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ESA Document - Emits - ESA

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4.4.5.3.2 GNC equipment<br />

HMM<br />

Assessment Study<br />

Report: CDF-20(A)<br />

February 2004<br />

page 349 of 422<br />

The MEV will be fully three-axis stabilized control entry vehicle.<br />

The MEV has to be able to deploy the drogue chute at a given Mach speed (Mach 2.0 is the<br />

baseline at about 10 km). This will be achieved by means of an IMU. This IMU will also be used<br />

during the powered phase. The mass and power budget can be found in the chapter 4.5.2<br />

explaining that phase.<br />

The time sequence for the deployment of the main chute and release of front cover will be<br />

implemented in the computer on-board. This equipment is taken into account in the Data<br />

Handling chapter 4.5.9.<br />

Figure 4-91 shows a schematic view of the foreseen GNC equipment. There is a possibility of<br />

manual control by the crew in case of failure of the automatic system.<br />

NAVIGATION<br />

IMU<br />

Altimeter<br />

LIDAR<br />

Camera<br />

GUIDANCE<br />

Backup manual<br />

control system:<br />

display + Joysticks<br />

On-board On board<br />

Computer<br />

CONTROL<br />

Automatic loop<br />

Off-line Off line<br />

reference<br />

trajectory<br />

Manual loop<br />

Thrusters<br />

Figure 4-91: MEV GNC equipment<br />

For stability and controllability reasons, the thrusting capability is as follows:<br />

• The design of the reaction control system is performed based on the attitude controller<br />

requirements.<br />

• The foreseen RCS system is composed of eight thrusters.<br />

With 8 thrusters, it is possible to provide thrust moment of yaw, pitch and roll, according to the<br />

following scheme:<br />

• for positive roll moment, thruster pods 1, 3, 5, and 7 are fired; no thrust force generated<br />

• for negative roll moment, thruster pods 2, 4, 6, and 8 are fired; no thrust force generated<br />

• for positive pitch moment, thruster pods 3, and 8 are fired; thrust force generated<br />

• for negative pitch moment, thruster pods 4, and 7 are fired; thrust force generated<br />

• for positive yaw moment, thruster pods 2, and 5 are fired; thrust force generated<br />

• for negative yaw moment, thruster pods 1, and 6 are fired; thrust force generated<br />

To generate yaw and pitch moments, forces also are generated. However, they will not have a<br />

significant impact on the point-mass motion of the spacecraft, because these forces are<br />

considerably lower than the aerodynamic forces.

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