See listAPR 21 196767-FM1-32FM/Deputy ChiefDescent engine gimbal polarity error
A serious misunderstanding between MIT and Grumman resulted in a situa- tion which would have been catastrophic to the AS-206 mission if it had not been discovered. Specifically, the direction the LM descent engine gimbals move when commanded by the spacecraft computer was opposite to the way they were supposed to. Upon discovery of this, Grumman immedi- ately dispatched a TWX widely distributed through MSC, and perhaps else- where, placing the fault for this inconsistency on MIT. Since it was easier to make the necessary modification in the software than the hard- ware, we chose to do that – thus giving further weight to the idea that the MIT work was faulty, which I simply do not believe to be the case. I am distributing the attached letter from MIT which explains the situa- tion in some detail in order to dispel the erroneous accusations you may have heard and believed.
Of course, finger pointing is not constructive, and I would like to em- phasize that a number of positive steps have been taken. Their purpose is to improve the understanding of the various parties associated with these interfaces and improving coordination of their testing to make sure a vehicle is never flown with anything as fouled up as this. Also, it is worth noting that this discrepancy was detected well in advance of the mission and in time that something could be done about it fairly easily. Even if we had done nothing, I would expect on future spacecraft that this sort of thing would be found sooner as a result of much earlier delivery of spacecraft computer programs and earlier readiness of the test facilities to verify its interfaces with a flight hardware.