11 April 2011

Forget space travel: it’s just a dream

Cosmos Online
The clash of two titans - physics and chemistry - are major barriers to human space travel to Mars and beyond, and may well make it impossible ... at least with existing technologies.
Hello from space

Spacecraft aimed at taking humanity beyond the Moon and across the vast reaches of the solar system are beset by physical and chemical limits. Credit: NASA

Human expansion across the Solar System is an optimist’s fantasy. Why? Because of the clash of two titans: physics versus chemistry.

In the red corner, the laws of physics argue that an enormous amount of energy is required to send a human payload out of Earth’s gravitational field to its deep space destination and back again.

In the blue corner, the laws of chemistry argue that there is a hard limit to how much energy you can extract from the rocket fuel, and that no amount of ingenuity will change that.

Start with a lightweight payload – a dozen astronauts collectively weighing less than a tonne. Now add the life support systems for a one-year journey, with sufficient food, water, oxygen and an energy source to keep their living quarters warm and bright. Fifty tonnes, perhaps?

Add the rockets and rocket fuel for mid-course corrections, and for landing somewhere interesting then taking off to return to Earth, and the mass spirals to excess.

The laws of physics are immutable. According to these laws, accelerating that large mass and fighting against planetary gravitational fields requires a tremendous amount of energy.

Now consider the laws of chemistry. You can’t change them by legislation. The energy content that can be liberated from rocket fuel, and the propulsion force that can be generated, depend on the mass of the fuel, the molecular bond energies and the temperature at which the chemicals burn.

Scientists and rocket engineers have known this for more than a century and have worked hard to optimise all the parameters. But at the end of the day, there is only so much that you can get out of the rocket fuel – and it’s not enough.

Somehow, the fact that this clash of the titans restricts our ability to undertake deep space flights doesn’t feel right. Surely the magic of our success in electronics and information systems should apply?

Moore’s law tells us that every two years the number of transistors in an integrated circuit doubles. Futurologists assure us that the total volume of humanity’s knowledge doubles every five years. Why, then, shouldn’t our ability to lift a payload double every five, 10 or even 20 years?

Sadly, the analogy does not apply. In the case of electronics and information systems, we are dealing with soft rules, related to the limits of human ingenuity. In the case of space flight, we are dealing with hard rules, related to the limits of physics and chemistry.

Rocket engineers and scientists have been battling these limits of physics and chemistry for years, with diminishing prospects for further gains.

Add to these hard limits the fear of failure from nervous governments worried about the political backlash if something goes wrong and, no surprise, the added weight for redundant safety and life-support systems makes return trips to other planets utterly impractical.

The solution, advocated in Cosmos by astrophysicist Paul Davies (“One-way ticket to Mars”), is to encourage one-way missions.

Davies’ hope is that the colonisers might be able to survive indefinitely by mining oxygen, water, hydrogen and other resources at the destination.

While possible in principle, this would be very difficult in practice because of the low grade of the resources. So the most practical solution is to offer people the opportunity to go on a one-way mission, with a peaceful end administered after many months or years of exploration and discovery.

I’d go. I bet lots of other seemingly normal but deeply inquisitive people would too.

What government would fund such a suicide mission? Probably none. So the much more realistic opportunities for manned space travel 50 years from now are orbital flights for tourism, and suborbital flights for high-speed travel from one side of the planet to the other, such as from Melbourne to London.

Let’s take orbital tourism. Too trivial, perhaps? Not if you consider the hundreds of billions of dollars that are spent every year on adventure for adventure’s sake.

Or take suborbital hops. Demonstrated as impractical by the dearth of supersonic airliners? Not at all.

Air breathing, winged supersonic airliners are impractical because they expend vast amounts of fuel overcoming air friction and create sonic booms that restrict their flight paths.

In contrast, suborbital flights – using the principles pioneered by Burt Rutan and Virgin Galactic – are likely to be quicker and more environmentally friendly: they don’t have to burn fuel in the air trying to push through our thick atmosphere for 20 hours or more; in the vacuum of space, they could traverse the distance between Melbourne and London in just a few hours. And there would be no restriction in the choice of routes and cities.

Wouldn’t it be great to have a taste of the future today? Yes: which is why I booked a flight on Virgin Galactic.

Alan Finkel is a neuroscientist and entrepreneur, and one of the founders of COSMOS. He is the Chief Technology Officer of Better Place Australia, and the Chancellor of Monash University.

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