

Why shuttle Atlantis will not be left attached to the ISS - soundsop
http://www.reddit.com/r/AskReddit/comments/fonzm/why_doesnt_nasa_leave_a_shuttle_in_orbit_attached/c1hhz90

======
Zak
It's interesting to see all the anecdotes in the reddit discussion about the
flight computer. It is variously claimed to be an 8086, to have less power
that a pocket calculator or that it could be easily replaced with a more
powerful modern computer. I'm puzzled by the fact that nobody in the thread
fact-checked these claims.

The shuttle's flight computers are, in fact five IBM AP-101s in a redundant
configuration. See <http://en.wikipedia.org/wiki/IBM_AP-101>

~~~
aperiodic
People might have that misconception due to hearing about the Apollo flight
and guidance computers, which were pretty janky. They had a really difficult
to use interface, and used core-rope memory[1] that was _woven together by old
ladies_.

[1] <http://en.wikipedia.org/wiki/Core_rope_memory>

~~~
gaius
"Janky"? You're right, they should have used Ruby on Rails. And, ermm, AJAX
2.0.

I'm sick of people slamming old tech with 50 years of hindsight. They were the
smartest people in the world doing the best work they could with what they had
available to them. And that's what they came up with - and it got the job
done.

~~~
rwmj
And those IBM mainframes are massively more reliable than the crap (software
and hardware) we use today.

------
js2
_Another reason is power. Now, a couple of years ago, they added something
called SSPS (Station to Shuttle Power System). This extended the docked
capability of the shuttle, but it is by no means a permanent solution. It
still uses a fuel cell to run some systems._

Apparently, it's SSPTS[1] and it was never retrofitted to Atlantis: _The SSPTS
also aided Discovery’s twice extended STS-133 docked mission, although STS-135
will not be able to benefit from this system, given the SSPTS is not installed
on Atlantis._ [2]

[1]
[http://en.wikipedia.org/wiki/Station_to_Shuttle_Power_System...](http://en.wikipedia.org/wiki/Station_to_Shuttle_Power_System#Station_to_shuttle_power_transfer_system)

[2] [http://www.nasaspaceflight.com/2011/05/sts-134-nasa-
managers...](http://www.nasaspaceflight.com/2011/05/sts-134-nasa-managers-
reviewing-endeavours-tps-dings)

------
bcl
I love the last point. The shuttle's computer can only count to 365 days.

~~~
bigbento
I can empathize. I've always found date-related bugs to be the hardest to
track down and messiest to resolve. Especially in applications consuming data
from a huge variety of buggy input formats ("So it's a server in Australia,
but their application layer adjusts time +36000 seconds and their durations
are listed in days, but it's daylight savings here...")

"Well, just don't fly the shuttle over New Year's" seems like a reasonable
enough workaround for an otherwise highly planned out program, especially
when, as a commenter in OP points out, the missions were only intended to run
weeks at a time to begin with.

~~~
pavel_lishin
It's a good thing there were never any emergencies on the station near the end
of December.

------
adrianwaj
Is there need for an escape vehicle? Just tethering it to the ISS in case of
an emergency could work. Who'd fly it down? Would it get damaged just sitting
in space? How long can it be left powered down awaiting an emergency so it
doesn't malfunction? How could it be accessed quickly in an emergency? How
could it be disposed-of eventually? What's the likelihood of an emergency?

~~~
Zak
The ISS keeps a Soyuz docked for use as an escape vehicle. It is very likely
better suited to that purpose than a shuttle.

See <http://en.wikipedia.org/wiki/Soyuz_(spacecraft)>

~~~
burgerbrain
Exactly. The Shuttle is so incredibly ill-suited for that task that I'd wager
the ISS would make a better escape vehicle from the Shuttle than the other way
around.

Soyuz crafts on the other hand are bloody brilliant at the job. Their modern
reentry safety record is unparalleled.

~~~
Zak
I know this was intended to be tongue in cheek, but aborting or interrupting a
shuttle mission by docking with the ISS and, if required sending the crew back
on a Soyuz or two is actually a reasonable response to certain mid-flight
emergencies.

------
JackWebbHeller
> _"The Shuttle suffers from its own Y2K problem"... "A software fix is
> possible, but it has never been worth the millions of dollars necessary to
> fix it."_

MILLIONS of dollars?!

~~~
ak217
Yes.

But I'm not sure if I understand why they would need the flight control
computers to stay on if it were to be permanently docked.

Of the reasons he listed, only the obstruction of docking ports strikes me as
valid. In any case, I think it would have been really cool if they spent a few
millions to retrofit the shuttle into a last-chance emergency crew return
vehicle (so enable avionics to survive an extended attachment to external
power). Then a few years later, if it's not needed, have it land on autopilot
in Mojave (or ditch into the Pacific if something goes wrong).

~~~
smithian
There are other reasons than the ones he listed. For instance, one reason that
the Shuttle can remain docked to the ISS without damaging the docking
connector is that the two vehicles employ their respective Reaction Control
Systems (RCS) to keep precisely in alignment. The Shuttle RCS is Hypergolic
and has limited fuel. You would need to totally redesign the system to keep
the shuttle attached to the station long term. There are lots of other reasons
as well. The Shuttle was not designed to be in orbit for more than a few
weeks. For a crew return vehicle, it would probably be a lot cheaper to finish
up an x-38 than retrofit the Shuttle. (and cheaper still to just keep doing
what we are doing now, which is use Soyuz capsules)

------
noonespecial
Last chance for the Americans to bring down any secret stuff that was on the
station?

~~~
joeyh
There does not seem to be any impediment to anyone of any nationality,
including space tourists, visiting any part of the ISS, so color me doubtful
on that theory. People do seem to avoid the cramped Russian side mostly, and
who knows what goes on socially that NASA PR hides from us.

Anyway, the US military has their own, apparently unmanned, shuttle
replacement and do plenty of launches of secret stuff on conventional rockets.
This is not surprising when you consider the relative budgets.

Disposing of the station's trash seems a large enough logistical problem that
getting one more shuttle-load out could be the real motivator. Sorta sad to
think that the last shuttle will be essentially a garbage scow on landing. At
least they didn't stuff it to the gills and send it down to burn up on
reentry, like is done with the majority of craft that dock to the ISS.

~~~
schwabacher
Do you have any more info on the military shuttle replacement? That sounds
like it could definitely provide some interesting reading

~~~
Joakal
[https://secure.wikimedia.org/wikipedia/en/wiki/Military_spac...](https://secure.wikimedia.org/wikipedia/en/wiki/Military_space_shuttle)

~~~
schwabacher
Very cool, thanks!

