By Angadh Nanjangud, Queen Mary University of London, The Conversation
Of all the things that Donald Trump’s return as US president could mean, one is that Elon Musk’s plan to use Starship rockets for long-distance flights on Earth could move forward. Dubbed Starship Earth to Earth, this would see passengers transported by rocket between cities. They would briefly leave the planet’s atmosphere during the journey before flying back down to reach their destination.
Musk claims it will be possible to travel to anywhere on Earth within an hour. His rocket company, SpaceX, has given examples such as New York to Paris in 30 minutes and London to Hong Kong in 34 minutes. In response to a post about it on his X platform, Musk responded: “This is now possible.”
Unlike previous governments, this Trump administration appears focused on reducing regulatory barriers hindering technological progress in all areas. This could make it easier for Musk to rapidly push towards realising this futuristic travel option. But what hurdles must be overcome first?
On whether Musk is right about the technical feasibility, the answer is “sort of”. The necessary technology was arguably first proven when Nasa achieved a Mars landing in 2012.
This was the first to land retropropulsively, meaning touching down softly on a planetary surface with rocket engines (technically called retrorockets). In contrast, previous Mars landings had used parachutes for the entry phase and airbags for the landing phase.
The 2012 landing opened the door to rockets and boosters becoming reusable, thereby greatly reducing the cost of launch. It was repeated in SpaceX’s historic Falcon 9 rocket landings in 2016, using some of the same Nasa engineers who had worked on the Mars landers. This technological shift has been vital for rockets becoming an economically viable alternative to aircraft.
Starship’s Earth to Earth journeys would involve visiting low Earth orbit (LEO), some 110 miles to 1,240 miles above the Earth’s surface. To do this, the rocket would use two stages. The first, known as the super heavy booster, would lift it through the dense lower atmosphere, approximately 5 to 9 miles above the Earth.
This would break away some 40 miles above the Earth, then begin a controlled descent back to the planet’s surface. SpaceX has matured this technology by leaps and bounds in the past decade, including better heat shields, adjustable lattice fins, improved aerodynamics and state-of-the-art landing algorithms.
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The second stage – known just as Starship – would contain the passengers and take over the flight to reach LEO after the first stage has detached. There is still work to be done before this is passenger ready, as demonstrated when a second stage blew up during a Starship testflight on January 16.
There will be no more Starship launches until the US Federal Aviation Administration (FAA) has completed its formal investigation into the cause. On the upside, the incident occurred within predefined hazard areas to ensure public safety.
Of course, this is the very purpose of a testflight: to learn what could go wrong and iteratively solve it, meaning repeatedly making improvements after each failure. No one can compete with SpaceX’s cost-effective iteration process, for example in its crewed trips to the International Space Station (ISS).
The malfunction of Boeing’s Starliner spacecraft in August was a recent reminder here: it left two Nasa astronauts stranded on the ISS, awaiting a return trip on SpaceX’s Dragon capsule in the coming weeks.
Other considerations
Other long-term challenges pertain to how passengers access the vehicle. Videos of astronauts boarding the Space Shuttle indicate that entering one’s seat in a vertically parked rocket takes a few people to help buckle you in. Making that workable over the length of a rocket will require clever engineering.
Building spaceports in different countries also won’t be trivial; we’ve seen considerable pushback against efforts to build a UK spaceport, for instance. The same goes for worldwide regulatory approvals. It’s already standard for rocket companies to need a launch licence per flight, while America’s FAA also requires them to obtain re-entry licences before launch.
Of course, regulatory hurdles can be overcome for transformational tech (once it’s proven to be safe and reliable). No doubt lawyers will have many things to say about these issues, though I doubt any will be insurmountable. And SpaceX must know a thing or two about dealing with regulations, having launched the world’s largest constellation of satellites into orbit.
Finally, rockets expel significant quantities of microscopic particles (particulates) into the upper reaches of the atmosphere. This would have seriously detrimental effects if they were flying in anything like the numbers of long-distance airliners.
Starship’s Raptor engines use methalox, a combination of liquid methane and liquid oxygen. Unlike the kerosene that has traditionally powered rockets, liquid methane prevents the build-up of sooty residue in the engine and is also safer to work with than liquid hydrogen. While Starship still burns vastly more fuel per trip than conventional aircraft, its potential to slash intercontinental travel times could drive critical research into carbon-neutral methane production. This would be integral to making a viable long-haul alternative.
At present, UK rocket companies Skyrora and Orbex are among those developing alternatives to traditional fuels. Skyrora is developing Ecosene, an aerospace grade kerosene made from unrecyclable plastic waste. Orbex’s Prime rocket will make use of a BioLPG derived from plant and vegetable waste.
Both tackle different sustainability problems, but are unlikely to meet the performance demanded by larger Starship-class vehicles. Another promising alternative is nuclear-powered engines, but using them close to Earth will likely be fiercely resisted by environmental campaigners.
In sum, we are in uncharted territory with landing second stages of rockets, but the general trend from 2012 to today indicates that such technical challenges are solvable. Doing so with crews will be even more challenging, but it does align with SpaceX’s mission to make humans multiplanetary. The same technology will be used to land humans safely on Mars, so developing it is probably inevitable.
Uncrewed Starship launches to Mars are supposed to happen in 2026. Crewed Mars missions will follow, without the same landing-related regulations as would be required on Earth. I suspect crewed Earth-to-Earth transport will only be approved after humans have landed on Mars safely.
If there’s one team that can’t be bet against turning visions into reality, it’s the SpaceX engineers who have been revolutionising launch vehicles for over ten years.
Angadh Nanjangud, Lecturer in Aerospace/Spacecraft Engineering, Queen Mary University of London
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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