OPAG Reports, Formal proposals/evaluations of future outer SS missions Options

[AscendingNode]

Where would you send it? Once it entered Europan orbit, basically the only way out is down.

There may be orbits of Europa that are stable for hundreds of years. It just is a big undertaking to calculate them (i.e. the mission needs to be funded before such an effort could be paid for). But by proposing to impact Europa in a safe way, they still have a viable mission if such stable orbits can't be found... and they still have the freedom to use such an orbit if it's found.

Also, although it would be costly to leave a low Europa orbit like that proposed by the EE study... if an elliptical orbit like JSO proposed were used at Europa it could lower the DV down into the realm where 'nudge' would be a good word.

[tasp]

Exploration of the Europan Hill sphere via earth bound computer simulation would be interesting. Analogs to our moon's path about the earth and sun might exist, and the interesting trajctory of Messenger as it interacts with Mercury might be applicable, too.

[JRehling]

I think the planetary protection protocols, such as they are, have to be taken with a grain of salt. Suppose Galileo had catastrophically failed at some point after JOI, leaving it in the orbit that it was in when the failure took place, until close encounters with the satellites tweaked the orbit. That would have meant a significant probability (about 20%, I would guess, but certainly more than 1%) that it would eventually impact Europa. And given the history of spaceflight, I think you'd have to grant at least a 1% probability (given the radiation dangers, I would think much higher) that any Jupiter orbiter might fail suddenly and without warning. If we were really taking the planetary protection protocols seriously, we wouldn't send any orbiter there without making sure it was thoroughly sterilized first.

Given that we're not really taking the protocols seriously, what's the difference between perhaps a 2% probability of Europa impact and just making Europa impact part of the plan anyway? Then if you want to worry about safeguards, put them at the point in the process where they belong -- minimizing the probability of an impact being harmful. We do this with surgical equipment and so on, with human lives at stake.

[tedstryk]

Regardless of one's opinion on planetary protection, it is important to note that because Galileo was designed at a time when no one was really thinking about life in the Jovian system being even a possibility, it did not undergo the sterilization procedures that, for example, a Mars Lander would. EE would certainly be sterilized, so the concern about Galileo hitting Europa doesn't really carry to EE.

[nprev]

Not to ignite a debate on this topic, but aren't orbiters at Europa's distance from Jupiter & closer largely self-sterilizing? The radiation environment is horrendous; you would think that models for biological survival might indicate a very, very small probability of viable organisms reaching Europa's surface if PPPs were applied pre-launch in addition to this.

As my 9th-grade biology teacher used to say, "We know there's life on Mars...after anything from Earth hit the surface, it's a certainty". Seems to me that the Jovian environment as described is somewhat less friendly; not too worried about a putative EE impact on Europa.

[AscendingNode]

Not to ignite a debate on this topic, but aren't orbiters at Europa's distance from Jupiter & closer largely self-sterilizing? The radiation environment is horrendous; you would think that models for biological survival might indicate a very, very small probability of viable organisms reaching Europa's surface if PPPs were applied pre-launch in addition to this.

The problem is that there is shielding on the electronics to protect them from the radiation, and this shielding could protect any microbes behind that same shielding.

I've heard some joking suggestions of putting thermite bombs in radiation vaults to sterilize a spacecraft at end of life. (of course, that would be a huge single-bit-upset risk)

[rasun]

Regardless of one's opinion on planetary protection, it is important to note that because Galileo was designed at a time when no one was really thinking about life in the Jovian system being even a possibility, it did not undergo the sterilization procedures that, for example, a Mars Lander would. EE would certainly be sterilized, so the concern about Galileo hitting Europa doesn't really carry to EE.

Well... does that mean that they will sterilize Juno?

[tedstryk]

Well... does that mean that they will sterilize Juno?

Probably not, since they are crashing it into Jupiter at the end of the mission.

[ugordan]

Probably not, since they are crashing it into Jupiter at the end of the mission.

Maybe rasun was getting at the point that now Europa is recognized as a potential habitat to life (unlike when Galileo was designed) and what JRehling mentioned about the very real possibilty of a craft suddenly and catastrophically failing at any time in Jovian orbit. Do those two facts now impose a must for sterilizing Juno even if it's not meant to come close to Europa?

Personally, I think the issue of contamination is blown way out of proportion and this is just playing devil's advocate a bit on my part.

[JRehling]

I think a dead craft in Juno's orbit would have virtually no chance of ever impacting Europa, since it will be a polar orbit with apojove well past Callisto and perijove way inside Io. No big satellite flybys means no big adjustments to the orbit anytime soon, although I suppose a game of billiards and procession over the millennia could eventually turn things sour.

The principle still should apply. I think an estimate of how likely it is that a crash onto Europa's surface would infect the ocean probably has a lot of zeroes in it, whereas an estimate of how likely it is that an orbiter intended to avoid Europa might actually impact it has only one or two zeroes in it, so the "pain point" is in the sterilization, not the intended endgame.

[AscendingNode]

I think a dead craft in Juno's orbit would have virtually no chance of ever impacting Europa, since it will be a polar orbit with apojove well past Callisto and perijove way inside Io. No big satellite flybys means no big adjustments to the orbit anytime soon, although I suppose a game of billiards and procession over the millennia could eventually turn things sour.

Jupiter's J2 and the Sun's gravity cause the orbit to rotate. Although initially it crosses the orbit planes of the moons well outside of Callisto, over time the periapsis and apoapsis move to higher latitudes and the crossing of the plane of the moons moves inwards and crosses near Europa and then below Europa. It then moves outward again as the orbit rotates and so on. Over hundreds of years through this cycle, there is a good chance of hitting one of Jupiter's moons.

[nprev]

Personally, I think the issue of contamination is blown way out of proportion and this is just playing devil's advocate a bit on my part.

I gotta agree in the case of a Europan surface impact by a spacecraft. Seems as if the ambient radiation alone would wipe out the bugs in very short order, if the vehicle had undergone even a modest (not excessive) amount of PPP preparation beforehand.

Natural selection on Earth hasn't produced very many microorganisms capable of surviving sustained levels of radiation due to our magnetic field and nice thick atmosphere; betting that any exceedingly tiny putative Europan surface critters could kick Earth bug's behinds in this regard!

[ugordan]

wipe out the bugs in very short order

Ahh... Imagine wiping out software bugs with radiation...

Seriously, greatest concern is often expressed about RTGs since they're inherently very warm and could sustain suitable temperatures. It's still hard to imagine microbes surviving in the Jovian radiation environment in the radiation shielded parts and then finding themselves neatly warmed up on the surface right on top of an disassembled RTG. A Europa orbiter would give impact speeds probably on the order of 1 km/s which isn't too unsurvivable for some materials (RTG casings?). A flyby craft (a-la Juno/Galileo) would have an impact speed probably in excess of 10 km/s and that's when kinetic energies begin to skyrocket.

[ngunn]

Natural selection on Earth hasn't produced very many microorganisms capable of surviving sustained levels of radiation due to our magnetic field and nice thick atmosphere;

More than you'd expect is what I've heard. (This has been invoked to support the idea of panspermia.) Our ignorance of life's place in the grand scheme is very great, truth be told. To have any chance of reducing it by studying our small available sample of nearby worlds absolutely requires that we don't barge around like a bull in a china shop. Minute risk maybe, but incalculable potential consequences. It's not worth trying to calculate zero times infinity. I can handle a reasonably low accidental risk of littering Europa, but doing it deliberately when it certainly isn't necessary? Surely not.

[rlorenz]

Nature News piece on the Flagships is out

http://www.nature.com/news/2007/071212/ful...931a/box/1.html