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Post by PhantomWolf on Sept 7, 2006 16:50:44 GMT -4
I noticed on From the Earth to the Moon: Part 4 - 1968 that when Apollo 8 was flying to the Moon they put into into a "standing up" position where if you were to draw a line between the Earth and the Moon, instead of pointing towards one or the other, it would have been sitting on its tail with one to each side. Now I already know that you can orientate the craft in any direction once it's fired its SME and it will still go in that direction so that's not a problem, and I'm guessing that it might be easier to do the turn for LOI in two stages as well as letting them probably see where they had been and where they were going, but I do have to ask, did they actually travel in this orientation mode? And if so, why, rather than keeping the nose pointed towards the moon until they were ready to do their turn? I'm guessing they did, because otherwise they probably couldn't have seen the Earth from inside the CM, but it's just something I've never thought about before.
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Post by echnaton on Sept 7, 2006 17:53:51 GMT -4
I think that the position was used because it gave even exposure to the sun over the spacecraft. A8 traveled outbound during a new moon. Pointing at the moon or earth would have exposed the CSM stack to very uneven heating.
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Post by ajv on Sept 7, 2006 20:32:05 GMT -4
The Apollo 15 Flight Journal has some information on PTC. the longitudinal axis of the spacecraft is brought perpendicular to the ecliptic which guarantees that the Sun (which is always in the plane of the ecliptic) will strike the spacecraft side on as it rotates. For the first PTC on A15, the stack was oriented to a pitch of 090, yaw 000 with respect to the "PTC Orientation REFSMMAT". For the first PTC on Apollo 8 it's more complicated. The flight plan gives pitch 331, yaw 331. This was changed by Collins (at 005:39:18) to pitch 242, yaw 020. However, the Flight Journal authors believe at this point the orientation was respect to the launch pad REFSMMAT. From the A8FJ: While compiling the Apollo 8 journal, it has been striking to compare the documentation associated with the mission with Apollo 15, the journal we worked on prior to this. Throughout Apollo 15, the spacecraft's orientation reference, the REFSMMAT, was always explicit, and was changed regularly as the mission progressed. On Apollo 8, these procedures are much more primitive, presumably because of the unknowns and the mission's pioneering nature. Apart from launch, this author (Woods) has seen no definition of the reference they are using for their guidance platform.
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