Michael BuschJul 28, 2023

Data downlink from Voyager 2 lost due to a pointing error on its antenna: https://blogs.nasa.gov/sunspot/2023/07/28/mission-update-voyager-2-communications-pause/

Although if I understand this correctly, the carrier is still detectable - it's just faint enough that the modulation isn't.

The spacecraft is expected to automatically repoint in mid-October.

Mission Update: Voyager 2 Communications Pause – The Sun Spot

Show threadMichael BuschAug 5, 2023

Voyager 2 was able to receive the "repoint now" command.

QT @canberradsn
2023 August 4

Two-way communications have been restored with #Voyager2
The good news was received through our 70-metre antenna dish, Deep Space Station 43 at 2:29pm AEST, 4th August. #DSS43

Show threadBarry GoldmanAug 5, 2023
@michael_w_busch @canberradsn how the hell we punch a signal STRONG enough to reach that mispointed ~10foot antenna 10billion miles away??? i'ma gonna have to learn me some physics!
Show threadAkaSci 🛰️Aug 5, 2023
@barrygoldman1 @michael_w_busch @canberradsn
This screen capture from DSN is from June 2022.
Tx power to Voyager 2 was 19.22 kW. It's a 70-m dish, so the beam width is around 0.1 degrees for the S-band 2.11 GHz signal.
Also see this thread from today for a possible explanation for why the 2 degree mispoint may not have been so bad for the S-band uplink.
https://fosstodon.org/@AkaSci/110831480704126540
AkaSci 🛰️ (@[email protected])

Attached: 1 image How can Voyager 2 decode a signal when its antenna is mispointed by 2°? The graphic below shows the "antenna pattern" of the Voyager antenna. Most of the downlink energy is located in the narrow main lobe, but there is some energy in the side lobes too. The graphic shows 2 such sidelobes. The uplink signal strength has similar but wider lobes, so it is possible for V2 to decode a high power signal from the DSN at a 2° offset. Here's hoping that it does 🤞 https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_new.pdf #Voyager 2/n

Fosstodon
Show threadBarry GoldmanAug 5, 2023
@AkaSci @michael_w_busch @canberradsn i gotta learn some physics. i stopped my physics education before E&M alas. 0.1 degrees? the beam can stay that tight? at 10billion miles thats still an area of ... like a millionth of a sphere at 10billion miles is still humongous area spread out.
Show threadMichael BuschAug 5, 2023
@barrygoldman1 @AkaSci Beamwidth is approximately (wavelength)/(antenna diameter). 2.1 GHz uplink -> 14 cm wavelength -> 0.002 radian beamwidth on a 70 m dish -> 0.115º.
Show threadBarry Goldman

@michael_w_busch @AkaSci ok here's my q: wouldn't light be more efficient? or would it get too scattered by spacedust? does the sun put out more light than radio, to swamp a light signal?

sure, light would suck to use when its cloudy.

Aug 5, 2023 at 2:13amWeb
Show threadMichael BuschAug 5, 2023

@barrygoldman1 @AkaSci Optical communication with spacecraft can be more efficient, but it runs into quantum mechanical limits: you need to have several photons per bit. And it doesn't work when it is cloudy.

Also, the Voyager spacecraft were built well before high bandwidth optical communication with spacecraft existed. It is only now being demonstrated over large distances: https://www.nasa.gov/mission_pages/tdm/dsoc/index.html

Deep Space Optical Communications (DSOC)

NASA.gov brings you the latest images, videos and news from America's space agency. Get the latest updates on NASA missions, watch NASA TV live, and learn about our quest to reveal the unknown and benefit all humankind.

NASA
Show threadBarry GoldmanAug 5, 2023
@michael_w_busch @AkaSci see? i know no physics. how do i relate frequency~energy to # photons per bit? hmm...
Show threadAkaSci 🛰️Aug 5, 2023
@michael_w_busch @barrygoldman1
I presume there would be challenges in keeping a laser beam well pointed at large distance, in both directions.
Show threadMichael BuschAug 5, 2023
@AkaSci @barrygoldman1 Pointing is a challenge, but more importantly optical beams going through Earth's atmosphere are limited to ~1 arcsecond beamwidth (absent some improvements with adaptive optics). The gain can still be ~10,000x what radio communication can provide; but the energy/photon is higher by a comparable factor. For low-bandwidth signals, radio can be equivalent or better. For higher bandwidths, optical can do better than radio - but only if there are enough photons to work with.