May 2019 meeting

Dave Nordling, Secretary, RRS.ORG

The RRS met for our monthly meeting on Friday, May 10, 2019, at 7:30pm at the Ken Nakaoka Community Center in Gardena, CA. We were not as well attended this month, but we did have three new people join us at the meeting. With Mother’s Day weekend and graduation ceremonies happening at this time of year, many had other commitments.

The RRS welcomed David Minar and John Krell to the May 2019 meeting.

I must admit my error this week. I did realize too late that my monthly email to announce the meeting was not sent this week. Typically, I do send an email reminder to our active membership list (or anyone else who wants to know) on the Monday before meeting which also contains a copy of the agenda. Next month, I will not forget as this unintended experiment has shown that our reminder emails can be valuable to our membership.

The RRS has our monthly meetings always at 7:30pm on the 2nd Friday of each month. I usually mark my whole calendar each year with all of the 2nd Fridays to avoid schedule conflicts, but this is only a suggestion. Our meeting location is at the Ken Nakaoka Community Center in Gardena, unless otherwise announced in advance.

Also, in about the week prior to the meeting around the first of the month, I will gather up the agenda topics expected for the next month and post . All members are welcome to send their suggestions and ideas for agenda topics. We especially want short topics (5 minutes) on things related to rocketry, chemistry, payloads or just any kind of project you’re working on. The society is about sharing knowledge. Send an email to the RRS secretary or any of the executive council and we can put it on the agenda. Some of our members who aren’t in town have submitted things to be presented at meetings in the past which is also something the society can share in our meeting if the materials are clear enough and sent well in advance.

After calling the meeting to order and the reading of the treasury report, we began our agenda for May and covered most of the topics leaving some for June 14, 2019.

Waldo Stakes (left reclining) and new RRS member, Kent Schwitkis, a professor at Compton College. Kent joined us at the 2019 RRS symposium and we bid him welcome at the May 2019 meeting.

(1) Discussion of the 2019 RRS Symposium

The 2019 RRS Space & Rocketry Symposium held on Saturday, April 27th, was a success. We had a few different presenters this year in our lineup, welcomed a few new exhibitors and were very well attended over most of the day. According to Frank, we broke last year’s attendance by a small margin. RRS president, Osvaldo Tarditti, was very pleased with the amount of support we got from our membership in the night before and early morning of the symposium. Also, the RRS was very glad to have support we did at the end of the symposium in tearing down and cleaning up at the close of the day. These often overlooked simple details make running the symposium a real pleasure even at the end of a long day.

Frank Miuccio, RRS Vice President and Symposium Coordinator. The RRS thanks to Frank for all of his hard work in bringing together many people and many things to make this 2019 symposium another success.

We had our first opportunity to discuss the positive things at the symposium at the May meeting and this took up most of our meeting time. We were very happy to see so many groups come out including Spaceport LA, ROC and two organizations within the US Air Force (SMC at LA AFB and AFRL from Edwards AFB). The food truck vendor was also a great success. Many people enjoyed the pleasant weather and good food we had on site at lunch time. The outdoor exhibits were also a big hit. We are also thankful to LAPD CSP and the Los Angeles county sheriff’s department. The society will take notes to help with improving and expanding our next symposium still in planning for April 2021.

Some things that could have been better was sound quality. It was generally agreed that better speaker placement and the cloth barriers behind our audience rows was not sufficient to dampen out the noise from several running exhibits and the general foot traffic. It was my suggestion that we return to the 2017 format of having our presentations in the separate meeting room in the back and keep our exhibitors in the ballroom and at the main entrance.

We have also discovered that our exhibition seems to do well starting first thing in the morning and lasting until mid-afternoon. However, our audience attendance for our speakers tended to be better starting in the late morning and lasting all the way to the end of the day. The RRS is considering having fewer presenters but keeping the duration and range of content the same. Our audience seems to enjoy the topics that our speakers have been offering, so we will continue in this direction. The RRS will likely discuss more of our member and attendee impressions of the symposium at the next meeting on June 14, 2019.

(2) Terry Price’s presentation on composite materials used in rocketry – delayed to next month

Terry was unable to attend the May meeting, however, he did say that he could join us next month. Terry gave a great hour and a half presentation of composite materials at the EAA 96 monthly meeting in April. I hope he can bring some of the same excitement that he generated at the Compton Airport to our June 14 meeting in Gardena.

Terry Price, retired, formerly at Cerritos College and a nationally recognized expert in aerospace composite materials

(3) Upcoming events at the RRS Mojave Test Area

The rocket build event with Spaceport LA planned for early May was cancelled. We hope to reschedule a similar event with them very soon. The RRS is always interested in supporting these rocket build events with public and private groups if there is sufficient interest. Larry Hoffing is our events coordinator and the point of contact for setting up these kinds of events. – Larry Hoffing

UCLA will be having their rocket launch event at the end of the Spring Quarter 2019 on Saturday, June 1st. Several model rocket motors will be fired as part of Dr. Mitchell Spearrin’s undergraduate class. We have been glad to support UCLA for three years running in hosting this event. The RRS has also been glad to support their liquid and solid rocket motor teams over recent years.

At this same June 1st launch event, Osvaldo and I talked about securing the alpha thrust stand and having a series of static hot fires to generate more thrust curves for our micrograin alphas. From the one and only thrust curve we made, it appears that the RRS standard alpha qualifies as an “I” sized motor. We had a setback last year when the concrete slab to which the rocket and thrust stand was secured proved to be an insufficient foundation to react the swift impulse loading of an alpha. We have this footage of this defective hot-fire test on our Instagram account. It’s almost comical, but we must do better for the sake of safety and good science. Further, we need more data. The RRS does not intend to commercialize the standard alpha, but for the sake of future projects using this vehicle as a test bed, it would be good to have more recent motor performance measurements.

First of ten alphas right at liftoff

Some of our membership had indicated interest in building payloads to fly inside of the RRS standard alpha rockets we fly at each of these school events. Nearly all of these payload tubes are empty and are available to members able to build and supply their payloads before the event. Contact the RRS president for more details on alpha rocket payload tube specifications.

Frank has confirmed another rocket build event starting this summer in June through the LAPD CSP program. LAPD has been an ardent supporter and our rocket build programs are a big hit with the kids. The final part of the project is the launch event at the RRS Mojave Test Area (MTA). This will likely take place on Saturday, July 13th. We often have at least six alphas and sometimes as many as a dozen rockets at these events.

(X1) A brief word to potential users of the RRS MTA

Our membership is welcome to bring more tests and flights to the manifest. The only requirements the RRS has is that all participants download and submit a Standard Record Form available from the RRS.ORG forms library. This document provides a basic description of the project that members or other authorized attendees intend to execute at the RRS MTA. Supporting illustrations and documents are encouraged to help explain the task and operations for the supervising pyrotechnic operator. Approval of all activities at the RRS MTA are at the discretion of the supervising pyrotechnic operator and the RRS.

For those outside of our membership wishing to use the RRS MTA, the society requires submission of Standard Record Forms for all proposed activities. These must be submitted to the RRS president at least 14 calendar days in advance of the planned MTA event. Details of these tests can be held confidentially, but the RRS must have the opportunity to review, understand and approve all activities at the RRS MTA well in advance of the event. The RRS would prefer to have at least a month’s notice if not more. The RRS has been glad to assist more and more groups particularly with universities, however, we can not always support events particularly when we get little or no advance notice.

In the professional aerospace industry, it is a common practice to schedule a date with the testing site many months in advance and use this calendar deadline to help motivate the team to achieving meaningful results in time for the pre-set date. Scheduling a test date as an after-thought in executing a project often leads to disappointing results. Also, the society strongly recommends that users consider using times of the year other than at the end of semesters or quarters. If an event is planned well in advance, we will keep it on our calendar and can more easily have the personnel and resources ready.

The RRS must coordinate our activities with several parties and the better informed we are and the more notice we have will result in the RRS being better able to serve our prospective membership and clients. For any questions about RRS policy or practices, please contact the RRS president. The RRS is a volunteer organization and will always make our best effort to support rocket programs and projects.

(4) Pyrotechnic Operators for Rocketry in California

The RRS has been on a campaign to get more of our membership to apply and attain their pyrotechnic operators license. We’ve enjoyed a lot of support from many of our licensed membership in getting the necessary letters of recommendation for the application process. The RRS has also been glad to have the advice and assistance of the California Fire Marshal’s office. Osvaldo Tarditti, Larry Hoffing, Drew Cortopassi, Chris Lujan and myself have been in the application process for the rocketry pyrotechnic operators license. At the May 2019 meeting, Alastair Martin indicated his interest in becoming a pyrotechnic operator also. With more pyrotechnic operators on the state roster, there is more opportunity for more groups to conduct events throughout California. The RRS plans to remain active in our support to the public.

It’s with pleasure that I announce that I have attained my 3rd class rockets pyrotechnic operator’s license from CALFIRE this month. This annually renewable license allows me to buy high powered solid motors and supervise launch events within this class of solid motors. I hope to soon announce more pyrotechnic operators at the RRS very soon. The RRS is also very glad for the support of the licensed pyro-operators in our society and outside of our society at Friends of Amateur Rocketry (FAR). It is through the mutual support of all rocketry organizations that we expand our voice in the state and maintain a high standard for safety and the bold tradition of experimentation made possible in the Golden State.

RRS’s newest pyrotechnic operator, Dave Nordling

It’s my intention to upgrade my license to rockets 2nd class to be able to supervise and manage the unlimited category of solid rocket motors. The RRS is an organization that regularly conducts flights and testing in the unlimited class of solid motors. Our proud tradition of responsible experimentation in solid rocket technologies has one of our perrennial activities for over seven decades from micrograin to composite motors.

For more information on the licensing process for pyrotechnic operators as it pertains to rocketry, please contact CALFIRE directly.

(5) RRS Constitutional Committee

Now that the 2019 RRS symposium is complete, the RRS Constitutional Committee will begin their task of systematically revising and updating the RRS constitution. This task was approved by the society earlier this year and the committee comprised of two regular members (Larry Hoffing and Bill Janczewski) and one executive council member (Frank Miuccio) were appointed to begin this task over the summer.

The RRS Constitution has been updated periodically through amendments and notices over the years. The society has decided that a full review and incorporation of all changes be made in an update to the constitution to be voted and approved by our active voting membership near this year’s end. The main intent of the committee is to examine the constitution and recommend changes to better reflect how the society operates today. RRS president, Osvaldo Tarditti, did offer a word of caution that the Constitution should not be too specifically worded to over-regulate our operations. He has recommended that the committee take a minimalist approach and the committee will take this under advisement. Frank already has copies of the last edition of the RRS Constitution and amendments. These materials are available to all society members and some may already be on the RRS website.

This new revision will be known as the 2020 Constitution. It is a big effort and the society looks forward to the committee’s draft to be presented at the September 13, 2019, monthly meeting where suggestions and discussions will first commence.

(6) RRS Social Media Improvements – Recurring Topic

Alastair Martin was able to talk a little bit about RRS social media improvements and advertising of RRS events in general. One of his suggestions was that the society examine the use of EDDM (Every Door, Direct Mailers). These are the large postcard advertisements that organizations use to go into the mailboxes of targetted audiences throughout a region. Alastair has used these in the past with some of his events and had great success. The cost is substantial, but the results could be many more people getting notice to come to future symposiums and other large events with the RRS.

RRS media officer, Alastair Martin, discusses his ideas for marketing future RRS events at the May 2019 meeting

I had offered a suggestion that the RRS consider the use of more forms of electronic payment to help our ability to sell items at events or take membership dues and application fees. Venmo is a smartphone application that can be convenient for some to make direct payments to the RRS. The society seemed open to the idea, but it seemed to require further discussion and a vote to implement the change. There may be other means of electronic payment to consider however we must be cognizant of the fees involved and how practical each means would be for the society. We can bring this subject up again at the next meeting on June 14, 2019.

Currently, the RRS only has a PayPal account which is connected to our “DONATE” button on the RRS.ORG website. We encourage new applicants to use the “DONATE” button to tender their application fee ($40) if they desire associate membership at the RRS. Also, for our current membership, annual dues payments are much easier if made through PayPal or using our “DONATE” button. The only we ask for online donors is that they make a note of what the contribution is for and who we have to thank.

The RRS still accepts payments by direct mail to our post office box shown in our RRS.ORG website. The mailbox is not very frequently examined so it is strongly advised that all persons making payments to the RRS by direct mail contact the RRS president or RRS treasurer by email in advance to let them know to inspect the mailbox soon after the mail arrives. It is not uncommon for our direct mail to sit for a week or more.

Lastly, Alastair made mention of the next Rocket Talk Radio podcast which Richard Garcia and I will be a part of on Saturday, May 25th. The subject of this hour-long program will be Robert Truax. Truax was a key figure in 20th century rocketry and an important pioneer in the decades before the so-called “NewSpace” movement.

(7) RRS Participation with the CALFIRE committee on rocketry

The RRS was invited to attend CALFIRE’s review of the state’s regulations and laws on rocketry. Both the RRS and FAR have been reviewing regulations and preparing suggestions for improvements and clarifications to CALFIRE legislation governing the practice of amateur rocketry in California. The state has been very open to hearing from the amateur rocketry community about ideas and common sense changes that would make regulation better for all participants. Osvaldo has been involved with this activity and will soon schedule a separate meeting for RRS pyro-op’s to share and review our ideas. The CALFIRE committee will meet again in November 2019 and the RRS will offer our views on how the law can best serve the public.

(8) Topics for next meeting

Time ran out in the May meeting. Next month’s agenda will include further discussion about the RRS involvement with the base11 organization and the liquid rocket project (LR101) at Tomorrow’s Aeronautical Museum (TAM).

Richard Garcia has indicated his interest in getting the first prototype of the RRS standard liquid rocket motor built and tested.

RRS members have been helping different university groups on their liquid rocket projects and we expect to greatly expand our activities in this area as this year unfolds.

Lastly, the quarterly update for the SuperDosa project will have be made at the July 12, 2019, meeting.

Our next meeting of the RRS will be Friday, June 14, 2019. We will likely have something to share from the MTA launch event with UCLA by then. If there are any corrections or additions to be made to this monthly meeting report, please notify the RRS secretary.

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.

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,

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.