4 Final Report - Emits - ESA
4 Final Report - Emits - ESA 4 Final Report - Emits - ESA
4 Final Report Figure 4.5-10: Baseline AOCS configuration Table 4.5-11: AOCS equipment and modes Sensors Actuators Mission phase Coarse GYP Earth IRES Star STR Sun BASS Fine LiASS IMU MBW CPS Transfer & Acquisition � � � � � On station: Normal mode � � � On station: Station Keeping � � � � Safe mode Transfer � � � Safe mode On-Station (�) � � 4.5.7 Propulsion System The Propulsion System of the mission is composed by: • Chemical Propulsion System (CPS): it is intended for GTO-GEO Transfer and, in the option without EPS, also for Station Keeping, wheel off-loading and de-orbiting. • Electric Propulsion System (EPS): it is optional and, if present, it is intended for reaction wheel off-loading or for active pointing (for an AOCS without reaction wheels). The following table summarises the possible options and the tasks allocated to CPS and EPS. Table 4.5-12: Propulsion System Options for Geo-Oculus Option 1 2 3 No EPS EPS + MBWs EPS only GTO-GEO CPS CPS CPS NSSK + EWSK CPS EPS EPS Deorbiting CPS CPS EPS Wheel off-loading CPS EPS / Pointing Manoeuvres / / EPS The main propulsion requirements, as deriving from AOCS analysis, are the following: • Transfer ΔV: 1500 m/s + 50 m/s margin, Page 4-66 Doc. No: GOC-ASG-RP-002 Issue: 2 Astrium GmbH Date: 13.05.2009
4 Final Report • De-orbit ΔV: 10 m/s • NSSK ΔV 400 m/s, • EWSK ΔV 10 m/s • Wheel off-loading + Rate Damping + Safe Mode = 15 kg (applicable to CPS only) The main trade-off regarding the propulsion system is about the use of EPS: • no EPS onboard (propulsion tasks entirely performed by CPS, all attitude control tasks performed by reaction wheels) • EPS only for reaction wheels downloading (GTO-GEO transfer and de-orbiting performed by CPS, fine pointing manoeuvres for image acquisition performed by reaction wheels) • EPS for attitude control (GTO-GEO transfer and de-orbiting performed by CPS, no reaction wheels) In this scenario, the results of the various propulsion system options are then to be analysed in a trade-off analysis at system level, i.e. involving also AOCS and main satellite level design choices. Therefore, the purpose of this section is just to prepare the input for such trade-off analysis. In following sections, the mass budgets (main trade-off criteria) for the options in Table 4.5-12 are derived from requirements and briefly analysed. 4.5.7.1 CPS Geo-Oculus is a geostationary mission. Astrium has a long heritage of supplying geostationary spacecraft, dating back to the 1970s. In addition to the telecom fleet there is a successful fleet of scientific and earth observation missions including Mars Express which has achieved two years in Mars Orbit, Venus Express currently in Venus orbit, and Rosetta and Cluster missions which are now flying with bipropellant NTO / MMH propulsion systems. The combined experience of this wealth of heritage shall enable Astrium to complete the study and return conclusions for the optimal CPS to meet the Geo-Oculus mission requirements. Astrium currently has 3 generic platforms for geostationary missions which can be considered for Geo- Oculus. These are: Eurostar 2000+ MON-3/MMH bipropellant propulsion system, an evolution of the Eurostar 2000 platform, featuring 4 propellant tanks, on a central cylinder supported structure Eurostar 3000 MON-3/MMH bipropellant propulsion system, a larger version of the E2000+ platform. The design has been expanded to include larger tanks to increase the mission capabilities of the design, featuring 4 propellant tanks on a central cylinder supported structure, in 4 sizes Eurostar 3000C The E3000C is an evolution of the E3000 design, based upon the successful Mars Express and Venus Express spacecraft. It remains a MON-3/MMH bipropellant propulsion system, with heritage from E3000 and Mars/Venus Express, but the platform is smaller than both E3000 and E2000+ to suit a smaller payload requirement. It features 2 propellant tanks are (supported by a “single H” type structure, demonstrated by the Mars/Venus Express spacecraft). As with Eurostar 3000, the tank size is interchangeable. Doc. No: GOC-ASG-RP-002 Page 4-67 Issue: 2 Date: 13.05.2009 Astrium GmbH
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4 <strong>Final</strong><br />
<strong>Report</strong><br />
• De-orbit ΔV: 10 m/s<br />
• NSSK ΔV 400 m/s,<br />
• EWSK ΔV 10 m/s<br />
• Wheel off-loading + Rate Damping + Safe Mode = 15 kg (applicable to CPS only)<br />
The main trade-off regarding the propulsion system is about the use of EPS:<br />
• no EPS onboard (propulsion tasks entirely performed by CPS, all attitude control tasks<br />
performed by reaction wheels)<br />
• EPS only for reaction wheels downloading (GTO-GEO transfer and de-orbiting performed by<br />
CPS, fine pointing manoeuvres for image acquisition performed by reaction wheels)<br />
• EPS for attitude control (GTO-GEO transfer and de-orbiting performed by CPS, no reaction<br />
wheels)<br />
In this scenario, the results of the various propulsion system options are then to be analysed in a<br />
trade-off analysis at system level, i.e. involving also AOCS and main satellite level design choices.<br />
Therefore, the purpose of this section is just to prepare the input for such trade-off analysis.<br />
In following sections, the mass budgets (main trade-off criteria) for the options in Table 4.5-12 are<br />
derived from requirements and briefly analysed.<br />
4.5.7.1 CPS<br />
Geo-Oculus is a geostationary mission. Astrium has a long heritage of supplying geostationary<br />
spacecraft, dating back to the 1970s. In addition to the telecom fleet there is a successful fleet of<br />
scientific and earth observation missions including Mars Express which has achieved two years in<br />
Mars Orbit, Venus Express currently in Venus orbit, and Rosetta and Cluster missions which are now<br />
flying with bipropellant NTO / MMH propulsion systems. The combined experience of this wealth of<br />
heritage shall enable Astrium to complete the study and return conclusions for the optimal CPS to<br />
meet the Geo-Oculus mission requirements.<br />
Astrium currently has 3 generic platforms for geostationary missions which can be considered for Geo-<br />
Oculus. These are:<br />
Eurostar 2000+<br />
MON-3/MMH bipropellant propulsion system, an evolution of the Eurostar 2000 platform, featuring 4<br />
propellant tanks, on a central cylinder supported structure<br />
Eurostar 3000<br />
MON-3/MMH bipropellant propulsion system, a larger version of the E2000+ platform. The design has<br />
been expanded to include larger tanks to increase the mission capabilities of the design, featuring 4<br />
propellant tanks on a central cylinder supported structure, in 4 sizes<br />
Eurostar 3000C<br />
The E3000C is an evolution of the E3000 design, based upon the successful Mars Express and Venus<br />
Express spacecraft. It remains a MON-3/MMH bipropellant propulsion system, with heritage from<br />
E3000 and Mars/Venus Express, but the platform is smaller than both E3000 and E2000+ to suit a<br />
smaller payload requirement. It features 2 propellant tanks are (supported by a “single H” type<br />
structure, demonstrated by the Mars/Venus Express spacecraft). As with Eurostar 3000, the tank size<br />
is interchangeable.<br />
Doc. No: GOC-ASG-RP-002 Page 4-67<br />
Issue: 2<br />
Date: 13.05.2009 Astrium GmbH
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