Citizens of the Imperium

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-   -   Gravity greater than M-drive potential (http://www.travellerrpg.com/CotI/Discuss/showthread.php?t=36107)

atpollard May 10th, 2016 03:40 PM

Quote:

Originally Posted by mike wightman (Post 538484)
Typical Traveller ships do not have rocket drives, they don't throw reaction mass out of the back and don't have to worry about delta-V or orbital mechanics. The magic 1g maneuver drive provides a constant 1g of thrust.

Don't take off like a rocket, take off like an aeroplane - you accelerate along the ground until you achieve sufficient speed to become airborne thanks to lift - your ship is streamlined remember.
You now keep accelerating and climbing, getting faster and faster until your horizontal thrust is matched by air resistance, so you climb to lesson the air resistance, your thrust remains 1g and you keep climbing and getting faster.
When you reach an altitude where their is too little air to provide lift you will be going fast enough to point the nose up and achieve orbit - gravity falls off with distance and even if you only have effectively 0.01g of net acceleration for this 'rocket' stage of the flight you will still achieve orbit. It won't be as fast as just blasting off with a 2g drive, but you will get their.
Taking off from a 1g world with a 1g ship is easily doable.

Except you don't.
At 1 G thrust on a 1.2 G world you scrape that flat plate that the ship rests on along the ground, throwing sparks and carving a groove in the tarmac until the landing strut fails. ;)

A ship COULD be built to use lift.
The Classic ships (and starports) in the illustrations are not.

QED: That is why class A & B starports have Highports and class C & D starports have shuttles. Now they actually get some use.

aramis May 10th, 2016 04:09 PM

The Dragon Article, Exonidas Spaceport, by Jeff Swycaffer (Issue 76), puts a HG repulsor in the starport for launching ships ...

mike wightman May 10th, 2016 04:45 PM

Quote:

Originally Posted by atpollard (Post 538487)
Except you don't.
At 1 G thrust on a 1.2 G world you scrape that flat plate that the ship rests on along the ground, throwing sparks and carving a groove in the tarmac until the landing strut fails. ;)

Ever hear of the wheel? Last time I looked a 0,6g aircraft can take off just fine from a 1g world, ergo a 1g ship can lift from a 1.2 g world, you just have to hope the additional gravity means a thicker atmosphere so you can get high enough and fast enough that you can achieve orbit.
Hmm, how high do you have to be that the gravity has fallen to 0.99g?

Quote:

A ship COULD be built to use lift.
The Classic ships (and starports) in the illustrations are not.
If they are streamlined they do. The illustrations of ships are as much use as Aslan pictures.

hdan May 10th, 2016 05:28 PM

IMTU, I don't like M-drive overthrusting for routine operations like liftoff from a high-G world.

Instead, I have any TL8+ streamlined and standard hulls outfitted with lifter modules (like an air/raft uses). Those lifter modules can raise the ship, and are used for moving the ship around the port landing facility. On liftoff, the ship uses its lifters to get clear of the starport buildings, then activates the M-drive to climb to orbital altitude (and of course to gain velocity if trying to establish an orbit).

The lifters themselves are not capable of very fast acceleration, though of course they technically *could* lift the ship out of the atmosphere, given enough time.

For simplicity's sake, I consider lifters to be part of the cost of the ship's hull. And once or twice, I've had players have to deal with damaged lifters.

atpollard May 10th, 2016 05:42 PM

Quote:

Originally Posted by mike wightman (Post 538493)
If they are streamlined they do.

Please prove it?

Quote:

Originally Posted by TTB,Pg60
Atmospheric Streamlining: The hulls specified are rough deep space configurations incapable of entering atmospheres. They may be streamlined by so indicating in the design plans, at a cost of MCr 1 per 100 tons of ship. This streamlining includes fuel scoops which allow the skimming of unrefined fuel from gas giants and the gathering of water from open lakes or oceans. Streamlining may not be retrofitted; it must be included at the time of construction.

Says nothing about 'lift'. Like the Apollo Capsule, the streamlining simply provides a shape that is stable in atmosphere ... like a bullet. Without streamlining, parts break off. With streamlining, all the parts stay on.

I have no idea why the game provides such wonderful opportunities for High Ports and Shuttles and all sorts of adventures and local color, and then people want to engage in such mental gymnastics to render High Ports useless, and shuttles pointless and wave our arms while frantically shouting "overclock" and discarding all of the rich visual texture of the illustrations as "that's not what it is like".

How about if we embrace "High Ports" and "Shuttles" and "1G means 1G" and all of the artwork ... and a hand full of 1.2 G worlds become just a little more interesting when the SPA directs you to a parking orbit and you get five comms from competing shuttle companies that can transfer people or cargo from orbit to ground at different rates and prices. Do you spend several hours as a slow launch makes lots of trips (and save some money)? Do you spend extra for a 6G passenger service?

What is so terrible about this?

shaunhilburn May 10th, 2016 06:38 PM

Quote:

Originally Posted by mike wightman (Post 538313)
Al that is necessary is streamlined hull generated lift, an airframe hull does so with even greater efficiency.

Absolutely. Aerodynamic lift is available at TL 5 and doesn't just vanish once spaceflight is introduced.

Also, load factors should be considered. What is the acceleration of a Type A free trader with a full cargo hold? What is the acceleration with an empty hold? Since F=ma, acceleration cannot be the same in both situations. Less payload = more lift; so A Type A trader should be able to depart the most massive terrestrial worlds by leaving with less cargo.

Enoki May 10th, 2016 08:08 PM

Even if there were no atmosphere, the ship could still use forward momentum to build up to escape velocity climbing away from the planet at less than a vertical climb. This is akin to a missile that doesn't use lift but has less than a 1 to 1 weight to thrust combination.

So, it might have to skim the planet's surface for quite a distance slowly building speed to then start climbing away from it.

whartung May 10th, 2016 08:14 PM

Quote:

Originally Posted by atpollard (Post 538498)
I have no idea why the game provides such wonderful opportunities for High Ports and Shuttles and all sorts of adventures and local color, and then people want to engage in such mental gymnastics to render High Ports useless, and shuttles pointless and wave our arms while frantically shouting "overclock" and discarding all of the rich visual texture of the illustrations as "that's not what it is like".

If you look at the bulk of Traveller art, ships are depicted landed at a dirt side space port of some kind.

Also, folks tend to like the idea ala Firefly, ala Star Wars, to "set it down over there" in some appropriate clearing and then able to leave without, ideally, sparking off the largest wild fire since Tokyo '45.

The High Fantasy of Traveller is ships buzz around night and day, in and out of planets, with little more than a pleasing, cool humming sound, using little more than a large button and, perhaps, several levers with colorful knobs on them.

Think too hard on it and, yea, you have to come up with things like "Lifting bodies" and such.

LBB 1-3 and TTB are Traveller at is Space Opera-ish, Highest Fantasy-ist.

Issues like this aren't detailed, and don't come up because they don't matter.

Streamlining, fuel scoops, buoyancy, crush depth, lifting bodies, thrusters, heat exchange, blah blah blah -- TMI for the basic premise of getting characters in and out of Adventure™.

Whipsnade May 10th, 2016 08:20 PM

Quote:

Originally Posted by whartung (Post 538511)
Streamlining, fuel scoops, buoyancy, crush depth, lifting bodies, thrusters, heat exchange, blah blah blah -- TMI for the basic premise of getting characters in and out of Adventure™.


Very neatly put.

As always, the issue arises when the needs of those who play Traveller come into contact with the needs of those who play with Traveller.

Between the late 70s and early 90s, I ran countless sessions, adventures, and campaigns for players ranging from high school students to active duty military members to college students to war gamers to just plain folks and not one ever bothered with this question. Ships took off, ships landed, and the fun continued.

Please note: None of those two styles of play are superior to the other. They just have different goals and thus different requirements.

tjoneslo May 10th, 2016 08:40 PM

I recall an early article in IIRC, White Dwarf, where it was possible to purchase a one-time use rocket on high gravity worlds. This was attached to your ship for take off. It would produce something between 0.2 and 0.5 G, and long enough to get your ship into orbit. Cost a few hundred credits. Enough to be painful, but not enough to ruin a good trade.


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