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I. Design Overview
The telemetry system for MidSTAR is being designed for simplicity and reliability. This is a very vital system to the spacecraft and all systems onboard the spacecraft rely on getting information from the telemetry system. It is designed to convert all data into a 12-bit digital format which is transmitted directly to the ground. Once in the ground station computers, the software will perform an Engineering Unit Conversion to all data to convert it into the type of data needed (i.e. current, voltage, temperature, etc.). There will be between 90 and 100 telemetry points in the final flight hardware to measure; therefore, a considerable challenge will be present in compacting all of the measurement boards into the C&DH box with all of the associating wires.
II. Design
The following link will take you to a working spreadsheet that will lay out all of the telemetry points. This is a document in progress and will frequently be updated as the design process gets further along.
There are currently 10 circuit boards that are performing voltage reductions so that the Analog-Digital converter gets a maximum of 2.5 Volts. The exact resistor values are under design still, but we are currently using a 20:1 voltage divider to measure the battery voltage. The following document shows our current layout of the boards and what telemetry points will be measured with which board. The actual layout of the boards is inaccurate due to some recent design changes in our Express PCB boards. Currently the plan is to mate each one of these boards with a programmed Easy Web board and use that for flight hardware. However, our backup plan is to use a commercial custom made board for our flight hardware. I am currently working on the design layout for these boards within the C&DH box.
Calibrations will need to be made before flight to match the output values of the A-D converter to the values we are looking for. Coefficients will be generated for the conversion software to be able to convert it to an appropriate value. I have already completed a preliminary calibration for 5 voltages that were being measured earlier this semester. These voltages were the power supply and the four battery voltages. The following document will show the output of this work. This will not be done until later in the process for the time being, but was done earlier in order to give the software designers some coefficients to work with.
Calibration Spreadsheet with graphs
The following is a report created when the initial calibration was completed.
Currently both Voltages and Currents are capable of being measured. We tried to do a current calibration; however, there was a problem with the setup and was unable to do it. At this point telemetry design is on hold until progress is made with the flight software. This should get up and running again sometime in the May-June timeframe.
It has been decided to use thermistors as our temperature measurement device. Accounting for many different temperature ranges I calculated a value of 500 kOhms for the 2nd resistor in the divider. The first one is the thermistor itself. However, we will probably have to design each type of thermistor divider separately to get accurate measurements since different parts of the spacecraft will be subject to different temperature ranges. There would be no benefit to have one design and have it account for one large range because the thermistors would have no range of measurement.
III. Presentations/Goals
The latest presentations given to the Department Head are located below which give short and long term goals for the telemetry system. These will be added on a monthly basis until the end of the semester.
January-February Presentation (includes all other departments)
March Presentation (telemetry contribution)
There was no April briefing by
students to Professor Boden.
On Wednesday, 26 APR 06, students briefed a team from the Space Cadre
on the status of MidSTAR-1. Other small
satellite program projects were presented as well. Below is the link to just the telemetry
contribution for easy viewing as well as the Full MidSTAR presentation.
Space Cadre Telemetry Contribution
This page is also available at our new website by clicking here. (New website is currently down due to technical difficulties)
This webpage is a work in progress. Any questions, comments, or suggestions may be submitted to: Midn 1/c John Fisher
Updated: 28 APR 06