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Author Topic: Apollo 5 50th Anniversary  (Read 541 times)
indy91
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« on: January 16, 2018, 09:55:24 AM »

On January 22nd it will be the 50th anniversary of the Apollo 5 mission, the first and only unmanned test flight of the Lunar Module. For this occasion I have put in some work to make this mission as flyable as possible. Previously there were some major challenges to launch a LM with its systems running on our Saturn IB. These restrictions still apply, so I essentially had to rebuilt the Saturn IB meshes, thrusters etc. around the LM class. But with this fairly hacky solution the mission is now completely flyable.

We are lucky to have the LM software version flown on Apollo 5 for the Virtual AGC, which is called Sunburst120. Sunburst is controlling most of the major mission events. It has all the major tests scheduled automatically, so there is nothing to do for the NASSP user here, just relax and enjoy the show. Sunburst can also control various LM systems through a device called the Lunar Module Programer. By sending commands to the programer it can control RCS pressurization, RCS valve opening and closing, DPS and APS engine arming and much more. The real programer controlled the systems by having devices all over the LM that closed the contacts between circuits. One shortcut I took when implementing the programer is that I did not modify all our systems in the LM to accomodate the LM-1 specific configuration. Instead the programer is setting switches on the LM panels. That also has the advantage that one can watch what Sunburst is doing with the LM systems at any time.

There is no flight plan for Apollo 5 that I could find, after all the flight plan is mostly for the astronauts to follow and there were no astronauts on board of LM-1. The best document with all mission events is the Spacecraft Operational Trajectory (https://www.ibiblio.org/apollo/Documents/HSI-209584.pdf), the major mission events start at PDF page 23. Sunburst will follow this event schedule very closely. I have also added support for our MCC feature to Apollo 5 and it will command the sequence of RCS tests at the end of the mission. Here are some mission highlights of Apollo 5:

-Simulated Descent Orbit Initiation (first DPS burn). This mission phase uses guidance equations that were deleted from Luminary, so they never flew on a lunar mission. I think this would have been program 61 in the LGC, or so.
-Simulated Powered Descent (second DPS burn). This includes a simulated braking phase (P63 in Luminary, P42 in Sunburst), a simulated approach phase (P64 in Luminary, P43 in Sunburst), a throttle test with a bunch of random throttle settings (P44), followed by full thrust for 1 second, abort staging, and a short APS burn (P71). This is the so called Fire-In-The-Hole (FITH) test, the most important of the scheduled Apollo 5 tests. The timeline for this long event is in the PDF above on pages 44 and 45.
-Simulated Powered Ascent (second APS burn). This mission phase simulates the powered ascent and will fire the APS propellant to depletion. This will causes a thrust failure and program alarm on the DSKY, but that is the expected behavior.
-RCS tests. After the main mission is done, there were still a few tests scheduled concerning the RCS. These are not programmed in Sunburst, but will be commanded by MCC uplinks. Again, the user doesn't have to do anything, it's all automatic. The first RCS burn will fire system B to depletion. The 3 following and shorter RCS burns would have been done to test how the RCS deals with one system depleted and how much the helium supply of the empty system is messing with RCS performance. The 5th and last RCS burn is firing system A to depletion. The whole mission takes 13 hours, but the important events with DPS and APS burns end at about 6:30h.

As is well known, the Apollo 5 mission did not complete this planned schedule at all. At 4 seconds into the first DPS burn the LGC shut down the engine and the running program, due to a lack of thrust caused by DPS propellant pressure that didn't develop quickly enough. So all these awesome computer tests that were scheduled were never done on the real mission. But in NASSP they can now be attempted and they seem to work quite well.

I had already written extensively about Sunburst last year, when we first tried to run it in the Virtual AGC. See this post (http://www.ibiblio.org/mscorbit/mscforum/index.php?topic=178.msg26093#msg26093) for an overview of the programs in Sunburst and the procedure for the prelaunch alignment. I would suggest using the T-60s scenario I provided, but if anybody wants to try the launch scenario, it starts at T-1 hour and still has all the LM systems powered down, including the AGC.
« Last Edit: January 16, 2018, 10:16:06 AM by indy91 » Logged
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