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Moonlander
CPE 101: Fundamentals of Computer Science

Purpose
To gain experience writing functions that return values or perform I/O operations, as well as integrate a collection of
functions into a complete program.
Description
Download the project files at:
http://users.csc.calpoly.edu/~dkauffma/101/moonlander.zip
moonlander.py   Starting file for your program’s functions
test[1-3].txt   Test cases for the full program
Use the wget command to download the archive to the CSL server:
wget http://users.csc.calpoly.edu/~dkauffma/101/moonlander.zip
Unzip the archive:
unzip moonlander.zip
Background
You are tasked with writing a program that simulates landing the Lunar Module (LM) from the Apollo space program
on the moon. The simulation starts when the retro-rockets cut off and the astronaut takes control of the LM. The LM
starts at a user-specified altitude with an initial velocity of zero meters per second and has a user-specified amount of
fuel on board. With the manual thrusters off and the LM in free-fall, lunar gravity is causing the LM to accelerate
toward the surface according to the gravitational constant for the moon. The pilot can control the rate of descent using
the thrusters of the LM. The thrusters are controlled by entering integer values from 0 to 9 which represent the rate of
fuel flow. A value of 5 maintains the current velocity, 0 means free-fall, 9 means maximum thrust; all other values are
a variation of those possibilities and can be calculated with an equation that is provided below.
To make things interesting (and to reflect reality) the LM has a limited amount of fuel – if you run out of fuel before
touching down you have lost control of the LM and it free-falls to the surface. The goal is to land the LM on the
surface with a velocity between 0 and -1 meters per second, inclusive, using the least amount of fuel possible. A
landing velocity between -1 meters per second and -10 meters per second (exclusive) means you survive but the LM is
damaged and will not be able to leave the surface of the moon – you will be able to enjoy the surface of the moon as
long as your oxygen lasts but you will not leave the moon alive. Velocities faster than (less than) or equal to -10
meters per second mean the LM sustains severe damage and you perish immediately.
The initial conditions of 1300 meters altitude and 500 liters of fuel were used in the original simulation and were
chosen so that an optimal landing should use approximately 300 liters of fuel. It’s a considerable challenge at first, and
you may enjoy trying it.
Implementation
Instructor Executable
Moonlander http://users.csc.calpoly.edu/~dkauffma/101/moonlander.html
1 of 5 3/15/19, 1:23 PM
Before you begin, try the instructor’s executable with the command /home/dkauffma/moonlander.exe on
one of the CSL servers. Start at 1300 meters with 500 liters of fuel and see how you do.
Function Definitions
In the first part of this project, you must write and test the functions that will eventually be used to complete the
finished Moonlander program. All function definitions must be written in moonlander.py, which has already been
started for you. These functions fall into two categories: those that calculate and those that do I/O (input/output). Test
your functions that calculate using assert statements in a file called mltests.py. You will test your functions that do I/O
using the Python interpreter.
I/O Functions
See the executable for the exact text to be displayed with these functions.
show_welcome() – NoneType
Display the welcome message.
get_altitude() – int
Prompt the user for an integer in the interval [1, 9999]. If this value is invalid, display an error message and prompt
the user again; otherwise, return this integer. This function must use a while loop.
get_fuel() – int
Prompt the user for a positive integer. If this value is non-positive, display an error message and prompt the user
again; otherwise, return the integer. This function must use a while loop.
get_fuel_rate(fuel: int) – int
Prompt the user for an integer in the interval [0, 9]. If this value is invalid, display an error message and prompt the
user again; otherwise, return the lesser of the user-entered value or the amount of fuel remaining on the LM (the
argument passed to this function). In other words, the user cannot use more fuel than the amount remaining in the
lander. This function must use a while loop.
display_state(time: int, altitude: float, velocity: float, fuel: int, fuel_rate: int) – NoneType
Display the state of the LM as indicated by the parameters, using Python’s string format function to ensure that all
values are properly lined up. If the lander is out of fuel, display the corresponding message instead. At the start and
end of the game, this function should also print the corresponding “LM state” message.
display_landing_status(velocity: float) – NoneType
Display the status of the LM upon landing, conforming to one of three possible outputs depending of the velocity of
the LM at landing, which are:
Status at landing – The eagle has landed!
Print if the final velocity is between 0 and -1 meters per second, inclusive.
Status at landing – Enjoy your oxygen while it lasts!
Print if the final velocity is between -1 and -10 meters per second, exclusive.
Moonlander http://users.csc.calpoly.edu/~dkauffma/101/moonlander.html
2 of 5 3/15/19, 1:23 PM
Status at landing – Ouch – that hurt!
Print if the final velocity is ≤ -10 meters per second.
Calculate Functions
The subscripts in the formulas below indicate whether the value is of the previous or next time step and will help you
determine the order these functions must be called in the second part of the project. Subscripts should not be included
as part of variable names.
update_acceleration(gravity: float, fuel_rate: int) – float
Return the new acceleration based on the provided inputs and the formula:
acceleration1 = gravity * ((fuel_rate1 / 5) – 1)
Use 1.62 as the gravitational constant for the moon when calling this function.
update_altitude(altitude: float, velocity: float, acceleration: float) – float
Return the new altitude based on the provided inputs and the formula:
altitude1 = altitude0 + velocity0 + (acceleration1 / 2)
(As the surface of the moon stubbornly limits an altitude to non-negative values, ensure your code does the same).
update_velocity(velocity: float, acceleration: float) – float
Return the new velocity based on the provided inputs and the formula:
velocity1 = velocity0 + acceleration1
update_fuel(fuel: int, fuel_rate: int) – int
Return the new amount of fuel based on the provided inputs and the formula:
fuel1 = fuel0 – fuel_rate1
main Function
Begin this part with your fully tested moonlander.py file. Now you must write a main function that simulates the
advancement of the LM from time period zero to landing, calling the functions written previously along with some
additional code to connect them together. Don’t hesitate to ask your instructor questions early in the process to help
make sure you understand what you are supposed to be doing. You will probably go down some dead ends and need
to remove and rewrite code, so be sure to allocate enough time.
In main, you do not need to write nested loops, nor do you need to write a loop followed by another loop. The
problem may be solved in both of those ways, but it should be solved more simply by writing a single loop.
The main function should not do any I/O; that is, do not call input or print inside main.
Testing
Calculate Functions
Moonlander http://users.csc.calpoly.edu/~dkauffma/101/moonlander.html
3 of 5 3/15/19, 1:23 PM
Test these functions using assert statements in mltests.py. You must provide at least 3 tests per function. Each test
should be written with its own assert statement.
I/O Functions
Test these functions in the Python interpreter:
1. import moonlander
2. moonlander.show_welcome()
3. Repeat Step 2 for other functions you wish to test
You should also test with invalid inputs to functions. For example, try entering a negative number for the initial
altitude and ensure the proper error message is displayed. You need not test with inputs other than integers.
main Function
Use the diff command to compare your program’s output against that of the moonlander.exe executable using the
provided test cases. Be sure to test the program using other inputs as the instructor’s test suite has additional test cases
(in other words, some test cases are hidden from you).
Run the executable until you are familiar with how the code should behave. Then run your code by typing the
command below, making sure your moonlander.py file is in the same directory.
python3 moonlander.py
If your version does not behave the same as the solution, modify the appropriate functions in moonlander.py
and test some more. Once you are confident that your code behaves just like the instructor’s version, go to Step
2.
1.
Run the executable with the test1.txt file and save the results in a file called exe.txt (though you can name it
anything):
/home/dkauffma/moonlander.exe < test1.txt exe.txt
2.
Run your moonlander.py module with the test1.txt file and save the results in a file called my.txt (or, again, any
name you prefer):
python3 moonlander.py < test1.txt my.txt
3.
Compare both files to see if they match:
diff exe.txt my.txt -sy
The -s option will let you know if both files are equal (otherwise it succeeds silently). The -y option will
display the content of both files side-by-side, with a | symbol indicating that that line has a difference.
4.
Continue modifying moonlander.py and comparing its output to the instructor’s version until the diff command
reports that the files are identical.
5.
6. Be sure to perform the above steps with the other provided test cases as well as any other cases that you create.
Submission
On a CSL server with moonlander.py and mltests.py in your current directory:
Moonlander http://users.csc.calpoly.edu/~dkauffma/101/moonlander.html
4 of 5 3/15/19, 1:23 PM
/home/dkauffma/casey.exe 101 moonlander
Moonlander http://users.csc.calpoly.edu/~dkauffma/101/moonlander.html
5 of 5 3/15/19, 1:23 PM

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