Why hasn't there been a dedicated mission to an ice giant?

[Unstung]

Voyager 2 only made it to Uranus and Neptune because it was in good shape yet not part of the plan instead of a Pluto flyby, IIRC. Science still hardly knows anything about those two planets, with most of the information coming from Voyager 2. The flybys showed us there is still much to know about the two planets ranging from Neptune's moon Triton to Uranus' magnetic field. Currently Cassini is still orbiting Saturn and Juno is going to Jupiter. Multiple other missions have visited those planets; the "grand tour" only included Jupiter and Saturn I believe and Cassini was launched well over a decade ago. Even New Horizons will visit Pluto because of its short-lived atmosphere.

However, no probe was ever planned to fly by the two "ice giants." I wonder why this is. Surely the Voyager craft proved the endurance of interplanetary probes. Many more well-known proposals to visit the two closer gas giants exist and their moons (which are still of great interest nonetheless).

I discovered a few months ago while searching this subject about a mission supported by over 100 scientists called the Uranus Pathfinder (although a horrible sounding name in English). Despite the backing, it might launch in 2021 and take quite a long cruise to Uranus (arriving half a century after Voyager 2); but what do you expect; under a relatively small budget - 400 million Pounds (compared to Juno and Cassini, as examples). I would consider a mission like this to be a higher priority and should have possessed scientific interest for many years; maybe even something with a lander like the Huygens probe destined for Triton.

Maybe NASA just deserves more funding or to allocate more to science rather than failed manned spaceflight projects. The agency, of course, hardly gets anything compared to the overall budget yet has great potential especially for missions like these. I still cannot see why I haven't found any other missions to an ice giant given serious thought.


http://newswatch.nationalgeographic.com/2011/01/03/europe_asks_to_probe_uranus/
http://news.discovery.com/space/uranus-pathfinder-mission-to-the-mysterious-ice-giant.html

 

[SiberianTiger]

Space is vast... Have patience. And mind

 

[Wishbone]

It makes no sense to plan missions which will come to fruition only after the death of principal investigators. Conversely, it takes a lot of delta-V to ensure speedy transit and capture of a with a meaningful set of instruments. When space agencies are faced with choice between sending (say) three probes to Mars and one probe to Uranus, they would behave rationally by choosing Mars, not only because of higher absolute payoff, but also because of lower risk when sending several missions instead of betting on one.

 

[agentgonzo]

Conversely, it takes a lot of delta-V to ensure speedy transit and capture of a [probe] with a meaningful set of instruments.

This is also compounded by the problem that if you want to use gravitational assists, you're basically going to have to go past Jupiter, and the alignment of Jupiter for this doesn't happen that often.

For instance, to get to Saturn we sent the pioneers and Voyagers through on one alignment of the planets. We sent Cassini-Huygens through on the very next alignment. They don't come up particularly often - Jupiter takes 12 (earth) years to orbit the sun and get back into alignment.

There have been easier and better targets to get spacecraft to previously.

 

[Unstung]

This is also compounded by the problem that if you want to use gravitational assists, you're basically going to have to go past Jupiter, and the alignment of Jupiter for this doesn't happen that often.

For instance, to get to Saturn we sent the pioneers and Voyagers through on one alignment of the planets. We sent Cassini-Huygens through on the very next alignment. They don't come up particularly often - Jupiter takes 12 (earth) years to orbit the sun and get back into alignment.

There have been easier and better targets to get spacecraft to previously.

I keep forgetting the alignment; 'Pathfinder is must preform a gravity assist at Jupiter. Hm, waiting for an alignment between Earth, Jupiter, Uranus and any other required planets must take a while. But why spend relatively a small amount on a mission that is so beneficial and so rare? It's quite an opportunity. (See last paragraph.)

As for better targets, the ice giants are still significant and we know little about them. NASA has already performed many successful flybys to reach their destinations for decades (even ones as complicated as MESSENGER or Cassini), so insertion shouldn't be a problem when working with NASA. This mission shouldn't be particularly more difficult.

It makes no sense to plan missions which will come to fruition only after the death of principal investigators. Conversely, it takes a lot of delta-V to ensure speedy transit and capture of a with a meaningful set of instruments. When space agencies are faced with choice between sending (say) three probes to Mars and one probe to Uranus, they would behave rationally by choosing Mars, not only because of higher absolute payoff, but also because of lower risk when sending several missions instead of betting on one.

I doubt it would be any different for the investigators to launch in 2021 or a few decades earlier. The 15-year cruise to Uranus shouldn't kill any sufficiently young person.

New Horizons passed the orbit of Uranus in five so propellant is definitely a concern (as I said, "but what do you expect" referencing its cruise time. I'll be much older in 2036 which sounds depressing). Will it be using an ion thruster? Aerobraking has already been proven, but is it practical or possible to use considering the atmosphere and gravity of Uranus.

The 'Pathfinder is only allotted 400 million Pounds, which is eclipsed by the budget for the MSL, a single martin rover ($2.3 billion). Juno is over $1 billion yet will destroy itself after only a year of research. 'Pathfinder certainly musn't be one of the more advanced probes with the most spectacular array of instruments.

 

[RisingFury]

The alignment comes about once every 15 years or so, but getting the probe to the target is easy compared to capturing it once it arrives there.

New Horizons is RACING towards Pluto and still it'll be 10 years from launch to arrival. Once it gets to Pluto, it will have about 30 minutes to do the science before the opportunity is lost.

If you want to capture you need to arrive at the planet at the lowest possible velocity. That means it'll take a lot of time to get there. Cassini-Huygens took almost 7 years from launch to orbit insertion and the mission is going now for another 7. Such missions are tough to execute.

 

[T.Neo]

I suggest superduper nuclear-electric propulsion for space probes! :hmm:

 

[RisingFury]

I suggest superduper nuclear-electric propulsion for space probes! :hmm:

Yea, and what would the power source be?
Solar panels are pitiful at Jupiter, RTG is pitiful everywhere...

 

[Unstung]

The alignment comes about once every 15 years or so, but getting the probe to the target is easy compared to capturing it once it arrives there.

New Horizons is RACING towards Pluto and still it'll be 10 years from launch to arrival. Once it gets to Pluto, it will have about 30 minutes to do the science before the opportunity is lost.

If you want to capture you need to arrive at the planet at the lowest possible velocity. That means it'll take a lot of time to get there. Cassini-Huygens took almost 7 years from launch to orbit insertion and the mission is going now for another 7. Such missions are tough to execute.

I was saying having a shorter transit time only has sentimental value. Of course it needs to go slower. New Horizons has a date with Pluto's atmosphere anyways.

If the proper alignment only takes fifteen years, that means there would have been two other opportunities between Voyager 2 and Uranus Pathfinder. This makes me revert to my original question: why hasn't there been a dedicated mission to an ice giant?

 

[T.Neo]

Yea, and what would the power source be?
Solar panels are pitiful at Jupiter, RTG is pitiful everywhere...

Nuclear. As in fission.

[ame="http://en.wikipedia.org/wiki/Jupiter_Icy_Moons_Orbiter"]JIMO[/ame] would have used nuclear fission. In addition to powering its propulsion system, the reactor could apparently have provided "opportunities like flying a full scale ice-penetrating radar system and providing a strong, high-bandwidth data transmitter".

Cancelled for the VSE. What a pity.

 

[RisingFury]

I was saying having a shorter transit time only has sentimental value.

No, it's not just sentimental. Spacecraft are designed to survive a certain time in space and it's difficult to create equipment that survives for a long time. The problem is as much an engineering one.

Processors, electronics and measurement equipment is exposed to radiation, power source degrades (RTGs expire), there's increased risk of collision with a micro-asteroid, increased risk of mechanical failures,...

Just recently the Akatsuki JAXA mission failed to enter Venusian orbit after spending only months in space - just imagine the disaster if Cassini failed to enter orbit!

why hasn't there been a dedicated mission to an ice giant?

Because it's hard to get the probe there and because it's hard for it to STOP there. If you're gonna design expensive equipment, you won't waste it on a flyby.

 

[Unstung]

Yes, the RTGs don't last forever but quite a while and their decreasing output over time is predictable. Voyager's still running, which is nice. I don't think of every aspect while writing these but I'm sure a decade-plus transit won't be a colossal concern to the RTGs with the longevity of other probes.

Just recently the Akatsuki JAXA mission failed to enter Venusian orbit after spending only months in space - just imagine the disaster if Cassini failed to enter orbit!

I know that; it's currently in hibernation until Venus can catch up to it in a few years. JAXA has much less experience than NASA. It seems to have disappeared from the news since so I can't tell how frustrated JAXA was.

Because it's hard to get the probe there and because it's hard for it to STOP there. If you're gonna design expensive equipment, you won't waste it on a flyby.

We've already done it with Saturn, Jupiter, Mercury, Venus, Vesta, and so on. It's disappointing how Uranus and Neptune are such low priorities.

EDIT: I just found this article. For NASA, such a mission would cost around $2 billion. Of course, I would think it's worth it (since the next chance is in another fifteen years from then). Congress, on the other hand, is too busy wasting money and playing political games.

 

[Ark]

Money, the same reason we haven't done a Mars sample return or a Europa submersible or any of the other things we really need to do.

Though with Dawn proving how well ion propulsion works, you would think we would be putting that drive system in probes left and right.

 

[Unstung]

Money, the same reason we haven't done a Mars sample return or a Europa submersible or any of the other things we really need to do.

Though with Dawn proving how well ion propulsion works, you would think we would be putting that drive system in probes left and right.

Ironically, a Mars sample return and Europa orbiter are the top two on NASA list, according to the article I linked. I don't see how a seemingly even more risky mission - returning some rocks from Mars - is worth it over an orbiter of Uranus like Cassini. Hell, since we're returning samples from Mars, why bother sending a few missions there (assuming they aren't canceled)? NASA does a better job at unmanned exploration anyways.

 

[Tychonaut]

Have you checked out this page? While most of those mission concepts will never fly, at least not this decade, they make for interesting reading.

 

[Wishbone]

Re: Mars sample return. The most intriguing space-related task nowadays (and for 30-40 years ahead) is searching for life outside Earth. This is the reason why getting samples back from Mars (where liquid water has been proven to exist) is top of the list, not missions to ice giants.

EDIT: The payoff from MSR is very uncertain. With top regolith layers sterilized, it is quite probable that picking a pound of rocks at random will not find signs of life. Deep intelligent drilling is beyond a simple robotic mission.

 

[Unstung]

Hm, I recognize some of those missions. All of them would be nice of course, but I still prefer the Uranus mission. You can get anybody up to speed with everything known about Uranus on the back of an envelope, but maybe that's a slight exaggeration.

I hope the Uranus orbiter, although third priority, will make it as a flagship mission. We have New Horizons, Juno, and the MSL this decade (but all are cheaper than the three 2013-2022 missions), so hopefully there will be another three over the next ten years. I'm strongly in favor of the Uranus mission being second in priority; a Mars sample return mission sounds even more complicated and Mars gets much more attention. I'm glad for the Europa mission, however.

I've read about the use of solar panels on an Uranus orbiter. That sounds outrageous.

EDIT: As you said, even finding life by drilling a bit is uncertain. Much more can be learned for over a billion less by sending something to Uranus. There are collaborations around for the Jupiter and Mars missions, but none for Uranus which makes it less likely unfortunately. I'm betting against the SLS, but if NASA is planning for it, why bother spending a few billion to pick some rocks? Samples are surely covered in the new manned exploration project.

 

[Wishbone]

I've read about the use of solar panels on an Uranus orbiter. That sounds outrageous.

:facepalm:

EDIT: As you said, even finding life by drilling a bit is uncertain. Much more can be learned for over a billion less by sending something to Uranus. There are collaborations around for the Jupiter and Mars missions, but none for Uranus which makes it less likely unfortunately. I'm betting against the SLS, but if NASA is planning for it, why bother spending a few billion to pick some rocks? Samples are surely covered in the new manned exploration project.

As a matter of fact, robotic sample return has so far been a pre-requisite for a manned martian landing (both from astrobiology and landing site geology viewpoints). Things may change, however, with budget shifts and other stuff. I'm curious what MSL may bring in terms of carbon content and isotope ratio analysis.

It is definitely necessary to have Martian samples examined by human eyes, under optical and electronic microscopes, nothing else can spot microfossils.

 

[agentgonzo]

New Horizons is RACING towards Pluto and still it'll be 10 years from launch to arrival. Once it gets to Pluto, it will have about 30 minutes to do the science before the opportunity is lost.

Where are you pulling this figure of 30 minutes from? This blog posting shows the detailed breakdown of what each instrument is doing at which target for the Pluto encounter and it shows the 12 hours around closest approach with a flurry of activity.

 

[Tychonaut]

I've read about the use of solar panels on an Uranus orbiter. That sounds outrageous.

Are you sure the solar panels were to power the orbiter? As I recall, some variants of the ice giant and Chiron missions propose using solar-electric propulsion as far as the asteroid belt. The SEP stage would then be jettisoned and the actual orbiter (or flyby probe) would use ASRGs for power and storable chemical propellants for propulsion after that.
As you suggest, solar power at Uranus doesn't make any sense. From what I've read powering Juno with solar is pushing the envelope, and they only opted for that to preserve Pu-238 stocks.