First off, who is Donald Bren? Is he another DS millionaire?

This kind of reminds me of Bill Gates investing in vaccines.

Anyway, this is a demonstration project, so something to watch and be aware of.

One of the features:  

MAPLE (Microwave Array for Power-transfer Low-orbit Experiment): An array of flexible lightweight microwave power transmitters with precise timing control focusing the power selectively on two different receivers to demonstrate wireless power transmission at distance in space.

 Donald Bren:

SSPP got its start in 2011 after philanthropist Donald Bren, chairman of Irvine Company and a lifetime member of the Caltech Board of Trustees, learned about the potential for space-based solar energy manufacturing in an article in the magazine Popular Science.

Intrigued by the potential for space solar power, Bren approached Caltech’s then-president Jean-Lou Chameau to discuss the creation of a space-based solar power research project. In 2013, Bren and his wife, Brigitte Bren, a Caltech trustee, agreed to make the donation to fund the project. The first of the donations (which will eventually exceed $100 million) was made that year through the Donald Bren Foundation, and the research began.

Bren said, “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.”

https://oilprice.com/Alternative-Energy/Solar-Energy/SpaceX-Rocket-Sends-Solar-Power-Prototype-Into-Orbit.html

Reasons for concern:

In order to provide a worthwhile transfer of power, any focused beam of microwaves will deliver substantial power to the receiver. Like megawatts. A typical home microwave oven is around 1 kilowatt. Humans make pretty good receivers at many different frequencies. But it’s not necessary for people to start “frying” to do damage. A focused beam of energy at TV frequencies over some time can slowly cook internal organs, or cause or health effects.

Keep in mind, microwaves are non-ionizing, so I'm not concerned about radioactive energy. But the ability to focus substantial power to a target on the ground means the ability to choose many different targets, like an outdoor concert, or an indoor stadium.

Here's a little info on high power radar and RF. This was not microwaves (> 1000 MHz), so more likely to penetrate into internal organs.  

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1757548/pdf/v055p00144b.pdf

Effects of acute exposure to ultra high radio frequency radiation on three antenna engineers EDITOR ,—Schilling1 reports the health problems of three men overexposed to ultrahigh frequency (UHF) TV radiation (785 MHz, >20 mW/cm2 for 1–3 minutes). Their symptoms included immediate sensations of heating and pain, and later erythema lasting a few days. Two had diarrhea for one to three days. Subsequently all three had headaches, dysaestheasia, lassitude, and loss of stamina which slowly improved over some three years.

And a naval officers first hand experience:

https://www.quora.com/Would-anything-happen-if-you-stand-in-front-of-a-powerful-military-radar-at-the-point-when-its-strength-is-the-greatest

Brad Pearce - Former Lieutenant Commander, USN at United States Navy (USN) (1983–1995)Author has 118 answers and 356.1K answer views5y

When I was (1) on active duty and (2) inport (a rare event), an unqualified and junior salior climbed aloft on one of the surface ships a couple of piers over while the ship’s fire control radar was being tested. The sailor died from the radar exposure.

I don’t recall whether we had a fleet wide safety stand-down, but we definitely were reminded about safety procedures.

Radar, especially fire control military radar, can be very strong.