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The Japanese SS520-5 nanosat launcher has a payload of 5kg or so to LEO on an all solid fuel rocket with a total mass of about 2.6 tons. To reach LEO its delta-V totalled over all three stages must be about 10 km/s, which is more or less what is needed to get from Mars surface to Earth intercept. Furthermore it's entirely solid fuel, so should survive the journey to Mars (at least from a time perspective).

Which brings me to my question -- if you had one of these (with reasonable adaptations) on the surface of Mars, could you use it to return a few kg of samples and heatshield to Earth, thereby eliminating one step in the current Mars sample return mission plan?

Secondary (but really part of the same question)? Just how hard would it be to get one there? It's about three times the mass of Curiousity or Perseverance, and a rather awkward shape.

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    $\begingroup$ About the rocket - I suppose there are at least two problems. First - to deliver the rocket to Mars. It weights over 2600 kg, and also long and thin - not the best shape for atmospheric reentry. (altough the latter can be redesigned). Second - it should be usable at Martian temperatures. For Mars Sample Return mission a special cover for thermal conditioning is planned AFAIK. $\endgroup$
    – Heopps
    Commented Aug 11, 2020 at 12:57
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    $\begingroup$ Different but related: How do spherical SRB's compare to long skinny ones? What do their thrust curves look like? $\endgroup$
    – uhoh
    Commented Dec 13, 2020 at 23:15
  • $\begingroup$ Previous US Earth entry vehicles (Stardust, Genesis, OSIRIS-REx) all used a ~45 kg, 60° sphere cone design, MSR currently looks to be evolving to a new generation entry vehicle (no parachute!), and similar weight (iirc). Hayabusa(& -2) used a smaller ~19 kg entry vehicle so existing designs are still a ways away from ~5 kg, if that number maths out for the Mars case. $\endgroup$
    – BrendanLuke15
    Commented Feb 21, 2022 at 15:37

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Could you use it to return a few kg of samples to Earth? Technically, yes, but practically, no.

From a straight orbital-mechanics standpoint, an SS-520-5 would have no trouble launching a payload from the surface of Mars to an Earth intercept. The 9400+ m/s delta-V to get to Earth orbit is well in excess of the approximately 6300 m/s needed to get from Mars surface to Earth intercept*, giving you room for a larger payload or a smaller rocket (maybe the two-stage S-520?).

The problem is in the details. The SS-520-5 is a pure solid-fuel rocket. This means that once you fire a stage, you can't stop it until it burns out. If any of the stages is running even a little fast or a little slow, you're going to miss the Earth entirely -- the entire planet is less than 1 m/s wide when launching from Mars, and the survivable re-entry corridor is much narrower than that. You really want a liquid-fuel or hybrid upper stage, so you can shut the engine down at exactly the correct moment. Ideally, it would use hypergolic fuels so you can do multiple mid-course correction burns if needed.

* Your 10k m/s for Mars surface to Earth intercept appears to be including the 3200 m/s for circularizing in low Earth orbit. You don't need to do that -- you can aerobrake the whole way down. You just need a heat shield that can handle it.

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