European Space Agency

Objectives

Demonstration of an integrated AODS based on the MosaicGNSS receiver with the AGGA-2 and complemented by star sensors and optional gyros for multimedia applications.


Higher level signal processing functions and software algorithms (GPS receiver, star sensor and gyro) are centralized on a single DSP.


The common hardware platform for these components is the GPS/AODS Demonstrator Hardware.


 click for larger image

Challenges

Integration of an AODS (Attitude and Orbit Determination System) demonstrator, being a sensor system that provides full state information and having a large degree of autonomy. The system comprises the following components:



  • MosaicGNSS receiver that provides position, velocity, time and attitude,



  • 3-axis star sensor, inertial 3-axis attitude information can be provided with spacecraft rates up to typically 2 deg/sec,



  • Optional gyroscopes for inertial rate measurements.

Benefits


  • Compact integrated AODS, stand-alone unit and slide-in module,

  • Portability, Modularity and Flexibility,

  • GPS Rx and Star Sensor and Gyro SW share MosaicAODS board:


    1. Reduction of mass, volume, power consumption costs,

    2. Easy to implement module interconnections,

    3. Improvement in robustness,

  • Radiation tolerant (up to 100 krad),


  • Short initial acquisition,

  • Fit for LEO / MEO / GEO missions,

  • Relative navigation.

Features

The GPS/AODS demonstrator will consist of three boards:



  • MosaicGNSS Receiver Base Board, comprising the DSP with program memory and data memory, a GPS ASIC developed by Astrium for signal preprocessing, board and boot control (BBC) and communication interfaces(UART/HDLC, SpaceWire, MIL-STD-1553), a boot PROM containing the primary boot loader, an EEPROM bank containing the application software. The base board has all the hardware required for a software correlator based GPS signal reception.



  • AGGA-2 Extension Board, comprising one AGGA-2. The AGGA-2 is connected to the DSP using the data bus extension of the base board. Four RF front-ends, one RF multiplexer (MUX) and three RF power splitter (PS) will be used to route the RF signals as required for the different modes.



  • Power Converter Board with the required DC/DC converters.

Since the GPS receiver as well as the star sensor require significant processor load, the key is the implementation of all functions on a single DSP. This is made even more difficult by the limitation of the DSP clock frequency (20 MHz) due to radiation requirements.






     click for larger image

The MosaicAODS system is composed of the following components:



  • A GPS receiver that provides full PVT information. The use of GPS receivers in low Earth orbits is common practice. Also, commercial applications in geostationary orbit and eccentric orbits are envisaged,



  • A 3-axis star sensor. Inertial 3-axis attitude information,



  • Optional gyroscope

Plan

Project start was the 1st of January 2003. The Baseline Design Review is planned 4 months after the project start. A Mid Term Review (MTR) is planed 11 months after the project start. The Final Review (FR) is planned for December 2005. 

Milestones in this activity are: 


















Project StartT0January 2003
BDR:Baseline Design ReviewApril 2003
MTR:Mid Term Review December 2003
FP/FR:Final Review December 2005


   
   

Current status


  • Start date of the project was 01.01.2003,

  • Successful BDR at ESA/ESTEC in Noordwijk, 28.04.03,

  • Successful MTR at ESA/ESTEC in Noordwijk, 08.12.03,

  • The system architecture of the GPS/AODS Demonstrator has been revised and a MIL-STD-1553 Bus interface has been added to the system architecture,

  • Adaptations of parts of the GPS attitude determination software have been performed,

  • The AGGA-2 breadboard has been used for differential phase measurement in full parallel attitude mode and in hybrid-multiplexed mode,

  • Adaptations of O/S and Interface SW using the AGGA-2 breadboard have been done,

  • GPS/AODS DC/DC converter manufactured,

  • RF Multiplexer PCB manufactured,

  • AGGA-2 extension board manufactured,

  • Successful board level tests and first functional tests,

  • Successful environmental and functional tests.

Status date

Wednesday, November 23, 2011 - 13:13