Reentry and landing.

[aramis]

Keth's Type R is at least 13.5m across, and at least 9m tall, with 48m length. (as evidenced by the plans in S7 and TTA).

A 747-300 main body is roughly 7.5 m tall, and 4.5m wide. 70.7m long.

So, type R is about 4x the volume by unit length, and half as long.

The flat bottomed oval shape is quite similar in profile. Note that the cargo volume listed for the 747-300 isn't the same as its interior volume, and has a significant divergance - because the smaller dimensions means more waste space for break-bulk and even more for containerized cargo.
So, main body wise, it's about 100-110 tons, counting the upper deck (which isn't cargo capable) and circumferential lost-space.

And that's a good match, as the Type R cargo and supercargo volumes are about 262 tons (200 Td cargo, 52 Td staterooms, and 10 Td LB. We also get a 3m width increase in the last 9m). The R is also less tapered - one end only, and a much shorter taper zone.

The big difference is in wing volumes. Over 1/4 of the volume of the Type R is in the wings; around 1/10th on the 747. (remember - they're essentially wedges... and you can stack 5 roots high and not fill the length.)

http://ialcargo.com/specs/b747.pdf
https://www.boeing.com/resources/bo...istorical/747-100_-200_-300_-SP_passenger.pdf

 

[Condottiere]

My view is that gravitational lifters directly reject gravity, which is why they peter out so soon when away from the principal source of it.

Thrusters could be the manipulation of gravitational force, or even the creation of gravity itself.

 

[Grav_Moped]

...
And aren't there air rafts that are enclosed/air tight ?

Not in LBB3 ('81). It's an obvious thing to do, though, and there's no reason they couldn't be (of course life support and such, and the added weight of a roof would use up some of the cargo capacity). If I had to guess, I'd say the game authors took their conception of the vehicle from a particular book or series, and didn't go far beyond that.

Neither the GCarrier nor the Speeder descriptions mention being sealed airtight, either.

 

[Grav_Moped]

You are describing an air/raft at an orbital altitude that is gravitationally 'buoyant' but it is not in orbit. It is not in orbit until it has built up 7-8km/s orbital velocity, ie it can switch off its grav modules and remain in orbit. If it does not have this velocity then it will fall back to the planet when it switches its grav modules off.

LEO is between 200 and 2000km.

Exactly. And of course if it's trying to rendezvous with something in orbit, it will rendezvous at 7-8km/s closing speed. Hilarity ensues.

Applying this to a nominal 1G starship (positing that it's running at 10% over rated capacity for 1.1G) doing the same thing, the lateral acceleration to achieve orbital velocity would be a bit less time-consuming as it would be able to progressively divert thrust from lift to lateral acceleration as it approached orbital velocity. I don't assume a purely grav vehicle can do that.

 

[Grav_Moped]

I am not sure if you actually believe that or are just looking for an argument. As I stated previously, there is a point where my "willing suspension of disbelief" ends, and the air raft getting into orbit is well beyond that point. It is your version of the Traveller Universe. It is not mine. I am out of the discussion.

Modeling the air/raft's operational envelope on that of a helicopter is entirely reasonable given the novels from which the concept of an air/raft was borrowed -- so I can't say you're wrong.

That said, I absolutely believe that they're capable of reaching orbit. It's explicitly supported in the vehicle description.*

I would say that, given late-'70s future-tech assumptions, actually executing the maneuver would have required installing a Hand Computer as an autopilot to calculate the flight plan, plus Ship's Boat skill in addition to Grav Vehicle skill. Under current technology assumptions, it'd be a standard app in the stock autopilot system and you could probably just tap the screen and go.

There are good reasons for an air/raft to not be your first choice as a surface-to-orbit vehicle (orbiting debris, solar flares, etc.). But it's at least possible, as the vehicle is described. It's in the same league as riding a Vespa from Inverness to Dover** -- it can be done, but unless you're trying to prove a point or have no other choice, it probably won't be.




* The autopilot would do its best to talk you out of it, likely refusing if you couldn't prove to it that you and any passengers were in vacc suits with sufficient air reserves for the ascent and a subsequent descent (such proof being a space-Bluetooth pairing from the suits to the air/raft).

** US localization: San Francisco to San Diego

 

[JimMarn]

Not in LBB3 ('81). It's an obvious thing to do, though, and there's no reason they couldn't be (of course life support and such, and the added weight of a roof would use up some of the cargo capacity). If I had to guess, I'd say the game authors took their conception of the vehicle from a particular book or series, and didn't go far beyond that.

Neither the GCarrier nor the Speeder descriptions mention being sealed airtight, either.

Understood. Some of the air raft symbols in Cosmographer from Profantasy look like they are enclosed, and some look like sport cars with the canvas tops down.

 

[JimMarn]

@Xerxeskingofking

My memories of the Apollo flights to the moon mentioned reaching the balance point, but not the distance. They may have mentioned L-1, but that memory has faded.

 

[Xerxeskingofking]

@Xerxeskingofking

My memories of the Apollo flights to the moon mentioned reaching the balance point, but not the distance. They may have mentioned L-1, but that memory has faded.

fair enough, I am far too young to have watched the Apollo landings (I wasn't even a twinkle in my dads eye at that point). I wasn't seeking to prove you wrong as much as provide the data for what you were talking about, which happened to be slightly different to your memory, but that happens. I mentioned L1 by name since once you know the name, its much easier to find out more about it.

 

[infojunky]

Some of the air raft symbols in Cosmographer from Profantasy look like they are enclosed, and some look like sport cars with the canvas tops down.

What symbol library are those in?

 

[Ulsyus]

This brings up a whole point for me re: grav drives that makes me itchy.

Fine on anti-gravity being a neutralization AND a push against fields.

Fine on gravitic manipulation being able to create artificial gravity.

What I don't get is the getting velocity to go towards a planet as though you have thrust towards it, outside the gravity of the planet itself.

Seems like in orbit you have to use your thrust part for lateral push against velocity so you would naturally deorbit, but that's not the same as pushing the engines 'down'.

Also seems to me that if there is no 'pull' option like the 'thrust/push', that your gravtank isn't anywhere as maneuverable as a conventionally thrusting rocket or jet in that your down speed is dependent on planetary gravity.

And if you DO have an 'attract towards gravity field' option for lifters/M-drives, why aren't there tractor beams?

Now you've gone from WHAT to WHY. Do you really want to do that? What I mean is that is the direction of Weber-ish and Trek-ish technobabble which has no real meaning and is only of use in internal justification of plot. Do we really need an explanation of WHY and HOW AG/CG and M-Drives work, or can we craft a game around just the effects? I tend to lean towards the latter.

 

[BlackBat242]

Now you've gone from WHAT to WHY. Do you really want to do that? What I mean is that is the direction of Weber-ish and Trek-ish technobabble which has no real meaning and is only of use in internal justification of plot. Do we really need an explanation of WHY and HOW AG/CG and M-Drives work, or can we craft a game around just the effects? I tend to lean towards the latter.

Exactly - it is a GAME, not a physics or engineering doctoral dissertation!

Everything that does not contribute to the flow and substance of the GAME needs to be cut away.

 

[kilemall]

Now you've gone from WHAT to WHY. Do you really want to do that? What I mean is that is the direction of Weber-ish and Trek-ish technobabble which has no real meaning and is only of use in internal justification of plot. Do we really need an explanation of WHY and HOW AG/CG and M-Drives work, or can we craft a game around just the effects? I tend to lean towards the latter.

I'm almost always of the school of game first science second.


But there is also suspension of disbelief, and the key to achieve for a sciencey background sort of game is consistency and plausibility.


That implies a functional background/techbook sort of thing, if only for cinematic continuity.


The description of 'how things work' is not consistent with the game effects technology described so far IMO- but I am missing the TNE and T5 components, and I wouldn't mind having tractor beams as a gameplay option, definitely miss the repulsors.

 

[Grav_Moped]

Ok, let's look at an air/raft:
It can cancel slightly more than 1G, which means it's contents (driver, passengers, cargo) could well be in free-fall when the grav drive is running. Awkward. Perhaps it creates 1G of artificial gravity within itself? If so, could one then turn off the 1G "cancellation" while leaving the 1G artificial gravity on? That would provide 1G downward force (in addition to gravity)!

This isn't something you'd want to do for long, as it would take 10 seconds of upward thrust at 0.1G to counteract 1 second of downward 1G thrust.

 

[kilemall]

Ok, let's look at an air/raft:
It can cancel slightly more than 1G, which means it's contents (driver, passengers, cargo) could well be in free-fall when the grav drive is running. Awkward. Perhaps it creates 1G of artificial gravity within itself? If so, could one then turn off the 1G "cancellation" while leaving the 1G artificial gravity on? That would provide 1G downward force (in addition to gravity)!

This isn't something you'd want to do for long, as it would take 10 seconds of upward thrust at 0.1G to counteract 1 second of downward 1G thrust.

Air/rafts are easy. Whether it is just pure repulsion off the planet's grav field or a buoyancy/cancellation effect along with thrust, down is 1 G with the field turned off.



I'm talking about a 4G maneuvering grav tank, what gives it the ability to 'thrust' down the same way a jet does? Should grav vehicles have the same 'agility' as aerospace vehicles in atmo without additional thrust components or a radically different gravitic tech?


Or a maneuvering starship for that matter, in a pure gravitic M-drive environment what allows that ship to 'thrust' towards the planet at 4G especially outside the planet's immediate G-effect?

 

[JimMarn]

What symbol library are those in?

Annual issue 99 has air rafts, enclosed air rafts, fighters, cutter, air rafts that remind me of an 18 wheeler, system defense boat, delivery truck size, and a triangular pirate.

Some are 'standard' colors, and some are vari-color.

Standard is mostly silver/metal looking with some air rafts of red, gray, blue, white color or highlights. One truck looking air raft is bright green and another is pale blue.

 

[JimMarn]

fair enough, I am far too young to have watched the Apollo landings (I wasn't even a twinkle in my dads eye at that point). I wasn't seeking to prove you wrong as much as provide the data for what you were talking about, which happened to be slightly different to your memory, but that happens. I mentioned L1 by name since once you know the name, its much easier to find out more about it.

I'm also old enough to have seen the Thor-Able launches that failed, along with Walter Chronkite talking about the early V-2 launches at White Sands, New Mexico. Ham the companzee, the little squirrel monkey going up to orbit, and the hurrah in the news when Sputnik orbited the Earth.

But I'm not old enough to remembger listening to a battery powered radio, battery recharged by the blacksmith, with plastic headphoes. That would be my mother's era.

I don't remind memory refreshes.

I've read so many books and watched so many documentaries, I rarely remember where I got a particular fact. And I do make mistakes.

 

[infojunky]

Annual issue 99 has air rafts, enclosed air rafts, fighters, cutter, air rafts that remind me of an 18 wheeler, system defense boat, delivery truck size, and a triangular pirate.

Some are 'standard' colors, and some are vari-color.

Standard is mostly silver/metal looking with some air rafts of red, gray, blue, white color or highlights. One truck looking air raft is bright green and another is pale blue.

Cool, Now off to acquire a Annual...

 

[Grav_Moped]

Air/rafts are easy. Whether it is just pure repulsion off the planet's grav field or a buoyancy/cancellation effect along with thrust, down is 1 G with the field turned off.



I'm talking about a 4G maneuvering grav tank, what gives it the ability to 'thrust' down the same way a jet does? Should grav vehicles have the same 'agility' as aerospace vehicles in atmo without additional thrust components or a radically different gravitic tech?


Or a maneuvering starship for that matter, in a pure gravitic M-drive environment what allows that ship to 'thrust' towards the planet at 4G especially outside the planet's immediate G-effect?

Then again, if it's just manipulation of planetary (or other massive body), the effects should be limited to (or at least constrained by) the local effective gravity. The fact that in canon, it's not, implies some sort of reactionless thruster rather than just antigravity.

Of course, reactionless thrusters are a pretty simple derivative of being able to turn gravity on and off.

 

[kilemall]

Ok, let's look at an air/raft:
It can cancel slightly more than 1G, which means it's contents (driver, passengers, cargo) could well be in free-fall when the grav drive is running. Awkward. Perhaps it creates 1G of artificial gravity within itself? If so, could one then turn off the 1G "cancellation" while leaving the 1G artificial gravity on? That would provide 1G downward force (in addition to gravity)!

This isn't something you'd want to do for long, as it would take 10 seconds of upward thrust at 0.1G to counteract 1 second of downward 1G thrust.

Then again, if it's just manipulation of planetary (or other massive body), the effects should be limited to (or at least constrained by) the local effective gravity. The fact that in canon, it's not, implies some sort of reactionless thruster rather than just antigravity.

Of course, reactionless thrusters are a pretty simple derivative of being able to turn gravity on and off.

I guess you'll have to spell it out for me as it's not so clear to me that turning gravity 'off and on' would translate to an effective drive.


Only thing that comes to mind is that the ship generates gravity forward of the ship and the ship 'falls' towards the artificial gravity. The classic 6G limit then becomes whatever the limit is to generate that much gravity, indeed it starts sounding awfully Alcubierre.


If one had a drive capable of that, then that would make for quite a potential for defending against missiles and possibly creating confusing signal returns for enemy sensors.

 

[Adam Dray]

Main Sequence has screens that bend space momentarily to ward off attacks, but it requires perfect timing, as the screens stay up less than a second.

They're great for deflecting missiles and lasers, but not great for cloaking. Besides the gravity waves produce a distinct signature that is very detectable.