Author Topic: General ISS Q&A thread  (Read 879601 times)

Offline Jim

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Re: General ISS Q&A thread
« Reply #960 on: 04/02/2009 02:07 pm »
ISS Expedition is "mission" designation for a specific crew

Increment is a planning phase that may cover multiple expeditions, shuttle and Soyuz launches.  It some times brackets large configuration changes to the ISS

Mods move this to ISS Q&A

Offline rjb23

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Re: General ISS Q&A thread
« Reply #961 on: 04/04/2009 06:02 pm »
Comparing the baselines for upcoming flights, I don't understand the plan for the SGANTs.  STS-127 is bringing up a spare SGANT (stored on ESP-3).  STS-132 is bringing up another SGANT, SGANT boom and has an EVA task for installing both on Z1.  Is the STS-132 objective to replace the current SGANT on Z1 or install a second SGANT while leaving the current one untouched?  If replacing the current one, I didn't see a uninstall task anywhere - is that a stage EVA objective?  If installing a second SGANT, does this alleviate the no-KU periods caused by structural blockage?  If installing a second SGANT, will both be managed concurrently or will one be a hot backup?

Offline Suzy

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Re: General ISS Q&A thread
« Reply #962 on: 04/05/2009 06:22 am »
Do the exteriors of the ISS windows ever get cleaned? Some of the photos taken through them look a bit spotted (like this one).

Offline MKremer

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Re: General ISS Q&A thread
« Reply #963 on: 04/05/2009 06:49 am »
Do the exteriors of the ISS windows ever get cleaned? Some of the photos taken through them look a bit spotted (like this one).

The problem is, what would you clean them with (that would be usable outside in the space environment), and can it be guaranteed that the result would be more transparent than just leaving a couple of small spots alone?
(ever clean spots or dust off your glasses or sunglasses and find you'd made things worse because you've now smeared a thin oily film over the surface and bright areas in your vision now have a faint halo effect?)

There's also the possibility that the 'spots' are the result of microscopic MMOD impacts. In that case, attempting any kind of cleaning will do no good (and could probably make things worse).
« Last Edit: 04/05/2009 06:51 am by MKremer »

Offline MKremer

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Re: General ISS Q&A thread
« Reply #964 on: 04/05/2009 07:00 am »
Comparing the baselines for upcoming flights, I don't understand the plan for the SGANTs.  STS-127 is bringing up a spare SGANT (stored on ESP-3).  STS-132 is bringing up another SGANT, SGANT boom and has an EVA task for installing both on Z1.  Is the STS-132 objective to replace the current SGANT on Z1 or install a second SGANT while leaving the current one untouched?  If replacing the current one, I didn't see a uninstall task anywhere - is that a stage EVA objective?  If installing a second SGANT, does this alleviate the no-KU periods caused by structural blockage?  If installing a second SGANT, will both be managed concurrently or will one be a hot backup?

The first spare could really be just a spare ORU. Those dishes with the horns, along with their electronics/positioning mount, are pretty large. (They've occasionally had them out for testing in the SSPF over the last several years.)

It's very likely that they're too large to be transported by anything other than in the orbiter cargo bay, in which case it's best to get the spare up and stored on orbit while the Shuttles are still flying.

Offline Spacenick

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Re: General ISS Q&A thread
« Reply #965 on: 04/05/2009 10:14 am »
Why don't they measure the weight of ISS by means of F=ma if the force applied by reboost thrusters is known and you measurecd the acceleration then it would be no problem to deduce the mass of the station. So why calculate the mass for every kg brought to the US when measuring would be so easy...

Offline AnalogMan

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Re: General ISS Q&A thread
« Reply #966 on: 04/05/2009 11:45 am »
Why don't they measure the weight of ISS by means of F=ma if the force applied by reboost thrusters is known and you measurecd the acceleration then it would be no problem to deduce the mass of the station. So why calculate the mass for every kg brought to the US when measuring would be so easy...

Its because as well as the total mass they also need to know how that mass is distributed for calculating center of mass, and the forces (torques) acting on various sections/joints of the station during maneuvers.

Mass is tracked to the nearest 1/10 of a lb (currently 685930.9 lb) which is better than one part per million - the accuracy with which the force of the thrusters is known will be orders of magnitude less than this.

EDIT:  A good example of what happens when you get mass distribution calculations wrong: during EVA 2 of the recent STS-119/15A mission the ISS lost attitude control because the Control Moment Gyroscopes (CMGs) were programmed with the wrong parameters.  These were based on the Mobile Transporter (MT) being at worksite 4, when in fact it was actually at worksite 1.

All was well though, because the orbiter took over station control and maintained correct attitude.
« Last Edit: 04/05/2009 02:43 pm by AnalogMan »

Offline Analyst

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Re: General ISS Q&A thread
« Reply #967 on: 04/05/2009 12:47 pm »
They will install a second SGANT including boom on Z1, STS-127 brings up a spare ORU SGANT without boom.

Analyst

Offline rjb23

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Re: General ISS Q&A thread
« Reply #968 on: 04/05/2009 02:42 pm »
Thanks Analyst.  Any insight on the operational implications of having 2 SGANTs on Z1?

Also, are there other components of ISS that will be "doubled up" over the remaining flights?

Offline Spacenick

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Re: General ISS Q&A thread
« Reply #969 on: 04/05/2009 10:00 pm »
Do the CMGs rely only on the mass estimates or do the have some kind of control feedback loop with accelorameters? i had thought that a lot of the the attitude control and other parts of spacecraft conrtol could be done with feedback loops and acceleration meassurement, maybe meassuring on different parts of the spacecraft.
If it is based on calculation rather then direct measurement, does this practice have it's roots in the age of the technology involved which for the most part was established many years before small accurate acceleration sensors became available?

Does the Soyuz also base it's thruster firings on caclulation rathern than on sensor measurements?

Offline Jim

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Re: General ISS Q&A thread
« Reply #970 on: 04/06/2009 02:47 pm »
Do the CMGs rely only on the mass estimates or do the have some kind of control feedback loop with accelorameters? i had thought that a lot of the the attitude control and other parts of spacecraft conrtol could be done with feedback loops and acceleration meassurement, maybe meassuring on different parts of the spacecraft.
If it is based on calculation rather then direct measurement, does this practice have it's roots in the age of the technology involved which for the most part was established many years before small accurate acceleration sensors became available?


The mass has to  be known for the gain settings (even with accels).  This is customary for most feedback systems

Offline Spacenick

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Re: General ISS Q&A thread
« Reply #971 on: 04/09/2009 08:51 pm »
I've a kind of silly question I've been thinking about for years.
Can a human propel himself backwards by blowing as strong as he can when in zero-g? i mean he definitely can to some extent otherwise F=ma  wouldn't be true, but is it enough so that one feels it?

Offline A_M_Swallow

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Re: General ISS Q&A thread
« Reply #972 on: 04/09/2009 10:43 pm »
I've a kind of silly question I've been thinking about for years.
Can a human propel himself backwards by blowing as strong as he can when in zero-g? i mean he definitely can to some extent otherwise F=ma  wouldn't be true, but is it enough so that one feels it?

The person has to breath in as well as breathing out.
Heads can be turned to point (nearly) the opposite direction.

Offline nomadd22

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Re: General ISS Q&A thread
« Reply #973 on: 04/09/2009 11:03 pm »
 He might do better with burritos and a Zippo.

Offline Spacenick

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Re: General ISS Q&A thread
« Reply #974 on: 04/10/2009 10:20 am »
Yeah but breathing in is much slower and therefor it should be possible to propel onself when blowing very strongly, however I'm unsure how great the effect would be.
I doubt burritos would work better though, even if it were pure methane the flame wouldn't speed up the molecules in one particular direction therefor you won't get very far with that, appart from doing that in a space station is neither nice nor acceptable from a safety point of view, while blowing is probably safe.

Offline hop

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Re: General ISS Q&A thread
« Reply #975 on: 04/11/2009 04:09 am »
Can a human propel himself backwards by blowing as strong as he can when in zero-g? i mean he definitely can to some extent otherwise F=ma  wouldn't be true, but is it enough so that one feels it?
Density of air at sea level is roughly 1.2 kg/m^3 =  0.0012 g/cc

Amount of air a typical adult male can exhale in one breath ~4.6l = 4600cc => 5.52g

Not sure what velocity you can exhale at, but lets say 10 m/s as a WAG*.

Assuming a 70kg (with a lung full of air) astronaut...

Plugging in dV =  10 * ln (70000/69994.48)**
= ~ 0.00079 m/s

Assuming I haven't messed something up, this is not going to get you anywhere in a hurry.

* this feels optimistic, but a sneeze may be better.

** OK, with a mass ratio like this you don't really need the rocket equation, but this is spaceflight gosh darnit ;)

Offline nomadd22

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Re: General ISS Q&A thread
« Reply #976 on: 04/11/2009 05:52 pm »
I doubt burritos would work better though, even if it were pure methane the flame wouldn't speed up the molecules in one particular direction
No problem. You just need a properly designed nozzle. And Russians are way to tough to complain about the fragrance. You might need to disable the fire suppression for a second though.
 And if you don't think you could get a respectable ISP from burritos, you haven't tried Jumburrito in Midland, Texas.

Offline NavySpaceFan

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Re: General ISS Q&A thread
« Reply #977 on: 04/22/2009 05:29 pm »
Sorry to break into the "fun with methane" discussion ;), but I was wondering can individual modules be remotely depressurized?  For example, if there is a hull breach in Destiny, can Unity be depressurized in order to ingress Destiny and make repairs?
<----First launch of DISCOVERY, STS-41D!!!!

Offline Life_Support_32

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Re: General ISS Q&A thread
« Reply #978 on: 04/22/2009 11:15 pm »
Sorry to break into the "fun with methane" discussion ;), but I was wondering can individual modules be remotely depressurized?  For example, if there is a hull breach in Destiny, can Unity be depressurized in order to ingress Destiny and make repairs?

The only module with that capability always activated is the US Lab.  Columbus and JPM contain that capability that would require some software configuration and the US Airlock would require crew action to reconfigure.  Node 1, Node 2 and the Russian Segment do not have the automated capability to do so.  There's always ways you could do this manually, but that's complex and not very attractive from the consummables standpoint.

Offline NavySpaceFan

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Re: General ISS Q&A thread
« Reply #979 on: 04/23/2009 12:09 am »
Sorry to break into the "fun with methane" discussion ;), but I was wondering can individual modules be remotely depressurized?  For example, if there is a hull breach in Destiny, can Unity be depressurized in order to ingress Destiny and make repairs?

The only module with that capability always activated is the US Lab.  Columbus and JPM contain that capability that would require some software configuration and the US Airlock would require crew action to reconfigure.  Node 1, Node 2 and the Russian Segment do not have the automated capability to do so.  There's always ways you could do this manually, but that's complex and not very attractive from the consummables standpoint.

Great response, thanks!!!!
<----First launch of DISCOVERY, STS-41D!!!!

 

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