Winston
Lorenzo von Matterhorn
- Joined
- Jan 31, 2009
- Messages
- 9,560
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https://www.hq.nasa.gov/alsj/a11/a11.landing.html
[In a post-mission analysis, Apollo Descent and Ascent Trajectories, Floyd Bennett notes that, at PDI, Eagle was about 3 miles farther downrange than planned, due to "small delta-V inputs to the spacecraft state in coasting flight. These inputs were from uncoupled RCS attitude maneuvers and cooling system venting not accounted for by the propagation of the predicted navigates state at PDI."]
[Journal Contributor Ron Wells calls attention to discussions in Gene Kranz's Failure is Not an Option which attribute the positional error at PDI to residual pressure in the tunnel between the LM and CSM at undocking at 100:12:00. In a 2002 e-mail, Kranz elaborates, "Floyd's note was correct on the velocity-induced position error at the start of the descent. There were several interrelated navigation problems, i.e. known deficiencies in the R2 lunar (gravitational) potential model, down-track (along the flight path toward the landing site) and cross-track (left or right, perpendicular to the flight path) propagation errors (errors that start out small but become larger as the flight proceeds), and errors induced by maneuvering of the spacecraft. The principal error induced by maneuvering of the spacecraft was, however, the incomplete vent of the tunnel propagated over one orbit after separation. We made a change in all future missions to get a MCC go-nogo on tunnel delta P before giving the crew a Go to undock. Page 82 of the Apollo 11 post mission report says ....'because of uncoupled attitude maneuvers such as hot fire tests, undocking impulse, station keeping, sublimator operation and possible tunnel and cabin venting. The net effect of these perturbations was a sizeable down-range miss.' To my recollection, the trajectory reconstruction determined that with the exception of the tunnel venting, most of the other perturbations were essentially self canceling. Further the post mission review indicated that the delta P gauge was too gross, the markings misleading and the tunnel had to be vented earlier in the timeline and the valve left in the tunnel vent position rather than returned to off."]
[And, finally, Hamish Lindsay, author of Tracking Apollo to the Moon notes that imperfect knowledge of the effects of mascons (mass concentrations) may have also contributed. In 2006, Hamish consulted with Jerry Bostick, who served as Flight Dynamics Officer on Gene Kranz's White Team. Bostick tells us, "It's one of those things that is hard to definitely prove one way or the other, but my opinion is that it was a combination of the tunnel pressure and us not completely understanding - being able to accurately model - the mass concentrations."]
[Armstrong - "We ended up three miles long."]
[Aldrin - "I think it's pretty remarkable that, this early in the burn, we could estimate that. Good guess."]
[Armstrong - "We picked a number of landmarks (to look at) while we were still in the face-down mode."]
[Aldrin - "I appreciate the 'we'. But you did (the tracking), because I wasn't looking out the window. I could care less about the landmarks. If it wasn't in the AGS or the DSKY, (then Buzz didn't see it)."]
[In a post-mission analysis, Apollo Descent and Ascent Trajectories, Floyd Bennett notes that, at PDI, Eagle was about 3 miles farther downrange than planned, due to "small delta-V inputs to the spacecraft state in coasting flight. These inputs were from uncoupled RCS attitude maneuvers and cooling system venting not accounted for by the propagation of the predicted navigates state at PDI."]
[Journal Contributor Ron Wells calls attention to discussions in Gene Kranz's Failure is Not an Option which attribute the positional error at PDI to residual pressure in the tunnel between the LM and CSM at undocking at 100:12:00. In a 2002 e-mail, Kranz elaborates, "Floyd's note was correct on the velocity-induced position error at the start of the descent. There were several interrelated navigation problems, i.e. known deficiencies in the R2 lunar (gravitational) potential model, down-track (along the flight path toward the landing site) and cross-track (left or right, perpendicular to the flight path) propagation errors (errors that start out small but become larger as the flight proceeds), and errors induced by maneuvering of the spacecraft. The principal error induced by maneuvering of the spacecraft was, however, the incomplete vent of the tunnel propagated over one orbit after separation. We made a change in all future missions to get a MCC go-nogo on tunnel delta P before giving the crew a Go to undock. Page 82 of the Apollo 11 post mission report says ....'because of uncoupled attitude maneuvers such as hot fire tests, undocking impulse, station keeping, sublimator operation and possible tunnel and cabin venting. The net effect of these perturbations was a sizeable down-range miss.' To my recollection, the trajectory reconstruction determined that with the exception of the tunnel venting, most of the other perturbations were essentially self canceling. Further the post mission review indicated that the delta P gauge was too gross, the markings misleading and the tunnel had to be vented earlier in the timeline and the valve left in the tunnel vent position rather than returned to off."]
[And, finally, Hamish Lindsay, author of Tracking Apollo to the Moon notes that imperfect knowledge of the effects of mascons (mass concentrations) may have also contributed. In 2006, Hamish consulted with Jerry Bostick, who served as Flight Dynamics Officer on Gene Kranz's White Team. Bostick tells us, "It's one of those things that is hard to definitely prove one way or the other, but my opinion is that it was a combination of the tunnel pressure and us not completely understanding - being able to accurately model - the mass concentrations."]
[Armstrong - "We ended up three miles long."]
[Aldrin - "I think it's pretty remarkable that, this early in the burn, we could estimate that. Good guess."]
[Armstrong - "We picked a number of landmarks (to look at) while we were still in the face-down mode."]
[Aldrin - "I appreciate the 'we'. But you did (the tracking), because I wasn't looking out the window. I could care less about the landmarks. If it wasn't in the AGS or the DSKY, (then Buzz didn't see it)."]
