BX34 – RETINA (Real-time Experiment for Thermal management, Inertial Navigation and Attitude)

Sapienza University of Rome, Italy

Launch Date: October 2024

The integration of Artificial Intelligence (AI) for inertial-sensor-based attitude estimation represents an innovative approach to the attitude determination problem. While traditional deterministic algorithms and filters have proven flight heritage, extensive application specific calibration is required to ensure precise attitude estimation. The main advantage of an AI-driven solution is the wide range of applicability since the training required is not application specific, allowing the solution to be applied to different types of systems.
Inspired by on-going research into Artificial Intelligence, RETINA (Real-time Experiment for Thermal management Inertial Navigation and Attitude) will perform the first in-flight demonstration of attitude determination through AI algorithms, testing the accuracy and reliability of a robust neural network in a real life scenario. Using data from a high-quality IMU, the AI will overcome adaptability issues commonly associated with changing environmental conditions and different sensor performances to produce attitude estimates, which will then be compared with those produced by flight-tested, embedded software within the aforementioned IMU.
Since considerable computational power will be required for the AI experiment, heat fluxes produced by the dedicated AI computer inside the BEXUS module will be managed by RETINA’s thermal management experiment, which will conduct the first in-flight demonstration of a miniaturized thermal two-phase cooling system to control heat exchanges.
Together with the AI system, RETINA also aims to test and validate different real-time attitude and positioning data fusion algorithms using measurements from an array of low-cost COTS IMUs. Their performance in position and attitude estimation will be compared to estimates produced by the high-quality IMU’s software.
Finally, RETINA will perform the first in-flight demonstration of a Flexible Time-Triggered Ethernet (FTTE) network, allowing for communication speeds up to Gbps between different end systems. This demonstration will pave the way for future applications in launch vehicles, where current generation systems are limited by their Mbps bandwidth.

BX32 – SBGA (Miniaturized Multi-Sensor Box for spaceborne geodetic Applications)

Technische Universität München

Launch Date: 24 September 2023

The main objective of this experiment is to measure the vertical gradient of Earth’s gravity field and to assess the applied instruments’ quality. For this purpose, the Miniaturized Multi-Sensor Box for Spaceborne Geodetic Applications (SBGA), which is an inertial measurement unit enhanced by additional sensors, will be used. It is mounted on the BEXUS gondola and will contain two low-cost accelerometers, a magnetometer, a barometer as well as a GNSS receiver. Optionally, one low-cost accelerometer will be replaced by a miniaturized high-precision opto-mechanical accelerometer, which is currently being developed for CubeSat applications and will be integrated as a tech demonstrator. We will measure the gradual changes of the gravity field during the ascent and descent phases of the balloon’s flight and analyse the data using a Kalman filter. The results will be compared to existing gravity field models, and this will validate the accuracy of the used instruments. The results of this experiment will provide valuable insight on the operation of small cost-effective sensor boxes and miniaturized instruments for airborne gravimetry and CubeSat applications.

BX28 – TARDIS (Tracking and Attitude Radio-based Determination In Stratosphere)

Sapienza University of Rome, Italy

Launch Date: 25 October 2019

The TARDIS experiment aims at testing an alternative in-flight attitude and position determination system based on the processing of the VOR signal and a radio-based tracking system. The VOR (VHF Omnidirectional Range) is a radio-navigation system for aircraft which relies on a wide infrastructure of ground stations. The main information decoded from the VOR signal is the radial, which indicates the bearing angle of the receiver with respect to the station. The experiment position will be calculated in real time by analysing the received VOR signals and intersecting the decoded VOR radials. The experiment attitude will be deduced by evaluating the VOR received signals power from different antennas, using their radiation patterns to determine the received signal direction. The tracking system will use a steerable antenna which will be maintained pointed towards different VOR ground stations throughout the flight. If the behaviour, accuracy and reliability in stratospheric flight of the tested systems will be confirmed, they could be employed on HAPS (High Altitude Platform Stations), stratospheric platforms that are meant for pseudo-satellite applications. While the tested navigation system could improve the reliability of the traditional inertial and satellite systems, the tracking system will demonstrate target pointing capabilities and could be used for various pseudo-satellite tasks.

TARDIS Student Experiment Documentation v5

BX29 – R2C2 (Radar Recognition of Chaff Clouds in the stratosphere)

Luleå University of Technology, Sweden

Launch Date: 23 October 2019

The R2C2 (Radar Recognition of Chaff Clouds in the stratosphere) experiment concerns the navigation of high altitude aerostatic balloons. To navigate such balloons, it is critical to know oh which wind directions are available in the close vicinity of the balloon and with which intensity the wind is flowing. As of now, the only possible way to determine how the wind layers are moving around the balloon is through trial and error. This means changing the altitude of the balloon in the hopes of finding a wind current that will take it in the desired direction. The primary objective of this experiment is to determine the speed and direction of the wind layers below the balloon and to analyze the data gathered in order to determine the feasibility of this method to navigate balloons at high altitude. To do this, chaff will be used. Chaff consists of small conductive metal pieces. When released mid-air it forms a “cloud” and slowly drifts away following the air currents before eventually dispersing. This chaff cloud can be tracked with a radar. To use this method for navigation, the tracking would ideally be done from the balloon. The R2C2 experiment would ideally use an on-board radar system as chaff tracking system. However, to keep the workload of the experiment at a reasonable amount, the team plans to use a ground radar system instead. Secondary
objectives include analyzing the aforementioned data regarding the wind structure of the stratosphere and comparing it to the typical model of horizontal wind layers; study the dynamics of chaff clouds and the effects of different chaff foil shapes and sizes; and developing a secure system to release chaff clouds from a balloon. This experiment would be focused on atmospheric research.

R2C2 Student Experiment Document v5-1

RX25 – PR3 (Payload for Radiation measurement and Radio-interferometry on Rockets)

Eindhoven University of Technology  & Radboud University of Nijmegen, Netherlands

Launch Date: 11 March 2019

The goal of the PR3 experiment is twofold: our primary objective is to demonstrate the feasibility of using radio-interferometry to track to location and orientation of REXUS in flight. Our secondary objective is to use commercially available off-the-shelf camera modules to measure radiation during flight. When correlated, these two objectives can provide a very accurate mapping between radiation dose and position/orientation of the camera sensors.

The radio-interferometry experiment will carry three transmitters on REXUS as a payload. Each of these transmitters will be tracked by several ground stations placed near the launch site. Based on what the ground stations measure, the position and orientation of the rocket can be established. The goal is to provide real-time tracking of REXUS while in flight.

The radiation measurement experiment will carry several off-the-shelf cameras on REXUS as a payload. When a particle strikes the camera sensor a flash will occur at one or more pixels. The brightness and number of pixels that light up give an indication about particle energy. The goal of this experiment is to establish what camera properties work best for particle counting.

PR3 Student Experiment Documentation v5

BX26 – IMFUSION (Reliable, miniaturised and universal localisation system for aerial vehicles)

Hochschule Nordhausen, Germany

Launch Date: 17 October 2018

The IMUFUSION experiment idea is to create a trajectory of the balloon within BEXUS campaign by the help of an Inertial Measurement Unit (IMU)-based System. A typical application of an IMU is the sensor part of a mechatronic stabilization system of Unmanned Aerial Vehicles. The project is focused on the design, the prototype, and the practice test of a reliable and failure tolerant IMU-based position- and attitude-logging system with diagnosis capability. All functional components of the system are redundant and contain self-test procedures. The main components are: energy management, microcontroller unit (MCU) with contained redundant memories, rotational speed, acceleration, and magnetic field sensors. The challenges of the project are: a) reliable system design, and b) real-time data fusion of the sensor data.

RX24 – SPAN (SPAce Navigation using Signals of Opportunity)

Faculty of Engineering University of Porto, Portugal

Launch Date: 4 March 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.