posted 07-30-2004 12:03 PM               

Which direction would the CSM be pointing on the trip out to the moon? Was it going backwards (engine bell towards the moon) or forwards?

I would assume backwards since they have to turn around to pick up the LEM but I remember what my mom said about assuming things.

posted 07-31-2004 11:28 PM            

quote:

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Originally posted by sts205cdr:
The CSM/LM stack was oriented perpendicularly to the flight path and rotated slowly to evenly absorb and radiate heat.

--John

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Am i right in saying the ships' alignment on all axes was constantly tweaked to take manual visual sextant/navigation readings?

posted 08-03-2004 11:30 AM               

--John

posted 08-04-2004 09:34 AM            

Here its is again copied to Notepad then copied here. Let's hope the weird cahracters dissappear :-)

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I don't know if this will help but here goes !

All Apollo missions used a Basic Reference Co-ordinate (BRC) system - an orthogonal inertial co-ordinate system - whose origin was either the centre of mass of the Earth or the centre of mass of the Moon.

The IMU's used values from matrixes that transformed elements of a vector in the BRC system. These matrices were called REFSMMATs.

There were usually eight REFSMMAT's used - one of which was called the Passive Thermal Control (PTC) or 'barbecue roll mode. The PTC REFSMMAT was used for MCC-1,-2,-3,-4,-5,-6 and in the J-3 missions for SIM Bay door jettison. Each REFSMMAt was a unique matrix locating an IMU stable member axis (X,Y,Z) in the BRC space co-ordinate system.

The BRC changed from earth centred to moon centred at the 64,373,760 metre distance.

For the PTC REFSMMAT the X-axis was in the ecliptic plane and perpendicular to
the Earth-Moon line projection in the ecliptic plane at the average time of TEI
for monthly launch window and azimuthal range. The Y-axis completed the Right hand system while the Z-axis was perpendicular to ecliptic directed 'south'

This is why the IMU (with its gyros etc) was critical to the success of an Apollo mission. Just before launch, there was a countdown step that ensured that the correct values for X,Y,Z for LC-39A (or B) for that launch day and azimuth were uploaded along with an accurate time. This was the 'start position' .There was a block house for an accurate position device at LC-39A/-B to determine this. From this point onwards everything would 'revolve' around the IMU values using the various REFSMMAT's . Because of small errors in hardware, electronics, gyro drift and other factors, it was important that all along the flight path ,at selected times, the astronauts used the telescope and sextant to make star readings to determine the IMU orientation with respect to BRC system that would then be used in REFSMMAT matrices to give updated IMU values. A lot of the numbers you see in the Apollo mission transcripts or hear on mission audio recordings are values that were to be used in the various REFSMMAT's.

If Sy is reading this thread maybe he will be able to add more info ?

Phill Parker
UK

posted 08-04-2004 12:12 PM            

"Apollo 11, this is Houston. Evasive _ aneuver SPS G&N: 63481, plus 095, minus 020; GETI 004 40 0100, plus 00051, plus all balls, plus 00190; ...etc"

I know it's to do with navigation , but is it gyro stuff (as in the gyro's are spheres) , or star/sextant lingo, as it kind of sounds like old sea mariner language.

Thanks

Andrew

posted 08-04-2004 07:02 PM               

I am very surprised - the "natural" angle always seemed to me to be spinning along the long axis, in effect like a rifle bullet, with the nose pointed in the direction of travel (though with the view blocked by the LM on the outward leg.)

I am doubly surprised, because as I said earlier, in every movie and documentary (eg in any CGI sequences) I've always seen it depicted as I imagined it was and never sideways.

posted 08-04-2004 08:57 PM               

"The last P52 aligned the X-axis of the IMU platform with the ecliptic and at right angles to the Earth-Moon line; its Z-axis was aligned southward, perpendicular to the ecliptic. If the spacecraft were aligned to match the platform, it would have its longitudinal axis aligned with the ecliptic with the Earth and Moon to either side. By pitching 90°, as called for in the Flight Plan, 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."

"Changing the selected omni-directional antenna from C to B will restore Mission Control's capability to switch between antennas B and D. Since these are on opposite sides of the spacecraft, Houston will be able to maintain communications as the spacecraft rolls slowly around."