Scaled Composites Tier One

• 1. Introduction

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  On the 17th of December 2003, Scaled Composites' Tier One program completed its first powered flight test. In the same announcement, the identity of its secret backer was revealed: Paul Allen, co-founder of Microsoft. He was then ranked 48th among the world's wealthiest people. Allen had put up an estimated 20 to 30 million dollars, never intending the spacecraft to carry paying passengers. That sum was at least twice the size of the prize Tier One was chasing. The Ansari X Prize offered 10 million dollars to the first non-governmental team to reach space in a reusable crewed vehicle. Burt Rutan had designed both SpaceShipOne and its carrier aircraft White Knight from the ground up. Before he started, he catalogued three specific engineering barriers that were making private spaceflight seem impossible. Preliminary development had already been running in secret since 1999. Even White Knight's first flight, on the 1st of August 2002, went publicly unacknowledged.

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• 2. Three Barriers

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  Rutan's list of obstacles began with propulsion. Liquid propellants, used in most conventional rockets, are dangerously explosive and expensive to handle. Solid-fuel motors present the opposite challenge: once ignited, they cannot be shut down. Getting back from space without burning up in the atmosphere was the third problem. SpaceShipOne used a hybrid rocket motor that burned nitrous oxide. Nitrous oxide can be handled as a bulk commodity and pumped into the spacecraft at the test site, unlike the volatile liquid propellants used elsewhere. For re-entry, SpaceShipOne flew to only about 100 km altitude. The Space Shuttle re-entered at Mach 25 from an orbital altitude of 400 km. SpaceShipOne reached Mach 3. At that speed, the thermal challenge of return was far less severe. The craft then glided unpowered to a horizontal runway landing. Adjusted for inflation, the entire Tier One program cost roughly 1/100 of the X-15 program. The three X-15 aircraft logged almost 200 test flights in total. Tier One would complete its prize-winning work with far fewer.

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• 3. Mobile Ground Systems

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  The road-going truck that served as Tier One's mobile mission control bore only the Scaled Composites logo. Nothing else marked it as unusual. Inside, computers and radio equipment tracked SpaceShipOne's telemetry at a range of up to 280 kilometers. A system called the DRS, or data reduction system, automatically directed antennas toward whichever craft was being monitored. SpaceShipOne's avionics displays were fully replicated inside the truck, so controllers could follow every instrument reading in real time. The mobile center also provided temperature control for both White Knight and SpaceShipOne cabins when needed. A second trailer handled nitrous oxide delivery. Tier One called it the MONODS, short for mobile nitrous oxide delivery system. Its tank held 6.5 cubic meters. Commercial suppliers delivered the oxidizer at about minus 17 degrees Celsius and 2 megapascals; MONODS then warmed it to room temperature, raising its pressure to 4.8 megapascals. A third piece of mobile equipment, the test stand trailer, replicated SpaceShipOne's oxidizer tank exactly. Ground-based engine firings therefore also tested the spacecraft structure under realistic vibration and heat. The test stand used a nozzle with an expansion ratio of 10 to 1 on the ground. The actual flight nozzle had a 25 to 1 ratio. The test stand replicated SpaceShipOne's structural components precisely but left out the crew cabin. That component would only join the system when the program moved to piloted flights.

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• 4. Flying Without a Tunnel

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  Twelve display computers generated the images surrounding SpaceShipOne's cockpit replica, all running commercial graphics software. Eleven monitors and one projector screen made up the display wall. The program driving them used computational fluid dynamics rather than a simplified flight model. Instead of encoding how SpaceShipOne behaved overall, it calculated the aerodynamic forces acting on each surface. This was the same modelling approach used during the original design process. It made SpaceShipOne one of the first modern aircraft designed without wind tunnel testing. Flight test data refined the model over time, keeping it accurate even in unanticipated flight modes. The cockpit itself was mounted on a static base and could not simulate acceleration. Rutan's team used White Knight for that. Equipped as a moving-base simulator, the carrier aircraft reproduced the physical sensations of acceleration a SpaceShipOne pilot would face in flight. Ground crew and engineers used the simulator too, learning procedures and testing avionics hardware and software before any flight. Stick force feedback was the one element the static cockpit could not model in real time. Pilots would encounter that sensation only in the physical aircraft itself.

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• 5. From Concept to Prize

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  The concept for Tier One originated in April 1996, five years before full development began. New programs at Scaled Composites were kept secret as a matter of policy. On the 18th of April 2003, that secrecy ended. SpaceShipOne and White Knight appeared before media for the first time at a rollout attended by between 550 and 600 people. The coverage triggered such interest that a planned Family and Friends Day on April 24 became a second media event. SpaceShipOne's first flight test, designated 01C, followed on the 20th of May 2003. Months of glide tests preceded the program's first powered flight. Increasingly ambitious powered flights followed, each reaching a greater altitude than the last. The team announced the program's first spaceflight attempt in advance. About 11,000 people traveled to Mojave Spaceport to watch. The flight was televised and structured as an airshow, with SpaceShipOne and chase planes making takeoffs and landings before the crowd. On the 21st of June 2004, SpaceShipOne completed flight 15P, achieving the first privately funded human spaceflight. The competitive flights for the Ansari X Prize came quickly after. Flight 16P on the 29th of September 2004 and flight 17P on the 4th of October 2004 were both successful, and Tier One claimed the prize. SpaceShipOne was retired shortly after, and responsibility passed to a successor project.

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• 6. The Commercial Road Ahead

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  When Scaled Composites expressed early hopes for the program, the benchmark they named was a luxury cruise. By about 2013, they had hoped, a member of the public might pay something similar for a suborbital spaceflight. To manage the technology's commercial future, Allen and Rutan established Mojave Aerospace Ventures. The company held the intellectual property from Tier One and managed all commercial exploitation. On the 25th of September 2004, a deal was struck with Virgin Galactic. The agreement called for a spacecraft based on a scaled-up SpaceShipOne, to be built by a company called The Spaceship Company. This became the SpaceShipTwo program. Tourist flights did not begin until 2023. The program concluded in June 2024 with only a handful of passengers having flown. Rutan himself sketched a longer trajectory. In the documentary Black Sky: The Race For Space, he outlined a three-tier naming scheme. Tier One covered suborbital flight, now completed. Tier Two would extend to orbital flight. Tier Three would reach beyond Earth's orbit, including the moon and other planets. He displayed designs for an orbital spacecraft built around SpaceShipOne, with a rocket roughly twice SpaceShipOne's length mounted to the ship's rear.

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