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NEOWatcher
2008-Sep-22, 12:34 PM
This weekend I was hearing radio talk of the upcoming HST mission and heard a common misconception repeatedly voiced.

"The ISS can not be used because the HST is at a much higher orbit."

But; It got me thinking about the energy needed to change the orbit from one inclination to another.

I started picturing the two orbits as vectors with direction as a delta in direction, and the length as the amount of energy needed to achieve orbit. (both vectors originating at rest at (0,0))

In the simple case*, would the amount of energy needed be as simple as vector made by subtracting one from the other?

*Same altitude, circular orbit. Not actually HST to ISS.

Larry Jacks
2008-Sep-22, 01:23 PM
Orbital inclination changes are discussed here (http://en.wikipedia.org/wiki/Orbital_inclination_change) and here (http://www.cdeagle.com/omnum/pdf/maneuvr1.pdf). The HST is in an orbit inclined about 28 degrees to the equator. The ISS is in an orbit inclined about 51.5 degrees to the equator. Not only that, but the orbits are almost certainly in different planes (e.g. right ascention of ascending node values.

The energy involved to change orbital planes is substancial. The energy involved to change planes from that of the HST to the ISS is far in excess if the Shuttle's capability. It simply can't be done.

NEOWatcher
2008-Sep-22, 05:22 PM
Orbital inclination changes are discussed here (http://en.wikipedia.org/wiki/Orbital_inclination_change) and here (http://www.cdeagle.com/omnum/pdf/maneuvr1.pdf).