The Engine Powering the Future of Civilian Spaceflight Enters the Collections

SpaceShipTwo’s historic rocket motor lands at the National Air and Space Museum

This cylindrical vessel, known as the Case/Throat/Nozzle (CTN), is the portion of RocketMotorTwo donated to the museum. It is one of the only non-reusable components of SpaceShipTwo. (NASM)
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Eight-year-old George Madden is wandering the “Moving Beyond Earth” gallery of the Smithsonian’s National Air and Space Museum on a blustery day in February. Clad in an orange spacesuit, he is examining the artifacts—the main engine from the Space Shuttle, flight suits, a rotating chair from a 1992 Spacelab mission—and lingering near a display about space travel. He gazes up at words printed in large white text on the wall: “When I grow up, I want to be an astronaut.”

His father, 52-year-old Michael Madden, will soon make history as one of the first 1,000 people to travel to space. Madden is a paid customer of Virgin Galactic, one of six “future astronauts” in the crowd who will be among the first wave of passengers to be carried into space by SpaceShipTwo when the company begins its commercial flights, maybe as soon as before the end of the year. Madden and his son, along with other space aficionados, are in the museum for a donation ceremony. Sir Richard Branson, founder of the Virgin Group, and Enrico Palermo, president of the Spaceship Company, are turning over the hybrid engine that powered Virgin Galactic’s SpaceShipTwo, VSS Unity, on its first space flight on December 13, 2018.

The crowd hushes as Ellen Stofan, the director of the museum, steps to the podium. “SpaceShipTwo’s rocket motor is an exciting addition to the national collection of milestone spaceflight artifacts,” she says. “It is a unique piece of history that represents a new era in space travel and is sure to inspire the next generation of innovators and explorers.”

Wearing his orange space suit, 8-year-old George Madden, who hopes to ride into space, met with Sir Richard Branson and others at the National Air and Space Museum on the day Virgin Galactic donated a hybrid engine to the Smithsonian's collections. (NASM)

The famously informal Branson takes the stage dressed in a leather jacket and jeans. “We’re proud to be making history as we work toward launching the world’s first commercial space line,” he says. The engine will go on display in the upcoming “Future of Spaceflight” exhibition, set to open in 2024 following the museum’s seven-year renovation now underway.

Embodying the future of spaceflight, SpaceShipTwo is the first commercial vehicle designed for space tourism as an air-launched reusable system that will carry up to eight people—two pilots and six passengers—into suborbital space. In a typical flight, the aircraft is carried to an altitude of approximately 9.5 miles by the four-engine, dual-fuselage jet WhiteKnightTwo that wraps around both sides of SpaceShipTwo like a protective parent holding either hand of a child.

Once launched, SpaceShipTwo’s hybrid rocket motor, predictably named RocketMotorTwo, activates and propels the aircraft into the mesosphere, an outer layer of Earth’s atmosphere. On the way down, SpaceShipTwo uses a unique “feathering” method for descent. The aircraft is able to change shape for a more aerodynamic landing, floating back to Earth in a motion similar to the way a badminton birdie moves through the air. Four years ago, a fatal crash of a SpaceShipTwo spacecraft occured in the Mojave Desert when one of the pilots unlocked the feathering system too early.

But on December 31, 2018, after four test flights, SpaceShipTwo travelled its farthest yet from Earth’s surface, reaching a peak altitude of 51.4 miles—high enough, some have argued, for the pilots to be classified as astronauts.

(A debate is underway as to whether this is technically reaching “space.” In 2018, astrophysicist Jonathan McDowell recalculated the official indicator of the lower border of space, the so-called Karman line, and determined that it begin at 50 miles rather than the previously agreed upon 63 miles above the Earth. Some are still holding to the initial estimate as the true boundary into space—but regardless of technical classification, SpaceShipTwo has flown to record heights for a commercial passenger aircraft.)

RocketMotorTwo is a hybrid rocket motor that combines the simplicity of a solid propellant rocket engine with the controllability of a liquid propellant engine. The motor consists of two main parts—a large tank which stores the liquid oxidizer (nitrous oxide), and the cartridge which stores hydroxyl-terminated polybutadiene (HTPB) solid fuel. This combination, known as the Case/Throat/Nozzle (CTN), the guts of the engine, is the portion of RocketMotorTwo donated to the museum. It is one of the only non-reusable components of SpaceShipTwo.

“The operation is very simple,” says Palermo. “We pressurize the nitrous oxide in the main tank, we open the valve, flow the nitrous into the CTN, ignite it and propel our spaceship forward.”

RocketMotorTwo is one of the key parts of SpaceShipTwo that makes it safer for commercial space travel, one of Virgin Galactic’s main goals in “democratizing space.” Due to the hybrid nature of the motor, if at any point in the flight the pilot needs to end the ascent, the motor can be stopped by shutting a single valve—a safety feature demonstrated in the December 2018 test flight.

Aside from its safety components, the RocketMotorTwo is impressively powerful. At the donation ceremony, a surprise guest from the Guinness Book of World Records stopped by to award the team behind the rocket motor with the Guinness World Record for most powerful hybrid rocket motor used in manned flight.

At a panel discussion following the donation, Byron Henning, the director of spaceship propulsion at The Spaceship Company, advanced the way forward. “The next milestone I think we need to achieve is doing it routinely,” he says. “With that much data we will learn how to build a product that will become routine, like commercial travel is today, and I think that’s really the future from the technology standpoint.”

As for young George Madden, the idea of commercial space travel can mean the difference between achieving dreams of spaceflight and not—like his hero Sir Richard Branson, Madden is dyslexic, as well as color blind, and therefore is unable to ever pilot a spaceship. With the possibility of routine commercial space travel, Madden could fly to space as a passenger. Virgin Galactic’s SpaceShipTwo allows Madden’s spaceflight aspirations to be more than just a fantasy. “These things are majorly impactful,” says his father Michael Madden. “It’s allowing us to inspire all kids to get more involved.”

The rocket motor is currently on view at the National Air and Space Museum’s Steven F. Udvar-Hazy Center in Chantilly, Virginia.

About Anna White
Anna White

Anna White is an editorial intern with Smithsonian Magazine. She was born and raised in Seattle, Washington, and will graduate from Northwestern’s Medill School of Journalism in March 2019.

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