Mission Analysis and Design of Formation Flying InSAR Remote Sensing Missions with Electric Propulsion
- Paper number
IAC-06-C1.6.09
- Author
Ms. Stefania Cornara, DEIMOS Space S.L., Spain
- Coauthor
Mr. Vicente Fernández, DEIMOS Space S.L., Spain
- Coauthor
Dr. Luis F. Penin, DEIMOS Space S.L., Spain
- Coauthor
Mr. Juan-Carlos Bastante, DEIMOS Space, Spain
- Coauthor
Mr. Jose Gonzalez del Amo, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Bernardo Carnicero Domínguez, European Space Agency (ESA)/ESTEC, The Netherlands
- Coauthor
Mr. Michael E. Price, Qinetiq, United Kingdom
- Year
2006
- Abstract
The increasing number of European Earth Observation programmes and missions has brought to the fore the need for an assessment of innovative concepts to cope with the requirements and the implementation of Remote Sensing (RS) mission scenarios. To contribute to address this need, a Study on RS Spacecraft with Electric Propulsion (EP) has been carried out in the frame of an ESA contract with the primary aim to identify RS missions that would significantly benefit from the exploitation of the maturing EP technology, and to quantify those benefits in terms of system improvements (i.e. mass, power) or innovative payload operation concepts.
Within the innovative concepts, formation flying (FF) rises as a natural option. Within the study a detailed assessment of an Interferometric SAR (InSAR) FF Mission Scenario has been carried out. This scenario consists of a master satellite (SAR emitter) and a formation of three receiver satellites behind the master at 630 km altitude. Two main cases have been considered for comparison purposes, depending on the value of the SAR frequency band used:
- L-Band InSAR. The reference mission taken into account for L-band SAR imaging is the TerraSAR-L Mission with 40x40 m baselines.
- C-Band InSAR. The interest in C-band SAR imaging is brought to the fore for example by the GMES Sentinel-1 satellite series. Baselines of 200x200 m are considered.
The main issues addressed to analyse the EP implementation option for a Formation Flying mission encompassed Mission Analysis (for formation design) and GNC system specification (for FF maintenance). The analysis rationale for InSAR FF configurations indicates that the application of EP to InSAR satellite formations cannot be understood independently from mission analysis issues and from GNC design issues. Ultimately, the control strategy required for formation maintenance drives the selection and the design of the propulsion system (either impulsive or EP, performance needed in terms of thrust level, thrust throttling/resolution, noise spectral density, etc.).
The formation design process resulted in the definition of a CarPe configuration, which is a Cartwheel-type interferometric constellation, where two satellites fly in a "Pendulum" configuration and the third one in an eccentric Cartwheel orbit. The "Pendulum" configuration offers the advantage that along-track and cross-track baselines become de-coupled, which is not possible if a pure Cartwheel configuration is used. In addition, since in the CarPe configuration no relative deltas in inclination and eccentricity exist, this FF design proves to have a great stability with respect to the orbital plane drifts due to the J2 perturbation.
Analyses conducted in open loop indicated that an adequate formation control scheme is necessary in order to maintain the interferometric baselines within the required bounds for long periods of time. The main factors leading to this conclusion are: differential drag between the flyers due to different ballistic coefficient, navigation errors leading to initial dispersion in position and velocity, quickly augmented by the propagation of relative motion dynamics and differential drag of the flyers with respect to the emitter satellite.
A control scheme based on the application of electric propulsion was then designed for the two reference missions in L band and in C band. This control scheme was based on the use of different types of EP Thrusters: T5, Mini GIE, FEEP High-Thrust, FEEP Low-Thrust. After detailed numerical simulation (whose results will be presented in the final version of the paper), it was demonstrated that EP can be regarded as a truly enhancing technology for the InSAR FF Mission Scenario considered in this analysis. This conclusion can be established on the grounds of:
- Interferometric baseline stability achieved by continuous low thrust.
- Low propellant consumptions due to the high efficiency of EP thrusters.
- Much lower complexity and risk of the continuous formation control implementations compared to the impulsive alternatives.
- Abstract document
- Manuscript document
IAC-06-C1.6.09.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.