Shuttle vs ISS Orbital Debris Risk

On Fri, 5 Sep 2003, Alan Pretre wrote:

"Jan C. Vorbr=FCggen" wrote in message
...
Is there an RCS on the ISS?
Several.

Jan, hi.

When are they used? When does the ISS need to "maneuver"? Are the beams
sticking out, such as for solar panels, extremely rigid to avoid periodic
motion?

ISS needs to "maneuver" for a number of reasons; mostly the RCS on the
station are used to maintain attitude (for docking and holding the best
position for the station's solar arrays), desaturate the momentum
gyroscopes, raise altitude (overcoming the very slight atmospheric drag
that would cause the station to fall out of orbit), and for collison
avoidance.

And don't worry; within reason the station's truss and solar arrays are
designed to handle the loadings from dockings and thruster firings.
-Mike

stmx3 wrote in message ...
Herb Schaltegger wrote:
In article , stmx3

Ahhh...that makes sense. If this is true then it would mean the ISS
Level 1 requirement was more stringent than the shuttle's, probably in
light of weight considerations.

Thank you.

In a way it is historical, orbit debris was , of course, known before
the Orbiter was ever flown, but it was only in the 80's that a focused
program was established with NASA to study it. At JSC it grew to a
respectable set of three groups, modeling the space debris
environment, ground observations of orbit and hypervelocity impact.
These groups established very precise criteria for shielding space
craft. That is why the ISS is better shielded than the Orbiter. And
yes all components of the ISS have to meet a specific shielding
requirement.
Alas, the budget for Orbital Debris at NASA has been reduced ,
especially since the last 90's. The areas of environment modeling and
observations have really taken bad hits. In fact last year for some
reason unknown, headquarters, in the 03 budget ,Space Debris was
zeroed out!! ,for about a week , before the operations guys at JSC
realized they could no longer do that risk analysis! The whole effort
in orbit debris at Nasa is still under funded.
For instance go to:

http://orbitaldebris.jsc.nasa.gov/

There used to be a useful web page there, but they laid off the
webmaster, so its gone!

in article , Doug... at
wrote on 9/6/03 2:24 AM:

In article , says...
Hi,

I'm wondering why the shuttle orbital debris risk (or "Critical
Penetration Risk) is 1 in 200 while ISS per-mission risk is 1 in 1200.
Is it because of different orbital inclinations? Is the ISS orbiting
along a relatively clean path?

In addition to other answers (which are valid), there is also the fact
that the Shuttle is smaller than the ISS. Increase the total exposed
surface area and you increase penetration risk. Especially if your
definition of "critical penetration" is penetration into a pressurized,
inhabited space. ISS has considerably more pressurized crew space than
the Shuttle does.

I take it that your answer concerns the design requirements of ISS vs.
Shuttle. I.e. Since ISS has a larger surface area, it must be designed with
a lower CPR in mind.

Thanks for the response.

in article , Al Jackson at
wrote on 9/6/03 7:53 AM:

stmx3 wrote in message
...
Herb Schaltegger wrote:
In article , stmx3

Ahhh...that makes sense. If this is true then it would mean the ISS
Level 1 requirement was more stringent than the shuttle's, probably in
light of weight considerations.

Thank you.

In a way it is historical, orbit debris was , of course, known before
the Orbiter was ever flown, but it was only in the 80's that a focused
program was established with NASA to study it. At JSC it grew to a
respectable set of three groups, modeling the space debris
environment, ground observations of orbit and hypervelocity impact.
These groups established very precise criteria for shielding space
craft. That is why the ISS is better shielded than the Orbiter. And
yes all components of the ISS have to meet a specific shielding
requirement.
Alas, the budget for Orbital Debris at NASA has been reduced ,
especially since the last 90's. The areas of environment modeling and
observations have really taken bad hits. In fact last year for some
reason unknown, headquarters, in the 03 budget ,Space Debris was
zeroed out!! ,for about a week , before the operations guys at JSC
realized they could no longer do that risk analysis! The whole effort
in orbit debris at Nasa is still under funded.
For instance go to:

http://orbitaldebris.jsc.nasa.gov/

There used to be a useful web page there, but they laid off the
webmaster, so its gone!

All this lends credence to the complacency concerning foam strikes in the
shuttle program. I'm sure the orbital debris folks used phrases like
"accident waiting to happen" more than once.

Thanks for the info.
--
A constant crank: a crank observed |
in at least 2 separate, rational reference |
frames (aka "crank invariant") |

Doug... wrote in message ...
In article , says...
Hi,

I'm wondering why the shuttle orbital debris risk (or "Critical
Penetration Risk) is 1 in 200 while ISS per-mission risk is 1 in 1200.
Is it because of different orbital inclinations? Is the ISS orbiting
along a relatively clean path?

In addition to other answers (which are valid), there is also the fact
that the Shuttle is smaller than the ISS. Increase the total exposed
surface area and you increase penetration risk. Especially if your
definition of "critical penetration" is penetration into a pressurized,
inhabited space. ISS has considerably more pressurized crew space than
the Shuttle does.

The Orbit Debris problem was known in the 70's , but not in detail
until the late 80's.
So it is just as shielded as the ISS is.
Pressurized inhabited space is not the only components you need to
shield.
The carbon carbon leading edge , the wheel well and the fluid loop of
the radiators when the payload doors are open. See:

Protecting the Space Shuttle from Meteoroids and Orbital Debris (1997)
(ISBN 0309059887), Committee on Space Shuttle Meteoroid/Debris Risk
Management, National Research Council.

One thing, the windows of the Orbiter have a scouring 'lifetime' due
to micro particle impact, these windows have had to be replaced 2
times as often as the orbit environment model predicts, this is a
problem that has not been solved , as far as I know.

(Al Jackson) wrote in message . com...
Doug... wrote in message ...
In article , says...
Hi,

I'm wondering why the shuttle orbital debris risk (or "Critical
Penetration Risk) is 1 in 200 while ISS per-mission risk is 1 in 1200.
Is it because of different orbital inclinations? Is the ISS orbiting
along a relatively clean path?

In addition to other answers (which are valid), there is also the fact
that the Shuttle is smaller than the ISS. Increase the total exposed
surface area and you increase penetration risk. Especially if your
definition of "critical penetration" is penetration into a pressurized,
inhabited space. ISS has considerably more pressurized crew space than
the Shuttle does.

The Orbit Debris problem was known in the 70's , but not in detail
until the late 80's.
So it is just as shielded as the ISS is.

That should have read : "It is NOT as shielded as well as the ISS is."
In fact to take care of hits the Orbiter flys at special 'safe' attitudes,
which some time caused problems with various observing experiments.
At the moment, when going to the ISS and docked at the ISS some of the 'safe'
attitudes cannot be flown.
(Safe Attitude means flying with least exposure to orbital debris.)

Al Jackson wrote:
(Al Jackson) wrote in message . com...

Doug... wrote in message ...

In article , says...

Hi,

I'm wondering why the shuttle orbital debris risk (or "Critical
Penetration Risk) is 1 in 200 while ISS per-mission risk is 1 in 1200.
Is it because of different orbital inclinations? Is the ISS orbiting
along a relatively clean path?

In addition to other answers (which are valid), there is also the fact
that the Shuttle is smaller than the ISS. Increase the total exposed
surface area and you increase penetration risk. Especially if your
definition of "critical penetration" is penetration into a pressurized,
inhabited space. ISS has considerably more pressurized crew space than
the Shuttle does.

The Orbit Debris problem was known in the 70's , but not in detail
until the late 80's.
So it is just as shielded as the ISS is.


That should have read : "It is NOT as shielded as well as the ISS is."
In fact to take care of hits the Orbiter flys at special 'safe' attitudes,
which some time caused problems with various observing experiments.
At the moment, when going to the ISS and docked at the ISS some of the 'safe'
attitudes cannot be flown.
(Safe Attitude means flying with least exposure to orbital debris.)

Thanks for the clarification. I assume that's why the shuttle flies
with main engines along the velocity vector. Do you know if it is in
this attitude when docked with ISS?