Spaceship Design

[GAHD]

then how do you get from deck to deck? if they're all spinning at different rates it'd be hard to allign a ladder or stairwell. oh and the spin towards center would be *faster* if you wanted to keep 1g of fake gravity constant throughout.

[TheBigDog]

Spinning concentric rings gives a different gravity for each ring. For a space station that might me ideal for doing research at varying levels. Maybe even manufacturing if the launch costs could be controlled. So crew could spend majority of day in normal ranged g's but perform tasks in areas ranging down to zero G.

 

Bill

[Jay-qu]

cone shaped is one solution - it also helps because if the apex (virtual or real) of the cone is pointing behind us then the tilt of the cone will help compensate for acceleration due to thrust :shrug: but would have to be somehow adjusted for coasting.. otherwise there would be a tilt.

[GAHD]

Yeah that's kinda the idea I was going with for my design. You have the rotating tub as a second hull basicly. The zero-g Stuff is outside the hub, while you have acess in a hollow center region at a relitively low difference in speed. It gives the crew a rotating 'bomb shelter' of sorts, just incase the outer zero-g area gets a leak.

 

Now the outer hull is where you try to keep a good portion of the ship's mass, so you hide the nuclear fuel and reactors out here. as well the bulk of supplys can be stored out there, like landers, probes, kill-o-bots, etc...

 

now the whole bit about the rotating body geing gyroscopic is troublesome...what about if it was a magneticly levitated sphere with cylindrical decks? :confused:

[Kayra]

now the whole bit about the rotating body geing gyroscopic is troublesome...what about if it was a magneticly levitated sphere with cylindrical decks? :lol:

 

Put the gyroscopic effect to good use.

Apply thrust to the rotating rings at 90 degrees to intented direction change.

The ship is gyro stabilized, not gyro imobilized.

[CraigD]

How does everyone envision getting gravity on a ship?

From the previous poll, the mandate appears to be “antimatter”. Let’s assume this implies the ship propelled by an antimatter-powered “steam” rocket motor. This is a high-pressure vessel into which is introduced antihydrogen or antiprotons and water, with a nozzle opening that allows the resulting superheated, unbonded H and O nuclei to escape at as high a speed as the physical limitations of the vessel can allow.

 

Assuming an adequate supply of antimatter – kilograms, not micrograms – such ships should have extraordinarily high maximum thrust and specific impulse – that is, they should be capable of acceleration limited primarily by the requirements of the human crew, and be able to sustain that acceleration for long periods (months to years) with extraordinarily small ratio of water reaction mass to total ship mass.

 

For such a ship, providing the crew with a simulation of normal Earth surface gravity would be trivial. In flight, the ship would be made to nearly always accelerate at about 10 m/s/s (1 g). All that’s necessary is that the ships decks be positioned for that 1 g to be downward.

 

A great potential advantage of antimatter rocket ships over lower-powered alternatives is their potential for even very large ships to be capable of Single-Stage-To-Orbit “amphibious” operation. I think the requirement to operate in an atmosphere (thought not necessarily at as great a speed or maximum acceleration as current rockets – escape velocity is not as meaningful a concept for a ship capable of sustained thrust as for current thrust-and-coast ships) will be the main driver of its design. Such ships will need some amount of streamlining and limited frontal area, so will likely resemble a small-footprint high-rise building on the inside, and an current-day rocket on the outside – that is, a long, narrow cylinder or prism with floors, elevators, and stairs inside, and a nose cone on top, all with some sort of “feet” capable of supporting the ship without sinking into an ordinary surface (gravel, etc).

 

In appearance, not as shiny and pointy, but not completely unlike what Heinlein envisioned in the 1950 movie ”Destination Moon”. There are actually many similarities between the 1940s fictional design of the nuclear thermal rocket presented in this old movie, and current design thought about antimatter rockets. The major difference is that the energy source for a nuclear rocket, uranium, is abundant, and even after the necessary refinement, cheap, while antimatter is staggeringly rare and expensive, and would require an engineering program dwarfing all the national space programs to date before it became plentiful and anything like “cheap”.

[Jay-qu]

For such a ship, providing the crew with a simulation of normal Earth surface gravity would be trivial. In flight, the ship would be made to nearly always accelerate at about 10 m/s/s (1 g). All that’s necessary is that the ships decks be positioned for that 1 g to be downward.

 

I had thought of this, but would that acceleration not be taxing on the structure of the ship? and also fuel consumption? - also if the ship is to remain in orbit above a planet where would our gravity come from then?

[cwes99_03]

Major problem with that propulsion theory is the expense of water. Haven't read the whole thread here, but where do you suggest getting such quantities of water?

[Kayra]

I hate it when I keep failing to understand a simple concept ;)

 

CraigD, could you explain to me how we can harness antimatter for propulsion when we are limited to ultra high temperature materials capable of 2,800 Celcius? These materials can operate in the 22-2400 range, and should give an SP of approx 800-1200. Even a standard nuclear reactor is capable of creating temperatures far exceeding any material we can make.

 

The Nuclear Pulse and Nuclear Salt Water propulsion systems seem to solve the problem by having the reaction occur behind the ship, but have technical issues of their own that need to be solved. While this throws considerable energy away, there seems to be plenty left over for propulsion somehow.

 

Could the engine be designed such that a continious stream of matter and antimatter meet at a point external to the ship? If that is the case, perhaps we could look into Antimatter catalysed fission or fusion.

 

I think I just answered my own question, sorry about the confusion.

[cwes99_03]

I think the problem with having the anti-matter and matter streams collide outside of the ship is that the explosion will not be controlled and vented properly to propel the ship. Basically it is like setting dynamite under the tires of your car to start yourself rolling. While it will begin the movement of the car, it will likely also lift the car up in the air and do all sorts of damage.

 

However, there is the possibility of using magnetic and electric fields to shape the exhaust from the matter/anti-matter explosion, but if we can do this outside of the ship, why not do it inside the ship and vent the resultant energy out the ship in a more controlled way.

[Kayra]

I think the problem with having the anti-matter and matter streams collide outside of the ship is that the explosion will not be controlled and vented properly to propel the ship. Basically it is like setting dynamite under the tires of your car to start yourself rolling. While it will begin the movement of the car, it will likely also lift the car up in the air and do all sorts of damage.

 

However, there is the possibility of using magnetic and electric fields to shape the exhaust from the matter/anti-matter explosion, but if we can do this outside of the ship, why not do it inside the ship and vent the resultant energy out the ship in a more controlled way.

 

So you want to contain a streaming nuclear event with magnetic fields? The magnetic field required just to contain an accelerate heated by RF energy turns out to require considerable power and mass. It can be done in a fusion reactor, but have you seen the size of the magnets required? Now multiply that by a factor of .. 5?.. 10?.. 100?

 

A matter Antimatter explosion is as powerful as it gets. The radiation from this explosion is mostly gamma and fast neutrons (I think). These are very detrimental to the engine itself.

 

As to the damage you mentioned it might cause, consider that you are trying to contain that very same energy. Ever hold a smallish firecracker tightly in your hand, then light it? It can take part of your hand off.

 

The consequences and design of pulsed and continuous nuclear events occurring behind the ship to propel it has been considered and designed by folk far more knowledgeable then I.

[Jay-qu]

matter/antimatter annilations only yield energy - I dont think neutrons are a product.

[CraigD]

For such a ship, providing the crew with a simulation of normal Earth surface gravity would be trivial. In flight, the ship would be made to nearly always accelerate at about 10 m/s/s (1 g). All that’s necessary is that the ships decks be positioned for that 1 g to be downward.

I had thought of this, but would that acceleration not be taxing on the structure of the ship?

I don’t think this is a significant concern. Nearly every structure conceived and built by mankind must endure the equivalent of a constant 1 g of acceleration, by virtue of being on the surface of the earth. The technology is mature

…and also fuel consumption?

In terms of antimatter – assuming, as I have, a state of technology where antimatter is very (kilograms) plentiful, fuel consumption really isn’t an issue. For a 10^8 kg ship (slightly more massive than the largest current aircraft carriers) 1 g of acceleration requires 10^9 W. Multiplied by a flight time of 10^8 seconds (about 4.5 years), this is an energy requirement of 10^17 J – the equivalent (per E=mc^2) of the annihilation of a “mere” .5 kg of antimatter – an insignificant fraction of a 10^8 kg ship’s total mass.

 

What’s likely to be more critical is the amount of reaction mass (water in my example) required, which depends in turn on how high an exhaust speed the rocket motor can produce, which depends on many complicated factors, a major one being how high a temperature and pressure the engine can contain. A major improvement in such a motor would be to have it contain the heat and pressure of the matter-antimatter annihilation heated water without physically touching it, by means of magnetic force. Since the annihilation is so powerful that it would almost certainly be able to ionize the water, this is likely to be feasible, but a terribly complicated engineering problem, similar to those faced by engineers attempting to magnetically confine super-hot plasma to produce “hot” nuclear fusion.

- also if the ship is to remain in orbit above a planet where would our gravity come from then?

One could maintain a powered orbit – an orbit with a velocity precisely greater than the freefall orbital velocity that it require a constant 1 g in/downward acceleration to maintain its radius, though this seems an appalling waste of energy (Even if antimatter becomes abundant and reasonably “cheap”, it’s hard to imaging wasting it like this!).

 

If the planet is massive and solid-surfaced enough, one could simply land on it, and have its surface gravity for free. A ship is, after all, intended to get you from one place to another, not be the destination place once you get there.

[Kayra]

matter/antimatter annilations only yield energy - I dont think neutrons are a product.

 

Sorry Jay, I was assuming that the annihilation would occur in the presence of reaction mass.

[Jay-qu]

No apology need - just clarification, its a beautiful thing :hihi:

 

so you think fast moving neutrons are useless to us?

[CraigD]

so you think fast moving neutrons are useless to us?

In an antimatter “steam” rocket motor, neutrons (and protons) are essential as the most massive particles in its exhaust.

 

Here’s a very simplified diagram of an antimatter steam rocket reaction (in glorious ASCII):

[input      ] [Reaction                                                             ][Exhaust]
|P- (the    |
|“antimatter|                  |many   |
|stream")   |>-            /->|photons|>--->|many   |>-------------->|Everything|   |hot, ionized |
               _anhilation_                 |photons|>->|e- (in  |>->|else (in  |>->|dissasociated|
|P+ (in H2O|>--/            ->|exotic   |>-/            |cool H2O|   |cool H2O  |   |H + O        |
|molecules)|                   |particles|               /            /
                                                       /            /
|the rest  |>------------------------------------------/------------/
|of the H2O|

So the annihilation produces, ultimately, photons, which heat the unannihilated water into plasma “steam”, which escapes the engine as exhaust, causing thrust.

[cwes99_03]

You still haven't answered my question on the quantity of water needed to create sufficient thrust.