Bibliography

Description

Current TT Progress and Plans

Goals

Colin Eaton

Undergraduate Senior SAWDRIP Intern Code 551 (Optics)

Trans-Track (TT):

– … is a 6-DOF object-transformation functionality in

the Spatial Analyzer (SA) metrology software

– …is currently used in real-time precision applications

for assembly and collision avoidance

– e.g. Mounting science instruments (SI) to

payload structures

– …uses Laser Trackers (LT) to record locations of

various spherically mounted retroreflectors (SMR)

attached to the moving object

– One LT monitoring 3 SMRs completes 6-DOF,

discrete TT system

– Three networked LTs monitoring 3 SMRs

provides real-time updates for 6-DOF TT

– …utilizes watch windows to monitor relationships

between corresponding source and target SMRs during

assembly, and updates the net distances/angles to the

destination position/orientation

Trans-Track with Laser Tracker Laser Radar Applications

– Monitor 6-DOF motion required to guide a moving

object through a static environment

– Both discrete and real-time

– Adapt a warning mechanism feature to the software

in order to alert the operator if objects are within a

given tolerance and/or if the minimum clearance is

violated

– Audio and/or visual feedback

– Develop a simplified mating assembly to

demonstrate features that can be used in full-scale

applications

– e.g. An IATF-ISIM scenario on behalf of the

JWST project

– Utilize the Measurement Planning (MP)

functionality of SA to help automate the processes

Spherically Mounted

Retroreflector (SMR)

Networked Laser

Trackers (LT)

Houston, we

have a problem

with the

tolerances.

< 0.001”

Acknowledgements:Mentors and *Lab Associates:

Joseph Stock, SGT, Inc.

Joseph Hayden, Sigma Space Corp.

*Henry Sampler, NASA/GSFC

*Phillip Anz-Meador, NASA/JSC

*David Parker, Lockheed Martin Corp.

Sponsors:

NASA Goddard Space Flight Center

Stinger Ghaffarian Technologies

University of Michigan – Ann Arbor

College of Engineering

Michigan Space Grant Consortium

– Explored the Interferometry (IFM) and Absolute Distance Meter (ADM) settings on the LT to establish

advantages and disadvantages of each:

– Successfully simulated discrete Trans-Track translation using 3 SMRs and one LT

– Associated SMR locations with their base in SA

– Observed discrete translation of target locations and base in SA

using instrument updates

– Near completion of audio and video feedback features with MPs

– Scheduled time for access to all three GSFC LTs

– Plan to perform real-time TT testing on (to be assembled) simplified IATF setup

– Will present findings to Optics division for potential uses and feasibility for full-scale applications

Base

SMR Nests

ADM Mode IFM Mode

•Records absolute distances from a known coordinate system,

and does not need initial reference measurement

•Only capable of measuring relative positions and thus needs an

initial reference measurement

•Utilizes automatic target-locking feature when the line-of-sight

between the LT and the SMR is compromised

•Break of beam requires “homing” of SMR to known location

•Internal integration times slightly delay measurements and

introduce source of error when measuring moving objects

•Near-immediate measurements induce no loss in accuracy in

measurements of objects moving slower than ~3m/sec

> Used for discrete TT applications > Used for real-time TT applications

– Following the impressive results of the RSU

scans, it was proposed that the LR be used to

analyze the micro-meteorite impacts on the

radiator of the Wide Field Planetary Camera 2

(WFPC2)

– The LR was networked into the reference

frame via scans of retro-targets and key

features of the face plate – specifically the

corners and two port hole centroids

– Hi-resolution scans were performed on the two

largest craters (numbered 13 and 14)

– These scans proved to be beneficial in the

analysis of the impacts, and may be

considered as a viable alternative for similar

applications in the future

LR Trans-Track LR vs. PG– Photogrammetry (PG) is currently the primary

method employed in optical metrology measurements

under cryogenic conditions

– PG is derived from photographic images and the PG

camera system is tested and calibrated through the

multi-layer windows of the cryogenic chambers

(which induce Snell’s Law image distortions)

– It has been suggested that the relatively new LR

technology be adapted to take cryogenic

measurements as a cross-check for PG

– Research has been done to analyze the window

distortion effects on LR measurements, and the

results are promising

– Current plans:

– Determine the most robust method of

centroiding the PG targets from LR scans

– Characterize the LR returns on PG targets at

different incidence angles

– Compare relative accuracy between LR and PG

on the same PG targets

– Test the repeatability of LR measurements

Hubble Ex-Flight Hardware Scans

– On Hubble Servicing Mission 4 (SM4), the

astronauts were unable to place one of the

Rate Sensing Units (RSU) in its mounting

plate

– As per the request of Code 442 scientists,

LR scans of the feet and pinholes on the

bottom surface of two RSUs were taken (one

that fit, and the one that didn’t fit)

– Relative locations and other requirements

were analyzed, and it was deduced that all

dimensions were well within their

respective tolerances (within ~30microns)

– The RSU was transported to the Hi-Fidelity

Hubble Mock-up at GSFC and was easily

placed into its respective mounting plate

– Original plans to utilize the laser radar (LR) included

scanning the envelopes of objects in the system as an

alternative/addition to simply translating the CAD

models

– An anomalous effect intrinsic to the LR was

discovered in the process, where scans of flat

surfaces yielded oscillatory patterns (nicknamed the

“Metrology Genome Effect”)

– This problem was resolved when the Decimation

setting was returned to its default position (it is still

unknown how/when this setting was manipulated)

– Once the LR was fixed, it was realized that the

tooling ball (TB) measurement feature of the LR

could be used in place of the LT for discrete TT

– Discrete TT with the LR has been successfully

tested and compared to the LT method

– Slightly longer delay between measurements

– Equivalent accuracy

Gyros WFPC2

Side view of the scan of a flat

metallic surface. Horizontal

scale is around 10mm, and

vertical scale of oscillations

ranged from 100-300 microns

(0.1 - 0.3mm)

PG targets are retro-reflective

surfaces that reflect light very

efficiently back to the light

source

LR surface scans

of the bottom

surface of the ex-

flight RSU super-

imposed onto the

dimensioned CAD

model

Photograph of crater “big 13 .“

Hole diam. <2mm

LR surface scan of crater 13

JWST: James Webb Space Telescope

ISIM: Integrated Science Instrument Module

IATF: ISIM Alignment Target Fixture