Shuttle vs ISS Orbital Debris Risk

On Thu, 04 Sep 2003 20:28:35 +0000, stmx3 wrote:

Herb Schaltegger wrote:
In article , stmx3 wrote:


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?


It could also be because ISS segments (at least U.S., Japanese and
European ones) were baselined to survive a defined orbital debris
environment as part of their Level 1 requirements. The U.S. modules
actually have a definite Meteoroid/Debris Shield (MDS) surrounding and
encompassing the pressurized elements. I don't know if the Japanese
Kibo or European Columbus modules have such a shield. They may as well.


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.

Just for fun the meteor buffer things Herb speaks of are spec'ed to
takes hits from orbital-velocity debris of up to 1 cm diameter.

The orbiter... is not.

--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying algebra?"

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?

Herb Schaltegger wrote:
In article , stmx3 wrote:


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?



It could also be because ISS segments (at least U.S., Japanese and
European ones) were baselined to survive a defined orbital debris
environment as part of their Level 1 requirements. The U.S. modules
actually have a definite Meteoroid/Debris Shield (MDS) surrounding and
encompassing the pressurized elements. I don't know if the Japanese
Kibo or European Columbus modules have such a shield. They may as well.


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.

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.

The debris/meteor shield uses the sample principle as modern tank armour:
you put part of the shielding at some distance of the hull, so that anything
that hits the object (ISS or tank) first hits and destroys part of the shield,
thereby spreading the energy of a much larger area on the hull, which can then
take the hit with no or much smaller penetration.

No way you can put something like this on the shuttle, all considerations of
weight aside.

Jan

Shuttle vs ISS Orbital Debris Risk

ISS is much larger thus more likely to be hit/ I figure t will be a small fast
moving impact that will cause the biggest problem since it cant be tracked.

Andrew Gray wrote:
In article , stmx3 wrote:

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.


It's not just that - ISS has been in constant habitation on-orbit now
for just shy of three years, and Shuttle has that much time on orbit *in
total* (give or take a few months - 113 flights at an average of ten
days is ~37mo) over twenty-two years.

ISS has a lot more time, overall, for something to hit it... it makes
sense to give it more resilience.

(... the Shuttle has, say, a ten-day mission and an overall risk of
1/200 - that's 1/2000 per day, so a 180-day ISS expedition would have a
~9% chance of an equally dangerous strike... these numbers are very
back-of-envelope & nebulous, since ISS can survive a lot of what would
give a shuttle a really bad day - it has no TPS to damage, for example,
and internal sections can be sealed - but you get the idea)


The CAIB numbers state current "per mission" risk guideline for shuttle
is 1 in 200, and cumulative risk over 113-flight history is calculated
to be 1 in 3.

The report also does state that it is the ISS's micrometeoroid and space
debris protection system which "reduces its critical penetration risk to
five percent or less over 10 years, which translates into a per-mission
risk of 1 in 1,200 with 6 flights per year, or 60 flights over 10 years."

Apparently, a pre-mission estimated risk and an actual as-flown risk
value are determined. So, for STS-107, the estimated risk was 1 in 370
while the actual value is 1 in 356. So, if that's typical for all
shuttle flights, then the 1 in 3 number is probably more like 1 in 5 or
1 in 6.

Jan C. Vorbrüggen wrote:
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.


The debris/meteor shield uses the sample principle as modern tank armour:
you put part of the shielding at some distance of the hull, so that anything
that hits the object (ISS or tank) first hits and destroys part of the shield,
thereby spreading the energy of a much larger area on the hull, which can then
take the hit with no or much smaller penetration.

No way you can put something like this on the shuttle, all considerations of
weight aside.

Jan

Ahhh...so the debris/meteor shield must be what gives rise to those
raised "puffy" panels on the various ISS elements. I remember one of
TransHabs selling points being its more robust, layered shielding.

Thanks for the info.

Shuttle vs ISS Orbital Debris Risk

ISS is much larger thus more likely to be hit/ I figure t will be a small
fast moving impact that will cause the biggest problem since it cant be
tracked.

Nonetheless, the total risk is lower for ISS because of its shield, size
notwithstanding.

It needs a seperate calculation what the most likely debris size to cause
damage would be: while smaller pieces result in less (or even no) damage to
the hull, they are more plentiful than the larger pieces.

Jan

"Jan C. Vorbrüggen" wrote in message
...
The debris/meteor shield uses the sample principle as modern tank armour:
you put part of the shielding at some distance of the hull, so that
anything
that hits the object (ISS or tank) first hits and destroys part of the
shield,
thereby spreading the energy of a much larger area on the hull, which can
then
take the hit with no or much smaller penetration.

Even if the energy of the impact is absorbed without penetrating the ISS
hull, is it possible, if hit in the right spot, for the ISS to have an
orbital change or go into a rotation? Is there an RCS on the ISS?

-- Alan

Even if the energy of the impact is absorbed without penetrating the ISS
hull, is it possible, if hit in the right spot, for the ISS to have an
orbital change or go into a rotation?

I think that's unlikely - too little total energy and momentum.

Is there an RCS on the ISS?

Several.

Jan