Nanosatellite and microsatellite refer to miniaturized satellites in terms of size and weight. Microsatellites are artificial satellites, with a mass of 11–100 kg (including fuel mass) while nanosatellites are artificial satellites weighing between 1 and 10 kg, and measuring around 30 cm × 10 cm × 10 cm. ‘CubeSat’ is one of the most popular types of Nanosatellites with standard dimensions (“U” or Units) of 10 × 10 × 11. These satellites can be 1U, 2U, 3U, or 6U in size, and typically weigh less than 1.33 kg (3 lbs) per U.
These are the fastest-growing segments in the satellite industry. One of the major advantages of nano and microsatellites is the low cost of building and operating these satellites. The growth in small satellites is driven by the miniaturization of electronics and sensors and the availability of high-performance commercial off-the-shelf components, significantly reducing the cost of hardware development.
The other rationale for miniaturizing satellites is to reduce the launch cost; heavier satellites require larger rockets with a greater thrust that also have a greater cost to finance. In contrast, smaller and lighter satellites require smaller and cheaper launch vehicles and can sometimes be launched in multiples. The access to orbit and economy of these spacecraft is also improved through the availability of secondary launch payload opportunities, especially for small satellites which conform to standardized form factors. They can be launched ‘piggyback’, using excess capacity on larger launch vehicles. The introduction of reusable space launch vehicles, which could be used for multiple missions, is expected to further reduce the costs associated with small satellites. This is expected to result in an increase in the adoption of microsatellites and nanosatellites.
The demand for these satellites has increased significantly over the last few years, owing to their lightweight attribute, shorter development cycle, high capability of performing complex computational tasks, and lower cost for development and launch. Comparing with the traditional geostationary earth orbit (GEO) systems, LEO satellite constellation has the advantages of low propagation delay, small propagation loss and global coverage.
Miniature satellites, especially in large numbers, may be more useful than fewer, larger ones for some purposes – for example, gathering of scientific data and radio relay. Another major reason for developing small satellites is the opportunity to enable missions that a larger satellite could not accomplish, such as: Using formations to gather data from multiple points, In-orbit inspection of larger satellites.
A satellite constellation is a group of artificial satellites working together as a system. Unlike a single satellite, a constellation can provide permanent global or near-global coverage, such that at any time everywhere on Earth at least one satellite is visible. Satellites are typically placed in sets of complementary orbital planes and connect to globally distributed ground stations. They may also use inter-satellite communication.
Satellites in Medium Earth orbit (MEO) and Low Earth orbit (LEO) are often deployed in satellite constellations, because the coverage area provided by a single satellite only covers a small area that moves as the satellite travels at the high angular velocity needed to maintain its orbit. Many MEO or LEO satellites are needed to maintain continuous coverage over an area. This contrasts with geostationary satellites, where a single satellite, at a much higher altitude and moving at the same angular velocity as the rotation of the Earth’s surface, provides permanent coverage over a large area.
Today, consumers not only routinely download high-definition movies but also play games and shop online, consuming vastly more bandwidth. In addition, entirely new demand segments, including in-flight airline connectivity, have emerged. Other markets, such as telecom backhaul, have greatly expanded with increased mobile usage. The large LEO-constellation providers aim to fulfill this demand by providing a price-competitive alternative to terrestrial solutions, by significantly reducing costs, from manufacturing to launch to the user equipment.
In tandem with increased demand for connectivity, service expectations have risen. Both businesses and consumers seek high-bandwidth connections and, for many applications, low latency. Significantly, these expectations have spread beyond technologically sophisticated users to virtually all consumers in developed economies and many in emerging markets. Only people with limited connectivity options accept lower performance.
For some applications, in particular digital connectivity, the lower altitude of MEO and LEO satellite constellations provide advantages over a geostationary satellite, with lower path losses (reducing power requirements and costs) and latency. The propagation delay for a round-trip internet protocol transmission via a geostationary satellite can be over 600 ms, but as low as 125 ms for a MEO satellite or 30 ms for a LEO system
Large growth in Microsatellite and Nanosatellite constellations
Major and upcoming companies, such as Planet Labs, GomSpace, Sierra Nevada Corporation, among others, are launching constellations of micro and nanosatellites to offer near real-time remote sensing data.
It is expected that numbers of satellites in orbit are going to increase more than linearly with about 8000 spacecraft in orbit in 2024 due to constellations only. Over 2500 nanosats are estimated to be launched in 2021-2027.
Nanosatellites and microsatellites find application in scientific research, communication, navigation and mapping, power, reconnaissance, and others including Earth observation, biological experiments, and remote sensing.
Race for Global Satellite Internet
More than half of the world’s population does not have internet access today, and in some places it is still not cost effective to take the terrestrial and fibre optic network. To fill this gap many companies including Starlink, One Web, and Samsung have proposed the concept of using satellite constellations in Low Earth Orbit (LEO) for communication to provide efficient global coverage. Unlike traditional satellite internet, these plans involve the use of satellites in low Earth orbit, which can be operated cheaply and with lower latencies.
Starlink internet is potentially a game-changer for satellite internet. With faster speeds, lower latency and unlimited data, Starlink will allow residents of rural households who currently are unable to work and learn remotely, to finally be able to do so.
Starlink, a SpaceX project, already has more than 1,700 satellites in low-Earth orbit, and the company says it has about 90,000 people currently testing the service, each paying $99 a month (plus a $499 fee for the satellite dish) for the privilege.
Starlink, which aims to deliver broadband internet around the world via 42,000 satellites, is already being used by a small number of people in the UK and North America. Starlink speeds currently range between 50 and 150 Mbps.
However, as more satellites enter the network, Starlink’s speeds will likely increase up to 300 Mbps. The greatest difference between Starlink and other satellite companies has to do with latency. Starlink’s latency is significantly lower than HughesNet or Viasat, which means it will be easier for users to work or learn from home using Starlink.
And rival service OneWeb, though not yet ready for customers, has resumed launching satellites after being rescued from bankruptcy by Indian conglomerate Bharti Global and the UK government last year. OneWeb, has over 350 satellites in orbit now, about half the total it plans for its constellation
Backed by Virgin Group, OneWeb is building a new global knowledge infrastructure accessible to everyone, particularly in rural areas in just 10 years, according to Greg Wyler, the founder of the company. One Web that aims to deploy a low-orbit constellation of 648 microsatellites each weighing as little as 250 pounds to provide low-latency, high-speed internet access to rural areas through Wi-Fi, LTE, 3G or 2G connections. Additionally, the new satellite constellation will provide networks for global emergency and first responder access.
The satellites will each be able to deliver at least 8 gigabits per second of throughput. OneWeb has started to work on terminals that use antennas that combine mechanical steering and a phased-array antenna. They will provide internet access at 50 megabits per second. The company says it has developed Progressive Pitch technology in which satellites turn slightly so its low-orbit satellites won’t interfere with signals from existing Ku-band satellites in geostationary orbit.
Amazon’s Project Kuiper
Amazon is the latest in a string of companies with plans to use a network of thousands of satellites to offer broadband around the world. Amazon’s Project Kuiper will consist of satellites at three different altitudes: there will be 784 satellites at 367 miles, 1,296 satellites at 379 miles, and 1,156 satellites at 391 miles.
These satellites will offer internet in areas ranging from 56 degrees north (roughly in line with the middle of Scotland) down to 56 degrees south (which is below the southernmost tip of South America). This area, theoretically, covers over 95 percent of Earth’s population.
Amazon recently announced that, by the end of 2022, a startup called ABL Space Systems would deliver two prototype satellites for Project Kuiper, the company’s effort to build a low-Earth orbit, or LEO, satellite constellation that can beam internet connectivity down to Earth. Amazon says it will eventually deploy 3,236 such satellites “that will provide fast, affordable broadband to unserved and underserved communities around the world.”
The project will also require a network of Earth stations for the satellites to communicate with. Amazon has already launched AWS Ground Station, a cloud computing service that will enable space-to-ground communications.
The Hongyun project, launched by CASIC in September 2016, has the goal of building a space-based communications network of 156 small satellites in orbit about 1,000 kilometers above the Earth. It would become operational about 2022. China in Dec 2018 launched its first communication satellite to provide broadband internet services worldwide in an apparent bid to rival Google and other international firms. When the Hongyun project is complete, it will cover the whole world and offer round-the-clock communication services to users in polar regions, who now have difficulties accessing telecommunication and internet services, Zhang said. “Hongyun will enable our users to enjoy broadband internet service no matter whether they are in the desert, on the sea or onboard an airliner,” he said, adding that it will help connect people in underdeveloped areas with the outside world.
Galaxy Space, founded in 2016, wants to put hundreds of its satellites into low Earth orbit to provide global 5G coverage, according to state media. Beijing-based China Head Aerospace Technology plans to create a 48-satellite constellation called Skywalker with applications for shipping, earthquake monitoring and imagery. The company, which built a 45kg satellite launched last year, has partners in several countries taking part in China’s “Belt and Road Initiative”, including South Africa.
Telecom and aerospace giants Samsung and Boeing are also sending internet satellites to orbit. In Samsung’s case, the plan is to begin deploying the first of 4,600 satellites to LEO by 2028. Once operational, this interconnected constellation will provide a 200-GB per month service in the V band for up to 5 billion users. A new report from tech giant Samsung entitled Mobile Internet from the Heavens predicts that by 2028, 5 billion Internet users around the world will be collectively requiring at least 1 zettabyte per month data, and propose that a fleet of roughly 4,600 micro-satellites orbiting Earth could satisfy our requirements. Boeing has similar plans for a 2,956 constellation that will provide enhanced broadband (also in the V band).The first part of this system will consist of 1,396 satellites deployed to an altitude of 1,200 km (746 mi) within the first six years.
Iridium is also partnering with Orbital ATK, the commercial aerospace company, to make their constellation happen. And whereas other companies are focused on providing enhanced bandwidth and access, Iridium’s main goal is to provide safety services for cockpit Wi-Fi. These services will be restricted to non-passenger flights for the time being, and will operate in the L and Ka bands.
“The biggest challenge will be affordability,” CCS Insight analyst Kester Mann said. “Space is a huge and risky investment. “And it may take many years before devices fall sufficiently in price to become appealing to the mass market. “This will be particularly relevant in emerging markets.” And that means costs will have to be recouped from consumers. SpaceX charged $99 (£75) per month for its initial trial offering in North America, plus a one-off $499 fee for the hardware. And that came with a warning that, at least at first, the service might not always work.
A myriad of new IoT satellite communication competitors (Eutelsat ELO, Kineis, Astrocast, Lacuna Space, Myriota, and many more), are presently growing to provide low cost IoT communication channels with worldwide coverage, encompassing the whole planet through low orbit satellite constellations. These organizations will contend with existing M2M Satcom vendors including Inmarsat, Thuraya, Globalstar, Orbcomm.
In many cases, IoT devices are distributed in remote areas (e.g., desert, ocean, and forest) in some special applications, they are placed in some extreme topography, where are unable to have direct terrestrial network accesses and can only be covered by satellite. Furthermore, revision of existing IoT protocol are necessary to enhance the compatibility of the LEO satellite constellation-based IoT with terrestrial IoT systems.
Eutelsat Communications revealed its ELO constellation project, targeting the Internet of Things (IoT) market. The 25 nanosatellite ELO constellation aims offer global IoT coverage enabling objects to transmit data, regardless of their location.
Internet of things satellite connectivity startup Myriota plans to provide low-cost, power efficient direct satellite connectivity for IoT uses, including industrial applications like equipment monitoring and measurement of environmental measures like groundwater levels. Myriota has four satellites on orbit already, with a plan to expand that to 25 by 2022. The Adelaide-based company has developed its own proprietary low-over iOT communications technology, that claims big advantages over existing solutions in terms of battery life, security, scalability and cost.
Radar microsatellite constellation
Satellite imagery has traditionally been produced via optical sensors. In recent years, however, satellite imaging increasingly relied on synthetic aperture radar (SAR). This technology boasts benefits over sensors, such as the ability to achieve clear imaging even in darkness and cloud conditions. It also can gather data such as elevation and moisture levels. By leveraging small satellite developments, several companies have made strides toward providing high-quality SAR imaging at lower costs. In doing so, they are paving the way for widespread adoption of SAR while ensuring uninterrupted, on-demand visibility of life on earth.
Capella Space, which was founded in 2016, has been working on a constellation to provide SAR imagery across the world. Capella Space has successfully launched the first satellite in that 36-satellite constellation. The microsatellite, named “Sequoia,” orbits at approximately 500 km while operating in the X-band. Capella Space claims Sequoia and the forthcoming satellites in the constellation will be able to detect sub-0.5-meter changes on the Earth’s surface. With this system’s ability to provide on-demand imaging – even through clouds and darkness – it has garnered interest and contracts from military, intelligence, and government agencies for applications ranging from virtual reality (VR) software to missile defense and enhanced threat prediction capabilities.
ICEYE, a startup from Finland, also is bringing SAR imaging capabilities to small satellites. Early achievements included 0.25-meter resolution for a small SAR satellite and quick turnaround time for capture data delivery (taking five minutes from when data begins its downlink connection to ground stations to when processed images are available for customers to use on their own systems). The company has raised $87 million to continue to grow its operational constellation. ICEYE launched five SAR satellites so far.
Umbra, based in Santa Barbara, California and previously known as Umbra Lab, is preparing to launch its first microsatellite in 2021 to provide Synthetic Aperture Radar (SAR) imagery with a resolution of better than 25 centimeters. “Umbra has agreements to deliver data to the United States government and commercial geospatial intelligence firms,” according to a Jan. 31 news release. Umbra has not announced contract awards. However, AFWERX, the Air Force organization focused on spurring innovation, lists Umbra as a Small Business Innovation Research awardee.
US-based EOS Data Analytics Inc. (EOS), a space portfolio company of Noosphere Ventures, unveiled EOS SAR – a project to develop its own synthetic aperture radar (SAR) sensors intended for deployment in a constellation of microsatellites. “EOS learned that the remote sensing market has strong demand for high-resolution high-quality SAR data, but low supply of such data. The choice of SAR technology is driven by the need to image Earth’s surface through dense cloud cover, in any season and all weather. It is critical for users to have access to uninterrupted, persistent situational awareness,” said Max Polyakov, CEO of EOS and Managing Partner at Noosphere Ventures.
EOS engineers have already designed a radar prototype and are moving ahead with the development of a low-cost high-performance SAR payload for small satellites with ultra-high resolution down to 25 cm. EOS SAR satellites will operate in Stripmap and Spotlight modes (including interferometry) and will cover a wide range of applications. EOS is also considering dual-frequency SAR in X-band and S-band on a single satellite. Dual-band operation increases versatility for all weather imaging and improves object-ground contrast. A special configuration of the radar front end allows for imaging of selected areas in both bands in a single orbit.
European ESA’s Disaster Monitoring Satellite Constellations
ESA’s Sentinel-2 mission is a land monitoring constellation of two satellites that provide high resolution optical imagery and provide continuity for the current SPOT and Landsat missions. The mission provides a global coverage of the Earth’s land surface every 10 days with one satellite and 5 days with 2 satellites, making the data of great use in on-going studies. The satellites are equipped with the state-of-the-art MSI (Multispectral Imager) instrument that offers high-resolution optical imagery.
The lower cost of platform development and the ability to be launched in larger numbers has also driving growth in small satellite constellations, having ability to perform many simultaneous and distributed measurements or observations. A key feature of multi-plane systems of these satellites is increased temporal resolution of collected data (e.g. shorter revisit times) over single plane. Furthermore the presence of multiple satellites in each orbital plane can facilitate a more graceful degradation of system performance on the occasion of individual satellite failures.
Some of the successful microsatellite-class constellation missions are Disaster Monitoring Constellation (DMC) and Rapid Eye Earth observation missions and the ORBCOMM satellite communications system. Two examples of larger multi-plane constellations of smaller satellites are the Planet Labs (Flock-1a:28satellites, Flock-1c:11satellites) and Skybox Imaging (24satellites).
Microsatellite constellation geolocates RF signals
Space Flight Laboratory (SFL) has launched three formation-flying HawkEye 360 Pathfinder 15-kilogram, 20 x 27 x 44-centimeter microsatellites designed to detect and geolocate radio frequency (RF) signals. The target signals emanate from VHF radios, maritime radar systems, automatic identification system (AIS) beacons, very small aperture terminal (VSAT) communication systems and emergency beacons. HawkEye 360 applies advanced RF analytics to the data to assess suspicious vessel activity, survey communication frequency interference and direct search-and-rescue.
Precise formation flying is critical, as the relative position of each satellite must be known to accurately geolocate transmission sources. The satellites carry space-qualified GPS receivers and high-performance attitude control systems to keep them stable in orbit.
Flying in formation, two or all three satellites may receive the same transmission when it originates from their common footprint. The signal’s different times of arrival at each satellite and their different apparent center frequencies (Doppler) will enable onboard comparison of time-of-arrival and frequency-of-arrival measurements to then calculate the transmitter’s position.
The onboard GPS receivers provide precise estimates for the position and velocity of the receivers, information required for multilateration. The satellites further synchronize their clocks using GPS receivers, which also stabilize the phase-locked loops governing the tuning frequency in the RF tuners. The satellites were built by Deep Space Industries of San Jose, California, and University of Toronto, Institute for Aerospace Studies/Space Flight Laboratory (UTIAS/SFL). They were launched in December 2018 into low-Earth orbit.
Technical Challenges and Enabling technologies
In addition to better use of spectrum, advances in active antennas and processing have raised throughput per individual satellite, increasing constellation capacity:
- A satellite can now deploy more spot beams, and greater power can be delivered through each beam.
- Intersatellite links (ISLs) improve connectivity and confer particular benefits to large constellations, including improved throughput and management.
- Improved data-compression methods reduce bandwidth requirements without reducing the quality of communications.
Traditionally, satellites have been accessed and tracked via parabolic-dish antennas. This equipment is poorly suited to LEO constellations, which will have numerous satellites all rapidly crossing a ground receiver’s field of view at the same time.
Antennas with electronically scanned apertures (ESAs), also called electronically steerable antennas, can shift beams (and track and access large numbers of satellites) without physical movement. ESAs can also be designed for modular assembly, which could allow manufacturers to produce large numbers of basic parts for use in both constellation ground stations and consumer equipment, thereby improving economies of scale.
Likewise, ISL advances that increase throughput also reduce backhaul costs and improve satellite control and network latency. Combining these elements would promote the autonomous and semiautonomous control and management of spacecraft, reducing staffing requirements.
Technical challenges in the construction of small satellites may include the lack of sufficient power storage or of room for a propulsion system. This large number of satellites in orbit has also thrown many challenges.
For example, the current ground segment infrastructures will probably not be able to monitor the status and control such a large number of satellites. Therefore ground service providers need to invest for new infrastructure development. However, important advances in ground equipment include new predictive analytics and network-optimization techniques that use available ground-entry points more effectively. Recent advances in analytics, combined with improved computing power and artificial-intelligence algorithms, can assist with these functions while reducing response times and operating costs.
One concern involves communication, with the RF spectrum becoming possibly overcrowded and the required data-throughput increasingly larger. Lastly, but probably most importantly, the rise of the space traffic and debris which may prevent the safe and successful operation of spacecraft with a higher probability of collisions.
Current satellite concepts will initially be as expensive as or more expensive than their predecessors. Although costs continue to evolve and many uncertainties remain, estimates for deploying an operational system generally range from $5 billion to $10 billion.
Annual operating costs will be high: the cost of replacing satellites alone will total $1 billion to $2 billion for a large constellation if their life span is about five years. The ground segment, even if largely automated, will require a substantial number of sites and antennas, which entail significant capital and operating costs.
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