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Station Crew Docks Dragon Capsule to ISS

nasa.gov

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Re: Station Crew Docks Dragon Capsule to ISS

#41

Post by Shivetya »

FranOntanaya wrote: post #5
aidos wrote: post #3

Whenever I see ISS dockings I wonder why the arm isn't computer controlled. There's no specific information on this page but I'm assuming it was a manual docking. Can anyone explain why the process is still manual?

I bet the trainers that certify an astronaut is precise enough to get it done are a lot cheaper than the engineers required to certify a computer wouldn't karate chop the station.

considering the first flight where they were rewriting code while it sat outside the station; reconfigured the LIDAR on the fly; I would put it down being overly cautious, maybe a bit of fear? Let us be honest, with all the difficulty of getting that module into space docking isn't that big of a deal. If there were no people on board no one would care.

Plus I have to ask, if a thruster suddenly misfires or goes haywire who is going to be faster? In Apollo days I would put odds on the astronauts, today - I am betting on a computer. We will sooner trust a car to drive itself before we allow a freighter to dock with a space station.

Re: Station Crew Docks Dragon Capsule to ISS

#42

Post by lotsofmangos »

Ankaios wrote: post #37
antimagic wrote: post #19

Earlier quoted context omitted.

It's common for pretty much all of engineering really. It's ludicrous to make calculations a bit more complicated by using weird non-SI units. The fact that NASA managed to crash a probe into Mars because they hadn't yet learned the lesson says it all really. Just use SI units and stop worrying about it.

No, the important lesson is to always label your units, and another one might be to always be careful passing dimensionful numbers between codes and teams. You can run into the same problem by accidentally even forgetting to convert between, e.g., newtons and millinewtons.

Even if you label your units, you get conversion errors that can easily multiply up into something nasty that goes boom.

Re: Station Crew Docks Dragon Capsule to ISS

#43

Post by arjunnarayan »

andyjohnson0 wrote: post #32
Zuph wrote: post #10

Earlier quoted context omitted.

Although the Dragon is reusable, SpaceX's contract with NASA stipulates that new capsules be used for each resupply mission. Not sure if the contract allows SpaceX to refurbish the capsules for other commercial missions, but the other CRS Dragons are being used for showpieces at the moment.

Interesting - I didn't know that. Do you know if this is due to NASA being general cautions with a new, relatively unproved vehicle? Or is it a condition of human-rating the Dragon?

General caution.

Re: Station Crew Docks Dragon Capsule to ISS

#44

Post by Tloewald »

Ankaios wrote: post #37
antimagic wrote: post #19

Earlier quoted context omitted.

It's common for pretty much all of engineering really. It's ludicrous to make calculations a bit more complicated by using weird non-SI units. The fact that NASA managed to crash a probe into Mars because they hadn't yet learned the lesson says it all really. Just use SI units and stop worrying about it.

No, the important lesson is to always label your units, and another one might be to always be careful passing dimensionful numbers between codes and teams. You can run into the same problem by accidentally even forgetting to convert between, e.g., newtons and millinewtons.

SI units don't include millinewtons, so the problem wouldn't arise. That's part of the point.

You measure mass in kg, not g, not tonnes.

You measure distance in metres. Not kilometers. Not nautical miles.

You measure time in seconds.

A Newton is a derived SI unit — 1 kg m / s^2

Incidentally, this is why engineering notation works the way it does. You pick your units and you get the significant figures from the mantissa and the descriptive prefix (giga, nano, micro, kilo, etc.) from the exponent.

Re: Station Crew Docks Dragon Capsule to ISS

#45

Post by rst »

andyjohnson0 wrote: post #32
Zuph wrote: post #10

Earlier quoted context omitted.

Although the Dragon is reusable, SpaceX's contract with NASA stipulates that new capsules be used for each resupply mission. Not sure if the contract allows SpaceX to refurbish the capsules for other commercial missions, but the other CRS Dragons are being used for showpieces at the moment.

Interesting - I didn't know that. Do you know if this is due to NASA being general cautions with a new, relatively unproved vehicle? Or is it a condition of human-rating the Dragon?

NASA was unwilling to believe any discount offered for use of a refurbished spacecraft until they'd actually done it, so the bid was made on the basis of a new capsule for each mission.

(The human-rated Dragon is going to be a different version anyway, with altered docking support, much beefier propulsion, altered solar panels, and of course, internal controls and life support. Current plan is new spacecraft permission there, too, though, perhaps for the same reason.)

Re: Station Crew Docks Dragon Capsule to ISS

#46

Post by pimlottc »

Tloewald wrote: post #44
Ankaios wrote: post #37

Earlier quoted context omitted.

No, the important lesson is to always label your units, and another one might be to always be careful passing dimensionful numbers between codes and teams. You can run into the same problem by accidentally even forgetting to convert between, e.g., newtons and millinewtons.

SI units don't include millinewtons, so the problem wouldn't arise. That's part of the point. You measure mass in kg, not g, not tonnes. You measure distance in metres. Not kilometers. Not nautical miles. You measure time in seconds. A Newton is a derived SI unit — 1 kg m / s^2 Incidentally, this is why engineering notation works the way it does. You pick your units and you get the significant figures from the mantis…

His point (I believe) is you always need to label units regardless of system. You could have the same problems with microseconds vs nanoseconds.

Re: Station Crew Docks Dragon Capsule to ISS

#47

Post by jjoonathan »

pimlottc wrote: post #46
Tloewald wrote: post #44

Earlier quoted context omitted.

SI units don't include millinewtons, so the problem wouldn't arise. That's part of the point. You measure mass in kg, not g, not tonnes. You measure distance in metres. Not kilometers. Not nautical miles. You measure time in seconds. A Newton is a derived SI unit — 1 kg m / s^2 Incidentally, this is why engineering notation works the way it does. You pick your units and you get the significant figures from the mantis…

His point (I believe) is you always need to label units regardless of system. You could have the same problems with microseconds vs nanoseconds.

Tloewald's point was that microseconds and nanoseconds are not SI base units, so standardizing on base units eliminates the ambiguity (the second alone is the SI base unit of time). Of course additional mechanisms of double and triple checking are probably still warranted to account for human fallibility.

Re: Station Crew Docks Dragon Capsule to ISS

#48

Post by Already__Taken »

vermontdevil wrote: post #40
TeMPOraL wrote: post #35

Earlier quoted context omitted.

Meanwhile Russians could successfully auto-land a shuttle in high wind. http://en.wikipedia.org/wiki/Buran_%28spacecraft%29#Flight_i... Buran was an amazing piece of technology. It's sad it didn't get its chance.

The US Air Force has one up there now - X-37B. It's completely autonomous. http://en.wikipedia.org/wiki/Boeing_X-37

18 years. Took them long enough.

Re: Station Crew Docks Dragon Capsule to ISS

#49

Post by nanofortnight »

gambiting wrote: post #26
MrBra wrote: post #16

Is it common to use metric system when launching rockets to space or is it a peculiarity of SpaceX? I heard the speaker on SpaceX channel always referring to kilometers and kilometers per second when talking about height and speed.

Is there any sort of engineering anywhere that is not done in SI units nowadays?

The US is behind on this unfortunately.

Re: Station Crew Docks Dragon Capsule to ISS

#50

Post by toomuchtodo »

Already__Taken wrote: post #48
vermontdevil wrote: post #40

Earlier quoted context omitted.

The US Air Force has one up there now - X-37B. It's completely autonomous. http://en.wikipedia.org/wiki/Boeing_X-37

18 years. Took them long enough.

"You can always count on Americans to do the right thing - after they've tried everything else." -- Winston Churchill
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