Texas Two Step launched at 1921 PDT on Saturday, April 27, following a trouble-free integration except for a part we had to have driven out from LA. This flight was notable for a few reasons. First, Texas Two Step is basically two rockets in one, the most complex vehicle RPL has ever built. It was the first flight of an 8" motor case - Traveler will be the next. It was also the first time we used the launch tower.

Showing off the launch tower to the National Geographic film crew.

Sliding the rocket into the tower.

There were a few signs of trouble before launch, such as a malfunctioning first-stage igniter and the sustainer avionics reporting after a few minutes that they would be unable to light the sustainer. With about 10 minutes to sunset, we didn't have time to troubleshoot anything except the booster igniter, which finally worked. Texas Two Step looked incredible zooming through the tower:


Shortly after clearing the tower, the vehicle pitched slightly into the wind, adding to the angle that it already had from the tower. It continued straight for a while, then seemed to pitch down even more near the end of the burn. There was no sustainer ignition, either due to the software angle lockout or the electronics problems mentioned earlier. The booster drag-separated as planned at about 12,000' AGL. Avionics in the nosecone fired the CO2 cylinder to deploy the recovery harness. This was the first time we have successfully used the CO2 system in flight, a great plus for Traveler!


Because of the high horizontal velocity at apogee, the shock cord broke on both ends and the two pieces of the sustainer cartwheeled and fell in the lakebed 3.2 miles from the launch site. We received dozens of BigRedBee GPS pings during the flight, and were able to immediately postprocess them and view them in Google Earth, giving us a good idea of the landing location. Then, a few minutes later, we found that our SPOT satellite messenger device was still working, and we drove and walked in the darkness to the exact location it gave us. The sustainer and nosecone were about 20 meters apart, both with significant damage. The nosecone shell, a few fins, and the airframe were cracked. Fortunately, the propellant had not ignited on impact. We looked for the booster for a few minutes, but weren't able to find it. This weekend, when we return to the MTA to fire Tim's GOX-GH2 aerospike, we'll look for it some more. It should be easy to find in daylight on the lakebed. Because it is so unaerodynamic by itself, there's a good chance we'll be able to get video from the five cameras on board even if the recovery harness broke.

The recovery team.

Acceleration and barometric altitude data. Note the large spikes in acceleration at deployment and impact.

Though this launch didn't go according to plan, we're much more confident from the performance of the booster motor, the launch tower, and the avionics that Traveler will be a success when it flies this September at BALLS. An even more important milestone for that flight will occur May 20, when we fire the full Traveler motor in an aluminum case on a new thrust stand. If that works, it will be the largest motor RPL has ever successfully fired by a factor of three! We're already producing a new motor for the flight this fall.

We'll be posting lots of video and pictures of the flight and build process in the coming week, as well as more information about the static fire.

Kiwi pulled off another successful static fire on Saturday, February 23. We had originally planned to fire three grains, but actually used only 10% oxamide, due to a combination of grain curing problems and an intense sandstorm. Our data acquisition system performed well again, including three pressure transducers (two at the head end and one at the aft end), load cell, and thermocouple.

We had a much smaller crew of RPLers at this firing, due to midterms - about 12 people in all. One benefit of this was that more people got experience preparing the motor.

The main way in which this firing was different from the previous series (besides the propellant composition) was the nozzle and forward motor bulkhead. We remade the nozzle out of steel, with a shorter graphite insert. Both the nozzle and the new aluminum bulkhead had face O-ring grooves to seal a leak path for combustion gases and thereby protect the inside of the motor case.

The nozzle, showing the face O-ring grooves and pressure transducer stems.

Integration went smoothly, apart from having to apply a little more force than usual to compress the motor stack longitudinally due to the face O-rings. After Kiwi was on the stand, the DAQ equipment was hooked up:

Tim and John working on DAQ.

The beginning of the sandstorm.

As promised, RPL is returning with Kiwi to Mojave this weekend to conduct another series of up to three static fires. The grains will be selected out of 72/10, and 5% oxamide, and 10% oxamide as time permits. Data should be even better than last time due to some new pressure transducers we got, a new setup for the transducers that can find the pressure differential between the forward and aft ends of the case, and a calibrator that we built.

Kiwi itself will consist of the same motor case, now becoming a little charred on the inside, with a new bulkhead and nozzle. There will be o-rings on the faces of the forward and nozzle bulkheads in order to seal a leak path and protect the inside of the case. We remade the nozzle carrier out of steel instead of aluminum, and the graphite throat has more efficient contours.


Some of the firings will be ignited with our head-end system. We plan to try both composite and black powder igniters, seeing how quickly they work in order to choose one for use on Texas Two Step. (We don't want the igniter to take too long or the upper stage could pitch over.)

We'll try to get video that lives up to the quality of last time. Stay tuned!

Before discussing the Kiwi project, I want to mention that our blog has a new, modern format. If you're reading this on the RPL website, you can check it out at uscrpl.blogspot.com!

January 26 was a very successful and productive day for RPL. We were in the full swing of setup by 0930 hours, and conducted the firings at approximately 1300, 1500, and 1600. The first firing was with our normal 72/10 propellant, the second with oxamide, and the third with melamine. See the previous post for an explanation of why we wanted to investigate these additives.

Integration was mostly trouble-free; the data acquisition setup, by our DAQ chiefs John Rising and Tim Ellis, was among the smoothest RPL has ever had. Video and photography capturing of the firings was superb, with two cameras close to the motor behind protective stands, a GoPro overlooking the motor, multiple keychain cameras all over the place, and many handheld cameras in the blockhouse and bunker. Some of the videos are truly astonishing, none more so than the one from a keychain camera taped to the igniter dowel on the third firing. Watch for that in our highlights video, which will be posted soon.

The filament-wound carbon fiber motor case stayed in good condition throughout the firings, except for a small bit of sealant damage at the head end. The case has now been fired four times, double the total of RPL's previous record holder, Trunnion. The insert and leads of the head-end ignition system showed little degradation.


Now for the data analysis. Our DAQ equipment consisted of an S-beam load cell, a pressure transducer, and a thermocouple. We used a new method for mounting the pressure transducer -- instead of screwing it directly into the upper bulkhead, we put it at the end of a grease-filled tube, in a successful attempt to keep it relatively cool and avoid damaging it. The thermocouple was attached near the pressure transducer to verify that it remained cool. In actuality, the transducer never got above 25 degrees C, so we will use this method on future tests.


Clockwise from top left on the below graphs, we have the time histories of the total thrust of the motor, the pressure at the head end, the thrust coefficient (a property of the nozzle geometry), c-star (a measure of the propellant chemistry), and specific impulse (the overall "efficiency" of the motor). Each graph contains one curve for each propellant formulation, with "Billy Mays" referring to oxamide and "Big Mel" referring to melamine. Due to switching to a different pressure transducer shortly before the test, the tops of the pressure curves went above the transducer's limit, so the curves in those intervals have been inferred based on the thrust data.


The performance of each propellant was close to our calculated optimum values. The 72/10 propellant produced 150 pounds of thrust and fired for about 4.5 seconds. The oxamide and melamine grains produced lower thrust, about 100 pounds, but fired for 6 to 7 seconds. Since they fired longer, their total impulse is about the same as that of the 72/10, meaning that the burning rate suppressants do not significantly lessen the energy release of the propellant. In fact, the slower-burning propellants would have produced even better performance had we used a nozzle with a smaller throat in order to bring their chamber pressure up by about a hundred psi to our usual level.

If you have any questions about the graphs or the propellants, please post in the comment section.

Kiwi will be back in late February for another series of static firings, for which we have already started preparing hardware. We'll try different concentrations of oxamide, different throat designs, and maybe even an aerospike!

In other news, our 8" and 6" diameter two-stage rocket, Texas Two Step, is deep into construction. The nosecone is complete, as are many miscellaneous bits of hardware. We are currently working on the nozzles and fins. Daily updates are being posted at twitter.com/uscrpl!

Tomorrow, USCRPL will be conducting our first operation of 2013: a series of three static fires in our 4" filament-wound motor case. The primary objective of the tests is to gather performance data on our usual propellant formulation as well as on burn rate suppressants.

Each test has one grain weighing about 3.3 pounds. The first grain is our normal propellant made of ammonium perchlorate and aluminum. The second has some oxamide, (CONH2)2, which according to motor chemistry calculations should slow down the rate at which the propellant burns. Oxamide has been tried by the lab before with inconclusive results, but this time we have a more homogenous grain and better data gathering capabilities. The third grain has melamine as an additive, C3H6N6, which is an another burning rate suppressant.

The benefit of slowing down the burn is that a high-performance vehicle such as Traveler would lose less energy due to drag, not need as much thermal protection material, and not be subjected to as high an acceleration. The data we gather during tomorrow's firings will inform the design of our future vehicles.

It's also worth noting that this will be the third time USCRPL has used a filament-wound motor case, and the first time that one will be reused. That will be a noteworthy achievement in itself.

One final technology that this project is helping develop is head-end ignition. Usually, to light the motors on our rockets, we insert an igniter up through the nozzle and connect it to a ground-based power source. But for the upper stage of Texas Two Step (...more details on that soon...) we need the avionics to send current to an igniter below the motor bulkhead. We'll be testing our method for doing that during these firings, albeit without avionics involved. Basically, we have an insulating insert in the forward bulkhead, with screws going through it to transmit the electricity.

You may be wondering about the name for this static fire -- Kiwi. Our hope is that the motor will remain as flightless as the bird.

If you hunger for more frequent updates, be sure to follow us at twitter.com/uscrpl! We post short updates there several times a week, in addition to meeting and work schedule notifications. We'll also be tweeting immediate updates tomorrow.