Encyclopedia Astronautica
HARP 5-3

HARP 7 & 5 in probes
From left to right: HARP 7-1, 7-2, 5-1, and 5-3.
HARP 5 inch Gun
Canadian earth atmosphere satellite. Study 1960. The HARP 5-3 probe was developed during HARP to reduce the complexity of the 5 inch vehicles and in particular the nose eject system used by the HARP 5-1 probe.

Although simple in design, the components which made up the nose eject system of the 5-1 probe constituted a considerable portion of the 5-1 probes manufacturing resources. To simplify the manufacturing of the 5 inch probes a new probe design was considered that replaced the 5-1 tapered boat tail with a straight tail and permitted payloads to be ejected out the rear of the projectile at altitudes of up to 61 km.

The 5-3 probe retained the general characteristics of its predecessors with a flight weight of 10.4 kg, a major diameter of 66 mm and an over length of 116 cm. The forward body retained the same general shape as the 5-1 and it used the same sabotry. The tail boom of the 5-3 probe was significantly modified, with a straight tail boom and 6 fins (versus the 4 finned tapered tail boom of the 5-1). This straight tail boom was hollow and provided a payload chamber that ran nearly half of the length of the probe's body.

The payload ejection profile for the 5-3 was simplified as well. To prevent gun gases from entering the probe's rear payload compartment during launching the base of the tail boom was fitted with a simple shouldered plug. This plug used O-ring seals to prevent entry of gun gases and had a slightly oversized lip which allowed aerodynamic forces to blow the plug off of the probe body after launch. After the base plug was separated the payload would be retained by small shear pins. At launch a single mechanical fuse would be activated. This was similar to the 5-1 probe, but instead of using a pyrotechnic charge to eject the payload, the timer would break the seal on a small CO2 cartridge which would pressurize the compartment and force the payload out.

The rear ejection technique of the 5-3 probe was a very successful method of deploying payloads without the complexities of the 5-1 probe. The design of the 5-3 was not without its disadvantages. The straight tail boom of the 5-3 exhibited poor aerodynamic characteristics compared to the tapered base of the 5-1. This reduced the 5-3 probe's apogee to only about 61 km (versus the 76 km of the 5-1). The lower altitude of the 5-3 was not considered too much of a concern, at the time. The majority of the flights conducted with the 5-3 were parachuted Metsondes. Above 60 km parachutes provided limited support, so there was no major loss of payload performance.

The 5 inch HARP gun probes were a remarkable successful instruments and some 300 flights were conducted over a 5 year period during HARP. With the main propulsion stage (the gun launcher) being a reusable ground based system the launch costs were in the range of about $300-$500 each flight providing a remarkably low cost launch system, which was more then capable of fulfilling its HARP role.

by Richard K Graf

Gross mass: 10 kg (23 lb).
Payload: 0.90 kg (1.98 lb).
Height: 1.16 m (3.80 ft).
Span: 0.13 m (0.42 ft).

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Associated Countries
See also
  • Gun-launched Artillery dominated military ballistics from the earliest use of gunpowder. In 1865 Jules Verne could only realistically consider a cannon for a moon launch in his influential novel. Even after the rocket established its primacy as a method of accessing space, Canadian Gerald Bull began a life-long struggle to use guns for cheap access to space. His successes could not generate funding to continue. Others since then have pursued the technology, convinced it was the only way for low-cost delivery of payloads to orbit. More...

Associated Launch Vehicles
  • 5 inch HARP Gun Canadian gun-launched sounding rocket. When most people think of the HARP Program they usually think of the big 16 inch guns roaring skywards as they launch test probes into the upper atmosphere. What most people do not realise was that even before HARP small portable gun launchers were used for the same purpose and even during HARP hundreds of high altitude flights were conducted using small guns. The 5 inch gun-launch system was initially designed to satisfy the requirements of the Meteorological Rocket Network This required that an 0.9 kg (2 lb) payload be carried to an altitude of 65 km (40 miles). Typical payloads were radar reflective chaff ejected at apogee, which was tracked by radar to yield wind data, and small Metsondes which drifted to earth under large parachutes and returned radio telemetry of temperature, humidity and the like. More...

Associated Manufacturers and Agencies
  • Bull Canadian manufacturer of rockets, spacecraft, and rocket engines. Bull, Canada. More...

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