THE pilot is counting down over the intercom: 鈥淥ne minute鈥�30 seconds鈥� 20鈥︹�� I am 6 kilometres above the Atlantic Ocean and about to lose a lot of weight.
They call this the vomit comet 鈥� and with good reason. When the pilot reaches the end of his countdown, he will pull back on the joystick, sending the aircraft into a 45-degree climb. A kilometre or so higher into the blue, he will cut back the engines. The plane鈥檚 momentum will take it soaring upwards until our ascent slows and stops and we begin to drop out of the sky. After a short while, the pilot will bring back the power and pull out of the dive. And then he鈥檒l do it all again and again and again. In the next 3 hours, we are going to experience 31 of these gut-wrenching parabolas.
These manoeuvres are not just for fun: flights like this one have long been used for carrying out a wide variety of research where gravity would get in the way (see 鈥淏eating the pull鈥�). For 23 seconds of the parabola, everyone on board will feel as if they are weightless. With the space shuttle still grounded, research slots on vomit comet flights are very much in demand.
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鈥淭en seconds鈥ive鈥︹�� This had seemed like such a good idea when I first got the call. A team from the University of Aberdeen in Scotland was planning to test their new exercise equipment for astronauts aboard a parabolic flight. The idea was to find out if a kind of vibration therapy could help bones and muscles resist the damaging effects of long-term weightlessness (see 鈥淕ood vibrations鈥�). Did I want to come along and watch? I signed up on the spot. By the time I鈥檇 discovered just what it involved, it was too late to back out.
In the months before the flight, I tried to prepare myself by going on fairground rides, and reading the instruction manual sent to me by Novespace, the French aerospace firm that provides the European Space Agency鈥檚 flights. It was hard to tell if the author had been attempting humour or was a master of understatement: first-timers 鈥渁re strongly advised to remain calm鈥�. Easier said than done, I decide as the first parabola rapidly approaches. 鈥淭hree鈥wo鈥ne鈥ull up!鈥� The climb subjects you to forces of about 2 g 鈥� equivalent to accelerating from 0 to 100 kilometres per hour in 1.5 seconds. My cheeks are being pulled downwards (or rather, being left behind as the rest of my body is pushed upwards) in what I have no doubt is a highly unflattering manner. Then comes the warning for zero gravity 鈥� 鈥淚njection鈥�. We brace ourselves.
Roller coaster
Though I follow instructions to remain in my seat for the first parabola, my body knows something strange is happening. It鈥檚 like going over the top of a steep roller coaster, when your stomach does that unnerving flip-flop as your insides rise up, then return to their natural place 鈥� except this time my stomach doesn鈥檛 go back down again. I realise there is a distinct gap between my bottom and the seat cushion, and my hair is floating up around my head like Medusa鈥檚. It is just so鈥dd. I loosen my seat belt to the maximum so that I float up closer to the ceiling and flop my arms and legs around like a rag doll.
After what seems much longer than 23 seconds, the pilot announces we are about to pull out of the parabola: cue another brief cheek-stretching period of 2 g, and then a return to normality. Cheered by the fact I鈥檓 not vomiting yet, I leave my seat and join the researchers in the work area. The plane has been converted into a zero-g lab by ripping out many of the seats, leaving only a few rows at the front and tail ends. In the vacant central space, every available surface is covered with white leather padding and festooned with straps, handholds and ropes strung vertically between ceiling and floor.
Losing contact
When the next parabola begins, I kneel on the floor holding on to one of the vertical ropes. In this position the 2 g phase feels even more disconcerting: the force pushes my head and neck down until I am bent over like a hunchback. Then the weight suddenly lifts. My knees are losing contact with the floor; I try to hold onto the rope more tightly only to find my legs drifting out behind me. The more I try to right myself, the worse things get.
By now I am practically horizontal and the researchers are in serious danger of getting a kick in the face. I am as helpless as a baby 鈥� and with good reason. As infants we learn to take control of our legs and arms by using muscles in complex configurations that move the limbs while simultaneously compensating for gravity. Even when we are just standing upright we are constantly using muscles in our feet, legs, bottom and back to resist that inexorable downward pull. Take away that force and all those instinctive actions seem to do nothing more useful than send us upwards.
While I am busy making a fool of myself, the researchers have work to do. Sadly, the Aberdeen crew have been banned from turning on their vibrating equipment: the ESA staff are concerned it could affect the aircraft鈥檚 instruments. So the team have to content themselves with taking leg muscle measurements during ordinary exercise in zero g. Other experiments are going on too: researchers from around Europe are investigating how weightlessness affects soldering repairs, an enzyme, a home-made robot, and even the behaviour of fish.
Research can鈥檛 be easy under the circumstances: the students have to fit their experiments into 23-second slots, while ensuring that neither they nor their experiment float away. All the equipment is tightly secured, right down to the last spare screw. Even something weighing a couple of grams could do serious damage if it floated up to the ceiling, then dive-bombed the cabin during the 2 g phase.
But as the parabolas continue, the chief hazard of working on the vomit comet is making its presence felt. Every so often people turn pale and hurriedly return to the seating area. While they barf up their breakfast, an ESA crew member waits in the background, as discreet as the maitre d鈥� at the Ritz. Once the bag has been filled, they whisk it away to somewhere near the cockpit.
Heroic heaving
Recovery seems relatively quick. Perhaps it鈥檚 down to the anti-motion-sickness medicines we had been prescribed, but most manage to return to work within 5 or 10 minutes of being sick. One brave soul, who was throwing up almost from the start of the first parabola, hasn鈥檛 even left the research area. She heroically carries on with her work between heaves, and we politely ignore her retching.
Anyone who has a spare moment gravitates towards the 鈥渇ree-floating zone鈥�, a small netted-off area set aside for messing around. It is here that I discover the joys of mid-air acrobatics, laughing and shrieking like an idiot as I bounce off the ceiling. We can鈥檛 resist staging photos where we support someone else鈥檚 weight with one finger, or pretend we are sitting on a flying carpet. It is impossible to convey just how much fun this is.
But sometime around parabola 23, my stomach decides it has had enough, and I bid a hasty retreat to the seating area. I manage a temporary recovery, but by parabola 28 I鈥檝e relapsed and have to sit down for the rest of the flight. Believe me, when you are fighting to keep control of your stomach contents, there is nothing you鈥檇 less like to do than zero-gravity somersaults.
鈥淚t鈥檚 impossible to convey just how much fun this is鈥�
Fixing my eyes on the dial that counts how many parabolas have been completed, I will the number upwards. When the final one comes around I hear groans of disappointment from the free-floating zone, but I can鈥檛 help feeling relieved.
So, what of the scientific progress? At the debriefing later that day, the research teams report how their experiments went. A few had suffered technical difficulties, but the robot moved around a bit, and the soldering worked. The Aberdeen researchers were pleased with their results. And the fish, it turns out, were somewhat taken aback by the weightlessness and didn鈥檛 swim around as much as usual.
I can鈥檛 say I blame them.
Beating the pull
鈥淢ICROGRAVITY opens up a new dimension for humanity to explore,鈥� says Vladimir Pletser, an ESA physicist and the coordinator for the vomit comet flight. 鈥淲e are still really at the beginning.鈥�
Philips engineers, for example, are going on parabolic flights to improve the design of highintensity- discharge (HID) lamps, a type of light bulb that is very energy-efficient but requires high power input. During weightlessness, they can study the de-mixing of the two gases inside the bulb, an effect normally masked by convection currents due to gravity. They are using the data to design HID lamps that can operate from the domestic power supply and be even more efficient.
Maurice Hinsenkamp, an orthopaedic surgeon at the Free University of Brussels (ULB) in Belgium, uses parabolic flights to study bone healing after breakages. He has even taken some of his patients on the flight with limbs held together by external metal rods screwed into the bone. Through these rods Hinsenkamp measures internal forces within the bone that are normally masked by gravity.
And a team from Bremen University in Germany have been using parabolic flights to investigate better ways of making metallic foam. This is a strong but extremely lightweight material with numerous potential industrial uses. It is made by heating a metal such as aluminium until it melts, injecting gas, and then quickly cooling the mixture so it solidifies as a foam. Current manufacturing techniques create a foam with unevenly distributed bubbles, as gravity causes the liquid to sink downwards and the bubbles to float upwards. The Bremen researchers are using the snatches of zero-gravity on parabolic flights to create 鈥減erfect鈥� foam with homogenous bubbles, and to work out ways of doing so back on earth. 鈥淚f you switch off gravity, it helps you optimise the process,鈥� says engineer Stefan Odenbach, who leads the Bremen team.
Good vibrations
IF THE manned space programme is ever going to take off for distant planets, we will need to be able to protect astronauts against the long-term effects of weightlessness. Without regular exertion against gravity, people鈥檚 muscles get flabby and their bones become brittle.
To counteract this, the crew on the space station are supposed to spend several hours a day exercising. All sorts of ingenious contraptions have been lugged into orbit to keep the astronauts fit, such as a treadmill with bungee cord harnesses that stop runners from floating away. But the crew are notorious for giving their keep-fit regimes low priority. And apparently the bungee cords tend to chafe.
What they need is a less time-consuming way to get the benefits of exercise. And that鈥檚 the idea behind the Aberdeen researchers鈥� vibration therapy. For reasons that are not entirely clear, when people stand or lie on a plate vibrating up to 50 times a second, muscle and bone tissue are stimulated much as they are by exercise.
Vibration therapy is being investigated as a way to boost muscle and bone strength in patients who are bed-bound, but it could also benefit astronauts, saving them precious time and increasing the effectiveness of some of their exercises.
鈥淭he problem they have now is that the intensity of the exercise is not strong enough to stimulate bone remodelling,鈥� says Marco Cardinale, an exercise physiologist at Aberdeen and adviser to ESA. 鈥淎dding vibration would help.鈥�
