The Balloon Experimental Twin
Telescope for Infrared
Interferometry (BETTII)
Dr. Stephen Rinehart
NASA’s Goddard Space Flight Center
Laboratory for Observational Cosmology
What is BETTII?
As proposed, BETTII looked something like this…
24 February 2014 BETTII: FISICA Workshop 2 Evolution…
By December 2012, the design looked like…
24 February 2014 BETTII: FISICA Workshop 3 Current Design
•  And now (February 2014)
Siderostat Dewar Primary Telescope Assembly Exoskeleton Metering Truss •  Essential design elements are unchanged…
24 February 2014 BETTII: FISICA Workshop 4 What can it do?
24 February 2014 BETTII: FISICA Workshop 5 Key Science Features
•  8-meter baseline + Double-Fourier =
–  Angular Resolution of ~0.5” at 40 µm
–  Spectral Resolution of up to R~200
•  Wavelength Coverage from 30-90 µm
•  Sensitivity: ~20 Jy in 10 minutes
–  The Negative Spin: Require bright targets
–  The Positive Spin: Can do targets that saturate for
Spitzer and Herschel
24 February 2014 BETTII: FISICA Workshop 6 Science Goals
NGC 1333 Serpens Cep CW NGC 7029 24 February 2014 NGC 2071 BETTII: FISICA Workshop 7 Spectra of Cores
Herschel beam
Herschel sees a blend
of multiple sources
Partially embedded
disk system
24 February 2014 Deeply embedded
YSO
BETTII: FISICA Workshop YSO with Water Ice
Feature at 43 µm
8 A Tale of Three Systems
Instrument/Cryostat External OpTcs Control System (Exoskeleton) 24 February 2014 BETTII: FISICA Workshop 9 Metering Truss
•  Must be stiff, strong, and light
–  Made of carbon fiber tubes with
stainless steel nosecones and nodes
24 February 2014 BETTII: FISICA Workshop 10 The Completed Truss
•  Light (~70kg)
•  Strong – can take
a 10g load with
factor of 2 margin
•  Stiff: first mode at
23.0 Hz.
24 February 2014 BETTII: FISICA Workshop 12 External Optics
8 meters Primary Flat Secondary K-­‐mirror 24 February 2014 Warm Delay BETTII: FISICA Workshop TerTary 13 The Telescope Assembly
Primary Secondary Flat TerTary 24 February 2014 BETTII: FISICA Workshop 14 The Instrument
•  Double-Fourier instrument
LHe Tank
–  FIR channel for science
–  NIR channel for angle tracking
and fringe tracking (maybe)
LN2 Tank
He3 Fridge
Science/FIR
Volume (4K)
•  TES Bolometer Arrays (BUGs)
Tracking/NIR
Volume (77K)
24 February 2014 BETTII: FISICA Workshop 15 Instrument Optics
•  Key features of the internal optics:
–  Optical relay for cold pupil
–  Cold delay line
Delay
Line
Collimated
input beam
–  FIR beam splitter
–  FIR dichroics
Long #1
Short #1
Detector
Detector
Long #2 Asphere
Tracking
Channel
Short #2
Near-IR
dichroics
24 February 2014 Asphere
Optical
Relay
50/50 OAPs Far-IR
dichroics
Beam
Splitter
BETTII: FISICA Workshop Detector
Detector
16 The Layout
Detector Arrays
Dichroic
Cold Delay
line
Cold
Pupil
Relay Optics
24 February 2014 BETTII: FISICA Workshop 17 Opto-Mechanical
24 February 2014 BETTII: FISICA Workshop 18 The Control System
•  Exoskeleton
•  Computers
•  Housekeeping
24 February 2014 BETTII: FISICA Workshop 19 Control Scheme
Momentum dump
ACTUATION LOOP
CCMG wheel angle
Siderostat
Rotation stages
Conversion to
elevation and
cross-elevation
errors
Elevation
error
Warm
delay line
CCMG
Cross-elevation
error
Attitude error
Slew mode
SENSOR LOOPS
Tracking mode
24 February 2014 Target pixel
for guide star
Tip/Tilt
Position
Target velocity
and position
Tip/Tilt
mirrors
Angle
Sensor
Gyros & star
camera
BETTII: FISICA Workshop 20 Overall Status
•  Proceeding well: upcoming milestones
–  Cryostat complete by April 2014
•  Internal optics installed and aligned by August 2014
–  Detector delivery in June 2014
•  Detector testing/characterization through August 2014
–  Delivery of telescope assemblies in August 2014 (!!!)
•  Alignment of external optics by November 2014
–  Control system testing ongoing
•  Performing better than expected!
•  On track for launch in Fall 2015 from Fort Sumner
24 February 2014 BETTII: FISICA Workshop 21 Thanks
The BETTII Team:
• 
•  R. Barry
• 
•  D. Benford
• 
•  P. Calhoun
• 
•  W. Danchi
• 
•  A. Dhabal
• 
•  D. Fixsen
• 
•  C. Jhabvala
UK Collaborators:
• 
•  P. Ade
• 
•  E. Pascale
• 
•  R. Juanola-Parramon
Collaborators:
• 
•  R. Lyon
• 
24 February 2014 Undergraduate Students
D. Leisawitz • 
• 
S. Maher
• 
L. Mundy
• 
M. Rizzo
R. Silverberg • 
J. Staghun • 
• 
T. Veach
M. Griffin
L. Spencer
G. Savini
A. Kogut
J. Mather
• 
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J. Doiron
S. Gore
B. Hoffman
W. Tierney
R. Curley
T. Kale
T. Handleton
S. Shapoval
M. Canaparro
D. Andrade
J. Stokes
C. Gibbons
J. Gibson
• 
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S. Weinreich
J. Alcorn
A. Rau
S. Padder
P. Nehme
L. Oliveira
H. Spooner
C. Wagner
A. Cotto
N. Mihalko
Y. Okafor
P. Taraschi
Y. Huertes-Morales
And the Far-­‐Infrared Telescope Experiment (FITE) team in Japan (H. Shibai, PI) BETTII: FISICA Workshop 22 

program in pdf - First Fisica Workshop