In the 1990s, NASA embarked on an ambitious project to create a space plane capable of single-stage-to-orbit (SSTO) flight, a concept designed to revolutionize space travel by eliminating the need for multi-stage rockets. Known as the X-33, the program aimed to drastically reduce the cost of sending payloads into orbit. However, the program was eventually canceled in 2001 due to insurmountable technical challenges.
Now, more than two decades later, Radian Aerospace, a Seattle-based company, is breathing new life into the SSTO dream with its innovative space plane, the Radian One. Co-founded in 2016 by Livingston Holder, who previously led the X-33 program, Radian Aerospace is leveraging advancements in materials and propulsion technology to overcome the hurdles that once grounded the SSTO concept.
The Radian One introduces a novel approach to space launches by replacing the traditional vertical rocket launch with a rocket-powered sled. This sled accelerates along a two-mile rail, reaching speeds of up to Mach 0.7 (537 mph) before releasing the space plane, which then ascends into orbit using its own engines. This method aims to bypass some of the fundamental limitations of the “rocket equation,” which traditionally necessitates multiple stages to achieve the velocity needed to escape Earth’s gravity.
Jeffrey Hoffman, a professor of aeronautics and astronautics at MIT and a former NASA astronaut, explains the challenge: “To reach orbit, a rocket needs to reach a speed of about 17,500 miles per hour, but 95% of its mass is devoted to fuel, leaving little room for anything else.” The multi-stage rocket system was devised to address this problem, with each stage jettisoned once its fuel is spent. By contrast, Radian One’s SSTO design aims to do away with stages entirely, offering the potential for significant cost reductions.
(Radian Aerospace)
Radian One’s design incorporates three key innovations: the rocket sled launch system, landing gear optimized solely for landing, and wings that reduce the thrust required by providing lift during flight. This combination of features allows the space plane to carry a full tank of fuel upon release, significantly enhancing its efficiency.
With a reusability factor of up to 100 missions, Radian One is set to carry two to five astronauts and will have a 48-hour turnaround time between flights. Holder envisions the space plane serving a variety of roles, from deploying satellites to providing disaster relief by delivering payloads to areas where traditional runways are unusable.
Livingston Holder, Radian Aerospace’s CTO, previously worked for NASA on the X-33.
Despite skepticism rooted in the history of failed SSTO attempts, Holder remains optimistic. “You have to be able to put yourself in the technology of today versus the technology of the past in order to see whether or not it’s viable,” he says. The Radian One project, set to begin flight tests by 2028, aims not only to achieve the technical milestone of SSTO but also to do so in a way that is economically competitive with existing launch systems, such as SpaceX’s Starship.
As the space industry watches with anticipation, the success of Radian One could mark a significant breakthrough in the quest for cost-effective and reusable space vehicles, potentially ushering in a new era of space exploration.
