Its maiden flight carried out a demonstration mission with the CASSIOPE satellite on 29 September 2013, the sixth overall launch of any Falcon 9.

[11] Beginning in April 2014, the Dragon capsules were propelled by Falcon 9 v1.1 to deliver cargo to the International Space Station under the Commercial Resupply Services contract with NASA.

[12] This version was also intended to ferry astronauts to the ISS under a NASA Commercial Crew Development contract signed in September 2014.

Falcon 9 v1.1 was notable for pioneering the development of reusable rockets, whereby SpaceX gradually refined technologies for first-stage boostback, atmospheric re-entry, controlled descent and eventual propulsive landing.

[15] It includes realigned first-stage engines[16] and 60 percent longer fuel tanks, making it more susceptible to bending during flight.

[1] The stage separation system was redesigned and reduced the number of attachment points from twelve to three,[15] and the vehicle had upgraded avionics and software as well.

[18] As part of SpaceX's efforts to develop a reusable launch system, selected first stages include four extensible landing legs[19] and grid fins to control descent.

[28] Grid fins were implemented on the Falcon 9 v1.1 on the CRS-5 mission,[29] but ran out of hydraulic fluid before a planned landing.

[33][34] The main propellant supply tubes from the RP-1 and liquid oxygen tanks to the nine engines on the first stage are 10 cm (4 in) in diameter.

[36] The interstage, which connects the upper and lower stage for Falcon 9, is a carbon fiber aluminum core composite structure.

[39] SpaceX uses an all-friction stir welded tank, a technique which minimizes manufacturing defects and reduces cost, according to a NASA spokesperson.

[41] Testing of the new fairing design was completed at NASA's Plum Brook Station facility in spring 2013 where acoustic shock, mechanical vibration, and electromagnetic electrostatic discharge conditions were simulated.

NASA concluded that the most probable cause of the strut failure was a design error: instead of using a stainless-steel eye bolt made of aerospace-grade material, SpaceX chose an industrial-grade material without adequate screening and testing and overlooked the recommended safety margin.

[54] The Falcon 9 v1.1 includes several aspects of reusable launch vehicle technology included in its design, as of the initial v1.1 launch in September 2013 (throttleable and restartable engines on the first stage, a first-stage tank design that can structurally accommodate the future addition of landing legs, etc.).

[45] In March 2014, SpaceX announced that GTO payload of the future reusable Falcon 9 (F9-R), with only the booster reused, would be approximately 3,500 kg (7,700 lb).

[58] Several missions of Falcon 9 v1.1 were followed by post-mission test flights calling for the first-stage booster to execute a flip around maneuver, a boostback burn to reduce the rocket's horizontal velocity, a re-entry burn to mitigate atmospheric damage at hypersonic speed, a controlled atmospheric descent with autonomous guidance to the target and finally a landing burn to cut vertical velocity to zero just before reaching the ocean or landing pad.

[10] The next test, using the first stage from SpaceX CRS-3, led to a successful soft landing in the ocean, however the booster presumably broke up in heavy seas before it could be recovered.

[60] The first stage of the CRS-6 mission managed a soft landing on the platform; however, excess lateral velocity caused it to quickly tip over and explode.

[61] SpaceX CEO Elon Musk indicated that a throttle valve for the engine was stuck and did not respond quickly enough to achieve a smooth landing.

[63] NASA resupply missions to the ISS—which include the provision of the space capsule payload, a new Dragon cargo spacecraft for each flight—had an average price of $133 million.

The contract was for a specific amount of cargo carried to, and returned from, the Space Station over a fixed number of flights.