Proceedings of KGCOE-MD2004: Multi-Disciplinary Engineering Design ConferencePage 1
MD2004-04036
Copyright © 2004 by Rochester Institute of Technology
Proceedings of KGCOE-MD2004: Multi-Disciplinary Engineering Design ConferencePage 1
Meteor: High Altitude Rocket PLatform
The application of micro-technology to space exploration
Michael Wilson/RIT / Joshua Shreve/RITCaitlin Vanderbush/RIT / Jared Schott/RIT / John Shoots/RIT
Nathaniel Stockey/RIT / Stephanie Sprague/RIT
Copyright © 2004 by Rochester Institute of Technology
Proceedings of KGCOE-MD2004: Multi-Disciplinary Engineering Design ConferencePage 1
Abstract
The METEOR project is a multi-disciplinary research project whose ultimate goal is the application of micro-technology to space exploration. A critical part of this goal is the development of a stabilized platform that is raised to a desired altitude utilizing zero-pressure balloon technology. Launching rockets from a platform at an altitude in the mid to high-ranges of the ionosphere presents a number of benefits that include (1) less air resistance and drag, (2) the ability to change the latitude that the launch occurs and, (3) eliminating the need for ground based launch equipment. Research has been conducted to build upon established altitude deliverance methods while incorporating the METEOR goals. The 2004 METEOR team has concentrated on establishing a communications link to the desired altitude, testing the performance of critical electronic components, as well as designing a sub-system to orient the payload, which in future missions will aim a rocket.
introduction
The objective of the 2004 METEOR team is to provide a base of knowledge and concepts for future teams by analyzing past amateur balloon missions and conducting a preliminary test mission. The components that will be evaluated in the mission will include the flight computer, communication system, GPS tracking, recovery system, various sensors, a payload orientation system as well as a high definition camera (acting as the payload) to take atmospheric pictures and a low definition camera to monitor the payload. The scope of the 2004 project is to develop a final design, which will integrate various subsystems, both electrical and mechanical, and can serve as a base for future METEOR teams to build upon. The design process must address concerns such as heat dissipation, effects of electro magnetic radiation, power consumption, ability to direct the payload, as well as establishing a communications link.
Nomenclature
FAA – Federal Aviation Administration
FCC – Federal Communications Commission
GPS – Global Positioning System
XCVR – Transceiver
TX – Transmitter
RX – Receiver
ATV – Amateur Television
OSD – On Screen Display
BACKGROUND RESEARCH
High altitude balloons have been used for meteorological research since the 1890s. [1] The highest altitude reached was 170,000 ft (51,820 mi) from Chico, California in 1972. Many amateur groups and universities have conducted experiments by launching modules into the atmosphere to collect data. Some of these groups are the University of Kansas, University of Washington, and the Central Iowa Technical Society. Groups such as HABET (High Altitude Ballooning Experiments in Technology) have done extensive research and conducted multiple launches that established a communication link to their payload in near space. [2] All of these launches involve sending a small payload into the upper atmosphere to collect data. Many of these payloads are no more than 30 lbs. To our knowledge, the concept of rocket deployable platforms has not been explored at the university level. Some of the lessons that the METEOR team took from previous research are to limit weight, create redundancy in critical systems where possible, and try to plan for the unexpected. The team also learned that the FAA is responsible for evaluating the safe operation of unmanned free balloons.
CONCEPT DEVELOPMENT
Once the design team had gained a better understanding of the scope of the project and defined the needs and requirements, time was spent generating concepts. A brainstorming technique was employed to generate a number of concepts whose effectiveness would later be evaluated. The following section describes the various aspects of the project the team fealt required the most attention.
Large Scale Model
One design concept answers the need to deliver a large-scale rocket, approximately 50 lbs, to an altitude of 80,000 ft. This design incorporates a balloon, a parachute, and a mission stage. The architecture of the main system can be seen in Figure 1. The parachute attaches to a shroud ring, which ensures the tethers extending to the platform will not tangle and that the chute will open. The mission stage consists of a platform which houses the electrical components in sealed boxes. The structure must protect the components from the cycling of environmental conditions as well as shielding them from impact.
Figure 1-
Stages of Design
The platform itself consists of a truss made of aluminum tubes to allow for a weight reduction and minimize the effects of drag. [3] Aluminum is chosen due to its high strength to weight ratio. [3,4,5] The rocket is housed inside the platform and is attached to an extendable arm, which could raise and lower the payload via a winch system. The large scale Design can be seen in Figure 2. The FAA-required cut-down mechanisms are sections of NiChrome wire wound around the tether that attaches the balloon to the parachute. An electrical current sent through the wire will heat up and burn through the tether, resulting in separating the parachute and platform from the balloon. Inert gas jets are included to orient the platform and ensure that the rocket is aimed in the desired direction. This concept may prove useful to METEOR teams in the years to come.
Figure 2 - Large Scale Model
Small Scale Model
A second design concept is developed to deliver a small-scale rocket, approximately 2 lbs, to Low Earth Orbit. This small-scale model must adhere to a 6 lb weight limit, which is divided among the electrical components, payload, and the orientation device. The NiChrome cut-down design is implemented in this model as well. The shroud ring is eliminated since the tethers are attached to the platform at equidistant locations, limiting the possibility of tangling. The small-scale model is made up of an aluminum plate to which all the electronic components are mounted on with a motor assembly mounted underneath. The motor assembly will connect to a payload that can be oriented to within 1.8 degrees of accuracy. A shaft extends from the bottom of the motor to which the payload can be attached. The electrical board and motor are housed inside a polystyrene structure covered in Mylar. The foam will regulate temperature and dissipate impact forces, while the Mylar will reflect any radiation. The legs of the foam insulator will also aid in protecting the payload upon impact.
CONCEPT SELECTION
The 2004 METEOR team chose the Small Scale Model. The FAA requires a number of safety measures to launch a payload greater than 6 pounds, which would have been impossible for the team to develop within the time limitations. The Small Scale Model does not have such limitations since the payload is 6 lbs or less. Also, there is a much smaller threat to property and persons with launching a smaller payload.
Final Design
The proposed design by the 2004 METEOR team consists of a flight vehicle composed of an ascent stage, a mission stage containing the electrical board and motor, a recovery stage, and a ground station, which is used to control and track the system.
Ascent stage. The ascent stage consists of the balloon, two independent cut-down systems, and tether attachments. The balloon is filled with a total volume of 358 ft3. This volume provides enough buoyancy force to account for the weight of the system and for 20% free lift. A nylon cord with a tensile strength of 30 lbs attaches the balloon to the top of the parachute. The two independent cut-down systems are attached to this tether. Both of these systems include a section of NiChrome wire wrapped around the tether. When current is delivered through the NiChrome wire it heats up and melts the nylon chord. One system is operated remotely from the communications ground station via the flight computer while the other utilizes a micro-controller to engage the system after a predetermined length of time.
Mission Stage. The mission stage is composed of both mechanical and electrical components. The electrical board has several electrical systems and is mounted on top of the orientation motor. These electrical components are the NIOS board, GPS, XCVR, Video TX and OSD, batteries, cut-down TX, diplexer, antenna, various electrical circuits, and a non-system 2m beacon in case of system failure. The board is capable of receiving information from the GPS (LAT/LON), a variety of sensors (internal temperature, external temperature, pressure, accelerometer, etc.), an Amateur TV signal, and can also receive commands via the Ground Station to control the motor for the payload and activate the cut-down device. The motor includes an attached protruding shaft where the payload will be attached. For this mission, our payload consisted of a high definition camera in place of the rocket.
Recovery Stage. The recovery stage consists mainly of the parachute and a non-system beacon. The parachute hangs freely with eight separate tether attachment points leading from the edge of the parachute to the platform or mission stage. The parachute will automatically deploy after the balloon is cut free due to air resistance. Although the atmosphere at such an altitude lacks density, there is still enough of a force to react against the parachute. There is also a beacon attached to an independent battery in case of system failure that will allow for recovery of the platform.
Ground Station. The Ground Station consists of a 2m XCVR, several kinds of antennas (Mobile, Yagi, etc.), a TV/VCR to monitor the 70cm ATV link with overlaid telemetry data, handheld GPS, and five linked laptop computers which are used to view and track the dynamics of the balloon, sensor readings, communications link, payload, and overall mission status for coordination of subsystems. These positions are stationed inside a vehicle, which allows for mobility to follow the balloons path. The Ground Station will transmit commands to the platform via the 2m communications link to move the motor for the payload (high resolution camera), take pictures, and activate the wireless cut-down device to start the balloons descent.
Flight Tracking and Prediction. Both Balloon Track, a free program written by Rick von Glahn, and a Matlab based graphical user interface, written specifically for this mission will track the balloon. Balloon Track will be used for monitoring the current position, bearing, and velocity of the payload. The Matlab program will be used to gain more accuracy in predicting the flight path of the platform. The Matlab interface uses a dynamic model and makes far less assumptions than Balloon Track. Balloon Track assumes constant ascent and decent rates while the Matlab program constantly calculates the drag forces on the balloon and platform, making for a far more accurate prediction. The Matlab GUI plots the flight path and allows for an updated simulation using the most recent location, bearing, and velocity data. It reads in all of the past APRS packets and plots the flight path and the simulated path after every APRS data packet. This enables real time tracking and prediction of the platforms movement. This assists in the decision of cut down times, allowing for the platform landing site to be targeted to avoid problematic landing areas. The GUI also allows for zooming in on the map to get a closer view of the flight path and landing area. Running Balloon Track allows for constant monitoring of the balloon by multiple team members while the Matlab GUI gives the ability to get constantly updated flight predictions.
The 2004 METEOR team established procedures and checklists for ground station preparation and duties. These checklists divide up the duties and responsibilities among the team members. This will give the team a communications system to maintain organization during the mission. This will also prove to be valuable to future METEOR teams who wish to conduct balloon launches.
PROTOTYPE FABRICATION
The success of the flight depends on all subsystems working correctly, however, the two main components which will be discussed further are the electrical board layout as well as the motor package.
Electrical Board
Electrical Board Schematic
Figure 3 – Layout of Electrical Board
This electrical board, seen in Figure 3, is the main subsystem that provides all power and communication to the team. The board layout includes various battery packs, a transceiver, an independent beacon, the flight computer, environmental sensors, video, and an antenna to communicate with the ground station.
Motor Package
The main component in the mechanical package is the stepper motor mount. This package, seen in Figure 4, is capable of securing the stepper motor underneath the electrical board, and couples with an output shaft to which a payload can be attached. The motor is powered by the onboard batteries and is able to rotate the attached payload according to inputs transmitted from the ground station.
The motor selected is a Hurst H17040440 Hybrid Stepper Motor. This particular motor is able to transmit relatively high torques, yet is very compact and lightweight. This is an ideal configuration since weight is to be minimized and various payload configurations may be attached.
Holding everything together is the mounting bracket and the standoffs. Both are fabricated from 6061-T6 aluminum, which has a high strength-to-weight ratio.
The motor shaft is attached to a flexible spider coupling which allows for minor shaft misalignments and directly couples to an output shaft. This output shaft rotates inside a Nylon flange bearing through the bottom of the mounting bracket and is secured with the spider coupler and a built-in flange which mates with the bearing.
The design minimizes weight while providing the necessary capability required to properly orient a rocket. The adaptability of the shaft allows the platform to be adapted for other uses, such as scientific experiments that need to be conducted in the upper atmosphere.
Figure 4 – Motor Package
Final Assembly
The integration of the electrical board and motor package creates the final flight vehicle. The final assembly can be seen in Figure 5 below:
Figure 5 – Final Assembly
This assembly provides an efficient and practical method for the incorporation of environmental sensors, GPS, flight computer, motor orientation device, payload, and power supply while respecting the 6 lb weight limitation.
Prototype Testing
Preliminary tests were conducted on various components of the assembly. The cut down system was tested by hanging a six pound weight from a length of nylon chord that has NiChrome wire wrapped around it. When an electric current is applied to the wire, it heats up which causes the NiChrome wire to melt the tether. Another aspect of the cut-down system is tested to determine what effect the cut-down system will have on the parachute once it is activated and descends from above, possibly tangling with the parachute. To test this, the parachute and cut-down system were dropped simultaneously from a height of about 40 feet. The balloon trajectory software is developed in MATLAB. Data is entered to test the ability of the software to estimate the trajectory of the platform. The video output was also tested. Also, testing was conducted to verify the communication link between the flight computer and the ground station.
Results
To determine the amount of current that needed to be applied to the cut down system, a power supply was used to gradually increment the current level. It was determined that the cut down system needed to deliver 1 amp of current to the NiChrome wire to melt the tether. Once a full Amp was applied, the tether separated almost immediately. This led the team to decide that a high capacity battery must be selected to power the system.
The cut-down device was attached to the parachute and thrown off of a 3-story building to determine the effect it would have on the parachute’s performance. The cut-down package did not inhibit the parachute from opening, although possible detrimental effects were observed. The cut-down tests show that the battery circuit will stay activated, but will not harm the parachute since it falls beneath the chute almost immediately.
The video output from the camera as well as serial data from the Nios board is sent to the Video OSD. The Video out from the OSD is then sent to the Video TX. The OSD allows for telemetry data to be overlaid onto the TV signal. This provides redundancy in tracking the platform because there are two different communication links transmitting the location of the platform. The video signal can be viewed on Cable Channel 60. This output is viewed through a television monitor and is also streamed over the internet.
The ultimate test of the launch vehicle will be the first launch. The true near space environment cannot be simulated. Once the first launch has been conducted a number of questions will be answered and technologies verified.
Conclusions
From the results of the design and testing procedures, the METEOR team has been able to determine which facets of the design will be carried onto successive launches and which aspects need improvement.