Mars Telecom Orbiter reduxe

[vjkane]

Question; Would it be more efficent to send one big comsat to Mars or a cluster of smaller "mini-comsats"?  Sats that are larger than cube sats, but smaller than regular comsats.

It depends on whether you want temporal coverage or higher data rates.  If you want more comm sessions, then more satellites are better.  If you want higher data rates, then bigger comsats with larger solar panels and higher power comm systems are better.

If you have just one landed asset (or multiple that are relatively close together), you can have both: a large spacecraft with lots of power in geosynchronous orbit.

[nadreck]

The answer is that a lot more than two will need to be in operation before a human surface mission is attempted, and this capacity needs to be forward-looking if we want permission to do that human surface mission this century.

While I totally agree that we need more surface examination before manned landings, and that multiple rovers and other probes are needed, and that a communications GPS constellation around Mars is needed and I imagine already 100% in the cards in the Musk universe of Mars exploitation. I have to ask what authority did you have in mind that can grant permission for manned Mars landings?

[kevin-rf]

GPS? It is not currently needed, and should not be needed for the initial manned landings at specific site(s). It has not been needed by the rovers and was not needed during Apollo.

[vjkane]

GPS? It is not currently needed, and should not be needed for the initial manned landings at specific site(s). It has not been needed by the rovers and was not needed during Apollo.

Rovers, no.  But would be useful for planes (several have been proposed; I doubt that any will fly).

[nadreck]

GPS? It is not currently needed, and should not be needed for the initial manned landings at specific site(s). It has not been needed by the rovers and was not needed during Apollo.

It hasn't been available which means that missions have never been designed around it's use. Lets put it this way, if you put a communications/GPS/monitoring/surveying constellation around Mars so that all the information available from the satellites including positioning could be received and processed in a 100gm/100mW device. What capabilities and missions could you dream up for the subsequent generation of probes? GPS would be used if it was available, especially if rendezvous with a sample return craft was necessary by a sample collecting rover. However in performing better site surveys, geology, mapping, etc the GPS will certainly improve the work as will all the other features of such a constellation.

[Burninate]

The answer is that a lot more than two will need to be in operation before a human surface mission is attempted, and this capacity needs to be forward-looking if we want permission to do that human surface mission this century.

While I totally agree that we need more surface examination before manned landings, and that multiple rovers and other probes are needed, and that a communications GPS constellation around Mars is needed and I imagine already 100% in the cards in the Musk universe of Mars exploitation. I have to ask what authority did you have in mind that can grant permission for manned Mars landings?

Crossposted to a separate thread to prevent this from going offtopic: http://forum.nasaspaceflight.com/index.php?topic=37244.msg1355699#msg1355699

[zubenelgenubi]

For a single, communications-relay satellite, whose prime function is relaying from multiple surface assets:
What is the optimal orbit?

Polar Low Mars Orbit ? (PLMO, to coin an acronym)
Molniya orbit?

I deduce that an areosynchronous orbit would not be useful, as a surface asset or assets could permanently be at a Martian longitude over the planet's limb from the satellite's perspective.

Zubenelgenubi

[hop]

For a single, communications-relay satellite, whose prime function is relaying from multiple surface assets:
What is the optimal orbit?

FWIW, the original Mars telecom orbiter was targeted at a 5000km orbit: http://web.archive.org/web/20050924232548/http://mars.jpl.nasa.gov/missions/future/mto.html

The spacecraft will be in contact with Earth almost around the clock, because its orbit will place it 20 times farther from the planet's surface than other spacecraft, meaning it will nearly always have a direct line of sight to Earth. The Mars Telecommunications Orbiter will fly above the surface of Mars at a distance of 5,000 kilometers (3,000 miles).

[vjkane]

For a single, communications-relay satellite, whose prime function is relaying from multiple surface assets:
What is the optimal orbit?

If communications is your only goal, and your landed assets are going to be in the equatorial zone, then you'd want to have an orbiter with an orbit that goes no further north or south.  That will result in more communication passes than with a polar orbiter.  Of course, if you are only going to have polar landers, than a polar orbit would provide a number of passes.

[zubenelgenubi]

For a single, communications-relay satellite, whose prime function is relaying from multiple surface assets:
What is the optimal orbit?

If communications is your only goal, and your landed assets are going to be in the equatorial zone, then you'd want to have an orbiter with an orbit that goes no further north or south.  That will result in more communication passes than with a polar orbiter.  Of course, if you are only going to have polar landers, than a polar orbit would provide a number of passes.

Good point differentiating requirements of "tropical" surface assets vs. polar assets.  My mental image was of several assets spread wide in latitude and longitude.

Do any "serious" agencies or organizations have serious upcoming plans for polar landers or rovers?

[vjkane]

Do any "serious" agencies or organizations have serious upcoming plans for polar landers or rovers?

Chris McKay and his team are proposing the IceBreaker mission that would return to the polar regions to follow up on the Phoenix mission for this coming Discovery competition.  The mission would launch in 2021.

The challenge is that the new orbiter, if it flies, needs to support missions of the mid- to late-2020s and early 2030s.  No one has a real idea of what they would be except the Mars community wants to send a mission to pick of the samples collected by the 2020 rover.  That latter mission is roughly constrained to the equatorial regions.

A comm orbiter with a serious ion engine and lots of time can shift from an equatorial to a polar and back to an equatorial orbit.

[baldusi]

I understand that the north pole of Mars is very shallow and thus has the most atmosphere, which makes EDL simpler. And it has a lot of water ice, thus, is the easiest place to land and a very interesting scientific place. I would hazard a guess that it is required coverage for a comm sat.

[notsorandom]

I understand that the north pole of Mars is very shallow and thus has the most atmosphere, which makes EDL simpler. And it has a lot of water ice, thus, is the easiest place to land and a very interesting scientific place. I would hazard a guess that it is required coverage for a comm sat.

If the comm sat is going to be carrying remote sensing instruments of some sort. Many of those will prefer a sun synchronous orbit which gives most site on the planets two fly overs a day. Odyssey for example is in a sun sync orbit. One is at night the other day. If the communications orbiter were in such an orbit it should be able to cover the polar regions pretty well.

[Blackstar]

Do any "serious" agencies or organizations have serious upcoming plans for polar landers or rovers?

Chris McKay and his team are proposing the IceBreaker mission that would return to the polar regions to follow up on the Phoenix mission for this coming Discovery competition.  The mission would launch in 2021.

The challenge is that the new orbiter, if it flies, needs to support missions of the mid- to late-2020s and early 2030s.  No one has a real idea of what they would be except the Mars community wants to send a mission to pick of the samples collected by the 2020 rover.  That latter mission is roughly constrained to the equatorial regions.

A comm orbiter with a serious ion engine and lots of time can shift from an equatorial to a polar and back to an equatorial orbit.

The ion engine adds an interesting dimension, including optimizing the orbit based upon what is on the ground on Mars.

But I suspect that a mission like IceBreaker, which is Discovery class and would have a limited lifetime, would have relatively little impact on deciding the comm-relay needs. They're going to design the comm relay solution to cover the most important and broadest range. A single mission to the poles that would only operate for a relatively short time would not justify major changes to the relay architecture.

[redliox]

Do any "serious" agencies or organizations have serious upcoming plans for polar landers or rovers?

A comm orbiter with a serious ion engine and lots of time can shift from an equatorial to a polar and back to an equatorial orbit.

The ion engine adds an interesting dimension, including optimizing the orbit based upon what is on the ground on Mars.

But I suspect that a mission like IceBreaker, which is Discovery class and would have a limited lifetime, would have relatively little impact on deciding the comm-relay needs. They're going to design the comm relay solution to cover the most important and broadest range. A single mission to the poles that would only operate for a relatively short time would not justify major changes to the relay architecture.

Considering we're starting to get ion engines with Earthly communication satellites it makes sense to put them aboard a Martian one, not so much for orbit insertion but so it can remain stable in orbit for not just 5 or 10 but perhaps even 20 years.

I have a feeling the first manned landing will be equatorial; heck if you look at the current operating rovers you'll notice even they are pretty much equatorial.  So a synchronous (or otherwise in a high orbit) satellite won't be a disadvantage.  If we have to settle for a single comsat, I'd suggest putting it in a 12 hour equatorial orbit so I can get coverage over the majority of Mars at least twice a day.