RFI: Calculated orbital decay rate of an unbooster ISS?

....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.

OM
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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

On Wed, 18 Jun 2008 02:43:25 -0500, Pat Flannery
wrote:

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.

....And then there's the 11-year cycle to contend with, which is what
helped kill Skylab early *and* helped kill CB Radio when the fad
finally started to decline thanks to all the skip killing local
traffic.

....So what do you say, Jorge? Worst case being ~160 days, then?

OM
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] OMBlog - http://www.io.com/~o_m/omworld [
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] an obnoxious opinion in your day! [
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OM wrote:
On Wed, 18 Jun 2008 02:43:25 -0500, Pat Flannery
wrote:

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.

...And then there's the 11-year cycle to contend with, which is what
helped kill Skylab early *and* helped kill CB Radio when the fad
finally started to decline thanks to all the skip killing local
traffic.

...So what do you say, Jorge? Worst case being ~160 days, then?

No, 180. The altitude is varied to keep the predicted lifetime above the
minimum. The heavyweight shuttle assembly flights have coincided with
the solar minimum allowing ISS to fly at a lower altitude. ISS will
gradually be boosted back up as the shuttle program ends and the next
solar maximum approaches. It may surprise you to learn that NASA has
improved their solar flux models in the (almost) three solar cycles
since the Skylab reentry.

"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.

h (Rand Simberg) writes:

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

Once the shuttle no longer visits, has there been any thought of raising the orbit to reduce drag?

Lou Scheffer

On 25 Jun 2008 15:33:35 -0800, in a place far, far away, Louis
Scheffer made the phosphor on my monitor glow in
such a way as to indicate that:

(Rand Simberg) writes:

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

Once the shuttle no longer visits, has there been any thought of raising the orbit to reduce drag?

Good question. Probably not.

But maybe Jorge knows otherwise.

Louis Scheffer wrote:
h (Rand Simberg) writes:

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

Once the shuttle no longer visits, has there been any thought of raising the orbit to reduce drag?

Already answered earlier in the thread:

"ISS will gradually be boosted back up as the shuttle program ends and
the next solar maximum approaches."