RFI: Calculated orbital decay rate of an unbooster ISS?

OM wrote:
...Has anyone done any estimates of roughly how long ISS could remain
in orbit without any boosts from the Shuttle, Soyuz or Progress
resupply missions? The issue has come up over on a BSG group, and I
actually haven't been able to find anything on the NASA sites about
this.

Depends on where the station is within the reboost cycle, but IIRC it's
a minimum of 180 days.

Jorge R. Frank wrote:

Depends on where the station is within the reboost cycle, but IIRC
it's a minimum of 180 days.

Once all eight solar panels are on it (there are six on it now), its
drag goes up, and it takes more reboosts to maintain altitude.
Mass also increases with the new modules that are being added to it, and
that doesn't help either with the reboost energy needed to maintain it
in orbit.
It was designed to use the Shuttle OMS burns to lift its orbit on fairly
frequent visits to it, and without further Shuttle missions to the ISS
after its retirement, it's going to be a bit hard-pressed to keep it
from reentering, as Progress cargo loads will need to be cut to give
them enough reboost fuel.
ESA's Jules Verne may be the only thing that keeps it viable in this
regard after Shuttle retirement.

Pat

"Pat Flannery" wrote in message
one...


Jorge R. Frank wrote:

Depends on where the station is within the reboost cycle, but IIRC it's a
minimum of 180 days.

Once all eight solar panels are on it (there are six on it now), its drag
goes up, and it takes more reboosts to maintain altitude.
Mass also increases with the new modules that are being added to it, and
that doesn't help either with the reboost energy needed to maintain it in
orbit.


True, but higher density helps reduce the decay rate.


It was designed to use the Shuttle OMS burns to lift its orbit on fairly
frequent visits to it, and without further Shuttle missions to the ISS
after its retirement, it's going to be a bit hard-pressed to keep it from
reentering, as Progress cargo loads will need to be cut to give them
enough reboost fuel.
ESA's Jules Verne may be the only thing that keeps it viable in this
regard after Shuttle retirement.

Pat



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On Wed, 18 Jun 2008 02:43:25 -0500, in a place far, far away, Pat
Flannery made the phosphor on my monitor glow in
such a way as to indicate that:



Jorge R. Frank wrote:

Depends on where the station is within the reboost cycle, but IIRC
it's a minimum of 180 days.

Once all eight solar panels are on it (there are six on it now), its
drag goes up, and it takes more reboosts to maintain altitude.
Mass also increases with the new modules that are being added to it, and
that doesn't help either with the reboost energy needed to maintain it
in orbit.

No, but more mass reduces the number of reboosts needed.

On Jun 18, 3:43*am, Pat Flannery wrote:
Jorge R. Frank wrote:


It was designed to use the Shuttle OMS burns to lift its orbit on fairly
frequent visits to it, and without further Shuttle missions to the ISS
after its retirement, it's going to be a bit hard-pressed to keep it
from reentering, as Progress cargo loads will need to be cut to give
them enough reboost fuel.
ESA's Jules Verne may be the only thing that keeps it viable in this
regard after Shuttle retirement.

Pat

Incorrect. The shuttle OMS has never been used to reboost the ISS,
nor was the ISS designed for it. The shuttle SOMETIMES does an RCS
reboost when it has surplus propellant. The ISS was designed to be
reboosted by Progress provided propellant from the beginning with the
Progress or the SM engines being used. The ATV flights are a bonus,
they do reduce the number of progress flights but the ISS could
survive without them
BTW, ATV is the ESA's resupply vehicle, Jules Verne is just the name
of the first one.

Jorge R. Frank wrote:

Depends on where the station is within the reboost cycle, but IIRC it's
a minimum of 180 days.


Does this mean that in worse case scenario, the ISS would burn up 180
days after the last reboost ?

Or is this more of a case that with more than 180 days between reboosts,
the amount of delta V needed to bring it back to a normal orbit would
exceed a single Progress/Shuttle's reboost capability ?

On Jun 18, 5:28 pm, John Doe wrote:

Does this mean that in worse case scenario, the ISS would burn up 180
days after the last reboost ?


You can get an idea of ISS orbital decay between reboosts by looking
at the "Height of the ISS - how does it vary with time" graph in
http://www.heavens-above.com/

See also http://ccar.colorado.edu/asen5050/pr...ons/Image2.gif
for a longer-term picture.

wrote:
can get an idea of ISS orbital decay between reboosts by looking
at the "Height of the ISS - how does it vary with time" graph in
http://www.heavens-above.com/

At what altitude would the ISS be considered to be re-entering ? How is
this altitude defined ? When there is enough drag to start ripping the
solar arrays apart ? When there is noticeable heating on the skin ?

Based on the graph above, basically drops by 10km altitude in close to
3.5 months.

I assume that the rate of decay would increase as the altitude goes
down. So dropping from 334 to 324 would take less than 3.5 months.

On Jun 19, 10:28 am, John Doe wrote:

I assume that the rate of decay would increase as the altitude goes
down. So dropping from 334 to 324 would take less than 3.5 months.

Yes, but as you say, the decay rate goes up as the altitude decreases.
There's a strong dependency on the solar cycle, but in general
altitudes in the 250-300 km range are getting parlously low.

See
http://www.ips.gov.au/Educational/1/3/8
and
http://www.seva.net/reg/satellite/no...y/image001.gif

wrote:
It was designed to use the Shuttle OMS burns to lift its orbit on fairly
frequent visits to it, and without further Shuttle missions to the ISS
after its retirement, it's going to be a bit hard-pressed to keep it
from reentering, as Progress cargo loads will need to be cut to give
them enough reboost fuel.
ESA's Jules Verne may be the only thing that keeps it viable in this
regard after Shuttle retirement.

Pat


Incorrect. The shuttle OMS has never been used to reboost the ISS,
nor was the ISS designed for it. The shuttle SOMETIMES does an RCS
reboost when it has surplus propellant. The ISS was designed to be
reboosted by Progress provided propellant from the beginning with the
Progress or the SM engines being used. The ATV flights are a bonus,
they do reduce the number of progress flights but the ISS could
survive without them


My bad.
I should have thought about the OMS engines - they would be too powerful
given the way the Shuttle is docked to the station.
Are the front or rear (or both) thruster groups used when the orbit is
boosted?
There is a updated ISS orbital height graph he
http://www.heavens-above.com/IssHeig...alt=0&t z=CET
It doesn't appear to have gotten a boost from the last Shuttle mission.
That website has a lot of info for satellite trackers:
http://www.heavens-above.com/
Although I still think that the NASA real-time J-Track 3D is the most
fun, as it turns your monitor into something like Space Command would
have: http://science.nasa.gov/Realtime/jtr.../JTrack3d.html
FEDSAT is getting ready to pass overhead.

BTW, ATV is the ESA's resupply vehicle, Jules Verne is just the name
of the first one.


What will the next ones be named? Any list out there?
If they are all science fiction related, I imagine Cyrano de Bergerac
and H.G. Wells can't be far behind.

Pat