# Presentation: 124376

## SCIENCE OVERVIEW

- Dr.  Ed  Cheng

## Topics

- What is WFC3?
- Scientific Goals
- Scientific Requirements Flowdown
- Science Management and the Facility Instrument

## What Is WFC3?

- WFC3 is a facility instrument being developed on behalf of HST user community (several thousand astronomers).
- Assures continued world class HST imaging science to end of mission
- By 2010 WFPC2, STIS and ACS will be 17, 13 and 9 years old, respectively
- Funded with re-programmed HST research funds (UPN459)
- No Guaranteed Time Observer (GTO) team, no GTO observing time, no GTO funding (saves >$20M)
- Scientific Oversight Committee (SOC) chartered by Code S
- “Badgeless” development team, led by HST Project

## What Is WFC3? (cont)

- WFC3 will be the first “panchromatic” camera on HST.
- Two channels cover Near-UV to Near-IR without cryogen
- UVIS CCD channel backs up ACS while providing unique NUV capability
- NIR HgCdTe channel improves upon NICMOS science
- Improved field of view, resolution, sensitivity
- Reduced wavelength range

## Scientific  Mandate

- Backup imaging capability for HST.
- Ensure an imaging capability through 2010 (lifetime).
- Address on-orbit CCD degradation issues (photometry).
- Radial bay operation not thermally constrained (efficiency).
- No aft shroud cooling system
- Provide a wide field and wide spectral range imaging capability.
- Statistical studies of rare objects require large field-of-view.
- Current scientific models need input from a “panchromatic” approach to observations.

## WFC3 Improves HST Imaging Sensitivity

## The Importance Of Panchromatic Science

- A synoptic view of the Universe requires knowledge over a wide spectral band.
- Astrophysical models are becoming very sophisticated.
- Galaxies look very different in the near-UV than in the near-IR.
- UV highlights star-forming regions and areas of energy production.
- IR highlights dusty regions and areas that absorb and redistribute (“recycle”) energy.
- A complete architectural model of a galaxy needs to understand all these components.

## The Panchromatic Galaxy

**I R**

## HST Imaging FOV

- WFC3  UVIS

- WFC3  IR

## The Importance Of Field-Of-View

- Statistical studies or discoveries of rare (dim, far away, or exotic) objects require large areas of sky coverage.
- Distant galaxy clusters need to be studied as a group.
- Studies of large objects are far more efficient without the need for extensive mosaicing.
- The stars within globular clusters need to be studied as a group.

## 30 Doradus What’s Inside A Star Forming Region?

## The Importance Of Near-IR Observations

- IR observations are a unique handle on the structure of the early Universe.
- Redshifted light at restframe UV and visible shows up in the IR.
- IR observations can look through dust to observe previously hidden regions of the Universe.
- Star forming regions and galactic centers are particularly interesting.
- HST is warm, but can be **very competitive** at wavelengths shorter than 1.8 um.

## How Much Energy Is The Universe Hiding In The Near-IR?

## Instrument Definition:The Science White Paper

- The WFC3 Science White Paper highlights areas where one may expect the contribution of WFC3 to be “ground-breaking.”  We have considered programs in each of the following themes:
-  **High-z Universe** (Sect. 4.2 and 5.1)
-  **Nearby Galaxies** (Sect. 6.1)
-  **Resolved Stellar Populations** (Sect. 4.1)
-  **Stars and Interstellar Medium** (Sect. 6.2)
-  **Solar System** (Sect. 5.2 and 6.3)

## Instrument Definition: Design Reference Mission (DRM)

- A set of 43 observing proposals.
- Based on the contents of the Science White Paper.
- Designed to stress the capabilities of the instrument.
- We have developed tools to rapidly assess instrument performance given varying instrument configurations.
- Provides 0th order assessment of the impacts of performance trades.
- The DRM may evolve somewhat as the SOC updates science goals

## Scientific Requirements Flowdown

- The Critical Science Review (CSR) has ensured that the instrument design satisfies the scientific requirements defined in the Science White Paper and Design Reference Mission.

## The Critical Science Review

- Conducted as the main part of the July SOC meeting.
- 24-25 July 2000 at STScI.
- 5 hour presentation by the Science IPT covering:
- Scientific requirements flowdown process,
- WFC3 scientific capabilities (focus on unique capabilities),
- Science-related instrument specifications,
- CEI Specifications (review of changes from prior discussion), and
- Estimated instrument performance and ability to meet scientific goals.
- SOC organized itself into 5 sub-committees.
- Discussed consensus conclusions and debriefed the HST Project Scientist and the STScI Director
- Delivered an 11 page report on 3 August 2000.

## CSR Report Summary

- “We feel well informed about the status of the Project and the current design.”
- “We find that the present WFC3 design does indeed meet the scientific performance specifications we expected.”
- “We believe that the Contract End Item Specifications reflect the best compromise between scientific performance and the stringent constraints on budget and schedule within which the Project must work.”
- “It is our judgement that the WFC3 Project is well managed and properly configured to deliver the camera within its budget, in time for the 2003 HST Servicing Mission.”

## CSR Detailed Comments

- “Since the detectors are the most critical items on the path to a successful instrument, we commend the Project for establishing the Detector Characterization Laboratory and for the recent progress in placing contracts with the two principal detector vendors and with a backup CCD vendor. We urge unrelenting attention to the issue of detector delivery.”
- “We recommend that the SOC and the Science IPT develop concrete plans for a candidate set of Key Projects for WFC3.”
- “We believe that the greatest current threats to budget and schedule lie outside the HST Project. NASA must maintain a more reliable schedule of Shuttle launches and not penalize the budgets of scientific payloads for delays beyond their control.”
- “The realized WFC3 will be essential to the success of HST in its final decade of operation and a critical pathfinder for the Next Generation Space Telescope.”

## CSR Concerns And Actions

- All items have been resolved with the SOC
- Shuttle schedule and associated budgetary impacts.
- Completion of contract negotiations with external contractors.
- Schedules for detector delivery at Marconi and Rockwell *“must be pursued with unrelenting scrutiny.”*
- Planning for I&T and SMOV needs development and SOC role needs to be defined.
- CEI clarifications requested on 7 items:
- CCD cosmetics, cross-talk, UV spec on backup devices.
- IR long l cutoff, scattered light.
- SOC updates on status of filters (esp. F300X).
- ETC development (enhancements to www page).

## Additional Recent External Reviews

- June 1, 2000 – NASA Headquarters - chartered “Simmons” Review.
- High-level technical and programmatic review.
- Positive comments from the panel.
- June 13, 2000 – Origins Subcommittee presentation.
- Positive comments regarding the instrument.
- Concern over potential cost overruns.

## Internal Reviews Completed

- June 10, 2000 – HST Project programmatic review.
- Reestablished that the budget and schedule are credible.
- Reconfirmed HST Project commitment to build WFC3 for the established budget and schedule.
- July 26, 2000 – WFC3 Subsystem Peer Reviews completed.
- A total of 15 detailed subsystem reviews covering all major technical areas of the instrument.
- Actions are being tracked.  Those that are reasonable to close before the CDR have been closed.

## Science Management

- WFC3 is a facility instrument.
- Selected to provide an extremely capable instrument for the entire HST community.
- Led by an Instrument Scientist in the role of the traditional PI.
- Supported by a Science Integrated Product Team (SIPT) in the role of the traditional “Science Team”.
- Guided by a Scientific Oversight Committee (SOC) to ensure that community interests are properly balanced.
- Not selected to perform a particular scientific program under a PI-led science team.
- SIPT is an integral part of the development project.

## SOC Roles

- Establishes the overall scientific balance of the observations that the instrument will perform.
- Creates the “Science White Paper”.
- Creates the Design Reference Mission.
- Participates in the tradeoffs of instrument design and technical feasibility.
- Participates in planning for the on-orbit performance verification phase.

## Scientific Oversight Committee

## SIPT Roles

- Supports the SOC in all its activities.
- Creates the instrument CEIS.
- Interacts daily with the instrument developers, making trades as necessary.
- Runs performance predictions against the DRM.
- Trades with significant scientific impact are brought back to the SOC.
- Selects the flight detectors.
- Plans and executes the instrument ground calibration.
- Plans and executes the on-orbit performance verification.

## Conclusion

- The “facility instrument” concept is new to HST and most of Code S.
- WFC3 is a trailblazer for future endeavors.
- To date, this has been an unqualified success.
- Serious scientific trades and discussions have been rapidly and productively concluded.
- The (justified) skepticism of many at the start has subsided.
- Interactions with the WFC3 developers and the HST Project are close and productive.
- The currently conceived WFC3 will have an unprecedented ability to produce outstanding, breakthrough scientific results.