Path: utzoo!utgpu!watmath!iuvax!rutgers!rochester!dietz From: dietz@cs.rochester.edu (Paul Dietz) Newsgroups: sci.space.shuttle Subject: Reentry blackout (was Re: Space Program-related acronyms) Keywords: plasma frequency Message-ID: <1989Aug12.005558.6729@cs.rochester.edu> Date: 12 Aug 89 00:55:58 GMT References: <135@sdcc10.ucsd.EDU> <298@opus.NMSU.EDU> <1015@accuvax.nwu.edu> <14531@bfmny0.UUCP> Reply-To: dietz@cs.rochester.edu.UUCP (Paul Dietz) Organization: U of Rochester, CS Dept, Rochester, NY Lines: 21 In article <14531@bfmny0.UUCP> tneff@bfmny0.UUCP (Tom Neff) writes: >The re-entry ionization blackout has more to do with the severity of >radio noise from the fireball than it does with who's listening, I >thought. There have been "light" distruptions in the past, I recall, >but I don't know what the common denominator is. If TDRSS somehow does >it, I'd like to know how. Any plasma has a frequency, called the plasma frequency, at which the electrons & ions in the plasma can oscillate against one another. This frequency is a function of electron density and temperature. I had always thought (I could be wrong) that the blackout on reentry was due to the use of RF frequencies below the reentry plasma's frequency, so the radiation could not penetrate (just as shortwaves are reflected from the ionosphere, or light from a metal). Perhaps the TDRSS lets them use higher frequency microwaves, above the reentry plasma's frequency? Paul F. Dietz dietz@cs.rochester.edu