After "crunching the numbers," Zenefits CEO and founder Parker Conrad told us:
A two-stage Falcon 9 rocket rises from its launchpad, and at an altitude of fifty miles the first-stage booster separates. The payload continues into space, riding on the second stage. The first stage coasts to about a hundred miles in altitude, then begins to descend.
Three of nine engines from the first stage reignite. The rocket has its own guidance- control system, which gimbals (orients) the Merlin 1D engines to rotate the rocket between 120 and 180 degrees. This aims the rocket toward the drone ship. The booster is traveling at nearly 3,000 miles per hour.
The center engine ignites to slow the descent and gimbals itself to help the booster become fully vertical. Four grid fins extend to stabilize and further brake the cylinder. Each moves independently to control roll, pitch, and yaw. The rocket's speed drops from 3,000 miles per hour to about 560.
The engines initiate a final burn to slow the craft to about five miles per hour. Four carbon-fiber-and- aluminum-honeycomb landing legs unfold, powered by compressed helium.
The booster lands on the floating pad. Technicians on a vessel positioned miles away head over to board the drone ship and secure the rocket to the deck with metal shoes and vent any leftover gases. The drone ship ferries the first stage to shore, where it can be processed, cleaned, and reused. Flight length: about nine minutes. ￼
The drone ship is equipped with a dynamic positioning system that uses azimuth- thruster engines to keep it at a specific GPS point hundreds of miles (in the case of the January test, about 200 miles) away from the launchpad, give or take ten feet. ￼