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Old software keeping space missions alive

bbc.com

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Re: Old software keeping space missions alive

#61

Post by 3pac »

hilbert42 wrote: post #48
3pac wrote: post #28

Earlier quoted context omitted.

It also has a vidicon tube for gathering images, although that can no longer be switched on.

Do we know the reason? Heater/cathode failure or HV supply would be likely reasons, or is there now insufficient power from the Pu source to run it? (The HV supply on a vidicons is usually about 700V—that's high enough to be quite stressful on P/S components.)

There is a heater for the vidicon which had to be shut off due to power budget. This heater had been on since launch. After being switched off, turning on this heater back on, or the vidicon's cathode filament (itself a separate heater) would have cracked the tube due to the cold of space.

Re: Old software keeping space missions alive

#62

Post by justinator »

deepspace wrote: post #44
justinator wrote: post #5

Earlier quoted context omitted.

There's a little more to it. If your original team retires because of old age, that's a lot of wisdom lost. Not everyone wants to learn COBOL to keep planes in the air and the IRS running, imagine needing to figure out the low level code on something millions of miles away with half the hardware broken, the battery cracked and leaking – and if the software update doesn't work, the entire mission is over? It's altoget…

The article calls software from the 90s "old". Nobody used COBOL for mission-critical software at that time. There is embedded software I wrote in the 80s and 90s still running in the field, mostly written in C.

I didn't wrote that COBOL was used in aerospace, but used it as an example in different industries.

Re: Old software keeping space missions alive

#63

Post by justinator »

ericbarrett wrote: post #20
justinator wrote: post #5

Earlier quoted context omitted.

There's a little more to it. If your original team retires because of old age, that's a lot of wisdom lost. Not everyone wants to learn COBOL to keep planes in the air and the IRS running, imagine needing to figure out the low level code on something millions of miles away with half the hardware broken, the battery cracked and leaking – and if the software update doesn't work, the entire mission is over? It's altoget…

COBOL is really quite straightforward and readable. I don't think a developer who's already familiar with a modern language or two would have a hard time picking it up. The system it's operating is domain-specific knowledge anyway, and would be something a newcomer would have to learn (or be familiar with) regardless of language.

>I don't think a developer who's already familiar with a modern language or two would have a hard time picking it up.

You're probably correct, but it's more about if they would want to pick up a language that has no future, except maintenance of already existing systems. (see: Perl).

Re: Old software keeping space missions alive

#64

Post by deterministic »

cryptoz wrote: post #16
snickerbockers wrote: post #4

jesus christ, i dont think ive ever seen an article that beats around the bush for as long as this one does before finally getting to the point. anyways, for those who don't have the patience, the title is misleading. it's just some old software from the 90s. It's only ancient if you're one of those people who completely rewrites their entire code base from the ground up every two years because to pad out your resume…

Software does degrade with age, though. Simply the fact that vulnerabilities are found over time means that our understanding of a piece of software and how it works changes. But it's not just vulnerabilities being found, it's protocols used that may be unsupported etc. That change is a kind of a rot like people call 'bit rot' but it's a specific software rot that does happen. Systems are complicated.

Brand new software made yesterday is full of bugs and will kill or maim you if you try to use it for safety critical systems. I trust 10+ years old code that has been proven in combat. Not crappy new code written by some arrogant young “Ninja” who has no clue on how little he/she/it knows.

Re: Old software keeping space missions alive

#65

Post by dr_orpheus »

hilbert42 wrote: post #57
dr_orpheus wrote: post #10

Earlier quoted context omitted.

Yes travelling wave tubes are still very common on modern satellites. They tend to be used most on high power (>50W RF power)/high frequency (K-band and higher) systems. I don't know the exact rationale, but for space systems in the higher frequency and power regimes travelling wave tubes are still more reliable than solid state power amplifiers. Traveling wave tubes are still in the 40-50% efficiency range so they'r…

Right, although I've worked with TWTs, klystrons, etc. in terrestrial equipment and have some familiarity with them, I've only casually thought about the TWTs in the Voyagers and in space use generally. Given the remarkable longevity of the Voyagers, what I'm surprised about is that there hasn't been much discussion about their componentry and why they've been so reliable. For example I've seen nothing written about…

> I'm surprised about is that there hasn't been much discussion about their componentry and why they've been so reliable

I think part of this might be because it is still considered proprietary information. Kind of crazy, but there is really only one company in the US that makes space qualified TWTs which is Stellant systems (formerly L3, formerly Hughes microwave) who made the Voyager TWTs as well.

Re: Old software keeping space missions alive

#66

Post by dr_orpheus »

hilbert42 wrote: post #45
AlanYx wrote: post #6

Earlier quoted context omitted.

It does! But the really interesting thing is that travelling wave tubes are still being used for quite a few modern satellite designs. For example, SiriusXM used them in SXM-9/10, and is probably using them in SXM-11/12.

In recent years I've occasionally wondered what the type/part number of that TWT is. Given its history, its heater and cathode emission seems to have held up remarkably well. Another question I'd like answered, do the Voyagers cycle down or turn off the heater during TX downtime? Turning it off risks metal/cycling fatigue, leaving it on risks reducing the cathode life—or even poisoning it from stray ions. A final poi…

> Another question I'd like answered, do the Voyagers cycle down or turn off the heater during TX downtime? Turning it off risks metal/cycling fatigue, leaving it on risks reducing the cathode life—or even poisoning it from stray ions.

I suspect that now the heaters are turned off during Tx downtime, but I think this is probably because they Pu power is much lower and so thy want to conserve as much power as possible. Even if they did have more power, Voyager only makes contact once per day so I think the increased thermal cycling is not much compared to reduction in cathode life so they probably go this route anyway. I do know that other missions I have worked on that have much more frequent contacts, we do keep the Tx heaters on so there is probably some number of cycles where one becomes more dominant.

> A final point, presumably the TWT's output has dropped over the decades, how is this monitored and do we know the percentage drop in power output (from the TWT not the Pu power source)?

This is telemetry from the TWTAs on the helix current and the anode voltage. Along with the DC power draw of the TWTAs I think you can interpret some of what the power output is and how it changed over life. Some of this might be curve fitting to ground-based life tests so there could be some estimation. The ground is also certainly measuring the received power so they can estimate power output from the spacecraft from that as well.

> The fact the TWT is still working seems quite remarkable

You're not the only one. From this article [0] a JPL engineer says "Nobody can explain why the Voyager TWT is still working".

[0] https://spinoff.nasa.gov/Traveling-Wave-Tubes-Travel-Far

Re: Old software keeping space missions alive

#67

Post by hilbert42 »

dr_orpheus wrote: post #65
hilbert42 wrote: post #57

Earlier quoted context omitted.

Right, although I've worked with TWTs, klystrons, etc. in terrestrial equipment and have some familiarity with them, I've only casually thought about the TWTs in the Voyagers and in space use generally. Given the remarkable longevity of the Voyagers, what I'm surprised about is that there hasn't been much discussion about their componentry and why they've been so reliable. For example I've seen nothing written about…

> I'm surprised about is that there hasn't been much discussion about their componentry and why they've been so reliable I think part of this might be because it is still considered proprietary information. Kind of crazy, but there is really only one company in the US that makes space qualified TWTs which is Stellant systems (formerly L3, formerly Hughes microwave) who made the Voyager TWTs as well.

I'd forgotten about Hughes, Voyager and TWTs, but now that you mention it, it does ring a bell.

You're likely right about the proprietary nature of such manufacturing but perhaps I'm reading too much into this. As I mentioned in an earlier post the emission in the CRT of my 43-year-old Sharp TV is still OK—at least as far as the quality of the image is concerned.

The technology used in the Wehnelt cylinder in my TV's CRT is of a similar vintage to Voyager (I'm pretty sure the TV was manufactured around 1979), and given the millions of CRTs made to similar a quality around that time it's likely that manufacturering techniques and reliability figures were widely known throughout the industry by then.

Anecdotally, I've noticed that CRTs made from the early '70s onwards had much better longevities than their earlier '50s counterparts, whether this was because the formulation of cathode emitters had changed or manufacturing techniques had improved or both is an open question.

Of course, such comparisons are tenuous but that's all I've got to go on, for starters, the Wehnelt in the Voyager's TWT would have been deigned to carry more current. Perhaps NASA has some spare TWTs that one day someone will reverse engineer and we'll know for sure.

Nevertheless, it seems to me that knowledge about component reliability is critical to NASA, so it's likely the answer already exists somewhere in the depths of NASA's archives.

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