All systems are go as SpaceX and NASA are counting down to the launch of a Falcon 9 booster and Dragon capsule to the International Space Station. Liftoff is scheduled for 12:45:23 AM EDT from Space Launch Complex 40 at Cape Canaveral Air Force Station.
In a rare occurrence, a number of Kennedy Space Center facilities will be closed for the duration of the launch due to a potential risk from toxic fume dispersion should there be a launch anomaly. Perhaps surprisingly, it is not the planned first stage booster return which is triggering the precautions, but instead a process improvement instituted by SpaceX in the aftermath of last year’s launch failure on the CRS-7 mission.
In the immediate hours after that incident, SpaceX founder, CEO and CTO (Chief Technology Officer) Elon Musk observed somewhat ruefully that the CRS-7 Dragon capsule might have been saved has it ridden to orbit with its Draco thrusters and emergency detection system engaged. The latter, supplemented by the much more powerful SuperDraco thrusters are an integral part of the crew abort system designed to make it one of the safest boosters to ever carry astronauts. Musk went on to state that in the future, every Dragon cargo ship would lift off with the abort systems standing by.
For this evening’s launch, the same weather system which is bringing a 90% chance of “go” conditions happens to be supplying a steady on-shore breeze, and that is the main reason for concern. Should a mishap take place early in the launch sequence while the stack is still at a fairly low altitude, an aborted Dragon capsule descending via parachute could be blown towards shore and a possible hard landing. That could result in the dispersion of the highly toxic, pressurized hypergolic propellants which power the Draco engines. Given the critical nature of this mission, and the fact that any mishap would inevitably result in the destruction of the IDA-2 docking adapter riding unprotected in the Dragon’s trunk, it is a precaution which everyone hopes is utterly unnecessary.
Assuming all goes well, following stage separation SpaceX will once again attempt to recover the first stage, this time via a return to the concrete pad at Landing Zone 1, formerly Cape Canaveral’s SLC-13.
Tonight’s return attempt will closely mirror that of the historic first, and so far only return to land which took place on December 21st 2015. The principle difference lies not with speed or altitude, but with trajectory, as launches to ISS require a northerly flight path to reach the station’s 51.6 degree inclination.
The Boost Back is the first of three burns will be required to bring the Falcon home, and will take place approximately 2 minutes and 20 seconds after liftoff, lasting for 40 to 50 seconds as the first stage, still in near-space, will reverse its trajectory and begin its trip back towards Cape Canaveral. The Entry Burn will take place 6.5 minutes after liftoff, and will slow the rocket as it re-enters the atmosphere, protecting the exposed engines from the searing heat which has been an issue on high-energy GTO flights. Finally, and aided by the grid fins which provide directional control, the Falcon 9 will light its center Merlin 1-D engine one more time for the Landing Burn, some 8 minutes after it blasted off from several miles up the Cape.
Speaking at a pre-launch press conference held on Saturday, SpaceX VP of Mission Assurance Hans Koenigsman described the overall return profile as very similar to that which took place on the Orbcomm-2 mission, going on to state that the remaining propellant level should be sufficient to remove any question of running out at the last second. In other words, SpaceX is fairly confident that this flight will result in a healthy, and salt spray-free Falcon 9 first stage sitting on the pad.
If that is indeed the case, then SpaceX will have in its hands the second readily reusable Falcon 9, both of which are the products of NASA Commercial Resupply missions. Responding to another question, Koenigmann indicated that the booster which lofted the NASA CRS-8 mission and was the first to land at sea, is slated to become the first to be re-flown. Presently, SpaceX is in discussion with launch insurance providers to outline its flight re-certification process. Following that, the company will need a willing customer, which is not likely to be a problem, and then a launch date can be set.