Author Topic: SpX Mars Communication Constellation?  (Read 32929 times)

Offline guckyfan

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Re: SpX Mars Communication Constellation?
« Reply #40 on: 04/22/2018 03:32 am »
Actually, this is not a problem.

At a little after entry into the Martian atmosphere, instead of actively maintaining your trajectory into the atmosphere aerodynamically, you do the opposite.
This bounces you out to an eccentric Mars orbit. A few tens of m/s at apogee, and you can make it an orbit which only intersects the edges of the atmosphere at the bottom.

Unload the cargo, taking as much as a few hours to do it, and then reenter as normal.

Payloads circularise and do other manoevering gradually using aerobraking as mars climate observer did, as well as slow thrusting from a small ion engine.


If you additionally have hardware that doesn't mind if it's on Mars or in low mars orbit, this can actually increase the payload to Mars quite notably.

There is one problem as I see it. The orbit of the deployed satellites would go quite deep into the atmosphere, deep enough that BFS has used the atmosphere for very significant braking. Those satellites either need a heat shield to survive the next pass or they have a very short time to deploy their solar arrays, get active and do an orbit raising maneuver.

Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #41 on: 04/22/2018 03:36 am »
The satellites have significant delta-v. They can do their own insertion maneuvers. No aerocapture or whatever needed.
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Offline swervin

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Re: SpX Mars Communication Constellation?
« Reply #42 on: 04/22/2018 03:57 am »
Delivering this capability w/ BFS assumes no desire or need to have this capability in place when BFS arrives and heads to the surface. SpX will have enough to handle at that moment, let alone managing the roll-out of a comm sat capability, simultaneously. I’m a strong advocate of an advanced launch, a cycle prior (2 years) to BFS heading to Mars. This capability needs to be in place, shook out, and ready to roll — at BFS entry interface.

Splinter

Offline speedevil

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Re: SpX Mars Communication Constellation?
« Reply #43 on: 04/22/2018 04:28 am »
This bounces you out to an eccentric Mars orbit. A few tens of m/s at apogee, and you can make it an orbit which only intersects the edges of the atmosphere at the bottom.

Unload the cargo, taking as much as a few hours to do it, and then reenter as normal.

Payloads circularise and do other manoevering gradually using aerobraking as mars climate observer did, as well as slow thrusting from a small ion engine.


If you additionally have hardware that doesn't mind if it's on Mars or in low mars orbit, this can actually increase the payload to Mars quite notably.
The orbit of the deployed satellites would go quite deep into the atmosphere, deep enough that BFS has used the atmosphere for very significant braking. Those satellites either need a heat shield to survive the next pass or they have a very short time to deploy their solar arrays, get active and do an orbit raising maneuver.
See bold. The size of the delta-v depends on how accurately you can tailor the exit velocity to a bound but high orbit.
It could be quite small indeed.

Offline guckyfan

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Re: SpX Mars Communication Constellation?
« Reply #44 on: 04/22/2018 07:18 am »
I agree it could be small, I got that from your post. My issue is that it would need to be done by BFS and then a deorbit burn. Not much but something. The time to get the satellite operational and do it by itself is just short. In earth orbit they need some time, days, if not weeks, to get a satellite checked out and operational.

Offline Bob Shaw

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Re: SpX Mars Communication Constellation?
« Reply #45 on: 04/22/2018 11:20 am »
NASA *does*use ground stations. Ever heard of the DSN?

Offline joek

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Re: SpX Mars Communication Constellation?
« Reply #46 on: 04/22/2018 11:56 am »
NASA *does*use ground stations. Ever heard of the DSN?

I believe the context of this discussion is Mars assets--not Earth/DSN-based assets: Would a Mars ground-based/fixed communication infrastructure be preferable vs. orbital?  Certainly additional and robust Mars ground-based communications infrastructure will be needed/desirable in the future.

Efficient intra-Mars communications will certainly minimize Earth-based assets such as DSN.  Efficient Mars-Earth communication may involve DSN.  In any case, the question for Mars-Earth communication is primarily: What does the Mars-side look like?

Offline guckyfan

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Re: SpX Mars Communication Constellation?
« Reply #47 on: 04/22/2018 12:01 pm »
The DSN and its basic structure are not appliccable for SpaceX needs of efficient Earth Mars communication. By the time SpaceX lands assets on Mars at least an initial Starlink constellation is deployed. IMO the logical way to go is having dedicated sats with large laser mirrors in orbit that feed into Starlink and data can be downlinked wherever convenient without the need of large dishes all over the world to maintain contact while the Earth spins.

Offline speedevil

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Re: SpX Mars Communication Constellation?
« Reply #48 on: 04/22/2018 12:52 pm »
IMO the logical way to go is having dedicated sats with large laser mirrors
This begins of course to look like a pretty generic satellite you can throw anywhere nearby.
Add a few more panels, an ion engine to the bus, and make sure you specify the option to swap the LASER for a commercial-grade imager when you want to look at something.

Fails - meh - it cost $3M. Doesn't fail, free relay node for missions further out, and suddenly imagery of bodies in the inner solar system becomes a _whole_lot_ better.
Outer solar system is more complex of course.

Online Eer

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Re: SpX Mars Communication Constellation?
« Reply #49 on: 04/22/2018 01:05 pm »
This discussion helped me realize the value of a slower, lower arrival delta v to orbit transfer path to Mars orbit for some things. Not everything needs to get there fast, and you don’t want to burden everything with aero capture shields to slow down. Keep it simple. Use FH to loft comm sats that will be captured by mars gravity without needing aero capture and let them circularize with onboard Hall thrusters or similar. They don’t all have to go at the same time, but we’ll ahead of mission need. Send some to Sol-Mars Lagrange points to provide relays around sun for when that’s needed. Use them all as relays from Asteroid mining and survey missions. Later when BFS is available send more to fill out the coverage.
From "The Rhetoric of Interstellar Flight", by Paul Gilster, March 10, 2011: We’ll build a future in space one dogged step at a time, and when asked how long humanity will struggle before reaching the stars, we’ll respond, “As long as it takes.”

Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #50 on: 04/22/2018 02:14 pm »
Delivering this capability w/ BFS assumes no desire or need to have this capability in place when BFS arrives and heads to the surface. SpX will have enough to handle at that moment, let alone managing the roll-out of a comm sat capability, simultaneously. I’m a strong advocate of an advanced launch, a cycle prior (2 years) to BFS heading to Mars. This capability needs to be in place, shook out, and ready to roll — at BFS entry interface.

Splinter
The existing Mars fleet (MRO, Mars Odyssey, MAVEN, ExoMars, Mars Express) has relay radios (I don’t think MOM does?) and may be sufficient along with DSN for uncrewed BFS. Crew will need more bandwidth.
« Last Edit: 04/22/2018 02:20 pm by Robotbeat »
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Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #51 on: 04/22/2018 02:37 pm »
What’s interesting is that the US doesn’t have any new orbiters approved for Mars in the foreseeable future. So data relay could be a problem. EXCEPT there are a bunch of international orbiters planned, and NASA usually offers a free relay radio package to any orbiter going to Mars. Mars is about to get a lot more international. UAE, China, Japan, and India have new orbiters planned in the next 6 years.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline guckyfan

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Re: SpX Mars Communication Constellation?
« Reply #52 on: 04/22/2018 03:24 pm »
Later with regular flights they will want to send all BFS fast and get them back in the same synod. That's not necessary for the first and second launch window.

Since they send 2 cargo ships in the first window they could send one fast to test EDL as planned and one slow on a Hohmann trajectory. The slow ship could drop a constellation of sats in the cruise phase. The sats can do orbit insertion on their own. Until the Mars constellation is ready they would have to rely on DSN assets, but that's only temporary.

I am very sure they will want uninterrupted fast connectivity for their crew missions from the beginning. Which would mean they have to deploy comm capabilities a window earlier.

Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #53 on: 04/22/2018 04:36 pm »
They could just launch them like regular commsats but to a very high, elliptical Earth orbit. They can do the trans-Mars-injection and Mars-orbit-insertion burns themselves, using their amply-provided electric thrusters.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline CuddlyRocket

Re: SpX Mars Communication Constellation?
« Reply #54 on: 04/22/2018 05:25 pm »
NASA mostly uses orbiters to relay data from ground assets. I fail to see why SpaceX wouldn’t do the same thing. It’s not at all an overcomplication as it simplifies the ground infrastructure.

If you think using a ground station alone is so great, then you better be able to explain why NASA doesn’t do it.

Because NASA's current ground assets on Mars have severe limits on the amount of power available and on the size of any antennas. A human Mars base or settlement can have far more power available and much larger antennas. There's a reason NASA uses the DSN and not orbiting satellites for communicating over interplanetary distances.

Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #55 on: 04/22/2018 05:36 pm »
Of course. Long-term, Mars will not rely just on the existing Mars relay orbiters. But likewise they’re not just going to use ground stations direct to Earth! They’ll use relay satellites, just better, SpaceX ones.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline guckyfan

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Re: SpX Mars Communication Constellation?
« Reply #56 on: 04/22/2018 08:17 pm »
The DSN has functions other than Mars. It connects to probes far out and needs very large antenna dishes for the very weak signals. It needs multiple dishes for continuous coverage.

Multiple dishes on Mars are not an option. Not yet and not for a long time. So a local constellation ensures continues connectivity from a Mars location. Laser links ensure high data rates without the need of very large dishes.

Offline DistantTemple

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Re: SpX Mars Communication Constellation?
« Reply #57 on: 04/22/2018 08:37 pm »
The DSN has functions other than Mars. It connects to probes far out and needs very large antenna dishes for the very weak signals. It needs multiple dishes for continuous coverage.

Multiple dishes on Mars are not an option. Not yet and not for a long time. So a local constellation ensures continues connectivity from a Mars location. Laser links ensure high data rates without the need of very large dishes.http://www.sciencetimes.com/articles/14680/20170509/nasa-s-deep-space-network-can-be-overwhelmed-by-mars-traffic-jams.htm
It seems that the DSN might be at full capacity at the 2020 synod. That doesn't bode well for SX to get lots of bandwidth exactly when it want/needs it. And this is without SX's onslaught, BFS, or humans!
Quote from: sciencenews.com
For the year 2020, the list of Mars mission is too long. Not only NASA will be launching any spacecraft, but other nations are also in the list. This clearly shows how much NASA's Deep Space Network needs to work out from future telecommunication problems. The list has NASA's Mars 2020 rover, China's orbiter, European Space Agency's ExoMars 2020 rover, United Arab Emirates' Hope orbiter, and India's Mars Orbiter Mission 2.
I'm sure EM will want independence, and everything he does seems like lining up for future turns in a chess game... (IMO) He will want to get in position for future huge expansion, and before that for safe human landings, and before that for reliable robotic setup of ISRU, water mining, and robotic site preparation. (in 2022)
So IMO his use of DSN, if any will be brief at the initial stages, or a backup if he has issues at the beginning.
2020 would be a good time for a handful of initial comms, sensing, and navigation sats on a couple of FH's. These would constitute a minimum network, high quality sensing of his favourite landing site, and link to Earth.
(I can also immagine a Red Dragon or other lander with rover to drill for water etc at his preferred landing site.)
We can always grow new new dendrites. Reach out and make connections and your world will burst with new insights. Then repose in consciousness.

Offline Robotbeat

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Re: SpX Mars Communication Constellation?
« Reply #58 on: 04/22/2018 08:57 pm »
Not "his" but SpaceX. SpaceX is now much more than just Elon.
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Offline Ludus

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Re: SpX Mars Communication Constellation?
« Reply #59 on: 04/22/2018 11:42 pm »
NASA mostly uses orbiters to relay data from ground assets. I fail to see why SpaceX wouldn’t do the same thing. It’s not at all an overcomplication as it simplifies the ground infrastructure.

If you think using a ground station alone is so great, then you better be able to explain why NASA doesn’t do it.

A satellite constellation for data relay from Mars isn’t hypothetical. It has been a reality for decades. It is the status quo. There is a fleet of 5 satellites around Mars that are used for data relay from the surface. Today.

By the same standard it already exists around earth too. In both cases the purpose of the Starlink type constellation is for future demand and applications. NASA finds it hard to justify investing in infrastructure to meet future demand. Businesses would find the sort of narrow planning that NASA does with no hope of covering costs equally impossible to justify.

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