Bench Talk

On February 6, 2018, SpaceX’s Falcon Heavy rocket launched into space. It’s currently the most powerful space vehicle in operation, using 27 rocket engines to lift a staggering 64,000kg into orbit—more mass than a 737 jet. One might note, however, that the Saturn V rocket greatly exceeded this payload capacity (almost 50 years earlier), and the Space Shuttle, while not capable of carrying as much cargo, could produce more thrust.

What really sets this flight apart from those that came before it is that the Falcon Heavy rocket was able to control the booster trajectory so well that the side boosters fell back to earth in a controlled manner and landed vertically on predesignated landing pads (Figure 1). To be fair, the third central booster core was not able to land successfully, but seeing the outer two boosters touch down simultaneously was like something out of a science fiction film.

Figure 1: Falcon Heavy side boosters landing on LZ1 and LZ2 (Source: SpaceX)

Trajectory

The main purpose of this flight was to demonstrate that this type of rocket—the two side boosters of which were already recycled—could indeed launch a payload into space and out of Earth’s atmosphere. This trajectory was accomplished in two stages, the first of which used 27 rocket engines in three separate cores. The second stage used only a single engine setup to operate in the vacuum of space and capable of restarting several times to release payloads at different velocities.

This flight culminated with the release of a Tesla Roadster into space with the hope of achieving a Hohmann transfer orbit that sweeps from Earth to Mars around the sun with a driver—dubbed Starman—at the wheel (Figure 2). The Hohmann orbit is an elliptical orbit used to transfer a satellite or spacecraft from one circular orbit to another. Unfortunately, Mr. Starman was released with too much velocity and is now on a trajectory that will pass through the asteroid belt. Regardless, one would have to call the lack of an immediate “rapid unscheduled disassembly (RUD)” a success and something that can be corrected next time.

Figure 2: SpaceX launches the Tesla Roadster into space. (Source: SpaceX)

With their job done, the side boosters were automatically flipped using cold-gas thrusters. Firing their engines, they headed back to the original launch site. The center booster stayed with the assembly for a while longer before doing its flip maneuver and heading to the drone-ship landing pad, which is affectionately named “Of Course I Still Love You.”

Simultaneous Landing

Once headed toward Earth, the boosters deployed their grid fins, which steered them to the correct position like a dart heading to a bullseye. Finally, when close enough to the pads, the engines were fired again in a controlled manner, and along with the grid fins and cold gas thrusters, with landing legs deployed to allow them to stand, the rockets were placed on landing pads. Seconds later, however, the center core would not make a successful landing on Of Course I Still Love You, apparently because of multiple engines running out of igniter.

Still, one must marvel about what had to go right for even two out of three of these rockets to land. Not only do systems used in rockets have to withstand the heat and violence of take-off, the precise guidance of re-entry, and more heat and violence during landing, but all of them must work perfectly. Doing some quick math: If you have just 1,000 parts that all need to work for a successful mission, and each functions correctly 99.9 percent of the time, your chances of success are .999^1,000, or just shy of 37 percent. Given that the space shuttle had 2.5 million moving parts, even if the Falcon Heavy had a tenth of that number, they must be made many orders of magnitude more reliable to have had a realistic chance at success.

While it might seem that the odds were stacked against the success of this mission, with over 5,000 employees spread throughout several locations and with suppliers spread throughout the US, the end result is a real testament to what people can do when working toward a common goal. It’s easy to concentrate on one amazing event, but the flight required the coordinated efforts of all these people, years of trial-and-error, and the knowledge of space pioneers, researchers, and, perhaps even, an odd sci-fi movie for the ultimate success of this mission to come to pass!