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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.lang.fortran
Subject: Re: Vintage Lunar Lander Game
Date: Sun, 23 Jun 2024 07:56:38 -0000 (UTC)
Organization: A noiseless patient Spider
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On Sat, 22 Jun 2024 08:37:00 -0000 (UTC), I wrote:

>     real(kind = useprec), parameter :: G = 0.001

OK, I figured out, this is lunar gravity in miles/second/second.

>     real(kind = useprec), parameter :: Z = 1.8

This is I think the rocket specific impulse.

>         delta_v = time_subinterval * fuel_rate / mass_total

This is not actually the change in velocity, it is the proportion of 
spacecraft mass being expelled over the subinterval.

>                     Z &
>                 * &
>                     ( &
>                         delta_v &
>                     + &
>                         delta_v2 / 2 &
>                     + &
>                         delta_v2 * delta_v / 3 &
>                     + &
>                         delta_v4 / 4 &
>                     + &
>                         delta_v4 * delta_v / 5 &
>                     )

I think this contribution to the velocity comes from the rocket equation. 
It’s a truncated power series; interestingly, it’s one with poor 
convergence.