Rockoon Update

Our final project for the semester is to assemble our design into a very large poster (it's like four feet wide). I'd like to share it with you! But instead of just posting a little picture of it, I've re-written it in post form so you can actually read it. That said, here it is:

ISU Rockoon

Goals/Objectives

The objective of the Rockoon Project is to build a fully reusable, economic, lightweight and stable sounding rocket to be assisted by a high-altitude balloon. The rocket will be launched near the stratosphere, to an altitude of at least 140,000 ft.  

The Rockoon will be powered by a L-class impulse rocket engine to carry video and communication systems (allowing the entire rocket flight to be live video-streamed), GPS tracking system, navigation-sensor systems, telemetry system and any payloads of interest to be used for experimental flights. Recovery systems will be used for safe return of the rocket and platform to the ground, making the Rockoon system reusable.

History

The concept of a Rockoon was first developed in 1949 by the Aerobee Rocket engineering crew and consisted of a sounding rocket that was launched from a balloon, rather than from the ground to achieve higher altitudes. James Van Allen was the first to use the rocket-balloon combination to study the atmosphere in 1952. In 1953 Rockoons fired off Newfoundland detected the first hint of radiation belts surrounding Earth. The low-cost Rockoon technique was later used by the Office of Naval Research and The University of Iowa research groups in 1953-55 and 1957, from ships in sea between Boston and Thule, Greenland.

Launch Platform Design

The launch platform is essentially the fundamental component of a Rockoon system, as it is the part the actually connects high powered rocketry with high altitude ballooning.  The platform needs to be durable and lightweight, but able to house the rocket and electronics, and be able to successfully launch the rocket.  The platform will be a “cannon” like design connected to a multiple balloon system, with the rocket sitting in the middle of the platform surrounded by three side rails.  These side rails will hold the rocket in place while it’s being towed to launch altitude, along with keeping the rocket stable while it reaches a sufficient launch velocity.  The platform will also house electronics that will allow us to track the platform and actually communicate with the rocket prior to motor ignition.

Electronics

The electronic systems for the launch platform have to perform four basic functions: (1) Monitor the motion of the launch platform, (2) Receive command to launch the rocket, (3) Track the launch platform via GPS, and (4) after ignition of the rocket, cut-down from the balloons so that the platform would return to Earth. The first flight of the launch platform will be to test the reliability of the launch platform and electronics without the launch of a rocket. Several cameras will monitor the motion of the balloons and the platform. An onboard accelerometer and gyro sensor will record motion data to an onboard micro-SD card. These functions, along with the ignition and balloon cut-down will be controlled by an Arduino MCU, and are depicted schematically in the figure below.

Rocket Design

The rocket design is based off of a carbon fiber airframe that was passed down to us from our predecessors. It will be a minimum diameter rocket that is just over eight feet tall made completely of carbon fiber. The nose cone has a metal tip to help burst through balloons if needed.  This rocket will be flown on a Cesaroni 4-grain, level-two L motor.  Payloads will consist of a GPS, CO2 pressure ejection system for recovery,  an accelerometer, and a camera with the possibility of a live video stream.  Initial RockSim simulations predict a maximum altitude of 157,000 feet, and a maximum velocity of 2427 feet per second (Mach 2.4). 

The design for this rocket has a center of gravity of 76.7 inches and a center of pressure of 91.8 inches, giving a static margin of 4.8 caliber. If the launch were to occur from the ground this margin would be too high, but since the launch will occur at higher altitudes, the perturbing effects will be much less effective due to the lower air density. Due to launching at high altitudes, bigger than normal fins will be used and an exit velocity of about 150 feet per second from the platform will be needed for stable flight.

Flight Performance Analysis (RockSim)