A US tech start-up wants to turn night into day. The question is why?

For billions of years, life evolved on Earth under conditions of roughly equal periods of dark and light in most places.

The sun rose and set. Night followed day.

Now, one of Earth's species — humans — plans to tweak this arrangement.

This week, the US federal communications regulator approved a Californian start-up's plan to launch a low-Earth orbit satellite, Reflect Orbital, with movable mirrors to reflect sunlight back to Earth.

The 5-kilometre-wide roving patch of illumination will be initially weak, but other mirror satellites may follow.  Reflect Orbital proposes 50,000, perhaps enough to make the lit-up area as bright as midday and extend the effect for up to an hour.

The question is why?

And who decides what hangs in the heavens?

'Let there be light'

The Reflect Orbital story reads like it's been assembled from a bingo card of big tech stereotypes.

In 2021, two American college-educated young male engineers, Ben Nowack and Tristan Semmelhack, founded a company to sell sunlight to Earth.

The company raised $US20 million ($28 million) in seed funding from Silicon Valley venture capitalists and took an office across the road from Elon Musk's SpaceX near Los Angeles.

The founders pitched their idea far and wide, getting media attention. The Crown Prince of Dubai expressed interest.

Sleep scientists and "chronobiologists" around the world wrote letters in protest, asking them to pause a plan that could upset the body clocks of humans and wildlife attuned to night-time darkness.

The founders argued their idea would help "solve climate change".

"We're here because, for some reason, people just accept the Sun goes down at night," Mr Nowack said in a 2025 media interview, describing why the company existed.

Billions of dollars' worth of solar farms around the world get no sunlight after the Sun goes down, he said.

"But what if all the sunlight that's missing the Earth can power the solar farms at night?"

"We can basically sell the sunlight like it's a resource."

Reflect Orbital was essentially pitching a partial alternative to grid-scale energy storage.

Instead of discharging stored solar energy from batteries during the evening peak, solar farms would pay Reflect Orbital to direct sunlight to their panels.

But powering solar panels wasn't the only reason for deploying tens of thousands of Olympic-pool-size mirrors into space, according to a spokesperson for the company in a statement to the ABC.

"Farmers will grow more food per acre to feed more people, more reliably; cities will have safer, evenly lit streets without carbon emissions," they said.

"The [regulatory approval] follows extraordinary global demand for our lighting and energy services, including most recently numerous requests to assist search-and-rescue efforts — and to save lives — in the aftermath of the tragic earthquake in Venezuela."

But will anyone be willing to pay for this? And if so, at what price?

The ABC spoke with a former Reflect Orbital employee as well as other experts to answer these questions.

The short answer: Selling sunlight for illumination or energy may not stack up.

'I really was not a fan'

Robert Salazar joined Reflect Orbital in 2023 as the founding engineer, responsible for designing the orbital mirrors (called heliostats). He departed the company this year.

"When they first marketed this thing, I really was not a fan of it," he told the ABC this week, speaking from a hotel room in London.

"The way they marketed it, that they're selling sunlight, as if they found some clever way of selling something that everybody has, I absolutely hated it."

The company's mission, he said, should be "sustainability".

"I think it is important now that they [the co-founders] really reframe what the real mission of this company is, and it's to provide very careful and wise stewardship over the energy demands of our planet in a way that no other technology can."

"We have an opportunity to provide the world with a renewable energy source that can actually scale with civilisation as we know it."

However, he admitted the light from a single satellite would not generate significant solar power on the ground.

"It would take many satellites to produce many moons' worth of irradiance onto a solar farm."

Instead of boosting solar power generation, orbital reflectors may be better suited to providing moonlight levels of illumination to parties and other events, he said.

"Maybe there's some, you know, grand party in the desert. It could be anything."

"Somebody throws an event and they want their event lit from space. Reflect is not just a power company."

Are orbital reflectors cheaper than batteries?

For all their complexity, Reflect Orbital's proposed reflectors are basically souped-up space blankets.

The orbital mirrors would be made from super-thin reflective aluminised mylar, kept under tension to minimise wrinkles.

In the 1990s, Russian scientists successfully deployed a 20-metre mylar reflector to shine a spot of light across Europe.

Orbital mirrors can reflect sunlight to the Earth's surface, but there are constraints.

Because a beam of light diverges, a satellite has to be in a relatively low orbit (about 625km, or a little bit higher than Starlink satellites) so the light it reflects forms a relatively bright spot on the surface of Earth.

At that orbit, the illuminated patch of ground would be about 5km across, and the light from an 18-metre wide mirror might be several times brighter than the Moon.

That sounds bright, but it's not.

Moonlight on a clear night is about 0.3 lux (the standard measure of illuminance). Office lighting is about 500 lux. Midday sunlight is about 100,000 lux.

Michael Brown, an astronomer at Monash University, calculated Reflect Orbital would need 3,000 satellites, each equipped with 54m-wide mirrors (ie several times larger than the pilot satellite's), to achieve 20 per cent of the illumination of the midday sun.

In low-Earth orbit, satellites move very fast to resist the pull of gravity.

Each would be able to provide light to a given location for no more than 3.5 minutes.

So, that's 3,000 satellites for 3.5 minutes of very weak sunlight.

Reflect Orbital has suggested it will charge $US1,000 an hour per satellite, Dr Brown said.

Beaming an hour of sunlight to any one location would require tens of thousands of satellites.

"Which would mean that to get daylight sun for an hour at one location, it would be about $US10–$US20 million ($14–28 million)," Dr Brown told the ABC.

"It doesn't stack up."

If these figures are accurate, battery storage of energy for the grid is a lot cheaper.

The cost of lithium-ion battery packs has fallen more than 20 per cent since Reflect Orbital was founded in 2021.

What would the orbital mirrors look like from the ground?

For optimal utilisation, the satellites would be deployed in a sun-synchronous orbit, following the line dividing night and day as it moves west across the Earth's surface, Mr Salazar said.

The mirrors would be potentially visible anywhere on Earth around dusk and dawn.

This also means they would be unavailable for party lighting, assisting in search and rescue, or any other potential purpose, outside of those times (i.e. for most of the night).

If you were standing in the patch they illuminated, they would appear like very bright stars.

Outside of this area, the satellites would be "absolutely invisible", Mr Salazar said.

When moving between target areas, the beam of light would "be travelling at thousands of miles in second" or "faster than the human eye can perceive".

"The same way that when an aeroplane flies between the Sun and we see a shadow for a moment, this is much faster."

Reflect Orbital could operate "responsibly", he said.

But Mr Salazar and Reflect Orbital were unable to convince scientists who said the company's plans could disrupt sleep and ecosystems worldwide.

Earlier this year, the presidents of international scientific societies representing thousands of researchers from more than 30 countries raised concerns in letters to the US regulator, the Federal Communications Commission (FCC).

Oliver Rawashdeh, a biologist studying the effects of time on living organisms (a chronobiologist) and president of the Australasian Chronobiology Society, co-authored a submission.

"It's ridiculous," he told the ABC.

"Half of the time, evolution happened in the dark. The dark is not just the absence of light. It has its own purpose equal to sunlight."

Migrating birds relying on celestial cues may lose their way. Coral may spawn prematurely. Nocturnal mammals may find themselves in daylight. Pilots in mid-air may be temporarily blinded. Sensitive astronomy sensors may be fried.

Dark Sky International, the global non-profit dedicated to combating light pollution, said in a statement it opposed Reflect Orbital's "long-term vision for a large constellation of orbital reflectors", citing impacts on wildlife, astronomy, public safety and the night-time environment.

In Mr Salazar's vision of the future, spots of reflected sunlight would sweep across the land at dusk, from the solar farm of one client to the birthday party of another.

"I met with folks from Dark Sky International, and we've had many conversations on this topic," he said.

"And we had these conversations in a city with a lot of light pollution."

Mr Salazar suggested light pollution from orbital reflectors, even ones owned by a private company serving commercial clients, was analogous to that from cities.

As with cities, the focus should be on how to emit light "responsibly", rather than on not emitting light at all.

"Let's be innovative and control the light, get it where it needs to go."

Despite its stated aspiration to limit light pollution, Reflect Orbital is commercially motivated to sell as much sunlight as possible, including to populated areas such as cities.

A Reflect Orbital spokesperson said in a statement "most people, and most places, will never see this light."

"We intend to avoid service over exclusion zones that cover endangered species, as defined by applicable regulations.

"We don't plan to operate over at-risk migration corridors."

Who decides what goes in orbit?

The FCC approved Reflect Orbital's pilot satellite launch this week.

The company will need further FCC approvals to launch more satellites, but the process won't assess potential harms caused by the proposed satellites.

In a statement, the FCC said its role was to authorise use of radiofrequency spectrum, and nothing else.

There's also an emerging issue of jurisdiction, or who should be able to make decisions on behalf of the planet.

The FCC is a US organisation, with a board of commissioners nominated by the US president, yet its decisions affect every other country.

With launch costs plunging, the FCC is being asked to approve a huge number of what it calls "emergent space activities".

There are proposals for orbital AI data centres, solar panels beaming power down to Earth, space hotels, and a "golden dome" missile defence system for America.

Ideas of what to put in orbit appear to be partly shaped by science fiction.

Orbital reflector constellations have recurred in science fiction for more than a century.

And now, finally, for some reason, someone may build one.

"It won't be surreal for me until the first light is on the ground and we're standing in the beam and we're seeing the brightest star anyone's ever seen," Mr Salazar said.

"That will really be something."

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