Tonnage Rule of Thumb

[Icosahedron]

I've said it before, I'll repeat it again, as you so kindly practically quoted the bit, note that is says "reach" orbit. As in climb to orbit. Not "de-orbit" as in come down from orbit. Guess what happens to an air/raft that tries to de-orbit? :toast:

Why is the air raft :toast: when it comes in? I think I'm with Aramis on this one.

And I imagine most of the '8 hrs time to orbit' will be spent accelerating to orbital speed once you're beyond atmospheric friction - it won't take that long to travel the vertical 100km or so.

If you take 8 hours to de-orbit too, I don't see a problem - apart from getting shot at.

 

[far-trader]

Well tell me this, what is the lifting thrust of the Air/Raft? It must be minimal whatever it is for it to take 1 hour per size code of the world to reach orbit. Starting slow and gaining lift and speed as the effect of gravity is reduced you eventually claw your way to orbit with a very high final velocity.

Now, how do you propose to reverse that procedure? You'll be starting fast with very little effective thrust to slow you down. That's a hot reentry. Which for an unstreamlined vehicle is :toast: (extra crispy). Or maybe a skip.

Unless you want to argue the language of the text is sloppy. I think they knew what they intended and worded it appropriately. An Air/Raft can climb to orbit, slowly, but it cannot de-orbit.

Regardless of all the (GURPS I think) rulings that CG allows even bricks to float down from orbit through an atmosphere the intent of the rules for streamlining are clear. Unstreamlined cannot enter an atmosphere from orbit. Period. If you try, you die. Period. Or at the very least, the vehicle attempting it does. To enter an atmosphere from orbit you need a streamlined vehicle. Period. Then it becomes routine and quick.

 

[coliver988]

Well tell me this, what is the lifting thrust of the Air/Raft? It must be minimal whatever it is for it to take 1 hour per size code of the world to reach orbit. Starting slow and gaining lift and speed as the effect of gravity is reduced you eventually claw your way to orbit with a very high final velocity.

I would think the opposite: closer to the gravity source the faster (isn't gravity an inverse square thing?). So that you are actually moving faster, vertically speaking, near the beginning of the trip as you have more gravity to react with. Or at least that's how I envisioned CG: the more gravity the more effective it is (up to the point where gravity is stronger than your CG, then you are out of luck. Which is my in MTU you needed maneuvering thrusters out in the middle of deep space [err, does deep space have a middle?] since you need a gravity source to push against, and I don't like the idea of a universal or galactic background gravity).

Now, how do you propose to reverse that procedure? You'll be starting fast with very little effective thrust to slow you down. That's a hot reentry. Which for an unstreamlined vehicle is :toast: (extra crispy). Or maybe a skip.

That's assuming you are actually in orbit - which means going fast enough to maintain your orbit against gravity. With CG you simply keep the power on to maintain orbit. If you want to maintain orbit w/o CG then you need the speed. So you can keep floating up higher & get to orbiting height without needing orbital speed. So for me the reverse would seem right as well - you don't need to start with orbital speeds if you have CG. But then I'll admit to not having a physics class in 20+ years and we didn't get too deep into orbital mechanics then. Think of a hot air balloon that has high-atmospheric tolerances: they can get sub-orbital and not burn up. And waft gracefully back to Earth, or Regina, or wherever you happen to be.

Unless you want to argue the language of the text is sloppy. I think they knew what they intended and worded it appropriately. An Air/Raft can climb to orbit, slowly, but it cannot de-orbit.

Maybe not sloppy, but as with everything, open to a lot of interpretation. YMMV

Anyway, as I said, CG (or anti-grav, or grav tech, or whatever one wishes to call it) changes a LOT of assumptions.

 

[aramis]

given that an air-raft has at least 1.1g's of acceleration, which, BTW, is more than the Space Shuttle in orbit, just a matter of decelling in orbit at 0.1 while holding altitude with somewhat less than 1 G...

And, given Scaled Composite's 'recent' suborbital flights, should be no problem. I suspect a major part of that time is above atmosphere, making orbital speed.

 

[whartung]

Funny, I've always considered anti-gravity to be, effectively, a means to achieve neutral buoyancy regardless of mass. So, if I have neutral buoyancy, I can, effectively, "float" and then use thrusters to move. Since velocity is not my mechanic for breaking the gravity well, I don't need velocity to make orbit.

Actually, to be clear, yes, you DO need velocity to maintain orbit, but with gravitics, I don't need velocity to break the gravity well in order to gain altitude to where I can achieve orbit. Thus I can "float" up to orbit altitudes, and then use thrusters to position myself in to a stable orbit, using gravitics to compensate until I actually reach oribtal velocities.

In order to deorbit, I reverse thrust and velocity, increasing gravitic compensation until I can safely enter the atmosphere. With a properly shielded ship, you can enter the atmosphere at a higher velocity than a less shielded craft. But as long as you have full compensation available from the gravitics (and enough thrust/fuel), you should be able to land a paper plane without burning it up.

Now, I can easily see having something like an air raft not have enough grav "power" to "work" higher in the gravity well, or something like that. But the truth is, gravity is quite powerful in orbit.

Throwing things in to atmospheres with heat shields is done because in general, it's cheap and easy compared to burning fuel on "retro rockets". But with thruster plates and gravitics, you should be able to float down with a hum instead of a trail of fire if you like.

 

[leo knight]

Funny, I've always considered anti-gravity to be, effectively, a means to achieve neutral buoyancy regardless of mass. So, if I have neutral buoyancy, I can, effectively, "float" and then use thrusters to move. Since velocity is not my mechanic for breaking the gravity well, I don't need velocity to make orbit.

I recently found a book titled "Floating to Space", which proposes using airships to get to orbit. Here's the Wikipedia article:

http://en.wikipedia.org/wiki/Orbital_airship

There are three stages: Airship to mesosphere, a mesosheric 'dark sky station', and the final ascent to orbit craft. It would take about 9 days for the craft to climb that distance, and a like amount to descend. No heat shields, no toast. It's why they go slow.

 

[tbeard1999]

Seems to me that if an airraft was capable of reaching orbit, but would burn up on reentry, the rules would point this out. Since the rules only state that it can reach orbit, I think that the most reasonable position is that it can also reenter the atmosphere and land safely.

The amazing utility of grav vehicles is a major reason that they do not exist IMTU.

 

[far-trader]

Seems to me that if an airraft was capable of reaching orbit, but would burn up on reentry, the rules would point this out. Since the rules only state that it can reach orbit, I think that the most reasonable position is that it can also reenter the atmosphere and land safely.

(obviously not trying to convince you tbeard, you don't use them for the reasons being argued against by me...)

So because the rules say one thing (only) - that the Air/Raft can reach orbit - but do not say it can deorbit, you take that to mean it can? o:

Granted my references to :toast: are exaggeration (meant only for a high speed attempt) but you can't believe the designers intended it to be done. At least not routinely or safely.

I think it's more honest to say IF the designers intended it to break the rules about only streamlined craft (with the same grav lift as the Air/Raft I think you're all saying) being able to enter an atmosphere from space they'd have spelled it out in no uncertain terms, especially after going to the trouble of mentioning it can reach orbit. That they didn't speaks volumes.

Look, I'm don't even really disagree that CG should allow anything to slowly deorbit into an atmosphere. It's an issue the designers didn't seem to think out. BUT...

...the intent of the rules is clear in several places. Only streamlined craft can enter atmosphere from space. Period. So anything else that seems to "cheat" this rule has to be interpreted in such a way as to not break it.

Saying the Air/Raft, an open topped, unstreamlined, unarmored, ungainly (extremely subject to wind effects), primarily low altitude atmospheric vehicle can deorbit just because it doesn't say it can't in the write-up that bothers to say it can achieve orbit (only) slowly makes no sense at all.

The amazing utility of grav vehicles is a major reason that they do not exist IMTU.

Whereas I'd rather say grav exists and works, just not the way some would like. It may be magic but (to borrow the answer I so justly deserved above ) it ain't pixies.

 

[tbeard1999]

(obviously not trying to convince you tbeard, you don't use them for the reasons being argued against by me...)

So because the rules say one thing (only) - that the Air/Raft can reach orbit - but do not say it can deorbit, you take that to mean it can? o:

Yes. I think it's the most reasonable inference. Seems to me that MM would have mentioned something as important as "but if it tries to reenter, it will burn up..."

I think it's more honest to say IF the designers intended it to break the rules about only streamlined craft (with the same grav lift as the Air/Raft I think you're all saying) being able to enter an atmosphere from space they'd have spelled it out in no uncertain terms, especially after going to the trouble of mentioning it can reach orbit. That they didn't speaks volumes.

Have you considered that air-rafts might be considered streamlined? Any craft that flies in the atmosphere would benefit from streamlining so it seems reasonable to assume that air rafts are streamlined.

 

[BigBadRon]

I think it's more honest to say IF the designers intended it to break the rules about only streamlined craft (with the same grav lift as the Air/Raft I think you're all saying) being able to enter an atmosphere from space they'd have spelled it out in no uncertain terms, especially after going to the trouble of mentioning it can reach orbit. That they didn't speaks volumes.

As I recall, in CT, there is no mention of ships having the same CG capability as an airraft.

The nature of the M-drive is not addressed, except to mention that interplanetary travel involves constant acceleration, turn over at mid-point, and constant deceleration (which sounds more like some sort of thruster technology, rather than something which manipulates gravitic fields).

 

[far-trader]

As I recall, in CT, there is no mention of ships having the same CG capability as an airraft.

It is implied by the simplification of the process of landing and taking off ignoring local gravity and solely reliant on the full maneuver drive rating, iirc. An implication later affirmed by it being explicitly stated as a part of the ship (in MT I think).

 

[far-trader]

Have you considered that air-rafts might be considered streamlined?

Actually, no. Seems odd that I'd not ever given that a thought but I didn't. Worth considering I suppose, but for the mention of it being "extremely subject to wind effects" implying an awkward shape.

Any craft that flies in the atmosphere would benefit from streamlining so it seems reasonable to assume that air rafts are streamlined.

It would, but I don't take that to mean it was. Illustrations don't generally show a shape I'd consider streamlined in the atmospheric sense. No more so than a convertible sports car.

 

[BigBadRon]

It is implied by the simplification of the process of landing and taking off ignoring local gravity and solely reliant on the full maneuver drive rating, iirc. An implication later affirmed by it being explicitly stated as a part of the ship (in MT I think).

Just as the ability of an airraft to reenter an atmosphere is implied by the lack of any mention that they can't.

 

[tbeard1999]

Actually, no. Seems odd that I'd not ever given that a thought but I didn't. Worth considering I suppose, but for the mention of it being "extremely subject to wind effects" implying an awkward shape.

Doesn't the following sentence from Mercenary strongly imply that grav vehicles are capable of reaching orbit *and* landing again:

"[Grav] Gunships mounting rapid pulse X guns and heavier Z guns are virtually indistinguishable from orbital craft."

 

[atpollard]

Cannon balls are incapable of atmospheric flight in CT (High Guard lists a sphere as partial streamlined only) while unstreamlined ships are explicitly capable of landing on a vacuum world.

The Saturn rockets of the Apollo Era are incapable of atmospheric flight in CT, but are capable of flight in MT (cylinders).

I have very littile confidence that any of the rules were THAT carefully considered or worded.

 

[atpollard]

Actually, no. Seems odd that I'd not ever given that a thought but I didn't. Worth considering I suppose, but for the mention of it being "extremely subject to wind effects" implying an awkward shape.

"extremely subject to wind effects" could also imply a low thrust craft unable to resist strong lateral forces - like flying an ultra-light in a hurricane.

 

[Icosahedron]

Whartung has the technically correct answer.

Gravity at 'skimming the atmosphere' height is essentially the same strength as surface gravity.

I think an air raft would be able to reach orbital height, but I'm not sure it would have the fuel to accelerate to orbital speed, unless it's fusion powered.

Streamlining would include control surfaces required for accurate manouvering in atmosphere. Either the air raft is streamlined or it uses a form of G-drive that has more finesse than that found in a flying brick unstreamlined ship.

 

[aramis]

Contragravity: added in TNE, not MT.

Gravitic explanation for M-Drives: MT specific, but implied in at least one adventure before that, and plenty of illos in CT.

General rule for RPG's: If it isn't explicitly forbidden, and isn't illogical, it's allowable. (This is implied in Book 0.)

(This is the opposite of Wargames & boardgames, where if it isn't explicitly allowed, it is forbidden.)

Given that Air/Rafts are explicitly able to reach orbit, by slow and steady, and that real world knowledge shows that slow and steady is the safest way to reenter, there is no logical reason they can not reenter slow and steady. Given the lack of logical reason, and no rules bar to so doing.

All it requires is slowing down relative to the atmosphere without falling to the atmosphere while at speed. This requires a vertical thrust in excess of local gravity.

 

[far-trader]

General rule for RPG's: If it isn't explicitly forbidden, and isn't illogical, it's allowable. (This is implied in Book 0.)

(This is the opposite of Wargames & boardgames, where if it isn't explicitly allowed, it is forbidden.)

My grognards are showing :smirk:

 

[coliver988]

My grognards are showing :smirk:

my eyes!

I've enjoyed this thread: it's always interesting to see how different people interpret the same rules in often very different ways. Or, in this case, the lack of a specific rule (until the later supplement came out). I always played the 'if it goes up then it must be able to come back down' version of the air/raft, with the assumptions previously stated about grav drives. I can see the other viewpoint, and I'd accept that if someone else were reffing besides me and accept that. I just never managed to play Traveller often enough, as it was just me and a good college friend who had the books & wanted to play (we did manage to drag several other people into playing, but never refereeing) and we had a similar style of play (well, other than that one time we misjumped into a DnD Universe, but that was because we wanted to switch to DnD for a while but with our current characters. It was an interesting experiment).