NGAO System Design Phase: Work Scope Planning Sheet

WBS Element Title:	Wavefront Sensors	
WBS Element Number:	3.2.3.5
Work Package Lead:	Viswa Velur
Work Package Participants:	J. Bell, A. Moore, C. Neyman, V. Velur
1.	Work Scope
	
WBS Dictionary Entry: 	Develop a design concept for each of the required NGAO wavefront sensors:

3.2.3.5.1 High Order LGS Wavefront Sensors:  Given the functional and performance requirements, develop a design concept for the laser guide star high order wavefront sensors. Take into consideration the possible need for both open and closed loop wavefront sensing.

3.2.3.5.2 High Order NGS Wavefront Sensor:  Given the functional and performance requirements, develop a design concept for the natural guide star high order wavefront sensor(s). Take into consideration the possible need for both open and closed loop wavefront sensing.  Include consideration of ADC packaging (ADC design is covered in WBS 3.2.3.8).

3.2.3.5.3	 Low Order NGS Wavefront Sensors:  Given the functional and performance requirements, develop a design concept for the low order natural guide star wavefront sensors for the purpose of determining tip/tilt and other low order modes in laser guide star observing mode. Take into consideration the possible need for both open and closed loop wavefront sensing.  Include consideration of ADC packaging (ADC design is covered in WBS 3.2.3.8).

3.2.3.5.4 Calibration Wavefront Sensor:  Given the functional and performance requirements, develop a design concept for the calibration wavefront sensor which will use natural guide star light as a truth wavefront.  This sensor will be periodically used to reset the references of the high order wavefront sensors in laser guide star mode.  Include consideration of ADC packaging (ADC design is covered in WBS 3.2.3.8).

Requirements: 	

Assumptions: Will be based upon those in the FRD.

2.	Inputs:	 
	a.	Functional requirements document.
	b.	Final optical design of the Cascaded relay.
	c.	Mechanical drawing(s) w/ space constraints and packaging issues clearly stated for the of Cascaded relay.
	d.	Type of each WFS (SH/ PYR)
	e.	What order/ # of sub-apertures.
	f.	The position each sensor in the Optical Relay.
	g.	The FoR for each sensor
	h.	Positioning accuracy
	i.	Specification on pick-offs for the WFSs (including the ones shared by the TT(FA) sensors inside the d-NIRI) and rotation if necessary.
	j.	Choice of detector(s) for each WFS (pixel size).
	k.	Pixel geometry specifics like guard bands, pixel geometry and spot size (for LGS with appropriate elongation) for each WFS
	l.	Centroid-ing accuracy, dynamic range, and linearity specifications from FRD for each WFS
	m.	The Field Stop/ Spatial filter specification

3.	Products:	
	a.	First order optical design.
	b.	Zemax design of each type of WFS (no tolerancing, 				commercial optics/ lenslets, not optimized for wavelength etc., 			no transmission budget).
	c.	First order Mechanical packaging 
	d.	Design for a generic spatial filter/ adjustable field stop 			that can be used for all WFS's
	e.	Preliminary mechanical design and 3D model (at least a cartoon showing the envelopes occupied by the WFSs.
	f.	Acceptance and completeness of the design effort w/ information on what needs to be done during the detailed design phase.
	g.	Preliminary costing
	h.	Documentation for all the above.

4.	Methodology:	
	a.	Based on the inputs from section 2. a first order optical design shall be worked out and shared with the rest of the WFS team for scrutiny. This will be documented and sent to the EC for further inputs.
	b.	A Zemax design based on above first order design and inputs from the WFS team will be released.
	c.	Based on the Zemax design a preliminary mechanical design shall be made and integrated into the rest of the Cascaded Relay Architecture.
	d.	Meeting with the WFS (w/ other invitees, if necessary) to have a mini-review for the optical design.
	e.	Design for a generic spatial filter/ adjustable field stop that can be used for all WFS's (may be just specify it, not design it).
	f.	Last meeting to understand risks and look at the acceptance of the work and design with the WFS design team.
	g.	Documentation of the designs with design risks.
	h.	After consensus on the design a preliminary sub-system costing will be performed for the hardware, optics and associated electronics and add it to the documentation.

5.	Estimate of effort:
	a.	First order design: 
LGS WFS : 16 hrs.
NGS HOWFS: 8 hrs.
TT and TTFA sensor : 12 hrs.
TWFS/ Calibration WFS: 8 hrs.
Total : 44 hrs.

Zemax designs for each WFS:
LGS WFS : 40 hrs.
NGS HOWFS: 20 hrs.
TT and TTFA sensor : 10 hrs.
TWFS/ Calibration WFS: 16 hrs.
Total: 86 hrs.

Meeting with the WFS (w/ other invitees, if necessary) to have a mini-review for the optical design ( half a day with 4 people) : 16 hrs.

First order Mechanical packaging
LGS WFS : 8 hrs.
NGS HOWFS: 4 hrs.
TT and TTFA sensor : 16 hrs. (need to talk to the IWG)
TWFS/ Calibration WFS: 4 hrs.
Total : 32

Preliminary mechanical design and 3D model (at least a cartoon showing the envelopes occupied by the WFSs. (1.5 X?)
LGS WFS : 16 hrs.
NGS HOWFS: 12 hrs.
TT and TTFA sensor : 24 hrs. (need to talk to the IWG)
TWFS/ Calibration WFS: 16 hrs.
(the hrs. above also include the time required to integrate the design into the Cascaded Relay ME design).
Total: 68 hrs.

Design for a generic spatial filter/ adjustable field stop that can 			be used for all WFS's : 20 hrs. (may be we must just specify it for 			lack of time) - no detailed design.

Last meeting to understand risks and look at the acceptance of the work and design with the WFS design team.: (4 people x 1 day) : 40 hrs.

Documentation of the designs with design risks:  20 hrs.

Costing and adding it to the documentation: 20 hrs.

6.	Approvals:			
Intially allocated: 240  hours
Estimated: 326 hrs.

Control	Name
Date				
Authored by:
Viswa Velur
Sept. 5, 2007					
Approved by:
WBS X.X Lead					
	NGAO EC Chair