The Space Reviewin association with SpaceNews

Brian Binnie
Brian Binnie speaks at the Heinlein Centennial conference on July 6, with an image of the Earth taken during his October 2004 suborbital spaceflight behind him. (credit: J. Foust)

An experience that sells itself

As the last several years have demonstrated, there is significant interest in the emerging market of suborbital space tourism. A number of companies have announced vehicles, in various stages of development today, and are actively signing up customers on the basis of computer-generated animations and other illustrations of what the flights will be like. However, these marketing materials many not adequately describe what the suborbital spaceflight experience will really feel like to future passengers, in part because these vehicles have yet to fly, and there’s very little experience to date with other similar vehicles.

One of the few people who really can describe what the suborbital spaceflight experience will be like is Scaled Composites test pilot Brian Binnie, who flew SpaceShipOne on its first powered test flight in December 2003, and again on its final, Ansari X Prize-winning flight in October 2004. In a talk at the Heinlein Centennial conference in Kansas City this past weekend, Binnie described the various phases of flight for SpaceShipOne (SS1) and its successor, SpaceShipTwo (SS2). While specific to those vehicles to some degree, his comments provided insights into what people may experience—and feel—on a wide range of future commercial suborbital spacecraft.

“If there are any concerns, fears, doubts, gremlins, or demons lurking between your ears as to why you’re doing this, they’re going to come home to roost during the hour-long climb up to altitude,” Binnie warned.

Both SS1 and SS2 have five general phases of flight: an hour from takeoff until the vehicle is dropped from its carrier aircraft, a period of about 90 seconds as the spacecraft’s engine fires, several minutes of weightlessness as the spacecraft coasts through the apogee of its suborbital trajectory, 90 seconds of reentry, and then a glide phase of up to a half hour before landing (a part of the flight Binnie didn’t go into much detail about during his presentation).

While both SS1 and SS2 have the same general phases of flight, Binnie did note that the flight paths of the two vehicles would be somewhat different. While SS1 remained close to Mojave Airport during its suborbital flights, Binnie said that, on its initial flights out of Mojave, SS2 and its White Knight 2 carrier aircraft will fly west out beyond the Pacific coast before turning back to the east to release the spacecraft. SS2 will then fly its trajectory up over the coastline, gliding back to land at Mojave. If SS2’s engine fails to light, however, it won’t be able to coast back to Mojave. “If we have any problems with the rocket motor at that point in time,” he said, “we’re still in glide range of several fields, including Vandenberg [Air Force Base].”

Regardless of the flight path, that hour-long flight to the launch point poses problems of a different kind. “This is really the phase of flight that I think is going to have the most interest, variation, and potential difficulty for us,” Binnie said. “If there are any concerns, fears, doubts, gremlins, or demons lurking between your ears as to why you’re doing this, they’re going to come home to roost during the hour-long climb up to altitude.”

The way to deal with this, he said, is by giving passengers some training before the flight so they better understand what the overall flight experience will be like. That will include weightless aircraft flights, like those currently offered by Zero Gravity Corporation, as well as possibly flights in aerobatic aircraft.

Any anxiety people feel will transform into something else when the vehicle is released and lights up its engine. Binnie described what people might feel when SS2 is released from its aircraft. “There’s separation, and a little lightening of the seat, and you’re free,” he said. “And you’re kind of thinking to yourself, ‘I can handle that.’ It’s kind of quiet since you’re separated from the jet engines, but just when you start to feel your oats you see a yellow light come on in the front cabin; that means the rocket motor has been armed. Then another light comes on, that means the firing sequence has commenced, and perhaps the large numeral ‘5’. That’s the number of seconds before the rest of your life is changed pretty much forever.”

“It goes to ‘4’, and you really start to feel the adrenaline start to kick in,” he continued. “It goes to ‘3’, and you look at your neighbor, and sort of see them have similar angst. It goes to ‘2’, and maybe you say a quick prayer, even if you don’t pray. And then ‘1’.”

“And when the rocket motor lights off, it is though a tsunami sweeps through that cabin,” he said. “Your ‘fun meter’ goes from hard right to left, from fun to fear, you go from the top to the bottom of Maslow’s charts [of hierarchy of needs], and away you go.”

The experience is so jarring, he continued, “you have nothing in your DNA to tell you whether this is good or bad. For the first three or four seconds, you’re running on fear, and then you realize you’re still alive, so the faith part kicks in that says, ‘Well, this is sorta like how they told me this would be. I’m still breathing and thinking, so we must be doing alright.’”

At launch, “your ‘fun meter’ goes from hard right to left, from fun to fear, you go from the top to the bottom of Maslow’s charts [of hierarchy of needs], and away you go.”

About ten seconds into the flight the vehicle passes through the transonic regime, ending the worst of the shaking and buffeting, although there’s still a lot of noise and shuddering. As the vehicle climbs at an attitude that becomes more and more vertical, “you look out and see the sky turn darker and darker shades, eventually to purple and then, around the one-minute mark, it starts to go black,” he said. “It’s a thrill. It really is.”

When the engines finally do shut off (after, in the case of SS1, sounding like “a shrieking cat” in its final seconds as the oxidizer go through a gas/liquid transfer phase), you “cross a dimensional boundary of peace and quiet,” he said. “Three wonderful things happen, I call it the holy trinity of spaceflight: the shaking, the shuddering, the vibrations, they go away. The noise, the shrieking, it goes away, and you become instantly weightless.”

He described the ability for SS2 passengers to float out of their windows and look out either at the blackness of space or the view of the Earth below, and the “bright blue electric ribbon of light”—the atmosphere—separating the two. “Everywhere you look, it’s wow. And everything you feel about you, because you worked pretty hard to get there, is wow.”

That all-too-brief euphoric experience in weightlessness, though, comes to an end as passengers face what Binnie called the “unique and memorable” experience of reentry. He described a “pinging” sound in the cabin as the spacecraft first starts to experience reentry, something he likened to the first drops of rain that fall on a car’s windshield at the onset of a thunderstorm. “The intensity builds and builds and builds,” he said, “and, along with it, the acoustic environment.”

As the same time the pinging noise starts to build, so does gravity. “You have about 20 seconds from when you realize that you’re no longer weightless to get back to your seat or find a place on the floor to stretch out and get comfortable,” he said, because after those 20 seconds the forces will have built up to 2 Gs, at which point it becomes rather difficult to move around the cabin.

The peak reentry forces will depend on the vehicle’s flight profile—the higher the maximum altitude of the flight the higher the forces upon reentry—but Binnie said they plan to set a limit of 7 Gs for reentry. “We think that 7 Gs, lying flat, is about as much anybody is comfortable with taking” and still come away thinking the flight was an enjoyable experience, he said. “Seven Gs lying flat is going to be the equivalent of 3–4 Gs sitting upright, which is what most normal people willing to expose themselves to this environment are comfortable with taking,” he said. He later added that the seven Gs is not a constant value throughout the entire reentry period: the G profile is actually more like a bell curve that peaks at 7 Gs, with about 20 seconds where the G forces exceed 4 Gs.

“I’m fully convinced that it will sell itself because that’s just how grand it is.”

Other companies are looking at ways to minimize reentry G forces. Last week Benson Space Company announced an approach called “Variable Ballistic Coefficient” that it plans to use during the reentry of its suborbital spacecraft. That system, which utilizes dive brakes and other vehicle configuration changes, keeps the G forces from exceeding 3 Gs during reentry. Binnie said that while such an approach is interesting, it’s more complex, and that he preferred the easier approach of feathering the wing and having the passengers lie down during reentry.

Despite all these physical and psychological factors, Binnie said that the overall spaceflight experience is more than worth it. “I don’t believe I can oversell it,” he said. “I’m fully convinced that it will sell itself because that’s just how grand it is.”