The allure of the space plane has always been the cost saving associated with the fact that every major component can be reused. The rocket fuselage, its engines the crew accommodations, all of the electronics, hydraulics, avionics, virtually everything is preserved.
The United States’ space shuttle was the only operational space plane to date, although the Buran of the former Soviet Union did make one unmanned flight.
Great Britain’s effort was centered on a program known as the Horizontal Take-Off and Landing (HOTOL) design. The program began in 1982 and was cancelled in 1988 when a lack of progress on technical issues discouraged the British government from providing further funding.
In 1989 Alan Bond and two rocket engineers from Rolls Royce secured private funding and founded Reaction Engines Ltd. All three were alumni of the HOTOL program. The purpose of the company was to perfect the HOTOL design.
On July 12 2016 ESA signed a contract with Reaction Engines to provide €10 million to further development of HOTOL’s successor, the company’s SABRE engine. The British government is providing £60 million for the same purpose.
These announcements follow a £20.6 million investment in Reaction Engines in November 2015 by BAE, in exchange for which BAE received a 20% stake in the company.
Reaction Engines says it now has the funds in place to build a ground based demonstrator of its SABRE engine, the heart of Skylon, its reusable space plane plan.
SABRE is the acronym for Synergistic Air-Breathing Rocket Engine. At the start of a flight SABRE is an air breathing engine becoming a conventional rocket engine after achieving a speed of Mach 5.5.
A key feature of SABRE is its use of a rocket engine chamber to burn atmospheric oxygen for the initial phase of flight and then liquid oxygen once the plane’s speed exceeds 1,900 miles per hour and can no longer breathe oxygen. Use of atmospheric oxygen at lower speeds of the rocket’s initial flight rather than liquid oxygen used for a traditional rocket’s initial stage results in significant weight saving.
Thee American company SpaceX has set about addressing reusability in a different way, namely designing rockets which can land vertically after launch rather than be crashed into the ocean or burned up in the atmosphere falling back to Earth.
In December 2015 Ashley Dove-Jay a Ph.D. researcher at Bristol University wrote an excellent article for The Conversation laying out the advantages and disadvantages from a financial perspective of Skylon.
Dove-Jay compares Skylon with SpaceX’s Falcon 9 and Falcon Heavy. His conclusion is that the Space X rockets will be cheaper to operate than Skylon which he believes is about a decade away from being operational.
Quoting Dove-Jay from his article:
“In terms of tackling the problem of expendable rockets, it seems that Reaction Engines are about a decade too late.”
The only area not addressed in the article is cargo capacity and capability and there is not a lot of information readily available to provide comparisons.
Skylon, for example, can be configured to take up to thirty astronauts into space at one time. The cargo bay seems to provide a space-shuttle-like flexibility which the Falcon rockets do not.
Cost projections based on emerging technologies should probably also include some factor for the unforeseen. Nothing ever goes according to plan.
Perhaps most importantly it should be pointed out that Dove-Jay’s analysis does not address the “cool” factor and Skylon The Space Plane is definitely pretty cool!
But Ashley-Dove’s article is a great insightful review of the rocket reusability options before us.