Monday, January 19, 2004

Algorithmic Cooling on Mars II: Mars (by guest blogger Scott Aaronson)

OK, now Mars. I'm sure you've all read about the dramatic successes of the Spirit rover, which incidentally raise two computer science questions:

  1. Can a lander be programmed to scout a safe, interesting landing site during its 6-minute descent phase? (Sending pictures to Earth takes too long; the round-trip time for radio signals is about 20 minutes.) As far as I know, Spirit took photos only to gauge its speed relative to the surface, not to scout landing sites.
  2. Can (and should) the Internet be extended beyond Earth's atmosphere? During the periods when Spirit is not in Earth's line of sight, two existing Mars orbiters are pressed into service as relays -- so in some sense a Martian communications network already exists. Will denial-of-service attacks and Viagra offers soon plague the solar system?

I'm sure you've also all read about the Bush administration's new vision for space exploration, which includes a manned Mars mission at an unspecified future date. Despite my no-politics mandate, Lance has often discussed science funding in this blog, so I will too. The usual rule is that sending humans somewhere (the Moon, Mars, low-Earth orbit) costs 100 to 1000 times as much as sending robots to the same place. Part of the reason is that, letting ε be the probability of a catastrophic failure, the cost of a mission increases asymptotically as ε approaches 0. Unmanned Mars landers have done well with ε around 2/3. For manned missions, by contrast, any estimated ε above (say) 1/1000 is unacceptable (although ε will always be higher in practice, as we were recently reminded).

But is human spaceflight worth the costs? Lest this post become too polemical, I'll skip the usual arguments and their rebuttals (if you don't know them, read What's New by Bob Park), and end with a question for readers. If you were the President's science adviser, would you suggest gutting the Shuttle, the ISS, and all work towards a moon base or manned Mars mission, and diverting the funds toward basic science? If so, a followup: suppose the NSF budget for theoretical computer science were quintupled tomorrow. What would be the best way to spend the money?

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