Will Starship Earth-to-Earth Really Take Off?
Will it really be possible to fly from New York to Tokyo in an hour?
|Oct 22, 2019|
When SpaceX’s ITS rocket (now known as the Starship rocket) was first unveiled in 2016, it left myself and many in the space-observing community in awe. Never before had a fully reusable rocket system been envisioned that would be large enough and powerful enough to open up transportation to and from the Moon and Mars. For the first time, a company had figured out (at least on paper) a viable way of making space truly accessible. It came as a surprise then, in 2017, when SpaceX showed the same rocket performing Earth-to-Earth (E2E) transportation. SpaceX, it seemed, was going terrestrial and targeting airlines and the travel industry here on Earth as well.
Since then, SpaceX has given a few updates on this concept. Meanwhile, critics have poked holes in the E2E system, arguing that it would never be safe enough or cost-effective enough to work. Regardless of whether or not the critics are correct, it is refreshing to have someone thinking big about the future of transportation. Since the 1970s, the most innovative ideas in aerospace seem to be limited to seat layouts and single-digit improvements in fuel efficiency. Even supersonic flight, once considered to be the next logical step in travel, is a distant memory.
Indeed, the E2E concept sounds implausible on its face. The Starship rocket, a rocket that is physically larger than the Saturn V rocket that took us to the Moon, would take off from a floating platform out at sea. The first stage would separate and land back on Earth at its launch platform (much like the Falcon 9 rockets currently do) while the second stage, carrying cargo and crew, would propel itself out of Earth’s atmosphere before reentering in a ball of flames and using its own engines to land softly on another floating platform at the destination.
The concept seems implausible for two reasons 1) Rockets are very expensive and 2) Rockets blow up (on occasion.) The former, I firmly believe, will be disproved in the next five years. Rockets are, for all intents and purposes, just engines with fuel tanks, and in many respects, much simpler than aircraft. In fact, early in the jet age, both liquid-fueled rockets and jet engines were not seen as all that dissimilar from each other; jet engines operate on similar principles. The primary difference is that jet engines burn oxygen from the air while a rocket brings oxygen with it. SpaceX is proving that it is possible to quickly and cheaply build rockets out of stainless steel. The Starship rocket, for example, is being built outside (sans a factory) in a manner that is reminiscent of the days of building transatlantic ocean liners in the early 20th century.
Spacecraft construction is looking alike ocean liner construction.
Furthermore, if the rocket can be used many times (like an aircraft), the cost of building that rocket is amortized over every flight. I explored this in greater detail in here. The challenge, therefore, becomes the issue of rapidly and cheaply refurbishing the rocket between flights. This is especially important because part of the economics of E2E transportation will depend on the frequency of flights. Ticket prices can be more comparable to airlines for long-distance flights if the Starship proves able to fly the same routes more frequently than traditional airlines.
The first stage of the Starship rocket, called the Superheavy booster, should be quite cheap to reuse, even when compared to the Falcon 9. Superheavy, with its larger size, should have a better wet/dry mass ratio than Falcon 9, resulting in a lower payload penalty for reuse. Second, its stainless steel construction should be able to withstand more flight cycles due to better fatigue resistance when compared to Falcon 9’s aluminum alloy. Third, the use of methane fuel will reduce soot buildup that might clog up the engine’s plumbing and allows for autogenous pressurization that completely eliminates the need for expensive helium on every flight. Fourth, and perhaps most importantly, the thermal characteristics of stainless steel enable it to withstand much higher temperatures. The Falcon 9 requires a thermal protective coating on the body of the rocket with a water-cooled heat shield at its base. Stainless steel will require no such shielding. This saves weight, eliminates failure points, and reduces turnaround times and expenses…you can’t spend time and money maintaining something a part does not exist…and a part that does not exist cannot fail. It is also worth noting that Superheavy will have six landing legs (and these legs appear fixed in place) alongside multiple redundant landing engines that should ensure higher landing reliability than the Falcon was ever capable of.
…you can’t spend time and money maintaining something a part does not exist…and a part that does not exist cannot fail…
The Starship upper stage, however, remains a big question mark. The upper stage will have to survive aerodynamic and thermal stresses akin to the Space Shuttle due to a much higher reentry velocity. The Space Shuttle could only survive reentry through the use of tens of thousands of heat shield tiles. These tiles were expensive, difficult to remove and replace, and extremely fragile. As a consequence, the Space Shuttle was unsafe, extremely expensive, and time-consuming/difficult to maintain. Rockets can only make money when they are flying, so if Starship is grounded for months while engineers take out/glue in replacement tiles, the economics could end up worse than an expendable rocket (as it did with the Space Shuttle).
Starship, however, is starting out with some important advantages over the Space Shuttle. Again, the stainless steel construction itself is able to take a great deal of the reentry heating. On the cooler leeward side of the craft, no heat shield will be needed at all, saving weight, and reducing maintenance costs and time. The windward side, however, will still require tiles. SpaceX has not revealed much about how they intend to overcome the Space Shuttle’s tile issues. We do know that the thickness of the tiles is a function of the spacecraft hull’s max thermal tolerances; stainless steel’s high melting point reduces the need for insulation. This allows either thinner/lighter tiles or perhaps thinner/more robust tiles to be used. Additionally, the science of heat shield tiles certainly has advanced since the 1970s. Stronger and lighter materials will likely be used. Finally, it appears that SpaceX is going to bolt them to the hull of the craft rather than glue them as was done on the Space Shuttle. This makes tile replacement much faster and cheaper as there is no need to wait for the glue to set.
Starship on Reentry
Even so, SpaceX has their work cut out for them. Developing a safe, and low-cost heat shield alongside the “brakerons” that help control its fall from the heavens is going to be a monumental challenge. But if SpaceX gets this right, there could very well be a path forward for point to point transportation, at least as a niche service that compliments the existing airline industry. Furthermore, Elon has hinted that the Starship craft alone might be able to achieve E2E without the need for the Superheavy booster. If this is indeed the case, this would dramatically reduce the fuel and logistics costs of the E2E concept and improve safety.
Nevertheless, I suspect that point to point rocket transportation would begin as many cutting edge technologies do: with the military as an early adopter. I imagine that the military would be attracted to the idea of being able to ship large payloads and personnel anywhere in the world on a moment's notice. The military is not a commercial enterprise and would likely be more comfortable taking on the risks that a new transportation mode entails. Of course, this all depends upon government support. Furthermore, if indeed Starship does pave the way to Martian/Lunar colonies, point to point transportation might be a necessity to travel between distant colonies that exist on the same celestial body. After all, there is air on the Moon and the atmosphere on Mars may be too thin for flight. In the absence of other transportation infrastructure, this might be the only means of long-distance transportation.
It is not likely that Starship will be taking paying customers around the world anytime soon, but the fact that SpaceX and Elon Musk are thinking big and pushing the boundaries of technology brings me hope that the future will not be one of stasis but one of inspiration and wonder.