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Mechanical System Design & the StarLight Project

Andy Jarski

Mechanical Systems Engineer

Ball Aerospace & Technologies

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Overview

• Brief Intro to Mechanical Design process

• StarLight as an example

• Some designs I’m working on

• Conclusions

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Quick Look at the Design Process

• Identify the requirements– Mission– Launch Environments– Instrument / Payload Accommodations

• Create Preliminary Configurations– Subsystem requirements (size, location, FOV)– Accessibility– Producibility– Structural Characteristics (load paths, stiffness)

• Design Options– Materials (strength, stiffness, weight, CTE, corrosion resistance, cost, etc.)– General shape / layout

• Validation of Requirements– Test Criteria– Design Criteria

• Iterations– Until requirements are met

• Detailed design goes to production

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StarLight is the 1st of it’s Kind

• Demonstrate 2 key technologies of particular importance for Terrestrial Planet Finder:

– Autonomous Formation Flying– Separated-Spacecraft Interferometry

• Mission uses 2 spacecraft, launched together which then separate to 600-1000m to simulate the performance of a single large telescope

• JPL provides interferometer instruments and formation flying sensors

• Ball provides 2 spacecraft, integration and test, and operations for the spacecraft

• Heliocentric, earth trailing orbit to eliminate gravity field perturbations

• Two spacecraft formation-flying to 2 cm accuracy

• Low-jitter spacecraft to permit interferometer to lock on fringes

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Black Magic of Interferometry

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Formation Flying, in the Dark

26º Half Cones of Shadow(all components are shaded)

42º Starlight View Range

Intra InstrumentLine of Sight

52º Starlight View Range

Collector Optics

Combiner Instrument

X

Collector S/C

Combiner S/C

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Who’s Driving our Configuration?

• Fit both spacecraft within the 3m, 3 stage, Delta II Fairing Envelope– Interface to the standard Delta 37” clamp band

– Keep the CG within launch vehicle limitations

• Accommodation of Interferometer instruments and Formation Flying Sensors

• Provide unobstructed fields of view for– StarLight interferometer

– intra-interferometer starlight link

– Formation Flying sensors

– Star Trackers

– Antennas

– Thrusters

– Sun sensors

– Solar arrays

• Maintain CG balance after fuel depletion

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Launch & Cruise Configurations

Delta II 3m-3 Stage Fairing

Combiner S/C

Collector S/C

37’’ Interface Ring

108”

100”

Star 48B3rd Stage Motor

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These Spacecraft are Nicely Equipped

High Accuracy FormationFlying Sensors

Low ImpulseCold Gas thrusters

(x16)

Star Trackers (x2)

Sun Sensors (x14)

UHF antennas(Inter s/c comm)

Solar Panel106 in./270 cm dia.

Deployable Sunshade134 in./340 cm dia.

Interferometer

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Interferometer

Main Bus Assembly

2-Piece Solar Array

Hatch

Propulsion Module

Modular Designs Reduce Risk

Formation Flying SensorModule

• Modularity reduces I&T complexity and time required

• Modularity improves accessibility

• S/C bus components housed in Main Bus Assembly

• Instrument is it’s own entity

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• StarLight uses nearly identical composite structures to

– closely match the characteristics of the interferometer optical benches

– minimize mass

• Commonality helps to– Reduce I&T complexity – Reduce risk– Lower cost

Commonality is Important

Relay Box

Reaction Wheels (x4)

Telecom “gear” X-Band Transponder

SCU (Computer)

IMU

Battery

Propulsion “gear” Transceiver

Star Trackers (x2)

Hatch

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Structural Requirements

• Minimum natural frequency of the launch stack– 15 Hz Lateral– 35 Hz Axial– 35 Hz Secondary– Applied to all components except the fixed sun shade

• Max Axial Load: 9.5 g axial combined with 0.1 g lateral

• Max Lateral Load: 2.8 g axial combined with 3.0 g lateral

• Minimum factor of safety– Yield: 1.25– Ultimate: 1.50

• Other requirements (acoustic, random, etc.) not expected to be critical

• Alignments

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Launch ConfigurationCollector Spacecraft

Combiner Spacecraft

StarLight FEM

• Finite element models– of Launch Configuration for structural modes analysis– of separated s/c to analyze on-orbit disturbances

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Modes Analysis

1st Lateral Mode of 15.3 Hz

1st Axial Mode of 38 Hz

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Connector

SeparationSpring

SeparationNut

Separation Plane

Deployable is a Dangerous Word

• Inter-Satellite Separation Mechanisms– Tolerance analysis– Separation dynamics– ABSOLUTELY MUST WORK!

• Sunshade– Material selection crucial

• RF transparent• Visibly opaque

– Stiffness– ABSOLUTELY MUST WORK!

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Some Other Thoughts

• Some basic engineering principles I think are important– When you start a design, just get something down on paper– If you leave something as a placeholder, document it as such and make sure

to go back and fix it– Allocate lots of time for test, this is where everything comes together, and

that is the point, isn’t it? – Test early, test often, test it again– Never compromise your ethics

• If the design isn’t working, is behind schedule or over budget, say so, don’t mislead anyone, they may be able to help

• If you see a problem, speak up

• Getting involved is the best way to learn– Space Grant provided opportunities I couldn’t get anywhere else

• Great exposure to industry• Opportunities you don’t always get in industry

– Learning in a classroom is one thing, but applying your skills in a “real world” environment with real accountability and responsibility is where the challenge and fun are.

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Questions?