Endeavour to land in California
Published on Nov 30, 2008 at 12:42 pm.
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Filed under space shuttle.
The weather forecast in Florida is not looking good for the STS-126 mission to land at KSC today, and tomorrow’s forecast isn’t looking favorable, either. So, mission controllers have decided to have the Endeavour land at Edwards Air Force Base, in California, instead. Landing would occur on orbits 25o or 251 this afternoon. I’ve included the landing ground track for orbit 250 here.
The Space Shuttle takes off like a rocket and lands like an aircraft (glider). The idea is that the orbiter is reusable, and this is supposed to save money. That was the sales pitch, that is. In reality, Space Shuttle flights are not any less expensive than disposable spacecraft for most missions. There are a few instances where they may save some money, but overall, the program has not lived up to its potential. But, the idea that it would save money was based on a fast turn-around (something that has not materialized) and dozens of flights per year (something else that has not materialized). I am not going to go into the reasons for all of that at this time.
The Space Shuttle is a large craft. It is the largest spacecraft flown by the United States. In that statement, I distinguish the craft from the booster lifting it. The Saturn V is the largest rocket that we’ve flown. Landing such a large spacecraft as the Space Shuttle is a bit of a challenge. Our earlier spacecraft, from the days of Mercury, Gemini, and Apollo, all landed in water. At the end of their mission, they entered the atmosphere, slowing down, deployed drogue chutes to slow further, and then parachutes to slow them to a survivable speed for them to hit the water. They aimed at the oceans. Precision landing was not generally possible in those days, so landing anywhere within several miles (or even dozens of miles) from the landing site was fine. The vast empty expanse of the oceans made missing the landing target spot acceptable. However, the Space Shuttle is a different matter. It lands like an aircraft, so it needs a long smooth surface on which to land. The first landings were at Edwards Air Force Base on a dry lake bed. There, the runway was simply painted onto the flat surface. Missing the landing spot simply meant landing by a little bit was also acceptable, because the ground was flat and smooth even where it wasn’t painted for landing. The problem was that the unpaved surface kicked up small pieces of debris that damaged the heat protective tiles of the orbiter. But, by the time of the Shuttle program, we knew more about reentry and the upper atmosphere. Missing landing by large distances was not likely. And, since the Space Shuttle is able to glide, missing the orbiter can easily fly to correct for missing the landing site by small distances. Soon, the landing was shifted to paved runways, reducing the landing damage from debris kicked up by the landing gear. A suitable paved runway exists at the Kennedy Space Center. What makes the runway suitable is that it is longer than the average runway, and wide enough for the Space Shuttle to land. Remember that the orbiter is landing like a glider, but it doesn’t really glide well. So, if there is something wrong with the landing approach, then there is no option to fly around and try again. It can’t abort landing. Once it enters the atmosphere, landing is ensured, whether the landing strip is ready or not, and whether the orbiter is lined up properly or not. That makes landing very stressful for NASA (both the astronauts and the controllers).
There are only a few landing sites suitable for the Space Shuttle. The preferred landing site, of course, is at KSC, since that means that the orbiter is landing where it will next need to be located for processing for another launch. If it lands anywhere else, it must be ferried to KSC on the back of a modified Boeing 747. That is time consuming and expensive, so NASA obviously doesn’t want to do it unless necessary. For STS-126, though, it looks like it will be necessary. If Edwards is not available, then the Space Shuttle can (and has) landed at White Sands Missile Range in New Mexico. There are other places where the Space Shuttle can land where airfield personnel have the proper training and emergency procedures to handle an emergency landing, such as airfields in Spain and Gambia. However, in a real emergency, if the Shuttle has to come down and the primary landing facilities are not available, there are about a two dozen other airfields with runways suitable for landing the Space Shuttle. However, landing the Space Shuttle at one of these emergency landing sites leaves it stranded there, since you can’t just get a lot of guys together to pick it up to set it on top of its modified 747 carrier. Thus, if at all possible, NASA will land the Shuttle at KSC, Edwards, or White Sands. Fortunately, those three are spaced out enough that the chances of the weather being bad at all three for several days straight is unlikely, and there has never been a time that NASA has had to choose any site other than one of those three.
But, of course, this does mean that the Space Shuttle can not just land anywhere. The Apollo, Gemini, and Mercury capsules couldn’t land just anywhere, either, but since they landed in the ocean, the options for landing were far greater. Most of the Earth’s surface is covered in ocean. The problem with an ocean landing, though, is that NASA did not have the capabilities of retrieving the spacecraft on their own. They required assistance from the Navy or Coast Guard (somebody with large ships). And, of course, those naval assets had to be in place and ready to recover the spacecraft, so that somewhat limits landing sites, too. With plans to have dozens of launches per year, the idea of using military assets for recovery for every mission was unappealing. It is far less expensive and easier for NASA to handle their own recovery. Thus, the landing site at KSC is by far preferred. The Orion Crew Exploration Vehicle (CEV), due to replace the Space Shuttle, was originally going to go for a land-based landing, similar to what the Soyuz does. However, plans have changed. Now, the CEV is expected to return to a water-based splashdown. That means that once again, NASA will likely have to rely on naval assets to recover the vehicle. But, at this time, no one is expecting there to be dozens of launches and recoveries per year. It might make sense, though, for NASA to have their own recovery teams and vessels for primary recovery operations off the coast of Florida and rely on the Navy or Coast Guard for backup operations if the weather is bad at the primary recovery zone. That would be similar to the way that things are run today.
-Astroprof
Image courtesy NASA
