|
Temperature SystemHow is DS1's heat balance maintained? |
During almost all of the mission, internal electrical power generation and direct solar energy (radiation from the Sun) are the only heat sources. The solar panels on DS1 are 22% efficient, which means that 22% of the sunlight that comes into them is made into electricity. The rest of the solar energy turns into heat. Heat also comes from the current traveling through the wires in the electrical system.
The ion engine is a significant source of heat, getting to temperatures as high as 300 degrees C during peak thrusting, but almost no heat from the ion thruster dissipates back through the spacecraft. There is an 18 inch separation between the back of the thruster and the rest of the spacecraft, and the spacecraft side of the thruster is blanketed with insulation. Since heat radiates in the direction of the greatest difference in temperatures, and space is hundreds of degrees C colder than the spacecraft, the heat radiates almost completely into cold space, rather than back through the spacecraft.
Very early in the mission, heat is absorbed from the Earth, but this is an insignificant heat source by the time that the prime portion of the mission starts and the ion thruster is turned on. During the launch and ascent portion of the mission, heat is also absorbed from the launch vehicle, from aerodynamic heating (frictional heating), and from solar energy reflected from the atmosphere (albedo heating). But these heat sources are only significant for the first hours of the mission.
In addition, DS1 has active heaters; some work automatically, using sensors to detect when the heaters should be turned on or off. Other heaters are controlled by command. For example, some of the subsystems produce heat when on. Heaters can be turned on to replace the heat those subsystems produce if the subsystems are off.
What could go wrong on DS1 if it gets too cold?
What components are where on DS1?
