Launching a payload and recovering the first stage
Falcon 9 uses two stages. The first provides initial acceleration; after separation, the second continues delivering satellites to orbit. Rather than discarding the spent first stage, SpaceX developed return and landing procedures for it.
The ORBCOMM-2 mission delivered communications satellites to low Earth orbit and tested first-stage landing. After staging, ascent and return proceeded separately.
Bringing a descending booster to an upright landing
After separation, engine burns changed the first stage’s trajectory toward a Florida landing zone. Controls adjusted attitude and velocity during descent, followed by a final braking burn and touchdown on landing legs.
High-speed flight, re-entry and terminal landing formed one sequence. Onboard systems controlled the engines against changing altitude and speed to arrive in a suitable landing attitude.
December 21 locally, December 22 in UTC
The launch and landing occurred on the evening of December 21, 2015, in Florida, already December 22 in UTC. The first stage landed upright at Cape Canaveral’s land-based zone, while the satellite-delivery mission also succeeded.
This was Falcon 9’s first successful first-stage landing on land after an orbital launch. The two dates describe the same flight in different time zones.
Recovery preserves the flown hardware
A recovered stage can be returned for inspection of engines, structure and thermal protection. Engineers can compare flight data with physical wear, gaining both hardware and post-flight evidence.
Reuse also requires inspection, maintenance and another flight. The 2015 landing accomplished recovery and supplied experience for later repeated use, extending a launch vehicle’s operations into return and ground handling.