The perilous road to Mars

January 2019

I see from the latest issue of Aerospace America that VASIMIR, for Variable Specific Impulse Magnetoplasma Rocket, has risen again [“The perilous road to Mars,” November 2018]. It’s been around forever. Arc jets have flown, Hall thrusters have flown, and ion thrusters have flown. But VASIMIR has never flown, and it’s hard to believe it ever will. I think there should be more critical discussion of such issues in the magazine, and not just pie in the sky.

Thomas R. Brogan
AIAA associate fellow
Burlington, Vermont
tcon4@juno.com

Next-generation search and rescue

The article “Next-Generation Search and Rescue” [November 2018] asked: “Why not simply transmit your GPS coordinates to the rescuers?” Cospas-Sarsat does so. The Cospas-Sarsat system has accepted forwarded GPS position data from emergency beacons since 1997. All popular personal locator beacons now sold in the U.S. transmit the user’s GPS location. The Doppler processing detailed in the article provides a valuable layer of redundancy for situations where GPS service is questionable.

Richard A. Fowell
AIAA senior member
Los Angeles