Space magnetometer sensors are normally mounted on deployable booms, in order to minimise the influence of spacecraft generated magnetic fields. The boom will typically be some metres in length and will weigh more than the magnetometer instrument. Unwanted magnetic signals, due to the presence of magnetic materials on the spacecraft or stray fields caused by current loops will contaminate the real ambient field measurement at the magnetometer. On many missions some level of data cleaning in addition to instrument in-flight calibration is required before the magnetic field data are of scientifically usable quality. In some cases the interference can be so bad as to degrade the quality of science analysis that may be performed.
One way of mitigating the interference problem is the use of multiple sensors. Quite often our spacecraft feature two magnetometer sensors mounted on the boom – one outboard and one inboard for the purpose of redundancy with the outboard sensor supplying the nominal scientific data. However, operating both sensors at equal data rates allows for the use of the magnetometer instrument as a gradiometer. The dual measurement provides a means of estimating and tracking the spacecraft dipole moment and provides a useful input into data cleaning algorithms. Such a scheme has been successfully applied on board the Equator-S, Double Star and Venus Express missions. However these schemes still require the need for a moderately long boom as well as some kind of magnetic cleanliness program during the spacecraft build phase.
Our group is studying ways of using multiple sensors to better characterise spacecraft field rejection techniques without the need of a dedicated boom. This project is a combination of modelling and experimental work and will include the development of a proto-array using miniaturised solid state magnetic sensors distributed around a model spacecraft surface. The longer term aim is to integrate the modelling work and sensor development into the Group's CubeSat activities.
There are numerous potential benefits to such an approach including:
Mass savings by reducing (or even eliminating) boom lengths
Reduced magnetic cleanliness program costs
Compatible with low cost missions featuring very small spacecraft
Standardise field rejection techniques suitable for constellation missions