On a cool, clear evening in May 2023, Caltech electrical engineer Ali Hajimiri and four members of his lab gathered on the roof of the Gordon and Betty Moore Laboratory of Engineering to await a signal from the heavens.
In preparation, the researchers had strewn portable floodlights across the floor and erected a collapsible canopy in a corner of the roof to shelter instruments and monitors stacked atop a small folding table. Two antennae perched nearby on heavy-duty tripods, their electronic gazes steadily tracking an invisible target drifting more than 300 miles overhead. The signal—if it came—would arrive in the form of a weak microwave beam transmitted from the Space Solar Power Demonstrator (SSPD-1), a 110-pound set of Caltech payloads that had launched into space five months earlier aboard a SpaceX rocket on the Momentus Vigoride-5 spacecraft. SSPD-1 is the first spaceborne prototype from Caltech’s Space Solar Power Project (SSPP). [Caltech story]