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Old 10-05-2018, 07:55 PM   #1
nukesnipe
 
Join Date: Oct 2007
Default Triplanetary: Launching from a planet

Launching from a planet

The short question: Must a ship spend at least 1 turn in orbit prior to leaving orbit?

The longer question:

Per the rules:

1. "Boosters provide an acceleration of one hex from the world or satellite to an adjacent hex."

2. "The planetary surface gravity immediately cancels takeoff velocity, leaving the ship stationary in the gravity hex immediately above the base. Unless fuel is spent on the next turn, the ship would fall back to the planet and crash."

3. By expending a point of fuel, the snip may enter clockwise or counter-clockwise orbit. On a later turn it may burn fuel to leave orbit to return to the planetary surface or venture into space."

In #1 above, should "acceleration" read "velocity"?

The wording of #2 seems to contradict the rules regarding gravity which state that "gravity takes effect on the turn after an object enters the gravity hex." It would seem that, applying the gravity rules, on the turn after launch, without burning fuel, the ship would move one hex directly away from the planet (beyond the gravity hex), then "fall" back into the gravity hex for a net velocity of zero. On the following (third) turn, provided no fuel is burned, the ship would fall into the planet.

It would seem, following the gravity rules, that if I burned fuel directly away from the planet on the turn after launch the ship would end up two hexes above the planet with a velocity of 1.

However, #2 and #3, combined, imply that on the turn after launch the ship's net velocity is zero and its only option is to burn fuel to enter orbit. On the third or subsequent turn the ship can burn fuel to leave orbit.

So, a literal reading of the rules implies that it takes a minimum of three turns to leave a planets orbit: one to get off the planet, one to enter orbit and a third to leave orbit.

Is that how it is supposed to be?

Thanks for the help!
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Old 10-07-2018, 09:24 AM   #2
RogerBW
 
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Default Re: Triplanetary: Launching from a planet

This is not an official answer.

The way I've chosen to interpret it, in light of the second edition rules which I also have, is thus. (Assuming strong gravity.)

On turn N you launch from planetary base (effectively, the planet hex) to a gravity hex - let's call it eastwards. Your velocity at this point was 1 hex eastwards, but you've just entered a gravity hex so it's now zero for your next turn.

On turn N+1 you can:
  • Do nothing; as a special case, I rule that staying in the same hex causes gravity to be applied again. You now have a velocity of 1 west. On your next turn, if you still do nothing, you will crash (or land where you started).
  • Thrust west. You crash.
  • Thrust north-west or south-west. You have now entered a new gravity hex, so your velocity of (e.g.) 1 north-west gets 1 south-west added to it to become 1 west. You are in orbit.
  • Thrust north-east, east, or south-east. You are now travelling freely in space.
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Old 10-07-2018, 01:40 PM   #3
RogerBW
 
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Default Re: Triplanetary: Launching from a planet

For clarity: this does allow for overloading on turn N+1.
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Old 10-07-2018, 06:14 PM   #4
nukesnipe
 
Join Date: Oct 2007
Default Re: Triplanetary: Launching from a planet

Quote:
Originally Posted by RogerBW View Post
This is not an official answer.

The way I've chosen to interpret it, in light of the second edition rules which I also have, is thus. (Assuming strong gravity.)

On turn N you launch from planetary base (effectively, the planet hex) to a gravity hex - let's call it eastwards. Your velocity at this point was 1 hex eastwards, but you've just entered a gravity hex so it's now zero for your next turn.

On turn N+1 you can:
  • Do nothing; as a special case, I rule that staying in the same hex causes gravity to be applied again. You now have a velocity of 1 west. On your next turn, if you still do nothing, you will crash (or land where you started).
  • Thrust west. You crash.
  • Thrust north-west or south-west. You have now entered a new gravity hex, so your velocity of (e.g.) 1 north-west gets 1 south-west added to it to become 1 west. You are in orbit.
  • Thrust north-east, east, or south-east. You are now travelling freely in space.
Thanks for the response!

My college son has participated in several NASA events and informed me that while it was conceivably to lift off and enter the right trajectory to get to one's desired destination, it was much more prudent to enter a stable orbit before leaving the planet's gravity well.

So, unless overridden by SJG "officials", I'll play it to where you have to enter an orbit after launch, even if it's for only one turn. I believe that's how your explanation works, so I must be in good company. ;-)
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Old 10-07-2018, 11:15 PM   #5
Tom H.
 
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Default Re: Triplanetary: Launching from a planet

It looks like RogerBW has already provided a helpful response.

I had some thoughts as well.

Quote:
Originally Posted by nukesnipe View Post
The wording of #2 seems to contradict the rules regarding gravity which state that "gravity takes effect on the turn after an object enters the gravity hex."
I just saw launch from a planet's surface as a special case. Your ship's boosters are accelerating against earth's gravity just to get you to a break even point at orbital altitudes.

Quote:
Originally Posted by nukesnipe View Post
My college son has participated in several NASA events and informed me that while it was conceivably to lift off and enter the right trajectory to get to one's desired destination, it was much more prudent to enter a stable orbit before leaving the planet's gravity well.
Good to hear. I wondered about this, but was sure an answer could come from real world space travel. I was also going to refer you over to the GURPS forums where there appear to be several posters with lots of technical knowledge of topics like this.

I'm guessing that you can save energy or delta V (or whatever) by tapping into some of the orbital energy before you decide to sling out.

I just remember as a kid seeing diagrams of the missions to the moon where the trajectories circled the earth and did the same on reaching the moon presumably to aid in deceleration.
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Old 10-25-2018, 02:18 PM   #6
Jack O'All Trades
 
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Default Re: Triplanetary: Launching from a planet

Quote:
Originally Posted by RogerBW View Post
On turn N+1 you can:
  • Do nothing; as a special case, I rule that staying in the same hex causes gravity to be applied again. You now have a velocity of 1 west. On your next turn, if you still do nothing, you will crash (or land where you started).
  • Thrust west. You crash.
  • Thrust north-west or south-west. You have now entered a new gravity hex, so your velocity of (e.g.) 1 north-west gets 1 south-west added to it to become 1 west. You are in orbit.
  • Thrust north-east, east, or south-east. You are now travelling freely in space.
I think the rules are that you should have a 1 west velocity vector on turn N+1. You can still thrust any direction under this interpretation, including a 'stand still' by thrusting east. Notably this would mean you apply the gravity again regardless the next turn - but still an option for when you want to 'freeze' the orbit.

Notably if you thrust northwest or southwest you can skip orbiting and have an escape velocity under this interpretation on N+1, but there is no option to shoot straight out from the planet in the 'direction' of the 'launch' on N+1.

On Board Game Geek the interpretations tend to be either the same as mine (start with velocity 1 West, no special case) or only allow orbit moves on N+1 (which is essentially a special case by disallowing the 'stand still' or the 'thrust down and to the side to shoot by the planet on your way out' maneuvers).
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Old 11-01-2018, 06:09 AM   #7
RogerBW
 
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Default Re: Triplanetary: Launching from a planet

The core problem here is that there has been an explicit change of text from 2nd to 3rd edition. In 3rd, we have:

Quote:
By expending a point of fuel, the ship may enter
clockwise or counter-clockwise orbit. On a later
turn it may burn fuel to leave orbit to return to the
planetary surface or venture into space.
In 2nd (1981), we have:

Quote:
By expending fuel, the ship may enter clockwise or counter-
clockwise orbit (or otherwise maneuver as desired). When in
orbit, the ship may then leave orbit to return to the planetary
surface or venture into outer space by burning fuel to change course.
Clearly, "or otherwise maneuver as desired" has been removed. What a lot of us have been asking is: was this intended to be a deliberate rule change to force ships to enter orbit after takeoff, or was it coincidental?
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