Will An Air Raft Operate Outside Of A G Well? [Answered]

[Solomani666]

Will an air raft work at all outside of a gravity well?
Will it work in micro gravity, say in proximity to an asteroid?
A am leaning toward a 95% "No".

Any input?

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[AndrewW]

Will an air raft work at all outside of a gravity well?
Will it work in micro gravity, say in proximity to an asteroid?
A am leaning toward a 95% "No".

Any input?

.

The technology is there for it to, spaceships operate outside the gravity well of a planet for example.

 

[far-trader]

Will an air raft work at all outside of a gravity well?
Will it work in micro gravity, say in proximity to an asteroid?
A am leaning toward a 95% "No".

Any input?

The rules answer seems to be yes* it will work fine, with exactly the same performance regardless. Never made sense to me though, my interpretation has always been that grav vehicle performance is directly related to the local gravity field. The ratings are for 1G standard and you multiply by local gravity for local performance since it is a counter-grav (CG) device.

* at least as I've seen the question widely answered and interpreted by others, and with that bit about "reach orbit" in the rules and the example of the Belter's Buggy (an enclosed Air/Raft for use in mining/exploring asteroids)

So a 100kph speed rating is for 1G worlds, operating near the surface. The higher your altitude the slower your speed and the less your lift capability. Grav in MTU can most certainly not attain anything close to low earth orbit.

EDIT: At least not most grav vehicles. Some high performance ones, like the classic Speeder can. MgT took a step towards making the rest more probable of this ability by upping the speed ratings, kudos there, I'd still probably not give the Air/Raft, Grav-Belt, or Lifter the capability, but the G-Carrier might do it.

The same 100kph speed rating on a world with .25G would have only a 25kph top speed and a likewise reduced operational ceiling.

Go for a cruise on a 1.2G world though and you have a performance boost with a top speed of 120kph.

And of course on a 0G world (and at sufficient altitude of any world) your speed and lift are 0, you don't go anywhere.

And yes, the nature of CG in MTU is such that they ride like they are on rails and brake like they have high traction grip, they perform as well or better than a high performance car for acceleration and deceleration, at least when close to the ground.

 

[far-trader]

The technology is there for it to, spaceships operate outside the gravity well of a planet for example.

A different (related) technology there though, imo. One suited to large scale application but not small vehicle scales. And vice-versa.

 

[Solomani666]

The game next week will probably involve the characters using a air raft to investigate a derelict vessel.

I will only allow slow speeds however in the assumption that the grav drive operates minimally as thruster plates.


Thanks for your replies.

Now feel free to digress.



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[Blix]

So a 100kph speed rating is for 1G worlds, operating near the surface. The higher your altitude the slower your speed and the less your lift capability. Grav in MTU can most certainly not attain anything close to low earth orbit.

Earth's gravity at surface: 9.80665 m/s2
Earth's gravity at 100km altitude: 9.51 m/s2 (96.9% of surface value)
Earth's gravity at 400km altitude (approx ISS space station altitude) : 8.68 m/s2 (88.5% of surface value)

Also gravity falls off with the inverse square, not linearly. If grav performance is related to gravitational field strength then there should not be a significant difference between its performance at the surface and its performance at 100 (or even 400) km altitude (on Earth at least).

 

[far-trader]

Yeah I know the sums, it doesn't feel right to me to follow the progression though

I figure there is an efficiency scale effect that limits it more than the simply gravity would. It might not even be a directly gravity related effect but one more akin to a ground-effect lift mechanic. The local multiplier effect is simply an easy hand-wave game mechanic.

Short story long, it is the top speed as much as anything that says to me, no, you won't achieve orbit (at least in any meaningful sense) in an Air/Raft. And it's mainly a MTU feel I want that such tech spoils. You can float and cruise along, but you can't fly high and fast, with CG alone.

 

[DFW]

I've split the "grav"tech into 2 different things in MGT. 1) Grav vehicle (CG). 2) Space Craft Tractors.

#1 relies on a gravity well & is limited by the strength of the well being pushed against. (similar to fartraders example above)

#2 "grabs" the fabric of space itself and pulls over & over very quickly. There is a limit to how fast the craft is going in relation to real space. Liken this to you sitting in a wagon next to a rail and, using your hands to grip and pull. At a certain velocity you can't accelerate as your arm can only go so fast.
This limit keeps the space craft from using constant acceleration to reach c.

With the rules above; lower thrust CG craft (air raft) can't move in true zero G. Maybe, inside a solar system, they can do ~1kph. But, not enough thrust to reach orbit unless the GC drive is very high thrust.

This can be problematic of you push off from a craft in high orbit. You're going to have high velocity by the time you reach an altitude where you have enough thrust to start slowing. Could get very hot... :twisted:

 

[Blix]

Yeah I know the sums, it doesn't feel right to me to follow the progression though

So long as it is understood that gravity doesn't vary with altitude as much as you think it does (or at least, would like it to!).

I figure there is an efficiency scale effect that limits it more than the simply gravity would. It might not even be a directly gravity related effect but one more akin to a ground-effect lift mechanic. The local multiplier effect is simply an easy hand-wave game mechanic.

With your "scale effect", how do spacecraft lift off the ground with their grav/thruster plates? If a vehicle cannott "make orbit" then why would a spacecraft? It just seems like an artificial limitation made for its own sake.

You can either keep adding "handwave game mechanics" and exceptions or you can go with something consistent. I would rather go with the latter myself.

 

[Mithras]

...and in MTU contragrav simply counteracts gravity and a secondary engine , jet turbine, ducted fan, whatever provides propulsion. I don't allow air/rafts to reach orbit, only speeders, i assume they have ramjets or scramjets or something similar.

I really am wary of giving grav vehicles too much utility, I want to save a place for the ships boat, but I also bring in grav vehicles at TL 10 so I can give lower tech worlds some interesting world specific forms of transport.

So my answer would be, yes but slowly, but not in MTU mate!

 

[hdan]

I've split the "grav"tech into 2 different things in MGT. 1) Grav vehicle (CG). 2) Space Craft Tractors.

That's pretty much how I see it too (though possibly the exact opposite? LOL) - Contra-Grav (CG) like air/rafts only works in a gravity well, and is limited to reaction against that gravity field. Thruster Plates work in "deep space" or for any high velocity applications since they are "raw acceleration" instead of "relative to the local gravity well positioning".

Canonically, Air/Rafts *can* reach orbit. For emergency purposes, I have CG vehicles reach and return from low orbits, considering their maximum listed velocity to actually be an NoE maximum (or at least an in-atmosphere based maximum). But the best way into orbit is a real spaceship.

For my spaceships, I've decided that a streamlined hull has CG lifters that help "in port" maneuvering where the thruster plates are not subtle enough. Use the lifters to get off the pad, away from the port and in the correct orientation for your orbital burn, then light the thruster plates (or reaction drives if you are in that TL between the arrival of CG and thruster technologies) to burn up to orbit.

To be honest, the main reason for the hull mounted CG lifters is to give the ship owner and engineer more stuff to worry about and spend maintenance money on. Those lifter modules seem to be forever going out due to excess heat or debris. Fortunately, there is one per 10 tons of ship, and a module can just lift 15 tons, so generally it's not a serious problem, just a minor annoyance.

That is, until the crew is down a few modules and needs to land on a high-G world....

Swapping out a dodgy lifter module is a Mechanic - Routine (10d6 minutes) task if the ship is in port. (It becomes one level harder in Zero-G, but a Zero-G skill test can help.)

 

[Blix]

It is quite possible to come up with any number of other reasons why an air-raft cannot climb to orbit - for example, the components may not be built to handle it, or there are built-in and non-overridable safety factors installed by the manufacturers, insurance companies don't cover flight above a certain altitude, legalities of air-traffic control may restrict it, etc.

Any of those are reasonable limitations that one might expect to encounter here, and they seem better to me than contriving technological reasons for the grav drives to magically fail to work at higher altitudes.

 

[far-trader]

It is quite possible to come up with any number of other reasons why an air-raft cannot climb to orbit - for example, the components may not be built to handle it, or there are built-in and non-overridable safety factors installed by the manufacturers, insurance companies don't cover flight above a certain altitude, legalities of air-traffic control may restrict it, etc.

Any of those are reasonable limitations that one might expect to encounter here, and they seem better to me than contriving technological reasons for the grav drives to magically fail to work at higher altitudes.

Certainly you can go that way, but they are no less contrived. They are perhaps even less enforceable and open to more questions than my "magically fail" solution for the magic flying dust that makes them work in the first place

Will an Air/Raft work in a vacuum? Almost certainly yes as described. That kind of blows the components not rated for high atmosphere function.

Insurance issues aren't going to stop players. Neither will legalities, even on some high law worlds, certainly not on a barren backwater nothing world.

And I'm sure you know nothing is tamper proof given the right knowledge and tools. Both of which the players are going to want to get if that is the impediment.

Yeah, I'll stick to my universally constant and consistent physical (ye kenna change the laws of physics cap'n) limitations on the magic flying dust

Your suggestions may work for yourself or others though. They open up different adventure possibilities.

 

[Blix]

OK, so why not go the other way and say that air/rafts can make it into orbit?

To be honest I really cannot see why that would be a problem. The whole point of grav is that it blurs the line between the various modes of travel (in the tech level charts it superseded land and sea and air travel), so why should it not be able to blur the line at the air/space interface too?

The problem then simply becomes a matter of practical application. Yes, it can make it into orbit, but then the passengers are limited by air and food supply and power consumption (the fuel cells that power the air/raft may not be able to keep the air/raft accelerating for very long by the time it is in space).

Air/rafts could be used to get small numbers of people from surface to space, replacing larger launches and shuttles, but are not much use for larger groups. Then again using multiple air/rafts may be cheaper than a using single shuttle.

In fact, this approach would make more sense to me than limiting their capabilities.

 

[atpollard]

OK, so why not go the other way and say that air/rafts can make it into orbit?

In fact, this approach would make more sense to me than limiting their capabilities.

I agree.

Just note that if the world has an earth-like atmosphere, the 200+ mph jet streams will make part of the trip fairly exciting, and travelling thru the Van Allen Radiation Belts (if you intend to head to the moon) will be unpleasant in a vacc suit and open air/raft.

... but Hell Yeah it is doable!

(just like climbing Mt Everest.)

 

[Blix]

Just note that if the world has an earth-like atmosphere, the 200+ mph jet streams will make part of the trip fairly exciting, and travelling thru the Van Allen Radiation Belts (if you intend to head to the moon) will be unpleasant in a vacc suit and open air/raft.

... but Hell Yeah it is doable!

Yes, and that will serve to somewhat limit its application as a surface-to-space vehicle.

That said, it may also force the design to evolve into something that is more useful for such a purpose too.

 

[far-trader]

OK, so why not go the other way and say that air/rafts can make it into orbit?

Because that's the issue for me, sorta the whole point of my posts.

Air/Rafts are vehicles, meant to be a quick way around the surface of a planet. Small craft such as launches are meant for orbital and short space flights, usually attached to an unstreamlined ship for that purpose. If a grav vehicle will do the same job then why bother with the distinction? Why the huge cost difference and size difference? If a ship with an Air/Raft is streamlined why does the Air/Raft need to have orbital flight capability? For that matter if a ship needs to be streamlined to permit flight between the surface and space how do you justify an unstreamlined vehicle like an Air/Raft doing it at all? Why not just have open topped spacecraft to save money and require all occupants to wear vacc-suits

It also strikes me as unnecessarily gimmicky.

Grav vehicles replacing/blending land and air travel is not the issue. Crossing it into space travel, no matter how minimal, is an issue.

Obviously it's not an issue for you, and some others. And that's fine too.

 

[Blix]

Air/Rafts are vehicles, meant to be a quick way around the surface of a planet. Small craft such as launches are meant for orbital and short space flights, usually attached to an unstreamlined ship for that purpose. If a grav vehicle will do the same job then why bother with the distinction? Why the huge cost difference and size difference?

Why indeed? Perhaps the game's designers did not think the implications through properly. It would not be the first time this has happened, after all (see near-c rocks, piracy, ecoomics etc).

If a ship with an Air/Raft is streamlined why does the Air/Raft need to have orbital flight capability?

Why do some people need such vast amounts of processing power in their modern desktop computers when all they do is check email on it? Why do people drive powerful cars that can reach a 150 mph if they never go much faster than 75 mph? Just because an Air/Raft has such capabilities, does not mean that they have to be used.

For that matter if a ship needs to be streamlined to permit flight between the surface and space how do you justify an unstreamlined vehicle like an Air/Raft doing it at all?

The streamlining issue only really applies when the craft is travelling rapidly through an atmosphere. Unstreamlined craft will encounter difficulties, turbulence, etc - streamlining will minimize these issues.

Landing and taking off depends on the structural tolerances of the craft. Streamlined craft would be able to handle the stresses, unstreamlined craft would not.

And I would argue that Air/Rafts must be streamlined anyway, in the same sense that cars are.

Why not just have open topped spacecraft to save money and require all occupants to wear vacc-suits

You could, but such a spacecraft would have limited use. It would not be able to jump, things would go flying off into space (in fact, how would one define the upper boundary of the volume that an artificial grav plate can affect without a roof/ceiling? I would say that artificial gravity only works in enclosed volumes), the crew would be subject to radiation, micrometeorites etc. It would theoretically be possible, but not very useful.

It also strikes me as unnecessarily gimmicky.

I am not sure how you can say that. The "gimmick" in question here is the artificial limitation of the capabilities of grav vehicles, my suggestion is to remove that!

Crossing it into space travel, no matter how minimal, is an issue.

Obviously it's not an issue for you, and some others. And that's fine too.

I think you are making it an issue when it does not have to be. But then it appears that your primary concern is to stick to OTU canon no matter what, in which case this discussion becomes somewhat pointless.

However, I suspect that there are some readers who are interested in exploring the possibilities of the technology, unfettered by artificial limitations of "canon", and hopefully my suggestions are more useful to them.

 

[DFW]

Why indeed? Perhaps the game's designers did not think the implications through properly. It would not be the first time this has happened, after all (see near-c rocks, piracy, ecoomics etc).

I hear this every once in a while. What is a near c rock?

 

[far-trader]

...it appears that your primary concern is to stick to OTU canon no matter what, in which case this discussion becomes somewhat pointless.

lol, hardly. You are the one on the side of OTU or be damned of the two of us in this case. The rules clearly say Air/Rafts can reach orbit. I disagree. And canon can be damned, as I've clearly stated this is an MTU opinion. I think you're just looking for a fight where there is none, trying to pick one with the old OTU canonnista insult stick. Fail...

However, I suspect that there are some readers who are interested in exploring the possibilities of the technology, unfettered by artificial limitations of "canon", and hopefully my suggestions are more useful to them.

Sorry, I didn't realize you wanted to make a contest out of this, lol. Go ahead though, but by the time your suggestions have been ironed out I suspect you will have changed the Air/Raft into a full fledged space craft. Or at the very least a Speeder. At which point, as I noted earlier, much of my concerns evaporate.