By Dave Nordling, President, Reaction Research Society
The society had a small work event at the Mojave Test Area on August 4th, 2022. The purpose was limited to starting the build of a new launch pad foundation for Bill Claybaugh’s upcoming large solid motor powered vehciles. The summer heat and tough soil limited progress but it was useful to gauge what the next steps should be. Launch is scheduled for mid-October.
Many thanks to Rushd Julfiker and Joe Dominguez for volunteering their support to Bill on that day. A new and larger launch pad is designed to support Bill’s larger adjustable launch rail system which will be useful to the larger sizes of future rocket projects at the RRS. New developments will be reported in the near future.
by Dave Nordling, President, Reaction Research Society
The University of Michigan came to the Mojave Test Area for another static fire campaign starting Monday, July 25th and ending July 31st. Pyrotechnic operators, Jim Gross, Osvaldo Tarditti and myself supported this protracted campaign in the July heat. The weather was challenging during that week with few heat-related problems other than slow progress which is understandable given the conditions. New RRS member, Rushd Julfiker, and long time member, Jim Gross, assisted me in the cold flow and hot-fire testing. MASA’s academic adviser, Professor Mirko Gamba was also present at the MTA for the days of cold flow and hot-fire testing.
University of Michigan held a Test Readiness Review on Sunday, 7/17/2022, with RRS members present. Many good questions were raised but few corrections were needed. MASA proceeded with packing and departed campus for the MTA on Friday, 7/22/2022.
The team arrived at the MTA on Monday night (7/25/2022) and began to unpack their gear and assemble the mobile test trailer. Leak checking went more smoothly due to design improvements. Problems with the igniter channel would prove to be a recurring concern.
On Friday (7/29/22), gas bottles and cryogenic liquids were recieved from the supplier. Delays in receiving these consumables allowed sufficient time to verify systems were ready. MASA achieved significant progress towards hotfire after completing four valve timing coldflows and one abort test. Analysis of the data from our tests in preparation for hotfire tomorrow.
Saturday (7/30/22) was the first attempt at hot-fire which was unsuccessful due to an igniter failure. The cause was traced back to an intermittent problem with the switch in the junction box. The prior igniter test demonstrated the igniter would fire in the cold flow conditions the day before. Comparing data sets, the team found that a simple verification of continuity in the voltage data stream during the countdown would safely identify a failed igniter firing circuit and allow a safe abort if it were to repeat.
In the last hour of the last day (Sunday, 7/31/22) of the campaign, MASA completed a successful 1 second hot-fire of the 2,000 lbf RP-D2 engine. The chamber and injector remained intact and the system safed itself properly.
After examining the data, pressures were significantly off from the expected profile, but the engine passed the visual inspection After further consideration, the team opted not to proceed with a longer 4-second burn due to the uncertainty about our data values and pressure drops seen from hot-fire. MASA would conduct a more thorough examination of the data and hardware back at the university.
The MASA team began cleaning up the test site on Sunday night and continued throughout the night to prepare for the 1800 mile jouney home. University of Michigan was extremely happy with the result of their campaign and were grateful to our pyro-op’s and membership that supported every day with the MASA team.
The RRS was glad to provide our testing site, resources, experience, labor and insight to this successful testing campaign.
For inquiries about using the RRS Mojave Test Area, contact the RRS president.
Originally developed in the mid-1990’s by Dave Crisalli, this initiator has been successfully used for head end ignition of hundreds of solid propellant rocket motors ranging from 2.5” to 9.0” diameter. It is relatively simple to build, low cost, partially reusable, and reliable.
II – Construction
The initiator consists of four parts: a standard stainless steel AN-4 male plug modified as discussed below, a 9/32” outside diameter aluminum tube with a 0.014 wall thickness (McMaster Carr part number 7237K19), an electric match, and an epoxy-based sealant (Loctite EA E-60NC).
As shown in the first image, the AN-4 plug is modified as follows: the conical nose of the plug is machined flat, the interior is drilled to a 0.281 (“K” sized letter drill) diameter, and two 0.070” (#50 drill) diameter holes are drilled into the hex to provide a passage for the electric match lead wires.
The aluminum tube is cut to the design length (typically 2.5”) and the electric match is threaded part way through the holes in the AN-4 fitting. Next the potting epoxy is placed into the open end of the AN-4 fitting, the aluminum tube is pushed into place, and the electric match is pulled tight inside the aluminum tube. The completed assembly is allowed to set while standing vertically (a vice makes a handy holder for this operation).
III – Testing
Once set, the initiator can be tested by screwing the threaded end into a three to six-inch length aluminum bar drilled length-wise and with an AN-4 port machined into one end; an appropriate high-pressure connection is machined on the other side. Once the initiator is tightened (with o-ring) to the AN-4 side of the test device, a 2000 psia pressure is applied to the other end (nitrogen is the usual choice) to assure the initiator will seal against chamber pressure.
IV – Use
Once the initiator is tested, it can be stored until time of use. At the launch site, the aluminum tube is about half filled with a 0.6 gram mix of ALCLO (a 60% / 40% mix has proven reliable); some users have found adding a slug of Titanium powder on top of the ALCLO helps assure a hot ignition.
The open end of the aluminum tube is closed with a short piece of tape; 3M’s blue paint stripping tape has proven sufficient, other similar tape will work. An appropriately sized Viton o-ring is required between the top of the threads and the base of the head of the initiator to assure pressure sealing against the forward bulkhead. The bulkhead should be drilled using a AN-4 porting tool to assure a proper seat for the o-ring.
For small motors (up to 2.5” OD) the initiator has been found to work fine without augmentation. Larger motors (6.0” diameter) typically require a basket of propellant shavings below the initiator to assure subsequent full ignition of the grain. Still larger motors (9.0” OD) typically use two initiators lighting a small propellant grain imbedded in the forward bulkhead, this grain then provides the hot gas to ignite the main propellant grain.
V – Reuse
The modified Stainless Steel AN-4 fitting can generally be reused by re-drilling the three holes; a good hex collet fixture is useful for holding the fitting while it is being cleaned out. Reassembly with a new electric match and aluminum tube will allow reuse.
VI – Other Uses
A short (1” length aluminum tube) version of the initiator using Nitrocellulose as a gas generator has proven effective as a source of hot gas for actuating valves and other pressure actuated systems. Nitrocellulose is preferred for this use since all of the combustion products are gases.