I'm reading these articles on Wiki and wherever bemoaning how difficult space travel is, how much energy is needed, how far the stars are, etc. Here's some quick research that isn't doom and gloom.

First, we don't need to go to the stars, at least not yet, and not for a long time. There's a huge amount of surface area in our Solar System comprised of the planets, asteroids and Kuiper Belt objects.

Second, there's a neat thing called the acceleration of gravity. On Earth's surface, this is conveniently called 1 g. If you accelerate in space at this rate, namely 1 g, it feels like you're standing on Earth. You don't lose bone or muscle mass, or suffer any of the symptoms of weightlessness. Any more than 1 g, and you're going to be uncomfortable. Any less, and you're not getting there as fast as you can. Ideally, you go 1 g until you're half way there, turn around and deaccelerate at 1 g until you get there.

The third is how the solar system becomes human-scaled when you're travelling at 1 g. Some examples:

  • 400,000 km (distance to the moon) - takes 3½ hours
  • 0.5 AU (distance from Earth or the moon to Mars) - takes 2 days
  • 3.7 AU (distance from Mars to Jupiter) - takes 5½ days
  • 50 AU (distance to the Kuiper Belt) - a bit more than 20 days
  • 100 AU (from one side of the Solar System to the other) - a bit more than 28½ days

(Just Google 'constant acceleration rockets' for the formulae.)

The fourth is how slow you're going relative to the speed of light c. From one side of the Solar System to the other, your top speed would be about 2% of c. We're not approaching any kind of significant relativistic effects here.

So going as fast as we comfortably can, we can visit any part of the Solar System in under a month, with a top speed of 2% of c.

To be fair, a constant acceleration rocket that can provide 1 g for an entire month is still a formidable engineering challenge, but several feasible solutions have been proposed, dating back to the 1950s. Most of these involve nuclear fusion of some sort or other, and were abandoned because the costs of "going to the stars" were insurmountable, or from the public's negative perception of nuclear devices in space.

I say, forget about going to the stars, let's work on short term 1 g rockets, and making them more efficient, so they run for longer times with less fuel. The goal is one month of 1 g, but even two days will get us to a primary target!

Personally, I think Mars has only theatrical value. However, just a little farther out, Ceres is a planetary body smack dab in the middle of a bunch of nickel and platinum group of asteroids ... commercial incentives are much more effective!

"The Exploration of Space" is a work of non-fiction written by Arthur C. Clarke, published in a first edition in 1951 and in a second edition in 1959. I read the second edition, which was published after the launch of Sputnik.

Although Clark was known more as a science-fiction writer, this book is written very technically, explaining the basic scientific principles of rocketry and communications in space travel. As with most things written in the past detailing the progress of technology, much of the interest for the modern reader comes from seeing just how right Clark was on some things, and how off he was on others. We do indeed have satellites in geostationary orbit broadcasting television to anywhere in the world--- but Venus is not a warm and comfortable swamp world ripe for human colonization. In general, like much written in the early Space Age, the predictions about flight technology were very optimistic (the book talks about moon bases and manned expeditions to other planets) while its predictions about information technology were pessimistic (such as saying that television signals could probably never be received from other planets).

The problem with making predictions is that true predictions often turn out to be obvious in retrospect, while untrue predictions seem ridiculous. Clark predicted that satellites would change communication, and that we would have space stations and space shuttles now seems commonplace, although they were revolutionary ideas at the time. On the other hand, moon bases, colonies on the swamps of Venus, and interstellar travel have all failed to materialize and now seem somewhat silly. But by reading this book in context, we can understand how clear and prescient of a thinker Clark was.

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