RFI: Calculated orbital decay rate of an unbooster ISS?

Brian Thorn wrote:

Yes, but ion thrusters have miniscule thrust. At ISS's altitude, you'd
need many of them just to counteract the atmospheric drag. Ion
thrusters are power hungry, so you'd need more solar panels (the ISS's
panels are already spoken-for)

Considering the station will end up smaller than originally anticipated,
isn't there spare power to be had from the arrays ? Or is that spare
going to be consumed by the russian segment because their own solar
"tower" is still vapourware ?




And as Jorge noted, all this would have to be wired to the Russian end
of the Station (the US propulsion segments S2 and P2 were never built
and cannot be added now).


Actually, couldn't engines be added to the truss segment ? The end of
the truss doesn't look too strong, so perhaps the engines could be hung
under the truss like a jet engine under a wing. Yes, it would require
some form of articulation so its exhaust would be "aft" no matter what
orientation the station would have.


From a structural point of view, since drag is being produced by the
arrays on the truss, having ion engines on the truss would eliminate the
torque issue of having an engine on Zvezda pushing the whole stack.


How narrow is the "exhaust" of ion engines ? is it very focused ? If so,
the engines would be far enough from the station modules and that
wouldn't be an issue. They would just have to build an engine "pylon"
that would put the engine
fare enough below the solar panels that would be aft of engine so that
the exhaust doesn't affect the panels.

On Sat, 28 Jun 2008 01:58:45 -0400, John Doe wrote:

Yes, but ion thrusters have miniscule thrust. At ISS's altitude, you'd
need many of them just to counteract the atmospheric drag. Ion
thrusters are power hungry, so you'd need more solar panels (the ISS's
panels are already spoken-for)

Considering the station will end up smaller than originally anticipated,
isn't there spare power to be had from the arrays ? Or is that spare
going to be consumed by the russian segment because their own solar
"tower" is still vapourware ?

It seems not, given that NASA is worried about not having enough power
for JEM Exposed Facility next year if the starboard SARJ is inop, and
after JEM EF we still add Node 3 and Russia's new
whatever-its-called-this-week module, which also need US power.
There's going to be some excess power (power intended for the
abandoned Hab and CAM will now go to the Russian Segment) but not
nearly enough to feed an ion thruster array.

Last I heard the Russian power module was cancelled.

And as Jorge noted, all this would have to be wired to the Russian end
of the Station (the US propulsion segments S2 and P2 were never built
and cannot be added now).


Actually, couldn't engines be added to the truss segment ? The end of
the truss doesn't look too strong, so perhaps the engines could be hung
under the truss like a jet engine under a wing.

They'd interfere with the radiators. S2/P2 would have provided
clearance in a segment between the radiators and the arrays.

Brian

Brian Thorn wrote:
On Sat, 28 Jun 2008 01:58:45 -0400, John Doe wrote:

Yes, but ion thrusters have miniscule thrust. At ISS's altitude, you'd
need many of them just to counteract the atmospheric drag. Ion
thrusters are power hungry, so you'd need more solar panels (the ISS's
panels are already spoken-for)
Considering the station will end up smaller than originally anticipated,
isn't there spare power to be had from the arrays ? Or is that spare
going to be consumed by the russian segment because their own solar
"tower" is still vapourware ?

It seems not, given that NASA is worried about not having enough power
for JEM Exposed Facility next year if the starboard SARJ is inop, and
after JEM EF we still add Node 3 and Russia's new
whatever-its-called-this-week module, which also need US power.
There's going to be some excess power (power intended for the
abandoned Hab and CAM will now go to the Russian Segment) but not
nearly enough to feed an ion thruster array.

Agreed on the CAM, situation with the hab is not nearly as clear-cut.
Modules themselves consume little power - mostly shell heaters and the
like. The bulk of the power is consumed by the racks they contain, and
the hab racks will still be on ISS, just scattered across multiple
modules. So the excess power is not that which was needed by the hab
racks, but that needed by the racks that have now been displaced by the
hab racks.

"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.

Actually, the reboost energy only depends on the drag over time.

The mass of the station impacts how often you have to reboost. For a given
mass, a lighter station means more reboosts, but it takes less energy to do
each of the reboosts. A heavier station means fewer reboosts, but an
indiviual reboost takes more energy. However, over time, the mass of the
station does not impact the total energy needed to maintain the 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.

You mean ATV. Jules Verne was the name of the first ATV.

It's possible that COTS providers will help here as well, but I wouldn't
hold my breath. With NASA pushing hard for Ares I and Orion, they've got a
ready made solution for ISS visits. The strategy is that you sell Ares I
and Orion as a necessary replacement for the shuttle, which gets you part
way to developing Ares V for lunar missions (i.e. the J-2X engine and 5
segment SRB both get developed). But this strategy also puts Ares I/Orion
in (long term) direct competition with potential COTS providers.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

In sci.space.history message ,
Tue, 1 Jul 2008 09:44:15, Jeff Findley
posted:

The mass of the station impacts how often you have to reboost. For a given
mass, a lighter station means more reboosts, but it takes less energy to do
each of the reboosts. A heavier station means fewer reboosts, but an
indiviual reboost takes more energy. However, over time, the mass of the
station does not impact the total energy needed to maintain the orbit.


To first order only. For a given loss of energy, a heavier Station will
sink into higher-drag regions by a smaller amount.

--
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Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
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"Dr J R Stockton" wrote in message
news
In sci.space.history message ,
Tue, 1 Jul 2008 09:44:15, Jeff Findley
posted:
The mass of the station impacts how often you have to reboost. For a
given
mass, a lighter station means more reboosts, but it takes less energy to
do
each of the reboosts. A heavier station means fewer reboosts, but an
indiviual reboost takes more energy. However, over time, the mass of the
station does not impact the total energy needed to maintain the orbit.

To first order only. For a given loss of energy, a heavier Station will
sink into higher-drag regions by a smaller amount.

Since reboosts are somewhat spaced out in time to provide for extended
periods of microgravity, this is an excellent point.

Jeff
--
A clever person solves a problem.
A wise person avoids it. -- Einstein

On Jul 3, 1:26*am, "Jeff Findley" wrote:
"Dr J R Stockton" wrote in

To first order only. *For a given loss of energy, a heavier Station will
sink into higher-drag regions by a smaller amount.

Since reboosts are somewhat spaced out in time to provide for extended
periods of microgravity, this is an excellent point.

Also a heavier station won't necessarily need proportionally larger
solar panels, which means drag per kg will be lower.