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Posted by: paranoid123 Dec 1 2006, 01:18 AM

I just read this press release about having relay satellites in "stable" lunar orbits for continuous Earth - Shackleton Station communication.

http://science.nasa.gov/headlines/y2006/30nov_highorbit.htm

It says "High-inclination, highly elliptical orbits being cheapest and most stable for communications satellites around the Moon? To Earth-centered satellite engineers used to thinking in terms of circular equatorial orbits, "it's a new paradigm," Ely declares."

Now, I'm no engineer or designer or anything, but wouldn't several line of sight relay stations, or probably a really really long fiber optic to a transmitter placed somewhere on the moon that faces the earth be much cheaper than the launch and operations of three relay satellites?

Or am I reading too much into this article?

Posted by: AlexBlackwell Dec 1 2006, 01:25 AM

How exactly are you going to place all of that infrastructure on the lunar surface? Call me crazy, but I'll assume you'll have to launch and land on the lunar surface, then complete the assembly, either robotically or by humans. And you think that's cheaper than placing three satellites into lunar orbit?

Posted by: Phil Stooke Dec 1 2006, 01:30 AM

Aren't those elliptical orbits basically the kind the Russians have used for a long time? - Molniya orbits? Hardly a new paradigm, if so. But I don't know much about this.

Phil

Posted by: AlexBlackwell Dec 1 2006, 01:34 AM

You're right, high-inclination elliptical orbits for communications (or even SIGINT, e.g., NRO Jumpseat spysats) is nothing new. And the now-defunct Mars Telecom orbiter (and even earlier iterations of Marsat constellations) had similar orbits as an alternative architecture to areostationary monitoring.

There are tradeoffs, but that's show biz

Posted by: helvick Dec 1 2006, 09:57 AM

[A] Line of sight relays. Assuming 4m masts you will need one surface relay station every 5km or so. You'll need to come down to around 70N or so. My back of the Envelope http://spreadsheets.google.com/pub?key=pNkQ_0mEEOPoMFsp9oLmpXw. Each of those has to be landed, commissioned and powered for the duration of the mission. A mass of around 500kg per relay seems optimistic to me but even at that we are talking about delivering close to 60 tons to the lunar surface with extremely precise positioning.

[B] Run a cable of some sort from the base to a main Earth Relay station at 70N (or thereabouts). Single armoured submarine comms cables come it at http://www.hegroup.com.tw/english/esubmarine.htm. Even assuming that we could do a lunar comms cable for two orders of magnitude less than this you are still talking about laying 30tons of cable across 600km of the lunar surface and getting all that mass to the lunar surface safely (along with the laying equipment).

[C] 3 x Molniya type satellites in lunar orbit. These would probably weigh in the region of 500-1000kg.

Practicality and cost are directly related to the amount of mass you need to use - the satellite solution is cheaper and easier by at least an order of magnitude.

Posted by: djellison Dec 1 2006, 10:16 AM

Several infact. $800m will build, launch and upgrade groundstations for three TDRS sat's which can each do 400 (or even 800) Mbps from GEO - $250m..ish..each. You'd drop some of the bandwidth - but a TDRS asset plased at some sort of L2 point would probably make most of the problem go away, for something like $400m including launch and augmentation of the bus for a greater fuel load and a larger LV to get it off the ground.

In the new mould of COTS etc...I would personally have thought that this is something that could be just handed to one of the big Sat manufacturers with a big cheque and told "make it so"

Doug

Posted by: Phil Stooke Dec 1 2006, 04:43 PM

"Line of sight relays. Assuming 4m masts you will need one surface relay station every 5km or so. "

Not so many, bacause you wouldn't measure to a flat horizon (as that must assume), you would naturally transmit from peak to peak - for instance, I think Schrunk and others have shown Malapert Mountain is within line of sight of Shackleton rim, 5 degrees or 150 km away. With good planning you might only need 5 or 6 relays.

I still prefer satellites, though, just making a point.

Phil

Posted by: helvick Dec 1 2006, 06:16 PM

Good point. I am compelled to add as a parting shot that however difficult landing a series of relays out on a lunar plain might be I suspect that landing a handful on the peaks of the four or five tallest Lunar mountains around the pole would be quite an interesting challenge.