# Another Apollo question - CM/SM systems interface. **URL:** \ **Category:** Factual Questions\ **Created:** [June 15, 2009, 8:08pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869 "2009-06-15T20:08:40Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MrFloppy](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)\ **Post date:** [June 15, 2009, 8:08pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/1 "2009-06-15T20:08:40Z")
On the the underside of the Apollo Command Module was the ablative heatshield, essential for the return to earth. When the Command Module was attached to the Service Module how did electrical power, oxygen and other services ‘get’ from the SM to the CM? Did these services pass through ‘conduits’ in the heatshield and if so, how did these conduits not compromise the heat shield’s effectiveness? I have always wondered this and have been unable to get a good answer. ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [June 15, 2009, 8:44pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/2 "2009-06-15T20:44:26Z")
The connections go along the exterior of the spacecraft, as shown here: [http://www.perspectx.com/store/proddetail.php?prod=0014](http://www.perspectx.com/store/proddetail.php?prod=0014) ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [June 15, 2009, 8:55pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/3 "2009-06-15T20:55:29Z")
For several years my office was about 100 feet from the real Apollo 11 command module, so I can tell you there were no breaks through the heat shield. [Here’s](http://www.rjprice.co.uk/Gallery/NAmerica/washington/dsc_1281.jpg) a picture of it. And [Here’s](http://upload.wikimedia.org/wikipedia/commons/c/c0/Apollo_CSM_lunar_orbit.jpg) another shot of the external connection gizmo **Terminus** beat me in finding. ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [June 15, 2009, 9:20pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/4 "2009-06-15T21:20:20Z")
> [@commasense](#): > > …URL=“[http://upload.wikimedia.org/wikipedia/commons/c/c0/Apollo\_CSM\_lunar\_orbit.jpg](http://upload.wikimedia.org/wikipedia/commons/c/c0/Apollo_CSM_lunar_orbit.jpg)”]Here’s another shot of the external connection gizmo **Terminus** beat me in finding. As an old space-geek I know this is a shot of Apollo 13 with its blown-out section of the Service Module! 😉 Seriously, I am guessing that the jettisoned panel exposes radiators for the fuel cells. Facts on this? ---
**Author:** ![Terminus\_Est](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/terminus_est/32/3087_2.png) [@Terminus\_Est](https://boards.straightdope.com/u/Terminus_Est)\ **Post date:** [June 15, 2009, 9:22pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/5 "2009-06-15T21:22:31Z")
Radiators don’t work very well in space, so there must be a different reason. ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [June 15, 2009, 9:48pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/6 "2009-06-15T21:48:36Z")
> [@MonkeyMensch](#): > > As an old space-geek I know this is a shot of Apollo 13 with its blown-out section of the Service Module! 😉 > > Seriously, I am guessing that the jettisoned panel exposes radiators for the fuel cells. Facts on this? I think the opened panel exposes the [Scientific Instrument Module](http://www.nasm.si.edu/collections/imagery/apollo/AS15/a15los.htm) (diagram of module components at the link) used in Apollo 15-17. I think the radiators are the white panels running around the top and bottom of the SM. ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [June 15, 2009, 9:49pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/7 "2009-06-15T21:49:30Z")
Ah, the gears of memory grind slowly, but exceeding fine. I remember now the later Apollo missions had some camera (I think) equipment in the SM that had to be retrieved by hand after trans-Earth-insertion. I remember David Scott’s description of the retrieval and it sent shivers through me. Maybe that was the panel that exposed the equipment… And radiators work perfectly well in space… _Convectors_, on the other hand, are worthless. ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [June 15, 2009, 9:51pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/8 "2009-06-15T21:51:03Z")
Or what **Omph** just said… ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [June 15, 2009, 10:17pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/9 "2009-06-15T22:17:00Z")
And now that I’ve Googled, it turns out that it was Alfred Worden’s description that I’m recalling. Ah, age. The more you remember, the more you forget. ---
**Author:** ![MrFloppy](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)\ **Post date:** [June 16, 2009, 1:19am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/10 "2009-06-16T01:19:02Z")
Ok. I see the external connection gizmo. Thanks for that. Now, it looks like it would hinder a clean separation of teh CM and SM prior to re-entry so how does that work? Does the gizmo itself get separated form both the SM and CM and then the CM and SM separate? ---
**Author:** ![MrFloppy](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)\ **Post date:** [June 16, 2009, 1:36am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/11 "2009-06-16T01:36:55Z")
Never mind. Found it. The ‘gizmo’ is officially called the SM/CM Umbilical. The separation of the SM and CM is done automatically by a controller installed in the SM. Cutting of the connectors, the transfer of the control of the electric system and jetting of the SM RCS engine to draw CM and SM apart are done almost instantaneously at the time of the separation. First, before the separation, astronauts pressurize the CM RCS by using electrical power provided by the SM. The separation sequence begins when either one of two switches on the main console is toggled. The electrical transfer through the CM-SM umbilical is disabled first. After 10 seconds, the tension ties that connect the SM with the CM are separated. At the same time, the stainless steel guillotine cutter is fired by explosives, cutting the cables and wires in the CM-SM umbilical. Finally, the RCS engines of the SM fire for five seconds, the flight course of SM is changed to avoid a collision with the CM. Until the fuel is used up or electric power is expended, the SM RCS keeps firing to ensure that the SM’s flight path stays away from the CM. ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [June 16, 2009, 1:55am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/12 "2009-06-16T01:55:46Z")
> [@MonkeyMensch](#): > > As an old space-geek I know this is a shot of Apollo 13 with its blown-out section of the Service Module! 😉 Another reason that photo couldn’t possibly be Apollo 13 is because there wasn’t a time while they were circling the moon when the LEM wasn’t attached to the CM. Likewise, who would’ve taken that picture with the moon in the background? ---
**Author:** ![MonkeyMensch](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@MonkeyMensch](https://boards.straightdope.com/u/MonkeyMensch)\ **Post date:** [June 16, 2009, 2:42am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/13 "2009-06-16T02:42:22Z")
> [@USCDiver](#): > > Another reason that photo couldn’t possibly be Apollo 13 is because there wasn’t a time while they were circling the moon when the LEM wasn’t attached to the CM. Likewise, who would’ve taken that picture with the moon in the background? Hence the winky smilie… ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [June 16, 2009, 2:50am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/14 "2009-06-16T02:50:58Z")
Right, I knew that of course! :smack: ---
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [June 16, 2009, 10:19am UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/15 "2009-06-16T10:19:03Z")
Thank you all for those photos. I had been wondering the same question as the OP for several decades. I was in high school throughout the Apollo program, and do remember hearing about the “umbilical”, but I don’t ever recall seeing such a large, bulky, rectangular box on the side there. Thanks for the memories. ---
**Author:** ![MrFloppy](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@MrFloppy](https://boards.straightdope.com/u/MrFloppy)\ **Post date:** [June 16, 2009, 1:13pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/16 "2009-06-16T13:13:51Z")
> [@MonkeyMensch](#): > > As an old space-geek I know this is a shot of Apollo 13 with its blown-out section of the Service Module! 😉 That is Apollo 15. The Command Module was named Endeavor. ---
**Author:** ![Cliffy](https://avatars.discourse-cdn.com/v4/letter/c/59ef9b/32.png) [@Cliffy](https://boards.straightdope.com/u/Cliffy)\ **Post date:** [June 16, 2009, 7:28pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/17 "2009-06-16T19:28:12Z")
Was the umbilical exposed during liftoff? I guess it was – none of the diagrams I see show it, but given its position, I guess it’d have to be. I always thought it very weird that the Service Module was exposed to the elements at launch – and especially, that the thrusters were. It seems like they’d be something you’d want to ensure didn’t shear off when cutting through the atmosphere. Well, I guess that’s why I’m not the engineer. –Cliffy ---
**Author:** ![fiddlesticks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fiddlesticks/32/18129_2.png) [@fiddlesticks](https://boards.straightdope.com/u/fiddlesticks)\ **Post date:** [June 16, 2009, 8:49pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/18 "2009-06-16T20:49:04Z")
[Here’s](http://history.nasa.gov/ap11ann/kippsphotos/69-HC-717.jpg) a picture of the Apollo 11 on the pad. It clearly shows the umbilical exposed even with the escape tower/protective cover laid over the CM itself that stayed on through most (all?) of the flight to orbit. Lots of great pictures of the Apollo 11 assembly process [here](http://history.nasa.gov/ap11ann/kippsphotos/saturn5.html). ---
**Author:** ![ElvisL1ves](https://avatars.discourse-cdn.com/v4/letter/e/5daacb/32.png) [@ElvisL1ves](https://boards.straightdope.com/u/ElvisL1ves)\ **Post date:** [June 16, 2009, 11:03pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/19 "2009-06-16T23:03:35Z")
FWIW, a hole through the heat shield is not unfeasible. The Gemini-derivative spacecraft that would have served USAF’s Manned Orbiting Laboratory had personnel hatches in theirs. ---
**Author:** ![Cliffy](https://avatars.discourse-cdn.com/v4/letter/c/59ef9b/32.png) [@Cliffy](https://boards.straightdope.com/u/Cliffy)\ **Post date:** [June 16, 2009, 11:24pm UTC](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869/20 "2009-06-16T23:24:01Z")
Thanks! –Cliffy [Next page](https://boards.straightdope.com/t/another-apollo-question-cm-sm-systems-interface/499869.md?page=2)