Speaker
Dr
Sérgio Brás
(National Trainee @ ESA/ESTEC)
Description
Earth observation data is key for a more efficient use of land and natural resources, better land and sea monitoring, more informed political decisions, and better understanding of the weather, climate, and land changes.
Many Earth observation satellites are operated in low Earth orbits which provide a good trade-off between revisit time and spatial resolution. Repeat ground track orbits are of particular interest as they allow the acquisition of the same scene at fixed time intervals. Additionally, either for calibration or nominal operation proposes, many satellites are required to overpass an exact location on Earth.
For missions comprising spacecraft constellations, accurate orbit phasing is also needed. Hence, the satellite manoeuvres should be carefully planned to control the ground track drift so that the desired longitude at ascending node crossing are achieved.
This paper describes a tool and the associated mathematical framework that automatically computes an orbit acquisition plan that minimize the duration of the orbit acquisition phase or the required Delta-V given the spacecraft characteristics and mission constraints.
The automatic algorithms are built upon on a perturbation analysis of the nominal orbit and provide the necessary information to perform preliminary analysis of orbit acquisition phases of Earth observation satellites.
Two kinds of simplified orbit acquisition plans can be computed: i) continuous semi-major axis change and ii) impulsive semi-major axis change. In the former, constant Delta-V per time interval is applied to the spacecraft, which is suitable when several small impulsive manoeuvres can be approximated by a continuous manoeuvre and also when there is no detailed information about the manoeuvring capacities and constraints. The latter is based on impulsive semi-major axis changes, which allows a more detailed plan where practical consideration such as the existence of calibration and touch-up manoeuvres are taken into account.
The tool also allows the analysis of several semi-major axis launch dispersions and launch dates providing for each case the resulting acquisition duration, required Delta-V, and mean local solar time drift. In particular, to insert another spacecraft within a constellation, a trade-off needs to be made regarding the requested orbital elements offset at orbit injection (in terms of semi-major axis, inclination or mean local solar time). Taking into account the spacecraft manoeuvre capabilities, the operational constraints of LEOP, the constraints preparing and implementing manoeuvres, launch date constraints and the agreed (or expected) launch dispersions, the tool identifies the consequences of all the possible scenarios (all cases are analysed together), which can then be used to define the orbital offset to be requested.
Some examples are given that illustrate the potential applications of this tool.
| Applicant type | First author |
|---|
Primary author
Dr
Sérgio Brás
(National Trainee @ ESA/ESTEC)
Co-authors
Mr
Berthyl Duesmann
(ESA/ESTEC)
Ms
Itziar Barat
(Deimos @ ESA/ESTEC)
