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

LED-based attitude reconstruction and back-up light communication: Experimental applications for the LEDSAT CubeSat

Optical observations are intensively applied to space debris monitoring for the achievement of orbit determination and for gathering information on their attitude motion, even if constrained by light conditions. Light Emitting Diodes (LEDs) installed on the external surfaces of a satellite could increase the visibility interval to the whole eclipse time. LEDSAT (LED-based small SATellite) is a 1-Unit CubeSat aimed at demonstrating the effectiveness of LEDs for the improvement of space debris optical monitoring algorithms. The LEDSAT experimental mode includes flashing patterns that will allow the CubeSat attitude reconstruction and the testing of a back-up light-based communication method. This paper will describe the features of the LEDSAT experimental mode, by describing the needed measurements for achieving the satellite LED-based attitude reconstruction and the features of the back-up LED communication

Experimental investigation on the effect of microgravity and immunotherapy in melanoma cells. Marge experiment

MARGE (Melanoma Apoptosis Reduced Gravity Experiment) is an experiment proposed for an orbital platform that aims at testing the combined effect of microgravity and target therapies on melanoma cells. The experiment is based on recent studies that prove that microgravity can induce apoptosis in student cancerous cells. MARGE aims at testing melanoma cells in microgravity conditions in combination with pharmacological treatment using check point inhibitors to evaluate the mechanisms underlying the biological modifications of the cells to identify adjunctive therapeutic targets. The experiment is structured as an autonomous small-scale cell culture laboratory containing the samples suspended in culture inside flasks. It will be internally divided by an insulation panel in order to maintain two different temperatures for the whole duration of the experiment in orbit: one set to guarantee the optimal growth of the cells (37C) and one to preserve the drugs (4C). The samples will be maintained in culture by providing nutrients, oxygen and regulating PH, temperature and humidity through a hydraulic and heating system. The cellular growth will be monitored through a turbidimetric analysis performed by a portable spectrometer. The experiment will be replicated on ground in normal gravity conditions. After the retrieval of the samples a post flight analysis will be conducted to compare the results achieved in orbit with the ones on ground. The facility will be compliant to Ice Cubes requirements and will be approximately the size of a 6U CubeSat. The idea has been conceived in late 2019 by a group of Aerospace Engineering and Medicine students from Sapienza University of Rome, supported by the S5Lab (Space Systems and Space Surveillance Laboratory) and the Laboratory of Cutaneous Physiopathology of the San Gallicano Dermatological Institute IRCCS (IFO), in Rome, Italy. In this paper the features of the MARGE experiment will be described through the mission objectives, the outline of the on-board system, together with an analysis on the compliance of the system with the launcher and hosting facility requirements. The expected results and outcome from the experiment will be discussed together with the future perspectives

Development and qualification of a LED-based payload for a CubeSat platform: LEDSAT mission

LED-based payloads can offer improved optical tracking of small satellites by extending the observable interval from the time when the satellite is sunlit to the whole eclipse phase. LEDSAT (LED-based small satellite) is a 1U CubeSat mission aimed at demonstrating the capabilities of LED based boards to be installed on the external surfaces of small satellites. The nano-satellite will host 140 LEDs on all the six CubeSat faces. The satellite has been conceived by Sapienza University of Rome and the University of Michigan and it has been integrated in June 2020 at the S5Lab at Sapienza University of Rome. The satellite project is participating in the ESA Fly Your Satellite! Programme and in the ASI IKUNS Programme. The LEDSAT LED flashing patterns have been optimized to enhance optical orbit determination, attitude determination and back-up light-based communication. Functional testing on the satellite will take place at Sapienza in between July and October 2020, while environmental qualification of the satellite will be performed at ESA/ESEC Galaxia in Redu, Belgium, in Q4 2020. The launch is schedule for Q1 2021. The LED-based payload has already been qualified for spaceflight after undertaking radiation, UV, vibration and thermal vacuum testing between 2017 and 2019. LED long-range observations have been successfully completed by University of Michigan, through a high altitude balloon launch that observed LEDs at a distance of 54 km, and functional testing of the ground segment at approximately 10 km of distance by Sapienza University of Rome. All the AIV (Assembly, Integration and Verification) cycle phases have highlighted challenges and advantages of equipping LED-based payloads on-board small satellites. Furthermore, the lessons learned from the satellite payload design and integration are important for a future wider implementation of LED boards on-board small satellites with different missions and form factors. This paper describes the LEDSAT design and capabilities, especially the subsystems development, assembly, functional and environmental qualification. The satellite mission objectives will be outlined in the introduction. The CubeSat architecture will be described with a report on the satellite assembly. The completed functional and environmental tests for the LEDs and at system-level will be reported, with focus on the LED-based payload features, testing levels and testing campaign results. Applicability of LED-based payloads to other concepts and form factors of nano- and micro-satellite platforms will be outlined, with focus on the generalized usage of LED payloads for small satellite platforms

Optimization and standardization of Light Emitting Diodes (LEDs) patterns for improved satellite tracking and monitorability

Installation of Light Emitting Diodes (LEDs) payloads on satellites for ground-based optical tracking can significantly improve the period of satellite tracking and the achievable tracking precision. The optical tracking of a satellite equipped with LEDs is extended from the sunlit region (when the ground-based telescope is in darkness and the satellite is in sunlight) to the whole eclipse phase, with a consequent improvement of the availability of optical measurements. The optimization of patterns for LED boards can introduce an improvement in the achievable measurement quality. If executing orthogonal patterns, such as Pseudo-Random-Number codes, the ground segment can discriminate satellites among a large cluster or identify the satellite faces pointing towards the observer for attitude reconstruction. To achieve a more precise orbit determination, alternated long and short flashes can contribute to the satellite identification and celestial coordinate identification. More specialized patterns can highlight the satellite functional status, especially for the execution of the satellite safe mode or to indicate that the satellite is facing specific issues, e.g. a component failure, excessive temperatures, currents or voltages on components and power lines, or to indicate that the satellite has entered its De-Commissioning mode. The improved tracking of the LEDs and the increased knowledge of the satellite functional status can contribute to Space Situational Awareness (SSA) and Space Traffic Management (STM). This will improve the sustainability of the LEO environment, especially if LEDs are adopted by a large number of satellites. From this perspective, the standardization of LED flashing sequences could further enhance the tracking and monitorability of spacecraft. The effectiveness of LED-based payloads is currently being tested by LEDSAT, a 1U CubeSat conceived by Sapienza University of Rome and University of Michigan, participating in the ESA Fly Your Satellite! and ASI IKUNS Programmes. The satellite is undergoing ambient testing at Sapienza and will be launched in 2021. During its orbital lifetime LEDSAT will test various patterns for verifying the aforementioned possibilities of the satellite. This paper deals with the optimization of the LED patterns for implementation and execution on satellite missions. Different study cases and LED functionalities will be described in the perspective of the near-future STM and SSA tasks. The actual LEDSAT patterns will be used as a case study for the paper, reporting the optimizations undertaken for producing the satellite flashing sequences. The paper will present the future perspectives for LED implementation on satellites and the possible standardization of LED patterns

Usage of light emitting diodes for small satellites tracking, early identification after launch and light-based communication

With the increasing number of cluster and mega-constellation launches, there is a urgent need for new spacecraft tracking techniques during all the mission phases, from in-orbit deployment to disposal. In this framework, the usage of Light Emitting Diodes (LEDs) on the spacecraft external surfaces can provide significant improvements to the small satellites early identification after launch in large clusters and for orbit and attitude determination. When applying the conventional RF-based identification to large cluster launches, strong uncertainties on the identity of small satellites of the same cluster remain even months after the launch. The implementation of LEDs can provide immediate recognition after deployment, if assigning specific flashing patterns to each satellite, as for aircraft recognition in trafficked airfields. The implementation of LEDs can also improve the precision achievable by optical orbit determination, making the satellites traceable throughout the eclipse phase. Any optical observatory can acquire the satellite LEDs flashes, thus with a great improvement of the spacecraft optical traceability and of the achieved precision in orbit and attitude determination. The LED-based orbit determination is focused on the celestial coordinates acquisition with respect to the background stellar field. Attitude reconstruction is possible when implementing LEDs, executing different flashing patterns, on different surfaces of the spacecraft. The improvement of orbit determination could help to augment the situational awareness for the small satellites population, as well as performing less and more accurate collision avoidance manoeuvres. The attitude determination can be applicable both for an improved trajectory estimation at low altitudes, when heavily influenced by drag force, and for planning future Active Debris Removal (ADR) missions. As example of LEDs in-orbit applications, the LEDSAT CubeSat, conceived by Sapienza University of Rome and by the University of Michigan, is equipping LEDs on all its external faces. The CubeSat is part of the Italian Space Agency (ASI) IKUNS Programme, it has been selected for the second edition of the ESA Fly Your Satellite! Programme, and it will be launched in 2020. This paper will describe the solutions offered by the implementation of LEDs on the external surfaces of small satellites for early recognition after deployment in large clusters and orbit and attitude determination. All the improvements offered by the LEDs in the framework of orbital debris mitigation, improved orbit determination and clusters early identification will be presented. Finally, an example of LED-based operations will be presented with an overview of the LEDSAT CubeSat mission

Lessons learned from the S5Lab hands-on student activities on the ledsat, greencube and WildTrackCube-SIMBA nanosatellites

Hands-on activities on University nano-satellites can be complementary to more theoretical education for engineering students at all stages of their academic curriculum. The development cycle of a nano-satellite, from design and paperwork to testing, launch and operations, allows the students to acquire practical skills and hands-on knowledge that will create the foundations for their professional career in bigger aerospace engineering projects. When coping with a simultaneous development of multiple nano-satellites, more advanced production concepts and study topics shall be explored, allowing students for access to a broader knowledge on manufacturing skills and hands-on projects management. The S5Lab (Sapienza Space Systems and Space Surveillance Laboratory) research team at Sapienza University of Rome is currently developing three CubeSats, to be launched between Q2 2020 and Q1 2021, involving students in space engineering at all academic levels in the development process. The three satellites present different mission objectives, form factors and payloads, but they share the same bus which has been already operated by the S5Lab team with the participation in the 1KUNS-PF CubeSat, launched in May 2018. LEDSAT (LED-based small SATellite) is a 1U CubeSat project conceived by S5Lab and University of Michigan equipping a Light-Emitting Diodes payload for ground-based optical observations. The project is participating in the ESA Fly Your Satellite! Programme and in the ASI IKUNS Programme. WildTrackCube-SIMBA (Wildlife Tracking CubeSat-System for Improved Monitoring of the Behavior of Animals) is a 1U CubeSat equipping spread spectrum modulation receivers for improving the tracking of wildlife in the Kenyan National Parks. The satellite, developed by Sapienza, University of Nairobi and Machakos University, has won the IAC 2019 Launch Opportunity offered by IAF and GK Launch Services. GREENCUBE is a 3U CubeSat developed by Sapienza, ENEA and University of Naples “Federico II”, with the support of ASI, that will test an autonomous laboratory for the cultivation of microgreens on-board a CubeSat platform. The satellite has been selected by ESA for a launch opportunity on-board the VEGA-C maiden launch. This paper presents the major lessons learned by the students participating in the three satellites project. After a brief description of the three satellites design, manufacturing and testing, the lessons learned related to the simultaneous development and testing of different satellites sharing the same bus will be provided. The paper will describe the activities with focus on the students involvement in the hands-on activities for completing testing and qualification for the mentioned international CubeSat projects

Development and testing of a LED-based optical data link for the LEDSAT CubeSat

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 matched to 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

From stratospheric experiments to CubeSat development: Lessons learned from the S5Lab participation into ESA hands-on educational programmes

The Sapienza Space Systems and Space Surveillance Laboratory (S5Lab) at Sapienza University of Rome offers hands-on projects opportunities, focused on space systems development, to students in aerospace engineering. Particular effort has been dedicated in the recent years, to enhance the laboratory students participation within the European Space Agency (ESA) hands-on educational Programmes. At the moment, S5Lab is one of the only laboratories in Europe to be simultaneously involved into two of these ESA programmes. In late 2018, a group of ten students, predominantly third-year BSc, has been selected for the REXUS/BEXUS Programme, managed by SNSA (Swedish National Space Agency), DLR (German Aerospace Center) and ESA, for designing, manufacturing, testing and launching their experiment, named TARDIS, on-board a BEXUS stratospheric balloon. Another group of students from S5Lab is participating since 2017 in the ESA Fly Your Satellite! Programme, addressed at offering launch opportunities to University students team willing to manufacture, test and launch their CubeSat. The laboratory is participating with LEDSAT, a 1-U CubeSat equipping Light Emitting Diodes (LEDs) on all the satellite external surfaces, which will be launched in 2020. The participation into these Educational Programmes is a great opportunity to extend and complement the education of students at all academic levels, improving their soft skills, practical experience on real flight hardware and teamwork capabilities. Furthermore, these Programmes schedules can fit into the students academic curricula and comply with the gained knowledge at different stages of their University years. In particular, the manufacturing of a stratospheric experiment is usually applicable to third-year BSc or first-year MSc, even without any previous experience in small hands-on projects. A second-year MSc student, along with PhD students, is involved into nanosatellites development and testing. Last but not least, the students have the possibility to practically access Space Agencies' technical reviews procedures in their education years, as significant preparation step for their involvement in future space projects. The acquired knowledge during these hands-on projects represents the robust fundamentals for the prosecution of the students' career after graduation, both in the academic or industrial framework. This paper describes the lessons learned from the involvement of students at all levels in ESA hands-on educational programmes. By using the two on-going projects as study cases, the paper will focus on the obtainable education improvements offered when complementing academic theoretical education with the hands-on projects activities. Furthermore, examples of educational return during specific experiences or events will be discussed