# Presentation: 622432

## Mission Overview

**Michael Levi**
**     ****Lawrence Berkeley National Laboratory**
**09  July 2002**

## Mission Overview

**Talk Outline:**
**Introduction**
**Review Charge**
**Mission Overview & Requirements**
**Observing Plan**
**Orbit/Telemetry**
**Launch Vehicle**
**R&D Issues**
**What’s New**
**Prelim. Project Organization**
**Prelim. Project Schedule & Costs**
**Summary**

- SuperNova /Acceleration Probe

-   R&D Plan

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

## Pre-conceptual Design Period

**SNAP currently in pre-conceptual design period**
**Development of collaboration **
**Performing critical R&D of new technologies, cost mitigation**
**Requirements development**
**Feasibility and early trade studies**
**Transition to conceptual design Jan 2003**
**Currently at an annual funding rate of $1.4M from DOE/HEP.**
**Maintain current expense rate until Jan 2003**
**During 18 month Conceptual Design period through August 2004:**
**Complete R&D**
**Mission optimization**
**Engineering trade studies**
**Cost & Schedule development**
**Development of conceptual design report and associated documentation**

## Why are we here?

**The subject of this Review is the SNAP R&D in its current pre-conceptual design phase and its preparations to start the conceptual design phase in the future.  **
**Endorsement by HEPAP subpanel for funding SNAP R&D**
**NAS/NRC Turner Panel Report**
**DOE Occasional Paper**
**In performance of a general assessment of progress, current status, and the identification of potential issues, the committee should address the following specific items:**

## 1. Does the proposed project meet the scientific objectives described by the Turner panel report?

**The Turner panel clearly states that the full understanding of Dark Energy requires a “wide field telescope in space (such as the Supernova Acceleration Probe)”  **
**SNAP can determine key cosmological parameters.                             ****<See Perlmutter and Ellis in plenary>**
**The project meets the objectives described by the Turner Panel Report of exploring the nature of the dark energy.**
**We have performed a complete detailed end-to-end simulation of SNAP. ****<See Bernstein in plenary and Kim in SC1>**** **
**We have made a detailed analysis of the science reach analytically.    ****<See Linder in SC1>**
**We have made a detailed analysis of the science reach with the new tools. ****<See Perlmutter in SC1 breakout>**** **
**The Type Ia Supernovae are at the leading edge of this new science. ****<****See Nugent and Aldering in SC1>**

## 2. Can the suite of instruments proposed carry out the scientific program proposed?

**The suite of instruments are the basis of the simulation ****<See Bernstein plenary,  Kim and Perlmutter in SC1>  ****and meets the needs of the SNAP program:**
**The telescope is neither too big, nor too small ****<Perlmutter in SC1> **
**The field-of-view is neither too big, nor too small ****<Lampton> **
**The optical and near IR detectors provide the photometric information needed, but can use risk reduction. ****<Bebek> **
**The spectrograph provides spectra needed for identification and characterization of Type Ia supernova over the full range of redshift. ****<Ealet> **
**Suite of instruments are at the technological forefront, but not beyond ****<See Bebek, Tarle, Ealet, Roe, Lampton in plenary>**
**The scope of the instrument is similar to an H.E.P. vertex detector**
**There is margin in the specifications of the reference model             ****<See Mission Definition and Requirements Document>**

## 3. For this instrument concept, does the R&D plan address the appropriate technical issues?

**We have selected items for intensive R&D that:**
**Have technological risk**
**Have schedule risk**
**Have cost risk**
**Some of the subjects of the R&D plan have combinations of the above.  The purpose of the R&D plan is to mitigate or eliminate these risk areas. ****<see System Managers Talks, & R&D Plan>**
**The major technical issues are the optical and NIR detector technologies. ****<Holland and Prieto in SC4>**
**The major schedule issues are the electronics for these technologies. ****<Roe in plenary, Walder in SC4>**
**The major cost risk is the telescope. ****<Lampton in plenary/SC3>**

## 4. Is the cost estimate consistent with the planned R&D program? 

**The cost estimate is a bottoms-up engineered estimate with ****<see Cost Book, WBS, System Manager Talks>**** :**
**Deliverables**
**Schedules**
**Milestones**
**Manpower, etc.... **
**How do we know that the cost is correct?**
**The staff that created the estimate is experienced and understands their requirements and the scope of the activity. **
** ****The management understands the requirements and the scope of the activities.**
**The size of the project during the R&D is largely level-of-effort, where we already know the staff and what they will be doing.**

## 5. Have the major risks and uncertainties been adequately identified for the current stage of the proposed project?  

**We have identified our major risks in ****<see Harvey in plenary and System Managers Talks>**** :**
**Technology**
**Schedule**
**Cost**
**We have been through an intensive study at Goddard to look at mission risks that has backed-up our own assessment. ****<see IMDC study on web>**
**We have been through an intensive study at Goddard to look at instrument & optical technology risks that has also backed-up our own assessment.    ****<see ISAL study on web>**
**The estimate for the contingency for the R&D and the conceptual design development is based upon a scoring depending upon the origin of the particular cost estimate. ****<see cost book>**

## 6. Is the proposed schedule reasonable and appropriate in view of the necessary R&D tasks and projected funding?

**The number and scope of tasks is limited and well-defined. ****<see System Managers Talks> **
**We believe that the important issues can be managed within the schedule & funding constraints. ****<see System Managers Talks> **
**The effort is reasonable with the requested budget profile ****<see Harvey in Plenary and SC6, cost-book, and DiGennaro in SC6>**

## 7. Is the management structure adequate and appropriate for guiding the proposed project?

**Strong commitment from Laboratory Directorate at LBNL and at SSL. ****<very significant financial/personnel support>**
**Project Manager has extensive experience on space systems.**
**Deputy Project Manager with a track record of successful project execution.  **
**Cost and schedule tracking is integral to the project plan.**
**Project office and cost tracking active. ****<Janus>**
**Key experienced system managers active.**
**Collaboration up and running. **
**Well defined reference model. ****<see MDRD>**
**R&D Plan is in place. ****<see R&D Plan>**

## Optimizing the SNAP Mission involves an interplay of telescope diameter, field-of-view, detector noise, observing plan and other parameters
At this time we have created a working reference model based on a 2-meter telescope and a 0.7 square degree instrumented field-of-view.
This reference model is the anchor point for our trade-studies and assessments.
The parameter set for this reference model is internally self-consistent and achievable.
The full optimization will result from the ensuing effort and will be the basis for the Conceptual Design Report

**At this time we have created a working reference model based on a 2-meter telescope and a 0.7 square degree instrumented field-of-view.**
**This reference model is the anchor point for our trade-studies and assessments.**
**The parameter set for this reference model is internally self-consistent and achievable.**
**The full optimization will result from the ensuing effort and will be the basis for the Conceptual Design Report**

**SNAP Reference Model**

## Mission Objectives

**How to obtain both data quantity AND data quality?**
**Batch processing techniques with wide field -- large multiplex advantage,**
**Mostly preprogrammed observations, fixed fields**
**Uniform data set where selection criteria can be applied without bias**
**Very simple passive experiment**
**Follow-up observations with spectrograph**
**Obtain over 2000 “clean” Type Ia Supernova **
**Quantity:  Field-of-View: 0.7 square degrees instrumented**
**Quality:  Cross-wavelength calibration, from 350 - 1700 nm**
**Distribution:  Ability to accurately study supernovae as far away as *****z*****<1.7**
**Minimum data set criteria: **
**1) discovery within 2 days (rest frame) of explosion,**
**2) multiple high S/N photometry points on lightcurve,  **
**3) high quality peak spectra**

## Mission Design

**Mission Design**

**SNAP design meets these objectives**
_**Satellite: **_**Dedicated instrument, few moving parts**

## Mission Design

**SNAP design meets these scientific objectives**
_**Telescope:**_** 2 meter aperture sensitive to light from distant SNe**

- Telescope Lead: Michael Lampton (SSL)
- Design is result of huge trade study!
- Flat focal plane
- Delivers < 0.04 arcsecond FWHM geometrical blur over field
- Provides side-mounted detector location for best detector cooling

- TMA63:

## Mission Design

**Mission Design**

**SNAP design meets these scientific objectives**
_**Telescope:**_** 2 meter aperture sensitive to light from distant SNe.**

## Mission Design

**SNAP design meets these scientific objectives**
_**Photometry:**_** 1****° FOV half****-billion pixel mosaic camera, high-resistivity, rad-tolerant p-type CCDs (0.35-1.0 ********m) and, HgCdTe arrays (0.9-1.7 ********m).**

- Instrument Lead/Deputy: Chris Bebek/Natalie Roe
- IR Lead: Greg Tarle
- 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

**SNAP design meets these scientific objectives**
_**Photometry:**_** 1****° FOV half****-billion pixel mosaic camera, high-resistivity, rad-tolerant p-type CCDs (0.35-1.0 ********m) and, HgCdTe arrays (0.9-1.7 ********m).**

- Step-’n’Stare: Drag star through multiple fixed length exposures in multiple filters
- Focal plane is rotationally symmetric

## Mission Design

**SNAP design meets these scientific objectives**
_**Integral field optical and IR spectroscopy:**_** 0.35-1.7 ********m, 3”x3” FOV, low resolution, high throughput.**

- Spectrograph Lead:
- Anne Ealet/Eric Prieto (France)

## Mission Design

**Mission Design**

**SNAP design meets these scientific objectives**

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

## Mission Design

**SNAP design meets these scientific objectives**

- shutter

- Focal plane

- Spectrograph

- electronics

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

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Mission Design

## Observation Concept

- Imager
- First survey field we’ll look at is near the North Ecliptic pole.
- Survey field is a skinny strip 1.3O x 8.0O  (7.5O sq. after subtracting edge/gap effects).
- Step across survey field in a predetermined pattern.
- Fields revisited every four days (gets average of 2 days post explosion).
- All objects see all 9 filters.
- Four exposures per position
- To implement dithering pattern -- at each position move couple of pixels in 2x2 pattern.
- This improves the spatial and photometric resolution
- To eliminate cosmic ray pollution.
- Defects in the image are eliminated by this procedure
- 300 sec fixed length exposures determined by a shutter.
- After the set of four exposures shift over by 0.05O – half the pitch of a detector.
- 132 positions altogether, with 4 exposures each
- Takes 16 months to measure 2,000 raw Type Ia SNe

## Observation Concept (continued)

- Spectrograph
- 40% of the time the spectrograph is turned on and the satellite points to the supernovae
- During spectroscopy the exposure time increases to 1000 seconds.  Both spectrograph and imager are active.
- Total integrated exposure time for spectroscopy is ~ 8 hours for a z=1.7; varies as 6th power of 1+z.
- SNe candidates are scheduled for spectrographic measurement near peak luminosity.
- Analysis done on ground to roughly identify Type Ia and roughly determine *z,* using imaging data to decide which transient events deserve a spectrum.
- Note peak luminosity is 23 days to 48 days after discovery for *z *= 0.3 and 1.7, respectively.

## Observation Program

- After launch:
- Correct initial orbit for injection errors, station-keeping
- Two-three months check out of spacecraft/instrument systems, including commissioning, alignment, and cool-down
- 16 month survey of the North Survey Field
- 2.5 month Wide Weak Lensing Survey and one month follow-up of SNe survey
- 16 month survey of the South Survey Field
- 2.5 month Wide Weak Lensing Survey and one month follow-up of SNe survey
- Additional surveys, Guest Observer (GO) program as appropriate
- At end of mission, lift orbit into 7 day perturbed orbit, eventually ejected

## Weak Lensing Survey

- Weak Lensing survey takes 5 months
- Survey size is 300 square degrees.
- Each field is observed in all 9 filters.
- Exposure time is increased to 500 seconds long.
- Maintain 2x2 small dither pattern
- Richard Ellis will describe the Weak Lensing Science in his plenary talk.

## Requirements Development

**Requirements Development**

**Science**

- Measure *M* and 
- Measure *w* and *w *(*z*)

**Data Set Requirements**

- Discoveries 3.8 mag before max
- Spectroscopy with ~100
- Near-IR spectroscopy to 1.7 m

**Statistical Requirements**

- Sufficient (~2000) numbers of SNe Ia
- ...distributed in redshift
- ...out to *z* < 1.7

**Systematics Requirements**

- Identified and proposed systematics:
- Measurements to eliminate / bound each one to +/–0.02 mag

**Satellite / Instrumentation Requirements**

- 2-meter mirror	Derived requirements:
- 1-degree imager	 • 	High Earth orbit
- Low resolution spectrograph	 • 300 Mb/sec bandwidth    (0.35 m to 1.7 m)

- •
- •
- •

- •
- •
- •

## SNAP Level 1 Science Requirements

**Four Key Level 1 Science Requirements:**
**Quantity**
**Quality**
**Spectroscopy**
**Surveys**

- 2000

- From the Mission Definition and Requirements:

| 1.1 | Obtain over 2000 Type Ia supernovae for analysis in the redshift range 0.3 < z < 1.7  |
| --- | --- |
| 1.2 | Fit peak of supernova lightcurve on average to SNR of 50:1. |
| 1.3 | Obtain supernova spectrographic observations near peak intensity with a resolution R~100 over 0.35 to 1.7 microns wavelength. |
| 1.4 | Perform deep multi-color photometric surveys with field sizes of approximately 10 and 300 square degrees |

## Tools for Requirements Definition

- SNAP*fast* Monte Carlo implements **detailed list of systematics**
**Event generator** - Create an object list with fluxes.  Ingredients:
- 	Supernova types, Type Ia subclasses
- 	Galactic, host, and gray dust
- 	Gravitational lensing
**Image simulator and SN extraction** - Measure photometry, spectra from images
**Data simulator** - Generate light curves and spectra
- 	S/N calculated based on observatory parameters
- 	Calibration errors
**Detection efficiency** - Measure contamination of non SNe Ia and Malmquist bias
**Light curve and spectrum fitter** - Simultaneously fit key parameters of SNe
**Cosmology fitter** - Determine best fit cosmological and dark energy parameters

## SNAPfast

- With the Monte Carlo:
- Have simulated SNAP with detector characteristics and observing program
- Have simulated other potential experiments including ground-based instruments
- Use state-of-the-art SNe models that simulate SNe population drift with redshift
- Included systematic effects and calibration errors
- Have demonstrated mission need
- Can optimize SNAP
- Can generate error ellipses for cosmological parameters
- This represented a major effort on the part of the collaboration to develop this tool.
- See long list of sophisticated analyses provided, will be discussed in the science breakout.

## SNAP Space Studies

- Dec 2000	Spacecraft RFI to 5 vendors
- Jun 2001	NASA Integrated Mission Design Center
- July 2001	Rockwell Corp. for IR detectors
- Sept 2001	Telescope RFI to 4 vendors
- Dec 2001	NASA Instrument Synthesis & Analysis Lab
- Dec 2001	NASA/Goddard Orbit/Telemetry Study
- Jan 2002		Boeing Launch Vehicle Study
- May 2002	SAGEM, Primary Mirror for Telescope (in progress)
*Now**	**	**-----------------------------------------------*
*June 2002**	**The Aerospace Corp, independent cost study *
*July 2002**	**STScI data pipeline study *
*Oct 2002**	**NASA Integrated Mission Design Center** **	** *

## Preliminary Studies Undertaken

**Completed Pre-conceptual Studies:**
**Spacecraft (GSFC & SSL)**
**Focal Plane Layout (U.Mich., LBNL) – See C. Bebek/G. Tarle**
**SNAP Orbital Properties (SSL & LBNL)**
**Launch Vehicle Study (Boeing)**
**Telemetry (SSL) – See M. Bester (breakout)**
**Telescope Optics (SSL) – See M. Lampton (plenary)**
**Telescope Stray Light (GSFC, SSL & LBNL) – See M. Lampton (breakout)**
**Thermal Study (SSL) – See D. Pankow (breakout)**
**Focal Plane Guider (SSL, published) – See M. Lampton (breakout)**
**Calibration (IU, STScI, SSL, AAS) – See S. Deustua (breakout)**

## Study: NASA GSFC/IMDC & ISAL

- Propulsion Tanks

- Sub-system
- electronics

- Secondary Mirror
- and
- Active Mount

- Optical Bench

- Primary Mirror

- Thermal
- Radiator

- Solar Array
- Wrap around, body mounted
- 50% OSR & 50% Cells

- Detector/Camera
- Assembly

**from GSFC - IMDC study**

***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***

## Study: SNAP Orbital Properties

-  3 day synchronous orbit,
-  Perigee = 2.56 Re (geocentric), eg. 10,000 km altitude
-  Apogee = 24.94 Re (geocentric)
-  This orbit is in the plane of the moon and is stable against lunar perturbations.  Also,  	simultaneously maximizes solar, lunar, and earth avoidance angles.
-  Time passage through radiation belts = 11.2 hours
-  During this time SNAP is not observing, rather performing data dump.
- 	This corresponds to an 86% operational efficiency.
-  Total proton dose from belts negligible

## Study: SNAP Orbital Properties

-  Orbit perigee remains over Berkeley without adjustment.
-  5.2 hour ground pass over Berkeley
-  ~300 Mbit/s downlink requirement
-  375 Gbytes storage requirement
-  Requires 0.5m 6W Ka-band Xmit, with 10m ground station

## Study: Launch Vehicle

- Launch vehicle [Delta IV 4240] is capable of lifting 2020 kg to that orbit with significant mass margin held in Perigee, Apogee, SC-propulsion.  Can use equivalent Delta III, IV, Atlas, or Sea Launch.

## Study: Calibration

**Fundamental part of mission.**
**Will be hardware devoted to calibration both on the ground and in orbit.**
**Realization that our physics is largely insensitive to black-body temperatures.  Looking at 2800K NIST standards, and ~40000K WD.**
**Able to relax calibration requirements **
**Calibration working group augmented with experts: R. Bohlin, etal.**
**Calibration error model propagated through simulation to see effect on our measurement of the dark energy parameters.**
**Preliminary Calibration document distributed.**

## How Mission Operations map onto the Instrument Concept

**Reliability**
**No large diameter filter wheel,**
**Minimal onboard data processing.**
**Satellite**
**Body mounted radiator and solar panels provide a stable platform for long exposures,**
**Passive, radiative cooling,**
**Orbit and telemetry**
**3 day orbit period a good match to data generation,**
**Generated data volume per orbit compatible with available solid state recorders.**
**Telemetry band width and dwell time over ground station compatible with down-linking an orbit’s data buffer.**

## Technology Readiness Issues

***Instrument***
_**NIR sensors**_
**HgCdTe detectors are begin developed for ESO, WFC3/HST, & NGST**
**Need to demonstrate performance requirements for SNAP **
_**CCDs**_
**We have demonstrated radiation hardness that is sufficient for the SNAP mission**
**Industrialization of CCD fabrication has produced useful devices. Need to demonstrate volume.**
_**Electronics**_
**ASIC development is required (in progress for HgCdTe devices for NGST)**
_**Filters**_** **
**	****Investigating three strategies for fixed filters:**
**Suspending filters above sensors**
**Gluing filters to sensors**
**Direct deposition of filters onto sensors**
_**Spectrograph**_** **
**Throughput optimization**

## Technology Readiness and Issues

***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**
**Ka-band telemetry, and long ground contacts are required. Goddard has validated this approach.**
_**Calibration **_
**There exists a draft plan, this needs to be extended to all aspects of calibration.**
_**Pointing**_
**Feedback from the focal plane, plus current generation attitude control systems, may have sufficient pointing accuracy so that nothing special needs be done with the sensors**
**Fuel Slosh**
**Will require full-up opto-mechanical simulation**
_**Telescope**_
**Primary mirror, thermal, stray light, alignment, contamination, I&T**
_**Software**_
** ****Data analysis pipeline architecture**

## What’s New Since Last Review

| Last Review | Now | Comments |
| --- | --- | --- |
| Optical system delivered beam to three separate instruments | Only one integrated focal plane | Greatly simplifies optics, facilitated by common operating temp. |
| Large complex filter wheel | Filter wheel eliminated in favor of fixed filters. | Facilitated by observing strategy. |
| 4% of SNe (above z>1.2) | ~1/3 SNe are above z>1.2 | Smaller FOV, but larger IR system. |
| FOV = 1 square degree | FOV = 0.68 square degrees | Smaller instrumented region. |
| Lunar assist orbit
(19 x 57 Re) | Highly Elliptical 3 day synchronous (2.6 x 25 Re) | Eclipse time was 5.5 hrs, now < 2.2 hrs.  Launch vehicle delivers us to final orbit. |
| 3 ground stations, 25W xmit | 1 ground station, 6W xmit | Data stored for transmission, downlink overlapped with time in radiation belt.   |
| Ejectable telescope cover | One time hinged door | Meets orbital debris policy. |
| Fast Steering Mirror/Pointing | Fast Guider on focal plane | Simpler. |

## Questions from Last Review - Science

**Response Document, with cross-references to major studies**
**All questions have been responded to with simulations or studies.**
**Proven Mission Need (can the same expt. be done from the ground?)**
**See E. Linder “ Importance of Supernovae at ***z >1.5 ***to measure Dark Energy”**
**We’re trying to determine if the dark energy is: 1) a vacuum energy density, *****w=-1***** and constant, or 2) a dynamical scalar field.  SNAP can uniquely measure *****w***** and its time evolution.**
**See S. Perlmutter “Simulation Results Talk”**
**Cannot do this from the ground, need to consider population drift & dust**
**Lots of supporting documents including detailed simulation studies.**
**Have examined coupling SNAP to ground-based telescopes, or NGST**
**Have Relaxed Requirements for Color Calibration**
**See R. Miquel “Effect of Calibration Errors in the Determination of Cosmological Parameters”**
**See S. Deustua “Calibration Program” for means to achieving goals.**

## Questions from Last Review - Instrument

**Expanded Trade and Simulation Studies, including Instrument Concept and prioritizing instruments**
**Obtain Astronomical Data from LBNL CCD’s, and reduce effort on CCD’s**
**Moving parts need to be thought out**
**Better define observational requirements for the IR system**
**Consider thinned HgCdTe devices**
**Investigate Spectrograph Throughput**
**Now have a simpler prism-based system**
**Acquire HgCdTe multiplexors and increase budget**

## Issues/Responses

| Harvey awarded satellite proposal study | Heetderks new project manager coming off ISUAL in Sept. (experience from EUVE, FAST, IMAGE ...). |
| --- | --- |
| Growth of LBNL R&D activity required increased oversight | DiGennaro, Dep. Project Manager, coming off SNS now. |
| H.E.P. flat funding and future loss of SNAP LDRD | Brought about prioritization in Physics Division and RIF.  SNAP is division’s highest priority.   |
| H.E.P. Pathfinder to NASA & Astronomy Communities | Working with NASA/SEU, AAS membership and meetings, collaboration now grown to 1/3 astronomers, |
| Calibration needed more support | Bringing in more experts, converted from a working group to a subsystem with funding. |
| IR detector development | Required higher level of funding and more technological oversight, |
| Spectrograph effort needed focus | France provided project management and leadership. |

## Slide 51

## Phase A Schedule

**Phase A Schedule**

## SNAP Phase A Organization

## SNAP Collaboration Organization

## Collaboration:  Built strong international collaboration, includes experts in space, and in the key technologies, continuing to expand in depth and breadth. 
Management: Very strong institutional support, team is in place.
R&D:  Have made huge strides in developing major technologies.  These need to be completed.
Space Worthiness:  Have demonstrated feasibility and confirmed/studied by others (eg. IMDC).  Directorate is establishing external space advisory board.
Concept:  Have developed a self-consistent reference model.  
Studies: Simulation advanced, significant early trade-studies completed

Ready to develop a full conceptual design and cost estimate

**Management: Very strong institutional support, team is in place.**
**R&D:  Have made huge strides in developing major technologies.  These need to be completed.**
**Space Worthiness:  Have demonstrated feasibility and confirmed/studied by others (*****eg*****. IMDC).  Directorate is establishing *****external space advisory board*****.**
**Concept:  Have developed a self-consistent reference model.  **
**Studies: Simulation advanced, significant early trade-studies completed**
**Ready to develop a full conceptual design and cost estimate**

**SNAP Pre-project Development Geared toward a Successful Mission**