Nanosatellite and microsatellite refer to miniaturized satellites in terms of size and weight, in the range of 1-10 Kg and 10-100 kg, respectively. These are the fastest growing segments in the satellite industry. ‘CubeSat’ is one of the most popular types of miniaturized satellites. CubeSats were made possible by the ongoing miniaturization of electronics, which allows instruments such as cameras to ride into orbit at a fraction of the size of what was required at the beginning of the space age in the 1960s.
The trend toward small-sized spacecraft continues in government applications and is even increasing in commercial space endeavors that are funded by venture capital. Small spacecraft, including nanosatellites, microsatellites, and small satellites (smallsats), are an attractive alternative to traditional, larger spacecraft due to reduced development costs, decreased launch costs, and increased launch opportunities. CubeSats reduce launch costs in two fundamental ways. They don’t weigh that much, which means a rocket doesn’t need a lot of fuel to heft them. In most cases, they also share a rocket with a larger satellite, making it possible to get to space on the coattails of the heavier payload.
One of the major advantages of nano and microsatellites are reduction in delay and low cost of building and operating these satellites. This means strongly reducing spacecraft lifecycle costs and lead time, without reducing (and most likely increasing) performance. In turn, this would allow the full potential of space to be exploited and space-based systems to be competitive with ground-based systems that provide similar services.
Modern small satellites has not only small size, light weight, high technology, good performance, high reliability, short development cycle, but also adaptability, ease of management, low risk, and thus has a broad development and application prospects. It can be used as a single satellite, but also satellites constellation.
Nanosatellites and microsatellites find application in scientific research, communication, navigation and mapping, power, reconnaissance, and others including Earth observation, biological experiments, and remote sensing. There is also growing utilization of miniaturized satellites for military and defense applications. Defense organizations have been launching communication nanosatellites and microsatellites to provide communication signals to soldiers stationed in remote locations or in dense forests. The military needs more data bandwidth and reliable communications infrastructure for its UAVs, which can be fulfilled using constellations of nano and microsatellites.
A significant disadvantage, however, of a small spacecraft is its reduced or limited capabilities. The physical size of the small spacecraft reduces the size of the payload and/or the number of payloads that it can host, its propulsion capabilities, and its power. To build such small, lightweight and intelligent spacecraft poses tremendous challenges.
Small spacecraft are most commonly used in low Earth orbit, limiting the number of observation opportunities for a particular area of the Earth or space and the number of ground station downlink opportunities for stored data. These constraints affect the complexity and types of applications that small spacecraft can serve. Using multiple spacecraft that work together can overcome many of these limitations and expand the utility of small spacecraft. Two concepts for cooperative groups of spacecraft are constellations and clusters.
Micro-nano satellite platform Challenges
The basic design of a CubeSat is a 10-centimeter (4-inch) cube with a mass of less than 1.33 kilograms (2.93 lbs.), But variations on the theme are possible. CubeSats can also be designed to encompass two, three or six 10-centimeter units for more complicated missions.
To build such small, lightweight and intelligent spacecraft poses tremendous challenges. The biggest challenge is miniaturization, virtually every spacecraft subsystem needs breakthroughs in fully functional miniaturized components in order to make the intelligent nanosatellite constellation feasible.
A key technical challenge for small spacecraft, constellations, and clusters is communication of data. Communication challenges exist for accommodating varying numbers of users, serving high user densities in a given geographical area, and providing a consistent quality of service for different types of applications (e.g., Internet access, voice communication, machine-to-machine).
The electronics are smaller and are therefore more sensitive to radiation. Because they are small, they cannot carry large payloads with them. Their low cost also means they are generally designed to last only a few weeks, months or years before ceasing operations (and for those in low Earth orbit, falling back into the atmosphere.)
Some of the technologies are integrated design of micro-nano satellite technology are multiple system on chip, SoC, MEMS, 3D multi-system integration technology to integrate the all functions into a chip or multi-chip package. New technologies are being pioneered to improve the use of CubeSats, such as a 2017 NASA parachute project that could land the small satellites without the need of boosters.
Micro-nano satellite platform can be divided by function: on-board computer, attitude and orbit control, monitoring and control, thermal control, promotion, construction and power management seven aspects.
Centralized computer unit.
The use of centralized data processing mode, will merge computing resources ,such as attitude, orbit control, on-board management and ambient temperature, using a single high-performance computing unit for centralized management. Current computing requirements can be satisfied by 100MIPS processor, embedding more than 1M memory, which fully meet the data processing requirements of micro-nano or small satellites. Centralized data management to reduce the complexity of the system, redundant design increases the system reliability.
Miniaturization of space electronics requires an understanding of all aspects of packaging technology, from the bare die level to the systems level. Cost, performance, schedule, and reliability are the primary drivers in the electromechanical development of space electronics.
Miniaturized sensors actuators
The small size of micro and nanosatellites constrains the small size and mass requirements of Sensors, actuators, and other structural elements needed for a specific mission. In all of these systems the minimization of power facilitates overall mass reduction and is an important design parameter.
Under 1-meter resolution radar imagery achieved by ICEYE
CEYE, a small satellite synthetic-aperture radar (SAR) technology company, achieved better than 1 meter resolution imagery from under-220 pound SAR satellites. The company has continued to launch more satellites, the latest in July 2019 with two new units. With new satellites being launched, ICEYE continues to develop and optimize its imaging capabilities further for customers in both commercial and government segments.
ICEYE’s newly deployed Spotlight imaging mode enables under 1 meter radar imaging from the company’s satellites. With Spotlight imaging, the satellite focuses its energy on a smaller area for a longer time, resulting in more data received from the same location. This in turn can be processed into more detailed imagery. Very high-resolution radar satellite images are helpful for both distinguishing small objects, and for accurately classifying larger objects such as vessels. These added capabilities of ICEYE’s SAR satellites are valuable in resolving challenges in sectors such as emergency response, finance, civil government, and maritime security
The optimization of navigation system.
Application of MEMS technology can be effectively optimized for navigation guidance sensors, such as gyroscope and accelerometers, MEMS technology designed gyroscope area has been reduced to a few centimeters, monolithic integrated three-axis gyroscope gradually realized, and significantly reduce the satellite navigation sensor size and power consumption. MEMS systems can replace some of the existing machinery and equipment, to achieve the sensing of environmental and location. Therefore, the design of micro-nano satellites can be used the Local MEMS devices, for laying the foundation for an multi-system integrated assembly in the future.
Microsat Power Systems and the IPS
Traditional spacecraft power systems that typically require some level of ground management incorporate a solar array energy source, an energy storage element (battery), and battery charge control and bus voltage regulation electronics to provide continuous electrical power for spacecraft systems and instruments. The cost-effective operation of a microsat constellation requires a fault-tolerant spacecraft architecture that minimizes the need for ground station intervention by permitting autonomous reconfiguration in response to unexpected fault conditions. The microsat power system architecture provides unregulated voltages that can be distributed to spacecraft systems and instruments in a traditional manner or used to power dedicated spacecraft loads through linear regulators or power converters.
Lynk First to Connect Satellite Directly to Standard Mobile Phones on Earth
Lynk has achieved a historic “first”—sending the world’s first ever text message from an orbiting satellite to a standard mobile phone on Earth. We are the first (and only one so far) to test from space, the first to prove it works, and we will be the first to market. This technical breakthrough is the next step on our mission to connect everyone, everywhere on their phone with broadband connectivity. We’re the only company that has launched a real satellite “cell-tower-in-space” to test the ability to talk to standard mobile phones on the surface of the Earth. To date, we have launched four “cell-towers-in-space” satellites; that is one satellite cell-tower launched every 6 months.
“In less than a year, we will begin commercial operations of the world’s first “cell-tower-in-space” to provide everyone everywhere services in a $1 trillion a year industry. Working with almost 30 mobile network operator partners, we will connect all 5.2 billion mobile phones on the planet, everywhere. This represents a $300-400 billion market opportunity. By being the first company to connect satellites directly to unmodified mobile phones, we are opening communications for everyone, everywhere, including people and emergency responders in remote areas.”
Communications using Software Defined Radio (SDR)
The Microsatellites also carry a radiation-hardened SDR transponder that leverages existing designs and enhance capabilities in the commercial sector. A Software Defined Radio (SDR) concept uses a minimum amount of analog/radio frequency components to up/downconvert the RF signal to/from a digital format. Rest all other processing (filtering, modulation, demodulation, etc.) is done in digital domain in software. This allows Software to be reused across products, reducing software/ hardware costs dramatically. As new telecommunication technologies emerge, incorporating them into the SDR fabric will be easily accomplished with little or no requirements for new hardware. New features and capabilities, such as encoding and decoding algorithms, filters, and bit synchronizers, can be added to the existing infrastructure without requiring major new capital expenditures, allowing implementation of advanced features in the communication systems.
Internet of Things (IoT) start-up Fleet Space Technologies has signed a contract to launch two of its satellites onboard the next Rocket Lab flight, dubbed “It’s Business Time.” The launch is scheduled to occur in November 2018 from New Zealand. Proxima I and II were both designed and built by Fleet. The two satellites will mark the first commercial tests of the company’s software-defined radios (SDRs), enabling the company to move data in both S-band and L-band frequencies in space. SDR is a key technology being used by a number of small satellite start-ups.
Optical Communication on CubeSats
The purpose of a telecommunication subsystem for a microsatellite is to serve as a communication link between the microsatellite and the ground station. Currently, CubeSats rely completely on radiofrequency communications using amateur low-speed UHF systems (with omnidirectional dipole antennas) due to its availability and lower cost, with rates in the order of kbit/s or tens of kbit/s from Low-Earth Orbit (LEO). As a result, the potential of most CubeSat missions is being limited by their communication capabilities, therefore there is a tendency to move to higher frequencies, especially to X-band, where more bandwidth is available, as an alternative to achieve higher data rates with smaller ground antennas. The Earth-imaging company Planet, has shown a remarkable success in these X-band communication systems, using COTS components and 5-m class ground antennas to achieve sustained data rates in the order of 100-200 Mbit/s with the latest generation of their ‘Dove’ CubeSats.
“Small satellites can’t use these bands, because it requires clearing a lot of regulatory hurdles, and allocation typically goes to big players like huge geostationary satellites,” said Cahoy, who also has an appointment in MIT’s Department of Earth, Atmospheric and Planetary Sciences. Furthermore, the transmitters required for high-rate data downlinks can use more power than miniature satellites can accommodate while still supporting a payload. For these reasons, researchers have looked to lasers as an alternative form of communication for CubeSats, as they are significantly more compact in size and are more power efficient, packing much more data in their tightly focused beams.
Space optical communications could play an important role by improving of several orders of magnitude in the transmission capacity, while keeping a low size, weight and power, thereby enhancing the potential of CubeSats with growing bandwidth requirements. The key components of a CubeSat lasercom system are the optical-power generation and the pointing capability. Generating several Watts of optical power imposes requirements that go beyond what a CubeSat can usually deliver, although an effective strategy to alleviate this is to include secondary batteries in the power management system.
FPGA’s & ASICS
At the chip level, custom and semicustom ICs and field-programmable gate arrays can integrate many functions onto the fewest number of ICs to reduce the parts count in the implementation of the electronics. Fewer components enhance reliability as well as reduce weight and volume. Among other important aspects in the design and development of application-specific ICs, besides cost and schedule concerns, are the radiation tolerance of the design and its implementation on the selected IC foundry line.
Multi-system assembly techniques
Multi-system assembly techniques, composed of a sensor unit, a data processing unit and a FPGA (implement diversity peripheral interface or bus), use 3D packaging technology to achieve integration. Multiple chips of the electronic systems are integrated or assembled in a single package, so that you can effectively achieve minimum micro-nano satellites. Multi-system technology assembly technology uses of micro-nano assembly technology, system in package(SiP) technology and other assembly techniques, completing multi-system interconnect and communicate.
SoPC Flight Control Design and Implementation
On-chip multi-system integration technology as a technology platform has now completed a chip for the function of control, data processing and navigation, mainly for the application of small satellites and onboard flight control. Design objectives and requirements: 100MIPS computing power, storage space is greater than 10M, programmable space, I2 bus, satellite navigation, inertial platform interface, high speed digital to analog conversion. The general requirements for flight control, there must be a high-performance computing power and flexible software and hardware programming capabilities, navigation and positioning capabilities.
Integrated electronics and Architecture
This includes the use of highly integrated electronics technologies as well as the integration of functions classically implemented in separate elements with the IPS, which combines energy storage, solar array electronics, and charge control electronics into a single structural element. With a compact electronics architecture, the electronics must be designed to incorporate the fewest components on boards that can be integrated in the most compact format possible.
At the component level, parts selection focuses on the integration of the smallest outline packaged parts (i.e., chip scale packaging) that are available for space use. Indeed, the smallest area required for the implementation of electronics involves mounting just the IC die itself and dispensing with the housing package for the die. The overall architecture is also important, with a conventional satellite electronics architecture, functional electronics subsystems are connected with wiring harnesses distributed throughout the satellite, adding considerable weight and volume. Typically, the harness is about 7% of the dry spacecraft weight.
With an integrated electronics module (IEM) approach, however, much of the onboard electronics are packaged onto electronics boards that are integrated into a single housing in which the boards are connected in a backplane fashion. This can result in considerable weight and volume savings. Standardized microsatellite platform helps the system integration and miniaturization.
Low power electronics
For power savings, the design of low-power electronics factors in power management techniques and considers low supply voltages. The power dissipated in CMOS integrated circuits (ICs) is a function of C*sqr(V)*f, where C is the load capacitance, V is the supply voltage, and f is the clock frequency. Research in the development of ultra-low power <1 V CMOS ICs suitable for space is encouraging and will likely result in major reductions in power dissipation in digital electronics. A study showed that the use of ultra-low voltage IC technology can yield a 20 to 50% saving in power, largely from a reduction of digital electronics power consumption.