Communications Strategies, How can the Deep-Space Network be improved on? Options

[Greg Hullender]

Given the recent news that Cassini will lose some data during the Phoenix landing due to contention for DNS access:

http://www.unmannedspaceflight.com/index.p...ic=4831&hl=

It seemed reasonable to create a topic to discuss where the DNS might be going.

Jasedm suggested a relay station at the Earth-Sun L2 point, which I think might be discussing (despite the expense) assuming the relay station could use laser communication with space probes, while beaming data to Earth via microwaves.

I know that experiments with laser communications were part of the now-abandoned Mars Telecommunications Orbiter, and I know that there was even a recent laser experiment involving Mercury Messenger.

http://www.space.com/missionlaunches/060104_laser_comm.html

These seem intended to support laser communications with ground-based receivers, though -- something that seems much too risky if remote space probes can't store days of data allowing for multiple retries.

Obviously a relay station would have its own risks -- you'd probably need two for redundancy -- and it'd be fabulously expensive, but it might also include quite a few savings as well. I've looked for figures for what the DSN costs to run, but I haven't found them yet. Not sure how large a part of a given mission (if any) is charged to the DSN, but it seems to me that a relay satellite ought to be a good bit cheaper to operate, and for far higher bandwidth.

Also, a laser transmitter ought to be lighter and consume less power than an equivalent microwave transmitter. That alone could result in huge savings for outer-system missions.

The only time I saw a serious proposal for a laser-to-satellite communications system was in a description of options for the "Grand Tour" that later became Voyager. (Assuming that counts as serious.) :-) With DSN needing more and more maintenance, I wonder if anyone is seriously considering laser for the future.

--Greg

[edstrick]

"...still have this image in my head of an antenna farm consisting of 10,000 old DirecTV and/or Dish Network 50cm dishes..."

The idea is not bad, but there's an optimum antenna size that balances antenna size, tracking mount size, and microwave components <feed horn, amp, whatever>. As pointed out above, antenna farm arrays are viable, but more in the scale of C-Band satellite dish, or small commercial dishes for communicating with synchronous sats.

[helvick]

The idea is not bad, but there's an optimum antenna size ..

The expense that would result from the multiplication of the tracking, control, cooling and low noise tx\rx circuitry (for a start) would make an array of domestic satellite TV dishes very expensive very quickly. To get into the range of the signal to noise levels from a single 35m antenna you would need something like 4000 of the small home satellite TV dishes.

The SKA seems to be opting for 12-15m component dishes as that appears to be the economic sweet spot - you still need 34 of those to give you the equivalent of a single 70m dish (in terms of S/N ratio).