4 Final Report - Emits - ESA
4 Final Report - Emits - ESA 4 Final Report - Emits - ESA
4 Final Report Table 4.5-4: Comparison of HEMPT 3050 and microHEMPT HEMPT 3050 microHEMPT Force 30-50 mN 100-500 µN Mass flow 1.2 mg/s 12 µg/s For the final suggestion of preferred actuators for the Geo-Oculus mission, the properties of above options in terms of pointing performance, agility and fuel consumption is checked for attitude control tasks and manoeuvres in the following. 4.5.6.4 Attitude control performance The attitude control performance of Geo-Oculus has been derived from simulations using a high performance attitude control simulator as already applied in a similar project. The baseline sensor suite has been used for simulations for both the MBW and EPS option. Below follows a summary of the attitude performance figures for steady state attitude control and manoeuvres. MBW system and performance The configuration of a MBW based actuator system is equal to that of a ball bearing reaction wheel system. Four or five MBW can be selected, depending on the impact zero-crossings has on the pointing accuracy. Five wheels are needed if zero-crossings are judged to be of importance, as a five wheel system will not experience zero-crossings even if one of the wheels should fail. A four wheel configuration is the minimum for redundancy, but will have wheel zero-crossings if one wheel should fail. The worst values of the analysed performances are • APE 14.1 μrad, AME 11.3 μrad, PDE 0.32 μrad/100ms (all values for 100% probability). All performance values are better than the requirements of Table 4.5-3. EPS system and performance: The EPS analysis is based on the recently finished HOPAS-3 study, investigating the use of EPS as the sole actuator on spacecraft in GEO. The study has been done for DLR by EADS Astrium GmbH. The baseline EPS configuration is derived from this study. The EPS based attitude control system will have a 12 thruster configuration based on the microHEMPT. A HEMPT 3050 based system has been analysed and rejected based on its high fuel consumption (~100 kg over 10 years) and problems with meeting the given minimum lever arm and torque level requirements. Also, the high power consumption of the HEMPT 3050 (1.2 kW per active thruster) does not allow more than 4 thrusters for attitude control to be active at the same time. This impacts the attitude control performance, especially after the completion of manoeuvres, when only attitude control thrusters are used for settling. In comparison, the microHEMPT can operate six thrusters at the same time, with a total power consumption of 0.2 kW. The attitude control thrusters are configured with four thrusters around each axis, as can be seen in Figure 4.5-8. The special configuration has been developed especially to meet the lever arm and thruster plume direction requirements, and at the same time provide decent torque levels and fuel consumption. Page 4-60 Doc. No: GOC-ASG-RP-002 Issue: 2 Astrium GmbH Date: 13.05.2009
4 Final Report Figure 4.5-8: EPS thruster configuration The analysed performance values are • APE 32.7 μrad, AME 11.3 μrad, PDE 0.21 μrad/100ms (all values for 100% probability). The APE and AME steady-state performances are well below the requirements with the APE being slightly worse than for the MBW solution. The EPS attitude performance is largely a function of the thruster controller dead zone. The dead zone determines the level the torque command must reach before the thruster will start firing. It is there to avoid excessive thruster firing due to noise and must be selected large enough to prevent continuous firing and counter firings. A small dead zone gives higher pointing accuracy whereas a large dead zone reduces the fuel consumption. The PDE steady-state performance for a EPS system is better than that for the MBW system, due to the lower torque exercised on the system from the EPS thrusters. The power and fuel consumption is acceptable but it may be further decreased by a larger dead zone. This is possible since there is still a good margin to the absolute attitude requirements. Doubling the dead zone from 1/6 of the available torque to 1/3 reduces the fuel consumption by more than 80%. The attitude performance is reduced but still within the requirements. Doc. No: GOC-ASG-RP-002 Page 4-61 Issue: 2 Date: 13.05.2009 Astrium GmbH
- Page 26 and 27: 2 Final Report Erosion / Sediment T
- Page 28 and 29: 3 Final Report 3 System Requirement
- Page 30 and 31: 3 Final Report Furthermore, the mis
- Page 32 and 33: 3 Final Report better than 0.5 SSD
- Page 34 and 35: 3 Final Report • Image post integ
- Page 36 and 37: 3 Final Report Table 3.3-1: Baselin
- Page 38 and 39: 3 Final Report Manoeuvre Times and
- Page 40 and 41: 3 Final Report Cloud Amount [%] Num
- Page 42 and 43: 3 Final Report cloud scenes where t
- Page 44 and 45: 4 Final Report Alternative solution
- Page 46 and 47: 4 Final Report The achieved ground
- Page 48 and 49: 4 Final Report board image processi
- Page 50 and 51: 4 Final Report 4.3.3.2 UV-VNIR foca
- Page 52 and 53: 4 Final Report Column decoder 4 out
- Page 54 and 55: 4 Final Report 4.3.3.5 Mechanical a
- Page 56 and 57: 4 Final Report 4.3.3.7 Electrical a
- Page 58 and 59: 4 Final Report 4.3.4 PLM budgets Th
- Page 60 and 61: 4 Final Report 4.4.2 Microvibration
- Page 62 and 63: 4 Final Report Figure 4.4-2: Struct
- Page 64 and 65: 4 Final 4.5 Satellite Report 4.5.1
- Page 66 and 67: 4 Final Report Star Tracker Figure
- Page 68 and 69: 4 Final Report (Spacecraft Computer
- Page 70 and 71: 4 Final Report This is based on a w
- Page 72 and 73: 4 Final Report Reception of the ins
- Page 74 and 75: 4 Final Report Table 4.5-2: Charact
- Page 78 and 79: 4 Final Report Table 4.5-5: EPS fue
- Page 80 and 81: 4 Final Report manoeuvre. It also h
- Page 82 and 83: 4 Final Report Figure 4.5-10: Basel
- Page 84 and 85: 4 Final Report The CPS considered f
- Page 86 and 87: 4 Final Report PPU B* FU XST Page 4
- Page 88 and 89: 4 Final Report Table 4.5-17. EP mas
- Page 90 and 91: 4 Final Report The primary structur
- Page 92 and 93: 4 Final Report Direction MTG Scaled
- Page 94 and 95: 4 Final Report 4.6.1.1 High Level F
- Page 96 and 97: 4 Final Report shorter. As a conseq
- Page 98 and 99: 4 Final Report 4.6.2.4 Cloud Cover
- Page 100 and 101: 4 Final Report management functions
- Page 102 and 103: 4 Final Report 4.6.2.8 Ground Stati
- Page 104 and 105: 5 Final Report based on EUMETSAT im
- Page 107 and 108: A Final Report Annex A Abbreviation
- Page 109 and 110: A Final Report ICU Instrument Contr
- Page 111: A Final Report Doc. No: GOC-ASG-RP-
4 <strong>Final</strong><br />
<strong>Report</strong><br />
Figure 4.5-8: EPS thruster configuration<br />
The analysed performance values are<br />
• APE 32.7 μrad, AME 11.3 μrad, PDE 0.21 μrad/100ms (all values for 100% probability).<br />
The APE and AME steady-state performances are well below the requirements with the APE being<br />
slightly worse than for the MBW solution. The EPS attitude performance is largely a function of the<br />
thruster controller dead zone. The dead zone determines the level the torque command must reach<br />
before the thruster will start firing. It is there to avoid excessive thruster firing due to noise and must be<br />
selected large enough to prevent continuous firing and counter firings. A small dead zone gives higher<br />
pointing accuracy whereas a large dead zone reduces the fuel consumption. The PDE steady-state<br />
performance for a EPS system is better than that for the MBW system, due to the lower torque<br />
exercised on the system from the EPS thrusters.<br />
The power and fuel consumption is acceptable but it may be further decreased by a larger dead zone.<br />
This is possible since there is still a good margin to the absolute attitude requirements. Doubling the<br />
dead zone from 1/6 of the available torque to 1/3 reduces the fuel consumption by more than 80%.<br />
The attitude performance is reduced but still within the requirements.<br />
Doc. No: GOC-ASG-RP-002 Page 4-61<br />
Issue: 2<br />
Date: 13.05.2009 Astrium GmbH
Change language