10
$\begingroup$

News in May, 2018:

News in July, 2018:


The news items above are included as background information that got me thinking of the following question.

For a similar mission of covering significant distance carrying a given experimental/observational package together with a robotic arm to pick up samples, what would be the differences between a rover build for the Moon versus a similar one built for Mars?

Would it be fairly straightforward to make small changes to a rover built for one body to optimize it for operation on the other body, or are there issues that would end up making one very different from the other?

For the purposes of this question let's call the "rover" the equivalent of a satellite's bus, and the experimental package and robotics as the "payload", and assume the payloads are identical or at least similar. Let's also assume the terrain is similarly "rover-friendly" in that there are no large rocks or extreme slopes in either case. However, there may be differences in regolith that can't be ignored, as one body has always had much more of an atmosphere than the other.

$\endgroup$
  • $\begingroup$ We're likely to see several rovers on the Moon as well as on Mars in the 2020's and the similarities and differences in their design is really interesting. Instead of (the two) silent close votes for "too broad", why not leave a helpful comment for how the question might be adjusted to avoid being too broad from your point of view? $\endgroup$ – uhoh Jul 10 '18 at 2:06
13
$\begingroup$

Would it be fairly straightforward to make small changes to a rover built for one body to optimize it for operation on the other body?

Small? No. If you design with both bodies in mind, making it modular where needed, then possibly so, although the design would be suboptimal. If you design for one, you're straying from the other quite far.

First, matters of guidance. 3 seconds of ping are quite manageable after proper training, for fully interactive control. The minutes to hours in case of Mars will require either partial self-driving capacity, or long wait periods. Similarly, the lunar rover on near side of the Moon can communicate with ground stations directly. The Martian one will require either a freakishly strong radio or a relay satellite.

Next, energy. Martian winter still gets enough sunlight to sustain the heaters to keep the batteries from dying - although in general the amount of sunlight is much lower. Moon gets two weeks of total darkness with not even the thin atmosphere to keep the deep space from sucking heat out of everything. More violent temperature changes, way deeper, much longer night, much brighter, hotter day. Completely different energy and heat management systems. (...unless you go with RTG. On a commercial craft? U mad?)

Surprisingly, for landing it's not that different. Don't pack the parachute and heatshield for the Moon. Rocket-based skycrane will be of comparable requirements for both. Unless you go for airbag landing on Mars, which is just not viable for the Moon.

The lunar rover will operate in full vacuum, so all mechanics must be vacuum-proofed. The Martian rover will travel through vacuum for a long time though, so unless you choose to make the landing capsule (heatshield/skycrane) airtight and minimally pressurized (to Martian levels?) you'll need to vacuum-proof it, at least partially.

The lunar regolith is more abrasive... but in the large scale of things that's not as big a problem unless you want another rover with 5000%+ lifetime expectation exceeded. But without wind, don't count on dust devils cleaning the solar panels - OTOH dust will only fly and settle on the panels if you arouse it. So these considerations are pretty different.

It remains to be determined how much would be left unchanged - and if it would be worth it; e.g. if a system must be more robust to fulfill needs of one body, it will work just fine on the less demanding one - but it will be more expensive than necessary. Will it be more expensive than developing a dedicated cheaper version would? That would need an in-depth analysis.

In short, the idea is technically viable, but its economy is questionable - and that's developing a rover for both bodies since moment one. If you develop for one, then try to adapt for the other, you're not getting nearly any savings.

$\endgroup$
  • 1
    $\begingroup$ @uhoh: AFAIK, everything since Spirit had partial autonomy when choosing route, avoiding obstacles; later upgrades to Opportunity added even autonomy at picking own science targets (if it spots an interesting rock, it stops to analyze it instead of rolling towards the designated destination). Sorry, if you want info on the rovers weathering the interplanetary travel, you need to ask someone else. $\endgroup$ – SF. Jul 9 '18 at 16:05
  • 1
    $\begingroup$ "Don't pack the parachute and heatshield for the Moon. Rocket-based skycrane will be of comparable requirements for both." While the skycrane was whizzy new technology, this massively undersells the role of the other parts of the EDLS. The heatshield and parachute do almost all the work of slowing you down for Mars entry (6000 m/s at entry, down to 500 m/s using the heatshield, and then down to 120 m/s using the parachute). A rocket-only system that can go from arrival speeds to a soft landing is a completely different beast. $\endgroup$ – djr Jul 9 '18 at 22:00
  • 1
    $\begingroup$ Don't forget the 2.5 times difference in gravity gravity means drivetrain design will be different too. More traction, but more weight to move on Mars. $\endgroup$ – Lesser Hedgehog Jul 10 '18 at 2:22
  • 1
    $\begingroup$ @LesserHedgehog: I believe this is one point where 'more robust fits both' is the correct choice. It will have to withstand similar stress of landing anyway, and not much is to be saved by making the Moon wheels extra-flimsy. $\endgroup$ – SF. Jul 10 '18 at 9:16
  • 1
    $\begingroup$ Note that airbag landings on the Moon are not only viable, but in fact were done twice successfully by the USSR on Luna 9 and 13. $\endgroup$ – Mark Adler Jul 10 '18 at 16:04
3
$\begingroup$

While you could set out to design a modular space probe, considering the costs of getting it to moon or Mars, I think it would be more wise to design the probe fully purposed for the mission. actually the only possible benefit to a modular probe would be any reduction in probability of losing a probe over all its missions due to similar design, if there is a reduction.

First, your roving sections mass and volume will have different envelopes for each mission due to distances and the aerodynamic requirements of Mars. For the cost of getting the rover to the surface mass and volume should be maximized thus proving unlikely the two optimal points coincide.

Additionally you would also have to consider how different chemistries and the presence of atmosphere or different pressures effect the scientific experiments size, mass.

Additionally communication and power requirement are probably going to be larger for Mars. Energy more difficult to obtain on Mars, higher gain and thus larger and less efficient antenna requiring more power.

They are literally two separate world. The better question may be what can be accomplished with a modular design to even persuade the consideration? To me it seems not much is gained outside of opportunity to prove designs that have commonality, possible reducing uncertainty in performance. I don't think there would be a cost benefit as a useful modular design may be more complex and perform poorer than a purpose built design.

$\endgroup$
  • $\begingroup$ Thanks for your answer! Can you add some specific examples? If another answer says something like one design could be easily modified to work as the other at substantially less cost and time than two independent efforts, then both answers would be pretty much opinions. For a good Stack Exchange answer, you should support your statements with detailed reasoning or even cite some supporting references. As you've mentioned antennas, a look into how Curiosity or the much smaller Spirit and Opportunity rovers already manage to exchange information with Earth might be a good avenue to explore. $\endgroup$ – uhoh Jul 9 '18 at 11:35
  • $\begingroup$ I did provide detailed reasoning, frankly as you have not define rigorous design parameters, and haven't specified concrete requirements, in the English syntax alone, doesn't constrain anything other than opinion. Additionally there is a surprisingly large amount of design choices in space travel. Look at SpaceX vs other space enterprise solutions. They very drastically and as of late they all solve the same problem, unmanned Leo and geo. Also providing cute little articles doesn't really accomplish much but thanks for the opinion. $\endgroup$ – marshal craft Jul 13 '18 at 8:32
  • $\begingroup$ But to give a trivial example consider a modular design that has a heat shield. Clearly for a moon landing it is useless and considering the cost per kg to lunar orbit, you are paying glarge amounts to bring a useless heat shield along. That is trivial case but a discrete design choice. For many things the design variables are continuous sets, having optimal points for other variables that are held fixed. It's not true that both Mars and moon lander share optimal design parameters in general. In fact it is probably rare. So it is probably easier to search for cases where they do. $\endgroup$ – marshal craft Jul 13 '18 at 8:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.