Question regarding GURPS SPACESHIPS formulas

hal · 11-04-2017, 03:08 PM

Hello Folks,
Was working on some space craft for my Cyberpunk campaign - thinking I'd give GURPS SPACESHIPS a whirl to see what it could do. Knowing that my buddy doesn't much like dealing with Math during gaming, I thought I'd put together a spreadsheet that has all of the Formulas from the first book GURPS SPACESHIPS on it, and I'd simply enter the values as necessary.

Under "Space Travel with Reaction Drives" page 37, it talks about deltaV and moving between Mars and Earth. More specifically, it talks about accelerating for a bit, and then having to drop down to a final velocity of 2.1 miles per second to reach orbit around Earth.

But my question is this:

The ship starts off with a velocity equal to that required to escape the Mar's velocity (or .93 MPS). If it accelerates to 25 MPS, it would have needed an additional 25 MPS (its target speed) less that it already had, or 24.07 MPS.

So, in the example given - shouldn't the formula have been working of off the 24.07 MPS rather than 25? Likewise, if the ship needs to slow down to 2.1 MPS, it requires a delta V change of 25-2.1 or 22.9 MPS which would require its own calculation?

"Example: Since Princess of Helium has an acceleration of 0.5G and wants to reach 25 mps, it spends 25 x 0.0455/0.5 = 2.3 hours accelerating to cruising speed near Mars. In the process, the occupants experience a gentle one- half of an Earth gravity acceleration. The ship will need to decelerate for the same time at the other end of its trip."

Just checking to insure that I'm doing this right, which is why I'm following the examples given in the book - step by step so that my answers agree with what is in the book.

Thanks.

Hal

11-04-2017, 03:08 PM	#1
hal Join Date: Aug 2004 Location: Buffalo, New York	Question regarding GURPS SPACESHIPS formulas Hello Folks, Was working on some space craft for my Cyberpunk campaign - thinking I'd give GURPS SPACESHIPS a whirl to see what it could do. Knowing that my buddy doesn't much like dealing with Math during gaming, I thought I'd put together a spreadsheet that has all of the Formulas from the first book GURPS SPACESHIPS on it, and I'd simply enter the values as necessary. Under "Space Travel with Reaction Drives" page 37, it talks about deltaV and moving between Mars and Earth. More specifically, it talks about accelerating for a bit, and then having to drop down to a final velocity of 2.1 miles per second to reach orbit around Earth. But my question is this: The ship starts off with a velocity equal to that required to escape the Mar's velocity (or .93 MPS). If it accelerates to 25 MPS, it would have needed an additional 25 MPS (its target speed) less that it already had, or 24.07 MPS. So, in the example given - shouldn't the formula have been working of off the 24.07 MPS rather than 25? Likewise, if the ship needs to slow down to 2.1 MPS, it requires a delta V change of 25-2.1 or 22.9 MPS which would require its own calculation? "Example: Since Princess of Helium has an acceleration of 0.5G and wants to reach 25 mps, it spends 25 x 0.0455/0.5 = 2.3 hours accelerating to cruising speed near Mars. In the process, the occupants experience a gentle one- half of an Earth gravity acceleration. The ship will need to decelerate for the same time at the other end of its trip." Just checking to insure that I'm doing this right, which is why I'm following the examples given in the book - step by step so that my answers agree with what is in the book. Thanks. Hal