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Rocketoon

Rocketoon Project

Last updated: May 28, 2005

Rocketoon flies! On May 10, 2005 we went to Camp Roberts, CA at about 7:00 in the morning. All our team’s efforts and hard work paid off with a successful launch.

We arrived at Camp Roberts at about 8:00AM, only to be met by a large herd of sheep. The MPs chased them away, allowing our launch crew to continue to the site. We were all unpacked and ready to set up the launch site by around 9:00AM. It took us about an hour and a half to get everything ready for launch. It would have been shorter, but much of the time was spent recuperating from a parachute charge that went off on accident.

A big part of launch prep is filling and loading the NOx tank. Our Propulsion Team spent a lot of time and did a lot of tests in the weeks before this launch to get this filling procedure right. All this effort paid of in spades: it all went without a hitch. In fact, they made it look easy.

With the NOx tank filled we had to pack the parachute, charge the batteries, load and switch on the electronics, couple together and lock down the airframe and we are ready for launch! A count-down, then push the button.

The rocket took off beautifully. The motor burned for about 10 seconds, but it seemed like the rocket never really got enough speed to get stable. In tests, our motor produced about 70 pounds of peak thrust, and 40 pounds sustained. The rocket weighs a little over 20 pounds. At about 1000 feet, the rocket started to tip and then lose altitude. We tried to pop the chute, but it was a little too late and the rocket suffered some scrapes on landing.

The parachute failed to stay connected to the rocket and as a result, there was heavy damage to almost the entire rocket. In honor of its successful flight (before the parachute), we have officially and permanently retired the vehicle in its entirety of pieces up in the hanger. Special congratulations go out to the Propulsion Team as our hybrid motor worked perfectly this morning. This is the first time CPSS has designed a motor from scratch and to have it designed, built and working within a school year is a great accomplishment. We should also give props to the structures team who came up with an excellent rocket design, significantly better than last year (we’ll just use some epoxy to fill in the scrapes on this year’s model). Also, our electronics worked very well. This was truly a team effort and we couldn’t have done it without everyone’s hard work.

We learned a lot from this flight. But the real win today is that our own motor, designed a built here, worked like a champ!

HM1 Hybrid Rocket Motor

The task of the Cal Poly Space Systems Propulsion Team was to provide a hybrid motor for use in the Rocketoon project. Previously CPSS had used a Rattworks K240 hybrid motor for Rocketoon testing, but these tests were limited to ground tests only because the K240 lacked the ability to store the oxidizer liquid over long periods of time. Because a balloon launch required a safe storage mechanism for the liquid oxidizer it was decided that the Propulsion Team would design and create a hybrid motor capable of storing the oxidizer for a period of time before igniting and firing.

CPSS Hybrid Motor Version 1 (HM1) was designed with the Rattworks K240 as a reference. HM1 used the same polypropylene fuel grains as the K240. This meant that the HM1 and K240 combustion chambers had the same diameter and length, about 2.5 x 12 inches. Also, the amount of nitrous oxide needed would be the same. An aluminum Catalina Cylinders 9007 tank with storage capacity of 103 in3 was given as a sample to CPSS at no cost. The Catalina 9007 tank is rated to 1800 psi, and provides a safe means of storing nitrous oxide. On the K240, the combustion chamber and nitrous oxide container are in the same aluminum tube. Using a separate tank for nitrous oxide in the HM1 allowed for the weight of the oxidizer fuel to be moved forward in the rocket and thus move the rocket CG forward and increase stability. During early testing of HM1, standard industry tank valves were used for sealing the nitrous oxide tank. However, through testing it was found that standard tank valves were either too large for the Rocketoon body or did not allow for enough mass flow. Also, the lack of a good vent system on standard valves made filling the oxidizer tank a difficult task. CPSS with the help of the Cal Poly Mechanical Engineering hangar machine shop machined a tank fitting to both seal the oxidizer tank and enable gas venting during filling.

Oxidizer flow was controlled with a Holley Performance Super Pro Shot solenoid specifically designed for automotive nitrous systems. Even though the Super Pro Shot is rated at requiring 12 volts and 8.6 amps the CPSS Electronics team found a way to cut the power usage of the solenoid to the point where it could be used onboard the Rocketoon.

The combustion chamber and oxidizer injector provided a machining task that was far beyond the capabilities of CPSS. Duke Energy of Morro Bay generously offered to machine the HM1 combustion chamber and injector at completely no cost. Many hours went into the machining and the result was a pristine aluminum chamber and injector. It is no exaggeration to say that without the help of Duke Energy, Cal Poly Space Systems would not have been able to build a hybrid motor.

Successful static firing of the CPSS Hybrid Motor Version 1 was first made on January 27 at the Cal Poly Test Cell. The first two test firings both used a direct oxidizer line from the large nitrous oxide storage tank. The third test firing used the flight capable Catalina Cylinder 9007 tank. After three successful static tests it was decided to move onto tests for measuring thrust. A swinging horizontal test stand was build to be used in thrust measurement tests. The decision to use a horizontal test stand was prompted by the large hole in the asphalt cause by the successful vertical firings of the hybrid motor. After several failed firing attempts a successful thrust measurement test was made on May 5. The peak thrust was 70 lbs and the average thrust was 41 lbs.

CPSS wanted to be the first private group to put an object into space. Well, we weren’t. However, we still plan to be the first amateur team put an object in to space.

Figure 1Figure 2Figure 3Figure 4

The Rocketoon Project is a combination of a high-altitude launch platform and a rocket. The launch platform is made using balloons; it carries the rocket up through the dense air to around 100,000 feet. The rocket then launches from the balloon platform and travels to the edge of space, about 62½ miles above the earth. Using the same process developed from the StarBooster™ Project, we will start small and build up to the final vehicle. The Rocketoon Project started in the Fall of 2003.

We started the project the project by building a series of 2-ft tall model rockets and a balloon based launch platform. Our goals were to test recovery systems and onboard electronic packages. The first series of rockets were flown from the ground to determine which had the best flight characteristics. The best performing rocket was then remotely launched from a balloon launch platform shown in Figure 1. The launch platform consisted of a lightweight rocket launcher held up by six helium balloons, each with an approximate diameter of three feet. The balloons went up 100 ft above ground, then we launched the rocket by computer from the ground. The rocket fired successfully on a size G solid rocket motor. The rocket pierced one balloon as it left the launcher, but the parachute opened at apogee and the rocket was recovered safely. The launcher was tethered so we could pull it back to ground without incident. The purpose of the launch was to gain experience with how much weight a helium filled balloon could lift and to test the remote firing capability. Both objectives were met and we started to plan for the larger rocket.

In the next phase of the project we built a 5-ft tall rocket with an auto recovery capability. We planned to launch this rocket from the ground to prove that all the electronic and mechanical systems worked. The rocket design included recovery fins that we controlled from the ground; we plan to use this same design on the full-scale rocket. The goal is to have some control over where the rocket lands after launch.

A major new aspect of the 5-ft rocket was a hybrid rocket motor instead of a traditional solid propellant. We did not have any experience with hybrid motors, so the motor was test fired on the ground several times before being used for the actual rocket flight. The motor is shown being prepared for a test fire in Figure 2. The fuel propellant for the hybrid motor was polyurethane and the oxidizer was nitrous oxide. We used data gathered from our static firing tests to find out what pressure the oxidizer tank needed to be at before the fuel would fire efficiently.

While the motor was being built and tested, another part of our group built the rocket. Both rocket and motor were ready for flight in May, 2004. The group reserved a large open field at Camp Roberts Army Training Facility in Bradley, CA for the launch. The skies were calm at the time of launch, but for the first attempt the igniter didn’t fire. The entire launch sequence was aborted and the igniter reloaded. On the second launch attempt, the rocket, shown in Figure 3, fired and got to 1000 ft. The parachute ejected correctly after apogee (shown in Figure 4) and the rocket landed safely. The on-board electronics showed altitude, pressure and acceleration during the flight. Video of the flight shows some control coming from the fins, but we need more testing to determine if this system will work at higher altitudes.

We concluded that this flight proved very promising and immediately began making plans for a high altitude launch to take place next year, in 2005. At the end of the school year, CPSS still had 35 very active members from seven different majors. Overall, the project is on track to be a success. The goal for the 2004-2005 year will be to launch a rocket off a balloon at high altitude.