I design machines. I sketch their shapes and calculate their strength, specify their construction, and listen to their heartbeats to make sure they've been assembled correctly. The little critters can go anywhere - hard vacuum, cryogenic temperatures, interplanetary deserts bombarded by deadly cosmic rays, or even to the bottom of the sea. I like the challenge and the chance to accomplish something human hands can't do alone.

Right now I'm nearly finished with a deployment mechanism to lower the next Mars Rover - a robotic vehicle as large as some cars - on ropes underneath a descending rocket stage that will set it down on Mars like a helicopter delivering cargo. Aerospace-grade lowering devices have been around for decades and NASA has flown three to Mars already, but this latest project calls for something above and beyond the heritage hardware. For more than three years I've been a historian and detective, sorting data and developing scripts to simulate various systems and explore their behaviors. I've optimized a design, built CAD models, made engineering drawings and assembly instructions, and given the cold hard steel and titanium parts a life-giving coat of grease. They didn't even blink at 65C below zero! Comforting results.. because the life of a billion-plus dollar space vehicle will hang from three slim cords strung around my creation.

I was hired at JPL in 2001 from Rensselaer Polytechnic Institute, where I was studying mechanical engineering. Within weeks I'd left behind the frozen confines of my upstate New York college town and settled in a paradise of palm trees where street names were straight out of song lyrics. In short order I was working in the California desert where fighter jets roared overhead and dropped bombs on distant hillsides while my colleagues prepared to load a rocket motor onto an instrumented sled and shoot it down a four-mile-long track built in the 1950s to test missile guidance systems at supersonic speeds. This was to try out a new radar system to be used for landing on Mars. I worked on the 2003 Mars Exploration Rover mission, developing a prototype rock abrasion tool and helping with shock mitigation for an antenna release device and with tests of the descent rockets. I also built an environmental enclosure with thermoelectric cooling and control circuitry for a helicopter test platform that proved the image processing algorithms used to generate firing commands for lateral stabilizing rockets in the last moments of descent to Mars.

I put a microwave spectrometer in an ER-2 aircraft, a U2 spy plane outfitted to fly civilian research missions 70,000 feet in the sky. This instrument studied atmospheric composition over hurricanes and rainforests. For another task, I designed a radar antenna structure and installed it on a Twin Otter aircraft. Over the Gulf of Mexico, I flew in NASA's KC-135 Low Gravity Lab airplane with an experiment that tested a sample collection system for asteroids and comets. Imagine being chest deep in water but without the resistance of liquid, almost floating - that's what lunar gravity feels like. Martian gravity is more like being a helium balloon skittering along the ceiling, except inverted. And in zero-g, the sand in our test chamber swooped around like a cloud of tiny insects until gravity returned to send the grains crashing down like ocean surf.

I designed parts of an earth orbiting x-ray telescope and lander concepts for the planet Venus. For the new Mars Rover mission I established the fundamental designs of the vehicle chassis, robotic sampling arm, and mass balancing system. I've written both proposals and requests for proposal, been involved with subcontracts and large procurements, prepared design reviews and test plans, and brought three separate tasks from concept to flying hardware. Working on these projects in the company of fantastic engineers has been a superb learning experience.

• Gradziel, Holgerson. "Mechanisms for Lowering Tethered Payloads: Lessons Learned from the Mars Exploration Program." Proceedings of IEEE Aerospace Conference, 2-8 March 2008, Big Sky, MT.;
• Hoffman, Rivillini, Slimko, Dahya, Agajanian, Knight, Sengupta, Thoma, Webster, Gallon, Gradziel. "Preliminary Design of the Cruise, Entry, Descent, and Landing Mechanical Subsystem for MSL." Proceedings of IEEE Aerospace Conference, 3-10 March 2007, Big Sky, MT. Pg. 1-18;
• Askins, Bao, Bar-Cohen, Chang, Dolgin, Gradziel, Peterson, Sherrit. "Folded Resonant Horns for Power Ultrasonic Applications." NPO-30489. NASA Tech Brief Vol. 27, No. 4, 04 Apr. 2003. US Patent App. #10/612,200;
• Sherrit, Askins, Gradziel, Dolgin, Bao, Chang, Bar-Cohen. "Novel Horn Designs for Ultrasonic/Sonic Cleaning, Welding, Soldering, Cutting, and Drilling." SPIE Vol. 4701, p. 353-360, Smart Structures and Materials. 2002;

Here are pictures of some of my less-technical projects: