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I've heard discussion of the Mars Curse, with the very high failure rate of missions to the planet. Comparing NASA Mars missions to NASA outer solar system missions since the beginnings of the 1970's is there really a "curse" for NASA

My numbers are based on Wikipedia entries for NASA Mars missions and overall missions, please edit if they are inaccurate.

Since 1971 there have been 23 NASA missions to Mars, with 4 of them failing (5, but I'm not counting launch failures), and 11 missions to the outer planets and none of them failed. Does the difference in the success rate simply come down to the "Faster, Cheaper, Better" program being a mistake?

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    $\begingroup$ You may not compare Mars lander missions to outer planet flyby missions. But mission counts are too small for comparison of success rates anyway. $\endgroup$
    – Uwe
    Dec 1, 2019 at 14:21
  • $\begingroup$ @Uwe Weren't 2 of the 4 missions that failed in the 1990's orbiter missions. I get it that lander missions should not be compared to flyby missions. Are orbiter missions substantially more difficult than flybys? $\endgroup$
    – Bob516
    Dec 1, 2019 at 14:34
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    $\begingroup$ The curse is due to the thin martian atmosphere being unable to brake spacecraft coming from orbit sufficiently, so that the slightest mistake in velocity computation leads to the loss of the lander. This effect obviously doesn't play a role for any other planet. $\endgroup$
    – AtmosphericPrisonEscape
    Dec 1, 2019 at 17:58
  • $\begingroup$ More maneuvers and changes in environment equate to more risk because of possible failures in the systems designed to perform those maneuvers or adapt to those changes in environment. $\endgroup$
    – CourageousPotato
    Dec 3, 2019 at 2:17
  • $\begingroup$ I think orbiters often pass very close to Mars. $\endgroup$
    – ikrase
    Dec 7, 2019 at 10:00

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While more outer planet missions have not 'failed' it is worth noting that many of them have had major problems. Juno was not able to reach target orbit, Galileo had antenna and other issues, Genesis sample return failed to deploy parachute and voyager 2 lost a transmitter among others.

Generally lander and to a lesser extent orbiter missions are more weight constrained since they must carry fuel or heat shield for stopping at their destination so spare systems and redundancy get deleted to make up, making events like the ones above 'mission failure' rather than just a complication to the plan. Similarly with more complex missions there is more room for failure or design error to cause problems. A flyby with a couple of % trajectory error still achieves the flyby and be called a success (at least in public), an orbiter/lander will generally fail entirely in this case.

Risk managment is also a factor. Mars mission windows are every couple of years and take a couple of years to complete while outer planet missions are every decade out to every 175 years and run for decades. For this reason it can be worthwhile doing things that massively increase mission costs to test and verify things before launch or other critical phases of an outer planet mission, where for a Mars mission a test set that will double the mission cost but reduce risk by 25% might be better spent on building next years mission.

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