Subluminal Travel

[Vondy]

Hey - I was hoping we had some hard science or physics buffs out there who could help me with something. I'm going to be running a Jovian Chronicles game, which is essentially a hard-science setting that occurs within Earth's solar system.

 

I want (after things get rolling) to add the development of subluminal interstellar travel, which would be well beyond the reasonable scope of the particle combustion chambers (a high-energy magnetic "bottle" to hold a micro-fusion reaction) - and are still limited by reaction mass.

 

In other words, its going to be a major, experimental, development in the game.

 

As such I need a theoretically sound drive concept that would propell a ship at velocities that could cover a light year every 2-3 years (so .5c or higher), so that a star such as Alpha Centauri could be reached in 8-10 years (or closer to 5 years if light speed was approached). Does anyone know enough about "hard" theoretical physics to make suggestions?

 

In addition, how does one go about shielding 1) the crew from the force of acceleration, and 2) the ship from potentially lethal phenomenon such as micro-meteors and the like. I have no idea about the first one, but the setting does have limited mag shields, would that pheasibly work with meteorites?

[lemming]

Re: Subluminal Travel

 

Originally posted by Von D-Man

I have no idea about the first one, but the setting does have limited mag shields, would that pheasibly work with meteorites?

IIRC, meteorites are mainly iron so I would expect so.

I would assume it would also work as shielding against radiation, much like the earth's magnetic field does.

 

I'll have to look up some data on the acceleration parameters.

[keithcurtis]

A light sail driven by a honking powerful laser can deliver a lot of accumulated thrust over a long period of time, perhaps enough to get you up to ramjet speed. It's been to long since I did this reseearch for my Solar Colonies game to give any authoritative answers.

 

 

As for the micrometeorites, you put a very thick shield in front of you and pray. They're not that common in interstellar space, but I don't know of anyway to make evasive maneuvers from something virtually indetectable coming at .5c.

 

Keith "Bull in a China Shop Helmsman" Curts

[L. Marcus]

This site might help: Warp Drive When?

[Intrope]

Another great site: Wikipedia's Spaceship Propulsion

 

For non-rubbery, your best bet appears to be Nuclear Photonic drive (Isp: 5,000,000) but I have no idea if that would get you anywhere near the .5c mark you want. Not that you can't exaggerate it's effectiveness.

[Ghost who Walks]

Originally posted by Von D-Man

In addition, how does one go about shielding 1) the crew from the force of acceleration, and 2) the ship from potentially lethal phenomenon such as micro-meteors and the like. I have no idea about the first one, but the setting does have limited mag shields, would that pheasibly work with meteorites?

You could skip the crew (multi-year journey, after all) and have everything automated. Would greatly reduce the amount of area that needs shielding. Crew could then be either in hot sleep/popsickle form, or could be in embryonic stage...designed to be born and raised by the ships computer after arrival.

[Seenar]

Re: Subluminal Travel

 

Originally posted by Von D-Man

Hey - I was hoping we had some hard science or physics buffs out there who could help me with something. I'm going to be running a Jovian Chronicles game, which is essentially a hard-science setting that occurs within Earth's solar system.

 

I want (after things get rolling) to add the development of subluminal interstellar travel, which would be well beyond the reasonable scope of the particle combustion chambers (a high-energy magnetic "bottle" to hold a micro-fusion reaction) - and are still limited by reaction mass.

 

In other words, its going to be a major, experimental, development in the game.

 

As such I need a theoretically sound drive concept that would propell a ship at velocities that could cover a light year every 2-3 years (so .5c or higher), so that a star such as Alpha Centauri could be reached in 8-10 years (or closer to 5 years if light speed was approached). Does anyone know enough about "hard" theoretical physics to make suggestions?

 

In addition, how does one go about shielding 1) the crew from the force of acceleration, and 2) the ship from potentially lethal phenomenon such as micro-meteors and the like. I have no idea about the first one, but the setting does have limited mag shields, would that pheasibly work with meteorites?

 

 

Robert L. Forward has done good work on this. Rocheworld (click on name for link) using a light sail. Accleration is low but over long time. The sail detaches on the way and is used to bounce the light back to the ship to decellerate it to the star.

 

For fast travel, Anti-mater or Fusion drives are non-rubber as both should be possible. Clark suggests using a cone of Ice (hexagons, of course) in Songs of Distant Earth that sounds convincing.

 

Hope this helps.

[Snarf]

Originally posted by keithcurtis

A light sail driven by a honking powerful laser can deliver a lot of accumulated thrust over a long period of time, perhaps enough to get you up to ramjet speed...

In case you haven't heard of ramscoops Von-D Man, a ramscoop is a device that magnetically grabs the loose particles of hydrogen floating in interstellar space and compresses them for a fusion reaction. You have to be going fast already for it to work at all (thus the laser/light sail for launching) but once it's running you don't need to carry any fuel and it can go fast. It's theoretically possible to do all of this, but the technology to magnetically scoop up and compress hydrogen, and protect the ship from radiation and meteors is needed. Since you're already are using mag shields in that campaign that stuff sounds pretty reasonable.

[Snarf]

For fast travel, Anti-mater or Fusion drives are non-rubber as both should be possible. Clark suggests using a cone of Ice (hexagons, of course) in Songs of Distant Earth that sounds convincing.

Another thing about that book. The fuel source in that spaceship was extracting energy from empty space. This is theoretically possible - physicists have theorized that space is a bubbling foam containing an unbelievable amount of energy - but of course nobody has the faintest idea how we could get that energy.

[lemming]

Using the poorly written code below, I get 9.07 years for an acceleration of 1G and a top speed of 1/2 the speed of light.

 

Acceleration needs to be at least 0.6 if we're assuming acceleration until the midway point. I threw in a calculation at the end showing what speed you'd achive assuming constant acceleration until you got to the midway point.

 

#!/usr/bin/perl
use strict;
use warnings;

# Light Year (y) = 9.4605 * 10^14 meters
# Speed of Light (c) = 3.0 * 10^7 m/s
#
# Acceleration (a) = 10 m/s^2
# Distance to Alpha Centauri (j) = 4.3 * y
# Top Speed (t) = .5 * c
#
# time to t (x) = t/a
# Distant accelerated (w) = 1/2 * a * x^2
# Time to get to ac = (j - 2w) + 2x

my $y = 9.4605 * 10**15;
my $c = 3.0 * 10**8;
my $a = 10;

my $j = 4.3 * $y;
my $t = .5 * $c;
my $x = $t/$a;
my $w = 1/2 * $a * $x**2;
my $total_time = ($j - 2 * $w)/$t + 2 * $x;

printf "%1.2e meters\n", $j;
printf "%1.2e m/s light speed\n", $c;
printf "%1.2e m/s Top speed\n", $t;
printf "%1.2e seconds to top speed\n", $x;
printf "%1.2e meters to accelerate\n", $w;

printf "%1.2e seconds - %10.2f years\n", $total_time, $total_time/(365.25*24 * 60 * 60);

$x = sqrt($j/$a);
$t = $a * $x;
printf "%1.2e m/s Top speed\n", $t;
printf "%1.2e seconds - %10.2f years\n", $x, $x/(365.25*24 * 60 * 60);

[L. Marcus]

Originally posted by Snarf

Another thing about that book. The fuel source in that spaceship was extracting energy from empty space. This is theoretically possible - physicists have theorized that space is a bubbling foam containing an unbelievable amount of energy - but of course nobody has the faintest idea how we could get that energy.

I've been fiddling with this for a SF-campaign, and technobabbled it as a result of deflector screen technology. Really rubbery, you know . . .

[Intrope]

Re: Re: Subluminal Travel

 

Originally posted by Seenar

Clark suggests using a cone of Ice (hexagons, of course) in Songs of Distant Earth that sounds convincing.

 

Hope this helps.

 

Given mass is the big limiting factor for low-rubber space ships, I'd guess that Ice would be out, and Chobam(sp?)-like armor would be in; basically, you'd want the most penetration resistance per kilo. But admittedly in Songs the Ice did make some sense 'cause they were planning on replenishing it during the voyage (and they weren't apparently heavily mass limited).

[McCoy]

Think most has been covered.

 

On thing implied I would like to emphasize, instead of protecting crew against high acceleration, you are better off with smaller accelerations over a longer period of time.

 

Speed is distance over time. Acceleration is distance over time squared. Lower accelerations are more efficent.

 

Lightsail or ramscoops are probably your best non-rubber bet, but some in the fringe of physics say that the "reactionless" drive (Dean Drive or something like) is not impossible.

[Outsider]

I dont think accleration shielding will be necessary. Every hard sci-fi interstellar drive I've read about doesnt provide all that much oomph. They provide a little oomph continuously over a long period, generally.

 

Velocity = Accelleration*Time

1 Gravity = ~9.8 m/s^2

0.5 light speed = ~150,000,000 m/s

Relativistic effects are pretty minimal, even at 0.5 light.

Distance covered = average velocity*time

 

So, accellerating at a full G to 0.5c takes only 15,306,122 seconds (about 6 months)

 

Distance to Alpha Centauri : 4.25 LY (Proxima = 4.2 LY, Alpha/Beta, 4.3 LY)

 

Acceleration : Time to 0.5C : Distance covered during accel/decel : Coast distance : Coast time : total trip time

0.06 G : 102 mnths : 4.25 LY : 0.00 LY : 0.00 years : 17 Years

0.10 G : 60 months : 2.50 LY : 1.75 LY : 3.50 years : 13 Years 6 Months

0.20 G : 30 months : 1.25 LY : 3.00 LY : 6.00 years : 11 Years

0.30 G : 20 months : 0.83 LY : 3.41 LY : 6.83 years : 10 Years 2 months

0.40 G : 15 months : 0.62 LY : 3.62 LY : 7.25 years : 9 Years 9 Months

0.50 G : 12 months : 0.50 LY : 3.75 LY : 7.50 years : 9 Years 6 Months

0.60 G : 10 months : 0.42 LY : 3.83 LY : 7.67 years : 9 Years 4 Months

0.75 G : 8 months : 0.33 LY : 3.92 LY : 7.83 years : 9 Years 2 Months

1.00 G : 6 months : 0.25 LY : 4.00 LY : 8.00 years : 9 Years

2.00 G : 3 months : 0.12 LY : 4.12 LY : 8.25 years : 8 Years 9 Months

Instant : 0 months : 0.00 LY : 4.25 LY : 8.5 years : 8 Years 6 months

 

 

The first line (0.06 G) is the minimum accelleration transit that reaches 0.5c (at turnover). The last lineis the minimum time transit that reaches 0.5c (instantaneously!)

 

 

Increasing your max. velocity will reduce the time, but require a slightly higher accelleration for the minimum accel transit. A 0.8c max, would, for example, have a 10.6 year minimum accel (0.15 G) transit, and a 5.3 year minimum time transit.

[Outsider]

Bah, McCoy beat me to the accelleration shielding comment while I was putting together my table. ah well.

[McCoy]

Originally posted by Outsider

Bah, McCoy beat me to the accelleration shielding comment while I was putting together my table. ah well.

But you did it better.

[Tim]

When I saw the thread titla I thought it read "SUBLIMINAL" Travel.

 

Between each step, you skip a large area.

[McCoy]

Originally posted by Outsider

Acceleration : Time to 0.5C : Distance covered during accel/decel : Coast distance : Coast time : total trip time

0.50 G : 12 months : 0.50 LY : 3.75 LY : 7.50 years : 9 Years 6 Months

1.00 G : 6 months : 0.25 LY : 4.00 LY : 8.00 years : 9 Years

2.00 G : 3 months : 0.12 LY : 4.12 LY : 8.25 years : 8 Years 9 Months

Outsider's chart also illustrates what I said about the lower accelerations being more efficent. Note doubleing the acceleration from .5 G to 1 G knocks only six months off the trip time. Quadrupling it to 2 G saves a total of 9 months.

 

For dramatic/campagine purposes, decide how long you want it to take, then that's how much acceleration is possible with the engines.

 

Another point, lightsails would take considerable "ground" support from the home system, while a ramjet or reactionless drive ship would be totally independent after launch.

 

So if you want the possibility of sabotage after launch, go with laser driven lightsails.

[McCoy]

Originally posted by Tim

When I saw the thread titla I thought it read "SUBLIMINAL" Travel.

 

Between each step, you skip a large area.

So did I. "Travel, no conscious control." "Hey, how did I get HERE?"

[SSJ Archon]

physics

 

You can get energy out of empty space. Sort of. Not really.

 

Its actually a quantum effect, that for short periods of time, particles and there antiparticle twins can appear out of no where. They, normally, imediately annilate. The trick is, if you keep them from annilating, the mass/energy DOES come from some where, usually the biggest field effect causing mass, like you. So you would lose mass. Effectively, you'd be slowly burning yourself off. The biggest problem is one of enginneering. By the time you harvest this miniscule amount of energy, you wasted millions of times more. Forget about it.

 

Antimatter is your best bet in my opinion. You'd mostly have a special station orbiting the sun at close range, gathering energy and using particle accelerators to, bit by bit, scrape together some antihydrogen. This would be stored in a magnetic "barrel" which would be put onboard your ship.

 

Theoretically, because antimatter-matter reactions are 100% energy output, you could reach speeds that approach the speed of light, no problem.

 

This is infact is the system I use in my SH campaign, as well as singularity dilating.

 

---fixed grammer---

[Dr. Anomaly]

Another possibility for low-rubber propulsion would be using kernels (Kerr-Newman black holes) as your power/propulsion source. Well, it's low-rubber if you concede the possibility of substellar-mass singularities...

 

It's possible to store energy in, or extract energy from, the ergosphere of a black hole using rapidly-moving charged particles or magnetic fields. Depending on the exact physical parameters of the black hole in question, as much as 49% of its mass may be available for extraction...that is, in an extreme case, up to 49% of the mass of a black hole may be in rotational energy (mass-equivalence) as opposed to 'actual' mass. Given that even a microscopic black hole would weigh in the hundreds of millions of tons, think about the possibilities of being able to extract up to 49% of that mass as usuable energy during a voyage...that is a humungous amount of available energy, even by the standards of subluminal interstellar travel. It's almost half as good as a matter/antimatter reaction in efficiency, but you don't have to worry about containing the antimatter...the black hole's gravity makes it self-containing. Also, with a matter-antimatter drive, you'd either have to carry enough antimatter along for both legs of the round trip, or somehow manufacture more at your destination. With a kernel, you can "refuel" it at your destination star by using ordinary fusion reactors (with fuel harvested from local sources, like ice comets or gas giant atmospheres) to "recharge" it (spin up the rotation again), or even use solar power to do the same thing. That's a lot simpler (at least in theory) than containing or manufacturing antimatter.

 

For a better idea (in fiction) of the near-real possibilities of using kernels for power/propulsion, check out The McAndrew Chronicles by Charles Sheffield. The stuff with kernels is in the first couple of stories...the later stories deal heavily with very high acceleration drives powered by zero-point (vacuum fluctuation) energy, which are probably far too "rubber" for your taste.

[Vondy]

Those of you who did math and prepared charts I salute you! I see the point about relatively normative acceleration (~1G being sufficient). Would anyone be willing to do math for speeds in excess of .5C, but not quite lightspeed?

 

I intend to have the crew in some sort of hibernation (be it hot or cold sleep on the way to the destination). I've been doing some research and there is a process they have discovered that allows them to "freeze" people without the formation of ice crystals in the brain and critical tissues.

 

As for the drive type - I've been looking at the ones suggested, as well as some I found on the jet propulsion laboratory's site.

 

There's also an interesting theoretical physics program at the UW focusing on an MMPP drive, which I'll write up a paragraph or two on when I figure out how the concept could be "applied"

 

Hmmm... subliminal travel: astral projection.

[lemming]

Ok at 1G acceleration using above code:

top speed |  time
.5 c           |  9.07 y
.6 c           |  7.73 y
.7 c           |  6.80 y
.8 c           |  6.13 y
.9 c           |  5.63 y
.99 c         |  5.28 y
1               |  5.25 y

[megaplayboy]

umm, has anyone factored in the relativistic effects?

 

I know the reason you can't exceed 'c' is because of the requirement to generate an infinite amount of energy.

 

going up toward .5, there's going to be a slight increase in the amount of energy requred to maintain a constant acceleration(about 40 percent).

 

I suppose some sort of carbon nanofiber coating would be useful for protecting the ship against collisions with micro-meteor-whatevers.

 

The solar sail idea is cool because you don't have to have 70 percent of the ship's mass be reaction fuel.

 

Perhaps a hybrid system(giant laser stations positioned in-system to accelerate unfurled solar sails, the fusion/ion/antimatter or whatever rockets engage once out of laser range, then the destination system uses lasers to help slow down the ship) might work.

[Outsider]

Lemming's code will give you a more accurate answer, but for a quick estimate :

 

 

For any Maximum velocity and distance to be covered :

 

Accel : Boost time

0.05 G : 40.0 Years

0.10 G : 20.0 Years

0.20 G : 10.0 Years

0.30 G : 6.67 Years

0.40 G : 5.00 Years

0.50 G : 4.00 Years

0.60 G : 3.33 Years

0.75 G : 2.67 Years

1.00 G : 2.00 Years

2.00 G : 1.00 Years

4.00 G : 0.50 Years

8.00 G : 0.25 Years

Instant : 0.00 Years

 

V = Desired maximum velocity (as a fraction of Lightspeed) = V

B = Boost Time (Accel and Decel portions) from chart

D = Total distance to be covered

T = Total trip time

 

T = 0.5*B*V+D/V