Monday, September 13, 2010

Lunar Communications Relay Constellation

I was watching one of the Apollo documentaries and was struck by how many critical burns happen during radio blackout from Earth: Lunar orbit insertion, trans-Earth injection, and I think the pre-burns for powered descent as well. During those times, there's no telemetry for the ground, so no fall back if something happens that the crew cannot detect or diagnose. The lack of relay options other than the CSM also limited real-time uplink of imagery and data, which in a modern lunar mission would seem to be something to plan on, what with cameras being pretty cheap. If I were able to, I'd have cameras on everything. One for each astronaut (still and video, maybe combined), one or more on any rovers, some on the lander both for site visuals and also maybe diagnostic applications. Maybe have one streaming that users could control (pan/rotation/zoom) from a website? I bet that server crashes due to requests after ten seconds. But all of it requires more robust data connections and relays than can be obtained by simply repeating Apollo's comm set up.

So now you're talking about relay satellites, not in orbit of Earth, but in orbit of the moon. What will they need to have on-board? How many do you need to provide coverage? Where do you put them to get the coverage you want/need? It's a hairy problem, and I can't say I understand all of it. Heck, there's areas where I can do nothing more than admit my lack of knowledge and move on. However, it seems like a worthy goal to explore if we're going to be serious about further exploration and perhaps even development on the moon. I have more to say based on my research and talking to others more knowledgeable, but I fear writing more when I have to wake up at 8 AM tomorrow to be lectured about sizing our plane for Aerodesign Team this year. I'm not going to be lead on that this year, but I owe it to myself and next year to make sure I'm awake enough to give it my best effort at comprehension.

1 comment:

  1. The ground wasn't totally blind of what happened on the lunar far side. The LM and CSM both had tape recorders specifically designed to capture voice and telemetry when the spacecraft was out of contact with earth and to dump that data (possibly at high speed) when contact was regained. The CSM could also relay some data from the LM.

    But you're right this wouldn't help analyze a catastrophic accident that kept the spacecraft from ever regaining contact with the ground.

    I think your best bet for a continuous real-time relay would be a satellite in a halo orbit around the earth-moon "L2" point, i.e., beyond the moon with a continuous view both of earth and the far side of the moon. It would have to be in a halo orbit around L2 or else the moon would continually block it from earth view.