NASA Mulls Missions To Neptune and Uranus, Using the Space Launch System

MarkWhittington writes: According to a story in Astronomy Magazine, NASA is contemplating sending flagship sized space probes to the so-called "ice giants" of Uranus and Neptune. These probes would orbit the two outer planets, similar to how Galileo orbited Jupiter and how Cassini currently orbits Saturn. The only time NASA has previously had a close encounter with either of these worlds was when Voyager 2 flew by Uranus in 1986 and then Neptune in 1989. Each of these missions would happen after the Europa Clipper, a flagship-class mission scheduled for the mid-2020s.

Comments

And the timeframe for getting another probe

[Rei]

... to Titan will be approximately three weeks after never :P

Well, at least they're not planning to follow up the wasteful 2020 flagship to Mars with yet another flagship to Mars as part of their ongoing Mars obsession at the cost of the rest of the solar system.

Re:And the timeframe for getting another probe

[Anonymous Coward]

Well, at least they're not planning to follow up the wasteful 2020 flagship to Mars with yet another flagship to Mars as part of their ongoing Mars obsession at the cost of the rest of the solar system.

While you seem to be one of those who sees those missions with disdain, there is a good logic for them.
1) Public favor. People got bored of the moon after a few visits, and Mars is the next most probe-able remote object to test probe tech on.
2) Theory testing. Mars probes have dealt with a fair deal of "that's interesting, but what about this other question?" that has lead to more advanced probes and rovers.

So, Mars is a good playground since they can't get funding to do live tests with major probes and landers on the moon anymore.

This logic is predicated on the assumption that NASA are logical and curious rather than being lead by a bunch of political appointees trying to manipulate the citizenry for votes. Or possibly "despite" instead of "rather than."

Re:And the timeframe for getting another probe

[Rei]

Mars is not the "next most probe-able remote object". Venus and Mercury have more frequent launch windows. And more abundant solar power. Capture is much easier at Venus, although surface survival is more difficult.

There are far more significant unanswered questions about bodies other than Mars that need "theory testing". Mars is the most studied body in the solar system outside of the Earth and the moon. And ranking the moon higher than Mars is at this point starting to get questionable. There are massive unanswered questions about many other bodies in the solar system. The incremental benefit for Mars is very low. Example: Venus is Earth's evil twin - such a close match for us in diameter and mass, formed right next to us, and yet it's a greenhouse hellscape without a magnetic field. We really don't know why. How much more of a fundamental geology question can you get than that? And as for fundamental biology questions, Titan is probably the best laboratory in the universe, while if the search is for actual extraterrestrial life, Enceladus probably gives you the best odds for your exploration dollar.

The public does not decide which NASA projects get funding, NASA does (except for a few big things mandated by congress). Nobody had a gun to their head and made them choose Mars 2020 or all of the others. In fact, with all of the craft we already have operating at Mars there's going to be a continuous stream of Mars news for the public for a long, long time. And really, what's been the biggest space stories of late, that show up say on the front page of Google News? New Horizons. Dawn. Rosetta. Cassini's latest flybies. The public likes pretty pictures and weird news, no matter where it comes from. And even congressional mandates these days are often for robotic probes to other worlds. When was the last time that congress mandated a probe to Mars like they did recently with the Europa probe mandate? They've insisted on general Mars policies, but nothing that specific in recent memory that I can recall.

Re:Flagship-sized probe to Uranus?

[Rei]

Herschel, its discoverer, wanted to name it "George". ;)

Really, Uranus was a naming mistake - in keeping with the names of the other planets, it should have been named Caelus.

Re:Flagship-sized probe to Uranus?

[Chris Mattern]

Herschel, its discoverer, wanted to name it "George". ;)

And he wanted to love him and hold him and squeeze him and pet him...

Use RTGs for ion propulsion then comm.

[wisebabo]

NASA's needs Pu to get to Uranus (puns intended). If they can manage to get the correct isotope of Plutonium then a space probe that uses ion propulsion would have the necessary electrical power to drive the extremely efficient drive even when, as in this case, it is very far from the sun. Since the space probe DAWN has proven that multi-year thrusting of ion engines does work quite well, this would enable a "flagship" (read "big") mission to get to the very outer planets in less than a decade. It could spend roughly half its time accelerating to a high cruising speed then almost as long decelerating to be captured into orbit.

Then, once the mothership has arrived in orbit then, like Cassini, smaller spacecraft could be employed to explore the various moons and atmosphere of these gas giants. (Unfortunately since the moons of Uranus and Neptune may not be large enough to effectively permit gravity assists like Cassini uses with Titan or Galileo used with the four large Galilean moons, you might need smaller probes because the ion drive may have too low a thrust for dynamic orbital changes). Now the RTGs, having powered the spacecraft to the far reaches of the solar system, could be "gainfully" (ha ha) employed to power a high bandwidth radio transmitter/laser communicator. This would enable the small probes exploring the system to send lots of data back to earth without each carrying a huge antenna, only the mothership.

Why all spacecraft don't utilize the extremely high energy/weight RTGs for deep space PROPULSION is beyond me. I (maybe mistakenly?) think that the RTGs, since it generates its power from the natural decay of a radioactive element, is constantly "on" and if you don't use the power being generated YOU LOSE IT (anyone please correct me if I'm wrong!). So it would seem to be ideal for a space probe that needs to go somewhere far far away from the sun and for which a low thrust high impulse drive (like ion propulsion) that requires large amounts of electric power is ideal. Maybe it's because the DAWN probe needed to prove the ion technology before NASA could commit a flagship mission to it.

Too bad that the isotope of Pu that they need for the probe isn't the same that is used in nuclear bombs, that would be the most apt fulfillment of the biblical(?) phrase "beating swords into plowshares". Oh well, Congress needs to fund the reactor that is used in the nuclear fuel cycle that manufactures this critical resource for space travel.

Of course this is only a stopgap until we get either the Lockheed Martin or MIT (mini) fusion reactors working!

Re:Use RTGs for ion propulsion then comm.

[Rei]

Why all spacecraft don't utilize the extremely high energy/weight RTGs for deep space PROPULSION is beyond me

First off, even with the little we use today, we already have a serious shortage of it. At least funding has been reestablished to produce more. But production rates are going to be very slow and expensive, and this means that the fuel will continue to be expensive. Unfortunately, 238Pu needs to be thought of as a manufactured product, not a waste product. It's impractical to extract from nuclear waste - you have to first separate out neptunium (which isn't too common to begin with, which means lots of reprocessing, which is expensive), and then you have to bombard it with a lot of neutron flux for a long time (neutron flux being very valuable, as it's what you can use to make power (by bombarding a fissile target) or medical/ industrial isotopes). And you need a lot of plutonium to be useful for space probes (kilograms), not the sort of ng/ug/mg quantities usually used in medicine and industry.

The net result is that RTGs are almost always the best option from Saturn on out, usually the best option for Jupiter, sometimes the best option for Mars and the asteroid belt, and seldom for Earth on inwards.

Re:Use RTGs for ion propulsion then comm.

[Rei]

1) RTGs are not being "phased out". They're actually going to become more common in the coming years, now that 238Pu production has restarted.
2) Computer power consumption has dropped, not increased.
3) For outer planetary missions, there is literally no better solution to produce X number of watts, whatever number X may be (up until you get into the many-dozens-of-kilowatts range, where it probably pays to start developing an outright fission reactor)
4) Few people would consider 238Pu to have a "long half life". There are certainly things that it's long in comparison to, but as far as "long lived radioactive" products are considered, it's not even close to being considered one.
5) Plutonium is not "rejected by the human body", it's accumulated in the bones, and alpha radiation inside the body has 20 times the destructive power of beta and gamma per MeV (also, with beta decay, 2/3rds of the energy is usually lost as a muon antineutrino)

Note: Please don't misinterpret this, I'm pro-RTGs. I just wanted to correct the facts.

Re:Ehh

[Rei]

Flagship is a technical term. NASA missions are divided into categories: Discovery, New Frontiers, Explorer, and Flagship. Flagship are the most expensive, and most infrequently launched. Flagship missions cost over a billion dollars, usually $2-3B. Because they're so expensive and infrequently launched, one expects a huge scientific return out of them - for example, although Cassini-Huygens cost $3.26B, it's returned such a treasure trove of data and incredible discoveries about the Saturn system that I doubt anyone would say it's not worth it. Is Mars 2020 going to return anything that worthwhile? Not even close. The sort of scientific territory it's exploring is far too well tread already; it's exploring small details, not huge unanswered questions. The Uranus or Neptune probes may or may not prove to be worth their price tag, but at least they stand a better chance. I know a lot of people for example itching to find out more about Triton after Voyager's tease, which was conducted with 1970s tech.

Retrieves Popcorn...

[trooper9]

This is gonna be awesome.