The 100 Year Starship Study
By Steve Morris, 13 Mar 2013
The 100 Year Starship project is a joint project by NASA and the US Defense Advanced Research Projects Agency (DARPA) to build an interstellar spaceship within the next 100 years. It began in 2012, so there are now only 99 years to wait!
The initial funding of around $1 million won't be enough to take us to the stars, but is intended to kick-start thinking about ways to get there. Already there are plenty of ideas on the table. You may be surprised to learn just how much work has already been done on starship design.
How far to the stars?
The nearest star to us is Proxima Centauri, located a distance of 4.2 light years away. Using existing technology, Voyager 1 would take approximately 73,000 years to reach Proxima Centauri, travelling at a speed of 38,000 mph.
Our galaxy, the Milky Way is approximately 100,000 light years in diameter. Other galaxies are millions of light years away.
Clearly something a lot faster the Voyager 1 is going to be needed to make interstellar travel a reality. Fortunately, there are already teams of scientists and engineers working on designing starships.
Faster, faster, faster
The fundamental problem to be addressed in interstellar travel is speed. The fastest speed theoretically possible is the speed of light, and it would take 4.2 years to reach the nearest star even travelling at light speed. Voyager 1, travelling at 38,000mph is moving at less than a hundredth of one percent of the speed of light.
The reason why conventional rockets move so slowly is that they generate all of their thrust during a short period of time - perhaps minutes. Yet it's easy to reach speeds close to light speed if you can continue to generate thrust over a sustained period. Imagine a very modest acceleration of 1g (9.8 metres per second per second). That's much less than in a fast car. If you can sustain this acceleration for a month, you'll reach 8% of light speed. So, sustained thrust is the key. That's why conventional rockets won't take us beyond the solar system - the amount of fuel needed is prohibitive. To travel to the stars we need a completely different kind of engine.
Nuclear pulse propulsion
Project Orion, initiated in 1958, looked at the feasibility of using nuclear bombs to propel a spacecraft - a system called nuclear pulse propulsion. In this conceptual design, a series of nuclear bombs would be detonated behind the spacecraft, each resulting in a huge "kick" forward.
In theory, a nuclear pulsed spacecraft would be capable of reaching Proxima Centauri within around 100 years from launch, but the practicalities of constructing such a craft seem extraordinarily challenging. While probably not practical for interstellar travel, a nuclear-bomb-powered spacecraft could feasibly be used to deflect an asteroid on collision course with the Earth. It would be capable of delivering a large amount of kinetic energy on impact with the asteroid (the equivalent of many nuclear bombs).
Nuclear powered rockets
Project Longshot, initiated by NASA in 1987, explored the somewhat safer option of using a small nuclear reactor to power laser beams that would in turn generate a nuclear fusion reaction to provide thrust.
This design seems less dangerous and violent than throwing nuclear bombs around. The proposed spacecraft could reach a maximum speed of around 5% the speed of light, reaching Proxima Centauri within around 100 years.
A fusion rocket design has been studied in Project Daedalus and its successor, Project Icarus. In this concept, pellets of deuterium and tritium would be ignited by electron beams and the resulting nuclear fusion reaction would power the rocket. Calculations suggest that such a craft could reach speeds of 12% the speed of light, reaching Barnard's Star, a distance of 5.9 light years within around 50 years. However, at present, nuclear fusion as a practical energy source has still not been demonstrated.
The USS Enterprise in Star Trek was powered by matter-antimatter reactors. Maybe one day this will become a reality. Certainly, reacting particles of matter with their antimatter equivalents is a very efficient means of generating power. The problem at the moment is that it's extremely difficult to create antimatter particles in the lab. But on a timescale of 100 years, who knows?
An alternative concept of powering interstellar craft is based on using gigantic light sails pushed by sunlight.
Another photon-based idea is to use lasers or high-energy particle beams based on Earth or the Moon to accelerate a spacecraft on its journey.
The amount of thrust generated by such methods may be much smaller than the nuclear-powered designs, but if the spacecraft itself is very lightweight, then very high accelerations could still be reached. In particular, if the spacecraft is unmanned and needs to carry no fuel or propulsion systems onboard, it could be very lightweight indeed. A micro- or nano-probe of this kind could also sustain continuous acceleration over a long period of time, enabling it to reach speeds close to light speed. That could make the journey time to the nearest star a matter of a few years.
Robot probes could even travel in advance of manned missions, finding suitable planets and starting work on making them habitable before humans arrive later.
A speculative concept for a nuclear fusion rocket that collects its hydrogen fuel as it travels through interstellar space has some appealing features. The proposed design would use an electromagnetic field thousands of miles in diameter to collect hydrogen atoms dispersed in space. Such a rocket would not need to carry its own fuel, and so it could weigh very little.
Manned interstellar exploration
Travelling to even the closest stars will take a long time. Even if you could travel at the speed of light, it would take 100,000 years to cross the galaxy. How could an astronaut survive such a journey?
In sci-fi, the answer is cryogenics, where the astronaut's body is frozen is suspended animation and then revived at the journey's end. But there might be a much simpler solution.
As a spacecraft approaches the speed of light, according to the Theory of Special Relativity, time slows down on board the craft. If the spacecraft can travel fast enough, then the journey time experienced by an astronaut on board would be much less than that observed from Earth. So, a journey of 100 years as measured by people on Earth might take just 10 years for the astronaut to complete. Of course a return journey would be problematic, since the astronaut would arrive back on Earth 20 years after leaving, only to find that 200 years had elapsed back on Earth.
Faster than light travel
According to Einstein's Theory of Relativity, it is impossible for anything to travel faster than light. We might just have to accept that we won't be able to hop across the galaxy for our holidays. That might turn out to be a good thing, since it could also prevent the kind of galactic war that could destroy humanity even once civilisation spreads across other star systems.
But just because Relativity says you can't do it, it doesn't stop people trying to find loopholes. One of the most obvious loopholes isn't a loophole at all. It's a wormhole. Some astronomers have speculated that black holes might connect distant parts of the universe via wormholes in spacetime. But even if that were true, we probably couldn't control where those wormholes went, and there's also the minor inconvenience of being crushed to death by the black hole that created them.
Another loophole makes use of the fact that while objects travelling in space cannot exceed the speed of light, spacetime itself can expand more rapidly than light speed. In fact, in the early universe, spacetime expanded many orders of magnitude faster than light speed. Of course the energy required to manipulate spacetime in this way is enormous, but the physicist Miguel Alcubierre has proposed a possible way of achieving faster than light travel without breaking Einstein's laws.
Why travel to the stars?
If we stay on Earth, sooner or later something will go wrong. It might be a giant asteroid, or it might be the sun frying us all to death in a billion years or so. If we want to survive in the long term, we'll need to find a new home. Ideally lots of new homes, to avoid the risk of extinction.
As Konstantin Tsiolkovsky said, "Unless mankind leaves the Earth, it will surely die there."
A first logical step might be colonising other planets in the Solar System. Then there are probably loads of habitable planets orbiting nearby stars, and many others that could be made habitable if we're prepared to put in some DIY effort. Humans are nothing if not curious, and the lure of such planets is going to be hard to resist, given all the pressures on Earth.
The journey begins
A journey of a thousand miles begins with a single step. And if you bear in mind that 100 years elapsed between the publication of Jules Verne's novel From the Earth to the Moon to the first manned mission to the Moon, then the timescale proposed by the 100YSS doesn't seem at all unrealistic. After all, Jules Verne had no idea how space travel might realistically be achieved, but as I've tried to show in this article, we already have plenty of ideas about how to travel to the stars.
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