A shift from small constellation system of large satellites towards large constellation system of small satellites in space architecture
Abdul Sami, Ph.D. Fellow/ Early Stage Researcher (TESLA project H2020-MSCA-ITN) at the Microwave Components Group (MCG), Department of Electrical, Electronic and Communications Engineering, Public University of Navarre (UPNA)
Satellites are objects or machines orbiting around the earth for a purpose. There are two types of satellites. Natural satellites and artificial satellites. A basic example of natural satellite is moon orbiting around the earth which exists naturally, therefore, moon is a natural satellite. Artificial satellites are man made machines which orbit around the earth for special purposes. The purposes include communication, defense, weather forecasting and research etc. Constellation system is a group of satellites combine to enhance operation capabilities in space. Traditionally, small constellations of large and complex satellites have been installed in space to carry out desired operations. But form the last decade, a new trend has been initiated by space industries where the idea of large constellations of small satellites has emerged in the market. This new idea is become feasible due to the rapid advancements in technology in the recent years. In this article, I will discuss the strengths and weaknesses of both constellation systems, evolution of space architecture, the current challenges for large constellation of small satellites and the market trends.
Constellation system of small satellites
Satellite mass is generally related with complexity and cost. Therefore, satellites are classified into different classes based on their mass at the time of launching. Satellites which have mass 1200 kilograms or less are categorized as small satellites, similarly satellites in the mass range between 1201 to 2500 kilograms are classified as medium, 2501 to 4200 kilograms are intermediate, 4201 to 5400 kilograms are large, 5401 to 7000 kilograms are heavy, 7001 and above are extra heavy satellites. Small satellites are further classified into six sub-categories from femto to small. Satellites of mass 0.01 to 0.1 kilograms are classified as femto, 0.11 to 1 kilogram are pico, 1.1 to 10 kilograms are nano, 11 to 200 kilograms are micro, 201 to 600 kilograms are mini, and 601 to 1200 kilograms are small satellites. The difference between the mass of smallest to the largest satellite categories represents the development in the space technology and shift in the space architecture. Currently, small constellations of large and complex satellites have dominated the commercial space industry. This dominance is measured in terms of mass shared by currently active large and small satellites in space architecture. The Union of Concerned Scientist (UCS) has shared the mass of 225 out of total 235 active European commercial satellites in their database. There are 163 pico to small satellites out of 225 satellites which represents 72% share by number while the mass share of these satellites is 16%. Similarly, there are 8 medium satellites and their share by number is 4% and by mass is 5%, 19 medium satellites with 8% share by number and 21% by mass, 12 large satellites with 5% share by number and 20% by mass, 19 heavy satellites with 8% share by number and 38% by mass. Even though the large and complex satellites have dominated the current commercial space market in terms of capabilities and investment, small satellites are also emerging as alternate options for investment in the space market. The growth in number of small satellites installed in recent times is seen because of the lower cost, greater capability now possible with small satellites and the possibilities of large constellation systems. In the recent past, Planet a space company has completed a constellation system of 175 small satellites for optical imagery purpose . A huge constellation of small commercial satellites is initiated by OneWeb and Airbus for global internet service. Currently, they are planning a constellation of 720 satellites with weight of 150 kilograms of each satellite and per unit cost varies from $500000 to $1 million . Installation of constellation has been started in 2019 and is projected to start services by the end of 2020. This project is planned to add more 1260 satellites until 2027 . Projects like these show that the number of small satellites in space will grow in the coming years. According to a forecast, a number nearer to 11600 small satellites are planed by different space companies to be placed in orbit between 2018 to 2030 with an annual average of approximately 1000 satellites . These numbers still suggest that large and costly satellites will dominate the space industry for at least one more decade but still a major shift will be observed towards large constellation systems in the space market. Trends in the miniaturization in electronics and other related technologies to satellites and satellite launch cost and launch vehicles will shape the small satellites market.
The miniaturization trends in various technologies like communication equipment, electronics, computing, and sensors has benefited all type of satellites. The most important are electronics and computing for space industry. Both these technologies have achieved significant improvement in the miniaturization in the past years. Today’s smart phones have greater processing power than mainframe computers a few decades ago. Apart from computing technologies, other technologies like mechanical parts and sensors have also experienced significant improvement in miniaturization. These trends not only enable to reduce the size of satellite payloads but also reduce the cost. Because of the above miniaturization trends, the capabilities of small satellites have been improved and developed small satellite market. Despite all these advancements, launch cost is still a big challenge to small satellites. Small launch vehicles are very less efficient than heavy launch vehicles which makes launch cost a big challenge for small satellites. The important point is when will the space industry be able to develop cost effective small launch vehicles. It is still not very clear but according to some observers, a big break through is expected soon.
It is very much expected in the coming years that big constellation systems of small satellites will be more cost-effective with respect to small constellation of large satellites due to the miniaturization and more importantly due to launch cost. These trends can be predicted due to the placement of small constellation of large satellites in geostationary orbit (GEO) which is 35700 kilometers above the earth whereas large constellation of small satellites are placed in lower earth orbital (LEO) which is some hundred kilometers above the earth. So, LEO much nearer to earth than GEO. Due to large distance between earth and GEO, these satellites must be equipped with high power communication equipment and high cost sensors than satellites in LEO. Currently, small satellites are not cost effective when compared with large satellites mainly due to the launching cost. Small launch vehicles or micro launchers are used to launch small satellites up to 350 kg in LEO while medium and heavy launch vehicles are used for launching both GEO and LEO satellites. Micro launchers are like taxis for small satellites where they deliver small satellites at the exact points but at higher costs. On the other hand, medium and heavy launchers are like public buses for satellites which are less expensive but slower and lower availability (satellites must wait for their time slot to be launch). Therefore, medium, and heavy launchers are more efficient for big constellations but in case satellites are required to place in different orbits then it is better to use micro launchers and place satellites in their final exact orbit one by one. Moreover, large number of small satellites are launched to LEO in case of big constellation system whereas few satellites are launched to GEO in case of small constellation system, therefore, overall launching costs of LEO is relatively high when compared with GEO. In Spain, a space company called PLD Space has developed two micro launchers called Miura 1 and Miura 5. Miura 1 is designed for sub-orbital flights (where the launcher does not reach to orbit) to enhance scientific research and technology under microgravity conditions. Miura 5 is mainly designed for launching small satellites. There are 100s of companies in the world offering (or promising to offer in the future) launching services: some of them will survive, some others will disappear. There are companies that launch small satellites from airplanes. This is nice but less reliable and expensive. While some companies launch small satellites from platforms in the middle of the sea, but these are not cost effective if we do not launch many satellites per year (maintenance costs). There are also political issues with them. There is also a risk of failure involved in micro launchers. Although constellation system of small satellites shows more resistant to such type of failures than the traditional heavy launchers, but still high failure rate which may be technically acceptable may create safety concerns in populated regions. That is why PLD Space performs its trails from very low populated coastal regions in the south of Spain. In this short discussion, I have briefly discussed the weaknesses and strengths of LEO and GEO. In practical, there are many tradeoffs involved while designing a constellation system. It is far more complex process than the process I discussed here.
Satellites orbits around the earth.
I am pursuing PhD in Electrical Engineering at UPNA, mainly focused to develop techniques to design passive components (filters) aiming for low cost fabrication to be used in small satellites in future. I am a part of European research group called TESLA where UPNA is one of the beneficiaries of the project. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 811232.
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