Station Crew Docks Dragon Capsule to ISS • Hacker News Board

Re: Station Crew Docks Dragon Capsule to ISS

#11

Post by drzaiusapelord » Tue, Sep 23, 2014, 1:45 PM UTC

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?

The cynical part of me thinks because manned spaceflight, at least in the context of being stuck in a LEO tin can, is of questionable utility and we try to find things for people to do? We can automate quite a bit of this, in fact, the ESA's Automated Transfer Vehicle just docks itself. Wikipedia:

At a distance of 249 m, the ATV computers use videometer and telegoniometer data for final approach and docking manoeuvres. The actual docking to Zvezda is fully automatic. If there are any last-minute problems, a pre-programmed sequence of anti-collision manoeuvres, fully independent of the main navigation system, can be activated by the flight engineers aboard the station.

http://en.wikipedia.org/wiki/Automated_Transfer_Vehicle

Or what's that apocryphal story about early astronauts fighting with NASA engineers to put in pilot controls with manual override so these guys could claim to be pilots and not mere passengers? The ugly truth is a lot of this stuff is best left to automation, robots, etc.

Re: Station Crew Docks Dragon Capsule to ISS

#12

Post by mzaccari » Tue, Sep 23, 2014, 1:46 PM UTC

bvm wrote: post #4

It's technically a berthing, not a docking as it mates under the power of the Candarm, not under its own steam.

Thank you for the clarification. I corrected the title

Re: Station Crew Docks Dragon Capsule to ISS

#13

Post by tomswartz07 » Tue, Sep 23, 2014, 1:47 PM UTC

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.

I think that the arm was designed specifically to be manually controlled.

Even though it might be possible to 'computerize' the control, realistically there's no benefit to doing so.

Re: Station Crew Docks Dragon Capsule to ISS

#14

Post by idlewords » Tue, Sep 23, 2014, 1:54 PM UTC

bvm wrote: post #4

It's technically a berthing, not a docking as it mates under the power of the Candarm, not under its own steam.

MATES UNDER THE POWER OF THE CANADARM

Re: Station Crew Docks Dragon Capsule to ISS

#15

Post by idlewords » Tue, Sep 23, 2014, 1:57 PM UTC

drzaiusapelord wrote: post #11

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?

The cynical part of me thinks because manned spaceflight, at least in the context of being stuck in a LEO tin can, is of questionable utility and we try to find things for people to do? We can automate quite a bit of this, in fact, the ESA's Automated Transfer Vehicle just docks itself. Wikipedia: At a distance of 249 m, the ATV computers use videometer and telegoniometer data for final approach and docking manoeuvre…

In the Shuttle, the landing gear control was intentionally left outside computer control so that the vehicle could not be flown unmanned. Flight control software could autoland the shuttle from orbit, but it took a human being to let the wheels down. So I don't think your cynicism is excessive.

Re: Station Crew Docks Dragon Capsule to ISS

#16

Post by MrBra » Tue, Sep 23, 2014, 1:58 PM UTC

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.

Re: Station Crew Docks Dragon Capsule to ISS

#17

Post by Intermernet » Tue, Sep 23, 2014, 1:58 PM UTC

idlewords wrote: post #14

bvm wrote: post #4

It's technically a berthing, not a docking as it mates under the power of the Candarm, not under its own steam.

MATES UNDER THE POWER OF THE CANADARM

Out of context, this sounds like a line from a very bad book. Have an upvote.

Re: Station Crew Docks Dragon Capsule to ISS

#18

Post by jimktrains2 » Tue, Sep 23, 2014, 2:01 PM UTC

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.

It's common in science in general to use Metric and not Customary. NASA is a/the notable hold out. Engineering is sometimes done in customary because of contracts and such, especially when dealing with government agencies.

While I love Customary volumes (powers of 2 base units), the rest could stand a change and am glad SpaceX is using Metric.

Re: Station Crew Docks Dragon Capsule to ISS

#19

Post by antimagic » Tue, Sep 23, 2014, 2:02 PM UTC

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.

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.

Re: Station Crew Docks Dragon Capsule to ISS

#20

Post by icegreentea » Tue, Sep 23, 2014, 2:02 PM UTC

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.

The arm almost certainly has a control system that can resolve that. Since humans suck at higher order control, the arm almost certainly has a control system that takes the operator's desired output (which will be a series of joint angles), and converts into the required motor torques. In this process, the control system almost certainly also does sanity checks to prevent self-intersections, collision with the space station, overtorqeuing the motors, and etc.

Replacing the human with a computer program therefore likely doesn't literally involve verifying that it will not karate chop the station - lower level control will take care of that for you.

However, as anyone who has worked with robot manipulators before, actually getting good performance out of them in variable environments (ie, not a controlled factory assembly line) is quite a bit of work - work that probably isn't worth it.