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RobertDyck

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From: Winnipeg, Canada

Registered: 2002-08-20

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Going Interstellar

Interesting video from NASA Innovative Advanced Concepts (NIAC).
Going Interstellar
It's a video, but I'll transcribe the important part.

We know how to get to relativistic speeds in the laboratory, we do it all the time. Then when we go to the macroscopic level, with things like aircraft, cars, spacecraft, we're pathetically slow. So the question is, can we bridge that gap between what we do in the macroscopic level with chemical binding energies to relativistic speeds which are done with electromagnetic acceleration. The Shuttle when it would take-off, or the SLS when it will take-off will have a power off the launch pad of between 50 and 100 gigawatts. Turns out to get to relativistic speeds with the spacecraft we're talking about you need basically the same power level. And for about the same amount of time. It takes 10 minutes to get to orbit with Shuttle, it takes us 10 minutes to get to 30% the speed of light, with about the same power level. Just using different technology. We could propel a 100kg robotic craft to Mars in a few days. If you want to push something like the Shuttle class, it takes you roughly a-border a month to get there.

He's talking about a particle accelerator. The key difference is power source, fuel, and thrust are not on the projectile. Basically, the particle accelerator is a high-tech cannon. Is he proposing sending astronauts in Orion launched with a cannon? If you did, how would it slow down? Imagine people in a capsule hitting the atmosphere at 30% the speed of light. Can you say "boom"? But then he changed his estimates, he said 100kg to Mars in a few days. That's not 30% C. Mars is between 4 light minutes and 20 light minutes away, depending on relative positions of Earth and Mars in their orbits about the Sun. To go 12 light minutes in 3 days would be 1/600 of the speed of light. Still, hitting the atmosphere at (299,792,458 metres/second) / 600 = "boom"! There is propulsive capture, but if you use a big electromagnetic cannon to fire an Orion spacecraft from Earth, how do you slow down?

This guy says "we" do it all the time. That means he's working in a physics lab. So let's work out the physics, how much energy is that?
Kinetic energy: KE = 0.5 • m • v²
1 Joule = 1 kg • m²/s²
(For GW Johnson: I coped the "²" symbol from the character map in my computer, found in the start menu under "system tools".)
I came up with 12 light minutes as a very rough estimate of distance, and translated "a few days" to 3. So let's make this simpler, round the speed of light to C=3*10^8 m/s so our speed is C/600 = 500,000 m/s. Orion capsule mass (not including service module or launch abort system) is 10,387 kg = 22,900 lb.
0.5 • (10,387 kg) • (500,000 m/s)² = 1,298,375,000,000,000 Joules = 1,298,375 GigaJoules
Nuclear bombs are often expressed in tons of TNT: 1 ton TNT = 4.184 GigaJoules
Therefor energy equivalent = 310,319 tons TNT. That's less than a megaton, 310 kilotons to be more precise.
Any volunteers?

(Image from the 1902 movie "LA VOYAGE DANS LA LUNE")

Last edited by RobertDyck (2016-02-21 12:55:54)

SpaceNut

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From: New Hampshire

Registered: 2004-07-22

Posts: 29,431

Re: Going Interstellar

Well lets put this in the Orders of Magnitude of energy with 8.8×1010 J total energy released in the nuclear fission of one gram of uranium-235....
with the likes of the Little Boy atomic bomb dropped on Hiroshima in World War II (15 kilotons)....of which puts the use of energy in the realm of the Nuclear underground weapons testing I would thimk that we are ready for such energy useages but many are still caught up in other directions still.