Cooling Pump Malfunction On ISS

eldavojohn writes "On Saturday at 8pm GMT, the crew of the International Space Station awoke to alarm bells as one of two ammonia pumps shut down due to a spike in power. Their backup cooling (Loop B) is functioning as designed and NASA released an official statement: 'The crew is in no danger, but will need to work additional troubleshooting on Sunday to keep the station in a stable configuration, including the installation of a jumper cable to maintain proper cooling to the Zarya module in the Russian segment.'"

Comments

HOWTO: Fixing stuff in space

[tomhudson]

1) Where's the Duct Tape?

2) Duct tape something ("including the installation of a jumper cable to maintain proper cooling to the Zarya module in the Russian segment");

3) Problem solved!

Is Feature!

[DWMorse]

Our cooling pump is now, for your convenience, a heating pump. For survival in the cold of space.

Re:Sounds like Russian thing: JUMPER CABLES IN SPA

[human-cyborg]

What's weird about jumper cables in space? A set of heavy gauge wires that can take lots of current, with universal connectors on either end? Sounds incredibly versatile. I'd never leave Earth with out them, packed right next to my towel.

You much be one of those people who take your car to the dealer to get an oil change.

Hmm...

[fuzzyfuzzyfungus]

I'm surprised that they would be using ammonia coolants, rather than something more exotic and less toxic.

Ammonia makes perfect sense in industrial ice plants and rink chillers and stuff, being dirt cheap, and not especially dangerous when you have an entire planet's atmosphere to dilute the leaks. Plus, it doesn't have the Ozone-eating properties of the CFCs.

In space, though, everything is expensive by default, having been carried into earth orbit, there isn't much of an ozone layer to worry about, and you really don't have enough breathable atmosphere available to risk contaminating it with anything unpleasant. Ammonia seems like a curious choice.

Anybody know why they would have gone with that?

Re:Hmm...

[vlm]

I'm surprised that they would be using ammonia coolants, rather than something more exotic and less toxic ... Anybody know why they would have gone with that?

IF its an absorption cycle system, you just can't do better than ammonia. Its hard to find any refrigerant gas that dissolves better in water... absorption cycle is nice on planet earth, no moving parts, no lubricant compatibility issues. In space you need pumps, however.

On the other hand, if its a vapor-compression system like your fridge at home, yes it is in fact a pretty cruddy choice and any of the freon series would kick its butt (as a refrigerant, anyway)

On earth you can play games with gravity to prevent/reduce slugging the compressor in a vapor-compression system. Not sure how you do that in space. Slugging a compressor is when load/airflow is low and you feed a gulp of liquid into the intake instead of moderately hot gas. Its kind of a shock to the innards, its the pump equivalent of eating at Taco Bell...

http://en.wikipedia.org/wiki/Refrigeration#Cyclic_refrigeration

Re:Hmm...

[DerekLyons]

The problem is that the ISS ultimately rejects heat by radiating it away through radiators mounted on the solar array wings - and water would freeze and plug up the radiators.
 
So instead, they use a water loop to cool the atmosphere and equipment, and then transfer that heat to the ammonia system which then circulates through the radiators. (It's pretty easy to design the system such that there is minimal ammonia piping (and thus a minimal chance of an accident) inside the manned spaces.) Since ammonia freezes at a much colder temperature than water, this means it's much easier to keep the coolant moving at a rate where it radiates enough heat to be useful but still stays warm enough to not freeze.
 
It's going to be a complex trade off to choose a coolant, and few people seem to realize that NASA does take into consideration cost and availability when making their choices. They aren't so good at controlling costs as they might be, which is understandable since overall they're working at the bleeding edge of engineering, but that doesn't mean they don't try.
 
And really, there's isn't much of a difference between ammonia or anything more exotic because even something 'safe' (like nitrogen for example) is still going to rapidly displace the oxygen from the air (that is, reduce the effective partial pressure) if there's a leak because of the small volume of the breathable atmosphere.

Re:Hmm...

[vlm]

Reason 3 which I forgot to include, is radiation turns ammonia into harmless H2 and N2. Little to no effect on the equipment or thermodynamic properties at any reasonable concentration. If you catch enough gammas to break down 50% of the refrigerant, roughly 50% of the crew mass would have been broken down, indicating bigger problems.

Radiation turns fluorocarbons into fluorine and assorted debris. fluorine, at any concentration, is not good in anything except fluorine tanks. Anthropomorphizing it a bit, F likes to halogenate hydrocarbons like pump oil or plain ole oily contaminants leading to all kinds of entertainment. Its just nasty stuff even at the lowest concentrations. I suppose you could design and install a nice heavy halogen trap, but you'd never Really Know about the internal corrosion levels of the pumps and pipes without very expensive continuous maintenance. The entire refrigeration system would need to be halogen compatible. On earth its not an issue due to low radiation levels and frankly if my A/C pipes corrode out its not life threatening anyway. But not so good of an idea in space.

Finally ammonia is high temperature stable and if you somehow manage to dissociate it anyway, the N2 and H2 are mostly harmless and can be flushed out. On the other hand, SOME of the fluorocarbons have pretty nasty icky byproducts if you overheat them, by, say, the pump shutting down in full sunlight for a long time.