The Space Training Simulator (STS-400) at the NASTAR Center. Image credit: Charles Black

Mar 12, 2015 OMG-force. Training for a suborbital spaceflight

Sen—As a future suborbital spaceflight participant, I decided to undertake a space training course at the National AeroSpace Training And Research (NASTAR) Center to prepare for the physiological and psychological effects of spaceflight.

I didn't know what to expect, but the application form was quite extensive and that should have given me a clue that it's a serious course. Before you can enroll you need to pass a class 3 medical as defined by the Federal Aviation Administration (FAA) which regulates U.S. spaceflight.

The FAA provide a list of doctors—known as Aviation Medical Examiners (AMEs)—who are qualified to provide the relevant class of medical certificate. The AME uploads all your details of the medical, including height, weight, eyesight and, in my case, a missing right finger which got chopped off when I was about one year old!

Armed with my medical certificate, completed application form and passport, I headed to the NASTAR Center which is located in Pennsylvania, between New York and Philadelphia.

On arrival, my fellow trainees and I were met by Brienna Henwood, Director of Space Training and Research. My 'teammates' attending the course with me were Allan Gray, Jim Clash, Karin Nilsdotter (all signed up with Virgin Galactic), Renata Rojas and Pedro Henrique Doria Nehme. Pedro had won a suborbital flight aboard the Lynx spaceplane being developed by XCOR Aerospace and was accompanied by his own AME from the Brazilian Space Agency, AEB (Agência Espacial Brasileira) who was there to monitor his physiology during the training.

Before sitting down to a series of lectures, we were given a tour of the training facility which includes an altitude compression chamber and various simulators, as well as classrooms. The walls are decorated with signed photos of the many astronauts who have visited the NASTAR Center, including Buzz Aldrin and spaceflight participants Anousheh Ansari and Greg Olsen.

Finally we were shown the main centrifuge. Its proper name is the Space Training Simulator (STS-400), and it's a serious bit of kit—in fact we were told it's the most advanced high performance human centrifuge in the world. With a 25 ft arm and a full motion, fully enclosed capsule, the centrifuge can simulate the launch and reentry profiles of most spaceflights, including those of Virgin Galactic SpaceShipTwo and XCOR Lynx.

It's designed to expose you to the G forces you will experience on a spaceflight and to increase your "G tolerance". To ensure it doesn't become unstable when in motion it's secured to the floor by four large bolts which are buried in 30 feet of bedrock. It's one of the reasons why the NASTAR Center is where it is—the bedrock is close to the surface, ideal for securing an incredibly powerful centrifuge. Another centrifuge (now decommissioned) just down the road at the Naval Air Development Center (NADC) was used to train Mercury and Gemini astronauts. 

Before our turn in the simulator we had lectures on three key areas—the space environment, the vehicle itself and the effects on the body of altitude.

A key part of the education was on G forces, the changing effect of different forces of gravity during spaceflight. G forces are explained as having different effects depending on the position you are in when you experience them—Gz are those that come from the vertical axis (imagine a vertical line running from your head down to your feet); Gx are those coming at you from the horizontal axis (imagine you are lying on your back and the force is coming from above from front to back) and Gy, which are sideways forces.

Another thing we learnt is that it's not just about the amount of G you experience, but the duration. We all experience heavy G loads from time to time, such as braking sharply in a car, but these are only for a second. Spaceflight generally exposes you to heavy G over longer periods, such as 20 to 30 seconds during suborbital flights.


Diagram showing the difference between Gz and Gx forces during spaceflight. Image credit: Sen

During the training, we learnt about the G force profiles of the Apollo spacecraft, which transported astronauts to the Moon, the Space Shuttle, the Russian Soyuz TMA capsule and also the predicted G forces for the suborbital flights of Virgin Galactic's SpaceShipTwo and XCOR's Lynx.

Astronauts launching and reentering in orbital capsules like Apollo and Soyuz don't experience any material Gz effects because they basically go straight up and down with astronauts positioned supine (on your back facing up). If you were standing up in the capsule during launch and reentry you would experience Gz, but because the astronauts and cosmonauts are lying on their backs they only feel the Gx effect.

With spacecraft more akin to a plane (SpaceShipTwo, Lynx and the Space Shuttle), their launch and reentry profiles have curved trajectories which mean at various points the G forces are felt vertically, from head to feet, meaning you encounter Gz as well as Gx.

Although astronauts experienced a maximum of about 2Gz during Space Shuttle reentry, the G forces were sustained for quite a long period—nearly 20 minutes—which I can only imagine made it very tough. Shuttle crews were also returning from spending time in a weightless environment, making the Gz effects even more difficult.

Ben Filippini, Chief Instructor at the NASTAR Center (who as a former fighter pilot ate G for breakfast) taught us how to counteract Gz forces with an Anti-G Straining Manoeuvre—an AGSM—a technique designed to stop the blood draining from your head when the vertical G forces (Gz) hit you. We were shown, and practiced, how to tense all our muscles from the stomach downward and how to manage our breathing. After practising our AGSM we were ready for our first go in the centrifuge.


The centrifuge seats one at a time, so when you take your place your teammates listen and watch from a viewing gallery, lined with screens showing everything that's going on inside and outside the centrifuge, including dashboards showing the level of G forces being experienced.


Here I am in the simulator before the G forces came on. Via a video link your teammates can watch and listen to what's going on whilst you are in the centrifuge. Image credit: Charles Black

On day one of the training your first go in the centrifuge exposes you to 50 per cent of the maximum G forces, both Gz and Gx, that you will endure on a SpaceShipTwo flight. If you are ok after this, they turn it up to 100 per cent.

When it came to my turn, I entered with some trepidation, not knowing what to expect. You get strapped into the seat with a five-point harness and all the safety checks are done. Then the door is shut and you're ready to go.

The first flight is for you to experience Gz, taking you up to 2Gz for 10 seconds. That didn't sound bad, but even 2Gz made me think 'this is going to be tougher than I thought'. In the control room were several NASTAR Center staff, and chief instructor Ben who was holding our hands over the radio. The worst bit at first was the anticipation, with Ben calmly asking how you are feeling before counting you down "OK, the Gs are coming on in 3, 2, 1 ..."

Though 2Gz was ok, 3.5Gz for 20 seconds was shocking. OMGz! After 20 seconds the Gs came off and Ben asked whether I had experienced any dizziness or changes in vision (tunnel vision, grey outs and black outs are common effects from extreme G forces). I explained that I had experienced some dizziness as the Gs came off (apparently that's normal and everyone experiences some disorientation) but my vision had been ok.

I carried on to the next two simulations which generated Gx, the horizontal G forces. First with a short burst at 3Gx then up to 6Gx for 10 seconds. The Gx were less offensive than the Gz because you didn't have to worry about your AGSM; instead you had to concentrate on your breathing whilst you soaked up the forces.

To get up to 6Gx the acceleration in the capsule is intense, then you feel like you are being pinned down by a giant invisible force. Wow, 6G felt oppressive, but bearable if you concentrate on your breathing.

A short video filmed from the gallery of the STS-400 centrifuge in action on day one of our training, going up to 6 Gx. Video shown with the permission of the NASTAR Center. 

That was it for day one, each team member taking it in turns. It's not unfair to my fellow trainees to say that each and every one of us came out of the centrifuge a bit stunned by the intensity of the G forces. There were some common effects, like very dry mouths, but some of us dealt better with the Gz and others with the Gx.

For me the Gz was tougher to endure. Teammate Allan Gray said: "I put my training to full use and was able to experiment with the AGSM exercises we had been taught to counteract the forces on the body which mainly affected my vision. As soon as I began the exercises my tunnel vision instantly disappeared."

One of the team, adventure journalist Jim Clash, observed: "As a Forbes adventure journalist I have done my share of unsettling things, including a parabolic weightlessness flight over Russia, a MiG-25 Mach 2.6 ride to 84,000 feet, driving Indy cars at 200 mph through turns on high-banked oval tracks, and bobsledding with the Olympic team. Never before had I felt the surreal experience of six times my body weight—6Gs—crushing my chest. It is formidable, and not to be underestimated."

For day two we all knew what the G forces felt like, and knowing what to expect made it easier to deal with. After further lectures we returned to the simulator for four flights.

The centrifuge was programmed with the flight profiles for the both Virgin Galactic's SpaceShipTwo and XCOR's Lynx suborbital flight. Your first flight is at 50 per cent of the G forces, followed by 100 per cent. As this recreates the flight profile, you experience a combination of both Gz and Gx at different times, rather than separately. The experience is made as realistic as possible by visuals, so from your seat you get an idea of what you will see on an actual flight. You also have dials showing the altitude and G forces.

By day two, the power of the G forces felt less shocking as I started to get used to them. After the SpaceShipTwo simulations, I did the full Lynx experience. With the Lynx flight you remain upright in your chair and there's a challenging Gz experience on reentry, up to 4.4Gz. I felt good after the final simulation and left the centrifuge feeling confident. The G forces are still extreme, but your tolerance improves quickly as you acclimatise to the sensation.


View from inside the centrifuge during one of the simulated spaceflights. Image credit: Sen

I imagine the real flight will be noisier and bumpier, but at least I have a good sense of what the G forces will be like, and how I can deal with that aspect of the spaceflight. I know that when SpaceShipTwo is released from the mothership I will tense my muscles and do my AGSM ready for the violent burst of rocket power and Gz. I will know that when we begin to descend to relax and concentrate on my breathing. Before my spaceflight with Virgin Galactic I will also benefit from three days of further training which all participants undertake.

Having done the training I would encourage anyone going into space aboard Virgin Galactic or Lynx to do it, it's essential to know what the G forces will be like. As Jim Clash observed "If this assault-on-the-senses had first happened riding a real rocket, I would not only have been uncomfortable, but probably scared out of my mind.

"To get the most from a suborbital space ride, Virgin Galactic ticket holders should definitely do this training before they fly. It is as close to a real space flight as you can get on Earth, and will allow a much more engaging ride when the real day comes because you have simulated the entire flight—and know what to expect!"

The experience had a positive effect on the rest of the team too. Allan Gray said: "I hadn’t considered the rocket ride element of my space journey as something to look forward to before now but I’m more excited than ever to go into space and experience the rocket ride, the view, the weightlessness and re-entry—the real thing!”

The training was a very valuable experience. What seems oppressive on day one does get easier with each simulation as your G force tolerance improves and you gain experience as to how to deal with them. My teammates and I left NASTAR feeling confident, better prepared and looking forward to our real spaceflight more than ever.


Adventure journalist and future Virgin Galactic astronaut Jim Clash in the simulator. Image credit: Sen