# Presentation: 656007

## SNAP Systems EngineeringWBS 1.3

**David Pankow**
**Space Sciences Laboratory,**
**Mechanical Engineering Department**
**University of California Berkeley**
**July 2002**

## SNAP Engineering Overview

- Mission Profile
- Spacecraft and Instrument Overview
- Optical Telescope Assembly (OTA)
- Telescope Packaging (TMA-63)
- Stray Light Baffle
- Mechanisms Overview
- Telescope Thermal
- Camera (passive) Thermal
- Trade Studies and Present Status
- R & D Activities, Manpower, & Schedule
- Summary

## SNAP DESIGN PHILOSOPHY

**Passive Cold Biased Bus & Baffle / Warm Optics**
- Active Coolers are not Mature, Cryogen's are Short Lived
- High Earth Orbit allows Passive Cooling and Stable Pointing
- Build, Test, and Fly Warm Optics (...*like Hubble*)
- Cold Optics would be a Significant Cost & Schedule Driver
- Compact Telescope with the Longest Light Baffle that will Fit !
**Generic *****and*****  Rigid Spacecraft**
- One Mission Thermal Attitude   ...near Sun Line Normal Viewing
- No Appendages and Minimal Mechanisms
- On Board Momentum Management
- Structural Noise Isolation at the Sources
- Generic RSDO spacecraft with Needed Upgrades

## SPACECRAFT CONFIGURATION

- Main Baffle Assembly

- Door Assembly

- Primary Solar Array

- Secondary Mirror Hexapod
- and “Lampshade” Light Baffle

- Secondary Metering Structure

- Primary Mirror

- Optical Bench

- Instrument Metering Structure

- Tertiary Mirror

- Fold-Flat Mirror

- Spacecraft

- Shutter

- Instrument Bay

- Instrument Radiator

- Solar Array, ‘Dark-Side’

**SPACECRAFT CONFIGURATION**

## CANDIDATE LAUNCH VEHICLES

-  **Delta 2920H-10L**
- Lift Capacity and Fairing Volume ***Marginal***
-  **Delta 3940-11**
- Lift Capacity and Fairing Volume Adequate
- GSFC “actual” Cost Estimate is $80M to $84M
- NASA & Boeing Describe this as a ***TRANSITION VEHICLE***
**Atlas IIIB **(or larger)
- Lift Capacity Comfortable, Fairing Volume Tight but Adequate
**Zenit 3SL w/ Block DM-SL restartable upper stage (SEA LAUNCH)**
- Liftoff Capability Comfortable, Fairing Volume Comfortable
-  ***Not a US Owned*** (majority holder) Company
**Delta 4240-12 *****(BASELINED)***
- Liftoff Capability of 2020kg Direct to Selected Orbit
- Fairing Volume Adequate

## SNAP Mission Profile

**SNAP Mission Profile**

**Delta IV M+ (4240) Launch from KSC**
- 2.6 x 25 Re Injection to Final 28 Inclination Orbit
- Phased for near Ecliptic Plane Orbit
- Our Plus: *The perigee is Stable Over Berkeley !*
**Commissioning Phase - several overlapping weeks**
- Spacecraft Turn On Activities
- Structured Cool Down of the Telescope
- Slow Roll, or Auxiliary (rear) Solar Arrays
- Degassing & Dry Out Period
- Optics Turn On – Open Cover, Focus, etc.
**Mission / Science Operations (Routine Survey)**
- Alternate Near N/S Ecliptic Pole Observing
- Observing is Suspended below 9 Re (radiation issues)
- High Speed Data Down-Link & Onboard Maintenance

***Delta IV fairing***

## ACS Concerns Expressed by IMDC

**Jitter **
- Isolate fundamental wheel frequency through detailed analysis from manufacturer
- Must tune wheel isolators - type, size and interface
**Flexible Mode Analysis *****( >5 Hz)***
- Require extensive analysis to avoid control - structure resonance interactions
**Solar Wind Tipping, given the Large Baffle C****p****-C****g**** offset**
- Smaller offset will minimize thruster firing frequency and propellant required for daily momentum unloading (est. 30 Nms wheels)
- Offset will migrate with mission life, will get better with fuel depletion
**Fuel Slosh Disturbance Analysis will be Needed**
- Minimize fuel tank Cg offset
**Sun Avoidance - VERY RELIABLE SAFE HOLD ! ...and Shutter Blocking**
*Considering Dedicated Gas Jets or Momentum Wheels*
**Earth & Moon Avoidance *****(mostly solved in the Chandra-like orbit)***

## SNAP Resources Allocation

**ELECTRICAL POWER REQUIREMENTS**

| Instrument & Electronics | 214 | Spacecraft Structure |   160 |
| --- | --- | --- | --- |
| Telescope Mirrors | 293 | Spacecraft Systems |   314 |
| Telescope Structure | 262 | Hydrazine Fuel |   172 |
| Stray Light Baffle | 228 | SPACECRAFT total (kg) |   646 |
| SCIENCE  total (kg) | 997 | MISSION total (kg) | 1643 |

|  | PEAK | AVG. |  | PEAK | AVG. |
| --- | --- | --- | --- | --- | --- |
| Instrument (Camera) |   41 |     8 | Command & Data | 103 | 30 |
| Inst. Electronics | 109 |   59 | SS Recorder |   50 | 30 |
| Thermal Control | 126 |   63 | Communications | 187 | 78 |
| SCIENCE total (watts) | 275 | 130 | Attitude Control | 193 | 89 |
|  |  |  | SPACECRAFT (watts) | 533 | 227 |
|  |  |  | MISSION total (w) | 808 | 357 |

**MASS ALLOCATION (~25% margin) *****2020 kg Direct to Orbit Launch Capacity***

**MISSION REQUIREMENTS**
- Complete Document Posted at ***SNAP.LBL.GOV***

## SNAP ELECTRICAL BLOCK DIAGRAM

**spacecraft bus****instrument**

## SNAP GROUND DATA SYSTEM

## Corning ULE Ultra-Low Expansion Glass
Face Sheets Bonded to Honeycomb Core
Achieves 85-90% Light weighting
Extensive Manufacturing History
Meets our Performance Requirements

Schott Zerodur Glass/Ceramic Material
Solid Blank, weight Relieved by Milling Backside
Achieves 70-85% Light weighting
Extensive Manufacturing History
Meets our Performance Requirements

Astrium/Boostec Sintered SiC (a distant 3rd)
Relatively New in Astronomy, Limited Flight History
Appreciable CTE is a Concern
Ongoing Work in France and Germany, also JPL

- Face Sheets Bonded to Honeycomb Core
- Achieves 85-90% Light weighting
- Extensive Manufacturing History
- Meets our Performance Requirements
**Schott Zerodur Glass/Ceramic Material**
- Solid Blank, weight Relieved by Milling Backside
- Achieves 70-85% Light weighting
- Extensive Manufacturing History
- Meets our Performance Requirements
**Astrium/Boostec Sintered SiC ***(a distant 3**rd**)*
- Relatively New in Astronomy, Limited Flight History
- Appreciable CTE is a Concern
- Ongoing Work in France and Germany, also JPL

**TELESCOPE MIRROR OPTIONS**

## Optical Telescope Assembly (OTA)

**TMA-63 OPTICAL PATH***-  2.0m****** ****Primary Mirror**-  0.45m**** Secondary Mirror**-  Folding Flat Mirror**-  0.70m**** Tertiary Mirror**-  0.70m ****Focal Plane **	**-  Instruments in 140K Dewar*

**DEWAR PACKAGING***-  Conical Thermal / Cosmic Ray Shield**-  Isolated Mounting of Focal Plane **-  Thermal ‘Flex Link” coupling to Radiator**-  Warmer Shutters cover Front Aperture*

## Optical Telescope Assembly (OTA)

**Optical Telescope Assembly (OTA)**

*SECONDARY MIRROR SUPPORT STRUCTURE*

*OPTICS “COFFIN” BELOW*

*PRIMARY OPTICAL BENCH*

**COMPOSITE PROPERTIES ***(driven by ppm Optic Stability)*- High Modulus & Conductivity Fibers        *for sub-ppm/****C Stability*-  Quasi-Isotropic Patterning- Cyanate Ester Matrix       *provides low CME (moisture)*- On Orbit Temperature Control- ***These are Today’s Technology !***

**OPTICS, THERMAL, AND GEOMETRIC DEFINITIONS ARE COMPLETE****DETAILED DESIGN AND FEM ANALYSIS NOW IN PROGRESS**

*with Three STIFF Metering Beams*

## Optical Telescope Assembly (OTA)

**Optical Telescope Assembly (OTA)**

**LONG STRAY LIGHT BAFFLE***-  Interior Kept COOL by**      Over Wrap of MLI Thermal Blankets*

**BAFFLE MOUNTED SOLAR ARRAY PANELS***-  Conductive Thermal Isolation**-  GaAs – OSR Striping for Front Surface Heat Rejection*

*GENERIC **SPACECRAFT**BELOW*

## STRAY LIGHT BAFFLE DESIGN

**STRAY LIGHT BAFFLE DESIGN**

**FUNDAMENTAL BAFFLE DESIGN CONSIDERATIONS**-  **Top Cut Angle Chosen to Block Sunlight in All Science Attitudes****-  Earth-Light Region must be Well Baffled****-  Baffle –to- Lamp Shade –to- Stove Pipe diffraction line dictates the “Hat Size”**  **Studies Indicate an Ordinary Aluminum Shell Construction is Adequate !**

## MECHANISMS OVERVIEW

**ACTIVE IN SCIENCE OR OBSERVING MODE**
** ****Camera Shutter ***(momentum compensated)*
** ****Momentum Wheels*** (long flight heritage)*
**ACTIVE ONLY IN ENGINEERING MODE *****(below 9 Re)***
-  Secondary HEXAPOD Focus Mechanism
-  High Gain Antenna Steering Mechanisms
-  Propulsion Thrusters
-  Baffle Door *(One Shot & then Captured)*
-  *TERTIARY HEXAPOD ADJUSTER IS AN  OPEN OPTION*
*** ******PRESENT BASELINE IS NO MOVING FILTER WHEELS !***

## MECHANISMS OVERVIEW

## TELESCOPE THERMAL

**OPTICS: Build,Test, & Fly Warm... like Hubble !**

**KEY DESIGN FEATURES**
** ****High Earth orbit (HEO) to minimize IR Earth-glow loading**
** ****GaAs cell - OSR striping of the (hot) solar array panels**
** ****Front surface heat rejection OK**
** ****Optical Solar Reflectors are back silvered Quartz tiles (*********** *****~ 8%, *********** *****~ 80%)**
** ****Low emissivity silvered mirrors**
** ****Thermal Isolation mounting and ****	****Extensive MLI blanketing**

## CAMERA THERMAL

**RECENT SSL MISSION EXPERIENCE**

**HESSI COLD PLATE ASSEMBLY**
**supports Germanium Detector Assembly under Vacuum**

**HESSI DETECTORS**
**Extensive T****h****ermal Isolation**
**Only ~3W of active cooling**

|  | HESSI | SNAP |
| --- | --- | --- |
| Detector Temperature | 73 K | 140 K |
| Cooling Budget | 3 W active | 20 W passive |
| Detector (Cold) Mass | 38 kg | Est 32 kg |
| Orbit | LEO | HEO |
| “Focal Plane” Precision | mm | microns |

## CAMERA THERMAL

*130K PASSIVE*
*RADIATOR*

**PASSIVE GIGA-CAM 140K DEWAR THERMAL BUDGET**
** ****32 w ****	****Radiating Capacity from 2m****2**** unobstructed 130K Radiator to Space**
**< 4w>****	****Radiator Thermal Isolation Mounts & MLI behind**
- 		**RADIANT COUPLING LOSSES**
**< 6w>****	****CONICAL Cosmic Ray Shield - MLI outside (********** ************ *****~ 1%)**
**< 4w>****	****Open End CONE Blackbody Loss to warm Coffin Cavity**
- 		**CONDUCTIVE COUPLING LOSSES**
**< 1w>****	****Giga-Cam Thermal Isolation Mounts**
**< 2w>****	****Dewar Thermal Isolation Mounts and Cold Plate Gaskets**
**< 1w>****	****Electrical “Flex-Print” (~ 5800 traces)**
**< 8w>****	****Average Electrical Power Dissipated in HgCdTe & CCD’s**
** ****~ 6w** 	**CURRENT MARGIN**
**~10°C ****	****Gradient allocated for Cold Plate, Radiator, and Flex-Links**

*THERMAL SHIELD*

*COLD*
*PLATE*

*SHUTTERS*

## R&D ACTIVITIES

**Typical Instrument Engineering Team**
**Instrument Manager, Structural, Thermal, Cryogenic, Mechanisms, Optics, Quality Assurance, Contamination, Configuration Management, Procurement**
**Typical Spacecraft Engineering Team**
**Bus Manager, Integration & Test manager, Ground Segment manager, Launch manager, Structure and Mechanisms, Thermal control systems, Attitude control systems, Flight Dynamics, Electrical power systems, Command & Data Handling, Telecommunications, Flight Software**
**Develop the “Proof of Concept” Spacecraft & Instrument Designs**
** ****Detailed Camera and Dewar Mechanical, Thermal, and Electrical Designs**
-  **Partner with Industry(s) to develop Telescope and OTA Structure**
** ****Develop Compatible Primary, or the Load Bearing Spacecraft Structure**
** ****Conceptual Design of Test / Ground Support Equipment needs**

**“****Expand the Instrument and Spacecraft Project Office Infrastructure that will be needed to properly ‘Architect’ the SNAP Mission”**

## R&D ACTIVITY HIGHLIGHTS

** ****Major Design Activity Flow Downs, or Design Related Activities**
** **Preliminary Coupled Loads Analysis (includes Launcher)
-  Preliminary  Observatory Level Integrated Thermal Model
-  Generate Viable Optics Test Plan, and the General Bus I&T Plans
-  Develop DRAFT Instrument & Spacecraft Interface Documents
-  Science and Mission Requirements Review(s)
** **Budgeting *(mass, power, etc.)* will be formalized as the Designs Mature
** ****Generate the Long Lead Item Optics Procurement Plan**
** ****Generate an EM Spacecraft & Telescope Plan and Schedule**

## Systems: R&D Schedule

## Deliverables WBS 1.3 Systems

## ENGINEERING STATUS

** ****CAMERA **needs and viable approaches are known and actively pursued
-  Thermal management calls for continuing vigilance
** ****TELESCOPE **packaging options and requirements are well defined
-  Several Light-weighting Options are Actively being Considered
-  Our team’s desire is to maintain technology/vendor flexibility
** *****OPTICS PROCUREMENT IS THE LONG LEAD ITEM***
** **
** ****SPACECRAFT **can be a generic ***(interagency)***** RSDO** procurement
-   Instrument - ACS interactions calls for studies & tracking
** ****LAUNCH VEHICLE **– Track the Options and New Development Maturity

## SUMMARY & COMMENTS

** ****Delta IV Is Not Mature Today, but NASA Is Committed.**
** ****Delta 4 build in process at KSC for EUTELSAT *****...summer ’02***
** ****USAF Launch of DSCS-B6 now planned for Nov. ‘02**
**SC Bus has its Challenging Aspects, but No New Technology**
** ****SNAP has Several Lightweight, Low CTE Mirror Options**
**Composite OTA Structures Are Well Understood and this Technology Continues to Advance **
**Build, Test, & Fly Warm is both Proven and Cost Effective**
**Passive Thermal Approach is Viable for Camera **