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Misc /
FirstGenCubeSatThe CubeSat ProgramStarted in 1999 by California Polytechnic State University (Cal Poly) and Stanford, the goal of the CubeSat program was to make launching a satellite an attainable goal for universities. This was achieved through a standardized specification that was small enough to be able to easily piggy-back on other satellite launches. This was further advanced by Cal Poly's development of the P-POD launcher, which carries up to three CubeSats into space and then allows for separation. A CubeSat unit is 10cm by 10cm by 10cm. A CubeSat may be up to 3 units long, making for a satellite which is 30cm by 10cm by 10cm. Each unit weighs under 1 kilogram. Cost to launch varies; I have seen quotes from $12,000 to $80,000 per unit (likely on the lower end in recent years). Regardless, this is significantly less than conventional satellites. Launched into a Low Earth Orbit (160 to 2000 kilometers), a CubeSat's orbit will decay resulting in short missions ending in a fiery death (This may not be the case: the CanX-7 is designed to test a deployable drag-sail for the purpose of deorbiting a small satellite within 25 years. This may be intended only for higher altitudes. Other limiting factors may be a lack of radiation hardened hardware and the number of charge cycles the batteries can handle). For example, the YamSat was expected to initially orbit at about 650km for about 1 month. While intended and largely used for academic purposes, CubeSats have been used as research platforms. They also provide an inexpensive means to test cooperating groups of satellites. A satellite can be broken down into roughly nine categories (from work):
Below are some examples of CubeSats intended to give an overview of their systems and architecture. CanX-1The first of a continuing series of CubeSats developed by the University of Toronto Institute for Aerospace Studies, Space Flight Laboratory (UTIAS/SFL). The CanX-1 satellite (detailed here) had a payload of two CMOS imagers intended to a) take nifty pictures and b) attempt to track stars, and used an ARM7 core as the basis for its onboard computer (labeled OBC below). Attitude Determination and Control was achieved a three-axis magnetometer and three torquer coils. The magnetometer is used to sense the Earth's magnetic field, and the coils can be activated to provide a torque by being repulsed or attracted to it. The B-dot control algorithm was used for detumbling (which appears to be fairly standard for satellites of this size). CP1Cal Poly State's CP1 (initial design described here) had a payload of a sun sensor and a student built magnetorquer to test. This payload generates little data to down-link, unlike the the image sensors on the CanX-1. This allowed the Cal Poly State team to focus more upon tracking the CP1 with a simple communication protocol specifically designed so that amateurs could aid in capturing transmissions, translating them, and sending them along to Cal Poly State. Redundant transceivers where built in. Uniquely, the CP1 does not have a battery charging circuit, and there are two separate batteries. The secondary battery seems to fulfill the role of a typical single battery setup; running the system while the solar panels are not suppling enough power and recharging when there is a surplus. It is lithium ion and has a protection circuit to prevent over and under charging. The team was concerned about the possible failure of the solar panels, so the primary battery (a lithium metal cell with a capacity of 7Ah) was included to power the satellite for several weeks even in the event that the solar panels fail. The power requirements of CP1 are low enough that the panels alone can power the system at reduced functionality. Similar to other CubeSats, CP1 used a COTS processor and computer board. The system lacks radiation hardening and redundancy. Thus SEUs can case errors, although this risk is fairly low. To help mitigate it, watchdog timers are used to reset the system if it becomes unresponsive. This may leave a possible application for a more sophisticated system of fault recovery. YamSatDeveloped by Taiwan's NSPO (National Space Organization), the YamSat A was (detailed here)intended to launch with the first batch of CubeSats in 2003 (the designs B and C were developed for demonstration and experimentation purposes; not orbit). Unfortunately this did not happen for apparently political reasons. Glossary and Acronyms
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