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Download and ShareSome satellites orbiting the Earth peer outward into space, observing the Sun, planets, our galaxy, even distant galaxies and beyond. Some satellites, on the other hand, peer back down toward Earth. NASA’s Glory satellite was designed to orbit the Earth tracking the distribution of aerosols in the atmosphere and also measuring total solar irradiance.
Aerosols are tiny particles like dust, mist, or fumes that are suspended in air. In the atmosphere, aerosols affect how rain forms inside clouds, and they also affect how much sunlight gets reflected back into space. By tracking and measuring the distribution of atmospheric aerosols, Glory’s instruments would support and inform global climate models. Glory’s second goal - measuring solar irradiance – would help determine the Sun’s effects on Earth’s climate.
Glory’s orbital path crosses the poles in what’s called a polar orbit. Glory’s is a special class of polar orbit – a sun-synchronous orbit - that lets the satellite pass over the same part of the Earth at the same local time every day. This type of orbit allows scientists to collect and compare precisely-timed data.
Glory contains sensitive scientific instruments, but it’s also an engineering feat designed to withstand not only the strong vibrations of launch but also the extreme temperature changes it experiences in space. In its orbit, Glory cycles through day and night in very short cycles, every 100 minutes. That means Glory experiences huge temperature changes (about +/- 100 degrees C) over short periods of time. Since temperature changes affect material properties, Glory’s testing process was designed to replicate the conditions Glory would confront in space.
As heat is added to a system or absorbed by materials, the molecules that make up the material move and vibrate faster and with more energy. Thermal energy – heat – causes most materials to expand. For a satellite cycling through extreme temperatures, such fluctuations could be problematic, but NASA engineers designed Glory to maintain its structure and stability as it orbits. One way engineers can stabilize a material against thermal expansion is to make it harder and denser. With more molecules packed together more closely, a material is less likely to respond negatively to thermal fluctuations. But for objects launched into space, scientists try to minimize size, weight, and volume. So, NASA engineers had to work out creative ways to produce Glory so it’s as light and compact as possible, as strong as possible, and would withstand thermal expansion and contraction. The core of Glory is an aluminum chassis, with the whole system – including its two sensors – about the size of an oil drum. NASA engineers built on prior experience and knowledge to produce a compact, efficient satellite that can withstand the vibrations and thermal effects of launch and orbit.
Before Viewing
While Viewing
After Viewing
Classroom Activity: Thermometer-meter
The expansion and contraction of the liquid inside a thermometer demonstrates thermal expansion. Thermometers are designed to take advantage of this fact! In this exercises, students focus on the thermometer itself.
Materials
For each student or group of students: two thermometer (designed so the liquid expansion / contraction is obvious), two beakers, ice water, warm water
Students set up the two beakers, one with ice water and the other with warm water. They put a thermometer into each one and observe and track the movement of the liquid inside each thermometer. When the temperatures have stabilized, students switch the two thermometers and observe the reaction of each.
Discussion Questions
Additional Activity Follow-up
Add another container of water – this one at room temperature. Students put one hand in the warm water and the other in the cold water. After they adjust to the two, students put both hands into the room temperature container. The two hands will experience the water differently based on the temperature of the previous container.
Questions: What does each hand experience? Why do you think there’s a difference? Which one is “correct?” How does this demonstration make the case for using instruments like thermometers?
John Satrom: The environment of space is very harsh on any hardware we put up, whether it be satellites or rockets or the space shuttle, and I think it’s one of the things that the average person doesn’t really appreciate.
The Glory mission is going to fly in what’s known as a low Earth polar orbit. It will fly around the poles of the Earth. We’re in a particular orbit called a Sun synchronous orbit such that when we come over the equator, at every pass, the Sun is in the same relative position. When you think about that, on every orbit we’re going from Sun into darkness and Sun into darkness, and so the spacecraft can cycle through temperature extremes of 100° centigrade from high to low. And so you just think about going from the hottest place in the summer to the coldest place in the winter every 45 minutes. That extreme thermal cycling is very tough on the spacecraft.
So what we do on the ground is we try and expose the spacecraft to the environment that it will see in space as much as we can before launch, to try and work out all those kinks.
Starting at the component level, we do vibration and thermal testing, and then up to the instrument levels, with the APS and TIM instruments, they’ll go through a full environmental test program. And then once we put the whole thing together, we expose the spacecraft with the instruments to a series of vibration tests, and then we put it in a vacuum chamber and pump out all the air to simulate the vacuum of space. And we’ll cycle it through those temperature extremes, and again, try and replicate all those environments it will see out in space before we launch it to make sure we’re worked out all the kinks.
The thermal cycling, and the vibration of being launched on a rocket, all those things are very harsh on the spacecraft, and if you don’t check them out in advance, there’s a good possibility you could induce failures. And if you induce failures on the way up, you know, there’s no way to go grab the spacecraft and bring it back down and fix it, so you’ve lost the mission if you’ve done that.
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