A led-based technology to improve the orbit determination of LEO satellite

The tracking of LEO objects, by means of large field of view (FOV) optical telescopes, is very challenging. Generally, optical tracking is only possible when the LEO satellite is in sunlight and the ground station is in darkness. This limits the tracking availability to morning and evening twilight for maximum five minutes at a pass. At worldwide level, several activities and studies are currently under development in order to improve the space surveillance capabilities. To this aim, Sapienza - University of Rome, together with the Astronomy Department of University of Michigan, are collaborating in the framework of the LEDSAT (LED-based SATellite) project. A LEO 1U CubeSat, equipped with LEDs (Light Emitting Diodes) is used as calibration target for optical observations for tracking the CubeSat. Through active illumination on the nanosatellite, the possibility to observe LEDSAT, by using ground-based telescopes, will increase since direct Sun illumination is no longer needed. The payload will flash with different patterns, on the basis of an accurate timing generated on-board. In this way, high timing precision on the ground-based system is not necessary. Thus, very simple and currently operating optical telescopes can be used for tracking, i.e. those in the amateur astronomy community. This paper describes the LEDSAT concept and the related science case. Moreover, the detectable LED-based payload configuration and the studies performed on the orbit determination feasibility are presented. In particular, the detectability is validated by Signal to Noise Ratio and Apparent Magnitude analyses. In addition, simulations of a tumbling LEDSAT with different flash patterns are shown. The reliability of the orbit determination is demonstrated by a batch filter. Furthermore, Monte Carlo runs show the achievable accuracies on the basis of different frequencies measurements and instruments precisions. Moreover, the architecture of the LEDSAT ground segment is outlined, with particular emphasis on the optical Ground Stations Network, which includes six observatories

LEDSAT: In-orbit demonstration mission for LED-based cluster launch early identification and improved LEO surveillance

The increasing number of small satellite cluster launches leads to a greater risk of confusion and collision soon after their deployment in orbit. In particular, the possibility to identify each CubeSat and to monitor their trajectories with passive optical methods could allow mitigating the possibilities of impacts among them. Thus, several researches in this field are currently on-going to improve the capabilities in space surveillance for satellite early identification. To this purpose, the LED-based small SATellite (LEDSAT) mission aims at testing the performances of a technology based on Light Emitting Diodes (LEDs) on-board the spacecraft able to autonomously illuminate the spacecraft and to allow ground-based telescopes to observe the CubeSat for a longer time window when the station is in darkness. The idea has been conceived and designed by an Italian student team from University of Rome “La Sapienza”, in cooperation with the Astronomy Department of University of Michigan (Unites States). This project is part of the educational activity carried on at the Sapienza Space Systems and Space Surveillance Laboratory (S5Lab) and LEDSAT has been selected for the 2ndedition of the ESA Fly Your Satellite (FYS) programme 2017. The on-board payload will operate in orbit by flashing with different patterns in order to simplify the possibility to distinguish different objects by minimizing the confusion between them. In addition, the on-board payload will allow testing different LED-based techniques for the nanosatellite tracking, attitude reconstruction and for the communication with ground in case of the Telemetry, Tracking, and Command (TT&C) subsystem failure. The design and the main features of this CubeSat have been defined to allow its detection by analysing the optical measurements collected during night-time by the observatories involved in the project. In particular, the optical network is composed of six observatories located at medium and equatorial latitudes. The LEDSAT mission willing to explore new and promising techniques conceived for gathering important information about the status of orbiting objects in Low Earth Orbit (LEO). Through active illumination on the nanosatellite, it will be possible to increase the possibilities for observing it by using the available ground-based telescopes without the need of direct sun illumination. The paper outlines the LEDSAT mission and scientific background, by offering a complete overview about the CubeSat design and the system architecture

Improved Orbit Determination of LEO CubeSats: Project LEDsat

Project LEDsat is an international project (USA, Italy, and Canada) designed to improve the identification and orbit determination of CubeSats in low Earth orbit (LEO). The goal is to fly CubeSats with multiple methods of measuring positions on the same spacecraft: GPS, optical tracking, satellite laser ranging (SLR), and radio tracking. These satellites will be equipped with light emitting diodes (LEDs) for optical tracking while the satellite is in Earth shadow. It will be possible to compare the orbits determined from different methods to examine the systematic and random errors associated with each method. Furthermore, if each LEDsat has a different flash pattern, then it will be possible to distinguish closely spaced satellites shortly after deployment. The Sapienza University of Rome 3U CubeSat URSA MAIOR with LEDs and retro-reflectors was launched in June 2017 and is working on orbit. Sapienza has designed a 1U CubeSat follow-on mission dedicated to LED tracking, which was selected for possible launch in 2018 in the European Space Agency's (ESA) 'Fly Your Satellite' program. The University of Michigan is designing a 3U version with LEDs, GPS receiver, SLR, and radio tracking. The Royal Military College of Canada (RMC) is leading a Canadian effort for a LEDsat mission as well. All three organizations have a program of testing LEDs for space use to predict the effects of the LEO space environment

Differences in the performance of NK1R−/− (‘knockout’) and wildtype mice in the 5‑Choice Continuous Performance Test

Mice lacking functional NK1 (substance P‑preferring) receptors typically display excessive inattentiveness (omission errors) and impulsivity (premature responses) when compared with wildtypes in the 5‑Choice Serial Reaction‑Time Test (5‑CSRTT). These abnormal behaviours are analogous to those seen in humans suffering from Attention Deficit Hyperactivity Disorder (ADHD). Here we used the 5‑Choice Continuous‑Performance Test (5C‑CPT) to ascertain whether NK1R-/- mice also display excessive false alarms (an inappropriate response to a 'no-go' signal), which is another form of impulsive behaviour. NK1R-/- mice completed more trials than wildtypes, confirming their ability to learn and carry out the task. At the start of Stage 1 of training, but not subsequently, they also scored more premature responses than wildtypes. When the mice were tested for the first time, neither false alarms nor premature responses was higher in NK1R-/- mice than wildtypes but, as in the 5‑CSRTT, the latter behaviour was strongly dependent on time of day. NK1R-/- mice expressed excessive perseveration during all stages of the 5C‑CPT. This behaviour is thought to reflect compulsive checking, which is common in ADHD patients. These findings point to differences in the 5‑CSRTT and 5C‑CPT protocols that could be important for distinguishing why the cognitive performance and response control of NK1R-/- mice differs from their wildtypes. The results further lead to the prediction that ADHD patients with polymorphism of the TACR1 gene (the human equivalent of Nk1r) would express more perseveration, but not false alarms, in Continuous Performance Tests when compared with other groups of subjects