RX24 – SPAN (SPAce Navigation using Signals of Opportunity)

Faculty of Engineering University of Porto, PORTUGUAL

Launch Date: TBD 2018

One of the many problems in the aerospace domain is assisted navigation. GPS receivers used in LEO satellites are very expensive and a big part of the total budget is used to buy these components. The main objective of the SPAN experiment is to use signals of opportunity to navigate, integrating timing information extracted from the signals to obtain the relative position from a known starting point. Signals of opportunity are signals which are used for other purposes that are not their primary ones. In this specific case, we will use DTTV, GSM and LTE signals. These signals are naturally slaved to a precise atomic clock, have significant power and bandwidth and are transmitted continuously or are never too long without being transmitted. Using a SDR and an on-board Rubidium Atomic Clock in a rocket module, will allow the team to receive the signal and couple it with the synchronized signal given by a timing signal generator that will be calibrated with the clock. Extracting the delay between a received symbol and the timing marker generated by the SPAN experiment, it is possible to calculate the relative distance between the transmitter and the receiver. Knowing the start position, the evolution of this delay gives the trajectory done by REXUS rocket. The ultimate goal of SPAN is to develop a compact methodology for future LEO satellites navigation, possibly integrated with communications.


BX22 – STRATONAV (STRATOspherical NAVigation experiment)

La Sapienza, University of Rome, Italy

Launch Date: 5 October 2016

The experiments main goal is to test the VOR (VHF Omnidirectional Range) navigation system and to evaluate its accuracy above its estimated Standard Service Volume. Through an in-situ testing campaign investigation, it might be possible to determine a future operational range extension of VOR to stratospheric flights. STRATONAV aims at tuning its VHF receiver to the optimal VOR ground station frequency nearby during the whole BEXUS flight and at recording the measured VOR radials. The STRATONAV equipment will be able to compute the BEXUS ground track by interfacing two or more measured radials simultaneously due to the network of VOR ground stations located in the area around the launch-site and to their multiple service volume intersections. The VOR accuracy will be evaluated by comparing the collected data with the estimated balloon path during its floating phase in the stratosphere. The main possible advantage that this experiment could offer is the possibility to use a well-established, mature and available navigation system as a stand-alone positioning system method or as add-on of current and future other space-borne positioning systems.


BX23 –  SIGNON (SIGNals of Opportunity for Navigation)

University of Porto, Portugal

Launch Date: 5 October 2016

The goal of SIGNON experiment is to use radio signals of opportunity, such as FM broadcast stations, DTTV stations and ADS-B signals transmitted by passing aircraft, to obtain navigation information during a stratospheric BEXUS flight. For this purpose software defined radio (SDR) receivers, tuned to these signals of opportunity, will be used. Post-processing by correlation with equivalent data gathered by a small set of reference stations in known locations allows computing distances between transmitting stations and the balloon and, consequently, obtain the balloon trajectory. Comparison with GPS data will provide an assessment on feasibility and accuracy for the use of these signals of opportunity for navigation at high altitude and for LEO satellites. The SIGNON experiment will also test the possibility of using DTTV signals for passive radar applications, measuring the signals scattered by the surrounding environment together with the direct signal from the transmitting stations. Combination of such measurements along the flight trajectory will enable to produce a scattering map of the vicinity of the flight trajectory.


BX19 – TORMES 2.0 (TOpography from Reflectometric Measurements: an Experiment from Stratosphere)

UPC Barcelona Tech, Spain

Launch Date: 8 October 2014

Reflight of TORMES. The main changes of TORMES 2.0 are: to design and to manufacture an improved version of the PYCARO (P(Y) and C/A Reflectometer) payload and a new down-looking antenna array with higher gain, to use a new On Board Computer and to include an Attitude Determination Subsystem. Moreover, the team will analyse the bistatic coherent reflectivity during the float phase of the flight and perform GPS radio-occultation measurements for atmospheric sounding.


RX16 – HORACE (Horizon Acuisition Experiment)

University of Würzburg, Germany

Launch Date: 28 May 2014

The aim of the Horizon Acquisition Experiment (HORACE) is to test and demonstrate the capabilities of a new approach for attitude determination, which also works under stress conditions like uncontrolled tumbling or spinning with high rates. Therefore the experiment processes optical data with image processing algorithms on an embedded system, so that the line of horizon is detected in the frames and a vector to the 2D projection of the center of the earth can be calculated. Unlike existing earth sensing systems using the IR spectrum to detect the earth, HORACE processes video frames of an ordinary camera, which is sensitive to the visible spectrum. Thus, there is strong emphasis on the software components of the system and we imagine a future system which could only be a software package capable enough to use data from existing payload-cameras for attitude determination in emergencies. During the experiment both video and calculated data are collected to provide qualitative and quantitative evidence about the robustness and accuracy of the horizon acquisition and the calculated earth vector, as well as for the general approach after post flight evaluation. The flight on REXUS provides a good setting for the experiment, because the launcher’s rotation is similar to uncontrolled tumbling or spinning movements and the reached altitude is high enough to take realistic, space-like images. HORACE has been initiated by five students of Aerospace Information Technology at University of Würzburg in close  ooperation with and support of the Chair of Aerospace Information Technology in October 2012. It will be implemented throughout 2013 and launched in spring 2014 as payload of REXUS 16.


BX17 – TORMES (TOpography from Reflectometric Measurements: and Experiment from Stratosphere)

UPC Barcelona, Spain

Launch Date: 10 October 2013

The Global Positioning System (GPS) was first conceived and implemented for navigation purposes, but it has also been used for Earth Observation. Recently, new applications explore the possibility to use the GPS signals scattered off the Earth’s surface and sensed by an airborne or spaceborne receiver in a bistatic radar geometry, as a means of performing altimetry and scatterometry. At present, the ultimate influence of the different GNSS‐R (Global Navigation Satellite Systems Reflectometry) parameters in the precision and accuracy of the altimetric products is still being analysing. The impact of different noise sources as well as the theoretical height precision expectations and the corrections of different bias terms must be correlated with results obtained in a real scenario. The main goal of this experiment is to test PYCARO (P(Y) & C/A ReflectOmeter). PYCARO is a new reflectometer developed at UPC (Universitat Politècnica de Catalunya‐Barcelona Tech), which uses the conventional GNSS approach (Cross correlation of the reflected and the direct signals with a locally generated replica of the transmitted signals), but taking full advantage of the latest developments in GNSS technology.


BX09 – NAVIS (North Atlantic Vessel Identification System)

Aalborg University, Denmark

Launch Date: 11 October 2009

The main objective of the NAVIS experiment was to flight-test two prototype Automatic Identification System (AIS) receivers and decoders – to be used for satellite-based maritime vessel tracking – in order to evaluate the quality of space based reception of AIS messages. The AIS is a ship identification and position exchange protocol used to enhance safety at sea. NAVIS was a subproject of AAUSAT3, the 3rd Cubesat currently being developed at Aalborg University, Denmark. The main payload of AAUSAT3 will be the two student developed AIS receivers, which were verified on BEXUS in a realistic environment so as to investigate the severity of message collisions for AIS receivers with an extended field of view. This is an important issue for satellite based AIS, and the main goal was to find out to what extent an increased FOV is acceptable. To investigate this, a high altitude balloon was flown carrying the prototype to an altitude of 24 km. The prototype performed as expected for the entire flight, and collected valuable sampled AIS data. More than 25,000 AIS messages were successfully received from ships in northern Scandinavia during the three hour flight. An analysis of the message reception ratio, based on interpolation showed that 15.9 % of expected transmission was received by the receivers. The satellite power supply and a newly developed communication system were also successfully tested.

NAVIS Conference Paper


BX06 – LOWCOINS (LOW COst Inertial Navigation System)

La Sapienza University of Rome, Italy

Launch Date: 8 October 2008

The purpose of the LOWCOINS experiment was to design and validate a low cost Inertial Navigation System comprised of COTS Micro Electro Mechanical Systems (MEMS). Inertial Navigation Systems’ (INS) are unusual in that they do not require any external reference points to determine position, orientation and velocity. As INS’s are completely self-contained, they are particularly relevant to the constrained environment associated with rocket and balloon applications. LOWCOINS was based on a strap-down design which used rigidly connected accelerometers, gyros and MEMS sensors to provide data on acceleration levels, angular momentum, magnetic field strength and direction, as well as atmospheric pressure and internal experiment temperatures. All of this information was used to determine the position of BEXUS throughout the flight. Once the experiment was recovered, the memory was dumped and an exhaustive post-processing procedure was conducted using all data gathered by the unit. During post-processing, the flight trajectory was reconstructed using several methods and compared against BEXUS’s GPS data. An exhaustive data analysis and comparison was then performed in order to gauge the maximum performance derivable from using these systems in extreme environments.