Zero-G on NASA's KC-135

The KC-135 is similar to the 707, but with the interior designed for experiements. The surfaces are padded to accomidate the microgravity experiments. There are about a dozen seats in the back for take-off and landing. No need for windows like a normal passenger aircraft.

 NASA photos

The microgravity condition is acheived with a dive from 34,000 feet down to 26,000 feet. The zero-G condition lasts for about 30 seconds at a time. At the end of the dive, the craft is pulled back up into a climb, resulting in a 2G condition.

One of the astronauts once told me that in zero-G, there is no up or down. Oh, sure, you can see what was once a ceiling or floor. But mentally, your mind does an immediate reset. No more up or down. It's hard to understand until you're in that situation.

Below, you'll see most people keep an "upright" orienation so it's easier to monitor testing equipment, maintain that earthly orientation, and prepare for returning to gravity.

The repeated cycles are done sequentially over the Gulf, in a maneuver called "plowing the field".

Notice the test subject in red shorts relative to the rest of the crew (above right, and below).

Common experiments include the testing of exercise equipment. Think about it: What exercises do you do that do not require gravity? That makes it difficult to exercise in space. Without exercise, each day is about a three percent loss in strength.

Notice the positions of the two green flight suits in the background.

The 0G-2G behavior results in the KC-135's hard earned nickname "Vomit Comet". If you use an airsickness bag on the last cycle, you've had a good day. If you begin using bags on the second cycle, expect one of the longest days you can remember. It's interesting that personal symptoms in the KC-135 are no indicator of how one will react in space.

Below, the red shorts are running laps around the cabin. And our forground subject is filling a bag. It'll be a long flight.

The reason for the emergency crew is that one day we lost hydraulic pressure. This isn't quite as tough as it may sound. When hydraulic pressure is lost, the wheels go into a locked brake mode. This requires the flight crew to litterally fly to a stop. Hence the automatic call to the rescue unit, even though there was no need. In close-up shot of the wheels, you can see how the tires skid to a stop and must be replaced before the next mission.