Gindex

SYSTEM DESIGN NOTE

SDN0014.01 - Instrument Handling

Prepared by	Date	Approved by	Date	Rev.	Rev Date
J Elias	6/2/99	N. Gaughan	6/8/99

1. Introduction

This design note is intended to cover the topic of instrument handling at Gemini facilities. Instrument handling at NOAO will be covered separately (SDN014.03). Access to the instrument for service is also covered separately (SDN014.02).

In general, the procedures outlined below are intended to conform to the Gemini documents, ICD-G0015 Gemini Facility Handling Equipment and Procedures and ICD 1.5.3/1.9 Instrument Support Structure to Science Instruments Interface Control Document. The procedures outlined below should be very similar to those used for handling and interfacing the Gemini ballast weight assemblies.

2. General Requirements

It must be possible to install the instrument on the telescope on either of the two side science instrument ports, or on the bottom (up-looking) port. This requires handling of the instrument in either a horizontal or vertical position. The installation procedure should not present risk of damage to either the telescope or the instrument.

In addition, it must be possible to transport the instrument within the telescope dome and at the Hilo base facility. It is not a requirement that this be possible in both orientations.

2.1 Instrument Handling Features

The spectrograph dewar uses several truss structures as interfaces. These are shown on the GNIRS web site (drawing numbers TBD) and are as follows:

Primary support truss. This truss mounts on the telescope Instrument Support Structure (ISS), and supports the weight of the dewar and the associated electronics. It is attaches to the “bulkhead” which is at the mid-section of the dewar. It must have sufficient rigidity to maintain the instrument aligned within tolerances on the telescope optical axis (displacements and tilts). It is therefore substantially more robust than is required strictly for handling. The details of the interface between this truss and the ISS are discussed below, in 2.3.

.Horizontal installation frame. This is a truss that also attaches to the bulkhead; it is designed to support the weight of the instrument when in the horizontal position, whether for transport, installation on the telescope, or assembly and service of the instrument. It must support the instrument safely, but has no additional flexure requirements. Ideally, it is a permanent part of the instrument, but we retain the option of removing it should its weight compromise either the weight budget or the location of the center of gravity. The truss interfaces to the Gemini air cart as discussed below (2.2).

Vertical installation frame. This is analogous to the horizontal installation frame, except that it is not used for assembly and service of the instrument. As with the horizontal installation frame, removal after installation on the telescope is optional.

Electronics enclosure support trusses. These trusses are used to attach the electronics boxes to the bulkhead.

Lift points will be provided at (at least) three locations on the trusses:

Two points will be provided on the sides of the primary support truss, near the front where it attaches to the ISS, at the mid-point of the sides.

A third point will be provided rear top center of the vertical installation frame (considered in horizontal orientation).

The instrument can be changed from the horizontal to vertical orientation using these lifting points and the Gemini handling equipment. If it is supported from the two forward points it will hang in a more or less vertical position; the rear lift point is used to raise that end to make the instrument horizontal.

2.2 Instrument Transport

The instrument is normally transported in the horizontal position on the Gemini air cart. It can be transported as well in the vertical position, but this is not recommended except as necessary for installation on the telescope, because of the center of gravity is at a much higher position.

There are sets of four mounting pads on the two installation frames that are matched to the pad locations on the air carts; these ensure that the instrument is properly centered on the cart. When in the horizontal position, the instrument can be placed in either of two orientations on the cart. The cart is designed so that when the instrument optical axis is along the length of the cart, the scissor lift can be at its lowest position (“lengthwise on the cart”). When the width of the instrument is along the length of the cart (“sideways”), the scissor lift cannot necessarily be lowered. The latter position is used primarily for corridor transport, where lengthwise orientation will not have sufficient clearance (see drawing 89-GP-1000-6000 for details). The “lengthwise” orientation is used for installation on a side port of the ISS.

The instrument can also be lifted and transported using the three lifting points described above (2.1). This is how it would be moved from one level to another in the dome, or removed from the air cart and placed on the floor (somewhere) for service.

The pads on the installation frames must be capable of supporting the instrument when it is placed on a level surface.

2.3 Telescope Installation

2.3.1 ISS Interface

The primary support truss attaches to the dewar “bulkhead” and to a mounting plate which is bolted to the ISS. The truss will be made of aluminum but the mounting plate will be made of steel in order to provide a good CTE match to the ISS. The truss is effectively attached at the four corners of the mounting plate, and thus accomodates temperature changes.

The overall instrument alignment is defined by the primary support truss, and final alignment of the telescope optical axis to the instrument can be done (if required) by remanufacture of the mounting points for the truss on the mounting plate, or of the mounting features discussed below. (One can think of these as effectively serving as shims.) It should be possible to determine alignment to the required accuracy in the lab, so that any adjustment will precede arrival at the telescope. The instrument can be used on any of three instrument ports; the absence of any adjustments in the mounting is due to the precision with which the ISS is made. The difference in the optical axis orientation at the three faces are roughly an order of magnitude below the overall instrument alignment requirements.

The instrument does not bolt directly to the ISS. Instead, four mounting pads are attached to the ISS; the instrument then attaches to these. The mounting pads are similar in design to those for the ballast weight assemblies, and thus also serve to align the instrument in the plane of the ISS surface as it is installed. This scheme ensures that if these alignment features are damaged for some reason, they can be readily replaced (which would not be the case if the ISS itself were damaged). It may be desirable to have the attachment points on the instrument mounting plate similarly modular, so that they too are easily replaced if damaged.

2.3.2 Installation Procedure

The installation procedures are described generally in Gemini ICD-G0015. The details of the final alignment of the instrument to the ISS (the last 5 mm) depend on the design of the alignment features. Note that if the mounting pads on the instrument are modular in addition to the ISS mounting pads, it is possible to have a slightly different alignment scheme for the up-looking and side-looking ports, taking the different gravity vectors into account.