4 Final Report - Emits - ESA
4 Final Report - Emits - ESA 4 Final Report - Emits - ESA
4 Final Report 4.3.4 PLM budgets The PLM budgets are computed for the baseline configuration with the following assumptions: • A 1.5 m diameter instrument with 5 focal planes. • Dual wing solar arrays, which is less favourable for thermal control efficiency because radiators on the NS walls have a reduced viewing factor. • Conventional 2.5 m baffle and Sun avoidance manoeuvres around midnight to keep the LoSto-Sun angle larger than 30 deg, i.e. preventing that Sun enters the telescope. • Remote Electronics Modules used for digital processing of the images are implemented in the SVM and accounted for in the SVM budgets. The PLM budgets are provided in the following figure: 2930 mm 2340 mm Mass Power Best estimate 505 kg 423 W Margins: 20% 101 kg 85 W TOTAL with margins 606 kg 508 W Figure 4.3-15: Geo-Oculus instrument interface budgets 650 mm Page 4-42 Doc. No: GOC-ASG-RP-002 Issue: 2 Astrium GmbH Date: 13.05.2009
4 Final Report 4.4 Line of Sight (LoS) Stabilisation Concepts 4.4.1 LoS stabilisation main issues: microvibrations and post-integration The LoS pointing stability requirements are very stringent for the aspects of the mission involving high resolution imaging. This is particularly the case during PAN imaging for disaster monitoring, since the 20 m resolution over Europe corresponds to 0.28 µrad nadir resolution, and to a lower extent when acquiring full resolution VNIR images (40 m resolution over Europe, 0.56 µrad nadir resolution) for disaster or fire monitoring. Image quality is then highly sensitive to LoS motion over the short integration time (up to ~100 msec) required to meet the moderate SNR requirements. On the contrary, the Marine applications, with a resolution relaxed to 80 m over Europe (i.e. 1.1 µrad nadir), are less sensitive to pointing stability over the image integration time. Nevertheless, since several images need to be post-integrated to reach high SNR requirements, image quality is more sensitive to pointing drifts over the total image acquisition time (several sec). LoS Stabilisation requirements derived from instrument design are summarised in the following table: RPE: Relative Pointing Error (stability over the integration time) RME: Relative Measurement Error (over image acquisition time) PDE: Pointing Drift Error (drift over integration time) 0.15-0.2 µrad peak-to-peak for high frequency jitter (>10 Hz) 0.1 µrad over 5 s max. acquisition time Marine applications: 10 µrad/s Fire/Disaster monitoring: 5 µrad/s Such specifications can not be met without proper management of the LoS pointing stability issue. Depending on the type of disturbances that challenge the LoS stability requirements, and in particular depending on the frequency band affected, different solutions might be proposed for Geo-Oculus : • High frequency perturbations, with period lower than typical integration time (100 msec), i.e. frequency > 10 Hz, require disturbance reduction techniques. Such disturbances are mainly due to microvibrations generated by moving parts (e.g. reaction wheels and cryocoolers). • Medium frequency disturbances (with period in the range of a few sec, corresponding to the time to acquire an image based on accumulation of several shots) require image processing techniques to enable post-integration. Such disturbances are mainly due to solar array flexible mode excitation after slew manoeuvres. • Low frequency disturbances are handled by the AOCS for those observed by the attitude sensors and by ground-based processing (so-called INR, Image Navigation & Registration) for LoS pointing errors due to orbit errors and thermo-elastic distortions between LoS and AOCS reference. Therefore, the LoS stabilisation issues to be addressed are: • Microvibrations: level reduction through careful selection of actuators and identification of potential other disturbances. • Post-integration: Evaluation of the technique to be used to estimate the shift between one image and another one before adding them. Doc. No: GOC-ASG-RP-002 Page 4-43 Issue: 2 Date: 13.05.2009 Astrium GmbH
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4 <strong>Final</strong><br />
<strong>Report</strong><br />
4.3.4 PLM budgets<br />
The PLM budgets are computed for the baseline configuration with the following assumptions:<br />
• A 1.5 m diameter instrument with 5 focal planes.<br />
• Dual wing solar arrays, which is less favourable for thermal control efficiency because<br />
radiators on the NS walls have a reduced viewing factor.<br />
• Conventional 2.5 m baffle and Sun avoidance manoeuvres around midnight to keep the LoSto-Sun<br />
angle larger than 30 deg, i.e. preventing that Sun enters the telescope.<br />
• Remote Electronics Modules used for digital processing of the images are implemented in the<br />
SVM and accounted for in the SVM budgets.<br />
The PLM budgets are provided in the following figure:<br />
2930 mm<br />
2340 mm<br />
Mass Power<br />
Best estimate 505 kg 423 W<br />
Margins: 20% 101 kg 85 W<br />
TOTAL with margins 606 kg 508 W<br />
Figure 4.3-15: Geo-Oculus instrument interface budgets<br />
650 mm<br />
Page 4-42 Doc. No: GOC-ASG-RP-002<br />
Issue: 2<br />
Astrium GmbH Date: 13.05.2009
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