The punch line to this story is that backup transmitter hasn't been used since 1981.
About two weeks ago, October 16, Voyager 1 put itself into a safe mode after receiving a transmission from its mission control via the Deep Space Network commanding the satellite to turn on one of its heaters. Because it takes just about a full day for radio transmission to get to the satellite and another full day before the response is known, they found out on October 18 that Voyager failed to respond.
According to a post from NASA, it took a little while to discover that Voyager had switched off its primary X-band transmitter and switched over to its secondary S-band radio transmitter, which uses less power.
Then, on Oct. 19, communication appeared to stop entirely. The flight team suspected that Voyager 1’s fault protection system was triggered twice more and that it turned off the X-band transmitter and switched to a second radio transmitter called the S-band. While the S-band uses less power, Voyager 1 had not used it to communicate with Earth since 1981. It uses a different frequency than the X-band transmitters signal [and] is significantly fainter. The flight team was not certain the S-band could be detected at Earth due to the spacecraft’s distance, but engineers with the Deep Space Network were able to find it.
While the first thought might be to turn the X-band transmitter on, the Voyager team is more cautious than that, wanting to understand what caused the fault protection system to trigger and switch the transmitters.
[T]he team sent a command on Oct. 22 to confirm the S-band transmitter is working. The team is now working to gather information that will help them figure out what happened and return Voyager 1 to normal operations.
Two days later on the 24th, the team was finally able to connect with the elderly
spacecraft, now in the 47th year of its four year mission. Voyagers 1 and 2 (a
few weeks older than 1) are the only man-made objects to reach and operate in
interstellar space. Their advanced age has meant an increase in the
frequency and complexity of technical issues and new challenges for the
mission engineering team. Which has met those challenges so far.
How do you hear a signal from a low power transmitter that's 23 light hours, that is, 16 billion miles
away? A high gain antenna. This the Deep Space Network antenna in Canberra,Australia. With a diameter of 70 meters, or 230 feet, the DSN stations are the three
most sensitive radio receiving stations on Earth. Image credi: NASA/JPL-Caltech
That's pretty cool. Too bad we don't have orbital antenna satellites to do the signal catching and then retransmitting back to Earth, and vice-versa.
ReplyDeleteWell, with Starship eventually coming on-line, it would be a good mission to put one up t here! And pretty cheaply, too!
DeleteI'm thinking that SpaceX/Musk will want their/his own solely controlled constellation of retrans satellites for only SpaceX missions outside Earth's orbit.
DeleteHe already has a system for in-orbit communications, that being all the friggin Starlink satellites cruising overhead.
I had an offer to work at the DSN in Goldstone.
ReplyDeleteBUT.....I had just met Sweet-Little-Wife-To-Be and I didn't want to move. Same with SBX. She would have loved to live in Hawaii, but I'd be gone 3~6 months at a time.....nope!
Clearly, when it comes to un-manned missions, NASA are proponents of the ‘under promise and over deliver’ action. But really, back in the day you have to admire their over-engineering foresight to have working Voyagers after 47 years in such an unforgiving environment as deep space. Oh, and not to waive credit to the telecoms engineers in the DSN either. Credit where credit is due!
ReplyDeleteI suspect engineers at SpaceX are in the same league.
The unmanned side of NASA and the JPL in particular strike me as the only parts worth saving. They've also gotten years out of Mars rovers. Like Opportunity, that was supposed to last 90 days but explored Mars for 15 years. There's a documentary about it on Amazon Prime called "Goodnight Oppy".
DeleteI just have this feeling that permanent institutions like that always devolve to take advantage of the permanence.
"Goodnight Oppy" was a very emotional viewing experience here in the Beans' household. Plucky little guys, both of them.
DeleteAs to overbuilding, since no-one really had any idea of the actual non-Earth space environment, they overbuilt because they had no idea how quickly the probes and such would last. Some said only a year or two, some said 10 years, maybe 20. Radiation damage, being struck by microparticles, dealing with the solar tides and waves.... Nobody expected the two Voyagers to last 40-50 years.
Now look at today's probes. Built to meet the expected environment, in many ways. And they don't last, much at all. The recent (in the last few years) of splattering the Moon with non-functioning and barely-functioning probes is a statement that we humans don't build them like we used to.
Spirit and Opportunity were built in the 'since we're going there anyways and we don't know what we're really going to find, let's overbuild it as much as possible.' And they did.
I wonder how big the sub-reflector is.
ReplyDeleteI would love to see a block diagram of the receiving system, with some description of each stage, that allowed them to receive such a signal.
ReplyDeleteThere's a bit of discussion of this in an old article I did on a look at Voyager from the design standpoint but with no block diagrams or that sort of detail. The most important part of the receiver is the antenna gain, which for the Deep Space Network was given as 82dB at X band.
DeleteI assume but don't know that they chill the DSN receiver's front end with liquid nitrogen, but possibly even colder, to reduce the noise temperature. Given the age of the transmitter and the power dropping out of the RTG, I'd redo that but with instead of 23 watts output power from Voyager, I'd drop that to 10 watts. I don't know what the ratings are for S band, but I'd start out assuming the antenna gain of both Voyager and the DSN are lower at ~ 2GHz rather than ~10 if it's X band.
SiG, you have hit some of the high points that had crossed my mind. The pre-amp is probably mounted at or near the feed point and super-cooled. As they get closer to absolute zero electronics get "different"; I've only heard of pre-amps being chilled by liquid nitrogen. Yes, the gain of the antenna will be lower at 2 GHz yet still far beyond what I can even imagine.
DeleteOne little point to add is that the LNA and cryogenic lines for cooling it are in that structure in the middle of the dish sticking up. It's like a radio version of a Cassegrain telescope: parabolic concave primary (the 70m diameter dish), and hyperbolic convex secondary, suspended above that that shielded thing in the middle. You can be certain the system was designed to set the Noise Figure Right Freakin' There.
DeleteThe gain changes with wavelength; I posted a couple of sample equations back here, so you could SWAG what the gain is at 2.5 and 10.5 GHz. Both of those are PFA numbers but kinda close. I think!