Autonomous Orbit Determination and Station Keeping Control for Competitive Telecom Missions – ESA CSC: Connectivity & Secure Communications

Objectives

Trade-off on different autonomous orbit-determination solutions including GNSS and optical-based navigation, and a trade-off on different station keeping strategies, to define the global autonomous system best suited for chemical and for hybrid chemical/electrical Telecom platforms on geo-stationary orbit. The chosen solution is based on GNSS and on classical Station Keeping strategy. Performances are assessed on a closed-loop functional software simulator, and on a closed loop real-time test bench including a MOSAIC® GNSS receiver, a LEON2 on-board computer, a SPIRENT GNSS stimulator, and a REDHAWK PC.

The objective of this activity is to develop and evaluate the performances of on-board algorithms for the planning and execution of station keeping manoeuvres on geo-stationary orbit for fully chemical and for hybrid chemical / electrical telecommunication platforms, using autonomous orbit determination based on optical navigation or on GNSS. It is a natural follow-on to two previous ESA studies: “Feasibility of GNSS sensors for AOCS Applications in GEO and Higher Altitudes” and “GEO Orbit Determination Using an APS-Based Navigation Sensor”.

Challenges

Autonomous orbit determination trade-off shown that pure orbit propagation and optical-based navigation are not sufficient for autonomous OD/SK requirements because of their insufficient accuracy (>0.02°) and because they require frequent calibrations. MOSAIC performance is sufficient to meet these requirements in nominal conditions, but better accuracy in radial position is required in degraded conditions. LION performances are expected to be sufficient in any conditions.

The chosen Station keeping strategy is similar to the one currently performed on ground because it offers a good ephemeris and manoeuvers prediction for at least the upcoming week, it has no overconsumption, and is well mastered by the operators.

Plan

1) State-Of-The-art in autonomous OD and SK => system level

requirements using inputs from telecom operators

2) Architecture and specification => high level requirements

3a) Design choices for orbit determination => trade-off on AOD

3b) Design choices for station keeping => trade-off on ASK

3c) Global trade-off => selection of two solutions (GNSS, APS)

4) Development of the prototype ASK SW

5) FVB and RTB development

6) FVB and RTB test campaign

7) Overall synthesis

Current Status

Main requirements for an Autonomous OD/SK system were good ground ephemeris prediction based on on-board orbit measurement and on foreseen maneuvers, no overconsumption and possibility for the ground to take over by uploading orbit measured on-ground, or maneuvers plan.

Trade-off on autonomous orbit determination systems outcomes (ordered from worse to best) :

Pure orbit propagation, Sun & Earth sensor, Star & Earth, Combined Star / Earth sensor, GNSS MOSAIC, GNSS LION.

The chosen ASK strategy is the one currently implemented on-ground because it provides good visibility on the upcoming maneuvers thus allows a good ephemeris prediction, has the same fuel efficiency, is well mastered by the operators.

Validation on the Closed-Loop Functional Validation Bench (software tests) outcomes :

ASK module is validated, APS navigator is not compatible with ASK, MOSAIC and LION navigator are compatible with ASK.

Validation performed on the Closed-Loop Real-Time test Bench outcomes:

RTB includes a MOSAIC, a SPIRENT, a LEON2 implementing the ASK SW, and a RT-Linux computer, two 7 days long tests with chemical & hybrid propulsion confirmed the adequacy of MOSAIC with AODSK in nominal conditions.

Additional tests performed has shown the sensitivity of SK performances to the radial position error which could be reduced by further optimizing the GNSS receiver filter.

Companies

Airbus Defence and Space (Friedrichshafen Site)

http://www.airbusdefenceandspace.com

Germany

Airbus Defence and Space (France)

http://airbusdefenceandspace.com/

France