Science Fun With A Scifi Concept...

[Spacescifi]

Full disclaimer... I am steering away from direct gravity manipulation with scifi SSTOs.

In favor of air manipulation. Because air manipulation is more obvious and thus looks and seems less fake... and it allows for lifting large loads without propellant usage since the air IS the propellant. Once the air thins out then you switch to rockets or external pulse pusher plate propulsion.

 

Scifi Tech: Acceleration screens. A glowing force-screen wall issuing from a port vent lining the inner walls of an open shaft or hollow cyinder... often multiple ones.

So what you have is an open shaft or cylinder filled with multiple screens inside so that the opening appears to glow solid white.

 

Function: The forcefield screen walls can suck any mass in contact with the screen through it at a high flow rate, add multiple ones in a single shaft or cylinder and you increase thrust since for every reaction there is a reaction.

Obviously the wider or longer your open shaft and OR the more force-screens  are installed, the more air that can be grabbed for higher overall thrust.

Uses: Flight obviously. Also a good mass driver.. especially with rate of fire. Just shoot through a screen and quadruple your projectile exit velocity.

What other uses could this have that I may have overlooked?

Edited August 25, 2022 by Spacescifi

[kerbiloid]

Air ain't a propellant, it's an inert working fluid. It doesn't provide energy.

[sevenperforce]

1 hour ago, Spacescifi said:

Function: The forcefield screen walls can suck any mass in contact with the screen through it at a high flow rate, add multiple ones in a single shaft or cylinder and you increase thrust since for every reaction there is a reaction.

So, propellers.

[Spacescifi]

2 minutes ago, sevenperforce said:

So, propellers.

More like a forcefield screen with uber vacuum suction.

 

Can toggle it on or off.

 

Basically I finally figured out a way to launch large heavy SSTOs without propellant.

 

Even less propellant would be used if it was a project orion using pure fusion bombs which do not require the critical mass that nukes do.

 

Could weigh less than a normal orion too.

 

Could use rocketry of course, but I love orion more.... since it is so much more uber and easuer to control than an uber rocket too.

[Shpaget]

4 hours ago, sevenperforce said:

So, propellers.

This. Put it in a tube and it's a ducted fan.

Add a few more similar, a few a bit different ones and some sprinklers and you get yourself a jet engine.

Then research a bit about existing and proposed air breathing engines and their role in getting to orbit.

[Codraroll]

19 hours ago, Spacescifi said:

Once the air thins out then you switch to rockets or external pulse pusher plate propulsion.

Have we still not succeeded in explaining to you what a horribad idea pusher plates are in atmosphere? One word: shockwaves. You really don't want to go about with explosive propulsion in a medium that can transfer the explosive force to the entirety of your craft.

But I digress. The problem here is that  "the air thins" is an event that will happen quite early in flight, as the rocket goes up first and then starts going fast sideways, because you don't want to go fast in an atmosphere for drag-related reasons. So a spacecraft's ascent profile tends to seek thin air before it starts building up the speed required to stay in orbit. In other words, the air-breathing engines will not be of use for more than the first short leg of the flight, but require their own wiring and plumbing and take up weight on the craft all the same. That's a particularly bad drawback on an SSTO. They're helpful for the first minute or so after take-off, and from there on they are dead weight. And you still need a different set of engines to actually take you to orbit.

You might be able to use the air-breathing engines as a first stage of a rocket, though. I think the first stage of Saturn V only flew in the lower parts of the atmosphere. But that means disconnecting that entire stage from the spacecraft after they have expended their usefulness.

Edited August 25, 2022 by Codraroll

[Terwin]

11 hours ago, Spacescifi said:

In favor of air manipulation. Because air manipulation is more obvious and thus looks and seems less fake... and it allows for lifting large loads without propellant usage since the air IS the propellant. Once the air thins out then you switch to rockets or external pulse pusher plate propulsion.

 

Scifi Tech: Acceleration screens. A glowing force-screen wall issuing from a port vent lining the inner walls of an open shaft or hollow cyinder... often multiple ones.

So what you have is an open shaft or cylinder filled with multiple screens inside so that the opening appears to glow solid white.

Nope, Aerokinesis is very powerful if you have a very large area, if you try to use a small area you run into problems like the speed of sound and creating a vacuum above your intake so that it stops doing anything useful. 

If you want aerokinesis to work for a heavier than air craft(lighter than air craft are awful for space travel in every way, so yes you do), then your field *must* cover an area many times the area of your vessel.  This means obviously magi-tech self-contained force-fields spanning hundreds of meters around your 10m ship(or several km around your 100m battleship), not magical ducted fans. 

 

You will not get a useful SSTO with a fuel ratio smaller than the SpaceX super-heavy that will not make a physicist roll their eyes.

Just go the star trek route and make it a flying van with magical engines bolted onto the sides, and be done with it.

[kerbiloid]

A huge, wide, force-field

Spoiler

trampoline.

 

Upd.
Btw...

The longer the craft is falling, the more the capacitor is charging. Every next push stronger than the previous one.
(And a pusher plate on the craft).

[Spacescifi]

2 hours ago, Terwin said:

Nope, Aerokinesis is very powerful if you have a very large area, if you try to use a small area you run into problems like the speed of sound and creating a vacuum above your intake so that it stops doing anything useful. 

If you want aerokinesis to work for a heavier than air craft(lighter than air craft are awful for space travel in every way, so yes you do), then your field *must* cover an area many times the area of your vessel.  This means obviously magi-tech self-contained force-fields spanning hundreds of meters around your 10m ship(or several km around your 100m battleship), not magical ducted fans. 

 

You will not get a useful SSTO with a fuel ratio smaller than the SpaceX super-heavy that will not make a physicist roll their eyes.

Just go the star trek route and make it a flying van with magical engines bolted onto the sides, and be done with it.

 

Good point and taken.

[Vanamonde]

Isn't this a flying Red October? 

If you're going to be grabbing air and throwing it around with forcefields, evolution has already put a lot of work into methods. It seems to me that you'd want to look at the ways fish use fins and imitate those motions with your force fields. 

Or perhaps I am misunderstanding the concept. 

[Pixophir]

Fins (of fish) in all their forms are extremely versatile and efficient instruments of propulsion and attitude control. But the density of the environment they work in is the same as the density of the bodies they are attached to.

So that won't bring a fish to space. Mammals, maybe, if there's a Star Trek spaceship at hand motivated to save the earth, or Dolphin's urge to say good bye is strong enough.

Edited August 25, 2022 by Pixophir

[Vanamonde]

I was thinking of fin-like motions but with force fields (as long as we're presuming they exist) projected over very large areas to make up for the lesser density of air. This preserves the original concept of using the air itself as reaction mass. 

[Spacescifi]

4 hours ago, Vanamonde said:

Isn't this a flying Red October? 

If you're going to be grabbing air and throwing it around with forcefields, evolution has already put a lot of work into methods. It seems to me that you'd want to look at the ways fish use fins and imitate those motions with your force fields. 

Or perhaps I am misunderstanding the concept. 

 

I already looked at helicopter blades made of forcefield in another thread.

 

The concept actually works if you ignore how in the world you make propeller shaped forcefield blades.

 

I decided against it.

 

Best to just go with what I like

[kerbiloid]

The problen is that the uniform atmosphere is just 8 km thick, so a rocket-shaped rocket has just 10 t of air per1 m₂ of cross-section area above.

So, its usage makes sense only for very small rockets.

Or you can ionize air in several kilometer wide area with lightnings from Tesla tower, and use a magnetic scoop on the rocket top to pull it inside and throw behind.

[sevenperforce]

17 hours ago, Spacescifi said:

17 hours ago, sevenperforce said:

So, propellers.

More like a forcefield screen with uber vacuum suction.

Can toggle it on or off.

So, propellers, which famously can be turned on or off. 

11 hours ago, Codraroll said:

You might be able to use the air-breathing engines as a first stage of a rocket, though. I think the first stage of Saturn V only flew in the lower parts of the atmosphere. But that means disconnecting that entire stage from the spacecraft after they have expended their usefulness.

The first stage of the Saturn V burned out at an altitude of 68 km and a speed of 2.76 km/s, which is quite high and quite fast. In comparison, the Skylon design, with its airbreathing SABRE engine, would close its intakes and switch to pure rocket propulsion at an altitude of 28.5 km and a velocity of 1.76 km/s. 

These "uber vacuum suction" propellers are still essentially airbreathing engines, even if they're not burning the air with fuel the way that a turbojet, ramjet, scramjet, or SABRE design would. They are using air as their reaction mass. Because they are using air as their reaction mass, their maximum attainable speed is limited by their exhaust velocity, as I will explain below.

19 hours ago, Spacescifi said:

The forcefield screen walls can suck any mass in contact with the screen through it at a high flow rate, add multiple ones in a single shaft or cylinder and you increase thrust since for every reaction there is a reaction.

Obviously the wider or longer your open shaft and OR the more force-screens  are installed, the more air that can be grabbed for higher overall thrust.

Let's think about this.

Apart from gravity, there is no such thing as suction in the universe; only pressure and the absence thereof. If you have a high-pressure region and a low-pressure region, then fluid in the high-pressure region will flow into the low-pressure region at a mass flow rate limited by the difference in pressure. The maximum flow rate for a given high-pressure region is achieved with incompressible fluids and an outlet pressure of zero (e.g., vacuum). Let's assume that these uber vacuum suction propellers (I'll call them uberprops for short) are so efficient that the flow can be treated as incompressible. Thus the maximum mass flow rate per intake unit area can be calculated directly from the inlet pressure and fluid density.

At STP, the atmospheric pressure is the familiar 101.325 kPa. To find the flow speed across the inlet, you simply use the dynamic pressure equation for an incompressible fluid and set dynamic and static pressure equal. The dynamic pressure equation is derived by merely taking the kinetic energy equation KE = m*v²/2 and dividing both sides by volume, yielding P_D = ρ*v²/2. Yes, pressure is the same as kinetic energy divided by volume, which means energy density has units of pressure. Pretty cool, huh?

Solving for v gives us v = sqrt(2*P_D/ρ).

So if 101.325 kPa of static pressure is perfectly converted into 101.325 kPa of dynamic pressure in a fluid with a density of 1.28 kg per cubic meter (that's atmospheric density at STP), then the inlet flow rate will be 398 m/s. Multiply this by the density of air (still 1.28 kg per cubic meter) and you derive a maximum propellant mass flow of 509 kg/sec for each square meter of inlet. That air is then yeeted out the back end of the uberprop at some exhaust velocity v_e. Let's say these uberprops produce similar thrust per unit area to an RS-25 SSME. The RS-25 at sea level produces 1.86 MN of thrust with a 2.4-meter nozzle, so in order to match that, the air will need to be ejected at approximately 808 m/s. Each square meter of uberprop produces 411 kN.

What happens after liftoff? Well, at first, good things happen. The mass flow rate at the inlet is no longer 509 kg/s; the airflow into your inlet adds to the amount of mass you can work with, giving you more thrust. At 50 m/s, you're scooping up 64 kg of extra air per second, so your mass flow is 573 kg/s. The air is entering at 50 m/s and exiting at 808 m/s, a net difference of 758 m/s, and your thrust has gone up to 434 kN. Nice.

At 100 m/s, your mass flow is 637 kg/s and your net exhaust velocity is 708 m/s so your thrust is 451 kN.

At 250 m/s, your mass flow is 829 kg/s and your net exhaust velocity is 558 m/s so your thrust is 463 kN.

But then a funny thing starts to happen.

At 400 m/s, your mass flow is 1021 kg/s and your net exhaust velocity is 408 m/s so your thrust is 416kN.

At 500 m/s, your mass flow is 1149 kg/s and your net exhaust velocity is 308 m/s so your thrust is 354 kN.

At 600 m/s, your mass flow is 1277 kg/s and your net exhaust velocity is 208 m/s so your thrust is 266 kN.

An airbreathing engine will initially have higher thrust as the flow rate of air increases, but then thrust will start to drop off as the forward airspeed approaches the exhaust velocity. A vehicle powered by an airbreathing engine cannot ever exceed its own exhaust velocity. This effect gets even worse because as you climb, the static inlet pressure and air density both start to drop. And this is before we even deal with the drag on the vehicle or heating effects.

On 8/24/2022 at 11:18 PM, Spacescifi said:

Even less propellant would be used if it was a project orion using pure fusion bombs which do not require the critical mass that nukes do.

As we have mentioned a thousand times previously, if you have pure fusion bombs without a minimum critical mass then you no longer need a pusher-plate design.

On 8/24/2022 at 11:18 PM, Spacescifi said:

I love orion more.... since it is so much more uber and easuer to control than an uber rocket too.

Orion has its advantages if you (a) are intent on launching massive payloads, (b) don't care about fallout, and (c) haven't mastered anything above thermonuclear fusion.

But "easier to control" has never been one of those advantages.