**SPACECRAFT DESIGN**

**and**

**MISSION OPERATIONS**

> **SNAP ORBIT**

-   \"Prometheus\" Orbit Baselined Following Preliminary Trade Study

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-   Uses Lunar Assist to Achieve a 19 X 57 Re Orbit with a Delta III
    8930 Launch Vehicle

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-   Good Overall Optimization of Mission Trade-offs

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-   Low Earth Albedo Provides Multiple Advantages:

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-   Facilitates Passive Cooling of Detectors

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-   Minimizes Stray Light in Telescope

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-   Minimum Thermal Change on Structure Reduces Demand on ACS

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-   Good Visibility from Berkeley Ground Station

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-   Outside Radiation Belts

-   Orbit Reachable with Available Launch Vehicle

> **SPACECRAFT DESCRIPTION**

-   Detailed Spacecraft Design will be Done in Collaboration with
    Teaming Partner

-   Intent of System Design is to:

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-   Keep Interfaces as Well Defined and Simple as Possible

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-   Utilize Experience and Strengths of Team Members

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-   Spacecraft System is Comprised of Four Major Functional Blocks

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-   Power System

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-   Propulsion/ACS System

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-   Telecommunications System

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-   Observatory Control Unit

> ![](media/image1.pct){width="8.497222222222222in"
> height="5.210416666666666in"}

**POWER SYSTEM**

-   Two 1 Square Meter Arrays of GaAs Cells Supply 340 Watts at End of
    Life

-   Arrays Fold Out after Launch and Lock in Place

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-   Gimbaling of Arrays is Not Required

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-   Controller Performs Battery Charge Management and Power Distribution
    Function

> **TELECOMMUNICATIONS SYSTEM**

-   S-Band Transponder with Two Low Gain Antennas Provides Uplink and
    Emergency Downlink

-   X-Band Transmitter with 25 Watt Traveling Wave Tube Amplifier and 50
    cm Steered Antenna Provides 50 megabit per second Link to Berkeley
    Ground Station

**POINTING STRATEGY**

-   Telescope Pointing Task is Broken into Two Parts

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-   Conventional 3 Axis Pointing System on Spacecraft Gives Accuracy of
    2 Arc-seconds in 3 Axes

-   Accomplished Using Mid to High End Conventional Components

-   Requires Careful Attention be Paid to Structure Stiffness and
    Damping

-   Stand Alone System on Spacecraft will be Spec\'ed to Required
    Accuracy

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-   Fast Steering Mirror System Augments Pointing Provided by Spacecraft
    to Achieve Required .03 Arc-second Pointing of Telescope

-   Roll Axis Accuracy of Spacecraft System is OK

-   Fast Tracking Mirror Corrects 2 Cross Axes

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-   The Two Systems are Completely Independent

-   No Exchange of Control Signals as on NGST

> **ACS/PROPULSION SYSTEM**

-   Strawman Design Provides Pointing Control on Spacecraft to 2 Arc
    Seconds

-   Two Ball CT 602 Star Trackers

-   Reaction Wheel Package Uses Ithaco Type B 16 nms Wheels with Special
    Balancing

-   IMU Package Comprised of Litton Hemispheric Resonator Gyros

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-   Dedicated Controller Separate from Data System

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-   This Accuracy is Adequate for Science Mission in Roll Axis

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-   Requirement on Cross Axis Pointing Effectively Met with Fast
    Steering Mirror in Telescope

> **ACS/PROPULSION SYSTEM** (continued)

-   Propulsion System Uses Mono Propellant Hydrazine

-   Single 10 Newton Main Engine

-   Redundant Set of Six 1 Newton Attitude Control Engines

-   System Dry Mass is 15 kg

-   49 kg Fuel Capacity

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-   25 kg Needed for Apogee Adjust

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-   5 kg Allocated for Navigation

-   5 kg Allocated for Reaction Wheel Management

-   14 kg Margin

> **OBSERVATORY CONTROL UNIT**

-   Primary Task is Receipt of High Rate Telemetry from Payload and
    Transfer to Downlink

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-   Receives and Processes Ground Commands

-   Controls Other Spacecraft Systems

-   Collects Engineering Telemetry and Performs Observatory Thermal
    Control

-   Performs Initial Acquisition and Spacecraft Safing Functions

> **SPACECRAFT STRUCTURE**

-   Careful Attention to Structure Design Essential to Meeting
    Requirements on ACS System

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-   Delta III Fairing Allows Separate Structure for Payload and
    Spacecraft

-   Math Modeling will be Done on the Combined Payload and Spacecraft
    Structure

> **LAUNCH VEHICLE**

-   Boeing Delta III 8930 will Deliver \>2800 kg to Prometheus Orbit

-   Spacecraft Propulsion System Used for Mid-course Correction and
    Apogee Reduction

-   Fairing will Accommodate All Telescope Designs Under Consideration

> **OBSERVATORY INTEGRATION and TESTING**

-   Large and Complex Task Requires Carefully Developed Plan

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-   Detailed I&T Plan will be Developed During Study Phase

-   Current Test Philosophy Includes:

-   Build Test Functions into Hardware

-   Perform System Level Tests as Early as Possible

-   e.g. Do Subsystem Interface Tests at Bread Board Level

-   Test End-to-End Whenever Possible

-   Ability to Support Tests is an Important Factor in Choice of Teaming
    Partners

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-   Strawman Plans Include:

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-   Optics Testing Done by Optics Subcontractor

-   Spacecraft Contractor will Deliver a Fully Tested Spacecraft

-   Mechanical and Electrical Integration will be Done in the SSL High
    Bay

-   Observatory Vibration and T/V Done in a Bay Area Facility

-   Final End-to-End Optical Test will be Done in an Appropriate
    Facility

> **MISSION OPERATIONS**

-   Mission Operations Center (MOC) at Space Sciences Using Berkeley
    Ground Station

-   Fully Automated System Tracks Multiple Spacecraft

-   Science Operations Center (SOC) at Lawrence Berkeley Laboratory
    Built Around NERSC Super Computer

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-   Multiple Terabytes Data Storage

-   High Speed Links to CPU Farms & Supercomputers

-   Intensive Processing Done on Supercomputer with Final Analysis on
    PC\'s

> OR

-   Grand Challenge-like Software System

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-   Operations are Based on a Four Day Period

-   Autonomous Operation of the Spacecraft

-   Coincident SOC Review of Data with Build of Next Target List

-   Upload Instrument Configuration for Next Period

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height="4.497916666666667in"}