Doug Hurley and Bob Behnken are the only two people who know what it's like to fly on a SpaceX rocket. On Friday, the pair revealed some more details about how it feels, and why the Falcon 9's design changes things.
Hurley and Behnken flew on the first crewed flight of the SpaceX Crew Dragon. The human-carrying capsule, designed to help NASA send astronauts to and from the International Space Station, was launched by a Falcon 9 rocket on May 30 from Kennedy Space Center's Launch Complex 39A in Florida. It was a momentous occasion: after NASA's space shuttle program ended in 2011, the agency had to send astronauts to the station with the help of Russian agency Roscosmos. SpaceX's crewed flight helped kickstart a new era for NASA missions, one that brings these flights a little clsoer to home.
In an interview with Spaceflight Now, Hurley described the launch as feeling "totally different than shuttle,” adding that “it was smooth. It got a little rougher.” Hurley, who was in charge of launching, landing and recovery for the Crew Dragon mission, also flew on the space shuttle's final mission.
Behnken agreed, saying that he was "surprised a little bit at how smooth things were off the pad." He told the publication:
“The space shuttle was a pretty rough ride heading into orbit with the solid rocket boosters, and our expectation was, as we continued with the flight into second stage, that things would basically get a lot smoother than the space shuttle did. But Dragon was huffing and puffing all the way into orbit. It was not quite the same ride the smooth ride as the space shuttle was up to MECO (main engine cutoff). A little bit less Gs, but a little bit more alive is probably the best way I would describe it.”
The main difference, as noted by Hurley, is the propellant in use. The space shuttle used two solid rocket boosters (SRBs) for flight, designed to send the vehicle up to 150,000 feet. Each SRB booster weighs 1.3 million pounds, with a motor that uses 1.1 million pounds of propellant. These worked with the main engines, so the boosters provided the thrust for the first two minutes of flight before giving way to the hydrogen-powered main engines.
Using solid fuel, unlike liquid, makes it easier to store and makes the development process cheaper. But the New York Times noted that solid fuel burns more "like a giant firecracker," as opposed to the easier-to-control liquid fuel as used on the Falcon 9.
This is perhaps why the launch phase felt smoother to the pair. The nine Merlin engines that power the Falcon 9 use super-cool liquid oxygen and rocket propellant to provide 1.7 million pounds of thrust at liftoff.
Behnken and Hurley will likely be joined later this year in the exclusive SpaceX flyers' club. The first non-test mission, "Crew-1," will send up astronauts Victor Glover, Michael Hopkins and Shannon Walker from NASA. They will be joined by Soichi Noguchi from Japan's JAXA agency. The mission is expected to take place in the third quarter of 2020.
The Inverse analysis – The comments demonstrate how SpaceX's entry into the rocket race is changing how astronauts experience spaceflight. Beyond the fuel switch, the Crew Dragon also uses a more futuristic-looking array of touchscreens on the inside, as opposed to the dials and levers better associated with traditional spacecraft.
As SpaceX gears up to fly the Starship, there could be more changes on the way. That ship, with the ability to send up to 100 people into space at a time, is set to be complete with an entertainment area and internal cabins. In the future, spaceflight may no longer be limited to the confines of a tiny capsule.