manuever node tutorial gives incorrect information about burn duration

[Dunbaratu]

Problem 1 : Tsiolkovsky delta-V not mentioned - crude version is claimed to be the real thing:

The maneuver node tutorial uses the crude approximation of burn time to achieve delta-V of just dividing maxthrust by mass to get accelleration, and then assuming accelleration is a constant.

The proper calculation that takes into account the Tsiolkovsky rocket equation should be at least alluded to, along with the fact that the value present in the tutorial is just a crude approximation.

It doesn't have to use the complex real calculation - the crude one is fine for tutorial purposes. But it shouldn't be making false claims to users that that IS the actual burn time, which is what it's doing right now, and that sort of makes us look like we don't know what we're talking about when someone who knows a thing or two reads it.

Problem 2 : The example is unnecessarily complex for steering

It tells people to do this:

set np to lookdirup(nd:deltav, ship:facing:topvector). //points to node, keeping roll the same.
lock steering to np.

It could just tell people to do this:

lock steering to nd:deltav.

And then it would also auto-update if the XYZ axes of the universe happen to rotate while waiting for the burn.

[hvacengi]

I agree that the rocket equation should be mention, so that the user knows to go look for a better calc once they start looking for ways to improve accuracy. We may want to consider providing a STAGE:ISP suffix to the users to help with this too. I've always preferred the current path, where users must iterate through engines to calculate ISP, but a more accessible method might be an easy tie in to this reference.

As for problem two, technically lock steering to nd. would the the easiest syntax. I'm not sure that it's well documented, but a maneuver node is (and was before the recent revision) a valid steering value type. I did not test it extensively when removing the maneuver node, but I'll make sure to do so now. It may null ref, or it may just end up pointing at v(0, 0, 0), or something more "Kerbal".

[hvacengi]

Close via #1341