Day 2 was all about the Phoenix centrifuge at NASTAR. After some instruction on techniques to increase blood pressure to avoid loss of vision and black out, we did a series of four flights in the morning. Because the centrifuge only accommodates one person at a time, and because there were a dozen of us, it took a while for everyone to get a ride. I was fifth to go. The four flights consisted of brief profiles of sustained acceleration along either the body’s plus X axis (into the chest) or the plus Z axis (down the spine). The latter pose problems for consciousness because +Gz makes it harder for the heart to pump blood to the brain. The Gx flights make it difficult to breathe, but are not generally likely to make one pass out, at least for the durations we were doing (about 20 seconds at a time).
I have previously had experience with two G’s on parabolic airplane flights. The first time I flew one of those flights, I oriented my body so that the two G’s were in the +z direction, and I got very sick after about a half dozen parabolas. On subsequent flights I lay flat on the floor of the plane, making those G’s in the +x direction and therefore much easier to bear. So I was concerned about our 2 Gz and 3.5 Gz flights, though they wouldn’t have the repetition of the “vomit comet” nor would they be interspersed with 0 G parabolas. On the 3.5 Gz flight I had to apply all of the body-tensing countermeasures we used because I started to get a bit of tunnel vision. The countermeasures worked. The Gx flights, at 3 and 6 G’s, were impressive. The sensation of going up very very fast was completely convincing. At 6 Gx it was a real effort to breathe, and speech was very difficult. All in all, the flights were smooth and didn’t make me sick.
In the afternoon we did two flights simulating the acceleration profile of Virgin Galactic’s SpaceShipTwo. One was at 50% of the total acceleration, and the other was full acceleration. These profiles involved both Gx and Gz at the same time, along with a visual simulation of what we would see through the window of the spaceship. These flights really gave the impression of going somewhere FAST. On the final run, I had to apply countermeasures to keep my vision as things started to go gray during the 3.8 Gz portion of the rocket burn. The peak accelerations are actually on re-entry, but they are Gx and so are easier to deal with.