Monday, June 10, 2013

A little rocket science

Something I've had my eye on for a little while has been the Kerbal Space Program.

I think I've mentioned it before a few times but it's only recently that I've opened up my copy and started to play. (Things like another Deus Ex run and not having the mental energy to learn something new have got in the way).

What is the Kerbal Space Program ?

It's a rocket simulator. You build your own rockets out of snap together bits and pieces, take it to the launchpad and watch it explode. Most of the time. Some of the time, you can try for escaping the orbit of the home planet and attempt to reach its Mun. Or even build huge ships out of multiple component launches and attempt to reach the other planets.

There's a lot of scope in the "game". Shouldn't really call it a game actually. Something as high quality as this is a stellar teaching aid. The building of the rockets is highly simplified and they are very easy to control. You have 3 axes of freedom plus a throttle. There's a stabilisation module that quickly stops your rocket tumbling out of control, if you've added the right bits.

The complication is hidden under the skin, with full physics orbital mechanics modelling at play. Going from Earth to the Moon isn't just about pointing the rocket at the Moon and throttling up the engines. The Moon will have moved by the time you get there and the course will curve due to all the little bits of gravity in play. KSP fully models all that complication, it lets you know what's happening and there's a couple of tutorials that let you know what's going on.

That shot's from one tutorial and shows the map view. The navball at the bottom helps you point in the correct direction (the green markings). The Mun is the big rock in the middle, the little grey triangle icon is my spaceship. The blue curve shows the partial orbit around the Mun. This is just after getting there, so it's not a properly formed orbit yet. There's a "Pe" for periapsis (point of orbit where you're lowest) and the little circle at the end of the line shows where your ship would escape the Mun's gravity if you did nothing. The thing to do here is to point backwards at "Pe" and then thrust to slow down. That should turn the escape into an orbit.

There's massively complicated maths but the visualisation tools in the program help you deal with it.
How did my attempts over the weekend go ?

Here's the first rocket ship attempt :

It's a fairly standard 2 stage rocket with a command module on top. The first stage has solid rocket boosters surrounding a main engine. The intention is that this stage gets your rocket to orbit. The second stage would then propel the command module to Mun orbit. This was early days so I was just looking to go Mun & back. Nothing fancy like an actual landing ...

How did this one go ? It got out of the atmosphere but never made the orbit. It needed more rockets. Actually needs another stage I think.

So - I add more rockets. And ...

Oops. Oh well. The little conical thing lying by the side of the support pylons is the command module. It survived ! And half a second before I took that screenie, good old Jeremiah Kerman was going "Let's do that again!". I think what I did this time was have the separators (which detach the boosters) firing before the boosters. Cue launching pad fireworks show.

I'm about to head back in again to see if I can make a working Mun rocket (without resorting to the wiki crib sheet!). But ... something like this can't really be described in words, so here's a Youtube video with someone talking you through the pictures.

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