Space Exploration Technologies Corp., better known as SpaceX is an American aerospace company providing cheap and reliable launch services as well as ferrying crew and cargo to and from the International Space Station as part of NASA’s Commercial Crew and Commercial Resupply Services program.
Falcon Heavy is quite possibly one of the most recognizable rockets flying today. Launching from LC-39A of the Kennedy Space Center, SpaceX’s heavy lift launcher is solidifying itself as one of the most versatile launchers in the industry.
First mentioned in 2005, the Falcon Heavy was going to be a variant and successor of the proposed Falcon 9 launch vehicle, which had yet to gain funding. However, the need for private heavy lift launch vehicles was a small niche in the industry, and the plans for the Falcon Heavy were put on hold as SpaceX began to further develop and iterate on the Falcon 9 and its landing sequence. Revitalized in 2011, the Falcon Heavy concept quickly rose in the priority list for the company to be utilized by private companies looking to place satellites into geostationary orbit, a high-traffic destination for satellites. However, the concept was harder to bring into reality than originally expected, and required major structural changes to the ‘basic’ booster used on the Falcon 9. By 2018, all structural challenges had been ironed out, and the first Falcon Heavy had been assembled in SpaceX’s Horizontal Integration Facility. Launching on February 6th, 2018, Falcon Heavy took to the skies carrying a dummy payload, Elon Musk’s personal Tesla Roadster, on a trajectory to Mars.
Falcon Heavy is what is called a tricore design, based off of SpaceX’s own Falcon 9 rocket. The Falcon Heavy uses three Falcon 9 derived cores, each of which provide thrust on liftoff. The two boosters on the sides are traditional Falcon 9 rockets, with many boosters having launched on Falcon 9 flights before and after a Falcon Heavy launch. The center core does not have this liberty; Because of the extra mass used for structural enhancements when constructing a core booster, they are not fit to operate as Falcon 9 boosters. The center core also supports the interstage and upper stage. The interstage, separating the center core from the upper stage, contains the Vacuum-Optimized Merlin engine. The Merlin engine first debuted as the main engine of SpaceX’s first rocket, the Falcon 1. As SpaceX moved on from the Falcon 1 onto their Falcon 9 design, the Merlin was the obvious choice for the launch vehicle, and was further refined to provide more efficiency and power to the Falcon 9. A variant of the Merlin optimized for the vacuum of space, or M-Vac, utilized the full diameter of the Falcon 9 concept to its advantage, filling the entire interstage. The upper stage of the Falcon Heavy is also identical to that of the Falcon 9, and is used to insert the rocket’s payload into its final orbit. The upper stage is the only part of the Falcon Heavy that is not able to be reflown as they are disposed of each flight.
One of the most notable and unique aspects of any of SpaceX’s rockets is the focus on refurbishment, reuse, and reflight. The Falcon Heavy takes that to heart, and is currently the most reusable rocket to reach orbit.
The Falcon Heavy is able to recover all 3 of its boosters and the two faring halves, leaving just the upper stage and its M-Vac engine to be disposed of each flight. However, depending on the constraints of the mission and the payload's anticipated orbit, recovery is not always possible or is limited to only the side boosters.
During a launch, the first recovery effort is seen on the side boosters. Because the side boosters run at higher thrust than the center core, the boosters deplete their fuel quicker and are dropped as the center core continues to power the flight into space. After the side boosters are dropped, they quickly flip their orientation, using controlled release of nitrogen to control the booster in the upper atmosphere. As the booster flips, the limited remaining propellant is used to power the boosters backwards toward the launch site, known as a ‘boostback burn’. The booster reorient itself again, with the engines facing down as the booster reenters the lower atmosphere. During this phase, the engines light for the third of four burns, using its engines to slow down its velocity as it reaches thicker atmosphere. Using four gridfins, akin to wings, located at the top of the booster, the avionics begin to hone into the landing pads located further down Cape Canaveral. The final of four burns is used to propulsively land the booster onto the ground, using what is known as a ‘hoverslam maneuver’ where the landing engine lights at the very last moment before igniting, allowing for more fuel savings later in the flight, which can be used to further propel the payload before separation. As the engine ignites, 4 landing legs are deployed from the exterior of the booster, that fall into place and lock steady, taking the brute of the impact force of the booster on landing. Land recoveries are titled Return to Launch Site landings, or RTLS landings.
Following the side boosters, the next recovery effort is with the center core, which has a similar recovery sequence to the side boosters. After the core has accelerated the upper stage to a high enough velocity, it also gets released as the second stage powers forward. Instead of performing a boostback burn, the core keeps moving forward and sets its trajectory to a droneship, a fully autonomous ocean landing pad used for Falcon 9 and Falcon Heavy launches. The droneship acts as an adjustable landing pad that can be placed wherever a booster needs to land, allowing for even higher performance overall. By cutting out the boostback burn from the core, it allows for more propellant to be spent before separation. Similar to RTLS landings, the atmospheric entry and landing sequences are identical. Ocean recoveries are titled ASDS, for Autonomous Spaceport Drone Ship. While none have launched yet, it has been theorized that a ASDS side booster landing is possible, where the two side boosters land on two separate drone ships, and the core booster is expended.
Lastly, the Fairings are the last part of the Falcon Heavy to be recovered. Separating shortly after the core is separated, the fairings fall back to earth naturally, and use their exterior as a heat shield, bearing the force of reentry heating. The fairings are self-stable and remain in the atmosphere until they reach a slow enough velocity to deploy a parachute. The faring then softly lands in the ocean, where a fleet of ships will pick up the fairing from the water and place it on its deck.
Following the recovery of the side boosters, center core, and fairings, all parts are brought back to SpaceX’s processing facilities across Cape Canaveral. These facilities inspect, clean, and repair the boosters and fairings for future flights. Most often, side boosters have the nose cone removed and are mated with a second stage and payload, and continue to operate as Falcon 9 rockets. The fairings are also reassigned to other missions, and repeat a similar recovery path on both vehicles. Core boosters are left out, as they are not versatile, only ever flying as Falcon Heavy core boosters.
Future Launch Sites
As of now, there is no demand for Falcon Heavy to operate outside of Kennedy Space Center’s LC-39A launchpad. However, the facilities to launch from SpaceX’s SLC-40 and SLC-4E, located in Cape Canaveral and Vandenberg, California respectively, have the necessary hardware to provide for Falcon Heavy. Boca Chica, Texas, was also a long rumored launchsite for the rocket, with rumors of a Falcon Heavy specific pad to be erected near the town. However, the idea was overtaken by the Starship project, SpaceX’s experimental Research and Development site for the replacement to the Falcon rocket family.
The Merlin engine is a rocket engine developed by SpaceX that uses a combination of rocket-grade kerosene and liquid oxygen as fuel. It is designed to provide high thrust and reliability for use in the company's Falcon 9 and Falcon Heavy rockets.
The Merlin 1D engine represents a significant improvement over its predecessor, Merlin 1C. It features a number of enhancements that make it more powerful, reliable, and efficient. The engine produces 190,000 pounds of thrust at sea level and 210,000 pounds of thrust in vacuum, which is more than 50% greater than the Merlin 1C engine.
The improved performance of the Merlin 1D engine is due to a number of factors. It has a higher chamber pressure, which allows for more efficient combustion and higher thrust. It also has an expanded nozzle, which allows for better expansion of exhaust gasses and higher thrust in vacuum. In addition, the engine features a more advanced turbopump that can deliver more fuel and oxidizer to the combustion chamber at a faster rate.
SpaceX began development of Merlin 1D between 2011 and 2012. The design goals for Merlin 1D were increased reliability, improved performance and improved manufacturability. Of which all primary design goals were met, if not exceeded.
CASSIOPE launch | Credit: SpaceX
SpaceX's first launch of the newly improved Merlin 1D engine was during the maiden flight of Falcon 9 v1.1 with the CASSIOPE mission on September 19th, 2013 from SLC-4E at Vandenberg Space Force Base (then Air Force Base).
The flight was a complete success with the CASSIOPE being deployed in its target orbit.
Merlin 1D static fire test | Credit: SpaceX
SpaceX tests every Merlin before it is fitted to a Falcon 9 or Falcon Heavy rocket. This is done at the company’s facility in McGregor, TX. Each Merlin undergoes a static fire test, typically lasting 142 seconds (slightly below the full duration of a Falcon 9 first stage burn). SpaceX tests many Merlin engines each week to keep up with the ever growing launch demand for Falcon 9 and Falcon Heavy.
SpaceX’s rigorous testing of Merlin, especially during early development, played a large role in the reliability of the engine and the rockets it powers.
Falcon 9 returns to Earth after successful flight | Credit: SpaceX
Reusability was a major factor during development of Merlin 1D. The engine is capable of multiple restarts, making it suitable for multiple missions. In addition, SpaceX recovers their first stage of their Falcon 9 and Falcon Heavy rockets where possible. This involves landing the first stage on a landing pad or drone ship after it separates from the second stage.
By reusing the first stage and the engines, SpaceX can reduce the cost of each launch and make access to space more ‘affordable’.
While reusability is a driving force to lowering costs, it also plays a factor in the incredible reliability of the Falcon family. When reused, Falcon first stages gain flight heritage which reduces risk of component failure.
Merlin 1D was used exclusively on the Falcon 9 Block 2 (V1.1). It had a sea level thrust of 654 kN, a vacuum thrust of 742 kN, an ISP at sea level of 282 seconds and an ISP in the vacuum of space of 320 seconds.
The first major upgrade was called Merlin 1D+. This Merlin 1D version was used on Falcon 9 Block 3 (V1.2). It had a sea level thrust of 845 kN, a vacuum thrust of 914 kN, an ISP at sea level of 288 seconds and an ISP in the vacuum of space of 312 seconds.
The last major Merlin 1D upgrade was called Merlin 1D++. Merlin 1D++ was used on Falcon 9 Block 4 & 5. It has a sea level thrust of ~990 kN, a vacuum thrust of ~980 kN, an ISP at sea level of 290 seconds and an ISP in the vacuum of space of 314 seconds.
The listed stats here aren't the only things to change over time. Other changed stats include the propellant mix ratios, chamber pressure, and pressure expansion rate.
Merlin 1D Vacuum is a vacuum-optimised version of SpaceX's Merlin 1D engine used on the Falcon 9 and Falcon Heavy second stages. It's often referred to as MVac.
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