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

MTA launch event, 2021-06-19

by Dave Nordling, Reaction Research Society

The society held a launch event at the Mojave Test Area on June 19th. With many people having other plans, we were sparsely attended but able to get a few things done. The winds were very low and sun was very hot that day (105 F) making it a challenge to operate at the site, but with each other’s help we managed. I was the pyrotechnic operator in charge that day. I had intended to bring my hybrid rocket for this event but wasn’t able to complete the rocket in time. It would be Bill Inman’s Solar Cat, a pair of micrograin alphas and witnessing the UCLA Prometheus team launch their hybrid rocket after getting a replacement nozzle from the motor supplier.

UCLA Prometheus team posing before bringing their hybrid rocket to the launch rail at FAR.


Bill Inman and Jon Wells made the journey from Nevada to demonstrate a new sun tracking system improvement to better automate the solar heating process with the parabolic mirror. Unfortunately, there were several problems with the installation that ultimately went unresolved for that day. A series of benchtop tests would be needed before bringing his combined solar collector and rail launcher back to the MTA for a launch.

Bill had also expressed concerns about vibration from over-the-road travel taking its toll on the structure. He was already considering a major rebuild of his parabolic collector with a wider aperture. The next iteration of the Solar Cat is also supposed to be larger in diameter and capacity. With the Solar Cat work at a halt, Bill and Jon came over to assist Manny Marquez and myself with the loading of a pair of RRS standard alphas.


Osvaldo Tarditti was unable to attend this event, but he did measure out the zinc and sulfur in separate pre-weighed bags and provided a clean pair of alpha parts complete with the nozzles and well-painted, turned and recovered aluminum nosecones. For our new members, the society likes to give the experience of micrograin rocketry. Manny, Bill and Jon would have their first experience loading and firing an alpha that day. The society hasn’t launched many micrograin rockets since before the pandemic.

Manny Marquez loads the pre-weighed charges of zinc and sulfur powders before closing up the mixing barrel.
With the generator powering the electric motor driven roller, the drum sits and gently rolls mixing the zinc and sulfur to a consistent mixture.

Manny was a big help getting the equipment out and running. I was able to train him in the old RRS tradition of micrograin rocketry. With only two rockets, we gave the loading duties to Bill and Jon. For their handling of the dirty task of slowly loading the propellant tubes, they each got the honor of finishing the build and preparing for launch.

New member, Jon Wells (left) and returning member, Bill Inman (right) hold the first of two loaded alpha propellant tubes.
Bill Inman doing the hook-up under oppressive heat.

I was able to teach Bill, Jon and Manny the safe procedure for hooking up back to the control box in the blockhouse. With a well rehearsed procedure including air-and-road checks, we notified FAR in advance of firing our two alphas for that day to prevent anyone from wandering downrange before we fired.

Still capture from the launch of Bill Inman’s alpha; fast as hell

We each got a good lesson in the value of teamwork and a renewed respect for the heat of summer. The micrograin rocket is a simple but powerful initiation into experimental rocketry.

We all brought a lot of ice and drinks for that day and it was a big help.

Our next event has not been scheduled but we do plan to return to the MTA in July 2021. For members interested in planning the next event at the MTA, contact the RRS president and the executive council.

MTA Launch Event, 2021-04-10

by Keith Yoerg (RRS Secretary)

The RRS held a launch event at our Mojave Test Area (MTA) on April 10, 2021, the day after our monthly meeting. COVID-19 still remains a threat so everyone continued to observe protective protocols – masks & physical distancing. For the first time in months, we had a day with great weather for launching rockets and we made the most of it! We had low-power, high-power, and experimental solid rocket launches, another launch of Bill Inman’s Solar Cat, the maiden voyage of Wolfram Blume’s Gas Guzzler, and a static fire of Larry Hoffing’s solid power motors. Osvaldo Tarditti was our pyrotechnic operator in charge.

Activity around 9:30 am at the MTA – prep work ongoing for CTRL+V (left) and Solar Cat (right)


Preparation for the first launch of the day: CTRL+V actually began the day before launch with motor integration and other preparation work taking place at the MTA site. On the morning of the launch, the team from the USCRPL installed the rocket on the launch rail, which was then raised into place south of the MTA’s vertical test stand. Wires running from the rail were staked to poles and hammered into the ground to provide additional stability for the rail. Several launch crew members can be seen prepping the rocket above, and a still image of the launch of the rocket can be seen below.

Launch of USC RPL’s CTRL+V, the smoke took a strange path up the rail faster than the rocket!

The rocket flew on a 6″ experimental rocket motor. A specific procedure was followed prior to launch, under the supervision of the pyro op, which included radio go/no-go call outs from several teams including tracking, avionics, and even a drone that took footage of the launch! All spectators and crew were in the bunker during takeoff at 11:04 am – ignition was prompt and rocket left the rail quickly and cleanly. The initial telemetry reported by the team indicated an altitude of over 11 km. Several members then went off on the daunting task of recovering the rocket from wherever it landed.


The next flight of the day came from with the rocket Lumineer. This launch was conducted from one of the pads just west of the vertical test stand. The flight took place around 1:20 pm on a commercial Cessaroni “N” motor and was livestreamed to a reported 9,000 viewers on YouTube. The rocket utilized a “fly-away” rail guide to provide stability and eliminate the drag of rail buttons, which can be seen still in the process of falling from the rocket in the image below. The target altitude was 10 km, but telemetry was lost shortly after takeoff so the actual peak altitude was unclear after launch, and the rocket was not recovered for some time.

Launch of Lumineer from

GAS GUZZLER (Wolfram Blume)

Wolfram Blume has been diligently making the pilgrimage to the MTA events over the last several months and the weather has been uncooperative for his chances of launching, but that finally changed in April! The maiden voyage of the Gas Guzzler took place from the pad just west of the vertical test stand. This flight was conducted to answer several questions about staging during the flight – so the ram jet second stage was flown empty and only the first stage, commercial solid rocket motor was used to power the rocket. A slow-motion (10% full speed) video of the launch can be seen here.

Launch of Wolfram Blume’s Gas Guzzler, it’s so calm the flag on the vertical test stand isn’t waving!

The ascent of the rocket was smooth, validating the rigidity of the rocket’s design and the stability when empty. The data from onboard altimeters confirmed that the ram air entering the 2nd stage was enough to separate the 2 stages immediately (0.1 second) after motor burnout which occurred at 1,440 ft. The parachute for the booster stage deployed successfully and that stage was recovered without damage. The ram jet, upper stage utilizes a dual-deployment of a drogue parachute at apogee and main parachute at 1,000 ft above the ground. While each of these deployments were successful, the main parachute did not pull out of the deployment bag so the stage landed hard and damaged a few parts. Fortunately, the 2nd stage is not the final parts intended for the full flight of both stages so there will not be delays to the project to rebuild. Wolfram collected lots of useful data and plans to add a GPS tracker and other upgrades before his next flight. We all hope the weather remains in his (and all of our) favor!


Up next was the 12th flight of Keith Yoerg’s rocket Charlie Horse. This was the first flight test of the LoRa GPS tracking boards discussed in previous reports. There are several difficulties with getting the units setup properly, not least of which being the frequent firmware updates required to pair the board with the mobile phone app (2 updates in as many months). Powering up the boards the night before would have helped eliminate these struggles, but a successful launch was still completed, a slow-motion (10% full-speed) video of the launch can be seen here, which was on a commercial Cessaroni I280-Smokey Sam motor.

Keith Yoerg’s Charlie Horse seen through the smoke of launch – the camera was tipping over!

One issue still to be resolved with the LoRa trackers is a setting within the Meshtastic mobile application which trades off tracking range for the speed at which new information packets are sent. The “medium” setting was used on this flight but for rocket flights it may be advantageous to reduce the range (which is purported to be up to 10 miles) in favor of more frequent location updates. More testing will be done on future flights in hopes of developing a cheap, simple GPS tracking available for rockets flying at the RRS.

SOLAR CAT (Bill Inman)

Bill Inman’s solar-heated steam-powered Solar Cat rocket took to the skies around 4:31 pm. While the weather was perfect for most of the projects, the light overcast that can be seen in the pictures above proved problematic for the solar heating required for the best flight. In addition by launch time, the solar collector was at its westernmost limit so no more heating was possible. At launch the water temp was 370 F and was at 130 psi.

Bill Inman’s Solar Cat takes to the skies for it’s 2nd launch at the MTA

The flight reached 41 mph speed and achieved a 60 ft altitude. While this was an improvement on the first Solar Cat launch at the MTA, with additional heating there could be even more impressive stats. While he can’t control the clouds, Bill hopes to arrive at the MTA site the night before a launch in the future to increase the chances  of getting off a good test and launch before reaching our western limit of travel for the solar collector.

THE YOERG CHALLENGE (Dimitri Timohovich & Keith Yoerg)

With this being Dimitri’s last MTA event before leaving to Alaska for the summer, some other RRS members need to step up to the plate to keep the “Yoerg Challenge” alive. I have put out the call for more RRS members to build low-power rockets to fly at the MTA, and have left my 5-pad PVC launcher at the site for future launches. IT’S CHEAP, IT’S FUN, IT’S A CHALLENGE (and everyone is a winner)! What’s not to love? So get out there and build some model rockets!

The remains of the “Space Crater” – not covered in raw egg!

The entrants this month included Keith’s Big Bertha, Baby Bertha, and Hi-Flyer XL rockets and Dimitri’s Space Crater – which carried eggs in honor of Easter this month. Fortunately, Dimitri’s wife had the foresight to hard-boil the eggs because his rocket took the “Crater” part of its name a bit too seriously (the remains are shown above). A few of Keith’s flights before the GoPro battery died can be seen here.


Larry Hoffing had some experimental solid rocket motors ready to test fire, but with all the other activity going on at the site he took the time to install a new “No Smoking” sign on the covered propellant loading area (shown below). Once things were a little less active, Larry was able to affix the motors and perform a test-fire. While the burns were long, they did not produce much thrust and need to be improved upon before use in a rocket.

No smoking sign added to the covered propellant loading area by Larry


In addition to everything detailed above, one of the USC RPL members flew a high power rocket to earn her Level 1 certification with the National Association of Rocketry, and Dimitri flew his water rockets with his son.

This was by far the most active event at the MTA in the past year and was an exciting day for anyone who likes to see rockets fly! Our next launch date has not been decided upon, but we hope to have an event in May to continue hosting at least one event per month at the site.