World Gravity
- Thread starter magmagmag
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far-trader
SOC-14 10K
If I recall correctly the answer is... maybe 
The basic MT rules (like CT) imply that no you could not lift off unless your maneuver thrusters were more than the surface gravity.
However the Starship Operator's Manual allowed a workaround. In that you could briefly overpower the maneuver thrusters by up to 400% so a 1G rated ship could for a short time perform as if it had 4G. This short time was enough to land or take off, not enough to count in combat. However I'm not sure how official that rule is.
Maybe somebody else knows a clear statement of the rule in the core MT books that gets around the surface gravity. One possibly confusing issue is the Travel to Orbit table (pg 92 MT Imperial Encyclopedia - US version) that implies a 1G can make orbit from any size world. Classic Traveller had a very similar table, but it also had rules that made it clear that local gravity influenced ships and had to be subtracted from maneuver rating before calculating actual Gs.
The basic MT rules (like CT) imply that no you could not lift off unless your maneuver thrusters were more than the surface gravity.
However the Starship Operator's Manual allowed a workaround. In that you could briefly overpower the maneuver thrusters by up to 400% so a 1G rated ship could for a short time perform as if it had 4G. This short time was enough to land or take off, not enough to count in combat. However I'm not sure how official that rule is.
Maybe somebody else knows a clear statement of the rule in the core MT books that gets around the surface gravity. One possibly confusing issue is the Travel to Orbit table (pg 92 MT Imperial Encyclopedia - US version) that implies a 1G can make orbit from any size world. Classic Traveller had a very similar table, but it also had rules that made it clear that local gravity influenced ships and had to be subtracted from maneuver rating before calculating actual Gs.
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Well, under CT, MG rules you couldn't. Although, I can think of one workaround. If you have a ship in MT with an airframe hull and you are on a planet with an atmosphere of thin or better you could use a runway to take off. Once airborne, constant acceleration would enable you to reach orbit.
The problem with airframe lift is getting both enough speed and enough altitude to beak out. given typical aircfraft T/W ratios run 0.8-1.2... an airframe should be able to fly given a standard atmo...
TNE's (and t4's) solution was "Contragrav" which negated 98% of the ship's weight (but not mass), the reducing the effective gravity to 2%; the ramifications include being able to take off from earth with high performance ion-plasma drives... the downforce causes roughly 0.2 m/s/s loss, so a 0.3 m/s/s drive (0.03G) should be able to get off world, and ships can hide in GG's to any depth above crush with only 1-2 G's... since 1G and Contragrav means anything short of 50G doesn't cancel your drive... It also means being able to cross a much lower point of no return around black holes and neutron stars, roughly 1/7th the distance from source.
MT's 400% is canonical for MT, optional elsewhere.
TNE's (and t4's) solution was "Contragrav" which negated 98% of the ship's weight (but not mass), the reducing the effective gravity to 2%; the ramifications include being able to take off from earth with high performance ion-plasma drives... the downforce causes roughly 0.2 m/s/s loss, so a 0.3 m/s/s drive (0.03G) should be able to get off world, and ships can hide in GG's to any depth above crush with only 1-2 G's... since 1G and Contragrav means anything short of 50G doesn't cancel your drive... It also means being able to cross a much lower point of no return around black holes and neutron stars, roughly 1/7th the distance from source.
MT's 400% is canonical for MT, optional elsewhere.
? Only the best military fighters have T/W ratio approaching even 1.0 and only for a limited time at that. Speed and altitude is no problem with constant accel & non-air breathing engine. But, the 400% is a much better option altogether. I used in MT but did't know it was cannon. Good to know.
Supplement Four
SOC-14 5K
Interesting question. I remember that the 400% was only for a short period--dunno if it would last 10 min or so to orbit.
far-trader
SOC-14 10K
Presuming of course a rolling chassis and sufficient hard runway. Neither of which is really addressed in any rules. They might be presumed in a setting with Airframe spacecraft, but funny thing there is CT and MT which need it for some worlds don't have it, and TNE which has it doesn't need it.
Really the solution is simple. In CT and MT ships with just 1G don't land on worlds of 1G or more gravity. They use orbital facilities or small craft.
I seem to recall MGT does have a rule (optional?) for eking out more performance. I don't think it's 400% though.
It wouldn't need 400% the whole way though, just enough to get off the ground and gain some speed. Heck even a fraction over 100% would be sufficient if maintained long enough. 110% of a 1G drive (1.1G) will get off a 1G world with a net thrust of 0.1G. It'll be a slow climb to start with but speed will build quickly. So if one wants to permit overpowering drives (I wouldn't) then you can just recalculate the time to orbit for the net thrust with what ever overpower you're comfortable with. Just realize such overpower has other ramifications.
I didn't know (or forgot) that the Starship Operator's Manual time to orbit was calculated on 400%. I vaguely recall them looking wrong though. That could be it. Thanks for the info aramis.
Personally, an idea I've been mulling over for ages is scrapping the time to orbit by thrust data since I'm too lazy to make the proper calcs for all situations of thrust, config, gravity, and atmo. My idea is to just use the rule of thumb CT did for Air/Rafts, 1 hour per world size to reach orbit or land. Realistic? No. Easy? Yes. Plausible enough too for my old favorite CT reaction thruster fusion engines (not to be used too close to a planet) so the ship lifts on it's own anti-grav just like the Air/Raft, before it is allowed/advisable to engage thrusters.
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This is one of those head-scratchers I've gone around and around on.
Part of me likes the simplicity of "if you have a 1G engine, you can't get away from a 1G+ world's gravity without assistance from aerodynamic lift or a "tugboat" - use the highport". Even thruster plates aren't going to provide "magic" beyond their reactionless thrust, and orbital mechanics and such are still relevant.
But if you assume air/rafts can fly even on high-G worlds AND you assume a streamlined or semi-streamlined ship includes some grav lifter modules (maybe that's part of the cost/tonnage for streamlining?) then the ship should be able to effectively cancel the world's gravity and accelerate away as necessary. It also makes takeoff look "Star Wars" ish - ships float up, orient towards their intended destination, then zoom off to the sky. And it allows more "flavor" opportunities to describe exactly what that maintenance cost is going to. (Captain, lifters 3 and 12 are only responding at 45%, we need to replace them if you want to lift more than 40 tons. I know a guy at the naval base who can get us some TL-12 surplus lifters on the cheap that should fit our frame with only minimal modification.)
And the part of me that's heavily influenced by the game Mass Effect likes the idea that grav engines cancel the effective weight of the ship to begin with, so even a lowly 1G engine can accelerate you away from a large gravity well without trouble.
(Interestingly, scientists have recently begun to suspect that there are multiple "flavors" of Higgs bosons, and that "inertial mass" may not necessarily be the same thing as "gravity mass" - a pretty radical idea if it pans out.)
Part of me likes the simplicity of "if you have a 1G engine, you can't get away from a 1G+ world's gravity without assistance from aerodynamic lift or a "tugboat" - use the highport". Even thruster plates aren't going to provide "magic" beyond their reactionless thrust, and orbital mechanics and such are still relevant.
But if you assume air/rafts can fly even on high-G worlds AND you assume a streamlined or semi-streamlined ship includes some grav lifter modules (maybe that's part of the cost/tonnage for streamlining?) then the ship should be able to effectively cancel the world's gravity and accelerate away as necessary. It also makes takeoff look "Star Wars" ish - ships float up, orient towards their intended destination, then zoom off to the sky. And it allows more "flavor" opportunities to describe exactly what that maintenance cost is going to. (Captain, lifters 3 and 12 are only responding at 45%, we need to replace them if you want to lift more than 40 tons. I know a guy at the naval base who can get us some TL-12 surplus lifters on the cheap that should fit our frame with only minimal modification.)
And the part of me that's heavily influenced by the game Mass Effect likes the idea that grav engines cancel the effective weight of the ship to begin with, so even a lowly 1G engine can accelerate you away from a large gravity well without trouble.
(Interestingly, scientists have recently begun to suspect that there are multiple "flavors" of Higgs bosons, and that "inertial mass" may not necessarily be the same thing as "gravity mass" - a pretty radical idea if it pans out.)
30 minutes.
Yep, it is a weird missing piece. Even MGT alludes and would require it per the rules but doesn't go into it. BTW, in MT you can push the M-Drive 40% over for days and 400% over for ~5 minutes.
Yeah, with my players stuck with a 1G ship that works very well 90% of the time, I just have them overdrive (and make skill rolls, etc.) the drives to take off from marginally high grav worlds.
That whole 'emergency agility' concept gets translated into emergency thrust for escaping size 8 and 9 planets. They tend to avoid the size 10 worlds outright, and thankfully there haven't been that many that would give them any reason to want to land so far.
That whole 'emergency agility' concept gets translated into emergency thrust for escaping size 8 and 9 planets. They tend to avoid the size 10 worlds outright, and thankfully there haven't been that many that would give them any reason to want to land so far.
My players gave me the same question (if the ship only has 1G can we take off from larger worlds than Earth?), And this was my response:
The spacecraft's engines do not move the ship by repelling or emission of matter / energy generating a force should be balanced against the force of gravity on the planet, but by manipulating the field of bosons (gravitational field, usually). The radiation resulting from these manipulations at the subatomic level is what causes the blue glow of the "thrusters" (actually, the engine section than remains off the ship, usually aft).
Older versions of the engine (and the grav vehicle engines.) Needed a gravitational field against which "push", so his performance plummeted once out of the planet's gravity (explained quite well in " hard times ")
Modern engines "produce" a field of bosons that replaces the planet's gravitational field (or generates a new, if not exist). Therefore, the external gravity does not compute when it comes to change the motion of the ship (as long as the motors are active.)
The only question is whether there is a gravitational field strong enough to "overcome" the physical manipulation of the engines of the ship (black holes, neutron stars, low orbits around O and B type stars, etc). However, I doubt that my players want to risk his characters in such a mission, so that the explanation was enough to satisfy and continue with the game ...
The spacecraft's engines do not move the ship by repelling or emission of matter / energy generating a force should be balanced against the force of gravity on the planet, but by manipulating the field of bosons (gravitational field, usually). The radiation resulting from these manipulations at the subatomic level is what causes the blue glow of the "thrusters" (actually, the engine section than remains off the ship, usually aft).
Older versions of the engine (and the grav vehicle engines.) Needed a gravitational field against which "push", so his performance plummeted once out of the planet's gravity (explained quite well in " hard times ")
Modern engines "produce" a field of bosons that replaces the planet's gravitational field (or generates a new, if not exist). Therefore, the external gravity does not compute when it comes to change the motion of the ship (as long as the motors are active.)
The only question is whether there is a gravitational field strong enough to "overcome" the physical manipulation of the engines of the ship (black holes, neutron stars, low orbits around O and B type stars, etc). However, I doubt that my players want to risk his characters in such a mission, so that the explanation was enough to satisfy and continue with the game ...
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