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Grav Vehicles


How do you guys play grav engines? Can they work in deep space? How far out from a planet can they go? Or, are they not reliant on any local gravity field, generating their own field? If the latter is the case then how do grav plates work, generating gravity when there is no field to work agaist?
So far, in the CT games I've played, Grav vehicles can make it to orbit, but anything beyond that they loose power. Getting to orbit is a streach too, as the decreasing gravity leads to decreasing power. Once they hit far orbit, any further and they better hope there's a search and rescue nearby.
I have very variant grave engines.

I have contragrav which "nullifies" the weight of the vessel - then I use jets to actually push them arround.

the End result is that I'm changing my vehicle design rules to something closer to GURPS.

Some other fun effects are that Grav vehicles are much more subject to recoil/impulse than land vehicles. So they tend to have energy weapons. But if you shoot at a grav tank with your rifle, you still ruin it's aim!

Other effects, Air rafts et al are good for ship->ground - but their accell is too low to be useful out from the planet. If they have jets rather than rockets, they can;t perform out of the atmosphere.
Originally posted by The Mink:
I have very variant grave engines.

I have contragrav which "nullifies" the weight of the vessel - then I use jets to actually push them arround.
Maybe not terribly variant, this is actually very like TNE's design rules, and I think (but it was ages ago so I may be wrong) MegaTraveller, so go for it. It's a better explanation imo.

Anybody with an official CT or T20 explanation for the way grav vehicles move?

I used to imagine (way back in my early CT days) that the contra-grav nullified the effects (mass of the vehicle) of the local gravity while generating an equal artificial gravity pull on the vehicle's contents. By shifting the vehicle's center of real mass around the contra-grav's center of nullified mass you would produce your desired acceleration at a rate in G's up to the local gravity, while the vehicle's body provided just enough lift, augmented at low speeds and altitude by small fans, to keep you from smacking the ground (falling and then catching itself, in a controlled manner, much like walking). If you 'fly' far enough, fast enough, you can even reach escape velocity for a low orbit (ala the air-rafts long trip to orbit). Not too sure it still seems plausible to me though ;)
I always assume that grav pods create an "illusion" of negative mass approximately the same size as the vehicle. This is repelled by planetary gravity, and depending on how it is adjusted the vehicle climbs, dives,or can even move laterally.

(Best of all, unlike Mink's cavourite, this isn't impossible. I stole it from Dr Robert Forward: look in his science-for-SF-writers book, Indistinguishable From Magic. I am using the technique he calls "dragging the metric")

The performance of these vehicles is porportional to local planetary gravity. Up to low orbit it still has 90% capability, but at orbital velocity a very small change in velocity needs a lot of energy (at 7 km/sec it takes 35 MJ to change the velocity of a 5 ton vehicle by 1 m/s). Even with a big engine it maneuvers like a 35' catamaran with a single trolling motor: you can get there, but ya gotta be patient.

In deep space it will work against solar gravity, but at planetary distances that is very weak. There is a similar problem with a low gravity moon or asteroid where a grav vehicle is very sluggish.
i also like grav bikes and scooters.....wide open at 9,000 ft.....down a canyon.....full of boulders......wow.....being chased by Vargr Cops.....whata rush!!!! :D
I always figured they worked by "redirecting" local gravity, so that (so far as the vehicle is concerned) gravity sometimes points up, forwards, sideways... Grav vehicles IMTU (CT) have a hull grid similar to the Jump Grid of a starship, so the change in gravity affects the engines and hull, but not the poor saps inside...
The motors also have the ability to "focus" the field, making it stronger (within limits imposed by the published specs of the vehicle) and allowing for multi-G accelerations. They produce a barely audible hum when operating normally, which rises to a really annoying high-pitched whine when forced to perform high-G maneuvers.
Any grav vehicle can operate in space, but since they need a gravity field to work with, their performance degrades rapidly. At Low Orbit the max acceleration is equal to the planet's surface gravity, and in Far Orbit it has dropped to a tenth of that.
Within an atmosphere (or within what would be the atmosphere if it wasn't a vacuum world) the acceleration is anything up to ten times the world's surface gravity, but not more than the vehicle is built to withstand.
I have always thought that the two (grav plates and grav vehicles) were related. And, since grav plates generate a 1G gravity field regardless of the stresses placed upon the vessel, and regardless of any local gravity field, that grav vehicles worked the same.

Grav Plates produce thrust, they are 'pulling' you down at 1G. The 'need' for grav plates to exceed this is limited, so they don't and have it hard-wired to not generate more gravity than is desired.

Grav Engines for vechiles work by producing gravity based thrust as well. They either push or pull depending on the vehicle design. They work independent of local gravity fields (thus low G worlds can have grav tanks on them such as high G worlds can. This means that not only are the grav engines being used to move the vehicle around regardless of it's location but that it's also generating a grav-plate like field for the occupants (it has to or they're jelly). This also means that grav engines can work in deep space.

This links into the question of how do maneuver drives work? The reactionless thrust thing hasn't really been explained and is 'accepted' as a magical thing (magic in a hard-science way). But, if it's gravity based -- the maneuver plates 'push' generating thrust up to they're G limit; then all these are fully related.

The reason I began thinking about this is that I had the thought to use the vehicle design rules to create torpedoes (i.e. giant missiles). Then I got the part of thrust....what to use? And thought about how grav engines would work. And, the rules as given, give the ability to generate unmanned vechiles that can travel at incredible accelerations (say 100+G).

just a few thoughts....
quick asside, there used to be a 6G limit at one stage. Is this still inplace or has it gone the way of the manual typewriter?

(ie were man drives/grav drives unable to "push" harder than 6G)
I thought that artificial gravity and contra gravity would be similar, but not just reverse of each other. It would make sense to me if it took a lot less energy to enhance a gravity wave (producing artificial gravity) than to reverse it. I like the "negative mass" concept. It would also answer another question I have had about grav propultion; can contra grav generators be armored?

The answer would have a significant effect on grav vehicle design. If the grav thruster produces it's own 'contra grav' thrust, then any armor protecting it would be pushed on with the same thrust? If the answer is yes, then combat grav vehicles would be ground hugging to protect the vulnerable grav thrusters. But if you use the negative mass concept, then the field generators could be located inside an armored hull and there would be no problem with high flying grav tanks.

Anyone have thoughts on armoring grav modules?

No, it's still there. Maneuver Drives are rated from 1G to 6G. But I've always thought of this as a limit of the Grav Plate techonlogy to handle the stresses of accelleration and not a limit of the maneuver drives themselves.

But, IMO, having a limit to accelleration of 600m/s is unrealistic. Hell, even a C-5 model rocket engine will accellerate at nearly 10G. The limiting factor is the amount of force, but the duration of burn as associtated with the specific impulse of the rocket.
Grav plates are wierd. I treat them as magic, and move on because the grav field they create is the illusion of tens of thousands of tons mass, without the inertia. Theoretically, if you roll over so you can look "up" at a planet, you should be drawn in at about, oh, 10,000 m/s2.

And attempting to explain congragrav and grav plates as one phenomena is pretty useless: the grav plates are at least 4-5 orders of magnitude more difficult to do. And trying to explain by talking about gravity waves just reveals you never studied field theory. Deck plates, not jump drives, is the real fantasy element in traveler.

Contra grav is comprehenible. For example, you can "drag the metric" to create a negative gravity field of about -5,000 Kg (without the 5 tons of inertia) that is repelled by the planetary gravity a little bit harder than a 4,000 Kg structure and payload is attracted, so the air-raft is lifted in the air. Of course, as we currently understand it a -1 ton grav pod will require control of a black-hole to build and contain a couple of gigatons of potential energy, but that's just engineering.

Maneuver Drive
Back in the seventies and eighties, I treated this as a Davis Mechanics device. Davis mechanics are a correction to the 3rd derivative of Newtons laws that allows angular momentum to be converted to linear momentum. These are real, from the 1960s, never proven but never disproven equations. (If you can convert the momentum, change in kinetic energy becomes minor if non-trivial.)

An alternative would be a Woodward drive based on Machs Principle. NASA has been looking into this, but I think it is going to require a lot more energy to be useful than people expect.
And from NASA's dying Breakthrough Propulson Physics office:
The entire concept of gravity is, I think, pretty much glossed over. You can install 'couches' into your small craft (i.e. gravity couches -- I don't think they mean sofas) which tends to give the implicit understanding grav-plates are not installed; but the effects of travelling at 6G are not addressed at all.

The book talks about grav tanks being very nimble fighters. We, at our tech7/8 are already capable of producing aircraft that can be flown with accellerative forces that are damaging to the pilots. So in this instance the gravity genererated for thrust and maneuvering must also generate gravity for the occupants.

It's an interesting concept on how it works.
1. via a gravity generating device
that acts in reaction to the local
gravity field?
2. creating of a gravity bubble that
both creates enough gravity to give
the crafta null gravity field (i.e.
make it gravitationally boyant)
*and* profide thrust via generation
of internal/independant gravity

If it is in the nature of gravity repulsion, then the gravatic device requires a local gravity field to react against. Also, it is not inherent that inertial gravitational control is part of this propulsion method. In that case, care must be taken for the survivale of the crew eitehr through limiting the performance of the craft or installion of an internal inertial dampening system. If this is in the form of a Grav-Plate as in the starships, then is there a 6-G (60m/s) limit on accelleration?

If gravatics is the second method then a local gravity field is not required for operation of the gravatics device. Also, the welfare and survivability of the crew are counted for as the gravity environment created is all encompassing of the vehicle in question. In fact, this method seems to be more akin to the 'flying saucer' performace capability in modern UFO mythology.

Vargrs have Cops???

I thought they were all pirates....

Originally posted by trader jim:
i also like grav bikes and scooters.....wide open at 9,000 ft.....down a canyon.....full of boulders......wow.....being chased by Vargr Cops.....whata rush!!!! :D
This may be true in some later versions, but Classic traveller draws a definate difference. 1st edition Striker gives design rules for grav that are incompatable with maneuver drives.
MT makes it clear that Gravitics are a thrust-based suspension; they are, in fact, gravitic thrusters which require a gravity well to operate within. (Matches the CT-Era Striker, BTW.) Early T-plates are similar in limit. TL 11+ plates can operate in system with full efficiency; MT never asserts a limit.