The peculiarity of an Inertial Navigation System (INS) is that does not require any external reference in order to determine position, orientation, or velocity. INS is the only self-contained navigation system, therefore it is specially suitable for applications on rockets or balloons.

Low.Co.I.N.S is a low cost inertial navigation system intended to be flown onboard BEXUS stratospheric balloon. Our experiment is based on a strapdown design that foresees the use of accelerometers and gyros rigidly connected to the vehicle. Inertial measurements are gained by MEMS-based motion sensing devices and a microchip PIC microprocessor  will collect those data, downlink to ground and store them into a flash memory.

Inertial navigation techniques recently faced important developments with the introduction of very low cost sensors, collectively labelled as Micro Electro Mechanical Systems.

Our experiment is a test of our  capability in the determination of the cinematic state of the Bexus payload gondola through the design and validation of an inertial navigation system built with low cost commercial off-the-shelf components.

The sensors involved in the experiment have to provide measurements of accelerations, angular rates, magnetic field strength and direction, as well as atmospheric pressure and internal experiment temperature. The accuracy of these data makes possible the determination of the position and the attitude of the Bexus payload gondola with a precision that we want to evaluate and increase as much as possible.

MEMS sensors may not be able to provide inertial measurements with a sufficient level of accuracy needed in cutting-edge inertial navigators, however they might be accurate enough to allow for navigation where pinpoint accuracy is not required or where periodic re-alignment is made available through other measurements (eg. GPS and/or magnetometers).

Our experiment consists mainly in the determination of the position and attitude of the payload gondola during the entire flight time. Accelerometers and gyros will sense acceleration and angular rates along three orthogonal axis, thus integrating those measurements in an opportune reference frame, the position and attitude of Bexus can be known once initial conditions have been specified.

Being a dead-reckoning process, where either attitude or position is evaluated using the state at the preceding time and adding the rate of change times the time interval, the calculated solution will sooner or later diverge from the true solution due to the accumulation of errors. Therefore it is necessary to periodically re-align the navigation platform using other references. These can be the Earth magnetic field vector that can provide the direction of the magnetic north as well as a reference around which is possible to determine the attitude. Barometric altimeter may be an effective reference and can be used to compare the calculated position along the vertical axis. Finally, during the post processing, also GPS data can be used for platform re-alignment as well as a benchmark.

Dead-reckoning also means that it is required to have an uninterrupted data flow from sensors, as if some measurements are lost, even for a small time interval, there is no more way to estimate correctly the cinematic state and the flight trajectory after the loss of data will be unrecoverable. That is why, even if we continuously downlink data to ground, we decided also to store all data gathered in a flash memory onboard. So, even a temporary loss of telemetry data stream will not affect the results of the experiment.

The reconstruction of the flight trajectory will be attended on the ground. Once the experiment has been recovered, the memory will be dumped and an exhaustive post-processing will occur with all the data gathered by the unit. During the post-processing the flight trajectory will be reconstructed in several methods and compared with GPS data, then exhaustive data analysis and comparison will be attended in order to find out the best solution.