Design Meeting - Aug 11, 1994

Design Meeting - Aug 11, 1994

An audio recording (11 MB) of the first 25 minutes of the design meeting is available. Seeker design issues and presentation content are discussed. The recording ends when the design group moves on to the computer room to view and discuss various optics design options.

Attendees


     Mark Cutkosky
     Sam Drake
     Larry Pfeffer
     JC Reddy
     George Toye
     Carolyn Valiquette
     Joe Wagner

Agenda 


09:00 am - 10:30 am: discussion on design issues 

10:30 am - 12:00 am: demonstration of the single axis test equipment
		     and further discussions

Lunch

1:30 pm - 5:00 pm: headover to EIT and have presentation matters
		   cleared out.

What happened?

The design discussions mainly concerned with the following issues: Filed of view: Field of view was earlier decided on about +/- 2.5 degrees. However, Sam has designed the optics for the effective focal length of 180 mm (field of view: +/- 1.5). Considering that the single axis test is running at about +/- 4 degrees, the group has expressed concerns over that being too small/tight.

Sam Drake agreed to decrease the focal length; but he would retain the existing design for the primary mirror (which has focal length of about 90 mm). He left the manufactured mirror (not the final one) here for experimenting. It means the secondary mirror has to be reworked (it is not yet manufactured, anyways).

Placement of the CCD: If the focal length is reduced and the CCD is to be mounted back of the primary mirror (along with a beam splitter), the secondary mirror gets to big and loss of light is huge. Also, the space available for placing the CCD in the back is going to be a problem since rate sensors are already taking a lot of space - having space for the CCD is going to be a little tricky.

Pros and cons of placing the CCD in the back of the primary with a beam-splitter or in the back of the secondary without a beam-splitter were discussed. Finally, conclusion was reached to place it behind the secondary since it will give more design alternatives (space) - more physical space available, and the secondary mirror gets smaller. On the other hand, some designs have to be reworked - design of the spider, for one. Sam agreed to do that. Although it was felt that that is not the most elegant solution, given lack of time to do experiments, it was an acceptable decision.

Encoders and Interface: Sam Drake brought some encoders from Jacobsen's lab at Utah. They were quite compact - but have only 10 bit resolution. However, if no velocity information is derived from the position info, they are just fine - so, if rate sensors work well and if we get good signal to noise ratio, we can use these encoders for position information. Interface of these encoders with PC is to be provided by Jacobsen's Lab - not clear what exactly will be given. Mark preferred two options: they provide an interface cord from which we can read directly; or we use a standard parellel port (serial will be too slow) and they give us 16 wires and the relevant information about how to read them, etc.

Rate Sensors: Rate sensors were brought by Sam Drake. He showed how they fit in the back of the primary mirror. Larry to test out how they work (in the current single axis test) and experiment with them to see if they can be used.

Manufacturing and Scheduling Issues: ?

JC