# Lander 101

Congratulations! You won a (one-way) trip to Mars in a cereal box. NASA was kind enough to donate the Lunar Excursion Module for this mission, so that's what you'll be flying.

Before you take off, you must go through some basic landing simulation. You shouldn't have to fly the lander if all goes as planned but, as they say, "better safe than sorry".

Your mission is to land the lander with a vertical speed of at most 10 m/s. There are two ways you can influence the lander's course: by adjusting its angle or by adjusting its thrust. In this simulation we only care about adjusting the thrust, expressed in m/s².

The [!python]`step()` function[/!][!scala|java|c]code[/!] that you should write now will be called every 0.1 second during the simulation. Make sure that your code does not last too long, with no while loop! It should only set the desired thrust of the next simulation step, by calling `[!java]void [/!]setDesiredThrust([!java]int [/!]desiredThrust[!scala]:Integer[/!])` where `desiredThrust` is some integer between 0 and 4 (that is, a thrust between 0 m/s² and 4 m/s²). You can only increment or decrement the thrust by 1 between two simulation steps, so if the current thrust is 2 and you ask for 4, you'll only get 3 in the next step. If you ask for less than 0 (resp. more than 4), everything will be as if you had asked for 0 (resp. 4).

In order to take informed decisions, you can query the lander's state. In this simulation you'll probably be interested in its vertical position: `[!java]double [/!]getY()[!scala]:Double[/!]`, and its vertical speed: `[!java]double [/!]getSpeedY()[!scala]:Double[/!]`. You can also ask for the thrust via `[!java]int [/!]getThrust()[!scala]:Integer[/!]` in case you don't remember what you asked for. Remember that Mars' gravity is 3.711 m/s², it might come in handy.

One last thing: the lander is pretty small so you don't have much fuel. At each step of the simulation the lander consumes as many fuel units as the current thrust. Once you run out of fuel you're in free fall so beware! You can consult the remaining amount of available fuel units using `[!java]int [/!]getFuel()[!scala]:Integer[/!]`.

Buona fortuna!