I think the precise formulas for that stuff may need to be designed for gameplay purposes. Most space-flight-sim games have fairly-quickly recharging shields that block all damage while they're up, and a hull that's only damaged when the shields are at zero, ala Wing Commander. This seemed pretty obnoxious from a gameplay perspective, because it means that long dogfights have the potential to last forever, as any brief opening doesn't produce lasting effects.

It seems like you're only considering shields that absorb some or all damage. The Star Control serious used a variety of shields that had a variety of effects:

Yehat Terminators's Shield: (from SC1)
Summary: short-term invulnerability
Blocks all damage from normal damage sources, but can only be activated for brief periods, and uses the same pool of energy that you need to shoot. Also, certain rare damage sources can ignore this shield, including collisions with planets.

Utwig Juggernaught's Shield: (from SC2)
Summary: damage to energy conversion
Similar to the Yehat's shield, except for a few key differences. An Utwig regenerates energy whenever it would otherwise recieve damage while shielding, and this is the ONLY way it can regenerate energy. However, it does not require energy to shoot its guns. An Utwig, unlike a Yehat, cannot fire while it's shields are active. Thus, if an Utwig shields without getting hit, and runs out of energy doing so, it is permanently out of energy and can not shield ever again, though it can still use its gun and engine just fine. Again, certain rare damage sources can ignore this shield, including collisions with planets.

Lk Sanctorum's Shield: (from SC3)
Summary: disable collisions
Collisions are disabled for this ship while its shields are active. It can maintain its shields for a fair while. It's shields draw power from the same power pool as its gun. Damage sources that don't require active collisions can ignore this effect (such as a cloud of poison/acid or a boarding space maring that has already hit the ship, but deals damage gradually over time).

Ploxis Plunderer's Shield: (from SC3)
Summary: reflect and "brainwash" enemy projectiles
A bubble appears around the ship when the shield is active. Any enemy projectiles that hit this bubble bounce off without dealing damage. Furthermore, projectiles that bounce off now belong to the Ploxis and can hurt whoever fired them or another enemy. Homing missiles even home in on the ship that fired them. The Ploxis' shields draw power from the same power pool as its missile launcher. Laser weapons are not reflected, though their damage is blocked. I don't remember what (if anything) can bypass this shield.

Other shield-like effects in various SC games include generating mini-spaceships to fly between you and the enemy to physically block their fire, healing ones regular health rapidly, an aimable shield that blocks all damage from a direction of your choice, a shield that turns on automatically if you get hit and have enough energy and costs a lot of energy to turn on but stays on relatively cheaply until you manually turn it off, several means of teleporting your ship out of harms way, a teleporter that teleports hostile projectiles away from you, guardians that orbit your ship and shoot down incoming projectiles, etc.

For the game I'm currently working on (in which customizing your ship is important), my intention is to have several types of shields that vary primarily in terms of
1. Directionality: omnidirectional or forwards-only
2. Effect: reduce damage or deflect projectiles
3. When: always on, or only for brief bursts, or some in-between
4. Stength: how much damage they can prevent, or amount of deflection
6. Regen: how quickly / if / under what circumstances they recover after taking damage
7. Specialization: which types of damage/projectiles they can effect to what degree

Technical note: in real freespace an Enterprise class ship and Spaceshuttle would have the same maneuvorability. You don't have there any friction. Also normal gun or better mass driver would be a superior weapon.

They have less energy. You need energy if you want to change the movement of a body.
Oh, there is no "Enterprise class". The original Enterprise is constitution class. The refit is of constitution-refit-class.
You can see that in Star Trek VI: The Undiscovered Country, Scotty is looking at some blueprints labeled Constitution Class (Refit).

Right, that was what someone originally pointed out, the problem with that, they said, is in the game play. -- something about long drawn out battles because it left too short of a gap of when you could hit them and deal damage...

I like a lot of the original ideas where some damage penetrates no matter what... it would also be cool if you could manually choose to reroute power from another system etc...

Of course thats easier said than implimented (since if you're playing with shields your ship is sitting dead in a dog fight, non-moving targets are easy to hit!) you could make it more rpg like and have engineers that get hired, and helms men also, and the better they are, the more they cost, and the better your ship manuevers when they pilot it/engineers make smarter decisions, etc...

Or it just hit me while typing, a player could define a list of actions to be taken under certain circumstances: ex1: shields get low -> reroute power from life support to shields; ex2: hotkey1 pressed, reroute power from shields to life support...

I was giving an example, but I still thing that there's no matter how the ship weights, if you have same engine you can move at same speed with Enterprice or Shuttle.

Yeah you're right I forgot about it.

It would be neat to have arcade style combat like you describe. (Aiming to knock out certain things) of course you'd need a pilot, and someone to choose a target (and I don't mean simple aiming turning a turret left and right, I mean actually choosing a target on the enemy ship and going for it -- I suppose an auto lock with a "next target/prev target would do..." and it could all be done two handedly -- fly & op the computer, aim, use tractor beams, etc...

maybe with a mouse... who knows... that'd be cool -- oh and like someone said -- with zelda like away missions ;-)