Conservation of angular momentum...

[BinocularSky]

... with CD players in microgravity:

https://video.twimg.com/tweet_video/C6ugewjV0AACAj_.mp4

[SilverAstro]

9 minutes ago, BinocularSky said:

... with CD players in microgravity:

https://video.twimg.com/tweet_video/C6ugewjV0AACAj_.mp4

No audio from them ( ?  checked in two browsers)  So it is true that no one can hear you scream in space then !

I like it though

Tonights homework :- why does the body of the CD player not counter-rotate ? (like a helicopter does without its tail rotor)

[Peter Drew]

Not all helicopters seem to have tail rotators these days. 

[SilverAstro]

4 minutes ago, Peter Drew said:

Not all helicopters seem to have tail rotators these days. 

That is true, but the ones that dont have a second, counter rotating, set of blades elsewhere    (or other counter reaction wheel)

[BinocularSky]

16 minutes ago, SilverAstro said:

Tonights homework :- why does the body of the CD player not counter-rotate ?

Watch carefully; it does (but very slowly, owing to its moment of inertia being so much greater than that of a CD). Perhaps also there are counter-rotating components in the CD player?

[SilverAstro]

2 minutes ago, BinocularSky said:

Watch carefully; it does (but very slowly, owing to its moment of inertia being so much higher than that of a CD). Perhaps also there are counter-rotating components in the CD player?

I once did some work on a spacecraft that rotated its whole body as a gyro stabiliser,  -  the only problem was --  to keep my high-gain dish pointed at the earth for the telemetry    > enter the de-spun platform to mount my gubbins on

Y'all be pleased to know we got good data back from Comet Halley

[niallk]

6 hours ago, SilverAstro said:

I once did some work on a spacecraft that rotated its whole body as a gyro stabiliser,  -  the only problem was --  to keep my high-gain dish pointed at the earth for the telemetry    > enter the de-spun platform to mount my gubbins on

Y'all be pleased to know we got good data back from Comet Halley

Hi SilverAstro - did you work on the Giotto mission?!!! Oh WOW!  Amazing engineering.

-Niall

[niallk]

7 hours ago, BinocularSky said:

... with CD players in microgravity:

https://video.twimg.com/tweet_video/C6ugewjV0AACAj_.mp4

I really like that

[SilverAstro]

15 minutes ago, niallk said:

 did you work on the Giotto mission

Yes well spotted, that's the one. From quite early,  I had a small part in the writing of the feasibility study (for the telemetry & telecommand) so I like to think I helped a little to win us the contract.

 

[niallk]

52 minutes ago, SilverAstro said:

Yes well spotted, that's the one. From quite early,  I had a small part in the writing of the feasibility study (for the telemetry & telecommand) so I like to think I helped a little to win us the contract.

 

Superb - what an accomplishment!!  That was an amazing mission: I remember well the pictures coming back in '86 when I was 10yrs old. It's a privilege to talk to you here on SGL

You know, I wondered how those spin stabilised probes communicated back: I didn't know about the counter-rotating dish platform! I guess some kind of feedback control is used to precisely match the rotations?  I must Google it!!

[SilverAstro]

13 hours ago, niallk said:

Superb - what an accomplishment!!  That was an amazing mission: I remember well the pictures coming back in '86 when I was 10yrs old. It's a privilege to talk to you here on SGL

You know, I wondered how those spin stabilised probes communicated back: I didn't know about the counter-rotating dish platform! I guess some kind of feedback control is used to precisely match the rotations?  I must Google it!!

you are too kind, it is my privilege to be (still ! lol) here to talk with you all

Exciting times, a lot was happening., I was young, not long qualified and still cant quite believe the stuff that landed on my desk ! Which is a long-winded way of saying - - I was too busy, I dunno, it was not my area of responsibility, I had to assume that when the attitude control bods said it would be pointing such&such a way, that it would be !

Yes, I think a Google is in order,,,,

 

 

 

[SilverAstro]

Lunch over, chores done, playtime ,, so here is a slightly longer reply with a little anecdote for amusement

I was saying  , , ,  >

when the attitude control bods said it would be pointing such&such way, that it would be ! My job was to say :-

given the data rate the science and housekeeping would need
the power that I was allocated,
the dimensions of the payload shroud of the launch vehicle (Arianne)
the Equivalent Noise Temperature of Rx front ends
the bit-error-rate that was acceptable
was it feasible ?

And the answer I gave was , , ,  no it wasnt !
Panic & Consternation when I said that a bigger dish was needed, they said "no. wont fit", I said then it will have to be squidged up a bit (sorry for that technical term) and un-furled when the shroud was jetisoned. Ha! mechanical actuators still dont have a good reputation, back then it caused mision planners to turn pale and cry
Somehow I was given a few more watts allocation and it all became good.

That all kept me quite busy, , , I do remember star finder/trackers were developed for spacecraft far from home (ie not in earth orbit) It looked for three bright stars, does that sound familiar !!!  (Fomalhaut, Sirius and Vega I think, no trees and houses in the way ) but cant remember if that was on Giotto or one of the others. That would have provided the ref. for the control system.

Not a lot on the interweb about its construction, all about (rightly) the science.