Author Topic: SpaceX's DSN plans  (Read 10832 times)

Offline UberNobody

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Re: SpaceX's DSN plans
« Reply #20 on: 09/23/2016 06:11 AM »
What kind of bandwidth are we talking about?  Megabits, hundreds of megabits, gigabits?  What are the limiting factors?

We need at least 6 live camera angles of the first manned landing, each one using 8k RED cameras ;) ;D

Offline savuporo

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Re: SpaceX's DSN plans
« Reply #21 on: 09/23/2016 07:06 AM »
1) So what Earth ground assets are likely to be implemented? There is a effort at Boca Chica right now for moderate size dish emplacement. Is there likely a plan for even larger ones?
For tracking and navigation, you need global continuous coverage, 3 dishes.

The data can be fed into the planned internet sat constellation. No need for big ground stations anywhere. Just route them to where you need them and download with a pizza box sized device.
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.
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Online AncientU

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Re: SpaceX's DSN plans
« Reply #22 on: 09/23/2016 07:28 AM »
I assume they would seriously consider a putting a relay satellite in a Mars-trailing orbit that would allow for comms relay around the sun during conjunction.

Why do you favor Mars trailing over earth trailing? Earth trailing is much easier to reach.
Even if the Earth local and Mars local ends are geosynch/areosynch, something has to deal with changing angles I think. If it's Earth trailing does that mean the Mars end has more angle change to deal with?

Low orbit like CommsX would use makes this worse I think? If the planet/first sat links are radio at both ends, that means fewer moving parts I think, with rf beam steering.  But how do you easily change laser beam angles without using moving parts?  just musing out loud here.

Changing angles are required no matter if RF or optical... Earth rotation, eclipses, and orbital mechanics make moving parts and multiple lines of sight a feature of any system.  GSO simplifies problem somewhat by mostly eliminating the eclipses.  Both RF and Optical have high directionality requirements, RF to get the needed gain and laser on both ends to establish and maintain the link.
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Offline guckyfan

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Re: SpaceX's DSN plans
« Reply #23 on: 09/23/2016 07:42 AM »
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

I don't think you quite understand how specific Mars communication with laser com sats from orbit to orbit will work.

Offline Hobbes-22

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Re: SpaceX's DSN plans
« Reply #24 on: 09/23/2016 07:51 AM »
Has laser communication been demonstrated at that distance yet?

Online AncientU

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Re: SpaceX's DSN plans
« Reply #25 on: 09/23/2016 08:28 AM »
Has laser communication been demonstrated at that distance yet?

Moon (Lunar orbit) to ground is best yet, I believe -- LADEE*.  One experiment APOLLO** links Earth to Lunar reflectors and back to 3.5m telescope counting individual photons, so theory behind comms is well established.

Pointing/acquisition is a solved problem.  Signal strength and data rate are trivially scaled in space; larger mirrors as collectors also trivially calculated, but harder to implement.  Down link through atmosphere is fairly trivial -- up link not so much because atmosphere distortions have much greater impact if on first segment of link instead of final segment.

*, **Links:
https://www.nasa.gov/sites/default/files/llcdfactsheet.final_.web_.pdf
http://www.physics.ucsd.edu/~tmurphy/apollo/apollo.html
« Last Edit: 09/23/2016 08:31 AM by AncientU »
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Offline Bob Shaw

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Re: SpaceX's DSN plans
« Reply #26 on: 09/23/2016 09:16 AM »
How will optical communication systems cope with the generally (and sometimes *very*) dusty Martian atmosphere?

Offline guckyfan

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Re: SpaceX's DSN plans
« Reply #27 on: 09/23/2016 09:20 AM »
How will optical communication systems cope with the generally (and sometimes *very*) dusty Martian atmosphere?

At least I don't suggest laser communication from and to any planetary surface.

My suggestion was for the interplanetary distance. With ground to orbit covered the way planned for the large array of small satellites.

Online AncientU

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Re: SpaceX's DSN plans
« Reply #28 on: 09/23/2016 11:17 AM »
How will optical communication systems cope with the generally (and sometimes *very*) dusty Martian atmosphere?

At least I don't suggest laser communication from and to any planetary surface.

My suggestion was for the interplanetary distance. With ground to orbit covered the way planned for the large array of small satellites.

I agree that RF comms are simplest to the surface... beamforming/signal relaying LMO sats should use same technology as planned LEO constellations.  Mobile surface platforms/individualy would not need to carry sat tracking hardware.

High data rate to/from the surface from fixed ground assets could generally use 1550 nm commercial laser which is fairly penetrating through dust, plus there is never significant atmospheric blurring (seeing) or thick cloud layers as on Earth.  This should prove to be much less challenging than Earth uplinking.
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Offline docmordrid

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Re: SpaceX's DSN plans
« Reply #29 on: 09/23/2016 01:47 PM »
NASA solar system internet using DTN networks

NASA article...

« Last Edit: 09/23/2016 01:49 PM by docmordrid »
DM

Offline Robotbeat

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Re: SpaceX's DSN plans
« Reply #30 on: 09/23/2016 01:50 PM »
Initially, use the standard UHF Mars radio that the existing Mars fleet uses for surface-orbit comms.
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Offline Lar

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Re: SpaceX's DSN plans
« Reply #31 on: 09/23/2016 02:52 PM »
I assume they would seriously consider a putting a relay satellite in a Mars-trailing orbit that would allow for comms relay around the sun during conjunction.

Why do you favor Mars trailing over earth trailing? Earth trailing is much easier to reach.
Even if the Earth local and Mars local ends are geosynch/areosynch, something has to deal with changing angles I think. If it's Earth trailing does that mean the Mars end has more angle change to deal with?

Low orbit like CommsX would use makes this worse I think? If the planet/first sat links are radio at both ends, that means fewer moving parts I think, with rf beam steering.  But how do you easily change laser beam angles without using moving parts?  just musing out loud here.

Changing angles are required no matter if RF or optical... Earth rotation, eclipses, and orbital mechanics make moving parts and multiple lines of sight a feature of any system.  GSO simplifies problem somewhat by mostly eliminating the eclipses.  Both RF and Optical have high directionality requirements, RF to get the needed gain and laser on both ends to establish and maintain the link.
Yes, changing angles are required no matter what. What I was driving at was: do certain design choices (which satellites are geo/areo synch, for example) reduce the amount of mechanical angle change compared to other design choices? I believe (based on gut) that mechanical angle changes (laser) are harder, more prone to failure, than radiative angle changes. But I could be all wet.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline savuporo

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Re: SpaceX's DSN plans
« Reply #32 on: 09/23/2016 03:50 PM »
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

I don't think you quite understand how specific Mars communication with laser com sats from orbit to orbit will work.

I'm eager to learn though. I mean, how does a currently functioning laser relay network like European EDRS have any inputs to spacecraft navigation ?
Specifically, without ground antennae and signal processing centers, how does one compute precise spacecraft velocity and location for example before and after mid-course trajectory correction maneuvers ?
Did someone invent a replacement for Delta-DOR, which replaces DOR correlators , VLBI receivers and all the other  equipment currently required for this ?
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Offline guckyfan

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Re: SpaceX's DSN plans
« Reply #33 on: 09/23/2016 04:18 PM »
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

I don't think you quite understand how specific Mars communication with laser com sats from orbit to orbit will work.

I'm eager to learn though. I mean, how does a currently functioning laser relay network like European EDRS have any inputs to spacecraft navigation ?
Specifically, without ground antennae and signal processing centers, how does one compute precise spacecraft velocity and location for example before and after mid-course trajectory correction maneuvers ?
Did someone invent a replacement for Delta-DOR, which replaces DOR correlators , VLBI receivers and all the other  equipment currently required for this ?

I was under the impression we are talking about high throughput data communications between earth and Mars.

You are now talking about something else entirely. Something that I believe may need radio communication between spacecraft and the ground on earth with rather low throughput.

Offline savuporo

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Re: SpaceX's DSN plans
« Reply #34 on: 09/23/2016 04:20 PM »
I was under the impression we are talking about high throughput data communications between earth and Mars.

You are now talking about something else entirely. Something that I believe may need radio communication between spacecraft and the ground on earth with rather low throughput.

Let me bold :
1) So what Earth ground assets are likely to be implemented? There is a effort at Boca Chica right now for moderate size dish emplacement. Is there likely a plan for even larger ones?
For tracking and navigation, you need global continuous coverage, 3 dishes.


I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

Orion - the first and only manned not-too-deep-space craft

Offline guckyfan

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Re: SpaceX's DSN plans
« Reply #35 on: 09/23/2016 04:27 PM »
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

So again, you have introduced an entirely new requirement into the discussion. My understanding remains that we are talking about a high speed data communications network between earth and Mars. You want to burden that with a totally different requirement. A sure way to increase cost and complexity while probably reducing capability.

Offline RonM

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Re: SpaceX's DSN plans
« Reply #36 on: 09/23/2016 04:42 PM »
I don't think you quite understand why Goldstone, Canberra and Madrid have 70m antennaes and what role do these things play in getting spacecraft going to where they need to be going.

So again, you have introduced an entirely new requirement into the discussion. My understanding remains that we are talking about a high speed data communications network between earth and Mars. You want to burden that with a totally different requirement. A sure way to increase cost and complexity while probably reducing capability.

The NASA DSN is used track to spacecraft position and velocity for navigation. Unless SpaceX is planning to use something like the NASA test DSAC, the SpaceX DSN will also have to be able to track spacecraft for navigation.

http://www.nasa.gov/mission_pages/tdm/clock/overview.html

Offline savuporo

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Re: SpaceX's DSN plans
« Reply #37 on: 09/23/2016 04:44 PM »
So again, you have introduced an entirely new requirement into the discussion.
I'm sorry : spacecraft tracking remains one of the most critical functions of a DSN network, any DSN - including Chinese, ESA, Indian and Japanese DSN networks. The other critical functionalities being command uplink and telemetry reception. I don't know what discussion of 'a DSN' would neglect these.
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Offline savuporo

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Re: SpaceX's DSN plans
« Reply #38 on: 09/23/2016 04:46 PM »
The NASA DSN is used track to spacecraft position and velocity for navigation. Unless SpaceX is planning to use something like the NASA test DSAC, the SpaceX DSN will also have to be able to track spacecraft for navigation.
DSAC alone would not replace DSN based tracking and navigation functionality. It would help navigation though
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Offline Robotbeat

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Re: SpaceX's DSN plans
« Reply #39 on: 09/23/2016 04:56 PM »
You could imagine an all-optical system for tracking and navigation as well as data transmission. Or a radio-based but all-in-orbit system for tracking and navigation that wouldn't require huge ground dishes.

If they go optical for bulk data transmission, I'd bet a hybrid system. They use radio for low-bandwidth commanding and rough tracking, then use optical for fine position tracking and bulk data transfer. Could use much smaller ground dishes.
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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

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