Aerospace and Electronic Systems Magazine June 2017 - 17

Photo Credit: NASA

sensors for the satellite and the attitude determination is dedicated
to the laboratory and cannot be utilized for space application.
These experimental setups provide an almost frictionless media
and are very useful instruments for testing the attitude control subsystem. Nevertheless, they have fundamental deficiencies for attitude determination, even the sensors used for attitude measurement
of the tables differ from those that are used in satellites. Generally,
laboratory verification of attitude determination is more complex
than the attitude control, because of the need to simulate operating
orbital conditions for real sensors. So the simulation of environmental conditions for sensors is considered a serious problem in many
researches. A Helmholtz cage and a sun simulator are employed in
the Space Dynamics Laboratory of Utah State University to simulate the space environment for sensors [11]. The satellite dynamics
and the actuators are simulated in MATLAB SIMULINK and assist
in constructing this HIL test bed. For attitude determination and
control evaluation of IRS and SROSS satellites, two methods were
introduced [12]. The first method is a simulation of motions using
a 3-axis air bearing platform with sensors, actuators, and control
electronics mounted on it. The paper doesn't mention simulation of
the space environment for attitude sensors. The second method is
a simulation of motions using a 3-gimbal servo table platform for
sensors with control electronics and actuators outside the platform
and the control loop closed through a digital computer, which simulates satellite dynamics and drives the servo table. The simulation
setup consists of an Earth sensor and gyros mounted on a servo
table with an Earth simulator. The attitude errors (table orientation
with respect to null conditions) as sensed by the Earth sensor and
gyros are interfaced to the processor outside the servo table. The
electronic processor generates torque signals for reaction wheels to
produce control torques on the satellite. The wheel currents are read
by the digital computer, which simulates the satellite dynamics and
in turn drives the servo table. Thus the servo table simulates satellite
motions for the sensors and the digital computer simulates satellite
dynamics. In the Air Force Institute of Technology satellite simulator (SimSat), a star field simulator system concept is developed to
benefit from star tracker in attitude determination of the platform.
This simulator is a valuable device for HIL tests of a satellite [13].
Complete versions of the HIL test bed for attitude determination
and control are those described in [14]-[16]. These test beds are integrated systems, which consist of a magnetic field simulator, a sun
simulator, and an air bearing platform. They facilitate test and veriJUNE 2017

fication of the complete ADCS which may include algorithms and
filters tests, communication tests between hardware and onboard
computer as well as satellite and ground segment, test of physical reactions of the system like direction of rotation, pointing, etc.
On the other hand, the platform represents the satellite bus and is
located totally inside the Helmholtz cage, so that the ferromagnetic
components of the table can affect the homogeneity of the magnetic
field. In addition, development of these systems for other elements
such as Earth simulator or star simulator has serious limitations. In
this article a new plan for attitude determination and control testing
is represented. This plan is based on the integration of distributed
components of the ADCS test bed and data transmitting between
different parts.
Unlike most of the previous works [1]-[13], we have designed
a new plan, including some real space sensors which are often used
in different satellites in simulated environments. Accordingly, the
reported tests have been performed in more real conditions. Furthermore, in comparison with integrated HIL test beds [14]-[16],
our innovative setup effectively reduces the interferences of different simulators and consequently facilitates the development for
other sensors, actuators, and required environments. Another advantage of this work is that the elements of the test bed can be used
individually or in an integrated HIL setup, without fundamental
modifications. In fact, here we have developed one setup for two
different applications which provide better efficiency and cost reduction in hardware resources.

SETUP DESCRIPTION
The block diagram of the new HIL setup is shown in Figure 1.
This test bed provides the possibility of evaluation of a satellite attitude determination and attitude control simultaneously. Simulating environmental conditions is one of the fundamental differences
between the proposed design and the others that were reviewed in
the introduction. Although similar to other designs, an air bearing
based platform simulates the attitude dynamic. We create environmental conditions for sensors in separate locations concurrently. In
other words, here the attitude determination and the attitude control operate in separate locations.
The proposed setup is structured of the following main elements:
an attitude control simulator, a sun simulator located in a dark room,
a 2 DOF controlled table and a sun sensor mounted on it, an Earth

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Table of Contents for the Digital Edition of Aerospace and Electronic Systems Magazine June 2017