# Presentation: 261785

## 2010

**Fundamental Understanding of the Universe: Dark Energy**

**2010**

**2001**

**Supernova Acceleration Probe**

**Development**

**Configuration**

**Launch**

**Physics**
**Discoveries**

**Assembly**

**Technology**

**Physics**

**Integration**

**Engineering**

## Critical Questions in Cosmology

***Time Magazine “Person of the Century”***

## Fundamental questions

**What is the nature of matter and energy at its most fundamental level?**
**What is the evolution and fate of the universe and how is it affected by the fundamental interactions of energy, matter, time and space?**
**Is general relativity the ultimate theory of gravity for the universe?**
**What is the connection between dark energy, gravity and the fate of the universe?**

## Some History

**Einstein 1917**
**How does the presence of matter effect the expansion?  Gravity should cause a deceleration****.**
**field equations show contracting or expanding universe, but the universe is static**
**Einstein postulated a cosmological constant, ******** (negative pressure) or Dark Energy to maintain a static universe.**
**E. Hubble 1924-1929**
**observation of galaxies, the universe is not static!**
**Einstein 1929**
**cosmological constant is unnecessary, ******** ******** 0**** **

## Type Ia Supernova

- Credit STScI

- Difference

- Reference

- Explosion

## Type Ia Supernova

**Type Ia supernovae are astronomical “standard candles”**
**Variations in SNe Ia light curves can be “corrected”  so their peak brightness can be used to measure distance (time) to the supernova.**

## The Accelerating Universe: Science’s Breakthrough of the Year

**Redshift of spectral features measures the expansion of the universe. **
**A magnitude vs. redshift plot provide a Hubble diagram measuring the expansion rate**
**Ground-based work thus far has uncovered a major surprise:**

## Accelerating Expansion

- Credit STScI

## Expanding Univserse

- Credit STScI

## The Implications of an Accelerating Universe

## Gravity should cause a deceleration. Supernova data shows an acceleration of the expansion! 
Remarkable agreement between Supernovae & recent CMB.

**Remarkable agreement between Supernovae & recent CMB.**

**SNe inconsistent with a ******** = 0 universe**
**CMB measurements ******** ********TOT**** = 1**
**Cluster measurements ******** ********M**** = 0.3**
** ******** ****= 0.7, ********M**** = 0.3 universe favored by SNe**
**Statistical uncertainties in SNe measurements only 2******** greater than known systematic errors.**

- Implications

## Composition of the Cosmos

- Credit STScI

## Why is the energy density so small?
120 orders of magnitude too small and yet not zero 
fine tuning?
Why now?
the energy density is about equal to the critical energy density
coincidence?
Will these be answered by new theories beyond Einstein?
quintessence
string theory...
“In string theory, to get  > 0 but extremely small is impossible” Ed Witten

*mysterious thing in basic science”*
- 	- Frank Wilczek
*“**This is the biggest embarrassment*
*in theoretical physics”*
- 	- Michael Turner

*“**Would be number one on my list of things to figure out”*
- 	- Edward Witten
*“**Right now, not only for cosmology but for elementary particle theory this is the bone in the throat”*
- 	- Steven Weinberg

***Why is the energy density so small******?***
**120 orders of magnitude too small and yet not zero **
***fine tuning?***
***Why now?***
**the energy density is about equal to the critical energy density**
***coincidence?***
***Will these be answered by new theories beyond Einstein?***
***quintessence***
***string theory...***
***“******In string theory, to get ************ > 0 but extremely small is impossible” Ed Witten***

- Theoretical Questions

***What is the Nature of the dark energy:***
***“******dark energy is energy associated with the simmering sea of particles living on borrowed time and borrowed energy that are the quantum vacuum of nature?” or, maybe***
***“******influence of hidden space dimensions as predicted by super-string theory?”, or ...***
***“******Our main achievement in understanding dark energy is to give it a name” – Michael Turner***

## How Can We Address These New Questions?

**It is necessary but NOT sufficient to find and study**
**more Sne Ia**
**farther Sne Ia**
**because the statistical uncertainty is already within a factor of two of the systematic uncertainty.**

## SNAP’s Target Results

**The most demanding SNAP requirements are devoted to eliminating and controlling all systematic uncertainties.**
**All data taken with single dedicated, instrument.**
**Above atmospheric interference**
**Imaging for discovery & photometry**
**Spectroscopy to classify Type Ia supernovae and for redshift**
**Reduce systematic errors to ********M < 0.02 **
**Need 1000’s of SNe to improve statistical accuracy. **
**Expected measurement uncertainties:**
********** ****to ******** 0.05,  ********M ****to ******** 0.02**

## Dark Energy Characterized by the Pressure/Density Ratio 

- Magnitude residuals (vs a =0.7 model)

- Pressure/Density Ratio **** *w* (Equation of State)

## Large statistics, ~2000 Sne Ia’s, distributed in redshift to z<1.7, with minimal selection bias and clean Ia ID.

- SNAP Baseline Sample

## What makes the SN measurement special?Control of systematic uncertainties

*Images*

*Spectra*

*Redshift & SN Properties*

*Lightcurve & Peak Brightness*

- data

- analysis

- physics

- M  and 
- Dark Energy Properties

- At every moment in the explosion event, each individual supernova is “sending” us a rich stream of information about its internal physical state.

- What makes the SN measurement special?Control of systematic uncertainties

## Advantages of Space

## Minimum data set criteria: 
Discovery within 2 days (rest frame) of explosion (peak + 3.8 magnitude), 
Ten high S/N photometry points on lightcurve,  
Lightcurve out to plateau (2.5 magnitude from peak), 
High quality peak spectrophotometry

How to obtain both data quantity AND data quality?
Batch processing techniques with wide field -- large multiplex advantage,
Wide field imager designed to repeatedly observe an area of sky
Mostly preprogrammed observations, fixed fields / spin filter wheel
Very simple experiment, passive expt.

SNAP design meets these scientific objectives
Dedicated instrument, essentially no moving parts
Mirror: 2 meter aperture sensitive to light from distant SN
Optical Photometry: with 1°x 1° billion pixel mosaic camera, high-resistivity, rad-tolerant p-type CCDs sensitive over 0.35-1m
IR photometry:  10’x10’ FOV or larger, HgCdTe array (1-1.7 m)
Integral field optical and IR spectroscopy: 0.35-1.7 m, 2”x2” FOV

**Discovery within 2 days (rest frame) of explosion (peak + 3.8 magnitude), **
**Ten high S/N photometry points on lightcurve,  **
**Lightcurve out to plateau (2.5 magnitude from peak), **
**High quality peak spectrophotometry**
**How to obtain both data quantity AND data quality?**
**Batch processing techniques with wide field -- large multiplex advantage,**
**Wide field imager designed to repeatedly observe an area of sky**
**Mostly preprogrammed observations, fixed fields / spin filter wheel**
**Very simple experiment, passive expt.**
**SNAP design meets these scientific objectives**
_**Dedicated instrument**_**, essentially no moving parts**
_**Mirror**_**:**** 2 meter aperture sensitive to light from distant SN**
_**Optical Photometry**_**:**** with 1****°x ****1****°**** billion pixel mosaic camera, high-resistivity, rad-tolerant p-type CCDs sensitive over 0.35-1********m**
_**IR photometry**_**:****  10’x10’ FOV or larger, HgCdTe array (1-1.7 ********m)**
_**Integral field optical and IR spectroscopy**_**:**** 0.35-1.7 ********m, 2”x2” FOV**

- Mission Requirements

## Mission Overview

**Simple Observatory consists of :**
**1) 3 mirror telescope w/ separable kinematic mount**
**2) Baffled Sun Shade w/ body mounted solar panel and instrument radiator on opposing side**
**3) Instrument Suite**
**4) Spacecraft bus supporting telemetry (multiple antennae), propulsion, instrument electronics, etc**
**No moving parts (ex. filter wheels, shutters), rigid simple structure.  **

## GigaCAM

- Depending on pixel scale approximately 1 billion pixels
- ~140 Large format CCD detectors required
- Looks like the SLD vertex detector in Si area (0.1 - 0.2 m2)
- Larger than SDSS camera, smaller than BaBar Vertex Detector (1 m2)

## Optical Photometry Parameters

- CCD

## Imaging Strategy

## GigaCAM detectorAnnular layout

- Layout is rotationally symmetric
- 142 3kx3k CCD’s

## One-square meter Silicon  Detector

- One-square meter silicon-strip detector arrays (five concentric layers, outer shown in fig)
- ~200,000 channels of electronics
- LBNL designed 10 Mrad tolerant IC’s (preamp, ADC, memory; 128 channels/chip)

## IR Photometry Parameters

## Shortwave HdCdTe Development

***Hubble Space Telescope***** Wide Field Camera 3**
**WFC-3 replaces WFPC-2 **
**CCDs & IR HgCdTe array**
**Ready for flight July 2003**
**1.7 ********m cut off**
**18 ********m pixel**
**1024 x 1024 format**
**Hawaii-1R MUX**
**NGST to use Hawaii-2RG**
**Dark current consistent with thermoelectric cooling**
**<0.05 e-/s at 140 K (compare to SNAP’s <0.1 e-/s zodiacal background)**
**Expected QE > 50% 0.9-1.7 ********m**
**Individual diodes show good QE**
**Effective CdZnTe AR coating **
**No hybrid device yet with simultaneous good dark current & QE**

**WFC-3 IR**

**NIC-2**

## Camera Example

**Components:**
**236 CCDs**
**24 2k x 2k HgCdTe**
**2 spectrographs**
**8 star guider CCDs**

**IR:**
**0.12 sq. deg.**
**0.125 asec/pixel**
**Visible:**
**0.88 sq. deg.**
**0.07 asec/pixel**

## Filters & Shutters

## IR Enhanced Camerawith Fixed Filter Set

## Camera Assembly

**Heat radiator**

**Filter Wheel**

**Folding**
**Mirror**

**Shield**

**GigaCam**

## Mosaic Packaging

**With precision CCD modules, precision baseplate, and**
**adequate clearances designed in, the focal plane assemble**
**is “plug and play.”**

**140 K plate attached**
**to space radiator.**

## CCD Subassembly

## Typical CCD’s

## Silicon Absorption Length

- Photoactive region of standard CCD’s are 10-20 microns thick
- Photoactive region of LBNL CCD’s are 300 microns thick

## High-Resistivity CCD’s

- New kind of CCD developed at LBNL
- Better overall response than more costly “thinned” devices in use
- High-purity silicon has better radiation tolerance for space applications
- The CCD’s can be abutted on all four sides enabling very large mosaic arrays
- Measured Quantum Efficiency at Lick Observatory (R. Stover):

## LBNL 2k x 4k

**USAF test pattern.**

**Trap sites found**
**by pocket pumping.**

## Industrialization of Technology

**The LBNL CCD technology, layout, and recipe were transferred to a commercial foundry.**

**Commercial 4” wafer run**
**completed:**

**Commercial 6” wafer run**
**in process:**

## Radiation Damage

**Solar protons — sub-100 MeV**
**Galactic cosmic rays**
**(we are ignoring electrons here)**
**Solar protons are most damaging to CCDs.**
**WFPC2 on HST developed losses up to 40% across its CCD due to radiation damage.**
**Hot pixels also developed.**
**Radiation testing is done at the LBNL 88” Cyclotron with 12 MeV protons.**
**SNAP expected lifetime dose 5 x 10****9**** protons/cm****2**

## Radiation Damage

**CTI is the charge transfer inefficiency**
**Q = Q****0**** ****(1-CTI)*N****transfer****, N****transfer**** ~ 2000**

## Spectrograph Parameters

- Optical Arm:

- IR Arm:

## Spectroscopic Integral Field Unit Techniques

## Integral Field Spectrograph Design with Image Slicer

- Complete spectrograph:
*0.6-1.7 microns *
*0.12 arcsec/resolution element*
*R~15A*

## Key requirements:
Minimize obscuration (<3.5%) & interference spikes
Dimensional stability
35 Hz minimum fundamental frequency
Baseline design: hexapod truss with fixed end
Simple design with low obscuration (3.5%)
6-spiked diffraction pattern
Ø 23 mm by 1 mm wall tubular composite (250 GPa material) struts with invar end-fittings.

**Minimize obscuration (<3.5%) & interference spikes**
**Dimensional stability**
**35 Hz minimum fundamental frequency**
**Baseline design: hexapod truss with fixed end**
**Simple design with low obscuration (3.5%)**
**6-spiked diffraction pattern**
**Ø ****23 mm by 1 mm wall tubular composite (250 GPa material) struts with invar end-fittings.**

- Secondary Metering Structure

## Key requirements and issues
Dimensional stability
High specific stiffness (1g sag, acoustic response)
Stresses during launch
Design of supports
Baseline technology
Multi-piece, fusion bonded, with egg-crate core
Meniscus shaped
Triangular core cells
Material
Baseline = ULE Glass (Corning)

**Dimensional stability**
**High specific stiffness (1g sag, acoustic response)**
**Stresses during launch**
**Design of supports**
**Baseline technology**
**Multi-piece, fusion bonded, with egg-crate core**
**Meniscus shaped**
**Triangular core cells**
**Material**
**Baseline = ULE Glass (Corning)**

- Initial design for primary mirror substrate: 334 kg

- Primary Mirror Substrate

## Spacecraft Assembly

- Movie courtesy of Hytec

## Observatory Parameters

- Edge Ray Spot Diagram
- (box = 1 pixel):

- Optical Solution:

- Primary Mirror
- diameter= 200 cm
- Secondary Mirror
- diameter= 42 cm
- Tertiary Mirror
- diameter=64 cm

## Optical Train

## Telescope Assembly

- Movie courtesy of Hytec

## Launch Vehicle Study

## Orbit Trade-Study

- Feasibility & Trade-Study

- Selected Lunar Assist “Prometheus” Orbit
- 14 day orbit: 19Re Perigee/57Re Apogee

## Orbit Optimization

- "Prometheus" Orbit Baselined Following Preliminary Trade Study
- Uses Lunar Assist to Achieve a 14 day (19 X 57 Re) Orbit, with a Delta III 8930 or Delta IV-M Launch Vehicle
- Good Overall Optimization of Mission Trade-offs
- Low Earth Albedo Provides Multiple Advantages:
- Minimum Thermal Change on Structure Reduces Demand on Attitude Control
- Excellent Coverage from Berkeley Groundstation
- Outside Radiation Belts
- Passive Cooling of Detectors
- Minimizes Stray Light

## Orbital Stability

**Semi-major axis (km) **
**Intrinsic stability of semi-major axis due to lunar influence**

**Inclination (deg) **
**Some reduction of inclination over lifetime of spacecraft**

**Perigee radius (Re) **
**Five year nominal stability**

## Project History and Status

**Project is being developed as a multi-agency partnership:**
**Team that produced current results was supported by DOE, NSF, and NASA.**
**Science review by SAGENAP of 260 page proposal March 2000: **_**strong endorsement of science, recommendation for study funding**_**.**
**Entire session at Jan. meeting of the American Astronomical Society devoted to SNAP: 9 talks, 4 posters.****  **
**Dark Energy a subject of the recent National Academies of Science Committee on the Physics of the Universe (looking at the intersection of physics and astronomy).  ****One of eleven compelling questions: “What is the Nature of the Dark Energy?”**
**SNAP to be reviewed by the NRC/”Committee on the Physics of the Universe” during 2001 as part of their Phase II review of projects.  **
**International collaboration is growing, currently 15 institutions.**

**Notes:**
Two GSFC scientists at both the DoE preview and SAGENAP.

## SNAP Collaboration

- G. Aldering, C. Bebek, S. Deustua, W. Edwards, B. Frye, D. Groom, S. Holland, 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, M. Metzger (CalTech)
- D. Huterer (U.Chicago -> Case Western)
- A. Fruchter (STScI)
- L. Bergstrom, A. Goobar (U. Stockholm)
- C. Lidman (ESO)
- J. Rich (CEA/DAPNIA)
- A. Mourao (Inst. Superior Tecnico,Lisbon)

## R&D Review

**Recent DOE/Science & R&D Review (Jan 2001):**
**“****SNAP is a science-driven project with compelling scientific goals.”**
**“****SNAP will have a unique ability to measure the variation in the equation of state of the universe.”**
**“****We believe that it is not an overstatement to say that the Type Ia supernova measurements will uniquely address issues at the very heart of the field...”  *****[Implications for particle physics]***
**Issues Raised at R&D Review:**
**Look at greatly increasing the near-infrared capabilities**
**Is the proposed IR spectrograph throughput adequate?**
**Look at a descoped instrument complement: Can the visible spectroscopy be done by ground-based facilities?**
**Develop a calibration strategy and plan.**

**Notes:**
Two GSFC scientists at both the DoE preview and SAGENAP.

## Science Goals

## N.Y. Times weighs in on Dark Energy

- N.Y. Times 4/10/01

## Time Magazine weighs in on Dark Energy

- Time Magazine 4/16/01

## Conclusion

**Type Ia Supernova:**
**Are light sources visible across the Cosmos**
**Show that expansion of the universe is accelerating through distance-redshift relation **
**Reveal evidence for a mysterious dark energy in the universe**
**SNAP:**
**Space observations of thousands of supernovae will provide the vital breakthrough in precision cosmology to characterize the dark energy**
**SNAP will measure the matter and energy densities with exquisite precision**
**SNAP will precisely determine the expansion rate of the universe as a function of time.**