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Unmanned Spaceflight.com _ Uranus and Neptune _ Uranus Orbiter

Posted by: Rob Pinnegar Nov 11 2005, 05:13 PM

Since the Neptune Orbiter thread has started to veer into talking about a Uranus orbiter as well, it seemed like a good idea to start a topic for Uranus.

Posted by: tasp Nov 11 2005, 05:46 PM

QUOTE (Rob Pinnegar @ Nov 11 2005, 11:13 AM)
Since the Neptune Orbiter thread has started to veer into talking about a Uranus orbiter as well, it seemed like a good idea to start a topic for Uranus.
*



Thanx. It is ok to move the Uranus orbiter post here if possible.

{I am imagining an era of NASA/JPL funding that results in the site being flooded with orbiter threads blink.gif }

Posted by: tasp Nov 11 2005, 06:08 PM

I admit a keen interest in Uranus. The mass ratios of the larger satellites to Uranus are not all that different from the Galilean satellites to Jupiter. Having two systems so grossly similar , yet with such huge differences, such as the axial tilt and the strength of the magnetic field, are so intriuging.

Would Hubble (or some of the larger ground based installations) be put to good use checking for co-orbital lagrangian moons of the larger satellites? I recall Voyager doing a thorough search closer in to the planet, but could small dark co-orbitals at Titania and Oberon have been missed?

That Jupiter seems to not have them, and Saturn having a few, it makes me all the more curious for a good inspection of Uranus to see where it stands regarding Lagrangian objects.

Finding some at Uranus might bump up the level of scrutiny Cassini is giving them at Dione and Tethys.

Posted by: Rob Pinnegar Nov 11 2005, 07:15 PM

QUOTE (tasp @ Nov 11 2005, 12:08 PM)
Would Hubble (or some of the larger ground based installations) be put to good use checking for co-orbital lagrangian moons of the larger satellites?  I recall Voyager doing a thorough search closer in to the planet, but could small dark co-orbitals at Titania and Oberon have been missed?

The four big Uranian moons are at about the same distance from Uranus as Tethys, Dione and Rhea are from Saturn. They also have similar masses. That being the case, you'd think that there would be at least one Lagrangian satellite somewhere in the Uranian system.

I wonder if the lack of co-orbital satellites for Ariel, Umbriel, Titania and Oberon has to do with Uranus itself, rather than the major moons? Uranus only has about 15% of Saturn's mass. Could this cause Lagrangian orbits to be less stable at Uranus?

Posted by: AlexBlackwell Nov 11 2005, 07:59 PM

QUOTE (Rob Pinnegar @ Nov 11 2005, 07:15 PM)
The four big Uranian moons are at about the same distance from Uranus as Tethys, Dione and Rhea are from Saturn. They also have similar masses.

Interestingly, a stronger comparison exists between Uranus and Jupiter, namely that both planets have similar planet/satellite mass ratios. In fact, in 2003 Andy Heaton and Jim Longuski published a paper showing that a Galileo-style tour is, unlike at Saturn and Neptune, possible at Uranus:

Feasibility of a Galileo-Style Tour of the Uranian Satellites
Andrew F. Heaton and James M. Longuski
J. Spacecraft Rockets 40, 591-596 (2003).
http://pdf.aiaa.org/jaPreview/JSR/2003/PVJAIMP3981.pdf

Posted by: tasp Nov 12 2005, 02:21 PM

QUOTE (AlexBlackwell @ Nov 11 2005, 01:59 PM)
Interestingly, a stronger comparison exists between Uranus and Jupiter, namely that both planets have similar planet/satellite mass ratios.  In fact, in 2003 Andy Heaton and Jim Longuski published a paper showing that a Galileo-style tour is, unlike at Saturn and Neptune, possible at Uranus:

Feasibility of a Galileo-Style Tour of the Uranian Satellites
Andrew F. Heaton and James M. Longuski
J. Spacecraft Rockets 40, 591-596 (2003).
http://pdf.aiaa.org/jaPreview/JSR/2003/PVJAIMP3981.pdf
*



I'll be darned! How 'bout that. I was aware of the mass ratio and distance scaling between Uranus and Jupiter, but I assumed there was an inverse square {or cube} law that prevents a 'quick' style tour of the Uranian moons. I thought I was really 'pushing' things suggesting a tour of the system lasting upwards of 20 years. {btw, a 20 year mission duration at Uranus is desirable for other reasons}

The lack of a strong resonance of three (or more) members of the Uranian system doesn't hurt the mission either. The lower radiation environment at Uranus would certainly be a relief after the ordeal Galileo experienced.

Appreciate the post!

Posted by: Rob Pinnegar Nov 13 2005, 01:49 AM

Yeah, thanks Alex -- that link was a good read. Very interesting.

Posted by: AlexBlackwell Nov 15 2005, 06:01 PM

QUOTE (Rob Pinnegar @ Nov 13 2005, 01:49 AM)
Yeah, thanks Alex -- that link was a good read. Very interesting.
*

I wish I could post the entire paper, which is fairly interesting, but AIAA is, like many organizations, very fastidious regarding copyrights, and Doug's forum is fairly visible.

Posted by: AlexBlackwell Nov 15 2005, 06:15 PM

QUOTE (tasp @ Nov 12 2005, 02:21 PM)
I'll be darned!  How 'bout that.  I was aware of the mass ratio and distance scaling between Uranus and Jupiter, but I assumed there was an inverse square {or cube} law that prevents a 'quick' style tour of the Uranian moons.

The most important thing for a "Galileo-like" tour is the availability of multiple satellites to utilize gravity assists, which adds flexibility to the tour design process. Cassini, on the other hand, can only use Titan and, consequently, must always return to Titan for a gravity assist to continue a given tour. This makes designing a "Cassini-like" tour very difficult, especially when multiple targets (e.g., Saturns icy satellites) are desired and the mission has severe operational constraints. Just ask the Cassini mission planners what they went though during the design process for the "T9-X" and "T18-X"-class tours.

QUOTE (tasp @ Nov 12 2005, 02:21 PM)
I thought I was really 'pushing' things suggesting a tour of the system lasting upwards of 20 years.  {btw, a 20 year mission duration at Uranus is desirable for other reasons}

I assume you're referring to monitoring Uranus' atmosphere and/or changing solar illumination?

QUOTE (tasp @ Nov 12 2005, 02:21 PM)
The lack of a strong resonance of three (or more) members of the Uranian system doesn't hurt the mission either.  The lower radiation environment at Uranus would certainly be a relief after the ordeal Galileo experienced.

Agreed.

QUOTE (tasp @ Nov 12 2005, 02:21 PM)
Appreciate the post!
*

My pleasure.

Trivia: For those who do happen to read the full paper by Heaton and Longuski, one might note that I get a brief mention in the acknowledgements section. I provided a couple of Uranus scientific references to Andy Heaton between the time he presented the paper at an AAS/AIAA conference and when he submitted the final for publication in J. Spacecraft Rockets.

Posted by: tasp Nov 15 2005, 06:16 PM

Without incurring copyright snags, of course, could I field a question about the ideas in the paper?

The portion available through the link ends with an intriguiging acknowledgement that the vehicle could enter orbit about Ariel after ~40 loops around Uranus.

Is this characteristic of the orbit tour similar (at least broadly) to the clever trajectory Messenger is utilizing to eventually end up in orbit about Mercury?

I realize the mass ratios of Sun - Mercury - Venus - Earth are quite different, but is there a correlation between the flight plans?

Amazing article, regardless!

Posted by: AlexBlackwell Nov 15 2005, 06:34 PM

QUOTE (tasp @ Nov 15 2005, 06:16 PM)
Without incurring copyright snags, of course, could I field a question about the ideas in the paper?

The portion available through the link ends with an intriguiging acknowledgement that the vehicle could enter orbit about Ariel after ~40 loops around Uranus.

Is this characteristic of the orbit tour similar (at least broadly) to  the clever  trajectory Messenger is utilizing to eventually end up in orbit about Mercury?

I realize the mass ratios of Sun - Mercury - Venus - Earth are quite different, but is there a correlation between the flight plans?

Amazing article, regardless!
*

Darn, wouldn't you know that I don't have a copy of the paper available on my system at the moment biggrin.gif

That said, I'll review it when I get home but from what I recall, the main concept behind the end-of-tour plan to insert into orbit at Ariel is based on orbital pumping and cranking, which not only changes inclination from the initial Uranian insertion, but reduces relative velocity so that the deterministic delta-V for insertion at Ariel can be handled by the orbiter's propulsion system. I can't remember whether the scheme also utilizes any "third-body" effects from Uranus or "fuzzy boundaries" but these might possible as was planned for the original Europa Orbiter insertion in europan orbit.

Whether this resembles, even in a broad sense, the MESSENGER trajectory through the inner solar system, is, I guess, in the eye of the beholder.

Posted by: tasp Nov 15 2005, 07:29 PM

{In re the 20 year mission life at Uranus}

I realize with Jupiters small axial tilt, we didn't see too many (any) seasonal effects with Galileo.

With Cassini, if we are lucky and have 7 years of probe life, we get to travel with Saturn roughly 90 degrees around the sun. We can see the rings from nearly full open to the sun to edge on. Assuming the rings look pretty much the same top and bottom (north and south?) we get to see the 'whole show' or at least be able to extrapolate it form a 7 year exploration of Saturn.

At Uranus, same thing. How does the ring look through forward scattering at edge on and full on to the sun? (I'm hoping for some phase effects, perhaps some of the Uranian ring particles are elongated and align radially to Uranus)

Additionally, if a probe arrived at Uranus with Uranian rings 45 degrees short of edge on to the sun (not that orbit for a probe would be easier to achieve in this orientation) and the probe could watch the rings go edge on then to 45 degrees further (in ~20 years), we could also get near 100% coverage in sunlight of all the surfaces of the main satellites.

A probe arrival with the rings full on to the sun, would also be desirable for other reasons.

{granted a probe with an even longer life would be great, but a factor of 2 or 3 increase from Cassini would seem technically possible}

Posted by: BruceMoomaw Nov 15 2005, 07:31 PM

Orbiting Ariel would be a remarkable ending to this mission -- especially given the assumptions I've been making until this month about the helplessness of a Uranus Orbiter. (I might as well say that Spilker told me that his own navigator for the Neptune Orbiter mission design took just a few days to reach a similar conclusion that a moon tour is perfectly feasible with a Uranus Orbiter; the only thing needed is experience with navigating a craft through a rapid-fire series of moon flybys, which Cassini has now given us. He didn't say anything about a finish-up at Ariel, though.)

Posted by: Bob Shaw Nov 15 2005, 10:13 PM

A long time ago (the early 1970s!), I suggested that there might be all sorts of odd effects around Uranus as a result of it's axial tilt - specifically, that at certain times of the Uranian year the relative velocities of both incoming spacecraft and meteorites, comets etc could be very much slower than expected (not so much a matter of traditional orbital dynamics as simply the summing of vectors). The end result might be a natural cache - as in Antarctica - of almost Kuiper Belt material, available for access in crater/canyon walls or by drilling on some of the icy moons. Or even interstellar material...

Bob Shaw

Posted by: hendric Nov 16 2005, 08:54 AM

QUOTE (AlexBlackwell @ Nov 15 2005, 12:01 PM)
I wish I could post the entire paper, which is fairly interesting, but AIAA is, like many organizations, very fastidious regarding copyrights, and Doug's forum is fairly visible.
*


For $450, Amazon claims it can deliver a copy of the proceedings:

http://www.amazings.com/sbb/reviews/review0494.html
http://www.amazon.com/exec/obidos/ASIN/0877034885/qid%3D1132130779/sr%3D11-1/ref%3Dsr%5F11%5F1/102-8920362-6213764

Posted by: BruceMoomaw Nov 16 2005, 09:23 AM

Well, shucks, how can anybody not jump at a bargain like that? However, they receive that journal at U.C.-Davis, which is within my driving range, so I'll photocopy it next time I'm down there. (That may be a while, though -- the advent of the Internet has tremendously reduced my need to go traipsing regularly to various university libraries for my astronautical information needs.)

Posted by: AlexBlackwell Nov 16 2005, 05:56 PM

QUOTE (hendric @ Nov 16 2005, 08:54 AM)
For $450, Amazon claims it can deliver a copy of the proceedings...

That's nuts.

I could post a scanned version of the Heaton and Longuski paper here (temporarily) but I'll let Doug decide since it's his forum. Of course, I'm assuming he's reading this thread.

Posted by: tasp Nov 16 2005, 06:19 PM

QUOTE (AlexBlackwell @ Nov 16 2005, 11:56 AM)
That's nuts.

I could post a scanned version of the Heaton and Longuski paper here (temporarily) but I'll let Doug decide since it's his forum.  Of course, I'm assuming he's reading this thread.
*



I confess a burning desire to see the whole paper.

An amazing finding I hope is employed in future exploration plans of Uranus.

Comparing the Uranian staellites close up to all the other moons would synergistically expand our knowledge of all the objects.

Posted by: AlexBlackwell Nov 23 2005, 01:49 AM

QUOTE (tasp @ Nov 16 2005, 06:19 PM)
I confess a burning desire to see the whole paper.

I dropped a line to Doug but I don't think he saw he it before his sojourn to Spain. I don't want to post it here without his permission. I guess I could email it to interested parties; however, maybe we should wait on Doug's return, especially since I don't know what the potential demand is.

EDIT (11/23/05): Anyone (as long as the number remains reasonable) who wants a scanned PDF version can drop me an email via this board and I'll send it via my own personal email account. A few members already have taken this route.

Posted by: tasp Nov 26 2005, 02:27 PM

QUOTE (AlexBlackwell @ Nov 15 2005, 12:34 PM)
Darn, wouldn't you know that I don't have a copy of the paper available on my system at the moment  biggrin.gif

That said, I'll review it when I get home but from what I recall, the main concept behind the end-of-tour plan to insert into orbit at Ariel is based on orbital pumping and cranking, which not only changes inclination from the initial Uranian insertion, but reduces relative velocity so that the deterministic delta-V for insertion at Ariel can be handled by the orbiter's propulsion system.  I can't remember whether the scheme also utilizes any "third-body" effects from Uranus or "fuzzy boundaries" but these might possible as was planned for the original Europa Orbiter insertion in europan orbit.

Whether this resembles, even in a broad sense, the MESSENGER trajectory through the inner solar system, is, I guess, in the eye of the beholder.
*


Have reviewed the Heaton/Longuski paper (Thanx!) now and have some comments.

The 'clever bit' of the Messenger trajectory, gravitational interaction with the target object to facilitate orbital insertion, isn't employed at Ariel. This technique is not addressed in the paper, but since utilizing it would take quite a while (if it were even possible at Ariel) and the paper was assuming 2 year long orbital missions the omission is not surprising. Also, the 1km/sec 'burn off' at Ariel doesn't seem excessive anyhow, so the utility of the technique at Ariel is less appparent. That the technique works at Mercury may be due more to Mercury's high density alowing the craft to approach closer to the planets center of mass to 'realize the math' than may be possible with an icy body like Ariel. It is not clear (to me) how the mass ratios and distances scale for this technique from sun/Mercury to Uranus/Ariel.

I am also amazed with the Heaton/Longuski trajectory in that in 2 years, 40 (!) encounters with Oberon, Titania, Umbriel, and Ariel are possible. A significant truth revealed in the paper is that since the Uranian system is 'scaled' smaller than the Galilean satelllites, useful distant flybys of Uranian moons also occur more frequently than they did for the Galileo spacecraft.

Inferring to Cassini, it seems the mass ratio of Saturn/Titan being so different from that of Jupiter or Uranus does allow Cassini much more flexibility in changing it's inclination around Saturn. I had wondered why this was not done with Galileo at Jupiter, and it seems many more satellite flybys would be required for a given inclination change than for Cassini at Saturn.

It does seem that an interesting mission could be orbited at Neptune following the Cassini style tour.

Also, granted the enormous delta vee needed to effect orbit insertion around Pluto, once that is achieved, an interesting mission at Pluto is possible utilizing Charons gravity for orbit shaping. Close observations of Pluto and Charon at a variety of inclinations seems quite feasible, and arbitrarily close approaches to the 2 new satellites seems 'easy' now. The big problem remains though, the difficulty in achieving orbit around Pluto due to the high approach speed of any reasonable spacecraft.

Posted by: BruceMoomaw Nov 26 2005, 09:23 PM

The best way to orbit -- or land on -- either Pluto or Triton seems to be Angus McRonald's suggestion for a big, heat-resistant ballute dragged behind the spacecraft on a cable to serve as an aerobrake in their extremely faint atmospheres. His preliminary studies show this to be quite workable. There was a little bit of discussion on it at COMPLEX, but as they said it will require quite a bit of technological work as compared to simple heat-shield aerocapture, which is almost ready to go right now. McRonald himself has become a victim of Ames Research Center's rather unselective layoffs, but some groups at Knoxville and Purdue U. are studying the question further.

As for a Neptune orbital tour, the plan already worked up for Tom Spilker's JPL design team involves a lot of orbital flexibility, but no actual switch from retrograde to prograde orbit at any point in the tour. (By the way, a lightweight but scientifically useful Triton lander that does most of its braking by ballute is seriously considered for addition to the Neptune Orbiter mission, if NASA hits the really big money.)

Posted by: tasp Nov 27 2005, 01:15 AM

QUOTE (BruceMoomaw @ Nov 26 2005, 03:23 PM)
The best way to orbit -- or land on -- either Pluto or Triton seems to be Angus McRonald's suggestion for a big, heat-resistant ballute dragged behind the spacecraft on a cable to serve as an aerobrake in their extremely faint atmospheres.  His preliminary studies show this to be quite workable. 
*



Wow, imagine watching the ballute go overhead while standing on the surface of Triton!

Would it radiate enough heat to flash the surface frost to vapor as it goes by?

Interesting to watch the surface after that if it did.

I assume that an accelerometer on the main body of the craft would cut the cable to the ballute when the craft slowed enough to enter orbit, but if the ballute didn't get deep enough into the thin atmosphere, the system wouldn't decel enough. Sounds stress provoking for the mission team at JPL.

Amazing concept, hope to live long enough to see one fly.

Posted by: BruceMoomaw Nov 27 2005, 03:17 AM

McRonald's best paper on the subject seems to be at http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17006/1/99-0422.pdf .

Posted by: tasp Nov 27 2005, 03:58 AM

QUOTE (BruceMoomaw @ Nov 26 2005, 09:17 PM)
McRonald's best paper on the subject seems to be at http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/17006/1/99-0422.pdf .
*



Doesn't look like it will burn off too much Tritonian frost. smile.gif

But what an amazing technique for getting to interesting places in the solar system!

Not sure a human payload will ever try this technique (shades of 2010), at least not at Pluto.

It is quite hard to imagine decel at up to 40 gees from such a thin atmosphere at hundreds of km above Pluto's surface. Still, the technique has great potential for orbiters and landers at a variety of objects.

Posted by: BruceMoomaw Nov 27 2005, 10:00 AM

Just keep in mind that -- because Pluto's gravity is so weak -- its atmosphere, thin though it is, towers up and up and up above the surface, with a huge scale height. In fact, there is speculation that some of it may get exchanged with Charon through tidal forces! High-altitude aerocapture in this situation is quite practical, if you have a moderately-sized ballute. (Ditto for Triton.)

Posted by: tasp Nov 28 2005, 04:45 AM

QUOTE (BruceMoomaw @ Nov 27 2005, 04:00 AM)
Just keep in mind that -- because Pluto's gravity is so weak -- its atmosphere, thin though it is, towers up and up and up above the surface, with a huge scale height.  In fact, there is speculation that some of it may get exchanged with Charon through tidal forces!  High-altitude aerocapture in this situation is quite practical, if you have a moderately-sized ballute.  (Ditto for Triton.)
*



I noted with interest in the referenced paper on the ballutes the one with a lens shape.

If this is not an original idea with me, my apologies; could such a near disk shaped ballute be angled during decel ? That advantage might be that a craft could manuever during the deceleration phase. The force applied by the ballute to the craft would not have to pass through the center of mass of the craft. The effect would be usable lift. The decel phase could be prolonged at a higher altitude while the craft arced further around the target object. Regions that perhaps would not be accessable from the 'standard' ballute might be reachable with a steerable one.

Should Pluto (or whatever) not be favorably aligned at arrival, this technique might still get you were you want to go.

Perhaps the decel could start over the far side (as seen from earth) and wind up on the fore side for the actual landing phase.

Another application might be (again using Pluto as an example) to enter the deceleration phase where convenient from the arrival trajectory, and manuver during decel and then exit the atmosphere on a path that leads to Charon (at a low enough speed that perhaps you could orbit or land there).

An application at Triton might be to decel in its' atmosphere, but not so much as to be captured by it, and wind up in an orbit favorably inclined about Neptune.

Aerocapture into Saturn orbit via ballute passage through Titan's atmosphere seems doable. Perhaps the manuvering technique would put the craft into an equatorial orbit about Saturn (for example) from a greater variety of incoming trajectory angles than any other technique?

Posted by: dvandorn Nov 29 2005, 02:32 PM

The biggest problem with using steerable aerocapture / landing trajectories is that you need to have a *very* good model of the atmosphere you're using to slow down with.

It's bad enough to have only a vague idea of the temperature/pressure profile of an atmosphere you're using to do straight-line drag braking. If you're designing into your spacecraft and trajectory a need for predictable changes in direction based on lift, *any* significant variation in the atmosphere's pressure, density and temperature profile from your model will result in completely different results.

They're talking about needing a Mars orbiter for day-to-day monitoring of the upper atmosphere in order to successfully land future probes -- apparently, Mars' upper atmosphere was so much thinner and extended than predicted during Spirit's EDL that she was very nearly dashed against the surface a la Beagle II. Cassini is seeing that Titan's upper atmosphere also seems highly variable in pressure/altitude. So, in order to successfully use Titan aerobraking for a Saturn orbiter, you'd almost need to already have a working Saturn orbiter there to tell you the detail you need about Titan's atmosphere at that moment...

Like many other elegant ideas, this one tends to fall apart when you look at it in greater detail.

-the other Doug

Posted by: tasp Nov 29 2005, 03:38 PM

QUOTE (dvandorn @ Nov 29 2005, 08:32 AM)
Like many other elegant ideas, this one tends to fall apart when you look at it in greater detail.

-the other Doug
*



{grasping at straws}

Can the craft itself scan ahead with a lidar device (or whatever would work) and adjust path 'on the fly' ?

Do we expect the Titanian weather reports to repeat precisely every Saturnian year?

Are Pluto and Triton far enough out that their atmospheres will model out quite stable in the the relavent altitudes?

Would a more 'structured' decel device be worth while? Maybe an RCC wing with some movable aerodynamic surfaces on the trailing edge. (I'm thinking of a shuttle type re-entry with hypersonic manuevuering capability, the craft flies to the appropriate density/altitude, executes the manuvuer wherever that layer happens to be).

I'm thinking the amount of gas over a particular surface area will be constant, but its' distribution vertically will vary. Set up something that tolerates the vertical gas distribution range expected and GO!

rolleyes.gif

Posted by: centsworth_II Nov 29 2005, 05:49 PM

What about a small,simple atmospheric probe that would fly ahead, similar to the way Huygens arrived at Titan before Cassini?

Posted by: BruceMoomaw Nov 29 2005, 09:23 PM

You don't need to grasp at straws -- Tasp's fears about the unusability of aerocapture due to uncertainties about the planet's atmospheric structure are, according to Jeffrey Hall of JPL, very seriously overstated. Hall's team has run almost 2000 simulated aerocapture entries into the atmospheres of both Titan and (more difficult) Neptune, inserting random changes in atmospheric structure to see if the written autopilot programs can cope with them -- without a single failure. (I can give you the URL for this actual report, once I track it down again in my records.)

He said flatly at COMPLEX that -- once a single New Millennium mission (maybe ST-9 in 2010) is flown to confirm the overall validity of the aerocapture autopilot programs -- the technology will be ready for use immediately at the smaller worlds (for instance, MEPAG was wrong in saying that an engineering test of aerocapture will be necessary at Mars) And he also went so far as to say that -- while aerocapture at the giant planets requires a radically different kind of boat-shaped heat shield, to provide the higher lift/drag ratio that will allow the autopilot to make corrective maneuvers faster, we won't even need another flight test for those aerocaptures; just some more ground work. Indeed, his cheerleading for this technology was one of the major pieces of news at the COMPLEX meeting, and seemed to effectively change the minds of the assembled members.

Posted by: BruceMoomaw Nov 30 2005, 08:29 AM

The document for simulation tests for a Neptune orbiter -- of which there were 2000 -- is at http://library-dspace.larc.nasa.gov/dspace/jsp/bitstream/2002/13082/1/NASA-aiaa-2004-4955.pdf . That for tests for the easier Titan orbit aerocapture is at http://www.inspacepropulsion.com/tech/pubs/2003_4951_Aerocapture%20Simulation%20and%20Performance.pdf .

Posted by: tasp Nov 30 2005, 04:36 PM

QUOTE (BruceMoomaw @ Nov 30 2005, 02:29 AM)
The document for simulation tests for a Neptune orbiter -- of which there were 2000 -- is at http://library-dspace.larc.nasa.gov/dspace/jsp/bitstream/2002/13082/1/NASA-aiaa-2004-4955.pdf .  That for tests for the easier Titan orbit aerocapture is at http://www.inspacepropulsion.com/tech/pubs/2003_4951_Aerocapture%20Simulation%20and%20Performance.pdf .
*



Amazing findings. Seems 'banking' the craft during the decel is the preferred technique. I thought perhaps pitch manuvers (or a combination of both) would be used. The banking technique seems (roughly) analogous to the hypersonic manuveurs the shuttle employs during earth atmosphere re-entry.

The banking technique would have obvious utility in expanding the cross range deflection for a lander type mission (at Titan, Triton, or Pluto).

Appreciate very much the information, it sure whets the appetite for future missions. Weird it may be easier to land on Pluto than Mercury . . . .

Posted by: vexgizmo Feb 2 2006, 07:46 AM

An excuse to post in the oh-so-obscure Uranus Orbiter thread!

----------

Uranus Pre-Equinox Workshop - First Announcement

2-3 May 2006, Pasadena, CA

Purpose: To ensure a comprehensive collection of Uranus System
Equinoctial observations, by gathering the community of Uranus system
observers, modelers, theorists, and lab experimentalists prior to
the 2007 equinox to coordinate both observations and analyses.

Who Should Attend: Those scientists planning either to make observations
of the Uranus system at equinox (including the atmosphere, rings,
and satellites), or to conduct theoretical and/or laboratory work
specifically pertinent to the Uranus system at equinox.

Date and Location: The meeting's timing and venue, 2-3 May 2006
in Pasadena CA, were selected to dovetail with the OPAG meeting on
the following two days, in order to minimize extra travel.

Next step if interested: Send email confirming your interest to
Heidi B. Hammel (...) with "uranus workshop" in the
subject line, and please indicate in the body of the message
the particular aspect(s) of the Uranus system you plan to study.
A second notice (and preliminary agenda) will be distributed in
late February.

Note: the primary purpose of THIS workshop is coordination and
facilitation of equinox observations and analyses, not review of
current science results. Some of us are considering hosting a
pre-DPS workshop to focus specifically on current atmospheric studies,
and similar workshops could be envisioned for other sub-fields.

Posted by: JRehling Feb 2 2006, 05:30 PM

QUOTE (tasp @ Nov 30 2005, 08:36 AM)
Weird it may be easier to land on Pluto than Mercury . . . .
*


It certainly is -- far easier. In fact, it takes considerably less delta-v to get a direct flight to Pluto than a direct flight to Mercury. It would take less delta-v to get a powered descent to Pluto's surface, and it just may be desirable to use that thin atmosphere to help more.

Dismissing the Sun, Mercury is the hardest place to fly to in terms of delta-v, and it has no atmosphere to help with a landing, so in two out of three categories, it is the hardest place to land. Among solid bodies, it ranks in escape velocity only behind the other three terrestrial planets, and so only Mars rivals it in terms of difficulty.

Not only is Pluto easier than Mercury -- they're near opposite ends of the spectrum!

Posted by: PhilHorzempa Apr 9 2007, 05:07 PM

Time to re-start this thread. Thanks to Cassini, we now have a better idea
of the diversity of all of the non-Titan moons of Saturn. This makes me feel that
an Uranus Orbiter should be flown before a Neptune Orbiter. Uranus is "only"
2 billion miles away, instead of Neptune's 3 billion. No matter which method one takes
to get there, the travel time will always be shorter to Uranus.

Also, for the meteorologists, the atmospheres of Uranus and Neptune are very
similar, except that Uranus is easier to get to.

Triton has always been thrown in as an extra Neptune bonus. It is a fascinating moon, I
must admit. However, as mentioned above, Cassini has shown us that even the smaller
icy moons of Saturn show complexity, perhaps even including zones of liquid water, e.g.,
Enceladus.

Uranus has 5 mid-size icy moons, with interesting possibilities for several of them.
We all know of Miranda's strange surface (Miranda is about the size of Enceladus)
The other 4 moons are in the size range of Dione and Rhea, which Cassini has shown are
more complex than Voyager led us to believe.
In fact, take a look at an image of Ariel and you will be reminded of recent views of
Dione's cracked and fractured surface.


My vote is for an Uranus Orbiter first.

Another Phil

Posted by: Cugel Apr 9 2007, 06:33 PM

Let's not forget that at Neptune Triton would also be used for orbital plane changes. For Uranus, lacking a big moon, that would take a lot of fuel.

Posted by: PhilHorzempa Apr 9 2007, 08:52 PM

QUOTE (Cugel @ Apr 9 2007, 02:33 PM) *
Let's not forget that at Neptune Triton would also be used for orbital plane changes. For Uranus, lacking a big moon, that would take a lot of fuel.


I refer you to some of the earlier posts in this thread, particularly #5, in which a paper,
entitled, "Feasibility of a Galileo-Style Tour of the Uranian Satellites," is referenced.
Because of the similarities in the planet/satelite ratios in the Jupiter and Uranus systems,
a spacecraft could execute quite the tour of Uranus' moons. In fact, the paper proposes
a 2-year mission that involves 40 flybys (!), ending with insertion into an orbit about
the moon Ariel.


Here is a link to a good view of Ariel. Doesn't it call to mind Dione and Enceladus?
Is Ariel hiding an ocean, or perhaps a lake, of liquid water?


http://www.solarviews.com/raw/uranus/ariel3.jpg


Another Phil

Posted by: Cugel Apr 10 2007, 12:12 AM

I stand corrected. I just wasn't following this thread 18 months ago....
Bruce's articles on SpaceBlogger.com kind of renewed my interest in outer planets exploration and I have the bad habit of catching up with threads starting with the last post.

Posted by: Greg Hullender Apr 10 2007, 12:53 AM

Apparently the big reason to prefer Neptune to Uranus, given that you could only do one in a ten (or twenty) year period was that by the time you got to Uranus, it'd be tilted on the side just as it had been for Voyager, ~40 years before. (Although, technically, it'd be the OTHER side.) Accordingly, they'd rather wait an extra 20 years and try to visit it at the next Uranian equinox. Maybe by my 100th birthday in 2058.

Pity is, if Alan could have sent NH2 there, it'd have got there at the Equinox -- more or less.

--Greg

Posted by: JRehling Apr 10 2007, 03:02 PM

QUOTE (PhilHorzempa @ Apr 9 2007, 10:07 AM) *
Also, for the meteorologists, the atmospheres of Uranus and Neptune are very
similar, except that Uranus is easier to get to.


They're made of the same stuff, and their gross dynamics are similar, but Neptune shows those huge cyclones which Uranus never has.

http://lasp.colorado.edu/~bagenal/3720/CLASS19/19GiantPlanets3.html

I agree that Uranus's larger satellites are made more interesting by forming a class with Saturn's midsize satellites. It would be interesting to see them upclose and from all angles.

Triton, though, is an understated "star". It has geysers being blown in the wind. Only Venus and Titan might match that doubly-impressive dynamism.

I don't think the gravity assist factor is all that important. Seeing what impressive results came from the single Voyager 2 trajectory, which was constrained by the need to get to Neptune, I think even a random orbit through the small Uranian system would produce some pretty good imaging of all of the satellites in time. The early tour could accomplish the satellite flybys, then a propulsive manuever at apoapsis could tilt the orbit to get some looks at the rings and the Uranian poles.

Posted by: dvandorn Apr 10 2007, 03:22 PM

The other attraction of Triton is, of course, that it is almost definitely a captured KBO. A Neptune orbiter would give you both a good look into the satellite system of an ice giant *and* an opportunity to study what may well be a prototypical KBO.

For my money, though, I think we need to wait for the next major breakthrough in propulsion technology. Then we may be able to launch an unmanned probe to *both* Uranus and Neptune -- and even have a chance of letting all of us see the data in our lifetimes!

-the other Doug

Posted by: JRehling Apr 10 2007, 05:37 PM

QUOTE (dvandorn @ Apr 10 2007, 08:22 AM) *
The other attraction of Triton is, of course, that it is almost definitely a captured KBO. A Neptune orbiter would give you both a good look into the satellite system of an ice giant *and* an opportunity to study what may well be a prototypical KBO.
-the other Doug


I think in bulk composition, perhaps, Triton is a prototypical KBO, but its got a history (and present) of tides that only one character in the neighborhood can churn up, and that character is Neptune. It's almost a thousand times the mass of anything else out there.

It may be that massive impacts or tight coorbital situations (like Pluto-Charon) may have melted the odd KBO or two, but Triton's probably pretty damned irregular by now, however it may have begun.

Pluto may be pretty irregular itself, being a tidally-locked world with a curiously patchy surface. And of course Triton and Pluto are both on the larger end of KBOs. Charon may be more like a typical KBO than either of them. Really, the post-Pluto encounter(s) by NH will be most important for a chance of truly seeing an ordinary KBO.

Posted by: hendric Apr 10 2007, 09:10 PM

QUOTE (JRehling @ Apr 10 2007, 12:37 PM) *
It may be that massive impacts or tight coorbital situations (like Pluto-Charon) may have melted the odd KBO or two, but Triton's probably pretty damned irregular by now, however it may have begun.


Actually, there was a recent update in Science about a presentation at the LPSC:

http://www.sciencemag.org/cgi/content/summary/315/5820/1789a?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=kbo&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT

Basically, someone sat down and did all the calculations for a large KBO, 1200 km, and found that with differentiation and a little ammonia anti-freeze that the KBO would retain a deep liquid ocean below the crust until present day. This could explain why some KBOs are bright, since any cracking would release water to the surface.

Posted by: Rob Pinnegar Apr 11 2007, 03:28 PM

A couple of random thoughts in favour of Neptune over Uranus (some already stated):

(1) Triton is a wickedly bizarre object worth a mission on its own.
(2) More atmospheric activity on Neptune.
(3) Nereid: captured, or scattered by Triton? If it's scattered, that's *very* interesting.
(4) Is Proteus primordial, or debris that assembled after Triton spoiled the fun?

And in favour of Uranus over Neptune:

(1) More large moons to study. Even Oberon may turn out interesting
(2) Miranda: a currently-dormant Enceladus?
(3) Small inner satellites: how stable are their orbits? Do they hit each other from time to time as has been hypothesized?
(4) Is Ariel still active, even at a "Dione level"?

In favour of both: How the heck did those magnetic dipole fields get tilted over at such crazy angles and displaced from the planets' centres? Something *weird* is going on inside those ice giants, and from a science perspective, at Uranus this could be the single most interesting thing to find out.

But of course, it's going to be Neptune, not Uranus, because no politician is ever going to publicly support a mission that is going to get laughed at on the Tonight Show. If we want that to change, then we'd better think of a different name for Uranus. They shoulda named it Minerva or Apollo or something.

Posted by: jsheff Apr 21 2007, 08:42 PM

Don't forget that both of them have ring systems - radically different from each other and from those of Saturn. Either one would teach us a lot.

Posted by: Jyril Apr 22 2007, 05:08 PM

And don't forget Neptune's second largest moon Proteus. It is larger than Mimas but still more or less irregular. Has it always been so?

We know so little about both of the planets so any mission to them would be scientifically very useful.

Posted by: David Apr 25 2007, 01:28 AM

QUOTE (Rob Pinnegar @ Apr 11 2007, 03:28 PM) *
(3) Small inner satellites: how stable are their orbits? Do they hit each other from time to time as has been hypothesized?


Just the huge number of fast-moving inner satellites means that a close-in orbiter is always going to have something to look at.

QUOTE
But of course, it's going to be Neptune, not Uranus, because no politician is ever going to publicly support a mission that is going to get laughed at on the Tonight Show.


No American politican, I guess you mean. Happily, there are other countries which don't base policy on stupid puns (in somebody else's language).

QUOTE
If we want that to change, then we'd better think of a different name for Uranus. They shoulda named it Minerva or Apollo or something.


They did name it something different. "Georgium Sidus"...

Posted by: Spirit Sep 22 2007, 11:45 AM

What about building two identical probes and launching one to Uranus and the second to Neptune? It will certainly lower the cost of the missions. And if we launch them at appropriate times, we can have the same team working on both projects - first on Uranus Orbiter and later on Neptune Orbiter.

Posted by: djellison Sep 22 2007, 12:12 PM

Sounds great! You paying?

Seriously - that'd be an ideal way to do it - but if they can't find money to do one of them, they're not going to be able to find the money to do both.

Doug

Posted by: brellis Sep 22 2007, 04:37 PM

A mothership with a bunch of micro-landers would be great. I wish Cassini had a few. Imagine dropping one into an Enceledan geyser!

Posted by: JRehling Sep 22 2007, 06:14 PM

QUOTE (djellison @ Sep 22 2007, 05:12 AM) *
Sounds great! You paying?

Seriously - that'd be an ideal way to do it - but if they can't find money to do one of them, they're not going to be able to find the money to do both.

Doug


Yes, I think just about any Outer SS science is looking marginal these days. Only the heavy-hitters (Europa, Titan, Enceladus, Jupiter and Saturn themselves) have a good shot at attention.

I will always be somewhat heartbroken that NH2 didn't come to pass, because the uranian flyby would have done an awful lot to address post-Voyager science there. With the extreme inclination and long seasons, the uranian satellites lose a lot of value as a potential target for the next *wince* 84 years. Given how long it was between Mariner 10 and Messenger, that sadly doesn't seem like such a long time.

I think the opportunistic use of a flyby en route to some deep-space (heliosphere) mission is the best bet that Uranus has, if we get a mission where the direction doesn't matter so much as the distance and we may as well point the ship at Uranus just to take advantage (and get a little gravity assist). But even such a mission would only carry nice camera in order to take imagery at Uranus, so it's not a total freebie.

Neptune/Triton carry a bit more clout, and lack the extreme seasonal constraints of Uranus, and I guess they'll get their closeup in, oh, about 30-40 years or so.

Posted by: AscendingNode Sep 23 2007, 05:18 AM

QUOTE (JRehling @ Sep 22 2007, 11:14 AM) *
I think the opportunistic use of a flyby en route to some deep-space (heliosphere) mission is the best bet that Uranus has, if we get a mission where the direction doesn't matter so much as the distance and we may as well point the ship at Uranus just to take advantage (and get a little gravity assist). But even such a mission would only carry nice camera in order to take imagery at Uranus, so it's not a total freebie.


Cassini could fly by Uranus as part of an end-of-life disposal. It could arrival anywhere from 2030 on (even at the equinox). There was another Longuski paper that talked about this at the AIAA/AAS Astrodynamics conference this summer. The big question, of course, is if Cassini could last that long. I hope they look into it to see if it could make it.

I've also calculated that you could launch something new horizon's sized to Uranus and not just do a flyby, but get it into orbit and do a tour. The flight time to Uranus would be 12 years, and the ops cost would probably be outrageous.... and you'd arrive at the solstice which wouldn't be great. So while it is possible with current launch and current chemical engines to do a Uranus mission, it is probably a lot of money to spend for a Uranus solstice mission.

And Neptune isn't even possible without some sort of new technology or 20+ year flight times. *sigh*

Posted by: JRehling Sep 23 2007, 05:56 AM

QUOTE (AscendingNode @ Sep 22 2007, 10:18 PM) *
Cassini could fly by Uranus as part of an end-of-life disposal. It could arrival anywhere from 2030 on (even at the equinox). There was another Longuski paper that talked about this at the AIAA/AAS Astrodynamics conference this summer. The big question, of course, is if Cassini could last that long. I hope they look into it to see if it could make it.


There's no way Cassini is going to visit any other planets, even if the theoretical possibility exists.

Its lifespan is primarily limited by the attitude-control propellant that is used up with every occasion in which the spacecraft is pointed in a particular direction (eg, for imaging during a satellite flyby). Now that it's in saturnian orbit, with Titan and Enceladus becoming more interesting the more we find out about them, the team is not going to stop using that attitude-control propellant on anything but Titan and Enceladus until the tank is empty. Saturn, the rings, and the other moons may get a few pictures here and there, but Titan and Enceladus will deservedly dominate the extended mission(s). Uranus can't hope to steal the show from those two heavy-hitters, especially with the exceptional risk involved in a 20 year cruise with the attitude-control propellant almost spent.

Put it this way: Imagine an upcoming mission could visit either Uranus or Titan and Enceladus. Which target would be more attractive? Now imagine that the craft is already AT Titan/Enceladus. The decision is extremely lopsided.

Posted by: ugordan Sep 23 2007, 10:41 AM

Regarding attitude-control propellant (i.e. monoprop for RCS thrusters), it is not the limiting factor, main engine biprop is. Cassini uses reaction wheels most of the time, only switching to thrusters if high slew rates are desired (mostly around closest approach observations) so it's pretty conservative about the RCS propellant. Even if that ran out Cassini would be able to do good science on reaction wheels alone. Apparently there's a way to offload built-up momentum solely via solar radiation pressure by taking advantage of the s/c assimetry. Using the very same thing that probably accounts for the majority of momentum buildup in the first place, rather neat.

It's the main engine fuel supply that, once exhausted, will lead to one of the endgame scenarios (regrettably, the crash-into-Saturn being most probable). Once you exhaust THAT, you can still control where you're pointed, but not where you're going.

Posted by: AscendingNode Sep 23 2007, 02:25 PM

QUOTE (JRehling @ Sep 22 2007, 10:56 PM) *
There's no way Cassini is going to visit any other planets, even if the theoretical possibility exists.

Its lifespan is primarily limited by the attitude-control propellant that is used up with every occasion in which the spacecraft is pointed in a particular direction (eg, for imaging during a satellite flyby). Now that it's in saturnian orbit, with Titan and Enceladus becoming more interesting the more we find out about them, the team is not going to stop using that attitude-control propellant on anything but Titan and Enceladus until the tank is empty. Saturn, the rings, and the other moons may get a few pictures here and there, but Titan and Enceladus will deservedly dominate the extended mission(s). Uranus can't hope to steal the show from those two heavy-hitters, especially with the exceptional risk involved in a 20 year cruise with the attitude-control propellant almost spent.


It don't think it would be a terrible hardship to reserve enough propellant for a single Uranus encounter. In any disposal scenario, there is going to still be propellant in the tanks (both monoprop and biprop). And if that propellant is need to insure a safe disposal, there's going to be margin on top of what is needed. And I maintain that that margin may be enough for worthwhile pointing during a Uranus encounter.

Also the spacecraft id disposed of as soon as it leaves Saturn.... (the spacecraft is guaranteed to escape the solar system after a cleanup maneuver) so the risk analysis only goes that far. Uranus can be viewed as a "lucky" event to be tried for, but that doesn't have to be insured.

Anyway, this can be calculated and verified along with other lifetime constraints... and the merits and demerits of a solar system escape disposal can be discussed if Cassini is interested in doing this.

QUOTE (JRehling @ Sep 22 2007, 10:56 PM) *
Put it this way: Imagine an upcoming mission could visit either Uranus or Titan and Enceladus. Which target would be more attractive? Now imagine that the craft is already AT Titan/Enceladus. The decision is extremely lopsided.


An upcoming mission to Titan/Enceladus would have to have better instruments than Cassini or do something different (like go into orbit) to be worthwhile.

It still is a valid argument that a mission to Saturn should stay at Saturn. But I just point out this alternative because it is interesting.... and because I don't think it should be ruled out without deeper study... I think the potential payoff is high enough to give it a shot.

Posted by: ugordan Sep 23 2007, 03:00 PM

QUOTE (AscendingNode @ Sep 23 2007, 04:25 PM) *
Also the spacecraft id disposed of as soon as it leaves Saturn.... (the spacecraft is guaranteed to escape the solar system after a cleanup maneuver) so the risk analysis only goes that far.

You're neglecting the nontrivial fact of exactly how many Titan flybys do you need to even escape the Saturnian system? Escaping the solar system? Can you lay down some concrete numbers supporting that?

As much as mission ending scenarios like that are nice and dandy, romantic and all that, I join the others in thinking wasting the last drops of fuel on planning an escape trajectory when you could be doing what you came here for (squeezing as much Saturnian system science as you could out of an aging spacecraft) is pointless.

The minute Cassini ignited its main engine on July 1st, 2004 to brake into orbit, it effectively determined its final resting place. I'm all for making as much out of that fact as we can. We have only just began scratching the surface of discoveries over there anyway.
Trying to get Cassini over to Uranus would IMHO be akin to trying to slingshot MRO to Jupiter via repeated Phobos flybys after its mission is over.

Posted by: djellison Sep 23 2007, 05:21 PM

Whilst orbital mechanics dictate that sending Cassini elsewhere is possible...it's not practically feasable, nor is it the best use of Cassini as a priceless scientific resource. It doesn't matter how long Cassini lasts - there will always be things for it to study in the environment for which its instruments were designed.

Doug

Posted by: tasp Sep 23 2007, 05:48 PM

I admit a burning desire for a Uranian orbiter (heck, even a targteted Pioneer 11 flyby), but Cassini is not the craft for the job.


High value observations at Uranus:

*confirmation of current (or recent) geophysical processes on Ariel

*(I wouldn't rule out Titania in that regard either)

* darkening agent (ala Iapetus' CR) discoloring Umbriel

*(Umbriel is otherwise DOA, BTW)

* 'big mountain' on Oberon

* ring morphology changes since Voyager II (maybe ongoing durin mission!)

* Uranian magnetic pole shift

*deep infrared observations of Uranian atmosphere

* BACK SIDE OF MIRANDA !!!!!!

Posted by: djellison Sep 23 2007, 06:11 PM

I think Neptune and Uranus orbiters are going to require a jump in technology before they become viable as anything other than a big flagship (and I don't think anyone would argue that we don't have enough on our plate in terms of targets for flagship missions already).

Aerocapture, NEP (or a large SEP for inner solar system accell), deep space flight tests Ka band - perhaps with a deployable HGA etc etc. All these things would make orbiters beyond Saturn a lot more achievable I think. Of course, we all want massive spacecraft to go everywhere, tomorrow...but we have to be realistic.

Doug

Posted by: JRehling Sep 23 2007, 09:07 PM

QUOTE (AscendingNode @ Sep 23 2007, 07:25 AM) *
An upcoming mission to Titan/Enceladus would have to have better instruments than Cassini or do something different (like go into orbit) to be worthwhile.


Expanded SAR coverage of Titan is reason enough to keep directing flybys that way. The fraction that has been covered by SAR is going to be about 25% when the main mission ends, and has just about no prospect for reaching past 45% when the extended mission ends. With that fraction mapped, we will have a peek at representative terrain for all of the major terrain types, but Titan is a place where a unique and fascinating feature may just be hiding in the last 10% that we'll get around to SAR-ing.

Titan's seasons (and Saturn's) are also an abundant justification for a long follow-up there. We haven't even seen Titan's north pole yet in ISS/VIMS.

In terms of terrestrial seasons, Cassini arrived when Saturn and Titan were at February 1, and 4 years of extended mission would only take us to about May 10. It will take 7 years of extended mission before we get to see Titan experience a solstice. As the seasons change, who knows what we'll see. Maybe the lakes in the north will shrink... or grow. Maybe the south will flood. Maybe midlatitude rains will lead to storm wash hitting the equatorial sand seas. Cassini's got the instruments to tell us quite a bit, but we have to stick around for 30 years before we've seen every season on Titan (15 years if there's north-south symmetry).

Enceladus also has more to show us, like the temperature profiles across the tiger stripes when they are in the darkness of seasonal polar night. And more observations to determine if there is temporal variation in the geysers.

Posted by: mchan Sep 23 2007, 09:09 PM

Will RTG power levels be sufficient to operate all the instruments in 2030?

Re-assembling a team to run 35 year old instruments on a 20-30 year old operational model could be costly compared to operations with the current technology of the time. While it would likely be cheaper than a future ground up Uranus flyby mission, the future mission would have better instrumentation for better science return.

Posted by: tedstryk Sep 24 2007, 10:11 AM

Well, 42 years, really. That's how long till the next equinox (shifting from north back to south at that time). I think the problem that we run into is that in the coming decade or two, if any money comes up for Uranus and Neptune, it will be for Neptune, thanks to the fact that it put on a better show for Voyager, plus the Triton factor. In addition to not having a moon the at is active (or known to be active), a Uranus orbiter would take a hell of a lot of fuel, since it has no Galilean Moons/Titan/Triton to use for gravity assists. NH2 would have been a cool mission. At equinox, a spacecraft could have flown by much as Voyager flew through the Jovian, Saturnian, and Neptunian systems, encountering a moon at a time, for the most part. If you look at the Voyager images on the PDS, you will notice that the amount of close coverage per moon pales in comparison to the other three planets Voyager encountered, because flying through the Uranian system near solstice, it passed through like it was hitting a dart board - all the closest approaches happened at the same time, so only a handful of images could be taken.

Posted by: ugordan Sep 24 2007, 11:05 AM

QUOTE (tedstryk @ Sep 24 2007, 12:11 PM) *
a Uranus orbiter would take a hell of a lot of fuel, since it has no Galilean Moons/Titan/Triton to use for gravity assists.

There was a paper Alex Blackwell referenced some time ago in http://www.unmannedspaceflight.com/index.php?s=&showtopic=1662&view=findpost&p=26445 about the feasibility of a Galileo-style tour of the Uranian system. In short, Uranus acts like a miniature version of the Jovian system in that interesting flybys are possible using the moons' gravities (feeble as they are).

Posted by: tasp Sep 24 2007, 12:51 PM

The Galileo style tour of the Uranian system is quite exciting. With the 'scale' being smaller, the mission generates very close encounters of Ariel, Miranda, Titania and Oberon in fairly a fairly short time interval.

Additionally, with even Oberon being less than (IIRC) 600,000 miles out from Uranus, you are having virtually continuous (well, not quite) reasonably close encounters with non-targeted moons on each orbit.

With the (IMO) near certainty of ongoing geological process on Ariel, and a good chance perhaps for Titania, too, a Uranus orbiter is looking like a pretty useful mission.

Our understanding of these smaller bodies grows synergistically with each one we study.

To learn more about the 'Enceladus phenomena', study Ariel.

And possibily, to learn more about Cassini Regio, study Umbriel.


A Uranus orbiter mission is a lot of bang for the buck.

Posted by: djellison Sep 24 2007, 01:52 PM

QUOTE (tasp @ Sep 24 2007, 01:51 PM) *
A Uranus orbiter mission is a lot of bang for the buck.


That may be true - to be honest, it would take a Uranus orbiter to find out. One thing that IS for sure, is that while it may be a lot of bang per buck...it'll also be a lot of buck.

Doug

Posted by: JRehling Sep 24 2007, 03:41 PM

I think one difficulty owing to the no-big-moon situation would be lifting the orbit out of the equatorial plane to get a good look at the rings. If the whole mission were spent in the equatorial plane, the rings would be very hard to study. Whereas if the mission were spent in an inclined orbit, satellite flybys would be severely limited. Either some fuel or a Titania boost would be needed to get the UO out of the equatorial plane on one pass, beginning a period of ring observations, and then back down there afterwards.

We could start a pool on which will happen first: a Uranus Orbiter mission or D.C. statehood.

Posted by: djellison Sep 24 2007, 03:46 PM

The paper cited above actually discusses the plane change issue.

Doug

Posted by: dvandorn Sep 24 2007, 04:32 PM

QUOTE (JRehling @ Sep 24 2007, 10:41 AM) *
We could start a pool on which will happen first: a Uranus Orbiter mission or D.C. statehood.

Frankly, I think you'll see the U.S. split up into several smaller polities before you see a Uranian orbiter... *sigh*...

-the other Doug

Posted by: AscendingNode Sep 24 2007, 05:34 PM

QUOTE (djellison @ Sep 24 2007, 06:52 AM) *
That may be true - to be honest, it would take a Uranus orbiter to find out. One thing that IS for sure, is that while it may be a lot of bang per buck...it'll also be a lot of buck.


It is very much not for sure that a Uranian tour spacecraft would be a lot of buck. I'd guess it could be done for ~ $1.5 Billion (or $75 mill a year for 20 years). And a big chunk of that could be saved if we could figure out how do do spacecraft hibernation better (i.e. improve upon New Horizon's hibernation). Sure that's more than a new frontiers mission, but it's about half a flagship mission cost.

Rough outline for a cheap mission: something New Horizon's like in the suite of instrument and in the mass of instruments, launch on a falcon 9, interplanetary trajectory like Venus-Earth-Earth-Jupiter, 12 year (mostly-hibernating) cruise, 1 year inclined tour with Titania flybys, 1 year equatorial tour with flybys of all of the moons. That's a 14 year mission, which is very much doable with current technology.

A Neptune mission on the other hand, would be a lot of buck since the interplanetary cruise times are beyond current technology unless we find a way to capture at Neptune from a high-energy transfer, which is also beyond current technology. Sure there are lots of technologies that could be developed... but that costs $$$.

Posted by: AscendingNode Sep 24 2007, 05:37 PM

QUOTE (JRehling @ Sep 24 2007, 08:41 AM) *
I think one difficulty owing to the no-big-moon situation would be lifting the orbit out of the equatorial plane to get a good look at the rings. If the whole mission were spent in the equatorial plane, the rings would be very hard to study. Whereas if the mission were spent in an inclined orbit, satellite flybys would be severely limited. Either some fuel or a Titania boost would be needed to get the UO out of the equatorial plane on one pass, beginning a period of ring observations, and then back down there afterwards.


Unless you arrive right at equinox, you'll start outside of the equatorial plane. If you arrive around solstice, you could have a very high inclination (60-80 deg). From this high inclination, you can then use Titania flybys to slowly bring you down into the equatorial plane. It takes a while, but it doable.

Posted by: djellison Sep 24 2007, 05:49 PM

QUOTE (AscendingNode @ Sep 24 2007, 06:34 PM) *
It is very much not for sure that a Uranian tour spacecraft would be a lot of buck. I'd guess it could be done for ~ $1.5 Billion (or $75 mill a year for 20 years).


$1.5B is low-end Flagship class. That's a lot of buck.

Doug

Posted by: infocat13 Sep 24 2007, 10:45 PM

QUOTE (Spirit @ Sep 22 2007, 07:45 AM) *
What about building two identical probes and launching one to Uranus and the second to Neptune? It will certainly lower the cost of the missions. And if we launch them at appropriate times, we can have the same team working on both projects - first on Uranus Orbiter and later on Neptune Orbiter.


Spirit,

I remember A while back NASA had idea much like yours , it was called Mariner Mark 2 I believe. You could goggle this.I think it is a great idea perhaps now in our era a massed produced space craft modeled after the Jupiter and Saturn orbiters could be built minus the instruments and electronics and stored(off the shelf)then as opportunities came up do to orbital mechanics science instruments specific to that mission would be added to the off the shelf spacecraft body and launched.
Questions I would have would be assuming we are using the Galileo design and we where building two space craft for Uranus Neptune and a re flight to Saturn and Jupiter IE 8 space craft with one atmospheric probe each. what would a JPL cost engineer cost these out as ?
Issues..................
(1) can a modular mass produce space craft design accept somewhat different scientific instrument suite for each outer planet?
(2) would a mass produced set off atmospheric probes work at each outer planet? each would need a somewhat different reentry cone?
(3) Could the Deep space network handle a outer planet mission launched every year or every two years?

http://en.wikipedia.org/wiki/Mariner_Mark_II

Posted by: AscendingNode Sep 25 2007, 12:12 AM

QUOTE (infocat13 @ Sep 24 2007, 03:45 PM) *
Questions I would have would be assuming we are using the Galileo design and we where building two space craft for Uranus Neptune and a re flight to Saturn and Jupiter IE 8 space craft with one atmospheric probe each. what would a JPL cost engineer cost these out as ?


A good way to estimate costs of doing multiple identical spacecraft (based off of MER experience, I think) is that if you build the spacecraft at the same time and they really are identical.... each spacecraft after the first costs 50% of the first. If anything is different or if you have time between when you build the spacecraft almost all of the savings is lost.

This is because almost all of the cost of spacecraft is in the brain-power used to build them. If you change something you have to think about all of the effects of the change and that often is as much work as designing from scratch. And if you have a gap in time between doing the designs, you probably need to get new people... so you have to pay full price.

As far as how much a mission costs... check out this link: http://www.lpi.usra.edu/opag/TitanEnceladusBillionDollarBox.pdf

This is the billion-dollar box study of what could be done at Titan or Enceladus for a billion dollars. (answer: not much) The main problem is that a new Saturn mission has to do something Cassini didn't (and Jupiter missions have to beat Galileo). For Uranus and Neptune you have to beat Voyager. Thinking that way, and looking at the cost of the mission ideas in the above study, I think a Uranus or Neptune mission would cost $1 billion at least. An that would be a very minimal mission.

But I think, for $2-$3 billion you could do something amazing that would be worth more scientifically than splitting that same number across 2-3 new frontiers missions. (Just look at all we got from one Cassini Iapetus flyby... that's a new frontiers-class science return from one flyby).

I think NASA needs to start thinking of outer planet exploration as a program that costs X dollars a year and then plan multiple flagships in that budget to overlap. Start with a Europa or Titan mission and then after it ramps up (maybe 5 years down the road), then start studying the next one. The flight times to the outer planets are so long that you can easily stagger the arrival times.

Posted by: nprev Sep 25 2007, 01:00 AM

Infocat, I and others on the board have had variations on the same idea before. However, as AscendingNode points out, requirements for planetary missions tend to increase & specialize over time as we build on the results of previous missions, complicated by the fact that technology changes rapidly. This applies even to the bus, not just the payload. Therefore, mass-producing modular "COTS" spacecraft for planetary missions just isn't feasible. (I know; I think it sucks, too!) sad.gif

Posted by: brellis Sep 25 2007, 01:30 AM

QUOTE
requirements for planetary missions tend to increase & specialize over time as we build on the results of previous missions, complicated by the fact that technology changes rapidly. This applies even to the bus, not just the payload. Therefore, mass-producing modular "COTS" spacecraft for planetary missions just isn't feasible. (I know; I think it sucks, too!)


It isn't "mass-producing". It's reproducing maybe a couple of dozen spacecraft that have common traits and interchangeable parts.

My area of work involves an analogy of sorts. I do soundtrack music for films. The technology involved requires a considerable investment of time to learn software, etc. At the dawn of the age of technology for us musicians, there was a feeling of exclusivity to our world.

When embarking on my music career, I tried to get the biggest, fastest, most versatile and bug-proof hardware/software available. The biggest part of this investment was a Synclavier. Almost 25 years later, I still use my Synclav primarily. The other software I use, ProTools, is almost 20 years old now, with lots of upgrades. It's not worth the effort to learn something that will be obsolete next year. It's worth it if there's a longterm possibility of success.

Spacecraft design must involve these longterm visions. Make the software easy to upgrade, and make the hardware as potent as possible, so it can be relevant 20 years hence. Build it and they will come. Send a fleet of well-built spacecraft to the outer planets, and the software designers will surely keep them relevant.

What made Galileo great was: first, they managed to launch it, and then, by hook or crook they milked everything they could out of the mission. Equipment failure didn't stop them. The philosophy of longterm investment of money, hardware, software and human effort was worth it.

Missions to the outer planets are worth the wait, and the machinery should be designed accordingly.

Posted by: tasp Sep 25 2007, 02:19 AM

Yeah, the Longuski paper describes a mission phase for reducing the inclination of the initial orbit to the equatorial plane.

Actually, this is an advantage.

We get a couple of years of excellent field and particles study at Uranus (fascinating magnetically anomalied orb that it is), and if we are encountering Titania (or Oberon) every orbit, we might have some pretty precise control of our other ring plane crossing point too. Maybe some close flybys of Miranda (not approached closely in 'Galileo' phaseof the mission, btw) and the inner 'rocks' too.

Wouldn't hurt to check out the extent of the ring plane debris prior to orbiting in it, too. I'm curious if there are any co-orbital satellites lurking there.

The paper contemplates 2 years in the ring plane, and maybe a year at mission end orbiting Ariel. I wouldn't think 2 or 3 years cranking down the incliniation would be unendurable. Cassini has been doing interesting things in all kinds of inclinations at Saturn.


A follow on New Horizon styled orbiter doesn't seem too useful too me at Uranus (in an orbit at Neptune with a period around ~ 1 year is another story).

The flybys happen pretty quickly, and NH is optimized for high data rate collection in brief spurts at long intervals, Uranus is pretty taxing all the time. ( a Neptune mission, OTOH, with perhaps a 20 year 'loiter' time there, and close Neptune approaches once a year seems pretty NH friendly to me. Neptune has a big Hill sphere, might as well exploit it.)

Posted by: nprev Sep 25 2007, 03:40 AM

QUOTE (brellis @ Sep 24 2007, 06:30 PM) *
It isn't "mass-producing". It's reproducing maybe a couple of dozen spacecraft that have common traits and interchangeable parts....
Missions to the outer planets are worth the wait, and the machinery should be designed accordingly.


Cannot disagree philosophically, but the problem is much more externally than internally driven.

We all know Moore's Law here, and that complicates long-term logistical support of software tremendously (older stuff gets REALLY expensive, really fast, to maintain; how to attract & retain coders for activities 30 years in the future?) Furthermore, achieving space qualification for IT hardware is not an insignificant effort. As of 2000, 80386 processors had finally achieved this for C-17 aircraft, which is a much lower level than that required for spacecraft. Add the fact that space exploration budgets do not generally enjoy stable long-term committments from decision makers for a variety of reasons...and thus very long-duration missions are correspondingly very difficult to sell.

A propulsion breakthough would obviate all this. Short of that, the overall risk profile for Cassini-equivalent outer-planet missions is questionable at best.

Posted by: JRehling Sep 25 2007, 05:03 AM

QUOTE (infocat13 @ Sep 24 2007, 03:45 PM) *
(1) can a modular mass produce space craft design accept somewhat different scientific instrument suite for each outer planet?
(2) would a mass produced set off atmospheric probes work at each outer planet? each would need a somewhat different reentry cone?
(3) Could the Deep space network handle a outer planet mission launched every year or every two years?


Jupiter and Saturn have already been revisted since Voyager, and followups to those systems (eg, a Europa Orbiter, Juno) are going to be more specialized.

Saturn, Uranus, and Neptune coincidentally have about the same cloudtop gravity, so entry probes hitting all three places would accelerate similarly. However, Saturn has a greater escape velocity, so the Saturn probe would arrive at a higher velocity. I guess though that with a very superficial difference in design, one approach could work for all three.

Jupiter presents very different parameters, and has already received an entry probe. Although a design that worked for Jupiter would work in the other places.

The extreme differential in flight times would mitigate any worries about DSN time. Moreover, with probes in elliptical orbits, the encounter-rich time in each orbit could be staggered from one mission to the next.

Posted by: dvandorn Sep 25 2007, 05:42 AM

QUOTE (nprev @ Sep 24 2007, 10:40 PM) *
...As of 2000, 80386 processors had finally achieved this for C-17 aircraft, which is a much lower level than that required for spacecraft.

I believe the most advanced processors being used in manned space flight today (on the laptops and integrated computer systems on the ISS, for example) are 80486's. We're not even into the Pentium era yet.

I could be wrong, of course... I haven't dug deeply into the latest news about ISS computers. I surely hope the Shuttles have upgraded their base computers from the PDP-8's they were originally fitted out with, though.

-the other Doug

Posted by: dvandorn Sep 25 2007, 05:51 AM

Anyone have any charts handy telling us when we have Jupiter gravity assists to each of the outer planets? Jupiter orbits once every dozen years (roughly) -- that means we ought to have a gravity assist trajectory to each of Saturn, Uranus and Neptune every dozen years or so, right?

The order in which we send probes to the outer planets would seem to be dictated more by the availability of gravity assists than by our 'druthers, I think.

-the other Doug

Posted by: mchan Sep 25 2007, 07:30 AM

To a first order, there can be Jupiter gravity assist trajectories every dozen or so years to Saturn, Uranus, and Neptune. Practically, a Jupiter gravity assist to planets further out is possible once a year for several years in a row.

The Jupiter flyby distance will vary from year to year depending on how much the trajectory needs to be "bent" and the energy of the orbit before the Jupiter flyby (which dictates the v-infinity of the hyperbolic trajectory around Jupiter). E.g., for "bend", compare that in the Saturn trajectories of Pioneer 11 vs the Voyagers and Cassini. E.g., for energy of orbit before Jupiter flyby, compare the "bend" in Jupiter flybys of Cassini (lower energy) vs. New Horizon (higher energy). Outer planet orbiters tend more to lower energy orbits to reduce orbit insertion delta-V, but must trade this off against longer flight times.

For an idealized calculation, Jupiter gravity assist opportunities are roughly spaced at the synodic period between Jupiter and the target planet.

For Saturn, 1 / (1/11 - 1/29) ~= 17.7 years
For Uranus, 1 / (1/11 - 1/84) ~= 12.6 years
For Neptune, 1 / (1/11 - 1/165) ~= 11.8 years

Time between Voyager (1979) and Cassini (2000) Jupiter flybys is 21 years which is within "several years" of the idealized calculated opportunities. Time between Pioneer 11 (1974) and Voyager (1979) was only 5 years, but look at how much Pioneer's trajectory got "bent".

Posted by: brellis Sep 25 2007, 08:42 AM

QUOTE (nprev @ Sep 24 2007, 08:40 PM) *
Cannot disagree philosophically, but the problem is much more externally than internally driven.

We all know Moore's Law here, and that complicates long-term logistical support of software tremendously (older stuff gets REALLY expensive, really fast, to maintain; how to attract & retain coders for activities 30 years in the future?) Furthermore, achieving space qualification for IT hardware is not an insignificant effort. As of 2000, 80386 processors had finally achieved this for C-17 aircraft, which is a much lower level than that required for spacecraft. Add the fact that space exploration budgets do not generally enjoy stable long-term committments from decision makers for a variety of reasons...and thus very long-duration missions are correspondingly very difficult to sell.

A propulsion breakthough would obviate all this. Short of that, the overall risk profile for Cassini-equivalent outer-planet missions is questionable at best.


Back to my Synclavier analogy - relevance can resist Moore's law. That said, I'm entering this post on a Mac G5 that NASA scuttled after one year of service unsure.gif

Let's have everything: better propulsion, longterm hardware design vision, flexible software. Designing boxes to last a lifetime would help reduce our landfill deposits on earth while making outer planet exploration more feasible. smile.gif

Posted by: JRehling Sep 25 2007, 02:46 PM

Another consideration, a happy one, is that for the biggest target in the uranian system, namely Uranus, there is a considerable and growing ability to monitor it telescopically from Earth at almost all times. Percentagewise, its distance from Earth is almost invariant. Excepting brief blackouts at solar conjunction, it is technically feasible to snap a multispectral image of Uranus practically *hourly* for years at a time.

Some images released in the press just a month back:

http://www.berkeley.edu/news/media/releases/2007/08/23_ringcrossing.shtml

And from 2004:

http://www.newscientist.com/data/images/ns/cms/dn6657/dn6657-1_370.jpg

The rings can also receive some useful studies from Earth. Obviously, the satellites cannot be resolved in any interesting way, so the scientific value of a UO mission depends most crucially on them. Since Miranda was wonderfully imaged (though only partially) by Voyager 2, the focus narrows even more.

In my mind, one of the key elements of interest in the uranian system is for us to have the contrast between many worlds of similar size that have nonetheless evolved differently. In the size range of 300 km to 1600 km, the Saturn and Uranus systems combine to give us 13 examples, all with approximately similar bulk composition and similarly low temperatures. Whereas the obvious view of exploration is that the unique places (like Io, Mars) deserve the most attention, you actually learn key things about the dynamics of planetary evolution by finding places that seem to have had similar initial conditions, but diverged. A good look at the uranian satellites would give us a pretty dense sample(s) of similar-sized worlds. At the top end of that group, there is a quartet: Rhea, Iapetus, Titania, and Oberon of almost identical size, and yet none of them look alike. There's really no opportunity in the solar system, except in the Kuiper Belt or among much smaller and less evolved worlds, to see a contrasting set of four worlds the same size and same bulk composition. (Since Mercury isn't made of the same stuff as Ganymede, Callisto, and Titan.)

None of this changes the fact that we'll have to wait a long time to get that next look at them. The main question is which multiple of 42 years we'll have to wait. (Alternate, worse possibility -- a flyby at an anti-Voyager solstice.)

Posted by: Spirit Sep 25 2007, 04:23 PM

Maybe we'll have another opportunity to flyby Uranus earlier. I am pointing to the http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Jupiter&MCode=JP&Display=ReadMore and http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Saturn&MCode=SFP&Display=ReadMore missions. If they get launched at the right time and have a technical capability to operate at Uranus orbit, we might be lucky. Yeah, we have a bunch of problems like power supply, telecommunications and money, but who knows.

Posted by: JRehling Sep 25 2007, 06:06 PM

QUOTE (Spirit @ Sep 25 2007, 09:23 AM) *
Maybe we'll have another opportunity to flyby Uranus earlier. I am pointing to the http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Jupiter&MCode=JP&Display=ReadMore and http://solarsystem.nasa.gov/missions/profile.cfm?Sort=Target&Target=Saturn&MCode=SFP&Display=ReadMore missions. If they get launched at the right time and have a technical capability to operate at Uranus orbit, we might be lucky. Yeah, we have a bunch of problems like power supply, telecommunications and money, but who knows.


Jupiter Flyby with Probes has most of the life taken out of it by Juno. Although an orbiter is technically a very different mission profile than a flyby with entry probes, Juno addresses many of the science goals that the multi-probe mission would have pursued. The AO for the New Frontier mission to Jupiter sort of expected entry probes but had a loophole that allowed a good remote-sensing mission to replace the actual entry probes, and Juno successfully convinced the powers that be that it will get the job done from orbit.

A Saturn entry probe is not what I'd call high on the list of missions to fly, but it is desirable sooner or later. When it does fly, it *could* work out that the bus/flyby craft could take a trajectory to Uranus (or Neptune, or some KBO), but I think the trajectory may be constrained by the need to get gravity data from the Saturn flyby.

On the other hand, Cassini might be able to fulfill that goal with a close dip over the cloudtops one or more orbits before its death plunge.

The Saturn flyby craft would *still* presumably have trajectory constraints as a data relay, etc. To my mind, top-down constraints would encourage planners to FIND a way to see two planets with the same mission, where feasible, and I don't think missions get enough credit for fulfilling off-prime science goals when selection time occurs. The Uranus flyby would have to end up coming almost for free, because if it increases the requirements (besides, obviously, a ground crew and DSN time) for a Saturn mission, it's going to be very unlikely.

To my mind, a $50 million (say) cost increase to a Saturn mission so it could fly by Uranus is like a $50 million mission to Uranus. But with bottom-up planning, that only looks like a complication of the "main" mission.

Posted by: algorimancer Sep 25 2007, 07:45 PM

Perhaps slightly off-topic, but there have been serious discussions recently about putting an interferometric telescope array in orbit which could resolve (2+ pixels) earth-sized planets about other stars. A quick back of the envelope calculation assuming an earth-sized planet 6 light years away corresponds to a resolution of 1 kilometer at the distance of neptune. Increase this by a factor of 10-100 and we're getting distinctly competitive with what spacecraft can do, without needing to venture much beyond earth orbit. Just playing devil's advocate here smile.gif Still, the polar regions would still be troublesome, and this would never compete with a rover on the ground or a dedicated orbiter. smile.gif

Posted by: tedstryk Sep 25 2007, 09:08 PM

QUOTE (algorimancer @ Sep 25 2007, 07:45 PM) *
Perhaps slightly off-topic, but there have been serious discussions recently about putting an interferometric telescope array in orbit which could resolve (2+ pixels) earth-sized planets about other stars. A quick back of the envelope calculation assuming an earth-sized planet 6 light years away corresponds to a resolution of 1 kilometer at the distance of neptune. Increase this by a factor of 10-100 and we're getting distinctly competitive with what spacecraft can do, without needing to venture much beyond earth orbit. Just playing devil's advocate here smile.gif Still, the polar regions would still be troublesome, and this would never compete with a rover on the ground or a dedicated orbiter. smile.gif


Ignoring the technical difficulties (such as that orbital motion and parallax would become HUGE problems at such high resolutions), there is also the problem of the fact that we see the outer planets at full or nearly full phases - high and moderate phase observations are impossible, so topographic mapping would be difficult. Also, building and operating an array with such imaging and tracking capabilities in orbit would cost a lot more than some orbiters and landers.

Posted by: algorimancer Sep 26 2007, 12:37 PM

QUOTE (tedstryk @ Sep 25 2007, 04:08 PM) *
...technical difficulties..., ...we see the outer planets at full or nearly full phases - high and moderate phase observations are impossible, so topographic mapping would be difficult. Also...would cost a lot more than some orbiters and landers.

I believe the notion was to place it in one of the earth-sun Lagrange points, rather than earth orbit, minimizing the problems of orbital motion. As to cost, I would guess several billion dollars. Definitely more expensive than sending a dedicated orbiter or lander, but far cheaper than sending orbiters and landers to every possible target in the solar system. I agree that the limited view & phase angles would be problematic for lot's of things, plus particles & fields would be out of luck. I'm just throwing the idea out there as a broad but imperfect solution which would in many ways be equivalent to sending flyby missions all over the solar system, not to mention the opportunity to do comparative planetology, since if you can resolve earth-sized bodies around other stars consider what you could do with the gas giants there.

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