June 29, 2012 12:11 am

Floating on air

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A bottle of water floats lazily past my ear, on a casual trajectory towards the windowless wall of the aircraft’s cabin. I too am floating, my path a complex intersection with that of the bottle. I easily scoop it up and return it to its owner.

Normally innocent objects can become painful unguided missiles when unrestrained by gravity. But in a flying laboratory designed to replicate some of the conditions of outer space, loose objects can also play havoc with scientific experiments that have been months or even years in the planning.

The meticulous briefings in the run-up to any flight on the European Space Agency’s Zero-G flight put particular emphasis on keeping everything secured in the micro-gravity part of the flight – whether pens, water bottles or full sick-bags.

The potential for feeling ill, possibly violently, formed a worrying large part of the preparation for my flight on Zero-G – or the “vomit comet”, as it is understandably known.

French company Novespace has been running weightless flights for ESA since 1988, and since 1996 with an Airbus A300. As a medium-range widebody airliner, the A300 can carry more than 260 passengers. For the micro-gravity flights, however, the strengthened Novespace aircraft carries maybe a dozen test-rigs bolted firmly to the floor, plus a few seats that the 40 or so scientists on board use for takeoff and landing.

The aircraft replicates the absence of gravity by flying a parabolic arc – it accelerates up one side of a steep arc, then, while still climbing, the engines are throttled back. For 20 seconds, while its momentum takes it up over the top of the arc and gravity pulls it down the other side, it is in freefall – and the effects of Earth’s gravity are cancelled out. The effect is weightlessness.

What is most curious is how natural it seems to remove the one force that has been more constant in my life than anything else. Every movement I make acts around my centre of gravity. It is Newtonian physics writ large, which is the reason these flights are so valuable to science.

For example, without gravity liquids form perfectly spherical droplets. The same is true for vapour bubbles in liquid. Studying the collapse of these bubbles away from the distortion of gravity, as one experiment on board the aircraft is doing, offers the chance to understand and even harness the huge forces and several-thousand-degree temperatures generated momentarily when these bubbles collapse. As scientist Danail Obreschkow jokes, the collapse of each bubble is like the creation of a black hole.

This is not a replica of spaceflight, though. The Zero-G flight consists of 31 parabolas – the odd number is a tradition, apparently – in sets of five. The pull-up at the start of the arc involves a sustained period of 1.8 times the force of gravity. And the pull-up at the end of the dive also involves about 1.8G. There is also sometimes negative G at the start or end of the weightless period. These positive or negative gravity forces are much more nausea-inducing than floating free, but the 20 seconds of weightlessness on each parabola are pure pleasure.

At first it is hard to avoid what some of the old hands, with thousands of parabolas to their name, call “swimming” – and of course flapping my arms and legs is ineffective in thin air.

The A300 that Novespace uses, the largest ever to be used for simulating zero gravity, is holding up well under the stresses it has to withstand – but its age means it must be replaced soon. Partly to help cover those costs, and partly to keep those of providing this valuable aerial laboratory at a less than stratospheric level, the company plans to offer weightless flights to members of the public. The details are still being worked out, but the likelihood is a shorter regime of about 15 parabolas, starting with low gravity – replicating that on the Moon or Mars – to dial flyers into the experience. And the cost? Possibly as low as €5,000.

That compares favourably with the sub-orbital, edge-of-space flights Virgin Galactic plans to offer at $200,000 per seat. And the public Novespace flights, which have now won approval from the French aviation authorities, could start as early as this year.

It struck me as I strapped back into my seat for the return to Novespace’s Bordeaux airport base that on these flights it is necessary to go through what for some is quite acute suffering, both before and after, in order to access to the benefits, and wonder, of the weightlessness in the middle. Which makes it the first time I have ever described parables in the air.

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