Global Positioning System (GPS)Constellation Status

Lieutenant Colonel Scott Shepherd, USAFJoint Staff/J6S (U.S. Department of Defense)

(703) 614-2917shephesf@js.pentagon.mil

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30 November 2000 2

Overview

• Overall GPS Constellation Health/Status

• GPS Constellation Age

• Status of GPS Satellite Subsystems

• U.S. Launch Forecast

• Summary

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30 November 2000 3

SVN 22PRN 22

SVN36PRN06

SVN 24PRN 24

SVN 51PRN 20

SVN 41PRN 14

SVN 25PRN 25

SVN 38PRN 08

SVN 27PRN 27

SVN 19PRN 19

SVN 30PRN 30

SVN 13PRN 02

SVN 35PRN 05

SVN 44 PRN 28

SVN 33PRN 03

SVN 31PRN 31

SVN 37PRN 07

SVN 46PRN 11

SVN 17 PRN 17

SVN 34PRN 04

SVN 21PRN 21

SVN 40PRN 10

SVN 23PRN 23

SVN 26PRN 26

SVN 43PRN 13

SVN 32PRN 01

A B C D E F1

2

3

4

5

SVN 39PRN 09

SVN 15PRN 15

MMD: II=9.22 yrs IIA=10.68yrs IIR=7.84yrs IIF=12.7yrs

28 Operational Satellites5- Block IIs18 -Block IIAs5- Block IIRs

Navigation Signal Availability

As of 28 November 2000

SVN 44PRN 28

SVN 29PRN 29

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30 November 2000 4

Constellation StatusLaunch through MMD

131917

211523

2425

26273229223137393534

36334030

4338

465144

Jan8

9

Jan9

0

Jan9

1

Jan9

2

Jan9

3

Jan9

4

Jan9

5

Jan9

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Jan9

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Jan9

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Jan9

9

Jan0

0

Jan0

1

Jan0

2

Jan0

3

Jan0

4

Jan0

5

Jan0

6

Jan0

7

Jan0

8

Jan0

9

Jan1

0

Contractual MMD Design Life New MMD New MMD to Today

Toda

y19 Past Contractual MMD15 Past Design Life 5 Past Updated MMD

Contractual MMD: 6 yrsDesign Life: 7.5 yrsBlock II MMD: 9.22 yrsBlock IIA MMD: 10.68 yrsBlock IIR MMD: 7.6 yrs

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30 November 2000 5

Constellation StatusAge by Plane

-2

0

2

4

6

8

10

12

19 25 27 39 38 13 22 35 30 44 31 37 36 33 17 15 24 34 46 21 23 40 51 26 32 29 43 41

Sa

tell

ite

Ag

e,

(ye

ars

)

Past Design Life (7.5 yrs)Past Contractual MMD (6 yrs)Below Contractual MMD (6 yrs)

A Plane B Plane C Plane D Plane E Plane F Plane

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30 November 2000 6

Constellation StatusSubsystem Assessment

SVN 41

SVN 44y gg gSVN 15

SVN 26

SVN 43

SVN 32

g

g

SVN 40

ySVN 34

g

y

g

g

y

g

SVN 23

g y

g

SVN 51

g g

y g

SVN 21

g

g y

SVN 24

SVN 46

SVN 36

SVN 33

SVN 31g

g

gSVN 17

SVN 22

SVN 30

SVN 13

SVN 35

F

LEGEND

SVN 25

SVN 38

SVN 27

SVN 19

A B C ED

SVN

1

2

3

4

5

g y

SVN 39g g

BU

S

NA

V

g

g

y

g

y

y

y

g

g

g

y y

g

y

y

y

y

gSVN 37

g

g

y

g y

g

g

ySVN 29

Bottom Line16 out of 28 vehicles are yellow

9 vehicles are yellow due to bus failures12 vehicles are yellow due to nav failures

>57% of constellation is degraded

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30 November 2000 7

Constellation StatusAttitude Control System

y

g

g

g

g

g

g

g

g

g

g

g

g

g

SVN 17g

g

gg g

g

g

g

g g

g

gg

gSVN 33

g gg

g

g

g

SVN 13

g g

gSVN 35

g g g

g

g

g

g

g

SVN 29

g

g gg g g

g

g

g

y

g

g g

g g

SVN 46

g

SVN 25

gy g ggg

SVN 30

g g

g g

g y

g g

g g

g

g

g

y y

g ygg

g

g

SVN 36

SVN 21

g

SVN 51 SVN 41

SVN 26

SVN 40 SVN 43

g

gW

HE

ELS

DC

EA

CS

CD

SE

NS

OR

S

WH

EE

LSS

PU

BLK IIR

SE

NS

OR

S

LEGEND BLK II/IIA

5 SVN 19 SVN 44gg

SVN 34 SVN 32g

SVN 15

g gSVN 23

F

1

C DA B ESVN 39 SVN 24SVN 22

SVN 37y

gg

g

g

SVN 31

g

g

g

4 SVN 27

g

g

2

3 SVN 38

g

Bottom Line8 vehicles with degraded attitude control3 Wheel, 2 Sensor, and 2 DCEA Failures

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30 November 2000 8

Constellation StatusReaction Wheels

g gg g

g gg g

g g

g gg g

r

g gg g

g gg g

g g

g gg g

g gg g

g gg g

r

g gg g

y r

g gg gSVN 23

g gg g

g gg g

g gg g

SVN 26

SVN 39 SVN 22

g gg

g gg g

LOW-LUBE DESIGN

SVN 15 SVN 29

WH

EE

L 1

WH

EE

L 2

WH

EE

L 3

WH

EE

L 4

LEGEND SVN

5 SVN 19 SVN 44g g

g4 SVN 27 SVN 35 SVN 37g gg gg g

g

SVN 34

SVN 41

SVN 30 SVN 33

3 SVN 38 SVN 13 SVN 31g gg

SVN 17 SVN 40

BSVN 36 SVN 24 SVN 51

A

2

E F

1

C D

SVN 25 SVN 46 SVN 21

SVN 43

g

g g g g

gg g

SVN 32

Bottom Line43% of low lube vehicles with at least one

failed reaction wheel

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Constellation StatusElectrical Power System

gg g

gg g

gg gSVN 25

g

gg g

g

gg g

gg g

SVN 30

gg g

gy g

g g

gg g

gg g

gg g

g g g

gg g

SVN 33

a g

SVN 40g g

SVN 39

g g

gg g

gg ggSVN 46

AR

RA

YS

BA

TTE

RIE

S

SE

NS

OR

S

SVN 15gy gg g

LEGEND SVN

ggSVN 29

4 SVN 27 SVN 35 SVN 37 SVN 34 SVN 23 SVN 32

5 SVN 19

3 SVN 38 SVN 13 SVN 31gg g

E

SVN 43

2

gg g

gg g

g

g

g

g

SVN 17

SVN 21

g

g

g

B

g

gg

SVN 51 SVN 41

SVN 26g

SVN 44

F

1

C DASVN 36 SVN 24SVN 22

g

Bottom Line3 vehicles with degraded EPS capabilities

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30 November 2000 10

Constellation StatusTelemetry, Tracking & Commanding System

SUSCEPTIBLE TO AUX LOCKOUT

g g g

g g g

g g g

g g

g g g

g g g

y g g g g g

g g g

g g g

g g g

g g gSVN 37

g

g g g

g

g g

y g

g

g g g

SVN 51

g

g g g

g g

SVN 41

SVN 25 SVN 30 SVN 33 SVN 46 SVN 21 SVN 26

SVN 39 SVN 22 SVN 36

SVN 29

SVN 34 SVN 23g

SVN 32

SVN 24

UP

LIN

K

DO

WN

LIN

K

LOC

KO

UT

SVN 15

g g

g g

LEGEND SVN

g g

SVN 17

5 SVN 19 SVN 44

y gSVN 40 SVN 43

4 SVN 27

3 SVN 38 SVN 13 SVN 31

SVN 35g

2

g g g

g g g

g g g

g

g g g

E F

1

C DA B

g g

Bottom Line3 vehicles with degraded TT&C capabilities

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30 November 2000 11

Constellation StatusNavigation Payload

g g g g g g g g

y g g y

g g g g

g

g g g y

g g g g

g y

g y g gSVN 40

g g

g g g g

g

g g g g

y g

g gSVN 34

g y

g g gg g y y

g g g

g g g g

g g g y

y g g g

g

g g g y

ggg

SVN 27

SVN 43

SVN 25 SVN 30g g y g g g

SVN 38 SVN 13 SVN 31 SVN 17

SVN 51SVN 22 SVN 36 SVN 24

SVN 33 SVN 46

gSVN 41

SVN 21 SVN 26

g g g g g g gy g g g

g y g

SVN 39

CLO

CK

SFS

UM

DU

L-B

AN

DBLK IIR

CLO

CK

SFS

DU

ND

UL-

BA

ND

LEGEND BLK II/IIA

g g g g

SVN 23 SVN 32

5 SVN 19 SVN 44 SVN 15 SVN 29

4 SVN 35 SVN 37g g g g g g g g

3

2

E F

1

A B C D

g

Bottom Line12 vehicles with degradedNav payload capabilities

3 vehicles single string in twoNav payload subsystems

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Constellation StatusClocks

g

g

y g

g g

g

r

g g

gSVN 17

g

SVN 44

g

g

g

g

SVN 33g g g g

r

g

g

gSVN 32

r

g

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g r

y

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y

gSVN 29

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SVN 23

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y

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g

SVN 46

y g

SVN 15

g

g

SVN 43

gg

g g y

y

g

g

SVN 40

r

g

g

gSVN 19

r

gg

r

g

SVN 34SVN 37r y g

g

g

SVN 26

g

g

y

g g

g

g

g

ggg r g r

g y

SVN 25 SVN 30

RB

1R

B 2

CS

3C

S 4

LEGEND BLK II/IIA

g g ggg

5

3 SVN 38 SVN 13g

4 SVN 27 SVN 35

gy

2

EA B

y ySVN 39 SVN 22

g g

RB

1R

B 2

RB

3

1

C DSVN 51SVN 36 SVN 24

gg g g

g Operational Clock

FSVN 41

g

g gSVN 21

BLK IIR

SVN 31g yy

g

Bottom LineSVNs 19, 24, 32,--on last clock

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30 November 2000 13

Constellation StatusBottom Line

• 19 SVs past contractual mean mission duration (6 years)• 15 SVs past design life (7.5 years)• 5 SVs past updated mean mission duration

(II--9.22, IIA--10.68, IIR--7.84)• 12 SVs one component away from navigation mission

failure• 9 SVs one component away from bus failure• No practical method to predict what component/SV will

fail next

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U.S. Launch Forecast for GPS

Programmed Launches:• FY 01: 3 IIR (9 Nov, 30 Jan, 11 Jun)• FY 02: 1 IIR (Oct)• FY 03: 4 IIR Modified• FY 04: 4 IIR Modified• FY 05: 2 IIR Modified,• FY 06: 2 IIR Modified, 1 IIF

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30 November 2000 15

Summary

• GPS is an aging Constellation

• GPS Constellation produces a Healthy Navigation Signal

– 28 Operational Satellites

• Scheduled launched and upgrades will improveperformance

– Continue to support world-wide users

– Moving towards meeting future requirements

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Back-Up Slides

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30 November 2000 17

Constellation Activity

• Recent constellation activity (since 18 August 2000)– SVN18 (F3) disposed due to DCEA and Wheel failure– SVN43 moved from F5 to F3– SVN16 (E5) disposed due to clock failures– SVN23 (E4) Yaw Sun Sensor (YSS) degradation– SVN21 (E2) anomaly– SVN24 (D1) last clock activated– SVN46 (D2) A2 step 3 completed but anomaly

unresolved

Constellation StatusSatellite Slot Location with 10 October 00 Vectors

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30 November 2000 19

Constellation StatusProblem Vehicles Summary

RED: lost redundancy incomponent required for

MISSIONBLUE: lost redundancy incomponent required for

DISPOSAL

Plane # SV SVN ProblemsA 5 19 Clocks, Reaction Wheels

25 NDU27 L Band

B 5 13 L Band, EPS, Yaw Sun Sensor, TTC22 TTC, FSDU30 NDU

C 4 31 NDU, L Band37 Control System Command Decoder

D 5 15 Reaction Wheels, Arrays, TTC24 Reaction Wheels, L Band, Clocks

E 4 21 L band23 Yaw Sun Sensor, Solar Array Drives, Power Level40 FSDU

F 4 26 Digital Control Electronics Assembly, L Band29 Digital Control Electronics Assembly, L Band32 Clocks, L Band

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Current Disposal Metric(NDS Ratings not Included)

0

50

100

150

200

250

300

350

400

450

NDS 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nav 350 36 350 233 70 10 198 126 9 18 117 67 70 70 58 27 18 0 0 0 0 9 0 0

Work 13 19 3 12 4 7 1 2 47 12 4 5 3 2 3 2 0 13 13 13 13 3 4 3

TTC 0 187 0 0 187 187 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

EPS 5 10 0 0 0 10 0 13 117 0 0 0 5 0 5 0 0 0 0 0 0 0 5 5

AVCS 58 117 0 58 0 6 0 58 6 117 0 6 0 0 0 6 0 0 0 0 0 0 6 0

24D1

15D5

32F4

19A5

22B1

13B3

31C3

26F2

23E4

29F1

27A4

21E2

40E3

30B2

25A2

37C4

34D4

44B5

46D2

51E1

43F3

36C1

17D3

33C2

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30 November 2000 21

Current Disposal Metric by Plane(NDS Ratings not Included)

0

50

100

150

200

250

300

350

400

450

NDS 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Nav 0 58 0 117 233 70 70 10 0 0 9 0 198 27 350 0 0 18 36 0 67 70 9 18

Work 2 3 3 4 12 4 2 7 4 13 3 3 1 2 13 13 4 0 19 13 5 3 47 12

TTC 0 0 0 0 0 187 0 187 0 0 0 0 0 0 0 0 0 0 187 0 0 0 0 0

EPS 0 5 0 0 0 0 0 10 0 0 0 5 0 0 5 0 5 0 10 0 0 5 117 0

AVCS 0 0 0 0 58 0 0 6 0 0 0 0 0 6 58 0 6 0 117 0 6 0 6 117

39A1

25A2

38A3

27A4

19A5

22B1

30B2

13B3

35B4

44B5

36C1

33C2

31C3

37C4

24D1

46D2

17D3

34D4

15D5

51E1

21E2

40E3

23E4

29F1

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30 November 2000 22

Special Topics

• Special Consideration Satellites

– SVN 19

– SVN 23

– SVN 29

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30 November 2000 23

SVN 19 Clock Status

CFS#3 is SVN19’s last usable clockWhat is the status of CFS#3?• CFS #3 - Operational from 11/1/89 - 1/2/92 (2.17 Years)

– Deactivated originally due to frequency stepping– Reactivated on 9/23/99

• One Day Stability ≅ 2.1E-13, Specification = 2.0 E -13– Equates to very marginal clock performance– Averaging 2.25 navigation uploads per day– Stability will only get worse, not better

• Beam Current = 1.39 nanoamperes– Typically, any beam current less than 2 nA is reason for concern– Beam current will continue to decrease

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30 November 2000 24

SVN 19CFS#3 Prognosis

What can be expected from CFS#3?

• Optimistically, CFS#3 may live another 2-3 months– The problem is that its performance will continue to degrade

• If CFS #3 does live another 2-3 months:– Stability will degrade beyond specification– The number of contingency uploads needed will increase– It may be very difficult, if not impossible, to maintain SVN19’s accuracy

within the current accepted tolerance

• Anticipated loss drove SVN 44’s orbital location

Bottom Line: The future performance of SVN 19’s CFS is very uncertain and anyperformance expectations beyond a few months are extremely unwarranted

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30 November 2000 25

SVN 23 Status

• 9.9 years on-orbit– Past contractual MMD (6 years) and design life (7.5 years)– 0.3 years short of updated Block IIA MMD (10.22 years)

• September loss of yaw led to discovery of sensor degradation– This eliminates scissoring as an option– Minimum of four critical supports per day for remainder of on orbit life

• Eclipse season from 3 Nov 2000 through 16 Dec 2000– Expect positive power balance problems– Battery reconditioning impossible due to orbital geometry– Ability to make it through this eclipse season without disabling secondary

payloads is unpredictable– Workload increases to > 6 critical supports per day during eclipse

Bottom Line: SVN 23 continued operations is dependent on disablingpart of the secondary payload.

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30 November 2000 26

SVN 29 Status

• SVN29 nodal position can not be controlled• Vehicle will occupy F1 node from 1 Dec 2000 to 2 April 2001• Following the 2 April exit, SVN29 will not be in a primary node

until it reaches the F4 slot (SVN32) in Nov 2003• SVN29 time on orbit = 7.9 years• Options for attempting a delta V

– Following nodal exit in 2001– As required by failures of other vehicles in the plane (SVN32

or SVN26)– Following a failure of SVN29

Recommendation: Delay decision until a time closer to nodal exit to gainbetter picture of entire constellation status

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30 November 2000

Current Transition Plan

– Upgrade Dedicated Monitor Stations and Ground Antennas withNew Digital Receivers and Computers

– Replace Existing Master Control Station Mainframe ComputerWith a Distributed Architecture

– Add Accuracy Improvement Initiative, Air Force SatelliteControl Network Interface with MCS

– Build Fully Mission Capable Alternate Master Control Station(AMCS) at Vandenberg Tracking Station

– Add IIF Command and Control Functionality

2-Step Plan: Replace Existing Mainframe With DistributedArchitecture Then Add Block IIF Functionality