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- Pridružio: 10 Feb 2005
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Ever wondered how astronauts feel when they are weightless? Alok Jha experienced a zero-gravity parabolic flight, 31 times in one day, to find out
At 25,000ft, the pilot cuts power to the engines. For the briefest of moments, there is silence. Then, the world inside the plane becomes a phantasmagoria: people gasp and scream as they are lifted, limbs moving chaotically. Bottles filled with coins rise into the air and the contents begin a serene dance, as if held by an unknown force.
Finally, 20 seconds after the Airbus A300 begins plummeting towards the Mediterranean, the engines roar back to life. The people inside, some of whom are pinned to the roof of the cabin, slam back against the floor. The quiet that follows is broken by a sharp hiss. A voice on the intercom razbijacles "Next parabola, one minute."
Feeling weightless is not something you do every day. As such, it is difficult to describe in everyday terms. It is nothing like floating in water. Nor is it like the butterflies in your stomach hurtling down a rollercoaster. It is the single strangest feeling I have ever had - a combination of shock, fear and immense euphoria.
My story began two days earlier at a military research base next to Bordeaux Merignac airport. Though it is part of a sprawling industrial park, the small, single-storey Novespace office sits alone next to the tarmac leading to the airport's runway.
When I get there, I find groups of people huddled around bits of foam, metal and plastic. The floor is littered with paper, electrical tape, wires, nuts, bolts, spanners and screwdrivers. Conversations hum in at least half a dozen different languages - these scientists have come from all over Europe to fly their experiments in zero gravity.
At one side of the building is a locked metal gate, beyond which rises the unassuming white shape of an Airbus. It wouldn't look out of place at any airport but for the lack of windows and the words "Zero G" daubed in blue multistorey letters on its fuselage.
"It's an incredible facility to have," says William Carey, of the European Space Agency's human spaceflight and microgravity exploration division. "A lot of scientists who will fly experiments on the space station will test equipment and procedures on a parabolic flight."
Thanks to these flights, scientists can, for 20 seconds at a time, test satellite components or predict problems with experiments destined for the International Space Station before they are sent into orbit. Falling out of the sky in an airplane is the only practical way to experience microgravity without leaving Earth.
At a safety briefing on the morning of my arrival, the pilot explains how the flight will proceed followed by a doctor who tells us how to survive the experience. Airplanes fly by forcing air over their wings in such a way that there is an excess of the upwards force, lift. While in the air, the plane stays up thanks to lift and moves forward because of the forward thrust provided by the engines. The aircraft battles against two forces trying to slow it down and pull it out of the sky - air friction and gravity. On a normal flight, the amount of thrust will be greater than the friction and the lift will equal the weight so that the plane stays up.
On a parabolic flight, thrust is set to equal air friction while lift is simultaneously removed. This leaves weight as the only force acting on the plane and, like any unpowered object fired into the air, it will move in a parabolic curve as it freefalls.
At this point, because everything inside the aircraft begins falling to Earth at exactly the same speed as the plane, the contents act as if they are weightless. That is not to say that the plane and its contents actually are weightless - gravity is still acting on the plane and everything in it. The effect on a passenger is a wonderful reminder of our animal past. The human brain gets so confused with the shifting sensations that it does what confused brains do best - induce vomiting.
The flight doctor explains how the sickness is caused by a conflict between information coming from the inner ear (responsible for balance) and from the eyes. The inner ear can't tell which way gravity is pointing during freefall, whereas the eyes see very little real difference. Cue the sickness.
The experience isn't cheap. Each campaign (usually three 31-parabola flights) costs half a million euros and ESA runs about four a year. As time is precious, most campaigns are limited to ESA-funded researchers. But, for the last eight years, ESA has run a campaign to give first-timers a feel for space research. The student parabolic flight campaign runs every summer and attracts applications from more than 100 teams of budding space researchers.
One of the successful British teams this year was backed by the highly regarded space research centre at Leicester University. Daniel Brandt, Jim Aldcroft, Keith Sprake and Richard Branch - fresh from sitting their physics finals - joined 28 other teams.
Their journey to Bordeaux had started almost a year before, when Aldcroft and Brandt came up with an idea to test how mixtures of particles of different sizes might settle in zero gravity conditions. "We're trying to observe segregation of granular matter in reduced gravity conditions," says Branch. In the presence of gravity, this separation phenomenon is more commonly known as the "Brazil nut effect", where the biggest nuts in a box of breakfast cereal, for example, rise to the top as the mixture settles.
This implies that the sizes of the particles in a mixture determine their final arrangement but no one has studied the role of gravity in the phenomenon. Out in space, how would a box of cereal settle? The idea has applications for planetologists trying to model how the debris resettles on small moons churned up after meteorite impacts.
"According to our theory, size shouldn't make a difference - what should make a difference is the density of the particles," says Branch. In zero gravity, Aldcroft and Brandt's idea was that particles of different densities would separate into bands along the length of the box. How could the Leicester team test this idea? Mixtures of materials (ball bearings, sand and simulated Mars dust, for example) were packed into clear plastic boxes and vibrated at various frequencies to force them to settle.
As well as the Leicester physicists, two other experiments from the UK made the flights this year. A team from Imperial College London studied the effects of zero gravity on the brain's ability to process spatial awareness and hand-to-eye coordination, while a group of students from Kingston University tested the practicality of unfurling kites in space.
The morning before the flight is frantic. The 14 experiments on the plane are checked and rechecked by the teams. Most (me included) have barely slept the night before and are nervously pacing the Novespace offices. The rooms fill with the sound of excited chattering.
People trade tips and rumours on how to avoid getting sick. Someone mentions eating oranges before the flight (they taste the same on the way out as on the way in, apparently). Another quietly counts the number of people sick on the flights the day before (four). The doctor warns us once more not to move our heads too much during the phases of near double gravity before and after the weightlessness - a sure recipe for nausea, he says.
At 8am, an hour before the plane takes off, the flight doctor opens his suitcase of drugs. He places a tiny white pill in my left hand with the word "hope" inscribed on one side - to help ward off motion sickness. In my right he places a much larger pill of caffeine, in case the first makes me drowsy.
I step onto the plane and make for a window seat at the back while flight safety attendants, dressed in vivid orange flight suits, pass through the cabin, handing out sickbags. An hour and a half later, we are in the air over the Mediterranean, with less than 10 minutes to go before the first parabola.
Not wanting to be held down in a seat for my first bout of weightlessness, I opt to lie on the floor in the central section of the plane, which has been cleared of seats and where the experiments are in place. Seconds before the plane begins to pull up, a conversation with the flight doctor rings in my ears: some people are sick on the first parabola, he had said. They just can't help it. "Then they are sick for every single parabola after that, too. The flight is not a good experience for those people."
And then the engines get louder and I am pushed into the ground, as if someone is sitting on my chest. I try lifting my arm and it feels as if it is made of solid lead. Breathing becomes difficult and I can feel my spine being gently pushed straight. The pilot calls out the angle of the plane: 10, 20, 30. At 40 degrees, he pauses for a breath before calling out "injection", the signal that the engine power is to be switched off.
And then the magic happens.
"There was a pause between injection and the actual feeling of weightlessness and then everybody just started screaming," Branch says later. "Surprise was the thing I saw on people's faces. Surprise and shock. Other people were just laughing because they couldn't believe what was happening to them."
I had been concentrating hard in the moments before the zero gravity so that I could remember as much as possible. But immediately after the pilot says "injection", I involuntarily let out a series of gasps. My body begins tumbling uncontrollably around the strap I am now clutching at with all my strength. My legs are moving themselves up towards the roof. Whenever I try to move in any direction (or even just lie still) my body steadfastly refuses to obey. Bodies are being thrown about all around me.
And it stops just as suddenly as it started. I crash to the ground and once again feel heavy as the pilot pulls the plane level. At the end of the parabola, I stand up and beam at the people next to me. One down, 30 to go.
Carey, a veteran of hundreds of parabolas, finds it difficult to describe the feeling of weightlessness. "You're describing something that isn't there. You're describing a loss of sensation," says Carey. "The closest somebody has come is like being on the bow of a ship when you get thrown up into the air and come down again." Branch finds it easier to describe what the feeling doesn't resemble."You imagine it's like floating in water without the water there but it's not," he says. "You're not being buoyed up by anything. You don't have the friction of the water to push off."
Weightlessness is a tremendous shock to the system. Picking something up or moving in a controlled fashion becomes a task of supreme concentration. But once I get used to it, I begin to understand what makes the feeling unique. It is not so much the physical difference but the mental confusion. Between my eyes showing me that things are (mostly) normal and my sense of balance refusing to work at all, my brain is getting a wealth of conflicting signals. Making a coherent narrative from these disparate and nonsensical signals begins to hurt my head.
I stay put for the first few parabolas and then begin trying out a few tricks the more experienced crew members are demonstrating - standing upside down on the ceiling, spinning around, flying from one end of the plane to the other. During the 10th parabola, I try staying completely still as close to the ground as possible. It's tougher than it sounds because as hard as I push, I can't seem to feel the ground beneath.
Working in these conditions takes some skill but the students on the plane - all of whom had only moments before properly experienced weightlessness for the first time - begin with gusto. By the third parabola they are all busy with their experiments.
Carey says that it is an invaluable experience for students to have the "opportunity to propose an experiment, to build it, to fly it and then to participate in something like a parabolic flight campaign where they get firsthand experience of what being in a non-gravity environment is like."
Another role of the student flight campaign is to tell others what space research is all about. ESA hopes it will turn the students into advocates for their space research programmes. "One of the problems in Europe is enthusing students and making them interested in science," says Carey.
The wow factor is enormous. Branch says that even weeks after the event, the flight is at the top of his team's thoughts. "The word injection, when we hear that, we associate it with a euphoric feeling."
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