Why valves are a spacecraft engineer’s worst nightmare

Observe the area business lengthy sufficient and also you’ll discover that an outsized variety of catastrophic failures of satellites or launch autos will be traced to a bodily small however ubiquitous half: valves.

Valves play a crucial position within the spacecraft’s structure, regulating the circulate of pressurents, like helium, and propellants. They can be discovered on launch autos, and by quantity they’re probably the most widespread subcomponents in these techniques. This actuality got here into sharp focus this week, when Astrobotic introduced that its Peregrine lunar lander would not be able to attempt a soft landing on the moon resulting from a mission-ending propulsion leak — with seemingly origins in a valve that didn’t reseal.

However Astrobotic is way from the one area firm to have a mission reduce brief by valve points throughout testing or on orbit. Boeing faced major mission delays for the second orbital check flight of its Starliner crewed capsule resulting from valve points, and again in 2019, SpaceX’s Crew Dragon exploded during a ground test resulting from a leaky valve within the propulsion system.

“There’s a thousand different ways you can make a valve unhappy,” mentioned Jake Teufert, CTO of Benchmark Area Techniques, a Vermont-based startup creating propulsion techniques for spacecraft.

Even a thousand is perhaps an understatement. Normally, valves are composed of a plunger that should reseat itself after being actuated, and that has to shut right into a seal. “If there are any issues with that, it can close wrong, it can cause leaks,” Grant Bonin, spacecraft designer and founder of gravityLab, mentioned.

However this description is simply too easy, to the purpose of being deceptive. Aerospace valves should be manufactured to ultra-high precision, be as light-weight as attainable and be capable of face up to a gauntlet of extremes: excessive temperatures, excessive fluids, excessive vibration environments and excessive pressures — typically as much as hundreds of kilos per sq. inch. Valves should even have ultra-low leakage necessities; Teufert mentioned that some valves have allowable leakage charges equal to leaking just one gram of helium over the course of 200 years.

Complicating issues even additional are the underlying bodily realities with which engineers and valve producers should contend. For instance, some fuels and oxidizers are incompatible with sure valve gasket polymers, and chemical incompatibility can result in issues like corrosion or cracking. Engineers should even be vigilant towards “foreign object debris,” or FOD, the tiniest particle of particles or impurity that may clog up a valve or forestall correct sealing. Even small leaks could cause runaway results, as a result of quickly increasing gasoline makes issues chilly, which might take the valve out of its acceptable temperature vary.

Engineers run spacecraft by means of a bunch of checks on the bottom, however the flight setting can solely be matched to an extent, Teufert defined.

“You can certainly throw something on the shaker table and do a [vibration] profile, but you may not be doing that while you’re also fully pressurized and exposed to oxidizer vapors, which is what’s happening in flight,” he mentioned. “Most test houses, if you put a full tank of nitrogen tetroxide on a shaker table, are going to tell you not ‘no’ — but ‘hell no’.”

On the finish of the day, engineers are up towards an impossibly lengthy record of failure modes and should in some unspecified time in the future decide their confidence within the testing. Plus, it’s not unusual for corporations to eat up all of their schedule margin with design, procurement and construct, leaving the testing division with essentially the most schedule strain.

“When you’ve got turnover internally, and when you’re working with a whole bunch of different vendors, it can be very easy to not test adequately, to miss some of these issues,” Bonin mentioned.

It is perhaps tempting to assume, why not add an extra valve, in order that if one fails to open, there’s a backup? However including two valves (or any extra subcomponents) can create entire new failure modes that you’d by no means have with one valve.

The opposite concern is provide chain. Regardless of the comparatively excessive volumes of spacecraft popping out of SpaceX’s Starlink program, Amazon’s Kuiper, OneWeb and the entire swath of rising area startups, spacecraft subcomponents are nonetheless very, very removed from being mass manufacturing.

“At it’s core, the problem is that space just is not a mass market,” Bonin mentioned. “Whenever anybody in aerospace talks about mass production, I chuckle, because we do things sometimes in intermediate volume, but we don’t do anything that’s truly mass production. So we’re not the high-priority clients for these companies.” Teufert echoed these ideas, saying, “As an industry, we are still so much at the point of being artisanal, handcrafted hardware, if it’s anything aerospace specific, and that definitely extends to valves.”

As a result of comparatively small volumes of product, manufacturing continues to be very a lot bespoke, with many valves made in a really small collection for particular propulsion techniques or spacecraft. However the competency of suppliers is just not essentially steady over time, as a result of the method is so boutique and depends a lot on tribal information.

“If it’s something that they’re making a large, true mass production run of per year, they have great processes and well distributed knowledge as to how to make that valve or other component reliably over time,” Teufert mentioned. “Whereas the weird little aerospace valve that they’re making 10 of per year for this niche market, that is [made by] some guy named Bob, who is in his early 60s, and has one foot in retirement. He’s making these every couple of years and then Bob leaves, and all that tribal knowledge goes out the door because there was no one to come up under Bob. I’ve seen that on a ton of components.”

Little doubt this isn’t true for each program; for instance, final summer time valve designer and producer Marotta announced it had delivered its 30,000th solenoid CoRe valve to SpaceX. However in different circumstances, smaller area corporations should cope with longer manufacturing timelines at smaller volumes, purchase business off the shelf or attempt to finagle an answer in-house.

SpaceX President and COO Gwynne Shotwell with Marotta reps. Picture Credit: Marotta

“I can buy the same part twice, but if Jim made Part A and Joe made Part B, even though they’re the same part number, they’re dramatically different quality,” Bonin mentioned. Or in case your lead technician had a shitty Monday, they could have skipped a step. There’s simply human error in all places on this stuff.”