1. Richard Barclay HGAS System Lead
SDO High-Gain Antenna System (HGAS) Overview and Pointing System Mission PDR
Richard Barclay
HGAS System Lead

2. Agenda Changes since SCR/HGAS Pre PDR System Requirements
S/C & HGAS Configuration
HGAS Mechanical Overview/Architecture
HGAS, HGADS, Gimbal, HGA
Changes since SCR/HGAS Pre PDR
Field-of-view
Electronics
Allocations
HGAS Pointing Budget
HGAS Pointing Calibration
Jitter
Development Approach, Flow
Schedule/Budget
Status
RFA Status

3. Requirements/Drivers
High data rate drives high carrier freq. High carrier attenuation necessitates waveguides and rotary joints for link margin. Insertion loss for HGAS verified by test, trended.
Link margin for system drives +/ deg. End-to-end pointing.
Near continuous coverage, orbit, sun-pointing, and 1-2 ground stations drives 2-axis gimbal with 360-deg azimuth (Az) and +60/ -51- deg max elevation(El) [at solstice, +45/-35-deg at equinox]. Additional range-of-motion included in design for alignment errors.
RF Attenuation, jitter, environment limit boom length.
System compromises between waveguide length, boom length, array shape, antenna size, amplifier power, pointing and jitter to meet FOV and link-margin requirements.
Single fault tolerance drives electrical redundancy. This combined with requirement not to need s/c attitude adjustment to meet coverage, necessitates 2 antenna systems.

4. High Gain Antenna System*
Boom
Hinge
HGA
HGADS, labeled. Also includes
rest of latching mechanism (not shown)
Launch Restraint Interfaces
Gimbal. Includes everything between HGA and Boom.
Gimbal
Rectangular to circular transition & circular polarizer
Hinge
Actuator
HGA
RF components: HGA, polarizer, rect-circular w.g. transition, waveguide, RF rotary joints.
*Also includes Gimbal Control Electronics (GCE) shown later
RF Rotary Joints
Harness & Cable-Wrap

5. S/C-HGAS Configuration
0.75-m diameter HGA dish
Azimuth-elevation gimbal with harmonic drive actuators, position sensors, and ECRA
Azimuth actuator and ECRA need to accommodate waveguide through center.
Single-hinged deployable rigid booms, (1.52m (60 in) from hinge to center of
WR34 waveguide, RF rotary joints—gimbal axes & boom hinge
Centrally located power amps, Ka band (26.5GHz nominal)
Tapered solar arrays to allow increased FOV, minimize handovers
Operations: 1 gimbal continuous for 6 months, then handover
Electrical redundancy, single-fault tolerance
1553 interface to electronics box, microprocessor controller
GCE also houses housekeeping thermistor monitoring ckts and additional switching ckts.
HGADS: spring w/fluid damper, restraints on boom and gimbal

6. Changes Since SCR/HGAS PDR
Longer Gimbal, shorter Boom, shorter overall length
SA resizing, S/C plan form changes, larger ECRA
Added fidelity to design and analysis
Developed restraint system w/ FEA analysis
Gimbal loads addressed
Actual design, not theoretical restraint for loads
Revised antenna bracket and HGADS interface
Detailed waveguide accommodation
FEA of feasibility study HGA-Gimbal interface, structural/thermal issues solved
Analysis
Bearing gradients, lubrication
Heater locations/accommodation—added thermal structure for elevation rotary joint.
Stowed loads, frequency
Deployed frequency
Thermal distortion for pointing includes whole HGAS (minus hinge)
Started jitter analysis
GCE
SPN split into Power Converter Card (PCC) and Low Power Switch Card (LPSC) (replaces ‘Ubercard’)
Increased GIC fidelity, parts selection, dissipation, area study
Increased Housekeeping fidelity, design, area study, SDN core interface
Firmed up software requirements/ICD

7. Changes Since SCR & HGAS Pre PDR
Then
Now

8. Changes Since SCR 1.2 m (47.2 in) 1.89m (74.3 in ) 2.1m (82.7 in)

9. Antenna Pointing Range-Of-Motion*
+Z, -66-deg El
-Z, +66-deg El
+Z, +66-deg El
-Z, -66-deg El
*360-deg continuous on Az

10. HGAS/Gimbal Design Detail
HGA Dish
HGA Dish Interface
Antenna Bracket/HGADS Interface
Waveguide
Boom
(with internal waveguide)
El Actuator
ECRA
(with internal waveguide)
Hinge Assembly
(Hinge, RJ, Damper, Cable Wrap)
RF Rotary Joint
Az Actuator
Boom-Gimbal Interface
Portion of Harness, Rest not shown

11. Life Requirement
48 times fewer cycles than TRMM (LEO, 3 cycles/orbit).
Slip/Roll-ring and Az rotary joint cycles same as Az output.
El rotary joint cycles same as El actuator output.
Hinge rotary joint life is gnd testing plus one, 90-deg on orbit.

12. FOV, October 6th
Each cylinder represents snapshot of HGA FOV required for given time in orbit.
Each ‘disk’ represents hourly progression of cylindrical HGA FOV over 1 day of given month.
At least one antenna will have clear FOV at all times.
‘+Z’, aka ‘HGA 2’, aka ‘Winter’ Gimbal
‘-Z’, aka ‘HGA 1’, aka ‘Summer’ Gimbal

13. FOV, November 6th

14. FOV, December 6th

15. FOV, January 6th

16. FOV, February 6th

17. FOV, March 6th

18. FOV, April 6th

19. FOV, May 6th

20. FOV, June 6th

21. FOV, July 6th

22. FOV, August 6th

23. FOV, September 6th

24. HGA FOV/Ops/Handovers

25. HGAS Interfaces/Overview
Have combination survival/operational heaters on gimbals. Heaters on survival heater bus (GCE not on at launch). Damper heaters in GCE.

26. Gimbal Control Electronics (GCE) Design
Box functions: HGA gimbal control (2, 2-axis gimbals), s/c thermistor housekeeping (48), power switching (heaters and gimbal drive power), HGAS hinge pot readout, RF switch toggling.
4 Cards per side (side A&B): SDN/HK, Gimbal interface , Low-Power Switch Card (LPSC), and Power Converter Card (PCC).
Nominal mode: receive position and velocity from ACS via 1553 and provide open-loop positioning. Loop is closed by ACS.
SDN microprocessor control of gimbals.
CPCI backplane
Single Fault tolerance
Gimbal interface supports motor drive and position sensors for 4 axes
Electrically redundant
Side A and B electronics (cross-strapped PSE power and 1553 externally, motor relays GCE-GCE)
Dual gimbal motor windings and sensors (not cross-strapped)

27. Allocations vs. Design
Mass allocation: 50 kg, current estimate: 45.6 kg includes: 2, kg gimbals, and 1 internally redundant, 15-kg HGAS electronics box. RF components including HGA kept separate along with HGADS. 9.6% margin to allocation, project holds 20% on allocation. Mission has 30% margin on current best estimate.
Power allocation 41W “normal mode”, estimate 39W; same for eclipse mode Project holds rest of margin. PSE interface is 10 A output module to supply all GCE power. Design draws <10A with estimated heater allocation and peak gimbal power over 21-35V.
End-to-end jitter: HGAS contribution to instrument jitter ~0.02 arcsec (1-sigma). Allocation under revision, but analysis of system-wide jitter meets requirement. HGAS contribution is small part of total jitter.
HGAS Pointing Budget. Preliminary analysis shows meet requirement with on-orbit calibration to remove static errors such as deployment.

28. Pointing Requirement vs. Design
SDO: +/ deg. end-to-end
Tighter than XTE and TRMM which did not require cal.
SDO: Better s/c pointing & Calibrate out launch shifts and deployment/static errors
Gimbal errors similar to XTE/TRMM gimbal allocation
~0.15 deg tracking
~0.03 deg thermal, ~0.14 deg orth.
~RSS +/-0.18 gimbal only
~RSS +/ deg total error
Actual requirement was larger
Gives confidence that this similar design will deliver similar performance. More stringent allocation on SDO; will be addressed with similar components and calibration to remove 1-time errors.
Analysis shows that pointing budget allocations are met.

29. HGAS Pointing Budget

30. HGAS Calibration Budgeted at +/-0.05 deg (TBR)
Working on method/details/simulation—T. Kenney
Ideal sim done. Adding noise sources.
Straight-forward approach, similar to other systems.
Use gnd commands to move HGA in pattern and correlate with ground signal strength to determine peak signal, call this zero.
ACS will have transformation matrix for new axes and send corrected gimbal positions. HGAS alignment errors will be measured on the ground.
Calibration addresses primarily deployment/1-time errors
Plan is for single calibration period in early orbit
Will trend signal strength after initial calibration
May need to calibrate seasonally although analysis shows we do not.
May need hourly tables to address thermal if worse than predicts
Will have ability for both as contingency

31. HGAS Jitter
Instrument pointing: ACS FEA/flexible body analysis shows HGAS contribution is small component of total jitter
HGAS pointing self-induced pointing jitter budget is 0.04 degrees.
ACS-induced HGAS pointing jitter budget is 0.02 degrees
Other spacecraft source-induced HGAS pointing jitter budget is 0.02 degrees (ie instrument mechanisms)
Will measure gimbal jitter and use modeling and analysis to predict impacts.
HGAS induced jitter avoidance plan uses duty cycle variability to dispense motor pulses at variable intervals providing slight lag/lead of required position while providing correct average rate
Nominally tracking: ~1 pulse/2 sec
Ex, 2 pulses every 4 sec

32. Development Approach Leverage proven components/designs/technology.
Comprehensive qualification/verification test program.

33. Development Flow Electronics (qualified separately)
GCE BB1: commercial backplane, bb sdn core, asd, gic, power supplies. Supports FSW development lab
GCE BB2: same as BB1 but stays with gimbal development, used for ETU, qual, and life testing.
ETU1: flt-like backplane, integrated sdn&asd, gic, lpsc, and pcc. Supports FLATSAT.
ETU2: same as ETU1 but supports flight gimbal testing.
FLT: redundant box.
Electronics tested with actuators, gimbals, and Dynamic Simulator (GDS) which simulates loads.
Gimbal (qualified separately)
BB: uses XTE/TRMM spare (approximates design).
ETU: uses flight-like components, sees environments. Is a pathfinder for assembly, test, design issues. If there are none, could become qual/lifetest unit. Used for GCE/APS testing, HGAS testing on SVU, and FLATSAT.
Qual/PT: built just like flight. Second fab cycle after ETU testing to include any mods. qualifies gimbal design. Sees PT environments and goes on to lifetest.
Flight(1&2): built along with Qual/PT, tested serially after qual unit before flt HGAS thermal sim.
HGADS
Development unit (DU) used with ETU gimbal for RF throughput test early.
PF units. One qualifed on SVU with ETU gimbal and spare HGA, other with mass sim.
HGA
Procured and qualified at vendor.
HGAS
Flight units assembled after component qual and see thermal simulation before observatory.

34. HGAS Verification Plan
Dev. Unit
(ETU)
HGADS
ETU Gimbal to Support Elec. Dev/Qual and FLATSAT
Offline Tests
Assemble
ETU HGAS
RF Throughput
ETU Gimbal
Offline Tests
Gimbal
Stiffness and
Strength Test
PT Gimbal Components
Random, Sine Vibe,
Strength, T-V
PT Stand-alone Tests
Sine Vibe,
Workmanship Random, T-Vac
Life Test
Dish (all three units)
Strength PF Qual
Acoustics PF Qual
FLT Gimbal Components
Random, Sine Vibe,
T-V
Gimbal
Stiffness Test
Gimbal Sine Vibe
(Acceptance level),
Workmanship Random
Gimbal
T-Vac (4 cycles)
PF HGADS Components
PF Strength: (1 each) Boom, Hinge, Latch
Stiffness: (2 each) Hinge, Latch
Random: (2 each) Hinge, Latch
T-V extreme functional: (2 each) Hinge, Latch
PF SVU Testing
Sine Vibe
Acoustics, Shock
Cold / Hot Deploy
Assemble
PF HGAS
System
Remove
PF HGADS
(2) FLT HGAS Orbital Sim
T-Vac
ETU Gimbal
Mass sim. Gimbal
Available
PF (FS) Dish
Available
Mass sim. HGA
PF Observatory Test

35. FLT GCE Integration & Qual
HGAS Subsystem
Subsystem & Element
CY 2003
CY 2004
CY 2005
CY 2006
CY 2007
CY 2008 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
4/8
8/03
3/04
5/04
2/05
MISSION MILESTONES
LAUNCH
SRR/
SCR
ICR
PDR CR
CDR
PER
PSR
S-Band Milestones
Mechanisms
11/17/03
11/3/04
PDR
CDR
Gimbal Control Electronics
GCE BB
1 = Spacecraft Integration
= Schedule Reserve
2 = Instrument Integration
3 = Environmental Testing
4 = Launch Site Operations
ETU GCE
FLT GCE
FLT GCE Integration & Qual
Gimbal Development
Gimbal Development
Design BB
ETU build/test
Qual Build & Test
Lifetest
SVU Testing Complete
FLT1 Build & Test
FLT2 Build & Test
FLT HGAS Thermal Sims
Del to S/C I&T
Procurements
ETU/QUAL/FLT1/FLT2
Actuator
Procure
Procure
Slip/Roll-Ring
Procure
ETU/QUAL/FLT1/FLT2
RF Rotary Joint
Procure
ETU/QUAL/FLT1/FLT2
HGAS System Tests
RF throughput w.g. Dev HGADS, ETU Gimbal
RF throughput w.g. PF HGADS, FLT Gimbal
FLT HGAS Thermal Sims
Spacecraft I&T 1 2 3 4
Launch

36. Issues Gimbal assembly life testing concurrent with flight gimbal I&T.
Concern: Life test unit failure after flight units tested.
Impact: Schedule and cost to address problem. Repeat I&T.
Mitigation: early component life tests, relatively benign life requirement, peer reviews/oversight all combine to reduce risk of gimbal life test failure. Performance monitored during test, possible early detection of problem. Spare long-lead parts.
Recovery: depends on possible failure. Gimbal life test completes 18 months before launch.
Component procurements are long-lead and are schedule drivers
Concern: Component development delays could impact system schedule
Impact: Could cause failure to meet delivery schedules.
Mitigation: Close oversight of component development. Leverage of existing designs/components.
Recovery: Parallel testing, reduction of second fab cycle.

37. Conclusion Review Status RFAs Developments: Documentation
Held HGAS Peer/PDRs in Aug ’03 and Nov ’03 and component reviews in Nov ’03.
RFAs
No show stoppers.
52 open, 40 recommended for closure
Most close as a result of design maturity.
Developments:
GCE GIC and ASD breadboard layouts pending
Gimbal preliminary design complete
Documentation
HGAS specification/requirements document being reviewed
HGAS Pointing Req Doc being reviewed
HGADS Req Doc being reviewed
Long lead procurement specs/sows in review, actuator RFI responses in.
Working ICDs
Ready to proceed with detailed design