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To the Stars

Entry 1931, on 2018-08-24 at 19:51:08 (Rating 1, Science)

The world seems very disunited at the moment. People have become increasingly tribal with big differences between the left and right becoming more apparent in recent times. What we need is a project which everyone can get on board with. In the 1960s the project was the attempt to land humans on the Moon, which was achieved in 1969. But we haven't been back since Apollo 17 in 1972, and even though there have been some significant achievements since then (the LHC and discovery of the Higgs boson, LIGO's discovery of gravity waves, etc) nothing has really captured the public imagination in the same way.

Sending humans to Mars seems like the next most logical mission which everyone could get excited about, but that is unlikely to happen soon for various reasons, which are partly technical (the flight is long, and keeping humans safe that long is really hard) and partly political (the cost involved is more than any one government would want to spend on a mission with limited practical benefits).

So why not send an automated mission to another star instead? Even though this would seem like a far more difficult task, it doesn't need to be. The nearest star - or more correctly the three stars in the Alpha Centauri system - are 4.2 light years away. That is 42 trillion kilometers. Mars is just 55 million kilometers away at its closest. That difference represents a factor of almost a million. At the same speed a spacecraft which took six months to get to Mars would take almost 400,000 years to get to Alpha Centauri.

That is a non-trivial difference! But there is one factor in favour of the interstellar mission: that it is automated and has no humans on board. That means that a very small spacecraft could be sent and this allows use of a new technology which can overcome the speed limitation of current rockets.

The problem at the moment is that rockets carry their fuel with them, making them really heavy. And the heavier they are, the more fuel they need, which makes them still heavier. So the problem is that the solution to the problem of propelling a heavier spacecraft by using more fuel makes the original problem worse.

The answer is to provide the propulsion from outside the spacecraft, and the most feasible way to do that now is to use a laser beam to push the spacecraft towards its destination.

By applying the laser for a few minutes near the start of the journey, the spacecraft could be accelerated at 60,000 Gs to a speed of 20% the speed of light, or 215 million kilometers per hour. At this speed it would take "just" 20 years to get to Alpha Centauri. To get an idea of how fast this actually is though, consider that it would take less than a second at that speed to travel completely around the Earth!

Laser technology is getting better at a rate that would make this mission possible in a few years. And there is another, equally important, factor. That is miniaturisation. When I said the interstellar spacecraft could be small I really did mean that. One possible implementation of this technology specifies a spacecraft weighing about as much as a paperclip!

This tiny object would contain all the electronics needed to gather details, including photos, of the stars and planets in the Alpha Centauri and send them back to Earth. Of course, even at the speed of light, the signal would take over 4 years to get back here.

There are many issues, including the fact that a collision with even a single atom at that speed could be disastrous, but a spherical shell surrounding the spacecraft could be used for protection. In addition, the heating from colliding particles could be used as a thermal gradient to generate power. And if the laser beam, which would actually be a beam from many individual laser sources, was made "hollow" (more powerful at the edges) it would push the craft back to the center.

It all seems very clever and - most importantly - practical. Except for a couple of issues...

First, despite it being many times less expensive than a manned Mars mission it still isn't cheap and could be accused of having no "practical benefits" (in other words, no one can make any money out of it). So funding would be an issue, although a Russian billionaire is considering funding one mission of this type called "Breakthrough Starshot".

Second, lasers of the power required would also make good weapons. In fact, unless the reflectivity of the sail used by the spacecraft isn't almost perfect it would be instantly vapourised! So politically, building these large lasers would be difficult. And there is already an example of scientific advances being reduced by political agreements because it is against international agreements to use nuclear power in space, even though it is often the logical choice.

But, despite all of these difficulties I would propose this technology as our next big project. Once the lasers are built they could be used for many projects, including sending many miniature spacecraft on long journeys, and even sending bigger craft to different destinations around the Solar System.

Multiple missions could be monitored by anyone on the internet, and people could participate in data analysis in a similar way to many projects today, such as SETI@Home.

I'm not naive enough to think that this would really make a lot of difference to political disagreements in the world today. People today are only distracted by anything for short periods of time. The coolness of anything would wear off fairly quickly and the political bickering would start again. But I still think the interstellar "nanocraft" is worth doing. Let's go to the stars!


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