By Paul Rincon
Science editor, BBC News website
Publishedduration1 hour agoRelated Topics
- SpaceX launch
image copyrightNASAimage captionCrew Dragon (right) next to the Falcon 9 rocket
Elon Musk's SpaceX has built the Crew Dragon to carry astronauts to the International Space Station. It's part of Nasa's plan to hand over space station flights to private companies. Here's our guide to the vehicle.
Elon Musk says human spaceflight had always been the fundamental goal for his pioneering company SpaceX.
The entrepreneur achieved that ambition on Saturday 30 May 2020, when the Crew Dragon spacecraft carried astronauts Doug Hurley and Bob Behnken into orbit for a rendezvous with the space station, or ISS. It was the first crewed vehicle to fly from US soil since the retirement of the shuttle in 2011.
SpaceX and Boeing have both been developing spacecraft to take over the job of crew transport from Nasa. The space agency filled the gap between the last shuttle flight and the Crew Dragon launch by purchasing rides to the ISS on Russia's Soyuz vehicle.
Crew Dragon evolved from an earlier spacecraft, called Dragon 1, which launched 20 times on missions to deliver cargo to the ISS between May 2012 and March 2020.
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An overview of Crew Dragon
In May 2014, Musk unveiled the seven-seat Crew Dragon concept during an event at SpaceX's headquarters in Hawthorne, California.
Like Dragon 1, it's a capsule design – like the Apollo command modules that carried astronauts to the Moon.
From launch up until shortly before re-entry, the capsule is attached to a section called the trunk, which has solar panels, heat-removal radiators, space for cargo, and fins to provide stability during emergency aborts. Together, the capsule and trunk stand around 8.1m (26.7ft) tall, with a diameter of 4m (13ft).
The Crew Dragon is equipped with 16 Draco thrusters that are used to manoeuvre the vehicle in orbit. Each Draco is capable of producing 90 pounds of force in the vacuum of space.
If anything goes wrong during lift-off, the capsule has a launch escape system (LES) consisting of eight SuperDraco engines that each produce 16,000 pounds of force. The LES quickly separates Crew Dragon from its rocket.
image copyrightSpaceximage captionThere are three different seat sizes with foam that is moulded to an individual's bodyInside the spacecraft
SpaceX engineer John Federspiel, says: "When we wanted to take Dragon and make it human-rated, I think we took a different approach to spaceship design than has previously been done, because we wanted this to feel like a 21st Century spaceship.
"Probably one of the biggest features of Dragon are the touchscreens on the inside. We designed them not just to be very functional, but with a user experience in mind."
The three large displays that allow the commander and pilot to monitor systems and control the spacecraft are a world away from the analogue buttons and dials that featured in the cockpits of previous vehicles such as the space shuttle.
As the first humans assigned to fly on Crew Dragon, Nasa astronauts Doug Hurley and Bob Behnken worked closely with SpaceX to get the capsule ready for its historic launch to the ISS in May 2020. Although they say the craft was SpaceX's design "from start to finish", the crew members provided vital input.
Hurley – who trained with the shuttle – admits that the touchscreen controls took a bit of getting used to.
"As far as actual physical feedback, you certainly don't get that from the touchscreen," he says.
"But what you do get is an indication of where you touched." That indication is a "return flash" on the screen that lets the astronaut know if the vehicle correctly recognised their input.
For the types of scenarios where astronauts might need to assume manual control of the normally autonomous craft, such as finishing off a docking sequence with the space station, the touchscreen controls are "much more than adequate", Hurley adds.
Behnken explains: "It just might not be the same thing you'd want to use if you were suited up and trying to fly an entry or descent, for example, like we could do with the space shuttle."
image copyrightSpaceXimage captionThe crew of the first operational flight to the ISS pose for pictures in their suits'A suit-seat system'
Tailoring the spacecraft to the user experience involved more than just the design of the controls.
John Federspiel says: "We have three different seat sizes, we even go so far as moulding the foam around the astronaut's body so there's not any pressure points and it's just generally a pleasurable journey into space."
When the astronaut gets ready to strap in, they plug an "umbilical" line from their seat into a port on the right thigh of their space suit. The umbilical provides the suit with life support systems, including air and power.
Those suits have been one of the bigger talking points about the Crew Dragon. The sleek, customised outfits contrast with the flight suits previously worn by astronauts. But their main purpose remains the same: to protect crew members from depressurisation, where air is lost from the capsule.
"The suit is really one part of the bigger Dragon system… we think of it as a suit-seat system," says Chris Trigg, space suits and crew equipment manager at SpaceX.
image copyrightSpaceXimage captionArtwork: The Crew Dragon has an innovative abort system if there's a problem during lift-offGetting to the space station
The Crew Dragon lifts off from Florida's Kennedy Space Center on a version of SpaceX's Falcon 9 rocket that's been adapted for astronauts.
In the event of an emergency on the pad or during the climb to orbit, the launch escape system will fire to propel the capsule and its crew away from the rocket. The vehicle then deploys its parachutes to bring the astronauts down safely.
Commenting on the LES, Doug Hurley says: "That perspective for me is huge compared to shuttle, where there were what we call 'black zones'… scenarios where it didn't really matter if you had the right combination of failures, you were likely not going to survive."
media caption"Go Nasa, go SpaceX. God speed Bob and Doug"
Hurley adds that the capsule design is safer than a winged vehicle under most circumstances.
Crew Dragon is also designed to be "two-fault tolerant". This means that any two things can fail, such as a flight computer and a thruster, and the spacecraft can still bring the crew home safely.
The vehicle is designed to dock with the space station autonomously – that is, without having to be guided in by a human. Jessica Jensen, director of Starship mission hardware and operation at SpaceX, says: "We have GPS sensors on Dragon, but also cameras and imaging sensors such as Lidar (laser range sensing) on the nosecone as it's approaching the space station.
image copyrightNASA / EPAimage captionCrew Dragon is able to dock autonomously to the ISS
"All these sensors are feeding data back to our flight computer to say: 'Hey, how far away am I from the space station? What's my relative velocity to the space station?'"
The flight computer then uses algorithms that determine – based on this information – how to fire the thrusters to most effectively get to the docking target.
The vehicle's lifetime in orbit is limited to a few months because of its solar panels, which degrade in the harsh environment of space.
Leaving for home
When astronauts are ready to return home, Crew Dragon undocks from the ISS and performs a de-orbit burn with its thrusters.
The vehicle's heat shield, located at its base, must survive temperatures hotter than the surface of the Sun as the craft screams through the atmosphere at up to 25 times the speed of sound.
The material used in the heat shield is ablative: it slowly burns away at high temperatures to carry away much of the extreme heat.
media caption"Thank you for flying SpaceX" – Doug Hurley and Bob Behnken return to Earth
There's a minor chance that the spacecraft's asymmetric design – driven by the placement of its emergency escape system – could cause it to roll too much. Elon Musk has said that the issue, known as roll instability, has been extensively studied, but that it still worries him.
"I think there's an argument that the return is more dangerous in some ways than the ascent," Musk says.
Then, after the fiery re-entry phase, the spacecraft needs to deploy four parachutes to slow its descent.
image copyrightNASA/Bill Ingalls
Finally, the Crew Dragon splashes down in the Atlantic Ocean, 450km off the coast of Florida, where recovery ships will take the astronauts to safety and retrieve the capsule.
The spacecraft can then be refurbished. Nasa has agreed to let astronauts fly on re-used Crew Dragons – and Falcon 9 boosters – as soon as SpaceX completes its third launch to the ISS with humans.
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