The problem of observing a given set of Earth target sites within an assigned time
frame is examined. Attention is given mainly to visiting these sites as sub-satellite
nadir points. Solutions to this problem in the literature require thrusters to continuously
maneuver the satellite from one site to another. A natural solution is proposed.
A natural solution is a gravitational orbit that enables the spacecraft to satisfy the
mission requirements without maneuvering. Optimization of a penalty function is
performed to find natural solutions for satellite orbit configurations. This penalty
function depends on the mission objectives. Two mission objectives are considered:
maximum observation time and maximum resolution. The penalty function poses
multi minima and a genetic algorithm technique is used to solve this problem. In
the case that there is no one orbit satisfying the mission requirements, a multi-orbit
solution is proposed. In a multi-orbit solution, the set of target sites is split into
two groups. Then the developed algorithm is used to search for a natural solution
for each group. The satellite has to be maneuvered between the two solution orbits.
Genetic algorithms are used to find the optimal orbit transfer between the two orbits
using impulsive thrusters. A new formulation for solving the orbit maneuver problem
using genetic algorithms is developed. The developed formulation searches for a mini mum fuel consumption maneuver and guarantees that the satellite will be transferred
exactly to the final orbit even if the solution is non-optimal. The results obtained
demonstrate the feasibility of finding natural solutions for many case studies.
The problem of the design of suitable satellite constellation for Earth observing
applications is addressed. Two cases are considered. The first is the remote sensing
missions for a particular region with high frequency and small swath width. The second
is the interferometry radar Earth observation missions. In satellite constellations
orbit's design, a new set of compatible orbits, called the "Two-way orbits",whose
ground track path is a closed-loop trajectory that intersects itself, in some points,
with tangent intersections is introduced. Conditions are derived on the orbital elements
such that these Two-way Orbits exist and satellites flying in these orbits pass
the tangent intersection points at the same time. Finally, the recently proposed concept
of observing a space object from onboard a spacecraft using a star tracker is
considered. The measurements of the star tracker provide directions to the target in
space and do not provide range measurements. Estimation for the orbit of the target
space object using the measurements of the star tracker is developed. An observability
analysis is performed to derive conditions on the observability of the system states.
The Gaussian Least Squares Differential Correction Technique is implemented. The
results obtained demonstrate the feasibility of using the measurements of the star
tracker to get a good estimate for the target orbit within a period of measurements
ranging from about 20 percent to 50 percent of the orbital period depending on the
two orbits.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3126 |
| Date | 12 April 2006 |
| Creators | Abdelkhalik, Osama Mohamed Omar |
| Contributors | Mortari, Daniele |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 4689937 bytes, electronic, application/pdf, born digital |
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