The NANOSATELLITES – Concept, challenges and prospects

1. 

   By Prof. Ahmed Hanafi, Professor of Electrical Engineering, Industrial Computing and Embedded Systems, Sidi Mohamed Ben Abdellah University in Fes Morocco (*).

   1. STATE OF THE ART OF NANOSATELLITES

   1.1. Classification of satellites

   To start the space age, three small satellites were the first to be launched into low Earth orbit (LEO) during the International Geophysical Year (IGY) from 1957 to 1958: Sputnik I, Explorer I and Vanguard 1:

Figure 1: Views of the space segments of the Sputnik I, Explorer I and Vanguard 1 missions [1] 

A classification system was first proposed by the Satellite Engineering Research Center at the University of Surrey in England, and it was readily adopted by the entire satellite community [2]. Table 1 summarizes this classification, where each class spans a range of deployed mass which is defined as the mass of the satellite plus that of the fuel.Table 1: Classification of satellites according to their mass

1.1. System description of a nanosatellite

From the system point of view, it is practical to subdivide a spacecraft or satellite into several functional elements as shown in Figure 2. We thus distinguish.

• A space segment commonly called a satellite.

• A ground segment made up of one or more ground stations whose role is to send commands to the space segment and to receive telemetry data and data from the onboard payload via a radio frequency link.

Figure 2: Global view of the system including space segment and ground segment

Each of the elements of the space system can be considered as a subsystem performing functions that will be associated with it, and interacting with the others according to the objectives and functional requirements of the mission.In the case of a nanosatellite, the space segment generally consists of two parts.·

  The payload which depends on the mission. Given the mass constraint of nanosatellites, this payload generally consists of carrying out scientific experimentation in space (evaluating, verifying and validating certain communication technologies and protocols).

• The space segment platform is made up of several subsystems that ensure the smooth running of the mission. For nanosatellites, these are generally the following subsystems:

Figure 3: Space segment subsystems

• Structure (STR) or chassis which provides, on the one hand, a mechanical interfacing between the space segment and the launcher, and on the other hand, a safe operating environment against the effects of space radiation.

• Attitude Control (ATT) ensures optimal orientation of the space segment in space according to the mission objectives.

• On-board Energy (EdB) whose main tasks are the production of electrical energy from solar cells, its storage in batteries, and its secure regulation/distribution to the various on-board subsystems in the space segment according to their consumption needs.

• Thermal Control (THER) which must guarantee the space segment a thermal environment allowing its nominal operation in a temperature range between -40°C and +80°C.

• Communication (COM) which is composed of a radio transmitter/receiver ensuring a reliable link between the space segment and the ground segment.

• On-board computer (OdB) which is the main system for processing data and remote controls. It must thus guarantee a stable operational state of the space segment by ensuring all the supervision and control tasks.

• Antenna Deployment Mechanism (ANT) which is a specific system for nanosatellites, with the main role of keeping the antennas in place during launch, and their deployment once the space segment is in orbit.

2. THE CUBESAT CONCEPT

   • Setups

The CUBESAT concept was proposed by Robert Twiggs (1999) and created following a collaboration between Stanford University and California Polytechnic University (Cal Poly). It was intended to meet the need to have a satellite that could be developed within 2 years, at a very low cost and with low weight to reduce launch costs.

This standard defines the space segment configuration, mass, volume, external dimensions, test procedures, and energy and operational constraints [3]. The best known configurations are the 1U, 2U and 3U Cubesats, where each “U” represents a 10 cm cube. For example, Figure 4 shows the planned integration of the MASAT1 academic nanosatellite space segment platform subsystems in a 1U configuration (nominal dimensions of 10 x 10 x 10 cm and mass up to 1.33 kg):

Figure 4: MASAT1 space segment 1U configuration

Table 2 summarizes some of the leading providers in the Cubesat market:

2.2 Technologies

Cubesats are currently designed for low Earth orbits (LEO) and the scope of their applications has increased dramatically over the past decade, largely due to technological advances in areas such as microelectronics, low-power communication modules , high efficiency photovoltaic solar cells, high energy density batteries, low power microcontrollers and high efficiency miniature motors/actuators.

Nevertheless, the small mass and dimensions specific to Cubesats considerably limit the amount of energy available in orbit, which remains a constraint both for the performance of the processors, for the use of redundant systems, for the communication which does not have enough power to transmit continuously, and for the choice of the useful mission.

             2.3 Deployment Systems

The key to the success of the Cubesat concept is to be able to use an in-orbit deployment system that meets a number of requirements, namely [3] [4]:

• The deployment system must protect the launcher and the primary load against any mechanical, electrical or magnetic interference from Cubesats which are considered secondary loads.

• The Cubesats must be able to be released from the deployment system using the minimum number of springs to minimize the probability of collision with the launcher and with the other Cubesats

.• All Cubesat components must remain attached during the launch and deployment process. No additional space debris should be created.The most used solution is a “container” called P-POD (Poly Picosatellite Orbital Deployer), developed by the Polytechnic University of the State of California (Cal Poly). Certified by a large number of launchers [5], the P-POD Mark III provides an enclosure strong enough to withstand a structural failure of the three Cubesats it can contain, while acting as a Faraday cage to protect the launcher primary payload: la charge utile primaire du lanceur :

Figure 5 : Système de déploiement P-POD [3]

Figure 5: P-POD deployment system [3]It should be noted that since the year 2008, the deployment of Cubesats from the International Space Station (ISS), which is located at an altitude of approximately 400 km, is possible thanks to the “KiboCUBE” module developed by the Japanese agency Aerospace Exploration (JAXA) [6]. This system is composed of an airlock and a robotic arm as shown in Figure 6:

Figure 6: KiboCUBE deployment system [6] 

3.   DEVELOPMENT PHASES OF A SPACE MISSION

The life cycle of a space mission typically progresses through 4 phases [7]:

• Phase 0 of initial study: This results in a broad definition of the space mission, functional and operational requirements, as well as constraints.

• Phase 1 of formal design: This results in the development of an engineering model of the nanosatellite with the design of the various subsystems that compose it.

• Phase 2 of production and deployment: This results in the creation of a flight model of the nanosatellite (development of flight hardware and software), and the establishment of an operational ground station.

• Phase 3 of operations: This involves putting the nanosatellite into orbit, monitoring it, operating it and maintaining it during the mission.As shown in Figure 7, these phases can be divided and named differently depending on the space agency chosen as reference: ESA or NASA. Each phase has a duration depending on the scope and objectives of the mission; and it must result in a deliverable document (review) that will be the basis to evaluate and validate the work carried out, and allow progress throughout the life cycle of the mission.As a reference framework for the MASAT1 project aimed at the realization of a Moroccan university nanosatellite, we partially used the ECSS (European Cooperation for Space Standardization) standards of ESA, designed to develop a unique set of coherent space standards to be used by the entire European space community [8].

More specifically, in the analysis phase of the MASAT1 mission, we applied the project planning and implementation standard ECSS-M-ST-10C which encompasses the entire process to be carried out to plan and execute a space project in a coordinated way; efficient and structured. This process includes the definition of project phases and the schedule to control the progress of the work in terms of cost, deadlines and technical objectives, as shown in Figure 8:

Figure 7 : Les phases de développement d’une mission spatiale

Figure 8: Tasks to be performed and Planning of the MASAT1 mission

2.   CHALLENGES AND PROSPECTS OF NANOSATELLITES IN MOROCCO

The project entitled MASAT1 is an applied research project which aims to produce the first Moroccan university nanosatellite. The project, launched in 2015 with the effective participation of the Sidi Mohamed Ben Abdellah University of Fez and the Al Akhawayn University of Ifrane, had as its main ambition to promote research and development in the field of space engineering, as well as making space scientific exploration accessible to Moroccan academics.In a context where the aeronautics and space sector have been identified by Morocco as a source of growth for the national economy, this project was of strategic importance, especially that according to SpaceWorks Enterprises, the nano/ low-cost microsatellites (1-50kg) were expected to experience an annual increase of 23.8% over the period 2014-2020 [9].The work carried out enabled us to achieve the following objectives:

• Acquire basic technology and knowledge on space engineering, through the complete development of the subsystems constituting the platform of the space segment of a Cubesat in 1U format. This knowledge covers varied fields such as orbital mechanics, electronics, telecommunications, real-time kernels, networks, systems modeling (UML and Sys ML) or CAD (Solidworks or Catia).

• Provide, for future Moroccan researchers in the space field, a complete and detailed literature concerning the state of the art and the design stages of nanosatellites, in order fill the gap in this field in Morocco.But the challenges remain enormous for the academics to carry out a project as complex as a space mission aiming at the realization of a nanosatellite. Some are presented as folllow:

• The method of financing university projects which causes delays in respecting the schedule set for the mission.

• The inadequacy of existing laboratories with the nature of testing and design work such as the lack of clean rooms.• The lack of efficiency, rigor and common vision in the collaboration between the different university structures. Regarding future prospects, we hope that this project will encourage the establishment of a center of expertise in the field of nanosatellites. The purpose of which will be:• The promotion of research and development in the field of space engineering.

• The launch of other 3U cubesat missions which will build on the future success of the MASAT1 mission.• The establishment of scientific collaborations with international university structures and private operators.

(*) Prof. Ahmed Hanafi, Professor of Electrical Engineering, Industrial Computing and Embedded Systems, Sidi Mohamed Ben Abdellah University

Higher School of Technology – FES, Department of Electrical & Computer Engineering

 

References

[1]     M. Gruntman, Blazing the Trail. The Early History of Spacecraft and Rocketry, Fig. 15.30, p. 375, AIAA, Reston, 2004.

[2]     Gallton, Daniel A., “The challenge of small satellite systems to the space security environment,” NPS Outstanding Thesis Collection, 2012.

[3]     CubeSat Design Specification (CDS) Rev.13 CubeSat Program, Cal Poly

[4]      Heidt, H., Puig-Suari, J., Moore, A., Nakasuka, S., and Twiggs, R., “CubeSat : A new generation of picosatellite for education and industry low-cost space experimentation,” Proceedings of the Utah State University Small Satellite Conference, Logan, UT, Citeseer, 2001, pp. 1–2.

[5]     Poly Picosatellite Orbital Deployer Mk. III Rev. E User Guide CubeSat Program, Cal Poly

[6]     Programme “KiboCUBE” de coopération ONU-Japon sur le déploiement de CubeSat à partir de la Station spatiale internationale (ISS) : http://www.unoosa.org/oosa/fr/ourwork/psa/hsti/ kibocube.html

[7]     W. J. Larson et J. R. Wertz, “Space Mission Analysis and Design,” Space Technology Library, Microcosm Press E1 Segundo, California, 2005.

[8]     M. Jones, E. Gomez, A. Mantineo and U.K. Mortensen, “Introducing ECSS Software Engineering Standards within ESA”, ESA Bulletin 111, Août 2002.

[9]     Buchen, E. and DePasquale D. “2014 Nano/Microsatellite Market Assessment, SpaceWorks Enterprises”, Inc. (SEI) 2014