Space X have finally put their teething problems behind them with total success for their fourth launch attempt of their Falcon I vehicle, which launched from Omelek island, Kwajalein Atoll.
NASASpaceflight.com covered the launch as a live event, with extensive background, live updates, images and video, all available on the link below (read more).
Falcon 1 is a two-stage, liquid oxygen and rocket grade kerosene (RP-1) powered launch vehicle. It is designed in-house from the ground up by SpaceX.
The primary structure is made of an aluminum alloy, graduated monocoque, common bulkhead, flight pressure stabilized architecture developed by SpaceX. A single SpaceX Merlin 1C regeneratively cooled engine powers the Falcon 1 first stage, while a single SpaceX Kestrel engine powers the Falcon 1 upper stage.
The Falcon 1 Flight 4 vehicle is carrying a payload mass simulator of approximately 165 kg (364 lbs), designed and built by SpaceX specifically for this mission.
Consisting of a hexagonal aluminum alloy chamber 1.5 meters (5 feet) tall, the payload attaches to the standard Falcon 1 payload mounting structure. It does not separate, but remains attached to the second stage as it orbits the Earth.
This launch was set to loft a Malaysian satellite. However, this was switched to the projected fifth flight – which will launch on a schedule that will be determined by the success of flight four – now expected to be in a few months.
The reason for the change relates to the three problems on the opening flights of the Falcon I – opened with a failure during first stage flight due to a fuel leak. The second flight managed to successfully achieve first stage flight, before failing shortly into second stage.
Flight three failed when the first stage recontacted the second stage seconds after separation. This was caused by a mistiming/miscalculation of the slightly modified turbopump purge pressure.
“On August 2, 2008, Falcon 1, Flight 3 executed a picture perfect first stage flight, ultimately reaching an altitude of 217 km, but encountered a problem just after stage separation that prevented the second stage from reaching orbit,” noted SpaceX’s investigation. “The origin of the problem arose due to the longer thrust decay transient of our new Merlin 1C regeneratively cooled engine.
“Unlike the ablative engine used previously by SpaceX in Flights 1 and 2, the regenerative engine had unburned fuel in the cooling channels and manifold that combined with a small amount of residual oxygen to produce a small thrust that was just enough to overcome the stage separation pusher impulse.
“SpaceX was aware of and had allowed for a thrust transient, but did not expect it to last that long. As it turned out, a very small increase in the time between commanding main engine shutdown and stage separation would have been enough to save the mission.
The resolution has only required a small change to the coding in the flight systems, which allowed for the speedy turnaround into flying this next mission.
“The fix was also very simple, requiring one line of code to be changed. We made the fix and immediately began work on Flight 4. Less than two months later, Falcon 1 Flight 4 is now on the pad at Kwajalein, ready for flight,” added SpaceX, who insisted the rest of the vehicle’s performance ahead of the failure was nominal.
“During Flight 3, the performance of the Merlin 1C and overall first stage was excellent. The stage separation system worked properly, with all bolts firing and the pneumatic pushers delivering the correct impulse. The second stage ignited and achieved nominal chamber pressure and the fairing separated correctly.
“The only untested portion of Flight 3 was whether or not we solved the main problem of Flight 2, where the control system coupled with the slosh modes of the liquid oxygen tank. We significantly improved the control logic, added slosh baffles to the second stage tank and will test the success of these improvements during Flight 4.”
Sunday’s launch was pre-empted by a static fire of the vehicle, which took place on September 20. The data from the static fire resulted in a decision to replace a component in the 2nd stage engine LOX supply line.
Following the successful launch and second stage flight through to SECO, SpaceX founder and CEO Elon Musk was lost for words in his review of the success.
“One of the best days of my life,” said Musk, shortly after thanking his workforce.