Planetary launch

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brazouck
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Planetary launch

Postby brazouck » Wed Sep 23, 2015 11:50 am

Hello,

how are ships that land on planet launched back in space ? ae their internal drive providing enought thrust or do they use magnetic rails and / or booster packs at starport ?

And if on internal drive, are they on a vertical ramp or do they take off like a plane ?

Thanks
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MongooseMatt
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Re: Planetary launch

Postby MongooseMatt » Wed Sep 23, 2015 12:04 pm

Their drives provide enough thrust - to actually lift off, they effectively use anti-gravity, so can take off vertically before transitioning to horizontal for speed.
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Re: Planetary launch

Postby brazouck » Wed Sep 23, 2015 12:13 pm

so they are on ground, use antigrav to leave ground, float some kilometers up, and then thrust main engine while being angled to leave atmosphere ?
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Re: Planetary launch

Postby MongooseMatt » Wed Sep 23, 2015 12:24 pm

I would say yes.
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ShawnDriscoll
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Re: Planetary launch

Postby ShawnDriscoll » Wed Sep 23, 2015 12:41 pm

They move like the Millennium Falcon does.
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Re: Planetary launch

Postby brazouck » Wed Sep 23, 2015 1:49 pm

ShawnDriscoll wrote:They move like the Millennium Falcon does.
I was thinking traveller was hard SF :?
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Re: Planetary launch

Postby Rikki Tikki Traveller » Wed Sep 23, 2015 2:58 pm

Contra-gravity has been around since the first issue of CT back in 1977. Ships of any thrust can reach orbit over any sized planet using contra-gravity.
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Re: Planetary launch

Postby brazouck » Wed Sep 23, 2015 3:23 pm

Rikki Tikki Traveller wrote:Contra-gravity has been around since the first issue of CT back in 1977. Ships of any thrust can reach orbit over any sized planet using contra-gravity.
ok thanks
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Re: Planetary launch

Postby High Orbit Drifter » Wed Sep 23, 2015 3:32 pm

Rikki Tikki Traveller wrote:Contra-gravity has been around since the first issue of CT back in 1977. Ships of any thrust can reach orbit over any sized planet using contra-gravity.
So how does a ship with 1g of thrust take off from a planet with a 1.5 gravity pull?
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Re: Planetary launch

Postby atpollard » Wed Sep 23, 2015 4:35 pm

High Orbit Drifter wrote:
Rikki Tikki Traveller wrote:Contra-gravity has been around since the first issue of CT back in 1977. Ships of any thrust can reach orbit over any sized planet using contra-gravity.
So how does a ship with 1g of thrust take off from a planet with a 1.5 gravity pull?
Depending on the Traveller rules version and group house rules:

1. it doesn't ... don't land in the first place unless you have a 2G ship.
2. the magic grav drives can briefly overclock to produce enough thrust.
3. the world has strap on boosters of some sort.
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Re: Planetary launch

Postby Jeraa » Wed Sep 23, 2015 4:59 pm

brazouck wrote:
ShawnDriscoll wrote:They move like the Millennium Falcon does.
I was thinking traveller was hard SF :?
Not really. Harder than a lot of others, however.
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Re: Planetary launch

Postby Condottiere » Wed Sep 23, 2015 5:32 pm

Give the Order Maximum Speed, which will gain you an extra one gee in acceleration.
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Re: Planetary launch

Postby spirochete » Wed Sep 23, 2015 6:23 pm

High Orbit Drifter wrote:So how does a ship with 1g of thrust take off from a planet with a 1.5 gravity pull?
By taking on less fuel and cargo. The lighter load will net more acceleration for the same thrust level, allowing you to reach orbit.
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Re: Planetary launch

Postby CosmicGamer » Wed Sep 23, 2015 8:38 pm

I'm no science whiz. This is how I always thought of it, but I could be wrong.

Aerodynamics and/or constant thrust.

G force isn't everything. Some cars can produce more G-Force than some planes! If the world has an atmosphere and the ship has lift surfaces... Even if it is just a wedge body with no wings I think it produces some lift.

Speaking of cars, think of a very fast car hitting the top of a steep incline and going airborne before gravity brings it back down. Now think many, many times faster. It is 1G of constant thrust not maximum speed. Unless you have 1G of drag, I think you can use a really long "takeoff" with that constant 1G thrust building up more and more speed until you reach an escape velocity.
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Re: Planetary launch

Postby hiro » Wed Sep 23, 2015 9:06 pm

High Orbit Drifter wrote:So how does a ship with 1g of thrust take off from a planet with a 1.5 gravity pull?
There's no mention of mass in the ship designs, it's hand waved and the ship does what it's crew wants and the GM aids and abets.

The different versions of Traveller rules have often been vague about this and how contra grav actually works. I'm pretty sure MgT doesn't specify it at all, it leaves it for you to decide or you can go read some of the previous versions of Traveller to see how they described it.

The question therefore gets bounced back at you, how do you want it to work? How do you want a 1G ship to land and take off from a planet with higher G?

A couple of possibilities:

Your GM insists the ship does it's business at the high port and if you want to go planet side you find alternative means to get there and back. Hailing a cab in space works fine just mind the vacuum.

Work out escape velocity from G, Earth's escape velocity is 11.2km/s, 1.5G would give a local escape velocity of 16.8km/s. If your ship can fly/generate lift cos it has aerofins from the ship design sequence, you can then calculate how long it takes to get to 16.8km/s in a 1G ship: 1G is 9.8m/s^2. I'll leave you to do the math :mrgreen:

As I mentioned at the start of the post, it's all hand waved anyway cos there's no mass figured into the ship specs.

If the ship is only streamlined, no aerofins, you're back to hailing that cab.
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Re: Planetary launch

Postby ShawnDriscoll » Wed Sep 23, 2015 10:40 pm

brazouck wrote:
ShawnDriscoll wrote:They move like the Millennium Falcon does.
I was thinking traveller was hard SF :?
Oh, no. Not the hard sci-fi thing again. There's no such thing.
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Re: Planetary launch

Postby hiro » Wed Sep 23, 2015 10:44 pm

Damn, I agree with SD on something.

No, Traveller is not hard sci-fi.

From what I know, the closest you can get to it in the Traveller ruleset is Zozer's excellent Orbital.

http://www.drivethrurpg.com/product/109 ... t_filtered
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Re: Planetary launch

Postby atpollard » Thu Sep 24, 2015 12:36 am

ShawnDriscoll wrote:
brazouck wrote:
ShawnDriscoll wrote:They move like the Millennium Falcon does.
I was thinking traveller was hard SF :?
Oh, no. Not the hard sci-fi thing again. There's no such thing.
I disagree, there is such a thing as Hard Sci-Fi ... It is just no darn fun.
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Re: Planetary launch

Postby haveahappy » Thu Sep 24, 2015 12:54 am

Hard sci-fi is still sci-fi.

There has to be SOME fi in your sci.
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Re: Planetary launch

Postby NOLATrav » Thu Sep 24, 2015 5:15 am

I figure every ship is actually generating twice its Thrust, half for Thrust (moving) and half for the deck plates (compensation).

So you turn off compensation and shunt that to Thrust and you can go 2G instead of 1G, but the people inside are now subject to 1G of maneuvering forces.

IMTU I allow acceleration couches (standard in staterooms and workstations) to offset 1G plus 0.25G per TL beyond 10. After that you need G-drugs, Improved Dampening for you deck plates, etc. Uncompensated G forces inflict damage every turn and cause -DMs on every task.

Works for me, now my players get how a 1G trader can refuel at a 1.5G gas giant and land on its 1.5G Mainworld moon.

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