About AAU CubeSat
A Student Satellite
AAU CubeSat is a student satellite
project at the University of Aalborg,
Denmark, which was initiated
in the Summer of 2001. The satellite project is a joint venture of
the following institutes
Institute of Electronic Systems,
Institute of Mechanical Engineering,
Institute of Computer Science, and
Institute of Energy Technology,
giving the students an unique chance to
experience a real engineering project with real engineering
problems. Currently the satellite is still under development and
will be delivered for P-POD and launch vehicle integration in January 2002 and then finally launched in April 2003.
The main purpose for the AAU CubeSat project is for the involved students to achieve a great deal of knowledge about desiging and constructing Space worthy technology, but the "scientific" mission of the AAU CubeSat is to take pictures of the
surface of the Earth and particularly of Denmark by using the on-board
The images recorded by
the satellite will later be transmitted to the ground station,
located at Aalborg University, from where they will be distributed over
the Internet and made accessible for the general public.
Several success criterias have been defined. A basic success criteria in this
case is, to develop and build a satellite which will be able to
survive the launch and the hazardous environment in its orbit. Another
success criteria is establishment of a communication link with the
ground station informing about the status of the satelitte.
Finally to point the on board camera towards a specific target on the
ground, to take an image and to send this data down to the ground
station, represents the final success criteria.
To summarize the above the missions sucess criterias are the following:
- That the involved students have achieved some useful knowledge of space technology.
- That communication is establised with the satellite and housekeeping information is retrieved.
- Take and download any picture.
- Test ACS performance.
- Take pictures of certain locations on earth.
- Take pictures of celestrial objects and experiment with the various subsystems.
Below a flyby over Denmark, while taking a picture, is shown, which is part of the 5th sucess criteria:
The Satellite Structure
The AAU satellite is a CubeSat, thus its measurements have to fulfill the
requirements set up by Stanford University and California Polytechnic institute, which originally developed the Cube-Satellite concept.
The size of the satellite has to be 10 x 10 x 10cm, while its mass is limited to below 1kg.
To archive this, light materials are used for the
structure of the satellite. Its design will be based on a frame
of aluminum with sides made of carbon fibres.
High requirements have been set regarding the structure of the
satellite and its integrity, as it has to withstand high temperature
variations (+80 and -40 C), vibrations and shocks,
radiation, and the vacuum in space.
However, the most vital task when designing the structure will be to keep
the weight limited and to be able to fit all necessary subsystems into
the structure. Below is the stucture with the different subsystems shown:
The Electronic Systems
The electrical subsystems of the satellite will be controlled from a central on board
computer (OBC) based on a C161PI micro controller from Infenion.
It features a 16-bit CPU providing 16 Megabytes of Linear Address Space. The
OBC uses three types of memory. A RAM module (4 MB) for picture data, dynamically allocated memory,
and buffers. A ROM module of 512kB for initial flightsoftware and 256kB of FlashRom used to upload new software after the satellite is
deployed in orbit.
The communication between the OBC and the other electrical subsystems are carried out by means of an
I2C bus, which connects the Power Supply Unit, the
Attitude Determination and Control and The Camera. The Communication Unit is connected directly to the OBC though a parallel interface. The connection between the subsystems can be seen on the figure below:
The Power Supply
The power supply will rely on batteries and solar panels, which will
be placed on the surfaces of 5 out of the 6 sides of the satellite.
The solar panels are triple-junction cells from EMCORE. They measure
68.96 x 39.55mm and will be placed in pairs on the satellites sides.
The four on board batteries are developed by DANIONICS and will provide
energy when the satellite is eclipsed or whenever the power use exeeds the power input
The available power on board the satellite will depend on the amount
of daily sunlight on the solar panels to re-charge the batteries as
well as on the environmental effects in the orbit.
The Communication System
In order to receive commands from the ground station as well as for
transmitting the on board status and the images recorded during flight,
an on board communication unit is used. In this case the on board
communication unit and antenna is purchased from OSSS and will
communicate with ground by using radio amateur frequencies. The
antennas attached to the satellite will be deployed after the satelitte is released from the launch vehicle
To be able to communicate with the AAU-Cubesat from ground a tracking
antenna will be used, which follows the satellite's motion over the
The main payload for taking the images of Denmark is the on board
It is in this case a digital CMOS camera chip based on a Kodak 1.3
megapixel kac1310, which has been provided by the Danish company
DEVITECH. It will take images of the ground with a
field of view of about 150 x 115 km and a resolution of 1280 x 1024 pixels
with a color depth of 24bit.
The lens in front of the CMOS camera chip is handmade with a diameter
of 2cm at a length of 5cm.
Attitude Determination and Control
To be able to take images of the earth, an attitude determination
and control system is required. It will point the camera towards the
correct target for imaging and for communication. Furthermore it will
point the camera away from the sun and point three of the satellites
sides with the solar panels towards the sun to ensure a maximum power
To control the satellites attitude in orbit three coils are
used, which are mounted on three of the satellites sides perpendicular
on each other. These will generate magnetic fields which interact with the
earths magnetic field, and hereby change the satellites attitude.
To determine the satellites attitude two types of sensors are used. A
magnetometer, build up with components from HONEYWELL, to provide
information on the direction of the earths magnetic field, and
sun sensors. These sun sensors are basically planar photo diodes placed
on each side of the satellite to measure the intensity of the incoming
Launch and Orbit
The CubeSat will be launched into space together with other CubeSats
inside a so called P-POD-deployer. It will be placed on top of the
launch vehicle as a secondary payload.
The launch vehicle itself will a
Russian Rockot rocket; a former ICBM.
The P-Pod will deploy its load of CubeSats including the AAU CubeSat,
in an sun synchronous Low Earth Orbit (LEO) at an altitude of
Here it will detumble to get a controlled attitude and to perform its
task of taking images. The lifetime of the satellite has been assumed
to be one year, after which it sooner or later will degrade due to
radiation and other environmental effects. The picture below shows the CubeSat in the P-POD: