Rotary Rocket

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For other uses, see Roton (disambiguation).
The Rotary Rocket Roton ATV on permanent display at the Mojave Spaceport.
The Rotary Rocket Roton ATV on permanent display at the Mojave Spaceport.

Roton was a concept developed in the late 1990s as a fully reusable Single Stage to Orbit (SSTO) manned spacecraft. Roton was intended to reduce costs of launching payloads into low earth orbit by a factor of ten. Gary Hudson championed the design and formed the startup Rotary Rocket, Inc, headquartered in a 45,000-square-foot facility at Mojave Airport. A full-scale test vehicle made three hover flights in 1999, but the company ran out of funds and closed its doors in early 2001.

Contents

[edit] Rotary Rocket design evolution

[edit] Helicopter to orbit

Gary Hudson's initial concept was to meld a rocket with a helicopter: spinning blades, powered by tip jets, would lift the vehicle in the earliest stage of launch. Once the air thinned to the point that helicopter flight was impractical, the vehicle would continue on pure rocket power, with the rotor acting as a giant turbopump.[1]

Calculations showed that the helicopter blades modestly increased the effective specific impulse (Isp) by about 20-30 seconds, essentially only carrying the blades into orbit "for free". Thus, there was no overall gain from this method during ascent. However, the blades could be used to soft land the vehicle, so the landing system cost nothing.

One problem found during research at Rotary was that once the vehicle left the atmosphere additional thrust would be necessary. Thus multiple engines would be needed at the tips as well as the base. Another issue would be noise- the rocket tipped rotor is likely to be extraordinarily noisy.

This version of the Roton had been designed with the small communications satellite market in mind. However, this market crashed, signalled by the failure of Iridium. Consequently, Roton had to be redesigned for heavier payloads.

[edit] Helicopter from orbit

The redesigned Roton was a cone-shaped launch vehicle, with a helicopter rotor on top for use only during landing. An internal cargo bay could be used both for carrying payloads to orbit and bringing others back to Earth. The projected price to orbit of this design was given as $1000 per kg of payload, less than 1/10 of the then-current launch price. Payload capacity was limited to a relatively modest 3 tons.

The company intended to use a unique rotating annular aerospike engine: the engine and base of the launch vehicle would spin at high speed 720 rpm to pump fuel and oxidizer to the rim by centrifugal force. Unlike the landing rotor, due to the shallow angle of the nozzles in the base rotor, the rotation speed self limited and required no control system. At the rim, 96 miniature jets would shoot the burning propellants liquid oxygen (LOX) and kerosene around the rim of the base of the vehicle, which gained the vehicle extra thrust at high altitude- effectively acting as a zero-length truncated aerospike nozzle.[2] A similar system with non-rotating engines was studied for the N1 rocket. The Roton engine had a projected vacuum ISP (specific impulse) of ~355 seconds (3.5 kN·s/kg), which is very high for a LOX/Kerosene engine — and a thrust to weight ratio of 150, which is extremely light.[3]

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. Further, the water metering system would have to be extremely reliable, giving one drop per second per square inch.

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 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. This 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. This composite construction was a world first.

[edit] Roton C-9 specifications

  • Overall dimensions:
    • Height: 63 ft (19.2 m)
    • Maximum diameter: 22 ft (6.7 m)
  • Cargo bay dimensions:
    • Length: 16.7 ft (5.1 m)
    • Diameter: 12 ft (3.7 m)
  • Total mass (estimated): 400,000 lb (180,000 kg)
  • Low Earth Orbit payload (projected): 7,000 lb (3,180 kg)
  • Orbit apogee (projected): 160 mi (260 km)
  • Engine thrust: 6,950 lb (30,860 N)
  • Engine specific impulse (vac): 340 sec
  • Number of engines: 72

(Projections are based on estimates reported in Aviation Week & Space Technology on October 5, 1998.) Also see: [4]

[edit] A new engine

In June of 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.[5] Although the company had raised $30 million, it still needed to raise an additional $120 million before entering service.

[edit] The Atmospheric Test Vehicle (ATV)

The ATV's cockpit was nicknamed the "bat cave" by its pilots because of its restricted field of view.
The ATV's cockpit was nicknamed the "bat cave" by its pilots because of its restricted field of view.

A full size, 63 ft (19 m) tall, Atmospheric Test Vehicle (ATV) was built under contract by Scaled Composites for use in hover test flights. The $2.8 million ATV was not intended as an all-up test article, since it had no rocket engine and no heat shielding. The ATV was rolled out of its Mojave hangar on March 1, 1999, bearing an FAA registry of N990RR.

The rotor head was salvaged from a crashed Sikorsky S-58, at a price of $50,000 — as opposed to as much as $1 million for a new head. Each rotor was powered by a 350-lbf (1,560 N) hydrogen peroxide jet, as intended for the orbital vehicle.[6] 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 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 "bat cave". 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.[7]

The second flight, on September 16, was a continuous hover flight lasting 2 min 30 sec, reaching a maximum altitude of 20 ft (6.1 m). The sustained flight was made possible by the installation of more powerful rotor tip thrusters and an autothrottle.[8]

The third and last flight was made on October 12. The ATV flew down the flightline at Mojave Airport, covering 4,300 ft (1,310 m) in its flight and rising to a maximum altitude of 75 ft (23 m). The speed was as high as 53 mph (85 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 ft (3,050 m) under its own power, before throttling back and returning for a soft landing.[9] At this point, given that further funding was then unlikely, safety considerations prevented the test being attempted.

[edit] Criticism of the design

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

On the one hand, Rotary Rocket demonstrated technical ability in the testing of actual hardware. The ATV flew three test flights and a composite propellant tank survived a full test program. As Jim Ransom, Rotary Rocket consultant, pointed out at the demise of the company, this was more than could be said for Lockheed Martin's X-33, which had a budget 30 times larger.[10]

On the other hand, these tests revealed problems. For instance, the ATV demonstrated that a landing of the Rotary Rocket would be 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 practically unflyable by anyone except the Rotary test pilots, and even then there were expected to be short periods where the vehicle was out of control. Still, further development and better controls would certainly have improved this.

Other aspects of the flight plan remained unproven. It is not known whether Roton could in practice have developed enough overall performance to reach orbit with a single stage, and return — although on paper this might have been possible. These doubts led some of the aerospace community to dismiss the Rotary Rocket concept as an impossible pipe dream.

Whether the full-up vehicle would have worked remains open to speculation.


[edit] The Last Days of Rotary Rocket

The Rotary Rocket Hangars at Mojave Airport, as seen in 2005. The taller hangar on the left is the Rotary Rocket Assembly Building.
The Rotary Rocket Hangars at Mojave Airport, as seen in 2005. The taller hangar on the left is 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 was forced to close its doors in 2001.

The timing of the venture was unfortunate: the Iridium fiasco was coming to a head, and the whole space industry was feeling the pinch. Ultimately, the company did not attract sufficient funding (even though numerous individuals provided a total of $33 million of support, including writer Tom Clancy).

Some of the engineers that worked there have since set up other rocketry ventures, notably XCOR Aerospace and t/Space.

The Atmospheric Test Vehicle was to be displayed at Classic Rotors, 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 35 knots. Instead, the Mojave Airport administration worked to keep this historic vehicle 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. To many, the Roton represents the program that launched Mojave into the Space Age, and this theme was echoed during the dedication ceremony that took place during the Veterans' Day celebration on November 11, at which Brian Binnie was the keynote speaker.

The Rotary Rocket hangars are now occupied by the National Test Pilot School.

[edit] Notes

  • 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. Amazon.com listing

[edit] References

  1. ^ Wired - Insanely Great? or Just Plain Insane?
  2. ^ United States Patent 5842665
  3. ^ Anselmo, Joseph C., "Rotarians." Aviation Week & Space Technology, October 5, 1998, p. 17.
  4. ^ http://www.spaceandtech.com/spacedata/rlvs/rotary_specs.shtml
  5. ^ Dornheim, Michael A., "Rotary Cuts Staff, Changes Engine." Aviation Week & Space Technology, June 28, 1999, p. 44.
  6. ^ Dornheim, Michael A., "Roton Test Craft Rolled Out." Aviation Week & Space Technology, March 8, 1999, p. 40.
  7. ^ Dornheim, Michael A., "Roton Hops Off Ground." Aviation Week & Space Technology, August 12, 1999, p. 36.
  8. ^ Smith, Bruce A., "Roton Test." Aviation Week & Space Technology, October 11, 1999, p. 21.
  9. ^ "Roton Achieves Forward Flight." Aviation Week & Space Technology, October 25, 1999, p. 40.
  10. ^ Agle, D. C., "Sounding: Elegy in the High Desert." Air&Space/Smithsonian Magazine, May, 2001. A short article on the death of Rotary Rocket.

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