Why building reusable rockets is so hard

When SpaceX announced that they were venturing into the manufacture of reusable rockets, my first question was, "Why is this happening only now?" Modern rocketry has been around since the mid-1900s and yet they were all single-use ones. It seemed like an utter waste of resources, effort, and time spent on building the complex machines. Diving deeper into why this advancement came so late, I found a number of reasons that justified this seemingly abnormal delay.

First, the cost spent on making the rockets reusable must be worthwhile. Building the rocket to withstand the damage done during launch, re-entry, and landing means more complicated - and costly - engineering. Also, the initial expense isn't the only cost to be borne in the business of reusable rockets. Maintenance does not come cheap, and it is not avoidable. Refurbishing and recertification usually cost more than manufacturing new engines. All things considered, rockets typically were not used frequently enough to justify the cost, so they were made to be disposable.

If you have watched a rocket launch, you must have noticed it shedding parts during different stages of flight. This is because they need to increase efficiency and reduce the amount of weight carried. When the fuel needed to achieve a particular height is used up, it is detached from the rest of the rocket and either falls back to Earth or is put into a decaying orbit (the distance between the rocket and the detached part is gradually increased).

Making a rocket reusable would mean that these parts will not be disposed of, adding to the weight that must be carried by the rocket. To compensate for this loss in efficiency, engines must be built to be more powerful, and launch may consume more fuel as well.

Heat is a major element that contributes to the reusability hurdle. Moving through the atmosphere at hypersonic speeds causes a significant amount of friction. Extra shielding is required to withstand the heat, which in turn contributes to our first problem - weight. Resisting heat also counts as a safety concern.

Looking at the safety aspect, considering the damage that a rocket goes through during a single flight, there must be high confidence that it is in good enough shape to fly again. This requires a considerable amount of testing and development to ensure that the parts used can handle more than a single launch. It also means that a lot of parts require replacement to guarantee safety, especially since the pioneers of reusable rockets - SpaceX and Blue Origin - have commercial use, or Space Tourism, at the forefront of their missions. According to Space X, the heat shielding of their Falcon 9 rockets needs to be replaced every 10th launch.

Coming back to the original question of why it took this long to start building rockets for multiple-time usage, on one hand, reusability wasn't a concern until private companies started thinking about commercial space flight. On the other, the technology needed to overcome all these obstacles simply did not exist until recent times. Heat shielding, propulsion technology, and guidance systems were a few handicaps, to name a few. The development of reusable rockets also requires the use of advanced materials that can withstand the stresses of repeated launches and landings. Finding materials that are lightweight, durable, and cost-effective has been a significant challenge.

SpaceX started working on the technology for vertical landing of rockets in 2011. Falcon 9's successful vertical landing in 2015 was a breakthrough in reusable rocketry that came about after years of multiple iterations, tests, and refinements. The landing succeeded after multiple failed attempts. As a member of the SpaceX team put it, "There are a million ways it could go wrong and one way it can go right."

If one can figure out how to effectively reuse rockets just like airplanes, the cost of access to space will be reduced by as much as a factor of a hundred. A fully reusable vehicle has never been done before. That really is the fundamental breakthrough needed to revolutionize access to space.
-Elon Musk