This response is filed on behalf of the National Radio Astronomy Observatory, headquartered in Charlottesville, VA. NRAO (http://www.nrao.edu)is a federally-chartered facility funded by the National Science Foundation for the purpose of constructing and operating radio telescopes in the pursuit of radio astronomy world-wide. Owing to a capital investment of over $1,000,000,000 in state of the art radio frequency astronomical instruments such as the eVLA, VLBA, Robert C. Byrd Green Bank Telescope and ALMA, NRAO and its user community are major stakeholders in the electromagnetic spectrum. They stand to be seriously impacted by testing, development and/or implementation of space-based solar power satellites (SPS) for terrestrial power generation. ~Some impact will occur, but they can find solutions until the SPS total is many gigawatts. By then, present equipment will be obsolete and the far side of the moon may be the main radio astronomy location which will not be impacted by even 1000 gigawatts of SPS~ The ill effects of SPS are hardly limited to astronomy nor have they lessened with the passage of time.

To capture and repackage as microwaves the same solar radiation which naturally falls on earth as sunlight, SPS would place huge (~75 sq km) solar collectors and multi-gigawatt rf transmitting systems into the heart of the geosynchronous satellite belt. Even in normal operation the presence of these transmitters could wreak havoc on other spectrum users (astronomy, terrestrial-satellite links and the like) because, with the inevitable leakage of even tiny fractions of gigawatt peak levels, it is impossible ~solutions will be possible in most cases~ to prevent interference across a broad swath of the spectrum. Moreover, generation of gigawatt power levels using literally millions of individual kilowatt power sources per SPS station will involve large amounts of spurious noise as the individual elements fail; even for a mean lifetime of 30 years, dozens of elements will fail each day at each station in high, geostationary orbit where servicing is extremely difficult. And even optical and infrared astronomy will not be immune because the SPS collectors will light up the sky at optical and infrared wavelengths day and night owing to reflection and heating of the solar panels. ~even 1000 gigawatts will be minor compared to the present light polution, cities world wide produce~

SPS systems have other liabilities. On the ground, they also require huge land preserves harboring rectifying antennas whose areas are comparable to what would be required to generate gigawatts of power from incoming solar power directly. The mean power levels beamed to earth as microwaves across these ground antennas by SPS are comparable to those of normal incident sunlight, but as microwaves they are well above human safety levels. ~True for the present standard of 0.1 watt per square centimeter, but considerably higher microwave energy levels are tolerated by humans at most frequencies, except on extremely hot days~ The need for such elaborate, remotely-sited ground receiving stations precludes use of SPS in case of sudden emergencies; it cannot be beamed wherever it might be needed. ~Some casualties from the beam is likely acceptable, if the energy allows the saving of many other lives~

It is a separate decision whether to entrust the national power supply to SPS ~1% is not entrusting/when and if we reach 1% we can consider if further scale up is prudent~ with it’s ~not~ obvious vulnerabilities. The vast amounts of rocketry needed may cause other bad side effects. NRAO recommends that the pursuit of SPS systems for terrestrial power generation should be abandoned, as the potential harm ~possibly~ outweighs the benefits. NRAO urges that the solar power research effort be turned toward development of appropriate technologies (such as power storage) which would allow ground-based solar collectors to be ~possibly~ adequate as a source of electric power. If development of SPS for terrestrial power generation proceeds, NRAO asks that the interests of all spectrum stakeholders be protected. ~using laser frequencies (instead of microwave) reduces most of these problems significantly. Neil~

It would deploy more solar cell array with one single launch as the ISS carries now after years of construction works.

Best wishes

Frank