=Paper=
{{Paper
|id=Vol-1490/paper29
|storemode=property
|title=Structure and algorithms of motion control system's software of the small spacecraft
|pdfUrl=https://ceur-ws.org/Vol-1490/paper29.pdf
|volume=Vol-1490
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==Structure and algorithms of motion control system's software of the small spacecraft==
https://ceur-ws.org/Vol-1490/paper29.pdf
Mathematical Modeling
Structure and algorithms of motion control system's
software of the small spacecraft
Filatov A.V.,
Progress Space Rocket Centre, Samara
Tkachenko I.S., Tyugashev A.A., Sopchenko E.V.
Samara State Aerospace University
Abstract. The paper is devoted to some features and algorithms of AIST-2D
experimental technological small spacecraft‘s Motion Control System Software.
Special Flight Control Software is embedded in Motion Control System. There
are several modes of software functioning depending on state of the spacecraft.
There are descriptions of the basic software algorithms in the paper.
Keywords: Motion Control System, Flight Control Software, Real-Time
Control Algorithm, Program Turn
Citation: Filatov A.V.,Tkachenko I.S., Tyugashev A.A., Sopchenko E.V.
Structure and algorithms of motion control system's software of the small
spacecraft. Proceedings of Information Technology and Nanotechnology
(ITNT-2015), CEUR Workshop Proceedings, 2015; 1490: 246-251. DOI:
10.18287/1613-0073-2015-1490-246-251
1. Introduction
Software is a very important part of every modern space project. The errors and
glitches of Flight Control Software could lead to critical consequences including
losses of expensive spacecrafts. Onboard computational opportunities are the basis for
successful execution of widespread spectrum of tasks in long space flights [1]. This
issue is important even for micro- and nano- satellites which represent the very fast
growing segment of the spacecrafts.
The Motion Control System (MCS) of the AIST-2D small spacecraft includes both
hardware (sensors, devices and aggregates) and software [2].
The MCS should perform the following:
─ quieting of the spacecraft after separation from the launch vehicle;
─ orientation of the spacecraft with a given accuracy in the Orbital Coordinate
System;
─ orientation of the solar panels’ surfaces towards the Sun with a given accuracy;
─ self-diagnostic information’s forming and transmission to Earth;
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─ form and send information about the spacecraft angular position to the Onboard
Control System (OCS) upon request;
─ support the mode without control pulses.
After the separation from the launch vehicle’s upper stage or after the Undirected
Flight Mode (UFM), the Mode of Compensation of the Initial Angular Velocity is
being started by activation of Executive and Sensing Elements Complex (ESEC).
When the angular velocity reaches the given value, Single-Axis Solar Orientation
Mode will start automatically. This mode supported until the moment of request from
the Onboard Control System to start Three-Axis Orientation in Orbital Coordinate
System Mode. The switching between the MCS modes is possible by transmission of
the special command messages. Timing Diagram of the MCS functioning is being
presented in Fig. 1.
So, in accordance with its purpose, MCS supports the following set of modes:
─ Compensation of the Initial Angular Velocity Mode (MCIAV);
─ Single-Axis Solar Orientation Mode (MSASO);
─ Three-Axis Orientation in Orbital Coordinate System Mode (MTAORS);
─ MCS experiments Mode (MMET).
Fig. 1. – Motion Control System Functioning Timing Diagram
2. Modes Description
Compensation of the Initial Angular Velocity Mode starts after its activation
and should compensate the angular velocity of the spacecraft. The mentioned angular
velocity could be formed after the separation from the upper stage or during the
Undirected Flight.
With decreasing kinetic moment of the apparatus to a predetermined value
(corresponding to the angular velocity of 0.07 degrees per second), the MCS
automatically activates (without control actions from the OCS) stabilization using the
Reaction Wheels.
Next, on the time interval of 100 sec, the process of angular velocity damping
process is being performed with the use of Reaction Wheels.
MCIAV ends automatically by the transition to Single-Axis Solar Orientation
Mode.
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Single-Axis Solar Orientation Mode designed to support orientation the surfaces
of the solar panels towards the Sun with a given accuracy.
The Mode starts automatically after the end of the MCIAV or by the request from
the OCS. The command message from OCS is being transmitted using the special
channel of information exchange.
The first operations of the MSASO are activation of the Orbital Solar Sensors
(OSS) and checking of the Sun’s detection. If the Sun detection process completed
successfully by at least the one OSS, the Program Turn into Solar Orientation will be
activated.
If the Sun cannot be detected, the spacecraft begins the rotation to find the Sun.
The maximal duration of the Sun Search process depends on angular velocity and
guaranteed review of the full sphere by the Sensor’s Visual Field. Thus, the maximal
duration of the search will not exceed 600 sec (excluding time of shadow).
The velocity of the search is 1 degree per second.
After the Program Turn, the stabilization in Solar Orientation begins. In this case,
the combination of the axis of OYSCS with the direction vector to the Sun in
Associated Coordinate System should be carried out.
The Mode continues until reception of command message from the OCS to change
the MCS mode.
Three-Axis Orientation in Orbital Coordinate System Mode should support
Spacecraft’s orientation in the Orbital Coordinate System with the given accuracy and
support the Program of Angle Motion Control. This Program implements the Time
Control Method and starts upon request from OCS.
The Mode starts by the command message from OCS via information exchange
channel.
The first actions of the Mode are the following. The Search of Earth (SOE) process
starts and it checks if the Earth detected in the spacecraft’s field of view. If there is no
Earth in the field of view in initial position, the SOE should be executed by the
spacecraft’s rotation.
The maximal duration of the SOE process depends on angular velocity and
guaranteed review of the full sphere by the Sensor’s Visual Field. The maximal
duration of the search is not exceeds 300 sec. The velocity of the search is 1 degree
per second.
After the successful end of Earth’s detection process, the pre-defined sequence of
algorithm’s segments will be implemented. After completion of the mentioned
segments, the spacecraft will have the right orientation in Orbital Coordinate System
and will be ready for implementation of Program of Angle Motion Control.
This Program can be initiated by the one of the following:
1. Array containing the time of turn’s start and the quaternion defines the position of
the Solar Coordinate System in the Orbital Coordinate System at the moment of
the end of turn;
2. Array of the parameters (Ai, ωi, φi) which define angle position of Solar Coordinate
System relatively to Orbital Coordinate System, by the three channels. In this case,
Program of Angle Motion Control is being formed by MCS in accordance with the
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expression: ψi = Ai·sin(ωi·t+φi), considering correspondingly the angles of roll,
yaw, pitch.
3. Array containing the polynomials of approximation – Program of Angle Motion
Control for the each channel.
The Mode executes until receiving the command message from the OCS to change
the mode of functioning.
MCS experiments Mode should support tests of the MCS equipment and
checking of the experimental algorithms of the MCS functioning.
The Mode starts by the command message from the OCS to implement the tests or
experiments. Which devices of MCS will be used, depends on the program of
experiment.
The Mode is active until the command message from the OCS to change the mode
of functioning.
To effective implementation of the all described modes of MCS functioning, the
development of the AIST-2D software includes the following steps:
─ Development of the technical overviews of the software algorithms;
─ Programming;
─ Unit testing;
─ Integration testing using the emulator of Earth’s Debug Testbed Complex;
─ Complex testing and debugging of the software using the Earth’s Debug Testbed
Complex.
All algorithms of the MCS’s onboard software can be divided into the following
categories:
System Algorithms:
─ Planning of the MCS functioning;
─ Collection of telemetry information and its output to OCS;
─ Forming of control information related to angle motion of the spacecraft;
Algorithms of the MCS Modes:
─ Solar System Coordinates Orientation of the spacecraft;
─ Orbital System Coordinates Orientation of the spacecraft;
─ MCS control in case of technical faults;
─ MCS tests and experiments;
Device control algorithms:
─ Fiber-optic gyroscopes control;
─ Reaction Wheels control;
─ Star trackers control;
─ Magnetic Executives control;
─ Magnetometers control ;
─ Optical Solar Sensors control;
─ Earth orientation devices control;
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Algorithms of Stabilization:
─ Spacecraft Motion Control by Reaction Wheels;
─ Kinetic Moment Clear;
─ Program Turn;
─ Calculation of Control Parameters;
─ Program of Angle Motion Control Forming;
─ Algorithms of Orientation Detection;
─ Solar Orientation;
Algorithms of Control:
─ Control of Redundancy in case of technical faults;
─ Control of Stabilization using Reaction Wheels;
─ Control of Magnetic System;
Algorithms of Experiments:
─ Orientation Detection using Angle Velocity measurement and data from Star
Trackers;
─ Orientation Detection in Inertial Coordinate System using Star Trackers.
3. Conclusion
Thus, algorithms and Flight Control software of AIST-2D small spacecraft’s MCS
provide:
1. Compensation of the angle velocity after the separation from the upper stage of the
launch vehicle (duration of the compensation process not more than 3 hours when
angle velocity less than 7 degrees per second and 2 hours 15 minutes when angle
velocity less than 3 degrees per second);
2. Orientation in Orbital Coordinate System with the error less than (with probability
Р = 0,96):
(a) by the angle position
(i) not worse than 30 angle minutes (without additional navigation
information);
(ii) not worse than 30 angle minutes in of pitch and roll channels и 10 angle
minutes in yaw channel (with usage navigation information);
(b) by angle velocity - 0,005 degrees per second;
3. One-axis solar panels orientation towards the Sun with the error not exceeds
(Р = 0,96):
(a) in angle position – 3 degrees;
(b) in angle velocity - 0,5 degrees per seconds in all channels;
4. Maximal angle velocities of the spacecraft during Program Turn – 1 degree per
second;
5. Maximal angle acceleration during Program Turn - 0,029 degrees per quadrate
seconds;
6. Transition from Solar Orientation into Orbital Orientation and in reverse order:
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(a) 10 minutes (using additional data about center of mass position);
(b) 25 minutes (without navigation information).
7. Reaching of maximal accuracy in Orbital Coordinate System for no more than 35
minutes from the moment of building of Orbital Orientation.
Acknowledgment
The authors would like to thank the reviewers for the valuable comments and
suggestions. Development of the Earth observation small spacecraft, including
development of the algorithms and software, is being carried out in accordance with
the Complex Project of Samara Progress Rocket Center and Samara Space Aerospace
University «Creation of the high-technology manufacture of small Earth observation
spacecrafts with the using of hyper-spectral devices for the social and economical
development of Russia and international cooperation» (this work is partially
supported by the Government of the Russia in accordance with Decree No. 218 dated
09.04.2010). This work was also supported by the Ministry of Education and Science
of the Russian Federation.
References
1. Journal Aircraft Engineering. Vol. 6: The results of science and technology VINITI.
Moscow, 1998. [in Russian]
2. Sevastyanov NN, Branets VN, Panchenko VA, Kazinskiy NV, Kondranin TV,
Negodyaev SS. The analysis of the modern opportunities of small Earth observation
satellites’ development. Proceedings of MIPT, 2009; 1(3). [in Russian]
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