Introduction: The on-board measurements available for control are a dual-slit sensor to find the elevation of the sun and a magnetometer to measure the orientation of the local magnetic field. Absolute magnetic field information is not available on-board, so it must be supplied from the ground. Torque is provided for control by an orthogonal pair of coils that interact with the Earth’s magnetic field to produce a torque. The total power available for ACS is 15 W.

Control mode:This includes: Detumble mode, spin up mode, and precession mode. During detumble mode, Control reduces the angular velocity. During spin up mode, CINEMA will speed up its spin rate to 4 RPM and align with its local z axis. After that, during precession mode, the local z axis aligns with the ecliptic normal.Simulation results:

Experiment structure :We are using a PIC microcontroller RS-232 port and a laptop serial port with our own protocol to construct the communication between the Simulink mode and the control software in the PIC. The following diagrams show the structures. The red diagrams present the PIC modules, the other diagrams present the Simulink modules .

Fig. (a) shows the time for the precession. Fig. (b) shows the power from the sun plus the effects from Earth’s albedo and the power consumed by the coils and PIC. This also includes the part of the orbit in Earth’s shadow

f Fig. (c) shows different initial deviations after S/C deployment. Fig. (d) shows the detumble and spin up mode. The initial angular velocity decrease to a small number then spin up omega z to 4 RPM. During the transition, it reduces omega x,y.

Fig. (e) Models of the sun sensor and solar panels. Fig. (f) Power from the albedo in the sun sensors and solar panels. One can find that they achieve their highest value when the satellite passes over Antarctica.

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

x 104

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

time(sec)

rad/

sec

omega vector

CINEMA: Attitude Control System

Yao-Ting Mao* David Auslander†

David Pankow‡

PurposeCINEMA (CubeSat for Ions, Neutrals, Electrons & MAgneticfields) will image energetic neutral atoms (ENAs) in the magnetosphere, and make in situ measurements of electrons, ions, and magnetic fields at high latitudes. Its nominal orbit will be 650 km high with a 72 degree inclination. The behavior of the satellite is described by three dimensional nonlinear dynamics with the variable of angular velocity in three axes. The desired attitude is with the spin axis normal to the ecliptic plane. The main purpose of this poster is to focus on the control of this three dimensional nonlinear dynamic system. The ultimate goal is to control the spin axis of nanosatellites such that they align with the ecliptic normal within 5 degrees and to maintain a stable 4 RPM spin rate.

Shadow analysis

Attitude dynamics from SimMechanics

Orbit dynamics

Albedo module

Gravity disturbance

Solar panels model

Sun Sensor model

Magnetometer model

Actuator model

Data space of Magnetic field and the Sun

Ground station

Battery modelTimer

Serial port send module

Serial port send module

Decode sensor module

Control logic

Exception module

Attitude estimator

Ecliptic plane CINEMA

Local z axis

Local x axisSun direction

* Graduate Student Researcher, Department of Mechanical Engineering, University of California, Berkeley † Professor, Department of Mechanical Engineering, University of California, Berkeley‡ Principal Dev. Engineer, Space Sciences Laboratory, University of California, Berkeley

0 0.5 1 1.5 2 2.5 3 3.5 4

x 104

0

10

20

30

40

50

60

70

80

90

100

time(sec)

degr

ee

deviation of the attitude with ecliptic normal

gravity torque effects

Solar panels

Sun sensors

light

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 100000

1

2

3

4

5

6

7

time(sec)

pow

er (w

)

storing and consuming power

solar panelsCoilsCoils+PIC

Detumble Spin up

Omega z=4 RPM

Omega X,Y

(a) average precession time

(b) storing and consuming power

(c) Settling Time vs. Initial Deviation

(d) omega vector

(e) solar panels and sun sensors

( f) power of the albedo per unit area

+x plane

+x plane

42o

5o0 0.5 1 1.5 2 2.5 3

x 104

0

10

20

30

40

50

60

time(sec)

wat

t/m2

power in the solar panel and the sun sensor

solar panelsun sensor