Caltech’s SSPD-1 Is a New Idea for Space-Based Solar

The concept of powering civilization from gigantic photo voltaic crops in orbit is older than any area program, however regardless of seven many years of rocket science, the idea—to collect near-constant daylight tens of hundreds of kilometers above the equator, beam it to Earth as microwaves, and convert it to electrical energy—nonetheless stays tantalizingly over the horizon. Several lately revealed deep-dive analyses commissioned by NASA and the European Space Agency have thrown chilly water on the hope that area solar energy may affordably generate many gigawatts of unpolluted vitality within the close to future. And but the dream lives on.

The dream achieved a form of lift-off in January 2023. That’s when SSPD-1, a photo voltaic space-power demonstrator satellite tv for pc carrying a bevy of latest applied sciences designed on the California Institute of Technology, blasted into low Earth orbit for a year-long mission. Mindful of considerations in regards to the technical feasibility of robotic in-space meeting of satellites, every an order of magnitude bigger than the International Space Station, the Caltech group has been very completely different approaches to area solar energy.

For an replace on what the SSPD-1 mission achieved and the way it will form future ideas for area solar-power satellites, IEEE Spectrum spoke with Ali Hajimiri, an IEEE Fellow, professor {of electrical} engineering at Caltech, and codirector of the varsity’s space-based solar energy undertaking. The interview has been condensed and edited for size and readability.

SSPD-1 flew with a number of completely different testbeds. Let’s begin with the MAPLE (Microwave Array for Power-transfer Low-orbit Experiment) testbed for wi-fi energy transmission: When you and your group went up on the roof of your constructing on campus in May 2023 and aimed your antennas to the place the satellite tv for pc was passing over, did your tools choose up precise energy being beamed down or only a diagnostic sign?

Ali Hajimiri: I’d name it a detection. The major function of the MAPLE experiment was to show wi-fi vitality switch in area utilizing versatile, light-weight buildings and in addition commonplace CMOS built-in circuits. On one aspect are the antennas that transmit the ability, and on the flip aspect are our customized CMOS chips which can be a part of the power-transfer electronics. The level of this stuff is to be very light-weight, to scale back the price of launch into area, and to be very versatile for storage and deployment, as a result of we need to wrap it and unwrap it like a sail.

Ali Hajimiri is the codirector of Caltech’s space-based solar energy undertaking.Caltech

I see—wrap them as much as match inside a rocket after which unwrap and stretch them flat as soon as they’re launched into orbit.

Hajimiri: MAPLE’s major goal was to show that these flimsy-looking arrays and CMOS built-in circuits can function in area. And not solely that, however that they’ll steer wi-fi vitality switch to completely different targets in area, completely different receivers. And by vitality switch I imply internet energy out on the receiver aspect. We did show energy switch in area, and we made numerous measurements. We are writing up the small print now and can publish these outcomes.

The second a part of this experiment—actually a stretch purpose—was to show that skill to level the beam to the proper place on Earth and see whether or not we picked up the anticipated energy ranges. Now, the bigger the transmission array is in area, the better the power to focus the vitality to a smaller spot on the bottom.

Right, as a result of diffraction of the beam limits the dimensions of the spot, as a operate of the transmitter measurement and the frequency of the microwaves.

Hajimiri: Yes. The array we had in area for MAPLE was very small. As a outcome, the transmitter unfold the ability over a really giant space. So we captured a really small fraction of the vitality—that’s why I name it a detection; it was not internet constructive energy. But we measured it. We wished to see: Do we get what we predict from our calculations? And we discovered it was in the proper vary of energy ranges we anticipated from an experiment like that.

So, comparable in energy to the indicators that come down in commonplace communication satellite tv for pc operations.

Hajimiri: But accomplished utilizing this versatile, light-weight system—that’s what makes it higher. You can think about growing the following era of communication satellites or space-based sensors being constructed with these to make the system considerably cheaper and lighter and simpler to deploy. The satellites used now for Starlink and Kuiper—they work nice, however they’re cumbersome and heavy. With this know-how for the following era, you may deploy a whole lot of them with a really small and less expensive launch. It may result in a way more efficient Internet within the sky.

Tell me about ALBA, the experiment on the mission that examined 32 completely different and novel sorts of photovoltaic photo voltaic cells to see how they carry out in area. What have been the important thing takeaways?

Hajimiri: My Caltech colleague Harry Atwater led that experiment. What works finest on Earth is just not essentially what works finest in area. In area there’s numerous radiation harm, they usually have been capable of measure degradation charges over months. On the opposite hand, there is no such thing as a water vapor in area, no air oxidation, which is nice for supplies like perovskites which have issues with these issues. So Harry and his group are exploring the trade-offs and growing numerous new cells which can be less expensive and lighter: Cells made with skinny movies of perovskites or semiconductors like gallium arsenide, cells that use quantum dots, or use waveguides or different optics to pay attention the sunshine. Many of those cells present very giant promise. Very skinny layers of gallium arsenide, particularly, appear very conducive to creating cells which can be light-weight however very excessive efficiency and far decrease in value as a result of they want little or no semiconductor materials.

Many of the design ideas for solar-power satellites, together with one your group revealed in a 2022 preprint, incorporate concentrators to scale back the quantity of photovoltaic space and mass wanted.

Hajimiri: A problem with that design is the reasonably slender acceptance angle: Things need to be aligned excellent in order that the targeted daylight hits the cell correctly. That’s one of many causes we’ve pulled away from that strategy and moved towards a flat design.

A view from inside MAPLE: On the proper is the array of versatile microwave energy transmitters, and on the left are receivers they transmit that energy to.Caltech

There are another main variations between the Caltech energy satellite tv for pc design and the opposite ideas on the market. For instance, the opposite designs I’ve seen would use microwaves within the Wi-Fi vary, between 2 and 6 gigahertz, as a result of low-cost parts can be found for these frequencies. But yours is at 10 GHz?

Hajimiri: Exactly—and it’s a significant benefit as a result of if you double the frequency, the dimensions of the programs in area and on the bottom go down by an element of 4. We can do this principally as a result of we construct our personal microchips and have numerous capabilities in millimeter-wave circuit design. We’ve truly demonstrated a few of these versatile panels that work at 28 GHz.

And your design avoids the necessity for robots to do main meeting of parts in area?

Hajimiri: Our concept is to deploy a fleet of those sail-like buildings that then all fly in shut formation. They are usually not connected to one another. That interprets to a significant value discount. Each one among them has little thrusters on the sides, and it accommodates inner sensors that allow it measure its personal form because it flies after which right the section of its transmission accordingly. Each would additionally observe its personal place relative to the neighbors and its angle to the solar.

From your perspective as {an electrical} engineer, what are the actually exhausting issues nonetheless to be solved?

Hajimiri: Time synchronization between all elements of the transmitter array is extremely essential and some of the attention-grabbing challenges for the long run.

Because the transmitter is a phased array, every of the million little antennas within the array has to synchronize exactly with the section of its neighbors with a purpose to steer the beam onto the receiver station on the bottom.

Hajimiri: Right. To offer you a way of the extent of timing precision that we’d like throughout an array like this: We have to scale back section noise and timing jitter to only a few picoseconds throughout your entire kilometer-wide transmitter. In the lab, we do this with wires of exact size or optical fibers that feed into CMOS chips with photodiodes constructed into them. We have some concepts about how to do this wirelessly, however we have now no delusions: This is a protracted journey.

What different challenges loom giant?

Hajimiri: The monumental scale of the system and the brand new manufacturing infrastructure wanted to make it is rather completely different from something humanity has ever constructed. If I have been to rank the challenges, I’d put getting the desire, sources, and mindshare behind a undertaking of this magnitude as primary.