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Tesseract makes spacecraft propulsion smaller, greener, stronger

Launch vehicles and their enormous rocket engines tend to receive the lion’s share of attention when it comes to space-related propulsion, but launch only takes you to the edge of space — and space is a big place. Tesseract has engineered a new rocket for spacecraft that’s not only smaller and more efficient, but uses fuel that’s safer for us down here on the surface.

The field of rocket propulsion has been advancing constantly for decades, but once in space, there’s considerably less variation. Hydrazine is a simple and powerful nitrogen-hydrogen fuel that’s been in use since the ’50s, and engines using it (or similar “hypergolic” propellants) power many a spacecraft and satellite today.

There’s just one problem: Hydrazine is horribly toxic and corrosive. Handling it must be done in a special facility, using extreme caution and hazmat suits, and very close to launch time — you don’t want a poisonous explosive sitting around any longer than it has to. As launches and spacecraft multiply and costs drop, hydrazine handling remains a serious expense and danger.

Alternatives for in-space propulsion are being pursued, like Accion’s electrospray panels, Hall effect thrusters (on SpaceX’s Starlink satellites) and light sails — but ultimately, chemical propulsion is the only real option for many missions and craft. Unfortunately, research into alternative fuels that aren’t so toxic hasn’t produced much in the way of results — but Tesseract says the time has come.

“There was some initial research done at China Lake Naval Station in the ’90s,” said co-founder Erik Franks, but it fizzled out when funds were reallocated. “The timing also wasn’t right because the industry was still dominated by very conservative defense contractors who were content with the flight-proven toxic propellant technology.”

rigel thruster test

A live fire test of Tesseract’s Rigel engine.

The lapsed patents for these systems, however, pointed the team in the right direction. “The challenge for us has been going through the whole family of chemicals and finding which works for us. We’ve found a really good one — we’re keeping it as kind of a trade secret but it’s cheap, and really high-performance.”

You wouldn’t want to rinse your face with it, but you can fuel a spacecraft wearing Gore-Tex coveralls instead of a hermetically sealed hazmat suit. Accidental exposure doesn’t mean permanent tissue damage like it might with hydrazine.

The times have changed, as well. The trend in space right now is away from satellites that cost hundreds of millions and stay in geosynchronous orbit for decades, and toward smaller, cheaper birds intended to last only five or 10 years.

More spacecraft being made by more people makes safer, greener alternatives more attractive, of course: lower handling costs, less specialized facilities and so on further democratize the manufacturing and preparation processes. But there’s more to it than that.

If all anyone wanted was to eliminate hydrazine-based propulsion, they could replace the engine with an electric option like a Hall effect thruster, which gets its thrust from charged particles exiting the assembly and imparting an infinitesimal force in the opposite direction — countless times per second, of course. (It adds up.)

But these propulsion methods, while they have a high specific impulse — a measurement of how much force is generated per unit of fuel — they produce very little thrust. It’s like suggesting someone take a solar-powered car with a max speed of 5 MPH instead of a traditional car with a V6. You’ll get there, and economically, but not in a hurry.

Consider that a satellite, once brought to low orbit by a launch vehicle, must then ascend on its own power to the desired altitude, which may be hundreds of kilometers above. If you use a chemical engine, that could be done in hours or days, but with electric, it might take months. A military comsat meant to stay in place for 20 years can spare a few months at the outset, but what about the thousands of short-life satellites a company like Starlink plans to launch? If they could be operational a week after launch rather than months, that’s a non-trivial addition to their lifespan.

“If you can get rid of the toxicity and handling costs of conventional chemical propulsion, but maintain performance, we think green chemical is a clear winner for the new generation of satellites,” Franks said. And that’s what they claim to have created. Not just on paper either, obviously; here’s a video of a fire test from earlier this year.

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