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Imagine rovers collecting samples on Mars and launching them to dock with a Mars-Earth transfer spacecraft. This vehicle would be in a Mars cycler orbit which passes near Mars and Earth every 7 years, for example. The sample in a cubesat sized probe and put in Earth orbit, possibly landing on Earth. It could also carry terabytes of data in solid memory chips brought together with the rock samples from instruments on the surface of Mars. All being low weight and cheap to accelerate, using the fuel stored in the Cycler.

The point would be to lower mass and complexity of the Mars ascent vehicle, so that for each return to Earth only one Atlas V class launch, or so, would be required to land it on Mars. Plus the one time larger launch of the reusable cycler. The cycler could provide fuel for Earth orbit insertion of the sample, and during the transfer also solar power, shielding, Earth communication, keeping the samples at Mars temperature if desirable. And maybe a capsule for direct Earth landing (storing one for each return mission foreseen). A sample return mission once every third conjunction (about 7 years) doesn't seem overly ambitious.

Could sample ascent, Earth landing and cycler transfer vehicles be made light enough to make this feasible today? Or would they need too much overhead equipment? Would the high velocities required for rendezvous with a cycler orbit eat up the benefits?

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    $\begingroup$ What's the point of a cycler for cargo anyway? The point of a cycler is to reuse life support equipment, cargo doesn't need life support, there's nothing to be gained. $\endgroup$
    – Loren Pechtel
    Nov 15, 2015 at 1:48
  • $\begingroup$ Minimizing the Mars ascent vehicle. The cycler could carry fuel, and even the heat shielded capsules, for Earth landings. On the other hand, the ascent vehicle might need more fuel to reach the cycler, than a one off vehicle in Mars orbit. I wonder if it is apparent how it adds up. $\endgroup$
    – LocalFluff
    Nov 15, 2015 at 6:22
  • $\begingroup$ Once you've matched orbits with the cycler there's little need of fuel because you return via aerobrake. All I can see to save is that the stuff for re-entry doesn't need to enter Mars orbit and that's expended upon return anyway--nothing to cycle. If you want to save mass do two launches--the probe and then the return capsule later to fly by Mars, meet the probe and bring the cargo home. I would be surprised if this was cheaper, though. $\endgroup$
    – Loren Pechtel
    Apr 5, 2016 at 5:51
  • $\begingroup$ I feel like a series of mars cyclers released from LEO and pushed into mars transfer orbit with a distance of 1 year inbetween them could be useful for data integrity. If the orbiters are programmed to recieve information from mars orbiters at their closest, then pass them back along the satellite chain, we may increase data accuracy and speed in wireless transfers. $\endgroup$
    – Magic Octopus Urn
    Aug 23, 2018 at 15:09

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I'm not sure data return in a physical format is worthwhile. Samples are another question, of course.

If we're already willing to wait seven years for it all to come in, why not transmit data slowly throughout that period via a relay satellite? This means you can start interpreting it early (and help inform the ongoing sample collection work); you avoid the "all your eggs in one basket" problem; you escape the risk of physical data corruption; and, best of all, you get flexibility. You can relay information from other orbiters, from other (non-sample-return) vehicles, etc.

But surely a relay satellite is too slow? Well, not really. Conveniently, we have a figure for the amount of data returned by the Mars Reconnaissance Orbiter over its first seven and a bit years; over 200 terabits, or 25 terabytes (TB). It's reasonable to assume that a dedicated relay satellite would have the ability to exceed this, and if we can transfer dozens of TB every seven years, we're seriously competing with the physical storage approach.

Only a small fraction of the data sent through MRO is relayed from the surface, but if we knew there would be a dedicated and high-capacity relay satellite, rovers and landers would no doubt be built to rely on that infrastructure, and high-bandwidth relay uplinks on them could be prioritised.

Yes, we'd still have to keep the data relay satellite working. But we're doing pretty well with Mars orbiters - every orbiter that's made it to Mars in the past fifteen years is still going - and if we built a cycler, we'd have to worry about keeping that going.

All told, from the data transfer perspective, it's probably unnecessary.

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  • $\begingroup$ If one returns rock samples anyway, the extra cost of putting a memory capsule in it is very small. Sensors develop and multiply, catching every photon from optical and chemical observations. Physical data transfer could complement select radio transfer. Data selection is hard while the unknown is being explored. Could also allow for engineering data to learn about how everything worked all of the time. 7 years would be (an example of) delivery interval. The travel time from Mars to Earth would only be about 7 months. $\endgroup$
    – LocalFluff
    Nov 13, 2015 at 5:01
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I think a more efficient method of data transfer would be relay from Mars orbit to Earth orbit. Of course this would involve beefing up both Mars and Earth satellites (most substantially, Mars). Of course, if you're talking about 100 TB of data, then we won't have any quick and efficient means of delivering that for a while.

As far as sample return, I can't see the need for sample return being that high anywhere in the near future. It is a lot more likely that we'll do more in situ lab work.

Now, could you? Sure, I don't see any reason why you couldn't have cargo instead of crew. I just doubt a cycler will be set up specifically for data and sample purposes, due to the cost of setup. If you already had a cycler system set up, it might be used for that as well.

More information on Mars data rates:

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    $\begingroup$ Labs on Earth are much much larger and better than anything sent to Mars. And whatever the radio data transfer rate is for select data, massive memory could bring home ALL data the instrument has collected. But the basic question is really about if a robotic Mars-Earth cycling spacecraft could make sense for repeated sample return to Earth. I think I ever only saw Mars cycles thought of as being crewed. They should be as good at returning samples as well. $\endgroup$
    – LocalFluff
    Nov 12, 2015 at 16:48
  • $\begingroup$ @LocalFluff I thought the general principle of cyclers was that they were not physically piloted--so I don't see any reason why you couldn't have cargo instead of crew. I just doubt it will be set up specifically for data and sample purposes. If you already had a cycler system set up, it might be used for that as well, for the reasons you mention. $\endgroup$
    – called2voyage ♦
    Nov 12, 2015 at 16:50
  • $\begingroup$ This talks about the general issue of data and sample return, but doesn't address the cycler concept in any way. It doesn't seem to me to answer the question. $\endgroup$
    – kim holder
    Nov 12, 2015 at 16:58
  • $\begingroup$ @kimholder edited comment into answer, how does it look now? $\endgroup$
    – called2voyage ♦
    Nov 12, 2015 at 17:00
  • $\begingroup$ Um, pretty vague... Why wouldn't a cycler system be set up for that? Too much investment, even for a micro version of it? Not enough science return? A technology gap? $\endgroup$
    – kim holder
    Nov 12, 2015 at 17:04

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