How close to interstellar space travel could humans get in the near future?

Let's do a calculation or two, shall we? (Note: All those wishing to skip the boring math can just read the lower portion of this answer.)

Finding the speed you're going for: $$v=\frac{15 \text { light-years}}{50 \text { years}} \times \frac{10,000,000,000,000,000 \text { meters}}{1 \text { light-year}} \times \frac{1 \text { year}}{31,500,000 \text { seconds}}= 95238095.24 \text { m/s}$$

Finding the energy needed to get to that speed: $$E_k=\frac{mc^2}{\sqrt{1-(v/ c)^2}}-mc^2$$ Assuming a mass of about $150,000$ tonnes (taking the Project Daedalus figure and tripling it), $$E_k=\frac{(150,000,000)(300,000,000)^2}{\sqrt{1-((95238095.24)/(300,000,000))^2}}-(150,000,000)(300,000,000)^2$$ $$=7.36 \times 10^{24} \text { Joules}$$

Can we do it? . . .

According to Wikipedia

In 2011, total world energy consumption was 549 exajoules

Multiply that by 50 years, and we still don't have enough.

I suppose we could use the Kardashev scale to figure out when humanity will have energy at that rate. Using this formula: $$K=\frac{\log_{10}P-6}{10}$$ and substituting in humanity's energy usage per year, we could calculate just when we'll reach that point. Just use $$P= \text { Joules/year}=2.34 \times 10^{16} \text { Watts}$$ $$K=\frac{\log_{10}7.36 \times 10^{24}-6}{10}$$

and we find we should be a Type 1.03692 civilization. Given that we're currently a Type 0.7 civilization, we should be at that point in about 100 to 200 years. Note, though, that this figure is for a ship using all of humanity's total energy, which is unrealistic. However, it shows that we won't be able to harness that energy at all for a while.

I would also be obliged if someone could check my calculations. I used this logarithm calculator, in case anyone wants to use it. Conversion ratios can be found easily online.

What are the major barriers mankind would have to overcome to reach those speeds?

If we're talking purely about travel at this speed, i.e. assuming we've figured out everything else, the main problem is propulsion. As the above result showed (for those who skipped it, you just have to know that we'd need a lot of power to reach these speeds.), it's not easy to travel fast in space. Here are some options:

• Bussard Ramjet - Take in hydrogen gas floating in interstellar space, compress it, begin fusion, and convert that into thrust. Obstacles: It has to be really big, and you have to be sure you have hydrogen in space. Oh, and you have to master fusion.

• Nuclear Pulse - Chuck nuclear bombs out the back of the spacecraft, and ride the shockwaves. This was used in the hypothetical Project Daedalus and the equally hypothetical Project Orion. Neither idea got off the ground (pun definitely intended). Obstacles: You have to make loads of nuclear bombs. Also, you have to find a nation that's willing to sacrifice a bunch of land for the launch pad, because that launch pad and the surrounding area will be completely destroyed.

  Alternatively, you could just use this idea in space, as Lohoris suggested.

• Solar Sail - Ride the radiation pressure from a star using a sail. Obstacles: You've got to make and deploy an enormous sail kilometers wide. Also, the acceleration is incredibly slow.
• Antimatter Rocket - I've saved the best for last. Put together matter and antimatter and harness the energy from the annihilation. Obstacles: Very expensive, because antimatter is expensive. Also, you'll have to make quite a lot of it at first, although you can start to coast at some point. You have to be very delicate, though. Veeeeery delicate.

posted over 9 years ago

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