According to Colwell

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.

Today we got a tour of the NASTAR center which has some impressive aircraft simulators and a gigantic centrifuge (11 ton, 25-foot arm, with bolts going 45 feet down into the bedrock and a huge mass of concrete underneath to keep it stable as it swings around). Then we had a course on the physiology of hypoxia (oxygen deprivation) and some basics on atmospheric physics before getting fitted with oxygen masks and heading for the altitude chamber. I’m not actually sure that’s the write term, but it’s a room with a dozen seats and ports for oxygen masks and can have its pressure adjusted to simulate various altitudes.

After 30 minutes of denitrogenation (breathing pure oxygen to remove nitrogen bubbles from the blood to reduce the likelihood of those bubbles expanding to painful size on ascent to high altitudes), we took our masks off and they took the chamber up to 18,000 feet. That is to say, they lowered the pressure in the room to what it is at an altitude of 18,000 feet. At that altitude, the pressure is about half what it is at sea level. So each breath delivers half the oxygen of a breath at sea level. We had some simple exercises to perform - simple math operations, some writing - to identify any degradation in mental function as we entered a hypoxic state. I noticed an increased heart rate, but no other symptoms. I have done two altitude “flights” in the past, about 10 years ago, with no noticeable effects. I could not tell if the increased heart rate was due to lack of oxygen or simple anxiety about possibly worse effects. After about 15 minutes, one member of our group passed out. By that time I was feeling a bit tired, but otherwise no overt effects of hypoxia. My simple math problems were done without error, as were the two mazes.

Today I flew to Philadelphia with my graduate student, Akbar Whizin, in preparation for a two-day course on suborbital spaceflight at the NASTAR center. With at least two companies readying commercial suborbital rockets to carry paying passengers to the lower limits of outer space, there is increased interest in the uses of these vehicles for science and education and not just high-priced sightseeing. NASA has long had a vigorous program of experimentation in suborbital sounding rockets. These new vehicles may soon find a place as laboratories for scientists and students who need quick and easy access to either the upper reaches of the atmosphere or a few precious minutes of high quality microgravity.

My own scientific interest in these vehicles lies in the study of the collisional behavior of small objects and aggregates of objects at low impact speeds. I’ve had one such experiment fly twice on the space shuttle and a similar experiment has flown several times on parabolic airplane flights. These experiments simulate in various ways the collisions that were common in the early stages of the formation of the solar system and are currently taking place in Saturn’s rings (and the rings of the other planets). It is not possible to perform experiments on these kinds of collisions without a microgravity environment. A few seconds of microgravity can be achieved in a drop tower, and 10-15 seconds of a relatively uneven low-gravity environment can be obtained on parabolic airplane flights. For many experiments a longer, more stable microgravity environment is needed.

Virgin Galactic has unveiled the first of its passenger-carrying suborbital crafts, the VSS Enterprise. Blue Origin has selected my experiment and two others to fly on a test flight of their New Shepard suborbital rocket. Other companies are developing rockets for passengers and some just for payloads. Someday soon, scientists may be flying alongside their experiments on these rockets, reacting to the performance and making real time adjustments to the operation of the experiment. And so I find myself getting ready to undergo two days of “astronaut boot camp” at the NASTAR center. Tomorrow features some hypoxia training and time in a chamber simulating high altitudes (low atmospheric pressure). Wednesday will be a full simulation of a flight on the VSS Enterprise. The final frontier awaits.