## Live from the Hubble Space Telescope

### UPDATE # 22

PART 1: Challenge Questions: last week's answer and a new puzzle

PART 2: Time change for the CU-SeeMe session

PART 3: San Francisco Bay Area teachers wanted

PART 4: Email HST experts your questions

PART 5: Skiing and software

### CHALLENGE QUESTIONS: LAST WEEK'S ANSWER AND A NEW PUZZLE

What special property must a target have in order for HST to observe it for a long time without interruption?

Props to help work on the question:

• globe (to represent the earth)

• piece of wire (to represent the circular orbit of HST around earth; HST is in a very low orbit, only about 600 km off the earth)

• bead (to represent HST in its orbit around earth)

• protractor (to help you make the orbit have an inclination of 28 degrees; inclination is the angle between the orbit and the earth's equator)

A target that has a declination near 62 or -62 degrees can be viewed for many days at a time. (Declination is sort of the celestial equivalent of latitude on the earth, but it doesn't turn with the earth.) This is because the earth does not block HST's view of the target. We call this the "continuous viewing zone" or CVZ.

How to use the props to see this:

1. Make a loop of wire that will fit around the equator of the globe with room to spare. (You might want to figure out exactly how far off the globe the wire should be to truly represent the height of HST off the earth.)

2. String the bead on the loop of wire.

3. Hold the orbit around the globe so that it is just above the equator. This would be a zero inclination orbit.

4. Now tilt the orbit so that the orbit crosses the equator, but the angle between the equator and orbit is about 28 degrees. (Remember that satellites orbit the center of the earth.)

5. So it is easy to demonstrate, make the orbit cross the equator at 90 degrees west longitude. and 90 degrees east longitude. Make the tilted up part of the orbit cross northern Africa and tilted down part of the orbit cross a little above New Zealand.

6. Now have someone stand with their hand directly above the Bering Straights (and at least a foot or two from the globe. Their hand represents the location of the CVZ (at about 62 degrees declination).

7. Move the bead around the orbit and notice that the earth never blocks the view of the CVZ point. (Note that there is also another CVZ point just east of the Sandwich Islands at about -62 degrees declination.)

8. Once you have that all lined up, forget about the positions on the globe, because the earth is actually turning around once every 24 hours while the stars in the sky stay still. The orbit is not fixed in space, but it turns more slowly than the earth. The orbit of HST precesses (just like a top precesses) once every 56 days. That means that the patch of sky which is in the CVZ now will be in the CVZ again in 56 days.

Challenge Question for this week:

There are many telescopes much larger than Hubble. The Hubble Space Telescope has a 2.4-meter mirror. At Mauna Kea Observatory alone, there are four telescopes with mirrors more than 3 meters across, including the world's largest telescope, the 10-meter Keck Telescope (more than 4 times bigger than Hubble!).

Why is the Hubble Space Telescope so special?

LAST-MINUTE TIME CHANGE FOR THE CU-SEEME SESSION

Today's CU-SeeMe session (April 17) occurred at 4:00PM Eastern time. This was different then the time originally announced. News about this time change was not shared widely due to some problems internal to the LHST team. We really regret any resulting problems we've caused teachers who planned around the original time.

### SAN FRANCISCO BAY AREA TEACHERS WANTED

We would very much like to identify several classrooms in the San Francisco/Silicon Valley area who plan to watch the April 23 program live. Please identify yourselves by sending a brief note to Geoff Haines-Stiles at ghs@passporttoknowledge.com. Please include your telephone number in your reply. Thank you.

### EMAIL HST EXPERTS YOUR QUESTIONS

As a reminder, we have arranged for HST experts to answer Email questions from classrooms. The folks at the NASA Goddard Space Flight Center (Greenbelt, MD), the Space Telescope Science Institute (Baltimore) and elsewhere are anxious to handle tough questions from your students. We are particularly encouraging questions about the Hubble itself and what it takes to keep it working properly. We'd prefer to receive questions whose answers are not easily found elsewhere.

### SKIING AND FLOWCHARTS

Jeane Ryan

April 10, l996
The Ryans are a HUBBLE family as both Joe and I work on the Hubble Space Telescope project at Goddard Space Flight Center in Greenbelt, Maryland. Also our children Kelly, Susan and Andrew have grown up with Hubble exposure for the last twenty years as Joe worked first on individual instrument development, then on the integration of instruments, mirror, solar arrays and all other parts to actually build the telescope and now on the Servicing Missions.

Hubble took us as a family to California in 1985 when only Joe worked on the project. He was assigned to Lockheed Missiles and Space Incorporated, Sunnyvale, California as the Government On-Site Director. We lived in California for almost three years. While in California we became more avid skiers and fell in love with the Lake Tahoe ski areas.

Early in 1996 we decided to take our holiday break from Hubble to ski. As both Kelly and Susan live out in the San Francisco Bay area and Andrew had lived out in the Lake Tahoe area last spring, Lake Tahoe seemed to be the perfect choice.

We were really lucky that our ski trip coincided with Comet Hyakutake's closest approach to Earth. It would be missing Earth by ONLY 9 million miles. It was discovered by and named for the Japanese amateur astronomer, Yuji Hyakutake (pronounced "yah-koo- tah-kay".

We drove up the Mt. Rose road from the rented Mountain Shadows condo to a scenic overlook at about 7,500 feet altitude. We parked the car and got out to stare up at the night sky.

We knew the comet was to be very near the Big Dipper, an easily spotted constellation. There were so many stars in the sky that it was difficult to find the Big Dipper! It was, however, not difficult at all to find the comet. Hyakutake and its tail were easily spotted as it was the next largest item in the sky besides the moon. The comet appeared brighter and the tail longer when we saw it from the corner of our eyes rather than from straight on. The main head of the comet was thumb size and the tail about six inches long. It was a spectacular sight to behold.

Here we were many miles from the HUBBLE project, on a ski vacation in the mountains and our thoughts turned to HUBBLE. We thought of ourselves here on Earth almost on top of a mountain looking at the comet and wondered what HUBBLE was seeing actually being up there amongst the stars itself.

Seeing this comet prompted many questions:
- Why were there so many more stars in the sky when we looked at the sky from the top of the mountain rather than from our home in Arnold, MD?
Why could we see the comet and its tail so easily?
How large is the comet?
How long is the comet's tail?
How often are comets like this discovered?

We are back at work now and looking forward to learning about what Hubble saw looking at Hyakutake and seeing the pictures that are sent back. But let me tell you about my job in the Systems Verification Group

The Systems Verification Group is on stand-by to run the Servicing Mission Ground Tests (SMGTs) as soon as the hardware is delivered and tested. We handle the work on these tests for Al Vernacchio who is the Servicing Mission System Engineer (SMSE) Manager for the Government. When a problem occurs during the test it is documented as a Test or Simulation Anomaly Report (TSAR).

Another SVG member, Francine Crum, has been working on creating a World Wide Web (WWW) Online TSAR creation and tracking system. A user that has discovered a problem during the test is able to enter the problem into this system. Al, the SMSE is able to assign it to a System Engineer to figure out why the problem occurred and determine what needs to be done to correct the problem.

At the present time I am working on diagramming the process flow for the WWW Online TSAR System. When software is designed, the different steps taken must be very detailed and explicit. The list of these steps and what must be done in each are called software "requirements".

To make the flowchart, I am using a program called MacDraw Pro to make diamonds (decision boxes) and rectangles (actions taken boxes) which are connected by arrows. The boxes are annotated with the YES/NO decisions being made and the actions being taken. It is a challenging task as you have to think very logically, step-by-step to make sure that the software system is designed to handle everything and once created actually does what it was designed to do.

Try your hand at making a flowchart. Make your flowchart illustrate the making and eating of an ice cream sundae. Use a rectangular box for an action taken and a diamond box for a decision box. For example, to get ready to make the sundae, you might use an action box to indicate opening the cupboard, finding a dish and spoon, and various other tasks that require taking an action. You might use a decision box to determine what flavor ice cream or syrup you want. For example, one decision box might read "Do you want Chocolate Ice Cream?" Draw an arrow from one point of the diamond and state YES; then draw an action box that lists the actions if chocolate is selected. Also draw an arrow with NO and list what would happen if chocolate wasn't selected.

The flow diagrams that I have produced will be reviewed by other people who will be using the system and the SVG person who is doing the system programming. Ask a friend of yours to review your Ice Cream Sundae Making flow diagram. Of course you could apply this to any task that might interest you. This is often done for a variety of tasks, like programming a computerized robot Just remember that the computer program must describe "EVERYTHING" that must be done. Your flow chart should reflect "EVERYTHING" as well.

In addition I am reviewing, editing and expanding on the User Guide that is being written to tell a new user how to use the TSAR system. Clarifying the requirements, creating flow diagrams, actually testing the software program (trying to break it) and writing the User Guide are what I do in my job working with the SVG group.

I think it is BIG time FUN.