4 Final Report - Emits - ESA

4 Final
Report
manoeuvre. It also has a close to linear torque response to the commanded torque within its torque
limits, something that favours the MBW option over the EPS solution.
In the following table the total times needed for the selected 3 typical manoeuvres are listed. The
criterion for the end of the manoeuvre is the fulfilment of the pointing requirements according to Table
4.5-3 where for the PDE the less stringent value has been considered (1μrad / 0.1sec).
Table 4.5-8: Total MBW manoeuvre time, including settling time for APE and PDE over 0.1 sec
Manoeuvre [deg] APE [s] PDE 0.1 s [s]
0.25 8 58
0.40 14 129
2.00 63 126
It can be seen that the APE settling time for all manoeuvres is within the allocated manoeuvre time of
70 seconds. However, the PDE settling is far longer due to vibrations of the solar array induced by the
manoeuvre. The length of the PDE settling can be possibly reduced by increasing the stiffness of the
solar arrays and by lowering the applied torque when performing a manoeuvre, thus increasing the
manoeuvre duration. Another option is to increase the simulated damping factor of the solar array,
thus reducing the PDE settling time. A conservative value of 0.3% is used as default, but increasing
the damping factor to 0.5% reduces the PDE settling from 126 to 74 seconds for a 2 deg manoeuvre.
It is assumed that if the manoeuvre is optimized further, it will be possible to reduce all settling times to
below 70 seconds.
EPS performance:
An EPS based manoeuvre system requires higher torques than the EPS based attitude control
thrusters can produce in nominal operations. Therefore an additional set of manoeuvre thrusters are
needed.
A manoeuvre system based on the HEPMT 3050 thrusters can produce a torque of ±85 mNm around
the x- and y-axis, giving the theoretical time optimal manoeuvre times and estimated fuel consumption
listed in Table 4.5-7.
It is also possible to use an additional set of microHEMPT thrusters, in combination with the attitude
control thrusters, for manoeuvres. This will cause the manoeuvre times to increase dramatically, as
the available thrust force only will be in the range of a few mN. This requires the microHEMPT thruster
to be able to operate at both 100 µN and 500 µN. The 100 µN operational mode is used for attitude
control and 500 µN for manoeuvres. If the two thruster pairs are operated at maximum force
simultaneously, a total of 2 mN will be available. To reduce total manoeuvre time additional sets of
microHEMPT thrusters can be added.
When using the HEMPT 3050 configuration the following performance can be achieved.
Table 4.5-9: Total HEMPT 3050 manoeuvre times, incl. settling time for APE and PDE over 0.1 sec
Manoeuvre [deg] APE [s] PDE 0.1 s [s]
0.25 18 20
0.40 153 57
2.00 300 160
It can be seen from Table 4.5-9 that the APE settling is the largest problem. Even though the time
optimal manoeuvre time for the HEMPT 3050 configuration is below the 70 seconds allocated to
Page 4-64 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009