On September 1, 2016, a SpaceX Falcon 9 rocket exploded on its launch pad at Cape Canaveral, two days before launch. The accident killed none, but destroyed the estimated $62 million rocket and its $195 million payload. The event, unsurprisingly, made international headlines and continues to be discussed in scientific and space-themed media outlets, even as a cause for the accident remains elusive.
The explosion occurred while the second stage of the rocket, which enters and returns from space, was being filled for a “static fire” test. This test was intended to ensure the proper functioning of the first stage of the rocket by firing the 9 first-stage engines for a short time. The rocket was securely strapped down and would not have moved during the test. Elon Musk, founder and CEO of SpaceX, took to Twitter one week after the accident, though provided unfortunately little detail. One tidbit he provided is that the investigation team is “Particularly trying to understand the quieter bang sound a few seconds before the fireball goes off.”
The satellite payload that was destroyed with the rocket was the Affordable Modular Optimized Satellite (Amos-6), owned by Israeli company Spacecom. The name is an allusion to the prophet Amos of the Hebrew Bible, who spoke about wealth inequality and social justice. It was designed to provide communications services for Europe and Africa, and was to be used by Facebook’s controversial Internet.org initiative among other clients. The communications payload itself was built by the Canadian firm MacDonald, Dettwiler and Associates Ltd., who are also responsible for the famous Canadarm and Canadarm2.
Despite the accident, SpaceX has been quick to point out that the Falcon 9 has a typical safety record. Over 29 launches, they have had 2 failures. That works out to a 93% success rate, compared to a 95% success rate that Bill Ostrove, an aerospace analyst at Forecast International, suggests is the industry average. It is unlikely that business will dry up as a result of this failure; Hannah Kerner, Executive Director of the Space Frontier Foundation, suggests that the demand for satellites is much greater than can be supplied, so SpaceX should be able to find customers regardless of the accident.
The Rocket
The Falcon 9 is a fairly large rocket, standing 70 m tall. It is dwarfed by the massive Saturn V rocket used in the Apollo program, which was 110 m tall and three times larger in diameter. Nevertheless, it is a giant structure capable of delivering 22 800 kg to Low Earth Orbit or, according to the SpaceX website, 4020 kg to Mars. The first stage of the rocket has nine Merlin engines that burn RP-1 (space-grade kerosene) and liquid oxygen (LOx) to get the rocket through the lower atmosphere. The upper stage uses one Merlin engine and the same RP-1/LOx fuel to bring the payload into orbit, and perform any orbital maneuvers required for the mission.
The Falcon 9 has many claims to fame. For instance, it was the first commercial rocket to be involved in an International Space Station rendezvous, delivering the SpaceX Dragon capsule to orbit so it could perform its resupply task. The most noteworthy aspect of the Falcon 9, however, is that the first stage can land back on dry land to be reused.
The goal of reusability in spaceflight has long been desired. It is hoped that the cost savings from reuse and the faster turn-around time from refurbishing—as opposed to newly constructing—can make spaceflight cheaper and more common. The space shuttle is a famous and rather terrible example. The cargo-bearing “shuttle” part of the shuttle, and the two solid rocket boosters were reusable. However, the inspections and refurbishing of the main body of the shuttle was so intense that the many of the expected cost and time savings were lost. The solid boosters, dumped via parachute into the ocean, had to be manufactured to withstand the corrosive properties of salt water. This lead to an expensive and inefficient mess, negating the entire purpose of reusability.
The Falcon 9’s reusability is much more promising. After the first stage separates from the rest of the rocket, it returns to a landing site near the launch pad, landing vertically on extendable legs and firing its rocket engines to slow down. This has the two advantages: landing vertically, so the rocket is subjected to the same forces as when upright on the launch pad, and thus does not need extra weight for reinforcements; and returning to near the launch site, which saves on transportation costs.
On return, the first stage is so light that a single engine, operating at its minimum thrust, can overcome the force of gravity. This means that the rocket is incapable of hovering; it will always be accelerating upwards. As a result, the rocket performs what is known as a “suicide burn”, so called because small miscalculations in the rocket’s motion will necessarily result in disaster. The single engine is activated at just the right time during the rocket’s decent so that it lightly touches down, and then the engine shuts out before it can start moving back upwards.
SpaceX has been one of the leaders of the commercial space venture, and they remain in that position despite this latest accident. With the Falcon 9, and their planned super-version, the Falcon Heavy, SpaceX will probably be able to shrug off the bad press, and continue its aggressive plan to make space flight cheaper and more regular.
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