Shuttle reentry ground track question

cr1

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It seems to me that NASA is always choosing a south-west to north-east direction ground track to land its space shuttles, and they never choose the north-west to south-east direction...
http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts126/news/landing.html
http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts124/news/landing.html
http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts123/news/landing.html
(etc.)

Why though?

(I'm not entirely sure I'm at the right section here... if not, feel free to move this thread to the appropriate forum thanks!)
 

garyw

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What you call n/w to s/e is actually called a descending node entry and there are a lot of reasons that they don't choose them. One of which is due to Columbia being on a descending node entry and scattering debris for some distance.

The favoured ascending node entry path keeps the shuttle over water for much of the entry plus I believe there are energy bonuses in flying that type of entry that someone like DaveS can probably throw more light on.
 

DaveS

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What you call n/w to s/e is actually called a descending node entry and there are a lot of reasons that they don't choose them. One of which is due to Columbia being on a descending node entry and scattering debris for some distance.

The favoured ascending node entry path keeps the shuttle over water for much of the entry plus I believe there are energy bonuses in flying that type of entry that someone like DaveS can probably throw more light on.
This is correct. One of the other prime reasons is that the descending node entries occur much later in the crew's day than ascending node entries. This leads to a more tired crew by landing time(early afternoon vs early evening in crew day time).
 

cr1

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Is it because an Earth orbit ground track shifts from "west" to "east" (on the Map MFD) that the descending node entry occurs later than the ascending node one?
What energy bonuses are there in an ascending node entry?



EDIT: Just noticed http://www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts119/news/landing.html (STS-119) which would use (edited) a descending node entry
EDIT2: STS-119 landing track link worked an hour ago (now broken)
 
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garyw

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STS-119 hasn't happened yet. It's scheduled for Feb 09.
 

David413

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Recent decending node landings

A year ago STS-120 actually made a decending node landing.

News item:

http://www.space.com/missionlaunches/071105-sts120-update.html

As noted in the article, there are typically concerns associated with noctilucent clouds, higher prop usage, etc. However, this landing provided a daylight opportunity.
 

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cr1

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I still do not really understand why a DN entry requires higher prop usage...
Even after reading http://en.wikipedia.org/wiki/Noctilucent_cloud I do not really understand why noctilucent clouds can create concerns for reentry (though in Orbiter I don't think this phenomenon would be present)

(Maybe there are too many things I don't understand, I hope nobody is annoyed at that :) )
 

Urwumpe

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I still do not really understand why a DN entry requires higher prop usage...

Remember that Earth rotates, while the orbit of the shuttle does not. the reentry conditions at the entry interface have to include the rotation of Earth. A descending node reentry has the strongest effect of Earths rotation to the flight path angle equation, which can be as large as 291 m/s for returns from the ISS.

Not compensating this effect means, the Shuttle reenters too shallow, and the shuttle allows only a few tenth of a degree tolerance for the reentry angle.

Even after reading http://en.wikipedia.org/wiki/Noctilucent_cloud I do not really understand why noctilucent clouds can create concerns for reentry

http://www.srh.noaa.gov/topics/attach/pdf/ssd02-31.pdf

For hypersonic vehicle operators who wish to operate at high latitudes (northward of 50°N) noctilucent clouds may pose a design problem. The Space Shuttle currently avoids re-entry trajectories which fly farther north than 50°N during the noctilucent cloud season around the summer solstice. Originally it was believed that noctilucent cloud nuclei were large enough to damage the thermal protection system of the Space Shuttle, but measurements since the late 1980s have suggested the cloud nuclei are 100 to 1000 times smaller than previously believed. Because of this, Space Shuttle flight design constraints may be changed soon to allow for high latitude re-entry trajectories during the noctilucent cloud season. Air-breathing hypersonic vehicles may still have to consider avoiding the clouds so as not to ingest the particles, but that is a question for engine and aircraft designers to answer. The cloud particles may also increase drag substantially from the standard atmosphere which would also impact vehicle performance and navigation.
 
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