SuperNova Acceleration Probe Research and Development Efforts

1
SuperNova Acceleration ProbeResearch and
Development Efforts

• Michael Lampton
• UCBerkeley Space Sciences Laboratory
• Chris Bebek
• UCBerkeley Lawrence Berkeley National Laboratory
• 7 May 2002

2
SNAP Collaboration
G. Aldering, C. Bebek, W. Carithers, S. Deustua,
W. Edwards, J. Frogel, D. Groom, S. Holland, D.
Huterer, D. Kasen, R. Knop, R. Lafever, M. Levi,
S. Loken, P. Nugent, S. Perlmutter, K. Robinson
(Lawrence Berkeley National Laboratory) E.
Commins, D. Curtis, G. Goldhaber, J. R. Graham,
S. Harris, P. Harvey, H. Heetderks, A. Kim, M.
Lampton, R. Lin, D. Pankow, C. Pennypacker, A.
Spadafora, G. F. Smoot (UC Berkeley) C. Akerlof,
D. Amidei, G. Bernstein, M. Campbell, D. Levin,
T. McKay, S. McKee, M. Schubnell, G. Tarle , A.
Tomasch (U. Michigan) P. Astier, J.F. Genat, D.
Hardin, J.- M. Levy, R. Pain, K. Schamahneche
(IN2P3) A. Baden, J. Goodman, G. Sullivan
(U.Maryland) R. Ellis, A. Refregier (CalTech) J.
Musser, S. Mufson (Indiana) A. Fruchter
(STScI) L. Bergstrom, A. Goobar (U. Stockholm) C.
Lidman (ESO) J. Rich (CEA/DAPNIA) A. Mourao
(Inst. Superior Tecnico,Lisbon)
3
Overview

• What is SNAP?
• SNAP Reviews Milestones
• What are our current RD efforts?
• Mission Development Optimization
• Optical performance trades
• Attitude Control System issues
• Shutter technology
• Bandpass filter technology
• Calibration plan
• IFU/Spectrometer technology
• Si CCDs
• HgCdTes
• Detector Electronics

4
SNAP Introduction

• Supernova data shows an acceleration of the
  expansion, implying that the universe is
  dominated by a new Dark Energy!
• Remarkable agreement between Supernovae recent
  CMB.

Credit STScI
5
Mission Design

• SNAP a simple dedicated experiment to study the
  dark energy
• Dedicated instrument, essentially no moving parts
• Telescope 2 meter aperture, diffraction limited
  beyond 1 micron
• Photometry with 1deg FOV half-billion pixel
  mosaic camera, high-resistivity, rad-tolerant
  p-type CCDs and HgCdTe arrays. (0.4-1.7 mm)
• Integral field optical and IR spectroscopy
  0.4-1.7 mm, 2x2 FOV

6
Primary Science Mission Includes
7
SNAP Motivation

• Precision cosmology to distinguish models
• There are a LOT of models
• Dark energy is not understood
• Early universe was dominated by gravitation,
  hence deceleration
• Only more recently could dark energy have become
  dominant
• Need an accurate redshift-magnitude diagram
• must extend a large range of redshifts
• small z recent epoch with acceleration
• zgt1.5 to probe possible early deceleration epoch
• must minimize systematics lt few percent
• must minimize statistics lt few percent

8
Standard Candles

• Cosmic accelerometer need lookback time and
  expansion for each of thousands of events
  distributed throughout universe.
• Standard candle redshift-magnitude diagram gives
  both
• expansion from redshift
• lookback time from apparent magnitude
• Type Ia supernovae are the best candles known
• WD receives mass from binary companion
• SN occurs when WD mass exceeds Chandrasekhar
  limit
• This limit is set by electron degeneracy pressure
• Empirically, Ias can be standardized to lt 0.2
  magnitudes
• therefore, tens to hundreds/bin give few percent
  precision
• Systematics are just as important as statistics
• Light curves are important to distinguish
  variants, trends...
• Spectroscopy is important to distinguish
  variants, trends...

9
How to achieve these goals?

• Huge amounts of uniformly-calibrated observing
  time gt space
• Need guaranteed reobservation each SN for light
  curve gt space
• Need to probe into the NIR, out to 1.7 microns
  gt space
• Need to go faint gt space
• detect at 29th AB magnitude at 1 micron
• spectrum precision photometry at 25th magnitude
• Spaceborne telescope and instrument complement
• approx 2 meter aperture, wide field optics
• large format imager/photometer, 1 deg FOV , 9
  bands
• repeatedly scans a survey region, 10 sq deg
• multiplex advantage half billion pixels
• processes entire field regularly, every few days
• low dispersion spectrometer
• observe each SN at peak for classification

10
Simulated SNAP data
11
From Science Goalsto Project Design
Science

• Measure ?M and ?
• Measure w and w (z)

Systematics Requirements
Statistical Requirements

• Identified and proposed systematics
• Measurements to eliminate / bound each one to
  /0.02 mag

• Sufficient (2000) numbers of SNe Ia
• distributed in redshift
• out to z lt 1.7

Data Set Requirements

• Discoveries 3.8 mag before max
• Spectroscopy with S/N10 at 15 Å bins
• Near-IR spectroscopy to 1.7 ?m

Satellite / Instrumentation Requirements

• 2-meter mirror Derived requirements
• 1-square degree imager High Earth orbit
• Spectrograph High bandwidth (0.4 ?m to
  1.7 ?m)

12
Other Benefits

• SNAP main survey will be 6300 x larger (and
  somewhat deeper) than the HST ACS survey
• SNAP will provide 9-band colors of every object
  within its survey region
• SNAP has time resolution
• revisit everything every few days
• span gt2 years
• Complementary to NGST target selection for rare
  objects
• Could survey 3000 sq deg in a year to I29 or
  J28 AB mag

13
SNAP Reviews/Studies/Milestones
Mar 2000 SAGENAP urged DoE to begin supporting
SNAP RD Sep 2000 NASA Structure and Evolution of
the Universe (SEU) Dec 2000 NAS/NRC Committee on
Astronomy and Astrophysics Jan 2001 DOE-HEP
Reviewed SNAP RD Program Mar 2001 DOE HEPAP
Reviewed SNAP science goals Jun 2001 NASA/GSFC
Integrated Mission Design Center July
2001 NAS/NRC Committee on Physics of the
Universe July 2001 Snowmass 2001 Workshop
Resource Book on Dark Energy Nov 2001 CNES
(France Space Agency) IN2P3, U.Marseille Dec
2001 NASA/SEU Strategic Planning Panel Dec
2001 NASA/GSFC Instrument Synthesis Analysis
Lab Jan 2002 AAS Washington 23 papers Dark
Energy SNAP Mar 2002 SAGENAP urged continuing
support Apr 2002 NAS/NRC CPU (Turner) Report
Published NOW -----------------------------------
------------------------- July 2002 DOE/SC-CMSD
RD (Lehman) Sept 2002 NASA/SEU Releases Roadmap
Oct 2002 CNES Review
14
RD Reviews

• Jan 2001 DoE Science and RD Review
• SNAP will have a unique ability to measure the
  variation in the equation of state of the
  universe.
• Look at greatly increasing the near-infrared
  capabilities
• Is the proposed IR spectrograph throughput
  adequate?
• Look at a descoped instrument complement Can the
  spectroscopy be done by ground-based facilities?
• Develop a calibration strategy and plan.
• Address NASA relationship
• June 2001 NASA/GSFC Integrated Mission Design
  Center
• Thorough analysis of launcher, shrouds,
  propellant, link margins, ACS, thermal....
• Generally high marks on mission concept,
  hardware, maturity
• Helped us plan a more cost effective orbit
• Nov 2001 NASA/GSFC Instrument Synthesis Analysis
  Laboratory
• Detailed review of telescope, shutter, focus
  mechanisms, ...
• Helped us identify shutter mechanisms and test
  plans
• Generally good marks urged us to develop and
  maintain a stray light model

15
Current Mission Concept

• 2.5 x 25 Re orbit, Delta III/IV or Atlas, KSC
  launch
• 29 deg inclination, 3 day period, perigee near
  Berkeley
• Science operations beyond 9 Re for lowest
  background
• Data downlink below 9 Re for best link margins
• Single ground station can handle all comm
• Survey region near north ecliptic pole
• least zodiacal light for best NIR sensitivity
• One side of vehicle is always within 45deg of
  sunward
• Opposite side always in shadow, passive cooling
  radiator
• Maneuvering around sun line for other targets
  (cal, SEP, ...)
• Onboard data storage for each orbits data
• no onboard processing, but 21 Rice compression
  of raw images
• 10 Mbit/sec average data generation rate
• 2.5 Tbit/orbit data recorder needed
• 6 hours AOS per orbit, Berkeley ground station
• 150 Mbit/sec actual downlink, Ka band
• Nominal 3 year mission, option to extend

16
Current Observation Concept

• Imager
• Step the entire focal plane through our dedicated
  observation field.
• Fixed length exposures determined by a shutter,
  typically 200 sec
• Multiple exposures per filter.
• To implement dithering pattern.
• To eliminate cosmic ray hits.
• NIR filters have twice the area of visible
  filters this combined with time dilation
  achieves desired S/N in CCDs and HgCdTe.
• All stars see all filters (modulo field edge
  effects).
• Field revisited every orbit. SNe will be
  followed throughout entire mission.
• Square-symmetric detector array layout 90 deg
  roll each 90 days.
• Spectrograph
• SNe candidates are scheduled for spectrographic
  measurement near peak luminosity.
• Light curve and color analysis done on ground to
  identify Type Ia and roughly determine z.
• Note peak luminosity is 14 days to 40 days after
  discovery for z 0 and 1.7 respectively.

17
Requirements Motivate Current RD

• Telescope
• SNR gt aperture, efficiency, stray light....
• SNR gt point spread function, Strehl ratio, ...
• discovery rate gt field of view
• PSF, focal plane size gt pixel sizes ltgt focal
  length
• materials limitations gt thermal control,
  focussing mechanisms...
• Instrumentation
• shutter precision
• detector performance
• spectroscopy performance
• Spacecraft systems
• attitude control system gt 0.02 arcsecond
  stability
• data generation and orbit downlink plan gt 2Tbit
  onboard storage
• Downlink Plan
• Orbit AOS Berkeley gt 6h contact time, 150
  Mbit/sec link rate
• Ka band transponder, transmit power, antenna
  size, ground station...
• Ground Computing
• must turn around SN detection in lt 14 days for
  spectroscopy
• sustained throughput requirement of 100Tbyte/year
  sizes systems

18
Ongoing SNAP RD Efforts

• Mission Development Optimization
• Telescope Development
• Payload structural static dynamic models
• Spacecraft ACS performance
• Shutter technology
• IFU/Spectrometer technology
• Bandpass filter stability
• Calibration Plan
• Si CCDs
• HgCdTes
• Detector electronics

19
Mission Development Optimization

• Start with any Universe
• Populate it with matter, dark energy, supernovae,
  lensing, ...
• host galaxy, reddening, evolution, ....
• Use a SNAP mission performance model to harvest
  that crop
• aperture, point spread function, attitude jitter,
  ...
• detector noise, linearity, CR hits, dithering,...
• produce simulated photometry data record
• perform triggering, spectroscopy, categorization
• Fit the Hubble diagram with model universes
• How constrained are they?
• Repeat for various SNAP designs
• wider / narrower survey region?
• more VIS? versus NIR?
• more objects followed? versus fewer objects,
  more time on each?
• These sims have driven (and will drive) our
  mission design

20
Telescope Development

• Three-mirror anastigmat does the job
• Existing manufacturing and test technologies are
  entirely suitable
• Policy Build, test, fly at 290 K
• RD phase task is to work with industry to create
  a biddable requirements document including
  comprehensive end-to-end test plan.
• Ongoing trade studies aperture, Strehl ratio,
  focal length, mfr/test plans

21
Structural/Dynamic Model
Forward baffle
Passive Radiator
SolarArray
Booster Attachment
22
NASA GSFC/IMDC Spacecaft Packaging
Secondary Mirror and Active Mount
Optical Bench
Primary Mirror
Solar Array Wrap around, body mounted 50 OSR
50 Cells
Thermal Radiator
Sub-system electronics
Detector/Camera Assembly
Propulsion Tanks
from GSFC - IMDC study
23
Attitude Control System Development

• Requirement 0.02 arcsecond RMS, 200sec exposure
• IMDC Recommendations
• Need complete flexural FEM to understand
  resonance modes and to guarantee system stability
• Use dedicated star tracker for coarse
  acquisition, gyros for dynamic feedback, and
  feedback from focal plane star guider for fine
  guidance
• Aerospace industry contractor Recommendations
• Compared SNAP to similar-size payload flown by
  another customer
• our planned rigid spacecraft will deliver
  needed stability
• Complete attitude model will be developed
• propellant slosh
• sensor noise spectra
• wheel rumble
• predict jittter, settling times, maneuver rates

24
Rotary Shutter Concept
1 sec to open 1 sec to close timing error
lt0.01sec reliability study 2003 zero angular
momentum
25
Calibration technology

• Identified as a mission driver
• Overall absolute relative errors lt 2, 0.4 to
  1.7microns
• SNAP working group is preparing an RD plan
• Four thrusts are being explored
• interpixel flat fielding by dedicated
  illumination system
• frequent comparisons with well-studied reference
  stars KOIII, DA WDs
• absolute irradiance standard comparison NIST
  reference sources ground, SOFIA, balloon, GAS
• adoption of hot DA WDs model atmospheres as
  known-slope calibrators

26
Bandpass filter technology

• Technology multilayer dielectric thin-film
  stack
• ion assisted deposition
• Fixed filters/substrates suspended above
  detector chips
• potential light loss from interface reflection
• Fixed filters deposited onto detector chips
• could offer improved QE
• could reduce detector yield
• Rotary filter wheel
• downside is additional moving part
• Goal extreme stability of bandpass curves
• ESA SUVIM/ISS, 2003, 7 bandpasses lt0.1
• NASA SORCE, Pegasus, 2003, 3 bandpasses lt0.03
• Berkeley have begun test evaluation of sample
  filters that have been directly deposited onto
  silicon

27
Conclusions

• Many aspects of the proposed SNAP mission have
  been reviewed
• Most of these do not require any RD
• However, development and/or definition are needed
  in these areas...
• Need gt2 terabit SSR, flight proven onboard data
  storage
• Spaceborne Ethernet? router? TCP/IP protocol?
  (CHIPS!)
• Posix/Linux in space?
• Need 5 watt solid state Ka band transmitter for
  high speed downlink
• Need thorough study test plan of our shutter
• Several calibration issues need planning
• accurate bandpass filters VIS-NIR
• absolute spectrophotometric standards
• benefits to many other missions NASA and
  community
• Ground data processing issues volume of data
  100TBytes/year
• Next up Chris Bebek, Detector RD