IEEE - Aerospace and Electronic Systems - August 2022 - 17

Avram et al.
Table 8.
Commercial ADCS RW Performance [35], and the Time Required to Reach the Input Body Frame's Maximal Angular Velocity
CubeWheel
small
Mass (g)
Dimensions (mm3)
Max. momentum storage
(mNms)
Max. torque (mNm)
Max. angular velocity (/s)
Time to reach vSET 3,max(s)
60
1.7
CubeWheel small
plus
90
28 28 26:133:4 33:4 31
3.6
0.23
1.2
19.4
the components of the corresponding input body frame's
angular velocity fvg obtained from (6). To maximize the
signal reception duration, the GS should point actively
toward the S/C during the orbital passage. Figure 15
reports the plot of the velocities needed by the GS's elevation
and azimuth actuators to continuously track the satellite.
The elevation velocity module is usually contained
below 1/s, while the azimuth velocity module is usually
contained below 7/s. As an example, the South Pole telescope's
maximal elevation speed is 2/s, and the maximal
azimuth speed is 4/s (see [34]).
The results of the attitude simulation are the driver for
the selection of the CubeSat ADCS subsystem. The maximum
S/C angular rate required to perform the pointing
maneuver is given by the maximum of the peaks shown in
Figure 14(b), it is possible to observe that, by using SET 3
(RAAN = 198.6 and AOP = 161.4) orbital parameters,
almost all input angular velocity peaks are below 0.72/s.
Table 7 shows the pointing maneuver maximal angular
velocity and the required maximal angular momentum
storage for the orbit configuration that maximizes the
mean contact time: SET 3 orbit (RAAN = 198.6 and
AOP = 161.4) and the one optimal for the maximum
overall number of contacts SET 3 (RAAN = 12.4 and
AOP = 111.7). Considering the preliminary design of the
6U nanosatellite, which has a
½IS/C¼
diagð0:057; 0:081; 0:031Þ kg/m2, the minimum required
RW angular momentum storage is 1 mNms.
Figure 14(c) shows the magnification over the orbital
period of the components of the required control torque for
the SET 3 (RAAN = 198.6 and AOP = 161.4) orbit. Control
torques are obtained by means of (9). The maximal
expected torque during the whole duration of the mission is
TRWmax ¼ð0:67 105; 1:59 105; 0:97 105Þ N m.
Table 8 shows the attitude control simulation results
compared with commercial ADCS modules, such as
CubeADCS [35], it is possible to see that all considered
RW configurations provide the required momentum
AUGUST 2022
1
2.5
4.5
CubeWheel
medium
150
CubeWheel
large
225
46 46 31:557 57 31:5
10.8
30
1
7.6
4.5
2.3
21.2
1.9
storage of 1 mN ms and the required torque 1:59 105
N m to perform the maneuver in the targeted time.
As it is possible to see from Table 8, the characteristics
of the RW in terms of mass and dimensions are compatible
with the integration in a CubeSat. Three RWs are
required to provide the requested three axes pointing
through the entire CubeSat lifecycle. Also for what concerns
the pointing requirements, we refer to the commercial
solution CubeADCS three-axis with CubeStar [35]
star tracker. CubeADCS three-axis is characterized by a
suite of sensors for attitude determination, such as Sun
and Nadir sensors, 3 MEMS gyro, 10 coarse Sun sensors,
and one magnetometer. For attitude control, it fits three
magnetorquers and three RWs. The performances of the
selected ADCS show that it is possible to achieve a pointing
accuracy equal to 4 arcmin (1-sigma), which is in line
with the positioning accuracy required for this application.
CONCLUSION
The ongoing development ofmore precise and compact satellite
instrumentation is expanding the possible use ofCubeSats,
which are being to date considered for complex commercial
and scientific missions by several SPACE AGencies and
industrial entities. In parallel, calibration ofground telescopes
is a critical aspect oftheir utilization, especially when deriving
information from unknown sources as in the case ofobservations
of a remote microwave background. Using relatively
small satellites to support the calibration of CMB telescopes
represents an innovative and high-potential application in
which the orbital calibrator can periodically serve different
sites around the globe, proving real-time information to compensate
for atmospheric distortions ofthe signal.
Starting from the requirements on the intensity of the
calibrator signal, a brute force search was presented to
estimate the optimal orbit parameters for a single calibrator
satellite that guarantees long visibility times for
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IEEE - Aerospace and Electronic Systems - August 2022

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