Questions_and_answers_SN-2019-15.pdf

1) Are we simply replacing an existing LN2 cooler on existing MCT IR detectors?

This is a request for information ONLY. Should we solicit later, the effort would be to replace a LN2 dewar with a Cryocooler, and to take the MCT detectors from the existing dewar and place them within the cryocooler. If using the US Forest Service existing MCT detectors from the LN2 dewar on a new cryocooler is not a possibility, then the US Forest Service will consider alternate solutions that require a new cryocooler with integrated MCT detectors.

2) If so, can you provide drawings of the interface between the existing LN2 dewar and the MCR IR detector?

Yes, if this goes to a formal solicitation the US Forest Service will share drawings and or solid models after a signed NDA is secured.

- I can probably adapt a stirling cooler to the existing housing shown in item #2 of the attachment if you can provide the details of the vacuum connection between the red LN2 detector dewar and the black housing below it.

In the photo you will see the side of the flange that currently mounts to the red dewar.

There is an O-ring that makes the seal between the flange and the red dewar. The O-ring mating surface is between the OD of the silver center and the first (inner most) circular pattern of holes.

- I may only need the drawing of the “cold shoulder” and I would probably have all the details I need to come up with the interface between the Stirling cooler and the detector.

The ½” cold finger extends below the base of the mounting flange for 7/8”, this is the point where the MCT detector is mounted using two #0-80 screws. The #0-80 screws are 3/8” apart and perpendicular to a line drawn between each MCT detector. The Germanium lens can be seen in the photo “Base mounting flange 1” the lens sits in a 1.01” recess at the end of the cold shoulder which is 1.1” outside diameter.

- Can you provide more pictures of the red LN2 dewar removed from the rest of the housing? I am interested in the vacuum flange and the connection with the cold shoulder.

The photos below show additional detail of the O-ring seal, vacuum port, and the SMA connectors.

SN-2019-15 Questions & Answers

3) What is the maximum acceptable level of vibrations from the cryocooler to the rest of the assembly?

The specific measure of acceptable vibrations is not known. Due to the fact that I have a fast focusing mirror (focal point is 6.5” from mirror surface), it was recommended that we use a split cryocooler system to minimize exposure to this potential problem.

4) Does the split Stirling cooler need to be flight rated?

No

5) Do you have any requirements on the input power of the Stirling cooler?

The main power on the aircraft is 28VDC. We also have 115VAC. Using the DC volts and a linear regulator if necessary is preferred. We refrain from using switching (ie pulse width modulated) regulators due to their tendency to be EMI noise sources. One goal is to maintain physical and electrical separation between the MCT detectors and their low noise amplifier and EMI or other electronic noise sources.

6) How many units would be required?

Should we issue a formal solicitation, the requirement would be for two units, with a possible option to purchase an additional unit within 5 years.

7) If multiple units are required, what is the expected lifetime of the project?

Should we issue a formal solicitation, two units would be required within about 120 days of an award.