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The Atmospheric Test Vehicle flying at Mojave Airport.

Three views of the Roton ATV demonstrator on its rollout.

A fascinating view of the evolution in SSTO design development by Gary C. Hudson, who played quite a part in many of these projects.

Type: demonstrator for SSTO launch vehicle

Type:

Program:

Powerplant: 1 x rotary RocketJet™ aerospike engine and several Derived Fastrac Engines
(to provide necessary thrust at take-off)

Important dates:
- 01/03/99: First Rollout
- 23/07/99: First liftoff to a controlled hover
- 16/09/99: 2nd flight to 20’ testing cyclic control (extended hover)
- 12/10/99: Final flight (first translational) to 75’ and flew 4,300’ at 53mph

The ATV was an approach-and-landing demonstrator for the Roton, a privately funded single-stage-to-orbit launch vehicle. The company Rotary Rocket was formed by space entrepreneur Gary C. Hudson to pursue the Roton™ design and after it raised enough funding to begin hardware development, the company attracted a tremendous amount of attention. As early as 1996, Hudson had begun working with Bevin McKinney, who had invented a radical SSTO concept that used a rocket-tipped rotor propulsion system. The rotors provided lift with the rockets and from the propeller effect while in the atmosphere. Furthermore, the spinning would provide pumping action on the fuel and thus eliminate the weight of separate pumps. The rotors would also provide for a helicopter-like landing.

Drawing from the general principles of that concept, Hudson and his newly-formed company aimed for the Roton to provide unparalleled operability, reliability, and safety while providing single-stage-to-orbit capability. To achieve the goal of an SSTO space vehicle required both high performance rocket engines and a lightweight vehicle structure to contain propellants and cargo. Several comsat constellation projects in low earth orbit began around this time and they promised to provide a solid market for a low cost vehicle that could carry replacement satellites to orbit. Excitement grew that finally low cost access to space was at hand.

Getting to orbit was only part of the challenge, however. The other key aspect of a reusable vehicle was return from space. The Roton was to accomplish this using conventional thermal protection to moderate the heat of reentry into the earth's atmosphere. The Roton would also utilize a deployable helicopter rotor to provide braking, stability and soft landing capability. The natural autorotation of the external rotors deployed during the return flight would enable a slow, controlled, descent to a soft precision landing. This would make the Roton capable of safely returning itself and its cargo to the ground at any point in flight, a technology dating back several decades. Vertical takeoff and landing also minimized land overflight and the effect of sonic booms, and needed only a small site for flight operations. The Roton would also land without any fuel on-board, enhancing safety. Reusability also ensured that individual vehicles could be flight tested repeatedly. Consequently, prior to achieving operational status, the Roton was to be put through more flight tests than many expendable rockets encounter in 10 years of operation.

High engine performance was achieved through the breakthrough technology of the RocketJet™ rotary aerospike engine. This engine featured an innovative blending of jet and rocket engine technology. RocketJet™ technology was proprietary to Rotary Rocket Company. The company's propulsion expertise was unique in the industry and ensured the propulsion system was exactly tuned to the vehicle, resulting in both high efficiency and high performance. This also gave the company total control over the key strategic business issues of engine cost and availability. The RocketJet™ engine automatically compensated for the decrease in atmospheric density as the vehicle ascended to orbit, maintaining outstanding engine efficiency and high vehicle performance. The engine rotated about the Roton's longitudinal axis, generating the centrifugal force necessary for pumping the propellants at high pressure to the engine's banks of multiple combustion chambers. This eliminated the need for complex and fragile turbo pumps as used in the Space Shuttle and most existing rockets. The engine would burn conventional jet fuel and liquid oxygen, and at take-off the Roton would carry less fuel than conventional transport aircraft. These propellants also produced an exhaust that was virtually benign to the environment. Tests of this innovative, patent-pending, propulsion system were conducted.

Powered by its rotary RocketJet™ aerospike engine burning liquid oxygen and jet fuel, the Roton was to deliver cargo to low earth orbit and return for reuse without discarding or expending any component. As with a conventional jet aircraft, only liquid propellant was consumed during a flight, and no refurbishment was required to prepare the vehicle for another flight. If a problem developed during flight the Roton could, in most instances, terminate the flight and return safely to the ground. A fleet of Rotons would provide fast, reliable and economical service in the same manner as any of today's airfreight companies, fundamentally changing the economics of carrying cargo to space. This contrasted strongly with the current industry practice of simply throwing away an expensive launch vehicle each flight.

A lightweight vehicle structure was obtained though the extensive use of sophisticated composite materials. These materials had already been used successfully in the DC-X program and in dozens of advanced aircraft, many of which (including the McDonnell-Douglas DC-X aeroshell) had been built by Scaled Composites, the integrating contractor for the Roton. Scaled was responsible for building the Roton's composite airframe, propellant tanks, cargo bay fairing, rotor, and thrust structure/heat shield. Rutan even named the Roton "the most important project ever to come in the doors at Scaled Composites."

"The third and last flight occurred on October 12, 1999. The ATV climbed to 75 feet and accelerated while traveling 4,300 feet down Mojave's main runway. We were shook by a thundering airframe vibration of about two Gs while in forward flight. The vibration disappeared in hover. We later discovered it was caused by the impingement of the rotor wake, which was energized by the rotor tip rocket exhaust, onto the airframe. The vibration caused several airframe components to break loose, including the propellant catalyst tank, which was found hanging by its plumbing lines. If the catalyst plumbing had failed, the tip rockets would have stopped, and the ATV would likely have crashed." — Marti Sarigul-Klijn, Cdr., USN (ret.)

Unfortunately, when Iridium and GlobalStar went bankrupt, investment in Rotary and several other startup RLV companies disappeared and Rotary closed in 2000. However, before the company shut down, it did manage to test the rotor landing system with three low altitude flights of the full scale ATV (Atmospheric Test Vehicle). Head of Rotary Rocket Gary C. Hudson left the company earlier to work at HMX and to pursue other interests. The Mojave facility was closed after an auction of most of its contents. Rights to the various technologies, e.g. composite fuel tanks, that were developed by the company were sold to XCOR, a company founded by several former Rotary employees.

the ATV was roughly comparable to the MDA DC-X in that it was a landing system technology demonstrator. However, it differed from the DC-X in that on completion of the ATV test flights, the Roton vehicle low speed aerodynamics and control laws would have been measured in full scale, rather than the subscale of the DC-X and the X-33. The ATV also tested the manufacturing methods for the liquid oxygen and kerosene tanks for the orbital Roton vehicle. The Roton was to enter base first, so the ATV did not need to perform comparable tests to the rotation maneuver which was necessary for the DC-X to demonstrate for the operational Delta Clipper side entry profile. The ATV was only a big, hydrogen-peroxide powered helicopter, but it demonstrated a level of commitment and follow-through toward an operational SSTO vehicle in its structures and configuration that the DC-X lacked.

Population: 1 [N990RR]

Specs:
Height: 64 ft.
Diameter: 22 ft. (at landing pads – 31 ft.)
Rotor type: Deployable Autorotative
Rotor blade diameter: 53 ft.
Gross weight: 15,000 lbs. (with hydrogen peroxide and pilots)
Empty weight: 9,700 lbs.

Crew/passengers: 2
(retired Navy Commanders Brian Binnie and Dr. Marti Sarigul-Klijn)

Following specs for unbuilt Roton C-9 PTV (Propulsion Test Vehicles)

Vehicle characteristics:
- Two-person piloted space vehicle (pilot and cargo specialist)
- Fully Reusable
- Single Stage to Orbit (SSTO)
- Virtually all-weather operation
- Vertical Take-off and Landing (VTOL)
- Controlled, soft, landing using autorotating rotor and tip mounted thrusters

Specifications:
- Height: 64 feet
- Diameter: 22 feet maximum
- Launch weight (GLOW): <400,000 lbs
- Main engine: Rotary RocketJet Aerospike
Engine speed: 720 rpm
+ 72 Derived Fastrac Engines on spinning arms creating Centrifugal Pressure to provide the necessary thrust at take-off
- Propellants: LOX (Liquid Oxygen) (70,000 lbs) and Kerosene (230,000 lbs)
- Expected Burn Time: 253 seconds
- Thrust: 500,000 lbs
- Payload: 7,000 lbs to low earth
- Target price per flight: $7 million

Cargo Environment:
- Capability: 7000 lbs to 50° / 160 nm orbit
- Cargo envelope: 144" dia x 200" high
- 4 g axial load limit on ascent
- 8 g axial load limit on return
- 1.5 g lateral load limit
- No pyrotechnic shock on payload release
- Ascent environment controlled to 32°C
- Cleanliness to class 100,000
- Flights out of Mojave, California

Description of a typical mission program for the Roton PTV.

Artist's rendering of the original Roton design with rocket tipped rotors.

A world of a difference between the Roton-C rotorcraft and the Roton SSTO.

Two snapshots of the Roton ATV's unusual two-place cockpit.

The Roton ATV preserved at the Classic Rotors Museum.

5,000 lb-thrust lox-kerosene engine fired at Rotary in 1999.

Superb artist's rendering of Roton PTV from Scaled's website.

Gary Hudson on the Roton/ATV debacle

If you were given $300 million today to build a RLV, would you still go with the basic Roton approach?

No. The Roton project was one of those train wrecks where everyone can see the bridge is out but the engineer can't slow the train down in time. And other people are throwing the switches. Bevin's original or "classic" Roton was a fun, cool idea. Using self-pumping and some aerodynamic lift augmentation up to about Mach 1.3, it could have performed the X-prize mission or put a couple of people and a ham sandwich into orbit. One feature that was particularly appealing was that the ascent lift augmentation (about 25-30 seconds Isp) paid for the weight of the rotor on orbit, and the rotor could be used to aid re-entry and provide soft, controllable landings. We felt that was a big win.

After we found funding for that vehicle, we also found ourselves in the position that our initial funds would not see us to flight, far from it. And our prime investor told us at the outset that we had to find other investors to fund the rest of the development. That was OK by me, and off we went. But we could not find any other investors willing to build a small piloted vehicle mainly configured for human spaceflight and small cargo, and were forced to either close our doors or retool the concept to meet the need for LEO comsats. The classic Roton might have been able to fly some of the early LEO spacecraft designs, one spacecraft at a time, but soon those grew in size many-fold and instead of a thousand pounds to LEO, we were facing 7000 pounds. The classic couldn't do that, and so the Roton everyone knows emerged. In hindsight, we'd have been better off walking away then, but no one suggested we do so.

In retrospect, are there any fundamental aspects of the Rotary Rocket project that you would do differently if you could do it over again?

(...) Short answer is yes, there are many things. A few key points: One is never start a project in the public eye that doesn't have all the cash in hand before you go public. (I might even amend that to wait until you are starting to fly before you go public!) Another is don't split your operation in two (in our case, the Bay area and Mojave). Third would be to control your hiring process carefully. A few hiring mistakes can consume huge amounts of management time to fix or mitigate damage. Having said all that, I am still very proud of the accomplishments of Rotary Rocket. We designed and flew, in one year's time, a full-size, piloted Roton demonstrator, that showed a lightweight SSTO with composite LOX tanks could in fact be in built. It was the only flying RLV demonstrator since DC-X. None of NASA's (or should I say the taxpayer's) billions produced anything that flew with humans. (...) They no longer have any artists, only managers. Systems engineering is an art, not a science. Folks like Kelly Johnson and Burt are aircraft artists. They blend equal parts vision, engineering and intuition to make successful design. Of course, in doing so, they also produce some stinkers. That is the price of this approach. The current industry doesn't select for such individuals, and I can see no way that it ever will.

Full interview on the HobbySpace.com website