Telecommunications Engineering needs recording.
AWA Field Engineers’ role in the NASA Apollo Missions
With all the excitement and reminiscing around the Apollo 11 mission and Man Walking on the Moon for the first time, Bob Rayner recalls details for this story.
Note: Parkes Telescope is Receive Only!
Have been reading and watching TV with interest regarding the Apollo 11 moonwalk mission particularly the almost exclusive coverage to the role played by the Parkes Telescope. This facility had a couple of drawbacks. It is receive only. It will not depress down to the horizon. Not good for orbits due to the horizon problem and the speed of movement. It is quite a massive structure, I have been up into it a few times.
How? Video Parkes and Honeysuckle Creek to OTC Sydney?
Getting to the point. No one has mentioned the problem of getting the video (analog those days) pics from Parkes Telescope and Honeysuckle Creek into the PMG (as this organisation was known) system to be passed to OTC and then Houston. Honeysuckle obviously had their voice and data circuits as it was being used for traffic both ways but apparently no video capability. Honeysuckle was a command station and transmits as well as receives. Had a 20 KW water cooled Klystron sitting under the dish.
Enter AWA Sydney and their Field Engineering section
Enter AWA Sydney and our little Field Engineering section. AWA at the time had several (don’t know how many) 7GHz Television microwave systems for hire. These were quite portable and housed in travel cum usage metal cases. Transmitter and receiver heads mounted directly behind the dish with a purpose made bracket which was bolted onto the dish and connected directly to horn feed. This then connected with a cable to the rest of the works in the travel cases. Dish and heads were normally then mounted on tripods and various means used to mount the whole thing to a tower or other site.
Maybe AWA’s involvement started with Apollo 8
I am not sure when our involvement started, memory a bit hazy and diaries long gone. It was when Apollo started sending pictures back in television video format I think. Probably about Apollo 8 or maybe a bit earlier. There must be records somewhere of this.
AWA Install Team heads to Canberra
Honeysuckle Installation / Transmission Issues
I headed up an installation team and off to Canberra. The object to install and commission a 7 GHz link from Honeysuckle via a passive repeater (about 400 Metres from Honeysuckle site), Active repeater at PMG site Williamsdale then to PMG site Red Hill Canberra. This was to be backed up by an ABC Outside Broadcast unit using the same passive repeater.
Williamsdale to Red Hill. All good, no problems.
Honeysuckle to Williamsdale.
Different story. Started with the passive repeater. This was simply 2 6ft dishes mounted on a temporary tower connected together with a 10ft length of Andrews oval corrugated flexible (???) wave guide. Unpacked this waveguide and found it kinked. Potential disaster and due to impending mission no time to have another made. VERY VERY carefully removed the outer sheath and found fortunately the copper corrugations had not cracked. Once again being VERY VERY careful we were able to straighten the waveguide out without cracking the copper. Found some lightweight steel angle and cut a couple of “splints” and secured the oval waveguide in the vee with stainless valstrap. Bound and sealed the whole lot up for weather protection and crossed fingers and toes that all well. Which it proved to be for the duration of the exercise anyway.
Honeysuckle 1st problem.
10Ft dish mounted on short tower with the same flexible?? waveguide run into the building where link TX to go. Waveguide fitted with rectangular connector and link TX has circular connector. Oh great. I believe circular connector ordered but once again no time to get replacement. Literally burned the midnight oil in the Honeysuckle machine shop which had quite a good lathe. I was able to fabricate an adaptor plate using a circular connector cut off a piece of discarded 7GHz waveguide. That problem seems to be overcome.
Honeysuckle 2nd problem.
A bit down on expected signal strength at Williamsdale. The receiving antenna here was a rather horrible huge exponential horn. Don’t know who found that. Very difficult for 1 person to handle. Finished up with a team of PMG linesmen waving this thing all over the sky until finally finding the main lobe. That problem solved.
Honeysuckle 3rd problem.
Having got signal level sorted we inserted a sawtooth video test signal. Horrible!!! These transmitters are fitted with a video monitor facility where you can monitor outgoing video quality. This sawtooth had a sine wave all over it of about 250mV on a 1V signal. I established that this was a re-transmitted standing wave or echo on the waveguide. Andrews urgently sent an engineer up to test the dish fully. All declared OK. Re-installed dish but what was causing this. Measured the time between sine wave peaks and found this equated to about 800 metres of signal travel. The passive repeater about 400 metres away!!! Inspection revealed that the mast had been erected with one face looking squarely at the TX dish. We were getting an echo off the mast face.
Prohibitive job to do anything about this at that time (running out of it). As said before these units are designed to fit directly on the dish and horn feed so waveguide mismatch errors are normally not a problem. Due to this a ferrite isolator is not required or fitted. There was not one readily available either. The waveguide connector used is quite long transitioning from rectangular to the oval shape over 200 – 250 mm. Idea! Drawing from tricks learned from an extensive association with John Van Der Ley I drilled and tapped a series of holes along the connector about one quarter wavelength apart. By carefully screwing brass screws in and out I succeeded in creating another echo of the wanted magnitude and phase to cancel the offending signal. Result was a nice clean sawtooth. During subsequent Apollo missions an isolator was obtained and fitted.
I don’t know if the ABC OB van had this problem.
Their microwave may have been fitted with isolators. After this first mission the ABC was unavailable so we duplicated out link.
This meant I now had 2 receivers and 2 transmitters in our tiny room at Williamsdale.
With the approach of Apollo 11 and moon walk somebody higher up decided that using the larger dish at Parkes was a good idea. Off to Parkes with another installation team to do the same thing. No repeaters required here just a direct shot to the nearest PMG site.
An aside, Careful where you park the car!
A bit of trivia. At this time this dish size had just been increased to 64M. One of the tecs parked his car in his usual spot and had it flattened to about 300mm when the dish was exercised. That is how close the edge came to the ground with the size increase.
Parkes to Honeysuckle Link
This Parkes signal had to get to Honeysuckle so another duplicated link was required from Red Hill – Williamsdale – Passive repeater – Honeysuckle. I now had 4 transmitters and 4 receivers in this little cubby hole at Williamsdale. quite a mess. I managed to borrow a couple of unused open channel racks from Honeysuckle, removed from cases and rack mounted everything. A lot tidier. This is when I found out the Americans used 21” racks. I had to arrange a dummy rail to mount our 19’’ equipment.
Gaps in Data Stream
Only one problem with this link. While running a test data stream from Parkes gaps were intermittently appearing in the data on the main link. Standby link OK. This was tracked to the receiver klystron flipping off frequency causing the sub carrier to drop off the side of NASA’s filters. Changing the klystron straight away would not have been a big problem but by the time permission was obtained from Houston to take the “prime” link out of service it was 10.00 at night.
Help Needed for Night Work
As I was on my own at this time I had enlisted the help of another AWA person from a project in the Canberra area to fix this link. Remember it was July in Canberra at this time and the klystron had to be changed some 50 or so feet up a tower with 2 plastic rain coats buttoned together for shelter and snowing quite heavily at 10.30 at night. Getting those little 6BA plastic klystron retaining screws in was no fun I can assure you.
Data Dump needs a Rock Solid Link
When the orbiting spacecraft is behind the moon all data is stored. When it comes into view this data was “dumped” at 16 or 32 times normal rate. During this period great care is taken to optimise everything so as not to lose any data. Hence the use of the higher gain Parkes facility. It was this data stream that our links carried to Honeysuckle. What became of it after is still a mystery. I was not aware of any television type video from Parkes on this link but I suppose there could have been, I don’t really know. If there was video our link was the only way off the telescope site. I saw the video from the moon while in the Honeysuckle control room. Slow scan (10 FPS) and pretty bad due to small bandwidth available at this stage. This was put through some pretty sophisticated video enhancing device before being sent on to Houston and the rest of the world via our links to Red Hill.
Apollo 13 Needs Link Re-Established Urgently
AWA equipment was removed from Parkes site and the telescope returned to its star gazing role until trouble was encountered during Apollo 13. An installation team led, I think by Vic Cowenberg, left Sydney urgently about lunch time and worked through the night to have our link re-established by early morning. I had left the mounting hardware on the PMG tower as it was doing no harm and I thought at the time it may be useful again. Little did I know at the time how useful. I believe AWA received a letter of thanks for the efforts during this emergency.
The Parkes facility effectively gave NASA another pair of eyes and ears until this problem was resolved by bringing the astronauts home.
AWA Staff Required to be On-Call 24/7
During all of these missions somebody was required in the area on call 24/7 in case of any malfunction. This also applied to the testing phase and during the mission one of us had to actually be on site. This was tasked to myself and Harry Bearon. Harry looked after the couple of times at Parkes and I the Honeysuckle/Canberra area. Harry filled in when for various reasons I was not available to go to Canberra. I do vividly remember one night in the early hours of the morning freezing my butt off at Williamsdale watching a vidicon tube being destroyed when the camera was accidentally pointed at the sun.
I asked could I stand down but was told to stay as they may be able to fix it!!!! Kidding I thought. Changing a vidicon is a bit of a fiddle on a workbench but on the moon with those big gloves?????
Valve Equipment Ran for Years
All up we managed quite a few missions. All a bit hazy now and I don’t recall exactly when our part finished and the equipment removed. This equipment (all valves by the way) proved very reliable and after the first few bugs just sat there humming away for a few years really. All we did was check it all before each mission which mostly entailed just rotating a switch checking meter readings to make sure nothing untoward was happening and plugging in a video test signal to check performance.
I hope this provides some sort of insight into one of the many small but not insignificant things that went on virtually in the background by many thousands of people during what was really a history making endeavour. I put forward this blurb as from what I have seen in the media is all about Parkes Telescope when in fact this played a small, but like the rest of us, vital part in the overall scheme of things. Apologise for being so long winded but I could not think of a shorter way to describe our part in this feat and thought it desirable to describe some of the problems and pitfalls encountered along the way.
Thanks for your patience, Bob Rayner (ex-AWA) <End>
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