Compact Spaceborne Magnetic Observatory (COSMO)
The Compact Spaceborne Magnetic Observatory (COSMO) is a 6U CubeSat with a simple, straightforward mission: measure the Earth’s magnetic field. Earth’s magnetic field is commonly represented via the World Magnetic Field Model (WMM). The WMM is used in a variety of realms including in your phone’s compass and for research purposes. Data for the WMM is currently taken from a mission called SWARM. The SWARM mission is to be commissioned in ~2023 and needs to be replaced. This is where COSMO comes into play. COSMO can provide WMM data at a low cost, ensuring sustainable measurement for decades to come.
COSMO may sound simple, but beneath the surface, this simple-sounding measurement is very difficult. We need to measure the magnetic field with an accuracy of one part in 100,000; we need to measure three vector components of the field, while also knowing the spacecraft orientation (attitude) to within a few arcseconds; and we need the spacecraft to be magnetically clean, i.e. it should not produce a large amount of magnetic noise. For this last reason, we need to design the CubeSat bus from the ground up, ensuring we take all precautions to avoid excess noise. In addition, the magnetic field created by each component of the bus must be characterized in order to ensure that the magnetic field data is not being corrupted by the CubeSat’s magnetic field and the measurements Earth’s magnetic field are to the accuracy and precision required.
COSMO may sound simple, but beneath the surface, this simple-sounding measurement is very difficult. We need to measure the magnetic field with an accuracy of one part in 100,000; we need to measure three vector components of the field, while also knowing the spacecraft orientation (attitude) to within a few arcseconds; and we need the spacecraft to be magnetically clean, i.e. it should not produce a large amount of magnetic noise. For this last reason, we need to design the CubeSat bus from the ground up, ensuring we take all precautions to avoid excess noise. In addition, the magnetic field created by each component of the bus must be characterized in order to ensure that the magnetic field data is not being corrupted by the CubeSat’s magnetic field and the measurements Earth’s magnetic field are to the accuracy and precision required.
Our Work
The design of COSMO began in summer 2018 and will continue over the next few years. The design has changed rapidly in order to develop an efficient low cost solution to meet the given requirements. The current design is a 1x6U CubeSat that is launched via a NanoRacks CubeSat Depolyer System into a sun-synchronous orbit. The 1x6U design was chosen to move the noisy components (solar arrays, electronics, and reaction wheels) as far away as possible from the magnetometer while not incurring the risks of a boom. The spacecraft will be powered via solar arrays and will be designed and built in conjunction with the Laboratory of Atmospheric and Space Physics and the Graduate Projects curriculum, ASEN 5018/6028-013. COSMO is scheduled to fly between 2021 and 2022.
The payload that will take the measurements onboard COSMO is also being designed and built as part of the project. This payload includes the attitude determination system and of course the magnetometer. The magnetometer being designed is a vectorized Rubidium optical magnetometer (VRuM). The design of this magnetometer is focused on minimizing volume, mass and power requirements while ensuring the accuracy and precision necessary for WMM. As the name implies, the magnetometer is consists of a Rubidium scalar magnetometer capable of taking scalar measurements that is adapted to take vector measurements as well. This vectorization method has never been done for Ribudium optical magnetometers to the precision and accuracy needed. In addition, a large effort is being made in the magnetometer development to ensure it is space qualified. Although COSMO’s magnetometer has little heritage, and its development effort is great, this magnetometer offers several advantages over other magnetometers that have already been developed for CubeSats. Most importantly, since an optical magnetometer’s operating principle is based on the effect of magnetic fields on atomic properties, its measurements are absolute, do not vary with time, are not sensitive to changes in temperature and do not exhibit offsets that need to be calibrated for. VRuM is scheduled to meet TRL 6 by late 2021.
The payload that will take the measurements onboard COSMO is also being designed and built as part of the project. This payload includes the attitude determination system and of course the magnetometer. The magnetometer being designed is a vectorized Rubidium optical magnetometer (VRuM). The design of this magnetometer is focused on minimizing volume, mass and power requirements while ensuring the accuracy and precision necessary for WMM. As the name implies, the magnetometer is consists of a Rubidium scalar magnetometer capable of taking scalar measurements that is adapted to take vector measurements as well. This vectorization method has never been done for Ribudium optical magnetometers to the precision and accuracy needed. In addition, a large effort is being made in the magnetometer development to ensure it is space qualified. Although COSMO’s magnetometer has little heritage, and its development effort is great, this magnetometer offers several advantages over other magnetometers that have already been developed for CubeSats. Most importantly, since an optical magnetometer’s operating principle is based on the effect of magnetic fields on atomic properties, its measurements are absolute, do not vary with time, are not sensitive to changes in temperature and do not exhibit offsets that need to be calibrated for. VRuM is scheduled to meet TRL 6 by late 2021.
Left: CAD rendering of COSMO’s 6U design, including VRuM, two star trackers, EPS, C&DH, ADCS system from Blue Canyon Technology and its radio. Middle: A partially assembled scalar Rubidium magnetometer that serves as the basis for VRuM. Its length is roughly 3 cm. Right: CAD rendering of the Helmholtz coil system that allows the scalar Rubidium magnetometer to have the capability of extracting the vector components of the Earth’s magnetic field.