Missions to the Ice Giants Uranus and Neptune

[clongton]

... for a Uranus-KBO option is that, at least without a major trajectory burn, most of the good KBOs, like Haumea or Eris, are on the opposite side of the solar system and better accessible from literally any of the other gas giants.

Exactly. That's why I am not in favor of coupling Kuiper belt objects to this study. BOTH ice giants should get orbiters with all the science that implies. It really sucks the big one that they want to de-emphasize Uranus, just because they can. Kuiper belt objects deserve their own dedicated missions. Don't sacrifice Uranus science for what is to me just an ego trip to fly past  more distant objects. I said before and I say again; money is **NOT** a hindrance. Congress will spend money like a leaking sieve if it wants to. There's more money available than even Congress can spend because if they want more they just print it.

[jbenton]

... for a Uranus-KBO option is that, at least without a major trajectory burn, most of the good KBOs, like Haumea or Eris, are on the opposite side of the solar system and better accessible from literally any of the other gas giants.

Exactly. That's why I am not in favor of coupling Kuiper belt objects to this study. BOTH ice giants should get orbiters with all the science that implies. It really sucks the big one that they want to de-emphasize Uranus, just because they can. Kuiper belt objects deserve their own dedicated missions. Don't sacrifice Uranus science for what is to me just an ego trip to fly past  more distant objects. I said before and I say again; money is **NOT** a hindrance. Congress will spend money like a leaking sieve if it wants to. There's more money available than even Congress can spend because if they want more they just print it.

If they want to do good science at the two Ice Giants and at several Dwarf Planets, it may be better to launch each orbiter with an ESPA ring mounting 6 small-sats each for Dwarf Planet flybys:

http://futureplanets.blogspot.com/2013/08/small-could-be-beautiful-planetary.html


Another interesting idea is assisting observations of Uranus' moons with CubeSats:
http://futureplanets.blogspot.com/2013/10/cubesats-to-planets-ive-seen-evolution.html

[redliox]

If they want to do good science at the two Ice Giants and at several Dwarf Planets, it may be better to launch each orbiter with an ESPA ring mounting 6 small-sats each for Dwarf Planet flybys:

http://futureplanets.blogspot.com/2013/08/small-could-be-beautiful-planetary.html

Intriguing, tricky, yet ambitious.  Given how Dwarfs and KBOs are the next batch of "sky vermin," it would be fitting to send equally numerous and diminutive probes to investigate them.  This would also get around the problem of compromising the orbiter missions both Ice Giants require.  The trick is can a cubesat survive long enough post-Neptune or post-Uranus to reach one major KBO; I would imagine it'd be lucky if a cubesat can include one or two New Horizon-esque instruments let alone the technical challenges.

On a side note, because of the Jupiter or Earth GAs required en route to reach the Ice Giants, the usual launch ring might not work.  However, some options for the Ice Giants suggest a SEP stage which flies along at least a lil past Jupiter; I could see a cubesat or 2 attached to this stage (which does get disposed of eventually); a KBO-sat could utilize this without bothering the main probes.

[ncb1397]

If you want to investigate small objects in the outer solar system, Uranus and Neptune are home to at least 41 of them. Why compromise comprehensive long term coverage in order to add in another one and make it 42. Why not flyby an asteroid on the way out or something (i.e. Galileo's flyby of Gaspra).

[jbenton]

If they want to do good science at the two Ice Giants and at several Dwarf Planets, it may be better to launch each orbiter with an ESPA ring mounting 6 small-sats each for Dwarf Planet flybys:

http://futureplanets.blogspot.com/2013/08/small-could-be-beautiful-planetary.html

...The trick is can a cubesat survive long enough post-Neptune or post-Uranus to reach one major KBO; I would imagine it'd be lucky if a cubesat can include one or two New Horizon-esque instruments let alone the technical challenges.

Just to clarify, the first article isn't about cubesats, but "small-sats" specifically. 100kg class. The idea presented is that you could give such a sat a mini-RTG and a small ion thruster and it could piggyback off of a GTO launch and send itself all the way to a centaur. I just thought NASA could kick that up a notch.

If you want to investigate small objects in the outer solar system, Uranus and Neptune are home to at least 41 of them. Why compromise comprehensive long term coverage in order to add in another one and make it 42. Why not flyby an asteroid on the way out or something (i.e. Galileo's flyby of Gaspra).

The second article mentioned using cubesats to complement the main orbiter, specifically for Uranus. The thought was at least 5 of the moons were interesting enough that they may want more eyes on target per flyby.

[zubenelgenubi]

<snip>
Why not flyby an asteroid on the way out or something (i.e. Galileo's flyby of Gaspra).

I see no reason why a search for suitable asteroids along proposed trajectories would not be done during mission planning.

However, there might be resources saved if the probe remains quiescent during passage through the asteroid belt?

On the third hand, an asteroid flyby would be a good test of the instruments and team.

[Blackstar]

Let's keep something in mind: EVERYTHING is a trade-off in multiple dimensions of mass, power, cost, schedule, operations, and risk.

So while the idea of adding smallsats to an ice giants mission might seem attractive at first glance, you have to consider how that is going to impact all the other aspects of the mission. If you add a smallsat, that takes mass away from something else, like fuel or redundancy. Is adding that smallsat worth shortening your main mission by a year?

And consider this simple fact--that smallsat is going to need its own power system and it is highly unlikely to be an RTG. So if it's a battery, then the smallsat has a short lifetime, probably measured in terms of days. Do you really want to trade tens of kilograms of mass for a mission that is only going to last a few days? What science is worth that kind of trade? The only missions that rise up in these kinds of evaluations are atmospheric probes and maybe a moon lander (particularly for Triton). Everything else is usually not even considered.

[TripleSeven]

Let's keep something in mind: EVERYTHING is a trade-off in multiple dimensions of mass, power, cost, schedule, operations, and risk.

So while the idea of adding smallsats to an ice giants mission might seem attractive at first glance, you have to consider how that is going to impact all the other aspects of the mission. If you add a smallsat, that takes mass away from something else, like fuel or redundancy. Is adding that smallsat worth shortening your main mission by a year?

And consider this simple fact--that smallsat is going to need its own power system and it is highly unlikely to be an RTG. So if it's a battery, then the smallsat has a short lifetime, probably measured in terms of days. Do you really want to trade tens of kilograms of mass for a mission that is only going to last a few days? What science is worth that kind of trade? The only missions that rise up in these kinds of evaluations are atmospheric probes and maybe a moon lander (particularly for Triton). Everything else is usually not even considered.

You observer things well and seem pretty tied into the planetary folks...does it surprise you that none of the design/scomments so far seem to be interesting in trying new technology (ie expandable, blowup etc) antennas to change the link equation?

I realize the Gallileo experience was traumatic

I agree with you on the small sats...for the outplanets they make little sense.

[Blackstar]

You observer things well and seem pretty tied into the planetary folks...does it surprise you that none of the design/scomments so far seem to be interesting in trying new technology (ie expandable, blowup etc) antennas to change the link equation?

Go get a copy of the 2011 planetary science decadal survey here:

https://www.nap.edu/catalog/13117/vision-and-voyages-for-planetary-science-in-the-decade-2013-2022

You can download that for free as a guest. Look in the sections on the ice giants science and mission proposals. That decadal survey is the guidebook (bible) for the NASA planetary program. You'll hear more about it next week. When the decadal survey team discussed ice giants missions they came to a pretty clear conclusion: the science is compelling and no new technology is necessary. If you took Cassini and put it in orbit around Uranus, the science results would be amazing, even with early 1990s era technology. Same for New Horizons, with its fewer instruments.

And developing new technology has risks (cost, time, possibility of failure). So the community thought this out and it was pretty simple to them. They just want a mission, and it is more likely they will get a mission if the cost is kept down and nobody tries to do anything complex. It's an easy calculation driven by the desire to just do it.

I think it's also the case that it's hard to see how any new technology would substantially increase the science results. There are certain targets, like Venus or Europa, where you may need technology to get science results. But with the ice giants, orbiting them is not any different than orbiting Saturn, and most of the instruments you would use there are common to many different kinds of spacecraft (like imagers, spectrometers, magnetosphere instruments).

[Blackstar]

There was one new technology that popped up as useful for Neptune, and that was aerocapture. Doing that at Neptune is uniquely different than doing it at other planets, and we haven't done it at other planets yet anyway.

I think that one other area that would be challenging would be a Triton lander. That would require some autonomous capability that we haven't really demonstrated. Probably not all that difficult, but harder and it would have to be proven out. As much as I think a Triton lander (or rover?) would be cool, I don't see it happening. The cost and complexity is rather high.


Additional note: there has been a NIAC-funded study of a Triton hopper. That's a neat idea, but the technology readiness is really low. I don't see that happening for decades.

[jongoff]

You know, trying to rigidly enforce a topic when people are having a discussion is a good way to stifle that discussion and kill the thread for good. The electrons are free, and if we wander around a bit and then come back to the topic, nobody gets hurt, no kittens will cry, and maybe, just maybe, we'll all learn something about what it is to be on this big journey we call Life.

I should put this in my sig line...

[TripleSeven]

You observer things well and seem pretty tied into the planetary folks...does it surprise you that none of the design/scomments so far seem to be interesting in trying new technology (ie expandable, blowup etc) antennas to change the link equation?

Go get a copy of the 2011 planetary science decadal survey here:

https://www.nap.edu/catalog/13117/vision-and-voyages-for-planetary-science-in-the-decade-2013-2022

You can download that for free as a guest. Look in the sections on the ice giants science and mission proposals. That decadal survey is the guidebook (bible) for the NASA planetary program. You'll hear more about it next week. When the decadal survey team discussed ice giants missions they came to a pretty clear conclusion: the science is compelling and no new technology is necessary. If you took Cassini and put it in orbit around Uranus, the science results would be amazing, even with early 1990s era technology. Same for New Horizons, with its fewer instruments.

And developing new technology has risks (cost, time, possibility of failure). So the community thought this out and it was pretty simple to them. They just want a mission, and it is more likely they will get a mission if the cost is kept down and nobody tries to do anything complex. It's an easy calculation driven by the desire to just do it.

I think it's also the case that it's hard to see how any new technology would substantially increase the science results. There are certain targets, like Venus or Europa, where you may need technology to get science results. But with the ice giants, orbiting them is not any different than orbiting Saturn, and most of the instruments you would use there are common to many different kinds of spacecraft (like imagers, spectrometers, magnetosphere instruments).

thank you for your comments.  I was just curious

I am sure that any probe to Neptune or Uranus with even Cassini technology is a vast increase of knowledge...and I am sure with the "era of big probes to the outer planets" over for a tad...the science crowd is eager for something.

thanks again

[JH]

Between Europa Clipper, JUICE, the Ultima Thule encounter, Lucy, and the significant unplanned extension of JUNO, the outer planets community is feeling less low level dread than they were a few years ago. This is about planning what's next (very necessary in this case, due to the long travel times involved for the missions to the Ice Giants and KBOs).

[TripleSeven]

Between Europa Clipper, JUICE, the Ultima Thule encounter, Lucy, and the significant unplanned extension of JUNO, the outer planets community is feeling less low level dread than they were a few years ago. This is about planning what's next (very necessary in this case, due to the long travel times involved for the missions to the Ice Giants and KBOs).

Europa clipper...yeah thats gonna happen

[JH]

Yes, it is. You might be thinking of the Europa Lander (which you'll notice I didn't bother to mention).

[vjkane]

... for a Uranus-KBO option is that, at least without a major trajectory burn, most of the good KBOs, like Haumea or Eris, are on the opposite side of the solar system and better accessible from literally any of the other gas giants.

Exactly. That's why I am not in favor of coupling Kuiper belt objects to this study. BOTH ice giants should get orbiters with all the science that implies. It really sucks the big one that they want to de-emphasize Uranus, just because they can. Kuiper belt objects deserve their own dedicated missions. Don't sacrifice Uranus science for what is to me just an ego trip to fly past  more distant objects. I said before and I say again; money is **NOT** a hindrance. Congress will spend money like a leaking sieve if it wants to. There's more money available than even Congress can spend because if they want more they just print it.

If they want to do good science at the two Ice Giants and at several Dwarf Planets, it may be better to launch each orbiter with an ESPA ring mounting 6 small-sats each for Dwarf Planet flybys:

http://futureplanets.blogspot.com/2013/08/small-could-be-beautiful-planetary.html


Another interesting idea is assisting observations of Uranus' moons with CubeSats:
http://futureplanets.blogspot.com/2013/10/cubesats-to-planets-ive-seen-evolution.html

SmallSats wouldn't make sense for the outer solar system, especially for flying to their own destination.  There are no small space-qualified RTGs.  The small antennas and limited power from a small RTG, if they existed, means the data that could be sent back would be minuscule.

[Comga]

(snip)
I think it's also the case that it's hard to see how any new technology would substantially increase the science results. There are certain targets, like Venus or Europa, where you may need technology to get science results. But with the ice giants, orbiting them is not any different than orbiting Saturn, and most of the instruments you would use there are common to many different kinds of spacecraft (like imagers, spectrometers, magnetosphere instruments).

As I see it, there was a new technology that would have had a major impact on outer planet missions:  The ASRG.

More power from each scarce pellet of Plutonium, or the same amount of power from a smaller fuel load and generator.

There would have been a number of missions, like continuously thrusting ion engine missions that would spiral out and slip into orbit at their destination.  I think some studies of these type of missions are referenced way, way back in this thread.

But we blew that.  The ASRG program failed.
We are left with the MMRTG, with its 110 W initial output.
It's not clear if we could even fuel a 300 W GPHS‐RTG systems as used for Cassini or (partially fueled to 245W) New Horizons.

And you discussed the issue of power, where a battery powered sub probe would be a huge burden and hard to justify, with the possible exception of entry probes like on Galilieo or Huygens, which would relay their data through the main probe.  Sub-probes can't go far.

For the foreseeable future missions to the outer planets will use a small number of these RTG sources. 

And for the poster who wondered "how much less capable the thrusters have to be to NOT go into orbit" please do a few calculations with the rocket equation.  With many km/sec needed to brake from a fast (<10 yr) approach trajectory to Neptune or Uranus, only a small fraction of the approach mass is left in orbit.  I heard one proposal for a Pluto orbiter had a probe half the mass of New Horizons and an Earth departure mass an order of magnitude larger. 
Orbiting gas giants is very hard to do.

edit: what vjkane said....

[AegeanBlue]

ASRG is still getting developed. Last week there was news that they managed to get the piston working for 12 straight years now, albeit with a generic heat source rather than a radioactive heat source. It is still years away from a flight model but there is, literally in the back burner, some development still taking place. JPL is developing the much lower risk eMMRTG which will use less Plutonium and last longer than the current MMRTG. At the February OPAG there was an update:

https://www.lpi.usra.edu/opag/meetings/feb2018/presentations/Zakrajsek.pdf

[Blackstar]

As I see it, there was a new technology that would have had a major impact on outer planet missions:  The ASRG.

An ASRG would not make an ice giants mission better. It would have only reduced the Pu-238 requirement, not enhanced the science.

Now all the other technologies, like imagers, spectrometers, electronics, etc., will still advance on their own. There will be a better imager 10 years from now compared to today. But the science community largely decided that nothing entirely new is necessary to do this mission. A 30-year old imager at Uranus would provide great science we don't have today.

[vjkane]

ASRG is still getting developed. Last week there was news that they managed to get the piston working for 12 straight years now, albeit with a generic heat source rather than a radioactive heat source. It is still years away from a flight model but there is, literally in the back burner, some development still taking place. JPL is developing the much lower risk eMMRTG which will use less Plutonium and last longer than the current MMRTG. At the February OPAG there was an update:

https://www.lpi.usra.edu/opag/meetings/feb2018/presentations/Zakrajsek.pdf

The enhanced MMRTG (eMMRTG) will not use less Pu.  Instead, it uses new thermoelectric couples that are both somewhat more efficient at the beginning of the mission but much more importantly degrade more slowly so 50% more power is available late in long missions.  eMMRTGs were, as I recall, one of only a couple of so new technologies the ice giant study team deemed enabling.  (I believe that heat shielding material for an atmospheric probe was the other technology.)  Flight times to ice giants are long and you'd like to have many years of operation there.  Even at Mars they would be useful.  If you read presentations on future plans for Curiosity, they are beginning to talk about the need for power management in a few years as the MMRTG power output drops.

Unfortunately, if selected, the Dragonfly mission will just miss out on being able to use an eMMTRG if the latter's development schedule holds.