Editing Project HARP (section)

== Martlet projectiles ==

Several models of test projectiles were fired or designed during Project HARP: These projectiles were fired on the island of Barbados and some were fired by the US Army's Ballistic Research Lab.<ref name=":11" /> The tube's slender design, which contained the rocket's payload, was very narrow and long, limiting what objects could be inserted into the tube. This limitation on size was extremely inconvenient when considering the future proposed payloads of Martlet rockets, including satellites and space probes. The cannon-like design also eliminated the capacity for crewed space travel as well as the launching of satellites carrying extremely sensitive scientific instruments and payloads due to the extreme acceleration placed on the projectile during firing.

=== Martlet 1 ===
The Martlet 1 was the first test projectile of the HARP program. Designed in 1962, it was a 16-inch (406&nbsp;mm) gun bore that weighed 450&nbsp;lb (200&nbsp;kg), was 6.6 inches (170&nbsp;mm) in diameter and 70 inches (1,800&nbsp;mm) long. Only four were manufactured, two of which were fired during the January and June 1963 test series.<ref name=":11" />

=== Martlet 2A, 2B, 2C family ===
The Martlet 2A, 2B, and 2C represented the earliest of the Martlet 2 16-inch (406&nbsp;mm) test projectiles. Martlet 2A was designed simultaneously with the Martlet 1 with a range of interest being 70 to 200 kilometers. Most carried multi-type research payloads studying the upper atmosphere and near-space conditions. Due to their low cost per missile launch, they were used to test out single payloads. Despite similarities in missile airframe, the Martlet 2A, 2B, and 2C featured differences in their structural materials and mechanical details. For the Martlet 2A, the liquid payload was loaded into an aluminum, tapered liner inside the missile body. But by the development of the Martlet 2C series, the aluminum insert was abandoned altogether to allow the liquid payload to be housed in contact with the steel body, increasing the quantity of the liquid payload that could be carried.<ref name=":11" />

=== Martlet 2G and 2G-1 ===
The Martlet 2G was an advanced test projectile with nearly all of its total 350&nbsp;lb (160&nbsp;kg) weight in the projectile. It was tested successfully with the Highwater gun and the Barbados gun but never proceeded beyond the engineering flight testing stage. The Martlet 2G-1 was a proposed space launch vehicle variant of Martlet 2G, which had a solid rocket motor in the projectile. The follow-on 2G-2 proposal was to have had a second rocket motor to place the second stage in orbit, though with little or no payload. After development, it underwent horizontal development firings from the Highwater gun in 1966 but failed to be properly tested in time.<ref name=":11" />

=== Martlet 3 ===
The Martlet 3 series consisted of advanced rocket-propelled projectiles. They were built and tested for the HARP project but were ultimately not successful due to restrictions in funding and a severe lack of technical information regarding large rocket grains' behaviour under high acceleration loading. When testing these projectiles, the danger of in-bore detonation was considered a severe potential problem.<ref name=":11" />

==== Martlet 3A ====
The Martlet 3A was an {{convert|18|cm|in|adj=on}} diameter, gun-fired rocket projectile that theoretically could reach 500&nbsp;km altitude. As HARP's first attempt at a low-cost sabotted rocket system, the projectile was built with [[fiberglass]] or aluminum bodies. A standard 6-inch rocket was bonded to an aluminum case. The rocket nozzle was supported by a pusher plate, which would impart the missile's acceleration through the aluminum wall casing. Fiberglass limited acceleration to 3600&nbsp;[[standard gravity|g]] (corresponding to a velocity of {{convert|3800|ft/s|m/s}} at rocket ignition). The Martlet 3A's original objective was to carry a 40-lbs payload to an altitude of 500&nbsp;km, which theoretically was feasible if the system could be launched at full gun pressures. The rocket motors' solid propellant deformed during firing and the design was never successful, despite several test firings.<ref name=":11" /><ref name="astronautix2">
{{cite encyclopedia
 | title= Martlet 3A
 | encyclopedia= Encyclopedia Astronautica
 | publisher= astronautix.com
 | url= http://www.astronautix.com/lvs/marlet3a.htm
 | access-date= 2016-01-22
 | url-status= dead
 | archive-url= https://web.archive.org/web/20160304000121/http://www.astronautix.com/lvs/marlet3a.htm
 | archive-date= 2016-03-04
}}
</ref>

==== Martlet 3B ====
The Martlet 3B was similar to the Martlet 3A but using steel casings and attempting to solve some of the 3A model's other problems. The casings survived {{convert|5100|ft/s|m/s}}, but the propellant failed at {{convert|3400|ft/s|m/s}}. This was solved for later rockets by filling the propellant cavity with liquid, but only after developing the 3B model had ended.<ref name="astronautix2" />

==== Martlet 3D ====
The Martlet 3D model was planned as a suborbital test rocket, using the first stage of the Martlet 4 solid rocket version. As the Martlet 4 was never built, no Martlet 3Ds were produced either.<ref name="astronautix2" />

==== Martlet 3E ====
The Martlet 3E was a solid suborbital rocket designed to be fired from a smaller, 7-inch (180&nbsp;mm) cannon used in the HARP project. Its basic concept revolved around packaging the rocket grain in a case with elastic properties to transmit the lateral strain to the gun tube. The 3E model utilized a new rocket grain construction technique that consisted of laminating sheet double-base propellant grain under hydraulic pressure.<ref name=":11" />

=== Martlet 4 ===
By July 1964, the Marlet 4 program pursued developing an orbit capable multi-stage rocket system to be launched from the 16" Barbados gun. Two versions of full-scale orbital launch vehicle projectiles were proposed in the Martlet 4 series. The first was to have used three solid rocket motor stages and was planned to orbit approximately 50 pounds of payload. The second used liquid rocket motors and was planned to have orbited 200 pounds of payload. Both were about {{convert|28|ft|m}} long and {{convert|16|in|mm}} in diameter, weighing about {{convert|2900|lb}} at launch. However, no Martlet 4 vehicles were built; the project was halted before the design was completed.

==== Martlet 4 Control Systems ====
A guidance and control system were developed for the orbital mission by Aviation Electric Limited of Montreal under the direction of McGill-BRL-Harry Diamond Laboratory group. [[Infrared]] horizon sensors and sun sensors were included in calculating [[Spacecraft attitude control|vehicle attitude]]. Information for on-board sensors was to be processed by the logic module, which provided commands to a cold gas thruster system which in turn adjusted the vehicle's orientation. The components of the guidance and control assembly were integrated into a 6.25-inch diameter test projectile. Sun sensors, horizon sensors, telemetry packs, receiving/transmitting antenna, hydraulic systems, logic modules, and gas thruster [[Spacecraft attitude control|attitude control]] systems were all test-fired to approximately 10,000 g's.<ref>{{Cite book|last=Bull, G. V. (Gerald V.)|title=Paris Kanonen--the Paris guns (Wilhelmgeschütze) and Project HARP : the application of major calibre guns to atmospheric and space research|date=1988|publisher=E.S. Mittler|others=Murphy, C. H. (Charles H.)|isbn=3-8132-0304-2|location=Herford [Germany]|oclc=24066021}}</ref>