"Preparing for a KAO Flight"

Junior Journals


Many thanks to Marilyn Kennedy Wall for graciously writing this Junior Journal based on Ben's original writing. Marilyn teaches at John Wayland Elementary School in Bridgewater, Virginia.

Sometimes getting ready to do my job on a KOA flight is very easy. When the astronomers are looking for bright starlike objects like stars, planets,and bright asteroids, my preflight preparaion is not hard. Once I find out where these objects are on my chart, I just have to tell the Video Star Tracker to "grab it" and "move it" to the what we call the "boresight". This is the spot in the camera field where their instrument is looking and tell the astronomers to start taking data.

Getting the Detection System Ready:
Most often, however, getting ready is not that simple. Tonight's KOA flight (September 27, 1995) will require more preparation. Tonight flying with us on this flight is astronomer and instrument owner Dr. Al Harper of Yerkes Observatory. Two other guest investigators will be there too: Dr. Jackie Davidson and Dr. Harold Butner. On tonight's flight they would like to investigate objects IRC +10420, L 1455, Saturn, L 1031B, IRAS 23568+6706, TMS 1A, GG TAU, and M42. The astronomers already know the infrared brightness of Saturn and IRC +10420, and they will use the known brightness of these two objects as a standard measure to make sure the detection system is working. Once everything is adjusted to what is known, then they can use the detection system to figure out the brightness of the unknown objects to be studied during the flight.

Getting out the Charts:
For this flight I have several things I must do. First, I have to get a list of the objects the astronomers want to see. I will also need the exact location of each object. Astronomers call these locations celestial coordinates; it's like the address of your house. Just like you find addresses in a phone book, I find the addresses of objects in the sky by using special catalogs. These catalogs tell the exact location, the exact coordinates, of each object I am looking for. There is also information about possible past measurements of infrared brightness made by other astronmers.

Next I check my files to see if there are already established charts for the objects we will be studying on our KOA flight. There are two important charts we must have on board for each object we want to find.

The Acquistion Chart:
The first chart I use to find the object is called an "acquistion" chart. This chart helps me find the general location of that object.The "acquistion" chart covers a larger region of the sky, and this chart measures the sky in degrees. It covers an area roughly about 8 by 12 degrees. It is on this "acquistion" chart that you would find the brighter stars, stars of 9th magnitude or brighter.

The Tracker Chart:
The second chart I must get from my files is called a "tracker" chart. This chart measures the sky even more precisely. It measures the sky in arcminutes. It covers an area in 25 by 18 arcminutes. The "tracker chart" shows the faintest stars that can be visible through the tracker telescope camera; it shows stars as faint as the 14th magnitude. The "tracker" chart also shows the locations or plotted points for all the infrared positions the investigators will study or observe.

Making charts with Pickles:
Sometimes, the objects have never been observed on the KAO . If there are no files for the object, then it is my job to create and make charts for that object and have it ready for our flight.

Before 1990, this kind of chart had to be made by hand, using special graph paper. It took hours and hours just to make one chart. Now, I use a special computer program called "Pickles". This program reads the Hubble Telescope Guide Star Catalog from a CD Rom and "Pickles" is able to plot the star's location very accurately. The Hubble Star Catalog can even plot stars as faint as the 16th magnitude, which is much fainter than even our cameras can see.

Setting up the D.O.G. and Using Guide Stars:
Once I have the charts, the real work begins. I must get a list of "guide star" coordinates for the YERKES D.O.G. (the Digital Offset Guider). The D.O.G. helps us find our way to object we want to investigate by using other visible guiding marks in the sky. It's like steering a boat to an unseen destination by using other visible landmarks. Imagine that you want to sail your boat to an island, an island that is not in view because it's beneath the horizon. You would use another island that is in view as your guide to get to your island. As you sail to your destination, you would calculate how far off the bow or the stern you need to keep the sighted island to find your way to the unseen island you want to reach.

Using the same guiding landmark idea, the D.O.G. uses the infrared brightness of nearby Guide Stars to help the find the object that is to be studied during the KOA flight. The Guide Stars must be at least 12th magnitude in brightness, and they must be nearby, no more than 10 arcminutes away. In most areas of the sky there are lots of nearby Guide Stars which are "dogable." Then, a list of coordinates for the Guide Stars and the objects to be studied are typed into the computer for reading by the D.O.G. (the Digital Offset Guider) program.

One Last Preparation Before Take-Off:
Making tracker Overlays When I look at the video monitor at my station, I have only a small viewing area. My field of view of the tracker telescope is a little smaller than the area of the full moon. To help coordinate our position in the sky, I must create tracker overlays. I go back to the "tracker" chart and trace the positions of stars and infrared sources onto a plastic sheet. I will use this overlay by holding it up to the video monitor and line up all my grease pencil marked stars with the real stars shown on the monitor screen. Although I can't see the optically invisible infrared objects on the video monitor (the tracker camera being sensitive to optical ight only), by overlaying my grease-penciled map on the real stars, I can see where on the screen the infrared objects are. Some day, perhaps on SOFIA, we will no longer use plastic overlays. In the future, the computer will give us our star positions.

So, with all these charts, overlays, and coordinate information, I can walk onto the plane and hope very hard that I haven't forgotten anything.

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