Pointing Accuracy and Stability Analysis of CMG Control ... · TSUBAME can still perform both the earth and astronomical observation –Shooting with a small maneuver can be performed

Pointing Accuracy and Stability Analysis of

CMG Control for Nano-satellite “TSUBAME”

Shota Kawajiri1, Hao Ting1, Masanori Matsushita1,

Kyosuke Tawara1 and Saburo Matunaga1,2

1. Department of Mechanical and Aerospace Engineering,

Tokyo Institute of Technology, Japan

2. Institute of Space and Astronautical Science, JAXA, Japan

2015/4/23 110th IAA Symposium on Small Satellites for Earth Observation

2

Outline

Mission

Analysis

Intro.TSUBAME Missions

Mission Requirements

On-Orbit Experimental PlanExperiment

Hardware ConfigurationADCS

OverviewDataflow in the Missions

Earth

Observation Mission

Astronomical

Observation Mission

Analysis Environment

Results and ProblemConclusion

Characteristics of TSUBAME

TSUBAME Overview

3

Outline

Mission

Analysis






Earth

Observation Mission

Astronomical

Observation Mission




TSUBAME Overview

Micro Satellite “TSUBAME”

Contents of the Presentation

Verification of the mission performance conducted

before the launch

On-orbit experimental plan

4

TSUBAME Overview

Developed by Matunaga Lab.

at Tokyo Institute of Technology

50 kg & 50 cm cubed

Launched on 6 Nov., 2014

Released into a 500 km

sun-synchronous orbit (LTDN:10:58)

5

Outline

Mission

Analysis






Earth

Observation Mission

Astronomical

Observation Mission




TSUBAME Overview

6

TSUBAME Missions

Micro CMG Demonstration

Earth

Observation

Astronomical

Observation

7

TSUBAME Missions


Earth

Observation

Astronomical

Observation

Demonstrate high speed & high accuracy maneuvering

with newly developed micro Control Momentum Gyros

(CMGs)

8

Micro CMG Demonstration Mission

CMGs: high efficiency

Reaction Wheel CMG

Power/Torque 250-2100 W/Nm 170 W/Nm

Weight/Torque 28- 290 kg/Nm 19 kg/Nm

Pyramid configuration

4 CMGs

skew angle: 54.7 deg

Micro CMG

9

TSUBAME Missions


Earth

Observation

Astronomical

Observation

With a small high resolution optical camera

Accurate and agile pointing using micro CMGs

10

Earth Observation Mission

CameraMultiple

point shooting

Continuous fixed

point shooting Resolution: 14 m

Developed by Kimura Lab.

at Tokyo University of Science

11

TSUBAME Missions


Earth

Observation

Astronomical

Observation

12

Astronomical Observation Mission

HXCP

GRB(NASA)

Gamma-Ray Burst (GRB)

Astronomical phenomena

Occurs suddenly at a random location

Lasts from a few seconds to 100 seconds

Observation in 15 seconds is desired

Sensors mounted on TSUBAME

Five Wide-field Burst Monitors (WBMs)

to detect GRBs

One Hard X-ray Compton Polarimeter (HXCP)

to observe GRBs

Developed by Kawai Lab.

at Tokyo Institute of Technology5 WBMs

1. A GRB occurs

2. Detects the GRB and determines the direction using

the WBMs

3. Finishes Maneuver in 15 seconds using the micro CMGs

4. Observes a GRB using the HXCP

13

Astronomical Observation Mission

Observation sequence of a GRB

14

Outline

Mission

Analysis






Earth

Observation Mission

Astronomical

Observation Mission




TSUBAME Overview

Unfeasible Missions

15

Characteristics of Micro Satellites

Feasibility

of Missions

TSUBAME

Challenging Missions with Low Cost

Development with Research

Requirements

Best effort

Performs missions in the range

of the performance even if the

requirements are not satisfiedNormal Satellites

Feasible Missions with High Cost

Requirements

Guaranteed to be satisfied

Pleiades (ESA)

Cost

16

Outline

Mission

Analysis

Intro.





Earth

Observation Mission

Astronomical

Observation Mission




TSUBAME Missions

TSUBAME Overview


17

Earth

Observation

Astronomical

Observation

Accuracy

[deg]

0.72 3.0

Stability

[deg/s]

0.50 N/A

Agility N/A 90 deg maneuver

in 15 seconds

Best Effort Requirements

18

Outline

Mission

Analysis






Earth

Observation Mission

Astronomical

Observation Mission




TSUBAME Overview

19

Sensors and Actuators of ADCS

MEMS Gyro x 3

Star Tracker x2

Magnetic Torquer

x 3

CMG x 4

ADCSCircuits

Sensors Actuators

GPS Receiver

Sun Sensors

x 6

Three-axis

Magnetometer

One-axis

Fiber Optic Gyro

x3

One CMG uses one CMG driver

Size Φ73.5 x 150 mm

Mass 1.0 kg

Maximum wheel angular

momentum

0.0527 Nms

(at 24000 rpm)

Maximum generation

torque53 mNm

Power consumption < 9.0 W

20

Micro CMGs and its Drivers

Size 100 x 102 x 60 mm

Mass 0.54 kg

Interface RS-422

Input Voltage 18 – 31 V

Power consumption 0.6 W

Micro CMG

CMG Driver

connected

21

Two CPUs of ADCS

Obtains sensor data

Receives CAN commands

Saves data to NAND

flash memory

Determines orbit

and attitude

Controls attitude

Drives actuators

Hardware configuration

22

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

GPSR, STTs, FOGs and CMGs are used in the mission

23

ADCS Dataflow in the Missions

GPSR

STTs

FOGs

CMGs

EKF

EKF

UKF

GSR

WSR

QF

t

q

ω ω est

q est

restr

Tref δ ref

．

Ω, δ

Schematic of Implemented Algorithms

and Dataflow for the CMG System of TSUBAME.

24

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

Software in the Loop Simulation (SiLS)

25


Control

Value

Sensor

Data

Control

Torque

Space Environment

Attitude Dynamics

Model

Sensor

Models

Actuator

Models

Σ

Disturbance

Torque

Orbit

Attitude

Embedded Software

Determine

Orbit & Attitude

Attitude

Control

Configuration of the SiLS

26

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

Continuous fixed point shooting

Target point: Tokyo Institute of Technology

Pointing control: Starts on 13 Mar., 2015 at 1:50 (UTC)

Shooting duration: 1:53 - 1:58

27

Simulation Scenario

1:55:30

1:58:00

1:53:00

Tokyo Institute

of Technology

Diagram of a simulation of continuous fixed point shooting

28

Conditions of the simulation

Initial attitude Sun pointing under

bias momentum controlInitial body angular velocity 0 0 0 T deg/s

Initial total angular momentum 0 0 − 0.111 T Nms

Inertia matrix (based on CAD model) 1.82 −4.4 × 10−4 −2.0 × 10−3

1.86 −7.8 × 10−3

𝑆𝑦𝑚. 1.95kgm2

CMG wheel rate 24000 rpm

Initial gimbal angle of CMGs 320 deg

Orbit determination algorithm Extended Kalman Filter

Attitude determination algorithm Extended Kalman Filter

Attitude controller Quaternion feedback

Control gains Kp = 0.09 I3x3, Kd = 0.9 I3x3

Steering logic Weighted Singularity Robustness Inverse

𝒖 = −𝑲𝐩Δ𝑞4𝚫𝝔 − 𝑲𝐝(𝝎 − 𝝎𝐫𝐞𝐟

Conditions of the Simulations

Requirement Performance

Accuracy [deg] 0.72 4

Stability [deg/s] 0.50 0.2

29

Simulation Results

1:53:00 1:55:30 1:58:00

Time from Control Start [sec]0 100 200 300 400 500 600

Po

inti

ng

Sta

bil

ity

[d

eg/s

ec]

0

0.5

1

1.5

2

2.5

3

3.5

4

Error

Requirement

200 250 300 350 400 4500

0.1

0.2

0.3

0.4

0.5

0.6

1:53:00 1:55:30 1:58:00

Not satisfy a best effort requirement

Time from Control Start [sec]0 100 200 300 400 500 600

Po

inti

ng

Err

or

[deg

]

0

20

40

60

80

100

120

140

Error

Requirement

200 250 300 350 400 4500

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Larger Kp yields better accuracy?

30

Discussion

e.g. Gain scheduling

An Improved controller is required

Attitude Oscillation

Kp = 0.12 I3x3, Kd = 0.9 I3x3

31

Can a shooting be performed?

Kp = 0.4 I3x3, Kd = 0.8 I3x3

A shooting with a small angle

maneuver can be performed

32

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

GRB Direction

Zenith 𝜃: 90 deg

Azimuth 𝜙: random

33

Simulation Scenario

Zenith 𝜃 and Azimuth 𝜙 of a GRB Direction

GRB Direction

Azimuth

Zenith

90 deg maneuver

Monte Carlo Simulation

Three hundred cases

Azimuth of a GRB is determined by a random number

Initial Conditions

the same as that of the earth observation

34

Conditions of the simulation

Settling Time: time to satisfy the accuracy requirement

Fastest : 30.1 seconds: not satisfy the agility requirement

Slowest: 98.0 seconds (with singularity problem)

35

Simulation Results (Best vs Worst)

Time from Control Start [sec]0 20 40 60 80 100

Po

inti

ng

Err

or

[deg

]

0

20

40

60

80

100

The fastest

The slowest

Requirement

30.1 sec 98.0 sec

An Improved steering logic is required

36

Simulation Results (Statistics)


Accuracy [deg] 3 Smaller than 3

Agility [sec] 15 42.5


Discussed with a science team

37

Reconsider the Agility Requirement

45 deg maneuver in 15 seconds is sufficient

to observe 3 significant GRBs in a year

GRB Direction

Zenith 𝜃: 45 deg

Azimuth 𝜙: random

38

Simulation Scenario

Zenith 𝜃 and Azimuth 𝜙 of a GRB Direction

GRB Direction

Azimuth

Zenith

45 deg maneuver

39

Simulation Results





Increasing the size of solar array paddles

large inertia moment of the flight model

40

Discussion -Reason for slow maneuver-

Inertia Moment

of the Flight model

Assumed value

in the early development stage

1.9 kgm2 > 1.2 kgm2

Larger CMG torque or

smaller inertia moment is required

In this maneuver speed, if size of GRBs are ignored,

TSUBAME can observe about 13 GRBs in a year.

41

How many GRBs can be observed?

Significant GRBs can be observed in a year

Big & significant GRBs Long-lasting and

easy to observe

42

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

Not yet conducted

& maybe will not be conducted

TSUBAME stopped receiving uplink commands

during initial checkout phase

Location of the faults

Peripheral circuit for communication is suspicious

43

On-Orbit Experiment

44

Outline

Mission

Analysis

Intro.




Earth

Observation Mission

Astronomical

Observation Mission



TSUBAME Missions



TSUBAME Overview

Performances in the missions are verified using software

in the loop simulation

Some best effort requirements are not satisfied

TSUBAME can still perform both the earth and

astronomical observation

– Shooting with a small maneuver can be performed

– Significant GRBs can be observed in a year

Future Work

Torque of CMGs, inertia moment, attitude controller and

steering logic should be improved

45

Conclusion

Appendix

46

TSUBAME Overview

Size 450×450×560 mm3

Mass 48.6 kg

Lifetime 1 year

Orbit500 km sun-synchronous

orbit (LTDN:10:58)

Power Supply

Solar cells

(Max. 130 W @ EOL)

Li-Po Battery

(16.2 Ah, 360 Wh)

Max. Power

Consumption68 W

Comm.Amateur Band (1200 bps)

S-Band (Max. 100 kbps)

Launch Date 6 November, 2014

47

48

Simulation Results (twice JCMG)

Objective Performance



Nearly satisfy the

best effort requirement

Documents

Pointing Accuracy and Stability Analysis of CMG Control ... · TSUBAME can still perform both the earth and astronomical observation –Shooting with a small maneuver can be performed