Quote from: TakeOff on 03/13/2017 06:17 pmOne mission might collect samples of Titan's upper atmosphere and of Enceladus' geysers and of ring dust, and bring it home to Earth. The transfer vehicle could park in high (or highly eccentric) Saturn orbit, drop off a daughter vehicle that "clips" the moons and rings to collect flyby samples. When it returns to the mothership, all mass is discarded except for the samples and the return to Earth power.Insanely expensive.One problem with any sample return from that distance is that it takes at least as long to return as it does to get there. So you end up with a mission that might take 18 years to complete, and you only get your science payoff at the end. So if the spacecraft dies in year 17, the whole thing has been a waste. And designing and testing a spacecraft to last 18 years is expensive.
One mission might collect samples of Titan's upper atmosphere and of Enceladus' geysers and of ring dust, and bring it home to Earth. The transfer vehicle could park in high (or highly eccentric) Saturn orbit, drop off a daughter vehicle that "clips" the moons and rings to collect flyby samples. When it returns to the mothership, all mass is discarded except for the samples and the return to Earth power.
Quote from: Blackstar on 03/13/2017 06:28 pmQuote from: TakeOff on 03/13/2017 06:17 pmOne mission might collect samples of Titan's upper atmosphere and of Enceladus' geysers and of ring dust, and bring it home to Earth. The transfer vehicle could park in high (or highly eccentric) Saturn orbit, drop off a daughter vehicle that "clips" the moons and rings to collect flyby samples. When it returns to the mothership, all mass is discarded except for the samples and the return to Earth power.Insanely expensive.One problem with any sample return from that distance is that it takes at least as long to return as it does to get there. So you end up with a mission that might take 18 years to complete, and you only get your science payoff at the end. So if the spacecraft dies in year 17, the whole thing has been a waste. And designing and testing a spacecraft to last 18 years is expensive.Cassini to Saturn cost about $3½B. A Falcon Heavy launch of about two-three times a Cassini mass sells today at $0.1B. So tenfolding the mass orbiting Saturn is a pretty trivial expenditure. Flying spacecrafts through comet tails to collect samples has already been demonstrated very successfully. A transfer spacecraft, maybe with fission electric propulsion with complementing chemical rockets taking advantage of "pericronus" for utmost eccentric orbital insertion, could enter an economic orbit of Saturn and release a small battery powered spacecraft to fly through the sample getting plumes, atmospheres and dust clouds. Then docking with the returning spacecraft with its microscopic payloads. Minimum mass sent into Saturn's gravity well.
Cassini to Saturn cost about $3½B. A Falcon Heavy launch of about two-three times a Cassini mass sells today at $0.1B. So tenfolding the mass orbiting Saturn is a pretty trivial expenditure. Flying spacecrafts through comet tails to collect samples has already been demonstrated very successfully. A transfer spacecraft, maybe with fission electric propulsion with complementing chemical rockets taking advantage of "pericronus" for utmost eccentric orbital insertion, could enter an economic orbit of Saturn and release a small battery powered spacecraft to fly through the sample getting plumes, atmospheres and dust clouds. Then docking with the returning spacecraft with its microscopic payloads. Minimum mass sent into Saturn's gravity well.Cassini was launched 20 years ago in October this year. It has made hundreds of orbits of Saturn, and it was built in the lousy early 1990s. Two decades is not in any way an upper limit for the duration of a space mission, as has been proven. But it would be more than plenty for a sample return from the Saturn system.
And then, well, here's the thing that I mentioned earlier: sample return usually means that the mission achieves its top science goals only when the sample is brought back. So for a sample return mission to Enceladus, that means that the science payoff only happens after 18+ years. And that's a heck of a long time to wait for the science return. And there are LOTS of other ways to spend that money that return science much much faster. So if somebody comes along and says "Give me that money and I will rewrite the science textbooks in 10 years" [like New Horizons] that's a much better return on investment.
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.
Quote from: TakeOff on 03/15/2017 01:12 amAfter having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.
For real world examples, see Genesis, Stardust and Hayabusa. All returned samples from targets much closer than Saturn, and two of them came very close to LOM failures in the return phase.
Quote from: hop on 03/15/2017 04:42 amQuote from: TakeOff on 03/15/2017 01:12 amAfter having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.What do you mean, of course one can? NASA missed the Moon when trying to hit it almost 60 years ago, but the precision of space navigation is fantastic today. The location of Saturn's center of mass is known to within one mile! A few grams of gas, ice and dust particles in a safe in a capsule with a heat shield and crash absorption zone, aimed at the middle of the Pacific, seems quite doable. If the return trip takes 7 years, nothing can go wrong with it since it doesn't need to do anything. It's a bullet on a trajectory.
Quote from: TakeOff on 03/15/2017 11:23 amQuote from: hop on 03/15/2017 04:42 amQuote from: TakeOff on 03/15/2017 01:12 amAfter having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail.This is incorrect. You can't lob a sample return capsule from Saturn and have it passively return to earth.What do you mean, of course one can? NASA missed the Moon when trying to hit it almost 60 years ago, but the precision of space navigation is fantastic today. The location of Saturn's center of mass is known to within one mile! A few grams of gas, ice and dust particles in a safe in a capsule with a heat shield and crash absorption zone, aimed at the middle of the Pacific, seems quite doable. If the return trip takes 7 years, nothing can go wrong with it since it doesn't need to do anything. It's a bullet on a trajectory.Well, in THEORY you could. However; there are numerous forces that can cause a deviation of course that would require both mid-course and terminal course corrections. Some of these are unpredicted gravitational interactions, radiation pressures, micrometeoroid impacts, and solar magnetic variations, just to name a few. Yes, for the most part, these are very minor interactions, but the changes that they can inflict, over time, can cause huge course changes at the distances that such a return probe would be traveling. This could cause a miss of anywhere from a few hundred to a few hundred thousand kilometers, absent at least one or two course corrections.
I think that NASA can recover a probe that lands in the Pacific Ocean, even if off by a thousand kilometers. It could transmit a radio signal once and again in order for its trajectory to be determined, and its atmospheric entry could be observed and it could have a radio or sonic beacon allowing it to be found after landing.
Solar pressure is well known and used in models that simulate tumbling asteroids for centuries. Solar magnetic variations is hardly a problem for space navigation.
And how could "unpredicted gravitational interactions" be possible? Astronomers have ephemeris in their blood and have taken care of it extraordinarily well. It is absurdly well known where things are and where they will be. Especially Saturn and Earth. Are you making stuff up just in order to try to argue against me?
A spacecraft can hit Earth from Saturn, I'm sure.
After having collected the samples the returning spacecraft (a simple capsule with a heat shield) would be of minimal mass and set on course to land on Earth. Nothing aboard that could fail. It could cruise for millennia, but it only takes a few years.
QuoteSolar pressure is well known and used in models that simulate tumbling asteroids for centuries. Solar magnetic variations is hardly a problem for space navigation.Really? Source please.Summary: no, solar effects are not well-modeled over such long distances and timespans.