## 5 Structure
The idea of reusability is founded on transforming rocket launches into something like airplane flights. However, the prerequisite is the high cadence of the rocket's flights. Sixty missions per year were expected for space shuttles. Despite efforts to secure the monopoly for shuttles to handle all defense payloads, the cadence of launches remainedvery low [38]. The Space Shuttle program conducted 135 flights over the whole thirty-year span, including two failures with 14 astronauts lost (Challenger in 1986 and Columbia in 2003) [81,82]. This equals four and a half flights per year on average. The Aldridge Commission (under the [PERSON] administration) recommended a transformation of NASA, including seeking to purchase services from private companies that truly compete with each other, and limiting its own role to those areas in which it could perform irrefutably well. In 2005, NASA started a USD 500 million program to resupply the International Space Station called COTS (Commercial Orbital Transportation System). Throughout its history, NASA has contracted with private companies to produce and service equipment based on cost-plus contracts. It means that the agency covered all proven costs, as well as assured markup. Of course, such a system did not create incentives to save money through cost discipline, efficiency, and innovation. However, it was intended to insulate contractors from the risk tied to the ambitious, extraordinary upfront investments. Contrarily, COTS contracts were based on a fixed-price model (also known as value-based pricing); namely, the agency requests a service for a set fee, putting the risk on the private firms. They receive, however, the possibility to create extraordinary profits if they are able to keep costs far below that fee. In this way, the agency has sown the seeds of revolution [38,83]. One of the first firms that awarded the first fixed-price COTS contract in 2006 was SpaceX. Money from NASA came at a crucial moment, supporting the company in the toughest time (between 2006 and 2008, three attempts to launch its small-lift vehicle Falcon 1 failed), allowing it to survive to the fourth, this time successful, flight. The fifth (2009) and last one was the only commercial one. It cost about USD 7 million, which accounted for around 14,000 per kg. In the next year, SpaceX introduced its medium-lift Falcon 9, which revolutionized the launch industry [38,70,71,78,79,80,84]. The COTS program was a success. At half the cost of the single shuttle flight, NASA supported the development of two new orbital rockets (Falcon 1 and 9) as well as a cargo vehicle, namely the Dragon capsule, which first docked with the ISS in 2012, thus fulfilling the SpaceX COTS contract. Satisfied with the results, NASA launched a larger follow-up program called Commercial Resupply Services (CRS) focused on routine cargo delivery to the ISS, thus continuing to support the private sector, including $1.6 billion for SpaceX. The next NASA program, Commercial Crew (CC), extended this new cargo model to astronauts. This new NASA approach (fixed prices) was an inflection point because the agency could be considered one customer among many for the first time in such a way, introducing more market-driven activities in the upstream and midstream dominated by a government-driven approach. Therefore, in line with the First Fundamental Theorem of Welfare Economics, the market proved to be an efficient way of organizing resource allocation [38]. Indeed, the money from NASA supported the further development of Falcon 9. The milestone was reached in 2015, when, just a few weeks after New Shepard's achievement, Falcon became the second private partially reusable rocket. The Falcon 9 achievement was much more important. While New Shepard is a suborbital rocket, spending a few minutes with tourists in microgravity, Falcon 9 was the first orbital-class rocket to successfully land after launching. To be clear, the landing part of the rocket is the first stage (booster). However, it is the most expensive part.