British Space Planes That Never Worked Out

book cover Review: HOTOL and Skylon by Jeff Foust Monday, July 13, 2026 HOTOL & Skylon: The Story of Britain’s Spaceplanes by Rob Coppinger British Interplanetary Society, 2026 hardcover, 268 pp., illus. ISBN 979-8198066182 US$26.87 Next week, the aerospace industry will convene outside London for the biennial Farnborough International Airshow. Space has a growing presence at the show, with a hall dedicated to space companies and a series of presentations on space industry topics, but Farnborough is still, well, an air show, dominated by aircraft companies and suppliers. The flight line is filled air aircraft ranging from widebody airliners to fighter jets to helicopters on static display, with nary a rocket or satellite around. “I’d say it was a dead end because, fundamentally, at the end of the proof-of-concept study, we never proved the concept,” said one engineer who worked on HOTOL. In an alternate universe, perhaps, that might be different. Spaceplane enthusiasts might imagine a Farnborough where one or more such vehicles found their place alongside more conventional aircraft. Those people would likely be particularly delighted if those spaceplanes were British: versions of HOTOL or Skylon studied by British companies for decades. Those two concepts were among the most ambitious designs for spaceplanes proposed during the Space Age: vehicles that would take off from a runway (perhaps with assistance from a rocket sled) and fly into space using an advanced engine design that started as an air breather and transitioned to a conventional rocket engine at higher altitudes. The designs promised to significantly reduce the amount of propellant the vehicle had to carry, since it could use atmospheric oxygen while in the lower atmosphere, while offering aircraft-like operations with lower costs and more frequent flights. The new book HOTOL & Skylon: The Story of Britain’s Spaceplanes by Rob Coppinger, editor of the British Interplanetary Society’s SpaceFlight magazine, offers a detailed history of these two decades-long efforts that attracted considerable publicity but never got close to actually taking off. Those efforts had their start at a BIS meeting in 1982, when aerospace engineers Alan Bond and Bob Parkinson attended a talk about the Hermes spaceplane France was proposing to develop for launch on the future Ariane 5 rocket. The two wondered if a single-stage-to-orbit spaceplane was possible; Bond had worked on an engine at Rolls-Royce called the RB.545 or “Swallow” that he thought could support such a vehicle. That led to British Aerospace beginning studies of HOTOL, or Horizontal Take-Off and Landing. The key to HOTOL would be that engine, which started as a conventional air-breathing engine but later switches to a rocket engine. Before that transition, though, HOTOL would reach speeds that superheat the air going into the engine. It required a heat exchanger, called a pre-cooler, to cool and densify the air before going into the combustion chamber. It would also be extraordinarily complex to develop. The project secured funding for a feasibility study and made progress on the design, but by 1988 it was clear the British government was not willing to fund further development of the spaceplane. (A version of HOTOL called Interim HOTOL, which used the Antonov An-225 as an air-launch platform, lingered into the early 1990s.) In 1989, Bond and two other engineers, John Scott Scott and Richard Varvill, established a new company, Reaction Engines Ltd., to continue their spaceplane ambitions. Their spaceplane was called Skylon and used an air-breathing engine concept called SABRE (Synergetic Air Breathing Rocket Engine) similar in concept to the RB.545 but different enough in details to avoid infringing on the Rolls-Royce patent on the engine. A big focus again was on the engine’s precooler, including how to prevent frost buildup that made it ineffective after just seconds of use. After years of effort, Reaction Engines started to win support and funding, including £6 million in 2009 and £60 million from the UK government in 2013. In 2015, BAE Systems, previously known as British Aerospace, took a 20% stake in Reaction Engines for £20.6 million. The company also had an American subsidiary to do engine testing in Colorado working with Defense Department agencies like DARPA. It seemed like SABRE and Skylon were on an ascending trajectory at last. But that momentum was not sustained. While Reaction Engines was able to secure additional investment, it was a tiny fraction of the amount needed to fully develop SABRE and use it for Skylon. The company raised £40 million in early 2023 in a round led by the UAE’s Tawazun Council, but its interest was in other applications of the heat exchanger technology needed for SABRE, from energy to desalinization. That funding was not sufficient, and in October 2024 Reaction Engines entered administration, the British equivalent of bankruptcy protection. Hayter recalled gifting a model of Skylon to Buzz Aldrin, who offered an indifferent response: “Still playing with that thing, are you?” The rise and fall of Skylon took place as another approach to reusability emerged. SpaceX pioneered recovery and reuse of its Falcon 9 booster, which has now performed 600 launches with reused boosters that, in some cases, have flown more than 30 times each. Blue Origin’s New Glenn has followed and, last week, China made its first booster recovery with its Long March 10B rocket. Who needs spaceplanes when you can land and reuse rockets? Varvill, one of the cofounders of Reaction Engines, congratulates SpaceX for its accomplishments but is insistent about spaceplanes. “But we still think that a reusable spaceplane is ultimately safer and capable of a higher launch rate from simpler ground facilities,” he says in the book. Others, though, have concluded the industry has bypassed spaceplanes. “There’s a step-by-step evolution of the vertical [rocket] launchers [and it] is not pointing at space planes,” says David Parker, who crossed paths with spaceplane development while in industry and later, at the UK Space Agency and ESA. “I think there are people that are emotionally attached to the idea [of a spaceplane] but it’s the scale of the project.” Developing a spaceplane, he says in the book, could cost up to 30 billion euros; SpaceX says it has spent about $15 billion developing its fully reusable Starship. Even a former CEO of Reaction Engines, Tim Hayter, acknowledged the high cost of developing Skylon, estimating the spaceplane would cost £10 billion and £3 billion for the SABRE engine: “it was just cuckoo land numbers.” And there’s continued skepticism that a spaceplane like HOTOL or Skylon is even technically feasible. “I’d say it was a dead end because, fundamentally, at the end of the proof-of-concept study, we never proved the concept and I don’t think it ever was proven,” said one person who worked on the HOTOL study in the 1980s. In the book, Hayter recalled gifting a model of Skylon to Buzz Aldrin, who offered an indifferent response: “Still playing with that thing, are you?” He didn’t disclose when the meeting took place but said it showed the project “lacked credibility because it had been around for so long.” The book interleaves the history of HOTOL and Skylon with other spaceplane projects around the world. It’s clear that spaceplanes are not dead, but have taken different technical approaches to the idealized form of a vehicle that takes off from a runway and goes directly to orbit. There are those that launch atop conventional rockets, such as the X-37B, China’s Shenlong and, eventually, Sierra Space’s Dream Chaser. There are also suborbital spaceplanes like Virgin Galactic’s SpaceShipTwo and its successor, simply known as SpaceShip, that air-launch. Dawn Aerospace in New Zealand has developed Aurora, which takes off under rocket power from a runway; the upcoming Mark II will be able to reach an altitude of 100 kilometers but with a payload of just 15 kilograms. It’s possible that, at a future Farnborough International Airshow, one of those spaceplanes might make an appearance. One could even imagine an Aurora Mark II performing a suborbital flight from the runway there. It just won’t dominate on the flight line in the same way a bigger vehicle, like HOTOL or Skylon, would have. Jeff Foust (jeff@thespacereview.com) is the editor and publisher of The Space Review, and a senior staff writer with SpaceNews. He also operates the Spacetoday.net web site. Views and opinions expressed in this article are those of the author alone.