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Author Topic:   Apollo LM Lunar Surface Sensing Probe
Apolloman
Member

Posts: 148
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 08-17-2019 02:17 PM     Click Here to See the Profile for Apolloman   Click Here to Email Apolloman     Edit/Delete Message   Reply w/Quote
Why the Apollo lunar module's lunar surface sensing probes did not cut automatically the DPS engine?

Is there a study of where is the choice to have the engine shut off manually, or is it an astronaut's claim?

oly
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Posts: 905
From: Perth, Western Australia
Registered: Apr 2015

posted 08-17-2019 09:12 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
The design of the Lunar Surface Sensing Probe was to illuminate a surface contact light on the instrument panel to advise the crew about the lunar module proximity to the lunar surface, in this case, 5'6" from the surface.

The lunar module Guidance and Navigation Computer had experienced a long and difficult development path, and the I/O configuration had been established. Introducing an additional control circuit to the rocket engine electrical control system would mean also introducing another failure path into the system, increased weight, and add additional complexity to the computer software.

The design goal could efficiently be achieved without introducing the additional complexity and weight to the Lunar Module systems through the use of an indicator light. Keeping it simple. From an Apollo Experience Report:

Attached to each of three of the footpads is a 1.73-meter (68 inch) probe designed to sense lunar-surface proximity and to signal the LM pilot so that he can initiate descent-engine shutdown.
And from a report about the landing gear:
A few months before Apollo 11, test data indicated that heating rates on the landing gear were much higher than anticipated. At approximately the same time, the LM flight crew expressed a desire to have the option of using either the probe mode or the pad mode for landing. The probe mode is the primary procedure for LM touchdown and consists of descent-engine shutdown initiation after probe contact with the lunar surface but before footpad contact. The pad mode is considered a backup landing mode in which engine thrust is terminated after footpad contact. Inclusion of the pad mode resulted in even higher predicted heating rates for the landing gear. Consequently, the Apollo 11 landing gear thermal insulation weight was increased to 31.03 kilograms (68.4 pounds). A refined analysis allowed reduction of the landing gear insulation weight on subsequent vehicles so that it represents approximately 8 percent of the total landing gear weight. This particular problem illustrates a hardware change made as a result of improved test data and a change in operational procedures.

Apolloman
Member

Posts: 148
From: Ledignan, Gard (30), France
Registered: Mar 2009

posted 08-18-2019 07:59 AM     Click Here to See the Profile for Apolloman   Click Here to Email Apolloman     Edit/Delete Message   Reply w/Quote
Thank oly.

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