4 Final Report - Emits - ESA

4 Final
Report
scan North/South and East/West, respectively. A summary of the manoeuvres required over 24 h is
presented in Table 4.5-6.
Table 4.5-6: Manoeuvre summary
Manoeuvre [deg] Daytime manoeuvres
over 9 h [-]
Nighttime manoeuvres
over 15 h [-]
Total manoeuvres
over 24 h [-]
Manoeuvre time
allocation [s]
0.25 27 0 27 70
0.40 27 0 27 70
2.00 324 720 1044 70
All manoeuvre performance data presented in this section are based on one-axis manoeuvres.
There are several options for manoeuvre actuators. The MBW option is clear, but also two EPS
options, using either the HEMPT 3050 or microHEMPT, have been considered. The MBW option uses
the same wheels for attitude control and manoeuvres, as the torque output from one wheel is
scaleable from 0 to 400 mNm. The wheel drive electronic quantisation is 55 µNm. The EPS can not
throttle its output to the same degree and an additional EPS system is needed for manoeuvres. The
first option is to use the HEMPT 3050 thrusters for manoeuvres which can produce a torque of ±85
mNm around each axis.
In the EPS analysis another option has been introduced as well. MicroHEMPT for attitude control has
a few advantages such as lower fuel and power consumption and system mass, and one obvious
drawback: the long resulting manoeuvre time. An overview of the theoretical, time optimal manoeuvre
time for the various options are listed in Table 4.5-7. Note that these numbers do not allocate time for
a settling period after the completion of the manoeuvre.
Table 4.5-7: Theoretical, time optimal manoeuvre times for HEMPT 3050 and microHEMPT based
configurations, and duty cycle over 24 h
Manoeuvre [deg] HEMPT 3050 (30 mN) MicroHEMPT (2 mN) MicroHEMPT (3 mN) MBW (400 mN)
0.25 24.2 s 132.6 s 108.3 s 9.4 s
0.40 30.6 s 167.8 s 137.0 s 11.9 s
2.00 68.5 s 375.2 s 306.3 s 26.5 s
Duty cycle over 24 h 84% 463% 378% 33%
Est. fuel consumption 635 kg
over 10 years
18 kg 27 kg 0 kg
In the following, the complete manoeuvres are assessed which includes the time where the actuators
are operated (corresponds to the manoeuvre times of above table) plus the settling time (mainly driven
by the solar array) needed to reach the pointing requirements. Only the APE and PDE are evaluated
according to the requirements of Table 4.5-3. The absolute measurement error AME shows the same
performance before and after a manoeuvre such that this parameter does not need to be checked.
From above figures, the EPS options could already be eliminated since the HEMPT solution needs too
much fuel (635 kg of noble gas) and the micro HEMPT system is not suitable because of a duty cycle
significantly higher than 100% which means that all the required manoeuvres can not be performed in
the required time frame. Nevertheless, all of above options are evaluated to give an impression what
is feasible with each of the options.
MBW performance
The MBW option has the most available torque for both the manoeuvres and the stabilizing after the
Doc. No: GOC-ASG-RP-002 Page 4-63
Issue: 2
Date: 13.05.2009 Astrium GmbH