Rocket Sled Image
A rocket sled is shown just before launch on the Holloman High Speed Test Track at Holloman Air Force Base, New Mexico.

In preparation for an increased demand of its services over the next decade, the 846th Test Squadron at Holloman Air Force Base, New Mexico, is working to get its hypersonic sled testing program up to speed by continuing a series of preparatory rocket sled tests that began last year at the Holloman High Speed Test Track (HHSTT). The tests are part of an initiative known as the Hypersonic Readiness (HSR) program. The planning stages for this program began around four years ago, with the first sled test conducted last summer.

The HSR program is an in-house project to prepare the 846 TS to carry out the Hypersonic Test and Evaluation Investment Portfolio (HyTIP), Air-Launched Rapid Response Weapon (ARRW) and other anticipated recovered hypersonic sled tests. The HSR program currently consists of multiple dynamic sled test velocities, sled designs, environments and different braking media.

Capability Development Lead Lee Powell said that sled testing in support of HyTIP is planned for 2021, starting with weather effects testing, such as simulated rain encounter. Such testing in support of ARRW is expected to get underway the following year. With this expected uptick in testing at the HHSTT and the testing already set to occur in the next calendar year, it was necessary for the 846 TS to revive, develop and rehearse hypersonic monorail sled test capabilities. The HSR program is primarily focused on the hypersonic 9-inch monorail sled test capability and includes the revival of old, as well as the development of new, high-speed braking capabilities.

“Historical hypersonic sled braking techniques have been retired and current braking methods do not allow entry at the speeds required to recover hypersonic monorail sleds,” Powell said.

Before the HyTIP missions slated for next year and the subsequent ARRW missions are carried out, alternative high-speed braking methods and workforce training must be developed and demonstrated. The HSR effort mainly consists of the development of rail-top braking methods to ensure the sleds launched during testing can be recovered on the rail for post-test analysis.

Four tests have been conducted at the HHSTT as part of the HSR program thus far, the first occurring on June 26, 2019, and the most recent on Aug. 6, 2020. The tests have called for the acceleration of a monorail sled to the supersonic or hypersonic regime. The sleds then coast from peak to speeds ranging from 2,299 feet per second to 2,900 feet per second before entering braking. A new braking wedge design was developed and used on the sleds to interact with rail-top water bag braking and induce a momentum exchange to slow the sled during the testing.

In addition to studying braking performance, the fourth and most recent test called for the sled to be exposed to a 400-foot section of the newly-upgraded 6,000-foot HHSTT “rainfield,” a sprinkler head system designed to simulate natural rain.

“The basic concept was to demonstrate exposure of a developmental material to a ‘rain environment’ in order to test the effects of water droplets hitting a test article at hypersonic velocities; think about the understanding of whether a missile will survive being launched through a rain cloud,” said Bryan Sinkovec, Capability Development Program manager. “The HHSTT rainfield was recently upgraded with a state-of-the-art fiber optic control and data collection system in time to support the 2021 HyTIP missions.”

After exposure to the rainfield, the sled was projected to enter braking at 2,900 feet per second, but it entered much faster than planned.

The three prior tests were considered successful in determining the effectiveness of the new sled design. Each test resulted in safely recovered sleds from the rail. The fourth test was considered a partial success because the sled departed the rail prematurely and was not recovered. However, some sled performance data was acquired.

At nearly 51,000 feet, the HHSTT is the longest facility of its type in the world. The rocket sled track, which is operated by the 846 TS, serves as a critical link between laboratory-type investigations and full-scale flight tests by simulating selected portions of the flight environment under accurately programmed and instrumented conditions. The sleds which serve as the test vehicles are accelerated to mission velocities by means of solid rocket motors, frequently in multi-stage operation.