Project Starshine and Parramatta High School

PROJECT DESCRIPTION Several small, optically reflective spherical "STARSHINE" student satellites, built by the U.S. Naval Research Laboratory, are being deployed by NASA from Hitchhiker canisters in Space Shuttle cargo bays, as well as from an Athena unmanned launch vehicle, into highly inclined low earth orbits at a rate of once every year or so. The satellites are covered by nearly 1000 small, front-surface aluminum mirrors that are machined by technology students in Utah and polished by tens of thousands of students all over the world.

...and Parramatta High School is involved, of course. Late in 2000, we registered our interest in the Starshine Project by asking for a mirror polishing kit to be sent to us. In March 2001 the kit was received, and we laboured (it was fun) to get the mirrors polished and returned to the U.S. by the end of the month. You can see the list of all schools worldwide which are participating here, but caution; this is a large (368kb) file, which must be downloaded entirely before it opens. I have saved a much smaller portion of the file here, with just the first dozen or so schools. (We're near the top!). Below is a chronicle of the grinding and polishing process, as undertaken by Parramatta High School.

Contrary to this site's conventions, the images in this section are not supplied first as thumbnails.
Instead, the size of the final images has been limited, and they are all displayed on this page. They should load sequentially. Apologies if this is inconvenient.

	The blanks (there were two) were supplied in as-machined state. This meant that there were very fine machining marks on the soon-to-be mirror surface. To assist in the fine-grinding step, the blanks were coloured in with a black marker pen, to exaggerate the depressions, making them easier to see during grinding.
The abrasive used for the grinding phase was Aluminium Oxide, supplied in a "creamy" solution for ease of handling and use.

	The Aluminium Oxide is applied to the glass grinding surface with the eyedropper. Initially, 10 drops or so of AlOx is used.
Initial grinding takes place in a gentle "figure-8" pattern (Whilst it appears from this picture that pressure is applied through the stem of the blank, it was actually applied through contact with the back of the mirror flat. In this shot, the blank is simply being positioned, ready for grinding.)

	As the grinding proceeds, the AlOx goes black. This is caused by the aluminium particles mixing with the white AlOx.
Here is one of the blanks after grinding. If you look carefully, you can see two faults - a spot and a line around 9 o'clock. The line is a drying artefact, and doesn't matter. The spot, on the other hand, is a machining mark which the grinding didn't remove - until we reground it!

	Cleanliness is paramount in this process. Many gallons of water were expended making sure that no abrasive particles were transferred from one step to the next. Likewise paper towels.
Polishing of the mirrors is not done directly on the glass surface. Instead, a small disc of "Kempad" polishing cloth is applied to the glass surface. This pad has a self-adhesive back, shown here being exposed.

	There were two stages to the polishing process. In this first stage, the 3µ diamond polishing paste is being applied to the pad with the supplied syringe. Eight drops of lubricant (not shown here) are also added - to assist the process.
Polishing proceeds in much the same fashion as grinding - making certain that the pad is not damaged.

	As the lubricant evaporates from the polishing mix, more is added as shown here. The mirror finish on the blank (in the background) is already visible.
Just as in the grinding phase, the abrasive mix turns black as the particles of aluminium mix with it.

	The fine polishing step is undertaken with 1µ diamond paste on a new polishing pad. This shows the blank (polished with 3µ), the bead of 1µ paste in the puddle of lubricant, and the reflection of the camera and the photographer.
The fine polishing phase proceeds as above.

	Here is the appearance of the two mirrors after polishing.
Testing of the mirrors' surface is by observing the interference patterns between the finished mirror blank and a supplied optically flat blank of glass. The interference rings are difficult to photograph, but can be just seen here.

	Perhaps the interference patterns are easier to detect here. Very few rings were visible by naked eye, too. Modesty forbids us to point out just exactly what that implies about about our polishing accuracy... (blush)
Here is the packet of two mirrors (and the optical flat), just prior to posting back to Alabama. Stay tuned for more news on this project. At this stage, launch is scheduled for August 31 2001, aboard an unmanned Lockheed Martin Athena I. We will certainly provides updates after the launch.