| MadSci Network: Astronomy |
Greetings:
The reentry phase of a space shuttle flight occurs at an altitude of 75 miles with the orbiter traveling at 5,063 miles per hour. During the reentry to the earth's atmosphere the shuttle must dissipate the tremendous amount of energy that the orbiter possesses when it enters the atmosphere so that it does not burn up (entry angle too steep) or skip out of the atmosphere (entry angle too shallow). The orbiter must also stay within structural limits so that the wings or tail do not break off. This is accomplished by using several sideways turns shaped like the letter S so the orbiter slows down but does not drop altitude too fast..
At approximately 50 miles the spacecraft enters a communications blackout. The blackout lasts until the orbiter reaches an altitude of approximately 30 miles. Between these altitudes, heat is generated from friction with the air as the spacecraft moves 5 times faster than a bullet. Ionizing atoms of air form a layer of ionized gas particles around the spacecraft. Radio signals between the spacecraft and the ground cannot penetrate this sheath of ionized particles, and radio communications with the earth are blocked for approximately 16 minutes.
Thermal protection tiles on the bottom of orbiter's outer skin protect the orbiter from temperatures that range from minus 250 F (-85 C) in the cold of space to entry temperatures that reach nearly 3,000 F (~1650 C).
When objects are heated to high temperatures they emit visible light; they glow.. The color of the light tells us how hot the object is. Often people will say something is RED HOT. The filaments of light bulbs are WHITE HOT (about 6,000 degrees F; 3,315 C) and other very hot objects are BLUE HOT (about 10,000 degrees F; 5,500 C). The red color of the space shuttle as it reenters the earth's atmosphere tells us that it is RED HOT .at a temperature of about 3,000 degrees F. If it got white hot the orbiter would burn up. You can see a picture of the red hot orbiter and many pages of information and pictures about it at the following Web site:
http://shuttle.nasa.gov/sts-82/landing/
If you have a lamp dimmer in your home you can conduct the following experiment. Put a clear light bulb in the lamp and turn the voltage (dimmer knob) up until the fillament in the bulb almost glows . You will feel the bulb heat up but you can't see the glow because it gives off -- infrared (heat) waves which human eyes cannot see. (Incidentlaly, the next shuttle mission is putting infrared cameras in the Hubble Space Telescope.)
Next, slowly turn up the voltage and the bulb will glow red hot. Now you know that the bulb fillament is about 3000 degrees F (1650 C).
DO NOT TOUCH THE BULB FOR AT THESE TEMPERATURES IT WILL BURN YOU.
When you turn the voltage all the way up the bulb will be WHITE HOT (about 6000 degrees F; 3,315 C). The bulb is designed so that it cannot be turned up to BLUE HOT for the parts would be so hot they would melt.
On a clear night you can see RED HOT, WHITE HOT and BLUE HOT stars in the sky. Now you know the temperatures of the surface of these stars! Measuring the temperatures of hot objects by the color of their glow is called OPTICAL PYROMETRY.
Regards, Your Mad Scientist
Adrian Popa
Try the links in the MadSci Library for more information on Astronomy.