Neptune Orbiter, Another proposed mission Options

[Guest_vjkane2000_*]

It is so difficult to get a craft to Neptune in a reasonable about of time (very high speeds are needed) and then slow it down enough to enter orbit (aerocapture appears to be required). You can probably solve the first problem by waiting to use a Jupiter gravity assist or a solar electric ion "boost stage". However, that aerocapture means that whatever you do will be a new design and new technology. At that point, there's probably good reason to spend more on the orbiter and instruments to get more bang from the bucks. As marvelous as the NH instruments are, heavier instruments built with the same level of technology would provide a higher science return.

If you want an inexpensive mission that could fly sometime in the reasonable near future, you could certainly take the core elements of NH and attach an atmospheric probe for a flyby mission. From what I understand of Triton's orbit, though, you can probably either have a close flyby of Triton or Neptune, but not both. Perhaps someone here knows. I also don't know if the relay from the atmospheric probe can be reasonably done if you go for the Triton flyby.

[tasp]

Tasp - NH is a flyby craft not an orbiter and its design is totally unsuited for an orbiter mission. There is no way to get something like it into orbit around anything without so much rework that it would end up being something completely different.

Yet New Horizons seems amply capable of Neptune encounters at ~1 year intervals. All the Jupiter data is coming back in less than a year, from its' recent encounter. It seems that characteristics of the Neptune system (such as the lower number of sizeable moons, Triton's favorable mass ratio with Neptune and the huge Hill sphere) might guide us towards a mission profile and probe design that would not be a 'flagship' mission. Cheap missions get flown far more often.

As I recall, the speed decrease for Cassini at Saturn for orbit insertion was ~1500 KPH, I don't have a figure for the Dv total expected for the Dawn mission, but that would be an item for discussion if someone knows. SEP at Neptune's distance seems iffy, I don't know how many RTGs it would take for a mission like this, but once the orbit insertion is over, residual power from the RTGs could power a NH derived clone
for decades.


Trade offs between aerocapture and ion propulsion are topics for discussion, off course. Engineering trade offs is the whole point here. Can a low cost, off the shelf derived, Neptune orbiter deliver 80% of the bang for 20% of the price?

[djellison]

You're talking about a flagship mission, which ever way you look at it.

Doug

[mchan]

Can a low cost, off the shelf derived, Neptune orbiter deliver 80% of the bang for 20% of the price?

Considering Cassini cost around $3.3 billion, and proposals for the Europa orbiter have project costs of $1.5 billion or more, a guess for the fagship Nepture orbiter costs could be ~$2 billion. Assuming this guess is realistic, 20% of the flagship Nepture orbiter cost would be $400 million which would not be enough to even buy another build of the original New Horizons spacecraft.

[tasp]

{For 'just wanting to throw out some ideas', it seems this topic has become a real grinder for me.}

A Cassini class flagship orbiter might go for 5 billion (over a decade of inflation mostly, and more rocket to get there, and upgraded dish and com system for Neptune's distance and a scan platform) so I'm thinking the 'cheap' Neptune orbiter might be <$1bil.

[Rob Pinnegar]

You're talking about a flagship mission, which ever way you look at it.

Not only that, but a flagship mission that (1) would have a good chance of failure due to the long travel time (and aerobraking risks) and (2) wouldn't make it to Neptune until after any political supporters would be retired.

This is going to be a tough nut to crack.

[J.J.]

Honestly, I'd just be happy with a cheap NH-type flyby of Uranus and Neptune, utilizing the advantages of equipment optimized for the light levels at those distances, and of course 30+ years of technological improvement. I'd dig seeing the other hemispheres of the Uranian moons, as well.

For instance, telescopic observations since Voyager have shown that Uranus's atmosphere shows much more detail in the near-IR than it does in the visual band--near-IR capability that neither spacecraft had. Sending a spacecraft so equipped to Uranus and Neptune could yield outstanding results, regardless if it orbited or not.

[JRehling]

I think to a considerable extent, Uranus and Neptune "meteorology" is eventually going to be more amenable to continuous survey from Earth than from pricey orbiters that provide outstanding spatial resolution but spotty temporal coverage.

This shows the best image that HST can provide now of either of these planets:

http://hubblesite.org/newscenter/archive/r...rmat/web_print/

If this resolution could be, say, doubled, either via a space telescope or future ground telescopes, then a lot of scientific goals regarding Uranus, Neptune, and Io (among other places) could be met by conducting temporal surveys on a "loose" basis: observing each of those worlds, say, at least three times a week (to see all latitudes as they rotate) and on an occasional "tight" basis, observing hourly or so. Certainly other places would fit on the same agenda, but imagine just those three worlds getting such a telescope's attention, with each of them observed weekly for years on end, and numerous "tight" surveys of each to get an idea of the fine-grained dynamics.

Note that Neptune and Uranus have essentially no variation in their distance from Earth (though each goes through a solar conjunction blackout), while Io's distance varies by 50%, so its tight surveys should obviously be done around Jupiter conjunction.

HST has a resolution of about 280 km/pixel at Uranus, 450 km/pixel at Neptune, and 65 km/pixel at Io. If that could be doubled (or even if not) an awful lot of the science you'd like to do with an orbiter could be done from terra firma (or LEO or L2). I think a single good flyby of each of Uranus and Neptune to "ground truth" the excellent temporal coverage with some close-ups would produce some good answers to basic questions. Obviously, magnetometers and satellite flybs would be part of the package.

Overall, I think there's a bias in the system against finding best-bang-for-the-buck options that do a pretty good job of exploring several targets without specializing for any one of them. Ultimately, a long-distance survey for time and close-up flybys for spatial resolution would accomplish a lot without the cost and "bother" of orbiters that have to sprint to the outer-outer solar system and then slam on the brakes to orbit a giant planet. The flyby craft for Uranus and Neptune would have obvious opportunities to also provide close-up views of other worlds along the way, including Io as a possibility for one or both of them, and perhaps KBO destinations like Sedna after their ice-giant flyby.

The real "victim" of this approach would be Triton, which can't be seen very well from 29 AU away and which deserves excellent coverage. A hedge to the approach would be to send two flybys to Neptune to capture opposite hemispheres of Triton and to catch two snapshots of its time-varying activity. A total of three flyby craft (and here we could talk in terms of NH analogues, if not clones) could visit Io three times, Uranus once, Neptune and Triton twice, and certainly get some KBO exploration done as well, possibly visiting some of the bigger KBOs.

I suspect this would be cheaper than a good Neptune orbiter and would let the next mission to the Neptune system be a Triton lander that could even spend some time looking skyward at Neptune and should be able to last a long time on the surface.

[Guest_AlexBlackwell_*]

It is so difficult to get a craft to Neptune in a reasonable about of time (very high speeds are needed) and then slow it down enough to enter orbit (aerocapture appears to be required). You can probably solve the first problem by waiting to use a Jupiter gravity assist or a solar electric ion "boost stage". However, that aerocapture means that whatever you do will be a new design and new technology.

For those with access, there is a pretty interesting paper in press with Advances in Space Research:

A Study of Trajectories to the Neptune System Using Gravity Assists
Adv. Space Res., In Press, Accepted Manuscript, Available online 1 March 2007
C.R.H. Solórzano, A.A. Sukhanov and A.F.B.A. Prado

Abstract

At the present time, the search for the knowledge of our Solar System continues effective. NASA's Solar System Exploration theme listed a Neptune mission as one of its top priorities for the mid-term (2008-2013). From the technical point of view, gravity assist is a proven technique in interplanetary exploration, as exemplified by the missions Voyager, Galileo, and Cassini. Here, a mission to Neptune for the mid-term (2008-2020) is proposed, with the goal of studying several schemes for the mission. A direct transfer to Neptune is considered and also Venus, Earth, Jupiter, and Saturn gravity assists are used for the transfer to Neptune, which represent new contributions for a possible real mission. We show several schemes, including or not the braking maneuver near Neptune, in order to find a good compromise between the ΔV and the time of flight to Neptune. After that, a study is made to take advantage of an asteroid flyby opportunity, when the spacecraft passes by the main asteroid belt. Results for a mission that makes an asteroid flyby with the asteroid 1931 TD3 is shown.

I believe this paper was presented at the recent 2007 AAS/AIAA Space Flight Mechanics Meeting in Sedona, Arizona.

[dvandorn]

I hate to say this, but I really think that extensive exploration of the outer Solar System is going to have to wait for a new generation of propulsion technologies. Uranus and Neptune orbiters, in particular, are very, very difficult to do with our present propulsion technologies.

We need some form of constant-thrust propulsion that doesn't require tons and tons of propellant in order to get out to the outer System in months, not decades, and that allows us to brake into orbit around the outer planets. Frequent energetic maneuvering, and even breaking out of orbit to travel to another planet, are also capabilities that we're going to need to develop eventually.

As long as we're stuck with either big-push-then-lots-of-coasting chemical propulsion and constant-but-really-miniscule-thrust ion propulsion, we'll never be able to afford more than three or four flagship missions to the outer planets in any one person's lifetime. That's just not going to get it done.

-the other Doug

[Stephen]

It's sure easy to forget the downlink bitrate in particular when talking about these deep outer system missions. Lasercomm really needs to be developed for future Flagship-class forays beyond Saturn. Cassini may well be the last one of these that relies on RF...

Hmm. Is Cassini a "beyond Saturn" foray or an "at Saturn" foray? If the latter, then as yet there have been no Flagship-class missions beyond Saturn (unless you count Voyager).

But I digress...

Wasn't there going to be a trial a laser communications system on the Mars Telecommunications Orbiter that was due to be flown in 2009?

Now MTO has been cancelled there will probably not be a test flown until at least the mid-2010s (hopefully on the putative MSO-MTO mission). But that in turn means that Flagship-class missions are unlikely to be able to start using it until at least the later 2010s.

Which in turn suggests that any Flagship-class missions to or beyond Saturn which go into the pipeline between now and then will be unlikely to be using laser communications, at least as its primary communications systems.

I guess that's just one more reason why a Titan mission is unlikely to be jumping the queue in front of a mission to Europa.

======
Stephen

[JRehling]

I guess that's just one more reason why a Titan mission is unlikely to be jumping the queue in front of a mission to Europa.

There's one outstanding reason which is that the data from Cassini hasn't been digested yet. As a rough sketch of the exploration process, I'd say that it tends to take a few years to understand the data from the previous mission before you can solidly know which investigations to undertake with the next one. (At least, when a world's exploration is in the early stages. We're farther along with, eg, Moon, Mars, Venus, Jupiter.) If Cassini were to last til 2010, it would be fair to estimate that it won't be any sooner than 2015 before you could count on the community having pretty well modeled Titan from that data. A 2020 launch would be sort of a rush job.

I think Europa is ready for planning the mission (the better part of a decade after the most productive Galileo flybys), and Titan isn't even in the same point in the queue for the two of them to be "competing". I think it's a dead issue. Even if Titan were intrinsically more desirable to visit next, Europa's time in the spotlight can come and go before the next Titan mission should be launched, unless we don't care about whether or not it's well-designed...

[PhilHorzempa]

It is so difficult to get a craft to Neptune in a reasonable about of time (very high speeds are needed) and then slow it down enough to enter orbit (aerocapture appears to be required). You can probably solve the first problem by waiting to use a Jupiter gravity assist or a solar electric ion "boost stage". However, that aerocapture means that whatever you do will be a new design and new technology.

I believe that NASA has considered the development of aerocpature to be one
of the enabling technologies for Outer Planet Orbiters. However, if you examine
NASA's proposed FY 2008 budget, then you will notice some more bad news for
Unmanned Spaceflight from Mr. Griffin. Take a look at p.130 in the Full Budget,
(accessible on NASA's budget page) where there is a list of proposed budgets for
the New Millenium Program for the next few fiscal years.
Griffin plans to reduce funds for NMP from $90 million to $65 million in FY08.
This is followed by "going-out-of-business" budgets for FY90 and FY10. NMP receives
only about $35 million in each of those years. Apparently, Mike Griffin is planning to
eliminate yet another part of our country's efforts to explore the Solar System.
In addition, in the FY08 Budget Proposal, the plan to delay the next NMP mission,
ST-9, by 2 years is also mentioned. This is bureaucratic talk that means that NASA
is essentially cancelling ST-9, just as it has cancelled SIM, TPF and MSR.
The cancellation of ST-9 is important in this thread because one of the technologies
that was a candidate for that mission was an AEROBRAKING demonstration.
You can now kiss that one bye-bye, courtesy of Griffin and the VSE. Our missions
to Neptune and Uranus and Titan and Mars just slipped that much further into the future.

Another Phil

[algorimancer]

Of course, Nasa administrators commonly change with presidential administrations. We have only a couple of years of Michael Griffin to worry about, then hopefully we'll get someone in charge who appreciates the science of space exploration (no surprise that an ex-astronaut doesn't). Personally I think that unmanned exploration really ought to be getting at least fifty percent of the Nasa budget, and that the science budget ought to be immune from scavenging to fund the manned exploration program. Things change, budgets, priorities, technology, people. Just have to be patient

[nprev]

True enough...just wish there was some way to program & lock in funds long enough to completely cover missions like a Neptune orbiter. We're talking about a probable 30+ year program duration from concept development to EOM, and even if we disregard the Galileo & Cassini delay debacles, don't forget that there was a serious proposal to shut down Voyager 2 while still enroute to Uranus to "save" a few bucks.

Sorry for the OT excursion into policy, but we've already seen that this does become an extremely serious consideration for missions to the outer planets. Wish that NASA program funding could be blocked out like military construction (10-year planning horizon vs. annual appropriations...in other words, they have ten years to spend their pot of money for a given project & in the interim it's not supposed to be touched). Maybe TPS should do some digging in this area & try to influence some policy changes; obviously, there's a precedent under current US law.