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
