The ability to observe resident space objects (RSOs) is a necessary requirement
for space situational awareness. While objects in a Low-Earth Orbit are easily ob-
servable by ground-based sensors, diffculties arise when trying to monitor objects
with larger orbits far above the Earth's surface, e.g. a Geostationary Orbit. Camera
systems mounted on satellites can provide an eff ective way to observe these objects.
Using a satellite with a speci c orbit relative to the RSO's orbit, one can passively
observe all the objects that share the RSO's orbit over a given time without active
maneuvering.
An orbit can be defi ned by ve parameters: semi-major axis, eccentricity, right
ascension of ascending node, inclination, and argument of perigee (a; e;
; i; !). Using
these parameters, one can create an orbit that will surround the target orbit allowing
the satellite in the Rock-Around Orbit (RAO) orbit to have a 360 degree view of
RSOs in the target orbit. The RAO orbit can be applied to any circular or elliptical
target orbit; and for any target orbit, there are many possible RAO orbits. Therefore,
diff erent methods are required to narrow down the selection of RAO orbits. These
methods use distance limitations, time requirements, orbit perturbations, and other
factors to limit the orbit selections.
The first step is to determine the range of RAO semi-major axes for any given
target orbit by ensuring the RAO orbit does not exceed a prescribed maximum al-
lowable distance, dmax from the target orbit. It is then necessary to determine the
eccentricity range for each possible RAO semi-major axis. This is done by ensuring the RAO still does not exceed dmax but also ensuring that the RAO orbit travels
inside and outside of the target orbit. This comprises one half of the rock-around
motion. The final step is to determine the inclination of the RAO orbit. Only a
small inclination different from that of the target orbit is required to complete the
rock-around motion while the maximum inclination is found by making sure the RAO
orbit does not exceed dmax.
It is then important to consider orbit perturbations, since they can destroy the
synchronization between the RAO and target orbit. By examining the e ffects of the
linear J2 perturbations on the right ascension of ascending node and argument of
perigee, the correct semi-major axis, eccentricity, and inclination can be chosen to
minimize the amount of fuel required for station keeping. The optimal values can be
found by finding the Delta v needed for di fferent combinations of the variables and then
choosing the values that provide the minimum Delta v.
For any target orbit, there are multiple RAO orbit possibilities that can provide
360 degree coverage of a target orbit. Even after eliminating some of them based
on the methods already described, there are still many possibilities. The rest of the
elimination process would then be based on the mission requirements which could be
the range of an on-board sensor, the thruster or reaction wheel controls, or any other
number of possibilities.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7473 |
| Date | 2009 December 1900 |
| Creators | Bourgeois, Scott K. |
| Contributors | Mortari, Daniele |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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