Deep Space Network Now: Status of communications with our deep space explorers | Hacker News Reader

Deep Space Network Now: Status of communications with our deep space explorers

eyes.nasa.gov

125 pointsCaliforniaKarl22 comments

The latest episode of the Off-Nominal podcast[1] had a great interview with Shannon Stirone[2] all about DSN. They go into just how critical the infrastructure is, how little support it gets, and just the insane level of planning required for any planetary mission. Definitely worth a listen. See also Stirone's longread[3] about the DSN.

1: http://offnominal.space/10

2: https://twitter.com/shannonmstirone

3: https://longreads.com/2018/03/15/welcome-to-the-center-of-th...

The thing I find really impressive is how weak the signals are.

From that page, the downlink from New Horizons is currently 1.89kbps at -143.72 dBm (4.25 x 10-21 kW). That's 0.00000000000000000425 W. Not a lot of signal to work with there, but the DSN is still able to extract a usable carrier. Amazing.

Dawn an Maven seem to be doing 10 b/s.

Apparently the signals from Voyager have a "received power 20 billion times weaker than that of a digital wristwatch."[0]

The DSN website is a really good read. Along with supercooling the amplifiers they also use "special techniques to encode signals so the receiving system can distinguish the signal from the unwanted noise."

[0] - https://deepspace.jpl.nasa.gov/about/

Wonder what the noise floor is at those receivers ;)

I found [1] which reports noise temperatures around 20–30 K for the 34 m antenna that receives Voyager data [2].

The equivalent noise spectral density is around -215 dB/Hz!

[1] https://descanso.jpl.nasa.gov/monograph/series13/DeepCommo_C...

[2] https://voyager.jpl.nasa.gov/mission/science/

Is it possible to keep cooling so we can keep receiving data?

Cooling the LNAs on the earth station? Yes. I doubt the LNA on Voyager is actively cooled.

I wonder if any feed components (prior to LNA) on the earth station are cooled? [1] does not indicate.

Read a paper recently on converting an old NASA earth station with beam waveguide over to a wideband feed. They had to put a rigid waveguide horn on place of the waveguide and actively cool it.

The capability to dig such a weak signal out of the noise is, indeed, a remarkable feat. I also think the ability to orient the spacecraft to point the antenna at where the earth is from a distance of a couple billion miles is pretty amazing. Obviously, a signal is going to spread a great deal over those distances but its still important to be close. I'd be curious to know how far off the pointing is from Voyager distance from boresight.

Actually, thinking about this, I made a mistake. Voyager isn't pointing its antenna at earth at that instant. It's actually pointing it to where the earth WILL be in 16 to 20 hours. Technically, that is probably no more difficult but my statement is more accurate.

Found this saying Voyager has a pointing accuracy of 0.1 degrees: https://www.quora.com/How-precise-are-spacecrafts-like-New-H...

From the distance of Voyager, I doubt it makes any difference where Earth is for pointing the antenna. As in, it is pointing to the same spot no matter the day or season. They probably dial in an inertial coordinate and that is it.

The difficulty of communicating from deep space spurred the development of error correcting codes. In particular, Concatenated codes [1] were developed for the Voyager program in 1977.

[1] https://en.wikipedia.org/wiki/Concatenated_error_correction_...

Dave Jones of EEVBlog has a nice series of videos talking to Richard Stephenson, Operations Supervisor at the DSN's Canberra site.

How To Contact The Voyager 2 Probe:

Part 1: https://www.youtube.com/watch?v=FzRP1qdwPKw&list=PLdytWBxFfp...

Part 2: https://www.youtube.com/watch?v=1rCrfQUcXDI&list=PLdytWBxFfp...

Part 3: https://www.youtube.com/watch?v=sP_hleOXTaU&list=PLdytWBxFfp...

(the playlist is a mess, and videos are unordered)

There are also a couple of Behinde the Scenes videos.

I'm about 15 mins into the first video, and I want to buy the camera guy a new taller tripod. I feel like I am a small child having to look up at the speaker.

Getting past that, it's a cool interview. Thanks for these links.

From what I can tell, this is an exact replica of what's displayed in the spaceflight operations facility in JPL.

The direction, speed, and density of waves are indicative of the direction, data rate, and data volume of the tx/rx from deep space missions.

Recently I read a wonderful review paper about some of the problems engineers faced with early space communication.

It's really amazing how fast things moved back then. From 1954 to 1962 they went from using the moon as a relay satellite to having Telstar in orbit, which was capable of live trans-atlantic TV broadcasts.

The paper was featured on Fermat's Library, it's a great read -> https://fermatslibrary.com/s/satellite-communication---an-ov...

It’s neat to look at, for example, Voyager and see the antenna azimuth track in real-time to compensate for Earth rotation.

What is the reason that "Wind Speed" is tracked and provided on this website. What does wind speed interact with communication between these antennas and the spacecraft?

It's hard to point a big dish accurately if the wind is too strong. They have wind limits above which they stow the dishes (by pointing them straight up to reduce the wind profile).

NASA has truly achieved some ridiculous feats. I hope that we see more of this in the future.

As they say - where there's a will, and funding for the willing, there's a way.

Watching YouTube from the New Horizon space craft would really suck. It’s 11.5hr round trip latency and the bandwidth is way worse than dialup!

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