A CanSat is a type of sounding rocket payload used to teach space technology. It is similar to the technology used in miniaturized satellites. CanSats do not go into space, but instead are released at an altitude of about 1 kilometer, using a rocket or a balloon.
In CanSat competitions, the payload is required to fit inside the volume of a typical soda can (66 mm diameter and 115 mm height) and have a mass below 350 g. Antennas can be mounted externally, but the diameter can't increase until the CanSat has left the launch vehicle. The CanSats are deployed from small rocket at height which varies depending on the competition. CanSats are equipped with a recovery system, usually a parachute, to limit damage upon recovery and to allow the CanSat to be reused. CanSats are used to teach space technology, because of their inexpensive price and small volume.
History
In 1998, about 50 students and faculties from 12 universities from the United States and Japan met at a symposium held in Hawaii. It was the first "University Space Systems Symposium". Here, Bob Twiggs, professor emeritus at the Stanford University, proposed the initial idea of what later would become the nanosatellite projects.Robert J. Twiggs, / cansatws / programandabstract.pdf "Introducing New Challenges for Future Space Missions", International CanSat Workshop, 23 February 2007 That idea was to launch a structure of the size of a soda can into space. Its volume should be around 350 milliliters and the mass, about 500 grams. This led to a project that began in 1999 called ARLISS, involving mostly American and Japanese Universities, carrying out the first launch on September, 11th of that year and continuing each year without interruption. The initial idea, still prevalent today, was to launch 3 satellites of 350 milliliters, or a satellite of greater volume. The means would be a rocket capable of moving 1.8 kilos and of ascending to 4000 meters, opening the door to low cost space flights -about $400.R. Walker et al., "ESA Hands-on Space Education Project Activities for University Students: Attracting and Training the Next Generation of Engineers Space " , 14–16 April 2010. In 2000, the missions were very different: for instance, calculating the opening of a landing system using data provided by the barometer or making use of a differential GPS system. The project came to a more complex situation in 2001 when the ComeBack category was added, according to which the satellite should be directed to a particular target. This mission was very successful and, in 2002, students of Space Robotics Lab of the Tohoku University went up to 45 meters from the target and, in 2006, this figure dropped to 6 meters. Interest in this type of satellite has been growing and spreading. In 2003, the University of Tokyo placed into orbit two satellites CubeSat, satellites of a size slightly larger than the CanSats, and cube shaped. In recent years, several competitions have been developed following the same concept proposed by Prof. Bob Twiggs and reflected in ARLISS both national and internationally.
Operation
Main elements
Some elements are shared by every CanSat:
Power supply The battery and/or solar panels supply power for operation of all systems. The systems must be able to be powered for four hours continuously and the battery should be easy to access. The most commonly used due to its performance and current-weight ratio are lithium polymer batteries (LiPo).
Microprocessor The microprocessor is the heart of the satellite, as it is responsible for receiving signals from external sensors (such as the altimeter, accelerometer or the transmitter) and also processes them to act as programmed.
CanSats generally use microcontrollers (MCU) and MCU boards which include an internal memory for data storage alongside the microprocessor, useful for storing information from various sensors during the flight. Some of the most common MCU choices are: STM32 NXP LPC ESP32 AVR
Secondary elements
Apart from the above-mentioned elements, others may be added in keeping with the mission it is entrusted with.
Barometer The barometer consists of a pressure measuring cell which is connected to the microprocessor and sends a signal with a voltage value according to the pressure it feels. The microprocessor uses the standard atmospheric conditions to get the altitude. Example of barometer used in devices of this type: SCP1000
Thermometer The thermometer carries out operations similar to the barometer but the voltage signal sent to the microprocessor depends on the temperature measured. The microprocessor interprets this signal by assigning a temperature value. These are examples of thermometers used: MAX6675 TMP102
GPS module The GPS is a land positioning system consisting of a satellite network orbiting around the Earth which continuously send their position and transmission time. From these data, the receiver triangulates its position with all the available satellites to get a higher accuracy. This position is sent to the microprocessor by a serial port as a data line.
At design level, GPS receivers should be located in a place where satellites vision line is as direct as possible in order not to be out of range with these ones during the flight. In a metallic structure CanSat, the receivers should be always located where the structure does not affect this vision line.
Camera A mini camera can be included in the CanSat to photograph anything during the time the CanSat is descending in the air. Bearing in mind that the CanSat can not receive orders to operate the camera when the robot is in air so the microprocessor must be the one that orders the camera to take a picture. This is an example of a camera for CanSat: CameraC328 Cansats can also be used for 3d mapping.
Accelerometer This system is made of one or more accelerometers in different axes. All the accelerometers aside allow to measure accelerations in coordinated axes. Accelerometers can be used to collect data or to determine position (by integration). The best accelerometers made to determine positions are called Inertial Navigation System INS. These are used on some CanSat models. The uncertainty of this system depends on the error when calibrating sensors. The pros of this system go from the fact that GPS is not needed, to immunity to magnetic interference. This allows multiple locations inside the CanSat. Some of the most used accelerometers are: ADXL345 LIS302
Electronic compass Sometimes, it is necessary to know the direction the CanSat is following (for instance, to perform a controlled descent), in which case a compass sensor is a very small sensor which like a traditional compass measures the angle between its direction and the north. This angle is transmitted to the microprocessor via a potential difference. The microprocessor interprets the incoming signal and acts accordingly. Thus, if the CanSat was intended to arrive to a target without using a GPS receiver, this sensor would play a crucial role. Some models of compasses used are: CMPS03 HMC6352 HMC5843
Types
There are mainly two types of CanSats, though a third category is usually added for those machines that do not fit in the two first:
Telemetry
This is the one whose primary purpose is to collect and transmit data from the flight and weather conditions in real time to be processed by a ground station. CanSats in this category do not use a steering system since its objective is not to fall at a particular point but to collect data while the descent (which is not usually controlled). Of the systems mentioned in the previous sections the most used are: barometer, thermometer, GPS and camera.
Comeback
The main task of these is to land in a controlled manner as close as possible to a target marked by GPS coordinates. These devices can be guided by GPS or by and Inertial Navigation System or INS. This position is sent to the microprocessor which compares the position of the target from the analysis of these data to calculate the angle at which it should turn to address the target and gives appropriate instructions to the steering system. This process is repeated continuously to make corrections. Such devices also store data on the flight but since the number of sensors that accompany them is less, information is more scarce than in the previous type. A ComeBack CanSat always carries a steering system that allows it to maneuver, to orient and to move towards the target. Normally such a mechanism is actuated by one or more actuators controlled by the microprocessor so that the servomotor rotates to one side or the other and so rotating CanSat. There are two main types depending on whether CanSat incorporates a parachute or glider or a rotor and wings.
CanSats with parachutes or paragliders
These devices generally have a steering system consisting of threads that move asymmetrically so as to generate a difference in lift of the longitudinal axis so the CanSat rotates in one way or another. It uses fairly simple mechanics. These devices are difficult to govern due to the generally low rate of descent and the large surface area lifts it.
CanSats with wings or rotors
Mechanically more complex and less vulnerable to weather conditions that CanSats with parachute or gliders. This kind of gadgets are much more harsh to govern and require an electronic system able to perform many more corrections per second due to its higher rate of descent.
Openclass In this category, any robot that is not included in any of the previous two categories can be submitted. Most CanSat presented in this category are robots testing new systems or new designs that have not yet been tested (technology demonstrators).
Educational interest
The low cost of implementation, short preparation time and simplicity of design compared to other space projects make of this concept an excellent practical opportunity for students to take their first steps in space. Students are responsible for choosing the way the mission is fulfilled, the CanSat design, components integration, correct operation verification, launch preparation, data analysis and team organisation by distributing the workload.Torbjørn Houge et al., A Hybrid Approach to Education Rocket, 2009 It is basically a scale replica of the design, creation and launch of a real satellite. The process required to develop a CanSat entails a learning process known as problem-based learning,Hmelo-Silver C.E., Problem-based learning: What and How Do Students Learn?. Educational Psychology Review, 2004 a new teaching method in which the student is the main character and the one who must solve the problems. The main characteristic of this type of project is being carried out by teams facing open problems driven by successive challenges. The support given by teachers is declining in keeping with the experience the group is reaching to recognize that systems engineering also has to deal with the complexity of development and research of their own abilities.Koichi Yonemoto et al., Educational Projects of Space Engineering in Kyushu Institute of Technology, 1 October 2008 Space engineering discipline is one of the most typical methods used in education because it provides a wide range of attractive themes.
Competitions
CanSat competitions are conducted in Europe, the United States and Asia, etc.
United States
CanSat Competition