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ericstoneking / 42

Simulation for spacecraft attitude control system analysis and design
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Questions: Regarding use of "Point" command in Inp_Cmd.txt #51

Open PeteBlanchard opened 3 years ago

PeteBlanchard commented 3 years ago

Eric,

Sorry to keep bugging you, I was trying to trace through the code myself, but there is quite a bit of it. When using the "Point" command in the 'Inp_Cmd.txt' file (say a lat/lon on Earth and using the PROTOTYPE_FSW), I had a couple questions:

Thanks in advance

annamaskolenko commented 2 years ago

Hello. Where do you see IdealTrq changing?

PeteBlanchard commented 2 years ago

Poor choice of words there...I saw IdealTrq set in flight software model initialization...

annamaskolenko commented 2 years ago

When I am trying to make SC_Simple to point to the Earth using the following command 10.0 Point SC[0].B[0] Primary Vector [0.0 1.0 0.0] at World[0] nothing happens. Spacecraft still rotates and from CAM window it is visually clear that the SC is not pointing to the Earth. Nevertheless, wbn output data produced is different from what it was with no pointing command. I am wondering if you figured out how to use the pointing command properly. I would be grateful if you could help me with it.

ericstoneking commented 2 years ago

I should point out that World[0] is the Sun. Earth is World[3]. For the complete list, see 42defines.h

annamaskolenko commented 2 years ago

Thank you! But still how quickly does the satellite turn? I have pointed its y axis towards World[3], i.e. Earth, but it is still rotating. Does PROTOTYPE_FSW use ideal actuators to execute the command?

ericstoneking commented 2 years ago

Hi Pete,

For whatever reason, I never saw this issue until yesterday, so sorry for the slightly slow response.

VectorRampCoastGlide's parameters are initialized in 42fsw.c:InitAC. My copy has a vmax of 0.5 deg/sec.

Yes, PrototypeCtrl will look at the spot you tell it to, whether that spot is visible or not.

Secondary vectors get populated by you. For the main body, if you don't define a SecVec, the sim should complain and crash. If it doesn't, I'd need to more about your setup. For an appendage, a PriVec and the constraints imposed by being an appendage are enough to fully define an attitude, so you don't need a SecVec.

Regards, -Eric

ericstoneking commented 2 years ago

Hi Anna,

Max slew rate is 0.5 deg/sec. PROTOTYPE_FSW does use ideal actuators. To monitor those, you may need to write them to an output file (see 42report.c to see how this is done in general) or use a debugger.

So, if it isn't pointing at the Earth, is there anything that it is pointing at? There may be clues there.

Regards, -Eric

annamaskolenko commented 2 years ago

Hi I do apologise in advance for such a long post. I have the following spacecraft's configuration:

<<<<<<<<<<<<<<<<< 42: Spacecraft Description File >>>>>>>>>>>>>>>>> 3-U Cubesat ! Description "Cube 3" ! Label GenScSpriteAlpha.ppm ! Sprite File Name PROTOTYPE_FSW ! Flight Software Identifier 0.2 ! FSW Sample Time, sec * Orbit Parameters **** ENCKE ! Orbit Prop FIXED, EULER_HILL, or ENCKE CM ! Pos of CM or ORIGIN, wrt F 0.0 0.0 0.0 ! Pos wrt F 0.0 0.0 0.0 ! Vel wrt F *** Initial Attitude LAL ! Ang Vel wrt [NL], Att [QA] wrt [NLF] 0.0 0.0 0.0 ! Ang Vel (deg/sec) 0.0 0.0 0.0 1.0 ! Quaternion 0.0 0.0 0.0 123 ! Angles (deg) & Euler Sequence Dynamics Flags *** KIN_JOINT ! Rotation STEADY, KIN_JOINT, or DYN_JOINT FALSE ! Passive Joint Forces and Torques Enabled FALSE ! Compute Constraint Forces and Torques REFPT_CM ! Mass Props referenced to REFPT_CM or REFPT_JOINT FALSE ! Flex Active FALSE ! Include 2nd Order Flex Terms 2.0 ! Drag Coefficient

***** Body Parameters **

1 ! Number of Bodies ================================ Body 0 ================================ 3.817 ! Mass 0.042 0.042 0.007 ! Moments of Inertia (kg-m^2) 0.0 0.0 0.0 ! Products of Inertia (xy,xz,yz) 0.0 0.0 0.0 ! Location of mass center, m 0.0 0.0 0.0 ! Constant Embedded Momentum (Nms) Cubesat_3U.obj ! Geometry Input File Name NONE ! Flex File Name

Joint Parameters 

     (Number of Joints is Number of Bodies minus one)

============================== Joint 0 ================================ 0 1 ! Inner, outer body indices 1 231 GIMBAL ! RotDOF, Seq, GIMBAL or SPHERICAL 0 123 ! TrnDOF, Seq FALSE FALSE FALSE ! RotDOF Locked FALSE FALSE FALSE ! TrnDOF Locked 0.0 0.0 0.0 ! Initial Angles [deg] 0.0 0.0 0.0 ! Initial Rates, deg/sec 0.0 0.0 0.0 ! Initial Displacements [m] 0.0 0.0 0.0 ! Initial Displacement Rates, m/sec 0.0 0.0 0.0 312 ! Bi to Gi Static Angles [deg] & Seq 0.0 0.0 0.0 312 ! Go to Bo Static Angles [deg] & Seq 0.0 0.0 0.0 ! Position wrt inner body origin, m 0.0 0.0 0.0 ! Position wrt outer body origin, m 0.0 0.0 0.0 ! Rot Passive Spring Coefficients (Nm/rad) 0.0 0.0 0.0 ! Rot Passive Damping Coefficients (Nms/rad) 0.0 0.0 0.0 ! Trn Passive Spring Coefficients (N/m) 0.0 0.0 0.0 ! Trn Passive Damping Coefficients (Ns/m) Wheel Parameters 0 ! Number of wheels ============================= Wheel 0 ================================ 0.0 ! Initial Momentum, N-m-sec 1.0 0.0 0.0 ! Wheel Axis Components, [X, Y, Z] 0.14 50.0 ! Max Torque (N-m), Momentum (N-m-sec) 0.012 ! Wheel Rotor Inertia, kg-m^2 0.48 ! Static Imbalance, g-cm 13.7 ! Dynamic Imbalance, g-cm^2 0 ! Flex Node Index ============================= Wheel 1 ================================ 0.0 ! Initial Momentum, N-m-sec 0.0 1.0 0.0 ! Wheel Axis Components, [X, Y, Z] 0.14 50.0 ! Max Torque (N-m), Momentum (N-m-sec) 0.012 ! Wheel Rotor Inertia, kg-m^2 0.48 ! Static Imbalance, g-cm 13.7 ! Dynamic Imbalance, g-cm^2 0 ! Flex Node Index ============================= Wheel 2 ================================ 0.0 ! Initial Momentum, N-m-sec 0.0 0.0 1.0 ! Wheel Axis Components, [X, Y, Z] 0.14 50.0 ! Max Torque (N-m), Momentum (N-m-sec) 0.012 ! Wheel Rotor Inertia, kg-m^2 0.48 ! Static Imbalance, g-cm 13.7 ! Dynamic Imbalance, g-cm^2 0 ! Flex Node Index **** MTB Parameters **** 0 ! Number of MTBs ============================== MTB 0 ================================= 180.0 ! Saturation (A-m^2) 1.0 0.0 0.0 ! MTB Axis Components, [X, Y, Z] 0 ! Flex Node Index ============================== MTB 1 ================================= 180.0 ! Saturation (A-m^2) 0.0 1.0 0.0 ! MTB Axis Components, [X, Y, Z] 0 ! Flex Node Index ============================== MTB 2 ================================= 180.0 ! Saturation (A-m^2) 0.0 0.0 1.0 ! MTB Axis Components, [X, Y, Z] 0 ! Flex Node Index * Thruster Parameters ** 3 ! Number of Thrusters ============================== Thr 0 ================================= 1e-6 ! Thrust Force (N) 0 1.0 0.0 0.0 ! Body, Thrust Axis 0.0 0.0 0.158 ! Location in B0, m 0 ! Flex Node Index ============================== Thr 1 ================================= 1e-6 ! Thrust Force (N) 0 0.0 1.0 0.0 ! Body, Thrust Axis 0.0 0.0 0.158 ! Location in B0, m 0 ! Flex Node Index ============================== Thr 2 ================================= 1e-6 ! Thrust Force (N) 0 0.0 0.0 1.0 ! Body, Thrust Axis 0.0 0.0 0.158 ! Location in B0, m 0 ! Flex Node Index *** Gyro **** 0 ! Number of Gyro Axes ============================== Axis 0 =================================== 0.1 ! Sample Time,sec 1.0 0.0 0.0 ! Axis expressed in Body Frame 1000.0 ! Max Rate, deg/sec 100.0 ! Scale Factor Error, ppm 1.0 ! Quantization, arcsec 0.07 ! Angle Random Walk (deg/rt-hr) 0.1 1.0 ! Bias Stability (deg/hr) over timespan (hr) 0.1 ! Angle Noise, arcsec RMS 0.1 ! Initial Bias (deg/hr) 0 ! Flex Node Index * Magnetometer **** 0 ! Number of Magnetometer Axes ============================== Axis 0 =================================== 0.1 ! Sample Time,sec 1.0 0.0 0.0 ! Axis expressed in Body Frame 60.0E-6 ! Saturation, Tesla 0.0 ! Scale Factor Error, ppm 1.0E-6 ! Quantization, Tesla 1.0E-6 ! Noise, Tesla RMS 0 ! Flex Node Index * Coarse Sun Sensor *** 0 ! Number of Coarse Sun Sensors ============================== CSS 0 ==================================== 0.1 ! Sample Time,sec 0 1.0 1.0 1.0 ! Axis expressed in Body Frame 90.0 ! Half-cone Angle, deg 1.0 ! Scale Factor 0.001 ! Quantization 0 ! Flex Node Index * Fine Sun Sensor * 0 ! Number of Fine Sun Sensors =============================== FSS 0 =================================== 0.2 ! Sample Time,sec 30.0 20.0 10.0 213 ! Mounting Angles (deg), Seq in Body 32.0 32.0 ! X, Y FOV Size, deg 0.1 ! Noise Equivalent Angle, deg RMS 0.5 ! Quantization, deg 0 ! Flex Node Index ** Star Tracker *** 0 ! Number of Star Trackers =============================== ST 0 ==================================== 0.25 ! Sample Time,sec 30.0 20.0 10.0 213 ! Mounting Angles (deg), Seq in Body 8.0 8.0 ! X, Y FOV Size, deg 30.0 10.0 10.0 ! Sun, Earth, Moon Exclusion Angles, deg 2.0 2.0 20.0 ! Noise Equivalent Angle, arcsec RMS 0 ! Flex Node Index ** GPS ** 0 ! Number of GPS Receivers ============================= GPSR 0 ==================================== 0.25 ! Sample Time,sec 4.0 ! Position Noise, m RMS 0.02 ! Velocity Noise, m/sec RMS 20.0E-9 ! Time Noise, sec RMS 0 ! Flex Node Index * Accelerometer ***** 0 ! Number of Accel Axes ============================== Axis 0 =================================== 0.1 ! Sample Time,sec 0.5 1.0 1.5 ! Position in B[0] (m) 1.0 0.0 0.0 ! Axis expressed in Body Frame 1.0 ! Max Acceleration (m/s^2) 0.0 ! Scale Factor Error, ppm 0.05 ! Quantization, m/s^2 0.0 ! DV Random Walk (m/s/rt-hr) 0.0 1.0 ! Bias Stability (m/s^2) over timespan (hr) 0.0 ! DV Noise, m/s 0.5 ! Initial Bias (m/s^2) 0 ! Flex Node Index

as well as the following orbit

<<<<<<<<<<<<<<<<< 42: Orbit Description File >>>>>>>>>>>>>>>>> Low Earth Orbit ! Description CENTRAL ! Orbit Type (ZERO, FLIGHT, CENTRAL, THREE_BODY) :::::::::::::: Use these lines if ZERO ::::::::::::::::: MINORBODY_2 ! World FALSE ! Use Polyhedron Gravity :::::::::::::: Use these lines if FLIGHT ::::::::::::::::: 0 ! Region Number FALSE ! Use Polyhedron Gravity :::::::::::::: Use these lines if CENTRAL ::::::::::::::::: EARTH ! Orbit Center FALSE ! Secular Orbit Drift Due to J2 KEP ! Use Keplerian elements (KEP) or (RV) or FILE PA ! Use Peri/Apoapsis (PA) or min alt/ecc (AE) 400.0 400.0 ! Periapsis & Apoapsis Altitude, km 400.0 0.0 ! Min Altitude (km), Eccentricity 53.0 ! Inclination (deg) 0.0 ! Right Ascension of Ascending Node (deg) 0.0 ! Argument of Periapsis (deg) 180.0 ! True Anomaly (deg) 0.0 0.0 0.0 ! RV Initial Position (km) 0.0 0.0 0.0 ! RV Initial Velocity (km/sec) TRV "EXAMPLE 1" ! TLE or TRV format, Label to find in file "TRV.txt" ! File name ::::::::::::: Use these lines if THREE_BODY :::::::::::::::: SUNEARTH ! Lagrange system LAGDOF_MODES ! Propagate using LAGDOF_MODES or LAGDOF_COWELL or LAGDOF_SPLINE MODES ! Initialize with MODES or XYZ or FILE L2 ! Libration point (L1, L2, L3, L4, L5) 800000.0 ! XY Semi-major axis, km 45.0 ! Initial XY Phase, deg (CCW from -Y) CW ! Sense (CW, CCW), viewed from +Z 0.0 ! Second XY Mode Semi-major Axis, km (L4, L5 only) 0.0 ! Second XY Mode Initial Phase, deg (L4, L5 only) CW ! Sense (CW, CCW), viewed from +Z (L4, L5 only) 400000.0 ! Z Semi-axis, km 60.0 ! Initial Z Phase, deg 1.05 0.5 0.0 ! Initial X, Y, Z (Non-dimensional) 0.0 0.0 0.0 ! Initial Xdot, Ydot, Zdot (Non-dimensional) TRV "ORB_ID" ! TLE, TRV or SPLINE format, Label to find in file "TRV.txt" ! File name *** Formation Frame Parameters **** L ! Formation Frame Fixed in [NL] 0.0 180.0 180.0 123 ! Euler Angles (deg) and Sequence L ! Formation Origin expressed in [NL] 0.0 0.0 0.0 ! Formation Origin wrt Ref Orbit (m)

using the following command script

<<<<<<<<<<<<<<<<< 42: Command Script File >>>>>>>>>>>>>>>>> 0.0 SC[0] qrl = [0.0 0.0 0.0 1.0]

100.0 Align SC[0].B[0] Primary Vector [1.0 0.0 0.0] with L-frame Vector [0.0 1.0 0.0] 100.0 Align SC[0].B[0] Secondary Vector [0.0 0.0 1.0] with L-frame Vector [1.0 0.0 0.0]

10.0 SC[0].Thr[2].PulseWidthCmd = 20.0

100.0 Point SC[0].B[0] Primary Vector [1.0 0.0 0.0] at World[3]

EOF

the issue still is present and my spacecraft spins throughout the simulation. If I am commenting out align commands and making pointing command active, the spacecraft still rotates randomly not pointing anywhere particularly. Thank you for responding to my questions. I do appreciate it

ericstoneking commented 2 years ago

No problem. I see a couple of things.

1) Replace KIN_JOINT with DYN_JOINT. The former is deprecated, and may not be hooked up to anything. (Sorry about that.) There is no downside to using DYN_JOINT, even if you don't have any joints. 2) You have zero wheels and MTBs, but you have inputs for three of each. This throws 42 out of sync. If we have zero of something, we leave one in place to serve as a template (see, eg, the Gyro section). Three is too many.

annamaskolenko commented 2 years ago

Thanks. I've made changes but no improvements. SC_Simple from Demo folder also does not execute written commands. The thing I have noticed, however, is that approximately 4000s into simulation both spacecrafts start to rotate in the opposite direction

ericstoneking commented 2 years ago

I think we're not going to solve this in a chat. I would recommend that you start over with a clean slate. Return all input files to their original state. (Maybe even take the opportunity to download the latest version...) Confirm that you can run the as-shipped InOut and Demo cases. Then change one thing and only one thing, and confirm that works. Build back up to your desired configuration one step at a time.

annamaskolenko commented 2 years ago

Thank you for all your help