Apologies if this is addressed later, but would it not be better for clarity to use (Vector3.back) instead of (-Vector3.forward)?
private void ProcessInput()
{
if (Input.GetKey(KeyCode.Space)) // Can thrust while rotating
{
rigidBody.AddRelativeForce(Vector3.up);
}
if (Input.GetKey(KeyCode.A))
{
transform.Rotate(Vector3.forward);
}
else if (Input.GetKey(KeyCode.D))
{
transform.Rotate(Vector3.back);
}
}