At the turn of the century, an in-orbit satellite would cost more than $17 million. These same capabilities can now be put into the same orbit for $200,000.
Satellites orbit a gravitating object – such as Earth – at a distance proportional to their speed, but the orbit may not be circular, and the exact path of the satellite can provide advantages in terms of capability and availability.
Some orbits will provide better coverage for certain countries, times of day, or antenna designs. They may be suitable for relaying data between other space resources, avoiding known belts of electromagnetic radiation, or reducing revisit times in certain areas.
Development of such orbits requires a detailed understanding of gravitational fields in four-dimensional space – including time – and several orbiters are protected by patents in their most useful applications.
Many new constellations of satellites are being launched Low Earth Orbit (LEO), less than 1,000 km above Earth’s surface. It provides good monitoring and communication services. But these satellites are also skimming our planet’s atmosphere, and can survive for about five years before de-orbiting and burning up to dust.
This constellation requires a constant replacement cycle – unlike satellites in geostationary orbit, which can use the same technology for 20 years. New services should be judged on the upgrades they plan to deploy — and their financial ability to support constant refreshes — over the capabilities they already deploy.
Communication satellites in Leo Offering low-latency communications, while commercial Earth observation satellites are photographing each location daily to provide time-based analysis. Much of the technology used in these “new space” projects is borrowed from the smartphone industry — efficient batteries, compact antennas and impact-resistant electronics — but much has been developed to address problems specific to working in space.
A circular orbit—around a planet’s equator—offered considerable utility, but as scientists gained experience working in space, it became clear that alternatives could open up new opportunities. Different altitudes – Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geostationary Earth Orbit (GEO) – provide a variable, but elliptical (expanded) orbit can support new use cases. Combinations of orbits can be used to maximize service availability and minimize idle time—an important factor in the profitability of a satellite constellation.
Several well-known orbits are already in common use Sun synchronous is an orbit, typically used at LEO altitude, that places the satellite at a fixed location on Earth every few days, at the same time of day. It is widely used by Earth observation (and spy) satellites to provide continuous shadowing of an observed region.
The orbit in which the satellite passes over both the poles is called polar orbit. It allows the planet to circle beneath it, enables the satellite to pass over every point on the surface and cross each pole every 100 minutes, and collect data from static sensors or take pictures of specific locations.
Molnea is a highly elliptical orbit, which increases the amount of time a satellite spends at a given latitude. It is commonly used to increase the availability of communication systems in northern latitudes such as Canada and Russia.
A geostationary orbit matches the Earth’s rotation and traces the equator, providing satellites that appear to hover over a fixed point on the surface. Such an orbit requires an altitude of 35,786 km to match Earth’s motion, resulting in high latency, but such an orbit enables dish antennas to be pointed at the satellite.
Different orbits and orbital altitudes provide different properties. Hybrid services combine LEO, MEO and GEO orbits to optimize the coverage, bandwidth and latency of a connection. GEO, for example, offers wide-area coverage, while LEO can provide low-latency communications.
A communications protocol, such as TCP/IP, can be broken down into layers that can be handled by satellites in different orbits – the channel being reassembled at the receiving equipment.
Management of data traffic, which is sensitive to latency, can be handled by satellites in LEO, while bulk traffic flows are delivered from satellites in MEO or GEO orbits. This enables the use of legacy assets, as well as reducing the need for high-capacity satellites in dense LEO orbits.
Network protocol for satellite communications
The TCP/IP protocol used for Internet communication requires that received packets be acknowledged within a specified time frame and sequence. This makes it very difficult to use TCP/IP with the MEO Constellation, and almost impossible to use on GEO without modification.
By providing recognition over LEO when bulk data is transmitted via MEO, a combined constellation can deliver data using standard TCP/IP communication. This enables, for example, interaction with a video service via LEO, when the selected video is delivered from a satellite in GEO.
Similar methods can be applied to other network protocols, providing the benefits of both orbits without the drawbacks of either. Such a combined constellation offers:
- Simplified application development: The ability to use standard Internet protocols without requiring proxies or protocol conversions simplifies the development of applications, as well as removes potential areas of incompatibility that could slow down deployment times.
- Reduced star density: MEO (and GEO) satellites have a much larger footprint, enabling customers to provide service over wide areas without the need for low-angle antennas, which are more prone to obstruction from buildings and trees. This allows a smaller, and more profitable, constellation to provide a comparable service.
- Greater availability of spectrum: Separating the control plane from the data plane allows for more efficient use of the radio spectrum, as these two components of the network stream can use different radio frequencies.
- Broad coverage: The larger footprint from higher altitudes allows for increased area coverage without the need for ground equipment and without the need for satellite-to-satellite communication systems.
- Exploitation of existing resources: Many companies have existing assets in Jio orbit. Complementing these with LEO services can enable these assets to compete with the full LEO constellation.
Potential for satellite comms
Various companies are looking for ways to increase the value of existing (deployed) orbital assets. The Quality of satellite data Rapid decline is occurring, as broadcast television is increasingly replaced by on-demand services, and the LEO constellation threatens the market for rural Internet access.
These companies may be optimistic that hybrid systems will have a long-term future, but much will depend on the development of low-cost endpoint equipment capable of supporting hybrid networks. They have a 15-year life, and while some new communication systems are being deployed in Jio, existing assets may continue to operate for another decade. This means the biggest opportunity is in the next five years.
As a final point, satellites in orbit often require large reflectors or antennas and almost always require extensive solar arrays to power the mission. Such objects are difficult to launch, so various technologies and techniques are needed to reduce the size during launch.
Techniques used include folding arms, springs, origami techniques, and memory metal. The best approaches offer a significant reduction in size while keeping weight low, but, most critically, can offer very high reliability.
Because reliability is so important, the technology behind such systems is rarely complex, so the interesting innovation is mostly in the way components are folded and unfolded and the method used to push them into place.
This article is an excerpt from the Gartner report, “Emerging Technologies: The Emergence Cycle for Satellite Systems”. Bill Ray A vice-president analyst at Gartner.