-- Rocket Motor Test Day #15
Held on Sunday, November 2, 1997 at the HALO Rocket Motor Test Facility
The following previously unpublished text would have been, given more time and space, part of an article by Ronnie Lajoie, which was to be published in the November-December 1997 issue of the Southeastern Space Supporter, newsletter of HAL5.
On Sunday, November 2, the HALO team held its 15th motor test firing day. This was to be the final test of the flight hardware of the SL-2 hybrid rocket motor. The new SL-2 combination oxidizer tank and motor casing had already been successfully hydrostatically pressure tested. The test stand had been enlarged to accomodate the 10-foot object. Since the flight hardware was being tested, the rocket motor would perform a complete 20-second beginning to end burn.
It was a very cold day, and it was very difficult to keep the nitrous oxide supply bottle warm. We ate lunch while waiting for the nitrous tank to warm up, but it never even reached 60-deg-F, and we wanted at least 70. A colder-than-desired nitrous oxide would mean that the tank pressure would be lower than desired, resulting in a longer-than-desired burn time -- as much as 60 seconds.
After a review of the possible dangers with such a long test (e.g., would the fiberglass motor casing hold up, would the nozzle burn through, etc.), a decision was made to proceed with the test. The test did not go as planned. The long burn time caused the nozzle to burn off the end of the motor, and it rolled away in a useless burning heap.
The burn lasted more than 60 seconds, and was almost over (into the gaseous phase) when the steel ring holding the motor inside the combination tank/motor casing finally succumbed to the heat. The motor shot out of the casing, but the top steel ring stopped the floating bottom of the oxidizer tank from coming out as well. The force of the gas expansion was tremendous, and the sudden stopping of the floating oxidizer plate turned the casing into a very large tensile strength test subject. Nature won. The combination tank/motor casing sheared apart near the base with a very loud BOOM! -- even though it was just the expansion of the remaining gaseous nitrous oxide in the tank. The top of the tank shot upwards into the air and landed on the other side of the barn. No person or property was harmed by this unfortunate incident.
Needless to say, the entire tank/motor assembly was ruined beyond repair. A HALO SL-2 Design Review was held shortly afterwards. Based on the disappointing results of the test, the entire SL-2 tank/motor assembly would be redesigned. This new design is the one which appears on the HALO SL-2 Web site.
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This file was last modified on Saturday, 15-Apr-2017 13:19:40 EDT