def Force_Gravity(mass_ship, altitude):
    """Calculates the force of gravity acting on the ship at altitude in meters
    Args:
        mass_ship (float): The mass of the ship at timestep i.
        altitude (float): The altitude of the rocket above Mean Sea level
    Returns:
        force_gravity (float): Calculated force of gravity at timestep i.
    """

    G = 6.674 * 10**-11
    MASS_EARTH = 5.972 * 10**24
    RADIUS_EARTH = 6.371 * 10**6  #meters
    STANDARD_GRAVITY = 9.80665  # m/s^2


    if mass_ship < 0:
        raise NameError("Mass error")

    force_gravity = G * mass_ship * MASS_EARTH / ((RADIUS_EARTH + altitude)**2)
    return force_gravity