Falcon 1 was a two-stage small-lift launch vehicle that was operated from 2006 to 2009[5] by SpaceX, an American aerospace manufacturer.

On 28 September 2008, Falcon 1 became the first privately developed fully liquid-fueled launch vehicle to successfully reach orbit.

But the Air Force did not want the launch of an untested rocket to occur until the final Titan IV flew from nearby SLC 4E.

The Falcon 1 first stage was powered by a single pump-fed Merlin 1C engine burning RP-1 and liquid oxygen providing 410 kilonewtons (92,000 lbf) of sea-level thrust and a specific impulse of 245 s (vacuum Isp 290 s).

[22] The second stage was powered by a pressure-fed Kestrel engine with 31 kilonewtons (7,000 lbf) of vacuum thrust and a vacuum specific impulse of 330 s.[20] The first stage was originally planned to return by parachute to a water landing and be recovered for reuse, but this capability was never demonstrated.

[23][24] At launch, the first stage engine (Merlin) is ignited and throttled to full power while the launcher is restrained and all systems are verified by the flight computer.

[citation needed] The second stage Kestrel engine burns for about six minutes, inserting the payload into a low Earth orbit.

Later, the Falcon 1e was to provide approximately 1,000 kg (2,200 lb) for $11 million, but the company withdrew the vehicle from the market, citing limited demand.

The DARPA payload was the United States Air Force Academy's FalconSAT–2, which would have measured space plasma phenomena.

The vehicle had a noticeable rolling motion after liftoff, as shown on the launch video, rocking back and forth a bit, and then at T+26 seconds rapidly pitched over.

The FalconSAT–2 payload separated from the booster and landed on the island, with damage reports varying from slight to significant.

A later review by DARPA found that the nut was properly tightened, since its locking wire was still in place, but had failed because of corrosion from saltwater spray.

SpaceX implemented numerous changes to the rocket design and software to prevent this type of failure from recurring, including stainless steel to replace aluminum hardware and pre-liftoff computer checks that increased by a factor of thirty.

In December the launch was rescheduled for 9 March, but delayed because of range availability issues caused by a Minuteman III test flight, which would re-enter over Kwajalein.

The launch attempt on 19 March was delayed 45 minutes from 23:00 GMT because of a data-relay issue, and then scrubbed 1 minute 2 seconds before launch at 23:45 because of a computer issue, whereby the safety computer incorrectly detected a transmission failure caused by a hardware delay of a few milliseconds in the process.

20 March attempt was delayed 65 minutes from an originally planned time of 23:00 because of a problem with communications between one of the NASA experiments in the payload and the TDRS system.

The rocket successfully left the launch pad at 01:10 GMT on 21 March 2007 with a DemoSat payload for DARPA and NASA.

This oscillation would normally have been dampened by the Thrust Vector Control system in the second stage, but the bump to the second-stage nozzle during separation caused an overcompensation in the correction.

[52] The rocket continued to within one minute of its expected duration and also managed to deploy the satellite mass-simulator ring.

[40] The SpaceX team planned both a diagnosis and solution vetted by third-party experts, believing that the slosh issue could be corrected by adding baffles to the second-stage LOX tank and adjusting the control logic.

The SpaceX team wished to work on the problem to avoid a recurrence as they changed over into the operational phase for Falcon 1.

[55] This flight carried the Trailblazer (Jumpstart-1) satellite for the US Air Force,[56] the NanoSail-D and PREsat nanosatellites for NASA and a space burial payload for Celestis.

Still within the specified window, the launch attempt was recycled, but aborted half a second before lift-off because of a sensor misreading.

Musk further explained the situation to Ars Technica journalist Eric Berger:[62] At the time I had to allocate a lot of capital to Tesla and SolarCity, so I was out of money.

Following the three prior failures, the SpaceX team assembled the fourth rocket using available parts in six weeks as a last chance for the company.

[63] Despite the challenges, the fourth flight of the Falcon 1 rocket successfully flew on 28 September 2008, delivering a 165-kilogram (363-pound) non-functional boilerplate spacecraft into low Earth orbit.

The rocket followed the same trajectory as the previous flight, which failed to place the Trailblazer, NanoSail-D, PRESat and Celestis Explorers spacecraft into orbit.

No major changes were made to the rocket, other than increasing the time between first-stage burnout and second-stage separation.

This minor change addressed the failure seen on the previous flight, recontact between the first and second stages, by dissipating residual thrust in the first-stage engine before separating them.

[76] Following the fifth flight, future launches of Falcon-1 were postponed, and eventually cancelled, and the vehicle decommissioned from service,[77] with SpaceX stating "We could not make Falcon 1 work as a business.