def Mass_of_spaceship(wet_mass, mass_flow, dry_mass, i):
    """Calculates the mass of the rocket at time t
    Args:
        wet_mass (float): The mass of the ship and fuel at time t=0.
        mass_flow (float): Amount of fuel expelled per timestep
        i (int): Iterator used for Euler's Method
    Returns:
        mass_ship (float): The new mass of the ship at timestep i.
    """
    TIME_STEP = .1
    mass_ship = dry_mass + wet_mass - mass_flow * TIME_STEP * i

    return mass_ship