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Baffle Mounting Points

There are three points on the top surface of the star tracker intended to receive a baffle. If a baffle has been provided by Sinclair Interplanetary, then these points will already be occupied. Otherwise, the customer may use these to attach a rigid or deployed baffle or other structure.

The three points are located on a 38 mm diameter bolt circle. Each will accept an M2.5x0.45 screw to a maximum depth of 4 mm. Stainless steel anti-siezing helical inserts are installed in these holes to prevent damage to the aluminum structure. The screw threads are grounded.

Vent

The star tracker is fitted with a filtered vent located on the bottom cover. This allows internal gasses to be released upon ascent on the launch vehicle. The vent is covered with a porous Teflon filter which will trap all particles 1.0 mm and larger. It will also prevent gross intrusion of liquids, making the sensor somewhat “splashproof”. Note that it will not prevent water vapour from entering the sensor and condensing inside.

User cautions associated with the vent are:

1. Ensure that the vent is not covered on the satellite, and in storage. If the star tracker is mounted to a flat plate there is adequate clearance for the vent.

2. Do not submerge the star tracker in cleaning solvents. Use great caution when cleaning the bottom surface to minimize the fluid that enters the vent hole.

3. Do not poke the vent hole with sharp objects.

4. Store the star tracker in a clean environment that is temperature and humidity controlled.

Fluorine Outgassing

Star trackers that use Rev 4 electronics (typically 4 V input voltage units) contain internal Tefzel type wiring that will slowly offgas minute quantities of fluorine. These units must be stored in a ventilated space so that fluorine does not build up and cause corrosion.

Star trackers that use Rev 5 or later electronics replace the internal wiring with a flex circuit. They do not produce any fluorine, and can be safely stored either in a ventilated clean space or in a sealed container with desiccant.

Lens Cleaning

When the baffle is not installed the lens is easily accessible, and can be cleaned using conventional camera-cleaning products. The front surface is glass, and so care should be taken to avoid scratching. Do not under any circumstances attempt to unscrew the lens from the star tracker body as the precision focus will be lost.

Once a baffle is installed it is extremely difficult to clean the lens. It is suggested that the star tracker be kept in a clean environment, or capped, at all times when a baffle is used.

Dust Covers

The star tracker is supplied with a black plastic cover on the lens. This must be removed before flight, and before the installation of any baffle.

Baffles are covered with a Kapton seal to keep them clean. This must be removed before flight.

The connector is recessed into the star tracker body such that a standard dust cap will not fit. If specified, the unit will ship with an attached connector saver.



Connector

The connector built into the star tracker is a Glenair part MWDM2L-9S-0J7-18B (rev 4) or MWDM2L-9S-5C3-.125B (rev 5 and later). It is built on the same line and to the same drawings as MIL-DTL-83513 parts, but is provided without the certifications to reduce the price. The built-in connector has socket contacts and is fitted with jackposts.

Star trackers may be supplied with a mating connector. This is Glenair part MWDM2L-9P-4J7-72M. It has pin contacts, and is fitted with jackscrews. There are nine flying leads, each 72” long. The leads are made from 24 AWG high-strength copper wire with ETFE insulation per M22759/33. Leads are identified by colour. Fluorine outgassing precautions must be observed with these materials.


Date: 2015-12-17; view: 593


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