4 Final Report - Emits - ESA

4 Final
Report
Direction MTG Scaled MTG Requirement Margin
Lateral 19.32Hz 18.86Hz 17.25Hz 1.61Hz
Longitudinal 40.65Hz 40.37Hz 40.25Hz 0.12Hz
4.5.8.2 Thermal Control
Thermal Environment
The Geo-Oculus spacecraft will circle the Earth in a geostationary orbit. It is positioned directly over
the equator and follows it’s path in the equatorial plane at a speed matching the Earth’s rotation. Thus,
the spacecraft completes one rotation around its North / South axis per day.
The sun will traverse through an angle of ±23.5° perpendicular to the orbit plane during the year. The
extremes will occur at the Winter Solstice and the Summer Solstice. Eclipses will occur during the
Equinox seasons, with maximum eclipse duration of 72 minutes. The North face of the spacecraft will
receive direct solar illumination for 6 months centred on the Summer Solstice, while the South face will
receive direct solar illumination for 6 months centred on the Winter Solstice. The other faces of the
spacecraft will receive varying solar illumination during each day.
The Earth varies it’s distance from the Sun over a period of 1 year. This means that the solar constant
at Earth’s location changes over the year from 1420 W/m 2 at Winter Solstice to 1327 W/m 2 at Summer
Solstice.
Thermal Control Concept
The Geo-Oculus spacecraft body thermal control will rely primarily on passive means supported by
electrical heaters. The North and South faces of the spacecraft are used as the main heat rejection
paths. Externally they will be covered by Optical Solar Reflectors (OSR). The exact area of OSRs
exposed to space will be regulated by the use of Multi-Layer Insulation (MLI).
The inside of the panels will have a black finish. Aluminium doublers and heat pipes, as appropriate,
will be used to spread the heat within the panel. All electronic units are mounted inside the spacecraft
primary structure. Heat transfer from the dissipating units to the radiators relies mainly on conduction..
Thermal Performance
The total dissipation of the equipments on the spacecraft is 1402 watts. 423 watts is the dissipation of
the externally mounted units, leaving 979 watts dissipated within the spacecraft body. The payload
electronics, 300 watts, is mounted on the North radiator. In addition, some of the bus equipment will
also be mounted on the North panel such that the total amount of heat rejection capability adds up to
479 watts. The rest of the spacecraft bus electronics, 500 watts, is mounted on the South radiator.
This allows the calculation of the radiator sizes and the required heater power. The analysis results
are shown in Table 4.5-20 and Table 4.5-21.
Page 4-76 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009