PROBA 1 F. Teston ESA/ESTEC D/TEC-EL Frederic.Teston@esa.int
PROBA 1 launch PROBA 1 has been launched on 21 October 2001 Orbital parameters: Altitude: 681-561 km Near polar (inclination of 97.9 ) Sun-synchronous Period 96.97min
PROBA 1 early activities start date stop date Activity 22 October 2001 Launch 22 October 2001 24 October 2001 LEOP 24 October 2001 April 2002 Commissioning April 2002 April 2003 Technology Demonstration mission April 2002 Start of CHRIS instrument calibration campaign & science mission Continuous Implementation and in-flight testing of improvements of the system and operations October 2002 Priority given to science mission Jan 2003 March 2003 Intensive campaign to further improve system stability and reliability in preparation of Scientific Utilisation Mission April 2003 now Scientific Utilisation Mission, main mission priority June 2003 Start of utilisation of Kiruna as additional downlink station
PROBA 1 Data (1) ESA technology demonstration program (GSTP) (1) In orbit demonstration of spacecraft technology (2) Payload complement CHRIS: Compact High Resolution Imaging Spectrometer HRC: High Resolution Telescope SREM, DEBIE, MRM: Earth environment monitors Operations centre located at ESA-Redu ground station (B)
PROBA 1 Data (2) Mass : 94 kg Volume : 80cm x 60cm x 60cm Power : 40 to 120 W High accuracy and agile ACNS
Mission management Main elements (related to CHRIS): PROBA 1 Steering Group (ESA) in charge of overall mission management CHRIS Steering Group (BNSC) in charge of CHRIS utilisation Campaign Unit (ESA) in charge of the definition and the organisation of the CHRIS Observation Plan RSAC (UK) in charge of CHRIS day to day planning SIRA (UK) in charge of level 0 processing and data distribution ESA Redu (B) in charge of spacecraft operations Industry in charge of technical project support
PROBA 1 status Spacecraft is operating on its nominal chain Degradation of power subsystem (solar arrays and battery) is compatible with the current mission and further extension is possible with some saving measures (limitation in summer of earth environment instruments) Degradation of radiation sensitive items (electronics, CCD) was observed but remains compatible with the mission and a possible extension Orbital natural decay and drift from SSO are very low (< 10 km semimajor axis) perigee height Ground segment status (addressed later) 6932 Drift of the orbital plane wrt the sun (i.e. drift from sun-synchronicity): <2 /year (< 8min) in the direction of noon. apogee height km 6930 6928 6926 km 7058 7056 7054 7052 7050 7048 7046 7044 7042 7040 7038 14-Sep- 01 14-Jan-02 16-May- 02 15-Sep- 02 15-Jan-03 17-May- 03 16-Sep- 03 6924 6922 14-Sep- 01 14-Jan-02 16-May- 02 15-Sep- 02 date 15-Jan-03 17-May- 03 16-Sep- 03 date
PROBA 1 EO related performances Spacecraft pointing performances are in line with expectations, Data link is nominal (some data loss on board), Thermal stability of CHRIS is adequate The main remaining issue is related to the spacecraft robustness which is acceptable but still includes anomalies causing losses of images (success rate addressed later).
Infant anomalies Platform stability, including onboard computer reboots The main problems still encountered on board after the end of the commissioning phase were the relatively frequent software reboots and the instable attitude control. Cold reboots resulting in the loss of not yet dumped image data and reconfiguration of the spacecraft into safe mode occurred typically once every 3-6 days or once every few weeks. Although the frequency of such events varied during the mission these events were found to be related and all had a potential impact on the spacecraft scientific return (less to the technology demonstration return). Depending on the case by case situation, this impact could consist in: the loss of planned imaging activities between two ground segment passes the loss of imaging data quality loss of imaging data Considerable effort has been put into the investigations of these events and into the definition and implementation of containment and corrective actions. As a result most of the mechanisms leading to these events were identified and corrected or worked-around, resulting finally in a complete resolution and a stable platform in April 1 st 2003. Centre times The CHRIS image times that the PPU manager takes from the ACNS represent centre times of the image. No factor was used to start the imaging sooner. Consequently, the selected target was not in the centre of the image, but always at the edge of the image (the image scan starts at the target). Therefore, the 5 images taken with CHRIS were not of the exact same area. Forward scans would show an area starting with the target and moving in the flight direction. Backward scans would also start at the target and move in the opposite of the flight direction. A patch in RAM has been uploaded with a configurable time offset, that will correct the values obtained from the ACNS. This patch successfully adjusts the start time of the CHRIS imaging, such that the target is located in the centre of the image. Depending on the image taken (e.g. number of lines), the time offset needed can be up to 5 seconds for a 10 second image. Furthermore, the presence of this patch provides the spacecraft operators to choose between overlapping images (images of the same area taken under different angles) or to pave the images in order to increase the actual field of view.
Thermal Subsystem (CHRIS) In orbit results: CHRIS Temperature 8.0 6.0 Transient from Bdot to Terrestrial CHRIS temperature ( C) 4.0 2.0 0.0-2.0 12.0 0.0 24.0 48.0 72.0 10.0 8.0-4.0 Measurements versus simulation results hours in terrestrial temperature ( C) 6.0 4.0 COLD_MODEL_CHRIS 2.0 HOT_MODEL_CHRIS MEASURED_CHRIS 0.0 0.0-2.0 20.0 40.0 60.0 80.0 100.0-4.0-6.0 orbit time (minutes)
Instruments
High Resolution Camera High Resolution Camera (HRC) Panchromatic 3D Packaging Technology CCD Fixed target pointing Strong requirements platform stability 8 m ground resolution Image size 4 x 4 km
Terrestrial : Fixed target pointing Fixed target pointing Used for HRC and WAC imaging and optimal ground contact HRC: 8 m resolution Off-track pointing of 25 possible HRC Image Line-of-sight of imager 4 km No scanning: ground speed = 0 m/sec
High Resolution Camera results
CHRIS Compact High Resolution Imaging Spectrometer (CHRIS) Bi-directional Reflectance Distribution Function measurements 19 spectral bands (415-1050 nm) Push-broom 20 m resolution Image size 15 x 15 km
Imaging mode: CHRIS BRDF images Terrestrial : Imaging 5 images per sequence in observation cone with 55 co-elevation angle Motion compensation of factor 5 wrt traditional push-broom! images takes 10 seconds 20 m resolution Off-track pointing of 25 possible Image5 Image4 Image3 Image2 Image1 End imaging Begin imaging Line-of-sight of imager 15km Scanning speed = 1/5 of spacecraft ground speed
Earth targetting Target prediction r r REL T cosγ = r r = REL T r r REL REL r T r T User-selected imaging target γ max Observation Cone γ Pitch r REL r Spacecraft Find the extrema of cosγ r T γ* d cosγ dt = 0 A( t)cosu( t) + B( t)sinu( t) = 0 α OBS Earth Prediction of the satellite flying by a target over the next day within some Roll constraints. Fine prediction and count down for fixed target pointing and CHRIS imaging. Used for sorting/selecting multiple targets and implement command sequence relative to fly-by (e.g switch on camera 100 sec before image taking).
Conclusion The PROBA mission - although designed as a technology demonstrator with a lifetime of 1 year has demonstrated adequate capabilities for science, disaster monitoring, education and outreach by the Earth observation community. The life time can be further extended for a period of at least 2 years (this extension is based on the status of the limited life on board items not on reliability estimation). The extension would require adequate support to cover technical support from project at ESTEC and industry in addition to the operation of the ground segment elements at Redu, Sira, RSAC, ESRIN. Depending on the mode of operations PROBA can support EO needs with a capability ranging from 2 sets of 5 multi-spectral, multi-angle scientific images to 50 push-broom 3 bands pseudo-colour images per day (depending on viewing opportunities and ground station visibility). Additional capability would require modification of the ground station locations.