Image copyright SpaceX Image caption Elon Musk has described hypersonic flight as “the ultimate rush”
The US military has launched three hypersonic rockets from a proving ground in California.
The hypersonic engines – two from SpaceX and one from United Launch Alliance – reached speeds of Mach 5.1 or more (3,600mph or 5,300km/h).
The tests – one earlier this month and two on Tuesday – were part of a programme to develop systems that will be used in warfare.
They are part of a complex US programme known as Strategic Capabilities Office (SCO) 5.
The SCO program is designed to allow “quick, agile and responsive” uses of hypersonic technology.
Image copyright SpaceX Image caption SpaceX’s X-37B aircraft flew a test flight in April 2013
“The hypersonic weapons layer is a key enabler for this capability,” SCO 5 project manager Brian Mueller said.
He said the SCO program would play a major role in US defense strategy.
“This layer will enhance the speed and survivability of our aviation, missile, and space systems,” he said.
“The SCO will be the spearhead of the US missile, air, and space operations, accelerating innovation, collaborating, and advancing US technology leadership and export policy.”
Testing has been taking place at the Vandenberg Air Force Base in southern California.
SCO 5 is comprised of 15 different projects.
The main aim is to test hypersonic flight technology “through demonstrator flight missions with a variety of payloads, environments, and weapons of the future”.
Development is being carried out under the Rapid Capabilities Office (RCO), which was set up in 2010 and is led by General William Shelton.
Mr Shelton’s office is involved in the Pentagon’s cyber and space warfare programmes.
The RCO’s main role is to choose projects that will have real-world applications.
Image copyright Getty Images Image caption General William Shelton’s office is involved in the Pentagon’s cyber and space warfare programmes
This is managed by the Defense Advanced Research Projects Agency (Darpa).
Darpa has previously conducted hypersonic test flights using military jets.
But these have not reached Mach 5, which is the Mach speed required to stay aloft.
Many missile and satellite launches have been carried out at Mach 5 or above.
The SCO 5 programme is being financed by a military budget of more than $1.2bn (£974m).
It is designed to develop and field hypersonic weapons systems and their technologies, technology and tactics by the end of the decade.
US missile defence programmes have tested hypersonic weapons systems. But these tests have often failed, and so far never used a launch vehicle designed to reach such a high speed.
Several of the top-secret US programmes involves X-37B autonomous spacecraft, similar to the Boeing Phantom Works Centaur T/U, which are reusable, autonomous semi-submersible aircraft.
These had their first test flight in April 2013. In June last year, it landed for the first time without reaching orbit.
It later made a second test flight in September and returned for a third time on 4 February this year.
The X-37B has not set speed records, but it does have the support of the US Department of Defense, which wants to develop vehicles designed to reach hypersonic speeds.
It will be part of the Pentagon’s deep-space exploration effort – called the Advanced Hypersonic Technology programme (HHTP).
Follow Alastair Jamieson on Twitter: @ajjamieson