How to Land Rockets

Updated: Mar 30

By William Huang


Picture a space rocket. It probably looks like a long, thin cylindrical tube with a fat bottom and pointy top, kind of like a tall, massive cone. Such rockets have been vital in every space mission, from the first moon landing to the Space Shuttle Program, to the modern day probe and satellite launches. Without this technology, escaping Earth’s gravitational pull would be nearly impossible. Despite their importance, launching rockets into outer space has one major drawback: they cannot execute a controlled vertical landing, and therefore cannot be reused – that is, until SpaceX came around. Before 2015, most people couldn’t imagine vertically landing such a spacecraft, and some even thought it was impossible. However, on December 22, 2015, SpaceX proved that notion false for the first time in history by successfully launching the Falcon 9 rocket into space, releasing its second stage into orbit, and finally landing the first stage vertically.

Falcon 9 rocket at a Cape Canaveral launch pad (SpaceX).


Why land vertically?


Before going into the complex mechanisms that allow vertical landings, we first have to understand the benefits behind landing vertically. As mentioned previously, one of the major drawbacks of most past and modern rockets is that they are not reusable. As a result, executing multiple space missions is extremely taxing, financially and in terms of the materials used. For example, although the main body of the space shuttle was technically reusable, its giant fuel tanks were discarded after every launch, and its side boosters landed in corrosive salt water after every flight, leading to a long, expensive process of retrieval and restoration.


In order to solve these problems and dramatically decrease costs of space transportation, SpaceX set a goal of producing a fully and rapidly reusable rocket system. Currently, the Falcon 9 rocket is not completely reusable and costs about $54 million to design, build, and launch; however, fuel only costs about $200,000 – a fraction of the total $54 million. Compared to the average commercial jet, each new plane costs about the same as the Falcon 9, but can fly thousands of trips before it is put out of service. Now imagine if the Falcon 9 could do that - the cost of space travel would decrease hundredfold.


How does the Falcon 9 land vertically?


Most rockets are designed to fly into orbit, then shortly after, fall and burn up in Earth’s atmosphere. However, from the beginning, SpaceX rockets - the Falcon 9 specifically - are designed and built with reusability in mind. The Falcon 9 is a two-stage rocket designed for the reliable and safe transport of satellites and eventually astronauts into space. As each stage of the rocket completes its purpose, it detaches from the main body, decreasing the

rocket’s weight and increasing fuel efficiency. The rocket is powered by a total of ten SpaceX Merlin engines with nine in the first stage and one in the second stage to fire in the vacuum of space. The Merlin engine is one of the most efficient and powerful rocket engines ever built. In fact, the Falcon 9’s first stage is built so that if two of its nine engines fail, the rocket can still launch and land safely. These engines are housed in a metal Octaweb structure, which reduces the length and weight of the rocket’s thrust structure, simplifying its design and keeping launch costs down.

The Falcon 9’s Octaweb structure in the first-stage. Eight engines form a circle around the center with one engine in the center (SpaceX).


The rocket has a few critical features that allows it to return and land on Earth. It can hold enough fuel to fly up to the International Space Station, dock, return, and land vertically on Earth. Once the rocket has separated into its two stages, cold-gas thrusters on the top of the first stage flip the rocket around as it falls back to Earth while the second stage goes on to complete its mission. The first stage’s engines then fire briefly to slow the descent. As the first-stage approaches the landing site, small, foldable heat-resistant wings called grid fins steer the spacecraft as it plummets through the atmosphere, and strong, lightweight retractable carbon fiber landing legs at the bottom are deployed. Right before touchdown, three of the engines are fired one last time - a “boostback burn,” as SpaceX calls it - to make

the craft almost hover then softly land. Once properly programmed, these systems are

completely autonomous after launch and only rely on real-time data from sensors to perform their jobs. Although a seemingly simple process overall, two failed attempts and hundreds of hours of calculations and planning went into the final successful landing of the Falcon 9. You

can watch a video of the Falcon 9 landing on a drone ship in 2016 here.

A Falcon 9 rocket touches down on a drone ship landing platform (SpaceX).


Since 2015, SpaceX and other companies like Blue Origin have made big strides in developing reusable rockets; however, a fully reusable rocket has not yet been built. If (or when) rocket reusability technology is fully developed, possibilities for human space exploration will become endless. According to Elon Musk, CEO of SpaceX, rocket reusability technology is “fundamentally required” to establish human life on Mars.



References

  1. Falcon 9. (2012, November 16). Retrieved from https://www.spacex.com/falcon9

  2. Parish, J. (2011, October 1). SpaceX says reusable VTVL rockets are the key to colonizing mars. Retrieved from https://www.theverge.com/2011/9/30/2460999/spacex-plans-fully-reusable-space-transportation-system.

  3. Teitel, A. S. (n.d.). How does SpaceX build its Falcon 9 reusable rocket? Retrieved from https://www.sciencefocus.com/space/how-does-spacex-build-its-falcon-9-reusable-rocket/.

  4. The why and how of landing rockets. (2015, June 25). Retrieved from https://www.spacex.com/news/2015/06/24/why-and-how-landing-rockets.

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