Home / Technology / AI & IT / Space threats require Space Based Sensors (SBS) to enhance Space Situational Awareness (SSA)

Space threats require Space Based Sensors (SBS) to enhance Space Situational Awareness (SSA)

There has been an exponential growth of space objects, including orbital debris that has increased the in-orbit collision risk. In the year 2019 alone, 385 smallsats were launched reaching a value close to 2900 in mid-2020 and still rapidly increasing. Moreover, taking into account all the applications filed by satellite operators to the relevant licensing authorities, more than 100,000 new spacecraft might be launched in orbit by 2030. And even if only 10% of these plans were realized, taking into account financial and market constraints, another 10,000 operational satellites could still be added to those currently in service,

 

In addition to polluting space, space junk poses risks for safely navigating spacecraft. In the year 2010 alone, space debris increased by over 75%, posing huge collision risks for spacecraft operating in the low earth atmosphere. NASA estimates there are 21,000 objects orbiting Earth that are larger than 10 cm, 500,000 between 1 and 10 cm, and more than 100 million that are less than 1 cm.

 

The large number of debris around Earth is a risk for the safety of operational satellites. Orbital debris of even 1cm size, traveling at an average speed of about 11 km/sec can cause partial or complete destruction of the satellite.  Any of the debris objects can cause harm to an operational spacecraft, where a collision with a 10-cm object could entail a catastrophic fragmentation, a 1-cm object will most likely disable a spacecraft and penetrate the satellite shields, and a 1-mm object could destroy sub-systems onboard a spacecraft.

 

Space situational awareness (SSA)

Space situational awareness (SSA) is the foundational element of space security, and it entails keeping track of all natural and artificial space objects, energy and particle fluxes and understanding how the space picture is changing over time. SSA is a system of systems dealing with space surveillance, space weather and NEOs.

 

The overall objective of space situational awareness (SSA) is to identify the location of every object orbiting the Earth, why it is there, what it is doing, and to predict what it will be doing in the future. Its aim is to track and understand what exactly is in orbit from either space or from the ground. This knowledge enables the management of space assets and the exercise of a level of control over the space environment.

 

SSA holds crucial importance for space safety owing to continuous monitoring of the presence of natural or man-made hazards like debris. SSA services document real-time information of space components while alerting satellite operators of potential accidents. It carries out Conjunction Assessment or identifying objects that can potentially hit satellites and generating the necessary warning in a suitable timeframe. In addition, SSA tracks space bodies that may interfere with a particular orbit while predicting their positions in advance for preventing collisions with satellites. The owner agency/country may then perform Collision Avoidance by maneuvering the satellite-based on the probability of collision and cost benefit analysis.

 

Militarization of Space and SSA

Space is also becoming increasingly militarized many countries are developing killer microsatellites and other antisatellite weapons (ASAT) that could be used to damage other satellites. There is also thrust on space robots that can perform the repair of satellites and could provide complete awareness of the adversary’s activities in space so that one can take counteractions. They could also be employed to deorbit adversary’s satellites.

 

There is an international effort to regulate debris and space warfare regulations. UK’s Exeter Law School has joined a consortium of founding institutions, including McGill University and the University of Adelaide, for the development of rules for space warfare. The Manual on International Law Applicable to Military Uses of Outer Space (MILAMOS) will also set out rules for war crimes in space and for the development of space-based weaponry, including lasers and missile defense systems. The manual will also look into the issue of who will be responsible for cleaning up space debris caused by military action.

 

However, militaries are going ahead to protect their space assets and formed space commands and space forces. The US Strategic Command defines SSA as “The requisite current and predictive knowledge of space events, threats, activities, conditions and space system (space, ground, link) status capabilities, constraints and employment — to current and future, friendly and hostile– to enable commanders, decision-makers, planners and operators to gain and maintain space superiority across the spectrum of conflict.”

 

SSA encompasses surveillance of all space objects, activities, and terrestrial support systems (satellites & debris), more detailed reconnaissance of specific space objects assets (mission identification, capabilities, vulnerabilities, etc.), discerning the intent of others who operate in space, knowing the status of our own forces in real-time, and analysis of the space environment and its effects (solar storms, meteor showers, etc.).

 

SSA is segregated into three service segments including space surveillance & tracking of various objects within the Earth’s orbit, space weather, and near-Earth objects. The near-Earth space extends to the Earth-radius of more than 100,000km to cover all man-made objects in the orbit. Space Situational Awareness (SSA)  concept revolves around monitoring and understanding the near-Earth environment, encompassing existing and predictive knowledge regarding natural and man-made objects within the Earth’s orbit. The ability holds a pivotal role in understanding space conditions, events, activities, threats, natural or man-made debris, and intentional or unintentional attacks on space assets such as satellites. It encompasses Signal Intelligence (SIGINT) to include Communication Intelligence (COMINT) and Electronic Intelligence (ELINT)) of adversary’s space assets

 

It also entails determining the various threats to space assets such as the growing number of debris, space weather, meteorites, orbital collisions and intentional attacks including directed energy attack, direct ascent and orbital ASAT, HAND events, etc. It also includes observation of adversary’s activities in space to include undeclared satellite launches, parasitic satellites, orbital parameters, in-orbit intentional maneuvers during conflict scenarios, malicious tests, experiments, space robotic activities and utilization of suspicious dormant satellites.

 

It involves the collection, processing, fusion, and assessment of data and information from many different sources and the dissemination of information to decision-makers and various users. Comprehensive SSA requires a networked system of radars and electro-optical sensors. Low altitude debris is usually observed by radar ground stations while high altitude debris is observed by optical ground stations. Bistatic, multistatic, and phased array radars are widely used. The optical telescopes have some disadvantages as they can only track objects that are illuminated while the telescopes are in darkness. Recently the trend is to use space-based sensors to provide timely detection, collection, identification, and tracking of man-made space objects from deep space to LEO orbits.

 

The information assists planners, operators, decision-makers, and commanders in gaining and maintaining space superiority through conflicts while thwarting attacks and potential collisions. SSA encompasses knowledge pertaining the space and ground-based capabilities. SSA covers space traffic management and space safety programs that include services intended to assist satellite operators in preventing physical or operational conflicts.

 

Recent events such as moon race and asteroid mining have made the cislunar space, the entire space extending beyond Earth to the moon next “high ground” a position of advantage or superiority that needs to be monitored and controlled.  The cis-lunar domain is defined as that area of deep space under the gravitational influence of the earth-moon system. This includes a set of earth-centered orbital locations in low earth orbit (LEO), geosynchronous earth orbit (GEO), highly elliptical and high earth orbits (HEO), earth-moon libration or “Lagrange” points (E-ML1 through E-ML5, and in particular, E-ML1 and E-ML2), and low lunar orbit (LLO). Now  with space competition and future militarization  has reached to Cislunar Space, militaries are extending the Space situational awareness (SSA) to this entire space between earth and moon.

 

The Space Based Space Surveillance (SBSS) system is a planned United States Space Force constellation of satellites and supporting ground infrastructure that will improve the ability of the United States Department of Defense (DoD) to detect and track space objects in orbit around the Earth. The primary SBSS contractor, Boeing, characterizes some orbiting space objects as, “Potential future threats to the United States’ space assets”.

 

The SBSS development work is being conducted in coordination with the Space Situational Awareness Group in the Space Superiority Systems Wing of the Space and Missile Systems Center. The commander of the Space Situational Awareness Group believes the SBSS satellite operations center, “Will transform Space Situational Awareness by providing a gateway to a responsive, taskable sensor. This capability is key to enabling the event-driven operations concept of the future”

 

The Space-Based Surveillance System (SBSS) has higher capabilities of data acquisition, identification, and tracking on space debris. Besides, the Space-Based Infrared System (SBIRS) constellation contains four satellites and infrared payloads in high orbits. 24 satellites are distributed in the Space Tracking and Surveillance System (STSS), further extending the coverage of the SBIRS. The STSS has stronger capabilities of orbital tracking and maneuver detection in complicated situations. Furthermore, the James Webb Space Telescope (JWST) integrates a telescope with near- and midinfrared cameras for ultra-far image acquisition and target monitoring.

 

Comprehensive SSA requires a networked system of radars and electro-optical sensors. Low altitude debris is usually observed by radar ground stations while high altitude debris is observed by optical ground stations. Bistatic, multistatic and phased array radars are widely used. The optical telescopes have some disadvantages like they can only track objects that are illuminated while the telescopes are in darkness. Almost without exception, objects are extremely difficult to monitor as they pass between the earth and the sun. Daylight observations, in general, pose a significant challenge for groundbased optical sensors. Space-based sensors can provide observations much closer to the sun, but all space-based sensors are still limited when the target is positioned between the sensor and the sun.

 

When considering only ground-based optical telescopes, the trade space ranges from large networks of small telescopes to small networks (or single copies) of large telescopes. The Russian International Scientific Optical Network (ISON) network represents an excellent example of a large network of what are mostly smaller telescopes. ISON has a very interesting mix of telescopes and optical designs, but most of their assets are in the 50 cm and smaller aperture class. What makes ISON interesting is that they have observation locations distributed
around the globe. One obvious weakness in their network is the limited coverage over the central to eastern Pacific Ocean.

 

Sensor suitability

Radar are very efficient and effective for less than 700 kms, however they can cover the full LEO region up to 2000 km altitude.  Below 1000 km altitude is very difficult to observe satellites / debris with ground optical stations. Above 1000 kms right upto GEO and HEO telescopes are being used.

 

The ground-based telescopes can detect GEO debris down to 10 cm in size, ground-based radars can detect LEO debris down to a few mm in size, and in-situ impact detectors can sense objects down to a few micrometres in size.

 

Space-based sensors

An emerging solution is to put radars and telescopes into orbit. Space Based Sensors (SBS) consist of a space segment, primarily consisting of constellation of radar satellites, and a ground segment including networked ground stations to control the satellites. SBS having the ability to track space objects from space, offer advantages over ground based systems since they are not affected by weather or atmosphere. This leads to improved sensor sensitivity and allows for the detection of faint objects including microsatellites and space debris. This in turn increases the probablity of collision event detection by improving the timeliness of detection for maneuver. Space based sensors will provide timely detection, collection, identification and tracking of man-made space objects from deep space to low-earth orbits.

 

For debris observations radar and optical stations are active, but also in situ measurements (e.g. optical observations from satellites) are efficient. Low altitude debris are usually observed by radar ground stations while high altitude debris are observed by optical ground stations.

 

Technologies

In a review paper recently published in Space: Science & Technology, Shuang Li from College of Astronautics, Nanjing University of Aeronautics and Astronautics, reviewed and analyzed research advancements in key technologies for space situational awareness, indicated the future directions of the key technologies, and emphasized the research prospects of multiagent and synergetic constellation technologies for future situational awareness, aiming to provide references for space-based situational awareness to realize space sustainability.

 

The Space-Based Surveillance System (SBSS) has higher capabilities of data acquisition, identification, and tracking on space debris. Besides, the Space-Based Infrared System (SBIRS) constellation contains four satellites and infrared payloads in high orbits. 24 satellites are distributed in the Space Tracking and Surveillance System (STSS), further extending the coverage of the SBIRS. The STSS has stronger capabilities of orbital tracking and maneuver detection in complicated situations. Furthermore, the James Webb Space Telescope (JWST) integrates a telescope with near- and midinfrared cameras for ultra-far image acquisition and target monitoring.

 

Low weight, precise, and broad observation are the significant advantages of the JWST. Following the United States, the European Union emphatically strengthens knowledge and early warning capabilities in the SSA, establishing the dual-mode detection system. Russia has advanced in debris tracking, early warning, and environmental monitoring, creating the Tree Canopy system. Overall, advanced space-based situational awareness systems constantly emerge in the United States and other countries.

Nevertheless, given the large power consumption of space-based devices and uncoordinated data processing methods, the current SSA systems are restricted by the number of detectors, detection capabilities, and location distribution, thus only concurrently possessing certain functions. In this case, the systems cannot realize accurate awareness of all space targets in real time, but only for task requirements. Therefore, the comprehensive situational awareness capability of the space-based SSA becomes a necessity.

Afterwards, the author reviewed and discussed characteristics of optical sensors and processing technologies, which plays a role of accurately acquiring the data of space targets. With the advantages of high sensitivity, rapid transmission, and strong anti-interference, optical sensors applied to the space-based situational awareness as the collectors of object data. As for the data processing, it represents the technology of processing and analyzing large spatial data, converting them into the key information of the targets. However, the increasing risky targets raise the requirements for processing massive data, and it also affects the accuracy and timeliness of situational awareness. Thus, data storage, filtering, and fusion are reviewed and discussed in order.

Then, the author presented and analyzed the technologies for target recognition. Firstly, object identification was the core section of target recognition in the space-based situational awareness. Laser radars had been dominant in object identification as sensors, while machine vision and ANN were highly explored as advanced identification algorithms. Secondly, parameter estimation, as an essential condition to acquire the accurate information of space objects, parameter estimation needs to be performed in the SSA after object identification.

Various parameter estimation technologies for space objects have been exploited so far. Photometric technologies had been more maturely developed, while optimal estimation technologies produced advanced algorithms in artificial intelligence. Thirdly, intention recognition was the process of the intention awareness and behavior inference of space objects through observed actions and effects on the situations, which were essential to improve the quality of early warning information and reduce the number of warnings, thus guaranteeing security. However, compared with the mature object identification technologies, intention recognition needs deeper research.

Furthermore, the author discussed the development of the target monitoring technology. In the steady period, target monitoring technologies emphasized orbital prediction, tracking, and maneuver detection, while early warning and collision avoidance dominated the risky period.

(1) Orbital prediction of space targets, as the foundation of collision warning mechanism and satellite measurement and control technology, had become a research hotspot in the SSA field. Nevertheless, the limitations of current orbital prediction methods are the low accuracy of target dynamic models, sensor measurements, and orbital determination. For instance, atmosphere drag models generated large uncertainty for the orbital prediction in low-earth orbits. Thus, the author c the orbital prediction method based on Analytical Prediction Models and Machine Learning Algorithms.

(2) Orbital determination and tracking were both important sections of target monitoring. They had been closely connected, where orbital determination was the premise and orbital tracking was the executing purpose. Nevertheless, only the line-of-sight observation from the optical sensors to the targets is available without range information. Considering that the assumptions are all satisfied, including linear dynamics, coasting flight, single sensor, and the sensor fixed in the center of mass, the well-known angles-only orbital determination need solutions to the lack of range observability. Thus, the author discussed the developments of Angles-Only Determination Algorithms and a series of Improved Filter Tracking Algorithms.

(3) Detecting the maneuvers of space objects with retrievable historical data has become an essential mission in the SSA, especially for active objects without available operational information. Real-time detection is required to react adequately to any spacecraft anomalies and possible threats to nearby space assets. The active objects’ maneuvers are detected, recording the patterns and trends in maneuver types and magnitudes. Thus, the author discussed the developments of the Sensitive Parameter Characterization Algorithms and the Joint Measurement and Processing Algorithms.

(4) Monitoring early warning technologies possessed significant advantages of wide monitoring ranges, diverse tracking means, and high warning accuracy. Therefore, early warning was promising as the mainstream direction and the future trends focus on the Space-based asteroid warning projects and the improvements of the timeliness, accuracy, and confidence.

(5) After receiving the early warning on space debris and asteroids, a vital part of the SSA was to predict and avoid satellite collisions to protect space assets. The research on collision avoidance technologies focused on collision prediction and maneuver strategies. The core of collision prediction was probability computation algorithms, while avoidance algorithms were the essence of strategy design. Thus, the author discussed the developments of the Collision Probability Computation Algorithms and the Maneuvering Avoidance Algorithms and Strategies.

Finally, the author summarized the four key conclusions and insights for the essential technologies:

(1) For the overall advance of the space-based SSA, full-dimensional and multilevel domain awareness and surveillance systems are activated. Space surveillance systems are expected to have larger coverage, higher accuracy, and shorter data updating. For system devices, the working frequency will be changed from the low to the high band. The fixed structures tend to be flexible, and a lightweight design is implemented. Furthermore, the working mechanism is evolved to the distributed and full digital array.

(2) As an essential part of the SSA, perfect target feature databases must be established to provide more prior information for accurate and rapid situational awareness. Relying on artificial intelligence and cloud computing, the development strategies of space big data should be formulated to promote new-generation information technologies. Furthermore, efficient space traffic management and commercial services are expected for higher sustainability and self-protection capability of space assets.

(3) The current intelligent algorithms for target recognition and monitoring mainly adopt small sample learning. Most models possess slow inference after deployment and cannot meet real-time requirements. Next, the current algorithms have insufficient generalization. Therefore, designing the classifiers of different categories in homologous sample space is necessary. The learning transfers of heterogeneous data should be studied to improve the model adaptability to the target intrinsic feature changes in small samples.

(4) Multiagent and synergetic constellation awareness overcome the limitations of payload allocation. Embodied intelligence and deep, general, and evolutionary learning can be applied to multiagent systems and constellations for realistic multimodal interaction, contributing to the intelligent evolution of situational awareness systems.

 

More information: Beichao Wang et al, Research Advancements in Key Technologies for Space-Based Situational Awareness, Space: Science & Technology (2022). DOI: 10.34133/2022/9802793

 

References and Resources also include:

https://phys.org/news/2022-07-scientist-key-technologies-space-based-situational.html

About Rajesh Uppal

Check Also

Navigating the Cosmos: Space Communication Protocols

Introduction In the vast expanse of space, where distances are measured in light-years, and obstacles …

error: Content is protected !!