As the use of smaller satellites in larger constellations increases, the need for faster communications between spacecraft will be needed for improved availability for intelligence, surveillance, telecommunications and reconnaissance applications.
The Defense Advanced Research Projects Agency this week announced a program called “Inter-Satellite Communication Links (ISCL)” it hopes will see the development of lightweight, low-power, and low-cost inter-satellite communications technology that could be used in a wide range of small Low Earth Orbit (LEO) satellites. Specifically, this program seeks to develop ISCLs with the highest practical data rates while having a per-link average weight of less than 2 pounds and an orbit-average power dissipation of less than 3 watts, DARPA stated.
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DARPA said rapid progress is being made in the development of low-cost microsatellites in the 10-100kg-weight range, which are expected to find application in a wide range of missions.
‘Many applications of these satellites will benefit from jam-resistant, high-data-rate (greater than1 Mbps), low-latency communications between satellites, whether for cooperative sensing applications or for data relay back to ground stations. Since ground stations may be unavailable in many locations, relaying data between satellites to reach one with a connection to a ground station is an attractive option when low data latency is needed,” DARPA stated. “The desire for rapid revisit rates or persistence from low-earth-orbit (LEO) satellites is also driving the development of large constellations of small satellites, potentially with about 100-400 satellites. In addition to performing their core sensing mission, such satellites also have the potential to provide inter-satellite data relay, providing a highly survivable mesh of nodes capable of relaying data before downlink to ground stations.”
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DARPA listed what it considered to be the major technical challenges for the ISCL program, including:
- Achieving the highest possible data rates within the tight weight and power constraints. This will entail getting high energy efficiency per-bit on each link, by optimizing transmit gain, receive aperture, transmitter power efficiency, receiver sensitivity, losses, and using energy-efficient waveforms and coding. Standby and static power dissipation of the system will also need to be minimized.
- Providing lightweight mechanical or electronic (e.g. phased-array) means to point the ISCL beam, antenna or optics toward a target satellite to acquire and maintain the communication without interfering with the host satellite operations.
- Having a robust approach for link acquisition with a desired neighboring satellite, and for maintaining that link. PAT and link maintenance can be particularly challenging for optical links, with their narrow beam widths. Proposals must address how reliable PAT and maintenance of links will be achieved.
- Being able to have the ISCLs fully developed, tested, and ready for integration onto an experimental satellite within 24 months is also expected to be a challenge.
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