Session
Session 7: Science / Mission Payloads II
Abstract
The collection of radio frequency (RF) signals by means of interferometry is an area that shows great promise for small satellite applications and is a shared interest of business and the scientific and military community. SIGnals INTelligence or SIGINT is one of the oldest missions for satellites, especially for its subfield, ELectronic INTelligence (ELINT), the analysis and localization of RF-signals. Unfortunately, the accuracy that customers demand from such systems in order to merit their costs is often incongruent with detection techniques that rely on single nanosatellites (such as Angle of Arrival methods). Accuracy is strongly related to aperture size; rigid antennas are therefore limited to the available surface area of small satellites. Typical accuracies that can be expected of AOA-techniques range from 0.1° – 1°1. Factoring in orbital altitude, this results in geolocation accuracies of 10 km or more for RF-sources close to the satellite’s nadir, increasing rapidly with distance from nadir for missions in LEO. Using a single CubeSat solution with rigid antenna systems limits the type of RF-emitters that can be geolocated with high accuracy (< 0.1°) to X-band (or shorter wavelengths). Deployable structures and small satellites that do not adhere to the CubeSat standard offer a limited solution as there is limited volume available for deployment mechanisms. One of the key benefits of using CubeSats is their lower unit and launch cost. This enables technical solutions that depend on distributing the desired functionality over many satellites, instead of investing in highly sophisticated single satellite payloads. This approach has in the past been studied for space-based interferometers like Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR) enabling far larger diameter “apertures” than could be fitted on a single satellite while at the same time simplifying the development and deployment2. The same technologies that enable these scientific missions are at the heart of satellite formations for the purpose of identifying and geolocating RF-emitters on the Earth’s surface, such as inter-satellite datalinks, station-keeping systems and precise avionics. The overlap is not limited to these enabling technologies but also extends to system level characteristics. One of the big obstacles for CubeSat missions beyond LEO is their reliability. CubeSat missions beyond LEO face two hurdles that amplify each other, on the one hand the radiation environment becomes significantly more hostile, complicating the use of COTS components and on the other hand the cost of replenishment increases drastically with distance from Earth. Missions such as OLFAR thus require a step change in the reliability of the subsystems in order for them to be affordable and cost effective. At the same time these same reliability improvements would further decrease the cost of ownership of LEO spectrum monitoring (or SIGINT) constellations.
SIGINT: The Mission CubeSats are Made For
The collection of radio frequency (RF) signals by means of interferometry is an area that shows great promise for small satellite applications and is a shared interest of business and the scientific and military community. SIGnals INTelligence or SIGINT is one of the oldest missions for satellites, especially for its subfield, ELectronic INTelligence (ELINT), the analysis and localization of RF-signals. Unfortunately, the accuracy that customers demand from such systems in order to merit their costs is often incongruent with detection techniques that rely on single nanosatellites (such as Angle of Arrival methods). Accuracy is strongly related to aperture size; rigid antennas are therefore limited to the available surface area of small satellites. Typical accuracies that can be expected of AOA-techniques range from 0.1° – 1°1. Factoring in orbital altitude, this results in geolocation accuracies of 10 km or more for RF-sources close to the satellite’s nadir, increasing rapidly with distance from nadir for missions in LEO. Using a single CubeSat solution with rigid antenna systems limits the type of RF-emitters that can be geolocated with high accuracy (< 0.1°) to X-band (or shorter wavelengths). Deployable structures and small satellites that do not adhere to the CubeSat standard offer a limited solution as there is limited volume available for deployment mechanisms. One of the key benefits of using CubeSats is their lower unit and launch cost. This enables technical solutions that depend on distributing the desired functionality over many satellites, instead of investing in highly sophisticated single satellite payloads. This approach has in the past been studied for space-based interferometers like Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR) enabling far larger diameter “apertures” than could be fitted on a single satellite while at the same time simplifying the development and deployment2. The same technologies that enable these scientific missions are at the heart of satellite formations for the purpose of identifying and geolocating RF-emitters on the Earth’s surface, such as inter-satellite datalinks, station-keeping systems and precise avionics. The overlap is not limited to these enabling technologies but also extends to system level characteristics. One of the big obstacles for CubeSat missions beyond LEO is their reliability. CubeSat missions beyond LEO face two hurdles that amplify each other, on the one hand the radiation environment becomes significantly more hostile, complicating the use of COTS components and on the other hand the cost of replenishment increases drastically with distance from Earth. Missions such as OLFAR thus require a step change in the reliability of the subsystems in order for them to be affordable and cost effective. At the same time these same reliability improvements would further decrease the cost of ownership of LEO spectrum monitoring (or SIGINT) constellations.
