STRATONAV (STRATOspheric NAVigation) is a scientific project which aims to test the VOR (VHF Omnidirectional Range) navigation system and to evaluate its accuracy above its estimated service volume. This investigation could determine a possible operational range extension to future stratospherical aviation.
The team is composed by students of Sapienza – University of Rome and Alma Mater Studiorum – University of Bologna.
The experiment has been selected for the REXUS/BEXUS programme 09 cycle and it will fly on the BEXUS stratospheric balloon in October 2016 from the SSC Esrange Space Center in Kiruna, Sweden.
What is VOR?
The VOR (VHF Omnidirectional Range) is an aircraft navigation system that convoys the old concept of sea mark navigation into radio frequencies. It has been used since late ’40s and there are over 3000 VOR ground stations all over the world.
Each VOR ground station transmits a complex signal (in VHF band), with the ID of the ground station, a reference signal indicating the magnetic North and a directional sine wave, changing its phase towards the transmitting direction.
By comparing the directional and the reference signal, a receiver is able to compute its radial, which is the angle between the magnetic North and the line between the receiver and the ground station. The radial does not match with the course (angle between the true north and the motion direction) or with the heading (the pointing direction of the aircraft’s nose)!
The VOR has been used for decades as primary flight navigation system: the pilot only had to divide his optimal route into straight segments among VOR ground stations and to follow the sequence of radials while tuning his onboard radio to the ground stations’ frequencies.
STRATONAV: our plan
The VOR service volume evaluation is based on calculations on the ground stations’ radiated power and it is approximated. The International Civil Aviation Organization (ICAO) prescribesstrict radiated power rates to each kind of VOR stations, but itgives no indications on the service volume.
We know that an high altitude navigation VOR station has to be able to serve civil planes cruising at high altitude (10-12 km). The VOR service should be guaranteed until 18 km in height.
What happens then?
We aim to test some VOR receivers in the stratosphere, flying on the BEXUS balloon until 25-28 km of height and to check the functionality and accuracy of the VOR system from the ground to the stratosphere. The launch area (Kiruna, Sweden, 150 km above the Arctic Circle) is served by a lot of VOR ground stations and the BEXUS flight could signify an unique chance to discover the real service volume end of the VOR.
We will collect the receivers’ VOR data and compare it to the GPS ground track of the balloon. If we are able to compute the balloon’s radial and position within an acceptable precision, we could set a milestone for future stratospheric flight navigation systems.
(PRELIMINARY DESIGN REVIEW)
The team has to highlight all the experiment objectives and requirements by submitting the Student Experiment Document (SED) to the Programme's assessors. The SED main aspects are discussed during the "Preliminary Design Review" (PDR).
(CRITICAL DESIGN REVIEW)
The team starts testing the experiment components and functionality while reviewing and completing the design. The tests are both physical (on COTS or bespoken parts) and numerical (FEM analyses, software tests, ecc.). All the work done is reported on an updated version of the SED and discussed during the Critical Design Review (CDR), that marks the half of the programme's cycle.
IPR and EAR
(INTEGRATION PROCESS REVIEW and EXPERIMENT ACCEPTANCE REVIEW)
The team continues developing the experiment by finishing the part manufacturing process and performing the last analyses. The experiment milestones are marked by two new SED updates and two reviews: the Integration Process Review (IPR), in July, and, when the experiment is ready to fly, the Experiment Acceptance Review (EAR) at the end of September. After the EAR, the experiment is sent to the SSC Esrange Space Center and the team members plan their way to the launch site.
The team stays at the SSC Esrange Space Center in Kiruna, Sweden, for 10 days for the last tests and to mount the experiment on the BEXUS balloon gondola. When the weather conditions are OK, the balloon is launched and STRATONAV reaches the stratosphere. After some hours of floating at really high altitude (around 25 km), the balloon is cut and the gondola, carrying all the BEXUS experiments, slowly falls to the ground with a parachute.
The programme does not end shortly after the launch. When the experiment is recovered, the team has to perform all the post-flight analysis in order to declare its mission accomplished or not. The SED comes to its final version and the results are ready to be presented in June 2017.
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