A two-stage-to-orbit (TSTO) or two-stage rocket is a launch vehicle in which two distinct stages provide propulsion consecutively in order to achieve orbital velocity. It is intermediate between a three-stage-to-orbit launcher and a hypothetical single-stage-to-orbit (SSTO) launcher.
At liftoff the first stage is responsible for accelerating the vehicle. At some point the second stage detaches from the first stage and continues to orbit under its own power.
Falcon 9 is a partially reusable, two-stage-to-orbit, medium-lift launch vehicle designed and manufactured in the United States by SpaceX. The first Falcon 9 launch was on June 4, 2010, and the first commercial resupply mission to the International Space Station (ISS) launched on October 8, 2012. In 2020, it became the first commercial rocket to launch humans to orbit. The Falcon 9 has been noted for its reliability and high launch cadence, with 568 successful launches, two in-flight failures, one partial failure and one pre-flight destruction.
The rocket has two stages. The first (booster) stage carries the second stage and payload to a predetermined speed and altitude, after which the second stage accelerates the payload to its target orbit. The booster is capable of landing vertically to facilitate reuse. This feat was first achieved on flight 20 in December 2015. As of December 2, 2025, SpaceX has successfully landed Falcon 9 boosters 526 times. Individual boosters have flown as many as 31 flights. Both stages are powered by SpaceX Merlin engines, using cryogenic liquid oxygen and rocket-grade kerosene (RP-1) as propellants.
View the full Wikipedia page for Falcon 9The Falcon 9 v1.0 was the first member of the Falcon 9 launch vehicle family, designed and manufactured by SpaceX in Hawthorne, California. Development of the medium-lift launcher began in 2005, and it first flew on June 4, 2010. The Falcon 9 v1.0 then launched four Dragon cargo spacecraft: one on an orbital test flight, then one demonstration and two operational resupply missions to the International Space Station under a Commercial Resupply Services contract with NASA.
The two stage vehicle was powered by SpaceX's Merlin engines, burning liquid oxygen (LOX) and rocket-grade kerosene (RP-1). Had the F9 V1.0 been used for launching payloads other than the Dragon to orbit, it would have launched 10,450 kg (23,040 lb) to low Earth orbit (LEO) and 4,540 kg (10,000 lb) to geostationary transfer orbit (GTO).
View the full Wikipedia page for Falcon 9 v1.0