IEEE - Aerospace and Electronic Systems - August 2022 - 4

Feature Article:
DOI. No. 10.1109/MAES.2022.3177392
Maximization of LEO Nanosatellite's Transmission
Capacity to Multiple Ground Stations: Orbit Selection
and Requirements on Attitude Control
Alexandru Andrei Avram , Carlo Bettanini , Sebastiano Chiodini ,
Alessio Aboudan
Padova, Italy
Marco Giuliani
, and Giacomo Colombatti , University of Padova, 35122
, Thales Alenia Space Italia, 00131 Roma, Italy
INTRODUCTION
Periodic calibration of an instrument is essential to verify the
measuring performance, mainly by assessing the variation of
sensitivity over time and evaluating the overall accuracy of
the measurement to correctly interpret the acquired data.
Thus far, telescope calibration has been usually carried out by
exploiting resources and facilities either fixed in space or artificially
created on the ground, but an innovative approach can
be conceived relying on a " Calibrator Satellite " concept especially
suitable to support the calibration needs ofa number of
different telescopes spread all over the globe. The satellite
provides a signal source (e.g., microwave signal) formillimetric
pointing, fully controlling the parameters under observation,
with the ability to switch the polarized (or nonpolarized)
microwave sources in different bands ofinterest. Many space
agencies and institutional entities could benefit from the proposed
concept to complement and support traditional procedures
for calibration, although a dedicated feasibility study is
required to investigate the details related to its viability. Satellite
visibility from ground stations (GS) is determined by the
orbital evolution of the spacecraft in relation to the geodetic
Authors' current address: Alexandru Andrei Avram,
Carlo Bettanini, Sebastiano Chiodini, Alessio Aboudan,
Giacomo Colombatti, University of Padova, 35122,
Padova, Italy (e-mail: andrei.avram18@gmail.com;
carlo.bettanini@unipd.it; sebastiano.chiodini@unipd.
it; alessio.aboudan@unipd.it; giacomo.colombatti
@unipd.it). Marco Giuliani, Thales Alenia Space
Italia, 00131 Roma, Italy (e-mail: marco.giuliani@
thalesaleniaspace.com).
Manuscript received 5 August 2021, revised 29
December 2021; accepted 13 May 2022, and ready for
publication 20 May 2022.
Review handled by Richard Linares.
0885-8985/22/$26.00 ß 2022 IEEE
4
position of the telescopes, with the GS operating in midinclination
or equatorial regions usually registering satellite orbital
passages less frequently than the polar ones. The calculation
oforbits with periodically repeated ground tracks can identify
a set of preferred orbits for the calibrator satellite evolution,
but it is not sufficient to fully address the overall mission scenario,
since a commanded attitude is needed to guarantee the
required pointing ofthe satellite to GS.
The satellite revisit time (RT), which is the time elapsed
between two successive observations by the satellite from the
same ground point on the surface ofEarth, shall be considered
to integrate the requirements ofground track repeatability with
satellite attitude control. In fact, RT is often used as a key performance
metric for LEO systems that do not have continuous
coverage ofan area of interest and a number ofmethods have
been presented in the literature for its calculation: Wertz [1], [2]
utilized simple analytical expressions to calculate coverage
and revisit metrics; simple ground track plots and point coverage
simulation methods are used to provide statistical data of
coverage with good accuracy. Bottkol and Didomenico [3]
described a numerical phase-based approach to the calculation
ofrevisit intervals,whereas Ulybyshev [4], [5] presented a geometric
analysis method for the calculation of RT within 2%
error agreement with commercial codes. Razoumny [6] also

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IEEE - Aerospace and Electronic Systems - August 2022

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