Falcon 9’s Merlin engines fire – launch date slipping
The next key milestone ahead of the historical SpaceX mission to the International Space Station (ISS) took place on Monday, as the integrated Falcon 9 and Dragon spacecraft underwent their full dress rehearsal for what was a May 7 launch – a date that is now slipping. Known as the Static Fire test, all nine of Falcon 9’s engines were fired at full power for two seconds, at the second attempt, following an earlier abort.
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The dress rehearsal firing of the Falcon 9 family of nine Merlin engines took place on the pad at Space Launch Complex 40 (SLC 40), with only the hold-down system restraining the rocket from flight.
The test, involving a full countdown and tanking of both the first and second stages, provided the exact environment the vehicle could expect to endure ahead of riding uphill – from the procedures for the controllers and ground crews, through to the thermal conditions for the Dragon sitting atop of the stack.
Based on the previous Falcon 9 pre-launch events, the countdown began two hours and thirty five minutes before launch, with flight controllers polled to begin the fuelling of the rocket. The strongback, a structure used to transport the rocket to the pad, raise it to vertical, and support it, was lowered 100 minutes before launch.
Fuel and thrust vector control bleeding on the second stage was performed at T-1 hour. At T-13 minutes, a final flight readiness poll was conducted, followed by the final hold point at T-11 minutes.
The terminal count began ten minutes before launch. Four minutes and forty six seconds before launch, the rocket transfered to internal power. The flight termination system, used to destroy the rocket in the event of a problem, was armed three minutes and eleven seconds before launch, and seven seconds later oxidiser topping ended.
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The flight computer started sixty seconds before launch, and the pad water system was activated. Forty seconds before launch, the propellant tanks were pressurized. Ignition – via the green glow of the first stage igniter source known as triethylaluminum-triethylborane (TEA-TEB) – occurred three seconds before launch.
UPDATE: The first attempt was aborted at T-47 seconds due to an improperly set criteria limit, an “overly restrictive redline on second stage engine position”. Following the reset of the limits, the countdown clock was recycled, ending with a successful test first of the Falcon 9 engines.
UPDATE 2: Meetings between the NASA and SpaceX teams on Tuesday concluded in the May 7 launch date being put in serious doubt. No official launch slip has been confirmed at this time. However, multiple sources are noting the launch date is under review and likely slipping – with extra information expected on Wednesday.
UPDATE 3: Still no official word from SpaceX. However, the Eastern Range have received a cancellation notice for the May 7 window, with no new date requested at this time. It is expected the launch will slip after the upcoming Soyuz launch, placing Dragon on a NET May 19 launch date target.
Following the firing of the engines, SpaceX engineers have been tasked with a thorough review of all data as part of the final preparations for the upcoming launch. This will result in one of the final reviews to clear the vehicle for its mission.
The most crucial item to be reviewed after the test will be inspections of the engines themselves, so as to ensure the issues of delamination are not observed.
It has been noted that SpaceX and NASA believe the engines on this flight are free of the defect, since they have been inspected with “lessons learned” from that recent isolated problem. However, in good operational practice, they will be looked at again after the static fire, either via ultrasound or just visually.
The Falcon 9 is a medium capacity partially reusable carrier rocket, which has been developed by SpaceX. It consists of two stages; both powered by Merlin engines burning RP-1 propellant in liquid oxygen oxidiser. The first stage, is powered by nine Merlin-1C engines, can generate 5 meganewtons (1.125 million pounds) of thrust at sea level.
The second stage, which is powered by a single Merlin engine modified for optimum performance in a vacuum, can produce 445 kilonewtons (100,000 pounds) of thrust. For Dragon launches, the rocket flies without a payload fairing.
A regular Falcon 9, with a payload fairing rather than the exposed Dragon spacecraft, would stand 54.9 metres (180 feet) tall, with a diameter of 3.6 metres (12 feet). It has a mass of 333,400 kilograms (735,000 pounds), and according to SpaceX figures, it is capable of placing up to 10,450 kilograms (23,050 pounds) of payload into low Earth orbit, or up to 4,680 kilograms (10,320 pounds) into a geosynchronous transfer orbit.
A proposed heavy-lift derivative, the Falcon 9 Heavy, would feature two additional first stages to be used as booster rockets, and would be able to place 32,000 kilograms (70,548 pounds) of payload into Low Earth orbit, or 19,500 kilograms (42,990 pounds) of payload into geosynchronous transfer orbit.
This third Falcon 9 will be the eighth overall flight for the Falcon family of rockets. Five previous flights have been made using the smaller Falcon 1, and have resulted in three failures and two successes.
The first launch, in March 2006, failed shortly after liftoff due to a fuel leak caused by corrosion. A number of problems, including an incorrect first stage fuel ratio and second stage fuel slosh, prevented the second test flight from reaching orbit.
The third launch failed after unexpected residual thrust in the first stage engines caused recontact during staging. Following these failures, two successful launches were conducted; the first in September 2008 with the RatSat demonstration payload, and the second in July 2009 with the RazakSat imaging satellite for ATSB of Malaysia.
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Thankfully, no major issues have been suffered by the Californian company’s vehicle since the teething problems with the Falcon 1, resulting in the rising confidence within both NASA circles – resulting in the commercial ISS cargo and crew advances – through to the commercial sector, with a launch manifest reaching out as far as 2017 via confirmed contracts.
However, this upcoming launch will be a major milestone for the company, as their combined COTS mission (C2+) aims to result in the berthing of their Dragon spacecraft with the ISS.
Due to the complex nature of the mission, the main objectives will be to conduct the original C2 elements of the mission, prior to conducting as many of the C3 objectives as possible. Failure to achieve the latter would not be a major setback, with another mission in the Summer set to try again should it be required.
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