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Specs and Documents for Instrument Builders

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New Instrument Procurement Models

Gemini is implementing a more flexible and enhanced approach to instrument procurement that facilitates development of new instruments and capabilities within the current constraints of our staff and financial resource budgets.  In its May, 2014 meeting, the Gemini Board approved new elements of an expanded procurement model, allowing Gemini to work more closely with build teams to support several varieties of in-kind contributions.  In the future, we plan both targeted calls for specific capabilities and open calls for the community to tell us what they want and can provide for us.  Through our visiting instrument program and ability to respond to ad-hoc requests, we also continue to be open to externally initiated opportunities.

In the November, 2015 meeting, the Gemini Board established some key principles for implementing this new approach.  The new tool added to our arsenal is an expanded use of telescope time in procuring new instruments and current instrument upgrades.  There are three ways we plan to use telescope time in these efforts:

  1. Telescope time can be awarded to the build team at various points in the project to reward successful and timely completion of milestones.
  2. We may elect to offer the equivalent of a long and large program to the science team associated with the build team to use the new (or newly upgraded) instrument for some initial investigations that will be scientifically valuable and provide a clear demonstration of the instrument's abilities.
  3. We can also allocate telescope time to the host institution or partner country of the build team(s) to compensate for in-kind contributions that reduce Gemini's cash outlay.

We have already implemented some of these concepts in our agreements with the GHOST and SCORPIO teams and regularly include them in our facility instrument and instrument upgrade calls.  We can also use them when we convert visitor instruments to facility instruments to recognize the visiting instrument team's contributions.  The Gemini Board reviews/approves each final agreement so they can help ensure we continue to meet the needs of the overall partnership.   These new approaches have already allowed us to continue to grow our overall capabiliities at Gemini while being even more responsive to community needs.

Specifications & Interfaces

This page describes key specifications and interfaces for Gemini instruments including interfaces for ISS-mounted instrumentsconsiderations for bench-mounted instrumentssystem services available, and the Observatory environments. Key interfaces are described in interface control documents (ICDs).

Gemini Specifications and Interfaces for Instruments

- Document ID Document Title Revision/Date
download INST-REQ-0001 Science and Facility Instruments Common Requirements Specification C 08/20/2018
download ICD 1.5.3/1.9 Instrument Support Structure to Science Instruments ICD E 07/18/2018
download ICD 1.9/2.7 Science Instruments to Facility Handling Equipment ICD E 04/27/2016
download | supplemental files ICD 1.9/3.6 Science and Facility Instruments to ISS System Services ICD J 08/03/2021
download ICD 1.9/5.0 Science and Facility Instruments to Transport, Observatory and Operational Environments ICD D 08/06/2018
download ICD G0014 Optomechanical Coordinate Systems B 09/08/2011
download ICD 1.1.13/1.9 Interlock System to Science Instruments ICD A 06/16/1997
(one package)
GIAPIBuilderReq-01302009 GIAPI Software Requirements for Instrument Builders 04 11/18/2014
GIAPIUse-08292006 GIAPI Design and Use 08 11/18/2014
GIAPIC++ICD50-02042008 GIAPI C++ Language Glue API 11 05/07/2014
ICD 20 Synchro Bus - Node/Page Specifications D 10/11/2013

Overview of Interfaces

Instruments mounted on the telescope Instrument Support Structure (ISS) must adhere to the following requirements and guidelines. The ISS webpage provides an overview of the ISS, telescope and observing floor.

Mechanical Interfaces 

See ICD 1.5.3/1.9 and ICD 1.9/5.0 for more details. 

Space Envelope: Instruments must satisfy the space envelope requirement as specified in drawing 89-GP-1000-0004 and ICD 1.5.3/1.9. Extension into the ISS (such as to add an entrance shutter) will require a waiver of the space envelope.

Mounting: Instruments must support mounting via use of Gemini ballast weight structures or using the standard Gemini physical interface specified in ICD 1.5.3/1.9. The ballast weight structures are empty frames upon which to mount instruments and add weight. 

Ports: There are three ports on the ISS available for science instruments: `side looking' or 'side ports' on Faces 3 and 5, and an `upward looking' or 'bottom port' on Face 1 (when the telescope is pointing towards zenith).    

Mass: Instrument weight on the ISS science instrument port faces must not exceed 2000kg. 

Thermal Control: It is preferred for instruments to minimize heat released to the dome environment and into the ISS structure. The threshold requirement for facility (non-visiting) instruments is 100W and 50W respectively.

Orientation: ISS-mounted instruments are normally subjected to changes in orientation as the telescope points from zenith to horizon and the Cass Rotator turns through its full range of 540 deg.

Vibration: Gemini telescopes are vibration-sensitive environments. Instrument builders should take care both to minimize induced vibrations, and to minimize the impact of vibrations coming from other sources. Gemini has experience with various cold head types and vibration mitigation techniques. External sources of vibrations include other instruments and other parts and components of the telescope system. This set of dome floor vibration measurements at GN is one characterization of the vibration environment, but it will vary depending on the site and on the instruments mounted on the ISS. Gemini has several sets of reports and data for various instruments. 

Flexure: ISS-mounted instruments will experience internal flexure due to variant gravity vectors, and may require passive or active flexure compensation. While every instrument will experience flexure in its own unique way, one characterization is given in two GPI papers on flexure modeling and flexure compensation.   

Optical Interface

See the Optics webpage for more details (telescope prescription, coatings, specifications, etc.)

Port: Instruments must be able to use Gemini's optical interface for the instruments, which is a circular port 400mm in diameter through which the telescope or calibration beam can be directed. The port is central to the ISS face and the beam emerges perpendicular to the interface plane. A machined land is provided to make a light tight seal with the instrument. Fastener detail for mounting a baffle component can be provided as needed. The nominal telescope F/16 focus is 300mm from the mechanical interface of the ISS. The plate scale at focus corresponds to 1.611 arc seconds per mm. The ports are detailed in ICD 1.5.3/1.9.

Guiding: Fast guiding is typically required at Gemini for good image quality. This is usually provided by a peripheral wavefront sensor (PWFS-2) that performs M1 active optics contract and M2 tip/tilt correction. Please see the Guiding and WFS webpage for more information. 

Flexure when guiding: Instruments using the PWFS for guiding may also notice flexure. The NIRI and GMOS webpages on guiding describe each instrument's experience using PWFS. Characterization of the NIRI-PWFS2 flexure was performed in 2008, plotting the change in pixels (also here) as the CRCS rotated from 180, to -180, back to 180 in 45 degree increments. 

Pointing Accuracy: Current blind pointing accuracy across the entire sky is +/- 6-8 arcsec, with average blind pointing errors +/- 2-3 arcsec. Use of A&G system puts a science target on any instrument within a positioning error induced by mapping (+flexure) of the guider. That error is +/- 1 arcsec for PWFS2 or +/- 0.5 arcsec with OIWFS. 

Calibration: GCAL is the facility system for flat field and wavelength calibrations. Please see the Calibration webpage for more information. 

Bench-Mounted Instruments

Gemini's Pier Lab has previously hosted BHROS, and will host GHOST, both bench-mounted fiber-fed spectrographs. The Pier Lab is located ~15m below the dome floor and having a ~800mm diameter shaft connecting the Lab to the dome floor. Lab geometry is described here.

  • Pier Lab internal usable diameter: 8,000 mm
  • Pier Lab nominal access door width (subtracting door thickness): 3,000 mm
  • Pier Lab nominal maximum height (subtracting structure and crane): 3,000 mm
  • Pier Lab ceiling hole: 800 mm
  • Uniform stationary Live Load capacity is 600 lb per square ft or 2929 kg per square meter.

System Services

See ICD 1.9/3.6 for more details. 

Gemini provides the following services to instruments via the Services Panel. For bench-mounted instruments, Gemini may provide the same or subset of Systems Services to another location on a case-by-case basis. Ideally instruments will have a patch panel to facilitate hook up to the service panel, and the instrument should come with equipment used in typical setup including interconnecting hoses, cables, etc. 

Coolant Dowtherm SR-1, 40 % by volume and water
Helium Closed Cycle Coolant GM Cooler Types
Compressed Air
Communications Wired ethernet only (GN) / Wired or wireless ethernet (GS)
Power UPS and MAINS
AC power frequency 60Hz (GN) / 50Hz (GS)

Gemini Observatory and Operational Environments

See ICD 1.9/5.0 for more details. 

This set of environmental measurements for both sites provides temperature, pressure and humidity data collected over two years. The data was taken from an external weather station near each telescope and the data sampling is not strictly uniform.

Altitude 4200m (GN) / 2700m (GS)  
Ambient air temperature  -15C to +25C
Ambient air temperature rate of change up to 1.3C/hr
Relative humidity 0% to 100%
Gravity component limits
(components vary continuously in discrete steps)
X axis +/-1g
Y axis +/-1g
Z axis -1g to 0g
Vibration  Varies between sites

Integration and Testing at Gemini

New instruments and systems will undergo several stages of integration and testing (I&T) with the final stage occuring at the telescope itself. Gemini sees value in working closely with instrument teams during both pre-delivery and post-delivery I&T. 

Pre-Delivery Expectations for I&T

Gemini advocates for a strong pre-delivery I&T program, for several reasons.

  1. To identify issues earlier if possible and to reduce risk.
  2. To identify issues while still at contractor site, where the development team is located and available to facilitate troubleshooting.
  3. To reduce the amount of problem solving performed at altitude, on the summit, where there is less oxygen as well as less in-person support.
  4. Pre-delivery I&T is an important time for knowledge transfer between contractor teams and Gemini staff who will be supporting the instrument.

Pre-delivery I&T is recommended to include:

  • Flexure testing.
  • Optical alignment.
  • Initial measurement of key performance parameters.
  • Software testing.

Post-Delivery Expectations for I&T

Post-delivery I&T may occur at both base and summit, or just at the summit. At this point, I&T should be focused on integration with Gemini systems which could not be simulated at the contractor site. We do expect to perform some re-assembly, re-alignment, etc. as some disassembly may be necessary for shipping. On-site contractor support will be expected for this. Much of the Gemini-focused I&T will require close collaboration with Gemini staff, and they will coordinate the ENTs and then the commissioning runs with Gemini operations.

Gemini Facilities for I&T

Gemini has lab spaces at GN base facility, and at both GN and GS summit facilities (3 labs total).

All of the lab spaces offer: 

  • Systems services as described in ICD 1.9/3.6 can be made available.
  • Connectivity to telescope software systems.
  • A flex rig for flexure testing. It is possible to simulate each angle the instrument may see and there is a calibration source to aid in measuring flexure too.
  • A small clean room. The rooms are limited in size and cannot fit an entire assembled instrument, generally, and there is no crane inside the clean room for lifting a complete instrument.

I&T Requiring Telescope Time

Gemini does not have test beds or simulations of the following. Time must be scheduled on the telescope in order to do I&T. Time is requested through engineering task requests ("ENTs"), and Gemini staff will assist in generating and submitting these.

  • Gemini telescope pupil / optical path.
  • Gemini calibration unit (GCAL).
  • Gemini acquisition and guiding unit (A&G).

Instrument Handling

Gemini provides facility handling equipment for handling, manoeuvering and installing instruments, as described in ICD 1.9/2.7. Newer instruments may provide their own handling carts.

Specs and Documents for Instrument Builders | Gemini Observatory


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