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

[jasedm]

Maybe a brief cloudburst over Madrid will be the least of our problems in the future. Having done a brief search, it appears that Earth-Sun L2 will get a tad busy in the coming years with the following planned missions to orbit there:

James Webb Space telescope
Terrestrial planet finder (may include multiple mirrors in close formation)
Darwin spacecraft (four or five separate free-flying components)
Gaia probe
Herschel space observatory
Planck surveyor

The WMA probe is already there observing cosmic background radiation, and probably many more missions wishing to take advantage of the small amounts of station-keeping propellant required, are in various stages of planning.
I'm not sure of the extent of the stable area available at L2, but it's going to get quite crowded (we may also find a few small but hazardous rocks there as well as the dust we know about)

Sooner or later I'm sure there will be some sort of solar-powered data relay at L2, especially as it could be maintained and upgraded by manned missions to mars which may use L2 rather than the moon, as a staging-point.

I think eventually the sheer number of demands on the DSN will make the space relay inevitable. Hopefully someone connected with the network reads UMSF and can enlighten us....

[djellison]

maintained and upgraded

That would include the replenishment of cryogenics to keep the receivers cool, the replacement of gyros (would gyros even work for a large dish?) and replenishment of thruster fuel to keep the think pointed.

It would cost an utter fortune, a fortune that would be much much better spent on array like DSN facilities on Earth, and upgrades to spacecraft that, with technology that is on the bench ready to go, take Mars-to-Earth comms up by two orders of magnitude over and above MRO.

Doug