It’s a matter of perspective

June 2021

Q: Three marine scientists and a former space flight controller board a boat before dawn off Florida’s east coast. “Whoa, look at that jellyfish!” the controller says. The marine scientists look down at the water, but the former controller points to the sky. The scientists are baffled and ask how there could be a jellyfish in the sky. What should the controller tell them?

Draft a response of no more than 250 words and email it by noon Eastern June 15 to aeropuzzler@aiaa.org for a chance to have it published in the July/August issue.

CROSSING THE INTERPLANETARY DIVIDE: We asked in the May issue whether it was true that travelers flying to Mars will pass a point after which they will no longer be in free fall toward Earth; they will be in free fall toward Mars. Astrophysicist and consultant Laura Forczyk reviewed your answers.

WINNER: For a spacecraft transiting from Earth to Mars, there are actually three major bodies that will influence the trajectory. For about the first 600,000 miles, Earth’s gravity dominates; and the last 300,000 miles of the trip are governed by Mars’s gravitational influence. However, the bulk of the journey takes place outside of those zones. During that intermediate part of the journey, the spacecraft is not “falling” toward either Earth or Mars — its trajectory is governed primarily by the sun! Gravitational force is governed by central body mass and distance from the central body; a “sphere of influence” calculation shows the distance where the planet’s gravity has diminished to the point where the sun’s gravity begins to take over.

Wes Dafler, an AIAA senior member, works on U.S. Navy projects as an air vehicle lead flight test engineer for Boeing Test and Evaluation.
Patuxent River, Maryland
wes.dafler@boeing.com