Aerospace and Electronic Systems Magazine July 2017 - 29

Pasand, Hassani, and Ghorbani
Table 4.

Orbital Parameters
Orbital Parameters

Value

Inclination, i

55°

Altitude, h

400 km

Right ascension, Ω

0°

Period, 

5,553 s

Eccentricity, e

0

Table 5.

Spacecraft, Modulator, and Controller Specifications
Spacecraft Specifications
Moments of inertia

Ix = 15.95 kg m2
Iy = 72.19 kg m2
Iz = 72.79 kg m2

Thrusters radial arm

R = 0.45 m

Thrusters x-direction arm

L = 0.4 m

Mass

m = 350 kg
PWPF Parameters

On threshold

Uon = 0.80

Off threshold

Uoff = 0.10

Gain of lag filter

Km = 3.00

Time constant of lag filter

m = 2.00
Attitude Control Gains

Proportional gain

Kp = 120

Derivative gain

Kdx = 200
Kdy = 200
Kdz = 200

reliable so that the mission success rate increases dramatically. At
the expense of overall system reliability, the system is subjected to
additional weight. In Table 3, the LR and the configuration matrix
of each configuration are represented. LR is specified using (1) and
its necessary and sufficient condition. As can be seen in Table 3,
the configurations with 6 thrusters have LR 0, the configurations
with 8 thrusters have LR 1, the configurations with 12 thrusters
have LR 2, and the configurations with 16 thrusters have LR 3. The
tabulated data are not valid for a general n-thruster configuration.

NUMERICAL SIMULATIONS
To evaluate the attitude control system performance of the proposed configurations, a typical mission is considered in Table 4.
JULY 2017

In Table 5, the detailed specifications of the applied spacecraft and
control gains and modulator parameters are given. The governing
equations and the mission's parameters are implemented in matrix
laboratory (MATLAB)-Simulink software. Then, numerical treatments are carried out that allow us an assessment of each configuration's merits. The simulation of each configuration is carefully
evaluated in terms of fuel consumption, attitude control accuracy,
number and width of PWPF modulator signals, and linear displacement. To achieve a meaningful comparison among configurations,
the maximum level of achievable torque for each configuration has
to be the same. For this purpose, the level of thrusters is normalized so that the maximum resultant torque corresponding to each
configuration equals 6.3443 Nm. In addition, fuel consumption is
calculated based on cold-gas RTs with a specific impulse of 70 s.

IEEE A&E SYSTEMS MAGAZINE

29



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