NASA Pulls Off Delicate Thruster Swap, Keeping Voyager 1 Mission Alive | Hacker News Reader

NASA Pulls Off Delicate Thruster Swap, Keeping Voyager 1 Mission Alive

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304 pointsStratoscope69 comments

I continue to be fascinated by how they:

1. Are able to diagnose the problems remotely at such distances and on such old hardware. How can they even measure the thruster tube apertures here?

2. Decide what actions to take. It's not like they have a local test device to experiment on is it? (Even if they did I can't imagine how they'd reproduce the conditions of the real thing.) And if they choose poorly, I'd assume the mission's over. There's no replacing Voyager 1 if they brick it.

3. Have such fine control over the hardware. For something built in the 70's when RAM was largely measured in kB, they seem to have an insane amount of flexibility to remotely reconfigure the equipment. Whatever they did, there must have been some real foresight.

In short, the Voyager spacecraft were designed (after considerable design and operational experience from Mariner and Pioneer spacecraft) to be able to operate for a long time largely automatically without too much hand-holding. All major systems are multiply redundant and may be remotely turned on and off. While there has been personnel turnover on the program, it has not been of a magnitude to jeopardize program continuation. Finally, program management has been media savvy and well politically connected ensuring that operations are still funded. (Contrast with other missions such as Magellan to Venus which was deorbited while it still had propellant reserve leaving some portions of the planet unmapped)

JPL has (or had?) a "retiree badge" program that permitted retired staff to continue to access their office. Many programs benefited from highly knowledgeable personnel essentially continuing to report to the office every day without pay (not being paid comes with the luxury of not having to worry about being laid off if your charge accounts don’t have enough funds!) It was an absolute privilege to learn from these people.

So, culture preservation is important for success of highly technical endeavours. Don't tell it to your run of the mill MBA.

I think it is inevitable that organizational "culture" changes. The tricky part is figuring out exactly what parts need change and what parts don’t.

For example JPL used to have beauty pageants ("Miss Guided Missile"). More recently, management appears to be trying to adopt policies and procedures from some venture funded commercial space companies. It is not clear how helpful these efforts will be given that these organizations are in fundamentally different businesses.

https://www.jpl.nasa.gov/images/slice-of-history-70th-annive...

Run off the mill MBAs are not allowed anywhere near to stuff as important as Voyager.

All the web apps, that run of the mill devs are implementing are nowhere near as important as voyager.

I think we are fine ;)

I guarantee you that a run of the mill MBA program will say something about institutional knowledge being important. You’re needlessly and unjustifiably finding an excuse to dunk on something that you know people here dislike, despite it having very little to do with the actual topic. Which…fine. But you’re also so keen to do it that you aren’t even correct. Please stop projecting every gripe you have with your boss onto this mythical “evil MBA”.

It also helps that JPL is a public good and not a wealth-extraction machine

but if someone is paid $0 it must mean they are worthless, surely the excel file doesnt lie

No, you need to think like an MBA.

It means that they are the most valuable employees, because their productivity per dollar is infinite.

It also means that when you sort all the (non-executive, of course!) employees by total comp in preparation for layoffs to make the budget look better, they are at the bottom of the list.

oh yes, you are absolutely right :D

Any idea how many people took advantage of the retiree badge program, or any individual people who continued to put in substantial hours?

We do something similar at my job for the greybeards that were very influential on our current projects. They "retire" but are retained as a very part time employee that only get paid if we need to bring them in for a day or two to help answer some questions. The managers love it because they don't need to find work for this person, pay for any benefits, or need to get approvals to pay them like contractors. As long as we keep doing relevant work to their expertise, they will continue being retained. There is a limit for how many hours they can put in because these people are incredibly expensive as they usually retire at the top engineer level and retain the equivalent hourly wage for that position.

Paying someone as sporadically as you would a contractor but they’re only getting their usual hourly wage? Doesn’t sound expensive to me. Sounds like a ridiculously good deal for the employer.

Yeah! Being almost 50 years old it's not like people is not working there anymore but that probably a bunch of people in the original project has already died!

Great forward thinking

What blows my mind is the organizational knowledge needed after so many years to keep it going. You don't just hand a guy some man pages when he comes onto the project. I'm sure people have aged out, yet they still understand the complexities in the design. That is something we need to understand and prioritize in the systems we build today.

When Voyager failed last year with a CMOS memory error, one of the big problems was that a bunch of low level information was gone or conflicting. For example, they sometimes had to guess assembler instructions because the code printouts were low quality photocopied pages. Or because there were handwritten comments or comments scratched out with pencil without any clue about why it was done.

One saving grace was the fact that the architecture and the code space was simple enough so that they could reason through the symptoms and actions to take, something that would have been much harder with modern spacecraft.

Check out this amazing talk: https://youtu.be/dF_9YcehCZo?si=W_b3NJ7vgxaYS1__

Thank you for this link!

Startup: "Do you remember when we inserted this quirky module running in AWS? We can use that to implement this next feature. That was a useful decision!"

Voyager: "Do you remember when our parents inserted this quirky module that has since left the solar system? We can use that to turn it off and on again. That was a mission critical decision!"

Not parents for most of us. Grand or great-grandparents. The senior engineers were highly educated and experienced, implying ages 30-50s during development. They are in their 80-100s now.

that aws module isn't supported anymore though, we need to npm install half the internet for the 2 line library that replaces it.

This thing hits me. True.

There's a documentary "It's Quieter in the Twilight" about the team keeping the Voyager missions alive: https://www.youtube.com/watch?v=8vJT8AW0wYw

Looks very interesting , thanks for sharing

Included with Amazon Prime in Canada

> It's not like they have a local test device to experiment on is it?

I would bet they have one or more simulators (“digital twin” in the parlance of our times). I’d want one simulator to always reflect the current state of the probe (with state data assimilated periodically from the real probe). Then other simulators can be used to test management changes to see how the system might respond.

> I would bet they have one or more simulators

Sadly they do not, but they are starting to write one.

And quite recently they also recovered from a faulty ram module, with a radio link speed that is maybe below the kbit/s now !

> Uplink communications is via S-band (16-bits/sec command rate) while an X-band transmitter provides downlink telemetry at 160 bits/sec normally and 1.4 kbps for playback of high-rate plasma wave data.

https://science.nasa.gov/mission/voyager/spacecraft/

The data playbacks were initially transmitted at 7200 bps, but this was dropped to 1400 bps in 2007 (https://voyager.gsfc.nasa.gov/Library/DeepCommo_Chapter3--14... - page 72).

RTT ~46 hours (one-way light time 22:49:59, per https://science.nasa.gov/mission/voyager/where-are-they-now/)

And you should see the ping times.

I suspect it’s far lower than that.

I would imagine if the design/assembly information was broadly available (internally) in the past, there's probably one or several "digital twin" emulations of the craft, or at the very least specific subsystems of it's computing resources. There must be some kind of analog/simulation of it's software just for proving "bugfixes" before upload, like the coms error and subsequent setting of the "solar system record" for "furthest distance remote code update" earlier this year.

There isn’t a simulator or digital twin for voyager. It has a bespoke processor made with 74* style logic. One guy will puts together a command and they will have a review where the other engineers will try and independently verify it. Then they copy and paste the command somewhere to “run it”. It happened, fairly recently, that the command had a typo that was caught in review, but the “wrong” pre-review command was used and the attitude became off by so much that they lost contact. It was only by cranking up the power at Goldstone that they got a command through. This fundamentally changed their understanding of the largest angle for which they could still communicate with the spacecraft. They just hadn’t wanted to try larger angles before because it was too risky.

That's the great thing about such a simple design, you can actually sit down with pen and paper and verify operations.

Forget about a digital twin, they don’t even have an assembler for the CPUs. It’s all hex values.

You should totally check out the talk from a few weeks ago that I link to in my other comment. It answers your 3 questions and more.

- "A fuel tube inside the thrusters has filled up with silicon dioxide, a side effect of age within the spacecraft’s fuel tank."

Where the heck do you get SiO2 from on a spacecraft? Some kind of silicone?

edit: "clogged with silicon dioxide, a byproduct that appears with age from a rubber diaphragm in the spacecraft’s fuel tank"[0] —I'm guessing that is a silicone rubber. I didn't know that rubber can decompose into sand.

[0] https://science.nasa.gov/missions/voyager-program/voyager-1/...

They expel the Hydrazine(N2H4) fuel out of a spherical Ti tank by inflating a rubber balloon that involve Teflon inside the tank using helium supply. I guess N2H4 was potent enough to degrade even those space age materials.

1: https://ntrs.nasa.gov/api/citations/19810001583/downloads/19...

Seems like silicone rubber is extracted from SiO2, so maybe it's impurities? Or maybe the Si and O are doing something to leave the polymer? (I have no idea if that last thing is even possible)

https://en.wikipedia.org/wiki/Silicone_rubber

It doesn't have to be silicone. SiO2 is a necessary ingredient in all rubber compounds.

2 weeks ago, Bruce Wagoner from the Voyager program gave a talk at !!Con about how they recovered from the CMOS memory issue that they had a year ago.

It’s basically blind debugging with a latency of 45 hours.

The talk is amazing and goes through the computer architecture of the spacecraft as well as the challenges of dealing with something that is so old, with so documentation that has conflicting information or unreadable etc.

https://youtu.be/dF_9YcehCZo?si=W_b3NJ7vgxaYS1__

The Voyager mission is such a wild achievement. Both the sublime design and craftsmanship that must have gone into the hardware, and the deep institutional knowledge required to keep it running is awe-inspiring.

Probably a better link: https://science.nasa.gov/missions/voyager-program/voyager-1/...

Great to see they bought her some more time.

I watched this excellent Voyager documentary recently:

https://www.itsquieterfilm.com/

I had the extreme pleasure of seeing Bruce Waggoner of the Voyager team give a keynote at !!Con just last month. The recording landed on YouTube just a couple days ago, so this is great timing: https://www.youtube.com/watch?v=dF_9YcehCZo

It's been operating for 47 years and it still has fuel left to make attitude corrections. I wonder how they managed that feat.

Not to downplay how impressive the Voyager probes are, but it seems they packed a fair bit of hydrazine. From "Engineering the Voyager Uranus mission":

While it was not a design requirement, the option for an extended mission past Saturn was always protected, unless it meant compromising a major mission objective at Jupiter or Saturn.

Even though the probability of Voyager 2 lasting another five years was calculated to be in the range of 60 to 70 percent -- well below NASA's usual acceptable probability-of-success threshold -- the decision was made to send Voyager on to Uranus.

After its Uranus encounter, Voyager 2 still carried 48% of the hydrazine initially loaded into its tanks, eight-and-a-half years before.

[1]: doi:10.1016/0094-5765(87)90096-8 (can be found on the hub of science)

IIRC They have some type of nuclear power. Not like a reactor but something much simpler that generates heat from radioactive decay.

the flow of electrons to allow systems to work is not the same as the expulsion of gasses to provide thrust

https://xkcd.com/2115/ The RTGs generated about 470 W of electric power at the time of launch. In 2023, it was 260W.

I presume solar power?

No, way too little sun out here. The sun is just a dot far away. The Voyagers both use RTGs, radioisotope thermoelectric generators. Decaying plutonium, essentially. That's for the electrically powered systems. The thrusters use liquid hydrazine, which is common for those kind of thrusters.

Edit: There's more about that in the NASA link in a sibling comment.

Solar has nothing to do with it. Voyager uses hydrazine, of which over 80% has been used up over the years. They simply use not that much of it as it's not for thrust, but for aiming at Earth more or less.

Even with something like an ion engine (which I'm not sure were available when Voyager was launched), you would need leftover reaction mass.

Lol. How would that work exactly?

> How would that work exactly?

Light sails. Laser propulsion. Photon rockets. None of which apply to Voyager. But none of which are laughably dismissible.

I've heard good things about some Voyager documentaries, and I've wanted to watch one with my daughter, but NASA keeps making the documentaries out-of-date and incomplete. How many amazing stories will there be to tell by the time Voyager is truly beyond our knowledge?

You mention voyager documentaries but fail to mention which one. There's lots, and its impossible to know which one is good until you finish it. Please tell us which one you wanted to watch.

It's sad how much documentation is honestly unreachable now.

Official release: https://science.nasa.gov/missions/voyager-program/voyager-1/...

(https://news.ycombinator.com/item?id=41505008)

Just another day at the office for the Voyager 1 team. Wow.

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