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Comment by jmpe | Hacker News Reader

"Dr. Tsou devised a way to capture comet particles and bring them back to Earth for NASA’s Stardust mission and has been suggesting a similar method for a spacecraft that would fly through Enceladus’ plumes and then return to Earth for scientists to examine.

The challenges are to make sure that the interesting particles would not break apart, to take precautions that any alien life would not infect Earth, and to fit it into the $500 million budget of one of NASA’s lower-cost planetary missions."

Why bring it back to earth? Wouldn't it be safer & less expensive to return it to ISS instead, (or is that what's implied) ?

Didn't know the carbon & nitrogen part of the story, read the article thinking only 1 thing: "when are you going to mention Europa".

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> Why bring it back to earth? Wouldn't it be safer & less expensive to return it to ISS instead, (or is that what's implied) ?

No, that would involve a very complicated and expensive breaking maneuver to slow down the spacecraft, not to mention getting in exactly the right orbit to rendezvous with the ISS. It's much, much easier to just the payload sturdy enough to survive atmospheric entry and a crash landing.

Expensive breaking is precisely what they're trying to avoid!

(Sorry, normally I wouldn't nitpick spelling when the meaning is clear, it was just a funny error!)

Hah! I had to reread twice to spot the mistake. That's too awesome; I'm going to leave it as-is.

What about crashing it into the moon? Higher cost, but much less chance of earth contamination. We could then check it out with cheap robots.

An object coming in from a rendezvous with Saturn would be traveling at a ludicrous speed. You would probably vaporize on lunar impact. The Earth's atmosphere can help slow it down to a reasonable velocity--otherwise you have to carry a lot more fuel to burn in a slow-down maneuver.

Similar to how a swing-by is used to accelerate a space-vehicle, I wonder if a swing-by could be used to decelerate as well.

According to Wikipedia, the MESSENGER mission to Mercury used a complicated series of fly-bys of Earth, Venus and Mercury to slow down.

It can. The boost is proportional to the cos(final exit trajectory in relation to the planet, velocity of planet) -- so if the probe leaves the planet opposite to the direction it goes around the sun, it slows down.

(that is, the probe as whole can still orbit the sun in the same direction as the planet, it just needs to do it slower.

Ludicrous speed?! I bet they have hyperjets on that thing!

(ducks)

Send two missions, one with the capture device, the other with a functioning remote-controlled robot laboratory. Leave them close to the region, set them up to explore for 50 years or so.

I know, I know, budgets. It'll 'never' happen.

But what if we just send a nano-factory with its own assembly/disassembly abilities? Feasible, 5 - 10 years on from now?

Well anyway, the point is: why bring it back, really? Just send more machines to do better jobs in space.

I doubt in orbit rendezvous with ISS would be safer and cheaper. It might be safer from planetary contamination standpoint, but complexity of such maneuver would handily offset that. On top of that there is a host of other issues due to the cramped space on ISS. For example: not enough space for proper isolation of sample, not enough equipment to properly study sample, and the fact that limited manpower would be available for examination.

Regarding planetary contamination, with the amount of meteorites hitting ocean I do not think we have anything to worry about.

That makes sense.

But regarding your last sentence: I'm not very fond of that risk analysis. Potentially introducing an alien aquatic micro-organism (that's what we hope to bring back, remember) into earth's system... No competition, paradise compared to its hostile home. No meteorite has ever been shown to carry life, but into this case we intend to deliberately introduce it, either controlled or uncontrolled.

NASA can bill me for the extra cost for taking it to ISS instead of earth's surface.

No competition?

A life form which evolved in a (relatively) low-energy environment (low temperature, low light level, lower pressure) is more in hell than in a paradise. Earth organism evolved to make the best of available resources on Earth, be it energy or materials; the organism would be teared apart in no-time.

That is, unless it is a highly intelligent and evolved life form with big environment alteration capacities, but then it might already be a problem, just one we aren't aware of.

Eh, I've played KSP, an orbital rendezvous in LEO on your return isn't that hard. If you have enough precision and fuel leftover to start a safe decent, you have enough precision and fuel to dock with the ISS.

I'm surprised that we aren't equally worried about contaminating Enceladus with terran microbes.

psst, kerbal is not a substitute for actual physics.

However, it turns out we can introduce actual physics into kerbal. http://forum.kerbalspaceprogram.com/threads/68502-WIP-Princi... + real solar system + realism overhaul.

You don't need any fuel to start a safe descent, except for a tiny amount for course corrections. The atmosphere does all the work.

KSP is intentionally a lot easier than actual Earth-based rocketry. Orbital velocities in KSP are much lower than in reality, and because the rocket equation is exponential that makes everything in KSP expenentially easier to do.

If you are coming in fast from interplanetary space, you'll either need to aerobrake or burn a good deal of fuel to get yourself into LKO. While aerobraking from interplanetary space to put yourself into a nice orbit is easy enough in KSP, in real life things are much more difficult (just for starters, in KSP your station is probably at 0 degrees inclination unless you went out of your way to put it somewhere else...).

Get FAR, RSS, Deadly Rentry, put your space station somewhere around 50 degrees inclination, then try it with suitably small probe. The Stardust spacecraft was 300kg; the sample return capsule was 46kg and reentered at nearly 13km/s.

Just one full small kerbal RCS tank puts you at 250kg, so you'll need to nearly empty that just for starters...

We're very worried about contaminating other worlds. But in this case, the plan (as I understand it) is to collect samples from the plumes of water that Enceladus shoots out into space, without ever landing on the surface.

> Regarding planetary contamination, with the amount of meteorites hitting ocean I do not think we have anything to worry about.

The amount of oxygen in the atmosphere helps a lot. The onset of photosynthesis caused a mass extinction ~two billion years ago.

https://en.wikipedia.org/wiki/Great_Oxygenation_Event

I love that name. It sounds like some kind of a party.

In regards to the contamination,

I don't think that would be a real risk. Earth life has spent billions of years both adapting and adapting to the environment to make it the best growing medium and even then it exists in exclusive bands. For example, put a polar bear in the desert or a fresh water fish in salt water. It is more likely that we would have to take extreme care not to kill any lifeforms we brought back than to worry about them killing us.

You're seriously underestimating this issue.

- rabbits/cane toads in Australia [0][1]

- Japanese knotweed [2]

- Tumbleweed (yep, not as native as Hollywood suggests) [3]

- Algae [4]

... and the list goes on and on, here's a top-100:

http://en.wikipedia.org/wiki/List_of_the_world%27s_100_worst...

[0] http://www.youtube.com/watch?v=pgPhn4tYxJQ

[1] http://en.wikipedia.org/wiki/Cane_toads_in_Australia

[2] http://www.environment-agency.gov.uk/homeandleisure/wildlife...

[3] http://en.wikipedia.org/wiki/Kali_tragus

[4] http://plants.ifas.ufl.edu/node/89

I don't think anyone is worried about space bears or space fish; but bacteria / viruses / other basic replicator forms have much bigger resistance to harsh environments.

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