The Final Frontier: Fake Space, Part 3: A Lunar Date

Cue orchestral music.

The alarms blared incessantly, terminal lights flashed over and over, and behind Bill Kerman's head he swore he heard a panel of the command pod's outer hull make a deep, sonorous creak. Either the ship was pulling apart at the seams or he was hearing things.  The latter would be excusable, seeing as the pod was spinning like a top - although tops normally just spin in place around one central point, whereas Bill's ship was twirling in three dimensions, like a ballerina break-dancing for dear life.  As the surface of the Mün approached faster and faster, Bill Kerman  remembered his astro-lessons, not so very long ago...

Three weeks earlier.

The campus was abuzz with talk of Jebediah Kerman, whose unprecedented methods of space flight, once considered idiotic, had proven wrong even the most senior experts.  It was like they had been trying to navigate their way through space with the map turned upside down; no, worse, it was as if the map had been drawn in crayon by a particularly unimaginative toddler.  Outer Space Ballistic High Jumps were a thing of the past. Jebediah's success had shown everyone the true possibilities of space travel, but it had come at a cost: the sudden pioneer reported that he was out of fuel, a situation that had never been a concern when ships simply fell back to Kerbin.  Jebediah was in orbit, and now destined to circle the planet endlessly.  If he had been wrong, he would been a laughing stock; but he was right, and stranded up there.

The Kerbalnautical Academy had swiftly reconstituted itself.  New lessons, new ship designs and two new goals: one part of the faculty looking to reach the Mün, another looking to gently nudge Jebediah's ship back home.  As much as Bill wanted his old friend back by his side, he had been assigned to the first group.  Recently promoted Professors barraged him with concepts and methods which they had learned mere days ago.  Supposedly they knew what they were talking about, but it was an open secret about campus that nobody fully understood the new ideas.

Everything had been gleaned from the ancient texts Jebediah had been poring over in the library, an obscure tome bizarrely named "The Entire Net".  Most of it was twaddle, absurd pictures of cats mixed in with poorly spelt, schizophrenic arguments about things long forgotten.  Jebediah Kerman had skimmed through the trash and found a gem buried there: detailed instructions on how to get into orbit, proof that these mysterious precursors had been intelligent, thoughtful people, before descending into madness.  All that was left in the final pages were barely understandable strands of gibberish, until eventually it just repeated the word "twerking" over and over again.

Back in the present...

So Bill was about to become the first Kerbalnaut to the land on the Mün, but he didn't much fancy doing it in a pile of wreckage as flat as a pancake.  As the featureless grey landscape drew closer, he hit the parachute release button in desperation, before recalling that the Mün had no air to catch him.  As his messy end drew near, for once he felt jealous of Jebediah.

If you want to catch up with the earlier segments of this blog series, you can find the first part here, and the second over here.  Without further ado, let's dive back into space!

Engines throttled all the way up, nothing happening.

Last time I talked about the frustrating but ultimately rewarding experience of cracking the problem of orbit.  It involved thinking a little bit outside the box (when I'm not shamelessly following the instructions of wiki pages, that is), most importantly getting the right idea of how to build a rocket that can actually go places.  In order to get Bill Kerman to the Mün, his rocket (sarcastically named "What-Could-Go-Wrong I") has to a) be nice and symmetrical, to make the delicate task of getting into orbit achievable, and b) have room for a decent supply of fuel, so that Bill doesn't end up like Jebediah.  There is a catch to the second part of that design philosophy, however, and it presents itself pretty quickly if you really try to load up on fuel.  Too much fuel, and the ship weighs so much it takes an age to climb up to the void - in fact, it's hardly uncommon to watch it sit obstinately on the launchpad, engines blazing to no effect whatsoever (see image above).  My initial reaction to this problem was to strap on more engines, or a more powerful thruster instead - but this often led to the rocket greedily guzzling all its fuel before it even left the atmosphere. Rather than fall into an endless loop of throwing more fuel tanks and engines at this problem, I went back to the drawing board, and tried to be a tiny bit more sensible when attaching fuel tanks.

Are we there yet?

I had the right idea with the huge orange tank, at least: the rocket needs a lot of fuel to get off the ground, but when once it's out of the atmosphere it's a lot more economical.  I kept the twin engines strapped to the side, but moved them up to the top, parallel with the command pod.  After a few adjustments, I had a build that could fly into orbit and still have some juice left in the tank.  Next stop, the Mün! Unfortunately, I was still stuck in Stupid Mode. My untrained instinctive strategy was to position the rocket (at this point having disconnected the orange tank and then the side-mounted engines) facing the Mün, wait for what seemed like the right point in orbit, and fire the engine full blast.  I was assuming this was what folks at NASA mean when they use the word "slingshot", but it seems I was a long way off.  Incidentally, I'm not going to make any assumption that what works in Kerbal Space Program works for the very smart people involved in real life space travel - the game seems to me to be based on realistic laws of physics, but that's a discussion for another time.  On with the matter at hand (things are about to get fairly technical again).

Keep going...

After running through most of KSP's final tutorial, I saw where I'd been going wrong. Getting to another point in outer space isn't like, say, driving a car from your house to the shops, a situation where you'd pick the straightest line available and accelerate towards your destination.  In space, one travels in curved lines (although actually, the Earth's surface is curved, so you could say we never travel in a straight line, but let's keep this as simple as possible).  Anyway, as the game's tutorial explains quite well, conquering that pesky Mün involves manipulating the trajectory of your orbit and those fun words, "apoapsis", and "periapsis" - remember, the former is the highest point in orbit, the latter is the lowest. You increase the apoapsis by waiting until the rocket is on or near the periapsis, and accelerating in the direction you're travelling. The blue oval gets more elongated as the apoapsis gets further away (see above). Here's the maniacally simple part: line things up so the Mün and the apoapsis will almost meet, and you're all set for a lunar meeting!


It can be a bit tricky lining things up just right, so that Bill's ship doesn't sail straight past the Mün. Get it right, and you'll see a yellow line with the magical words, "Mün encounter" (click on the image to the left for an enhanced look). The next step is to carefully warp time forward (the alternative is waiting about half an hour) until the rocket enters the start of that yellow line, at which point it is officially being affected by the Mün's gravity.  Bill's travelling too fast, however, and is on what's called an "escape trajectory" - that is, skipping off the Mün's gravity like a stone skimming the surface of a lake.  If I don't want him to end up like Jedgan Kerman (still circling the Sun), I have to wait for him to reach the Mün's periapsis (i.e. the line's closest point to the Mün) and fire retrograde, or basically, point the rocket backwards and throttle the engine up.  This slows the ship down until there's a nice blue circle around the Mün.

Orbit achieved.

An interesting thing I discovered while getting screenshots for this post, is that my initial strategy - the erroneous slingshot method - while very inefficient, was not entirely flawed.  Pointing the ship aggressively towards the Mün and just accelerating can in fact lead to a lunar event, which surprised me quite a bit. I suppose there's more than one way to skin a galactic cat. It also used up almost all the ship's fuel, which is why the tutorial's version is the best way to go.  By throttling up at the periapsis of Kerbin's orbit, you get more control over where the rocket's headed and - crucially - use much less gas. In Bill Kerman's case, this meant he probably had just enough left in the tank to actually head home. Unfortunately for him, I made the dubious decision to try to land him on the Mün.  I learned two things from his demise: that you need quite a bit of fuel (and probably more thrusters) to slow down a rocket's descent by firing retrograde; and that parachutes don't work on the Mün.  In hindsight, that second bit should have been pretty obvious.

Bill Kerman. A pioneer. A hero to millions. An idiot.