For the first time, the US Air Force has successfully recovered a reusable rocket sled traveling at hypersonic speed. The test in late March 2022 was part of the Air Force's Hypersonic Sled Recovery (HSR) project and successfully brought a sled traveling at 5.6 times the speed of sound to a stop.
Hypersonic flight technology has a great potential to revolutionize both military and civilian applications, but research in the field has always been extremely difficult stretching back to NASA's X-15 rocket plane project in the 1950s and '60s. One major problem is the intense heat generated in hypersonic flight of over five times the speed of sound. Temperatures can reach in excess of 1,800 °F (1,000 °C), destroying materials, disrupting avionics and flight systems, and putting large amounts of thermal strain on the airframe.
Because of this, engineers are very keen to study the effects of this heat as well as other factors. However, they don't get many chances in a post mortem because flight tests that involve dropping missiles from mother ships usually end with the test craft crashing into the ocean and being lost to the watery depths.
As an alternative, vehicles can be tested on hypersonic test tracks. The latest tests by the 846th Test Squadron's Holloman High Speed Test Track (HHSTT) at Holloman Air Force Base in New Mexico involved using a rocket to accelerate a vehicle riding a monorail at ground level. These spectacular hypersonic drag races pay particular attention to developing high-speed braking technology to recover the vehicle for analysis.
Such sled tests allow engineers to have much more control over the flight variables, which simplifies analysis. Flying at ground level is also useful because military hypersonic missiles will have to fly at low altitude if they are to become practical weapons.
According to the Air Force, the HHSTT is the only sled track that can recover hypersonic vehicles. Though previous rocket sleds have reached speeds in excess of Mach 8, these faster sleds were not recovered. In early March, a sled traveling at 6,400 feet per second (1,951 m/s) on a monorail track was successfully stopped.
"What you accomplished marked the fastest recovery of a monorail sled in over 30 years, and the first time we have recovered a planned reusable sled at those speeds ever," said Lieutenant Colonel Paul Dolce, Commander, 846th Test Squadron, congratulating the team. "Truly historic in my books. This could not have been done without everyone here who works at the track.
"These efforts will now set up our future HyTIP [Hypersonic Test and Evaluation Investment Portfolio] runs for success and add a new capability for our hypersonic customers."
Source: US Air Force
