MRO Telecommunications Options

[Guest_AlexBlackwell_*]

There's a new presentation entitled "Mars Reconnaissance Orbiter Telecommunications" on the JPL DESCANSO Design & Performance Summary Series web page (scroll to the bottom).

[Harder]

I hope it is sufficiently understood by all that there is a major inconvenience with the outage of DSS 55 near Madrid: http://www.space.com/news/060802_dsn_problems.html.

Till January 2007 according to this article. Probably a significant impact on HIRISE I would guess, but as the article states: the DSS teams have plenty of experience in delivering the impossible. Let us hope they will find a workaround this time as well.

[djellison]

An impact - but not a HUGE one - most of the downlink for MRO is 34m based. There are 14 Xband 35m passes per week, and only 3 70m passes. Yes - higher speed with the 70m, but given that it's only 3 passes, they can be offset away from the down-dish.

Colin Clark should be picked up on this one... "a result of a longer than planned shutdown of one of the three antennas that comprise Deep Space Network (DSN),"

The DSN is only 3 dishes is it Colin?... that's just lazy journalism..Each of the three sites has at least four dishes, and a total of 15 I believe.

However there is no doubt that the DSN is in need of serious investment - a good case could be made for several more 35m's at each site - that could be used in an array ( as has already been demonstrated ) for the typical 70m requirements. A concerted effort across the whole network (perhaps even internationally) to build perhaps 6 or 9 identical dishes to reduce costs would be a wise move.

Doug

[monitorlizard]

What JPL would like to build is an array of 400 antennas, each 12 meters in diameter, at each of the three
DSN sites. This would "increase downlink capability of DSN by two or three orders of magnitude". It would also have the obvious advantage of "graceful degradation" if one antenna would fail. Such an array would benefit every deep space mission, including MRO, but imagine what it would mean to New Horizons Pluto
spacecraft. It might increase communications distance enough to add a few more KBO's to the encounter list.

One paper discussing this type of antenna array technology is at:

tmo.jpl.nasa.gov/progress_report/42-160/160B.pdf

This technology is certainly closer to implementation than optical communications ! You'd also see improved data rates long before all 400 would be deployed.

[helvick]

What JPL would like to build is an array of 400 antennas, each 12 meters in diameter, at each of the three
DSN sites.

Rather than dumping all the eggs in single locations it would be useful if this exercise also extended it's brief a bit so that each of the three main sites had a backup at a similar longitude but was located in a zone with a very different climate to the primary site. For example Madrid could be paired with a South African site, Goldstone with a South American one and Canberra with someplace in Siberia. That way we'd have a practical "hot spare" environment.

It's not a cheap thing to try and implement but I believe that the global part of the Square Kilometer Array radio telescope project has these sort of requirements. I really do think that the SKA is a wonderful project but surely the DSN is more important?

[edstrick]

There was a South African DSN site, but that was abandoned during the sanctions era against the apartheid government. There should be paired DSN stations, one north, one south for each of the 3 longitude zones.

[djellison]

If you do the maths, and I'm sure it's just an accountants and engineers xls file that will do it..

For a given aperture you need either

A large number of small cheap dishes with a complex interconnection system
A small number of larger more expensive dishes with a less complex interconnection system

i.e. there's will be a graph - with points between 1 x 100 metre dish, and 10,000 x 1 metre dishes where the cheapest option exists....the challenge is to find that point, make it as easily deployable as possible, and then build it - or subsets of it, at various locations.

Doug

[RNeuhaus]

A good engineer, looks for the best equilibrium between few and large dishes and many and small dishes. However, anyway, there is a tendency that the future, the many and small dishes will be winner due to its advantages of redundancies required to meet to the increasing number of spacecraft navigating in the space. The time will dictate the best equilibrium.

Rodolfo

[nprev]

I had a post related in a way to this issue a couple of days ago here. Earth-Sun Trojan DSN relay satellites, anyone?

[RNeuhaus]

I had a post related in a way to this issue a couple of days ago here. Earth-Sun Trojan DSN relay satellites, anyone?

Your idea is brillant. This will eventually be justified their costs to build, send and operate relays satellites in the Lagrange points L4 and L5 only when the number of spacecraft operating abroad in space is overhelming. That will happen in some future day!

On the other hand, the relay satellites at the good Lagrange point is not related to the problem of the traffic of messages (more DSN) but it only is good for avoiding the telecommunications during any superior conjunction.
I might be wrong! but it is anyway an interesting topic.

Rodolfo

[nprev]

Thanks, Rodolfo. Always knew I was born 200 years too early!

[edstrick]

Ahem...

Look for George O. Smith's "Venus Equilateral"a book of stories by radio engineer George O. Smith, copyright 1942.

"The Venus Equilateral Relay Station was a modern miracle of engineering if you liked to believe the books. Actually, Venus Equilateral was an asteroid that had been shoved into its orbit about the Sun, forming a practical demonstration of he equilateral triangle solution of the Three Moving Bodies. It was a long cylinder, about three miles in length by about a mile in diameter...
This was the center of Interplanetary Communications. This was the main office. It was the heart of the Solar System's communication line, and as such, it was well manned. Orders for everything emanated from Venus Equilateral."

(found with a google for "Venus Equilateral")

[nprev]

Never read it...bummer...thought I had an original idea, there! Oh, well, fame and fortune remain elusive...

Within the framework of current technology, these Trojan relay sats could be linked to Earth-orbiting intermediate satellites in orbits (precessing "semi-Sun-synchronous" polar?) that would provide a continuous LOS path to them; in turn, you could use MUCH smaller (even commercial-off-the-shelf) ground stations & deploy a lot of them in order to maintain continuous contact.

[djellison]

You mean take TDRS and turn it interplanetary.

Doug

[mchan]

An aerospace engineering student at my alma mater wrote a paper in early 90's on Mars relay sats in halo orbits around the L1 and L2 points. Two satellites would provide near-continuous global coverage of Mars. The downside is that the greater distance between Mars and L1/L2 required the comm systems on Mars to be higher powered / use bigger antennas compared to that required by low Mars orbit relays. Tradeoff between coverage time and power / structure.