Team Vision for System-Level Design PhaseDuring the Systems Design phase, we planned to develop system level concepts, research parts, perform feasibility analyses, perform research on the environment, and more. We wished to understand the platform we will be building from a systems point of view and develop a high level design/plan.
We completed the weekly MSD assignments and our design phase goals. We thought of the functionality required to satisfy our requirements and developed various concepts. We performed bench-marking and compared and contrasted options to arrive at the most optimal solution. We spent time performing various analyses toward our design, including weight, power consumption, and transmit power analyses. We created an initial system level design. A lot of time was spent developing the system level design. Work has also been done toward narrowing down on parts to be used in the design.
Project Statement RecapHere is a re-cap of our project statement.
- RIT SPEX performs high altitude balloon launches
- An instrumentation platform is needed as a base system for these missions
- There have been launches in the past (like the METEOR project), but they were not all successful and did not provide a great deal of functionality
- A functioning design
- Acquire and transmit sensor data, location information, and video
- Interface with GPS and transceivers
- Receive and execute ground commands
- The final design is in conjunction with the HABIP-DAQCS team
Partner TeamOnce again, we are working with the High Altitude Balloon Instrumentation Platform Data Acquisition and Control Team. Their Systems Design page has other system concepts, research on batteries, research on environmental testing chambers, and more information that applies to both teams.
A functional decomposition was performed to understand system requirements and derive key system functions. We performed an independent functional decomposition for communication and thermal control functionality; it was combined with the functional decomposition done by the data acquisition and control team (HABIP-DAQCS) for an overall instrumentation platform functional decomposition.
This is the full functional decomposition (HABIP-COMMS & HABIP-DAQCS teams). The working document can be found here.
This is the HABIP-COMMS specific functional decomposition. The working document can be found here.
We observed previous high altitude balloon designs for how our desired functions were achieved.
We began research and comparison of the various parts needed for the communication system.
The working benchmarking document can be found here
Possible PartsWe looked into multiple options for each of the main components of the communication system: screen overlay device (OSD), GPS, 70cm ATV transmitter, 2m transceiver, structural materials, APRS, antenna, and a duplexer to allow one antenna to be used in the system.
We are currently considering the OSD-232+ device.
We are currently considering the Tracksoar device. It is open source with software available. The board and components can be bought separately; about $60 would be saved assembling the device ourselves.
The APRS modules we looked at have GPS devices. A redundant GPS could be added to the system.
We are currently considering the Ublox MAX-M8Q since that is the GPS used in the Tracksoar APRS device.
70cm ATV Transmitter
More research needs to be done for possible ATV Transmitter devices. In a previous METEOR project, the TXA5-RCb was used, but it is not available to be bought; perhaps it could be found on eBay or somewhere. The VideoLynx VM-70X was the only other device with the appropriate output power, but it has very high power consumption. A lot of options were either low range or high power consumption/high weight.
More research needs to be done for possible transceivers. In a previous METEOR project, a transceiver was created using the MC2833 transmitter and the MC3362 receiver. There are not that many COTS products available for the distance, weight, and power restrictions of the platform (and with a cost in budget).
- Option 1: Buying a transceiver
- Pros: Simple, saves time
- Cons: More power consumption
- Option 2: Making a transceiver
- Pros: Less power consumption
- Cons: Complex, takes time
If the transceiver was made, it could be made from scratch or from existing transmitter and receiver components.
If one antenna is used, a duplexer will be needed with the 70cm ATV transmitter and the 2m transceiver.
Concept Development and Selection
The working document can be found here.
A concept screening matrix method was used to find viable system concepts. The working document can be found here: Pugh Chart
The above image shows the various concepts that were selected to analyze. The reference concept was our initial thoughts on a high level system design.
The above matrix was used to screen the selected concepts based on our selection criteria. It narrowed down considerations to concepts A, C, and D as shown.
The above matrix is similar to the screening matrix, but with weighted criteria and a wider range of values. It narrowed down considerations to concepts A and D as shown.
Based on further discussion between the 2 teams, we have decided to create a short and wide cylindrical structure. It is easily manufacturable, it is more ideal for resisting wind forces, it could easily be made modular, and could be controlled in terms of stabilization.
Conformal coating will be used. From research of other designs, we may not need to conduct and dissipate heat; cold temperatures at certain elevations could be more of an issue (insulation would then be important). If heat is an issue, a thin aluminum coating and high emissitivity paint would be used.
A serial link will be used to communicate between the main processor of each team (between data acquisition and communications). Amateur radio bands (2m band) will be used for commands and data. Amateur TV (70cm band) will be used to transmit the analog video with a data overlay. APRS will be used to locate the platform.
A parachute will be used to allow the platform to descend from flight. Lithium polymer batteries will most likely be used for power.
Feasibility: Prototyping, Analysis, Simulation
Transmit PowerQuestion: How much transmit power will (theoretically) be required to delay data and video over the 70cm and 2m bands, respectively, back to earth?
Background InformationThe system must be able to travel 140,000 feet up in the air, which is 26.5 miles, or 42762 meters.
For ATV, we will be using the 70cm frequency band, which is dedicated to Amateur TV (ATV) use. This band uses a frequency of 421.25-445.25 MHz. We have a 70cm Yagi antenna in the METEOR Lab (brand: C3i, model: FO22-ATV). It has a gain of 17.9 dBi
For data and telemetry, we will be using the 2m frequency band. This is a common Amateur radio band. This band uses a frequency of (144-148 MHz). We have a 2m Yagi antenna in the METEOR Lab (brand: C3i, model: FO12-144). It has a gain of 12.6 dBi
The antenna used on previous METEOR designs (already purchased and installed) is a dual-band (70cm and 2m) Comet SBB-1, which had a gain of 1.5dB for 2m, and 2.15 dB for 70cm.
ATV (70cm)The following chart, sourced from an Amateur Radio website, relates the total gain of the antennas in the system to the transmission distance, for ATV. Based on the numbers above, the transmit and receive antennas have a combined gain of 20.05 dB.
In order to get the desired 26.5 miles of range, a 70cm transmitter of ~5W will be needed. In order to reduce this transmitter power, the total antenna gain could be increased, or the system could be designed to require less range.
Data and Telemetry (2m)Because a Distance vs Antenna Gain graph like above has not been found for the 2m band, the difference in free space path loss for the 2m band, versus the 70cm band, will be found. Free space path loss is how much a signal attenuates as it propagates through air. The formula for free space path loss is as follows:
Free space path loss has a logarithmic dependency on frequency. For a frequency of 420 MHz (70cm/ATV), this term in the equation is 172.46. For a frequency of 148 MHz (2m/telemetry), this term in the equation is 163.405. Therefore, the free space path loss for the 2m band is less by about 9dB, compared to the 70cm band. We can factor this in, and use the 70cm graph used above, but add 9 dB to the total antenna gain to adjust it for the 2m frequency.
Based on the transmit and receive antenna gains given in the background information section, the total combined antenna gain for the 2m system is 14.1dB. Adding 9dB to this, to adjust from 70cm to 2m, gives us a total gain of 23.1 dB.
This means we will need a 2m transmitter with a transmit power between 1W and 5W, or ~2W, in order to get a transmit distance of 26.5 miles.
An available ATV transmitter still needs to be found. Transceiver options also need to be further researched. One may need to be made for lower power consumption.
The working document can be found here: Power Consumption
One ATV Transmitter option is shown above. The output power can be adjusted; power consumption is based on output power. In the past, a 1.5W output power transmitter was used for a METEOR project. Based on the graphs above, the VM-70X would draw about 900mA at 12V (10.8W power consumption).
Environmental Factor Researchhere.
From the image, temperature will range from room temperature (about 23 degrees Celsius) to -57 degrees Celsius. In the Troposphere, temperature decrease 6.5 degrees Celsius per km; the jet stream is also at this level of the atmosphere. Weather takes place in the Troposphere. The Tropopause is the border between the Troposphere and Stratosphere; air temperature is constant in this layer. The Stratosphere includes the Ozone Layer, with most of the concentration at 20-30 km (65,617-98,425 ft). Temperature increases with height in the Stratosphere.here. Pressure decreases with height; with it, the amount of water vapor in the atmosphere decreases with height.
Atmospheric pressure decreases with height like density:here.
The Stratosphere and Troposphere (where the platform will be) are part of the Homosphere; it has uniform concentrations of N2 and O2.
Based upon previous HAB designs and parts, the components of the HABIP that majorly contribute to the weight of the system were analyzed. For parts that are not currently in our possession (e.g. the PCBs), an educated assumption based upon online data was used. The data is shown in the table below.
Some of the figures were slightly exaggerated, however there is still the possibility of exceeding 6 lbs which would be an issue. This analysis was important and the team will need to make careful design choices regarding any contributing factor to the weight.
Of the three possible scenario’s, which is most likely to happen?
1) The unit cannot generate enough heat and slowly cools to vacuum temperature (0 Kelvin)
2) The unit generates excessive heat and subsequently overheats
3) The unit generates and mitigates heat sufficiently during the flight operation
Temperature control of electronics at high altitudes can be a tricky situation due to the low density environment. The HABIP is comprised of several critical electrical components that need to be maintained within specific operating temperatures (typically industrial ranges) for both component health and data accuracy. For this reason it is necessary to determine the most likely operation mode based on preliminary design.
It has been suggested that there will be two possible avenues of failure - Overheating and chilling. Overheating is expected to occur due to the decreasing environmental density with increasing altitude. The opposite failure mode however has been experienced by similar projects - namely failures along the lines of cold camera failures. This theory contradiction prompted the analysis to determine the general trends the can be expected, and to plan and design accordingly.
As component selection is not finalized, only the internal environment can be analyzed. To do so the system was approximated as an aerated environment isolated from the ambient environment by polystyrene - which serves as both an insulator and condensate barrier. Since the internal environment is isolated, it can be approximated as a very low density solid allowing for temperature gradient analysis. This was done by discretizing both the internal air environment and structure into nodes and applying the appropriate boundary conditions of conduction, convection, generation, etc... in a simple linear fashion (See Figure T.2).
When analyzing the discrete system over different sets of heat generations a clear abet unique trend was found. According to model form, the low conductivity of air resists thermal transmittance so significantly that overheating the environment is assured when heat generation is non zero. Notice from Figures T.3 through T.6 that as the generation wattage increases the nodal temperatures of the air spike accordingly. The styrofoam structure however remains within roughly the same temperature range.
Figure T.3/6 : System Input Comparison | Left/Top : 0 W | Right/Top : .5 W | Left/Bottom : 1 W | Right Bottom : 5 W
The results presented in Figures T.3-6 suggest that either increased resolution / form is required as it is not believed that the internal temperature would rise to such increased figures. Increasing the discretizations and including synthetic parameters (linked to empirical data) would likely be the most advantageous route. Abet this realization, the data does provide a consistent fact that the the isolated environment will not prove helpful in transferring excess energy.
1) Increase Resolution / Fidelity
2) Create a Grand Canonical Model based on needs
3) Prototype test and verify against rough test data
4) Finalize design for analysis
System Block Diagram
This is our team's (the communication side of the system) high level system block diagram.
This is the full (DAQCS and COMMS team) high level system block diagram. The working document can be found here.
The working document can be found here.
The working Risk Management document can be found here: Risk Management
Design Review MaterialsThe following presentation was given on October 6, 2016: System Level Design Review Presentation
Notes from the design review can be found here: Systems Level Design Review Notes
Plans for next phase
Now that we understand the design better from a system level, we can begin to implement these design ideas. This will involve looking at each subsystem, as described in the system-level block diagram, and start the design. From a mechanical perspective, this would involve designing a common frame and structure design, to house all the individual subsystems and circuit boards. In addition, heating and cooling mechanisms will be specified, as components placement is planned. Finally, the stabilization control system will be evaluated and prototyping will begin. Electrically, details about each subsystem should lead to high level schematics, specifying communication interfaces, power requirements, and data storage details. The goal is to make the design modular, so repeated/redundant functions will attempted to be grouped together, to minimize hardware/software development efforts. Knowing the desired hardware architecture, a software operation diagram can also be built to prepare for the software that will have to be developed. Preliminary decisions about component redundancy will also be made.
The following Gantt chart describes our plan in detail:
The working Gantt Chart can be found here: Microsoft Project