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04/25/09 - Big Win at NASA USLI Competition and Hybrid Test Results
NASA USLI Rocket Competition Results
Seven Daedalus members traveled to Huntsville, Alabama on April 16th to participate in the University Student Launch Initiative rocket competition hosted by NASA. This was our first time participating in the NASA USLI competition. Because of the distance involved (and the proximity to the end of the semester) we decided to ship our rocket, Vertical Cruise Missile (VCM), ahead and fly to Huntsville. There was some slight damage to our fins from the shipping, but nothing a dremel and a steady hand couldn't fix. Upon our arrival we went through a quick hardware and safety check and we were ready to launch.
The next day the NASA USLI participants (19 University teams in total) were treated to a tour of NASA's Marshall Space Flight Center (MSFC). We toured quite a few labs but my overall favorite would have to be the propulsion department. In addition to electric propulsion and a wide range of ARES I show & tell, we were surprised to see the retired XRS-2200 linear aerospike engine originally built for the X-33 and the nuclear thermal rocket NERVA. Both engines are common house-hold names around the Daedalus labspace and they practically couldn't stop us from asking questions.
On Saturday we prepped the rocket for travel to the launch site. The NASA USLI competition was held at Bragg Farm in a large adjacent empty corn field. A total of 35 teams were participating in this launch; 19 University-level teams and 16 high school teams enrolled in the NASA SLI competition. The high school teams were scheduled to launch the next day but the weather on Sunday called for intense thunderstorms. The launch was VERY well organized and we didn't have much to do but quickly assemble our rocket and chat with other teams.
We ran into a few snags prior to the launch. Firstly, and most unfortunate, our payload just wasn't working. We still flew components of it, but it was not in working order prior to the launch. Not to worry though, our payload, the custom built flight computer, is a long term project. The goal is to eventually replace all onboard commercial flight computers since we have had a few fail on us in the past. We have two more VCM launches planned for the rest of the year and the flight computer should be up and running by then. At least the hardware is qualified for additional launches. The second worse problem was our altimeter(s). We were planning on flying an RDAS and ARTS, but our RDAS broke off a tiny LED during the test launch and will not initialize. We also ordered an ARTS (we lost one on the upper stage of DARTS) which we learned too late was never actually shipped. As such we needed at least one replacement. Fortunately, PerfectFlite told us that Huff Performance would be at the launch site, so we were able to buy a PerfectFlite MAWD directly from the vendor. This is probably the least advanced flight computer we've ever flown but it worked great. Thanks for your help Carey!!
After waiting a few hours we were finally ready to launch. Again, it is important to realize that the site was launching 35 rockets that day, nearly back to back as far as rocket launching goes. For our launch the weather was picture perfect and there was hardly any wind. The outcome:
Video: VCM_USLI_Launch.mpg [13.8mb]
Final altitude: 5,293 feet!!!
Did I mention the goal of this competition was to hit 1 mile (5,280 feet)? We missed the mark by 13 feet which is easily within the tolerance of our flight computer. We knew it would be close, but there are so many extraneous variables that we could not have planned for prior to the launch (wind speed and direction, launch angle, motor variability, etc.). If we had to launch again that same day we would likely be +/- 100 feet, as with most rockets. We did have a bit of a tangled chute on the way back down, but there was no damage to the rocket.
That same night was the awards ceremony hosted by ATK and NASA. The banquet was held under an actual Saturn 5 in the new museum at the U.S. Space and Rocket Center. We were awarded the Closest to Altitude Award, which was the most sought-after award given that night. The "Overall Winner " and "Rookie Winner " awards will be given at a later date after the Post Flight Analysis and Review papers are turned in and graded.
Great event overall and a lot of stiff competition; hopefully we can afford to travel back next year. This was a fantastic learning experience for the newer members on our team. The VCM USLI team leads AJ Colangelo and Matt Summers did a great job with the rocket, especially considering this was their first time taking the lead on a project. We are very happy to see younger members stepping up and taking responsibility. I'm very happy to say that this team will continue to do well long after the senior members are gone.
We'd like to thank our sponsors for making this entire event possible: NASA for putting this entire event together, Orbital Sciences for their generous donation and support of our program, Freescale for donating time and equipment towards our advanced flight computer payload, ATK Launch Systems for their motor and hotel donations, and of course our title sponsor Raytheon for their support over the years.
Stay tuned to the VCM homepage for more information, pictures, and videos of the launch.
[edit; 05/06/09] : The ASU Media Relations Department wrote up a short blurb about our participation in the NASA USLI Competition. The link is here: http://asunews.asu.edu/20090504_daedaluslaunch
[edit; 05/08/09] : The official NASA MSFC New Release on the competition has been uploaded: http://www.nasa.gov/centers/marshall/news/news/releases/2009/09-035.html
Hybrid Rocket Motor and Aerospike Nozzle Test Results
The same week as our return from the NASA USLI competition we were ready to test our new hybrid rocket motor and aerospike nozzle. Both projects were built as part of the Fulton Undergraduate Research Initiative (FURI) program by senior Daedalus members Jacob Dennis and Steven Shark. Their design work for hybrids and aerospikes also resulted in a win at the recent AIAA Region VI student conference in the team division. As such they will be heading back to Orlando this year for the AIAA International Student Conference at the Aerospace Sciences Meeting (ASM) conference.
Briefly described, our hybrid motor is 4 inches in diameter and uses N2O and HTPB as the oxidizer and fuel, respectively. The oxidizer mass flow rate is about 0.6 lbs/sec and is injected through a 60 degree swirl injector. This type of injector is known to drastically increase the regression rate of the hybrid and was investigated thoroughly by Justin Pucci, former Daedalus Project Director, during his own undergraduate career at ASU prior to leaving to MIT for graduate studies. The motor nozzle can be screwed onto the top of the motor case, resulting in added modularity when it comes to swapping nozzle designs. The motor was not built to fly, but weighing in at only 15 lbs with a load of HTPB fuel, we could certainly try it. The injector enclosure also has a forward-end ignition system on it, so it could be air-launched if required. Predicted thrust was around 250lbf.
The motor was fired on a new custom-built test stand designed and built by Daedalus members Jason Haubold and Weston Hanoka. As you can tell from the pictures, this test stand was designed with BIG motors in mind and can easily accommodate hybrid motors. The key design features include use of a thru-hole load cell so that we can run our N2O plumbing through the load cell without having to put any load on the feed lines. Also of note is the transverse motor retention with all-thread rods that can be moved to accommodate all sizes of motors. The motor was instrumented with a 2,000lb load cell, a pressure transducer, and read voltages from the solenoid relay to signal oxidizer start and end time. Unfortunately our load cell was not working for these tests, which is a real shame. We somehow managed to blow our op-amp during calibration and our DAQ just isn't sensitive enough to resolve the millivolts output by the load cell. The pressure transducer worked just fine, so we'll see what we can derive from that data.
Video: Hybrid_Firing_short.mpg [12.2mb]
As you can see, the hybrid motor tests with a standard bell-shaped nozzle worked just fine. It burned for just over 5 seconds though we could have gone for longer if we had wanted. However, we saw a few small chuffs in the flow and wanted to investigate into the pressure spikes prior to doing longer burns. Besides a larger chuff in the beginning and a small one at the end, the pressure curve looks practically even. The Arizona desert was about 101 degrees on Thursday, so the operating pressure was higher than expected. In fact, the solenoid valve liked to stick if the pressure was too high in the feed lines so it was tough to get it started. We chilled the tank a bit and opened it only just prior to ignition. We were very happy with the results and from our initial estimates the regression rate is over 1 mm/sec, which is really good. Not sure on the thrust yet, but we're confident from the video that we are around (or maybe over) 250lbf.
Truth be told, the above test was the second of the day, but I wanted to save the most interesting for last: the hybrid aerospike test. Prior to using the conical nozzle, we put in the aerospike nozzle designed by Steven Shark and built at the ASU student machine shop. We had a few small integration issues, but nothing we couldn't solve with a bit of Daedalus tinkering. The aerospike nozzle is expanded to 30kft I believe, meaning that it is perfectly expanded at all altitudes below 30kft. This kind of altitude compensation effect makes the aerospike much more efficient than conventional nozzles for a wide range of altitudes. However, this comes with a cost: mainly increased heating and integration issues. We solved the former by using a graphite nozzle insert, but there is still some more work to be done to ensure that the aerospike (especially the retention part) will not melt during long burns. We also used a graphite cowling to choke the flow without suffering from much erosion. The results were very promising but we identified some room for improvement.
Video: Aerospike_Firing_short.mpg [15.4mb]
Clearly something went wrong after two seconds. In fact, our pressure data shows that the pressure was increasing up until the point of ejection. That means our throat was closing during the burn. After checking out the ejected spike, it seems apparent that the bolt used to hold in the spike stripped the threads and the nozzle was slowly moving up towards the cowling lip. It is important to remember how very tiny the throat is; a gap smaller than 1/16 of an inch all around the spike. Some of the pictures show a bit of thrust asymmetry, providing further proof of slippage of the spike assembly. Though we never thought that'd be an issue, it seems that we need a longer bolt. Looking back, only 1/2 inch of threading was not nearly enough. If we had a longer bolt in there then we are confident that the aerospike would have stayed together for the duration of the burn.
Fortunately, besides the graphite cowling which was shattered, the spike itself is actually still in working order. This is despite the fact that it was shot into the air and landed roughly 20 yards away. If we wanted, we could re-build the cowling and test this same nozzle, though there are signs of cracking, perhaps from the expansion of the aluminum tip but more likely from the impact. As such we are planning on using a bit more steel, increasing the bolt length, using higher grade graphite, and perhaps some phenolic to try and mitigate the heating on the retention device.
We learned A LOT after about 10 hours of motor burning at our testing site in Florence, Arizona. Our proof of concept hybrid should be more than adequate for sustained burn times and high thrust. Our aerospike nozzle design works for the most part. We need to change a few things (materials and the main bolt), but the overall geometry can stay the same. We should have another ready for testing in less than a month. We hope to add all of the information on the motor and aerospike nozzle to our Propulsion section on this website once we get that up and running.
~ James Villarreal; Project Manager