Gravity

RocketPy provides a flexible way to model the gravitational acceleration in simulations. The gravity parameter can be set to various input types to define the gravity model used in the simulation. Below are the details on how to set and use the gravity model in RocketPy.

Gravity Parameter

The gravity parameter can be specified as an integer, float, callable, string, or array. Positive values indicate downward acceleration. If None, the Somigliana formula is used. For more information, refer to Environment.set_gravity_model().

Constant Gravity Acceleration

To set up an Environment object with a constant gravity acceleration:

from rocketpy import Environment


g_0 = 9.80665
env = Environment(gravity=g_0)

print("Gravity acceleration at 0m ASL: ", env.gravity(0))
print("Gravity acceleration at 1000m ASL: ", env.gravity(1000))
print("Gravity acceleration at 10000m ASL: ", env.gravity(10000))

Gravity acceleration at 0m ASL:  9.80665
Gravity acceleration at 1000m ASL:  9.80665
Gravity acceleration at 10000m ASL:  9.80665

Variable Gravity Acceleration

To vary the gravity acceleration as a function of height:

from rocketpy import Environment


def gravity(height):
    g_0 = 9.80665 # Gravity at sea level
    R_t = 6371000 # Earth radius
    return g_0 * (R_t / (R_t + height))**2

env = Environment(gravity=gravity)

print("Gravity acceleration at 0m ASL: ", env.gravity(0))
print("Gravity acceleration at 1000m ASL: ", env.gravity(1000))
print("Gravity acceleration at 10000m ASL: ", env.gravity(10000))

Gravity acceleration at 0m ASL:  9.80665
Gravity acceleration at 1000m ASL:  9.80357218600464
Gravity acceleration at 10000m ASL:  9.775937052994687

Somigliana Gravity Formula

The Somigliana formula computes the gravity acceleration with an altitude correction accurate for aviation heights. This formula is based on the WGS84 ellipsoid.

Tip

The Somigliana formula is the default gravity model used in RocketPy. If the gravity parameter is set to None, the Somigliana formula is used.