Here Come the Space Tugs, Ready to Tidy Up Earth's Orbits

SpaceX is teaming up with the maker of a space tugboat, which would nudge satellites around, clean up space junk, and do other orbital housekeeping.
a satellite
When satellites launch into orbit, they don't always arrive in the ideal orbit. Space tugs could help by steering them to a precise destination.Cosma Schema

For the low, low price of $2.25 million, SpaceX will put your small satellite on a big Falcon 9 rocket and shoot it to orbit with a bunch of similarly small satellites. It's part of a new initiative called the SmallSat Rideshare Program, and with a first flight in late 2020 or early 2021, it will carry only diminutive instruments, a boon for their makers. While a Falcon 9 carried out a similar rideshare mission last year, that launch was organized by another company. This time, SpaceX itself is promising "regularly scheduled, dedicated Falcon 9 rideshare missions," according to its website.

Typically, small satellites have to squeeze in, Tetris-style, alongside larger, more expensive satellites that dictate when the launch happens and what orbit the payload goes to. Smallsat operators never liked that scenario. If the big guy was late, for instance, the little guys had to wait. If the big guy wanted to go to a different orbit than the small satellites, too bad, so sad.

The paradigm has started to change, with rideshares like SpaceX’s and tiny rockets meant only for smallsats, like Rocket Lab's Electron, which more resembles a pencil than a space vehicle. The pencils will get the little guys exactly where they want to go, but, like bespoke anything, they are expensive. Although rideshares on big rockets don't necessarily set the pocketbook on fire, they also don’t always send your satellite where you want it to go. After all, they have tens or dozens of other customers to please. Mikhail Kokorich, founder of a space company called Momentus, likens it to being told, "You can fly from San Francisco to Atlanta, but you cannot fly to Charlotte.”

But Charlotte’s a nice place, you know? So Kokorich, along with others, is trying to engineer connecting flights, using vehicles called space tugs. (That’s short for “space tugboats,” the creators of the term possibly not aware of the unfortunate internet-connotations of the word “tug.”) These vehicles can, among other things, ferry satellites from the busy hub where they got dropped off to the less-popular orbits they want to occupy. That way, they can ride whatever cheap rocket to whatever generic spot and then just wave goodbye when the space tug arrives.

The various tugs on the drawing boards and in the engineering labs of Earth could—in addition to acting as puddle-jumpers—also cut down on space junk, by tugging satellites out of orbit, and keep useful satellites up longer, by boosting them to higher orbits. But because they don't quite exist yet, no one is sure how much demand there is for them. Momentus will be one of the first to find out: The company announced today that its tug will launch aboard SpaceX’s first SmallSat Rideshare mission, sending a few customers to the Charlottes of space.

Kokorich, who grew up in Siberia, helped create a satellite manufacturing company called Dauria Aerospace in 2011. He moved to the US from Russia in 2014, and started a satellite-and-data company called Astro Digital the next year. Momentus, founded in 2017, was born out of what he calls the “pain” of getting his other companies' satellites launched.

The company's tug, named Vigoride (okay, maybe somebody knew about the internet slang?), can carry multiple small satellites to multiple orbits, propelled by a “water plasma” engine. Solar panels generate electrical power, which the vehicle then uses to generate microwaves, which superheat the water up to Sun-surface temperatures. That produces a plasma that shoots out a nozzle, propelling Vigoride forward. Water could make a good space fuel because it is cheap, safe and not so prone to exploding, and available all around the solar system—meaning that some distant-future robots might one day dig ice out of asteroids and the Moon to refuel a visiting spacecraft. (Other companies are also developing water-based propulsion.)

Vigoride's prototype flew to space a month ago, and it has two more test flights planned. Momentus hopes those demonstrations will help them line up two or three takers for their first real flight.

In its initial incarnation, Vigoride is a one-and-done machine: It will vigorously drive its customers wherever they want to go, and then, with its job complete, it will be done with its life. The company plans to make future tugs reusable, able to suck up more water when they get dehydrated (source TBD), and keep on trucking.

Another space-tug hopeful, a company called Atomos, is planning for that reusability, too. “We don't want to launch our space tugs with customers,” says CEO Vanessa Clark, although they may do so at first. “We want to have a sustained presence in orbit.”

In other words, in mature form, Atomos will send a tug up solo. It will wait for its passengers, scoop them up, deliver them to their stop, and then wait for the next riders. Atomos, as its name alludes, plans to power its ever-circling vehicle with a nuclear reactor, starting in the mid-2020s. But with first launch happening, fingers crossed, around 2021, the tug will run on solar power.

With decoupled systems, though, there’s a wrinkle in spacetime: The tug has to snuggle up to the satellite and dock with it. If you’ve ever tried to hook up with something traveling 17,000 mph, or watched Interstellar, you have an idea of how hard docking can be. Especially because most satellites probably weren’t designed to dock with a nuclear-powered ferry.

But docking with things that were never meant for docking is potentially important to Atomos. Its tug could raise them to a higher orbit to help them live longer, or send them off on a different mission; it could also lower them down (with permission) so they don’t become space debris. Space tugs could more proactively deal with orbital litter, too: If engineers don’t have to make rockets that travel as high—because a tug can take care of the “last mile”—then their spent boosters will fall faster back to Earth.

Debris was top of mind for Spaceflight Industries, a company that arranges rocket rides for lots of satellite operators. Back in December 2018, they set up the SmallSat Express, which carried more than 60 little satellites to orbit on a SpaceX rocket. To release them all to the right place at the right time without causing a giant pile-up, the company built two deployment devices.

They were called “free flyers,” and they were based on the schematics of its own space tug, called Sherpa, but minus the propulsion. The satellites traveled up in the flyers, which detached from the rocket once they got to orbit. In a carefully orchestrated sequence, the free flyers set the satellites loose. “All of our customers were fine with the orbit we were going to,” says Jeff Roberts, Spaceflight’s mission director, so they could get away without using propulsion. When the show was over, big sails deployed from the free flyers and dragged them out of orbit so they didn't add to the junk.

From that launch and other rideshare work, Spaceflight has learned a few things: They probably won't do another launch with as many satellites as the SmallSat Express. It was a lot of logistics. And according The Verge, people had trouble tracking their satellites and communicating with them, a worry Wired reported on at the time of launch. Roberts says the company will probably now stick to missions involving “no more than 20 to 30 satellites at a time.”

Also: Roberts isn’t sure how badly smallsat operators need a space tug. “A lot of our customers are happy with the rideshare model, where you’re going to a specific orbit, and most of their missions have enough variability that they can accommodate multiple orbits,” he says. People who need that bespoke space positioning have to make a decision: Do they pay for a dedicated rocket like Rocket Lab’s, or do they pay for a space tug?

That question is still open, in part because space tugs still have to prove themselves and live up to their promise of reusability. “The current state of the space tug is, you pay for the entire Uber car, you drive it to one spot, and then you throw it away,” says Roberts.

All that uncertainty has led Spaceflight to pull back a bit on its own plans to tug. “We don’t want to go into it full-bore if there’s no market for it,” says Roberts. Sherpa is still technically an active program, but it doesn’t have any interested customers. And the company is looking into buying shuttle services from other people as needed (whether to pay for a tug or do it yourself being a perennial question).

Momentus, of course, has placed its bet on building the space tugs. And as SpaceX’s 2020 rideshare approaches, the industry will be watching see who takes them up on their offer of a vigorous ride, how smooth the sailing is, and what trajectory it charts for the future.

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