[Gardamorg]

A good Science Fiction oriented space craft would be a super light spacecraft.

If we had nano assemblers we could essentially give Aerogel a nanostructure that fortifies it's strength by composing it's structure with nanotubes such as these.

There is no limit to how strong we could make it, we just need to engineer a stronger structure, and this doesn't increase it's mass.

So imagine a spacecraft made of a material as light as Aerogel and as strong as Titanium or Diamond.

A 1000 pound spacecraft made of this material would have such volume that it would be a LOT faster, because it would take many times less thrust to push it.

A spacecraft made of this material could be 40 km tall and travel just as fast as a modern chemical rocket, but hold a massive amount of fuel, and burn just a little bit of it to travel at these speeds.

[CraigD]

Originally Posted by Gardamorg

A good Science Fiction oriented space craft would be a super light spacecraft.

Very low mass space craft are a good idea, with an established literature. Perhaps the lowest mass of any proposed is the Starwisp, an unmanned interstellar spacecraft massing about 1 kg.

Originally Posted by Gardamorg

If we had nano assemblers we could essentially give Aerogel a nanostructure that fortifies it's strength by composing it's structure with nanotubes such as these.

Carbon materials not only promise to dramatically reduce the empty mass of spacecraft, but is already has in several designs, such as SpaceShipOne. As Gardamorg suggests, nano-materials – whether assembled by nano-robotic assemblers or other schemes – promise to allow even lower empty mass spacecraft.

Although the performance improvement possible with such materials is appreciable, it’s not extreme, because even old rockets already have a high fuel/frame+skin mass ratio. For example, the Saturn V’s first stage is 94% fuel by mass, of which 2% of the empty mass are due to its engines. So if its conventional metal frame and skin could be replaced with an advanced material massing nothing, its fuel/frame and skin would be improved to 98%/2%, a significant, but still only incremental improvement.

Originally Posted by Gardamorg

There is no limit to how strong we could make it, we just need to engineer a stronger structure, and this doesn't increase it's mass.

Although nano-materials promise to be many times stronger than conventional carbon fiber materials, which are already many times stronger than conventional metals, there maximum strength is not unlimited. They are limited by the strength of the intermolecular bond strength of the atom of which they’re made.

Originally Posted by Gardamorg

A spacecraft made of this material could be 40 km tall and travel just as fast as a modern chemical rocket, but hold a massive amount of fuel, and burn just a little bit of it to travel at these speeds.

The problem – obvious is you read the preceding quote – is that a massive amount of fuel has, well, a large mass. A rocket with a large mass needs a large thrust to lift off the Earth, or accelerate in space, which in turn requires a large thrust force, which requires a large motor power, which in turn requires burning a lot of chemical fuel. The only ways to partially escape the vicious circle of needing more fuel, which requires more thrust, which requires more fuel+oxidizer and larger motors, which requires more thrust, etc, is to increase the specific impulse of the fuel/motor system, yet keep it’s total thrusts high enough to lift the fully fueled vehicle, use a separable part of the system (lower stages, as with the Saturn V, or a carrier aircraft, as with SpaceShipOne’s White Knight), and/or get much of your reaction mass from outside the system (as with the air-breathing jet engines on White Knight) to do part of the lifting.

Simply scaling up a chemical rocket to be 40000 m tall would need more than super-strong structural material (note that 40000 m would be about 50 times taller than the tallest structure yet constructed, the to-be 818 m Dubai Tower). If shaped roughly like most rockets, it’s mass would be about 64 million times as massive as a Saturn V, the largest rocket ever launched. If it used motors similar to Saturn V’s 5 F-1 motors, the largest ever built, it would need about 320 million of them! It would need about (about 600 billion barrels) of kerosene – about equal to about 200 year of the current total world supply. That’s an awful lot of rocket motors and fuel!

Nanotechnology will, I suspect, be vital to future engineering projects of many kinds, including spaceflight. However, I don’t think a 40000 m tall chemical rocket is likely ever to be built.

[Moontanman]

I prefer the idea of super strong to super light. A space ship should be strong, if it has to be heavy to be strong I prefer strong. But if it is heavy then how do you power it?

Since we don't have warp fields to lower the mass or antimatter to fuel the space craft what should we turn to?

The Saturn Five previously mentioned had engines that ran on liquid hydrogen and liquid oxygen. It was pretty much the best chemical rockets can do, the Saturn Five had a specific impulse of 450 Isp, the old Nerva nuclear rockets had a maximum Isp of about 900, pretty good but the reactor was so heavy if negated much of the increase.

What we need is a better and lighter power supply. The gaseous core nuclear reactor engine has an Isp of over 3000 to about 5000 that is as much as 10 times as good as the Saturn five rocket. This rocket can not only be operated safely but if it massed the same as the Saturn five rocket it could launch 2 million pounds of cargo into Earth orbit in one launch! Not only that it could also fly back down on it's own exhaust and carry cargo back to earth. It would be a true space ship, no multiple throw away stages. Just one space craft capable of doing almost anything we want it to do.

[Gardamorg]

Originally Posted by Moontanman

I prefer the idea of super strong to super light. A space ship should be strong, if it has to be heavy to be strong I prefer strong. But if it is heavy then how do you power it?

Since we don't have warp fields to lower the mass or antimatter to fuel the space craft what should we turn to?

The Saturn Five previously mentioned had engines that ran on liquid hydrogen and liquid oxygen. It was pretty much the best chemical rockets can do, the Saturn Five had a specific impulse of 450 Isp, the old Nerva nuclear rockets had a maximum Isp of about 900, pretty good but the reactor was so heavy if negated much of the increase.

What we need is a better and lighter power supply. The gaseous core nuclear reactor engine has an Isp of over 3000 to about 5000 that is as much as 10 times as good as the Saturn five rocket. This rocket can not only be operated safely but if it massed the same as the Saturn five rocket it could launch 2 million pounds of cargo into Earth orbit in one launch! Not only that it could also fly back down on it's own exhaust and carry cargo back to earth. It would be a true space ship, no multiple throw away stages. Just one space craft capable of doing almost anything we want it to do.

So combine the gaseous core nuclear reactor engine with a craft that is as light as Aerogel and....

[Moontanman]

Originally Posted by Gardamorg

So combine the gaseous core nuclear reactor engine with a craft that is as light as Aerogel and....

As I said before, strenth is more important than being light weight. There comes a point where it's far more important to be strong than it is to be light.

[Gardamorg]

Originally Posted by Moontanman

As I said before, strenth is more important than being light weight. There comes a point where it's far more important to be strong than it is to be light.

Nano Assembly would allow the spacecraft to be both strong and light.

With light fuel, and a light haul/craft, the craft will zip through space, as opposed to a craft with light fuel and a heavy craft producing drag.

We wouldn't need it to be any stronger than high class titanium or diamond.

[Moontanman]

Originally Posted by Gardamorg

Nano Assembly would allow the spacecraft to be both strong and light.

With light fuel, and a light haul/craft, the craft will zip through space, as opposed to a craft with light fuel and a heavy craft producing drag.

We wouldn't need it to be any stronger than high class titanium or diamond.

First of all what do you hope to achieve by making the space craft super light? Read this link, all of it.....

BRUCE BEHRHORST ARTICLE LIST

Once you get to a certain point lowering the weight just increases the risk of failure. When the space craft is already much lighter than the fuel, engine, and payload, to go even lighter just makes it weaker with no real increase of speed or acceleration.

In space you have no drag dude, mass simply resists acceleration but the gain of a couple of percent in acceleration isn't worth the risk of failure. Hydrogen is already as light as reaction mass is going to get, the Saturn five rocket was very light in comparison to it's fuel and payload weight but it was also on the ragged edge of failure. A reusable space craft needs to be more durable than that. The Saturn five was much lighter than it should have been to make up for the small Isp of it's engines. It would be very difficult to make a space craft any lighter. It's fuel tanks weren't much more than metal balloons as it was.

You seem to have a strange idea of what strong is, diamond is not strong, it's hard, there is a difference. I can smash diamonds quite easily, titanium is strong but it will bend and deform.

[Gardamorg]

Originally Posted by Moontanman

First of all what do you hope to achieve by making the space craft super light? Read this link, all of it.....

BRUCE BEHRHORST ARTICLE LIST

Once you get to a certain point lowering the weight just increases the risk of failure. When the space craft is already much lighter than the fuel, engine, and payload, to go even lighter just makes it weaker with no real increase of speed or acceleration.

In space you have no drag dude, mass simply resists acceleration but the gain of a couple of percent in acceleration isn't worth the risk of failure. Hydrogen is already as light as reaction mass is going to get, the Saturn five rocket was very light in comparison to it's fuel and payload weight but it was also on the ragged edge of failure. A reusable space craft needs to be more durable than that. The Saturn five was much lighter than it should have been to make up for the small Isp of it's engines. It would be very difficult to make a space craft any lighter. It's fuel tanks weren't much more than metal balloons as it was.

You seem to have a strange idea of what strong is, diamond is not strong, it's hard, there is a difference. I can smash diamonds quite easily, titanium is strong but it will bend and deform.

Do you know how light Aerogel is? In space it would weigh next to nothing, you're speed wouldn't increase by percentage, but it would multiply, saying the engine and parts and all are made of this nanotube enhanced aerogel.

I could literally push a craft made of aerogel at several miles per hour with my bare hands in a vacuum, so imagine what an antimatter powered rocket engine would do to it.

Now to decrease failure we could give it shielding, such as magfields.

[Moontanman]

Originally Posted by Gardamorg

Do you know how light Aerogel is? In space it would weigh next to nothing, you're speed wouldn't increase by percentage, but it would multiply, saying the engine and parts and all are made of this nanotube enhanced aerogel.

I could literally push a craft made of aerogel at several miles per hour with my bare hands in a vacuum, so imagine what an antimatter powered rocket engine would do to it.

Now to decrease failure we could give it shielding, such as magfields.

Well then since we are just wishing with no basis in reality at all I think we should have a space craft surrounded by a warp field that negates the mass of the space craft completely and structural integrity fields that make the metal of the space craft as strong as nutronium. Oh yeah lets go with a top speed of 10,000 times the speed of light.

[Gardamorg]

Originally Posted by Moontanman

Well then since we are just wishing with no basis in reality at all I think we should have a space craft surrounded by a warp field that negates the mass of the space craft completely and structural integrity fields that make the metal of the space craft as strong as nutronium. Oh yeah lets go with a top speed of 10,000 times the speed of light.

Okay I get the point....

What were you proposing exactly?

Lighter fuel as opposed to a lighter craft?