Rotary Rocket Company was a rocketry company that developed the Roton helicopter-rocket hybrid concept in the late 1990s as a fully reusable single-stage-to-orbit (SSTO) crewed spacecraft. The design was initially conceived by Bevin McKinney, who shared it with Gary Hudson. In 1996, Rotary Rocket Company was formed to commercialize the concept. The Roton was intended to reduce costs of launching payloads into low Earth orbit by a factor of ten.

The company gathered considerable venture capital from angel investors and opened a factory headquartered in a facility at Mojave Air and Space Port in Mojave, California. The fuselage for their vehicles was made by Scaled Composites, at the same airport, while the company developed the novel engine design and helicopter-like landing system. A full-scale test vehicle made three hover flights in 1999, but the company exhausted its funds and closed in early 2001.

Origins

Bevin McKinney had been thinking about the idea of a launch vehicle using helicopter blades for several years, when Wired magazine asked Gary Hudson to write an article on the concept. The resulting article resulted in a commitment of funding from billionaire Walt Anderson, which was combined with an initial investment from author Tom Clancy and allowed the company to get started. Hudson and McKinney were joined by co-founders Frederick Giarrusso, Dan DeLong, James Grote, Tom Brosz, and Anne Hudson, who together launched the company in October 1996.

Design evolution

Helicopter to orbit

Gary Hudson's and Bevin McKinney's initial concept was to merge a launch vehicle with a helicopter: spinning rotor blades, powered by tip jets, would lift the vehicle in the earliest stage of launch. Once the air density thinned to the point that helicopter flight was impractical, the vehicle would continue its ascent on pure rocket power, with the rotor acting as a giant turbopump. A similar system with non-rotating engines was studied for the N1 rocket. That application had a much smaller base area, and did not create the suction effect a larger peripheral engine induces. The Roton engine had a projected vacuum I<sub>SP</sub> (specific impulse) of ~, which is very high for a LOX/kerosene engine – and a thrust to weight ratio of 150, which is extremely light.

During reentry, the base also served as a water-cooled heatshield. This was theoretically a good way to survive reentry, particularly for a lightweight reusable vehicle. However, using water as a coolant would require converting it into superheated steam, at high temperatures and pressures, and there were concerns about micrometeorite damage on orbit puncturing the pressure vessel, causing the reentry shield to fail. These concerns were resolved using a failure-resistant massively redundant flow system, created using thin metal sheets chemically etched with a pattern of micropores forming a channel system that was robust against failure and damage.

In addition, cooling was achieved two different ways; one way was the vaporization of the water, but the second was even more significant, and was due to the creation of a layer of "cool" steam surrounding the base surface, reducing the ability to heat. Further, the water metering system would have to be extremely reliable, giving one drop per second per square inch, and was achieved via a trial/error design approach on real hardware. By the end of the Roton program, some hardware had been built and tested. The reentry trajectory was to be trimmed, similar to the Soyuz, to minimize the G loads on the passengers. And the ballistic coefficient was better for the Roton and could be better tailored. When the Soyuz trim system failed and it went full ballistic, the G levels did rise significantly but without incident to the passengers.

The vehicle was also unique in planning to use its helicopter-style rotors for landing, rather than wings or parachutes. This concept allowed controlled landings (unlike parachutes), and it was 1/5 the weight of fixed wings. Another advantage was that a helicopter could land almost anywhere, whereas winged spaceplanes such as the Space Shuttle had to make it back to the runway. The rotor blades were to be powered by peroxide tip rockets. The rotor blades were to be deployed before reentry; some questions were raised about whether the blades would survive until landing.

The initial plan was to have them almost vertical, but that was found to be unstable as they needed to drop lower and lower and spin faster for stability, the heating rates went up dramatically and the air flow became more head on. The implication of that was that the blades went from a lightly heated piece of hardware to one that either had to be actively cooled or made of SiC or other refractory material. The idea of popping out the blades became much more attractive at this point, and initial studies were made for that option. This rotor design concept was not without precedent. In 1955, one of five Soviet designs for planned suborbital piloted missions was to include rocket-tipped rotors as its landing system. On May 1, 1958, these plans were dropped as a decision was made to proceed directly to orbital flights.

Rotary Rocket designed and pressure-tested an exceptionally lightweight but strong composite LOX tank. It survived a test program which involved it being pressure cycled and ultimately deliberately shot to test its ignition sensitivity.

A new engine

In June 1999, Rotary Rocket announced that it would use a derivative of the Fastrac engine under development at NASA's Marshall Space Flight Center, instead of the company's own unconventional spinning engine design. Reportedly, the company had been unable to convince investors that its engine design was viable; the composite structure and gyrocopter reentry was an easier sell.

At the same time as this change, the company laid off about a third of its employees, lowering approximate headcount from 60 to 40. At this point, the company planned to begin its commercial launch service sometime in 2001. The rotor assemblage was tested in a rock quarry before installation on the ATV.

The ATV flew three successful test flights in 1999. The pilot for these three flights was Marti Sarigul-Klijn and the copilot was Brian Binnie (who later gained fame as pilot of Scaled Composites' SpaceShipOne on its second X-Prize flight).

The ATV made its first flight on July 28. This flight consisted of three vertical hops totaling 4 min 40 sec in duration and reaching a maximum altitude of 8&nbsp;ft (2.4 m). The pilots found the flying extremely challenging for a number of reasons. Visibility in the cockpit was so restricted that the pilots nicknamed it the Batcave. The view of the ground was entirely obstructed, so the pilots had to rely on a sonar altimeter to judge ground proximity. The entire craft had a low rotational inertia, and torque from the spinning rotor blades made the body spin, unless counteracted by yaw thrust in the opposite direction.

The second flight, on September 16, was a continuous hover flight lasting 2 min 30 sec, reaching a maximum altitude of 20&nbsp;ft (6.1 m). The sustained flight was made possible by the installation of more powerful rotor tip thrusters and an autothrottle.

The third and last flight was made on October 12. The ATV flew down the flightline at Mojave Air and Space Port, covering 4,300&nbsp;ft (1,310 m) in its flight and rising to a maximum altitude of 75&nbsp;ft (23 m). The speed was as high as 53&nbsp;mph (85&nbsp;km/h). This test revealed some instability in translational flight.

A fourth test was planned to simulate a full autorotative descent. The ATV would climb to an altitude 10,000&nbsp;ft (3,050 m) under its own power, before throttling back and returning for a soft landing. At this point, given that further funding was then unlikely, safety considerations prevented the test being attempted.

Criticism of the design

Rotary Rocket failed due to lack of funding, but some have suggested that the design itself was inherently flawed.

The Rotary Rocket did fly three test flights and a composite propellant tank survived a full test program, however these tests revealed problems. For instance, the ATV demonstrated that landing the Rotary Rocket was tricky, even dangerous. Test pilots have a rating system, the Cooper-Harper rating scale, for vehicles between 1 and 10 that relates to difficulty to pilot. The Roton ATV scored a 10 — the vehicle simulator was found to be almost unflyable by anyone except the Rotary test pilots, and even then there were short periods where the vehicle was out of control.

Other aspects of the flight plan remained unproven and it is unknown whether Roton could have developed sufficient performance to reach orbit with a single stage, and return – although on paper this might have been possible.

Last days

right|thumb|The Rotary Rocket Hangars at [[Mojave Air and Space Port, as seen in 2005. The taller hangar on the left was the Rotary Rocket Assembly Building.]]

Engine development ceased in 2000, reportedly two weeks before a full-scale test was due. The vehicle failed to secure launch contracts and Rotary Rocket closed in 2001.

The timing of the venture was unfortunate: the Iridium Communications venture was nearing bankruptcy, and the space industry in general was experiencing financial stress. Ultimately, the company did not attract sufficient funding – even though numerous individuals provided a total of $33 million of support, including writer Tom Clancy.

The Atmospheric Test Vehicle was to be displayed at Classic Rotors Museum, a helicopter museum near San Diego, California, but an attempt to move it there on May 9, 2003, via a short-line sling-load under an Army Reserve CH-47 Chinook failed when the Roton began to oscillate at airspeeds above . Instead, the vehicle was kept at Mojave, and on November 10, 2006, the Roton was moved to its permanent display location at the intersection of Airport Blvd and Sabovich Road.

Roton C-9 specifications

See also

  • Hiller Hornet, a helicopter with ramjets mounted on the rotor blade tips.

References

; Citations

; Bibliography

  • Petit, Charles, "Rockets for the Rest of Us." Air&Space/Smithsonian Magazine, March, 1998. A look at the early design of Rotary Rocket.
  • Sarigul-Klijn, Marti, "I Survived the Rotary Rocket." Air&Space/Smithsonian Magazine, March, 2002. The test pilot of the ATV describes the three test flights.
  • Weil, Elizabeth, They All Laughed At Christopher Columbus: An Incurable Dreamer Builds the First Civilian Spaceship. Bantam, 2003. An insider's view of the development of Rotary Rocket.
  • Space.com on test flights; archived copy
  • Space.com on helicopter museum trip
  • QuickTime footage of final test flight of Roton ATV, from the Air&Space Magazine website
  • Archives of original rotaryrocket.com website, from Internet Archive Wayback Machine
  • Tom Brosz's personal account of Rotary Rocket and fallout
  • Photos of the project from the Mojave Virtual Museum
  • Photos from the unveiling of the Roton