[Spaceships] Actually GMing a world with Pseudovelocity drives?

[vicky_molokh]

Greetings, all!

I'm curious: how problematic is the actual implementation of a setting where all space drives (or at least all Inertialess drives) are Pseudovelocity drives. Specific things that I suspect would warrant special consideration:

• missiles;
• shells from 'normal' guns;
• bombs;
• AKVs;
• the whole issue of breaking/deceleration and Reversals (or whatever it is called, from SS4);
• takeoff and reentry.

Anybody has good knowledge of these issues and their interaction with PV drives?

Thanks in advance!

[David Johnston2]

Well as soon a projectile left the pseudo-velocity sphere it would be moving at the ship's real speed plus it's acceleration. So I'd recommend not using guns and only using missiles with their own pseudo-v drives (meaning they'd do no momentum damage. You'd have to rely on the warhead).

[vicky_molokh]

Originally Posted by David Johnston2

Well as soon a projectile left the pseudo-velocity sphere it would be moving at the ship's real speed plus it's acceleration. So I'd recommend not using guns and only using missiles with their own pseudo-v drives (meaning they'd do no momentum damage. You'd have to rely on the warhead).

Well, just how much does it invalidate the use of shells and missiles?

[weby]

Originally Posted by Molokh

Greetings, all!

I'm curious: how problematic is the actual implementation of a setting where all space drives (or at least all Inertialess drives) are Pseudovelocity drives. Specific things that I suspect would warrant special consideration:[*]missiles;[*]shells from 'normal' guns;[*]bombs;[*]AKVs;[*]the whole issue of breaking/deceleration and Reversals (or whatever it is called, from SS4);[*]takeoff and reentry.[/list]
Anybody has good knowledge of these issues and their interaction with PV drives?

Thanks in advance!

Basically any attack form that uses kinetic energy is useless unless it can gain that kinetic energy somehow.

Thus if the pseudovelocity drive is capable of lifting a ship to orbit, that ship could then drop a bomb and let the gravity do the stuff.

This and other acceleration issues are a good reason to not allow pseudovelocity drives to work in strong gravity wells.

If the pseudovelocity drive was usable in lifting the ship up from a gravity well, the ship could just repeat: "raise, turn off pseudovelocity, dive to gain energy" until it has way too much potential energy thus loosing one of the main reasons in having psedovelocity drives. (no C-fractional strikes of starships on planets)

Originally Posted by Molokh

Well, just how much does it invalidate the use of shells and missiles?

In most likely scenarios the kinetic energy of a projectile is thus neglible, whereas in "more realistic" games kinetic energy is a true killer.

As said a missile with a Pseudo velocity drive is still fully usable if it can carry a warhead capable of damaging ships.

Ofcourse if the pseudovelocy drives have low acceleration then a short range kinetic missile using a non pseudovelocity drive would still work.

In general a raw pseudovelocity drive is most gameable if it is deep space use only or alternatively you say "normal physics does not work wih pseudovelocity drives" and wave away the problems.

[David Johnston2]

Originally Posted by Molokh

Well, just how much does it invalidate the use of shells and missiles?

"Our weapons fire at the speed of light and our engines move us at faster than the speed of light."

"So?"

"We just shot our own ship down."

Unless the projectiles have their own pseudovelocity propulsion, the ship will collide with them if it is firing forward at any speed worth mentioning. It could I suppose launch them rearward or to the sides.

[Ulzgoroth]

Or you could change your pseudovelocity. Make it 'sticky'. Objects moving with pseudovelocity retain pseudo-inertia even if they have no active pseudovelocity drive. Optionally, it could bleed off slowly enough not to pose a problem for your projectile weapons.

This is not going to negate the fact that pseudovelocity collisions are deeply weird. Two objects can slam into each other with a near-c closing pseudovelocity while their 'real' velocities are pointing away from each other...what happens?

This could be negated if you make the pseudovelocity system kill normal momentum relative to a locally privileged reference frame. Yes, physics is suddenly very upset with you, but at least you no longer have to know your target's native velocity before you can shoot them...

[thalassogen]

We are using (some kind of) pseudo-velocity drives in our GURPS Firefly game. The grav drive unit "just reduces the inertia of the ship" (as Serenity RPG states) by 99% for "forward motion" only. The real propulsion systems are fusion rockets/torches. While the grav drive is activated the rockets are 100 times as efficient (sAcc * 100, mps * 100). This affects only speed and travel time (as long as the drive is active), not kinetic/collision damage (that is just the 1% of real mps expended). Shutting down the drive immediately drops speed back to the real 1%.

Hope that helps.

EDIT: during fights grav drives are normally switched off, but switching them on is commonly used to escape; in general we try to avoid fights as they are too expensive

[Timolas]

Although I am using a pseudovelocity drive in my campaign, it does cause a number of serious headaches that I'm doing my best not to poke at too much...

Weapons are definitely a great big problem. Simple impulsive guns and missiles are useless, I would suggest, or at the very least, extremely limited. You'd have to keep a very clear idea of your intrinsic velocity, and target accordingly - perhaps jockeying for position so that when you finally shoot, the round's intrinsic vector aligns correctly with the target's location in time and space.

Lasers on the other hand do my head in - as you are translating your position without accelerating, I think that means you run smack bang into the situation that started Einstein off on that whole Relativity thang. Consider - using your nifty pseudovelocity drive you are flitting along just shy of lightspeed, and then you fire your multi megajoule laser cannon to forward... whaddya see? Does the laser pulse crawl slowly out of the barrel and inch away from you? Relativity says no.... but does it still even apply?

Of course if this thing is also your FTL drive then the answer is probably no... But then what happens if you try firing your laser while you are warping just slightly faster than lightspeed? Does your weapon blow up?

There are also more mundane problems - linked to the comment about hovering in a gravity well and building up an enormous KE straight down. Hoverbombs would be the ultimate weapon; and worst of all you daren't defuse them!

This issue of intrinsic velocity has a big impact on navigation as well. Supposing you are in low Earth orbit and then you warp off to Mars. Okey dokey, no problem. But then you settle into Martian orbit, switch off your drive, and realize that you have the same velocity vector you had in Earth's orbit - you'll need tens of miles per sec of delta v to sort things out. Or you can try hovering on the warp drive while Mars' gravity accelerates you to a sensible velocity ... But having tried it in Orbiter with the warp drive MFD, let me attest that it will take hours of painstaking manoeuvres hunting around for the sweet spot where the local gravity is doing the correct job for you.

So clearly there are some problems. If you haven't already, I'd recommend searching the web for 2300AD sites. That game is very hard SF, and it's Stutterwarp drive is one of the most carefully thought out pseudovelocity drives going. They bury what happens close to lightspeed in a blur of quantum uncertainty (very wise!), limit shipboard projectiles to missiles also using Stutterwarp, and combat to well below c (so lasers are okay). And finally big gravity wells like Jupiter are important navigational features, as ships can dive close to them to curve their intrinsic velocity into something useful, without needing to burn any delta v.

So, yes there are headaches with a pseudovelocity drive, but there are potentially reasonable sounding explanations for them all out there as well. And the other things you gain may make it all worth it.

For one thing - pseudovelocity is the best explanation I've heard for Star Wars and its imitators type spacecraft behaviour. Far better and more consistent with what we see on screen than the argument that these ships must be capable of thousands of g of acceleration... and yet for some reason all choose to spend most of their time doing nothing of the sort. If Luke was feeling pressured by Darth Vader as they roared down that trench - why didn't he just execute a few thousand g turns, lose the bad guys, and get back to shooting that exhaust port? Hmmm?

[Fred Brackin]

Originally Posted by Molokh

Greetings, all!

I'm curious: how problematic is the actual implementation of a setting where all space drives (or at least all Inertialess drives) are Pseudovelocity drives. Specific things that I suspect would warrant special consideration:[*]missiles;[*]shells from 'normal' guns;[*]bombs;[*]AKVs;[*]the whole issue of breaking/deceleration and Reversals (or whatever it is called, from SS4);[*]takeoff and reentry.[/list]
Anybody has good knowledge of these issues and their interaction with PV drives?

I used a pseudovelocity drive in 2 campaigns and found it far, far simpler than normal accleration and deceleration in combat.

The rules were:

There is no energy transfer between colliding bodies while even one of the two has the PV drive is on.

If two PV bodies do collide they stop but regular kinetic weapons may fire without PV effects. A standard weapon was a PV missile with a SEFOP warhead.

I also invented a "sustainer coil" that was cheap enough to put into shells and kept the projectile in PV for approx. 1 second after firing. Effective pseudovelocity (and therefore range) was roughly 1000x normal atmospheric and guns were very common weapons. I imposed TS-like heat restrictions on beam weapons.

Maneuvering was just like in atmosphere and special vaccuum-only maneuvers were not allowed.

<shrug> It was easy and I have no intention of running space combat with "normal" drives in my own campaigns. KE weapons in those situations are a major PITA.

[capnq]

Not being familiar with the [Spaceships] series myself, could someone who is familiar with both comment on whether GURPS Lensman's Technology chapter would be a useful resource on this question? (Specifically, its treatment of inertialess drives.)