Type: subscale rocket-powered, cable-mounted decoy
Powerplant: 1 x rocket engine
Significant date: April 1991
In 1992, a series of full-page ads was running in engineering and computer magazines, featuring Burt Rutan. This was a humorous ad for a CAD program called Ashlar Vellum, with a picture of Burt holding in mock-seriousness a propeller-head leather flying helmet and the caption "one of America's most thought-provoking engineers". In a way, it was a bit odd using Rutan to promote a CAD system, because as everyone knows, Rutan is a very bright guy and a skilled aerodynamicist, but his drafting skills have been the subject of insider-jokes among engineers for years. And Rutan openly admits he uses the program only for layouts and working out geometry and doesn't use the program for finished drawings. Yet Rutan was enthusiastic about the software’s capabilities as a conceptual design tool.
At the bottom of the ad was an example "engineering drawing courtesy Burt Rutan", an astonishingly crude drawing of a quarter-scale model airplane. It was called the SU-25 Roar, a crude design loosely based on the Soviet Frogfoot combat support aircraft, with all straight lines and a tail on the back, scarcely resembling anything Rutan has designed. The picture could have gone largely unnoticed and the sketch forgotten if not for a mention of the selfsame project in one of Rutan's online biographies, associating the project with Sandia National Laboratories, thus providing some clues as to the purpose of the decoy.
As early as the 1970s, Sandia National Laboratories developed a high-velocity impact testing technique, utilizing a tethered rocket. The technique involved tethering a rocket assembly to a pivot location with high-tensioned ropes and flying it in a semicircular trajectory to deliver the rocket and payload directly to a desired target location, at which point the ropes are terminated. test missile flew on the ropes to a precise hit-point controlled by the location of the rope anchors. Trajectory, angle of attack, velocity, and impact obliquity can all be controlled by rope length, rope tension and target placement.
Sandia led a series of 12 flight tests between May 9, 1989 and 22 March 22, 1990 involving tethered rockets. These proof-of-concept tests were designed to study the high-velocity impact of steel and aluminum materials using high velocity aircraft rockets (HVAR) and Zuni rockets. The test unit was mounted on a steeply inclined rocket launch rail assembly and tethered to a swivel anchor located approximately 200 ft. to the east. Tethered rockets were guided by the steeply inclined launch rail for the first 5 to 6 ft. of flight and then followed an arcing path to the impact area in the northeast portion of the graded area.
The White Sands Missile Range as well as the Rocketball, Model-On-a-Wire (MOW) Facility located at Redstone Arsenal, AL conducted similar research. All three facilities implemented a single cable pulled to a desired tension and used rocket motors and/or gravity to accelerate the payload to velocity for data collection including target radar cross-section, sensor development, and aircraft target representation, and all three documented peak velocities less than 300 m/s that were in the subsonic regime.
Then, in the early 1990s, Sandia went one step further in their research on the subject. An operational computer code, called ROAR (Rocket-on-a-Rope), was developed to simulate the three-dimensional transient dynamic behavior of the tether and motor/payload assembly. Integral to developing this testing technique was the parallel development of accurate simulation models. Burt Rutan's Scaled Composites was contracted to build a tethered sub-scale rocket-powered decoy that was test-flown in April 1991 to validate the program. The fact that it was designated SU-25 has prompted some to believe that the decoy either simulated an imaginary Sukhoi jet or was related in some way to the Army's Su-25 1/5 RPVT scale targets. However, despite the fact the "SU25 1/4 scale model" is a Frogfoot-shaped decoy, there is absolutely NO connection between the Sandia/Scaled rocket decoy and the Army's RPVT program.
Research on the ROAR program was taken one step further a decade later with development of the SROAR (Supersonic Rocket-on-a-Rope) test method, developed as a low-cost and high-fidelity alternative to sled testing. SROAR is the first method to use this technology to attempt velocities greater than Mach 1 or supersonic speeds. The basis of SROAR was a follow-on to Rocketball, a subsonic test facility at Redstone Arsenal used in radar and interceptor testing for active protective system development and evaluation.