# Presentation: 431285

## 2010

**Technologies for the SNAP – Supernova / Acceleration Probe**

**2010**

**2002**

**Supernova / Acceleration Probe**

**Development**

**Configuration**

**Launch**

**Physics**
**Discoveries**

**Assembly**

**Technology**

**Physics**

**Integration**

**Engineering**

**Michael Levi (LBNL)**

## 
Talk Outline:
Introduction
Science
Mission Overview
Focal Plane Technology
Orbit/Launch Vehicle
Project Status
Summary

- Talk Outline:
- Introduction
- Science
- Mission Overview
- Focal Plane Technology
- Orbit/Launch Vehicle
- Project Status
- Summary

**SuperNova /Acceleration Probe**

-  **Technologies**

- AN ARRAY OF DETECTORS  WILL BE ASSEMBLED INTO AN ANNULUS NEARLY ONE HALF METER WIDE, THE LARGEST AND MOST SENSITIVE ASTRONOMICAL IMAGER EVER CONSTRUCTED

*Overview*

## The Cosmological Constant

- Einstein 1917
- Field equations show contracting or expanding universe, but the universe was thought to be static.
- Einstein postulated a cosmological constant, called “dark energy” (with negative pressure), to maintain a static universe.

## Einstein’s field equations (1917)

-  and  *add* in determining H
-  and  *subtract* in determining acceleration of universe
- Danger! Runaway solution if  is large and positive!

## Hubble’s Law

- Measure the velocity of every galaxy.
- Nearly all are receding.
- Use Cepheids to measure distances to nearby galaxies.
- Result: The faster it’s moving, the farther away it is.

- Hubble’s Data (1929)

- Distance Mpc)

- Recessional Velocity (km/sec)

## The Universe, its Expanding!

- Hubble’s 1929 evidence  that the universe is not static.
- The Cosmological Constant is unnecessary
- 			-- Einstein’s proclaimed his “Biggest Blunder.”

## Future possibilities: expand/collapse

*Future possibilities: expand/collapse*

- Big Bang

## Borderline Universe

- Density ()
-   = density/critical density
-           = /c
-  c ~ 10-26 kg.m-3
-          ~ 6 H atoms per m3!

## Inflation

- Alan Guth....
- enormous (but brief!) cosmic expansion
- Age 10-33 sec to 10-31 sec
- Vast expansion, roughly 1066
- predicts a completely flat universe today
- in accord with Cosmic Microwave Background (CMB)
- predicts a nearly uniform universe today
- small fluctuations: accord with CMB
- One teensy problem:

- theory

- experiment

## Future possibilities: expand/collapse

*Future possibilities: expand/collapse*

- Future

- Past

- (today)

## Finding Supernovae

## Type Ia Supernovae

*Type Ia Supernovae*

**Type Ia supernovae can be seen from 10 billion light years away**

## Slide 13

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

- -accelerates
- -expands forever
- -slows but never collapses

## Evidence for Acceleration

## Current Results on Cosmological Parameters

*Current Results on **Cosmological Parameters*

## Energy budget of Universe

***Dark***
***Energy:***
***65%***

***Dark***
***Matter:***
***30%***

*Energy budget of Universe*

## What’s wrong with a non-zero 

## Fundamental Physics Questions

- What is the Nature of the dark energy?
- The dominant component of our universe.
- Dark energy does not fit in current physics theory.
- Theory proposes a number of alternative new physics explanations, each with different properties we can measure.
- Two key contrasting theories of dark energy.
-  vacuum energy, constant over time:
- Deep philosophical implications, why are the matter () and energy densities () nearly the same today, they have totally different time evolution.  Why now?  Why is  so small?
-  or, time dependent possibly a dynamical scalar field:
- Might explain  and so small, we’ve seen these fields elsewhere in particle physics and in the theory of inflation.  Points to new physics.

## Future possibilities: expand/collapse

**Need Lots of**
**Data to Study**
**This Region**

## Need Lots more Data!

- The 42 SNe from the SCP
- Project peters out by Z>0.6

*Need Lots more Data!*

- Turn 42 Supernovae  2500 Supernovae

## SNAP a dedicated experiment to study dark energy
Dedicated instrument, few moving parts
Mirror: 2 meter aperture sensitive to light from distant SN

- _Dedicated instrument_, few moving parts
- _Mirror_: 2 meter aperture sensitive to light from distant SN

*Supernova / Acceleration Probe*

## SNAP’s Target Results

*SNAP’s Target Results*

## Understanding Dark Energy

*Understanding Dark Energy*

## SNAP Collaboration

**G. Aldering, C. Bebek, J. Bercovitz, W. Carithers, C. Day, S. Deustua*, D. Groom, S. Holland, D. Huterer*, A. Karcher, A. Kim, W. Kolbe, R. Lafever, M. Levi, E. Linder, S. Loken, P. Nugent, H. Oluseyi, S. Perlmutter, K. Robinson, A. Spadafora (Lawrence Berkeley National Laboratory)**
**E. Commins, G. Goldhaber, S. Harris, P. Harvey, H. Heetderks, M. Lampton, J. Lamoureux, D. Pankow, C. Pennypacker, R. Pratt, M. Sholl, G. F. Smoot (UC Berkeley)**
**C. Akerlof, G. Bernstein(->U.Penn)*, D. Levin, T. McKay, S. McKee, M. Schubnell, G. Tarle , A. Tomasch (U. Michigan) **
**R. Ellis, R. Massey*, J. Rhodes, A. Refregier* (CalTech)**
**C. Bower, N. Mostek, J. Musser, S. Mufson (Indiana)**
**A. Fruchter (STScI)**
**P. Astier, E. Barrelet, A. Bonnissent, A. Ealet, J-F. Genat, R. Malina, R.Pain, E. Prieto, G. Smadja, D. Vincent (France: IN2P3/INSU/LAM)**
**R. Amanullah, L. Bergström, M. Eriksson, A. Goobar, E. Mörtsell (U. Stockholm)**
- http://snap.lbl.gov/

## SNAP a dedicated experiment to study dark energy
Large Field of View: to see lots of SNe, has half-billion pixel mosaic camera (~100x larger Field than Hubble)

- _Large Field of View_: to see lots of SNe, has half-billion pixel mosaic camera (~100x larger Field than Hubble)

*Space Mission*

## Mission Design

*Mission Design*

- _Telescope:_ 2 meter aperture sensitive to light from distant SNe

- Flat focal plane
- Delivers < 0.04 arcsecond FWHM geometrical blur over field
- Provides side-mounted detector location for best detector cooling

- TMA63:

## Camera

**Largest Astronomical Flight Camera**

*Camera*

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## New Technologies for SNAP

## Mission Design

- _Photometry:_ 0.7° FOV half-billion pixel mosaic camera, high-resistivity, rad-tolerant n-type CCDs (0.35-1.0 m) and, HgCdTe arrays (0.9-1.7 m).

- Field of View Optical ( 36 CCD’s) = 0.34 sq. deg.
- 	Four filters on each 10.5 m pixel CCD detector
- Field of View IR (36 HgCdTe’s) = 0.34 sq. deg.
- 	One filter on each 18 m pixel HgCdTe detector

- guider

- spectrograph

## Mission Design

- Shutters

- Cryostat/Cosmic Ray Shield

- Filters

- CCDs/HgCdTe

- Guiders

- Cold Plate

- Readout Electronics

- Spectrograph

- Thermal Links

- Radiator

*Mission Design*

- All detectors occupy same mechanical, thermal, & optical environment.

## Mission Design

- shutter

- Focal plane

- Spectrograph

- electronics

## Focal plane concept

*Focal plane concept*

- Coalesce all sensors at one focal plane.
- Imager sensors on the front.
- Spectrograph on the back with access ports through the focal plane.
- Common 140K operating temp.
- Fixed filter mosaic atop the imager sensors.
- Mechanical shutter near the folding mirror.
- Particle/thermal/light shield between folding mirror and focal plane
- Guide spacecraft from the focal plane.

## High-Resistivity CCD’s

*High-Resistivity CCD’s*

**New kind of Charged Coupled Device (CCD) developed at LBNL **
**Better overall response than more costly “thinned” devices in use**
**High-purity “radiation detector” silicon has better radiation tolerance for space applications**
**The CCD’s can be abutted on all four sides enabling very large mosaic arrays**

## High-Resistivity CCD’s

- LBNL “Red Hots”: NOAO September 2001 newsletter

**New kind of Charged Coupled Device (CCD) developed at LBNL **
**Better overall response than more costly “thinned” devices in use**
**High-purity “radiation detector” silicon has better radiation tolerance for space applications**
**The CCD’s can be abutted on all four sides enabling very large mosaic arrays**

## LBNL 2k x 4k

**USAF test pattern.**

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

- Back-illumination technology development completed
- for LBNL manufactured devices.

## Commercially fabricated 150 mm waferDALSA Semiconductor

- Front-illuminated 2k x 4k (15m pixel)
- Back-illumination technology development in progress

## SNAP Prototype CCD Test Image

- 2880 x 2880
- 10.5 m pixels
- Front illuminated

## Fe55X-ray spectrum

- =17.2 e-

*10.5 ****m pixel CCD*

## CTE Measurement

*Charge transfer efficiency in CCD bucket brigade*

**Notes:**
We measure CTE by irradiating the CCD with X-rays from an 55Fe source.
To calculate parallel CTE a stacking plot is used: the x-ray peak height vs row number is plotted, so that all x-rays from a single row are “stacked” into one column on the plot.
The most common x-ray charge as a function of row number can easily be seen. We obtain the CTE value from the slope of the fitted line.

## Radiation Damage

- 0.9990

- 0.9991

- 0.9992

- 0.9993

- 0.9994

- 0.9995

- 0.9996

- 0.9997

- 0.9998

- 0.9999

- 1.0000

- 0

- 200

- 400

- 600

- 800

- 1000

- 1200

- 1400

- 1600

**Dose (10**

**6**

**MeV/g)**

**Gain [CTE]**

- LBNL CCD

- HST/Marconi

- Tektronix

**Gain is measured using the ****55****Fe X-ray method at 128 K. **
**13 MeV proton irradiation at LBNL 88” Cyclotron**
**SNAP will be exposed to about 1.8********10****7**** MeV/g (solar max).**

**Notes:**
To compare the CTE degradation in our CCDs to results found in literature, obtained at different proton energies we choose the non ionizing energy loss (niel) as a measure of damage. The niel data for various proton energies can be found on the NIST website using the PSTAR calculator.
We observe a change in CTE of:
CTE=2.5x10-13 g/MeV (Standard LBNL devices)
CTE=9.6x10-14 g/MeV  (“Notch” implant LBNL devices)
In Literature we find:
CTE=1.9x10-12 g/MeV
for current CCD designs [1].

## Measurement of PSF

-         VSUB = 12V                                                     VSUB = 80V
- 1100 x 800 pixels, 300 m thick back-illuminated CCD, 15 m pixels

## CCD support electronics

- Goals:
- Photons-to-bits focal plane
- Eliminate large cable plant to reduce system noise problems.
- Reduce power dramatically relative to conventional implementation.
- ASIC Challenges:
- Large dynamic range from 2 e- readnoise and 130 ke- well depth.
- Radiation tolerance
- Operation at 140K to reduce cable plant and associated problems – requires low power

## Front end readout Concept

- Low noise:CCD + electronic noise  4e rms
- Large dynamic range:96dB from noise floor to 130ke well depth
- Readout frequency:  100 kHz
- Low power  200mJ/image/channel

- Operation at 140K and 300KAllow normal operation at 140K and chip testing at room temperature
- Compact
- Radiation tolerant 10 kRad ionization
- Robust, space qualified

- CCD

- Amplification

- Analog signal
- processing

- ADC

*Front end IC*

- Digital out

- Analog
-  input

- Clocks, control

- (One channel)

## Multi range ADC concept

*Multi range ADC concept*

**Gain 1**

**Gain 2**

**Gain 32**

**MUX**

**12 bits ADC**

- Input

- Digital out

**Signal **
**processing**

- (CDS + Integration)

- The dynamic range for the  signal is 96dB (16 bits)
- From 2 electrons  (CCD noise) up to 130000 electrons.
- The dynamic range is covered using 3 slopes and a 12 bit ADC.
- The readout chain should digitize the signal with an LSB size which depends of the signal amplitude such that the quantization noise is still below the Poisson noise.

- Gain 32
- quantization noise
- referred  to the input

- Gain 2

- Gain 1

- Poisson
- + elec noise

## Technology Survey

-  Selection criteria:
- Noise, Transistor performance
- Matching, precision
- Passive components availability and precision
- Expected production life time
- Radiation tolerance
- Two deep sub micron CMOS technologies were selected:
- Primary technology: **TSMC** 0.25 m
- Backup technology: **UMC** 0.18 m

***Technologies studied for noise and power performance***

**Minimum feature size:**

*Technology Survey*

## Measurement of 0.25m CMOS at low-T

*Measurement of 0.25****m CMOS at low-T*

**DC characteristic measurement of MOS transistors:**
** ****The main parameters varing with temperature are the threshold voltage and the mobility.**
** ****Measurements performed on transistors using a LBNL test chip.**
**Good agreement between measurement and simulation.**

**Mobility ratio NMOS 1u/0.24u**

**0**

**0.5**

**1**

**1.5**

**2**

**2.5**

**3**

**3.5**

**0**

**50**

**100**

**150**

**200**

**250**

**300**

**350**

**Temp (K)**

- Temp (K)

- Threshold voltage

## Radiation Tolerance

- No significant change of threshold voltage was observed (<50mV)
- Enclosed geometry prevents leakage at high dose (10 Mrad)
- Standard geometry could be used for dose <100kRad

***Standard geometry:***

***Enclosed geometry:***

*Radiation Tolerance*

## NIR System Concept

*NIR System Concept*

**150 NIR Megapixels:**
**36 (2k ******** 2k) 18 ********m HgCdTe detectors (0.34 sq. deg)**
**3 special bandpass filters covering 1.0 –1.7 ********m in NIR**
**T = 140********K (to limit dark current)**

- HgCdTe

## HgCdTe Fabrication

- Hybrid array has an array of HgCdTe detectors on one layer and charge collection and addressing circuitry (CMOS multiplexer) on another layer.  The  two layers are connected  with indium bump bonds.

**PACE** – Layer of CdTe is deposited on sapphire substrate by chemical vapor deposition followed by a layer of HgCdTe grown by liquid phase epitaxy.  Principally manufactured at Raytheon.
**MBE**** - **Rockwell has developed a process of fabricating detector layers in HgCdTe using molecular beam epitaxy (MBE).

## State of HgCdTe NIR Detectors

*State of HgCdTe NIR Detectors*

-  Hg**(1-x)**Cd**x**Te – **c** determined by x; this determines operating temperature.
-  Rockwell Science Center (RSC) is the principal source for Mercury Cadmium Telluride (HgCdTe) infrared focal plane arrays (FPAs) used in astronomy.
-  RSC has developed devices (NICMOS 256 x 256 FPAs, WFC3 1024 x 1024) for the IR channel on HST. Also U Hawaii, ESO, Subaru, JWST...

## Shortwave HdCdTe Development

*Shortwave HdCdTe Development*

*Hubble Space Telescope*         	Wide Field Camera 3
- WFC-3 replaces WFPC-2
- CCDs & IR HgCdTe array
- 1.7 m cut off
- 18 m pixel
- 1024 x 1024 format
- Hawaii-1R MUX
- Dark current consistent with thermoelectric cooling
- < 0.5 e/s at 150 K
- ~0.02 e-/s at 140 K
- Expected QE ~60% 0.9-1.7 m

**WFC-3 IR**

**NIC-2**

## Spectrograph:  IFU Slicer principles

- Aligned pupil mirrors
- Sub-Field imaged along an entrance slit

- 1

- 2

- 3

*Spectrograph:  IFU Slicer principles*

- How to rearrange 2D field to enter spectrograph slit:

**Notes:**
You should say here that there are in fact 20 slices in the SNAP concept.

## Mirror Slicer Stack(L.A.M. – Marseille)

*Mirror Slicer Stack**(L.A.M. – Marseille)*

## SPACECRAFT CONFIGURATION

- Main Baffle Assembly

- Door Assembly

- Primary Solar Array

- Secondary Mirror Hexapod
- and “Lampshade” Light Baffle

- Secondary Metering Structure

- Primary Mirror

- Optical Bench

- Instrument Metering Structure

- Tertiary Mirror

- Fold-Flat Mirror

- Spacecraft

- Shutter

- Instrument Bay

- Instrument Radiator

- Solar Array, ‘Dark-Side’

*SPACECRAFT CONFIGURATION*

## NASA GSFC Spacecraft Study

- Propulsion Tanks

- Sub-system
- electronics

- Secondary Mirror
- and
- Active Mount

- Optical Bench

- Primary Mirror

- Thermal
- Radiator

- Solar Array
- Wrap around, body mounted

- Detector/Camera
- Assembly

***Goddard/Integrated Mission Design Center study in June 2001: ******no mission tall poles***
***Goddard/Instrument Synthesis and Analysis Lab study in November 2001:  ******no technology tall poles***

## Orbit

**High Earth, 3 day synchronous orbit**
**Good Overall Optimization of Mission Trade-offs**
**Orbit Provides Multiple Advantages:**
- Minimum Thermal Change on Structure
- Excellent Coverage from Berkeley Groundstation
- Passive Cooling of Detectors
- Minimizes Stray Light

## Ground Station Coverage

- Orbit perigee remains over Berkeley for 3 years without adjustment.
- 5.2 hour ground pass over Berkeley

## Ka-Band Ground Antennas

- 12-m Prototype Antenna for NRAO’s 64-Element Atacama Large Millimeter Array (ALMA) Presently Installed at VLA Site in New Mexico

**Manufacturer:**
**VertexRSI, Santa Clara, CA**
**Aperture Diameter:  12 m**
**Surface Accuracy:     25 ****μ****m r.m.s.**
**Max. Frequency:       600 GHz**
**Pointing Accuracy:    0.6 arcsec**

## Launch in 2009

## Delta IV Main Engine Test Firing

- First launch scheduled for
- Nov. 16, 2002

## Current Status of SNAP

- SNAP currently in pre-conceptual design period
- Development of collaboration
- Performing critical R&D of new technologies, risk mitigation
- Requirements development
- Feasibility and early trade studies
- A major review of SNAP was performed by DOE in July, 02   (The “Lehman Review”)
- Transition to conceptual design Jan. 2003
- Technology development currently funded by DOE/HEP.

## 
Endorsement by HEPAP for development of cost, schedule, R&D
“We endorse R&D funding for SNAP from the high-energy physics program”.

SNAP reviewed by the NRC Committee on the Physics of the Universe (Turner panel) as part of their Phase II review of projects. 
“To fully characterize the expansion history and probe the dark energy will require a wide-field telescope in space (such as the Supernova/Acceleration Probe).”
“The Committee further recommends that NASA and DOE work together to construct a wide-field telescope in space to determine the expansion history of the universe and fully probe the nature of the dark energy.”

A major review of SNAP was performed by DOE in July, 02   (The “Lehman Review”)

**Endorsement by HEPAP for development of cost, schedule, R&D**
***“******We endorse R&D funding for SNAP from the high-energy physics program”.***
**SNAP reviewed by the NRC Committee on the Physics of the Universe (Turner panel) as part of their Phase II review of projects****. **
**“*****To fully characterize the expansion history and probe the dark energy will require a wide-field telescope in space (such as the ******Supernova/Acceleration Probe******).”***
**“*****The Committee further recommends that NASA and DOE work together to construct a ******wide-field telescope in space****** to determine the expansion history of the universe and fully probe the nature of the dark energy.”***
**A major review of SNAP was performed by DOE in July, 02   (The “Lehman Review”)**

*Current Status of SNAP*

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

## Technology Summary

*Instrument*
- _NIR sensors_
- HgCdTe detectors are begin developed for WFC3/HST, & JWST
- Need to demonstrate performance requirements for SNAP
- _CCDs_
- Industrialization of CCD fabrication has produced useful devices. Need to demonstrate volume, especially for commercially fabricated back-illuminated.
- _Electronics_
- ASIC development is required
- _Spectrograph_
- Challenging IR Detector Performance Requirements

## Technology Summary

*Spacecraft Systems*
- _On-board data handling_
- We have opted to send all data to ground to simplify the flight hardware and to minimize the development of flight-worthy software,
- 300 Mbit/s Ka-band telemetry,
_*large*_ Solid State Recorder – 375 Gbytes.
- _Pointing_
- Pointing requirements are challenging, but not state-of-the-art,
- Feedback from the focal plane, plus current generation attitude control systems, may have sufficient pointing accuracy,
- _Telescope_
- Primary mirror manufacture, stray light, end-to-end testing plan.

## Conclusion

- Exciting time for high energy and particle astrophysics.
*Dark Energy* and *Dark Matter* comprise 95% of the constituents of the universe yet we know nothing about them.
- New particles & fields yet to be discovered.
- Supersymmetry, extra-dimensions, quantum gravity, strings, etc...
- Needed data is accessible to experimentation
- Accessible to current or planned technology
- “My colleagues accuse me of wandering around the halls saying ‘We’re in a golden age of cosmology, we’re in a golden age of cosmology.’  Well, I’m proudly saying that we’re in a golden age of cosmology.” – Michael Turner

## Expansion History of the UniverseWe live in a special time when:- we can ask questions about the history and fate of the universe- and hope to get an answer!