Usage of Light Emitting Diodes (LEDs) for improved satellite tracking

With the increasing number of satellite launches, especially in Low Earth Orbit (LEO), optical tracking can offer a convenient enhancement of tracking precision and availability. Spaceborne active illumination devices, such as LED payloads, can offer a significant improvement to optical observations, extending the observability interval to the whole eclipse time and performing optimized flash sequences for identification, orbit determination, attitude reconstruction or low data rate communication. The main features of LED panels for optical tracking mounted on small satellites platforms (and with particular regards to nano-satellite platforms) are outlined in this paper, along with the description of the design drivers. The analysis of the performance is referred to Sun-Synchronous (at 700 km of altitude) and International Space Station (400 km) orbits, while the ground segment and the optical link budget reference design relies on a standard university space debris observation station architecture. The paper also outlines the advantages of using different observation techniques and the variety of flashing patterns. The LEDSAT 1U CubeSat, aiming at demonstrating the effectiveness of an LED-based payload for observation and tracking, is used as a study case for examples of the LED payloads and related operations that are reported and described in this paper

Horus: multispectral and multiangle cubesat mission targeting sub-kilometer remote sensing applications

This paper presents the HORUS mission, aimed at multispectral and multiangle (nadir and off-nadir) planetary optical observation, using Commercial Off-The-Shelf (COTS) instruments on-board a 6-Unit CubeSat. The collected data are characterized by a sub-kilometer resolution, useful for different applications for environmental monitoring, atmospheric characterization, and ocean studies. Latest advancements in electro-optical instrumentation permit to consider an optimized instrument able to fit in a small volume, in principle without significant reduction in the achievable performances with respect to typical large-spacecraft implementations. CubeSat-based platforms ensure high flexibility, with fast and simple components’ integration, and may be used as stand-alone system or in synergy with larger missions, for example to improve revisit time. The mission rationale, its main objectives and scientific background, including the combination of off-nadir potential continuous multiangle coverage in a full perspective and related observation bands are provided. The observation system conceptual design and its installation on-board a 6U CubeSat bus, together with the spacecraft subsystems are discussed, assessing the feasibility of the mission and its suitability as a building block for a multiplatform distributed system

VHF Omnidirectional range (VOR) reliability determination in stratosphere. Stratonav experiment

The VHF Omnidirectional Range (VOR) is a mature and reliable radio-navigation system, used since the late 1940s by civil and commercial aircraft. This navigational aid is still used nowadays as back-up for inertial, satellite and other radio-frequency navigation systems. The VOR architecture is based on ground stations transmitting a complex signal in VHF band and on passive and simple receivers able to extract the "radial information", equal to the angle between the Magnetic North direction and the line that connects the ground station and the receiver. The Airport Information Publications (AIPs) indicate the service volume of each ground station, that extends up to 185 km in range and 18 km in altitude. The service volume measures are based on prescribed minimum power density rates. The vehicles in charge of verifying the correct operations of the VOR stations are traditional fixed-wing planes, inherently unable to reach the guaranteed service limit height. However, simple link budget calculations indicate a possible applicability of the VOR to stratospheric aircraft. STRATONAV (STRATOspheric NAVigation) Experiment is a scientific project developed by a joint students team from both Sapienza - University of Rome and Alma Mater Studiorum - University of Bologna, aimed at evaluating the VOR accuracy rates in the stratosphere, above the prescribed service volume limit. The experiment was selected in December 2015 to participate in the ninth cycle of the REXUS/BEXUS Programme (Rocket and Balloon-borne EXperiments for University Students). STRATONAV was designed, developed and tested in the first half of 2016 and was launched on-board BEXUS 22 stratospheric balloon on October 5th, 2016 from Esrange Space Center in Kiruna, Sweden. The experiment collected VOR radials for nearly five hours, reaching a balloon float altitude of 32.2 km. The flight area was characterized by the presence of multiple VOR stations, whose dense service volumes intersection pattern allowed to perform a VOR-standalone-based ground track determination by interfacing two (or more) radials at a time. This paper deals with the STRATONAV Experiment design, development, test and flight. After a description of the experiment radio-frequency systems, VOR receivers and data collecting methodologies, a report of the experiment stratospheric flight will be provided. Finally, an overview of the achieved results and future applicability will be presented

LEDSAT 1U CubeSat thermal analysis and steady state calibration for thermal-vacuum testing

This paper reports the results from the thermal analysis, the steady state analysis and the thermal vacuum testing from the LEDSAT 1U CubeSat environmental qualification. While the thermal analysis has been computed to state the compliance of the CubeSat to the orbital environment, the steady state analysis has been performed to confirm the suitability of the selected thermal vacuum test levels for the survivability and operational ranges of the satellite components. The spacecraft system-level thermal vacuum testing has given satisfying results, with perfect functionalities of the spacecraft and with a successful qualification of the PFM for spaceflight

LEDSAT 1U CubeSat GPS receiver electro-magnetic interference (EMI) analysis

While Electro-Magnetic Compatibility testing is not often considered for CubeSat projects, the increasing complexity of nano-satellite platforms is suggesting to include such tests in their standard verification processes. This paper reports the followed approach and measurements set-up for an EMC anomaly regarding the LEDSAT 1U CubeSat Proto-Flight Model on-board GPS antenna. The anomaly was discovered and solved during functional testing campaign in 2020 and the satellite has been successfully qualified for flight

Space debris observation activities at s5lab: From telescope measurements to orbit and attitude determination

Nowadays, the space debris issue is on top of the list of all space agency in the world. Even more so with the advent of the new space economy which will increase even more the number of objects around the Earth and consequently impact risk between operative satellite and space debris. S5Lab has developed several tools in order to identify, classify and monitor object in orbit. Measurements acquisition occurs by means of a network of telescope around the Earth surface. In this paper will be shown all S5Lab's activities starting from image and measurements acquisition until attitude determination retrieved from the light-curve, passing for orbit determination and measure calibration. Moreover, a TLEs improvement procedure will be exposed

Experimental validation of VOR (VHF Omni Range) navigation system for stratospheric flight

This paper presents the results of STRATONAV experiment to test the precision of the VOR (VHF Omni Range) aircraft navigation system in stratosphere. The experiment has been conducted by the S5Lab research group at Sapienza University of Rome in the framework of the REXUS/BEXUS Programme. STRATONAV has been successfully launched on-board the BEXUS 22 stratospheric balloon from Esrange Space Center in Kiruna, Sweden, in 2016. The main payload was composed by two typologies of VOR receivers, a commercial portable receiver and a Software Defined Radio (SDR), alongside the bus and positioning, attitude and temperature sensors. STRATONAV succeeded in collecting VOR radials for the whole duration of the balloon flight. The results prove that VOR can be used as back-up navigation system for stratospheric platforms, ensuring a reliability improvement, while being applied to smaller payloads as primary system for a cost and complexity reduction of experiment developments. The paper analyzes the collected VOR data during the balloon flight. Accuracy and performance plots with respect to distance from the VOR stations and altitude are presented and discussed. The mean errors and standard deviations from all stations for both the receivers are shown with an analysis over the recorded errors. Finally, future perspectives, analyses and applicability of the research are exposed

Time difference of arrival for stratospheric balloon tracking. Design and development of the STRAINS experiment

In the recent years, an increasing interest towards enhanced and more frequent operations at high altitudes has been demonstrated both by aerospace industry and academics. In particular, many institutions and companies are developing the so-called HAPS (High Altitude Platform Stations, [1] - [3] ), high altitude balloons provided with low-thrust propulsion systems able to maintain their position over a target. These vehicles are provided with power generation systems and are able to perform long-term missions of weeks or even months. On the other hand, suborbital commercial missions are close to their starting point for both touristic and short-term scientific operations [4] , [5]. The mentioned new-generation vehicles require to maintain a certain level of reliability in the tracking and surveillance systems to assure their compatibility with the "conventional"air space operations of commercial aircraft and the needed safety levels for the conducted operations, with particular regards to manned missions

The Wildtrackcube-Simba Cubesat. Italian-Kenyan mission for wildlife monitoring

The WildTrackCube-SIMBA (System for Improved Monitoring of the Behavior of Animals) CubeSat project has been conceived by Sapienza University of Rome, Machakos University and University of Nairobi to demonstrate an innovative wildlife tracking system based on a nano-satellite project. The mission has resulted winner of the free launch opportunity contest offered by the International Astronautical Federation (IAF) and GK Launch Services in 2019. The proposing team was awarded at the 70th IAC in Washington DC. The spacecraft development is supported by the Italian Space Agency and by the Kenyan Space Agency. The satellite is the third Italian-Kenyan capacity building nanosatellite after 1KUNS-PF (launched in 2018) and LEDSAT (qualified for launch, to be launched in Summer 2021). Wildlife tracking has not only the aim of studying and monitoring the behavior of animals and tracking the migrant species, but also to prevent and avoid human-wildlife conflict incidents that can result in damage to cultivations or urban areas or even in the death of the animals or humans. Countries like Kenya that have a significant percentage of their surface area covered by a large variety of National Parks have the urgent need to monitor the movements of the animals within the Parks and to set-up methods for preventing the wildlife to cross the preserves boundaries. The 1U CubeSat carries spread-spectrum modulation antennas for receiving data from the radio-frequency sensors which will be deployed on the wildlife in Kenya. The acquired data will be down linked to ground to allow the biology team to track the wildlife and to study its behavior. The satellite has been qualified in late 2020 and integrated on the launch deployer in February 2021 at the GK Launch Services integration center in Moscow, Russia. The spacecraft is scheduled to be launched on-board the Soyuz-2 Soyuz/Fregat vehicle on March 20, 2021 from the Baikonur Cosmodrome in Kazakhstan. The mission marks an excellent occasion for a capacity building collaboration between Italy and Kenya which will be continued throughout the future years in multiple disciplines such as the development and improvement of space communication systems, biology and ethology. This paper will deal with the WildTrackCube-SIMBA 1U CubeSat mission. After a presentation of the mission space and ground segments, the paper will describe the conducted activities from satellite mission concept to launch and early operations of the spacecraft

Innovative tracking techniques approaches: From stratospheric vehicle testing to commercial space transportation applications

The future manned space transportation systems require safe, reliable, high-capacity tracking and surveillance systems to ensure safety of the operations. Differently as aircraft surveillance that is mainly performed by traditional primary and secondary radar systems, novel, dedicated tracking systems should be applied to space transportation vehicles due to the inherent differences between aircraft and spacecraft mission profiles in covered distance, speed range, typical elevation and elevation rate of the targets.. Quasi-passive tracking systems, exploiting multi-lateration techniques such as the TDOA (Time Difference of Arrival) and FDOA (Frequency Difference of Arrival), could offer a significant contribution to the achievement of acceptable safety levels of the tracking systems for space transportation vehicles. These systems rely on a spaceborne transmitter downlinking dummy signals (without any information content) and a distributed network of ground-based sensors achieving position and velocity determination through multi-lateration algorithms. The TDOA algorithm consists in retrieving the spaceborne target position by analyzing the reception times of the signals from multiple locations, while FDOA is able to reconstruct the velocity vector of the target on the base of the observed Doppler shift frequency from the distributed receivers. The reduced dependability on the effective transmitting system well-functioning compensates the great difficulties in building and managing active tracking systems, e.g. primary radars, needing to extend their range to near-space and space operational conditions. The effectiveness of those multi-lateration systems is being tested by the S5Lab research team at Sapienza University of Rome and ALTEC (Aerospace Logistics Technology Engineering Company) through the development and launch of a stratospheric experiment, named STRAINS (Stratospheric Innovative Systems), on a Zero-Pressure Balloon in the framework of the HEMERA H2020 Balloon Launch Infrastructure. The stratospheric experiment will be launched in September 2020 from the Esrange Space Center in Kiruna, Sweden, and it is under integration at Sapienza University of Rome. The results of the experiment, applied to a stratospheric vehicle and to the Near-Space environment, will be immediately applicable to the mission scenario of space transportation systems, with particular focus on suborbital spaceplanes for commercial and scientific missions. This paper describes the future perspectives of TDOA and FDOA tracking systems for Near-Space and space transportation vehicles. Particular focus will be given to the system architecture, to the experimental set-up and results of the STRAINS experiment on-board a stratospheric platform and on its future applications to space transportation systems, with regards to suborbital spaceplanes mission profiles