Reaching orbit with Air-raft

[MrBackman]

Various canon Traveller sources state that Air-rafts can reach orbit and in my Traveller campaign precisely that situation arose during my weekend session with my kids. I assume here that the ship we want to match orbit with is in Low Earth Orbit (LEO). The problem is much simpler if the ship is hovering on its contragrav above the planet but that is not what the canon sources say; 'orbit' does not mean outside the atmosphere, it means outside the atmosphere with enough speed for centripetal forces to match gravity.

Has anyone playing a fairly realistic Traveller ran into this problem and how did you solve it (ruling out air-raft to orbit is one solution)?

If you dig into the problem there are lots of complications that crop up:

Problems with the vehicle:
An open topped vehicle is hardly built for vacuum as this costs a lot extra, so I guess the instrumentation, upholstery etc will break in vacuum. Another problem is that an air-raft produces something like 0.1 G thrust for propulsion which mean (ballpark calculations here) that to reach say 5 km/s orbital velocity they must accelerate for over an hour (ca 5000 seconds).

Problems with the calculations:
To match the orbit of a ship the air-raft driver must eyeball the ship and vector (yes, LEO ships can be seen at dusk or dawn by the human eye) and then match that orbit by hand with the air-raft over a more than an hour long acceleration phase. The air-raft will have no instrumentation for orbit matching and the like, just an accelerometer based (Traveller vehicles does not rely on the crude GPS system we use) absolute positional instrument that also indicate height as well as speed gauges. Calculating the orbital mechanics and driving the air-raft to comply is in my opinion a really hard problem for a spaceship pilot and impossible for mere grav-jockeys.
If you think orbit matching is a piece of cake try it yourself with the free PC space simulator Orbiter.

IMTU: My TL progression differs from canon and GURPS Traveller and this causes even more problems:
(I don't add gravtech until TL 10, so I can have cultures with jumpdrives without grav and floorfield, 'Hard-SF with jump' if you will)
Jumpdrives TL 9
Floaters TL 10
Floorfield TL 11
Gravthrust TL 12
Floater gravbelts TL 13
Reactionless drives TL 13
Gravbelts TL 14
Tractor beams TL 15
Presser beams TL 16
Rattlers (high freq tractor weapons) TL 17

Floaters are grav 'thrusters' that can only negate gravity, they can never create upwards or lateral thrust, just negate the downward pull of gravity. Floaters and gravthrust have 'thrust' proportional to local gravity so a 1G (Thrust = mass) floater will negate gravity on all planets, regardless of gravitation (simplifies designing gravvehícles and 'explains' why gravthrust is useless for interplanetary travel). Floaters come at TL 10, are much cheaper and require much less power per 'thrust' than regular gravthrust. Regular gravthrusters produce floating at the cost of x1/10 thrust (a 1G gravthrust would use 0.1 G for floating and 0.9 G for propulsion for example).
My air-rafts are so cheap they use floaters powered by a fuelcell for lift and turbojet for thrust (both the fuelcell and turbojet are hydrogen powered and need an atmosphere with oxygen to work).

So IMTU the air-rafts cannot reach orbit at all, they cannot even operate in anything near vacuum, fitted with compressors they can work in Very thin atmospheres, but that's it.

[thrash]

Originally Posted by MrBackman

An open topped vehicle is hardly built for vacuum as this costs a lot extra, so I guess the instrumentation, upholstery etc will break in vacuum.

Don't forget that many of the worlds that Travellers visit are effectively or actually in vacuum. I don't think this is an issue for Imperial (i.e., non-local) gear.

Another problem is that an air-raft produces something like 0.1 G thrust for propulsion which mean (ballpark calculations here) that to reach say 5 km/s orbital velocity they must accelerate for over an hour (ca 5000 seconds).

The original sources said that reaching orbit in an air/raft takes one hour per thousand miles of planetary diameter, so this is optimistic if anything.

The air-raft will have no instrumentation for orbit matching and the like,

Why not? It's not that difficult, and virtually a necessity to use the air/raft around small worlds.

... just an accelerometer based (Traveller vehicles does not rely on the crude GPS system we use) absolute positional instrument that also indicate height as well as speed gauges. Calculating the orbital mechanics and driving the air-raft to comply is in my opinion a really hard problem for a spaceship pilot and impossible for mere grav-jockeys.

I sincerely doubt that anyone except a sport enthusiast or show-off ever eyeballs an orbit or tries to calculate an intercept by hand. How hard would it be to contact the ship and have its computer calculate an intercept course, and then feed you regular updates using its collision-avoidance sensors? Or call space traffic control and ask for the orbital elements of the ship, so you can run it through your hand computer's intercept application?

There are certainly situations where this is an intractable problem (uncooperative ship above an uninhabited world), but in most cases the orbital mechanics are the least of your problems. Do your gravitics allow floaters to reach orbit at all? If so, does anyone want to spend multiple hours in a vacc suit to get there?

[malloyd]

Originally Posted by MrBackman

If you dig into the problem there are lots of complications that crop up:

Problems with the vehicle:
An open topped vehicle is hardly built for vacuum as this costs a lot extra, so I guess the instrumentation, upholstery etc will break in vacuum.

Essentially nothing built in the Imperium will have a problem with this. If you are building for export you *don't* get to assume anything about the atmosphere your product will be operating in. If something other than a standard atmosphere would be a problem for it (and really vacuum is not that hard on most equipment, there are lots worse environments) it will be sealed.

To match the orbit of a ship the air-raft driver must eyeball the ship and vector (yes, LEO ships can be seen at dusk or dawn by the human eye) and then match that orbit by hand with the air-raft over a more than an hour long acceleration phase.

So? Reaching orbit isn't the same thing as matching a specific orbit. On the other hand I'm not sure why you assume an air raft has no orbit matching instrumentation - it's not really a tremendously hard calculation, well within the capability of an autopilot, assuming you don' simply hand the problem off the local traffic control system. If you are planning on using your air raft as an interface vehicle, buy one with decent electronics.

Floaters are grav 'thrusters' that can only negate gravity, they can never create upwards or lateral thrust, just negate the downward pull of gravity.

Do not attempt to stress this if your players are technically oriented types. It's inviting things like we'll use it to float relative to the gravity of the sun (or the galaxy) rather than the planet and.... Straight reactionless thrust with "contragravity" being a popular misnomer actually suffers from a lot fewer problems.

So IMTU the air-rafts cannot reach orbit at all, they cannot even operate in anything near vacuum, fitted with compressors they can work in Very thin atmospheres, but that's it.

Then problem solved. If you've redefined the air raft so it's very different from canon, why is it even an issue that it has different capabilities from canon?

[Apache]

/facepalms

[ak_aramis]

Canon already has a tech level with JDrives but without gravitics. The GT mangling of Tech Levels to fit GURPS rendered missing.

In actual GDW Traveller, not GT nor MgT, TL 9 has no artificial Grav nor gravitic thrust, but has Jump 1; gravitics come in at TL 10.

This not appearing to exist in GT is simply an artifact of GT's tech level compression past TL 8.

[thrash]

Originally Posted by ak_aramis

In actual GDW Traveller, not GT nor MgT, TL 9 has no artificial Grav nor gravitic thrust, but has Jump 1; gravitics come in at TL 10.

Air/rafts are TL8 (Book 3, pp. 15 and 23), as are GCarriers and Speeders (Book 3, p. 23).

[MrBackman]

Originally Posted by ak_aramis

Canon already has a tech level with JDrives but without gravitics. The GT mangling of Tech Levels to fit GURPS rendered missing.

In actual GDW Traveller, not GT nor MgT, TL 9 has no artificial Grav nor gravitic thrust, but has Jump 1; gravitics come in at TL 10.

This not appearing to exist in GT is simply an artifact of GT's tech level compression past TL 8.

Well, I wanted a TL with the so called contragrav things GURPS Spaceships use as well as TNE in that you get lift but not thrust, to allow flaoting grav thingys with jetegnines and the like.

MA Lloyd: My floaters merely negate any and all gravity from all directions so none of the problems you depict occur. 'Floaters' break the law of momentum conservation as does reactionless thrusters, you cannot really say that one is worse than the other.

When air-rafts where built using Megatraveller design system or Fire Fusion and Steel they didn't put radars etc needed for matching a ship in orbit. I am pretty sure that the air-raft in GURPS Traveller (built using GURPS Vehicles?) didn't have the needed instrumentation and sensor either.

I'm sorry if I offended anybody by pointing out some, in my opinion, unrealistic stuff from old canon. I am actually a bit surprised at the strong reaction, especially from mr Lloyd - is this the same Lloyd who wrote the awesome additions to Vehicles with audio signatures and realistic falloff for communicators and sensors, way back?

[MrBackman]

Originally Posted by thrash

Air/rafts are TL8 (Book 3, pp. 15 and 23), as are GCarriers and Speeders (Book 3, p. 23).

Thank's! The old LBB Traveller universe was kind of boring in that sense as the TL progression was kind of like this:

Various historical inventions appear all the way up to TL 7. After that they invent fusion, grav etc at TL 8, jump at TL 9 and from then on only small increment in capabilities occur.

[thrash]

Originally Posted by MrBackman

Various historical inventions appear all the way up to TL 7. After that they invent fusion, grav etc at TL 8, jump at TL 9 and from then on only small increment in capabilities occur.

At least GDW was relatively consistent about it: per capita GNP doubled between TL5 and TL6, TL6 and TL8, and TL8 and TL12, and arguably wouldn't have doubled again until TL20 (Striker, Book 2, p. 38, under "Integration with Traveller"). This implies that the differences between TLs become finer the higher one goes on the scale.

[MrBackman]

Originally Posted by thrash

At least GDW was relatively consistent about it: per capita GNP doubled between TL5 and TL6, TL6 and TL8, and TL8 and TL12, and arguably wouldn't have doubled again until TL20 (Striker, Book 2, p. 38, under "Integration with Traveller"). This implies that the differences between TLs become finer the higher one goes on the scale.

True. GURPS way of making each TL a separate culture works better but then maybe the different Traveller societys (Imperium, Zhodani, K'Kree etc) should have a TL rating and the planets should instead have a more fine grained production rating than the standard sequence: Low pop -> Non Industrial -> Regular -> Industrial.

I have been toying with the idea to have the population limiting what one can produce: 1 million inhabitants and they can produce items that cost 1 MCr in local currency, everything more expensive has to be imported or 'hand built' ie much more expensive. The population limit would not apply to Industrial planets, they are the heavy lifters of industrial production in Traveller.