NASA has posted the ground tracks for two opportunities for STS-120 Discovery to re-enter for landings on Wednesday. If one of these tracks is used, it will be the first time since the Columbia accident in 2003 that a shuttle re-entry has flown over the continental US. Of course, since then they have developed the ability to positively check the condition of the orbiter, and Discovery has passed that check. So the main interest now is that some people may have the opportunity to see the re-entering shuttle orbiter in the mid-day sky. It still depends on the weather - but NWS forecasts for Kennedy Space Center (KSC) look good so far, with the only potential problem being winds. So what does this mean?

The first opportunity will be on Orbit 238, landing at KSC at 1:02 PM US Eastern Standard Time. The second opportunity will be on Orbit 239 landing at KSC at 2:36PM. 238's entry will be making its highest latitude at it crosses the Pacific coast at southern British Columbia, Canada and cross the Lower 48 states from northwest to southeast. 239 will have made its highest latitude off-shore and cross the coast near Astoria, Oregon and continue southeastbound to Florida.

Let's point at some introductory info on NASA's site that they call "Landing 101". But we can add to that. Discovery is traveling at 17,000mph at an altitude of about 200 miles. It had to match the space station's orbit in order to dock with it. When landing time comes, Discovery will fire its orbital maneuvering system (OMS) rockets to change its orbit so that the low end (perigee) of the orbit dips down and intersects Earth's atmosphere. As it starts to hit the atmosphere, the shuttle maintains an altitude of 200,000 feet (40 miles or 65km) until it slows down enough that it can't any more. That's the "peak heating" period where you can see it pass you in the sky at night, and maybe even during the day. Then it descends to the landing site. It goes subsonic within the vicinity of the landing site, making the double-boom to be expected from any re-entering spacecraft.

Edwards AFB in California and White Sands Space Harbor in New Mexico are backup landing sites. But they are not being activated for the Wednesday opportunities. If Wednesday's opportunities are not used, those will undoubtedly be considered for Thursday. The orbiter has limited supplies, such as food and fuel. At this point they have an extra couple days to work with if needed.

See my photos from Atlantis' landing at Edwards in June.