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## Hypersonic Radio Black-Out Problem Solved88

KentuckyFC writes "Russian physicists have come up with a new way to communicate with hypersonic vehicles surrounded by a sheath of plasma. Ordinarily, this plasma absorbs and reflects radio waves at communications frequencies, leading to a few tense minutes during the re-entry of manned vehicles such as the shuttle. However, the problem is even more acute for military vehicles such as ballistic missiles and hypersonic planes. Radio blackout prevents these vehicles from accessing GPS signals for navigation and does not allow them to be re-targeted or disarmed at the last minute. But a group of Russian physicists say they can get around this problem by turning the entire plasma sheath into a radio antenna. They point out that any incoming signal is both reflected and absorbed by the plasma. The reflected signal is lost but the absorbed energy sets up a resonating electric field at a certain depth within the plasma. In effect, this layer within the plasma acts like a radio antenna, receiving the signal. However, the signal cannot travel further through the plasma to the spacecraft."
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## Hypersonic Radio Black-Out Problem Solved

• #### The shuttle doesn't (currently) black out (Score:5, Informative)

on Friday January 07, 2011 @02:19PM (#34793990)
http://en.wikipedia.org/wiki/Communications_blackout#Reentry_communications_blackouts [wikipedia.org]

Until the creation of the Tracking and Data Relay Satellite System, the Space Shuttle would, like Gemini, Mercury, Apollo, and others, endure a 30 minute long communications blackout before landing. However, the Shuttle can communicate with a Tracking and Data Relay Satellite during re-entry. This is because the shape of the Shuttle creates a "hole" in the ionized air envelope, at the tail end of the craft, through which it can communicate upwards to a satellite in orbit and thence to a ground station.

• #### Re:No, they haven't. (Score:5, Informative)

<bughunter@@@earthlink...net> on Friday January 07, 2011 @02:33PM (#34794176) Journal

FTFA:

Korotkevich and co say the weakness of the transmission signal doesn't matter because ground-based receivers can be made hugely sensitive, certainly much more so than mobile ones.

Considering we can communicate with interplanetary (and now some technically interstellar) probes with received signal strengths on the order of -200 dBm [baylorschool.org], and we can build arbitrarily large transmitters/receivers on the ground, and health and status telemetry doesn't require huge bandwidths (on the order of 10^2 bps), I'd say he's right.

• #### TFA is revealed! (Score:5, Informative)

on Friday January 07, 2011 @03:06PM (#34794620)

Well, I read the full introduction of the paper, and the conclusion, skipping only the detailed plasma physics models & calculations. They do mention the strategy of putting an antenna through the plasma which can last as long as one fuel tank before it ablates, but they instead propose that (more elegantly) a small commercially-available 3 kW high frequency klystron amplifier (a lot less power than the radar) be placed at the surface of the aircraft, where it will disrupt a very small region of the plasma in a manner that will scatter ~.7 - 2% of the original incoming signal (which will resonates in a layer of the plasma) back to the aircraft; that is enough power for a 5 m. antenna and a commercially-available high sensitivity GPS receiver to pick it up. There is an analogous explanation for outgoing signals. They account for quite a few confounding plasma effects, acknowledge that there are some others that can't be modeled so clearly (or maybe they didn't think of), but predict that getting the system to work would be a not-so-difficult engineering challenge.

My first thought was, "Boy, I hope all the space opera authors read this preprint: no more signal attenuation from the plasma engines in the atmosphere!" Now there is one more area in which reality is exceeding a certain segment of--rather soft--science fiction (that I am only familiar with--AHEM--because of Baen's visionary no-DRM any-format ebook policy).

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