MTA launch, 2019-04-06

Dave Nordling, Secretary, RRS.ORG

The Reaction Research Society (RRS) had another launch event at the Mojave Test Area (MTA). We had a nice cool day for the launch with a little wind. The winter seasonal rains left the land green which was a lovely change to the usual desert brown.

The RRS sign welcomes our guests to the MTA. The winter seasonal rains had turned the land green.
Desert flora in bloom downrange of the RRS MTA

We were pleased to be joined by California State Fire Marshal, Ramiro Rodriguez, who came out to see our amateur rocketry group in action. David Crisalli was our pyro-op for the event and I was glad to apprentice under him once again for this event.

RRS events coordinator, Larry Hoffing; RRS member and pyro-op, Dave Crisalli, California State Fire Marshal, Ramiro Rodriguez; and RRS secretary, Dave Nordling

Also joining us was the students at University of Southern California’s Rocket Propulsion Laboratory (USC RPL). The students had prepared a 6-inch solid motor for static fire test. They were demonstrating an improved carbon-phenolic nozzle design. They arrived the night before and made preparations all morning.

The name of USC’s 6-inch solid motor was “Poise”

USC still had a few more steps to go in their preparations before our other guests from Compton Elementary arrived. LAPD CSP and the RRS were glad to bring another class of young minds to see firsthand a rocket in flight. After all had arrived and settled, we held our safety briefing with our pyro-op, Dave Crisalli.

Students, LAPD officers, USC and the RRS gather in front of the George Dosa building for the safety briefing.
Ramiro relates practical advise on safety to the students of USC RPL.
Everyone safe in the observation bunker. We’re ready to launch.

We had six of our standard alphas made by the kids at Compton Elementary. This launch event is the final day in the educational sessions we do with local schools thanks to our partnership with the LAPD CSP.

5 of the 6 alphas sit in the rack; Osvaldo’s alpha with a parachute sits to the left.

We loaded each of the rockets in the numerical order they were labelled. Each team had their own color scheme to help make them unique. Reds and blues stand out well against the desert browns and green of the brush.

A very well timed shot of an RRS alpha just clearing the box rails.
A not-so well timed shot just a split-second too slow on the shutter.

After the last alpha from Compton Elementary, we launched Osvaldo’s alpha with a parachute recovery system packed in the payload tube. The parachute deployment system has a simple timer circuit that starts when a pin is pulled as the rocket speeds away off the rails. The red flagged plug in the photo is the safety pin to prevent accidental activation of the payload.

Osvaldo’s customized alpha rocket with a parachute recovery system (left in the photo).

Unfortunately, the parachute system didn’t deploy after launch. It’s possible that the timer deployed the parachute too early which the forward pressure against the payload tube may have held the system in place. The other possibility is the timer didn’t start at all. Either way, the recovery of Osvaldo’s rocket had to be done like all the others… with a shovel.

After the last of the alphas fired, LAPD CSP packed up Compton Elementary for the long ride home. The RRS is grateful for the chance to show young people the excitement of rocketry in the Mojave desert.

Dave Crisalli talks wtih USC as they made their solid motor ready for static fire. USC had several cameras ready to record the 11 second firing.
Dave oversees the careful installation of the igniter system into the core of the solid motor.

The USC RPL team was ready after waiting through our fusillade of micrograin alphas. With final preparations made and instrumentation checking out, the installation of the igniter package on the end of a long sacrificial stick was inserted to the proper depth. Standing back and bringing everyone to safety, USC began their countdown.

Still capture from video taken from the RRS MTA blockhouse. The motor ran full duration.
Post hot-fire inspection showed the carbon-phenolic nozzle still in tact.

USC had predicted a peak thrust of 800 lbf and a burn duration of 11 seconds. Actual burn time matched predictions, but thrust levels may have been short of expectations. USC was crunching the data as the RRS moved on to recovery of the alphas from down-range.

We were fortunate to find three of the alphas from the launch event. They were found north-west of the launch site which was unexpected. Another alpha from last year’s event was also found.

One of the three alphas we recovered later in the afternoon.

Osvaldo’s ratcheting extractor tool came in handy once again to avoid the back-breaking work of shoveling out an alpha once it’s found.

Securing the chain links in a circle near the nozzle throat gives the steel cable something to grasp as the ratchet progressively pulls the rocket from the ground in the same direction it entered.
Osvaldo’s alpha with a parachute was one of the alphas we recovered. Sadly, the parachute system did not deploy and the alpha returned ballistically with the parachute still packed inside.

The next RRS meeting will be Friday, April 12th, at the Ken Nakaoka Community Center in Gardena. This will be our last meeting before the 2019 RRS symposium on Saturday, April 27th. We’ll have more information posted here on RRS.ORG very soon.

Build Your Own Rocket Event with Spaceport L.A.

by Larry Hoffing, Educational Outreach Coordinator, Reaction Research Society

The Reaction Research Society (RRS.ORG) is glad to be a part of an upcoming event with Spaceport L.A. The “Rocket Workshop with the RRS” is an excellent opportunity for anyone who wants to get directly acquainted with rocketry. This event is meant for both professionals and non-professionals alike. From younger students to university students of all fields, to adults, this event is meant to give people the experience of assembling and flying your own rocket.

https://www.facebook.com/spaceportla
Spaceport L.A.’s Facebook page has their upcoming events

The event will begin on Saturday, May 4, 2019 with a subsequent launch of the rockets from the RRS Mojave Test Area (MTA) on Saturday, May 18, 2019. At this event, you can learn about the fundamentals and more practical knowledge of rocketry.

The event will be held at the HexLab MakerSpace in Van Nuys. This is laser-cutting service in the Los Angeles area. Check the Spaceport L.A. website for the details and updates.

HexLab MakerSpace is a place for creative people to have the tools they need to make their ideas real

The RRS standard alpha rocket is a very old, but reliable design still used in the society. Although micrograin propellant is not used anywhere else but at the RRS (where it was initially discovered in the 1940’s), it is a simple and powerful propellant combination that makes for an impressive show of raw power. I have attached an earlier description of the RRS standard alpha rocket below.

After the first session, on the second event, you can go out to the RRS’s private Mojave Test Area (MTA) at Koehn Dry Lake, east of Cantil, California in the high desert. The RRS will handle the propellants, you can see the impressive results from the safety of our observation bunker.

alpha launch 03-25-2017
RRS director of research, Richard Garcia, with his brick as a camera tripod
First of ten alphas right at liftoff
Xavier Marshall and Wilbur Owens; Wilbur gets his first RRS alpha

Amateur rocketry is our passion and purpose and the society is glad to hold this event with Spaceport L.A. and the public.

https://www.spaceportla.com/

Spaceport L.A., our sponsor for this Rocket Build Event with the RRS

For questions, look to the Spaceport L.A. official website linked above. For questions about the RRS rocket build event, contact the RRS Educational Outreach Coordinator, Mr. Larry Hoffing.

events@rrs.org

For any questions about the Reaction Research Society, go to our website at RRS.ORG

Liquid Rocket Components: Pyrotechnic Valves

by Tom Mueller


Editor’s Note: This is a reprinting of the original article written by RRS member, Tom Mueller on the subject of pyrotechnic actuated valves around 1995 (?). He mentions the build of two different rockets (the XLR-50 and the Condor) and a hypergolic rocket he intended to build after this article was written. We hope to gather more photos and details about these rockets and display them in future improvements to this posting. For now, please enjoy the subject matter as the information is very relevant today to amateur builders of liquid rockets. The RRS has been very active lately in re-exploring liquid rockets. The society thought this would be a timely and interesting subject to share with our readers.

For any questions, please contact the RRS secretary, secretary@rrs.org


For an amateur rocketeer seeking to build a liquid rocket, one of the most difficult components to obtain or build are remotely operated valves. A liquid rocket will require at least one valve to start the flow of propellants to the combustion chamber. In the two small liquid rockets I have flown in the last year or so, both used a pyrotechnic fire valve located between the pressurant tank and the propellant tanks. The propellants were held in the tanks by burst disks (or equivalent) in the propellant run lines. When the fire valve was actuated, the sudden pressure rise in the propellant tanks blew the burst disks, allowing propellant to flow to the injector. This method of controlling the flow to the rocket allows the use of only one valve, and eliminates liquid valves.

In the case of the first rocket, the XLR-50 which flew in October 1993, elimination of the liquid valve was important because the oxidizer was liquid oxygen, and a small cryogenic compatible valve is very difficult to construct.

For the second rocket, which flew in October 1994, the small size prevented the use of liquid valves. In fact, the single pyro valve I used was barely able to fit in the 1.5 inch rocket diameter. In this article I will describe the design of the valves that were used on these two vehicles, and variations of them that have been used in other rocket applications.

FIGURE 1: XLR-50 pyro-technic “fire” valve

The valve shown in Figure 1 consisted of a stainless steel body with a 0.375 inch diameter piston. The O-rings were Viton (material) and the squib charge was contained in a Delrin plastic cap. The Delrin was used to prevent shorting of the nichrome wire, and also to provide a frangible fuse in case the squib charge proved to be a little too energetic. In practice, I’ve never had the Delrin cap fracture.

The inlet and outlet lines to the tanks were silver brazed to the valve body. The valve was tested many times at inlet pressures of up to 1000 psi without any problems, other than the O-rings would need replaced after several firings due to minor nicks from the ports. To help alleviate this problem, the edges of the ports were rounded to help prevent the O-ring from getting pinched as the piston translates. This was accomplished using a small strip of emery cloth that was secured in a loop in one end of a short length of 0.020-inch stainless steel wire. The other end of the wire was clamped in a pin vise which in turn was chucked in a hand drill. As the wire was rotated by the drill, the emery was pulled snugly into the port, where it deformed into the shape of the inlet, and rounded the sharp edge. I used WD-40 as a lubricant for this operation, allowing the emery to wear out until it would finally pull through the port. I repeated this process a few times for each port until the piston would slide through the bore without the O-rings snagging the ports.

Another requirement is to lubricate the O-rings with a little Krytox grease. This helps the piston move freely and greatly reduces the problem of nicked O-rings.

FIGURE 2: Fire valve for a micro-rocket

The pyro valve I used in the 25 lbf thrust micro-rocket that was launched in October of 1994 is shown in Figure 2. This valve was identical in operation to the XLR-50 valve, with the major difference being its integration into the vehicle body. The valve body was a 1.5 inch diameter aluminum bulkhead that separated the nitrogen pressurant tank and the oxidizer tank. Because of the very small diameter of the rocket, the clearances between ports and O-rings were minimized, just allowing the valve to fit. The fuel outlet port was located at the vehicle center, providing pressure to the fuel tank by the central stand pipe that passed axially down the oxidizer tank. The piston stop was a piece of heat-treated alloy steel that was attached to the valve body by a screw. This stop was originally made from aluminum, but was bent by the impact of the piston in initial tests of the valve. The black powder charge in the Delrin cap was reduced and the black powder was changed from FFFg grade to a courser FFg powder, but the problem persisted. The stop was re-made from oil hardening steel and the problem was solved. In this application, the port diameters were only 1/16 inch so only a small amount of rounding was required to prevent the O-rings from getting pinched in the ports. The valve operated with a nitrogen lock-up pressure of 1000 psi.

FIGURE 3: Fire valve for Mark Ventura’s peroxide rocket

A more challenging application of the same basic valve design was used for the fire valve of Mark Ventura’s peroxide hybrid, as shown in Figure 3. This was the first application of this valve where liquid was the fluid being controlled, rather than gas. In this case the liquid was 85% hydrogen peroxide. The second difficulty was the fact that the ports were required to be 0.20 inch in diameter in order to handle the required flow rate. The valve was somewhat simpler than the previous valves in that only a single inlet and outlet were required. The valve body was made from a piece of 1.5-inch diameter 6061 aluminum, in which a 1/2-inch piston bore was drilled. The piston was also 6061 with Viton O-rings, which are peroxide compatible. The ports were 1/4-inch NPT pipe threads tapped into the aluminum body. The excess material on the sides of the valve was milled off, so that the valve was only about 3/4 of an inch thick, and weighed only 4 ounces. Even though the piston size was 1/2 inch, the same charge volume used in the 3/8 inch valves was sufficient to actuate the piston.

In testing the valve with water at a lock-up pressure of 800 psi, I was pleased to find that even with the large ports, O-ring pinching was not a problem. One saving factor was that the larger size of the ports made it easier to round the entrances on the bore side. The valve was tested with water several times successfully before giving it to Mark for the static test of his hybrid.

The only problem that occurred during the static test of hybrid rocket was that the leads to the nichrome wire kept shorting against the valve body. Three attempts were made before the squib was finally ignited and the engine ran beautifully. I have since been able to solve this problem by soldering insulated 32-gauge copper wire to the nichrome wire leads inside the Delrin cap. In this way, I can provide long leads to the valve with reliable ignition.

My next liquid rocket is a 650 lbf design that burns LOX and propane at 500 psia. This engine uses a Condor ablative chamber obtained from a surplus yard. For this reason, I call it the Condor rocket. This rocket uses a scuba tank with 3000 psi helium for the pressurant. I decided to build a high pressure version of my valve as the helium isolation valve for this rocket. When firing this rocket, just prior to the 10 second count, this valve will be fired, pressurizing the propellant tanks to 600 psi. I assumed going in to this design that the O-rings slipping past a port simply wasn’t going to work at 3000 psi.

At these pressures, the O-ring would extrude into the port. In order to get around this problem I came up with the design shown in Figure 4.

FIGURE 4: High pressure helium valve for Condor rocket

For this valve, the O-ring groves were moved from the piston to the cylinder bore of the valve body, so the O-rings do not move relative to the ports. The piston is made from stainless steel with a smooth surface finish and generous radii on all of the corners. The clearance between the piston and the bore was kept very small to prevent extrusion of the O-rings. The valve operation is similar to the one shown in Figure 3, and the valve body is made in the same way except female AN ports were used rather than NPT ports. When the valve is fired, the piston travels from the position shown in Figure 4a to that shown in Figure 4b. During this travel, the inlet pressure on the second O-ring will cause it to “blow out” as the piston major diameter translates past the O-ring groove. The O-ring is retained around the piston, causing no obstruction or other problems. This valve has been tested at 2400 psi inlet pressure with helium and works fine. It will be tested at 3000 psi prior to the first hot fire tests of the Condor rocket next spring.

As a side note, essentially an identical valve design as the one used on the Condor and Mark’s valve is a design shown in NASA publication SP-8080, “Liquid Rocket Pressure Regulators, Relief Valves, Check Valves, Burst Disks and Explosive Valves”.

A second pyro valve is used on the Condor system as shown in Figure 5. This valve is used to vent the LOX tank in the event of a failure to open the fire valve to the engine.

FIGURE 5: Emergency vent valve for LOX tank, Condor rocket

When the propellant tanks are pressurized by the helium pyro valve, the LOX tank auto vent valve (shown in Figure 6) closes. If the engine is not fired after a reasonable amount of time, the LOX will warm up, building pressure until something gives (probably the LOX tank). The pyro valve shown in Figure 5 is used as the emergency tank vent if the engine cannot be fired. The valve body is stainless steel with a stainless tube stub welded on for connection to the LOX tank. This valve has been tested to 800 psi with helium and works fine. In this case, some ‘nicking’ of the O-rings can be tolerated because the O-rings are not required to seal after the valve is fired. The ports in the bore are still rounded, however, to prevent the O-rings from getting nicked or pinched during assembly of the valve.

Even though it is not a pyro valve, I have shown the LOX auto-vent valve in Figure 6 because this design has proven to be very useful for venting cryogenic propellant tanks without requiring a separately actuated valve or control circuit. The valve uses a Teflon slider that is kept in the vent position as shown in Figure 6a.

This allows the tank to vent to the atmosphere, keeping the propellant at its normal boiling point. When the helium system is activated, the pressurant pushes the slider closed against the vent port, sealing off the LOX tank, as shown in Figure 6b. An O-ring is used around the slider to give it a friction fit so the aspiration of the LOX tank does not “suck” the slider to the closed position. This problem happened to David Crisalli (fellow RRS member) when he scaled this design up for use on his 1000 lbf rocket system. I have used this design on the LOX tank of my XLR-50 rocket, which used a 1/4-inch diameter slider, and on the Condor LOX tank, which uses a 1/2 inch slider. In both cases the vent valve worked perfectly.

FIGURE 6: Automatic LOX tank vent valve

The main fire valve on the Condor rocket is a pair of ball valves that are chained together to a single lever so that both the fuel and oxidizer can be actuated simultaneously for smooth engine startup. For static testing of the rocket, I will use a double-acting air cylinder to actuate the valves. For flight, however, I plan to use a pin that is removed by an explosive squib to hold the valve in the closed position. When the squib is ignited, the pin is pulled by the action of the charge on a piston, allowing the valves to be pulled to the open position by a spring. This method may not be very elegant, but it is simple, light, and packages well on the vehicle. David Crisalli has successfully employed this technique on his large rocket.

That covers the extent of the pyro valves I have built or plan to build so far. In the next newsletter, I will present the design and flight of the small hypergolic propellant rocket that used the valve shown in Figure 2.