New Semester... New Rocket Team; Update

Welcome Back
The fall semester began last month at SDSU and we have started working on rockets again. Hopefully we will start posting regular updates on this blog again. We would also like to use this blog as a way for our team members to communicate and post ideas, so I am going to add the entire team roster as blog publishers. Anyone else out there in the world wide web can also comment, share ideas and ask questions.

May Static Test Findings
We last reported that our May 27, 2007 static test fire ended in a fireball -- likely a hard start. I was hoping the telemetry data would yield valuable clues as to what went wrong, unfortunately the data does not show a smoking gun. In fact, the data looks jumbled and I suspect we have had some issues with our sensor, their calibration or electrical noise. Here is the data we captured at the time of ignition:
The ignition occurs around 800 seconds on the chart. The helium pressure looks to be at about the correct range 1400-1700 psi, although I don't understand the drop from 1700 to 1400 in the minute before ignition (cooling due to expansion, maybe???). The kerosene pressure trace seems errant (it could not have been 1200 psi... the tank would burst at ~750psi) . The combustion pressure could not have been 500 psi before ignitions, so this telemetry channel could have been switched with the kerosene since this was the pressure the kerosene tank was set to. The LOX channel is completely erratic before ignition. Since we were not using cryo rated transducers could we have damaged this one?

Hopefully we will do better on data collection/telemetry this year.

Here are a few suspicions I had:

(1) poor or weak igniter.
(2) purge not working as expected; propellants made there way behind the injector.
(3) Contamination in the LOX side plumbing.
(4) The LOX line was filled with GOX. By the time LOX reached the chamber, it was like having a fuel lead and hence a hardstart. If anyone can make any sense of our traces, please feel free to post your comments.

New Team Members
We have 7 or 8 new interested students this semester as well as 4 or 5 returning students. The team leaders are:
Alex Bautista
Eddie Corwin
Stephen Kirby

This is a great, enthusiastic, motivated group we have this year. I expect good things to come!

New Rocket... A Step Back
We had a long discussion on what we wanted to do this year and we came to the conclusion that the past rockets got too complicated. We decided to try to simplify our rocket. We would like to make a simple rocket and then as our program progresses we can incrementally improve the rocket and add performance to it. This is a philosophy similar to the CSULB/Garvey program, and they have been very successful and have grown a lot. we also want to spend a lot more time up front designing the rocket in the virtual world. We found ourselves throwing things together on the past rocket and reworking a lot. Here are the main changes we have committed to:

• ablative motor -- We are going to make our own ablative motor with a graphite throat. The motor design is based on a LOX/alcohol motor that the Reaction Research Society shared with me. The motor is rated for 600 lbf. of thrust, however we may up-rate it to 800 or more. The LOX/kerosene LR101 we had used has given us a fair amount of ignition problems, and LOX/alcohol is suppose to be a little more benign in ignition. Plus, alcohol is a lot more pleasant to work with than kerosene.
  

• blow down pressurization -- A blow down pressurization system fills the tanks half way with propellant. You then pressurize the space above (the ullage) . When you open the main propellant valves the pressure forces the propellant out of the tank. The ullage pressure gradually decays due to expansion as the tank empties. The simplifies pressurization and removes at least two regulators.

• Tanks/airframe -- Our past rockets used modified stainless steel fire extinguishers in a stringer/bulkhead airframe. Not very mass fraction efficient, but a very robust airframe. The biggest drawback of this structure is the airframe takes a long time to fabricate. This time around we are going to make our tanks the airframe. Paul Breed from Unreasonable Rocket has demonstrated 8" diameter aluminum welded tanks which were easy to fabricate and held 500 psi. We are going to add skirts to the these tanks and connect them with an inter-tank adapter. I think making the airframe from tankage will be much easier. The only challenge I see is making all of the valving fit within a 8" cylinder which we have already begun to address. We also have to run some plumbing along the side of the tanks. Here are some preliminary pictures of what we have in mind.

• Valves -- Steve K. came up with this cool way to actuate our main propellant valves (see pictures of simplified assembly below). It uses a pnuematic cylinder (or any linear actuator) as our past actuated valves, however, the clever linkage allows us to use the stock ball valves with out modifying the handles. In fact all the parts are off the shelf.
  

Fund Raising
We do not get any funding from SDSU :-( Up to now we have relied on donations from sponsors, alumni, etc. We are going to make a conscience effort to look for funds, grants, etc. Ideally we would like to partner with a corporate sponsor(s) who could provide hardware or financial contributions. If you have a company that would be interested in helping us or know of what please contact us on this blog. I think this project is a great educational tool and I hope some aerospace companies will recognize that. Some of our past students are working at great jobs such as NASA-Jet Propulsion Laboratory, Northrop-Grumman, Lockheed Martin, Boeing, Scaled Composites, Air Force Research Laboratory and so on. Most of them told me that their employers hired them because of the hards-on experience with the rocket project.

--- Carl T.
Faculty Adviser

Long Over Due Brief Update

Hello. Sorry for the long period of inactivety on this blog. We got real busy with midterms, finals and of course presparation for our static test fire which we conducted this past Sunday, May 27th at the Friend's of Amatuer Rocketry test site in the Mojave Desert.

Basically the test did not go so well. We experienced a hard start and a fireball engulfed our system. We are compiling all our video and data to try to determine what the cause of the failure was which I will post, however, in the meantime here is some video Paul Breed took. Ours is the fourth test about 1:42 into the video.

Video

--- Carl

Motor Integrated to Airframe

Not a whole lot to report from our past work party. The most significant event to occur was the mounting of our motor to the airframe. The kerosene flex line is a bit too long and will be more so when we add fittings to purge this line. The stainless steel braided hose can be seen in the photo below at the bottom of the motor.
We also need to figure out how to best plumb the lines from the main LOX valve to the LOX dome including fittings to purge this line as well. As you can see in the photo below the stainless steel braided LOX hose would need to make a tight radius bend to connect with the LOX dome flare fitting. Www.anplumbing.com has a great selection of aluminum Earl's AN fittings and has a 90 degree adapter fitting we may be able to use. The alternative is to route the line outside the airframe for the static test.
Paul Breed has gratiously donated new pressure transducers to us. These transducers have a 0-5VDC output and integrate better to the elctronics. We will be monitoring via telemetry pressure in the helium tank, LOX tank, kerosene tank and the combustion chamber.

We also changed out a valve on the SSPS to allow us to pre-fill the "dome-dump" accumulator more easily.

This upcoming week is spring break, so I'm not too sure how many students are planning on being in town. Once the motor is fully plumbed we can begin our final testing.

--- Carl

Motor Prep, Ignition and Oher Details

Motor Prep
Our missing LR101 motor was finally returned to us. After sitting idle for 6 months it has accumulated quite a bit of visible surface rust on the exterior. The motors are entirely 4130 steel except for a copper wire which spirals between the walls forming the cooling passages. We're not sure how much rust may be in the cooling passages since they are nearly impossible to inspect. I took this motor to Sheffield Platers to have them electroless nickel plate it. I'm hoping this will clean off all the rust and offer protection from further rusting. They said it will cost $90. In the mean time, Steve Harrington (our other rocket project adviser and head honcho at Flometrics... and my boss) has offered us one of Flometrics LR101 motors, which we have begun to modify for use in our system. This involves cutting off the spindles which were orginally used to mount & gimbal the motor. Also, a hole is tapped so that a AN fitting can be screwed to the motor to plumb the kerosene in (see picture below).



Rust has been an enemy to us in the past. We have had injectors completely clog up with rust particles that were in the cooling passages. If we use this motor we'll have to make sure the inside is free of rust since the cooling passages were never plated in the original Rocketdyne process. Someone in the past suggested we recirculate naval jelly through the cooling passages which seems to work pretty well, so we will do that as a precaution. Also, sometime ago I made the tooling to make filter screens for the LOX and Kerosene. The screens nest over the injector.


The LR101 is getting to be pretty rare. It's my understanding that Rocketdyne is no longer allowing them to go on the surplus market due to the liability. They now destroy any motors they do not use... what a shame :-( I have heard that these motors are starting to go for up to $4000. Our educational budget (is $0.00 a budget?) can not afford this, so we're talking about reproducing our own based on the LR101. We have two designs: A sheet metal formed/welded one (see pics below) and a machined design (Devin, can you post pics of your design... I don't have it).
I hope to send out drawings to have these parts quoted in the next week or two. I also need to talk to our welder to determine what details/features he will need to make these parts weldable. Ideally I'd like to have them made from stainless steel to, once and for all, put this rusting issue to bed, however, a proper thermal analysis will need to be done, since stainless doesn't have the thermal conductivity the existing 4130 steel has.

Igniters
The original motor used hypergols for ignition. I have been told by a Rocketdyne engineer familar with these motors that a pyrotechnic igniter will work and the flames should spread out radially as close to the injector face as possible to insure propellant ignition without letting too much liquid propellant build up in the combustion chamber. These are sometimes referred to as radial outward-firing igniters or ROFI's. As far as I know, all the amatuer groups lighting this motor use pyrotechnic igniters.

No one on our team has a pyrotechnics license, so we will have to count on others for an igniter. I don't really want to have to make igniters. I'm trying to get some experts to provide them. Ken Mason, who has fired hundreds of LR101's with legendary Bob Truax, makes his on ROFI's. Ken has been a valuable resource and knows so much about these engines. I am hoping that either him or Kevin Baxter at the Friend's of Amatuer Rocketry can help us with an igniter.
Just in case that falls through, we thought about using automotive flares to make an igniter. I'm assuming they are DOT legal so they should be okay to use by mortal folks like us. We took one apart and the flammable substance is some yellow powder (sulfur and something else is my guess... anyone know for certain the composition?). We carefully (slowly) drilled a 1/8" hole in the end and inserted a nichrome wire folded in half so that the two wire ends stuck out the end of the flare. We glued that in with some 5 minute epoxy (see below... they are road flares... not dynamite folks!).

We then cut off a 1.5 " section of the flare containing the nichrome wires and inserted them in a phenolic fabric tube which had 5 radial 3/16" diameter ports for the flames to emit from. We capped both ends with wooden dowel caps using 5 min. epoxy and allowed the wires to come out of two of the ports.

We tested it by connecting the nichrome wires to long leads and touching them to a 12VDC battery. As soon as I can figure out how to post videos, I'll do so! Just as expected fire came out of the radial ports, however, it wasn't as uniform as I would have expected. Maybe 5 ports was too many. Perhaps 4 1/8" diameter ports will create more back pressure and better distribute flamey stuff from all the ports. The flare igniter burned for over 30 seconds, but by 15-20 seconds the phenolic casing was starting to burn through.


Plumbing
The Soft Start Pressurization System was finally plumbed to each of the propellant tanks tanks. A check valve goes between the SSPS and each tank to insure that no cross-contamination from propellant vapors can occur.

A small leak was found in a helium fill line fitting. We fill the composite pressurant tank through the Circle Seal regulator in the SSPS. The fitting is a straight adapter -- 3/16" tube to 1/8" NPT. The tubing then has to make a 180 degree bend and was probably stressesd. We'll replace it with a 90 degree elbow adapter. I've ordered new fittings.

Next we will plumb the MPVA to the motor via flex hoses. If our motors aren't ready we'll probably add some orifices to each propellant line to similuate the pressure drop through the motor and start high pressure and cryotesting. Paul Breed has offered to let us use the balance of a LN2 dewar he just ordered.

--- Carl

Components Mounted in Airframe

This past Sunday's work party had 7 students in attendance: Alyson, Judy, Jerry, Eddie, Alex, Joquin and Devin, the project manager. Also present was Brett, an industry engineer helping the project and myself.

Soft-Start Pressurization System (SSPS)
The SSPS was tested at high pressure tested and mounted in air frame. During bench testing one of the brass AN nuts on a stainless steel braided hose was over-tightened and stripped. I new one was ordered. This didn't stop us from testing... it just meant we had to test each Mity Mite regulator independently, by swapping the remaining flex line between regulators. To test we connected the system to a 2200 psi air supply. I also put a ball valve on each regulator output with a .028" orifice to mimic the actual load and an upstream pressure gauge to make sure we were getting the required output pressure. With the ball valves closed we set the output pressure on the Circle Seal hand-loaded regulator. This is the regulator that will "reload" the domes and, hence, change the propellant tank pressure. We set this reg to 500 psi. We loaded the dome-dump accumulator (DDA) (the sphere in the system) to 100 psi just using shop air with an air nozzle gun. This would allow the regulators to initially pressurize the propellant tanks to 100 psi and hopefully start the motor in a benign manner. When we opened the ball valves on the reg output, air would flow through the orifice at a modest rate. Then we energized the dome-dump solenoid (DDS) with 12 VDC from a power supply. The gauge on the DDA changed from 100 psi to 500 psi in about 1 to 1.5 seconds and the air output of the mity mites immediately increased. I think this event happens much quicker than 1-1.5 seconds, but there is some dampening in the pressure gauge. We'll see when we test with water in our tanks and we can actually track the tank pressure with our pressure transducers. After testing, we mounted the SSPS in the airframe. At our next work party we'll replace the broken flex hose and plumb the Mity Mite outputs to the propellant tanks. we also need to reroute the helium fill line which allows us to remotely load helium into our composite pressurant tank. Here are some pics...



Main Propellant Valve Assembly (MPVA)
We tweaked the MPVA to allow full range of motion. Initially when we commanded the pnuematic actuator to open the ball valves they only opened about 70%. of the 90 degree rotation. We had made a geometry error when mounting the pnuematic actuator. We simply drilled new mounting holes for the actuator and that solved everything. Now we get 100% opening. The whole assembly is quite rigid and we cycled it at least 50 times that day. We probably overbuilt the structure it is mounted to, but we wanted to make sure it was rigid, unlike previous versions. We may add some lightening holes and machine away some material in it when we're ready to fly it, but for our static test this will do.

Motor Mounting Bulkhead
The titanium sheets covering the bottom bulkhead were giving us a real hard time. New sheet metal skins made from 6061 aluminum. Here it is mounted. The 8 small holes are what our engine mounts to. The large hole on the left is where the LOX line exits the airframe to connect to the motor. We need to add a hole for the kerosene plumbing.



Other:
Our electronics were built and donated by Paul Breed at Netburner (see Paul's blog: Unreasonable Rocket). Our electronics allow us to transmit data from the rocket to a ground station. Basically we monitor pressure in both the propellant tanks and the motor combustion chamber. If time and resources permit I would like to add a transducer to the helium supply and DDA. There is also an accelerometer which we could use to sense altitude and GPS which updates at 5 Hz. All this data is sent over a 1 Watt Maxstream transmitter.
Here the electronics are mounted in the airframe:

For the flight we are also going to try to have a wireless camera mounted to transmit live video of the flight from the rocket. We also will have two commercially available rocket altimeters to initiate the recovery via parachute deployment. We haven't selected altimeters at this time, so any recommendations or suggestions would be appreciated.

LOX tank insulated
We used fiberglass insulation to insulate the LOX tank. We left the top and bottom of the tank un-insulated so that we could leak check the fittings at the top & bottom. We will also need to insulate the LOX line leading to the MPVA.
Motor woes...
One of our former students was entrusted with our LR-101 motor and has gone MIA. We exhausted every effort to get a hold of him to get the motor back. This is a big deal! We have a spare motor, but we'll need to modify it to get it into a configuration for our vehicle. We'll start this at our next work party.


--- Carl

Valves, Pressurization, Motor Mounting Bulkhead

Saturday's work party was full of activity. I forgot to get a head count, but we probably had 9 or 10 student rocketeers. We focused on three areas:

• main propellant valve assembly
• bottom bulkhead/thrust structure.
• pressurization system

Main Propellant Valve Assembly (MPVA)
We use stainless steel ball valves with teflon seals and seats for both of our main propellant valves. We actuate these valves with a common pnuematic cylinder. During our last static test the mounting of the MPVA was a bit shoddy and we may not have had full range of valve motion. There was also a lot of slop in the linkage. We suspected that the fuel valve did not seat closed all the way and we had some leak-by when we pressurized our tanks, and hence a fuel lead instead of the traditional LOX lead. Needless to say we had a hard-start. We want to make sure the MPVA is rigidly mounted this time around and we get full range of motion from both valves. Here's some CAD...


Here they are mounted in the airframe... (the pnuematic cylinder is hidden slightly behind one of the aluminum stringers).


Pressurization System
In the past we have had a hard time with starting our rocket motor. We've had our fair share of hard starts and rapid engine disassembly. Our main propellant valves are not throttleable... just on/off... so our engine just starts full bore. We are building a pressurization system that starts the motor at low chamber pressure then switches to full throttle. Here's how it works...

We're using Mity Mite dome loaded regulators which will initially pressurize our tanks to a low pressure, like 100 psi. When we open the main propellant valves, propellants will flow into the engine with a LOX lead at a lower flowrate than nominal. Once ignition has been detected and Pc attains some minimal value like 70-80 psi we'll then "dump" 500 psi into the dome port of our Mity Mites which will bring our motor up to full throttle (1000 lbf. and 350 psi Pc). This "dump" comes from a 3rd regulator ( a Circle Seal IR10 reg) which is released via a solenoid valve into a spherical accumulator and then into the domes, therby changing the regs output pressure. We're calling this our Soft Start Pressurization System (SSPS).

Here are some CAD models of this scheme...


Here's the real thing....

During testing of the system we found that one of the Mite Mites was installed backwards, but other than that it worked fine at 150 psi when given an artificial external command signal. Next we plan to test it at operational pressures (500 psi) while under load.

Bottom Bulkhead/Thrust Structure
Our airframe is primitive. It is made up of a series of bulkheads attached by 4 stringers. All our propellant tanks, valves, etc... are mounted within this structure.


The bottom bulkhead also serves as our thrust structure since our motor gets bolted to it. This bulkhead is made from 3/4" marine grade plywood which is then skinned with sheet metal. This makes it into a strong, stiff sandwich structure. We usually just use sheet aluminum, however, some titanium sheet was donated to us, so we skinned the bulkhead with it. What we didn't expect was how difficult it would be to cut holes in. None of us are expert machinist, so it took us 2 hours to drill a 2" dia. hole through 1/16" titanium sheet using a hole saw. I looked in the machinist handbook and it said HSS was fine and slow, slow feed speeds which we abided by.

For now I think we'll go back to low-tech materials and leave the exotic stuff to NASA.


My plan is to try to post something at least once a week assuming we make progress. I also want the students to moderate and post updates, questions, etc.

--- Carl

Test post of the SDSU Rocket Project Blog

Welcome rocketeers, enthusiast, fans & followers of the SDSU Rocket Project. We've decided to blog about our rocket project.

The SDSU Rocket Project is a group of students, faculty and advisers at San Diego State University who are building incredible liquid propellant rockets. The project began in 2003 and we are now building our 4th rocket. These rockets are pressure-fed vehicles which use kerosene and liquid oxygen as their propellants and are pressurized with helium gas. Our rocket motor for the time being is a surplus Atlas LR-101 vernier motor which produces 1000 lbs. of thrust. The motor is regeneratively cooled with the kerosene fuel, so theoretically it could be run indefinitely.

We're hoping to do a static test in the next month or two, so we'll keep you posted and document our progress via this blog. We're hoping this blog will serve as a tool to allow you to see what we're doing and post questions and comments. We may even solicit advice from you, our blog audience.

Welcome all!

--- Carl