Solar power, long considered the leading contender among renewable energy sources, has advanced significantly over the past few decades. The cost of manufacturing and installing solar panels has dropped considerably, and efficiency has increased, making it price competitive with coal, oil, and fossil fuels. However, some barriers, like distribution and storage, still prevent solar power from being adopted more aggressively. In addition, there’s the ever-present issue of intermittency, where arrays cannot collect power in bad weather and during evenings.
These issues have led to the concept of space-based solar power (SBSP), where satellites equipped with solar arrays could gather solar energy twenty-four hours a day, seven days a week, three-hundred and sixty-five days a year. To test this method, researchers at the California Institute of Technology (Caltech) recently launched a technology demonstrator to space. It’s called the Space Solar Power Demonstrator (SSPD), which will test several key components of SBSP and evaluate the method’s ability to harvest clean energy and beam it back to Earth.
The SSPD launched at 06:55 a.m. PST (09:55 a.m. EST) on Tuesday, January 3rd, atop a SpaceX Falcon 9 rocket from Space Launch Complex 40 (SLC 40) at Cape Canaveral, Florida. The mission (Transporter 6) was a dedicated rideshare that transported dozens of small satellites to space and deposited them in a sun-synchronous orbit (SSO). The 50-kilogram (110 lbs) satellite was carried aboard a Vigoride spacecraft (provided by commercial space company Momentus) and consisted of three main experiments, each tasked with testing a different key technology.
The Space Solar Power Project (SSPP) began in 2011 when Donald Bren – philanthropist, chairman of the Irvine Company, and a lifetime member of the Caltech Board of Trustees – and Caltech’s then-president Jean-Lou Chameau came together to discuss the potential for a space-based solar power research project. By 2013, Bren and his wife (Caltech trustee Brigitte Bren) began funding the project through the Donald Bren Foundation, which will eventually exceed $100 million. As Bren said in a recent Caltech press release:
“For many years, I’ve dreamed about how space-based solar power could solve some of humanity’s most urgent challenges. Today, I’m thrilled to be supporting Caltech’s brilliant scientists as they race to make that dream a reality.”
While the technology behind solar cells has existed since the late 19th century, generating solar power in space presents some serious challenges. For one thing, solar panels are heavy and require extensive wiring to transmit power, making them expensive and difficult to launch. To overcome these challenges, the SSPP team had to create a satellite that would be light enough for cost-effective launches yet strong enough to withstand the extreme environment of space. This required envisioning and developing new technologies, architectures, materials, and structures.
Several times, the team enlisted the help of engineers at NASA’s Jet Propulsion Laboratory (which Caltech manages for NASA) and other commercial space entities based in southern California. The result of this was three prototype testbeds within the SSPD, which were designed and built by a team of 35 graduate students, postdocs, and research scientists at Caltech. The Caltech team will commence testing in the coming weeks and hopes to complete a full assessment of the SSPD’s performance within the next few months.
The ultimate goal is to test and mature technologies that will eventually go into making a kilometer-scale satellite constellation that’s essentially a power station in space. The three main experiments include the Deployable on-Orbit ultraLight Composite Experiment (DOLCE), the ALBA, and the Microwave Array for Power-transfer Low-orbit Experiment (MAPLE). According to Caltech, these experiments will carry out the following tasks:
DOLCE: A structure measuring about 3.5 square meters (6 x 6 feet) that demonstrates the architecture, packaging scheme, and deployment mechanisms of the modular spacecraft. ALBA: A collection of 32 different types of photovoltaic (PV) cells to enable an assessment of the types of cells that are the most effective in space; MAPLE: An array of flexible, lightweight microwave power transmitters with a precise timing control that focuses power selectively on two different receivers to demonstrate wireless power transmission from space.The fourth component is a set of electronics that interfaces with the Vigoride computer and controls the three main experiments. Some elements will be tested in the next few weeks, whereas others will require months to evaluate fully. The ALBA photovoltaics will need up to six months of testing before the team can determine what types of PV technology will be best for this application. The MAPLE experiment involves a series of tests that will evaluate the system’s performance in different environments over time.
The DOLCE experiment has two cameras mounted on deployable booms (with additional cameras on the electronics box) that will monitor the experiment and send video back to the Caltech team on Earth. Sergio Pellegrino, Caltech’s Joyce and Kent Kresa Professor of Aerospace and Civil Engineering, is the co-director of SSPP and a senior research scientist at JPL. As he explained:
“DOLCE demonstrates a new architecture for solar-powered spacecraft and phased antenna arrays. It exploits the latest generation of ultrathin composite materials to achieve unprecedented packaging efficiency and flexibility. With the further advances that we have already started to work on, we anticipate applications to a variety of future space missions. We plan to command the deployment of DOLCE within days of getting access to SSPD from Momentus. We should know right away if DOLCE works.”
The DOLCE experiment unfolding in the lab. Credit: Caltech
The MAPLE array, meanwhile, will test the potential for beaming energy via microwave arrays to receiving stations on Earth. As Ali Hajimiri, Caltech’s Bren Professor of Electrical Engineering and Medical Engineering (and co-director of SSPP), explained:
“The entire flexible MAPLE array, as well as its core wireless power transfer electronic chips and transmitting elements, have been designed from scratch. This wasn’t made from items you can buy because they didn’t even exist. This fundamental rethinking of the system from the ground up is essential to realize scalable solutions for SSPP.”
With the successful launch in their rearview, the Caltech team and project leaders are looking at several challenges moving forward. Very little is known about SBSP and its ability to transmit energy effectively to Earth. But that is the point of the experiment, and success and failure from the testbeds will be measured in a variety of ways. For DOLCE, the most important test will be deployment and ensuring that the structure completely deploys from its folded-up to its open configuration.
For ALBA, a successful test will provide a clear indication of which photovoltaic cells provide maximum efficiency and performance in the extreme environment of space. For MAPLE, success will mean the demonstrable ability to transmit power to specific locations Earthside on demand. Regardless of the outcome, said Hajimiri, the fact that the Caltech teams have created a prototype capable of being sent to space represents a significant achievement:
“No matter what happens, this prototype is a major step forward. It works here on Earth, and has passed the rigorous steps required of anything launched into space. There are still many risks, but having gone through the whole process has taught us valuable lessons. We believe the space experiments will provide us with plenty of additional useful information that will guide the project as we continue to move forward.”
Further Reading: Caltech
