ISS Utilization: ROSA (Roll Out Solar Array)
The ROSA technology is a new/innovative mission-enabling solar array system that will offer maximum performance in key areas and affordability for NASA's future space missions. NASA selected DSS (Deployable Space Systems) of Santa Barbara, CA, in 2012 to develop advanced solar systems to support advanced solar electric propulsion. After testing, both companies may compete for NASA funding to test their arrays in the harsh environment of space.
The DSS ROSA deployable array features an innovative "roll out" design which uses composite booms to serve as both the primary structural element and the deployment actuator – eliminating the need for motors. The ROSA engineering development unit is sized to provide nominally 20 kW of electrical power per array – enough for exciting new missions such as redirecting an asteroid to lunar orbit to enable in-depth studies by astronauts and commercial venturers. 1)
The solar array is configured for launch stows into a cylindrical volume less than two feet in diameter. Once the spacecraft is positioned, the arrays roll out to their full size, 6 m x 13.7 m (Figure 1). The very large solar array is able to be stowed so compactly because its solar cells are mounted on an innovative flexible blanket which is much thinner than the traditional rigid panels in current use.
NASA has partnered with DSS (Deployable Space Systems) and SSL (Space Systems Loral) to develop solar cell structures designed to power government space vehicles or commercial communications satellites. ROSA (Roll Out Solar Array) will work to convert the sun's rays into energy that could drive ion thrusters of solar electric propulsion spacecraft for NASA's Asteroid Redirect Mission and other deep-space exploration programs. 2) 3)
ROSA is one of the options eyed by NASA's STMD (Space Technology Mission Directorate) that could power an advanced solar electric propulsion spacecraft that makes possible such endeavors as the agency's Asteroid Redirect Mission—plucking a multi-ton boulder from an asteroid's surface, and then maneuvering that object into a stable orbit around the moon for human inspection and sampling.
Tapping into ROSA technology allows the conversion of sunlight into electrical power that drives the ion thrusters of a solar electric propulsion spacecraft. ROSA is expected to enable a number of space initiatives and is a cost-saving plus to transport cargo over long distances beyond the Earth.
Commercial satellite platforms: DSS has partnered with Space Systems Loral (SSL) of Palo Alto, California to apply the technology into SSL's heritage commercial satellite platform. SSL builds some of the world's highest power satellites. Higher power increases satellite capability, particularly for applications like broadband and ultra high-definition television, explains Al Tadros, SSL vice president for Civil and Department of Defense Business. ROSA is an enabler for SSL business, Tadros adds. "Higher power can translate to more payload and more revenue for our customers."
Scalable solar wings: In general, the solar array rolls up around a spindle to form a compact cylinder for launch. Those solar wings are then deployed via strain energy in rolled booms that form the outer sides of the structure. A low mass mesh material supports strings of photovoltaic cells that churn out electrical power. What's more is that ROSA is scalable. It can be configured and combined with other ROSAs for very high power levels, Michael Ragsdale says, Research and Development project manager at SSL.
SSL is working closely with space agency researchers at NASA/GRC (Glenn Research Center) in Cleveland, and its contractor DSS to qualify ROSA to become an integral part of SSL's 1300 satellite platform product line.
Figure 1: The ROSA (Roll Out Solar Array) technology undergoes testing (image credit: DSS (Deployable Space Systems), Inc.)
The U.S. Air Force has funded a test flight of the ROSA mechanism, now scheduled for a SpaceX launch in Spring 2017 to the ISS (International Space Station), where it will be deployed in space.
ROSA is groundbreaking, a low-mass technology that rolls up and stows into a very compact volume, explains Brian Spence, president of DSS. "NASA's investment in ROSA was important to elevate the maturity level of the technology and I am pleased to see a good return on investment of taxpayer dollars."
Looking into the future, Spence envisions ROSA technology as key for NASA's solar electric propulsion needs as well as robotic and human journeys to Mars and beyond. For example, excursions on Mars can benefit by deploying solar arrays, he adds, and then retract them for point-to-point travel across the rugged landscape of the Red Planet.
Launch: The ROSA assembly was launched to the ISS on June 3, 2017 on SpaceX Dragon/Falcon-9 CRS-11 (Commercial Resupply Services-11). ROSA will be hosted as an externally attached payload on the ISS via the ELC (ExPRESS Logistics Carrier). The launch site is KSC (Kennedy Space Center) LC-39A. 4) 5)
The external payloads manifested for this flight were:
• NICER (NICER/SEXTANT (Neutron-star Interior Composition ExploreR / Station Explorer for X-ray Timing and Navigation Technology)
• MUSES (Multiple User System for Earth Sensing)
• ROSA (Roll Our Solar Array)
Orbit of ISS: Near-circular orbit, altitude of ~ 400 km, inclination = 51.6º, period = 92.6 minutes.
Research overview of ROSA on the ISS: 6)
• ROSA is an innovative new solar array design that uses high strain one-piece composite slit-tube booms. The stored strain energy of the booms enforces the deployment actuation, and the booms provide the array's deployed structural stiffness and strength.
• The flight experiment is designed to characterize the performance of the array in a relevant combined space environment to compare to scalable model predictions and on-ground test data. The intent is to compare this on-orbit ROSA data to the model predictions that have been previously validated by on-ground measurements in a simulated environment.
• On-orbit data are used to fully develop the structural models for unique spacecraft applications and higher power levels. As such, the flight experiment is designed in a combined space thermal, vacuum, and micro-gravity environment in order to:
- Characterize deployment loads and kinematics
- Characterize the deployed structural dynamics
- Characterize the structural dynamics that occur going from eclipse to illumination
- Characterize blanket structural survivability and photovoltaic performance after launch and deployment
- Characterize retraction loads and kinematics.
• ROSA significantly improves the power density and stowage efficiency and scalability over current rigid panel array technology and shows high promise for consideration on all future NASA, DoD (Department of Defense) and commercial spacecraft.
Description: The research plan is broken into four main objectives with experiments designed around satisfying each of the stated objectives. The objectives include characterizing the Roll-Out Solar Array (ROSA) structure deployment loads and kinematics, the deployment torque, the deployment kinematics, and the velocities and accelerations of the array during deployment and blanket tensioning. The ROSA deployed structural dynamics and the changes in full-sun and full-shadow are measured, as well as the fundamental frequency and mode shape for the system bending mode and the blanket drum mode.
Many operational parameters such as structural damping, structural dynamics during eclipse exit, blanket structural survivability and photovoltaic performance post launch and post deployment, I-V (current -voltage) curve immediately following deployment and dynamics experiment, I-V curve each time the array is at optimal solar illumination throughout mission life, structure retraction loads and kinematics, retraction torque, retraction kinematics, velocities and accelerations of the retracting array and blanket tension release.
Operational Requirements and Protocols:
ROSA is stowed in the trunk of the SpaceX's Dragon capsule during launch. Once on orbit, the ISS robotic arm removes ROSA from the Dragon trunk and temporarily stows it on an ELC (ExPRESS Logistics Carrier). When ROSA operations are ready to begin, the ROSA is picked up by the ISS robotics arm and located in its operations location. The ROSA operations are conducted while attached to the SSRMS/SPDM for a duration of 7 days. During initial deployment of the array, video is required. Data are recorded using embedded sensors on the experiment. Testing is activated and commanded via the ground controllers. The Payload Health and Status and Experiment Data are downlinked via 1553 communications.
The deployment is monitored by cameras, limit switches, eddy current damper voltage, and accelerometers placed on the tip of the mandrel and the blanket. Visual markers are placed on the booms, blanket, and tip mandrel to provide a visual index of array deployed length. These same markers are used during the dynamics testing to infer the fundamental frequency and associated mode shape through post-processing. A sinusoidal actuation at the array root with a motor will sweep across a frequency range at various rates. The dynamic response is measured via accelerometers on the mandrel and ROSA dynamics response is further characterized during thermally induced impulse loading due to eclipse exit.
The blanket and photovoltaic performance are measured by collecting current-voltage (I-V) sweeps from near the open circuit voltage to near the short circuit current. Sweeps are performed approximately every two minutes for the duration of the mission. Temperature, sun angle and shadowing are measured in order to correlate the measured I-V data.
1) "Administrator Bolden Visits Company Rolling Out New Solar Array Technology," NASA, July 1, 2014, URL: https://www.nasa.gov/content/administrator-bolden-visits-company-rolling-out-new-solar-array-technology/
2) "Roll Out Solar Array Technology: Benefits for NASA, Commercial Sector," NASA June 9, 2016, URL: https://www.nasa.gov/feature/roll-out-solar-array-technology-benefits-for-nasa-commercial-sector
4) "New NASA Experiments, Research Headed to International Space Station," NASA Release 17-052, June 3, 2017, URL: https://www.nasa.gov/press-release/new-nasa-experiments-research-headed-to-international-space-station
6) "Roll-Out Solar Array (ROSA)," NASA, Jan. 18, 2017, URL: https://www.nasa.gov/mission_pages/station/research/experiments/2139.html