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



 
 
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  #91  
Old May 22nd 06, 08:16 AM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

John Doe wrote in :

"Jorge R. Frank" wrote:
And ISS does exactly that - they call the mode "Night Glider".



If the arrays are at an angle to direction of travel (with the sun in
the back), do they provide any lift at all ?


"Any", yes. "Non-negligible" (in terms of being useful for orbit
maintenance), no. The station isn't just hypersonic; it's in a "free-
molecular" flow regime. L/D is generally so poor ( 1) that ISS is better
off following a strategy of minimizing drag (even though lift goes to zero)
rather than maximizing lift.

Once the truss os fully deployed, if they were to put one side at 45
and the other at -45, would it create sufficient force to actually put
the station into a spin ?


It would generate a measurable aero torque, and could in theory generate a
spin over time, though the angular acceleration would be quite low (the
station's moments of inertia are very large) and would take a long time to
build up a visible rate, even in the absence of control torques.

Will the surfaces be large enough that they could use the arrays/truss
to help desaturate the CMGs ?


In theory, yes. The software accounts for this (rather than seeking gravity
gradient attitudes, it seeks torque-equilibrium attitudes that balance the
aero and gravity-gradient torques), but currently does not take advantage
of it.

--
JRF

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  #92  
Old May 22nd 06, 02:04 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"



Chuck Stewart wrote:

NASA PAO flack at a press confrerence:
"No one has ever done this before! It will be a
huge leap in space solar power applications that
will undoubtedly have many spinoff effects for life
on Earth... and also we're using RMS technology
engineered for the shuttle/ISS program so costs will
be reduced by a factor of 10!"



I'm still shaking me head at Deep Space 1 and the ion engine of wonder
that has never been done before and is like the one Scotty's going
ecstatic about in Star Trek TOS.
Of course it had been done long before, and powered by a RTG isotope
generator to boot.
What I can't figure out is why Scotty is so damn awed by an ion engine,
considering he's got a pair of antimatter powered warp field generators
to play with.
Maybe it's like running into a steam engine made out of titanium or
something.

Pat
  #93  
Old May 22nd 06, 06:02 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

Chuck Stewart wrote:

"Feather"...

(The zapkitty has a vision of ISS circling
the globe with the solar arays windmilling
freely in the breeze...


Except the idea of feathering is to *prevent* windmilling.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL
  #94  
Old May 22nd 06, 11:36 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

On Mon, 22 May 2006 17:02:45 +0000, Derek Lyons wrote:

Chuck Stewart wrote:


"Feather"...


(The zapkitty has a vision of ISS circling
the globe with the solar arays windmilling
freely in the breeze...


Except the idea of feathering is to *prevent* windmilling.


*ouch*
OK, I asked for that...
.... but what about the ISS autorotation drills?

D.


--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying algebra?"
  #95  
Old May 24th 06, 03:24 PM posted to sci.space.station,sci.space.history
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Default Oberg: "The real significance of the ISS thruster test failure"

JRS: In article , dated Thu, 18
May 2006 20:32:38 remote, seen in news:sci.space.station, Jorge R. Frank
posted :
Dr John Stockton wrote in news:$n9DF9AxAObEFwW9
:


What does the drag amount to in actual Newtons and pounds-of-force, for
a typical or mean attitude? It can hardly be 166 kgf/m^2.


Right, the ballistic number is not pressure (force per unit area) but
rather mass per unit area. So 166 kg/m^2 means the station has 166 kg of
mass for every square meter of projected area.

Drag force is F = 0.5*rho*v^2*Cd*A, drag deceleration is a = F/m. The
ballistic number is BN = m/(Cd*A) so drag simplifies to a = 0.5*rho*v^2/BN
or F = 0.5*rho*v^2*m/BN. m is around 185,000 kg, v is around 7700 m/s. I
don't have my atmosphere models handy so plug in your favorite value for
rho and chug away.


That's all very well, no doubt; but neither do I.

The Heavens-Above site indicates that, between boosts, ISS drops by
about 3 kilometres/month or 1 millimetre/second.

Now ISTM that dR/dt = A T / pi where T is the period (Does anyone
know if that is right?) which puts the deceleration A at around 0.05
micro-gee and the force therefore as about one centi-newton (1 gram).
Someone please check that!

--
John Stockton, Surrey, UK. Turnpike v4.00 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
 




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