Lt. Commander
Join Date: Dec 2007
Posts: 120
# 31
03-28-2012, 10:44 AM
Quote:
Originally Posted by hevach View Post
Antimatter isn't necessary... and for that matter, not feasible with current technology, or our current understanding of the stuff. We haven't found a way to produce it without expending more energy than it'll release in annihilation (not to mention the fantastic expense involved), we haven't managed to store multiple particles at once, or single particles for more than a few seconds, and don't even have a viable theoretical means to do so.

Acceleration doesn't need to be done all at once. Because of the distance involved and the need to be accelerating or decelerating for most of it to attain minimum travel time, sustainability is more important than output. Ion engines exist and are ideal for this kind of use, and you wouldn't even need something as exotic as fusion to power one.
It has nothing to do with the magnitude of the acceleration, and everything to do with how much energy can be extracted from the fuel. The less energy in the fuel, the more of it you will need. The bad news about that, though, is that fuel consumption increases exponentially with your desired maximum velocity.

To put this all in perspective, a spacecraft traveling at 0.999c has a relativistic kinetic energy equal to about ten times the energy of annihilating its rest mass in antimatter.

http://en.wikipedia.org/wiki/Rocket_equation

http://en.wikipedia.org/wiki/Specific_impulse

As such, to get 0.999c with fusion power would require literally trillions of times your payload mass in fuel unless a Bussard ramrocket can be made workable.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 32
03-28-2012, 10:59 AM
Quote:
Originally Posted by AAA2513
Utilizing the gravitational fields of stars starting with our very own sun to accerate and decelerate could reduce energy consumption considerably. Imaging the speed one could obtain over the severl months of droping in for close pass of our sun from a distance out past Pluto.
How exactly do you plan on turning the ship around after it is past Pluto? After you reach a speed of 617.5 km/s, the craft wouldn't come back anymore.

Using (1/2)m * v^2 for low speeds, that would only account for 0.0001% of the energy you'd need....
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 33
03-28-2012, 11:02 AM
Quote:
Originally Posted by AAA2513
Or forget the ramjet and go Orion Project all the way. A nuclear warhaed in the 1 megaton range can release about 4.184 petajoules, which is about 4.184x10^15, and there are much higher yielding devices than that.
Your new idea is to detonate 1,000,000 nuclear warheads to propel the ship?
I'm done here.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 34
03-28-2012, 11:17 AM
Quote:
Originally Posted by hevach View Post
The rest of my life trapped in cramped conditions living on strict rations with a large number of other people, constantly haunted by the knowledge that if the radiation doesn't sterilize us all before we make it to the heliopause, anything built by the lowest bidder will never last any longer than it takes those responsible to be safe from consequences?

Yeah, I'll pass.
Otherwise known as the Submarine service!! :p

Quote:
Originally Posted by hort_wort View Post
Hmmmmmmmm -scratches chin-

Let's also assume we have 100 humans to start a small colony.
Unfortunately, you'll need at least 200 people for proper genetic diversity (let's add 50 more, just as an engineering fudge factor) otherwise you'll end up like the Spanish line of the Habsburg royal family. More like a Family Stick, than a Family tree.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 35
03-28-2012, 11:23 AM
Quote:
Originally Posted by hort_wort View Post
Your new idea is to detonate 1,000,000 nuclear warheads to propel the ship?
I'm done here.
No, as In noted 1 megaton is on the small side, I was think 1000 to 3000 nuclear warheads depending on yield. but not all at once.

I am sure there are plenty of technical issues, but we are no further away with this approach than we are trying to build and supply a ship to make a trip that will take 200 to 300 generations to complete.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 36
03-28-2012, 04:15 PM
Perhaps we don't need to "slow down" the ship when it gets to its destination. What if it consisted of two sections: crew section and engineering (like the Galaxy class saucer and stardrive sections).

The Crew Section (the "saucer") is large enough to house the ship's crew and passengers, along with everything they need to survive. It also carries conventional engines.

The Engineering Section (the "stardrive") consists mainly of massive engines that run alongside the Crew section. These engines are responsible for propelling the ship at near-light speeds.

When the ship gets close to the target system, everyone gets inside the Crew section. The Crew section is fired like a bullet out of the back of the ship, getting left behind while the Engineering section flies on and self-destructs or something. Then the Crew section fires its own engines and finishes the voyage at conventional speeds ("impulse power").

I don't know if that's plausible or not, but either way it would make good sci-fi.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 37
03-28-2012, 04:21 PM
Quote:
Originally Posted by Ertwin View Post
Imagine if you will, that scientists were able to say definitively that Kepler 22b was habitable, and a generational spaceship was built to go there. Would you be willing to board?
Nope - and IMO it would be unwise until they sent an un-manned probe there (and yes I realize they would have to solve the tech hurdle of radio signnal degradation beyond 5 light years for such a probe mission to be feasable and be able to send back verifiable data on the enviroment.)

I'm all for calculated risks, but I'd need irrefutable proof that it was indeed habitable and sustainable food water and other needed resources were indeed available before I'd sign up.

If you are in fact saying all that all the above verifiableevidence was presented as proof of habitability - honestly, yes, I'd sign up.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 38
03-29-2012, 05:42 AM
Quote:
Originally Posted by ThePsycoticVulcan
Perhaps we don't need to "slow down" the ship when it gets to its destination. What if it consisted of two sections: crew section and engineering (like the Galaxy class saucer and stardrive sections).

The Crew Section (the "saucer") is large enough to house the ship's crew and passengers, along with everything they need to survive. It also carries conventional engines.

The Engineering Section (the "stardrive") consists mainly of massive engines that run alongside the Crew section. These engines are responsible for propelling the ship at near-light speeds.

When the ship gets close to the target system, everyone gets inside the Crew section. The Crew section is fired like a bullet out of the back of the ship, getting left behind while the Engineering section flies on and self-destructs or something. Then the Crew section fires its own engines and finishes the voyage at conventional speeds ("impulse power").

I don't know if that's plausible or not, but either way it would make good sci-fi.
Few problems I see with this:

1. It takes the same amount of energy to achieve the deceleration regardless of whether you do it instantly or over 300 light years.
2. Rockets tend to be efficient and easy to direct, explosions inefficient and difficult to direct, so attempting an explosive deceleration might take substantially more energy because of inefficiency and wasted force sent to the sides.
3. Rapid deceleration from relativistic speeds would probably be fatal to everyone inside. Sir Isaac Newton is the meanest SOB in space. There is a theory that suggests reducing inertial mass is possible with exotic particles (and thus decreasing the force needed for acceleration) but none to suggest you can escape the fundamental laws of motion.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 39
03-29-2012, 05:53 AM
Quote:
Originally Posted by AAA2513
No, as In noted 1 megaton is on the small side, I was think 1000 to 3000 nuclear warheads depending on yield. but not all at once.

I am sure there are plenty of technical issues, but we are no further away with this approach than we are trying to build and supply a ship to make a trip that will take 200 to 300 generations to complete.

I am with you on this. Even with the energy requirements being what they are I see that mission far less daunting than trying to build a generation ship that could survive such a huge duration.

What we are talking about is a vessel traveling at relativistic speeds, but consuming the equivalent of the entire global energy output for decades but could arrive in a single generation, versus a vessel that would have a journey that would last longer than all recorded human history.
Lt. Commander
Join Date: Dec 2007
Posts: 120
# 40
03-29-2012, 11:53 PM
Quote:
Originally Posted by ThePsycoticVulcan
I don't know if that's plausible or not, but either way it would make good sci-fi.
The idea of a multi-module ship with throwaway modules could work, but it would need a slightly different setup.

The "core" of the ship would consist of a long boom to which the other modules would attach. At the forward end (protected by any necessary anti-space-debris shielding) would be the Crew Module (crew quarters, command-and-control, and systems needed to land the module on the new planet). At the aft end would be the Engine Module, housing the main engines. So far, this gives us something resembling a scaled-up version of Discovery from 2001: A Space Odyssey.

Mounted along the boom would then be expendable modules containing all of the supplies--Fuel Tanks, Equipment Modules (containing all of the non-renewable supplies for the crew, like medicine, computer parts, and other stuff needed in-flight that can not be constructed aboard the ship), and Ecosphere modules (for food production and park/recreation space).

The Fuel and Equipment modules would be jettisoned as each one is exhausted, making the overall ship progressively lighter. Partway through the deceleration phase, the remainder of the Equipment and Ecosphere modules will be stripped of everything useful and they will be jettisoned as well. The supplies taken by them will be crammed into the Crew module (too bad that they'll be cramped for the last few months with all of that stuff, but they'll live with it). Such a mission profile would let no-longer-necessary mass be tossed away as soon as possible, which minimizes the amount of fuel and propulsion that will be needed.
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off


All times are GMT -7. The time now is 12:23 AM.