Saturday, April 24, 2010

What is Parking Orbit?

You might ask what Parking Orbit refers to? The answer is fairly simple; a temporary orbit by a spacecraft. The reasons for this maneuver, as explained in wikipedia is that:

  • It can increase the launch window. For earth-escape missions, these are often quite short (seconds to minutes) if no parking orbit is used. With a parking orbit, these can often be increased up to several hours.[1][2]
  • For non-LEO missions, the desired location for the final burn may not be in a convenient spot. In particular, for earth-escape missions that want good northern coverage of the trajectory, the correct place for the final burn is often in the southern hemisphere.
  • For geostationary orbit missions, the correct spot for the final (or next to final) firing is normally on the equator. In such a case, the rocket is launched, coasts in a parking orbit until it is over the equator, then fires again into a geostationary transfer orbit.[3]
  • For manned lunar missions, a parking orbit allowed some checkout while still close to home, before committing to the lunar trip.[2]
  • It is needed if the desired orbit has a high perigee. In this case the booster launches into an elliptical parking orbit, then coasts until a higher point in the orbit, then fires again to raise the perigee. See Hohmann transfer orbit. In this case the use of a parking orbit can also reduce the fuel usage of an inclination change, since these take less delta-V at high elevations.
For science fiction fans, it has been used to describe temporary visitation of a planet while members of the crew investigate the surface. An example would be the many times in Star Trek when the Enterprise comes to a new planet. It circles the alien globe while Kirk, Spock, and Co. beam down or land in a shuttle. After the mission is finished, they will leave the temporary orbit and go off to explore other strange new worlds.

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