As pointed out in this answer, on page 4 of NASA Technical Note TND-1366 The Orbital Behavior of the Echo I Satellite and its Rocket Casing During the First 500 Days (June, 1962) says:
Echo I has an effective cross-sectional area of 7,854 square feet. The launch weight of 157 pounds decreased to 124 pounds with the loss of 33 pounds of benzoic acid and anthraquinone which were used to maintain inflation for the first few weeks in orbit. Thus, the initial ratio of the weight to mean drag area for Echo I was 0.020 pound per square foot and reduced to 0.016 pound per square foot after several weeks in orbit.
Echo-1 was about 100 feet in diameter, so that change in weight of 0.004 pound per square foot of drag area corresponds to the 35 pounds mentioned.
- What kind gas would have been produced by this mixture, and what fraction of the initial mass would have been converted to gas? Could it have been all of it as suggested? (the idea is that after the gas leaked out the balloon would have become rigid enough to retain its shape while in orbit.
- Why both benzoic acid and anthraquinone? Did they react? Did they sublimate only? Is there any chemistry-related reason why both substances were used?
below x2: cropped and full size from Echo, NASA's First Communications Satellite