NASA "SAFER" Backpack

[Beowolf]

I ran across the Wikipedia page for NASA's "SAFER" emergency backpack, and am finding the specs confusing. It contains 1.4kg of nitrogen producing 3 m/s of delta-v, and some electronics to automatically stop a spinning unteathered astronaut.

...and it masses 38kg! Why?

Does anyone here know more about it, in-particular why it masses so much? 38kg for 3 m/s just seems outlandish to me. Heck, you could probably squeeze out an extra m/s by taking the empty unit off and throwing it!

NASA isn't crazy, so obviously there's a good reason for it being so heavy, but an hour's research came up empty.

Any info appreciated.

[TwoHedWlf]

Well, you've got got the weight of a tank to hold about 3000 PSI of pressure, some plumbing, some nozzles, some electronics, batteries to power the electronics, some gyros, some valves, some electronics to actuate the valves, some latches, a structural frame, some fabric...Obviously adds up.

[Beowolf]

Thanks for the input. You got me thinking about more details...

Google Books returned a section of "Walking In Space" describing the Gemini 4 Hand-Held Maneuvering Unit in detail. It had two 4000 PSI tanks along with minimal plumbing, nozzles, valves and such too. But it produced delta-v of 1.82 m/s with a total mass of only 3.4 kg. So double that to slightly exceed SAFER's 3 m/s: 7 kg.

With SAFER the plumbing will be 8 times as complex since it can stop spins without being manually aimed. But playing around with replicating the plumbing using off-the-shelf brass and copper parts from Home Depot I can't make it add up to more than 5 kg.

I don't buy the electronics amounting to much. A set of 3 commercial ring-laser gyros from Honeywell adds 1.4 kg and 6 watts of power consumption. That wasn't commercially available in 1990, but was common in military applications. Everything else would be sitting in standby until needed, but since it was designed back around 1990 I'll allow another 10 watts. Allowing 0.6 kg for the electronics and wiring is too much, but it puts my math back into round numbers.

For the structural frame, latches and fabric we can toss in an average aluminum-frame backpack: 2 kg.

My model is up to 16 kg and has everything but the batteries. But the standby power draw we've identified is only around 10 watts at 15 volts. My notebook's lithium-ion masses 1 kg and is enormous overkill.

So I was able to account for 17 kg. Could they need to heat the plumbing even when it's just on standby? That would require significantly larger batteries.

[razark]

Have you taken into account the environment it's meant to be used in? Insulation, cooling, heating, hardened electronics, redundancy, over-engineering for safety, etc?