Probes are being dispatched to explore the solar system, but will people follow them?by Martin Rees / April 20, 2011 / Leave a comment
On 17th March, Nasa’s Messenger space probe was injected into orbit around Mercury; it is now beaming back data from only 200km above the planet’s parched and cratered surface. The probe, which has already tripled the number of images of Mercury available, aims to solve questions such as whether water ice lurks at the shadowy poles of Earth’s smallest cousin.
Messenger is the most recent in a series of unmanned spacecraft launched to explore planets, moons, comets and asteroids. In the coming decades, huge numbers of miniaturised probes could be dispersed to explore the solar system more fully.
But will people follow? It’s 50 years since the Soviet astronaut Yuri Gagarin’s first flight; Neil Armstrong’s “one small step” came only eight years later. Yet it’s nearly 40 years since the last Apollo astronauts returned from the moon; today’s astronauts go no further than the International Space Station (ISS). At a cost of around $100bn, the ISS is the most expensive artefact ever constructed, but it is neither useful nor inspirational.
The US’s firm plans don’t even include further moon landings. Instead, Nasa envisages a less demanding but still progressive programme: an expedition to an asteroid, a number of lunar orbiters, and eventually a trip to Mars and back (perhaps alighting briefly on one of its small moons, Phobos or Deimos). The latter would be far easier than landing people, along with all the equipment needed for their return trip, on the red planet itself.
Nasa is too constrained by public and political opinion to be anything but risk-averse. In 130 attempts, only two shuttle flights have failed—a level of risk that astronauts or test pilots would willingly accept. But the shuttle has been promoted as a vehicle safe enough for civilians, and each failure has caused a degree of national trauma. The disintegration of the Space Shuttle Challenger in 1986, resulting in the deaths of its crew, was followed by an investigation and a 32-month hiatus in Nasa’s space programme. A similar process followed the 2003 Columbia shuttle disaster.
Future expeditions to the moon and beyond won’t be politically and financially viable unless they are cut-price ventures, spearheaded by individuals prepared to accept high risks. The US now contracts with private companies to undertake launches, rendering Nasa more like an airport authority than an airline. The Falcon 9 rocket system, developed by the entrepreneur Elon Musk’s company SpaceX, has successfully launched a payload into orbit. The involvement in the sector of credible and well-resourced figures such as Musk and Jeff Bezos, the founder of Amazon, is surely a positive step. Google, meanwhile, has offered a prize for whoever can build and launch a robotic lunar lander able to travel 500 metres and beam back a video.
Current launching techniques are as extravagant as air travel would be if the plane had to be rebuilt after every flight. Spaceflight will only be affordable when its technology comes closer to that of supersonic aircraft. Tourist trips will demand a step-change beyond the brief “lobs” above the atmosphere Virgin Galactic may soon offer, which could become routine for wealthy adventurers within a decade. But the use of the term “space tourism” is ill-advised. Participants should be seen as risk-takers, seeking thrills beyond those of mountaineering or round-the-world ballooning, or the first accident will be as much of a setback as the shuttle crashes were.
The next step would be a voyage around the back of the moon—going further from Earth than anyone has ever been, except (unintentionally) the crew of the Apollo 13 capsule in 1970. It’s my personal hope that some people now living will walk on Mars—and I think it’s possible. The stakes are high: a lucky few will experience a new world. Maybe the most-determined pioneers would be prepared to accept—as many terrestrial explorers did—the improbability of return. A Martian base would develop more quickly if its constructors were content with one-way tickets.
That said, space travel could be far more rapid and less precarious if more efficient propulsion were devised. At present, trajectories have to be planned with precision in order to minimise fuel consumption. The Messenger probe took more than six years to reach its destination, because it had to take a circuitous path that passed close to the Earth, then twice past Venus and twice past Mercury. This game of “planetary billiards” was calculated to gradually reduce the probe’s orbital energy, thereby reducing demands on the probe’s retro-thrusters.
If rockets yielded, say, ten times more thrust per kg than chemical fuel can supply, in-flight adjustments could be made less sparingly. Keeping a car on a winding road would be a high-precision enterprise if the journey had to be programmed before, with no chance of changes along the way. With plenty of power and fuel, space travel would be an almost unskilled exercise. The possible destinations are all in clear view; one just has to steer and use reverse thrusting to brake at the journey’s end.
Solar and nuclear power are the obvious sources for novel propulsion systems. It would help greatly if both the method of propulsion and the fuel needed to escape Earth’s gravity were on the ground rather than part of the cargo. One possibility is a “space elevator”: a wire, made of carbon fibre, extending 35,000 km up into space and held vertical by a geostationary satellite. This contraption would allow payloads to be hoisted from the grip of the Earth’s gravity by power supplied from the ground—but only if a method of joining carbon nanotubes together with sufficient strength can be found. The rest of the voyage could be powered by a low-thrust (perhaps nuclear) rocket. Writer and inventor Arthur C Clarke once said that a space elevator would be built “about 50 years after everyone stops laughing” about the idea.
Even if there is a hiatus of a decade or two in the US space programme, it remains plausible that 100 or 200 years from now, groups of intrepid adventurers may be living independently of Earth. Whatever ethical constraints we impose here, such pioneers would have powerful motives to genetically modify their progeny to adapt to alien environments. The post-human era, perhaps, would then begin.