Thursday, August 30, 2012

The Diamant A Launch Vehicle

The Diamant A was France's first orbital launch vehicle, making France the 3rd country with an orbital launch capability after the USSR and the USA. On 26 November 1965, the satellite Asterix was placed into orbit on the first try.

The Diamant A had a number of innovative aspects for its day which might be applicable to small launch vehicles. It had one of the first multinozzle solid motors with gimballing nozzles. It used a solid gas generator to pressurize the first stage liquid propellant tanks. The first stage motors were extremely simple, as liquid motors go, utilizing a graphite throat and film cooling. The Diamant rockets had no guidance system, only a control system, and were guided from the ground.

The Diamant A rocket was a final unifying effort from a multiple step development process. Each of the stages was tested in a separate sounding rocket program. Stage 3 and the Payload shroud were tested separate from the Diamant vehicle as the Rubis sounding rocket, Stage 2 was tested in the Topaz sounding rocket and stage 1 was tested in the Emerald and Saphire

The following table is an estimate of the performance of each stage and the vehicle, as a whole. The nose cone was ejected about 10 seconds into the flight of stage 2 so that stage is broken into two performance phases.

As can be seen, the 3-stage vehicle had a total delta-V of approximately 33000 feet per second (10.1 km/s).


Stage 1 was a pressure-fed liquid propellant stage with 21372 lb-m of Nitric Acid as the oxidizer and 6512 lb-m of Turpentine as the fuel. A 250 lb-m slug of furfuryl alcohol in the fuel lines ignited the propellants. This stage used a unique solid-propellant pressurization system whereby hot gasses from a solid gas generator plus steam generated from water coolant were used to pressurize the propellants to about 320 PSI.

Four fins provided atmospheric pitch/yaw control and two small rocket motors on the tips of opposite fins provided roll control.

The pressurized propellants were burned in the Vexin rocket motor which provided an average of about 69690 lb-f of thrust. The Vexin motor design was quite simple and used a graphite throat with film cooling. The following image shows the general plan of the motor. The motor was basically a steel tube and nozzle with a graphite throat. It also had a radial injection system, not seen on many other motors.

Based on published data fitted to combustion models, the likely characteristics of the motor were:

OF Ratio3.16
OxidizerNitric Acid
Chamber Pressure255 PSI
Sea Level Thrust63620 lb-f
Vacuum Thrust72929 lb-f
Sea Level Isp203 sec
Vacuum Isp233 sec
wdot313 lb/sec
Expansion Ratio3.6
Length~ 72 in
Throat Diameter15.9 in
Nozzle Exit Diameter30.2 in
Engine Weight816 lb
Thrust:Weight Ratio85:1


The Diamant's second stage utilized a solid rocket motor with four steerable nozzles. This motor provided about 33,700 pounds of thrust for about 44 seconds. The propellants were based on polyurethane binder with aluminum fuel and ammonium perchlorate as the oxidizer; this mixture had a trade name of "Isolane." The nozzles were offset from their rotation axis such that by rotating them, the nozzles could direct the thrust off-axis. Hydraulic pistons rotated each nozzle; by coordinating the nozzle rotation, the thrust could be directed as desired for pitch, yaw and roll control.

Design of Nozzles

The second stage also contained an equipment bay containing the telemetry system as well as a gyro-based attitude control system. There was also an interstage adapter which connected to stage 3.

About ten seconds after the second stage's ignition, the nosecone was ejected. The second stage remained connected to the third stage after burnout in order to provide orientation for the third stage. Eight cold gas jets at the base of the stage were used for proper orientation prior to igniting stage 3. The second stage initiated a tilt-over operation using the cold gas jets, and once oriented, the second stage had four solid rocket motors to cause a spin-up of both the second and third stage together. Once the third stage was oriented and spinning, it was ignited and separated from the second stage using two separation rockets on the second stage.


Stage 3 is a 275 RPM spin-stabilized vehicle utilizing a 25.6 in (650 mm) diameter by 82 inch (2100 mm) long solid rocket motor called P0.64. Powered by the same "Isolane" propellant as the second stage, the motor had a peak thrust of 11690 lb-f for an average thrust of about 8573 lb-f; it burned for about 45 seconds with an average Isp of 273 seconds. It had a 3.78 inch (96mm) graphite throat and the chamber pressure varied from a low of 20 atmospheres (290 PSI) to 40 atmospheres (594 PSI) during its burn time.

The motor was manufactured using a wound fiberglass-phenolic casing and a fixed silica-phenolic nozzle reinforced with glass-epoxy winding.


Simulations of the flight indicate that there is an aerodynamic loss of 459 feet per second for both stages 1 and 2. About 451 fps was lost to aerodynamics for stage 1 and about 8 feet per second was lost in stage 2.


Flight simulations indicate that there is about 4041 feet per second of gravity losses during the flight of stages 1 and 2. Stage 1 saw gravity losses of about 2715 fps and stage 2 saw gravity losses of about 1326 fps.


The Diamant A had no on-board guidance system, only an on-board control system utilizing gyroscopes for orientation control. Ground based tracking systems with an uplink control signal provided the guidance for the Diamant A launch vehicle.

  1. Capcom Space []
  2. Villain, J. "The Evolution of Liquid Propulsion in France in the Last 50 Years" Acta Astronautica Vol 22, 1990.
  3. Truchot, Mr A. "Design and Analysis of Solid Rocket Motor Nozzle," Agard Lecture Series 150, Design methods in Solid Rocket Motors, 1988.
  4. Uhrig, G.; Boury, D.; "Large Space Solid Rocket Propulsion in Europe Past and Future Developments," AIAA 1998-3980, AIAA 1998.
  5. Jung, Phillipe; Serra, Jean-Jacques; "VE 210 Rubis: Sounding Rocket on the Road to Space," IAC-05-E4.3.02, International Astronautical Federation 2005.
  6. DIAMANT A ROCKET, France's space agency, the CNES in 60'S [VIDEO] YouTube.

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