Large Binocular Telescope Observatory

Attachment A to the RFP for the
Mask Manufacturing Unit (MMU)

STATEMENT OF WORK

Technical Specification - 8 May 2009

 

TABLE OF CONTENTS

1. Background

2. Mask-Cutting Machine Requirements

3. Procedures

4. Drawings

================================================

1. Background

This Statement of Work (RFP) covers the purchase of a laser cutting machine designed to produce spectroscopic multi-slit masks for two scientific instruments currently being built for the Large Binocular Telescope in Arizona. The requirements and capabilities of this Mask Manufacturing Unit (MMU) are detailed below in this Statement of Work.

1.1 The Large Binocular Telescope

The LBT is an international collaboration among institutions in the United States, Italy and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota and University of Virginia.

The telescope consists of two 8.4-meter mirrors on a common mount, equivalent in light-gathering power to a single 11.8 meter instrument. Because of its binocular arrangement, the telescope will have a resolving power (ultimate image sharpness) corresponding to a 22.8-meter telescope when the light from the two telescopes is combined interferometrically. The telescope was completed in Italy and shipped to Arizona in the summer of 2002. Major construction work on Mt. Graham in south-eastern Arizona is complete, and the telescope is beginning limited scientific observations during the commissioning phase.

Additional information on the LBT Project can be found on the web at this URL:
http://lbto.org

1.2 The optical spectrographs: MODS

As part of the complement of first-generation instruments, The Ohio State University (OSU) is constructing two identical optical spectrographs for the LBT. Designated the Multi-object Double Spectrographs (MODS), these instruments are capable of both imaging and low-resolution (R=2000-8000) spectroscopy spanning the wavelength range from 330-1100 nm. A beam selector below the focal plane carries a dichroic that splits the incoming light from the LBT into separate red- and blue-optimized channels, each with its own collimator, grating, camera and detector. This allows simultaneous operation across the entire CCD band. The first MODS is scheduled to arrive at the LBT in fall 2009.

For multi-object spectroscopy, a custom-machined slit mask is placed in the focal plane of the telescope to isolate the light from up to ~72 separate astronomical sources (some applications could significantly increase this number). The MODS mask blanks are spherical shells that vary in thickness from ~140 microns at the center to ~170 microns at the edge. They are made of electro-formed NiColoy metal (Nickel-Cobalt alloy) coated with copper black. More details on these mask blanks and what needs to be machined in them are given below. Obtaining the laser-cutting machine to manufacture these masks, as well as the equivalent part for LUCIFER (below) are the focus of this RFP.

1.3 The infrared spectrographs: LUCIFER

As another part of the complement of first-generation instruments, the Landessternwarte (State Observatory) in Heidelberg, Germany is constructing two cryogenic infrared spectrographs for the LBT. Designated the LBT NIR-Spectroscopic Utility with Camera and Integral-Field Unit for Extragalactic Resarch (LUCIFER), these instruments provide seeing-limited and diffraction-limited imaging at wavelengths from 0.9-2.4 microns, as well as low-resolution (R<10000) spectroscopy.

As with MODS, multi-object spectroscopy with LUCIFER is accomplished using custom-machined slit masks. The LUCIFER mask blanks are 125-150 micron thick flat stainless-steel sheets. In the instrument they are held in a frame that bends them into a cylindrical shape that better matches the curvature of the telescope focal plane. More details on these mask blanks and what needs to be machined in them are given below.

1.4 Local infrastructure

The currently preferred location for installation of the MMU is at the University Research Instrumentation Center at the University of Arizona in Tucson.  

2. Mask Cutting Machine Requirements

The MMU is to be a computer-controlled 3-axis laser cutting machine, capable of cutting precision apertures in relatively thin metal with two different formats. The detailed requirements and capabilities of this Mask Manufacturing Unit (MMU) are detailed in this section. Note that the specifications in the following tables are the minimum acceptable requirements.

2.1 Mask Substrates

Handling of the mask substrates for MODS imposes two strong constraints on the capabilities of the MMU. First, the machine must have a working area at least large enough to handle the 330mm diameter MODS mask blanks. Second, the machine must be able to accomodate the height of the spherical shells and its holding fixture. The LUCIFER mask substrates are smaller than the MODS substrates and flat, so should not introduce any additional constraints on the MMU.

The table below summarizes the properties of the mask substrates to be machined by the MMU.

Raw Mask Substrates:

LUCIFER

MODS

Material:

125um Stainless Steel1

150um NiColoy2

Size:

<200mm square

330mm diameter

Format:

flat sheet, bent to cylinder shape with radius=1040mm after milling.

spherical shell, radius=1040mm, 12.8mm high at center.

1Type 304L (low carbon) vacuum annealed stainless steel.
2NiColoy is a proprietary electro-deposited Nickel-Cobalt alloy. The MODS masks vary in thickness: ~140 microns at the center of the shell and ~170 microns at the edge. The MMU must be able to handle this variation in thickness. The MODS masks also have a thin coating of copper black. For more information on NiColoy, visit this URL: http://www.nicoform.com/definitions/nicoloy

2.2 Mask Blanks as Cut from Substrates

The following table summarizes the physical properties and tolerances of the cut mask blanks for each instrument. The toleranaces in the following table are less stringent than those that follow, but they include the minimum working range of the XY stage.

Masks Blanks as Cut:

LUCIFER

MODS

Mask Size:

162 ± 0.3 mm square1

230 ± 0.1 mm square2

Mask Edge Roughness:

± 50um

± 30um

Mask Perimeter Cutting Speed:

N/A

>5mm/sec

Registration Slot Width:

2.00 ± 0.015 mm

2.00 ± 0.015 mm

Registration Slot Length:

3.00 ± 0.015 mm

3.00 ± 0.030 mm

Reg. Slot Position tolerance:

± 15um

± 15um

Reg. Slot Edge roughness:

± 15um

± 15um

Reg. Slot Cutting Speed:

N/A

>2mm/sec

1Example drawings of LUCIFER masks can be found at the bottom of this statement of work.

2Example drawings of MODS masks can be found at the bottom of this statement of work.

The final size and shape of the masks as they will be used in each instrument must be established by cutting them out of the substrate material with the MMU. The larger size of the MODS masks drives the primary constraint on the MMU: the XY stage must be large enough to allow cutting of the 230mm square mask blanks. LUCIFER's masks are quite a bit smaller and therefore do not impose any additional constraints on the capacity of the XY table.

For LUCIFER we will mount the completely cut masks into rigid frames that bend them into a cylindrical shape before installing them into the instruments. The mask substrates are flat metal sheet.

For MODS we will mount the round blank on a holding fixture, cut the slits and registration holes, and then trim the outside perimeter.  The holding fixture is still in the design phase. 

The masks are located in these frames through the use of registration slots on the masks and corresponding pins on the frames. The slots must therefore be accurately sized and placed to fit over alignment pins. The registration slots are elongated to allow for differential thermal expansion and contraction between the masks and frames.

2.3 Tolerances on Slit Placement and Quality

Accurate placement of the slits across the full focal plane is critical, as each slit must line up correctly with the targeted astronomical source. LBTO acknowledges that this will likely be one of the more difficult specifications to meet on the MMU. The required minimum tolerances are given in the table below, but proposals should discuss the potential costs associated with meeting a goal of tolerances a factor of two more stringent.

The following table summarizes the properties and tolerances of the spectroscopic slits or apertures to be cut into the science portion of the instruments' fields of view.

Slit Tolerances:

LUCIFER

MODS

Width:

0.15-0.6mm

0.15-1.2mm

Length:

<10mm (typ)

<10mm (typ)

Orientation:

±30°

±30°

Shape:

Arbitrary polygon or circle

Arbitrary polygon or circle

Width Tolerance:

±15um

±15um

Position Tolerance:

±15um

±15um

Edge Roughness:

±1.5um RMS over 150um

±1.8um RMS over 180um

Cutting Speed:

N/A

>2mm/sec

The two most critical issues for multi-object spectroscopy are accurate relative placement of the slits on the mask and roughness of the edges of the slits. For real-world astronomy, slits can have arbitrary shapes. Rectangular slots are used most frequently, but arcs and square or circular apertures will also be used. Slits can also have an arbitrary orientation, typically ±30° from the normal to the dispersion direction.

A typical metric for aligning slits to targets is to center the sources to better than 10% of the width of the smallest slit likely to be used. For both instruments, the minimum typical slit width is ~0.25 arcsec, equal to 150 microns in the telescope focal plane. This implies that the laser-machined slits must be accurately located on the mask to better than 15 microns.

The edges of the slits should also be smooth at detector pixel scales or larger. Very little re-cast, slag, or waviness can be tolerated. The edges of the (rectangular) slits need to be parallel and straight. In practice, the goal is to achieve rms deviations on the edge roughness of less than 1% of the narrowest slit the instruments are likely to employ. The minimum typical slit width for both instruments is ~0.25 arcsec, equal to 150 microns in the telescope focal plane. This sets the requirement that the edges of the slit are smooth to <1.5 microns RMS over a scale of 150 microns.

2.4 Laser Refocus to Follow MODS Shell

Since the MODS masks are spherical shells, the MMU must be able to follow the curvature of the mask (dynamic refocus, or a 2.5/3-axis machine). It is sufficient for the laser cutting to be done always perpendicular to the XY stage motion, it is not necessary to follow the normal to the surface of the spherical shell. The mask substrates are 12.8mm high, while the mask blanks cut from the substrates are 12.4mm high. In practice, cutting the MODS masks after mounting the blanks into their frames means that the MMU must accommodate a somewhat higher total vertical refocus.

2.5 Mask Processing Speed

The duty cycle for cutting masks with the MMU is fairly low, likely to be 10-20 masks per day on average. Given modern laser machining speeds and the fact that each mask will typically require less than 2 meters of total linear cut length to complete, each mask should require no more than 10-15 minutes of laser machining to complete. Thus, ease of set up and clean up will be considered.

2.6 Software Interface

The data defining the locations and dimensions of the slits or apertures to be cut into the masks will be generated in software that is outside the scope of this MMU project. The two instruments have yet to specify the format of the files output from the mask design software, but it is likely to be in some industry-standard format like DXF files or G-codes. This can be negotiated between the laser machine provider, the LBTO, and the instrument teams as needed. The MMU must be able to import these files and convert them into the necessary MMU control codes to successfully cut the masks.

2.7 Operational Safety

Safety is a primary concern. Persons employed to process the masks through the MMU will be trained, but unlikely to be expert laser-machinists. The MMU must therefore be fully enclosed and interlocked to prevent operator exposure to stray reflections of the laser light.

2.8 Ease of Use and Maintenance

Again, the MMU operators will be trained in its use, but not experts. Ease of use of the MMU, as well as minimizing routine maintenance will be considered in the selection of the machine.

2.9 Deliverable Documentation

Described in this section are all the plans, drawings and documentation that must be supplied as part of this Statement of Work. All documents shall be supplied in two (2) hard copies and one (1) digital copy. All the deliverable documents, once accepted by the LBTO, become property of LBT Corporation. These documents include:

2.9.1 Final Design Review

Prepare and submit for approval a Final Design for the MMU describing all major subsystem specifications. The Final Design should specifically address what infrastructure (power, cooling, ventilation, floor loading, etc.) is required in Tucson before installation of the MMU.

The Technical Representative shall comment on the design within 15 days from the receipt. In the event of no comment, the design is to be considered approved.

2.9.2 Acceptance Test Plans and Results

Prepare and submit for approval an Acceptance Plan describing test procedures and inspections that shall be performed prior to acceptance of the MMU. These tests should include machining of at least five test masks for each instrument with LBTO-supplied input files and raw materials, plus subsequent measurements of these masks to verify that they meet the required specifications. A representative from the LBTO will likely be present for acceptance testing of the MMU.

The Acceptance Plan must be submitted to the Technical Representative for approval prior to the start of the acceptance testing. The Technical Representative shall comment on the plan within 15 days from the receipt, and in the event of no comment the request is to be considered approved.

Similarly, test results must be submitted to the Technical Representative for approval once completed. The Technical Representative shall comment on the test results within 15 days from the receipt, and in the event of no comment the test results are to be considered accepted.

2.9.3 Operations Manual and Safety Guidelines

Prepare and submit for approval an Operator's Manual. It must clearly describe all operations that the MMU is capable of relating to its primary purpose (spectroscopic slit mask machining) and how to safely perform them. It must also address all procedures that must be followed for safe operation of the MMU. Include complete instructions for installation and initial checkout of the unit in its final operating location.

The Operator's Manual must be submitted to the Technical Representative for approval prior to the start of the acceptance testing. The Technical Representative shall comment on the plan within 15 days from the receipt, and in the event of no comment the request is to be considered approved.

2.9.4 Maintenance and Troubleshooting

Prepare and submit for approval a maintenance schedule and troubleshooting guide. The maintenance schedule should cover all aspects of routine maintenance for all subsystems of the MMU (XY stage, laser, interlocks, computer, software, etc.) and how to safely perform them. The troubleshooting guide must address and clearly describe major anticipated failure modes and the correct procedures to safely recover from them.

3. Procedures

3.1 Acceptance

The Work shall be accepted by LBTC upon delivery and completion of the Work (including the acceptance tests in the factory and a post-delivery inspection) in a manner at that time satisfactory to LBTC.

3.2 Technical Liaison

The Supplier shall provide access to all phases of the Work to the following LBTC Technical Representative(s):

Mark Derwent, Engineer

Ohio State University

Department of Astronomy

140 West 18th Ave

Columbus, OH 43210

USA

mderwent@astronomy.ohio-state.edu

Phone: (614) 688-5863 Fax: (614) 292-2928

and

David Thompson, Instrument Support Astronomer

LBT Observatory, University of Arizona

mailto:dthompson@as.arizona.edu

The Supplier shall maintain informal technical liaison with the LBT Observatory Technical Representative(s). These representative(s) shall be provided the following:

3.3 Technical Changes

All ECRs, NCRs, and Requests for Waivers or Deviations will be presented to the Technical Representative(s) for further evaluation, formulation of responses, and recommendations to the LBT Director.

3.3.1 Engineering Change Request

In the event that the Supplier deems it necessary to deviate from any specification or term of the Technical Specifications or the Proposal, the Supplier shall deliver to the Technical Representative(s) an Engineering Change Request (ECR) setting forth:

3.3.2 Non-Conformance Report (NCR)

The Supplier shall report all non-conformities from the Technical Specifications which occur during the manufacture, assembly, or testing at all levels of the Work. Each Non-Conformance Report shall set forth the following:

3.3.3 Request for Waiver/Deviation

A Request for Waiver may be issued during the manufacturing, test or integration of a deliverable item to:

A granted waiver does not lead to changes of any approved and released documents. The Request for Waiver shall include:

It shall be accompanied by all documentation required by the LBT Corporation to judge the acceptability of the waiver. If any change in the schedule or performance are expected, these points shall be clearly addressed.

3.4 Point of Delivery

All documents and hardware shipped as a result of this Statement of Work shall be sent to the LBT Observatory office in Tucson:

Large Binocular Telescope Observatory

The University of Arizona

933 N Cherry Avenue

Tucson, AZ   85721-0065

USA

telephone: +1 520 626 5231

telefax: +1 520 626 9333

4. Drawings

In case the drawings following the table are not visible, the figure numbers in the table below link to PDFs of the mask examples.  

Document Type

Fig. #

Description

LUCIFER Mask Blank

4.1

Mask blank dimensions for LUCIFER

Example LUCIFER Mask

4.2

Example mask for LUCIFER, including a single long slit.

Example LUCIFER Mask

4.3

Example mask for LUCIFER, including multiple slits across the full instrumental field of view.

MODS Mask Blank

4.4

Mask blank and registration slots as cut from the substrate for MODS.

Example MODS Mask

4.5

Example mask for MODS, including a range of rectangular slit widths across the full instrumental field of view.