Could we build a starship using current technology?

[generic mook]

Suppose you had limitless resources and political will, and you wanted to build a starship. Your goal is to maintain constant acceleration of 1g for a period of at least 1 year (long enough to travel to a distant station and recharge).
1/ Could we do this using existing technology?
2/ How massive would such a vessel have to be? (Assume a human crew of 6.)

[jeff_wilson]

Originally Posted by generic mook

Suppose you had limitless resources and political will, and you wanted to build a starship. Your goal is to maintain constant acceleration of 1g for a period of at least 1 year (long enough to travel to a distant station and recharge).
1/ Could we do this using existing technology?
2/ How massive would such a vessel have to be? (Assume a human crew of 6.)

1. Not even.
2. There is no way of knowing.

[Humabout]

For what it's worth, accelerating that much for that long would run headlong into relativistic effects that would sap all efficiency. After three or four months, you'll probably be going plenty fast enough to achieve your goal, and without using up nearly so much fuel.

Also, you'll make it far more feasible if you cut back the acceleration and increase the velocity of exhaust. That'll increase efficiency, reducing fuel costs and making year-long constant acceleration more possible.

Of course, fuel for a year's worth of constant acceleration is probably way too much to be doable today. Remember that the more fuel you amass, the more mass you have to move, which requires more fuel. The only real way around that is either refueling or getting a more efficient engine. And the latter requires better tech, and the former typically requires launching fuel out ahead of you, which requires a lot of planning, time, and even more fuel. It gets kinda crazy.

[Dustin]

For comparison, a proposed unmanned interstellar probe design (Project Longshot) using nuclear pulse propulsion and relatively few advances on current technology compared to other designs achieves an acceleration of .001g (.01 m/s2) after 70 years of flight, and twice that after 100 years of flight (when it reaches Alpha Centauri B).

[Humabout]

Why does acceleration increase over time? Usually, that's relatively steady and velocity increases over time - that is, when it isn't instantaneous like most modern rocketry uses.

[Balor Patch]

Originally Posted by Humabout

Why does acceleration increase over time? Usually, that's relatively steady and velocity increases over time - that is, when it isn't instantaneous like most modern rocketry uses.

Presumably mass decreases as fuel is consumed.

[Dustin]

Originally Posted by Balor Patch

Presumably mass decreases as fuel is consumed.

Yes, that's my understanding here. Thrust is fairly constant and the vehicle's mass is decreasing as fuel is consumed.

[Mailanka]

Originally Posted by Dustin

For comparison, a proposed unmanned interstellar probe design (Project Longshot) using nuclear pulse propulsion and relatively few advances on current technology compared to other designs achieves an acceleration of .001g (.01 m/s2) after 70 years of flight, and twice that after 100 years of flight (when it reaches Alpha Centauri B).

There's no way that graph is correct. For one thing, an orion drive is going to accelerate you much faster than 0.01g. We have chemical rockets that accelerate you faster than that. Blowing nuclear bombs behind you (what a nuclear pulse drive is) will certainly kick you forward faster than that. Second, you'll never get to alpha centauri in 100 years at a speed of 0.01 m/s after seventy years.

You can actually read up on the Orion Drive in GURPS Spaceships. One engine gives 2g acceleration and each fuel tank (at TL 8) gives 3 mps, which is really, really good compared to everything else we can use. The main reason we don't use them is that people are very skeptical of the safety of blowing up tons of radioactive, weapons-grade bombs to get off the planet (and even if you get it up into orbit with more conventional means and then start blasting it around, what if the rocket crashes on the way up? We won't have people seriously considering an Orion Drive until we can construct it entirely in space with radioactive material collected IN space, and even then, there's a substantial anti-nuclear sentiment that has people freezing up at the very mention of the idea).

Also, Alpha Centauri is not THAT far away. Yes, it's very very very far away, but not insurmountable with modern technology. It's just that there's not much reason to spend billions of dollars building a ship powered by weapons of mass destruction that will get there in back in a couple of centuries. What would you do with something like that? What's the point?

[Anthony]

Originally Posted by Mailanka

There's no way that graph is correct. For one thing, an orion drive is going to accelerate you much faster than 0.01g. We have chemical rockets that accelerate you faster than that.

Bear in mind that all the Orion drives at that link have an exhaust velocity of 120,000 m/s or lower, other than Orion MAX, which is just the hard limit on theoretical performance for Orion and is most certainly not near future. A viable interstellar drive requires at least 3,000,000 m/s (0.01c), and increasing exhaust velocity decreases thrust.

[reverse_atomic_roger]

Have a look at the 100 year spaceship project http://en.m.wikipedia.org/wiki/100_Year_Starship

Its a DARPA project, and they reckon its going to take about 100 years to develop the tech for a plausable interstellar space ship.

That said, most of the stuff they plan to have is only a small stretch ahead of what we had now, so if you were going a bit cinematic it'd probably be fine.