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

Chris Bennetts wrote:


Zarya isn't just fitted with fuel lines, it can store a significant
amount of fuel in its own tanks. I'm not sure where they are located
on the module (probably in the 'flared' section), but they are a lot
closer to the docking port in question than the aft end of Zvezda.


On the Cosmos TKS module from which it's derived they are external.

Pat

Jorge R. Frank wrote:

The ballistic number of the current config is 166.0 kg/m^2 while flying
in XVV (normal low-beta) attitude. That's a mass/area ratio; the higher
the number, the *less* draggy the station is.

The ballistic number of the station at assembly complete will be 70.02
kg/m^2, which is considerably less draggy than the current config.

Both of those numbers are average values to account for the changing
frontal area of the rotating solar arrays.



But there's also overall station mass to contend with as far as
accelerating it goes.

It's also obvious to me that the Russians are sitting on a nice fat
propellant reserve of over 4000 kg, and that if they really felt the
need, they could boost ISS up to a 425 km circular orbit any time they
wanted to and still have nearly 1000 kg of propellant left over for
attitude control.



Did we ever determine if the propellant feed could go to the Progress
from the station, rather than the other way around?

Pat

Pat Flannery wrote in
:

But there's also overall station mass to contend with as far as
accelerating it goes.

Henry addressed that.

It's also obvious to me that the Russians are sitting on a nice fat
propellant reserve of over 4000 kg, and that if they really felt the
need, they could boost ISS up to a 425 km circular orbit any time they
wanted to and still have nearly 1000 kg of propellant left over for
attitude control.

Did we ever determine if the propellant feed could go to the Progress
from the station, rather than the other way around?

Yes, it can.

--
JRF

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check "Organization" (I am not assimilated) and
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Jorge R. Frank wrote:

The ballistic number of the station at assembly complete will be 70.02
kg/m^2, which is considerably less draggy than the current config.



Oops - got that backward; the final config is more draggy.



Yeah, I kind of thought so with all the modules sticking out at the
front end.
Of course, that the final configuration actually is seems to change from
month-to-month.

Pat

Bruce Hoult wrote:

Hold it a second! Are you saying that the total amount of Newtons of
energy to move the ISS from one orbital altitude to another is unrelated
to the total mass of the ISS to be moved? This is a simple matter of
mass to the thrust applied to it to change it's velocity, and therefore
its orbital altitude.
Double the ISS' mass and the same amount of Progress delta v only
affects its orbital velocity by one half as much.



Yes, but if you double its mass then it'll only lose half as much
altitude between reboosts.


Assuming that drag stays the same; but as Jorge pointed out, drag is
going to increase as it grows in size.

Pat

Rand Simberg wrote:


This is a simple matter of mass to the thrust applied to it to change
it's velocity, and therefore its orbital altitude.
Double the ISS' mass and the same amount of Progress delta v only
affects its orbital velocity by one half as much.


But it only has to be done half as often. The total amount of
propellant required for reboost doesn't change over time. That is a
function of drag, not mass.


But the lower you stay, the more the drag increases.

Pat

Chuck Stewart wrote:


In other words to maintain a given orbital height
for ISS you need to counteract the amount of
delta-v lost to drag with an equivalent amount of
delta-v from the engines... and the denser the
station is the *less it's affected by LEO
aerodynamic drag.*


True; it's a matter of total frontal area versus mass (the classic case
being that spherical satellite we launched for measuring the Earth's
gravity field that had the covering of retroreflectors and the depleted
uranium core)
But at the lower altitude drag increases, and if it weren't for the
desire to boost maximum mass to the ISS' orbit, a higher orbit would be
better.
What's the specific trade-off? Does not decreasing the Progress
propellant cargo load enough to let it reach a orbit ten miles higher
let it carry enough extra propellant to make it worth letting the ISS'
orbit decay down an extra ten miles?
This makes sense in relation to non-propellant related cargo, but what
about the total delta v that the added propellant load can give the ISS?

Pat

Pat Flannery wrote:


Rand Simberg wrote:


This is a simple matter of mass to the thrust applied to it to change
it's velocity, and therefore its orbital altitude.
Double the ISS' mass and the same amount of Progress delta v only
affects its orbital velocity by one half as much.



But it only has to be done half as often. The total amount of
propellant required for reboost doesn't change over time. That is a
function of drag, not mass.



But the lower you stay, the more the drag increases.

Yes, so it requires a little more boost propellant, but not twice as much.

Pat Flannery wrote in
:

Jorge R. Frank wrote:

The ballistic number of the station at assembly complete will be 70.02
kg/m^2, which is considerably less draggy than the current config.



Oops - got that backward; the final config is more draggy.



Yeah, I kind of thought so with all the modules sticking out at the
front end.

It's not the modules that make up the bulk of the area; it's the solar
arrays and radiators.

Of course, that the final configuration actually is seems to change from
month-to-month.

The only major difference in frontal area between the config I quoted above
and the "current" config is the deletion of the Russian Science Power
Platform.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Jorge R. Frank wrote:

Yeah, I kind of thought so with all the modules sticking out at the
front end.



It's not the modules that make up the bulk of the area; it's the solar
arrays and radiators.


No, looking at the huge model (one of my favorites) you can feather the
solar arrays so that the present minimal drag to the ISS as she travels
forward through space, and the radiators are put in her drag shadow.
Christ; that thing's HUGE.



Of course, that the final configuration actually is seems to change from
month-to-month.



The only major difference in frontal area between the config I quoted above
and the "current" config is the deletion of the Russian Science Power
Platform.



Again, on the Intermountain Railways model....with the implied proviso
"get ****in real".
(anyone who hasn't built that model hasn't gotten any real idea exactly
_how_ big the original ISS proposal was intended to be. I've got a Mir;
I've got two Salyuts: I've got a Skylab.... that SOB is gigantic.)

Pat