Mastodawn

Dave Anderson Apr 27, 2023

Today I'm remembering one of the coolest space things ever: Voyager 2's S-band radio receiver has been broken for 44 years, and yet we can still talk to it.

Back in 1978 the primary receiver failed, and the team discovered the backup receiver had a faulty capacitor in the PLL circuit that adjusted for Doppler shift. Since then, Voyager 2's receive bandwidth has been much narrower, and the band-pass window wanders back and forth by a few hundred Hz with temp changes.

A lesser team would have declared the spacecraft lost after concluding the receivers were no longer working. But the badasses running Voyager figured out that they could make the Deep Space Network sweep the range of frequencies where V2's receiver _could_ be listening, then lock onto an adjusted frequency ground-side to compensate for the wonky receiver.

And so, for the last 44 years, every couple weeks, the DSN does a search to find where Voyager 2's receiver is hanging out today.

Dave Anderson Apr 27, 2023

What I'm saying is, the Voyager project team at JPL are ridiculously resourceful, tenacious people, and deserve to be celebrated more.

This ramble brought to you by today's news that the project team once again pulled a rabbit out of a hat, and figured out a way to stretch Voyager 2's dwindling power budget by several more _years_ before having to power down more science instruments.

Half a century later, still teaching those amazing machines new tricks.

Dave Anderson Apr 27, 2023

Today's happy news about stretching the science mission even more: https://voyager.jpl.nasa.gov/news/details.php?article_id=129

Hackaday's delightful rundown of the radio systems on the Voyagers: https://hackaday.com/2022/06/08/how-is-voyager-still-talking-after-all-these-years/

Voyager - NASA's Voyager Will Do More Science With New Power Strategy

Daniel Borges Apr 28, 2023

@danderson voyager is the demoscene of space

James Garry May 2, 2023

@msk @danderson

And TIL that they're running 18 bit CPUs!

<"Eeh, 18 bits? Luxury!">

Dan Sugalski Apr 28, 2023

@danderson I love how they were basically "protecting the instruments from voltage fluctuations doesn't get us much if that means there isn't enough power to actually run the instruments" and shut the safety system off. Kind of a genius move -- even if the instruments do ultimately get fried we still get science from them until then.

Pippin May 3, 2023

@wordshaper @danderson Personally, I find it even more impressive that the people designing the Voyagers' computer and communications systems back in the 1970s had the foresight to make them *so* flexible and remotely-configurable that it's possible now, 50 years later, to rewire a power supply from a distance of well over 12 billion miles!

(Also interesting to think that most of the people working on it now had probably not been born when humans last laid eyes on either Voyager.)

W6KME Apr 29, 2023

@danderson Here's some perspective on the brilliance of the DSN gang. The signal Voyager sends home is from a 23 watt transmitter. By the time we receive it, it's one tenth of a billionth of a trillionth of one watt. That's 10 to the minus 16th.

If that doesn't make your head spin, you weren't reading carefully.

Hopeful Humanizer May 2, 2023

@danderson The JPL team over the entire span of the voyager project deserve accolades. But what stands out is the philosophy of of making use of limited resources. Back here on earth, continuous improvement bloats software, which obsoletes hardware, which drives sales and creates e-waste. If only we treated the earth as a limited resource?
#earth #resources #software #bloatware #e-waste

none gender with left politics Apr 28, 2023

@danderson huh, how long does this process take? V2 is about 18.5 light hours away, and I would imagine it takes at least one round trip? I guess they probably just sweep until they hear a reply and then subtract the distance in light-minutes/hours/etc to see where they were in the sweep when they sent?

Dave Anderson Apr 29, 2023

@vikxin Yeah, it's described briefly in https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--141029.pdf (design of Voyager's telecommunications system), starting page 73: twice a week, the DSN sweeps around the last known "best lock frequency". In the downlink telemetry from Voyager 2, they have the signal strength as seen by the receiver onboard the probe. From that, they work backwards to what the new best lock frequency is.

Dave Anderson Apr 29, 2023

@vikxin For distance, DSN apparently does standard "ranging" transmissions: they send a known signal out, and make the Voyagers echo it straight back to earth (Voyager demodulates the S-band signal, remodulates it into X-band, and fires it straight back out). By listening for the ranging signal and with very, very good clocks on the ground, they can turn that delay into distance.

Dave Anderson Apr 29, 2023

@vikxin There's also amazing stuff like: after they transmit a command to make Voyager 2 do anything, there's a 3-day moratorium on sending anything else, because just receiving and processing the command generates enough heat to fuck up the damaged oscillator and the receive frequency goes nuts. They have to give it time to cool back down and stabilize.

none gender with left politics Apr 29, 2023

@danderson this is really amazing, just how fragile the system is and how they're able to actually accommodate it. Something I didn't realize until I was reading about JWST heat shielding prior to launch is that, while the vacuum of space is extremely cold (like 2K I think), actually cooling a solid mass off is extremely hard because there's no matter to absorb kinetic energy! Almost all heat has to be radiated via blackbody radiation, the slowest method of heat transfer

Roger Lipscombe May 2, 2023

@danderson @vikxin https://xkcd.com/303/ but "waiting for the oscillator to cool down"...

Compiling

xkcd