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During reentry phase into the Earth's atmosphere the heat produced by air friction does not allow any communication with the surface. Why does the heat interfere with electronic frequencies and signals?

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Heat doesn't.

The intense heat does, however, strip off electrons from molecules in the upper atmosphere, leaving an electrically charged plasma. This plasma interferes with radio communications to such an extent there is a complete radio blackout until the capsule has decelerated to such an extent plasma is no longer formed - this can take 30 seconds or more.

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    $\begingroup$ Nice answer, but one question in return. On the last flight of space shuttle Columbia, the signals of Columbia were relayed through a satellite back to mission control. It was the first flight with, well, technically uninterrupted radio contact during re-entry. Did they stick an antenna out of the plasma 'cloud' ... ? $\endgroup$ – s-m-e Aug 12 '13 at 19:44
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    $\begingroup$ They didn't have to. The plasma is pretty much between the shuttle and earth, so transmitting upwards is much easier. (In reality there is still a lot of interference but it is manageable) $\endgroup$ – Rory Alsop Aug 12 '13 at 20:28
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    $\begingroup$ The plasma doesn't exactly interfere with radio communications. Due to the physics of EM waves in plasmas, there is a critical plasma electron density for which EM/radio waves of a particular frequency (or lower) cannot propagate at all. The pressure caused by the bow shock causes the electron density to increase beyond the critical density for part of the re-entry. $\endgroup$ – binaryfunt Mar 19 '18 at 10:55

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