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While many terrestrial mobility platforms have been very successful, why are we spending millions to every rover device making it unique?

Sure enough, different worlds offer different conditions, but why not build a more or less general purpose chassis say for the Moon or Mars?

That is, will such make sense at some point of time with enough budget and sufficiently mature component technologies, or is there a reason why we will be ever creating unique mission-focused vehicles from scratch, never reaching a (low scale) mass production level? Or do they actually use already a more or less standard chassis being reconfigured by mission?

=== UPDATE ===

A "mobility platform" is meant to be a general purpose vehicle design which can be modified for different purposes and of course it should be developed over generations. True enough, after building first dozen of cars, nobody yet was thinking of that. Nevertheless, on long term modularity where it makes sense might pay off.

Example: UNIMOG. It does not seem like its wheels' design is much under influence of what they mount on top: sure enough it will have a range of acceptable parameters.

UNIMOG

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    $\begingroup$ You may rephrase your question as "is there any research". I suggest you go see how curiosity platform design was reused in mars2020 $\endgroup$ – Manu H Jul 10 at 6:38
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    $\begingroup$ Mass production is not a goal. Launching a payload to an extraterrestrial world is expensive on itself and thus not done very often. Many unforeseen technological evolution are done between 2 missions, possibly obsoleting previous (standard or not) platform. $\endgroup$ – Manu H Jul 10 at 8:45
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    $\begingroup$ You might note that we did not start out mass-producing identical (or even very similar) terrestrial mobility platforms. Early "horseless carriages" had many different designs, before they evolved into the ones we use today. FTM, we even breed different sorts of horses :-) $\endgroup$ – jamesqf Jul 10 at 16:59
  • $\begingroup$ The MMSEV is the Multi-Mission Surface Exploration vehicle. It’s likely the first choice of NASA for any habitable rover uses. $\endgroup$ – CourageousPotato Jul 10 at 20:12
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    $\begingroup$ Thank you for explaining that! $\endgroup$ – Tanner Swett Jul 12 at 10:18
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NASA have deployed 4 rovers to Mars, and are working on the fifth. ESA is working on nr. 6.

  • Sojourner: tiny, limited.
  • Spirit and Opportunity (MER): much larger than Sojourner. No reuse possible. Spirit and Opportunity were identical.
  • Curiosity: much larger than MER. No reuse possible - but it does use technologies proven on MER, like the suspension design. Mars 2020 will reuse Curiosity's design with small changes (wheel design, IIRC).
  • ESA ExoMars/Rosalind Franklin: seems to be a unique design, after cooperation with NASA didn't work out.

So even on this tiny number, standardization is being used.

The majority of the cost of a rover is not in the driving platform. It's in the scientific instruments, and those tend to be unique: each mission raises new questions, and a new rover is built to answer those questions. These instruments tend to be state-of-the-art or even beyond that, and that's where the cost is: in advancing technology to the point where we can build the instrument we need. The sample analysis instruments on Curiosity would ordinarily fill an entire laboratory, here they had to fit in a tiny box.

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  • $\begingroup$ The size is not the only constraint. You can also mention other adaptation to be fully functional in space (some experiments process may rely on gravity, all the instruments must survive launch vibrations and acceleration and space vacuum,...) $\endgroup$ – Manu H Jul 10 at 8:40
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    $\begingroup$ Dont know why but the last 2 sentences made me get impressed goose bumbs. That's so impressive :) $\endgroup$ – Zaibis Jul 11 at 5:40
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    $\begingroup$ @Zaibis: That's progress. A Hall effect sensor used to be thing that took a lab full of equipment to operate. These days, I can buy a tiny little IC that does the same task as that lab full of equipment - and it does it better and costs like 10 cents. $\endgroup$ – JRE Jul 11 at 9:28
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    $\begingroup$ Since I worked on it I feel I should point out that you missed ESA's ExoMars rover off your list - en.wikipedia.org/wiki/Rosalind_Franklin_(rover) - But your point about instruments driving design is spot on, different rovers provide different mass, volume and power limits for the instruments. $\endgroup$ – liamvharris Jul 11 at 9:41
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The question seems to be primarily about rovers, which is covered in Hobbes' answer. However, there have also been a large number of landers, which have seen a fair amount of re-use:

  • The Soviet Mars 2-7 landers of the 1970s were built in identical pairs. Even between the pairs, many components were re-used.
  • The two U.S. Viking landers were essentially identical.
  • Mars Pathfinder was a unique craft, as it was also used to land the Sojourner rover, in addition to having its own scientific instruments. It did not have the volume to hold the later rovers.
  • There have been three Phoenix-class landers:
    • The Mars Polar Lander crashed in 1999.
    • Mars Surveyor 2001 lander was a twin of the MPL, but cancelled after the failure of MPL. With some minor changes to its scientific instruments, its was later "resurrected" as the 2008 Phoenix mission, which was a success.
    • Spare parts of Phoenix were used to build InSIGHT, the only lander on Mars that is currently operational. This saved significant money on the project.
  • Beagle 2 failed when it could not deploy its solar panels. Its burrowing "mole" instrument was re-designed for the InSIGHT lander.
  • Schiaparelli crashed, but the design will be used for the upcoming Kazachok lander, which will also deliver the Rosalind Franklin rover.

It should be noted that if you want to re-use a spacecraft platform, all of the following must be true. Exceeding one or more of these parameters means you need a new design:

  • The new mission must fit in the volume of the platform.
  • The new mission must be less than the weight limit of the platform.
  • The new mission must require less electrical power than the platform provides.
  • The new mission must be able to survive the landing forces that occur when the platform lands.

As Hobbes points out, newer missions often require new instruments that exceed these parameters.

It does seem that some private space companies have talked about building massive delivery platforms, which will carry payloads from multiple customers. Such designs would be modular and re-used. Blue Origin has proposed such for their Blue Moon lunar lander. However, that approach is way too expensive for government-funded vehicles, and we will have yet to see whether the business model will be successful.

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  • $\begingroup$ Beagle 2 did not crash. It landed successfully, then failed to deploy two of its solar panels, which left its communications antennae blocked. $\endgroup$ – 8bittree Jul 11 at 19:05
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New technologies come along

In addition to "each mission's equipment has a different profile" requiring different parameters in the lander or the rover, we also keep developing newer technologies.

One of the main problems with Curiosity was that the wheels would get damaged and there being no Martian Jiffy-Lube to go to for repairs, the wheels would eventually deteriorate and result in the rover being unable to move (oh, it did that already). Also realize that the wheels are huge. 20 inches in diameter and 16 inches wide made of solid milled aluminum.

One research group is looking into finding a shape-memory alloy that would solve this problem. By finding an alloy that returns to its imprinted shape at the right temperature, that alloy can be woven into a wheel-shaped mesh, that acts as a tire. All deformation against that mesh would heat the alloy up (this is a physical process, you can do it with a paper clip) and that residual heat would be enough to cause the alloy to want to return to its imprinted original shape, effectively self-repairing all damage.

Here's a news article about the research (probably one such group).

And that's just one aspect of a rover's design. More efficient solar panels might come along, and if their weight profile is different, that could result in shifts to other parts of the rover design. Lighter panels might allow for extra instrumentation. Heavier ones might mean sacrifices elsewhere, but allow for higher power usage somewhere.

Every aspect of the rover and lander is influenced by need, (monetary) cost, weight, size, and available options. As we develop new parts, that list of options changes, offering new (game theory) costs and benefits. Imagine if we were still using a 1960s standard lunar lander today (in a hypothetical modern moon landing): it would still be running on 8 bit computers using delay line memory weighing hundreds of pounds! That's what would happen if you made a "standard lander" module "just add instrumentation." The core computer would be locked into a specific specification in order to allow for attaching standardized parts, using a standard amount of power provided by a standard solar array, designed to move a standard weight around the surface on standard wheels...

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  • $\begingroup$ I'm pretty sure the 1960s standard lunar lander used magnetic-core memory, not delay-line memory. $\endgroup$ – Mark Jul 10 at 20:15
  • $\begingroup$ @Mark I know that delay line memory was used at one point and its the delay line memory that was more relevant to the point I was making, so I'd be happy to fix it if I know what used it. $\endgroup$ – Draco18s Jul 10 at 21:10

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