The idea behind this Instructable is to provide an alternative method, however implausible it may seem, for cost-efficient rocket launches. With recent space technology developments being focused on lessening the cost, I thought it would be great to introduce the rockoon to a broader audience. This Instructables is divided largely into four parts: introduction, design, building, and results. If you want to skip the concept of rockoons and why I designed mine the way I did, go straight to the building part. I hope you enjoy, and I would love to hear from you about your thoughts on my project or about your own design and builds!!
Step 1: Background Information
According to Encyclopedia Astronautica, a rockoon (from rocket and balloon) is a rocket that is first carried into the upper atmosphere by a lighter-than-air gas-filled balloon, then separated and ignited. This allows the rocket to achieve a higher altitude with less propellant, as the rocket does not have to move under power through the lower and thicker layers of the atmosphere. The original concept was conceived during an Aerobee firing cruse of the Norton Sound in March 1949, and was first launched by the Office of Naval Research group under James A. Van Allen.
When I first started my project on rockoon, I had no idea what a rockoon was. It was only after I had finished up the documentation after my project that I found out there was a name for this device I had made. As a South Korean student who is interested in space technology, I have been frustrated at my country’s development of rockets since I was young. Although the Korean space agency, KARI, have made several attempts at space launch vehicles, and succeeded once, our technology is nowhere near other space agencies such as NASA, ESA, CNSA, or Roscosmos. Our first rocket, Naro-1, was used for all three launch attempts, two of which are suspected to have failed due to separation of stages or fairing. The next rocket to be made, Naro-2, is a three-stage rocket, which makes me question, is it wise to divide the rocket into several stages? The benefits of doing so would be that the rocket loses significant mass as the stages are separated, therefore increasing the efficiency of propellant. However, launching multiple-stage rockets also increase the chance that the launch will end up as a failure.
This made me think of ways to minimize rocket stages while maximizing propellant efficiency. Launching rockets from planes like missiles, using combustible material for rocket stage bodies, are a few other ideas I had, but one option that attracted me was the high altitude launching platform. I thought, “Why can’t a rocket just launch from a helium balloon, above most of the atmosphere? The rocket can then be a single-stage sounding rocket, which would simplify the launching process significantly, as well as lessen the cost.” So, I decided to design and build a rockoon myself as a proof of concept, and to share this Instructables so you can all try it if you want.
The model I build is called a HAAS, short for High Altitude Aerial Spaceport, in hopes that one day, rockoons won’t be just a temporary launching platform for rockets, but a permanent platform used for launching, refueling, and landing space launch vehicles.
Step 2: Design
I designed the HAAS based on intuitive shapes and basic calculations
Using Nasa's guide on "Designing a High Altitude Balloon" I calculated that I would need about 60L of helium to lift at most 2kg, the upper limit we set for the HAAS weight, taking into account that temperature and altitude will have an effect on the buoyancy force of helium, as mentioned in "Effect of Altitude and Temperature on Volume Control of an Hydrogen Airship" by Michele Trancossi. However, this was not enough, which I will talk about in more detail, but it was because I didn't take into account water vapor's effect on helium's buoyancy.
- Cylindrical shape in order to minimize wind effect
- Three layers (Top to hold rocket, middle for launching mechanism, bottom for 360 camera)
- Thick middle layer for extra stability
- Vertical rails for rocket placement and guidance
- 360° camera for footage
- Foldable parachute for safe decent
- Thin Cylindrical helium balloon for minimum rocket offset angle
- Microprocessor: Arduino Uno
- Launch methods: Timer / Digital Altimeter
- Method of activating propellant: By puncturing a hole in a high-pressure CO2 capsule
- Metal spike attached to springs
- Release mechanism consists of two hooks
- Released by movement of motor
I came up with several methods of releasing the spike with a motor movement.
Using a design similar to a keyed chain door lock, by pulling the metal plate until the end key aligns with the bigger hole, the spike could be launched. However, the friction proved to be too strong, and the motor couldn’t budge the plate.
Having a hook holding onto the spike and a pin locking the hook to a stationary object was another solution. Like the reverse of a fire extinguisher’s safety pin, when the pin is pulled out, the hook would give way and launch the spike. This design also produced too much friction.
The current design that I use is by using two hooks, a similar design to a gun trigger. The first hook holds onto the spike, while the other hook is caught in a small nick at the back of the first hook. The pressure of the springs holds the hooks in place, and the motor has enough torque to unlock the secondary hook, and launch the rocket.
- Propellant: Pressurized CO2
- Minimize weight
- Action camera integrated into the body
- Replaceable CO2 capsule (reusable rocket)
- All the main features of model rockets (nose, cylindrical body, fins)
Since solid rocket propellant wasn’t the best option to launch in a populated area, I had to opt for other types of propellant. The most common alternatives are pressurized air and water. Because water could damage the electronics onboard, pressurized air had to be the propellant, but even a mini air pump was too heavy and consumed too much electricity to have on the HAAS. Luckily, I thought of the mini CO2 capsules that I had bought a few days ago for my bike tires, and decided that it would be an effective propellant.
Step 3: Materials
In order to make a HAAS, you will need the following.
For the frame:
- Thin wooden boards (or any light & stable board, MDF)
- Long nuts & bolts
- Aluminum Mesh
- 4x Aluminum slider
- 1x Aluminum pipe
- 360° camera (optional, Samsung Gear 360)
- Large piece of cloth & rope (or a model rocket parachute)
For the launch mechanism
- 2x Long springs
- 1x metal rod
- Thin wire
- Some aluminum plates
- 1x Breadboard
- 1x Arduino Uno (w/ USB connector)
- Temperature & pressure sensor (Adafruit BMP085)
- Piezo Buzzer (Adafruit PS1240)
- Small motor (Motorbank GWM12F)
- Jumper wires
- Motor Controller (L298N Dual H-Bridge Motor Controller)
- Batteries & battery holder
For the air rocket
- CO2 bike tire refill cans (Bontager CO2 Threaded 16g)
- Several aluminum cans (2 for each rocket)
- Acrylic plates (or plastic)
- Elastic bands
- Long strings
- Action Camera (optional, Xiaomi Action Camera)
- Glue gun
- Epoxy putty (optional)
- Saw/Diamond cutter (optional)
- 3D printer (optional)
- Laser cutter or CNC milling machine(optional)
Beware! Please use the tools with caution and handle with care. Have someone else around to help if possible, and get assistance using select tools if you don’t know how to use them.
Step 4: Frame
- Use a laser cutter, a CNC milling machine, or any tool of your preference to cut the thin wooden board into the shape in the attached pictures. The top layer is consisted of two boards connected with bolts for stabilization. (For milling or laser cutting, the files are provided below.
- Cut the aluminum sliders into equal lengths, and insert them into the crevices along the inner ring of each layer. Using a glue gun, stick the layers so that there is room for the rocket at the top.
- Place the aluminum pipe at the center of the middle layer. Make sure it is stable and as vertical to the layer as possible.
- Drill a hole into the bottom layer and attach the optional 360° camera. I made a removable rubber cover for the camera, in case the camera receives a shock during the landing phase.
- Fold the large piece of fabric or cloth into smaller rectangles and attach 8 ropes of equal length to the farthest corners. Tie the rope at the far end so it doesn’t get tangled. The parachute will be attached at the very end.
Step 5: Launch Mechanism
- Make two hooks, one to told the metal rod and one to be the trigger. I used two different designs: one using metal plates, and one using a 3D printer. Design your hooks based on the pictures above, and the 3D printing files are linked below.
- In order to be able to release the trigger and launch the rocket using either a timer or a digital altimeter, the Arduino circuit specified in the picture above must be made. The digital altimeter can be added by connecting these pins.
- Arduino A5 -> BMP085 SCL
- Arduino A4 -> BMP085 SDA
- Arduino +5V -> BMP085 VIN
- Arduino GND -> BMP085 GND
- Add the circuit to the HAAS. Connect the trigger hook to the motor with a wire, and spin the motor to test if the hook can smoothly slide out.
- Grind the end of the thin metal rod and insert it into the aluminum pipe. Then, attach two long springs to the end of the rod, and connect it to the top layer. Bend the end of the rod so it can easily be hooked onto the launching mechanism.
- Test a few times to make sure the rod launches smoothly.
3D printing Files: https://www.thingiverse.com/thing:2759681
Step 6: Rocket
- Prepare two aluminum bottles. Cut the top part of one bottle, and the bottom part of the other.
- Cut a slight cross on the top of the first bottle, and the bottom of the second bottle.
- Use wire and cloth to make a holder for the CO2 capsule on the first bottle.
- Insert a CO2 capsule into the top part, and squeeze it into the bottom of the second bottle so that the entrance to the CO2 capsule is facing downwards.
- Design and cut fins with plastic or acryl, then glue them to the side of the rocket. Use any preferred material, in this case epoxy putty, for the cone.
- Cut a rectangular hole on the side of the rocket for the optional action camera.
To finish off the HAAS, after installing the launch mechanism, wrap the aluminum mesh around the frame, tie it to the small holes on the outside rim. Cut a hole on the side in order to reach into the device easily. Make a small casing for the parachute and place it on the top layer. Fold up the parachute and put it in the casing.
Step 7: Coding
The launch mechanism can be activated in two different ways: with a timer, or a digital altimeter. The Arduino code is provided, so comment out the method that you don’t want to use before uploading it to your Arduino.
Step 8: Testing
If you’re using timer to launch the rocket, test a few times with spare CO2 capsule at a few minutes.
If you’re using the altimeter, test if the launch mechanism works without the rocket by setting the launch altitude to ~2 meters and walking up the staircase. Then, test it at a higher launch altitude by going up an elevator (My test was set at 37.5 meters). Test that the launch mechanism actually launches a rocket by using the timer method.
Included are 12 testing videos of the HAAS
Step 9: Results
Hopefully by now, you’ve tried to make a rockoon yourself and perhaps even celebrated a successful rocket launch. I have to report, however, that my launch attempt ended in a failure. The main reason for my failure was that I underestimated the amount of helium needed to lift the HAAS. Using the ratio of the molar mass of helium to the molar mass of air, as well as temperature and pressure, I had approximately calculated that I needed three tanks of 20L helium gas, but I found out I was horribly wrong. Since it was hard to purchase tanks of helium as a student, I didn’t get any spare tanks, and failed to even get the HAAS above 5 meters off the ground. So, if you haven’t tried to fly your rockoon yet, here is an advice: get as much helium as you can get your hands on. Actually, it would probably be more reasonable if you calculated your needed amount, taking into account that pressure and temperature decreases as height increases (within our flying range), and that the more water vapor there is, the less buoyancy helium will have, then get twice the amount.
In the aftermath of the failed launch, I decided to use the 360 camera to capture an aerial video of the surrounding river and park, so I tied it to the helium balloon with a long string attached to the bottom, then let it fly. Unexpectedly, the wind at a slightly high altitude was heading in the complete opposite direction as the lower winds, and the helium balloon drifted into an electrical wiring installation nearby. In a desperate attempt to rescue my camera and not damage the wiring, I tugged on the attached rope, but it was useless; the balloon was already caught in the wire. How on Earth can so many things go wrong in one day? Eventually, I called the wiring company and asked them to retrieve the camera. Kindly, they did, although it took me three months to get it back. For your amusement, attached are some photos and videos from this incident.
This accident, although it didn’t occur to me at first, revealed a serious limitation of using rockoons. The balloons cannot be steered, at least not with a light and easy-to-control mechanism that can be installed on the HAAS, and therefore, it is almost impossible to launch the rocket into an intended orbit. Also, since the conditions of each launch are different and keeps changing throughout the ascent, it is hard to predict the rockoon's movement, which then requires the launch be done at a site with nothing around it for several kilometers, because a failed launch could prove to be hazardous.
I believe this limitation can be overcome by developing a mechanism of navigating on a 3D plane with drag from the balloon, and interpreting wind as vector forces. Ideas that I have thought of are sails, compressed air, propellers, better frame design, etc. Developments of these ideas are something I’ll be working on with my next model of HAAS, and will be looking forward to seeing some of you develop them as well.
With a bit of research, I found that two Stanford aerospace majors, Daniel Becerra and Charlie Cox, used a similar design and had a successful launch from 30,000 feet. Their launch footage can be found on the Stanford Youtube channel. Companies such as JP Aerospace are developing "Specialties" on rockoons, designing and launching more complex rockoons with solid fuel. Their ten-balloon system, called "The Stack", is an example of various improvements on the rockoon. I believe that as a cost-efficient way of launching sounding rockets, several other companies will work towards making rockoons in the future.
I would like to thank Professor Kim Kwang Il, for supporting me throughout this project, as well as providing resources and advice. I would also like to thank my parents for being enthusiastic about what I am passionate about. Last, but not least, I would like to thank you for reading this Instructables. Hopefully, environmentally friendly technology will be developed in the space industry soon, enabling more frequent visits to the wonders out there.