Basic attitude simulation

[mhmodayman]

In scenarios, there is a basic orbit simulation

isn't there a basic attitude scenario simulation for a satellite propagating around some planet?

I am struggling to develop such a scenario [I mean without attitude control - just simulation]

[mhmodayman]

not pointing, not control, not pointing in deepspace, just a satellite propagating around a planet

[schaubh]

The scenarioBasicOrbit.py simulation simulates a spacecraft doing an orbit about the Earth while the attitude is held inertially fixed. All spacecraft states are initialized to zero, so the MRP attitude and body angular velocity are zero here. However, note that the spacecraft object always contains 6-DOF. If you want to modify scenarioBasicOrbit.py to include some rotational motion, then you find the place where the spacecraft states are initialized:

    scObject.hub.r_CN_NInit = rN  # m   - r_BN_N
    scObject.hub.v_CN_NInit = vN  # m/s - v_BN_N

and add the desired attitude heading and rate at the initial simulation time. In scenerioAttitudeFeedback.py both the translational and rotation motion are initialized. The attitude motion is set using:

    scObject.hub.sigma_BNInit = [[0.1], [0.2], [-0.3]]  # sigma_BN_B
    scObject.hub.omega_BN_BInit = [[0.001], [-0.01], [0.03]]  # rad/s - omega_BN_B

The spacecraft object propagates the orientation using MRPs. You can readily translate these to quaternions, Euler angles, etc. Python support file src/utilities/RigidBodyKinematics.py has a range of functions to do just that like MRP2C() to convert MRP to a DCM, DCM2EP() to convert a DCM to Euler Parameters (aka quaternions), etc.

[mhmodayman]

Hello Dr. Schuabh @schaubh. I would appreciate it if you could take a look at the code below.
Thanks in advance

[mhmodayman]

@schaubh, can you please check the lines of code that I added to the basic orbit simulation scenario file to simulate attitude angles?

am I doing it right? specially the (arrows <<<<<<<) highlighted lines below.

and are these Euler angles of the satellite body frame with respect to the earth-centered inertial frame.

# Inertia of hub about point Bc in B frame components
scObject.hub.IHubPntBc_B = [[0.9, 0.0, 0.0], [0.0, 0.9, 0.0], [0.0, 0.0, 0.3]]  # kg*m^2

# define the spacecraft mass
scObject.hub.mHub = 2.6  # [kg]

# define offset vector of the origin point {B} of body frame relative to center of mass
scObject.hub.r_BcB_B = [[0.0], [0.0], [0.0]]  # [m]

scObject.hub.sigma_BNInit = [[0.0], [0.0], [0.0]]  # [rad] sigma_BN_B
scObject.hub.omega_BN_BInit = [[0.08], [-0.02], [0.03]]  # [rad/s] - omega_BN_B

posData = dataRec.r_BN_N
velData = dataRec.v_BN_N

sigmaDataBN = dataRec.sigma_BN  # angular angles           <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
omega_BN_B = dataRec.omega_BN_B  # angular rates           <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

dataEulerAnglesPitch = list()
dataEulerAnglesYaw = list()
dataEulerAnglesRoll = list()

for sigma in sigmaDataBN:
    eulerAngle = RigidBodyKinematics.MRP2Euler321(sigma)
    dataEulerAnglesPitch.append(eulerAngle[0])  # theta, pitch, about y
    dataEulerAnglesYaw.append(eulerAngle[1])  # psi, yaw, about z
    dataEulerAnglesRoll.append(eulerAngle[2])  # phi, roll, about x