These regimes are subsonic, transonic, supersonic, hypersonic, and hypervelocity flow. Transonic, supersonic, and hypersonic flows are all compressible flows. Aerodynamic heating is a concern for supersonic and hypersonic aircraft. This can lead to dramatic improvements in lift for supersonic/hypersonic aircraft. The Reaction Motors XLR99 rocket engine that powered the hypersonic research aircraft used liquid ammonia. Russia is the first country to deploy a hypersonic nuclear missile. Other methods of delivery could include orbital weapons, nuclear torpedo and hypersonic glide vehicles. The missile is also intended to be capable of carrying the Avangard hypersonic glide vehicle. The aircraft is called the Hypersonic Technology Demonstrator Vehicle. Two main types of hypersonic weapons are hypersonic cruise missiles and hypersonic glide vehicles. China is among the countries pursuing hypersonic vehicles as warhead delivery systems. The aircraft will also be capable of firing hypersonic missiles. Mach 11 flight at altitudes, and significant improvements for vehicles designed for continuous hypersonic flight. Most of the jet travels at hypersonic speed. The North American X-15 arrived and began to explore hypersonic and exoatmospheric flight.