The ram accelerator belongs to the transverse gas gun family because the hydrogen flow is transverse to the projectile direction. The minimum mass is 104 tons. The maximum velocity is unknown.


The original ram accelerator is a steel tube filled with a gaseous mixture of fuel, oxidizer, and diluent. The most popular gases are methane, oxygen, and nitrogen. To reduce the length of the tube, the mixture is pressurized. A projectile resting on a sabot is fired from a conventional powder gun into the ram accelerator. The projectile compresses the mixture to the point of ignition. Thrust is generated by the mixture expanding behind the projectile. The ram accelerator is plagued by ablation and premature detonation. Direct contact between the projectile and the tube erodes both of them.


A. Hertzberg and A. P. Bruckner,

David W. Bogdanoff, "The Ram Accelerator: A New Chemical Method of Accelerating Projectiles to Ultrahigh Velocities," AIAA Journal, Vol. 26, No. 2, February 1988, pp. 195-203.

P. Kaloupis and A. P. Bruckner, "The Ram Accelerator: A Chemically Driven Mass Launcher," AIAA Paper 88-2968, AIAA/ASME/SAE/ASEE 24th Joint Propulsion Conference, Boston, MA, July 11-13, 1988.

Ram accelerator at the University of Washington.

Ram accelerator at Army Research Laboratory, Aberdeen Proving Ground, Maryland.

Ram accelerator profile

Ram accelerator profile

Ram accelerator section

Ram accelerator section


The hydrogen core ram accelerator is a steel tube divided into two parts: the part near the axis is filled with hydrogen, while the outer part is filled with a mixture of fuel, oxidizer, and diluent. Ablation and premature detonation are reduced by immersing the projectile in hydrogen. Annular or helical dividers also prevent premature detonation. There are 3 variants of the hydrogen core ram accelerator:

  1. Balloon ram accelerator divides the tube with a disposable balloon. It takes lots of manual labor to remove the remnants of old balloon and place new the balloon in the tube.

    Balloon ram accelerator section

    Balloon ram accelerator section

  2. Gas vortex ram accelerator does not have a physical barrier dividing the tube. The gases are separated because they flow in the tube like a vortex. The flow is turbulent so the separation is not perfect.
  3. Powder vortex ram accelerator also employs the vortex to divide the tube. A fine powder of ammonium nitrate is used as the oxidizer. The centrifugal force keeps most of the powder away from the center of the tube. Powder in the center of the tube burns before impinging on the nose cone of the projectile. Helical fins maintain the vortex flow and generate turbulence which ensures uniform density of the powder in the outer part of the tube. Ammonium nitrate is hygroscopic and does not produce soot while burning in hydrogen.


  4. David W. Bogdanoff, "Ram Accelerator Direct Space Launch System - New Concepts," Journal of Propulsion and Power, Vol. 8, March-April 1992, pp. 481-490.
    David W. Bogdanoffand Andrew Higgins, "Hydrogen Core Techniques for the Ram Accelerator," AIAA Paper 96-0668, 34th Aerospace Sciences Meeting and Exhibit, Reno, NV, January 15-18, 1996.


This contraption also has the hydrogen core. The projectile is propelled by a high explosive. Plastic foam protects the steel tube from the explosion. The explosive ram accelerator is more expensive than the hydrogen core ram accelerator. Disposable designs forgo the foam to achieve higher hydrogen pressure.


E. T. Moore, D. Mumma, C. S. Godfrey, and D. Bernstein, "Explosive Gas Guns for Hypervelocity Acceleration," Fourth Hypervelocity Techniques Symposium, Arnold Air Force Station, TN, November 1965, pp. 457-484.

NASA Contractor Reports: CR-982, CR-1533, and CR-2143.

C. A. Rodenberger, "Obtaining Hypervelocity Acceleration Using Propellant-Lined Launch Tubes," NASA CR 10193, 1969.

C. A. Rodenberger, M. L. Sawyer, and M. M. Tower, "On the Feasibility of Obtaining Hypervelocity Acceleration Using Propellant Lined Launch Tubes," NASA CR 108699, 1970.

I. T. Bakirov and V. V. Mitrofanov, "High Velocity Two-Layer Detonation in an Explosive Gas System," Soviet Physics Doklady, Vol. 21, 1976, pp. 704-706.

A. E. Voitenko, "Principal Energy Characteristics of a Linear Jet Engine," Journal of Applied Mechanics and Technical Physics, Vol. 31, 1990, pp. 273-275.

V. I. Tarzhanov, "Massive Body Acceleration on the Detonation Wave Front," Combustion, Explosion, and Shock Waves, Vol. 27, 1991, pp. 130-132.

P. V. Kryukov, "BALSAD-Ballistic System for Antiasteroid Defence," Second International Workshop on Ram Accelerators," Seattle, WA, July 17-20, 1995.

G. Carrier, F. Fendell, and F. Wu, "Projectile Acceleration in a Solid-Propellant-Lined Tube," Combustion Science and Technology, Vol. 104, January 1995, pp. 1-17.

Explosive ram accelerator section

Explosive ram accelerator section

Curator: Al Globus
NASA Responsible Official: Dr. Ruth Globus
If you find any errors on this page contact Al Globus.
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