Author
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Topic: Did Gemini have a retrograde orbit like Mercury?
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DFBrunswick Member Posts: 40 From: California, USA Registered: May 2015
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posted 05-19-2015 01:10 AM
Once in orbit, the Mercury spacecraft flew 'backwards' as I recall so that the earth would be moving forward and away from the astronaut's perspective. What was the reason for this kind of 'retrograde' flight path? Also did the Gemini and Apollo spacecraft fly 'forward'? |
SpaceAholic Member Posts: 4494 From: Sierra Vista, Arizona Registered: Nov 1999
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posted 05-19-2015 03:10 AM
Mercury's flight path was pro-grade. What you are referring to is spacecraft attitude/orientation vice path. |
space1 Member Posts: 861 From: Danville, Ohio Registered: Dec 2002
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posted 05-19-2015 05:08 AM
The reason Mercury oriented itself that way was to be ready for re-entry at any time if needed, given the experimental nature of the spacecraft. Later flights (Gemini and Apollo) were oriented according to mission requirements.Gemini had orientation modes selectable by the astronauts that included "SEF" and "BEF," for Small End Forward and Blunt End Forward. |
Jim Behling Member Posts: 1488 From: Cape Canaveral, FL Registered: Mar 2010
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posted 05-19-2015 05:20 AM
The Mercury attitude "blunt end forward (BEF)" was so the vehicle was a near entry attitude and was able to perform entry as easily as possible, For Mercury, each orbit was conditional and a GO was given on each orbit to continue the mission.For Gemini and Apollo, the attitude was determined by mission requirement. Nose end forward (NEF) was required by Gemini during rendezvous so that the radar was pointed at the target. Once docked with the Agena, it was flown BEF so that the Agena propulsion systems could be used. On Apollo on the way to the moon, the vehicle would fly in attitudes determined by sun angles and mid course corrections. During LOI, it would have to be with the SM engine towards the direction of flight. Of course, rendezvous and docking with the LM dictated other attitudes. |
Headshot Member Posts: 891 From: Vancouver, WA, USA Registered: Feb 2012
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posted 05-19-2015 07:04 AM
Jim, where did you find the reference to NEF (nose-end forward)? I read one or two Gemini mission documents and recall the orientation being referred to as SEF (small end forward). Just curious. |
Lou Chinal Member Posts: 1332 From: Staten Island, NY Registered: Jun 2007
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posted 05-20-2015 08:51 AM
In Apollo you will see reference to the "Barbecue Mode." The engineers were trying to distribute the heat evenly by keeping the spacecraft in a slow roll. In Mercury, the mindset was "we have be ready to Retro-Fire forthwith." In Gemini they very often performed a rendezvous sideways (90') to the target. |