Evaluation of time difference of arrival (Tdoa) networks performance for launcher vehicles and spacecraft tracking

Time Difference of Arrival (TDOA) networks could support spacecraft orbit determination or near-space (launcher and suborbital) vehicle tracking for an increased number of satellite launches and space missions in the near future. The evaluation of the geometry of TDOA networks could involve the dilution of precision (DOP), but this parameter is related to a single position of the target, while the positioning accuracy of the network with targets in the whole celestial vault should be evaluated. The paper presents the derivation of the MDOP (minimum dilution of precision), a parameter that can be used for evaluating the performance of TDOA networks for spacecraft tracking and orbit determination. The MDOP trend with respect to distance, number of stations and target altitude is reported in the paper, as well as examples of applications for network performance evaluation or time precision requirement definitions. The results show how an increase in the baseline enables the inclusion of more impactive improvements on the MDOP and the mean error than an increase in the number of stations. The target altitude is demonstrated as noninfluential for the MDOP trend, making the networks uniformly applicable to lower altitude (launchers and suborbital vehicles) and higher altitude (Low and Medium Earth Orbits satellites) spacecraft

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

Remote airfields navigation and tower control through optical and radio-frequency data fusion

The civil aviation operations safety is enhanced by the Air Traffic Control (ATC). While en-route control is usually managed by centralized Area Control Centers (ACCs), that can operate without visual monitoring the controlled aircraft, in-situ visual surveillance on the aircraft position is often applied in terminal air applications, i.e. by Air Traffic Control Towers (ATCTs) in airports. However, the high manpower costs for operating ATCTs are often not justified by the low and discontinuous number of flights arriving and departing from remote or small airfields. Therefore, the vast majority of world's airports are Non-Towered Airports (NTAs), only offering procedures for take-off and landing, without the assistance of ATCT operators. The Remote and Virtual Tower (RVT) concept has led, in the last years, to the possibility of performing terminal air space surveillance without the physical presence of ATCT controllers at the airfield, but with a complex remote surveillance system aimed at providing situational awareness to operators located in a separate site. A further leap forward in ATCT coverage for NTAs could be represented by an Automated Virtual Control Tower, consisting in a surveillance infrastructure in charge of autonomously processing optical and Radio-Frequency data, in order to monitor the nearby aircraft correct position and speed, to communicate with the ATC and to provide navigational instructions to the pilots. The system takes advantage of an optical segment, addressed at determining the aircraft angular position, and of a Radio-Frequency sub-system, capable of ranging and measuring the approach speed of the target. Finally, an information segment will provide guidance to the vehicles through an automated mechanical voice radio channel, as for actual ATCT controllers. The surveillance and navigation system has been designed by considering up-to-date and low-cost technologies, such as motorized telescope stations, wide-field commercial cameras and Software-Defined Radios (SDRs), that could allow a significant cost reduction in the production and implementation. The applicable technologies are currently used, with high maturity, for space surveillance and space debris tracking, allowing their adaptation to the ATC field with reduced development costs. This paper will describe the functional definition and the design of an Automated Virtual Control Tower. In particular, the technologies adopted and the similarities between their utilization in the fields of space surveillance and aerial navigation and ATC will be outlined. Finally, the completed tests, the future perspectives and the possible applications to Unmanned Aerial Vehicles surveillance will be presented

Space hospital: How future space-based medical infrastructures could revolutionize tomorrow's health care system

After the first paying passengers on-board the International Space Station (ISS) between 2001 and 2009, a considerable number of space tourism mission concepts has risen, aiming at a large multiplicity of platforms, typically from already existing small size suborbital spaceplanes to future large-scale touristic space stations. On the other hand, many years of space-based research on biological systems has demonstrated how the space environment, and in particular micro-gravity, can introduce beneficial effects on humans for what concerns, as an example, cardiovascular and neoplastic pathologies. When considering the treatments for such diseases, microgravity and exposure of patients to the space environment could represent a visionary healthcare provision in the future space era where affordable, low-risk launch and space transportation systems will be granted and available to everyone. The healthcare space-based infrastructure would benefit from the advancements in space systems introduced by the touristic and commercial space outposts, but by specializing their mission for providing medical treatment to “patient astronauts”. In a far future scenario of an homogeneous, wide access to manned space infrastructures for the large majority of humanity, the patients could benefit from considering microgravity a treatment and a part of an international public medical infrastructure. As an example of the potential diseases to be addressed, microgravity can induce beneficial effects to patients experiencing cardiovascular diseases, such as heart failure, contributing with a pressure drop and a heart contractility improvement, while the microgravity-driven induction of a lower heart frequency can help patients suffering from atrial and ventricular fibrillation. In addition to cardiac diseases, neoplastic pathologies such as melanoma could benefit from being treated in microgravity, leading to a reduction of the neoplasm aggressivity and with a consequent increase of a therapeutic efficacy. Besides the user-end systems, represented by the space hospital station ECLSS (Environmental Control and Life Support Systems) for long-term permanence in space and by the systems devoted to actually treating patients, huge improvements in all fields of space engineering and manned space explorations shall be introduced. This paper presents a concept for a medical treatment “hospital” space station. After a description of the current trends for commercial and touristic large-scale spaceborne infrastructures concepts, the potential beneficiaries of microgravity treatments are outlined with the disease to be treated. Then, an outline of the space station subsystems and architecture is presented with a roadmap of the key technologies to be dramatically improved for the introduction of similar infrastructures

Distributed hybrid sensors architectures for launch vehicle avionics and future space transportation systems

Distributed architectures of hybrid sensors could greatly support the future launch vehicles navigation systems and avionics in the perspective of a significant increase of the space launches in the future years and decades. While the current architectures rely on high-TRL, costly, centralized sensors, similar performances could be reached by distributed networks of lower TRL, lower cost sensors. This paper introduces a concept for a hybrid network of sensors and will describe the prototypes and tests for several categories of implemented sensors

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

Vhf omnidirectional range (Vor) experimental positioning for stratospheric vehicles

The usage of aeronautical radio-frequency navigational aids can support the future stratospheric aviation as back-up positioning systems. Although GNSS has been extensively redundant in the last years of space operations, radio NavAids can still be supportive of navigation and tracking for novel mission profiles. As an example, in 2016, VHF Omnidirectional Range (VOR) has been proven to work well above its standard service volume limit on a stratospheric balloon flight with the STRATONAV experiment. While VOR provides the “radial” measurement, i.e., the angle between the Magnetic North and the line between the receiver and the transmitting ground station, the intersection of two or more radials at a time allows to perform ground track reconstruction for the vehicle to be tracked. This paper reports the results from the data re-processing from STRATONAV: the acquired radials have been intersected in order to achieve positioning. The radials interfacing method, the position calculation methodology, and the data acquisition strategies from STRATONAV are reported together with the data analysis results

Trajectory optimization for the Horyu-VI international lunar mission

The Horyu-VI nano-satellite is an international lunar mission with the purpose of studying the lunar horizon glow (LHG)—a still unclear phenomenon caused by electrostatically charged lunar dust particles. This study analyzes the mission trajectory with the hypothesis that it is launched as a secondary payload of the NASA ARTEMIS-II mission. In particular, the effect of the solar gravity gradient is studied; in fact, depending on the starting relative position of the Moon, the Earth, and the Sun, the solar gradient acts differently on the trajectory—changing it significantly. Therefore, the transfer and lunar capture problem is solved in several cases with the initial Sun–Earth–Moon angle as the key parameter. Furthermore, the inclination with respect to the Moon at capture is constrained to be equatorial. Finally, the problem of stabilization and circularization of the lunar orbit is addressed in a specific case, providing an estimate of the total propellant cost to reach the final orbit around the Moon

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

Italian approach to suborbital space transportation: From setup of harmonized framework to spaceport and ground segment evaluation for enabling operations in the Italian territory

Italy has increasing interest in Commercial Space Transportation and in particular in suborbital flights. A suborbital spaceflight system is an opportunity to involve the Italian industry in the development of new technologies, exploit opportunities of microgravity experimentation and pilots/astronauts training, as well as catalyse the national industry. The central position of Italy in the Mediterranean basin, the generically favourable climate condition, the touristic vocation resulting in hospitality at the highest level, pretty much allow year round suborbital operations and unique customer experience. Consequently, Italy is particularly suitable to host a Spaceport, even though the density of population has to be factored in as a key aspect, together with a proper environmental assessment. This paper outlines the basic Italian approach that, instead of focusing on the development of new Spaceport from scratch, evaluates the capabilities of existing airports and their possible upgrades to achieve the Spaceport license, when a proper regulatory frame will be established. Advances in the technical activities that are being conducted to assess various Italian sites of interest will be described, including trade off methodologies and ranking criteria. Different aspects will be considered, from the availability of civil and military airports, to the identification of the best location between coastline or inland sites but, first of all, in compliance to the safety requirements. Some specific Spaceport infrastructures and operational aspects will be described, along with their integration with the already existing ones. These include hangars, propellant storage facilities, ground support equipment, high and low airspace surrounding the airport area, ascent and descent corridors, as well as tracking telemetry station to support specific mission profiles in integrated fashion with the existing airport infrastructures and air traffic. The paper will also describe the approach to the definition of a harmonized cooperative regulatory framework, according to the Aviation Authority, that represents the basis to assess suborbital operations and allows the relevant missions execution. In this activity, basing upon an established Memorandum of Cooperation between FAA, ENAC and the Italian Space Agency, the existing FAA/AST regulatory work frame will be considered as reference benchmark and further tailored to the Italian case. Some considerations will also be developed relevant to initial challenges to be faced, by interested stakeholders, in starting commercial spaceflight initiatives as a new ground and emerging business opportunity