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ESA Document - Emits - ESA

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s<br />

3.3.5 AOCS<br />

HMM<br />

Assessment Study<br />

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

February 2004<br />

page 189 of 422<br />

The ACS system for the complete vehicle shall be modular as much as possible, trying to<br />

minimise hardware used and propellant consumption.<br />

The functions of the ACS during the whole lifetime are listed in Table 3-32:<br />

Phase ACS functions<br />

During LEO assembly None<br />

Between assembly<br />

completion and 1 st Aero disturbance rejection<br />

TMI burn Attitude control (no manoeuvre)<br />

No orbit maintenance<br />

Transfer to Mars phase – 3 Attitude control during non propelled phases<br />

burns<br />

No orbit maintenance<br />

Control during firing: TVC -> residual attitude rate 0.5<br />

degrees/s<br />

Mid-course manoeuvre after TMI are separated<br />

Transfer to Mars phase – Attitude control during non-propelled phases<br />

orbit correction<br />

Control during firing: TVC -> residual attitude rate 0.5<br />

degrees/s<br />

Transfer to Mars phase – Attitude control during non propelled phases<br />

orbit insertion<br />

Control during firing: TVC -> residual attitude rate 0.5<br />

degrees/s<br />

180 degree rotation manoeuvre (TBC)<br />

Mars orbit Attitude control<br />

Orbit maintenance<br />

Return to Earth – propelled Attitude control<br />

phase<br />

Control during firing: TVC -> residual attitude rate 0.5<br />

degrees/s<br />

Mid-course correction<br />

Return to Earth – cruise Attitude control<br />

Earth retargeting<br />

Table 3-32: ACS during mission lifetime<br />

To limit the dimensioning of the ACS components, and considering that each individual stage<br />

has to have some manoeuvring capability as a stand alone item, an integrated control system is<br />

proposed. This means that all the stages shall participate in accomplishing the functions of each<br />

mission phase.<br />

This results in a configuration of the ACS with actuators (i.e. thrusters) located along the vehicle<br />

in each "interstage". The thrusters’ locations are shown in Figure 3-46, corresponding to the<br />

points P1 to P6.<br />

The dimensioning of the control authority needed in each location is explained for each stage in<br />

the following chapters. The basic idea is to size the "higher" stages (from TMI to TEI and then<br />

MOI 3 rd , 2 nd and 1 st stage), only to fulfil the functions they have to accomplish in their part of the<br />

mission. This would avoid overdesigning the ACS of the stage that has to go to Mars and back.<br />

Any ACS would however contribute to the control of the vehicle (according to its capability)<br />

throughout the mission.

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