(CNN) –– In the 1990s, NASA designed an experimental space plane that was intended to be a cost-effective alternative to expensive rockets.
Called fall during ascent to reduce weight) and favors a unique, fully reusable spacecraft.
The X-33 was designed to launch vertically like a rocket, but land on a runway like an airplane, with the goal of reduce cost from sending half a kilo of payload to orbit from US$10,000 to just US$1,000.
However, the program was canceled in 2001 due to technical difficulties, and ended up on a list alongside other similar projects that have not materialized.
“I ran the former USAF astronaut and X-33 program manager, and now CTO of Radian Aerospace, a Seattle-based company he co-founded in 2016 to revive the SSTO dream.
“Things have changed dramatically since the X-33: we have composite materials that are lighter, stronger and can withstand a greater thermal range than what we had back then. And the propulsion is better than anything else we’ve had, in terms of the efficiency with which the fuel is burned and the weight of the systems,” he stated.
The product of this updated technology is the Radian Onea new space plane that will replace vertical launch with a very unusual system: a rocket-powered aircraft.
In order to escape Earth’s gravity and reach orbit, a rocket needs to reach a speed of about 17,000 miles per hour, according to Jeffrey Hoffman, a professor of aeronautics and astronautics at the Massachusetts Institute of Technology and a former NASA astronaut who has flown five space shuttle missions. “The problem is that as you go up, not only do you have to lift the rocket and the payload, but you also have to lift all the fuel on it,” he said.
A rocket capable of reaching that speed would have to devote 95% of its mass to fuel, Hoffman said, leaving very little room for anything else. “It would be a dream to reach orbit with a single stage,” he added. “But to achieve this, the rocket structure, engines and payload cannot represent more than 5% of the total mass of the entire system. “And we just don’t know how to build things like that.”
That is why all the rockets used to reach orbit have been multi-stage, although current rockets such as SpaceX’s Falcon 9 have fewer stages (two) than older ones, such as the Saturn V of the Apollo lunar mission, which I had three.
“Once all the fuel in the first stage is used up, instead of taking that structure with you to orbit, you simply drop it. And that allows you to carry much more payload for a given mass on the launch pad,” Hoffman explained.
Traditionally, spent rocket stages fall to Earth (usually in the ocean), burn up in the atmosphere, or end up in orbit as space debris. SpaceX has changed that paradigm by designing reusable booster rockets that can autonomously land on Earth. The premise of a single-stage space vehicle is to dispense with rocket stages entirely, with the promise of reducing costs even further.
It’s not easy to get around what Hoffman calls the “tyranny of the rocket equation,” or to solve the problem of having to carry the weight of fuel into space. Radian’s solution is a rocket-powered aircraft that runs along a 3-kilometer rail and accelerates to Mach 0.7 (864 kilometers per hour) before releasing the space plane, which then flies into orbit with the power of their own engines.
“There have been several attempts to develop single-stage vehicles for orbit,” Hoffman noted. “NASA and the Air Force tried it in the late 1980s and 1990s. They tried to solve the problem with what they call a ramjet engine, which would take the plane through the atmosphere and burn oxygen from there instead of having to carry it with him. “It’s a great idea, but technically it’s very difficult to build that kind of engine.”
“What Radian is doing with their rocket aircraft is kind of the equivalent of the ramjet,” Hoffman explained. “In other words, it’s about trying to achieve initial acceleration without burning the rocket propellant. “In that way, some of the limitations of the rocket equation are overcome.”
Radian is convinced he can overcome the obstacles to a successful SSTO thanks to three key technologies.
The first is the aircraft’s launch system, which uses its fuel not only to power its three engines, but also those of the spaceplane itself, leaving the plane’s fuel tank full just before takeoff. The second is the landing gear, which is designed only for landing and not takeoff, making it significantly lighter. And the third is the wings, which are not present on a vertical rocket but reduce the amount of thrust the system needs by providing lift as it flies into orbit.
“Once we get to orbit, the closest analogy is probably the space shuttle,” Holder said. “We have a smaller bay, but we can do many of the same types of missions. And when we return home, we will have a more robust exterior surface, and that will allow us to reuse the system over and over again with lower inspection requirements and faster response times.”
Radian said his spaceplane will be reusable up to 100 times and will carry a crew of two to five astronauts with a 48-hour turnaround time between missions. A scale model of the plane will be tested this year, according to Holder, and a full-scale version will begin flight testing (without reaching orbit) in 2028.
Like the shuttle, Radian One could deploy payloads such as satellites into orbit or perform missions using equipment located in the bay, such as Earth observations, surveillance and intelligence for military or defense entities. But, Holder added, the plane could also help with humanitarian aid in disaster areas when runways, for example, have become unusable, by dropping the payload out of the bay in a controlled re-entry through the atmosphere.
He drew an analogy with a construction site, where the rockets are the 18-wheel trucks that arrive with large equipment and the Radian One is the truck that carries smaller materials along with the crew. “I think there will always be a place for vertical launch rockets,” he added. “They’re going to carry the really heavy stuff up.”
He is aware of the skepticism that another attempt at SSTO will attract. The latest high-profile project that lost strength It was the British Skylon, a hydrogen-powered space plane that would take off from a reinforced runway and land back on Earth. The company behind the project said last year that a two-stage system in orbit is most likely at this point.
“I’m not criticizing people who are scratching their heads and wondering whether single-stage launch into orbit is feasible,” Holder said. “It took me almost a whole year on this show to convince myself again that it is. You just have to be able to compare current technology with that of the past to see if it is viable or not.”
The big question, according to Hoffman, is not only whether SSTO can be technically achievable, but whether it can be done at a cost that is economically competitive with other launch systems, such as SpaceX’s new spacecraft, which can carry hundreds of small payloads. useful in a launch and do it relatively cheaply. “That’s always been the reason for the single-stage dream to orbit: in principle, it should be less expensive,” he said.
“I hope they are successful,” Hoffman added. “Because it would definitely be a novelty, technically speaking, and we will see what happens with the economic aspects. “You never know until they demonstrate the capability and see who signs up to use it.”
