MTA Firing Report, 2022-01-15

by Bill Inman, Member, Reaction Research Society

A few of us met at the Mojave Test Area on Saturday, January 15, 2022, to conduct an elevated temperature burst test of a 5-gallon (20-pound) propane container partially filled with water, Dave Nordling was the pyrotechnic operator in charge for this event, The objective was to determine practical limits for use as steam rocket vessel. This was an extremely dangerous task and having only those necessary to conduct the test was prudent.

The 20-lb propane bottle that was to be failure tested was an old surplus asset retired from serivce, The capacity of this particular propane fuel cylinder was measured at 46.4 lbs. of liquid water (1285 cubic inches). Propane containers by regulations are only filled to 80% of their liquid volumetric capacity. The water fill level for this test, since higher temperatures than reached by normally reached in steam rocket operations were anticipated was only 4 gallons or 71% of the 5.57 gallon total to provide more internal room for thermal expansion.

Propane container with some of the heating shroud sitting in a metal frame
The test article being filled by siphon tube.

Filling of the vessel was done through a reducer bushing in the factory opening via a siphon tube from water bottles. Heating of the sealed vessel charged with water was done by a propane fired turkey fryer burner, The burner was positioned directly underneath the center of the bottle which was propped up by a metal frame. The positioning of the burner was both by eye and by feeling for the weld seam running around the middle of the tank. The propane fuel hose and pull cable to remotely pull away the burner if necessary were both on the right side as viewed from the blockhouse. Automotive brake line was used to connect a pressure gauge for visual readout at a distance and manual ball valve on a tee to allow remote venting of the setup if the need arose, Mechanical pull cables were carefully routed back to the blockhouse. All mechanical control devices were tested and safe operation verified before starting the heating process.

The test article sits on its side with a sheet metal shroud covering it to better control the heat applied from the burner below.

The test article on the north side of the vertical test stand just behind the large I-beam. The pressure gauge and the video camera recording the gauge readings were on the opposite side of the I-beam and all controls were remotely handled from the blockhouse.  Due to the expected destruction of most of the test stand and related components, everything was kept minimal, with no planned provision for securing it beyond the clamps holding the sheet metal shroud in place over the test article.

Large diameter pressure gauge was visible from the blockhouse. The ball valve used to remotely relieve the tank has a cable connected to the handle.

All operations went smoothly and everyone was safely secured in the blockhouse. The heating rate from the turkey fryer bunrer was somewhere over 100,000 BTU/hr based on literature which was sufficient for a steady increase in pressure which took just a little longer than 45 minutes. The propane container used to feed the burner had sufficient fuel to last 2 to 3 hours in effect limiting the test if no action was taken once the burner was lit. As long as all parties remained safely behind cover and at a safe distance, we only had to wait. If somehow, the vessel failed to burst and the manual valve would not open remotely by the mechanical pull cable from the blockhouse. the test article would be left untouched and we would allow 24 hours for the vessel to return to ambient temperature.

Listed design burst pressure was about 960 psig based on a four-fold safety factor of the nominal rating of 240 psig for propane service. As these containers are meant for public use and rougher handling at campsites, they are likely way over-designed. Conversely, these containers often get dented, abused and corroded over time. The exact failure point on any given vessel is not easily determined from so many uncontrolled factors. According to the graphs in the report of a testing program commissioned by the propane industry (1), the average as-tested burst pressure of used cylinders of this type appeared to be in the 1250 to 1600 psig range. But these vessels aren’t normally actively heated which makes analysis less certain, thus the reason for this testing program, and this being the first test. The cylinder chosen for this test had a fair amount of rust evident around the bottom and a few inches up from it. For the next test, a cylinder in better condition will be used to see how they compare.

Carrie Uetz and Bill Inman sits in the blockhouse as the vessel steadily heats and the pressure rises.

The vessel failed at 1135 psig in a sudden violent burst a little above the expected burst pressure but within the 1500 psig range of the gauge. The pressure wave was enough to shatter the row of cinder blocks put beside the test article to block the wind. The test article ruptured at the weld seam. The metal support structure was blown apart, converted into twisted pieces of steel, and the sheet metal shroud was shredded in numerous pieces scattered all across the area and crumpled up like aluminum foil. Some parts, including the largest piece of the tank weighing 10.5 pounds, were found almost 100 yards away. The I-beam deflected the debris away from the occupied blockhouse, but the shockwave, which was felt by us inside the blockhouse, managed to break one of the windows in the Dosa Building. The blockhouse with the blast windows continues to be a useful asset for the society.

The remains of the test article and surrounding debris was gathered up and the site cleaned up.
Clean up was extensive.

Preliminary answers to questions going in (pending confirmation of these results in a follow-on test):

What is the “real-world” burst pressure of a retired propane cylinder on it’s first use as it would be for a steam rocket motor, and would it be significantly less than that of a cylinder used only in normal propane service?

ANSWER: 1135 psig, and apparently some less (approximately 20.5%), although this one was not in pristine condition, either.

Is the prediction that it will fail along a seam (weld) true?

ANSWER: it appears to be, as there was a long tear along the seam, although there were many other tears in quite a few other locations as well. Six pieces were recovered but there is still over a pound missing compared to the starting empty weight, meaning there are at least seven pieces.

Will the area the burner flame impinges upon be weakened more than the rest of the tank?

ANSWER: It appears so, as the area where the longitudinal tear and the tear along the seam intersect shows evidence of the paint being more completely burned away than elsewhere. But again, there were many additional tears as well, so not sure exactly how to factor that into the analysis – and would an arrangement to keep the burner moving back and forth while heating reduce any such tendency?

Burst pressure data of several aged propane cylinders

Reference 1: National Propane Gas Association, Final Report on Testing and Assessment of CG-7 Pressure Relief Valve and Propane Cylinder Performance, Volume One: Results and Evaluation, January 31, 2003, by D. R. Stephens, M. T. Gifford, R. B Francini, and D. D. Mooney

December 2021 Virtual Meeting

by Keith Yoerg (RRS Secretary)

The latest meeting of the Reaction Research Society took place by teleconference on Friday, December 10th and had twelve attendees.

Screenshot of discussion during the monthly meeting


Keith kicked off the meeting with a recap of the first launch of his rocket “The Hawk” an 8-inch diameter 14-foot tall rocket that was flown from the RRS Mojave Test Area on November 28th. The rocket utilized the 1515 rail launcher which was secured in place to one of the concrete pads using sandbags and tie-downs. The motor was a 98mm Cesaroni M1790 Skidmark which features sparks in the trail.

First launch of Keith Yoerg’s rocket “The Hawk”

Keith shared some slow-motion video of the flight captured with a GoPro camera and other data from the flight, including a 3D flight path. The rocket reached an altitude of 4,846 feet as measured by the barometer on the onboard AltusMetrum Telemega flight computer, and was successfully recovered with only minimal damage to the body tube. The rocket is in the process of being prepared for another launch on December 17th to coincide with the anniversary of the Wright Brothers first flight.

Map of the flight path with barometric altitudes in red and GPS in blue. The GPS appears less reliable on this flight.


Election chairman Drew Cortopassi presented the results of the 2022 executive council elections. The RRS Executive Council for 2022 is as follows:

President:    David Nordling
Vice President:    Frank Miuccio
Secretary:    Keith Yoerg
Treasurer:    Larry Hoffing

The society members in attendance congratulated the incoming new president and other incumbent officers and expressed their gratitude to outgoing president Osvaldo Tarditti for his stewardship of the organization. Osvaldo noted that the future of the group looks bright, and promised to send anyone who asks him a question a photo of him fishing.


Osvaldo and Dimitri provided a recap of the lengthy solid rocket motor testing campaign that USC conducted at the MTA from December 4-5. On Saturday the 4th, the team worked through the night until around 2 am to be able to complete their goal of firing 20 separate grains of solid fuel by 2:45 pm on Sunday the 5th. The only reported mishap was that the U-Haul the USC team rented broke down just after leaving the dirt road to the MTA, which Dimitri suspected was because they had been using the battery from it to fire the rocket motors.

While the campaign was an ambitious one, the repetitious nature allowed them to get some of the younger students involved who wouldn’t normally be able to take part in on a day when only one motor is being fired. It was remarked that having more young members with hands-on experience is very good for the future of their program and the continuity of knowledge after the upperclassmen graduate. Dimitri mentioned that additional work will be needed to fill in the area of ground blasted away by all the recent USC solid rocket static firings – which has been affectionately named the “Trojan Trench.”

On the same weekend, a team at the FAR launch site launched their “Genesis” rocket – a hypergolic liquid propellant rocket that has been in development since the early 1980’s. Several RRS members had worked on the rocket at various times during its design and fabrication process. Unfortunately, the parachute system did not work and the tanks ruptured on the landing causing a small fire that self-extinguished but was visible from the MTA.


Our outgoing president, Osvaldo Tarditti, took a moment to extend a special thank you to RRS member Dimitri Timohovich for all of the recent work he has done in improving the facilities we have available at the MTA. Not only did he take the lead in the recent blockhouse roof repair which included several trips up to the site for the initial build, cutting the edges, and installing the tar paper, but he also donated four propane bottles for the society to use in the heaters and BBQ up at the Dosa Building.

The old blockhouse with a new roof.

In addition, Dimitri has agreed to take on the bulk of the work in building out the interior of the containerized bathroom. Three concrete pads have been poured at the MTA to accommodate this 20-foot high cube container as well as another one adjacent to it.

Future site of the RRS containerized restroom facility.

Osvaldo has procured most of the fixtures for the interior and plans to drop them off at Dimitri’s house – where the container will be delivered so that he can work on it more easily. Dimitri gave a tentative timeline of mid-January 2022 for when the container may be ready for transport out to the MTA.


Keith discussed his plans for a second launch of “The Hawk” on Friday, December 17th – this time on a Cesaroni N2600 motor. In addition, Dimitri has an RRS Standard Alpha rocket constructed and ready for launch and Osvaldo agreed to prepare one for Keith to get experience with the Zinc-Sulphur rockets. Dimitri volunteered to bring food for the group – award winning caribou chili made from meat they hunted, dressed, and prepped themselves in Alaska.


RRS member Dave Nordling informed the group that he recently learned that he passed his Class 1 Rockets Pyrotechnic Operator’s License exam. Congratulations Dave!

Office of the State Fire Marshall (OSFM) governs the licensing of pyrotechnic operators in California.

With additional members continuing to work towards earning their licenses, we can make sure that the RRS is able to accommodate a wide range of rocketry testing and schedule requests.


As a reminder – yearly membership dues are due January 1st. Please click on the yellow “Donate” button on the right panel of this website to pay online via PayPal, or mail a check to the society post office box in Los Angeles.

Reaction Research Society; P. O. Box 90933; Los Angeles, California, 90009-0933

The next RRS monthly meeting will be held virtually on Friday, January 14th at 7:30 pm pacific time. Current members will receive an invite via e-mail the week of the meeting. Non-members (or members who have not received recent invites) can request an invitation by sending an email to:

Please check your spam folders and add to your email whitelist to make sure you are receiving the meeting invitation.