Reshetnev University * makes space accessible

Is space exploration as an integral and conventional part of every-day life of the mankind a science fiction or reality? The mystery of the Space attracts many romantics, dreamers, and inventors. Back in the middle of the last century, people were sure that they would conquer the solar system, galaxy, and the universe. Despite the fact that since the flight of Yuri Gagarin less than 600 people have visited the Space, and the planet colonization is most likely in the distant future, everyone can take their own step to make this perspective a little closer. How can it happen? The Reshetnev University scientists answer the question. They are the University scientists who are creating small spacecraft of the CubeSat class.

Small spacecraft philosophy. Conventional spacecraft (SC) are often large and heavy. This is due to the tasks they deal with, which require high energy capabilities and large equipment. Such spacecraft in some cases can weigh several tons.

Small satellites belong to spacecraft weighing less than 500 kg. Advances in miniaturization of electronics have reduced the size and mass of many on-board systems, opening the way for miniaturizing spacecraft. The concept of small spacecraft, developed over the past 15-20 years, has become so widespread that many researchers have stated a new philosophy of designing small spacecraft, which differs significantly from the design methodology of conventional satellites.

Reasonable sufficiency in everything. The main idea of the philosophy of small spacecraft implies reasonable sufficiency in every phase to realize a successful mission. Mission goals should be specific and not overloaded with optional tasks. The space mission duration is precisely determined and does not imply an increase in length. Technical solutions laid down during satellite design (materials, structure, electronic component base, and others) should ensure an absolute fulfillment of the space mission tasks, but only for the planned period of spacecraft operation.

Minimum cost to achieve the result. Small spacecraft must be constructed quickly and have low cost. Mission objectives are compared with the cost amount. Costs should be minimal to achieve the desired result. Tasks to realize by small spacecraft should require much less money (than usual ones in the space industry) for design, launch, and operation of spacecraft in orbit. With proficient risk management, it is possible to organize a greater number of flights with time-dependent overlap and greater regularity, and thereby, ensure the continuity of the services provided to the space system users.

Proven commercial solutions. Low costs and high development speed is achieved primarily through the use of affordable and proven commercial solutions and components instead of excessively reliable and expensive components specially designed for space. Used commercial components, for example, commercial microcontroller microcircuits, memory, network interfaces and others, meet the current level of functionality while minimizing power consumption and size. Their low reliability is compensated by low orbits, where small satellites operate, and where the impact of the destructive factors of outer space is insignificant, and also by a short term of their active operational life at an orbit.

CubeSats as the brightest example of the small spacecraft. CubeSats fully comply with the small spacecraft concept, but along with their participation in the movement of small spacecraft, elements of standardization and unification are introduced and worldwide recognized.

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Figure 1 – Cubsats launched from the International Space Station (NASA photo)

A small spacecraft of the CubeSat type has got standardized dimensions and mass: a cube with a 10 cm edge and a mass of not more than 1 kg. This is a basic unit - 1U. CubeSat can have bigger dimensions, but they have to be a multiple of 1U: 1U, 2U, 3U, 6U. (Figure 1) The increase in dimensions allows locating more equipment or bulky devices.

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Figure 2 – Dimension picture.

Why do engineers need standardization? Usually launching a satellite is a minefield for developers. In case of CubeSat, a special launch container has been developed to carry up to three 1U devices or one 3U device. Standardization of the spacecraft dimensions and the development of a single launch device located in the launch vehicle, significantly reduce the number of issues to be solved in the anticipation of the launch.

Spacecraft structure. The satellite body is usually made of aluminum alloy and it is a frame inside which the devices are placed. The internal volume is not sealed, since up-to-date electronic components can operate in vacuum, temperature ratio and other conditions.

Inside there are modules of subsystems, which are usually represented by electronic circuit boards integrated into a stack (a rack, in simple words). On the outer faces of the body, there are solar panels that provide the device with energy. The device has antennas and a communications system with a ground control station that operate in the amateur radio frequency range, which greatly facilitates obtaining permission to use radio communications to control the spacecraft.

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Figure 3 – CubeSat Structure (Darbali-Zamora, Rachid & Cobo Yepes, Nicolas & Ortiz-Rivera, Eduardo & Aponte-Bezares, Erick & Rincon, Amilcar. (2018). Applying HOL/PBL to prepare undergraduate students into graduate level studies in the field of Aerospace Engineering using the Puerto Rico CubeSat project initiative. 10.1109/FIE.2018.8659049.)

The most sophisticated CubeSat system is the attitude determination and control system (ADCS). The difficulty lies in the technical performance of the system hardware devices, which must differ in minimum dimensions and power consumption for a CubeSat. The most important ability is to develop an executive control algorithm ensuring the satellite rotate to the desired position in the best way. Fig. 4 demonstrates a simplified diagram of the attitude determination and control system.

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Figure 4 – Attitude determination and control system block diagram

The required position of the device, set, for example, by a command from the ground station, is determined by the base coordinate system. The current actual angular position of the device is determined using the Sun, stars and the Earth sensors. By comparing the required and actual angular position, the position error is calculated. In order for the device to orient as required, the error must be reduced to zero.

The system controller, adhering to a certain control strategy (for example, maximizing the orientation speed, minimizing errors, minimizing the energy consumption for orientation), produces a control action on the system executive devices. Executive devices provide rotation of the spacecraft. Usually these are magnetic coils interacting with the Earth's magnetic field - the spacecraft rotates like a large compass needle. Since external forces (aerodynamic forces of atmospheric residues, the Earth’s gravitational field, solar wind, etc.) constantly impact the vehicle, its position gradually deviates from the set one. Therefore, the ADCS system works constantly in automatic mode, ensuring its required position in outer space.

To test the system algorithms, the scientists have developed a uniaxial iron bird rig to simulate the attitude determination and control system. The rig setup is suspended on a thread and rotates the platform of the vehicle around the axis of the suspension. The

control algorithms are developed in the SimInTech simulation environment. When the rig setup operates, the management controller works on a remote PC, receiving signals from real sensors and executive devices installed on the full-scale simulator of the spacecraft, therefore controlling the physical turns of the platform.

Universities are the driving force to CubeSat constructing. Actually, the CubeSat project was proposed by the university community in the USA and Japan in 1999 as a scientific and educational project. Since then, this class of spacecraft has been widely recognized in other sectors of the aerospace industry, primarily commercial, but universities still play a significant role in this project.

At Reshetnev University, the Small Spacecraft laboratory provides CubeSat constructing, designing CubeSat systems of 3U type.

Currently, several systems of the device have been manufactured: the body of the device for container launch, the on-board computer, and the engineering model of the power supply system. Other systems are under the design stage: a radio channel with the ground station, the attitude determination and control system, as well as facilities to develop the interaction of CubeSat with the ground stations, facility to test the power supply system and the attitude determination and control algorithms for the spacecraft.

Students and graduate students are involved in the development of CubeSat systems at Reshetnev University. Under the guidance of scientific supervisors, they are engaged in the development of models and software to realize spacecraft orientation and stabilization algorithms in outer space, software development for a functional facility to develop interaction between the spacecraft and a ground station, and to create a radio control channel.

It is assumed that the students’ active work of in the project will result in their interest in astronautics, will provide them with practical knowledge, and subsequently, will consolidate university graduates in the country's space industry. Therefore, simultaneously with the project realization, a scientific and educational course is created, and designed for wider audience.

The course syllabus covers the main sections related to the design and development of CubeSat: orbital motion and operating conditions of the device in outer space, the composition and description of all systems of the device, radio control of the device, CubeSat target use, including remote Earth sensing, issues of the spacecraft life cycle, as well as pre-design work, design, manufacture and launch. Therefore, the objective of the program is to give a holistic view of all stages and types of work, and tasks to be solved when designing, creating and launching small spacecraft using the example of CubeSat.

International Summer School as a platform to discuss promising areas in the field of space exploration. Now the educational program is actively developing. This year the International Summer School is planned for the first time, the school will allow participants to get acquainted with the stages of designing small spacecraft like CubeSat and its main systems, and it will also become a platform for communication of specialists involved in theoretical and practical research in this area.

Now there are hundreds of satellites in outer space, but humanity is at the very beginning of the journey. There are still many questions to answer and the most ambitious plans to realize. Although we do not have an answer to the question if the design of the "training" satellite will become a step toward large-scale space exploration, but we find the words by Konstantin Tsiolkovsky rather significant; he said: “every being should live and think as if they could achieve everything sooner or later.”

* Reshetnev Siberian State University of Science and Technology

 The material is prepared by

V.K. Khanov, D.M. Zuev, А.Т. Lelekov