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An atomic clock, ‘green’ propellant, and a sunlight-surfing sail are headed to space next week

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SpaceX’s Falcon Heavy is sending a bunch of new technologies to orbit

Image: SpaceX

On Monday, SpaceX is set to launch the third flight of its most powerful rocket, the Falcon Heavy. And this time, it’s carrying a host of new technologies into space, ranging from a new type of atomic clock to a thin sail that moves on sunlight. If they can survive the harsh environment of Earth’s orbit, then these new technologies could evolve into valuable tools for future space missions.

A combination of 24 satellites will fly to space on this mission, assembled from the Department of Defense, NASA, the National Oceanic and Atmospheric Administration, and universities. Getting all of these satellites to their intended orbits won’t be easy. The two dozen payloads need to be dropped off in three separate orbits, which means the Falcon Heavy will reignite its engine up to four times over the course of six hours to get the satellites where they need to go. SpaceX CEO Elon Musk claims that this complicated flight is the company’s “most difficult launch ever.”

A new atomic clock goes to space

On board one of the Falcon Heavy’s satellites is a small clock the size of a toaster. But it’s not an ordinary clock like the one you’d find on a wall or a watch you’d wear on your wrist. This clock is more accurate than any personal clock here on Earth. While the clocks we use eventually speed up or slow down over time, this particular clock, named the Deep Space Atomic Clock, would take up to 10 million years to get off by one second.

All clocks keep pace by measuring the time between some repetitive event. Old analog clocks, like grandfather clocks, will time the swings between a pendulum moving back and forth. Some modern watches will send voltages through quartz crystals, which then vibrate at the same frequency every second. An atomic clock, on the other hand, measures how long it takes for small particles to transition from different states of energy. That’s where these clocks get their names: they’re dealing with atoms.

The Deep Space Atomic Clock works by manipulating a specific type of charged atom known as an ion. Within the clock are tubes filled with ions of mercury — the same amount of mercury you’d find in two cans of tuna fish. Microwaves set at just the right frequency are used to perturb these ions, getting the mercury all excited. This causes the ions to shift back and forth between different states of energy. “That’s when the magic happens because that transition frequency is very well-known and very precise,” Jill Seubert, the deputy principal investigator of the Deep Space Atomic Clock mission, tells The Verge.

An artistic rendering of the Deep Space Atomic Clock heading to space.
Image: NASA

NASA has been using mercury-based clocks for a while on the ground, but the devices were typically the size of refrigerators and too large to fit on spacecraft. Other smaller atomic clocks have been sent to space on GPS satellites before, but they work by measuring elements like cesium or rubidium. While precise, these eventually stop being accurate, as their atoms get lost over time. “They get kind of embedded into the walls of their container,” says Seubert. Mercury-ion clocks like the Deep Space Atomic Clock are even more precise because the ions don’t bump into the walls of their container tubes, keeping the system intact.

Because they are so dependable, NASA has been working to miniaturize these systems, and now the Deep Space Atomic Clock will demonstrate if a mercury-based instrument this small can work in space. The team behind the instrument hopes to turn it on in August and then see if it works as intended over the next year. If so, the mission could lead to the development of other super precise atomic clocks that could help spacecraft not only keep time, but also navigate through deep space.

As of now, vehicles heading out of our planet’s orbit don’t have atomic clocks and must rely on commands from Earth for navigation. Engineers will send pings and then wait to get a reply from a vehicle, and that relay time will help them determine where the spacecraft is. That can be a long process, though, depending on the distance of a spacecraft. Vehicles at Mars, for instance, sometimes must wait between four and 20 minutes for commands from Earth. But if these vehicles had atomic clocks, engineers could send pings to the spacecraft, and their atomic clocks could calculate where they are, based on how long it took to get the signal. Then, spacecraft could navigate and change direction all on their own. “If we’re going to build a GPS-like network at other planets and moons, you would need to have an atomic clock, and this technology is the obvious choice there,” says Seubert.

Propulsion goes green

Many of the spacecraft on the Falcon Heavy launch will need to maneuver once they’re in space, either to keep their positions stable or to head to higher orbits. Typically, the chemicals used for these small engines are all the same toxic materials. But one spacecraft heading to orbit next week will be testing out a “green” type of propellant that’s a lot more user-friendly.

It’s all part of NASA’s Green Propellant Infusion Mission (GPIM). The vehicle will run on a new type of propellant developed by the US Air Force that’s meant to serve as an alternative to hydrazine, the current propellant of choice for most satellite engines. This new material could be an attractive option for satellite operators since hydrazine is particularly nasty stuff. It can be very reactive at room temperature and give off toxic fumes. Hydrazine has to be transported in certain types of metal containers and explosive-safe trucks, and people must wear protective gear when handling the propellant. All of these precautions add up, making development more expensive and time-consuming.

In contrast, the “green” propellant going up next week — hydroxylammonium nitrate — is much more palatable, with no noxious fumes. “You can have a jar on your desk, and you can’t smell anything on it,” Christopher McLean, the principal investigator for GPIM at Ball Aerospace, which developed the satellite, tells The Verge. “And unless the temperature is high enough, it won’t ignite at all.” That also makes transporting this material much easier, according to McLean. “We ship this stuff via FedEx in a plastic jug, and then put it into our loading equipment,” he says.

This green propellant also comes with an added bonus of being more efficient for satellites since it’s much denser. You can get 50 percent more fuel in a satellite engine’s tank with it than you can with hydrazine, according to McLean. That could potentially allow a satellite to last much longer in orbit, as it will have more fuel over time to change position or make maneuvers.

The one downside to this material is that when it does burn, it burns hot. When hydrazine reacts in an engine, it gets up to 900 degrees Celsius, while the green propellant gets up to 1,800 degrees Celsius. “That made it impossible to use standard hydrazine engines for this,” says McLean. “We had to develop new materials and technologies that were compatible with this higher temperature.”

Once in space, the GPIM satellite will test out this onboard propellant by manipulating its orbit from a circular one to a more elliptical one. The satellite will then spend about a year doing some experiments for the Air Force before it uses its propellant one final time to take itself out of orbit and plunge into Earth’s atmosphere.

Sailing on sunbeams

While NASA is testing out the green propellant, another organization will be testing out a way to propel spacecraft through the cosmos without using any fuel at all. Instead, it just needs light from the Sun.

The spacecraft is known as LightSail 2, and it’s the product of engineers at the Planetary Society, a nonprofit organization that advocates for space exploration. The vehicle is equipped with a very thin sail made out of mylar that’s designed to expand into a big square about the size of a boxing ring. This flat surface is meant to get pushed around by light coming from the Sun. Particles of light don’t have any mass, but they do carry momentum, which can cause very thin reflective materials to move through space.

“Once you’re above the atmosphere, you don’t need any fuel ever,” Bill Nye, CEO of the Planetary Society, tells The Verge. “You use solar pressure from sunlight to push you to all sorts of destinations in the Solar System.”

The idea of a solar sail was dreamed up by renowned astrophysicist Carl Sagan in the 1970s, and he even presented the concept on The Tonight Show Starring Johnny Carson. Now, more than four decades later, Nye, a former student of Sagan’s, has helped to turn this vision into a reality with others at the Planetary Society. “It’s just romantic,” Nye says. “It’s just fantastic, this idea that you could sail on sunbeams.” In 2015, the Planetary Society launched a precursor mission called LightSail 1 that was designed to test out the deployment mechanism for the solar sail. That mission was a success and proved the deployment could work (though the spacecraft did get zapped a few times by errant cosmic rays).

Now, the Planetary Society is looking to actually sail this time. LightSail 2 is riding into orbit tucked inside another spacecraft called Prox-1, which will eventually deploy the payload into orbit. Once on its own, LightSail 2 will expand its solar sail and then twist itself in space using an electric motor inside the spacecraft. That way, the vehicle can orient its sail to get the best boost from the Sun. As it travels around the planet, it will shift its position, coasting edge-on toward the Sun on the nightside of the Earth. Then it will twist its sail to catch the Sun’s rays on the dayside. This push will ultimately boost the spacecraft’s orbit over time, raising it to a higher orbit.

If this works, LightSail 2 will demonstrate a way for spacecraft to maneuver through space without the use of conventional propellants, which can take up a lot of room on a spacecraft. Instead, small satellites around Earth could be equipped with solar sails, giving them much-needed mobility and freeing up room to carry more instruments and sensors. Nye also foresees the possibility of using a solar sail to send materials to the Moon or Mars.

After the sail unfurls, there’s a chance that people on Earth may be able to get a glimpse of it as it reflects light from the Sun. The Planetary Society will provide a link on its website that includes where and when LightSail 2 will be passing overhead, giving us Earthlings prime viewing opportunity. “We’re very excited that it will engage people around the world because it’s literally visible from the surface,” says Nye.