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Author
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Topic: Mercury spacecraft reentry signal acquisition
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Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 06-02-2018 12:44 PM
   
The Mercury spacecraft were at a 75 mile high altitude above the Earth when re-entry heating would begin. At what altitude did the spacecraft have to plunge before reentry heating stopped altogether and radio communications could be restored?And as far as defining in general at what altitude a reentry typically ends, is it a question of what actual altitude the capsule has plunged down to or more a question of what speed the capsule has slowed down to? |
randy
Member Posts: 2231
From: West Jordan, Utah USA
Registered: Dec 1999
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posted 06-02-2018 02:32 PM
According to "We Seven," page 341, Friendship 7's altimeter read 80,000 feet about 12 seconds after AOS. I couldn't find any reference to altitude at LOS. |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 06-03-2018 01:03 AM
quote:
Originally posted by Jim_Voce:
...or more a question of what speed the capsule has slowed down to?
Speed. |
Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 06-03-2018 06:35 AM
At what speed does a spacecraft have to be slowed down to before atmospheric heating ends?So in the case of the Mercury or Gemini spacecraft, if it reenters at just under 17,500 (less than Mach 25) the reentry plasma sheath as I understand it can extend as far down as 10 miles above the earth (although Randy points out that signal acquisition for Friendship 7 was regained at a 15 mile altitude suggesting that Friendship 7's speed had slowed sufficiently to regain a signal). And a related question — A Mercury or Gemini spacecraft descending from a 100 mile altitude had to descend to about a 75 mile altitude before experiencing reentry heating as I understand it. But then there's the X-15 which on its highest flights starting in 1962 traveled in a zone of 50 to 67 miles altitude. This sounds like the X-15 was already in the "reentry zone" (75 miles and below) and in theory should have been experiencing a plasma sheath of some kind when flying in that zone until its speed slowed down enough. Is that correct? |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 06-03-2018 06:42 AM
quote:
Originally posted by Jim_Voce:
At what speed does a spacecraft have to be slowed down to before atmospheric heating ends?
Depends on many factors, like the shape of the entry vehicle. There is no real single answer. quote:
This sounds like the X-15 was already in the 'reentry zone'...
No, It is not an altitude related "zone" as stated before. It is speed related. Shuttle couldn't communicate with ground stations but that was because the Orbiter was a large planform, it could communicate up to TDRSS through the hole in the sheath. |
Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 06-03-2018 12:57 PM
Thank you Jim for clarifying that. But there is a specific altitude of increased atmospheric density when the plasma envelopment begins. And I think that is at about a 75 mile high altitude for a returning vehicle. Couldn't this be said to be the "re-entry zone"? I realize that it is still speed related in that a returning vehicle will still be a near orbital speed of under 17,500 mph. And it is that speed coming in contact with a certain atmospheric density where the ionization begins. Conversely, if a returning vehicle is 85 miles high in altitude and is traveling at 17,500 mph, it does not experience atmospheric heating as far as I know due to the thinness of the atmosphere. Or if it does, it is very slight at that point. I believe. And as far as the Shuttle being able to maintain radio contact during reentry, was that because it was an irregular shape relative to reentry characteristics (as opposed to a blunt body which allows full envelopment)? |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 06-04-2018 08:14 AM
quote:
Originally posted by Jim_Voce:
But there is a specific altitude...
There isn't a specific altitude. 400,000 ft. has been used the Entry Interface for Apollo and Shuttle but it was not the beginning of black out. It is mostly used for guidance purposes. Others used the Von Karman line, 100 km, as entry. KH-7 GAMBIT spacecraft had flown lower than 75 miles. quote:
...it does not experience atmospheric heating
It does see some heating. quote:
...was that because it was an irregular shape
No, it was because it was big. A big wide blunt body could do the same thing. |
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