On 16 August 1960, a US air force captain called Joseph Kittinger stepped out of a balloon. The balloon was 102,800 feet above the Earth. It would be an exaggeration to say that Kittinger jumped out of a balloon in space, as he’s sometimes said to have done, but there’s no denying that his jump was, in layman’s terms, seriously freaking high. There is some footage of the jump, taken by cameras on Kittinger’s chair-like parachute and on the balloon, and I find that its vertigo-inducing properties are so great I have to make a conscious effort to compose myself before watching it.

Kittinger set several records. One of them was for speed. Although gravity exerts an equal force on all objects, different bodies experience different degrees of air resistance depending on their shape, so in practice things stop accelerating at different speeds. That maximum falling speed is known as ‘terminal velocity’. A feather has a different terminal velocity from a mouse, which in turn has a different one from a cannonball. For a human being falling with arms and legs extended, like a starfish, that top speed is around 120 miles per hour; for someone falling with arms and legs tucked in, like a spear, the top speed is 200 mph.

At least, that’s the top speed at sea level. Go further up, and the air resistance is lower, and therefore the top speed higher. Go high enough up, where the air is unbreathably thin, and the air resistance becomes so negligible that a person can fall seriously fast. Kittinger was so far up that he set a number of records which still stand, including the highest ever balloon jump, longest ever free-fall and greatest velocity ever attained by a falling human: 614 mph.

Kittinger’s feat was brought to mind recently by James Cameron, the movie director, who has just done something almost as astonishing: in a newly designed submarine, he has gone to the deepest place on Earth, the Mariana Trench, in the Pacific Ocean close to the Philippines. The trench is 36,000 feet deep and the difficult thing about getting there is the opposite of what made Kittinger’s jump such a feat: it’s the pressure exerted by the force of water.

The unit of measurement of this pressure is the atmosphere, named after the weight of the air bearing down on us at sea level. We don’t normally think of the air as having weight, but it does. Hold your hand out flat, and imagine an invisible column of air above each of your fingernails stretching up from where you are to the top of the Earth’s atmosphere. That column weighs 1.03 kg per square centimetre – in other words, about one kilogramme’s weight of air bears down on each fingernail. That amount of pressure is one atmosphere.

The deeper underwater you go, the more water bears down on you; it’s water pressure rather than air pressure, but the principle is the same. As you go down, the pressure goes up. Recreational scuba divers descend to a maximum of about fifty metres, where the air pressure is six atmospheres, and world-class free divers go down to about a hundred metres, where the pressure is ten atmospheres – more than enough to tell the human body that it doesn’t want to be there. Normally functioning submarines, meaning subs not designed for the special purpose of ultra-deep diving, operate down to about four hundred metres, where the pressure is 41 times that at the surface; some Russian subs with titanium shells are thought to have operated down to a thousand metres, where the pressure is a hundred atmospheres. Cuvier’s beaked whale, a deep-diving specialist, is known to have gone down as far as 1900 metres, the deepest level ever attained by an air-breathing animal.

The Mariana Trench is 10,994 metres deep – 36,069 feet – and the pressure there is 1072 atmospheres. That’s 1072 kg pressing down on every square centimetre of its surface, more than 16,000 pounds per square inch. To resist that level of pressure is a technical challenge so formidable it should be no surprise that it has only been accomplished twice. Once was this recent trip of Cameron’s, in his specially designed submarine, Deepsea Challenger. The design of this vessel is, in Cameron’s phrase, that of a ‘vertical torpedo’: a cigar-shaped tube with the propellers on the top end, pointing downwards. Much of the effort and ingenuity of Cameron and his team went into making it possible to film while he was on the way down, and on the seabed, with a view to having something they can show in the cinema later. I think it’s a rare person who wasn’t hoping for at least one encounter with a colossal squid, maybe one which attacked the sub and was then fought off by an equivalent-size whale … Alas, Cameron reported that he didn’t see anything other than shrimp-like crustacea, amphipods, of about an inch long. The main impression, he said, was that the deepest place on Earth is a ‘barren, desolate, lunar’ spot.

An amazing thing for people to have done – but as I’ve said, this wasn’t the first time. That was on 23 January 1960, a few months before Kittinger stepped out of his balloon. The people who preceded Cameron to the bottom of the Mariana Trench were a US navy lieutenant, Don Walsh, and a Swiss oceanographer, Jacques Piccard, the son of the man who designed their Italian-built vessel, the Trieste. That wasn’t so much a submarine as a tube with a sphere attached to the bottom: the tube held the buoyancy mechanism, and the tiny ‘pressure sphere’ held the crew. They had a nervous four and a half hour trip to the bottom, during which a window cracked under the atmospheric pressure at about nine thousand metres down, and they spent only twenty minutes on the seabed, unable to take pictures because their arrival threw up so much silt. Then they spent three and a half hours coming back up.

The question thrown up by these adventures – Kittinger’s, Walsh and Piccard’s, Cameron’s – is two different flavours of ‘why?’. Why did anyone bother doing these stupendous things? And why, having done them, was it more than half a century before anyone tried to do them again? Put it like that and you’re part of the way to the answer. The practical answer to the first ‘why’ is weak. The substantive rationale for these feats, meaning the scientific, or the military, or the military-scientific rationale, is not especially robust. Kittinger’s experiments bore on the question of high-altitude ejection from jets, and Operation Nekton – the series of experiments which led to the Mariana Trench dive – was, broadly speaking, part of a Cold War investigation of what submarines could do. But the practical applications of these feats in truth seem pretty limited; they were dead-ends. The real momentum behind them came from the desire to do things just to see if they could be done. This principle was taken as far as it has ever been taken by the Moon landings that Kennedy announced as a goal on 25 May 1961. Why? Because we can – maybe.

That ‘maybe’ is another part of the reason these feats haven’t been repeated. They were seriously risky. Kittinger’s record-breaking jump was the third in a sequence of three. On the first, he was spun around at such speeds that parts of his body were experiencing 22 times the force of gravity – another, less welcome record. Kittinger blacked out and was saved by the automatic functioning of his parachute. It’s hard to imagine being the person who, once that has happened, goes back up in that balloon a second and third time, but it’s perhaps even harder, today, to imagine being the person in the chain of command who says it’s OK to carry on with the experiment. Neil Armstrong, the first man on the Moon, and Michael Collins, who circled the Moon while the first two men walked on it, years later admitted to each other that they privately put the mission’s chance of success (read: survival) at 50-50. That level of risk is no longer acceptable for anything carried on in the public eye.

Robots do some of these things better – that’s another thing. Hear about anybody doing anything risky for a scientific reason, count to ten, and you will be hearing another person explaining why that thing is done better and more cheaply by a robot. Space exploration? Send a robot. Deep-sea exploration? Send a robot. Killing people on the Afghan-Pakistan border? Send a drone. This is linked to the question of risk, since the main part of what makes experiments with humans expensive is the need to keep them alive. Take that away, and suddenly the Mariana Trench doesn’t seem so deep, or 102,800 feet so high, or Mars quite so far away.

Your attitude to these adventures depends, I suspect, to a large extent on your attitudes towards the technological sublime: whether it holds any romance for you. It doesn’t for many people, and no doubt they’re in the right. Speaking for myself, though, I do feel that romance, and often find myself wondering what are the secret, private, deep-down thoughts of men like Kittinger and Walsh, both of whom are still alive, and both of whom are involved in the attempts to follow up on the records they made. Walsh is attached to James Cameron’s Deepsea Challenger team, and Kittinger is still active in his own field too. He had an eventful life after his jumps – two of the other things he has done were to make the first ever solo Atlantic crossing in a balloon, and to get shot down by the North Vietnamese in 1972, leading to an 11-month stay in the ‘Hanoi Hilton’. At the moment he is working with Felix Baumgartner, an Austrian high-altitude specialist whose Red Bull Stratos project has the goal of free-falling from a balloon at 120,000 feet. If they pull it off, Baumgartner will become the first free-faller ever to break the sound barrier.

Do Walsh and Kittinger ever think about why it’s more than a half century since people tried to redo the things they did when they were young men – go to the place where the air pressure is lowest, where the water pressure is highest, just to see what it’s like? Do they feel as if we, the culture in general, have lost something, by losing our appetite for this for-its-own-sake adventurism? It might be that our current sense of the technological sublime is located elsewhere, in things which are more about bits and bytes, some of them objects we carry in our own pockets. Maybe it’s just that we’ve all grown up. Or maybe the fact that we’ve grown up and moved on is exactly the measure of what we’ve lost.

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