Requirements Doc

Attitude Determination and Control System
Science Requirements Document
TJ Trent; PJD Peterson; L Benson

Introduction

The Attitude Determination and Control System (ADCS) performs two main tasks, primarily it is responsible for detumbling the satellite then allowing the satellite to be pointed with reasonable accuracy. In order to do this magnetourques and magnetoresistors will be used to determine the attitude from the earth’s magnetic field, giving 3 axis control.

Attitude Determination

The current design involves a switching system that would allow three axes worth of analogue data from the magnetoresistors to feed one channel of the cubesatkit's ADC, or any other ADC. There is an option of either buying or building our own Circuit board for this purpose, here is a summary of these systems.

The LM324N is a small op-amp purpose built for low power applications by a company called National Semiconductor[1]. It actually carries four amps on one chip, which is very good for us in terms of space. It will run off 700 microamps regardless of the supply voltage, which can be 3-32V. It's temperature range is from 0-70ºC, which is tight but more tolerant versions are available (LM124 works between -55 and 125ºC).

The circuit board would be built using 2x 7555 chips, for use as a flip-flop gate. 3x AMRs (ansiotropic magnetoresistors), possibly all on the same chip. And 1x LM324 quad low-power op-amp to allow the outputs from the AMRs to communicate with the CPU, along with 17 resistors and 5 capacitors - I'll know the values once I know the power supply situation. The design uses around a 5V input, but most of these components are very flexible, and can be replacements with high-temperature versions if needed.

A suitable AMR is the Honeywell HMC 1053[2]. It's a readymade 3-axis package, so only one is needed. It will run of anything between 3 and 20V, and will draw about 5mA for each axis at 5V.

Mass and Costing

If we were to build our own board total cost should be less than £50 for the materials. Weight of all components would total approximately 40-50g. This will all fit on a board 50mm square, at most, with the components reaching no more than 5mm high

Honeywell HMC 1053[2] will cost around $62.40[4] (£30.94)[3]. It's a chip 7.366mm square, and 2.286mm thick (2.794mm if you include the pins). The weight is not known and we are still waiting on Honeywell for that information.

The IC is a standard dual-in-line configuration, 6.35mm wide and 18.80mm long, and 3.683mm thick up to the pin shoulder. The pins are 3.175mm long. 55 of them will cost us $0.32 (£0.16) [3] each, but there is a possibility of getting samples for free.

Attitude Control

The design for the control system involves three coils of copper wire, magnetourques, one mounted on each axis to create stability in that plane, giving three axis stabilization.

Mass and Costing

The mass of all three magnetorques will come to no more than 60g, but this is dependent on the number of turns, but each coil wouldn’t exceed 20g. This means that the overall mass should be under 100g. The copper can be bought over the internet for around €3.58 (£2.42)[3] a reel[5], the length and cost is dependent on the gauge.

[1] National Semiconductor
< http://www.national.com/mpf/LM/LM324.html>
[2] Honeywell HMC1053
http://www.ssec.honeywell.com/magnetic/datasheets/HMC105X.pdf
[3] Currency converter
http://currencyconverter.uk.com
[4]Price for Honeywell HMC1053
http://www.newark.com/jsp/Electromechanical+&+Industrial+Control/Sensors/HONEYWELL/HMC1053/displayProduct.jsp?sku=26H2816
[5]Conrad Electronics
http://www1.int.conrad.com/scripts/wgate/zcop_in/~flNlc3Npb249UDkwX0NPUF9FTjpDX0FHQVRFMDY6MDAwMC4wMTFmLjQyMTAwMGMwJn5odHRwX2NvbnRlbnRfY2hhcnNldD1pc28tODg1OS0xJn5TdGF0ZT00MTk0MzQ1MzI=?~event=home&~target=_top

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