Nanosatellites and cubesats
A satellite is an object that orbits around another one in space. There are both natural satellites such as the moon around the earth, and manmade satellites such as GPS satellites, communication satellites, and the hubble telescope.
A nanosatellite is a class of satellites. It is defined by the mass of the satellite. If a satellite is between 1 and 10 kilograms, it is considered a nanosatellite.
A cubesat on the other hand is defined by its outer physical dimensions. There are different sizes of cubesats. A 1U cubesat measures 10x10x10 cm. A 2U cubesat, is two 1U cubesats. So it would have dimensions of 10x10x20 cm. Similarly a 3U cubesat has dimensions of 10x10x30 cm. The key feature is that the cross-sectional area is always the same. That way cubesats can have common launching mechanisms.
The satellite design by the USST was a 3U cubesat, that only weighed four kilograms so it counted as a nanosatellite.
Why cubesats? Why nanosatellites?
Why is it important that the space industry move to a standard satellite dimensions such as the case of cubesats, and why is it significant to be working on making lighter satellites such as nanosatellites?
Having lighter satellites, such as nanosatellites is important. It is important because currently it is very expensive to launch objects into space, it can cost anywhere from $10 000 to $40 000 to get a single kilogram into space. By making lighter satellites, such a nanosatellites it possible to accomplish the mission of the satellite at a lower cost. It also makes it easier for smaller organizations to get their satellite into space.
Cubesats, are important because they are a standard small size. By employing such a design it is possible to create lower cost solutions for launching cubesats, enabling groups such as academics or students to place in space their experiments and platforms for research that were previously not possible.
(Left: Rendering of USST satellite without payload antennas by Myles Penner)
Canadian Satellite Design Challenge
The USST participated in the first annual Canadian Satellite Design Challenge. This a challenge for students attending Canadian universities. Their goal is to design a satellite with a unique scientific purpose or mission. By doing so these students are gaining experience in the design, construction, integration and testing of a satellite. Not only do the gain technical experience, but large amounts of management, and financial experience in running such a large program and project.
Teams also are expected to participate in outreach to other students and organizations in their community to promote and create awareness about space activities. It also enables the team members to encourage younger students in high school and elementary school to pursue education and training following the completion of high school. This has since become an important part of the USST's mission.
To find out more about this competition, please go here .
The USST worked towards this mission from September 2010 to September 2012.
Payload: Total electron content
The goal of the competition was to develop a unique scientific mission. This scientific missions is what is known as the satellite payload, or what special science, equipment or mission it was carrying. A payload can be anything from a telescope, to cameras, or in our case, hardware for a scientific experiment. Our mission was to measure the total electron content of the ionosphere, a part of the atmosphere.
The accomplished by members of the team was so ground breaking it was endorsed by a senior researcher from the United States Naval Research laboratory.
Satellite Bus: Structures
While our satellite's payload was a unique satellite mission, that is not the only component of the satellite, and only a small portion of our team was dedicated to developing that technology. The rest of the satellite is called the satellite bus, or the hardware in place to support the mission of the satellite (the payload). One portion of the satellite bus is the structure.
The structure of a satellite is the physical frame that the satellite is composed of. It must be designed so it can withstand the rigours of the launch into space, but also maintain its structural integrity when in space. The structure houses all the electronics, communications and power equipment. The USST designed their sructure from the ground up so all its hardware could fit, its entire structure was purpose built.
The design a frame and shelving that was unique to the teams that year, it included a rigid 3 sided outside structure with a removable front face. Internally the components were organized into shelving that could be removed through the front face of the satellite.
Satellite Bus: Power System
In order for all the electronics to run, satellites require a constant and reliable power supple. In order to accomplish this the USST design a power system including batteries, solar powers and a power distribution system that enabled our communication systems, control systems and all the necessary electronics to be powered.
As a part of this team members participated in a solar panel construction workshop. Two team members went to Ottawa to learn how to assemble, and manufacture their own solar panels for the satellite.
Satellite Bus: Attitude Determination and Control
When satellites are launched into orbit, they need to be able to properly orient themselves as they are arbitrarily spinning. It is important to both know how the satellite is spinning and what part of it is facing the earth, also known as the satellites attitude. This is important because depending on the payload of the satellite, or how the communications system of the satellite was designed a particular part of the satellite might be required to face the earth. So equally as important of determining how the satellite is behaving, is how to get the satellite to point the way you want it to. The combined system is called the attitude determination and control system, or ADCS.
Both the USST's payload and communications required a particular orientation in order to operate accordingly. In order to accomplish this USST designed a determination system based around sun sensors that would enable the satellite to located the sun. Using this it would have been possible to determine which end of the satellite was facing the earth, and approximately how fast it was spinning.
While that information was useful, we needed to control how the satellite was spinning. This was designed to be accomplished using two approaches, both a passive and an active approach. The passive method was the usage of a gravity gradient boom (GGB). The GGB deploys a mass a distance away from the primary satellite. Through this the center of mass, and center of gravity becomes separated on the satellite due the gradient in the pull of gravity in orbit (hence the name). This enables a pendulum like motion that points the satellite down towards the earth. This downward motion in constance no matter the location above the earth. A requirement both our communications and payload required.
This system is not perfect however, the satelite still requires some other methods to dump energy out of the satellite. On earth, air resistance would have been enough, however since there is negligible resistance an electromagnet was designed to react with the earths magnetic field at certain locations relative to the earth.
(Right: exploded view of the model for the gravity gradient boom deployment system)
Satellite Bus: Command and control
Command and control is as straight forward as it sounds. This module of the satellite is the command center. It interprets the commands it receives over the communication systems and turns that into actions on the satellite. This module connects with all of the other components (except of course the structure) of the satellite bus system. It makes decisions based on orbit locations, power levels and what the current payload priority is.
The USST designed a custom C&C module for the satellite. This enables all hardware to work together seamlessly at maximum efficiency as it was purpose built.
(Left: Image of the satellite model from the bottom with the GGB deployed)
Satellite Bus: Telemetry and Communications
Critical design review
The Critical design review (CDR) was the second major milestone of the Canadian satellite design challenge. At this point all teams should have completed their design which was then presented to a panel of experienced engineers and scientists. The USST was ranked third for this portion of the competition.
The photo seen to the left was taken of the team by David Stobbe at the USST press release prior to departing to the critical design review (CDR). This photo was further featured at the display "Canada's 50 years in space" featured at the Canadian Embassy in Washington.