The resources for getting down smoothly are much more of a mixed bag – and are riskier and more accident-prone too, especially if you are applying them on the far side of the solar system, when the whole procedure has to run on automatic. If your target planet has no atmosphere, of course, you have only one option. You have to cancel out the energy you wish to shed in the most direct way possible, by applying a braking force in the other direction. You have to do a powered descent, with a rocket engine burning all the way down, like the lunar module on the Apollo missions, riding down to the moon’s surface on a cushion of counteracting flame. But if there is any mantle of gas around the planet at all, the possibilities multiply. You can start exploiting friction.
For the first, massive reduction of energy, there’s aerobraking. You send your craft into the gravity well – or across it, because it’s possible to shave away an increment of velocity by taking a tangent through a handy atmosphere and coming out the other side – and you let the impact of the gas molecules wear down the speed. Every time you hit a speck of gas, it gets a bit more energetic and you get a bit less so. You need a heatshield, to protect the underside of the craft. And you need some kind of gyroscopic force, to keep the underside underneath. If your craft is surfing down through temperatures of several thousand degrees on its asbestos-coated arse, it needs to keep travelling arse-first. Most planetary landers deal with this by spinning as they fall, which encourages stability, but occasionally spacecraft have had actual gyroscopes on board. The successful Viking missions to Mars landed in 1976 with sets of them whirring away like crazy inside the aeroshells, all the way down to Chryse Planitia and Utopia Planitia. Then, after the gross energy loss of aerobraking, comes the subtler shape-changing opportunity of the parachute. Parachutes multiply the surface area that is resisting the atmosphere; but they also make the craft far more subject to whatever is happening in the atmosphere right there and then. In a thick enough atmosphere, strong winds may start to carry the craft sideways, away from its intended destination. Even in a thin atmosphere, like Mars’, there may still be a noticeable deflection to the planned trajectory. A 2° bend in the path to the surface can shift the point of landfall five or ten kilometres – which matters if the new site is a canyon or a spiky boulder field. There can be a sequence of parachutes, opening one after another as the craft slows. They can also be combined with powered descent, as with Mars 2. The retro-rockets then need not fire so powerfully that the counter-thrust collapses the parachute canopy: it’s a balancing act between the density of the atmosphere and the force of the motor. If the descent motor and its fuel add too much to the mass of the craft, there may not be much advantage in having it at all. On the other hand, if you have equipped the craft with some means of looking down, and it can distinguish between different kinds of terrain, a well-timed bit of thrust may be just the thing to alter course enough to avoid a hazard on the ground. As the ground approaches, there’s one last option. The Mars Pathfinder mission of 1997 pioneered the use of an airbag for the landing itself. If you’ve opted not to employ a rocket motor for the classic landing on extended metal legs, and your parachute won’t slow you enough on its own, you can now inflate a beachball around the craft and bounce to a halt.
These choices can be combined in a different ways, depending on your budget, and your destination, and your confidence in your ability to manage the different technologies. Heatshield–descent motor. Heatshield–parachute. Heatshield–parachute–descent motor. Heatshield–parachute–airbag. You pick the one you believe leads to the best chance of the desired final state where the energy of the journey has all dissipated peaceably and the craft rests intact on the sand, transformed from meteor into stationary suitcase. But whichever way you do it, success depends on getting things right at the few points of decision where the descent can be nudged onto the course you want. You can control the angle at which you make the initial insertion into the atmosphere. You can set times for the key events; or, more ambitiously, set up the onboard software to react autonomously to sensors and decide then and there when the parachute should unfurl, the motor fire, the airbag pump itself up. But there’s no turning back. You can’t turn round and fly back out again if things go wrong. Delicate nudges are all you can administer. Once the mission is committed to a trajectory, it is under the control of the physics of falling. As one of the Apollo astronauts said, ‘Mr Newton is doing the driving now.’
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Descent and ascent may be opposite problems in physics. But in human societies, what lets you bring a spacecraft down is just the same as what lets you put one up. Money.
On Christmas morning, 2003, a tiny British spacecraft less than one metre across will be poised over the Martian atmosphere. Its adventure in physics will be just about to begin. But getting the craft to the point where it can fall down the Martian gravity well will already have been an adventure in finance.
It began with a piece of scientific politics. In the mid-1990s, a set of reforms were pushed through at the European Space Agency at the urging of the Particle Physics and Astronomy Research Council in London, the new custodians of Britain’s never-increasing space-science budget. PPARC’s space budget never rose, but ESA’s costs did, inexorably, to the point where PPARC’s annual subscription to ESA ate up almost the whole of its resources, leaving too little over even to take proper advantage of the access the subscription bought. Needless to say, Britain had opted out of all the grandiose stuff at ESA, like Ariane and the long-range plans for manned spaceflight. In terms of extra spending on space, in relation to the size of its economy it ranked somewhere above Norway and somewhere below Ireland. It only paid the mandatory science sub to ESA; it had the minimum, plain vanilla membership in the agency. On the whole, it was a good deal. Only a few British experiments could fly free on NASA rockets, and this way Britain was able to take a share in missions it could never have afforded alone. For a set payment every year, PPARC won the right for British scientists to enter the bidding process by which it was decided which experiments would fly on each new science probe. Since the British experiments were usually excellent, they won the bidding disproportionately often. Britain paid for 14 per cent of ESA’s science spending and ended up designing 20–25 per cent of its science programme: a bargain. But having booked British scientists the right to participate, PPARC still had to be able to give them grants to build their experiments. It was not much use being theoretically entitled to a slot on a mission if you couldn’t then afford to build the instrument that fitted into the slot. And that was the situation PPARC was being pushed into.
What drove ESA’s costs up was a system known as juste retour, or ‘fair return’. Basically, it was an agreement to share the industrial pickings from ESA in proportion to the amount of money the different European nations put in. It meant that ESA did not look for the lowest bidder when assigning the big contracts. Other European governments felt comfortable with this as a form of indirect subsidy to their national space industries. But since Britain was stingy, British companies did not do well out of juste retour. They got more work from ESA building specialised components than the British sub strictly allowed, since their reputation too was excellent, so in that sense, like the British scientists, they still punched above their weight. But they hardly ever got the big items. The space division of British Aerospace was rarely prime contractor on ESA missions. (In desperation, it had just been merged with the French satellite builder Matra and the space interests of GEC to create Matra Marconi Space, an Anglo-French conglomerate that might be better placed.) Year by year, the shrunken British space industry, resolutely specialised in sensible areas, just ticked over, never growing, never able to take a decisive upward step.
PPARC argued for reform on the grounds of simple necessity. Soon, they were not going to be able to cover their 14 per cent of ESA’s spending. But they also pointed out that year by year ESA got far less science for its money than it might do if it sorted out the procurement process and concentrate
d on extracting value from the limited budget. The incentive to cut costs was the prospect of extra science. This was the kind of reform that the representatives of Thatcherised Britain constantly urged in every European institution, and French and German negotiators often looked with pity upon their British counterparts, who seemed to be obliged to talk about nothing but ‘best value’ and were never, never allowed to plan anything big. But this time, between the arguments of necessity (for the Brits) and opportunity (for everyone), PPARC carried the day. ESA streamlined its rules and its structure and started to look around for chances to try out its new style of science mission: faster and cheaper and less conducted as a complex exercise in multilateral pie-sharing.
The first chance came quickly. Europe had a package of experiments aboard a new Russian Mars probe named Mars 96. Mars 96 crashed straight into the Pacific Ocean when its Proton booster failed during ascent to Earth orbit. A swift calculation showed ESA that if they hired their own Russian rocket on the open market, perhaps the robust Soyuz rather than the temperamental Proton, and made the maximum reuse of existing hardware and software, they could put together a pared-to-the-bone replacement Mars orbiter for about €150 million – less even than the budget for NASA’s faster-better-cheaper Mars missions. There was a launch window available in 2003, when Earth and Mars would be at their periodic nearest to one another and you could cover the distance between the blue-green third planet and the red fourth planet in a meagre six months. ESA announced Mars Express in 1997. It usually took a good five years to get from initial mission design to the awarding of the development contracts to industry. Fired with a convert’s zeal for this exciting business of getting things done swiftly, they decided to race through the process in one year by doing the scientific planning and the industrial planning at the same time. They called for payload suggestions. Proposals, please, by February 1998. The Swedes proposed ASPERA, a sensor for detecting charged plasma in space. The French proposed OMEGA, an infrared spectrometer designed to scan Mars for ice and water. And in Milton Keynes the Planetary Sciences Research Institute of the Open University proposed Beagle 2.
The moving spirit behind it was the Professor of Planetary Sciences, Colin Pillinger. Pillinger had huge mutton-chop whiskers and a strong West Country accent that made him sound like a man perpetually leaning on the gate of science with a straw in his mouth. At weekends, he liked to relax with his herd of dairy cows. But as a young post-doc in Bristol in the early 1970s he had been a member of the team who got to analyse one of the precious lunar samples brought back by Apollo. He had opened the little grey canister sent to England by NASA; he had held a slice of moon. He never forgot it. From then on, he was a planetary scientist, not interested in distant quasars, or in star formation, or in the search for the neutrinos that zipped straight through the earth like elusive streakers. He preferred, as he put it once, ‘the solid matter in our solar system’. It was worlds he cared about, those other spheres which the human imagination intuitively recognises as places we can interpret; places where sublime, or toxic, or terrifying variations are played on the familiar themes of air and ground, as we know them on Earth. What about life, though? Were there parallels out there to Earth’s biology, variations on that theme too?
The solar system had looked definitively dead, back in the 1970s, when Viking’s life-science experiment reported negative results from Chryse and Utopia. Mars was the best candidate for life, and Mars seemed to have nothing going on. But since then, the intellectual odds had improved. Bacteria had been discovered in more and more hostile environments on Earth. If species of Archaea could live in volcanic vents in ocean trenches, and in caves washed in sulphuric acid, and in deep rock strata without access to light or to oxygen, then perhaps something similar could exist on Mars at six millibars of pressure, in temperatures that dropped to –150°C and never rose above –15°C. The one absolute essential seemed to be the presence of water. The camera on NASA’s Mars Global Surveyor had just started sending back high-resolution photographs from Mars orbit of dry valleys with classic riverine twists and turns, and wavery contours that might be the shorelines of lost lakes. Mars researchers were now theorising not only that Mars had been hotter and wetter when it was young but that the water might still be there, locked in the planet’s crust and cycling slowly in and out of the sparse atmosphere, with occasional tremendous liquid eruptions onto the surface. There was even a piece of incredibly ambiguous, incredibly controversial evidence from close to home. Pillinger had worked a great deal on meteorites – nature’s way of giving free samples to needy scientists, he joked – and he was agnostic about the teeny-weeny calcite tubes inside meteorite ALH 84001, which had flown from Mars to Earth and been quenched with a wet sizzle in the Antarctic. He didn’t know whether or not the tubes were fossil Martian bacteria, as NASA proclaimed. They were far smaller than any living organism known on Earth. Nobody had yet demonstrated how objects that size could contain the minimal materials required for self-replicating life. You couldn’t fit a cell’s worth of DNA into them. But he certainly thought there were questions to be answered. He certainly thought it was worth going and finding out. And if an ESA instrument platform was going to be orbiting Mars, passing by only 250 vertical kilometres away from the Martian dirt where the answer might lie, he thought it would be foolish not to drop down that last little distance. With the help of the Space Research Centre at Leicester University, he devised a Mars lander focused entirely on biology and named it, with no false modesty, after the ship that carried Charles Darwin on his world-changing field trip.
ESA’s evaluation committees liked Beagle 2. The only member state of ESA that voted against it was Belgium, because Belgian scientists had a rival idea. ‘They spend as much on space as we do,’ remarked Pillinger later of this act of temerity by the drinkers of raspberry-flavoured beer, ‘so they probably felt they had the right.’ Beagle 2 went forward as an official element of the Mars Express mission plan. But a problem immediately arose. PPARC itself was not keen.
No matter how small Beagle 2 was – and it was going to have to be unprecedentedly tiny to fit aboard Mars Express, which was an engineering problem in itself – it was still estimated that it would cost about £25 million to build, which it would be the responsibility of Beagle’s British sponsors to find, just as the French were stumping up the money for their infrared spectrometer and the Swedes were shelling out for their plasma detector. (ESA’s own Mars Express budget only covered the common infrastructure of the mission as a whole: the spacecraft ‘main bus’ to hold all the instruments, the power systems, the solar panels, the communication array, the mission computer.) PPARC did on occasion write big cheques. In 1997, they had given £7.7 million towards the Surface Science Package of the Cassini-Huygens mission to Titan, another Open University project. They were due to pay £23.6 million towards the 1999 launch of the XMM-Newton Observatory, an orbital X-ray telescope for studying black holes. But in 1998, when Pillinger’s hastily assembled consortium took soundings at PPARC about the possibility of support for Beagle, the cash they’d clawed back for spending that year, thanks to the reforms, they had already pretty much allotted. ‘Mars Express was a mission invented in a hurry,’ Dr Paul Murdin of PPARC told a House of Commons committee later. ‘It came at a time when, in principle, we had used up the quota of money we had available for ESA missions.’ More than that, though, they were sceptical about the very idea of Beagle. PPARC’s evaluators knew where they were with a project like the X-ray telescope. It fell comfortably in the hard-science mainstream. It was sure to return high-quality data. It fulfilled a verifiable need among astronomers and astrophysicists. And if nobody much except astronomers and astrophysicists cared about it, then in a funny way that furnished a kind of guarantee of scientific purity. It proved that all of the reasons for supporting it were legitimate, scientific reasons. You couldn’t say the same about a mission to search for life on Mars. The evaluators could immediately see a host of non-scientific reasons why peo
ple might want to do this one. Non-scientific reasons; pseudo-scientific reasons; frankly science-fictional reasons. Reasons with little green men in them. Reasons that made the words of the phrase ‘life on Mars’ drip and burble, like the horror-show typography of a B-movie poster. The long years of drawing in their horns, of getting things done with very little, had made British space scientists averse to the risks that came with even a hint of popularity. The consolation for operating on limited resources had been the knowledge that at least none were being wasted on projects that were merely eye-catching or spectacular. Something like a tacit policy of anti-glamour was in place. And Beagle broke it. Its science might be excellent – PPARC’s evaluators were themselves mostly astronomers and astrophysicists, so they hadn’t been reading the last decade’s worth of work on extremophile bacteria and the history of the Martian hydrosphere – but by definition, it had much further to go to prove itself than a nice dependable study of galaxy formation. Which meant that at a time when money was tight, as it always was, Beagle was low priority. Which meant that it wasn’t going to happen.
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