Author Topic: General ISS Q&A thread  (Read 879563 times)

Offline parham55

Re: General ISS Q&A thread
« Reply #920 on: 03/20/2009 05:31 pm »
Thanks, Jim.  You seem to know exactly what to search for or you have the whole site mapped in your head.

Offline rerickson

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Re: General ISS Q&A thread
« Reply #921 on: 03/20/2009 07:38 pm »
Why did the "target dots" turn out not to be usable for SSRMS navigation? This probably was a significant lesson learned, as it'd have been a good thing for Canadarm2 to be able to confirm its position autonomously, rather than depending on crewmembers with video monitors as a backup to the joint sensors. :( This would only have applied to relocation tasks with ample clearances; one could imagine the arm making a series of inchworm moves without human involvement, once you can trust the control systems.

By the way, is any (non-L2) speeded-up video available of the SSRMS relocating as an inchworm? I would've expected NASA to assemble a series of such moves, for the visual interest.

In reading the interesting 62pp of this thread, I found mention of the target dots' purpose, as well as their not being provided on recent modules because they didn't work as planned -- but nothing as to why they failed.

NSF is the best! Thanks.

Offline Jorge

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Re: General ISS Q&A thread
« Reply #922 on: 03/20/2009 07:41 pm »
Why did the "target dots" turn out not to be usable for SSRMS navigation? This probably was a significant lesson learned, as it'd have been a good thing for Canadarm2 to be able to confirm its position autonomously, rather than depending on crewmembers with video monitors as a backup to the joint sensors. :( This would only have applied to relocation tasks with ample clearances; one could imagine the arm making a series of inchworm moves without human involvement, once you can trust the control systems.

By the way, is any (non-L2) speeded-up video available of the SSRMS relocating as an inchworm? I would've expected NASA to assemble a series of such moves, for the visual interest.

In reading the interesting 62pp of this thread, I found mention of the target dots' purpose, as well as their not being provided on recent modules because they didn't work as planned -- but nothing as to why they failed.

NSF is the best! Thanks.

Inadequate contrast using real-world cameras in real-world lighting conditions displayed on real-world monitors.

Worked great in the ivory tower, though.
JRF

Offline MKremer

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Re: General ISS Q&A thread
« Reply #923 on: 03/20/2009 08:02 pm »
In reading the interesting 62pp of this thread, I found mention of the target dots' purpose, as well as their not being provided on recent modules because they didn't work as planned -- but nothing as to why they failed.

NSF is the best! Thanks.

Remembering the several times the space vision system was used in early station assembly and MPLM supply missions, they kept running into problems because it couldn't recognize all the targets consistently enough to depend on it to reliably and accurately position or move anything with confidence.

It ended up that Mark I eyeballs were much more reliable, versatile and accurate, which is what is used today with the help of alignment guides, targets, and multiple views.

Offline rerickson

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Re: General ISS Q&A thread
« Reply #924 on: 03/20/2009 11:15 pm »
That makes sense; a fixed-sized dot on a white background isn't very distinctive once you add noise and fuzziness. They should've put a distinctive pattern around the periphery of the white circle, so it would stand out under even adverse conditions. You could even encode a unique dot-id for increased navigation confidence.
Next station...

Offline Jorge

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Re: General ISS Q&A thread
« Reply #925 on: 03/21/2009 12:15 am »
That makes sense; a fixed-sized dot on a white background isn't very distinctive once you add noise and fuzziness. They should've put a distinctive pattern around the periphery of the white circle, so it would stand out under even adverse conditions.

Don't think that would help enough. The dots weren't visible at all in conditions of deep shadow. Sun reflection off shiny nearby surfaces could also cause the camera to "bloom" and white out, and sometimes the iris would close down and make the whole scene dark. The existing CCTV system simply doesn't have the dynamic range needed to handle all these conditions. The real fix is to replace the CCTV system, not the targets.
JRF

Offline parker

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Re: General ISS Q&A thread
« Reply #926 on: 03/22/2009 04:10 pm »
good morning,

I have a simple question re ISS size.
For the technolgy we have now is there a maximum size it can be build
& stay in orbit.
Reason for my question. Why we do not use each supply ship that is sent as an extra section, so it gets bigger & bigger,
I would guess, that the larger the size, the great effect on the pull of gravity to earth,
could this be overcome, by changing orbit a few miles.

Seems such waist when equipment  is just sent to burn up in re-entry,
maybe sent it to the moon ?? specific location ?
have so many questions, hoping to find all the answers here in this forum.

thanks

"a new visiter to site"

Offline Jim

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Re: General ISS Q&A thread
« Reply #927 on: 03/22/2009 04:24 pm »

1.   Why we do not use each supply ship that is sent as an extra section, so it gets bigger & bigger,

2.  I would guess, that the larger the size, the great effect on the pull of gravity to earth,could this be overcome, by changing orbit a few miles.


1.  No $$$$

2.  Size* or weight has no effect on the orbit of the ISS.  Once an object is in orbit, it will stay in the same orbit

* other posters don't muck up the discussion with drag

Offline jimvela

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Re: General ISS Q&A thread
« Reply #928 on: 03/22/2009 04:36 pm »

1.   Why we do not use each supply ship that is sent as an extra section, so it gets bigger & bigger,

2.  I would guess, that the larger the size, the great effect on the pull of gravity to earth,could this be overcome, by changing orbit a few miles.


1.  No $$$$

2.  Size* or weight has no effect on the orbit of the ISS.  Once an object is in orbit, it will stay in the same orbit

* other posters don't muck up the discussion with drag

Sorry, couldn't resist.  Aside from drag created by more modules, aren't there other reasons to limit mass?

+  As mass increases, the amount of reboost you can do per unit of available thrust decreases, meaning it gets harder and harder to keep the station at the correct orbit.

+  Similarly, as you increase mass, it gets harder and harder for CMGs and thrusters to change attitude, at some point making the existing systems ineffective.

+  Each module would need some amount of power, cooling, and ventilation to keep it conditioned for habitation, which at some point takes away from power needed to to meaningful work, and ultimately exceeds the capabilities of the station power systems.

+  The mass would soon exceed the ratings of the trusses, which requires further design and buildout to support the adding of more junk modules.

+  Modules need regular cleaning and maintenance so they don't end up with big blobs of water and crap floating around in them.  At some size, this becomes more than the crew can handle and still do meaningful work.

+  Modules need to be monitored for leaks, fire, etc.  There isn't provisions to do this with the existing systems.

I'm sure there are many other reasons that I'm missing.

Offline Jim

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Re: General ISS Q&A thread
« Reply #929 on: 03/22/2009 04:56 pm »
+  As mass increases, the amount of reboost you can do per unit of available thrust decreases, meaning it gets harder and harder to keep the station at the correct orbit.


 ;)  reboost is required because drag

Offline ChrisC

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Re: General ISS Q&A thread
« Reply #930 on: 03/22/2009 05:37 pm »
During last week's post launch news conference, there was some Q+A about expedition handover, overlap, crew changeout, etc.  One of the guys (Gerst or Suffredini) was talking about "direct handover" vs "indirect handover".  I didn't quite follow what he was talking about.  I think it was in the context of making sure that the expedition crews had a full 7-10 days of overlap in order to do a good transition, without the distraction of also having a shuttle mission docked, but I didn't fully understand the jargon.  Can someone explain?
PSA #1: EST does NOT mean "Eastern Time".  Use "Eastern" or "ET" instead, all year round, and avoid this common error.  Google "EST vs EDT".
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Offline Jorge

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Re: General ISS Q&A thread
« Reply #931 on: 03/22/2009 05:49 pm »
During last week's post launch news conference, there was some Q+A about expedition handover, overlap, crew changeout, etc.  One of the guys (Gerst or Suffredini) was talking about "direct handover" vs "indirect handover".  I didn't quite follow what he was talking about.  I think it was in the context of making sure that the expedition crews had a full 7-10 days of overlap in order to do a good transition, without the distraction of also having a shuttle mission docked, but I didn't fully understand the jargon.  Can someone explain?


erioladastra is probably the one to answer this, but my understanding is that direct handover means the new Soyuz docks before the old one leaves, allowing the new crewmembers to take the handover directly from the departing crewmembers, while indirect handover means the old Soyuz leaves first, so the handover is performed by the three "holdover" crewmembers. (Obviously only applies with a 6-person crew; an indirect handover with a 3-person crew leaves ISS temporarily uninhabited.)

The reason why this might be necessary is shortage of Soyuz/Progress/ATV docking ports. There are currently only three, and a direct handover will require all three (two for the old Soyuzes and one for the new one). That means that the Soyuz rotation schedule will be tightly coupled with the Progress/ATV schedule. Indirect handover frees up a port so that the Progress/ATV schedule can be kept independent (to some extent) from the Soyuz schedule.
JRF

Offline ChrisC

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Re: General ISS Q&A thread
« Reply #932 on: 03/22/2009 05:53 pm »
Ah, yes, that makes sense.  With 3-person crew, I knew they wouldn't have 2 depart and leave just the 1 person as the "holdover" crewmember until the next 2 showed up (or leave it unmanned).  I didn't think of 6-person crew.

It's going to be pretty tight for those 5 years ...
« Last Edit: 03/22/2009 05:55 pm by ChrisC »
PSA #1: EST does NOT mean "Eastern Time".  Use "Eastern" or "ET" instead, all year round, and avoid this common error.  Google "EST vs EDT".
PSA #2: It's and its: know the difference and quietly impress grammar pedants.  Google "angry flower its" .  *** See profile for two more NSF forum tips. ***

Offline erioladastra

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Re: General ISS Q&A thread
« Reply #933 on: 03/22/2009 07:59 pm »
During last week's post launch news conference, there was some Q+A about expedition handover, overlap, crew changeout, etc.  One of the guys (Gerst or Suffredini) was talking about "direct handover" vs "indirect handover".  I didn't quite follow what he was talking about.  I think it was in the context of making sure that the expedition crews had a full 7-10 days of overlap in order to do a good transition, without the distraction of also having a shuttle mission docked, but I didn't fully understand the jargon.  Can someone explain?


erioladastra is probably the one to answer this, but my understanding is that direct handover means the new Soyuz docks before the old one leaves, allowing the new crewmembers to take the handover directly from the departing crewmembers, while indirect handover means the old Soyuz leaves first, so the handover is performed by the three "holdover" crewmembers. (Obviously only applies with a 6-person crew; an indirect handover with a 3-person crew leaves ISS temporarily uninhabited.)

The reason why this might be necessary is shortage of Soyuz/Progress/ATV docking ports. There are currently only three, and a direct handover will require all three (two for the old Soyuzes and one for the new one). That means that the Soyuz rotation schedule will be tightly coupled with the Progress/ATV schedule. Indirect handover frees up a port so that the Progress/ATV schedule can be kept independent (to some extent) from the Soyuz schedule.

While that is true that is not usually what we mean by direct or indirect (but I guess some might use those terms).  Normally it means this:  Direct we schedule N hours of timne for the crew to go over a handover book or specific topic (e.g., emergency response).  Indirect is where we do handover by showing - for example robotics where the new person gets to feel the thing while the old person is there to guide and show features.

Offline eeergo

Re: General ISS Q&A thread
« Reply #934 on: 03/22/2009 10:33 pm »
Is Brazil still contributing to the ISS program with an ELC? If so, which of them is it? If not, what happened to the project and who's making up for the change?
-DaviD-

Offline Jim

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Re: General ISS Q&A thread
« Reply #935 on: 03/22/2009 11:03 pm »
GSFC is in charge of the ELC's

Offline Almurray1958

Re: General ISS Q&A thread
« Reply #936 on: 03/23/2009 04:04 pm »
question on CETA move:

Doesn't CETA have (unpowered) Grapple fixture attached? 
Why use astronaut as end-effector? 
- Al Murray

Offline Jim

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Re: General ISS Q&A thread
« Reply #937 on: 03/23/2009 04:12 pm »
question on CETA move:

Doesn't CETA have (unpowered) Grapple fixture attached? 
Why use astronaut as end-effector? 


No, it would be in the way
« Last Edit: 03/23/2009 04:16 pm by Jim »

Offline Ronsmytheiii

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Re: General ISS Q&A thread
« Reply #938 on: 03/23/2009 05:36 pm »
Isnt ESP-3 berthed to a UCCAS or  a PAS?  If so, when was the first deployed (UCCAS or PAS)?
« Last Edit: 03/23/2009 05:46 pm by Ronsmytheiii »

Offline The-Hammer

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Re: General ISS Q&A thread
« Reply #939 on: 03/23/2009 05:52 pm »
ESP-3 is berthed to the P3 Zenith UCCAS which was deployed February 08, 2007 during Expedition 14 EVA 4. ESP-3 was berthed August 17, 2007 during STS-118.
Grant Imahara: Oxygen deficiency alarm? Is that something I should be worried about?
NASA worker: Only if it goes off.

 

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