EVA limits on Shuttle flights.
c.wright
Twice now since the "Columbia" tragedy I have seen
postings that say that an EVA cannot be made to "orbit" the Shuttle and
visually, at least, inspect potential lift-off damage to the tiles, for
example. I must confess I am extremely puzzled by this statement.
Why on "Earth" is this the case? Surely the MMU could be used for this,
the delta V is minimal and the duration of such an inspection is much
less than some of the HST repair missions for example.
Also I am surprised that the ISS is kept in such a low rate of supply.
Now perhaps I will have to begin to agree with those who think it is a
total waste of money.
After the expense of billions of dollars we haven't even got an
emergency shelter in orbit!!!
Lets hope that these posters were wrong and that there is some sense
left in the space programme.
Regards Cliff Wright.
Robert Dale
Hint -- the Columbia is not part of the Space Station...
> postings that say that an EVA cannot be made to "orbit" the Shuttle and
> visually, at least, inspect potential lift-off damage to the tiles, for
> example. I must confess I am extremely puzzled by this statement.
Read the FAQ posted in the shuttle newsgroup.
> Why on "Earth" is this the case? Surely the MMU could be used for this,
What MMU?
> Also I am surprised that the ISS is kept in such a low rate of supply.
6 months is a low rate? How long do you think they should stock up for?
> Now perhaps I will have to begin to agree with those who think it is a
> total waste of money.
Why?
> After the expense of billions of dollars we haven't even got an
> emergency shelter in orbit!!!
That's not the purpose of the Space Station.
- rd
LooseChanj
> Why on "Earth" is this the case? Surely the MMU could be used for this,
> the delta V is minimal and the duration of such an inspection is much
> less than some of the HST repair missions for example.
The MMU was mothballed years ago. IIRC, they decided there was no
real need for it.
> Also I am surprised that the ISS is kept in such a low rate of supply.
> Now perhaps I will have to begin to agree with those who think it is a
> total waste of money.
Why? Because it's not stocked to the gills every other day or two
like your local supermarket? Well, it's *not* your local supermarket.
It costs a hell of a lot more to get supplies to it, so it is quite
understandable that only what is absolutely necessary is sent. And
they're not on a 5 year mission either.
> After the expense of billions of dollars we haven't even got an
> emergency shelter in orbit!!!
Compare how much is spent on other things. IMO, it's remarkable we've
got as much as we do!
> Lets hope that these posters were wrong and that there is some sense
> left in the space programme.
Oh, that's almost certain. Both that alot of posters are wrong and that
there's *some* sense left in the space program. If armchair quarterbacking
is difficult to be accurate, how much more so something as intricate as
space travel? Think about what you do, and how many misconceptions there
are about it.
Even if you flip burgers for a living you can relate.
--
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Chris Bennetts
"c.wright" <c.wr...@auckland.ac.nz> wrote in message
news:3E3F322F...@auckland.ac.nz...
> Surely the MMU could be used for this,
The last MMU flight appears to be STS-51A in *November* *1984*, the 14th
flight of the shuttle.
> Also I am surprised that the ISS is kept in such a low rate of supply.
> Now perhaps I will have to begin to agree with those who think it is a
> total waste of money.
???
> After the expense of billions of dollars we haven't even got an
> emergency shelter in orbit!!!
The problem is, you would need several emergency shelters in different
orbits. Since they would be in low earth orbit, they would need regular
reboosting, and maintenance would need to be performed on their systems.
This would require many shuttle missions just to keep the emergency shelters
in operation. It is simply not feasible.
--Chris
c.wright
Chris Bennetts wrote:
Cor!!
Now after these "flames", I'd better explain my position.
1. I am "fanatically" in favour of manned space flight, and space flight in
general. Noone of my acquaintance would ever consider me a "Luddite". I have
spent most of my life in scientific research and semiconductor engineering.
2. As and "oldie" I am obviously out of date. From photos I had seen on recent
HST refurbishing missions I had understood that manned manoevering units or some
improvement thereon were still in use, perhaps NASA has been expending its
budgets on new acronyms!
3. I am an amateur astronomer of 49 years experience and have a reasonable
qualitative grasp of orbital dynamics, dating back to Sputnik 1. So I don't
think my suggestions were either trivial or totally uninformed. Often time can
be traded for reaction mass when an orbital change is required for example. As
to needing many space stations in low orbit, a little maths shows me that the
amount of fuel needed for orbital change is trivial. If it isn't then the
shuttle is being run so near its limits that it is truly a "death trap".
4. Supply on the ISS. Since the "Columbia" another Proton supply craft has
reached the ISS with more supplies, so where is the problem there? Incidentally
our local media reporting NASA officials seems to show that all sorts of excuses
are being made about the ISS option.
I'm afraid that I'd have to have a lot of data about fuel on this flight, space
suit characteristics,
and EVA difficulties before my mind is even slightly at rest on these points.
What I'd like to see is facts rather than flames.
5. I fully understand that the ISS's orbit is so low that orbital decay requires
that it be boosted from time to time. This has NO bearing whatever on its use as
a temporary refuge for stranded astronauts. Ultimately of course if the shuttle
is not available it could in the worst case become the most expensive man made
meteor in history, but that depends on many factors.
Finally no one answered my question regarding EVA! Once again I ask, will
someone please inform myself and others, why it is allegedly impossible to
inspect the exterior of the orbiter while in orbit. As I remember several early
shuttle flights carried out such inspections when technology was 20 years older!
I hope that I have made myself clearer this time, and get some useful replies.
Regards Cliff Wright.
Chris Bennetts
> 2. As and "oldie" I am obviously out of date. From photos I had seen on
recent
> HST refurbishing missions I had understood that manned manoevering units
or some
> improvement thereon were still in use, perhaps NASA has been expending its
> budgets on new acronyms!
NASA has introduced devices called SAFERs (Simplified Aid For EVA Rescue) in
recent years, for use on station missions. They provide a limited propulsive
capability to allow an astronaut that had become untethered to make their
way back to the station, since the station (or a shuttle docked to the
station) can't go after them, an option that is available on non-docking
missions. They weren't carried on this flight, and I don't think they've
been used on HST flights either. They are completely different to the MMUs.
[snip]
> a little maths shows me that the
> amount of fuel needed for orbital change is trivial. If it isn't then the
> shuttle is being run so near its limits that it is truly a "death trap".
It's not trivial at all. I'm not sure whether his calculations are accurate,
but David Findlay just posted on sci.space.shuttle(Subject: How much energy
required to reach ISS from STS-107's orbit) his results for required
velocity change to get from STS-107's orbit to the ISS's orbit. He came up
with 15.6km/s. By contrast, the total normal orbital velocity in these
orbits is about 7.8km/s, and the shuttle uses SRBs and all of the fuel in
the ET to achieve that.
> 4. Supply on the ISS. Since the "Columbia" another Proton supply craft has
> reached the ISS with more supplies, so where is the problem there?
Progress can only do so much. It can carry much less cargo than the shuttle,
and there are only three or four launches per year. The station can't
survive without the shuttle.
> 5. I fully understand that the ISS's orbit is so low that orbital decay
requires
> that it be boosted from time to time. This has NO bearing whatever on its
use as
> a temporary refuge for stranded astronauts. Ultimately of course if the
shuttle
> is not available it could in the worst case become the most expensive man
made
> meteor in history, but that depends on many factors.
You're right, it doesn't, but I don't think anyone said that orbital decay
of the station was the reason that Columbia's crew couldn't take refuge
there. Both myself and others were saying that the capacity of the station's
life support system, the lack of a docking port in Columbia on this flight,
and the huge orbit change were the things that prevented going to the
station.
> Finally no one answered my question regarding EVA! Once again I ask, will
> someone please inform myself and others, why it is allegedly impossible to
> inspect the exterior of the orbiter while in orbit. As I remember several
early
> shuttle flights carried out such inspections when technology was 20 years
older!
I don't think that such inspections were ever carried out. Outside the
payload bay, there are no handholds for the astronauts to get around with,
and if they were installed prior to a launch, they wouldn't last long,
probably falling off during launch (and damaging tiles as they fell).
--Chris
Brian Thorn
<c.wr...@auckland.ac.nz> wrote:
>2. As and "oldie" I am obviously out of date. From photos I had seen on recent
>HST refurbishing missions I had understood that manned manoevering units or some
>improvement thereon were still in use, perhaps NASA has been expending its
>budgets on new acronyms!
It is called SAFER (Simplified Aid for EVA Rescue) and has a very
limited fuel life. It is meant to get an astronaut back to the Space
Station if his/her tether breaks (which happened once to a cosmonaut
on Russia's Mir space station, fortunately, his spacewalking partner
grabbed him.)
>3. I am an amateur astronomer of 49 years experience and have a reasonable
>qualitative grasp of orbital dynamics, dating back to Sputnik 1. So I don't
>think my suggestions were either trivial or totally uninformed. Often time can
>be traded for reaction mass when an orbital change is required for example. As
>to needing many space stations in low orbit, a little maths shows me that the
>amount of fuel needed for orbital change is trivial.
Orbital change in altitude requires little propellant, yes (although
the amount is not trivial for a move from Columbia's 140-or-so miles
to Space Station's 250 miles). But that is not the issue for moving
Columbia to the Space Station. For that, Columbia would have needed to
change its orbital inclination (move from 39 degrees to a 51.6 degree
orbit.) The fuel requirements to accomplish that are nearly as much as
for the original launch itself. Columbia had a tiny fraction of the
propellant necessary.
>If it isn't then the
>shuttle is being run so near its limits that it is truly a "death trap".
Columbia was flown well within the limits needed to complete its
mission. Something were disastrously wrong. End of story.
>4. Supply on the ISS. Since the "Columbia" another Proton supply craft has
>reached the ISS with more supplies, so where is the problem there? Incidentally
>our local media reporting NASA officials seems to show that all sorts of excuses
>are being made about the ISS option.
Those excuses being called "the laws of physics".
>I'm afraid that I'd have to have a lot of data about fuel on this flight, space
>suit characteristics,
>and EVA difficulties before my mind is even slightly at rest on these points.
>What I'd like to see is facts rather than flames.
You do seem to have an honest interest in this matter, however please
note that the sci.space newsgroups have been flooded with cranks since
the disaster. Honest questions are quickly lost in the noise.
>5. I fully understand that the ISS's orbit is so low that orbital decay requires
>that it be boosted from time to time. This has NO bearing whatever on its use as
>a temporary refuge for stranded astronauts.
Correct, the incompatible orbital inclinations outweigh all other
arguments about diverting Columbia to the Space Station. Although I
believe it is also true that Columbia did not carry enough propellant
to raise its orbit from 140 to 250 miles even if it had been in the
same plane as the Space Station.
>Finally no one answered my question regarding EVA! Once again I ask, will
>someone please inform myself and others, why it is allegedly impossible to
>inspect the exterior of the orbiter while in orbit. As I remember several early
>shuttle flights carried out such inspections when technology was 20 years older!
No, spacewalkers have never travelled beneath the Space Shuttle,
they've always stayed within line-of-sight from the Shuttle's payload
bay or overhead windows, for safety reasons.
EVA under the Shuttle to inspect the tiles is not possible because the
maneuvering backpacks were not available on this flight (they're only
needed on the Space Station... where a Shuttle cannot quickly undock
to go get a drifting astronaut.) Columbia also did not have the robot
arm on this flight (it wasn't needed to accomplish the mission) and
the robot arm doesn't have the freedom of movement necessary to reach
under the Shuttle. Without the backpack, there is no way for an
astronaut to control his/herself under the Shuttle. There are no
handholds on the outside of the Space Shuttle.
Even if they did have handholds down there, Columbia did not carry a
tile repair kit... no Shuttle has since 1981.
Brian
JF Mezei
> 4. Supply on the ISS. Since the "Columbia" another Proton supply craft has
> reached the ISS with more supplies, so where is the problem there?
Last Proton that was used was to bring Zvezda. It was a Progress vehicle that
docked to the station, it was launched by a much less powerful Soyuz rocket.
The Soyuz rocket, used to launch Progress cargo and Soyuz crew capsule is a
relatively small rocket.
Progress is a very versatile cargo ship. Very neat. But its capacity is
limited and you need more Progress the are currently sent to keep the station
running. The current schedule of Progress assumed a certain number of shuttles
(reboost+water) and MPLMs (supplies) each year.
So the question becomes: Can Russia increase its Progress production quickly
enough to keep the station manned. Folks would have to act quickly on this in
ternms of releasing funds to get things moving. Progress vessels and Soyuz
rockets aren't built overnight.
> 5. I fully understand that the ISS's orbit is so low that orbital decay requires
> that it be boosted from time to time. This has NO bearing whatever on its use as
> a temporary refuge for stranded astronauts.
That is correct. Orbital mechanics and lack of fuel are what prevented
Columbia from going to ISS.
> Finally no one answered my question regarding EVA! Once again I ask, will
> someone please inform myself and others, why it is allegedly impossible to
> inspect the exterior of the orbiter while in orbit.
EVA suits only have an emergency "get back to ship" mini thrusters (SAFER).
For main manoeuvrability, the astronaut needs to hold on to something, or he
will drift into space and/or not be able to turn a screwdriver or press a tile
into place since the action of pushing a tile into place would push him away
from the shuttle. There is also the question of the astronaut banging into the
tiles, causing more damage to the tiles.
There may be ways to develop systems, ropes, booms etc in conjunction with the
arm to allow crewmembers to move to the side and under the shuttle. Given a
mandate, I am sure they can find a way. But right now, there really are no
mobility aids to allow one to safely go under the shuttle.
JF Mezei
> The station can't survive without the shuttle.
I'd say that loss of Progress at this point in station life would be more
problematic than loss of Shuttle.
Shuttle does provide good reboosts and brings lots of water and experiments.
But it is unable to transfer fuel to the station fuel tanks which serve for
attitude control and reboost when Progress s not present. (attitude control is
normally done by the US CMGs, but from time to time they need to fire the
thrusters to desaturate the CMGs, and should another CMG fail, (one has
already failed and was due to be sent up on next shuttle), the thrusters will
be needed much more.
Chris Bennetts
"JF Mezei" <jfmezei...@vl.videotron.ca> wrote in message
news:3E407A33...@vl.videotron.ca...
> Chris Bennetts wrote:
> > The station can't survive without the shuttle.
>
> I'd say that loss of Progress at this point in station life would be more
> problematic than loss of Shuttle.
[Snip good, valid argument.]
Okay, I'll rephrase. Progress or ATVs are required to keep the ISS in orbit,
and the station can't remain in a stable orbit in a stable attitude without
them (unless a shuttle is handy every time you need to desaturate the CMGs,
but docking a shuttle requires use of the station's fuel anyway). If you
want to maintain a crew or worthwhile science, then the space shuttle
becomes almost essential.
--Chris
c.wright
Brian Thorn wrote:
Good Day Brian.
Many thanks for the most informative reply. I really must
do the calculations properly some time about changing orbital inclination. Your
figures were a great surprise to me, I must admit.
I did find it ironical however about full orbital inspections of the shuttle being
discouraged because of "risk factors", to me common sense suggests that the risk to
one astronaut which with the correct equipment seems to me to be quite acceptable is
totally outweighed by the deaths of the entire crew and the loss of an orbiter and
all its scientific data.
It is understood that the lower surface can have no attachment points, but how would
this prevent a visual inspection of any suspected damage?
Perhaps the real problem is that without a backup for rescue of the crew and orbiter
"ignorance is bliss" and chances are taken. Its just that this time it did not work
out well.
BTW do you happen to know why the tile repair kit was dropped? I understand that the
orbiters tiles are individual, but modern refractories should make some kind of
ablative patch for 1 emergency reentry possible
Best regards Cliff Wright..
Neil Gerace
"Brian Thorn" <brian...@yahoo.com> wrote in message
news:r4p04v87jfndv4saq...@4ax.com...
> Columbia was flown well within the limits needed to complete its
> mission. Something were disastrously wrong. End of story.
Shuttles and other spacecraft are always flown close to their limits. If the
limits were set higher, further away from the realm of normal flight, like
an airliner's are, the shuttle would be way too expensive to build, and way
too heavy to launch.
rgds
Neil