Saturday, May 19, 2007, 06:20 PM
Today the propulsion team worked on the rocket motor's ablative liner. This fiberglass tube lines the inside of the rocket motor's combustion chamber, protecting the steel walls from the 6000 degree flame inside the rocket motor. The tube is designed to burn away (ablate) during the motor's operation, and must be strong and uniform.
Today, the team applied layers of fiberglass cloth impregnated with epoxy resin to a mandrel, which is sized to the exact inner dimension of the ablative liner. In this picture, you can see Ed (volunteer) demonstrating proper epoxy application technique to the students:
These strips were applied to the mandrel at a 45 degree angle to the expected direction of combustion, decreasing the rate at which the ablative will burn away. In the next picture, you can see Amanda (volunteer) helping the students apply wet fiberglass to the mandrel:
Once the outer diameter of the ablative liner had reached the correct size, the still-wet ablative was vacuum bagged and allowed to cure. On the next work day (mid-June), the ablative will be cut down to the correct outer diameter (using putty to backfill voids, if necessary), polished, and then removed from the mandrel.
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Saturday, May 5, 2007, 05:49 PM
Today the propulsion team installed a new main valve actuator and added the final layers of insulation to the LOX system plumbing.
The original main valve actuator still works fine, and performed as expected during the water and cryogenic testing. We have recently received a new pneumatic valve actuator, though, and we decided that the safety improvement of this new actuator was worth the time required for installation.
Here is a link to a time-lapse movie of us replacing the main valve actuator:
Time Lapse Movie of valve actuator replacement (2MB)
The new valve actuator has an internal spring which forces the valve closed if pneumatic pressure is lost. The original valve actuator was a bi-stable valve meaning that if pneumatic pressure was lost it would remain in its current position. If this failure occurred while the rocket motor was operating, we would have no way to turn off the motor – a potentially hazardous situation.
The most likely cause for losing pneumatic pressure on our test stand is an electrical failure. We protected ourselves from this failure (and a generic actuator failure) by installing a backup shutdown piston which forced the valves closed if the main valve actuator failed. This system works, but only if pneumatic pressure is still available in the backup air tank.
By using the new “spring-return” actuator, we can sustain a loss of electrical power and/or pneumatic pressure during the test firing and still safely turn off the rocket motor - a definite safety improvement.
Here are the before and after pictures of the valve actuator replacement:
Original Valve Actuator
New Valve Actuator
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Saturday, April 28, 2007, 06:40 PM
The computer team has been endlessly testing their software and sensors for function and redundancy. The software has many safety “redlines” for temperature and pressure depending on the current phase of the motor test (propellant loading, actual operation, etc.), and each of them must be tested to the greatest extent possible without actual propellants. In addition to their rigorous testing, the computer team has re-wired parts of the test stand for redundancy and to avoid potential hazards with the propulsion system. The propulsion team continues to work with the computer team to assist this testing and improvement.
During part of today’s testing, two students developed a process for improving the insulation on the main liquid oxygen line, purchased raw materials, and installed the insulation.
Here is a general picture of the work day. Note the completed insulation on the liquid oxygen tank (the big white burrito):
On this work day we also applied the first layer of ablative material to the ablative mandrel. This first layer of the ablative liner serves as a structural support for subsequent layers, and will be allowed to dry for at least a week before adding subsequent material. The interior of the finished product will be the interior of the rocket motor (4.4”), and will burn away as the motor operates:
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