Could we build a starship using current technology?

[David Johansen]

No

But, that's assuming something new and groundbreaking doesn't come along in the next couple years.

Highly unlikely, mind you.

But really you absolutely need to have reactionless (which is to say impossible) drives to do 1 g for any astronomically significant period of time.

However, we should be able to build a solar powered soft launch plasma packet accelerator and a separate ship for it to push. Essentially you fire the fuel out of a cannon at a shield / sail so the ship doesn't have to carry its fuel. The resources required are considerable and the cannon facility itself has its limits. The cannon magnetically accelerates ionized matter like the stuff in a plasma TV rather than the hot death ray plasma of science fiction.

It's not 1G for a year by any means but it's probably the best bet at present. You probably do gravitic (use the target star's gravity to slow you down) or high atmosphere braking using the same sheild at the other end.

[generic mook]

What if you spent many trillions of dollars, and built a HUGE ion thruster in space? I mean, the size of New York City... and used it to propel a small ship.

[johndallman]

Originally Posted by generic mook

What if you spent many trillions of dollars, and built a HUGE ion thruster in space? I mean, the size of New York City... and used it to propel a small ship.

An ion drive needs to be mounted on the vehicle. Since the exhaust is charged particles, they repel each other, so the beam spreads out drastically and has no useful range. A fixed laser can propel a separate vehicle, but we don't know how to build one big enough to be useful.

[Fred Brackin]

Originally Posted by generic mook

What if you spent many trillions of dollars, and built a HUGE ion thruster in space? I mean, the size of New York City... and used it to propel a small ship.

Efficiency does not increase with size.

If you're talking about a ship that's 1% payload and the rest given to drive and fuel it still won't be anything like what you're hoping for.

If you used Spaceships and had 5% payload, 5% drive,5% power plant and 85% fuel you'd get something like 91.8 miles per second of Delta-
V.

This would allow you to leave the solar system but since you can only use half the Delta-V to accel and have to have the other half to decal you'll be travelling through interstellar space at only 45 miles per second.

At that speed it would take you over 78,000 years to get to Alpha Centauri.

[malloyd]

Originally Posted by scc

I calculated how fast a ship would be going after accelerating at 1 G for a year once, without accounting for time dilation, and if I remember correctly you're going at ~.99C

That's about right. The speed of light is just about a G-year (353 G-days).

Even playing a little loose with what you measure where, this is impossible now, or with any conceivable future drive. You'd have to turn something like 96% of your starting mass into energy to do this, even with a perfect mass to energy conversion system - which violates some nuclear force conservation laws.

[Anthony]

Originally Posted by generic mook

1/ Could we do this using existing technology?
2/ How massive would such a vessel have to be? (Assume a human crew of 6.)

No; a chemfuel rocket of the required size would have mass exceeding the mass of the observable universe and wouldn't manage 1g.