IEEE - Aerospace and Electronic Systems - July 2022 - 24

Development and Validation of a Canfield Joint as a Precision-Pointing System for Deep Space Instrumentation
Table 1.
Orbital Simulation Results
Date and time
08/27/22 10:20
AM
08/23/22 05:38
AM
08/31/22 03:01
PM
08/19/22 12:56
AM
08/26/22 04:16
PM
08/22/22 11:35
AM
08/30/22 08:58
PM
08/18/22 06:53
AM
Azimuth
(degrees)
93.879018
94.682791
93.238724
95.587958
Elevation
(degrees)
-82.481631
-82.455473
-82.431029
-82.356146
Earth clock angle
(degrees)
271.739947
272.602621
271.033913
273.55815
Clock rate (degrees/
sec)
0.3983337
0.3966137
0.3958337
0.3909377
275.43258
274.572886
276.046295
273.534183
82.408085
277.476278
82.386908
82.357489
82.296182
276.55851
278.154931
275.470391
-0.3919571
-0.3915869
-0.3887019
-0.3876241
the altitude may be bounded to a fairly circularized periapsis
of 255 km and an apoapsis of 320 km, as illustrated in
Figure 1 [13], [14]. This scientific orbit, optimized for
conducting surface observations, imparts a few significant
requirements on the communication payload. In selecting
an orbit for the spacecraft, a tradeoff exists between communications
and science gathering needs: Communications
is most easily accomplished with a large orbit that minimizes
occlusion time, whereas a closer scientific orbit
demands that the spacecraft spend a greater share ofits duty
cycle occluded by the planet and unable to communicate.
For the duration of the orbit, the spacecraft generally
maintains the alignment of the nadir deck toward the surface
of the planet to maximize the science gathering
potential. As depicted in Figure 3, between the limb-tolimb
portions of the orbit, the goal of the communications
payload pointing system is to maintain line-of-sight with
the Earth independent of the spacecraft attitude. During
the course of each orbit, the spacecraft operations may
alternate between science gathering and telecommunications
modes, so a wide FOR capability ensures that the telecommunications
system can easily accommodate varying
link windows as the result of both operations decisions
and orbital mechanics. An analysis was conducted by constructing
an orbital mechanics simulation featuring the
Martian orbiter maintaining a daily link with Earth and
gathering statistical data over a notional 2-year span of
operations. Selected datapoints are listed in Table 1 for
the reference frame shown in Figure 4, which illustrate the
required range in terms of azimuth and elevation. The
complete simulation results from which these are drawn
may be found in [15].
Figure 4.
Earth's clock angle is measured relative to a coordinate frame
where the positive X-axis is tangent to the satellite's path in the
direction of motion and the positive Z-axis is in the nadir direction,
i.e., pointing downward toward Mars. The clock angle is the
angle between +X and the vector pointing toward Earth in the
plane normal to +Z.
24
FIELDOFREGARD
Establishing the spacecraft as a parent coordinate system,
the maximum telecommunications FOR range to continually
address Earth independent of spacecraft pose results
IEEE A&E SYSTEMS MAGAZINE
JULY 2022
IEEE - Aerospace and Electronic Systems - July 2022

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