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Author
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Topic: Mercury: Advantages of a retrograde orbit
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Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 07-30-2016 08:15 PM
   
Is it true that the Mercury spacecraft was the only spacecraft to fly in a retrograde orbit and that Gemini and Apollo flew in a forward path?Was the retrograde flight path because it required less fuel to set up for an de-orbiting? And were their any Soviet manned spacecraft that used a retrograde flight path? |
SpaceAholic
Member Posts: 4494
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 07-30-2016 08:42 PM
Mercury was launched in a prograde orbit. |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 07-31-2016 09:40 AM
Mercury, the planet, goes through apparent retrograde motion.No manned spacecraft have done retrograde orbits. Not really practical for US east coast launches. Most orbital launches from VAFB are retrograde. Also, Israeli orbital launches are retrograde due to overflight issues. |
Jim_Voce
Member Posts: 273
From:
Registered: Jul 2016
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posted 07-31-2016 03:34 PM
quote:
Originally posted by SpaceAholic:
Mercury was launched in a prograde orbit.
Thank you for the correction. What I meant is that the Mercury capsule orbited the earth 'backwards' with the heatshield facing forward as it orbited. I wanted to confirm that no other American spacecraft (or Russian) flew in this fashion. And to ask if this was done on Mercury so as to minimize fuel assumption when de-orbiting. In other words, the spacecraft was already positioned to deorbit. |
oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 07-31-2016 09:32 PM
Mercury spacecraft launched pointy end up just like Gemini, Apollo and Orion. at some point in time during the flight they all need to manoeuvre into blunt end forward for re-entry to put heat shield forward. If this happens early on or later on in the flight does not make much difference because during the flight every way is up. The fuel used to rotate the craft 180 degrees would be similar. |
space1
Member Posts: 861
From: Danville, Ohio
Registered: Dec 2002
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posted 07-31-2016 10:19 PM
As a precaution the Mercury spacecraft was normally in orbit with the heat shield forward in case a system failure would prevent a timely maneuver. As far as I know this was not done on any other manned US program. |
SpaceAholic
Member Posts: 4494
From: Sierra Vista, Arizona
Registered: Nov 1999
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posted 08-01-2016 06:40 AM
quote:
Originally posted by oly:
The fuel used to rotate the craft 180 degrees would be similar.
Similar to what? Mercury RCS leveraged monopropellant H2O2 which was unique to that specific application (launch propellant was bi-pro hypergolic hydrazine and retro-fire used ripple fired solid propellant motors). Spacecraft attitude was not sustained in retrograde orientation throughout the entire flight. The crewmember could and would vary attitude to accommodate observation of the external environment and experimentation. |
oly
Member Posts: 971
From: Perth, Western Australia
Registered: Apr 2015
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posted 08-01-2016 07:34 AM
quote:
Originally posted by SpaceAholic:
Similar to what?
The quantity of fuel used (energy) to rotate a spacecraft 180 degrees along direction of flight would be similar if done at the beginning, middle or end of the orbital flight if done at same altitude, speed and mass. using the same motor, regardless of what type of motor is used. |
Jim Behling
Member Posts: 1488
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 08-01-2016 08:12 AM
quote:
Originally posted by Jim_Voce:
What I meant is that the Mercury capsule orbited the earth 'backwards' with the heatshield facing forward as it orbited.
As stated above, Mercury flew "backward" in case of system failures. Also for the earlier orbital missions, they flew at an attitude that would only last a few orbits. This way, if there were several failures, the spacecraft would be in entry attitude and be able to return with no further maneuvering.In addition to the "backward" attitude not being compatible with a maneuvering spacecraft or focusing rendezvous sensors on a target spacecraft, Apollo and Gemini had no need for this safety measure since they had multiple systems for attitude control and multiple means of providing the deorbit impulse. Apollo flew "backwards" towards the moon. And at some time Vostok and Voshkod had to fly "backwards." The durations would have to be supplied by somebody else. Since the Zenit-2 reconnsat was the same spacecraft as Vostok, it is likely it flew in a similar attitude. |
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