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Ammonia Leak Alarm On the ISS Forces Evacuation of US Side: Crew Safe
New submitter BabelBuilder writes: An alarm signaling a possible ammonia leak aboard the ISS this morning caused the crew to evacuate the U.S. side of the station. All crew aboard the station are safe. "Flight controllers in Mission Control at NASA's Johnson Space Center in Houston saw an increase in pressure in the station's water loop for thermal control system B then later saw a cabin pressure increase that could be indicative of an ammonia leak in the worst case scenario. Acting conservatively to protect for the worst case scenario, the crew was directed to isolate themselves in the Russian segment while the teams are evaluating the situation." They don't yet know whether it was caused by a faulty sensor, a problem in the relay box, or another malfunction.
When there are a thousand sensors it gets problematic to monitor all of them. That's why we invented electronic sensors, so that we could use software to do all the work of monitoring them, logging data, triggering alarms, etc.
If anybody knows about refrigeration it's probably the people that designed the cooling system on the ISS.
And, analog gauges are not magically immune to failure...
You want analog? Check this out. This is a 360 view of the engineer's station of a Convair B36. I'm not quite sure where I'd stash my slide rule, but I'm sure there's a spot somewhere.
Some mornings it's hardly worth chewing through the restraints to get out of bed.
A standard US shit ton = 2.65 metric shit tons, or 78.1 US crap-loads.
A computer once beat me at chess, but it was no match for me at kick boxing -- Emo Phillips
Do you also enjoy spending hours that could be used productively doing nothing but working your way through gauges scattered across a system? Because that's one of the hidden costs of analog gauges - either you keep the system simple and keep the gauges near the point of measurement, or make it more complex and heavier by introducing a method to transfer the measured quantity (fluid, gas, what have you) to a convenient location for the gauge? (And an awful lot of what people see as analog gauges are actually voltage or resistance meters - the measured quantity is measured locally and then transmitted to a distant gauge as an analog electrical signal.)
On top of that, you can only confirm false readings if it's not the gauge or measurement system itself supplying the false reading in the first place. Analog gauges do break and their calibration does drift. Piping used to transfer fluid or gas to a measurement point does get clogged up. (And people shut or forget to open gauge stops and isolation valves at the most inconvenient of times.) If it's a hybrid (analog mechanical and analog electrical) system, there's a whole additional level of potential for faults and drifting calibration (without any of the advantages that using the same wiring for digital provides).
The plural of anecdote is not data.
In my experience, the vast majority of people who pine for analog gauges have never dealt with an analog system other than their automobile dashboard (which after the late 80's is probably a hybrid (digital with analog displays) system anyhow) or something else equally simple and only having a handful of gauges (at most) in the first place. I have (USN Submarine Service, '81-'91), and I'll take a digital system over an analog system any day of the week. They're much easier to maintain, offer far more functionality, and are much easier to use.
I emailed a friend who worked on Station's ECLSS back in the 90's, and this was his reply:
"Ammonia has a great specific heat (ability to carry the thermal load), plus its boiling and freezing points work really well in space applications. It's also (aside from toxicity) a very well-known, simple, cheap and fairly easy material to work with. The way the TCS loops work on ISS, the ammonia loop is external; it never mixes with the internal (water) loops. There are external heat exchangers to pass the thermal loads from inside to outside; the water loops out of the pressure vessels through the end cones to the heat exchangers and back inside. The only way for ammonia to get into the water loop (it seems to me) would be a debris strike or something like that in a heat exchanger (and they're protected by MMOD shielding, as well as being rather out of the way)."