Reusable Rockets: The Next Challenge

Chances are, you've already heard of SpaceX's Falcon 9, a trailblazer in the realm of reusable rockets. However, did you know that NASA was already exploring this revolutionary technology back in the 1980s? In this article, we're going to delve deeper into the concept of reusable rockets, explaining their significance and impact on the future of space exploration.

What is a reusable rocket ?

Simply put, a reusable rocket is designed with components that, following recovery and appropriate maintenance, can be used again. This stands in stark contrast to traditional rockets, which are either entirely destroyed during re-entry or left to sink in the ocean. The primary motivation behind this innovation is economical. Developing rockets is an expensive endeavor. The minimum cost of a launch is 2720 dollars per kilograms nowadays (with the Falcon 9) but it can go up to tens of thousands per kilograms. With some component, such as an engine, costing between 100 and 200 million of dollars, it is easy to understand why space agencies are willing to reuse as many parts as possible on their rocket. However, a fully reusable rocket has yet to be produced. For now, the various space agencies managed to reuse only some part of their rocket.

NASA Space Shuttle

While the concept of reusable rockets has only recently captured public attention, space agencies like NASA have been exploring this territory for decades. In fact, the first spacecraft to feature reusable components was NASA's Space Shuttle, a project conceived in the 1960s and which saw its maiden flight in 1981.

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The Space Shuttle's design was innovative for its time. A reusable orbiter vehicle was attached to conventional rocket, enabling it to reach orbit. Once its mission was complete, the orbiter would reenter the atmosphere and land horizontally, much like an airplane. Capable of carrying up to eight astronauts and 25 tonnes of payload, the orbiter was a crucial component in NASA's vision for reusable spacecraft.

Six Space Shuttles were produced: Enterprise, Columbia, Challenger, Discovery, Atlantis, and Endeavour. Tragically, two of these - Columbia and Challenger - were destroyed in mission accidents, leading to the loss of 14 crew members.

The reusability of the orbiter was a key design requirement, but it had a significant impact on the payload capacity of the Shuttle (25 tonnes, in comparison to Saturn V's 140 tonnes). NASA hoped to offset this limitation with frequent launches (24 per year) and reduce costs per launch due to reusability. However, this ambition was never fully realized.

In 2011, after 135 missions spanning 40 years, the Space Shuttle made its final flight. Despite its pioneering nature, the program fell short of NASA's expectations: the cost per launch exceeded projections, the maintenance of reusable parts hindered the desired launch frequency, and critical safety issues led to two fatal disasters.

SpaceX's Falcon 9

Since 2005, SpaceX has been developing the Falcon 9, a partially reusable rocket. This spacecraft has seen numerous iterations, with each version improving upon its predecessor. The current model in operation is the Falcon 9 Block 5, which has been in use since May 2018.

The Falcon 9 is a two-stage rocket, designed with a first stage (or booster) capable of vertical landing for reuse.

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There are two ways for the first stage to come back to Earth, depending on the mission and payload of the rocket:

The autonomous droneship landing is used when the rocket does not carry enough fuel to go back to the launch site. It requires an autonomous spaceport drone ship (ASDS) : an ocean-going vessel, autonomous, and capable of precision positioning (3 meters deviation maximum).

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Autonomous droneship landing has been attempted 159 times, beginning in 2015, and succeeded 146 times (91.8% success rate).

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Whenever feasible, a landing zone landing is the preferred method as it eliminates potential errors related to ASDS positioning as well as other factors. Of the 33 missions that attempted a landing zone approach, only one failed, resulting in a success rate of 97%. In 2021, there were 31 Falcon 9 launch, which required only 2 new boosters, proving the efficiency of the solution.

Conclusion

Reusable rocket is a modern challenge in the space industry, even though the problematic was first tackled by the NASA decades ago. The improvement made over the last ten years are very promising, with the Falcon 9 successfully recovering its boosters at a very high rate, and being trusted enough to carry crew members to the ISS. However, there are still concerns about the efficiency of the method and its economic viability, and the challenge of producing a fully reusable rocket remains.

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