Design Meeting - Jul 13, 1994

Attendees


    Larry Pfeffer
    JC Reddy
    George Toye
    Joe Wagner

What was planned?

general update and future schedule
finalized optics design

What happened?

JC presented two detailed optics design options - both are cassegrian arrangements. Rough sketches of these designs are accessible: first, second.
The first one with effective focal length of 116mm preferred. However, it is suggested that we go for full 100mm diameter for the primary mirror (maximum possible). Accepted by the group. See below for additional changes.
Questions were raised about where to put CCD camera. CCD without lens is about 1.5" dia and 1" deep. With lens, it is longer. Where do we accomodate the camera if we decide to place in the front? In the back of the secondary mirror? In that case is there enough space?
Clearly, there is not enough place there since the total distance available in front of the primary mirror is only 2 inches (~50mm) - according to the current gimbal design (can be increased - but it would increase the overall size, may not be acceptable).
Sam Drake suggested beam splitters a while ago. However people were skeptical about what % of light will be lost if a beam splitter is used. CCD camera will be used in the back of the primary mirror as shown in the figure if the beam splitter is acceptable. There is a plenty of room in there.
Joe and Larry have done some experiments to see if beam splitters are ok. Qualitatively the losses are "not too much" (less than 10%), and image quality on the CCD seems ok. However, some additional questions were raised:
- CCD is quite small (smaller than PSD) and hence the field of view will be smaller for the CCD. It is clearly not acceptable. Do we need to use additional lenses in front of the CCD to increase the field of view. What are the details? Possible?
- Optics have to reworked out since PSD has to be moved back by about 25 mm to accomodate beam splitter and the CCD. Can we still get an acceptable optics configuration?
  Preliminary calculations by moving PSD by 25 mm back, keeping the effective focal length about 120 mm, and changing the curvatures of mirrors show that it might be - but we incur more light losses because of the blockage due to secondary mirror - about 22%; should be reduced.
Joe Wagner selected required CCDs from a catalog (from Supercircuits. Still to be finalized and ordered.
He also made available on the web three new catalog pages detailing video camera options. The current favorite configurations are using the PC-9XS camera alone--utilizing and a beam spliter and the seeker mirror to provide a 5 degree field of view, or the ML-12MM lens for a 18.4 degree field of view.
Group also discussed about what kind of velocity and position sensors we would need. Sam has already ordered rate-gyros and the lead-time on them is about 2 weeks. Larry has expressed concerns about that time being too late for the project deadlines. Sam also wanted to look into encoders Utah (Jacobson) lab manufactures. Larry decided that he would need atleast 13 bit resolution on encoders. It is still unclear as to what option is selected.
Finally future plans and logistics were discussed.
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Optics worked out ASAP.
7/13: Check on I/O board
7/20: hook PSD into computer

8/1: Stuff ready to send to Sam
8/8: full set up for control
8/15: final working seeker
8/24: sending for demo
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