The Martlet 3E was a full-bore, rocket-assisted, Fiberglas airframe vehicle 88.5 inches (2.25 m) long and 7.15 inches (18 cm) in diameter. The vehicle used six flip-out fins for stability, a straight tapered nose cone, and the recently-developed hydrostatic containment technique to support the rocket grain during launch. The launch weight of the Martlet 3E vehicle was 135 pound (61 kg) without payload, of which 94 pound (43 kg) was rocket fuel.
The Martlet 3E was initially designed to be launched at a velocity of 1200 m/sec (4000 ft/sec) from the HARP 7 inch guns with a 12 second ignition delay and a seven second rocket motor burn time. The specific impulse of the rocket motor was 280 sec./vacuum. The theoretical performance of the 3E would have allowed a 20 kg payload to be lofted to an altitude of some 250 km - well in excess of the Martlet 2 vehicles performance envelope. Higher launch velocities would have allowed heavier payloads or higher altitudes to be realised.
Considerable research went in to the development of the Martlet 3E with numerous test launches. Individual test programs were conducted to address design concerns with the rocket motor grain hydrostatic-support technique, the structural integrity of the motor's Fiberglas airframe throughout the launch cycle (including case wear), the new flip-out fins, and other aspects.
Most of the development flights of the Martlet 3E were conducted using surplus 155 mm smooth-bore guns (6.25 inch) in place of the 7 inch (7.17 inch actual bore diameter) guns. There were only a limited number of 7 inch guns available. The 155 mm smooth-bore guns were available in larger numbers and were expendable if development problems occurred. Once the primary design problems of the 3E were worked out it was intended to scale the design up from the 6.25 inch to 7.17 inch. The final high altitude vertical flight testing was to be conducted with the 7 inch gun systems.
With the launch costs of the Martlet 3E in the same range as a Martlet 2 vehicles it was intended that once the 3E became operational it would replace the Martlet 2 as the primary atmospheric sounding vehicle for the HARP Program. The use of the 3E over the Martlet 2 would allow portable soundings to be conduced all over the world. This would also free up the 16 inch gun for the future development and operation of a gun-launched satellite vehicle.
by Richard K Graf
Payload: 20 kg (44 lb) to a 250 km altitude.
Stage Data - Martlet 3E
Gross mass: 155 kg (341 lb).
Payload: 20 kg (44 lb).
Height: 2.15 m (7.05 ft).
Diameter: 0.18 m (0.59 ft).
Apogee: 250 km (150 mi).