Mars Sample Return Options

[Explorer1]

Largely about the differences in culture between the various centres involved, the fact that it's separate from the rest of the Mars Program, and the comparison/contrast with JWST, which was a similar long term large projects with ballooning costs, that nevertheless has been successful.
The fact that there's no overall PI for the project, like on a normal flagship mission, also struck me (not counting Perseverance, which does have one). Every other sample return I can think of has had one, so why is MSR different, simply because of the multiple launches and vehicles involved?

[mcaplinger]

The fact that there's no overall PI for the project, like on a normal flagship mission, also struck me (not counting Perseverance, which does have one).

Not sure what you're saying. MSL and M2020 do not have "overall PIs" nor does any flagship mission AFAIK, they have a PI per instrument and a project scientist who is not much like a PI. For example, Europa Clipper doesn't have an "overall PI". Only Discovery and New Frontiers missions do (discounting leftovers like MER and Mars Scout programs.)

The thing that's unusual about MSR is that it has no competed science instruments and thus no PIs at all, to the best of my knowledge.

[vjkane]

NASA's managers announced today that they are "pausing" or "slowing" down the Mars sample return mission development.

Links to two articles below.

Immediate future work will focus on the system to deliver the samples to orbit. The articles don't make it clear what that means. It could mean that NASA would launch the samples into orbit and then collect them some (maybe many years) later. I don't believe that's what is meant. A small canister in orbit could easily be lost to tracking, but alternatively the samples are safe if left on the Martian surface. I think that what this means is that NASA will focus on refining the launch and sample capsule designs. These were elements that the recent review stated were least defined but the definition of which had the greatest impact on the full design of the return architecture.

Space Policy Online: https://spacepolicyonline.com/news/nasa-pau...essing-options/

Space News: https://spacenews.com/nasa-slows-down-work-...et-uncertainty/

[mcaplinger]

A small canister in orbit could easily be lost to tracking...

Agreed, they can't possibly mean that. If the OS has to have a long-lived beacon, then it becomes a small spacecraft and things will snowball.

The Figueroa "report" (it's a viewgraph package, basically) https://www.nasa.gov/wp-content/uploads/202...nal-copy-v3.pdf has such gems as alternatives that include adding back the fetch rover (which was previously deleted to save cost) to reduce the annual cost, while driving up the total cost.

Honestly, words fail me.

[StargazeInWonder]

In 1999, the plan was to launch the Earth return vehicle in 2005. The distance between plans and reality of MSR have been greater than the distance between the Earth and Mars.

[mcaplinger]

Agreed, they can't possibly mean that. If the OS has to have a long-lived beacon, then it becomes a small spacecraft and things will snowball.

Looking at the Figueroa report again, they seem to have convinced themselves that with enough tracking of the OS by assets in Mars orbit (details unspecified?), they can find it again over a 10-year period even if the beacon is dead. Which seems like a thin thread to hang the mission on to me.

[StargazeInWonder]

The Figueroa report has some new-to-me discussion of the priority of a 500 g threshold of returned material, and how things are already making that look unlikely. I'm far from expert on the science of analyzing such samples, but that seems like an odd consideration. The point of retrieving different samples is that they represent distinct portions of the lake's history, and therefore to have value, they have to be analyzed on the basis of something more like 5-20g each. And in that case, the sum total of returned material seems, while not utterly irrelevant, a poor measure of the value of the return.

For the architecture of the return, it seems like risk mitigation is the top concern and that the best way to achieve that is to allow for a second chance to be taken for possible failures. That would mean launching the (primary) Mars ascent and Earth return vehicles at about the same time so that if either fails, the first version of the other is still alive in time for a second one of the other to arrive. It would also mean only utilizing half of the samples available so that a second entire effort could be made with the other half. In that case, the 500 g concern seems even more misplaced, because we would rather have a second chance at half the samples than one chance with all of the samples, right? And at the costs that are being mentioned, it seems like paying to get the second half returned would be unlikely if the first half is returned successfully.

[vjkane]

The Figueroa report has some new-to-me discussion of the priority of a 500 g threshold of returned material, and how things are already making that look unlikely. I'm far from expert on the science of analyzing such samples, but that seems like an odd consideration. The point of retrieving different samples is that they represent distinct portions of the lake's history, and therefore to have value, they have to be analyzed on the basis of something more like 5-20g each. And in that case, the sum total of returned material seems, while not utterly irrelevant, a poor measure of the value of the return.

In many ways, the sample mass is strongly related to the number of individual tubes returned. Each tube has a volume and likely mass.

Each study in a terrestrial lab will require distributing some of the sample, some immediately, some decades from now (as has been done with the Apollo lunar samples).

For ~$8B, how much volume and distinct sampling sites makes the effort worth it. Certainly not a single grain of sediment nor a single chip of rock.

I read this section as the review committee making a recommendation on the minimum mass and diversity of the collected samples that would make the expense worth it. That is a key driver of the entire effort.

[mcaplinger]

I read this section as the review committee making a recommendation on the minimum mass and diversity of the collected samples that would make the expense worth it.

The problem is that if all of the available tubes on M2020 were returned and they were all fully loaded, it might add up to 500 grams. Look at the 10 tubes in the backup cache, which one might have plausibly thought was the performance floor. No way that adds up to 500 grams. It's barely possible it would total a quarter of that or perhaps a bit more, but more likely less.

I don't disagree that 500 grams is a plausible number to spend all this money on, but at this point it seems like unhelpful moving of the goalposts.

[bobik]

I think it would have been far better if the OS and STA functionality would have been already integrated into M2020, however, it was decided to shift technical development and related cost into the future, which, by the way, introduced additional complexity to the MSR scheme.

[fredk]

Looking at the Figueroa report again, they seem to have convinced themselves that with enough tracking of the OS by assets in Mars orbit (details unspecified?), they can find it again over a 10-year period even if the beacon is dead. Which seems like a thin thread to hang the mission on to me.

I guess this means trying to fix the orbital parameters of the MAV/OS once and for all, after orbit insertion, and then hoping the parameters are known accurately enough to find the OS after a decade? I wonder if anyone has thought about this seriously. I guess you'd want to be well above the atmosphere. I don't know if Phobos could produce hard-to-estimate perturbations at higher altitudes. But even if such perturbations are negligible, there's still the question of initial parameter uncertainties, though it should be straightforward to propagate those forward 10 years. I guess that would include uncertainties in the gravitational field of the planet itself.

[StargazeInWonder]

Thinking (probably unhelpfully, brainstorming) outside the box, maybe a good place to store the samples would be ON Phobos. We won't lose that.

[vjkane]

I guess this means trying to fix the orbital parameters of the MAV/OS once and for all, after orbit insertion, and then hoping the parameters are known accurately enough to find the OS after a decade? I wonder if anyone has thought about this seriously. I guess you'd want to be well above the atmosphere. I don't know if Phobos could produce hard-to-estimate perturbations at higher altitudes. But even if such perturbations are negligible, there's still the question of initial parameter uncertainties, though it should be straightforward to propagate those forward 10 years. I guess that would include uncertainties in the gravitational field of the planet itself.

Any hardware to allow long term tracking - a beacon and presumably solar cells to power it -- adds to the mass that has to be launched off of Mars. The parking orbit also would need to be high enough to effectively eliminate long term atmospheric drag.

[mcaplinger]

Thinking (probably unhelpfully, brainstorming) outside the box, maybe a good place to store the samples would be ON Phobos. We won't lose that.

Come on. Then we have to design something that can get the samples down to Phobos, and something else that can pick them up again. I don't see how that's gonna save money, do you?

The samples are as safe as can be on Mars where they are now. The idea that they should be put into orbit and picked up later is, at best, driven by budget phasing considerations, not engineering reality.

[StargazeInWonder]

Certainly the surface is more known and safe than Phobos, but that's also in Mars's gravity well, so the point is that if we get outside of Mars's gravity well, where is the best place. Utah is better still, but that's not an apples to apples comparison.

"Down to" and "up" don't apply with Phobos. The escape velocity is 40 km/hour. That's a nudge, not a launch. Is two delta-V's equal to a basketball player's jump cheaper than years of monitoring, tracking, beacons?

The question is how to manage this tricky sequence of steps that depend upon other failures. Between the surface of Mars and Earth is something. The question is Phobos vs. purgatory in Mars orbit, not Phobos vs. Jezero. Putting the Earth return asset in place before leaving Jezero is probably the safest option. My point is that purgatory is Mars orbit while we wait years is not the best option.

I don't think that Phobos is the best option; it's in comparison to orbit without a next step ready.