DaveM wrote:
Why can't NASA use some kind of handshaking routine to coordinate data retrieval from MER-A and B? Wouldn't the weight of extra memory be trival compared to science that could be done?

Alex writes:
Mind you, I'm not a comm expert, but I doubt if the issue is simply one of the "trivial weight of extra memory." As a scientist I would love to see the comm relay capability at Mars boosted, but one should note the UHF relays aboard both 2001 Mars Odyssey and MGS are really just that - *relays.* These are not like Earth orbiting comm satellites, which are multiplexing "switchboards-in-the-sky." Odyssey's UHF relay, in addition to higher data rates, also has both uplink and downlink capability; MGS' MR can only receive data, which is buffered in the MOC memory, from landed or near-surface packages.

At any rate, from what I understand, the Odyssey and MGS comm passes, which involve low-flying, near polar orbiters, are very brief (on the order of ~8-10 minutes each), and involve interrogation and locking on to establish the link. I'm sure that present solutions do exist to accomodate both rovers from one orbiter, but NASA is taking the conservative route here, at least from an operational standpoint. Future plans, though, (e.g., the Italian ASI-supplied "Marconi" telecom orbiter) will undoubtedly have the capability for one orbiter (presumably from higher, more elliptical, maybe even areosynchronous, orbits) to loiter and communicate with a wide array of landed or near-surface packages simultaneously.

Alex R. Blackwell
University of Hawaii