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.
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.
"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.
Which made for hellishly long compile times. Core-rope memory was used because of the weight and volume savings. On Apollo every pound counted. If you look at the Wikipedia article you find a link to HAL/S which used to program the shuttle computers. A similar language (the same?) was used to program the Apollo computers and I believe the ground support computers. I do remember finding 3 punched cards per statement to be a bit bizarre. Yes, I was there at MIT Instrumentation Lab, but some of the details have become hazy. :-)
Edit: The compile times for core-rope memory were pretty long, so there were lots and lots of simulations. Going to core was an infrequent occurrence. The computers had a small amount of conventional core so that patches could be applied. Bug fixes half way to the moon were possible.
Perhaps some of the confusion comes from stories at the time that shuttle crews started carrying 486 (IIRC) laptops to "augment" the guidance computers. I dont think they were used in flight control, more likely for other routine tasks.
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]
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.
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?
Two Soyuz, actually. They need two because the ISS now has a six person crew and one Soyuz has only space for three people.
Using the Space Shuttle would also not be practical because you can’t swap it out. Those Soyuz don’t stay permanently attached to the ISS, they are swapped out whenever a new Soyuz arrives (every few months). The Soyuz spacecraft is only rated for six months in space (the Space Shuttle is likely rated for much, much less time).
Two Soyuz, actually. They need two because the ISS now has a six person crew and one Soyuz has only space for three people.
Also, I had no idea until just now that each seat is for a specific person, because the Soyuz seat is custom-fitted for its user to protect them against the forces involved.
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.
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.
Yeah. The problem is, for every joke you post somebody will have a counter-thrust they just have to post. I can't reply to every point. I don't have the breadth of knowledge. But I can and will reply to every joke, and there's hundreds of geeks just like me ;)
Then every thread goes: Point, counter-point, joke, counter-joke, counter-counter-joke, "touche", guy who didn't get the joke, "whoosh", and then troll-war over how the site is becoming slashdot.
I've always found that slashdot's moderation system does a great job of handling that particular problem by allowing users to be modded "funny" in particular, making it not count for anything, and allowing users to add a moderation modifier to "funny" moderations (so you can redefine a +1 Funny to be effectively -1 Funny, if you wish).
> "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."
Well, if it's a mission critical system with millions of lines of code that need inspecting by highly trained engineers, I don't think that's so far fetched. Some Y2K problems might require significant refactoring. Then pile on code auditing & certification before it can go back into production systems.
There were some comments here just a few days ago about NASA software:
The downside is that every change is prohibitively expensive. I didn't bookmark the article but remember to have read that the astronauts are taught lots of rules like "if the computer displays x and y, this means that z", stuff that would usually be a simple software feature. The new year bug seems to be quite similar.
I imagine for something like the shuttle, there would need to be an awful lot of testing to ensure nothing goes wrong. If a lot of systems rely on the Date code, they all need to be tested.
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).
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)
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.
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