At the NSS Boston Chapter meeting on March 6, 1997, Mr. William Letendre of the New England Affiliated Technologies (NEAT), Lawrence, Mass, gave a presentation describing a positioning device that his company is making for the alignment and calibration of NASA's Advanced X-ray Astronomical Facility (AXAF). The device is positioned on a kinematic optical mount for thermal stability. By the use of extensive software it can move the X-ray instrument assembly to keep it in line with the X-ray telescope assembly which is 60 feet in front of it, and is rotated about its aperture in three axes for alignment and calibration of the instrument module. The NEAT device must therefore rotate and shift the instrument module up, down and sideways to maintain the alignment with the pointing direction of the X-ray telescope.
     The device is used in a vacuum chamber, since the soft X-rays to be measured are absorbed by the atmosphere. There is a large chamber to house the AXAF and an eight foot diameter extension, 600 meters long for transmitting a narrow beam of X-rays to the telescope. To enhance the vacuum the chamber is cryogenically cooled causing any internal gases to stick to the chamber walls.
     The NEAT instrument module support weighs several tons and is about ten feet high. It is made of welded stainless steel which is electropolished for use in the vacuum facility, since it has a low outgassing rate. It is motorized and uses ball screws and gears for moving the instrument device to the commands of the software. Feedback is through rotary and linear encoders. Extreme cleanliness is also required, requiring that all mechanism use low outgassing, cryogenic suitable materials, and avoid greases and replenishing lubricants which outgas or give off dust particles.
     NEAT should be given a great deal of credit for the development of this device which has to operate accurately in a cryogenic vacuum which has created tremendous problems to be overcome. We are indebted to Bill Letendre for giving this excellent presentation.

Thursday, April 3, 7:30pm

"Hale-Bopp: Comet of the Century?"
by Jeff Foust, MIT

Comet Hale-Bopp promises to be a spectacular sight in the night sky over the next several weeks as it passes through the inner solar system. What makes Hale-Bopp different from other comets that have made appearances in recent years? What are the best ways to view this comet? Just what are comets anyhow? Jeff Foust, a planetary astronomer at MIT, will answer these and other questions about Comet Hale-Bopp in this talk.

PASA meets regularly for a business luncheon and formal meeting from 1-3 pm, the third Saturday of every month at Smart Alex Restaurant, Sheraton University City, 35th & Chestnut. 2 hours free parking with validation.
     Scheduled activities: April 3rd presentation to World Future Society (see below). April 4th & 11th Hale-Bopp comet viewing at Trenton State Museum at 6 pm. (Call Michelle Baker for details: 609/561-8867.) April 10th book signing by Jim Chestek at 7:30 pm at the Barnes & Noble bookstore in Abington. April 19th monthly meeting. May 11th trip to SSI Space Manufacturing Conference for summary session. May 17th monthly meeting. Call Dottie for details.
     March 8th meeting included the following reports: Earl Bennett discussed: the March 1997 Analog magazine article by G. Harry Stein on the X-33 and how NASA is trying to make it into a Shuttle-2 program; the new eyeglasses on the Hubble telescope; telemetry from Galeleo with images of Ganymede in improved resolution; and Silicon Carbide FET's which are usable at high temperatures (600C), and therefore can be sent to Mercury and Venus.
     Jim Chestek will join Michelle Baker at the March Storm initiative in Washington DC. Dottie Kurtz discussed a Planetary Society article on Mars rocks.
     Mitch Gordon finalized plans for the PASA Human Settlements in Space presentation to the World Future Society meeting on Thurs., April 3rd at 7 pm in Room 2023 of Drexel University's MacAllister Hall, 33rd & Chestnut Sts. Mitch, Earl, Michelle, Jim, Don Cox, and Jay Haines will present. Call Mitch for details: 215/625-0670. Mitch passed out copies of our trifold brochure.