ISS altitude maintenance/reboost plan?

wrote:
OBE, but of interest: Figure 4 in

http://www.spaceflight.esa.int/users...ion_prelim.pdf

Repeated with minor fixing as Fig 2-1 in
http://www.sbf.admin.ch/htm/internat...User_Guide.pdf

wrote in message
oups.com...

Jorge R. Frank wrote:

P.S.: And ISS is getting more massive...

Check your understanding of physics. More mass results in *less* drag
deceleration, not more.

Depends on how much (frontal) area comes along with the mass. In any
case, the actual point is that more mass does, no fooling, mean more
fuel is needed to make up a given decrease in altitude.

But more mass also means that it takes more drag (more time for the same
drag) to decrease altitude. If you look at the total specific impulse
(fuel) needed over say the course of a year to maintain altitude, you'll
find it's independent of station mass and depends only on drag (i.e. frontal
area).

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

Jeff Findley wrote:

But more mass also means that it takes more drag (more time for the same
drag) to decrease altitude. If you look at the total specific impulse
(fuel) needed over say the course of a year to maintain altitude, you'll
find it's independent of station mass and depends only on drag (i.e. frontal
area).

Yes, the frontal area combined with the air density at altitude
produces an average force that needs to be balanced by a counteracting
average force that comes from burning fuel. Note the air density part
of that -- drag isn't just a function of frontal area, of course.

Anyway, this gets slightly away from what was meant to be the original
question -- is there a plan for ISS altitude maintenance? And, since we
are assured and can believe there is such, what is it? On what
specific resources does it depend over the years ahead?

This is a subset of the larger and also interesting question, "What is
the ISS logistics plan?"

" wrote:

Anyway, this gets slightly away from what was meant to be the original
question -- is there a plan for ISS altitude maintenance? And, since we
are assured and can believe there is such, what is it? On what
specific resources does it depend over the years ahead?

Progress and (IIRC) ATV I believe are the main reboost resources for
the near term.

This is a subset of the larger and also interesting question, "What is
the ISS logistics plan?

Ship stuff up and hope like heck nothing has to be discarded that
cannot fit into existing craft.

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

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

wrote
This is a subset of the larger and also interesting question, "What is
the ISS logistics plan?"

Somethying like Bulvay's plan against the Wendl
in '13th Warrior' --
"ride out until we find them and kill them all".

Jim Oberg wrote:

Somethying like Bulvay's plan against the Wendl
in '13th Warrior' --
"ride out until we find them and kill them all".

You guys aren't helping... ;-)

I certainly wouldn't expect NASA to have a Teutonically(*) precise
ten-year plan for everything they're going to do with ISS -- launch
schedules tend to slip a bit, if nothing else. But it would be of
interest to see how they're planning to keep the thing up in the sky
and operating, whatever "operating" might mean. What supply vehicles
are needed, generally when they'll need to be launched, etc.

(*) No ethnic slur or derogation should be inferred.

" wrote in
ups.com:


OBE, but of interest: Figure 4 in

http://www.spaceflight.esa.int/users.../ISS_Users_Gui
de_Earth_Observation_prelim.pdf

I think there's some mislabeling.

Yes, I do believe the 80 and 180 day plots should be swapped.


--
JRF

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"Jeff Findley" wrote in
:


"Jorge R. Frank" wrote in message
...
Check your understanding of physics. More mass results in *less* drag
deceleration, not more.

And doesn't the total reboost total impulse (thrust times time,
right?) you need for a certain time period in orbit depend only on the
drag force, which depends on the frontal area of the station, not on
the mass of the station? In other words, two stations with different
masses, but with the same drag force (frontal areas) would need the
same total reboost total impulse over the same time in orbit, right?

That's right. The more massive station would need reboosts more
infrequently, but each reboost would require more propellant to achieve a
given delta-V due to the increased mass.

So adding more modules to ISS in such a way as to increase the frontal
area will increase drag and will require an increase the amount of
fuel needed to maintain its orbit, right?

Right, if the area is increased more propellant will be required for
reboost, regardless of whether mass is increased or not.
--
JRF

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