Author Topic: SpaceX and DSN  (Read 5834 times)

Online speedevil

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Re: SpaceX and DSN
« Reply #20 on: 03/19/2018 02:21 pm »
That assumes a new generation of deep space probes. Assuming they start developing them in a few years with new budgets they can fly in 10-20 years. But even only switching Mars to the new system should provide a lot of relief for the DSN. Much of the data stream comes from Mars.
Assuming that you can't do a deep space probe for $10M.

Online guckyfan

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Re: SpaceX and DSN
« Reply #21 on: 03/19/2018 06:35 pm »
That assumes a new generation of deep space probes. Assuming they start developing them in a few years with new budgets they can fly in 10-20 years. But even only switching Mars to the new system should provide a lot of relief for the DSN. Much of the data stream comes from Mars.
Assuming that you can't do a deep space probe for $10M.

You lost me.

Offline Jim

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Re: SpaceX and DSN
« Reply #22 on: 03/19/2018 06:45 pm »
Let me make sure I understand the commentary above:

If you have satellites in orbit to relay the signal, there isn't a need for the large ground based antennas used by DSN?

That's the way I read it. And with laser communication to Mars, you don't have to worry about cloud cover. I would assume that the Mars relay satellite(s) would be in orbit somewhat above GEO and only require one or two satellites. Looking farther into the future I would expect 2 relay satellites in an orbit around the sun so communication would be uninterrupted when Earth and Mars were on opposite sides of the sun.

No, then you still have to have "DSN" to talk to the relay sats. 

Other than direct to earth stations, GSO only other viable point for a receiver.   StarlinK?  nah.  Got to stop thinking space communications is like the internet.  That burned SpaceX on vehicles.  Telemetry (vehicle health) can't be packetized, it is needs to be continuous (until we get to airliner type operations).

Offline biosehnsucht

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Re: SpaceX and DSN
« Reply #23 on: 03/20/2018 08:19 pm »
It can be continuous unpacketized (or minimally, depending on the needs of physical layer) transmission from remote device (orbiting Mars or whatever) and more heavily packetized after it arrives at a relay, and then carried over Starlink from there.

Only the first hop needs to be capable of streaming data to get every last bit of data out in order, if that's a priority.

The speed of light means that you're not going to have realtime data no matter what, it's always delayed, so after you hit the first relay (which is probably not going to burst into flames in the middle of some critical data being relayed) you can buffer and store and forward in a more efficient / internet-y method and thus use Starlink as backhaul from there.

Hell you could orbit a few satellites in useful locations (around Earth, Moon, or even the Sun, etc) which have the necessary gear to listen for broadcasts normally sent to the DSN, using a mix of relevant hardware (might require more than one kind of antenna selected as desired, or even all operating at once, plus various other bits optimized to various bandwidths/frequencies) and software defined radio techniques, sample the data (you can do so in a way that you sample a wide range and can decode later) and store and forward back to Earth via Starlink laser comms or anything else you want. This would let you basically put a "DSN dish" anywhere you want. If a $20 USB dongle can tune from ~24MHz to ~1.7GHz with over 2 million samples/sec, then high end flying SDR's for DSN use should be trivial for anyone willing to spend some money on R&D.

Online Roy_H

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Re: SpaceX and DSN
« Reply #24 on: 03/21/2018 01:26 pm »
Let me make sure I understand the commentary above:

If you have satellites in orbit to relay the signal, there isn't a need for the large ground based antennas used by DSN?

That's the way I read it. And with laser communication to Mars, you don't have to worry about cloud cover. I would assume that the Mars relay satellite(s) would be in orbit somewhat above GEO and only require one or two satellites. Looking farther into the future I would expect 2 relay satellites in an orbit around the sun so communication would be uninterrupted when Earth and Mars were on opposite sides of the sun.

No, then you still have to have "DSN" to talk to the relay sats. 

Other than direct to earth stations, GSO only other viable point for a receiver.  StarlinK?  nah.  Got to stop thinking space communications is like the internet.  That burned SpaceX on vehicles.  Telemetry (vehicle health) can't be packetized, it is needs to be continuous (until we get to airliner type operations).

Starlink will have laser communications between satellites. I see no reason that same communications system can't have a dozen or so Starlink satellites able to connect with 2 satellites in earth orbit just above GEO. The link from these Earth to Mars relay satellites does not have to be the same Internet protocol on the Mars link side. BTW 1 satellite would do, I just think 2 for redundancy and always having at least 1 not blocked by Earth between satellite and Mars.
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Offline CuddlyRocket

Re: SpaceX and DSN
« Reply #25 on: 03/21/2018 09:19 pm »
StarlinK?  nah.  Got to stop thinking space communications is like the internet.  That burned SpaceX on vehicles.  Telemetry (vehicle health) can't be packetized, it is needs to be continuous (until we get to airliner type operations).

Just like on Earth, some communications are like the Internet and some aren't. Telemetry may need to be continuous, but not all communications are telemetry even in present-day space operations (ISS crew get email, for instance).

Online ThereIWas3

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Re: SpaceX and DSN
« Reply #26 on: 03/21/2018 10:52 pm »
Over such long distances, you can't ask for retransmission if you get a bad checksum.  All a checksum can do is tell you that the data you just received has been garbled, but not how.

Instead you use Forward Error Correction (FEC) which adds additional information so that you can actually correct errors up to some specified limit.  The actual algorithm used depends on what kind on interference you expect.

But FEC does require dividing the data into chunks/frames/packets.
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Offline oldAtlas_Eguy

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Re: SpaceX and DSN
« Reply #27 on: 03/22/2018 06:58 am »
If you can offload from the existing DSN the predominance of scientific and image data which is not real time, is highly compressed and heavily FEC encoded, then it will be a very good thing. Not all data from probes is do or die telemetry. Most of is plain packets of data streamed through the transmitter during spacecraft inactivity. If you could be able to ship this data at any time leaving the prime telemetry transmitter for telemetry only then the demands on the DSN Earth assets become less of a problem. At least for a while. But by then the DSN should be represented by a multi-planatary/stations distributed network joined via advanced interplanetary internet system.

What is being discussed is the interim between what exists now and what would exist once settlements are established.

What is suggested is a supplemental system for the predominance of non critical data and even streams a copy of the critical data in case the primary system has drops. This supplemental system, likely a laser system, would have 100X or more the data bandwidth that of the primary telemetry. The difference is that the primary telemetry does not assume a stable craft. This is also true for the command and control uplink.

The scenario is one where the expensive DSN assets are only brought to bare when the high data rate laser link fails, for whatever reason. Most do not realize that often no DSN asset is even listening to a probe. It only when a probe is transitioning states or performing some critical action that in many cases there is more than just one DSN asset listening.

Online Giovanni DS

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Re: SpaceX and DSN
« Reply #28 on: 03/22/2018 12:06 pm »
What is the problem with slight delays in transmission? I assume you can organize the information in packets and add time stamps from an high resolution "system time", that will allow reconstruction of real-time events downstream.

There would be no buffering, one packet is assembled while the previous one is being transmitted.

Lost information would amount to a packet transmission time, assuming the transmitter does not survive long enough.

Offline Robotbeat

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Re: SpaceX and DSN
« Reply #29 on: 03/22/2018 12:12 pm »
You can use a radio (which is what the Starlink satellites have) with different higher level protocols. No reason it HAS to be TCP/IP.
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Online DigitalMan

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Re: SpaceX and DSN
« Reply #30 on: 03/22/2018 12:42 pm »
You can use a radio (which is what the Starlink satellites have) with different higher level protocols. No reason it HAS to be TCP/IP.

There could be a lot of data that would benefit from a store and forward infrastructure.  Time sensitive data would benefit from having more specific protocols that could alleviate issues, such as multi-path.

Considering the constraints compared to terrestrial internet I am not sure one mechanism is the right path once you introduce time-sensitive data into the mix where remote humans are involved.  Just a thought.

Offline LouScheffer

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Re: SpaceX and DSN
« Reply #31 on: 03/22/2018 01:32 pm »
Previous discussion on this: https://forum.nasaspaceflight.com/index.php?topic=41240.0

It looks like one aspect need to be emphasized is DSN is not just for communication, but also for navigation.
DSN does  three main operations:
   a) Receiving data (science and telemetry)
   b) Commanding spacecraft
   c) Navigation - this has two parts - ranging and doppler shift measurement.

Function (a) you could do much more cheaply with an array of smaller antennas.  JPL itself has lots of studies on this, and astronomers use it all the time.  It's well developed technology.
 (b) is harder.  Deep space commanding needs an extremely strong signal, since you have to assume the target spacecraft could be pointed the wrong way, so you  get only the low gain antenna.   JPL uses big transmitters and big dishes combined.  Replacing this with an array is still research - the problem is, that unlike receiving, there is no phase reference.
 (c) is also harder to cheapen.  Both ranging and doppler rely on a strong uplink, as in (b).  Ranging by necessity (you need the round trip time) and doppler by technology (it's easier to have a super-stable oscillator on the ground). 

JPL now opts for the easiest, but most costly, solution.   They build all dishes at all stations capable of all operations.  Then, whenever they track a spacecraft, they do so by running the uplink and using the received data for both doppler and telemetry.  Sometimes they include ranging as well, but that takes modulation on the downlink and reduces telemetry rates.  (There is one exception which is Mars.  Here one spacecraft gets the uplink but multiple can downlink.  But this is the rare case where more than one spacecraft is within the antenna beam.)   

A new facility could do better by specializing.  Perhaps two big antennas at each site, for uplink and ranging.  Neither of these is super time consuming, so two rather than the 4-5 current antennas per site might suffice.  Then supplement this with a larger array of smaller antenna, for receiving only.   For the same expense, this could have 4-5 times more receiving area than the current solutions, with a corresponding larger science return.  The one thing you lose with this arrangement is doppler navigation data obtained simultaneously with downlink.  On some missions, this is a big deal, since this is the data needed for gravity modelling and other radio science.  But these missions could (very soon if not now) carry miniaturized, space rated, high accuracy atomic clocks.  These missions could then do doppler full time without requiring a constant uplink.

Overall, I don't think you could build a good DSN for much less than the current cost.   But you could make new stations several times more effective in terms of science return for the same money, if you are willing to change the use model




Offline docmordrid

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Re: SpaceX and DSN
« Reply #32 on: 03/22/2018 03:01 pm »
You can use a radio (which is what the Starlink satellites have) with different higher level protocols. No reason it HAS to be TCP/IP.

There could be a lot of data that would benefit from a store and forward infrastructure.  Time sensitive data would benefit from having more specific protocols that could alleviate issues, such as multi-path.
>

Like NASA's DTN (Delay/Disruption Tolerant Network), which they developed for a solar system internet?

https://www.nasa.gov/content/dtn



« Last Edit: 03/22/2018 03:04 pm by docmordrid »
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Offline Kansan52

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Re: SpaceX and DSN
« Reply #33 on: 03/22/2018 03:11 pm »
I think it is optimistic to plan for ST's Enterprise being in the loop (upper right hand corner).

Online DigitalMan

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Re: SpaceX and DSN
« Reply #34 on: 03/22/2018 03:22 pm »
That's interesting, looks like a good place to start. 

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