NASA JPL provided a minor update today about the status of the Voyager 1 spacecraft, indicating that the comm. problem that started more than 2 months ago has not been resolved yet. No other details.

Please check out the rest of this thread for more info on the problem where instead of sending science and engg. data, Voyager 1 has been stuck sending a 0101 bit pattern.

@NSFVoyager2
#Voyager
12/n

Two-way comms happening now between Voyager 1 and NASA DSN Canberra.

Of course, the results of the uplink commands will arrive 45 hours from now. The data arriving now left Voyager 1 22.5 hours ago.

Downlink rate is the lower 40 bps rate.
The DSN schedule for Voyager 1 shown below was modified and published yesterday.

Here's hoping that Voyager engineers are getting closer to a solution 🤞

https://eyes.nasa.gov/dsn/dsn.html
https://voyager.jpl.nasa.gov/pdf/sfos2023pdf/23_12_14-24_01_01.sfos.pdf
#Voyager
11/n

NASA did not provide a date but it looks like this issue was discovered and acted upon on Dec 7 or 8.

The graphic below shows the schedule for Voyager 1 comms via DSN, generated on Dec 7. Normally, the downlink rate is 160 bps. On Dec 8, it was switched to 40 bps. And again on Dec 10. Some special commands for the FDS were also sent.
Since then, the D/L rate has been switched between 160 bps and 40 bps a few times with additional FDS commands uploaded.

https://voyager.jpl.nasa.gov/pdf/sfos2023pdf/23_12_07-23_12_25.sfos.pdf
#Voyager
10/n

A similar but not identical problem afflicted Voyager 2 in 2010. Received science data (but not engg data?) was garbled.

The problem was traced to a flipped bit in the program stored in the FDS. A command was sent to flip the bit.

The issue was diagnosed by downloading a full memory image, which implies that engg data download was working.

This is probably what was done today with Voyager 1 today. Hopefully, it is a similar problem.

https://voyager.jpl.nasa.gov/news/details.php?article_id=16
@destevez
#Voyager
9/n

Voyager - Engineers Diagnosing Voyager 2 Data System

^{voyager.jpl.nasa.gov}

NASA DSN in Goldstone, CA is currently receiving the downlink from Voyager 1 at a reduced rate of 40 bps. No uplink at this moment.

Apparently, Voyager 1 switched data rate (160 -> 40 bps) & did a full memory read-out of her Attitude and Articulation Control Subsystem, Flight Data Subsystem, and Command Computer Subsystems A&B.
Transmission time = 6 hours
Download size = ~108 kBytes

Here's hoping that the received data is not 0101... 🤞

https://eyes.nasa.gov/dsn/dsn.html
#Voyager
8/n

In the blog post at https://blogs.nasa.gov/sunspot/, Voyager engineers point out the difficulty in diagnosing problems and crafting solutions for a spacecraft with a signal round-trip-time of almost 2 days and hardware/software developed over 46 years ago using technology long since obsolete.

"Finding solutions to challenges the probes encounter often entails consulting original, decades-old documents written by engineers who didn’t anticipate the issues that are arising today."

#Voyager
7/n

Richard Stephenson of DSN Canberra explains on twitter how NASA verified that the uplink is working.

They sent a command to Voyager 1 to switch between non-coherent mode and coherent mode transmission.

In coherent mode, the Transmission clock is derived from the Rx signal instead of from the AUX oscillator. This changes the Tx RF frequency a bit which was detected at the DSN.

https://science.nasa.gov/learn/basics-of-space-flight/chapter10-1/
https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_new.pdf
#Voyager
6/n

This schematic of the Voyager telecom system shows that the FDS sends data to the comm system over 2 serial interfaces - a low rate 10 b/s interface routed to the S-band transmitter and a variable rate 10 - 115.2 kb/s interface whose bits are sent via X or S band.

Also, from the 2 diagrams (this post and post #1), the outer coding (Reed-Solomon) is done in software!

What do you think might cause the data to be stuck not at 0 or 1 but at 0101?

https://descanso.jpl.nasa.gov/DPSummary/Descanso4--Voyager_new.pdf
@destevez
#Voyager
4/n

Voyager's computer systems were custom-built using 1960s technology, with clock speeds measured in KHz and RAM in kbytes, running hand-crafted software, crammed into 4K of 18-bit wide plated-wire memory (similar to but better than core mem).

And yes, it uses digital 8-track tape for storage.

The custom-designed hardware, (upgraded) software and instruments are mostly still functioning after 46 years in space!

https://history.nasa.gov/computers/Ch6-2.html
https://hackaday.com/2018/11/29/interstellar-8-track-the-low-tech-data-recorders-of-voyager/
@NSFVoyager2
#Voyager
3/n

The two Voyager spacecraft, launched on Sept 5, 1977 and Aug 20, 1977, have been traveling in space for over 46 years.

Voyager 1 is farther away from earth at 24.3 mil km (22.5 light hours), while V2 is 20.3 mil km away, located below the ecliptic. Both spacecraft are in interstellar space.

Here are the locations and some vital stats on the two Voyager spacecraft.

You can follow the real-time status of Voyager at https://voyager.jpl.nasa.gov/mission/status/
Graphic source: https://www.nasa.gov/solar-system/nasas-new-horizons-reaches-a-rare-space-milestone/
#Voyager
2/n