MRO Telecommunications Options

[nprev]

You mean take TDRS and turn it interplanetary.

Doug

Yep...but as mchan pointed out, the transmitter requirements for the actual planetary mission spacecraft may be prohibitive. Still, as tehcnology evolves, this might prove feasible someday.

[hendric]

Why does it need to be at L1/L2? Just stick it in an orbit interior to Earth, and half the time it will be closer to the target planet than Earth. You can choose to use the local DSN for when the planet is "behind" the earth, but for the rest of the time use your inner relay to zip the data back and forth around the sun. Plus, you can put large solar panels to boost the power going either direction.

[djellison]

err - very very very large solar panels. The transmitters on DSN assets are in the tens to hundreds of KW ( and the recievers cooled using LN2 in some cases I believe )

Doug

[nprev]

I think that advances in receiver sensitivity fueled largely by digital signal processing/processor speed progress combined with phased-array antennas might ultimately provide the ticket to make this work. For example, most newer airborne radars have amazingly low peak power outputs (one system I know of puts out much less than 50 watts--yes, watts, not Kw) and replaced an old system that blasted out more than 50Kw peak power yet had a shorter range and far inferior resolution.

If an analogous quantum improvement in complex waveform reception is ever realized, then Hendric might be right. The reason I originally went with the Earth-Sun Trojan points was to guarantee a clear LOS to any target location in the Solar System at all times, but if the effective SNR can be reduced enough than the Earth-Moon TPs would work just fine.

{EDIT} You know, after writing that I realized that developing such breakthrough improvements could be a huge selling point for this project. Isn't pioneering new technologies for transfer to the private sector one of NASA's long-time strategic objectives? Everybody loves spinoffs...

[mchan]

Clarification on the Mars relay sats in L1/L2. These are the Sun-Mars L1/L2, so they are strictly for Mars-centric comm relays. The advantage is near-continuous, near-global coverage for craft on the Martian surface with 2 spacecraft. Contrast this with architectures at the other end, i.e., there have been papers on Iridium or Globalstar type constellations around Mars, though with much smaller numbers of spacecraft, e.g. 8-12 instead of 48 to 66.

The halo orbits allow spacecraft landed on Mars to point to the Mars L1 comm relay without pointing directly at the Sun.

[nprev]

Oh, I'm sorry, mchan...did not mean to misinterpret, and the fault was mine. Still, if we could do this from the Earth-Moon TPs, it would be even better!

[mchan]

Nothing to apologize for. I was just mentioning another comm relay concept involving spacecraft in some other Lagrange points.

Regarding phased array antennas, I recall DSCS-3 featured them starting around early 80's. More recently, I have read that Messenger uses them. What have been their other applications in spacecraft communications?

[nprev]

Hmm. Frankly, I don't know...my main electronics experience base is airborne non-RF stuff like INS and instrumentation (G&C systems). I wonder what the commercial comsats are using, esp. high-rate data providers like DirecTV?