Have you seen the moon tonight?
Q: It’s the future. All around the world, people are running outside to see if it’s true, and it is. The face of the full moon is now rotating slowly in the sky. In your cranial implant, a planetary scientist explains, “The _ _ _ _ _ lock between the moon and Earth was broken when a large _ _ _ _ _ _ _ _ flew by.” Fill in the blanks and explain.
Send a response of up to 250 words that someone in any field could understand to firstname.lastname@example.org by noon Eastern Sept. 14 for a chance to have it published in the next issue.
From the July/August issue: EXPLAINING SPIN
We asked you to explain spin stabilization for satellites compared to knuckleballs in baseball.
WINNER: A spin stabilized satellite acts like a gyroscope, and assuming it is balanced so it doesn’t wobble, it will point in a fixed direction throughout its orbit. Think of a toy gyroscope balanced on the tip of your finger. As you tilt your finger, the gyroscope remains pointing vertically. Spinning the satellite is simpler and less expensive than having multiple gyros to control its attitude about each of its three axes. The spinning satellite’s spin axis is determined by its axis of maximum moment of inertia. A baseball has a spherically uniform distribution of mass, so its moments of inertia are the same about each of its three axes — this means it has no preferred spin axis. The baseball’s surface is not perfectly smooth, and it will experience aerodynamic effects induced by however the ball is spun when pitched. These two factors will determine the ball’s attitude and trajectory.
Anthony Richards, AIAA senior member
Anthony retired in 2005 from TRW, where he was a mass properties engineer specializing in spin-stabilized spacecraft.
Barton Smith, who reviewed your answers, couldn’t resist adding a knuckleball explanation: “The interesting thing about a knuckleball is that you can throw them with no spin and they will gain spin in some random direction due to asymmetric shear on the surface of the ball, generated by seams. There are no aerodynamics in space.”