Erectable S-Band Antenna Deployment
Copyright © 2010 by the Editors of Working on the
Moon.
Last revised 8 February 2010.
The antenna package, including a thermal/micrometeoroid cover
an end cap and various fastenings, had a terrestial weight of 6.1 kg.
When deployed, the umbrella diameter was 3 m. The tripod height
and base width were both 1.5 meters. Illustrations from pages 2-20 to 2-22
in Lunar Module Structures Handout, LM-5
Summary
The Erectable S-Band Antenna was first flown on Apollo 11 and was intended to provide a stronger television signal. Because time during the brief Apollo 11 EVA was so s precious, the expected 19-minute deployment of the antenna would have a major impact of productivity. Consequently, an assessment was made of the first few minutes of the B&W TV signal coming through the LM's steerable antenna. The signal was deemed adequate, so the Erectable S-Band wasn't deployed. It was deployed on both Apollo 12 and 14.
Deployment was intended to be easy enough that one person could do it. However, training convinced the Apollo 12 crew that they might have to work together when aiming the antenna at Earth. On both the Apollo 12 and 14 deployments, the astronauts worked as a team doing rough alignments and then, with one of them watching the sighting glass and making small adjustment to elevation using the flexible-cable crank, the other astronaut held the antenna to keep it relatively steady and to keep it from tipping over. The Apollo 12 and 14 deployments took 15 1/4 and 10 1/2 minutes, respectively. In both instances, the second crewman took part for about 5 minutes.
Detailed procedures can be found on pages 35 to 39 in the Final Apollo 12 Lunar Surface Operations Plan ( 6 Mb ).
Lessons
The low weight and high center-of-mass meant that the antenna was easy to disturb. Evidently, there was enough friction ("stiffness") in the crank mechanism to cause the structure to move or, even, tip over, unless the astronauts worked together to keep it steady while it was being aligned. This is probably a case in which mechanical forces became more important relative to gravity than had been the case on Earth.Offloading
As indicated, the following two-line decal was in the equipment bay to the right of the ladder, just below the stowed antenna. See Apollo 11 training photo S69-31055.
The handle is at the bottom of the
package in the following figure, in the astronaut's right hand.
The astronaut's left hand is on the carry bar. Click
on the image for a larger version. See, also, a detail from S69-31056.
Deployment
The following decal was on the top plate (end cap) of the package (unnumbered Apollo 11 training photo). The plan was to have the deployment in the field-of-view of the 16mm sequence (movie) camera mounted in the LMP's window. 'Gross pointing' may have involved holding the package upright and turning it around its vertical axis until an arrow on the top plate was pointed at Earth's azimuth (S69-31057). The antenna was supported on three telescoping legs, which were to be unlocked at this point. Finally, the top plate and underlying pad were removed (S69-31150) and discarded (S69-31151).
As indicated, the next decal was under the top plate. The antenna's transmitter-receiver was located at the top of a two-section, telescoping mast which, when extended (S69-31152) and locked, put the transmitter-receiver at the focus of the umbrella-shaped, wire-mesh dish. Once a second azimuthal alignment was done, the three, telescoping legs were extended upward (S69-31058). Then, once a tie-down strap was removed from each leg, they were allowed to rotate down, lying horizontal on the ground but attached at pivot points at the bottom of the main antenna body. At this point, a thermal/micrometeoroid cover (unnumbered Apollo 11 training photo) was removed from from around the bundled umbrella ribs and wire mesh. Finally, the antenna body was lifted vertically (unnumbered Apollo 11 training photo) to get the legs into position and locked. (During the Apollo 14 deployment, Alan Shepard removed the thermal cover after the lifted the antenna and got the legs locked.)
The final deployment decal was on one of the legs. The first steps are to remove the carry bar and a rib protector (Apollo 11 training photo). Next, a trigger lanyard was released (Apollo 11 training photo). This put the trigger about halfway down the legs (Apollo 11 training photo), which let the astronaut trigger deployment while keeping his helmet and backpack well out of the way of the quite dynamic unfolding (Apollo 11 training photo, Apollo 14 training film clip). Finally, the cable connecting the antenna to the LM was extended out from the MESA and connected.
Antenna Alignment
Alignment in both azimuth and elevation was done with a flexible-cable crank (detail from a training photo). A rough alignment was done, again, by sighting along the mast (training photo), while the final alignment was done by using the crank and a sighting 'glass' mounted on the elevation rotation axis. (Click on the following image for a larger version.)
The astronaut's found that use of the crank disturbed the antenna structure and threatened to overturn it. Consequently, one or both of the astonauts had to hold the legs to keep the structure steady. A final problem was keeping the OPS antennas clear of the wire mesh, particuarly when sighting along the mast or suing the sighting scope. Detailed commentary on the problems encountered during alignment can be found in the Apollo 12 and 14 Lunar Surface journals starting at 116:01:14 and 114:19:27, respectively.
Details of the Apollo 12 and 14 Deployments
Although the quality of the TV isn't great, we can identify the time of occurence for most deployment events from the audio/video record, supplemented by the audio transcript. For the Apollo 12 deployment, we have only a few seconds of TV relevant to offloading and, otherwise, only the audio and transcript. These allow times to be determined for some events, albeit with more uncertainty. The Apollo 14 deployment was the shorter of the two by about 5 minutes, due entirely to quicker alignment. Clearly, the Apollo 14 crew learned a great deal from the Apollo 12 experience and, pre-flight, probably worked out an effective way to get the alignment done. Because we have a more complete record of the Apollo 14 deployment, it occurs first in the following table. Crew comments can be found via the links to the relevant portions of the Apollo 12 and Apollo 14 Lunar Surface Journals| Event |
Apollo 14
Ground Elapsed Time (From Television) |
Apollo 14
Time from Start (mm:ss) |
Apollo 12
Ground Elapsed Time (From transcript*) |
Apollo
12 Time from Start (mm:ss) |
Apollo 11 Training Photographs |
| Total
Task Times |
|||||
| Start Offload |
114:11:32 |
0 |
115:53:42 | 0 |
|
| Finish Deployment |
114:22:05 | 10:33 |
116:08:59 | 15:15 | |
Deployment details |
|||||
| Start Off-Load | 114:11:32 |
0 |
115:53:42 | 0 |
S69-31055 |
| Carried package away from bay |
114:12:22 |
00:50 |
115:54:26 |
00:44 |
S69-31056 |
| Reached deployment location,
rough align, remove top plate |
114:13:12 |
01:40 |
115:54:53 |
01:11 |
S69-31057 S69-31150 |
| Discarded top plate |
114:14:04 |
02:32 |
S69-31151 | ||
| Has mast raised |
114:14:34 |
03:02 |
115:56:27 | 02:45 |
S69-31152 |
| Third leg raised |
114:15:06 |
03:34 |
|||
| Leg straps removed, legs
released, tripod raised and legs locked |
114:15:54 |
04:22 |
S69-31155 S69-31156 S69-31157 S69-31158 |
||
| Umbrella cover removed and
discarded |
114:16:01 |
04:29 |
115:58:11 | 04:29 |
S69-31159 With cover is in the foreground in this A11 training photo, with the carry bar on top of it. |
| Question from Houston about leg
penetration answered |
114:16:26 |
04:54 |
|||
| Removed and discarded carry bar
and rib protector |
114:16:51 |
05:19 |
115:59:25 |
05:43 |
S69-31159(detail) S69-31165(detail) Neil has the rib protector in his right hand and will let it slide down the leg on our right. |
| 2nd leg question answered |
114:17:01 |
05:29 |
|||
| Al worked on far side of the
antenna, probably deploying the trigger lanyard. Ed brought the
connecting cable from the MESA. Noticed
that the antenna was too far from the MESA. |
114:17:27 |
05:55 |
S69-31160 S69-31161 |
||
| Ed returned to MESA to see if he
has pulled the full cable length out. Returned. |
114:18:04 |
06:32 |
|||
| Antenna in final location |
114:18:33 |
07:01 |
|||
| Umbrella released but hung up;
antenna tipped 90 degrees so Mitchell could free. Returned to
upright. |
114:19:27 |
07:55 |
116:01:14 Didn't get hung up. |
07:32 |
S69-31162 S69-31163 Apollo 14 training film clip Didn't get hung up. |
| Shepard used the crank to set
approximate elevation. |
114:20:42 |
09:10 |
S69-31059(detail) S69-311179 KSC-70PC-0016 (Apollo 13 training photo showing Jim Lovell using the crank) |
||
| Mitchell on the sighting
"glass".
Shepard adjusted azimuth, looking from behind. They then fine-tuned
elevation and got Earth centered. |
114:22:05 |
10:33 |
116:08:59 |
00:00 |
S69-17211(detail) S69-31165 S69-31165(detail) unnumbered training photo |
* Times inferred from the Apollo 12 transcript are more uncertain than those from the audio-synched Apollo 14 TV record.
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