No, I agree that the Atlas V is the best option. The trajectories achieved for NH and MRO were excellent, saving valuable fuel for future scientific efforts. I also don't think that Juno is necessarily "settling" with the Atlas V choice. I was only saddened to just find out that the rocket had its first problem--I'm still catching up on lots of old news that I missed while on two months of summer fieldwork.

Anyway, Atlas V is back on track with another successful launch.

http://www.space.com/missionlaunches/sfn-0...-countdown.html

The Ariane 5? It's launched closer to the equator so can take advantage of more centrifugal forces than a California launch.

And in the real world with real money and real national interests (that rightfully keep the $190m spend on the Juno LV within the US) ?

Doug

The Juno team has added a couple of new videos to their site. They aren't anything too high-tech, but they give a visual description of the mission.

http://juno.wisc.edu/index_whatsnew.html

BTW, and this is all public information, of course, the launch problem previously mentioned was with the Centaur upper stage, which cut off a few seconds too early. Problem traced to a new fuel valve design; they went back to the old one for the WGS-1 launch, which went flawlessly.

Are you interested in science or Boeing's profits? The ESA has no problem contracting certain launches out to Russia. It's not like Boeing is going to go bankrupt if they don't get the Juno launch. It's not like you're contracting the launch to North Korea, Europe is America's ally, and they have an equally capable launch vehicle and better launch position. NASA should take advantage of it if they can.

Actually - the Ariane V is a slightly less capable launch vehicle, from a better launch position, resulting in a similar performance.

I'm not going to start ( or allow ) a political debate here - but the fact of the matter is that US tax payers pay their taxes, some of which goes to NASA, so that America can do good science and exploration. As a US tax payer, is one going to be interested in science and engineering jobs in the USA, or in France?

The Ariane V is not significantly cheaper than the Atlas V, and any difference is probably offset entirely by figuring out how much of the cost of an Atlas V launch goes straight back to the US government as income tax.

Yes - ESA and NASA colaborate on projects ( SOHO, STEREO, C-H, JWST ) - but on a trade basis...we'll build a lander, you make the orbiter - or we'll make some instruments to fly, and you can use them sometimes, or we'll launch it if you let us use it for a while..... but NASA writing a cheque to Arianespace for a launch of an American project isn't going to happen, and nor should it. This entire debate is academic as we're now down a road whereby Juno IS launching on an Atlas V- fact. However - were we to wind back history 5 years and have a significant European contribution to the project in terms of instrumentation and scientists - then perhaps the responsibility of launching the mission could become a European affair (as is happening with JWST). Writing big trans-atlantic cheques just makes no sense, for either party, and is not a sensible way to spend the respective taxpayers money.


Doug

Doug's right...plus, of course, it is in the best interests of the US to keep its domestic launch capability afloat. There really aren't all that many launches per year globally, and US commercial interests already outsource a lot of them to Baikonur and/or Ariane, so even one or two domestic Atlas flights become critical to keep the market attractive enough for the big aerospace companies to remain in the business (esp. with the pending demise of the Delta II, which will hurt UMSF). The profit margin here is really pretty slim.

I notice that Falcon 9 is promising to deliver essentially the same payload to LEO as an Atlas V for the same price as a Delta II launch. If SpaceX truely pulls this off, it seems to me it'll make it hard for the big aerospace companies to stay in the game at all. But it could be GREAT for UMSF. :-)

--Greg

But remember, Delta IIs only look cheap in comparison with Delta IVs and Atlas Vs. We're still talking significant expense. The expense of launchers has driven a lot of commercial users to less costly -- and less reliable -- systems.

What we really need is some revolutionary new propulsion technologies that will make access to LEO a lot cheaper than can be accomplished through the sole use of chemical rockets. (And while I'm wishing, I ought to toss in a good thought for World Peace, too, I guess...? )

-the other Doug

Falcon 9 is 9.9 to 10.4 tons to LEO

Atlas V is 10.3 to 20.5 (25 if you include the Atlas V heavy) to LEO

So really - the Falcon 9 fits inbetween the Delta II and Atlas V in terms of performance ( something of a sweet spot I would say - MRO took the cheapest Atlas V.a job that could perhaps have been done by an F9 in the future)

Now it gets exciting with the Falcon 9 heavy...27.5 ton to LEO.


Doug

So the only argument against big checks crossing the Atlantic is national pride? I thought we were part of the larger scientific community. If the Atlas V is the best LV for Juno, so be it. But if the Europeans provide a more suitable vehicle, ie. cheaper and more effective, then why should American taxpayers and the scientific community pay more for less?

Like I said, a single launch is not make-or-break for American rocketry. Science launches make up a small portion of total space launches anyways.

If you make the rocket, why not use it? And if you stop using -- and making -- it,
you may regret it down the line, after it's too late. US business certainly has not
been adverse to exporting other jobs when it helps the bottom line!

It, along with 99.999% of all human activity, is also a matter of individual incentive. A politician who helps conduct legislation that provides jobs where his/her constituents live is more likely to please those constituents than a politician who watches or helps the same jobs go somewhere else. Ultimately, the money for all of these projects come from taxpayers=voters. They are on average less interested in science than in avoiding unemployment, local recessions, etc.

National federal funding rarely leaves the country in substantial quantities, and it is never highly popular when it does. Likewise, state funding rarely leaves the state it arises in, ditto on other levels.

If you had a single system of government that raised revenues on both sides of the Atlantic, then these considerations would become somewhat less relevant. As it is, they are virtually laws of physics.

No, national interests.

Pride doesn't enter into it.

I don't think we're going to get any where with this debate. At this point, I'm considering the LV issue closed and any further posts on it will be culled.

Doug

PS: Clearly Geographer can't read what I just posted. Posts culled = 1.

Is Jupiter the furthest target that a solar powered mission could reach? Jupiter used to require RTGs but advancing solar technology has made those unnecessary, at least for this medium cost mission. How many advances in solar technology can realistically be expected; could there eventually be a Uranus or Neptune mission with solar?

I'll be surprised if it's ever cost-effective to use solar beyond Jupiter, now that the political opposition in the US to RTG-powered vehicles has largely disappeared. Note that there wasn't a peep about New Horizons using an RTG.

--Greg

I expect it *IS* cost-effective to use solar beyond Jupiter.... for very "quiet" missions. You basically need solar-sail concentrators aimed at solar panels. Not the sort of thing to easily and accurately deploy from a folded-for-launch configuration. But very deep space observatories doing things like low frequency radio work or interplanetary weather stations or other spacecraft that do not do extensive maneuvering, especially attitude changes, could relitively easily use solar power. These might be assembled/deployed in high earth orbit... L5 or whatever, and sent outbound with ion engines.

There have been several proposals for a Saturn atmospheric probe mission in which the carrier spacecraft is solar powered. I believe that the mission is New Frontiers class.

I once calculated the energy available at Uranus for a craft using the largest solar arrays flown on interplanetary spacecraft. It was harder to figure out than the simple geometry of light intensity loss because solar arrays can be tweaked to perform better under (if I recall correctly) different temperature ranges. (It may have been different light levels; this was awhile ago.) I even doubled the size of the arrays. No go -- just not enough light.

However -- the new stirling low cost nuclear power supplies that NASA is considering for Discovery missions probably would enable a small Uranus craft with a probe or two in terms of power. The cost would probably still fill a New Frontiers budget. I suspect that you would still need a battery to handle peak power demands.

I am admitting that I am having problems thinking of missions within a Discovery price tag that would be *enabled* by the Stirling power supply. I can think of several -- network landers on Mars or rovers on Mars -- that would be easier with such a power supply. However, my understanding is that there are fairly few missions that need just 100-200W of power (I forget the exact power offered by this generator) and that don't require expensive launchers such as anything going to Jupiter or beyond. Perhaps I'm just not clever enough.

Noticed that too, and was pleasantly surprised; it's absolutely key.

I think that even if solar cell efficiency increases ridiculously (think it's around 40% right now), RTGs are still the only game in town for outer-planet missions. The recent ISS array deployment difficulty shows how much risk there is with very large arrays for UMSF (and no way to fix them, unless you get really lucky with respect to failure mode). Furthermore, all the articulation needed to maintain optimum power levels after achieving orbit around the target not only adds weight & even more mechanical complexity, but also requires a lot of power to accomplish; motor torque eats current like so many peanuts.

When you're talking very infrequent launch opportunities combined with decades of cruise time for Uranus & Neptune, I don't think we want to roll those dice...

New Horizons probably didn't get the media fanfare that Cassini did. Cassini was the biggest probe ever launched, going to explore big, pretty, ringed Saturn. And it had 3 RTGs. And it was making a flyby of Earth, which of course brought out the doom-n-gloom crowd. Someone at NASA/JPL would have had to screw up pretty badly to send Cassini plummeting into the ground during a routine gravitational-assist flyby.

New Horizons had one RTG, and it was on a high-speed one-way trip away from Earth. There probably were some complaints (some of the extremists probably think that saying "plutonium" is enough to cause cancer), but they just didn't get much attention on the launch of New Horizons.

I don't mean to be political here, but I do wonder if some of it had to do with the fact that some of the anti-RTG folks may have realized that if the Clinton administration wouldn't stop a probe with three RTGs that would make an earth flyby, there wasn't a chance in hell the Bush administration would block a probe over one RTG with no earth flyby.

Back on the solar power for outer planets missions.

From what I understand, the ammount of power produced by solar arrays at Jupiter are practical (for some missions), but solar arrays degrade if they spend too much time in the Jovian radiation belts. Juno avoids this problem because its highly elliptical, polar orbit keeps it out of the radiation for most of the orbit.

Similarly, the furthur out your Jupiter periapsis, the less your total exposure. I think some of the orbiters being conceptualized for the Laplace mission have solar power since they have lower power requirements and stay furthur out. (I could be wrong about this, and the mission will keep evolving over the next couple years during the on going studies).

As for array deployment problems, I don't think it is a good apples to apples comparison to bring up the ISS troubles. Those arrays are huge, and involve a huge number of folds. If you look at ships like Juno, there are only a few panels to be unfolded. That being said, it's true that RPGs tend to have fewer deployment failure scenarios.

Hubble's SA1 arrays were much smaller than the ISS arrays, yet the astronauts had to toss one overboard when it failed to retract...

My whole point in bringing up the ISS array prob was to illustrate that minimizing mechanical complexity for long-duration, rare-window missions is a wise design heuristic. FWIW, I think solar power is certainly a viable option for some Jupiter & even some Saturn missions (though definitely setting hard constraints on feasible science objectives for either destination), but you very well might be talking about ISS-sized arrays or better for any place further out, which just doesn't seem prudent, practical, or affordable.

That's why RTGs are very robust; no moving parts. Well, unless you're talking Stirling RTGs. I don't know how I feel about the idea of having moving parts like that on long duration missions, even if the RTGs end up more efficient than old designs.

Oh, there was a peep or two from the usual hard core anti-nuke crowd. Google "space_4_peace" w/o the underscores.

Some of their demands so sadly illustrate a lack of any effort to understand what they are saying, e.g., after the Cassini SOI, they wanted Cassini to be redirected to impact the sun to avoid danger of it coming back to Earth. Some of these people would believe that NH was sending plutonium back to Pluto.

There were several anti-nuke letters in the NH RTG EIS (environmental impact statement). Which leads back to the topic of this thread since the EIS discusses alternate power options, e.g. solar, for NH.

Since RTG's are critical to Outer-planet exploration (at least), I do think it's really on-topic to seriously discuss the things that might limit their use -- even thought that involves talking a bit about.....CUT

..... things banned at UMSF. Sorry Greg. Rules are rules. : Doug

article at space.com regarding the Juno mission.

Here's the merchandise:
http://www.bookstore.caltech.edu/jpllab/sh...p;catalog_id=39

NASA Prepares for New Juno Mission to Jupiter

Is there any possibility of JunoCam (image of instruments on spacecraft here) getting images of the Galilean satellites of any decent resolution?

Or would that be a bad thing due to the solar panel requirements?

-Mike

[EDIT: Already discussed earlier in this thread (multiple times, best response here).]

Fortunately, JRehling is mistaken. In fact, Juno's orbit won't be fixed, it will rotate slowly as shown on the picture.
Baseline mission assumes 32 orbits in all. On 12-13th orbit Juno will intersect Jupiter's equatorial plane somewhere near the Callisto orbit, on 20-21th orbit close approach to Ganymede will be possible. In case of the extended mission even Europa can be explored (if only Juno can survive in the radiation belts).
I don't know whether such a "flybys" ever planned, but approaches to Galileans will be certainly much more close than those calculated by JRehling

And will Callisto be anywhere near Juno at that time? An orbit crossing doesn't mean a close encounter.

Yes, but if we have an opportunity for encounter why not make use of it? why not to synchronize orbits?

Because it's not a part of the mission goals and could potentially either take enormous amounts of delta-v or lead to unacceptable constraints on mission timing?

Also, Junocam only has a requirement to last for seven orbits.

Ouch! That's disappointing to hear. I realise though that this is a science mission, not a tourism mission... but images keep public interest alive.
Requirement to last for seven orbits... I remember hearing 90 days as the designed lifetime of the MER rovers. (of course Jupiter is a different story, radiation and such X_X)

I remember seeing a PDF of the instruments on Juno, and one page showed the power budget and how much each instrument would use during perijove and during cruise through apojove. JunoCam was listed as 0 watts for the entire cruise segment of the orbit. This makes it seem like it won't be turned on at all anywhere but closest approach.

Since the primary goal is polar imaging and the pole crossings are not typically at closest approach, this is not accurate; probably what you saw was a placeholder since we take little power and only image for tens of seconds at a time.

If someone wants to simulate the Juno orbit (public information is rather thin but see http://juno.wisc.edu/mission.html ) and see if any satellite observations are possible given that the spacecraft is spinning, I'd be happy to advocate such observations.

Has the team looked into the feasibility of imaging the cloud decks at perijove? Would the motion just result in a blur?

Junocam already has to work with the spacecraft spin. Orbital motion is only a small fraction of that, so perijove imaging would work fine.

Do you know what the resolution of the cloud tops will be at perijove?

15km/pixel

I think it's around 4 km/pixel. The 15 km/pix is for the polar case when perijove is near the equator.

Whoa, 4km/pix thats news to me; thanks for the info mcaplinger.

Is it too early to know if Juno might make an asteroid flyby or two? (i.e. Galileo style)

My understanding was that Juno's main focus was on Jupiter itself and its interior. I thought that the JunoCam was a sort of afterthought, for public outreach and schoolkids, becuase the Juno probe will be spinning and the imaging would be pretty crude, not unlike the Pioneers in the mid 1970s. How can meaningful science be achieved by trying to image the moons?

"Pretty crude"? I'm insulted. Despite the spacecraft spin. the Junocam images should be extremely good; comparable to or better than the best Galileo images of Jupiter. That said, we'd have to get pretty close to one of the satellites to get good images, because Junocam has a wide field of view.

As for asteroid flybys: I can't speak for the rest of the payload but for any plausible flyby distance, asteroids would be barely resolved from points by Junocam.

I believe that the best Galileo cloud deck images were in the 15-20km range partially because of the distance of most of Galileo's perijoves. When GLL did get in close, it tended to do pixel binning as a counter measure to radiation caused noise.

JunoCam will may provide more images of the cloud deck and at higher resolution than the Galileo mission. If it can achieve 4km/pixel at perijove, I believe that would be the highest resolution of the cloud deck ever. I just wish there was a near infrared band -- would have added a lot of science.

As for imaging satellites, the timing of Juno's orbits is selected to enable even spacing of Jovian longitudes for gravity mapping. Targeting a satellite for what would be fairly low resolution images (because JunoCam is a wide angle camera) would mess up a key goal of the Juno mission.

"Pretty crude"? I'm insulted. Despite the spacecraft spin. the Junocam images should be extremely good; comparable to or better than the best Galileo images of Jupiter. That said, we'd have to get pretty close to one of the satellites to get good images, because Junocam has a wide field of view.

As for asteroid flybys: I can't speak for the rest of the payload but for any plausible flyby distance, asteroids would be barely resolved from points by Junocam.

I apologise and stand corrcted Mcaplinger. Do you work on the Juno mission yourself? I didn't realise that Junocam would have 15km resolution. That's very adequate for tracking atmospheric changes and some moon imaging, like monitoring volcanic activity on Io.

Question: How does Junocam work if Juno itself is spinning? Is it a type of scanning photometer like on Pioneers 10 and 11?