The discussion revolves around the Apollo 11 mission, specifically focusing on the 1202 computer error code encountered during the lunar landing. Participants explore the implications of this error, the architecture of the onboard systems, and the historical context of programming and hardware used in the mission.
Participants express a mix of agreement and disagreement on various aspects of the discussion, particularly regarding the nature of the 1202 error, the decision-making process during the landing, and the historical context of programming practices. No consensus is reached on these points.
Participants highlight limitations such as the lack of modular code, absence of libraries or modern programming tools, and the severe constraints of memory size during the Apollo missions. These factors contribute to the complexity of the issues discussed.
This discussion may be of interest to those studying the history of space exploration, computer science, and engineering, as well as enthusiasts of the Apollo program and its technological innovations.
jedishrfu said:Summary: Perhaps the most dramatic moment of Apollo 11's mission to the moon was when the Eagle began its final descent to the lunar surface and the Apollo Guidance Computer became overloaded. Few were more nervous than the young computer programmer who had written the code for the landing. On the Apollo 11's 50th anniversary, WSJ sat down with programmer Don Eyles.
That might not be the whole story. Their ability to abort at that point may have seemed more risky than continuing. Remember that they admitted later that they did not have much faith in the ascent engine. Aborting would have meant maintaining control of the descent plus starting the ascent engine at the same time.Greg Bernhardt said:Unbelievable courage, continuing the mission after getting those errors and not really knowing what they meant! I'd need a new space suit!
It is hard for us today to imagine just how constraining the memory size was in those days. When I started in 66, the cost was about $1 per bit. (I worked at GE's Apollo Support Department in Daytona 1966-68) 1kB was an engineer's annual salary and more than one year's salary for a programmer. In a space module, cost was unimportant, but size and mass were still severe constraints.jedishrfu said:just the symbol index in the program listing if you chose to generate one and hopefully the programmer used a symbol like ERR1202.
if X=A then CASE=1
elseif X=B then CASE=2
else ERR=1202 'because there should only be 2 cases
assert X=A or X=B
Aborting the descent is what Apollo 10 did on purpose - as dress rehearsal for the landing, because that was considered to be safer than actually landing.anorlunda said:That might not be the whole story. Their ability to abort at that point may have seemed more risky than continuing. Remember that they admitted later that they did not have much faith in the ascent engine. Aborting would have meant maintaining control of the descent plus starting the ascent engine at the same time.
That is not really accurate. Apollo 10 LM was happily in lunar orbit (albeit a low one)) the whole time. At no time did the perform a true abort procedure although they did separate the lower stage and briefly fired the ascent engine to test it. I assume they did not perform an "abort" procedure because it was, in fact, too dangerous!mfb said:Aborting the descent is what Apollo 10 did on purpose - as dress rehearsal for the landing, because that was considered to be safer than actually landing.
mfb said:They didn't get that close to the Moon but they separated the descent stage in flight and fired the ascent engine - just as Apollo 11 would have done for an abort. With the difference that Apollo 11 would have needed the ascent engine to work quickly and fire for a while, it would have crashed into the Moon otherwise.
Use of AGS[edit]
There are few actual descriptions of the use of the AGS, as a landing abort was never needed during the Apollo missions. There were, however, four cases in which the AGS was used.
Its first use was for testing of the Lunar Module descent stage in Earth orbital flight during the Apollo 9 mission[6]. It was used again in the Apollo 10 mission, following separation of the Lunar Module descent stage prior to the APS burn. An incorrect switch setting[7] leaving AGS in Auto rather than Attitude Hold mode led to a prompt and pronounced deviation in attitude moments before staging[8]. The situation was quickly brought under control.
The next use of the AGS was during the lunar ascent phase of the Apollo 11 mission, when the LM crew performed a sequence of rendezvous maneuvers that resulted in gimbal lock; the AGS was subsequently used to acquire attitude control.[2]
The AGS played an important role in the safe return of Apollo 13 after an oxygen tank explosion left the Service Module crippled and forced the astronauts to use the Lunar Module as a "lifeboat." Supplies of electrical power and water on the LM were limited and the Primary Guidance and Navigation System used too much water for cooling. As a result, after a major LM descent engine burn 2 hours past its closest approach to the Moon to shorten the trip home, the AGS was used for most of the return, including two mid-course corrections.
Greg Bernhardt said:Unbelievable courage, continuing the mission after getting those errors and not really knowing what they meant! I'd need a new space suit!
jedishrfu said:Summary: Perhaps the most dramatic moment of Apollo 11's mission to the moon was when the Eagle began its final descent to the lunar surface and the Apollo Guidance Computer became overloaded. Few were more nervous than the young computer programmer who had written the code for the landing. On the Apollo 11's 50th anniversary, WSJ sat down with programmer Don Eyles.