Last month, Virgin Galactic's rocket plane Spaceship Two broke the sound barrier - and took a BIG step toward commercial space travel.
By next year, it could be taking tourists into space.
"Virgin Galactic has announced they've sold over 560 tickets already. X corp is selling tickets on their vehicle," says Dr. Jim Van der Ploeg, study leader and space medicine specialist at the University of Texas-Medical Branch.
And thousands more want to follow them.
Within a few years, experts predict more commercial space passengers than in the 50 years of government-supported flights.
At the NASTAR center in Bucks County, space doctors have launched a study to find out how ordinary people react to the intense gravitational, or g-forces, of launch & re-entry.
"All of the data we've had up till now has been on very healthy astronauts and cosmonauts. We have almost no data on the common citizen who wants to go to space," says Dr. Van der Ploeg.
He adds," There's virtually no data on people like me, who are 50, 60, 70 years old."
So Dr. Van der Ploeg ssays he actually WANTS volunteers with these common medical problems -
* High blood pressure
* Respiratory conditions like asthma or emphysema
* Heart problems, such as coronary artery disease, or abnormal rhythms
* Back or neck problems
Fellow researcher Tarah Castleberry was doctor to the Navy's Blue Angels, and for NASA astronauts headed to the International Space Station.
But now, in the centrifuge at NASTAR, she's getting her first taste of what space tourists will feel. First, as the 'space ship' takes off, there are 4 G's of force pressing down on the top of her head.
Then when she reaches the maximum height, there's the floating feeling of micro-gravity.
"Wheee - I'm weightless now," says Dr. Castleberry.
Finally, when re-entry comes, 6 G's of force push Dr. Castleberry to her seat and make breathing a challenge.
"It feels like you're getting a facelift, but it also feels like somebody is sitting on your chest," she notes.
"You have to work a little bit at breathing. You don't feel like you're going to pass out, but you just have to work at slowly breathing.," she says.
Volunteers taken into the study will spend 2 days at NASTAR, and take several trips in the centrifuge under constant medical monitoring.
"We're monitoring their heart rate, blood pressure, the amount of oxygen in their blood, their respiratory rate, and also talking to them during their flight," says Dr. Van der Ploeg.
Study leaders think most of us will be OK for space travel, but they want to make sure it's done safely.
As Dr. Castleberry finishes her second flight, she exclaims, "That was a whole lot more fun than I thought it was going to be."
For more information or to sign up for the study, click here to go to the study site.