4 Final Report - Emits - ESA
4 Final Report - Emits - ESA
4 Final Report - Emits - ESA
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
3 <strong>Final</strong><br />
<strong>Report</strong><br />
Ground Segment Requirements<br />
The ground segment requirements can be found in detail in RD [3]. It is based on a centralised Flight<br />
Operations Segment (FOS). Requirements have been specified for:<br />
• Functionalities of FOS;<br />
• S-Band TM/TC Ground Station and X-Band Ground Station for PDT;<br />
• Centralised Payload Data Ground Segment (PDGS);<br />
• Standardised User Portal;<br />
• Centralised processing facilities;<br />
• High-speed communication connections to the PDT receiving stations;<br />
• Interfaces to meteorological service providers for the provision of nowcasting and very short<br />
range forecasting information of cloud coverage.<br />
3.2 Major System Trade-Offs<br />
In this chapter the major system trade-offs performed after the MTR, leading to the proposed Geo-<br />
Oculus baseline, are summarised. They are discussed in detail within the dedicated chapters /<br />
documents.<br />
• Field of View vs. resolution<br />
The combination of instrument FoV and resolution is limited by the detector technology<br />
(number of pixels). Additionally, both the maximum FoV size and the resolution are limited by<br />
the telescope size. Due to the coverage requirements for the marine applications, the choice<br />
is to go for a maximum possible FoV size (300km x 300 km with the proposed telescope<br />
concept), with medium resolution. For disaster monitoring, the best resolution possible with<br />
the proposed telescope concept has been chosen. This leads to a smaller FoV size, which<br />
requires mosaic imaging for disaster monitoring.<br />
• Magnetic Bearing Wheels vs. Electric Propulsion for manoeuvres<br />
MBWs allow high torques and therefore short manoeuvre times. The drawback are the<br />
microvibrations, which are much lower than with ball bearing wheels, but still impact the<br />
image quality. EPS would create no microvibrations, but increase the manoeuvre time due to<br />
the relative small torque, which leads then to a small number of missions. Furthermore, the<br />
propellant demand is significant, especially for EPS with high thrust. As a consequence, it<br />
has been decided to go for the MBW solution.<br />
• Manoeuvre time vs. image post-integration effort<br />
The pointing instability impacts the image quality. With a good pointing stability, no postintegration<br />
(including image motion compensation) is needed, as long as the MTF<br />
requirements are met. The major contributors to pointing instability are microvibrations<br />
(which are not time varying at a short timescale) and solar array oscillations. The solar array<br />
oscillations are a direct function of the waiting time after a manoeuvre. The trade-off is<br />
therefore between a long manoeuvre time, needing no post-integration and shorter<br />
manoeuvre times, requiring post-integration.<br />
Doc. No: GOC-ASG-RP-002 Page 3-17<br />
Issue: 2<br />
Date: 13.05.2009 Astrium GmbH