July 21, 2009
If you have contacted me about the files, they will be ready for delivery this week. I am working out the last few kinks in the programming. When you receive the email, there will be several files attached. One will be a PDF document with instructions, but I am reproducing it below in case you can’t open that file. The other files will the program code. The file your child worked on is titled MoonTAG_Complete.py.
To run the program, complete the following steps:
- Visit http://www.vpython.org/contents/download_windows.html and download the following files: Python-2.6.2.msi and VPython-Win-Py2.6-5.11.exe to your hard drive.
- Double click on the file python-2.6.2.msi to install the Python interpreter. This file must be installed first.
- Double click on the file VPython-Win-Py2.6-5.11.exe to install the Visual libraries (required to run the animation).
- Create a folder on your desktop called MoonTAG. Copy the python files into that folder. There are six files: MoonTAG_Complete.py, Planet.py, SpaceShip.py, System.py, TimePiece.py, WindowEnvironment.py.
- Find the desktop icon VIDLE for Python 2.6 and double click to open it.
- In VIDLE, click on the “File . . . Open,” then navigate to the MoonTAG folder. Open the file MoonTAG_Complete.py. You will see the computer code for the program in the window.
- On the top menu bar, select “Run . . . Run Module,” or you can hit the F5 key. This will execute the program. (The first time you run the program, it will take a few minutes to run.)
Your child’s web page can be viewed at this address:
Replace ## with your child’s two-digit number. (Written down during class.) To log in and edit the page, use the following log in information:
- Username: MoonTAG0##
- Password: moontag0##
Both are case-sensitive. Replace ## with your child’s two-digit number.
Please contact me with any questions. I can provide any amount of help with the Python program. For help with the web page, you should contact Webs.com technical support.
My email address is dunningrb [at] longwood [dot] edu.
July 17, 2009
Yesterday was the 40th anniversay of the Apollo 11 liftoff. Monday (July 20) will be the 40th anniversary of Armstrong’s first step onto the lunar surface.
In the last class meetings students worked on a web page where they described what they learned in the TAG class. They also did a little Internet research to discover important facts about Apollo 11 and the Moon. Additionally, the learned how to add pictures, videos (YouTube), and simple games to their websites.
I had originally planned to distribute the final version of the computer program on CD, but burning 80 copies of the master CD would take about 16 hours. Right now I plan to distribute the student’s code through email to the parents. A separate post will describe how to install and run the program.
July 14, 2009
In all the classes the students have successfully landed a rocket on the Moon!
The procedure involved the following steps:
- Launch the rocket using the stage 1 engines.
- Move the rocket into a circular orbit about the Earth using the stage 2 engines and a brief burn from the stage 3 engines. The students had to figure out the correct amount of time to burn the stage 3 engines to achieve a nearly circular orbit where the rocket’s altitude stayed between 100 and 199 miles.
- After one and a half orbits, fire the stage 3 engines (exhausting the remaining fuel) to leave Earth orbit and travel to the Moon. Students had to determine the correct time to launch the rocket to ensure it rendezvoused with the Moon.
In the fourth period class, students began work on a web page that will summarize some of the exicting things they’ve learned in the course. Students in the other periods will start work on their web pages Wednesday and Thursday.
Students also attempted to execute a brief engine burn in lunar orbit in order to achieve a free return trajectory. This has proved challenging, and we’re still working on it!
July 8, 2009
In today’s class the students received their first exposure to the Python programming language. We started by creating a simple program that displayed statements to the screen, such as “My name is Johnny. I have two cats.” This made sure the computers were working correctly and that students could save their files in a home directory which they access for later classes.
Next, we ran our first visual program that created a model of the Earth with the Rocket sitting on the equator. (Pictures coming in future posts.) The students also learned how to manipulate the display using the mouse to zoom in and out, and rotate the point of view.
In most of the classes we also started work on the code that will make the Earth rotate on its axis. Everyone will be caught up with this by tomorrow, and also in tomorrow’s classes we’ll add the Moon and watch it orbit the Earth.
I’ll provide more details about the Python programming language and the VPython visual libraries (used to create the 3-D animations) in future posts. We’re on our way to the Moon!
July 7, 2009
In today’s class we learned about the physics of rocket flight by watching a 30 minute video that explained how the Space Shuttle and Saturn V rockets worked. The students made notes in an Astronaut’s Log Book about any interesting facts they saw during the videos, and any questions they had about what they saw. At four points during the movie we stopped the video to give students a chance to share what they observed and ask questions. Students noted the following interesting things about the space shuttle:
- The space shuttle uses five engines to lift off. Three are attached to the shuttle itself, and fed by a huge external fuel tank attached to the shuttle’s belly. After the shuttle reaches space, the external tank is cut loose and crashes into the Indian Ocean. The other two engines are attached to the booster rockets that appear on either side of the main fuel tank. (See the picture below.) The booster rocket tanks use parachutes to fall back to the ocean, where they are recovered and used again.
- Most of the shuttle’s mass at the time of launch is the fuel needed to propel it into space.
- The main fuel tank is filled with liquid oxygen and liquid hydrogen. When they react, they produce water vapor. The booster rockets use a solid fuel.
- Once the booster rocket engines are started, they cannot be stopped.
- The shuttle does not take off going straight up. It moves away from the Earth in a curved path as it establishes a circular orbit about the Earth.
- The shuttle launches from Florida toward the East to take advantage of the Earth’s rotational velocity, since Florida is close to the equator. The European Space Agency launches from South America, at a location that is even closer to the Earth’s equator.
- The shuttle’s three main engines are pivoted to direct the rocket thrust in just the right direction at take off.
- A few seconds before take-off, over 300,000 gallons of water are released onto the launch pad to suppress the noise created by the engines. Otherwise, the sound energy would reflect off the ground and damage the shuttle.
- A few minutes after take off the shuttle breaks through the sound barrier. It has to slow down a bit when doing this to reduce the stress on the ship.
- The booster rockets are cut loose a few minutes after take off. Later, the main fuel tank is also cut loose.
- It takes only 90 minutes for the shuttle to orbit the Earth, at an altitude of 400 km.
The students asked many interesting questions:
- Where do they keep the food for the astronauts? (Answer: I don’t know its exact location–but shuttle missions last too long to send the astronauts up without food and water, so it’s kept somewhere!)
- Why don’t the booster rockets and main fuel tank “float” in space like the shuttle? I.e., why don’t they orbit the Earth? (Answer:The booster rockets are cut loose while still in the Earth’s atmosphere, so air resistance slows them down and parachutes are used to provide a soft landing in the ocean. The main fuel tank has a small valve near the top that releases pressurized gas when it’s cut loose, causing it to tumble back toward the Earth—otherwise it will skip off the atmosphere and become a very large and dangerous obstacle in space!)
- Why doesn’t the shuttle use jet engines? The student pointed out that jet engines are easier to build. (Answer: At high altitudes, the decreasing air pressure and temperature will result in decreasing thrust from a jet engine. In space, a jet engine wouldn’t work at all.)
The last part of the video discussed the enourmous Saturn V rocket, which generated a massive amount of thrust to lift the Apollo astronauts into space on the way to the Moon. We learned about the three stages of the Saturn rocket, and how the astronauts orbited the Earth 1.5 times before the final engine burn produced the necessary velocity (about 11,000 m/s) needed to send the astronauts toward the Moon. The journey to the Moon requires four days. Nearly 98% of the Saturn V mass consists of fuel!
In the final minutes of the class, students learned about the general trajectory of the Apollo rocket toward the Moon. We learned that since the Moon is orbiting the Earth, the rocket cannot be launched directly toward the Moon. Sending the rocket to the Moon is kind of like playing catch with someone who is running while you are throwing the ball to them.
Tomorrow: We begin work on our computer programs.
July 7, 2009
In today’s class we launched an air-powered rocket using a bicycle pump to create air pressure in the launch cylinder of the rocket. The students used a stop watch to measure the rocket’s total flight time, from which they were able to calculate the rocket’s initial velocity and maximum height. We ignored air resistance in making these calculations. We repeated the experiment several times by varying the amount of air pressure in the launch cylinder. This gave different values for the initial velocity and maximum height of the rocket. Students learned that the greater the initial velocity leaving the launch pad, the greater the maximum height achieved by the rocket.
The formula for the rocket’s initial velocity is:
(initial velocity) = (1/2) * (acceleration due to gravity) * (total flight time)
At the Earth’s surface, the acceleration due to gravity is 9.8 m/s2. The longest recorded total flight time was 5.8 seconds, yielding an initial velocity of 28.4 m/s.
The rocket’s maximum height is given by
(maximum height) = (1/4) * (initial velocity) * (total flight time).
With a total flight time of 5.8 seconds and initial velocity of 28.4 m/s, the rocket’s maximum height was 41.2 meters.
After completing the calculations, we talked about the initial velocity necessary to escape the Earth’s gravitational pull: 11,000 m/s. We also talked about why real rocket’s do not leave the launch pad with such an enourmous velocity. The huge acceleration would be fatal to the astronauts!
Physics majors: You can derive the equations we used by starting with the kinematic equations, remembering that the rocket’s speed is zero at its maximum height. Remember also that we used the total flight time, since that was what we measured using the stop watches. The way the kinematic equations are ordinarily set up for max height calculations, t represents the time needed to reach maximum height (or to fall from maximum height), which is half of the total flight time.
June 22, 2009
The Lunar Reconnaissance Orbiter blasted off from Florida last week. Follow this link for the story.
The orbiter will send back all kinds of data, from day-night temperature maps to color imaging and UV reflection, NASA said. There is particular emphasis on areas of the moon that may have continuous access to sunlight and where water may exist.
Because building a lunar outpost implies extended periods on the moon’s surface, NASA is hoping the orbiter can help it identify safe landing sites and moon resources, and how the lunar radiation environment would affect humans.
The orbiter’s trip to the moon will take about four days. It will then spend at least a year in a low polar orbit around the moon, eventually orbiting about 50 kilometers (31 miles) above its surface, NASA said.
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