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SpaceX Falcon - Boost Back and Landing

According to SpaceX's "Capabilities & Services" statement, a single Falcon 9 rocket, fully loaded with fuel and launching the biggest payload it can carry to Low Earth Orbit (22.8 metric tons), costs $62 million. If Musk's marginal cost figures are at least somewhat correct, SpaceX's cost to a launch a newly built Falcon 9 is about $50 million. According to Elon Musk, the marginal cost for a reused Falcon 9 launch is about $15 million. He explained that the majority of this amount was represented by the $10 million it costs to manufacture a new upper stage. It is not reusable (and never will be), so it is necessary to make a new one for each launch. The Pentagon awarded SpaceX with five of the six GPS III satellite launch contracts to date. Those five launch contracts total $469.8 million, or $94 million per launch. In 2020 the Space and Missiles Systems Center modified the contracts for SpaceX’s next two GPS III satellite launches to allow reuse, a move that the military estimated will save about $64 million, or $32 million per launch. This indicates the price of a reused Falcon 9 is $62 million, not $15 million.

Boost-back and Landing in planned for many Falcon 9 and Falcon Heavy first stage boosters. After first stage engine cutoff and separation from the second stage, three of the nine first stage M1D engines are restarted to conduct a reentry burn. This reduces the velocity of the booster and places it in the correct angle for descent. Each booster has internal carbon overwrapped pressure vessels which are filled with either nitrogen or helium and are used to orient the position of the booster. Once the booster is in position and approaching its landing target, the three engines are cut off to end the entry burn. A final burn of one to three engines slows the booster to a velocity of zero for landing on the drone ship or at LZ-1 and/or LZ-2.

For missions involving boost-back and landing, SpaceX measures wind speed in the landing area using weather balloons. Measurements are taken at various intervals before launch and landing events and used to create the required profiles of expected wind conditions during the landing event. A radiosonde, which is approximately the size of a shoe box and is powered by a 9-volt battery, is attached to a weather balloon and transmits data to SpaceX and to vehicle onboard predictive systems. The balloon, which is made of latex, rises to approximately 12 to 19 miles and bursts. The balloon is shredded into many pieces as it falls back to Earth, along with the radiosonde, and lands in the ocean. The radiosonde does not have a parachute and would not be recovered.

LZ-1 and LZ-2 support preparations for and the landing of Falcon 9 and Falcon Heavy first stage boosters. They also support post-flight landing and safing activities which begin upon completion of all landing activities and engine shutdown. Once a booster(s) is safed, it is eventually transported to a SpaceX facility for refurbishment.

Following a nominal launch from LC-40 or LC-39A (including a polar mission), the first stage booster(s) would return to LZ-1 and/or LZ-2 for potential reuse (or land on a drone ship; see next section), rather than splashing down in the Atlantic Ocean. After first stage engine cutoff, exoatmospheric cold gas thrusters would be triggered to flip the booster(s) into position for retrograde burn, and three of the nine booster engines would be restarted to conduct the retrograde burn. This reduces the velocity of the booster and places it in the correct angle to land. Once the booster is in position and approaching its landing target, the three engines would be shut down to end the reentry burn. During the boost-back stage, sonic booms would be generated by each booster (the number of booms depends on the number of returning boosters).

The landing legs on the booster(s) would then deploy in preparation for a final single-engine burn that would slow the booster to a velocity of zero before landing on the pad. The detailed sequence of events for first stage booster landing(s) along with trajectory data would be provided in SpaceX’s Flight Safety Data Package submitted to the FAA prior to the operation. Although propellants would be burned to depletion during flight, there is a potential for residual LOX and RP-1 to remain in the booster(s) upon landing. Final volumes of propellant would be included in the Flight Safety Data Package. A small amount of ordnance, such as small explosive bolts and batteries, would typically also be onboard. Any hazardous materials would be handled in accordance with federal, state, and local laws and regulations. SpaceX has an established emergency response team and any unexpected spills would be contained and cleaned up per the procedures identified in the SpaceX Emergency Action Plan and Spill Control and Countermeasures Plan.

If SpaceX is unable to return the first stage booster(s) to LZ-1 and/or LZ-2, SpaceX would attempt a drone ship landing. SpaceX’s drone ship includes four outboard dynamic positioning devices which allow the barge to maintain a constant position for booster landings. In addition to the drone ship, SpaceX charters a crewed tug that tows the drone ship into position prior to launch. An accompanying crew boat also houses crew and communications equipment. Once on location, the drone ship positioning system is remotely activated, tow is broken, and the crew boat and tug boat fall back and stage themselves cross-range of the rocket’s flight path. This puts the nearest vessel approximately 5 nautical miles from the drone ship, and the furthest vessel no more than 12 nautical miles from the drone ship. The drone ship would be no closer than 5 nautical miles from shore, but could be located several hundred miles offshore in the Atlantic Ocean. This area is referred to as the “superbox”. For polar missions, downrange drone ship recovery operations could include areas of the Atlantic Ocean north and south of Cuba and west of the Bahamas.

Following a drone ship landing, automated and remotely operated systems are initiated to ensure the booster completes its landing and safing operations. Commands are transmitted through a satellite-based communication system that provides feedback and pertinent data about the systems to SpaceX controllers. The safing steps include venting pressure of stored helium and nitrogen, purging residual hazardous ignition fluid (TEA-TEB), and emptying remaining LOX from the booster. In some cases, the booster may fail to make a successful landing due to a number of variables (e.g., lack of fuel or hydraulic fluid, wind shear, etc.). In the case of an unsuccessful landing, any remaining fuel would ignite and burn off, and the wreckage would sink, similar to the fate of traditional non-reusable first stage boosters. A remote controlled robot device is used to secure the booster. Once the booster is remotely safed, SpaceX personnel board the drone ship to service the fluids system to further remove hazards and protect against corrosion. Operations are optimized to require a small amount of time with a small number of personnel on the drone ship. After safing and securing operations are complete, the drone ship is placed under tow and all vessels return to shore.

As the drone ship approaches shore, automated systems ensure the booster is in a safe-state to proceed into port. SpaceX personnel are mobilized at the port to receive and off-load the booster. The booster is then placed into processing fixtures on-shore that allow any residual fuel to be offloaded into storage tanks, landing gear removed, ordnance removed, and to ultimately facilitate on-road transport to a SpaceX facility for further processing.

While it is SpaceX’s goal to renter and land all first stage Falcon boosters for reuse, some payloads require additional propellant to reach desired orbits or destinations (due to increased weight or extended trajectory), and, as a result, not all the launches would include boost-back and landing. Approximately 75 percent of missions are expected to include a boost-back and landing. In the event SpaceX is unable to locate an expended first stage in the Atlantic Ocean, SpaceX expects the stage would sink and therefore not be recovered. If the stage lands intact, SpaceX would attempt to recover it. For Falcon Heavy boost-back and landing (which involves three first stage boosters), each of the three boosters would be controlled separately so their approach and landing would be managed independently. Not all of the boosters would land at CCAFS. Some would land on one of SpaceX’s drone ships in the Atlantic Ocean. For a conservative analysis, the FAA is assuming a maximum of 54 annual first stage boosters landing at CCAFS (LZ-1 and/or LZ-2) and 27 annual first stage boosters landing on a drone ship.

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Page last modified: 21-11-2021 12:30:26 ZULU