X-Ray Calorimeter Mission

hardtofindcurtainUrban and Civil

Nov 16, 2013 (3 years and 11 months ago)

394 views

I n t e g r a t e d D e s i g n C e n t e r / M I s s I o n D e s I g n L a b o r a t o r y

N A S A G O D D A R D S P A C E F L I G H T C E N T E R

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


X
-
Ray Calorimeter Mission

Attitude Control

Philip Calhoun, Dave Olney, Joe Garrick

Attitude Control Systems Engineering Branch

Code 591

2



6 April 2012


ACS,
p
2

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

ACS Overview


Sensors


Coarse Sun Sensor (CSS)


8 units aligned to provide 4
π

steradian

coverage of sky


Used for Safe mode sun acquisition


Gyro


1 internally redundant unit


Sense the attitude rate of change


Used in
Kalman

Filter to propagate and smooth state


Star Trackers


1 electronics and four heads


A star tracker head is used
for

attitude
determination (inertial frame)


Second star tracker head is used for
alignment between science instrument
components


Two pairs of star trackers provide fully redundant capability



Actuators


Thrusters


12


4.5 N (1
lbf
) thrusters for attitude control and orbit maneuvers


Thrusters full on for orbit maneuvers, off
-
pulsed for attitude control


Thruster on
-
pulsed for attitude control during momentum unloading


Reaction Wheels


4


75
Nms
, 0.2 Nm reaction wheels


Used to attitude actuation




ACS,
p
3

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

ACS Functional Block Diagram


Gyro

CSS

Tot.8

Safe Mode Att.

Determination

Mission Attitude

Determination

Attitude

Control

Momentum

Management

Reaction

Wheels

4 total

(pyramid about Z)

Thrusters


12 Total

(See slide #18)



ACS FSW

Sensors

Actuators

Star

Tracker

Orbit

Maintenance

ACS,
p
4

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Observatory Coordinate System

and Key Terms

+Z
OBS

points from the Mirror Node

to the Target

Z is the axis for ROLL

(the
Boresight

is aligned w/ Z)


Target

+X
OBS


points from the Mirror Node


towards the Sun,


X is the axis for YAW

Observatory Coordinate System

Origin is at the Mirror Node

+Y
OBS

points from the Mirror Node,


forming a right handed
orthogonal frame with X and Z

Y is the axis for PITCH

(side S/A’s are aligned w/ Y)

Sun

“FORE” is the
+Z (FMA) end
of IXO

“AFT” is the

Z
(Instruments)
end of IXO

ACS,
p
5

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Operations Requirements


Launch


Direct insertion into transfer orbit in full sun with continuous ground contact (have TDRSS capability)


Indefinite duration safe mode available immediately after LV separation


Deployments start right after LV separation


Cruise to L2


Start with one month commissioning phase for checkouts, calibrations


Continuous DSN contacts during commissioning, then twice daily for 30 minutes for OD during cruise


Correction burns as required


Mirror cover deployed after observatory outgassing


No exposure of aperture to sun light allowed for remainder of mission


Science observations may start during cruise


L2 Insertion


Performed in Operational configuration (10
-
3

g level forces only)


Observations


Pointing at a target for < 10
6
seconds


1


20 observations per week, re
-
pointing accomplished in less than an hour


Observing efficiency 85%


EOL disposal


Passivate

observatory, impart 1 m/s towards deep space


Mission Ops


Highly autonomous observatory, 8 x 7 ground staffing




Data latency 2 weeks required, 72 hours goal from completion of observation to product delivery, excludes bright
source observations

ACS,
p
6

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Requirements and Considerations


Requirements


3 year (5 year goal) mission lifetime at L2



Attitude Requirements


Pointing: 10
arcsec
,
Pitch/Yaw (3
-
sigma
); Roll number not provided by customer


Knowledge:


3
arcsec
,
Pitch/Yaw (3
-
sigma); Roll number not provided by
customer


Jitter:


1
arcsec
, all axes (3
-
sigma) over 1 seconds


Slew Requirement


Complete a 60 degree (yaw) slew in 60 minutes (including settling)


Considerations


Impact of changing pitch field of regard to +/
-

45 degrees



Impact
of Solar force center of pressure (CP) to Center of Mass (CM) offsets



Assumptions


HGA not slewing during science observations


Adequate calibration slews and observation time for sensor alignments


ACS,
p
7

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Earth

Sun

Target

H

Yaw:

+/
-
180



Moon

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Pitch: +/
-
25,
-
25


R潬o:


-
㄰1


䙩敬搠潦oR敧慲a


Pitch:
+25,
-
25
°

Yaw:
+/
-

180
°


Roll:
+/
-

10
°

Slew


Slew:
60
degrees in
60
minutes


Average # of slews per day: 2.5 during
first year of mission, less later

Requirements and Considerations (
cont
)

ACS,
p
8

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal


ACS Modes, Sensors and Actuators



Orbit Adjust Maneuvers (Delta
-
V Mode)



Gyros and thrusters



Full
-
on thrusters for orbit maneuvers



Off
-
pulse thrusters for attitude control




Momentum Unloading (Delta
-
H Mode)



Gyros, thrusters and wheels (spin down)



Attitude control on thrusters as wheels spin down to commanded momentum level




Science/Mission (Science Mode)



Gyros, star
t
racker, wheels,
Kalman

f
ilter



Inertial Pointing (point at sun during coast phase; target pointing during science)



Calibration slews (science and ACS sensor alignments)



Re
-
pointing slews (slewing to next science target)





Safe (
Safehold

Mode)



CSS, gyros and wheels



Point solar array at the sun

ACS,
p
9

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

ACS Sensors and Actuators

Star


Tracker

Model

Mass (kg)

Avg

Power

(W)

Max
Power
(W)

FOV

Degrees

NEA

Arcsec


1
-
sigma

Accuracy

Arcsec

3
-
sigma

Angular
Rate

Deg/sec

Update
Rate

Lifetim
e

Estimated
Cost

$ K

DTU

1 DPU

4 CHUs



0.56

0.25 (each)

3.6

0.7

3.6

0.7

18 x 16

(each CHU)

0.7 at 2 Hz

7.0

Up to 32
Hz

>

30

$2400

(4

heads)

Gyro

Model

Mass
(kg)

Avg

Power

(W)

Max
Power

(W)

Scale Factor
Accuracy

(
ppm

) 3
-
sigma

Bias
Stability

(deg/hr)

Angular
Rate

(deg/sec)

ARW

(sigma
-
v)

(
arcsec
/se
c^1/2)

AWN

(sigma
-
e)

(
arcsec
/Hz^
1/2)

Lifetim
e

(years)

Estima
ted
Cost

$ K

Northrop

SIRU(internally
redundant)

7.1

27

27

< 5

< 0.0015

7.0

0.009

< 0.003

> 15

$ 2500

Reaction

Wheels

Model

Mass
(kg)

Avg

Power
(W)

Peak Power
(W)

Momentum

(
Nms
)

Torque

(Nm)

Static
Imbalance

(g
-
cm)

Dynamic

Imbalance

(g
-
cm^2)

Lifetime

(years)

Estimated
Cost

$ K

Honeywell

HR16

Reaction

Wheels

( 4 units )

12

18

(22
max
spd
)

105

100

0.2

0.48

15.4

>15 years

$200

(each)

Coarse

Sun

Sensors

Model

Mass
(kg)

Avg

Power
(W)

Peak
Power (W)

Lifetime

(years)

Estimated
Cost

$ K

Honeywell

Analog

(8 units)

<0.1 kg

0

0



$15 each

ACS,
p
10

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Instrument Pointing Star Tracker Specifications

Micro
-
Advanced
Stellar Compass (
μ
ASC
)

ACS,
p
11

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

SIRU Instrument Pointing
Gyro Specifications

ACS,
p
12

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Honeywell Reaction Wheel

ACS,
p
13

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Coarse Sun Sensor:
Adcole


Adcole

analog
CSS detectors provide
close to


2
π

steradian

coverage (85 deg half angle)



8
detectors distributed across the

observatory provide
near
full

4
π

steradian

coverage




4 CSS on SA panel facing sunward




4 CSS on body facing anti
-
sunward


ACS,
p
14

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Solar Array size and position have been selected to make the center of mass (Cm) and
center of pressure (Cp) nearly coincident along longitudinal axis for a pitch angle = 0
degrees


Cp / Cm offset



along X axis (toward Sun) ~= 1m



along Z axis (11.5 cm)


For pitch

≠ 0

the Cp and Cm will not coincide



increased Solar Torque
















Solar Radiation Torque and its Effect on Wheel
Momentum Storage

25

o

Projected

silhouette


toward sun


Cp

Cm

Ref

Baseline (Pitch = 25
deg
)

-50
-40
-30
-20
-10
0
10
20
30
40
50
-200
-150
-100
-50
0
50
100
150
200
Momentum Buildup (21 day) due to Solar Pressure
Pitch Angle (deg)
Pitch Momentum (N-m-sec)
-50
-40
-30
-20
-10
0
10
20
30
40
50
-1
-0.5
0
0.5
1
1.5
x 10
-4
Solar Radiation Pressure Torque
Pitch Angle (deg)
Torque (N-m)
ACS,
p
15

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Four Reaction Wheels


Momentum Storage

RWA body alignment


RW1 RW2 RW3 RW4


| 0.6124 0.6124
-
0.6124
-
0.6124 |


| 0.6124
-
0.6124 0.6124
-
0.6124 |


| 0.5000 0.5000 0.5000 0.5000 |


(bias to X and Y axis, momentum accumulates mainly on
these axis)


Baseline (Pitch < 25
deg
)



Momentum per wheel = 100
Nms
, (HR
-
16)


Torque per wheel = 0.2 Nm


Plot shows momentum capacity (min = 130 N
-
m
-
sec)

> 165
Nms

within adequate range of +/
-

Y axis


Trade (Pitch < 45
deg
)



Momentum per wheel =
125
Nms

(HR
-
16)


Torque
per wheel = 0.2
Nm


Impact of 125 N
-
m
-
sec wheel


mass & imbalance increase





Allowable Range for
Momentum Buildup
along Y axis

Momentum Capacity ( 1
whl

= 100 N
-
m
-
sec)

Azimuth (deg)

Elevation (deg)

ACS,
p
16

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Slew Capability


Requirement: Slew 60 deg in 60 deg (allow time to settle)


Design:


Goal: Slew should not significantly impact momentum / control authority usage


Use 5% of minimum Momentum Capacity (~6.5 N
-
m
-
sec)


Use 10% of torque capability (~0.02 N
-
m) during ramp


5 min ramp time to minimize slew transients


Slew completes in 58 min, 2 min for settle



0
10
20
30
40
50
60
0
10
20
30
40
50
60
Time (min)
Slew Angle (deg)
0
10
20
30
40
50
60
-1
0
1
2
3
4
5
6
7
Time (min)
Slew Momentum (N-m-sec)
ACS,
p
17

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Science Pointing

Pitch and Yaw

Per Axis

Requirement

Predicted
Performance

10
arcsec

(3
σ
)

3.8
arcsec

(3
σ
)

Knowledge Error

Requirem
e
nt

3
arcsec
, (3
σ
)

Performance

2.25
arcsec
, (3
σ
)

Kalman

Filter

0.38

Science

ST2 align

0.16

ST1
-
ST2 align

0.16

ST1
-
Gyro

Align

0.2

IRU Quantization

0.1

ST1 spatial bias

0.25

Jitter

1.0

Jitter


(outside of Control System bandwidth)

Requirement

1.0
arcsec

(3
σ
)

Performance

1.0
arcsec

Cryo

Cooler

Info to analyze not
provided

HGA

0.0

(assume no motion
during science)

RWA

1.0 (allocation)

(static and dynamic)

Environment

negligible

Pitch / Yaw Error Budget

Control System

Requirem
e
nt

Performance

0.56
arcsec

Algorithm

0.5

Cycle Delay

0.06

RWA Torque
quantization

negligible

(large inertias make
this very small )


SUM

SUM

SUM

SUM

Note: RWA jitter is allocation (based
on experience of similar missions)

Few things in our favor:

1.
Large inertias (torque produces small angles)

2.

Motion in star tracker filters out biases

3.
Large observation times

Uncorrelated items can be
RSSed

but a more conservative
estimate is to Sum items

ACS,
p
18

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Thruster

Configuration

8 Thrusters canted 10


in two planes

4
Thruster
s canted
45


in
one
plane

Solar
Array

Lines
of
Action

Couple

Notion
al CG

Component


Vendor

Flight

Units

Thrust

Minimum

On

time

Thrusters

Aerojet

12

4

N

5
msec

ACS,
p
19

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Momentum Unloading


Thruster
Isp

= 210 sec


Wheel torque = 0.2 Nm



Momentum accumulation = 125 N
-
m
-
s about Y axis (worse case) every 21days (Baseline: Pitch < 25
deg
)


= 180 N
-
m
-
s about Y axis
(worse case)
every 21 days (Pitch < 45
deg
)



For 5 year mission, every 21 days is about 87 unloads



Max Thruster torque about each axis ~= +/
-

[1.4, 8, 8 ] N
-
m



Minimum on time thrusters =

5 m
-
sec



Thruster Pulsing Duration = 15.6 sec of thruster on
-
time to remove 125
Nms

(Baseline: Pitch < 25
deg
)




=

22.4
sec of thruster
on
-
time
to remove
180
Nms

(Pitch < 45
deg
)



Accuracy of unloading to < 0.03 N
-
m
-
s



Time to spin down wheels = 125 / 0.2 = 625 sec, about 10.5 minutes (Baseline)


180/ 0.2 = 900 sec, about 15 minutes (Pitch < 45
deg
)



Fuel usage = Total momentum (5
yr
) / (
Isp

* r * 9.8) = (125*87) / (210 * 2 * 9.8) = 2.6 kg (baseline)



= (180*87
) / (210 * 2 * 9.8) =
3.8
kg (baseline)



Assume r = 1m

ACS,
p
20

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Summary

Potential future work:



Need Jitter Assessment to determine impact to Pointing Budget


Reaction Wheel Imbalance


Cyrocooler



Passive isolators could be used to reduce jitter if needed


Ex: Chandra Reaction wheels mounted on isolator


Evaluate launch vehicle tip
-
off
rate damping,
thrusters and/or wheels


Issues/concerns:



Momentum Buildup due to Solar Pressure is driving to larger wheel size
for off pointing about Pitch axis


䩩瑴敲⁩湣牥慳e





ACS,
p
21

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Supplementary Slides

ACS,
p
22

Final Version

M i s s i o n D e s i g n L a b o r a t o r y

Do not distribute this information without permission

from Gerry
Daelemans

(gerard.j.daelemans@nasa.gov)


2


6 April 2012

X
-
Ray Cal

Kalman

Filter Performance

s
v

s
u

s
e

s
n

T
1

T
2

D
t

w

q

g

z

s
q
-

s
q
+

s
w
-

s
w+

asec/sec^0.
5

asec/sec^1.5

asec

asec

sec

sec

sec

asec/s

asec

[ ]

[ ]

asec

asec

asec/sec

asec/sec



SIRU/CT
-
633 (boresight)



2.79E
-
13

0.00E+00

0.118

30

86400

3600

1.00

0.0000

0.00

1.00001

1.00001

0.118

0.118

0.00E+00

0.00E+00







SIRU/DTU



4.68E
-
05

5.29E
-
07

0.118

3

86400

3600

0.20

0.0002

0.07

1.00077

1.00086

0.125

0.124

6.30E
-
10

6.30E
-
10







SIRU/DTU boresight



4.68E
-
05

5.29E
-
07

0.118

20

86400

3600

0.20

0.0002

0.07

1.00002

1.00005

0.204

0.204

1.63E
-
09

1.63E
-
09

MIMU/DTU micro ASC



0.300

7.03E
-
05

1.000

3

86400

3600

0.20

0.0207

20.02

1.05433

1.07672

1.197

1.112

2.11E
-
05

2.11E
-
05







MIMU/DTU micro ASC roll



0.300

7.03E
-
05

1.000

20

86400

3600

0.20

0.0207

20.02

1.00125

1.00463

1.927

1.918

2.12E
-
05

2.12E
-
05

s
u

gyro rate random walk standard deviation

s
e

gyro angle white noise standard deviation

s
n

measurement no楳e standard dev楡i楯i

q
1

long term time period for calculating rate random walk (drift)

T
2

shorter term time period for calculating angle random walk (angle drift)

D
t

Ka汭an f楬ter update per楯i

w

rate error after 吱⁴業e per楯i (dr楦t rate)

q

ang汥lerror after 吲⁴業e per楯i (dr楦t ang汥l

s
q
-
?
standard deviation of angle error after propagation, just before update (steady state)

s
q
+

standard deviation of angle error after update (steady state)

s
w
-
?
standard deviation of rate error after propagation, just before update (steady state)

s
w+

standard deviation of angle error after update (steady state)

Markley, "Analytic Steady
-
State Accuracy of a Spacecraft Attitude Estimator", Journal of Guidance, Control and

Dynamics, Vol. 23, No. 6, Nov
-
Dec 2000, pp. 1065
-
1067.