Editing Project Echo (section)

=== Echo 2 ===
Echo 2 was a {{cvt|41.1|m}}-diameter balloon satellite, the last launched by Project Echo. A revised inflation system was used for the balloon, to improve its smoothness and [[sphericity]]. Echo 2's skin was rigidizable, unlike that of Echo 1. Therefore, the balloon was capable of maintaining its shape without a constant internal pressure; a long-term supply of inflation gas was not needed, and it could easily survive strikes from [[micrometeoroids]]. The balloon was constructed from a {{cvt|9|µm}}-thick mylar film sandwiched between and bonded with two layers of {{cvt|4.5|µm}}-thick aluminum foil.<ref>Staugaitis, C. & Kobren, L. "''Mechanical And Physical Properties of the Echo II Metal-Polymer Laminate (NASA TN D-3409)''", NASA Goddard Space Flight Center (1966) {{PD-notice}}</ref> It was inflated to a pressure that caused the metal layers of the laminate to plastically deform slightly, while the polymer was still in the elastic range. This resulted in a rigid and very smooth spherical shell. A beacon telemetry system provided a tracking signal, monitored spacecraft skin temperature between {{cvt|-120|and|+16|C|F}}, and measured the internal pressure of the spacecraft between 0.00005 mm of [[Mercury (element)|mercury]] and 0.5 mm of mercury, especially during the initial inflation stages. The system consisted of two beacon assemblies powered by solar cell panels and had a minimum power output of 45 [[Watt|mW]] at 136.02 MHz and 136.17 MHz.<ref>{{cite web|title=Echo 2|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1964-004A|publisher=NASA|access-date=2019-01-30}} {{PD-notice}}</ref>