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Oberg: "The real significance of the ISS thruster test failure"



 
 
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  #21  
Old May 12th 06, 10:06 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Dale wrote:

I thought the Soyuz' shelf life was more an issue with its batteries, not
its thrusters (?)...



They're still somewhat closed mouthed about all this and the specifics
of what decays over time.
I'd be seriously concerned about what condition the propellant valves on
the motors would be in after all this time and given the corrosive
nature of the propellants, as well as all the hot/cold exposures they've
had over the years as the station passes through Earth's shadow.
If they had never been fired before it would be one thing, but these
motors have been fired and shut down six years ago.
I wouldn't try to start them, I'd be concerned something bad might
happen; that module is basically a souped-up Mir core module, and Mir
wasn't the most reliable thing ever made.

Pat
  #22  
Old May 12th 06, 10:42 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Jeff Findley wrote:

I thought the issue with Soyuz limited in orbit lifetime was due it's use of
hydrogen peroxide for the descent module's attitude control system. I
believe that the issue there is that hydrogen peroxide degrades over time
due as it slowly turns back into oxygen and water.

http://www.nasa.gov/mission_pages/st...ft_detail.html


I'd heard it was degradation of the propellant feed system and the
propellant tankage itself under the corrosive effects of the propellants.
Batteries? H2O2? Propellants? Maybe the whole thing just pretty much
goes to pot after a set amount of time.
If you think about it, having the whole thing pretty much break down
simultaneously would be a very economical way to design it; you wouldn't
have any part be overbuilt for its intended mission, and that concept
has Russian written all over it.
Until we started using them as lifeboats we could not get any specifics
of what a Soyuz's lifetime on-orbit even was, and just had to estimate
it from how long they'd kept one up. That was even the case back in the
Mir days, decades after it was introduced into service.
What gets me is how the Russians have suddenly decided to rev up the
engines to "see if they work"....there's got to be more to that story.


Pat
  #23  
Old May 12th 06, 10:51 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Jeff Findley wrote:

I'm not sure I understand this since the tanks on ISS can feed the thrusters
on a docked Progress (certainly one docked at the aft port, not sure about
other ports). It seems like this would be more useful for a collision
avoidance maneuver when a Progress isn't docked, or for some reason the
Progress engines fail to fire (from what I've read, you can still fire the
ISS thrusters even when a Progress is docked to the aft port).



We discussed this a couple of years back, when the loss of Columbia
ended the regular Shuttle reboosts.
The Zvezda module apparently has left-over fuel still onboard that could
give a significant boost to the ISS' altitude.

Pat
  #24  
Old May 13th 06, 05:05 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

"Jeff Findley" wrote in
:


"Pat Flannery" wrote in message
...
Those are hypergolicly fueled engines using N2O4 and UDMH, and they
don't trust the Soyuz, whose motors use the same propellants, after
six months.


I thought the issue with Soyuz limited in orbit lifetime was due it's
use of hydrogen peroxide for the descent module's attitude control
system. I believe that the issue there is that hydrogen peroxide
degrades over time due as it slowly turns back into oxygen and water.

http://www.nasa.gov/mission_pages/st...nts/soyuz/spac
ecraft_detail.html


That's what I thought as well, and it turns out to be true up to the Soyuz
TM. I've recently learned that the TMA uses an improved grade of peroxide
that increases the lifetime of the descent propulsion system from 180 to
270 days. However, Soyuz as a whole is limited to 200 days due to
certification of other systems. I don't know which systems in particular
are the limiting factors.



--
JRF

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  #25  
Old May 13th 06, 05:07 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

Pat Flannery wrote in
:

Jeff Findley wrote:

I'm not sure I understand this since the tanks on ISS can feed the
thrusters on a docked Progress (certainly one docked at the aft port,
not sure about other ports). It seems like this would be more useful
for a collision avoidance maneuver when a Progress isn't docked, or
for some reason the Progress engines fail to fire (from what I've
read, you can still fire the ISS thrusters even when a Progress is
docked to the aft port).


We discussed this a couple of years back, when the loss of Columbia
ended the regular Shuttle reboosts.
The Zvezda module apparently has left-over fuel still onboard that
could give a significant boost to the ISS' altitude.


Right. And as others have stated, Zvezda can interconnect to a docked
Progress on either port to reboost the station even if Zvezda's own engines
are inop. (And even if there is no Progress docked, don't forget that only
one Zvezda engine failed; they can still do single-engine burns if they
must.)

--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.
  #26  
Old May 13th 06, 05:13 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

Pat Flannery wrote in
:

John Doe wrote:

I don't think you can fault anyone for this at this point in time. We
have to wait to see how they react in the event they cannot fix the
thruster.


As to why they are keen to test them:
http://www.hq.nasa.gov/osf/station/images/issalt.gif
Without the Shuttle reboosts they are slowly but surely getting lower
despite the Progress reboosts.


That plot is not as alarming as it might appear. ISS is now flying through
solar minimum, so it can fly at a lower altitude while maintaining the same
orbital lifetime. And as you pointed out yourself, Zvezda has plenty of
propellant reserves that could be interconnected to Progress to boost ISS
all the way back up to its maximum altitude in a contingency. Right now the
Russians and NASA are taking advantage of solar minimum to optimize
Progress and shuttle payload.


--
JRF

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check "Organization" (I am not assimilated) and
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  #27  
Old May 13th 06, 05:18 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Jorge R. Frank wrote:

That's what I thought as well, and it turns out to be true up to the Soyuz
TM. I've recently learned that the TMA uses an improved grade of peroxide
that increases the lifetime of the descent propulsion system from 180 to
270 days.



It would be fun to know how they pulled that off- did they chill the
H2O2, or use a stabilizing additive of some sort?

Pat
  #28  
Old May 13th 06, 05:28 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Jorge R. Frank wrote:

Right. And as others have stated, Zvezda can interconnect to a docked
Progress on either port to reboost the station even if Zvezda's own engines
are inop. (And even if there is no Progress docked, don't forget that only
one Zvezda engine failed; they can still do single-engine burns if they
must.)



Looking at my Intermountain Railways model of the ISS, it looks like
Zvezda has a total of three open docking ports; the one facing toward
the rear of the station flanked by the two engines they are trying to
use, and two mounted to the "docking sphere" that are at ninety degrees
to the main axis of the station (up and down).
How's the Progress supposed to get its center of thrust to pass through
the ISS' center of mass from either of those two locations?

Pat
  #29  
Old May 13th 06, 05:47 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

Pat Flannery wrote in
:

How's the Progress supposed to get its center of thrust to pass
through the ISS' center of mass from either of those two locations?


It doesn't; the resulting torque would be controlled by the RCS thrusters
on Zvezda. Inefficient, but tolerable. The forward of the two nadir
locations is very close to the ISS center of mass for the current config
anyway. The loads from the Progress reboost engine are likewise tolerable
even in this off-axis state; remember that this reboost engine is smaller
than even a single shuttle primary RCS thruster.

--
JRF

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check "Organization" (I am not assimilated) and
think one step ahead of IBM.
  #30  
Old May 13th 06, 06:30 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Jorge R. Frank wrote:

That plot is not as alarming as it might appear. ISS is now flying through
solar minimum, so it can fly at a lower altitude while maintaining the same
orbital lifetime. And as you pointed out yourself, Zvezda has plenty of
propellant reserves that could be interconnected to Progress to boost ISS
all the way back up to its maximum altitude in a contingency. Right now the
Russians and NASA are taking advantage of solar minimum to optimize
Progress and shuttle payload.



Thought problem:
Something doesn't go right on the next Shuttle flight and it gets
grounded again.
The Progress reboosts are helping, but how long can they keep kicking it
up on there own once the Zvezda's fuel is expended?
Do they have to wait around for the new ESA Jules Verne module to raise
its orbit in lieu of the Shuttle if that occurs?
There is one ironic aspect to all this- if the ISS really had been
completed to the point it was supposed to be today on the original
schedule, it would have been a lot more massive than it presently is,
and those Progress reboosts would be having far less effect than they
presently are.
Having it lag so far behind schedule has kept it light enough for the
Progress' to keep its orbit up despite the two groundings of the Shuttle.

Pat
 




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