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View Full Version : Inter stella : energy needed querry



2002-Jan-27, 07:35 AM
I read a recent posting which states that the energy needed to get a ship to the closest star was equivalent to that stored in a Jovian giant.

Did this method assume that life was being supported through out the journey, or was E used only for thrust?

lpetrich
2002-Jan-27, 07:54 AM
It depends on how fast the spacecraft is to travel -- if it gets very close to c, it will need a very large volume of fuel compared to its empty mass.

However, if it is to travel relatively slowly, say, anything from a few to a few thousand km/s, it will then need much less fuel. However, such a slowpoke craft will not reach another star in a human lifetime, which is the goal of a near-c craft.

Azpod
2002-Jan-27, 09:31 PM
On 2002-01-27 02:35, RPN wrote:
I read a recent posting which states that the energy needed to get a ship to the closest star was equivalent to that stored in a Jovian giant.

Did this method assume that life was being supported through out the journey, or was E used only for thrust?


The numbers I saw assumed a payload the size of the Voyager probes and a 100 year timespan, using conventional hydrogen-oxygen rockets. The acceleration was applied evenly over the timespan such that the craft entered orbit at A. Centauri, ~4LY away. The required fuel was about the mass of Neptune.

The main thing that makes it so massive is the fact that you are not just accelerating the payload. You are accelerating the fuel needed for deceleration, as well as any unspend fuel remaining for acceleration.

More efficient rockets would affect this. Ion drives are about 10X more efficient than conventional rockets, but they would need some immense power source for the drive. But something 10th the mass of Neptune is still way too large of a ship to send to the nearest star. Fusion would make it small enough for us to be able to build, but it still would be absolutely HUGE. Antimatter would be the most efficient fuel, but it currently costs US$ trillions per ounce to make!

The best solultion is to make the craft incredibly small and to use as little onboard fuel as possible. Nanobots capable of attaching themselves to debris in orbit at the destination star and building copies of themselves would be a good solution to the problem. They would have a few grams (or less) of mass, could be launched to incredible velocities by any number of means before they leave Solar orbit and could use an onboard ion drive or a laser-powered sail to decelerate and enter orbit.

Once there, they could find a small asteroid or comet to land on and build a base. They would build hundreds of copies of themselves, use them all to build a powerful transmitter to Earth so that they could receive instructions. We could then send them designs for probes to build to explore the rest of the system.

The total transit time could be under 100 years, and we could still perform incredible amounts of science. The best part is, the main cost would be the infrastructure for the whole system, not the probes themselves. We could use this same system to send probes to all the stars within a dozen light-years or so. Humans may never visit the systems (unless we find some way to do a warp drive or macroscopic interstellar quantum teleportation or something else not out of place in Star Trek), but we could still explore them and colonize them with machines.

Chuck
2002-Jan-27, 10:01 PM
We could send people in cryonic suspension. We already have some "volunteers" in the freezers now. We could send them ahead slowly and send the technology to revive them with the microprobes later.

Azpod
2002-Jan-27, 11:42 PM
On 2002-01-27 17:01, Chuck wrote:
We could send people in cryonic suspension. We already have some "volunteers" in the freezers now. We could send them ahead slowly and send the technology to revive them with the microprobes later.


I don't know... do you think Walt would like waking up with only a few semi-thawed people around him, and the next nearest person several LY away?

Sounds like the makings of a bad sci-fi movie to me. /phpBB/images/smiles/icon_smile.gif

Silas
2002-Jan-30, 04:10 PM
John Boardman wrote an article for Ares Magazine, entitled, "No, You're Not Going to the Stars." He did some simple math showing that the fuel requirements (even using anti-matter/matter annihilation) were -- well, he was talking about hyperbolic sine functions, which get very big, but in ordinary common language, the fuel tanks would have to be "effin' ginormous!"

Silas

GrapesOfWrath
2002-Jan-30, 05:53 PM
On 2002-01-27 18:42, Azpod wrote:
I don't know... do you think Walt would like waking up with only a few semi-thawed people around him, and the next nearest person several LY away?
What do you think he would do to us?