Servicing ATLAST!
Bill Oegerle
Lloyd Purves
NASA/Goddard Space Flight Center
International Workshop on On-Orbit Satellite Servicing
University of Maryland, College Park
March 24-26, 2010
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ATLAST is the “Advanced Technology
Large Aperture Space Telescope”
Postman (STScI), PI
• Envisioned as the next-generation UVOIR telescope after HST
and JWST
• 3 point-designs considered:
– 8-m diameter monolithic mirror design for launch on Heavy
Lift LV (Stahl/MSFC, lead)
– 9.2-m segmented mirror design for launch on EELV (DeltaIV Heavy) (Oegerle/GSFC, lead)
– 16-m segmented mirror design for launch on Heavy Lift LV
(Unwin & Traub/JPL & NGST lead)
• All operate at SEL2 Lagrange Point
• Submitted in 2009 for consideration to the National Academy’s
Astro2010 Decadal Survey (results to be published in Sept
2010)
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3 Designs for ATLAST
(not to scale)
8-m monolith
(Hubble-like)
All concepts were
designed with
servicing in mind
9.2m segmented
(JWST-like)
16m segmented
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(JWST-like)
Servicing ATLAST-8m
The instruments in ATLAST-8m are easily accessible in a
bay below the OTA by an autonomous rendezvous vehicle
such as Orbital Express (Stahl, 2009)
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The ATLAST-9.2m design features
Similar to JWST, but different in many ways
 Primary mirror has 36 segments (instead of JWST’s 18).
 ULE glass mirrors (not Be); room temperature optics (easier ground
testing)
 Wavelength range 110nm to 1700nm (useful response to 2500nm)
 Diffraction limited at 500nm - 4 times tighter specs on wavefront error
than JWST
 Modified TMA design with Cassegrain channel for UV instruments and
high contrast imager.
 Cassegrain: Al+MgF2 coating on PM and SM for high UV throughput
 TMA: ~ 8 x 20 arcmin Wide field cameras in (silver coatings on
pickoff flat and TMA optics after PM and SM)
 Guider and wavefront control combined in one TMA sensor - active mirror
control every 5 minutes
 Pointing control with active hexapod isolator/pointing arm/reaction wheels
 Simple Sunshield - meant to block sunlight not provide thermal control
 Designed for servicing
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ATLAST-9.2m - Stowed configuration
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Deployment Sequence
RELEASE FROM
LAUNCH VEHICLE
RELEASE/DEPLOY
POSITIONING ARM
DEPLOY
SOLAR ARRAY
DEPLOY HI-GAIN
ANTENNA
DEPLOY
SUNSHIELD
DEPLOY MIRROR
ARMS
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ATLAST-9.2m - Deployed Configuration
PM Segment
36 ea.
Deployable PM Baffle
SSM Baffle
SM Assy.
SM Metering Structure
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ATLAST-9.2m Deployed Configuration
Instruments are
easily accessible
for servicing
from behind the
OTA.
Support Panel
2 ea.
PM Backplane
Frame
ISIM Envelope
Instrument
boxes can slide
in and out on
rails
instrument
Complement
(spectrographs &
Exoplanet instrument)
Hybrid FGS
WFS&C cameras
4 ea.
IC & DH
WFOV
camera
Lower Support
Structure
Junction box
2 ea.
ADU Box
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ATLAST-9.2m Spacecraft Bus layout
Top
view
SC
components
replaceable
Side
view
Bottom
view
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Servicing ATLAST-9.2m
Deployable telescoping
Manipulator arm
Deployable temporary
Stowage site (1 of N)
Carrier-Handler
with SIs and
ORU modules;
optimized for
each servicing
mission
PM segments
(with positioners
and latches
ATLAST ISS
with multiple
SIs,active
latches
CarrierHandler
bus
SM module
(with positioners)
Sun shield
Carrier-Handler
docking interfaces
SC bus with
Subsys modules
& modular
Restowable
appendages
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Servicing Thoughts
 Servicing required for large national space-based assets
 Replaceable items should have easy access for robots or
humans as part of mission design
 Observatory should have access ports or fixtures to allow
capture and maintenance by rendezvous service vehicles.
 Highly desirable to have a “standard” plug and play method of
removing and inserting “replaceable boxes” (instruments or
S/C components) - ie. standard rails, fixtures etc.
 For robotic servicing: in situ at SEL2 - replace whole
instruments - don’t try to repair them
 For human servicing: bring observatory back to EML1/2.
Could remove instruments and do intricate repairs inside
servicing depot
 Need consideration of how to replace non-standard items eg. mirror segments
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