Ahh...good thought, but not the case here.

This area isn't chilled down until fuel loading begins, and I believe that is just done by sending LH2, or possibly a brief helium purge, through at low volumes for a while...I think only 30 minutes. Then they just pumping it in at full volume until its full. I guess that's slow enough that thermal stresses aren't an issue, and contraction is dealt with in the design. The main concern is boiloff, but the thermal mass of the fuel is far greater than that of the tank, and the fuel is kept topped off until just a few seconds before launch. At the time when fueling begins, there's no access to the external tank, so I know for certain that no retorquing is done then.

Maybe it has something to do with cooldown times for components exposed to liquid hydrogen at -423 F.

According to a Mission Management Team memo (not officially published, but there happen to be a couple outlets good at getting details), it's torquing issue. Here's the specific quote I was referencing:

In the reinstallation of the flight seal, there is a 30 hour retorque requirement, that pushes us to a Monday launch. The team is looking to examine if there is some wiggle room in the 30 hr torque requirement, then we could potentially get a Sunday launch attempt.

Cooldown is part of the overall filling process and done during the countdown at T-6 hours. It lasts about two hours.

This mission was originally supposed to launch February 12. I know, because I bought tickets to go see it, and I ended up missing (KSC still makes for a great vacation though).

They got within a week or two of launch, and decided they still weren't happy with the analysis that had been conducted for troubleshooting an issue with the propellant lines that cropped up during Endeavor's STS-126 launch. A valve on a secondary fuel handling line had failed, and while it didn't appear to affect that flight there was concern that it would either result in metal particles from the valve causing issues downstream, or lead to excess hydrogen venting that could cause a fire. They spent the last month testing and quantifying the probability of these concerns, and figuring out additional safeguards to implement for this flight, since making new valves would be an additional two months.

The next possible launch window is about 23:30 after this one, but apparently the expected resolution for the leak is a multi-day process. The launch is now scheduled for no-earlier-than Mar 15 (19:43 EDT), but Mar 16 (19:21 EDT) sounds likely. As I understand it, re-installing the ground support hydrogen line on external tank requires a 30 hour waiting period before applying the final torque to allow the seals to compress...a typical factor when working with torque specs on plastic components. That 30 hours is on top of the time to demate and remate the hydrogen line, do leak checks, and reset to the proper point in the countdown.

Anyway, because they're working against a launch window before the next Soyuz launches to the station, they're losing at least one mission day, and if it slips to the 16th, they'll be losing another day, plus one EVA. That will mean they can get the last solar array installed, but not fully hooked up. I'm not sure if that EVA would be handed off to a future shuttle mission, or if it could be fit into the station crew's schedule. If the launch happens after Mar. 16, they'll have to wait until after the Soyuz mission.

There's a briefing going on regarding all this right now on NASA TV.

In a polar orbit like OCO would have been in, the satellite would regularly cover the entire earth's surface. The rovers had an expected range of a few hundred meters. Even the amazing dozen kilometers they've covered over their extended missions leaves each still within the major geological features they landed in.

The insurance policy of having a second rover for moderate (not minimal) cost was one factor. I think it increased the costs by about 25%, and put considerable extra strain on the team to get the second unit built in time for the launch window. Launch cost alone was an extra 10% or so.

The other factor was that a second rover allowed them to conduct similar studies of a much different location on Mars, giving the scientists good comparisons of very different geographies. It turned out to be a good thing, too. Opportunity, which landed second, has arguably accomplished much more than Spirit, in large part due to its location. That's not to say that Spirit hasn't also been extremely successful, but Opportunity has tended to steal the spotlight since day 1.

A second copy of OCO would have been producing nearly identical data as the first. Given that this mission was already under pressure just from politics, spending extra money to build a complete spare was unlikely.

However, NASA still has the design work done. We'll have to see if they decide to build a replacement, or simply settle for data from the related Japanese Greenhouse Gasses Observing Satellite launched last month.

The missions back in those "good old days" of space travel were much simpler both in scope, technical complexity, and duration. The longest of the Mariner missions, for example, was about 8 months, and it was only collecting data for a small fraction of that. We've already learned most of what we can (or at least what we can justify the cost of a launch for) with those simpler missions. This new Europa mission is going to be big. Even in physical size it will dwarf those old transistorized tin pots. NASA calls missions like this "Flagship" class. They are few, far between, and generally bring in floods of new information. This mission is on the scale of Voyager and Cassini.

Even back in the Voyager days, when the rocketry and resources (developed in the lull between Apollo and Shuttle) to launch such a mission were newly available, close visits to any of the planets beyond Mars were completely unprecedented, and NASA was anxious get underway it took five years. Cassini was first proposed 15 years and approved I think 10 years before it launched. Now that there's minimal hurry and a lot of other things to share the annual budget with, so the timeline is more like that for Cassini. The taxpayers don't want to pay out more per year, and besides, Europa isn't expected to go anywhere in the meantime.

As mission complexity and cost grows, getting the most out of it becomes increasingly important. You can't achieve that with a generic bus because it limits the instrumentation you can hang on it. Instead you tailor the bus to the power, thermal, geometric, stabilization, and other needs of all this really expensive and fancy instrumentation. If you need a 3-axis stabilized, nuclear-powered spacecraft with a large contiguous cavity for a big telescope like Cassini, you can't make effective use of a solar-powered spacecraft bus designed to be spin stabilized and provide a mount for a radar and a long magnetometer boom like Juno.

Instrumentation is another thing. Back in the Mariner days, they were generally taking the best instruments currently coming out of the labs and figuring out how best to use them for the mission. Lately, it's been more typical to examine what you want to know, what technically should be possible, and do the research, development, design and testing of an instrument optimized for its mission. As a result, science package development is often a primary pacing and budgeting concern for exploration missions these days.

Lastly, those ten Mariner probes in ten years were being concurrently developed, not one after the other. I'm not sure how many missions NASA had active or in development at any given time back in the 60's and 70's, or how much money was devoted to them. Right now, however, I'm aware of 13 solar system exploration missions currently operating, and five or six more in development. I'm really not sure how many earth and deep space observing missions there are (Hubble, Spitzer, Chandra, GALEX, WMAP, OCO, JWST, etc). All of these consume (I count 60+ total on NASA's website) consume less than a quarter of NASA's budget. It's rather impressive in the grand scheme of things.

Absolutely...I don't think it's at all far-fetched. They genuinely have a great museum, and I'm sure with the addition of the space exhibit hall (new since I've last been there) it's even better. Between that and their active leadership they'll likely end up on the short list of candidates. But my personal opinion is that NASA will ultimately choose museuems with a more direct tie-in to space exploration (Evergreen Aviation itself is just a small air freight company) and more conveniently located for a larger number of people.

Of course, since I live in Portland, I would be ecstatic if Evergreen were granted even Enterprise, much more so for one of the operational orbiters.

I can't find the original information, but I'm pretty sure the allocation of the shuttles won't be soley based on cash, but also on perceived value to the public for receiving one and consistency with the general mission of the museum. Keep in mind, the $42 million is supposedly for refurbishment for display, not to raise additional money. This first of all will mean cleaning up any potential hazards, like residues of hydrazine manuevering fuel. Of course, they get fairly weathered by each launch and re-entry, so there'll be some polishing to be done, and undoubtably ITAR-sensitive or high value equipment like the main engines will be removed and replaced with detailed replicas where applicable.

There's three orbiters surviving (Discovery, Atlantis, and Endeavor). I suspect Kennedy Space Center will keep one and house it near their Saturn V that's on display. This is consistent with another article that says two orbiters and six engine display kits will be made available according to the RFI. With public accessibility being a likely major consideration, the Smithsonian Air and Space Museum is almost guaranteed one of the actual orbiters, to replace the Enterprise aerodynamic test vehicle which is currently housed there.

That's going to make it a tough grab for the remaining orbiter. Because McMinneville is roughly an hour-long drive from the relatively small and aerospace-vacant city of Portland, I think their chances of getting an orbiter are relatively slim, even though they have a great facility and can probably afford it.

The Intrepid Museum in New York Harbor is certainly prominent enough, but they would need to make a rather substantial addition to protect the shuttle from the elements. It probably wouldn't be possible to deliver it to the waterfront an SCA flight to New York, but if they wanted to put it on a barge like the Concorde they have on site, they may be able to float it straight up from Florida that way. I think they're also at a disadvantage because there will already probably be two shuttles on the East Coast (Florida and DC).

I think Johnson Space Center in Houstan and Marshall Spaceflight Center in Huntsville are the two most likely locations not on one of the major coasts. Both of them already host two of the three remaining Saturn V's (the third is at Kennedy). On the west coast, I think the lead option is Boeing's museum of flight, partially because of their accessibility and ability to host a space shuttle, but also because of their involvement with the shuttle program (although that is due to their acquisition of Rockwell).

I would bet one of these three locations will get the third orbiter. That still leaves Enterprise after it leaves the Smithsonian, which only did glider and procedural tests, but would still be a major attraction. Maybe Evergreen has a chance at getting Enterprise, but I think more likely a second of the above three will get her. There is also a ground-test mockup called Pathfinder currently at MSFC in Huntsville that would likely get a new home if one of the orbiters went there, but it's only externally representative of the flight vehicles.

A commenter on another site had a fantastic idea, in my opinion: before sending the last of the orbiters to a musuem, use the SCA to take it on a tour of the US. This would be a great opportunity for millions to see it and the modified 747 together.