[Spaceships] Homebrew - Alternate Contragrav
 

Another new design switch suggestion for GURPS Spaceships:
Force Screen Variant

Gravity Screen: Provides no DR (although it does affect Tractor Beams[1] and Graviton Guns[2]) but instead lessens the gravitational effect of outside masses on the ship. Read "dDR" as the divisor applied to a planet's gravity to determine its effect on the ship*. You can have both a gravity screen and another force screen.

* The ship's mass remains the same however, so the rate of ascent in a vertical take-off would be A-G/dDR where A is the spacecraft’s drive acceleration in G, G is the world’s gravity and dDR is the gravity divisor. To find the effective escape velocity of planet while using the screen, divide its natural escape velocity by the square root of the dDR. (FWIW: The solar escape velocity from a planet's orbit is that planet's mean orbital velocity times sqrt(2).)

Example: An SM+10 (10,000 ton) ship with a gravity screen installed has an effective weight of 66 2/3 tons on a 1G planet. If that planet is Earth, its effective Ve would be 6.96/sqrt(150)=0.568 mps.

While not a defensive system, the gravity screen does have an effect on gravity-based weapons:

1. Tractor Beams: The force applied to a target with a gravity screen is divided by the screen's dDR.
2. Graviton Guns: Gravity screens protect with 1/10 dDR.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Should it be a high-powered component?

(Not with my books, so I don't remember whether that's already true of force screens.)

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Yes, force screens are already high-powered components.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Why is it a force screen variant? It's just a contragravity variant, and there's no reason the effect would scale with the size of the ship.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

its a little of both: it protects against a class of weapons and counter-acts gravity. In some universes its a very effective shield.

As for why it scales in size, the generator seems to effect things not based on the mass of what it effects, but a large area determined by the size of the generator.

That said, In a setting with this, I'd probably get a 1/3 or 1/10 one for my ship, because there is very little punishment for going undersized unless graviton beams are a dime a dozen. Its very effective at any size.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

FWIW, I worked out the effect of the Gravity screen on effective escape velocities (and thus orbital ones). Multiply the velocity by the modifier below.
For SM+16 and greater, divide the modifier for size-12 by 10. An important feature here is that this make geosynchronous orbits at a lower altitude possible. (I haven't worked out the table for that yet. )

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Against a weapon nobody would use considering that this would be a standard propulsion system if available. Actually I'd suggest making it effective against missiles as well, but not beam weapons.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Just curious, but what would be your in game reasoning / techno-babble as light is just as effected by gravity as matter?

Re: [Spaceships] Homebrew - Alternate Contragrav
 

Well, sort of. Gravity is generally more relevant to slow objects. A lot of 'gravity'-based drive systems are likely to have boundary conditions that would be problematic for low velocity projectiles, though I'm not sure why this particular system would.

Re: [Spaceships] Homebrew - Alternate Contragrav
 

No, not just as. My explanation is that the higher the mass the greater the effect.