“Screws can back out; things can break,” says Greg Tipton, a structural dynamics engineer at Sandia National Laboratories.
An early milestone for new missiles is showing they can withstand abuse without falling to pieces by surviving computer-simulations or large-scale field tests that shake and spin components.
High operational tempo sounding rocket program (HOT SHOT) tests – research rocket design iterations filled with experimental modules to determine capabilities – are critical to that proving-out process. Recent data analysis has revealed a way to improve these tests, providing an earlier, more accurate indicator of whether an experimental technology will succeed in flight. This could eliminate approximately a year’s worth of additional research and development.
Tipton and his team dressed the insides of several sounding rockets with pea-sized instruments to measure vibration, producing a more complete picture of flight vibrations now being used to create more accurate simulations and ground tests.
“Flight gives you combined environments that you wouldn’t get on the ground,” Tipton says. “So, it’s spinning and it’s accelerating and it’s vibrating, there are shocks. It’s a whole different kind of environment.”
The HOT SHOT program measures the effects of a rocket launch on missile prototypes. Sandia builds the rockets, integrates the experiments, and operates the launches for the National Nuclear Security Administration.
In May 2018, Tipton and his team built a mock component for the rocket, which they called the wedding cake, then decorated it with vibration sensors. After the launch, they played a mathematical game with the data. Knowing only vibration data from a few sensors, they calculated the readings on every other sensor.
“We showed we could do this and predict what the vibration environments were pretty much anywhere on that structure,” Tipton says.
They recently repeated the experiment, outfitting the payload sections of two rockets to measure vibrations on more experimental hardware. Initial data analysis suggests they can predict vibration at virtually any point within that section of the rocket.
The Sandia team must now recreate the HOT SHOT flight environment using ground test technology. If successful, this testing platform will generate more and better data than is usually available for missile technologies in early stages of development. The team is exploring acoustics and vibrating patches to recreate complex vibrational patterns that are difficult to reproduce using conventional shaker tables.
Olga Spahn, Sandia’s HOT SHOT payload integration manager, says better data early in development could reduce failure risk, allowing researchers to explore new, innovative ideas. It could also improve the overall performance of future missile systems by fostering development of components that reduce size, weight, and power requirements.