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Interface Specifications for VI

Specifications for Visiting Instruments

This page describes key specifications and guidance for visiting instruments (VI) including interfaces for ISS-mounted instrumentsconsiderations for bench-mounted instrumentssoftware interfaces, system services available, the Gemini operating environments and VI operations. Links to relevant drawings and interface control documents (ICDs) are included within the text.

PIs interested in bringing a VI to Gemini should first review the information below and Gemini's VI Policy. Initial coordination should then be done through the Associate Director of Operations, Andy Adamson.

ISS-Mounted Visiting Instruments

VI to be mounted on the Telescope Instrument Support Structure (ISS) must adhere to the following requirements and guidelines. See DSSI and TEXES for examples of ISS-mounted VI.

Physical Interfaces 

Space Envelope:VI 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 and must be coordinated in advance.

Mounting: VI 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. Gemini provides standard and long ballast weight structures for visiting instruments. The ballast weight structures are empty frames upon which to mount instruments and add weight. VI teams should request in advance any special items required for attaching the VI to the ballast weight structure or for general set up (bolts, straps, fibers, etc.).

Ports: VI should make any specific port requests in advance. 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). The upward looking port is preferred for IR instruments. The side looking ports have an extra reflection.

Mass: VI weight on the ISS science instrument port faces must be trimmed to be 2000kg. The moveable ballast weight system for the ballast weight structures includes metal plates and disks in multiple sizes to do this.   

Orientation: VI should provide any orientation restrictions in advance. 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. Any orientation restrictions must be specified in advance so that appropriate operating procedures can be defined to avoid mishaps (e.g. spilling of cryogens).

Vibrations: VI must provide any VI vibration specifications unless the VI is being used without backup queue. Gemini telescopes are vibration-sensitive environments and therefore potential sources of vibration (e.g. pumps, cold heads) should be known beforehand. 

Optical Interface

Port: VI 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.

Telescope prescription: Here is the Zemax file for GN and Zemax file for GS

Guiding: Fast guiding is typically required at Gemini for good image quality. For VI this is usually provided by a peripheral wavefront sensor (PWFS-2) that performs M1 active optics contract and M2 tip/tilt correction. If using the PWFS-2, Gemini will provide the telescope corrections.

Thermal Control

It is preferred for VI to minimize heat released to the dome environment and into the ISS structure. For comparison, the threshold requirement for workhorse instruments is 100W and 50W respectively.

Bench-Mounted Visiting Instruments

Advanced planning is required to accommodate bench instruments. Specifications for VI size and other environmental and operating conditions should be provided. See GRACES for one example of a fiber-fed bench-mounted VI. 

Software Interfaces

VI can be entirely self-contained if they do not need to control the telescope movements (e.g. do not need to nod or offset). If interaction with the telescope is required, the VI should use the VI Interface document and associated Wiki page form the Gemini Software Group (SWG) to facilitate integration.

System Services

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

Services Provided: see ICD 1.9/3.6 for complete specifications (e.g. couplings, flow rates, 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 Note differences in specs at GN and GS

Network Connections: Advance coordination with the Gemini Information Systems Group (ISG) is required to support VI communications needs. For VI teams at GN, note that Wi-Fi is not allowed on Mauna Kea so ensure your laptop has a built-in ethernet port or additional hardware to connect.

Cryogens: Advanced planning is required for VI using cryogens. Liquid nitrogen and helium are not readily available at Gemini and must be ordered in advance.  At GS liquid helium must be shipped from the US.

Gemini Operating Environments

VIs should be capable of operating in the following conditions. The instrument operating environment are those conditions experienced under normal telescope operations when the module is mounted on the ISS and in use. Complete information is provided in ICD G0013.  

Altitude Sea level to 4300m
Ambient air temperature  -5C to +20C
Median air temperature GN: 0C / GS: +9C
Ambient air temperature rate of change 0.8C/hr
Relative humidity 0% to 90%
Wind speed 0 to 5 m/s
Gravity component limits
(components vary continuously in discrete steps)
X axis 1g
Y axis 1g
X axis -1g to 0g
Vibration (this specification is currently under review) PSD 1x10-5g2/Hz, 20-1000Hz, 6db/oct drop-off to 2000Hz

VI Operations

Visitors should review general instructions and information on the Gemini Science Visitors page.

Instrument Configuration and Maintenance

In advance of their visit, VI teams must provide a description of anticipated activities for VI configuration and maintenance including daily and recurring ones. Coordination for Gemini engineer support and with other telescope maintenance activities must be done in advance.

The access required to perform configuration and maintenance should be included in the description. For instance, will a dewar need to be refilled and what part of the VI must be accessed to do so? Will masks or filters need to be changed and what part of the VI must be accessed to do so?