The giant 100-passenger spaceship that SpaceX plans to load with a billionaire and a clutch of artists may one day circle the moon, perhaps as soon as 2023.
But the ship also has to land safely back on Earth.
While presenting wealthy lunar-enthusiast and future SpaceX passenger Yusaku Maezawa to the public on Monday, CEO Elon Musk also showed a simulation of how the forthcoming Big Falcon Rocket, or BFR, will fall through the sky like a plummeting rock and eventually land upright back on Earth.
"It's very counterintuitive," Musk said. "It's not like anything people are familiar with. It's not like an airplane."
Indeed, compared to the way people expect a plane to land, a BFR landing would be radically different. But when it comes to landing such a large, reusable spaceship, the plan is in many ways quite sensible -- though by no means close to being realized.
In fact, the BFR may be following in the footsteps of NASA's retired space shuttles, the 184-foot-long craft that conducted missions in space for three decades until their retirement in 2011.
For most of their descent through the atmosphere, the shuttles didn't point their noses forward like an airplane. Instead, they positioned their noses up, using the shuttle's broad underside to catch lots of air friction and slow down.
"The space shuttle did the exact same thing," Brad King, director of the Space Systems Research Group at Michigan Technological University and CEO of Orbion Space Systems, said in an interview.
As the shuttle fell through the atmosphere, it acted "like a great big ram" as it collided with masses of air to brake in the sky, said King.
And this is Musk's plan for the BFR.
"What's interesting about this is he uses the body of the vehicle to lose most of the velocity," Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, said in an interview. "He kills a lot of the horizontal speed early."
And it's braking during this first, super high-speed descent through the atmosphere that's really the most critical. SpaceX has already mastered the last part, which is landing things upright -- even two rocket boosters at the same time.
"It's not the landing that’s difficult," said McDowell. "It's the horizontal speed of 18,000 mph that you have to kill."
Once the BFR brakes and loses forward momentum, then it will simply plummet straight downwards to its landing spot.
"It's what a stone would do," said King. "It just kind of drops out of the sky."
Hitting the precise landing spot, however, will be a challenge.
Unlike NASA's shuttles, once the BFR slows down and loses its forward motion, it also loses most of its ability to propel itself to a specific location. The shuttle could circle around in preparation to land. The BFR doesn't have that ability.
So, as soon as the rocket leaves space and begins descending through the sky, it will need to make the adjustments necessary to bring it within landing range.
"The decisions it makes high up in the atmosphere are absolutely crucial to where it lands," said King.
Though, the BFR -- in its current form -- will have a little bit of steering ability. It has three fins on the back, two of which can move around. So, once SpaceX is in pretty close range to its landing zone, it has some ability, though limited, to correct the spaceship's final course.
"That gives them controllability on the way down," said McDowell.
But, as both McDowell and King emphasized, these fins are not wings. They don't provide any lift like a plane. They simply allow the craft to move from left to right.
Landing a giant spaceship upright may seem like a somewhat fanciful endeavor. But SpaceX engineers have accomplished unprecedented landing feats for years now.
"It's a very interesting design and I look forward to them developing it into reality," said McDowell.
"When Elon and SpaceX put their mind to doing something, I wouldn’t bet against them," Tommy Sanford, executive director of the Commercial Spaceflight Federation, said in an interview. "It's sort of like NASA in the sixties -- you wouldn’t bet against them."
If it works, the BFR is designed to go well beyond the moon, out into the more distant solar system. And that's not so far-fetched a concept anymore, either.
"I think it's feasible and it's about time," said King. "As a spacefaring species, humans have known how to get a vehicle to Mars for some time."
In the coming five years, SpaceX might have a vehicle to not just get there and back, but land safely on earthly ground.
"I don’t see any technology here that requires a miracle," he said.
