NASA’s Small Spacecraft Technology Program is set to show technological demonstrations of advance communications and proximity maneuvering capabilities for the CubeSats mission. The Optical Communications and Sensor Demonstration (OCSD) mission will showcase the first-ever high-speed data downlink from a CubeSat to a ground station using lasers, in addition to maneuvering the pair of diminutive spacecraft to up-close proximity.
Also set for demonstration is the Integrated Solar Array and Reflect array Antenna (ISARA) mission. A reflect array is a relatively new type of antenna fabricated from standard printed circuit boards with an array of square copper patches etched on them. These innovative satellites were carried onboard Orbital ATK’s Cygnus advanced maneuvering spacecraft, a commercial resupply vehicle that will berth to the International Space Station (ISS). Atop the Orbital ATK’s Antares booster, the Cygnus commercial resupply mission launched from NASA’s Wallops Flight Facility in Virginia on November 12.
Once the Cygnus craft has completed its ISS servicing mission, it will detach from the ISS and move to a higher orbit. From there, the OCSD and ISARA CubeSats will be deployed to begin their respective missions. The Small Spacecraft Technology Program expands U.S. capability to execute unique missions through rapid development and in-space demonstration of capabilities for small spacecraft applicable to exploration, science, and the commercial space sector. The program enables new mission architectures through the use of small spacecraft, with goals of expanding their reach to new destinations and challenging new environments.
NASA’s primary mission for OCSD is demonstrating laser communications, by using a laser on the spacecraft to downlink data to the optical ground stations on Mt. Wilson in California. The laser communication data rates are orders of magnitude higher than what can be done on radio frequency. Laser communication offers data rates competitive with current high-end CubeSat communications systems, in a compact package, and with the potential for higher data rates. With each spacecraft carrying ultra-small star trackers, critical for precision pointing of the laser communications hardware, the laser is hard-mounted to the individual CubeSat body with the beam pointed by controlling the orientation of the entire spacecraft. The applications for high data rate communications include providing download capability for data-intensive missions in low-Earth orbit such as those engaged in Earth imaging.
Following laser communication testing, another OCSD objective is proximity operations where the two CubeSats will fly relatively close together in Earth orbit. To do so, the satellites use a combination of variable drag and bursts of propulsion from the spacecraft – using water exhausted as steam – to bring the two within 650 feet (200 meters) of one another. Both CubeSats have miniature cameras, laser rangefinders, and are dotted by light-emitting diodes (LEDs) to aide in a step-wise reduction of distance between them. The plan is to essentially have one of the satellites orbit the other at smaller and smaller distances.
Each OCSD CubeSat is about 4 inches x 4 inches x 6.7 inches (10 centimeters x 10 centimeters x 17 centimeters) and weighs approximately 5 pounds (2.5 kilograms). As for the benefit of CubeSats, the technology development aspect of this mission is proving worthwhile for follow-on missions. Also, the commercial sector is very interested in the technologies that come out of this work. Capabilities in proximity operations will enable multiple small spacecraft to operate cooperatively during science or exploration missions, to approach another spacecraft or object for in-space observation or servicing, or to connect small spacecraft together to form larger systems or networks in space.
The technology benefit of the ISARA mission is to enhance CubeSat with a blend of antenna and solar cells, to allow for higher data-downlink communications. It will use radio frequency Ka-band – the first time Ka-band uses a reflect array antenna– that will surpass the existing baseline CubeSat transmission rate of 9.6 kilobits per second to more than 100 megabits per second.
ISARA will be the first in-space demonstration of a reflect array antenna as well as that of an integrated antenna and solar array. As far now, no reflect array has ever flown in space. It has been discussed over the years, but now NASA is going to demonstrate it does work in the space environment. Distinct from a parabolic dish antenna, the flat reflect array panels are folded down flush against the CubeSat. Once the three antenna panels are deployed – electrically tied together through hinges – they narrowly focus the CubeSat’s radio transmission beam to a “sweet spot” in much the same way a parabolic dish reflector would. ISARA solar array and reflect array antenna is a very attractive package that enables high-speed data rates of more than 100 megabits per second. That’s the primary goal for this mission.
Signals from the reflect array antenna are to be transmitted to a ground station located at NASA’s JPL. Experts there will reconstruct the antenna signal pattern, contrasting that pattern against pre-launch ground tests to appraise overall quality of ISARA’s downlink transmission over months of mission duration. The mission is being carried out in partnership with The Aerospace Corporation (Aerospace). Aerospace built the CubeSat and also supports a ground station network that’s spread out across the United States that can be used to support the CubeSat demonstration flight.
Indeed, due to efficiencies in the ISARA design that provide extra stowage volume, along with spacecraft power provided by the technology, a secondary payload known as the CubeSat Multispectral Observation System (CUMULOS) is onboard - an experimental remote sensing payload from Aerospace.
These two missions are pushing technology forward, for infusion in future missions. Getting data down to the ground from space is always essential. Laser communication and improvements in CubeSat radio frequency communication will be key components of that future. Similarly, flying small sat constellations are important as well. ISARA and OCSD reflect how essential small satellites have become. The short period of development time, the frequency of flight opportunities, and the ability to fly hardware in space to see how it performs in a relevant environment – these small satellites give a low-cost avenue for in-space validation, verification and improvement of technology in an incremental fashion.
