Post MSL Roadmap Options

[dvandorn]

Thanks, Ted -- that's exactly what I was struggling to say, that Sojourner acted a lot more like a really long robotic arm than like a true rover.

The only true rovers that have been actually deployed, IMHO, are the Lunakhods and the MERs. All of which worked (or are working) pretty well, all things considered.

BTW, I had not heard that there had been significant information returned about the rocks under the dust on Sojourner's APXS. Well, OK -- I had heard that the only "clear" patches they had tested indicated andesitic basalts, but there was a lot of discussion at that point as to whether this reflected composition of the rocks or the dust. Especially since andesites weren't exactly expected.

-the other Doug

[Vultur]

OK, that makes sense.

What are the big problems of sample return from an engineering standpoint - why couldn't we do it now [if we had funding]? Carrying enough fuel to be able to lift out of the gravity well of Mars?

[nprev]

Well, from a VERY big-picture view, it's probably the most complex engineering problem ever proposed in a number of ways. Consider the sheer number of interdependencies & critical events that have to happen just right for it to work beyond the already-formidable problem of getting the orbiter/lander package into Mars orbit & then executing a successful EDL. MSR literally enters unexplored territory shortly thereafter.

A top-level functional decomposition/method decision tree for post-landing operations probably looks something like this (grossly oversimplified), and bear in mind the hundreds of not thousands of sub-functions required as well as the overarching paradigm that they all must be executed autonomously:

-Acquire samples.
--Deliver samples of max scientific value to Earth-return module with minimal contamination.
---Fly a sample-acquisition rover?
---Land near MSL & design MSR to accept a sample from it?
-Depart Mars with samples.
--DTE return? (Hard.)
--Mars orbit rendezvous? (Also hard, and complex.)
-Deliver samples to Earth.
--ISS rendezvous? (REAL hard.)
--Earth orbit injection with retrieval via dedicated manned flight? (Also hard, and expensive.)
--Direct re-entry? (Easier, but possibly more risky?)

...and that's all ridiculously incomplete, with far from all options & risks explored.

[vjkane]

Well, from a VERY big-picture view, it's probably the most complex engineering problem ever proposed in a number of ways.
...and that's all ridiculously incomplete, with far from all options & risks explored.

There's also the problem that the ascent vehicle and Earth return craft both must carry enough fuel from Earth to (1) achieve Martian orbit and (2) enter a low Martian orbit (aerobraking will help) and two break Martian orbit to return to Earth.

If I remember correctly, MSL is already pushing the weight and size envelopes. Anyone here know for sure?

There are some proposals to manufacture the ascent vehicle's oxidizer from the Martian air, but that's another piece of technology.

I suspect that our current suite of launch vehicles means that the technology push to minimize weight makes this even harder. If we could use Ares V, things would be easier. That though, is a development project in its own right.

[Vultur]

@vjkane: That was what I was asking about, the take-off fuel problem.

The idea of picking up samples from MSL is intriguing, but sounds really difficult (due to the precision landing necessary). Wouldn't it be easier just to drop in some very interesting region with abundant loose rock and dirt, extend an arm Phoenix-like to scoop stuff up, and then blast back to Earth? (Maybe a paired mission hitting 2 different spots, like Spirit & Oppy)?

What are the problems with DTE return? The others sound really complex ... why not just drop a sealed capsule in some un-populated zone, like Stardust did? I never realized that that wasn't the obvious option.

[vjkane]

@vjkane: That was what I was asking about, the take-off fuel problem.

Wouldn't it be easier just to drop in some very interesting region with abundant loose rock and dirt, extend an arm Phoenix-like to scoop stuff up, and then blast back to Earth?

We already have random samples of Mars. What is wanted next is carefully selected samples that address specific questions. There was once a proposal for a no rover sample return. That died when Opportunity landed. Just imagine if we had a sample return mission and couldn't collect samples from that beautiful exposed bedrock a few meters away...

What are the problems with DTE return? The others sound really complex ... why not just drop a sealed capsule in some un-populated zone, like Stardust did? I never realized that that wasn't the obvious option.

It's really a weight problem. For the same reasons that we use multistage launcher on Earth, you want a multistage launcher for Mars. If you carry the extra stage to the surface, you have to size the lander for it, carry the fuel to land the extra fuel.... The Mars orbiter essentially acts as that second stage.

[nprev]

Not trying to start a debate (& the mods will quickly stop one if it begins!), and definitely not expressing an opinion one way or another, but a capsule return al a Stardust or Genesis will have to also deal with the potential back-contamination issue. It's just another system element in this very, very complex construct.

[Greg Hullender]

In the case of Opportunity, it took a 250-ton rocket to send a 1-ton payload to Mars, which landed a 185 kg rover. So at 3300 tons, an Ares V ought to be able to land a 2-ton vehicle on Mars, all other things being equal.

Now it's easier to send something from Mars back to Earth than it is to send it to Mars, but even so, with a 2-ton rocket, you're not going to get a whole lot back -- even if you can get the money for an Ares V in the first place.

Of course there are lots of clever ideas to improve on that -- but that means "untested" and "we're not sure how to do it yet" and, more importantly, "we can't do it with what we've got today."

--Greg

[tedstryk]

If we want a really random mars dust sample, a cheap way to do it would be the old SCIM proposal http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1721.pdf

If we do an all-out sample return mission, being selective is important.

Dvandorn, going back to what you said about Sojourner, from a scientific standpoint, you hit the nail on the head (from an engineering demonstration standpoint, it was certainly more than a robotic arm, but that isn't what we are talking about here).

[Geert]

It's really a weight problem. For the same reasons that we use multistage launcher on Earth, you want a multistage launcher for Mars. If you carry the extra stage to the surface, you have to size the lander for it, carry the fuel to land the extra fuel.... The Mars orbiter essentially acts as that second stage.

True, plus a DTE burn from the surface direct to interplanetary earth trajectory would probably only be possible from certain latitudes on Mars and certainly only at very specific dates & times, the best trajectory would almost certainly be to burn to Mars orbit first and then do a TEI burn from Mars orbit. If you have to get into orbit first, then it makes a lot more sense to leave all fuel, engines, and complexities of the return trip in Mars orbit and dock the ascent stage with it before burning out of orbit back to earth. This is exactly the same problem which long ago let to the Apollo LOR method, it saves you a lot of weight if you use only a small lander which docks with an orbiting returnship for the homeward journey.

Personally I still think the best method is using a lot of small lander+rover units, who each shoot a small container with samples into mars orbit, then later have one or two dedicated orbiter missions collect all of those orbiting sample containers and bring them back to earth. This allows for simpler and lighter lander units as they won't need all the complexities of the return-to-earth part, and it allows you to sample a lot of different sites without having to fly a dedicated (& complex) return-craft for each of these missions. Only restriction will be that all those sample-containers will need to end up in the same orbital plane (unless you like to spend lots and lots of fuel from the orbiters for plane-changes), so this will restrict your landing-points somewhat but most of the surface will still be in reach. I don't think it is useful to design a whole mission just to sample one specific site. Mars is such a complex planet and there are so many different landscapes that you would always need samples from a lot of different (carefully selected) sites.

[vjkane]

Personally I still think the best method is using a lot of small lander+rover units, who each shoot a small container with samples into mars orbit, then later have one or two dedicated orbiter missions collect all of those orbiting sample containers and bring them back to earth... Mars is such a complex planet and there are so many different landscapes that you would always need samples from a lot of different (carefully selected) sites.

I'm with you. I think that a number of rover missions should be flown that characterize locations in depth. From ExoMars on, I believe they should be able to cache samples. However, even if they don't cache, we will know which site(s) are most worthy of sampling. Imagine spending $6B, flying to a new site, and getting skunked like we were at Gusev Crater.

As I armchair assess the risk, it seems to me that the high risk elements are first the Mars ascent vehicle and then the landing. For this reason, I would fly at least two lander/rover/ascent missions (probably in sequential Mars opportunities) and then fly the Mars orbiter/Earth return vehicle.

The science community will also have to look hard at the cost of Mars sample return. For the likely cost of that mission (~$6B, I hear), both a Titan/Enceladus and a Venus flagship mission could be flown. If a series of rovers find no sites with organics, then which is more valuable: carefully selected geological samples or a Titan orbiter+Titan balloon+Titan lander AND a Venus orbiter (radar imaging at 5m)+two balloons+two landers (~24 hour life)?

If any rover finds organics, then I'm all for Mars sample return. Otherwise...

[Geert]

If any rover finds organics, then I'm all for Mars sample return. Otherwise...

I don't like to turn this discussion to organics for obvious reasons, but I'm very worried about all the talk of 'finding organics'. I remember Viking all too well, all the PR about how it would 'prove' everything, and when it didn't Mars missions went belly-up for a very long time... You wont 'find organics', or at least not in the way the public expects, you get experimental results which 'might indicate', and then you get a debate which lasts for years and which should be done quietly within the science community and not on worldwide media!

They should put more emphasizes on HiRISE and the MER images, don't try to 'explain' everything but just show the public the beauty of those landscapes! I don't care whether there are organics or not, Mars is a fascinating place, every time I wander through HiRISE I find new wonders and we are still nowhere near to global coverage, this place is amazing! People spend thousands for a holiday to the Rocky Mountains or other similar places, they should see Mars just 'as it is'. You don't give people a guided tour through the Rocky Mountains while talking about difficult science questions, you show them the 'views', that's what they want to see!

Getting back to MSR, I think there is a moment when you just get diminishing returns from ('single trip') robotic missions, we haven't reached that moment yet but all the budget-overruns on MSL are a first indication. At a certain moment it just gets too expensive and too complicated (and too risky) to get all the equipment you would need down on the surface and then, in the end, it will be cheaper and better to get the samples back on earth. When we reach that moment, and only then, MSR should be ready.

Getting in some 'race' to get the samples would be the worst possible thing for Mars-science I guess. You can probably fly MSR today in the same manner as the Soviets flew their Y8E sample return missions from the moon (and as the Chinese will be repeating soon), those missions were scientifically close to worthless, they were extremely restricted in their landing locations (they could/can only land close to 60 deg longitude) and they could only randomly grab the nearest handful of sand and pebbles and take off. It is a 'quick and dirty' method of getting samples but scientifically I think you could save yourself the trouble...

I love to discuss MSR and the best method to fly it, but personally I don't think we are anywhere near to needing to fly it (yet). At the very least we would need global HiRISE and CRISM coverage first, and more rovers down on the surface. And sure, I'm all in favor of more flagship missions to Venus and to Jupiter/Saturn and their moons, there is beauty out there as well!

Once again, I guess the worst possible outcome would be some 'race to get the samples', that would be disastrous, you'll get a handful of close to worthless samples and the media will expect you to immediately solve all big questions...

[vjkane]

Getting back to MSR, I think there is a moment when you just get diminishing returns from ('single trip') robotic missions, we haven't reached that moment yet but all the budget-overruns on MSL are a first indication. At a certain moment it just gets too expensive and too complicated (and too risky) to get all the equipment you would need down on the surface and then, in the end, it will be cheaper and better to get the samples back on earth. When we reach that moment, and only then, MSR should be ready.

I think the argument from much of the scientific community is that we are already at that point. There are a number of questions about Mars that can only be answered with samples, and the mission has been endorsed by numerous blue ribbon communities.

I don't doubt the scientific value of the mission, but approach the question of when to fly from a different perspective. Whenever MSR flies, it will suck up much of the world's (since this will be an international venture) budget for planetary exploration for a decade. It will fly once in the professional lifetime of any but the youngest scientists. Therefore, I ask two questions. First, do we have excellent confidence that we know where to gather the sample from? I would argue not -- we have simply explored too little of the surface. We may explore a couple of the sites with clays, for example, and find that they are thin verniers. The other question I ask is whether MSR is more valuable than the missions that could otherwise be funded. None of the blue ribbon panels that I am aware of have stated which missions we should forgo to other targets to enable MSR.

My personal call would be to land a mid-range rover every opportunity for a decade (5 rovers plus Spirit and Opportunity, MSL, and ExoMars). If one of them shows that the site is absolutely compelling ("organics"), then move post haste to MSR. Otherwise, get the experience on the ground, and then decide which of the 9 sites explored is the one to go back to for samples.

[Geert]

Therefore, I ask two questions. First, do we have excellent confidence that we know where to gather the sample from? I would argue not -- we have simply explored too little of the surface. We may explore a couple of the sites with clays, for example, and find that they are thin verniers. The other question I ask is whether MSR is more valuable than the missions that could otherwise be funded. None of the blue ribbon panels that I am aware of have stated which missions we should forgo to other targets to enable MSR.

I fully agree with you on that!

My personal call would be to land a mid-range rover every opportunity for a decade (5 rovers plus Spirit and Opportunity, MSL, and ExoMars). If one of them shows that the site is absolutely compelling ("organics"), then move post haste to MSR.

Agree, but don't forget the orbiters! In a way one could argue that even Spirit and Oppy launched too early (or MRO too late), if we would have had those HiRISE images and CRISM data we have now they might have selected other landing sites. As of yet I don't think we have explored all the available options to get data from orbiting instruments and there are a lot of 'grey spaces' on the map.

With regards to rovers, they are wonderful marvels of engineering, but looking through the orbital images, there are so many sites which look extremely interesting but are simply out of reach for rovers. Maybe we need some 'climbers' or 'crawlers' or some kind of airship or helicopter-analog to reach some of the potential sample-points...

[vjkane]

Agree, but don't forget the orbiters! In a way one could argue that even Spirit and Oppy launched too early (or MRO too late), if we would have had those HiRISE images and CRISM data we have now they might have selected other landing sites. As of yet I don't think we have explored all the available options to get data from orbiting instruments and there are a lot of 'grey spaces' on the map.

Unfortunately, it will be the orbiters that will suffer the biggest impact of the MSL cost overrun. The Mars Science Orbiter (MSO) was to have a HiRISE-class camera, which meant that it would have also the precision pointing and high data rate that might also have enabled other precision imaging spectrometers. Even expanding the HiRISE spectral bands to another 4-6 to pick up key minerals would have greatly expanded our exploration of Mars. Alas, the camera (and more importantly for cost cutting, the precision pointing and high data rate) has been dropped from MSO plans.

I hope that NASA is funding the MRO extended mission sufficiently to get every last bit of science possible because the capabilities it has isn't likely to be repeated for another 20 years or more. Typically for extended missions, NASA reduces funding, which also reduces science activities per unit time. Does anyone know whether or not MRO is working as hard now as it did in its prime mission?