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

Student CEF at Sapienza - University of Rome. Preliminary design of Spec CubeSat with optical payload

Students attending the Spacecraft Design lectures in the framework of the Space and Astronautical Engineering MSc course atâ€La Sapienza†University of Rome have been involved in a Concurrent Engineering design for the CubeSat mission SPEC (Stellar Population and Evolution with Cubesat), conceived in collaboration with the Italian Space Agency. The SPEC mission is focused on the implementation of a small ad-hoc telescope and a sensor aimed at observing binary stellar systems in the near-infrared and infrared bands (i' and z' filters from the Sloan Digital Sky Survey) on-board a 6-Unit CubeSat. The mission is addressed to the observation of gravitationally bound groups (couples or more) of stars orbiting around a common centre of mass. The observations goal is to resolve (i.e. visually discriminate) the system members and perform spectrometric measures of the stars electromagnetic emission. Therefore, the mission requirements are mainly related to the Attitude Determination and Control System (ADCS) and to the payload optical performances and pointing precision. The project gives the students the opportunity to apply and improve the theoretical knowledge acquired during the academic courses by practising in a team working and project leading context. The whole class was involved in the design activities performed in the Concurrent Engineering Facility (CEF) by being organised into subgroups. Each subgroup took care of a subsystem or a mission feature. The CEF activities duration was set to slightly less than three months. Once concluded the CEF activities, the finalised configuration, obtained with several iterations on the sub-systems design, was delivered to the Professor in charge of the course for verification and evaluation of the contributions. A short introduction on the SPEC preliminary design was also presented during theâ€4th Space Debris Student Opportunities Workshop†at Sapienza - University of Rome in December 2017. In such framework, the students gave a public presentation about their work and achieved results. This paper outlines the SPEC preliminary design and how the CEF experience allowed the students to understand and practice on how a satellite design process is usually approached and carried out. Finally, the educational return offered by the course and related activities is discussed, with examples from the Concurrent Engineering nano-satellites design from the present and the past years

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

A concept mission for the Stellar Population and Evolution with Cubesats (SPEC)

Binary or multiple stellar systems, constituting almost a third of the content of the Milky Way, represent a high priority astronomical target due to their repercussions on the stellar dynamical and evolutionary parameters. Moreover the spectral study of such class of stars allows to better constrain the evolutionary theories of the Galactic stellar populations. By resolving the members of stellar systems through photometric observations we are able to perform more detailed measurements to infer their mass. In this paper we investigate the feasibility of a cubesat based mission including an optical payload to directly optically discriminate the members of a selected sample of binary systems. The scientific targets, consisting 11 M class dwarf stars binary systems, have been extracted from the already studied Riaz catalogue. These subset has been selected considering the star distance, the members angular separation, and the distance from the Galactic plane (due to limit the background and foreground contamination). The satellite concept is based on a 6 unit Cubesat embedding some commercial off the shelf components and an ad hoc designed optical payload occupying almost 4 units. The optical configuration has been chosen in order to fit the angular resolution requirements, as derived from the target characteristics. Moreover, according to the optical analysis and the computed field of view some requirements on the attitude control system have been inferred and fulfilled by the component selection. The paper is organized as in the following: a brief scientific introduction is made; consequently the project is described with particular attention to the optical design and the standard sub-systems; finally the conclusions are drawn and the future perspectives are investigated

LED-based optical communication on a nano-satellite platform

LEDSAT (LED-based small SATellite) is a 1-Unit CubeSat project equipped with a LED- (Light Emitting Diode-) - based payload, carried out by the S5Lab (Sapienza Space System and Space Surveillance Laboratory) research team. The satellite mission, conceived with the University of Michigan, has been accepted for the European Space Agency Fly Your Satellite! Programme and it will be launched in 2019. The project is primarily addressed at verifying and improving the current methodologies for satellites and space debris orbit determination by means of optical observations. One of the mission objectives relies in testing an encoded optical communication method to downlink basic telemetry data. This feature could support future CubeSats as back-up for traditional Radio-Frequency transceivers, providing redundancy and improving the reliability of these critical components. The LEDs are a promising payload for space communication thanks to their optimal performances in terms of radiated power and wide emission angle. While the high performances and small diodes dimensions allow to mount a high number of LEDs, sufficient to assure visibility from ground, on a small area of each satellite face, the wide emission angle allows a less strict on-board pointing requirement, which is usually a major constraint on a CubeSat. The light-based communication tests will be performed through three methods, at different data rates. The sidereal tracking method, consisting in shooting a long exposition picture to the target and acquiring its tracklet on a fixed stellar field, and the satellite tracking method, represented by the acquisition of a high frame rate video by maintaining the target in the field of view, will be exploited by means of a Charge Coupled Device (CCD). On the other hand, the high rate communication is achieved by using a telescope equipped with an amplified photodetector, able to convert the acquired light into an electric signal, thus allowing a faster flashes detection. The tests will be performed by the LEDSAT Ground Station network, which includes telescopes located all around the world, from the equatorial region (Kenya) to mid-latitude stations in both the hemispheres (Italy, USA, Switzerland, Chile). In order to decrease the background noise, telescopes are equipped with narrowband filters coupled with the LEDs wavelength emission. This paper will describe the LED-based light communication methods to be tested on the LEDSAT 1-U CubeSat. In addition to the data link design, the potential outcomes and further applications of LED communication for CubeSat will be discussed

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

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

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

Opportunities and technical challenges offered by a LED-based technology on-board a CubeSat: The LEDSAT mission

LEDSAT (LED-based small SATellite) is a 1-Unit CubeSat project conceived by the Sapienza - Space Systems and Space Surveillance Laboratory (S5Lab) research team at Sapienza - University of Rome, with the collaboration of the University of Michigan (USA). The project has been accepted for the European Space Agency Fly Your Satellite! Programme, it is under development with the support of the Italian Space Agency (in the framework of the IKUNS project) and it will be launched within 2020. The main mission objective is to test a payload composed of Light Emitting Diodes (LEDs) to verify and improve the current methodologies for orbit determination by means of optical data. The secondary mission objectives focus on testing LED-based methodologies for attitude reconstruction and on a basic light-based communication strategy. The implementation of a LED-based payload introduces a great number of technical challenges for the project. Indeed, the LED boards need to be qualified for being mounted on the outer surfaces of a satellite, for a Low Earth Orbit mission of one year. On this purpose, the research team has recently completed an Ultra-Violet radiation testing campaign and a gamma-ray Total Irradiation Dose (TID) test to assess the diodes survivability to the space environment. Then, the design of a self-illuminating system requires to perform a trade-off between the LED activation time and radiated power, that increase the probability of detection from ground, and the available peak power and energy storage on-board the nano-satellite platform. Moreover, the spacecraft shall be able to autonomously manage the LEDs activation time synchronization with the Global Positioning System (GPS) time, in order to allow the observatories to coordinate the data acquisition to the LEDSAT flashes. Finally, a various set of photodetectors will be implemented at ground for testing the spacecraft LED-based communication. In particular, while a low data rate is suitable for simultaneously determining the satellite angular position and acquiring the down linked data with a Charge Couple Device (CCD), higher data rates can be offered by Avalanche Photo-Diodes (APD) or P-I-N diodes. The performance of these devices will be tested by the S5Lab research team in the next months. This paper describes the LEDSAT payload, the technical challenges related to its design and the implemented solutions for the spacecraft production. In addition to this, the expected outcomes of the mission and the possible applications of LED boards on nano-satellites will be discussed

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