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Old September 13th, 2011, 11:24 PM
cryingblackoil cryingblackoil is offline
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Default Air/Raft

Ok. Quick question. There has been some discussion about whether grav technology, specifically air/rafts, can function in deep space without a sizable chunk of mass like a planet to push/pull against. Any thoughts?
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Old September 14th, 2011, 02:23 AM
kilmore kilmore is offline
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I would say yes, as it appears that maneuver drives function without pushing against anything, and if I recall correctly, the maneuver drives work on grav principles. I'd say the gravitic energy is pushing against the ship / air-raft itself.
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Old September 14th, 2011, 03:39 AM
E.D.Quibell E.D.Quibell is offline
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In MT Air Rafts use Standard Grav Drives that push against a gravity well. If you use these on a space craft you lose 50% of you drive potential past 10 diamiters of the planet.

Thruster on the other hand can fit into anything over 20 tons push on themselves, so never lose dirve potential.

In MgT I have no idea though.

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Old September 14th, 2011, 05:45 AM
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Note that T4 and T5, Thruster plates die at 1000 diameters...
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Old September 14th, 2011, 07:31 AM
BytePro BytePro is offline
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MgT is based on CT, which, as far as I know, did not have this concept... certainly haven't come across it in any of the MgT books.

I think the authors intentionally left this vague in MgT - especially if one looks at air rafts.

IMTU, gravitic systems 'create gravity' as well as manipulate existing 'gravitic fields' - so no 'external' gravity is required. Of course, this seems less believable, especially for small devices like grav belts', which I suspect is one of the reasons for the other versions of Traveller to make a distinction. For myself, I make it simple and keep gravitics purely in a fictional realm, rather than trying to tie it to real life physics and perceptions - which just means more effort for no real gain, as it will utterly fail for those of us not more gifted than Einstein.

Like all handwaves, there comes the question of suspension of disbelief - but gravitics (gravity control, not gravity) is fantasy, not science.
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Old September 14th, 2011, 11:07 AM
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IMTU, grav only works in a planet's gravity well.

A CT Air/Raft has a rather weak grav system, so is more closely tied to a planet.

IIRC correctly, there was something in the CT description of an Air/Raft as "a light duty grav vehicle that uses null-grav units to counteract gravity for lift and propulsion." If there is no gravity to counteract, there is no propulsion, but there is always some. I describe it to my players as being not enought to work with outside 100 diameters, and halved by 10 diameters.
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Old September 14th, 2011, 11:57 AM
far-trader far-trader is offline
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Quote:
Originally Posted by BytePro View Post
MgT is based on CT, which, as far as I know, did not have this concept...
Actually it does. As samuelvss notes, the CT grav vehicles can only make orbit, and only very slowly at that (except for the Speeder). Taking 1 hour per planet size digit. And orbit is as far as they can get before they are incapable of further thrust.

Ships and small craft on the other hand can make orbit in minutes and travel between planets at full thrust.

Two very different systems are evident and in use.

As you note, being based on CT, MgT should have similar notes and performance.

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I think the authors intentionally left this vague in MgT...
That wouldn't be my first conclusion
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Old September 14th, 2011, 12:05 PM
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In response to samuelvss' post (far-trader's got in between )

Ah - looked up the Book 3 CT description - yep, that's it, except my reprint says 'anti-gravity' in place of 'grav' - yet still uses the 'null-grav unit' for propulsion...

LOL - well, at least the writing style was consistent! Goes quite well with naming a vehicle, designed to operate in any environment, notably a vacuum, an 'Air/Raft'.

Like you said, since there is gravity generally everywhere, that really doesn't put any limits on things. However, the paragraph does state '...;passengers must wear vacc suits and interplanetary travel in an air/raft is not possible.' Of course, it doesn't state why - gravitics limits or range/exposure - though the game mechanic of an hour per planetary digit size to reach orbit implies that it cannot move as fast going away from a gravity well.

Love the very next sentence - 'Range in time or distance on a world is effectively unlimited, requiring refueling from a ship's power plant every ten weeks or so.' LOL - so, it is 'effectively unlimited' - just, uh, with a limit.

Using an Air/Raft (what a really dumb name for such) for off-world travel never came up in my games, but does seem to come up on forums. Perhaps another advantage to players not having rule books!

Last edited by BytePro; September 14th, 2011 at 12:10 PM..
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Old September 14th, 2011, 03:23 PM
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Quote:
Originally Posted by BytePro View Post
since there is gravity generally everywhere, that really doesn't put any limits on things. However, the paragraph does state '...;passengers must wear vacc suits and interplanetary travel in an air/raft is not possible.'
Well, I may have been vague, but what I meant was that there WAS a practical limit, though not a theoretical limit, to using an Air/Raft far enough out. The farther out, less gravity; at some point it is essentially small enough not to use.

There is an aspect to my ignoring stellar gravity wells here for the same erason I ignore them in jump mechanics: I'm too lazy to figure it out! I basically tell players they can't use an Air/Raft beyond the 100 diameter limit, an between the 10d and 100d limits, they are useful only for small movements (e.g.: moving a few 100 meters in EVA. A fire extinguisher would probably be better!).

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Originally Posted by BytePro View Post
Love the very next sentence - 'Range in time or distance on a world is effectively unlimited, requiring refueling from a ship's power plant every ten weeks or so.' LOL - so, it is 'effectively unlimited' - just, uh, with a limit.
Well, if I can drive my car 10 weeks without refueling, THAT's relatively unlimited. I must confess, though, that this 10 week figure is where I just break with canon IMTU. I assume it meant 10 weeks of very intermittent operation at full capacity or lighlty loaded, having designed a few vehicles in various design rules. I normally give them about 72 hours on continuous operation at full thrust, I use fuel cells to stretch the operation to almost 8 hours a day unloaded in an atmosphere. A fuel cell can be used, per NASA, in a vacuum, but both H2 and O2 must be brought along; thus operating one of my Air/Rafts in and atmosphere gets close to the 10 weeks by using ambient O2, and requiring less power, but only if lightly loaded or used intermittently. I put some precise SWAGs down elsewhere:

http://www.travellerrpg.com/CotI/Dis...hlight=ballard
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Old September 14th, 2011, 04:09 PM
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Nice writeup - Thanks for the link!

Never paid attention to most of the Air/Raft details, actually, especially the silly 10 week thing. Ironic, given the emphasis on ship fueling, and then the basic handwave on grav vehicles. IMTU, I usually used GravCars anyway, and they really weren't used for any altitude or duration - just a way to get around, along with GravCycles. Which never had enough fuel remaining for the ubiquitous high speed chase!

Always preferred micro-fusion powered small vehicles and such, especially for gravitics - when Back to the Future came out (2nd one, IIRC) the Mr. Fusion was an instant hit with me and my players, though I felt compelled to allow odd things for fuel after that...
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