Project HALO Status Report

Rocket Motor Test Day #2

Held on Sunday, April 15, 1995 at the HALO Rocket Motor Test Facility

The following text was taken, with permission, from an article by Tim Pickens, which was published in the May-June 1995 issue of the Southeastern Space Supporter, newsletter of HAL5.

Three weeks after the first test, on Easter Sunday, April 15, we began the second test.  The crew came out early to correct the data acquisition problems, and were getting very clean (non-noisy) data by 1pm.  Meanwhile, others prepared the motor for firing.  We also laid out rows of bricks over a steel plate as our new flame deflector.  We inserted an ignitor into the motor, strapped the motor to the test stand, and loaded the oxidizer tank.

After the final siren warning, we counted down five seconds, then threw the switch.  With a loud “snap”, the ignitor squib fired and started the ignition process.

In my eagerness, I threw the oxidizer valve switch too early (only one second later).  Raw N2O shot from the motor nozzle and rolled along the ground like a dense fog.  Eventually, the oxidizer pressure dropped low enough that motor ignition finally occurred, but only about 50 lbs of thrust was produced.  All was not lost however.  Data acquisition this time was great and Steve said that he could use this “cold flow” data to verify the mass flow.

Since we had another ignitor and the motor fuel grain was still mostly intact, we decided to try again.  But first, we feasted on a meal of hot dogs, cokes, and Mel’s delicious cookies, provided by Tim Pickens, and prepared by our hosts Herman and Chris Pickens.

The Second Motor Test

By now, night had fallen, but we were ready to try again.  After the “snap” of the ignitor, we were determined to wait a full two seconds before opening the valve.  We did so, but nothing happened after we heard the “snap” of the oxidizer valve squib firing.  The valve was still closed and the ignitor was still burning away creating more fuel vapor.

As soon as I realized what was happening, I pulled hard on the string serving as our backup, manual release.  By now five seconds had elapsed, and the chamber was filled with excess hot fuel vapor.  When the fuel and oxidizer finally mixed, the chamber pressure rose so high that it blew out the copper tubing running to our big pressure gauge.  The rocket motor roared to life, but some of the thrust went sideways out through the quarter-inch hole of our chamber pressure tap.  The test lasted for 16 seconds.

It was quite a sight to see, especially at night.  Since we had no way of stopping the test (this was later corrected), we just watched in awe as the powerful vertical thrust slid aside our flame deflector bricks (so much for that idea), while the less powerful (but more exciting) horizontal thrust spewed arc-welder-like sparks across the test stand where they bounced off the concrete wall (thankfully protecting our N2O supply bottle).

Lessons from the Second Test

The second motor test proved to be a turning point for our test oxidizer flow system.  We decided to abandon the unreliable ball valve design in favor of one which could be activated by a pyrotechnic charge.  There would be no room for failure in our flight vehicle.

We also decided to stop testing potential flight-capable oxidizer valves while trying to prove that the motor itself worked.  For ground tests, therefore, we switched to a sturdier pneumatically-controlled valve which could be closed by command, thus shutting off the oxidizer flow.  We also added a second one-way valve which would prevent any thrust from running back into the oxidizer tank.  Our last test revealed a fuel-rich condition and a low fuel regression rate; therefore we built a new injector which would allow more mass flow.

We replaced the broken copper tubing with a sturdier flexible steel hose.  We also added “snubbers” to all our pressure sensors, which would filter out big spikes in pressure and thus help to prevent another blowout.  Steve assembled a sequencer which would allow us to precisely control the time between ignition and the valve opening, and also to control the length of the burn.

Ad Astra per Ardua -- “To the Stars by Our Own Hands”

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This file was last modified on Saturday, 15-Apr-2017 13:19:39 EDT