Posted on by Adam

Odds & Ends News 14-2-2010

Happy Valentine’s Day to all you loveable Blog-ghosts who read this page.

I’ve been working on the dynamics of laser pushed reflectors – i.e. super-reflectors which can ‘reuse’ the beam thousands of times before it is absorbed and lost as heat. The concept was AFAIK originally discussed by Robert Metzger & Geoff Landis, but Young K. Bae has used it experimentally in a mock-up of a low-power position system for space-vehicles. Ignoring relativity, for now, and staying at close range to minimise diffraction loses, the final velocity over a range from Xo to X is pretty easily solved as…

v = sqrt[2.E/m*ln(X/Xo)]

…but then integrating, care of the Online Integrator from Wolfram’s Mathematica, to find the trip-time produces this horror…

t = 2.X.F{sqrt[ln(X/Xo)]}.sqrt[m/2E]

…F{…} is Dawson’s Function or Integral which is related to the Error Function that produces the Bell Curve. In otherwords there’s no easy way of computing the rotten thing.

Trawlling the Web produces some interesting finds, courtesy of the University of Arizona Press, a whole book online by Carl Sagan & James Pollack (both sadly deceased), Planetary Engineering ,which covers all the big questions of remaking the planets. Cool.

Sagan was a heavy-hitter in astrobiology & SETI – he worked on even while battling his ultimately fatal cancer and produced this paper, one of his last…

Scintillation-induced Intermittency in SETI

…which covers the fade & amplify effect that interstellar plasma can have on radio signals. Thus we might occasionally receive a signal from much further away, thanks to random drifts of plasma in the intervening void. Makes it very hard to get a repeat performance from such signal sources and the full implications are discussed here by his co-writer…

Now You See Them, Now You Don’t

…on his web-site (John Lazio’s page.)

Mentioned by the 1997 paper is an earlier SETI results paper, by Paul Horowitz & Sagan (again) from 1993…
Five years of Project META – an all-sky narrow-band radio search for extraterrestrial signals
…which reports a tantalising set of signals. Benford3 reference the paper in their duology…

Searching for Cost Optimized Interstellar Beacons

Messaging with Cost Optimized Interstellar Beacons

…which are deserving of a more detailed discussion next time.

5 Replies to “Odds & Ends News 14-2-2010”

  1. Luke Campbell said “I will note that explicit methods of calculating Dawson’s integral are given in the various Numerical Recipes books by Press et. al. (as I type, I’m looking at the implementation in Numerical Recipes in FORTRAN 77).”

    “The routine presented has an accuracy of about 2E-7, and it should be trivial to get accuracies near 1E-16 by using double precision arithmetic.”

  3. Guess I’ll have to try to write it in C or Java. Might be a worthwhile exercise. I found an approximation that seems reasonably accurate on the arXiv…

    astro-ph/0602124 v2

    …which is enough for now. But the Numerical Methods approach has piqued my interest, thanks.

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