ASTRO APS Star Tracker Qualification

Objectives

The objective of the project is the qualification of the ASTRO APS such as to obtain a new, highly reliable, up-to-date star tracker based on the Active Pixel Sensor (APS) technology.
The qualification process is based upon a predevelopment of Jena-Optronik’s
new generation APS star trackers. An elegant breadboard has been built and tested. The results achieved have demonstrated the technical feasibility and encouraged the next step towards a fully qualified sensor.
 
In particular the activity will include the following tasks:
  • Redesign of the electronics from the EM configuration to the EQM
  • Redesign of the S/W according to lessons learned from the EM tests and implementation of advanced acquisition algorithms
  • Re-work of the EM mechanical structure and optics for the usage in the EQM (if necessary) and optimization of APS detector cooling
  • Procurement of the DC/DC-converter
  • Surface Mounted Technology (SMT) Process Verification
  • Manufacturing, Assembly and Integration of the star tracker unit including baffle
  • Qualification test campaign of the star tracker including baffle
 Key feature of the Jena Optronik APS star tracker is the very compact mechanical design and robust acquisition and processing of star image data due to advanced processing techniques which will be of benefit to next generation satellite platforms.
 


Challenges

 The key-issues addressed in scope of this qualification are the following:

  • Redesign of the electronics from the EM configuration to the EQM
  • Redesign of the S/W according to lessons learned from the EM tests and implementation of advanced acquisition algorithms
  • Re-work of the EM mechanical structure and optics for the usage in the EQM (if necessary) and optimization of APS detector cooling
  • Procurement of the DC/DC-converter
  • Surface Mounted Technology (SMT) Process Verification
  • Manufacturing, Assembly and Integration of the star tracker unit including baffle
  • Qualification test campaign of the star tracker including baffle

Benefits

With the APS technology opening the door towards system miniaturization, the single box concept shows a significant saving in the power and mass budget compared to equivalent CCD based star trackers. The mass, power and envelope reduction is achieved through the high functionality and integration of the APS technology. APS detectors contain the whole analogue signal processing for driving and image data read-out known from CCD’s. Therefore, the analogue electronics effort can be reduced to a minimum in APS-based designs.
 
This project under ARTES3 is addressed to the re-design, manufacturing and qualification testing of the ASTRO-APS star tracker in order to establish a competitive and highly robust star tracker product for the international telecom satellite marked. The qualification is focused on the typical requirements for the star tracker application on large telecom platforms like the European large telecom platform AlphaBus. The ASTRO-APS star tracker is planned to accommodate as Technology Demonstration Payload (TDP#6) on the
AlphaSat telecommunication satellite.
 
The star sensor described herein has been introduced as “ASTRO-APS” in the Jena-Optronik GmbH star tracker ASTRO series product family [ASTRO1, ASTRO5, ASTRO10, ASTRO15].

Features

The APS Star Tracker (also labeled as “ASTRO-APS”, and belonging to the star tracker ASTRO series product family of the Jena-Optronik GmbH) provides autonomously high accurate 3-axis attitude information with regard to the J2000 inertial reference frame and 3-axis angular rate measurements of the spacecraft. The APS Star Tracker is accomplished as a compact single box on which a 26 deg baffle is mounted for suppressing the stray light.
High quality images of the celestial sphere are generated in the field-of-view of the autonomous Star Tracker by means of an well-corrected optics and an
APS (Active Pixel Sensor) detector. The digital signal processing performed in hardware and software carries out the star acquisition and attitude tracking. An on-board Guide Star Catalogue (GSC) together with dedicated algorithms facilitates the star identification that is prerequisite to the subsequent attitude determination as part of the attitude tracking.
The APS Star Tracker is characterised by the following basic features:
 
 Sensor Field of View  20deg
• Limiting Star Magnitude  5.8mi
• EoL-Condition  15 years geo-orbit @ TAPS-Chip = +30°C
• Sky Coverage  100 percent for ≥ 9 stars at EoL
• Sun Exclusion Angle  26 deg
• Axis Attitude Accuracy  4.3/26 arcsec (3σ) for the xy/z axes
 Angular Rate  up to 3 deg/sec
• Temperature Range  -30 … +60°C
• Dimension  12 x 12 x 22.5 cm, incl. baffle
• Mass  < 1.98 kg, incl.: baffle, 15 years geo orbit equivalent shielding, DC/DC converter
 Power  6 W @ 100 VDC without APS Peltier  cooling
   11 W @ 100 VDC with APS Peltier cooling
• Data Interface  MIL-1553

Current status

The ASTRO APS Star Tracker EQM successfully completed the qualification test campaign. The APS Star Tracker has shown excellent performance. It outreached the specified requirements especially in terms of accuracy and robustness to space environment (Moon, Radiation Robustness). The design expectations are very well met.
 
The ASTRO APS Star Tracker is well suited to fulfil the mission requirements of Alphasat, Small GEO, Sentinel-2 and EarthCARE, missions for which ASTRO APS us currently contracted for.

Contacts

Status date

Friday, September 25, 2015 - 15:37