Solar energy, long considered a leading contender among renewable energy sources, has evolved significantly over the past few decades. The cost of manufacturing and installing solar panels has fallen significantly and efficiency has increased, making them price competitive with coal, oil and fossil fuels. However, some barriers such as distribution and storage still prevent solar energy from being used more aggressively. In addition, there is the ever-present problem of disruption, where arrays fail to collect power during inclement weather and evenings.
These problems have led to the concept of space-based solar power (SBSP), in which solar cell-equipped satellites can collect 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 into space. Dubbed the Space Solar Power Demonstrator (SSPD), it will test several key components of SBSP and evaluate the method’s ability to harvest and radiate clean energy back to Earth.
The SSPD lifted off on Tuesday, January 3 at 06:55 PST (09:55 EST) on a SpaceX Falcon 9 rocket from Space Launch Complex 40 (SLC 40) in Cape Canaveral, Florida. The mission (Transporter 6) was a special ride-along that carried dozens of small satellites into space and deployed them in sun-synchronous orbit (SSO). The 50-kilogram satellite was transported aboard a Vigoride spacecraft (provided by commercial space company Momentus) and consisted of three main experiments, each tasked with testing a different key technology.
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The Space Solar Power Project (SSPP) began in 2011 when Donald Bren — philanthropist, chairman of the Irvine Company and lifelong member of Caltech’s board of trustees — and Caltech’s then-president Jean-Lou Chameau came together to discuss the potential for a space-based solar energy research project. By 2013, Bren and his wife (Caltech trustee Brigitte Bren) began funding the project through the Donald Bren Foundation, which will eventually surpass $100 million. As Bren said in a recent Caltech press release:
“For many years I have dreamed of how space-based solar energy could solve some of humanity’s most pressing challenges. Today I am very excited to support the brilliant scientists at Caltech in making that dream a reality.”
While the technology behind solar cells has existed since the late 1800s, generating solar power in space presents some serious challenges. For one, solar panels are heavy and require extensive wiring to transmit power, making them expensive and difficult to start. To overcome these challenges, the SSPP team needed to design a satellite light enough for inexpensive launches, yet strong enough to withstand the extreme environmental conditions of space. This required the imagination and development of new technologies, architectures, materials and structures.
On several occasions, the team enlisted the help of engineers from NASA’s Jet Propulsion Laboratory (which Caltech manages for NASA) and other commercial space companies based in Southern California. The result was three prototype testbeds within the SSPD, designed and built by a team of 35 graduate students, postdocs and research scientists at Caltech. The Caltech team will begin 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 feed into the manufacture of a mile-wide satellite constellation that is essentially a powerhouse 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 accomplish the following tasks:
- DOLCE: A structure approximately 3.5 square meters (6 by 6 feet) in size, demonstrating the architecture, packaging scheme, and deployment mechanisms of the modular spacecraft.
- ALBA: A collection of 32 different types of photovoltaic (PV) cells to allow an evaluation of the cell types that are most effective in space;
- MAPLE: A range of flexible, lightweight microwave power transmitters with precise timing that selectively focuses power to two different receivers to demonstrate wireless power transmission from space.
The fourth component is a set of electronics that connects to the Vigoride computer and controls the three main experiments. Some items will be tested over the next few weeks, while others will take months to fully evaluate. ALBA photovoltaics will be tested for up to six months before the team can determine which types of PV technology are best suited for this application. The MAPLE experiment is a series of tests that evaluate the system’s performance in different environments over time.
The DOLCE experiment has two cameras mounted on extendable booms (with additional cameras on the electronics box) that monitor the experiment and send video back to the Caltech team on Earth. Sergio Pellegrino, Joyce and Kent Kresa Professor of Aerospace Engineering at Caltech, is co-director of SSPP and senior research scientist at JPL. As he explained:
“DOLCE demonstrates a new architecture for solar-powered spacecraft and phased array antennas. It uses the latest generation of ultra-thin composite materials to achieve unprecedented packaging efficiency and flexibility. With the further advances we have already started to work on, we anticipate applications for a variety of future space missions. We plan to order DOLCE deployment within a few days of receiving access to SSPD from Momentus. We should know immediately if DOLCE works.”
The DOLCE experiment in the laboratory. Photo credit: Caltech
The MAPLE array, meanwhile, will test the potential for beaming energy via microwave arrays to receiving stations on Earth. As Ali Hajimiri, Bren Professor of Electrical and Medical Engineering at Caltech (and co-director of the SSPP), explained:
“The entire flexible MAPLE array as well as the electronic core chips and transmission elements for wireless power transmission were developed 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.”
Looking back on the successful launch, the Caltech team and project leaders consider several challenges ahead. Very little is known about SBSP and its ability to effectively transfer energy to Earth. But that’s the point of the experiment, and the success and failure of the testbeds are measured in different ways. For DOLCE, the most important test will be deployment, ensuring that the structure fully deploys from its collapsed to its open configuration.
For ALBA, a successful test will provide a clear indication of which photovoltaic cells are performing at maximum efficiency and performance in the extreme environment of space. For MAPLE, success means the demonstrable ability to transfer power to specific locations on earth as needed. Regardless of the outcome, Hajimiri said the fact that Caltech teams have created a prototype that can be sent into space represents a significant achievement:
“No matter what, this prototype is a big step forward. It works here on Earth and has passed the rigorous steps required for anything put into space. There are still many risks, but after going through the entire process, we learned valuable lessons. We believe the space experiments will provide us with much additional useful information that will guide the project as we move forward.”
Further reading: Caltech
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