IEEE - Aerospace and Electronic Systems - December 2021 - 6

Feature Article:
DOI. No. 10.1109/MAES.2021.3089233
Estimation of the CubeSat'sAvailable Energyfor
Free-Orientation Scenario
Alexander Lelekov , Federal Research Center " Krasnoyarsk Science Center of
the Siberian Branch of the Russian Academy of Sciences, " Krasnoyarsk
660036, Russia
INTRODUCTION
When designing an electrical power system for CubeSats,
the available energy is usually estimated first, then the
energy budget is calculated, taking into account the load
consumption. This is a simple operation if the exact
amount of available electrical energy is known; however,
sometimes it can be quite difficult to estimate it.
For example, how would we estimate the energy budget
for a CubeSat without an attitude control system
(ACS)? Or when the attitude control failed? When the
CubeSat is released from the launch container, it inevitably
begins to rotate, and it is difficult to predict in advance the
direction ofthe rotation axis and the magnitude ofthe angular
velocity, which are mostly determined by random factors;
so how much energy can we get from the solar array
(SA) in this case? Undoubtedly, these are quite important
cases that require an estimation ofthe available energy.
As is known [1], to estimate the energy budget, we
need to know the orbit average power, generated by SA. It
depends on many factors: orbital parameters (duration of
illuminated and shadow areas), electrical characteristics
of solar cells, their temperature, and state of health; this
parameter can be calculated or measured fairly easily. The
power of SA also depends on the illumination-the
amount of solar power that reaches the solar cell per unit
area. This energy is determined by the orientation scenario
(and attitude control method) of a CubeSat, since it
depends on the angle between the direction of sunlight
and the normal to the SA surface.
From an energetic point of view, all orientation scenarios
can be divided into three groups, differing in the
degree of certainty of the SA attitude relative to the sunlight
vector.
SA ATTITUDE RELATIVE TO THE SUNLIGHT VECTOR IS
PREDETERMINED AND KNOWN
This is the case when the SA is pointed toward the Sun, or
when CubeSat has an active three-axis ACS. The calculation
of the energy budget in this case is quite simple [2]-[4]: SA
illumination is calculated as a function of time in advance,
the best and worst cases ofthe load consumption are selected,
and the energy budget is calculated from them.
SA ATTITUDE RELATIVE TO THE SUNLIGHT VECTOR IS
PARTIALLY DETERMINED
Author's current address: Alexander Lelekov was with
the Federal Research Center " Krasnoyarsk Science
Center of the Siberian Branch of the Russian Academy
of Sciences, " Akademgorodok 50, Krasnoyarsk 660036,
Russia (e-mail: a.t.lelekov@yandex.ru).
Manuscript received November 16, 2020, revised April
11, 2021; accepted May 16, 2021, and ready for
publication June 11, 2021.
Review handled by Richard Linares.
0885-8985/21/$26.00 ß 2021 IEEE
6
This is the cases when CubeSat has a one-axis ACS, active or
passive (except, of course, when one of the axes is oriented
toward the Sun). This is, for example, the case when the
CubeSat axis is oriented along the local vertical for the payload
operation (nadir-oriented scenario) [5], [6]; passive orientation
by earth magnetic field with permanent magnet [7],
[8]; aerodynamic stabilization toward the velocity vector [9]-
[11]; spin stabilization ofthe CubeSat [12]. See power budget
calculation examples in references.
Here, the calculation of the available energy usually
involves the setting of restrictions on the CubeSat's attitude-its
angular position relative to the sunlight must be
known (functionally set) for any moment of time or its
orbital position [5]-[8], [11]. In the simplest case, its position
is constant, i.e., it does not rotate at all [12], [13]. But
the satellite still has degrees of freedom; SA illumination
can vary within certain limits, which introduces uncertainties
in the calculation of the energy budget.
IEEE A&E SYSTEMS MAGAZINE
DECEMBER 2021
https://www.orcid.org/0000-0003-1160-8997 https://www.orcid.org/0000-0003-1160-8997 https://www.orcid.org/0000-0003-1160-8997 https://www.orcid.org/0000-0003-1160-8997 https://www.orcid.org/0000-0003-1160-8997
IEEE - Aerospace and Electronic Systems - December 2021

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