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  Mercury - Gemini - Apollo
  Lunar Module Ascent to Descent Attachments

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Author Topic:   Lunar Module Ascent to Descent Attachments
Neil Aldrin
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posted 01-29-2011 11:37 AM     Click Here to See the Profile for Neil Aldrin     Edit/Delete Message   Reply w/Quote
I was wondering how the attachment and separation was made between the Lunar Module upper ascent stage and the lower descent stage that was left on the moon.

Was this done with frangible bolts/nuts and NSD pyros?

I understand that if an abort were to have been executed before touching the lunar suface they would have needed a method to quickly "dump" the descent stage and fire the ascent engine.

But what about on the lunar surface during normal departure? It would seem prudent to make a mechanical disconnect between the upper and lower stages, and verify this, prior to firing the ascent engine. As opposed to hoping that the release mechanism would operate as planned milliseconds before the ascent stage was fired.

Any thoughts on this or knowledge of the system? Thanks!

ilbasso
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From: Greensboro, NC USA
Registered: Feb 2006

posted 01-29-2011 01:13 PM     Click Here to See the Profile for ilbasso   Click Here to Email ilbasso     Edit/Delete Message   Reply w/Quote
It happened in three stages. First, the electrical connections were severed, then four interstage nuts and bolts were blown, and finally the interstage umbilical guillotine (pyro-initiated) severed the umbilical and water line between the stages. Of course, this all happened within a fraction of a second.

There's a famous story that when they fired the pyros to break the connections on Apollo 16, the Ascent Stage suddenly sank an inch or two. Charlie Duke said he had an "Oh Sh*t" moment in the tenth of a second or so before the ascent engine kicked in and Orion took off.

Neil Aldrin
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posted 01-29-2011 03:56 PM     Click Here to See the Profile for Neil Aldrin     Edit/Delete Message   Reply w/Quote
Thanks for the reply.

Interesting stuff. They sure had a lot of faith in the pyro devices all along the way. I would love to see photos and or diagrams showing these parts and how they operated.

I know that the electrical, water and oxygen connections had to be broken between the command and service modules as well, at jettison. Probably a similar sequence?

By the way, I see you post a lot of information with very deep knowledge and it is appreciated. What's your background?

Thanks!

ilbasso
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From: Greensboro, NC USA
Registered: Feb 2006

posted 01-29-2011 04:16 PM     Click Here to See the Profile for ilbasso   Click Here to Email ilbasso     Edit/Delete Message   Reply w/Quote
Thanks for your kind comments!

There's a NASA presentation about the pyros on the Saturn V and Apollo located here. Very informative. You're right - they did (and still do) rely a lot on pyros, even to start the engines. Most systems had redundant pyros on separate circuits.

Neil Aldrin
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posted 01-29-2011 07:09 PM     Click Here to See the Profile for Neil Aldrin     Edit/Delete Message   Reply w/Quote
Great Link!

That really gives me a much better understanding of the inner workings of those devices. I had no idea that Pyro charges were used so extensively (valves, etc.)

Thanks again!

moorouge
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Registered: Jul 2009

posted 01-30-2011 01:55 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
This description of the explosive bolts is taken from Results of the Second U.S. Manned Suborbital Space Flight. One assumes the LM bolts were roughly the same.
The explosively actuated side hatch was used for the first time on the MR-4 flight. The mechanically operated side hatch on the MR-3 spacecraft was in the same location and of the same size, but was considerably heavier (69 pounds as installed rather than 23 pounds).

The explosively actuated hatch utilizes an axplosive charge to fracture the attaching bolts and thus separate the hatch from the spacecraft. Seventy 1/4-inch titanium bolts secure the hatch to the doorsill. A 0.06-inch-diameter hole is drilled in each bolt to provide a weak point. A mild detonating fuse (MDF) is installed in a channel between an inner and outer seal around the periphery of the hatch. When the MDF is ignited, the resulting gas pressure between the inner and outer seal causes the bolts to fail in tension.

The MDF is ignited by a manually operated igniter that requires an actuation force of around 5 pounds, after removal of a safety pin. The igniter can be operated externally by an attached lanyard, in which case a force of at least 40 pounds is required in order to shear the safety pin.

Neil Aldrin
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posted 01-30-2011 10:38 AM     Click Here to See the Profile for Neil Aldrin     Edit/Delete Message   Reply w/Quote
Thanks for adding that information.

I had never heard the Charlie Duke story about the LEM, but after reading that link can see how it could happen once the mechanical link was severed.

Some of those early NASA pyros operated much the same as the seat belt and buckle charges in many modern cars with SRS, where they use the explosive charge to take up the slack in the belt or buckle.

Going a little further off-topic, I would like to learn more about the currently used Shuttle SRB hold-down nuts, bolts and pyros. I was told also that shuttle crew members are presented with the used nuts after their mission?

Byeman
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posted 01-30-2011 10:59 AM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Neil Aldrin:
I had no idea that Pyro charges were used so extensively (valves, etc.)
Still extensively used in current launch vehicles and spacecraft.

ilbasso
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Posts: 1494
From: Greensboro, NC USA
Registered: Feb 2006

posted 01-30-2011 06:36 PM     Click Here to See the Profile for ilbasso   Click Here to Email ilbasso     Edit/Delete Message   Reply w/Quote
If you watch the JPL video of the latest EDL (Entry, Descent, and Landing) system test for the MSL "Curiosity" Rover, you can hear three sets of pyros firing as the rover is lowered from the Skycrane and as the wheels are released from the cruise position.

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