# Safeguarding the Final Frontier: Optical Sensors for Persistent Space Domain Awareness

August 19, 2024

### Current State of Space Domain Awareness

There were less than 1,000 active spacecraft in orbit in 2010; there are over 8,000 active spacecraft in orbit today; and projections point upwards of 100,000 active spacecraft in orbit by 2030. In this period of exponential growth, space domain awareness (SDA) will remain the foundation for keeping these spacecraft and humanity’s near-Earth space environment safe and sustainable. But the SDA problem set is growing in tandem: unexpected payload separations and maneuvers threaten situational awareness in low Earth orbit (LEO), rendezvous and proximity operations (RPOs) demand vigilance in geostationary Earth orbit (GEO), and interest in new horizons is picking up in cislunar or “beyond GEO” (xGEO) orbits.

Ground-based optical sensors like the Slingshot Global Sensor Network bring a unique set of capabilities and insights to the space/satellite operator’s toolbelt, augment existing modalities, and help bring clarity to an increasingly complex orbital operating environment.

### Understanding Optical Sensor Systems

Ground-based electro-optical (EO) sensors collect astrometric and photometric data by detecting and measuring light signals reflected by objects in space. The Slingshot Global Sensor Network is a collection of over 150 optical sensors at 20+ global sites (with more coming online this year) that provide 24/7 tracking and monitoring of space objects from LEO to GEO and beyond.

Slingshot’s network consists of multiple proprietary optical sensor types including both taskable gimbaled telescopes and persistent staring arrays—all of which provide unique capabilities and work together to create a network that provides persistent day/night satellite tracking. These sensors produce high-accuracy optical measurements (at single-digit to sub-arcsecond astrometric accuracies) which, when processed through Slingshot’s proprietary software, enable industry-leading uncorrelated track (UCT) resolution, orbit determination (OD), and maneuver detection (MD).

_FoV = Field of View_

Specifically, Slingshot’s Tasking, Collection, Processing, Exploitation, and Dissemination (TCPED) pipeline turns this network of telescopes into a set of priority-scheduled and persistent data collectors – producing low-latency optical observations and actionable insights for satellite operators and space agencies.

#### Tasking

Sensor optimization algorithms use tracking prioritization inputs from Slingshot’s orbital analysts and customers to task each telescope in the Slingshot Global Sensor Network – ensuring that the network is appropriately scheduled to satisfy the customers’ varied mission needs and use cases. On-demand tasking requests from our customers are seamlessly integrated with automated sensor scheduling.

#### Collection

On-site servers autonomously monitor weather conditions, control roof/dome enclosures, and execute tasking through complex interactions with sensor hardware. High-accuracy pointing models accurately steer gimbaled telescopes to ‘rate-track’ satellites even at the lowest LEO altitudes. Visible, near-infrared, and shortwave infrared sensors collect sequences of time-tagged high data-rate images at exposure cadences varying from less than 0.1Hz to above 100Hz.

#### Processing

Patented, automated image processing algorithms reduce high-data-rate imagery streams into low-data-rate detections with line-of-sight and brightness measurements. These measurements are then calibrated against the latest star catalogs to produce high-accuracy astrometric and photometric observations.

Streams of observations from each sensor are grouped into “sensor tracks.” Slingshot’s Multiple Frame Assignment Space Tracker (MFAST) compares these sensor tracks with Slingshot’s existing orbit state estimate database and either correlates and extends an existing orbit state or, when enough data is available, identifies a new object through initial orbit determination (IOD).

#### Exploitation

Once the raw data has been calibrated, correlated (associated to known objects), and fused together to form updated orbital states, Slingshot’s indications and warning (I&W) data analytics components automatically produce alerts against maneuver detections, photometric change detections, conjunction reports, reachability analytics for assessing potential on-orbit threats, and other critical insights.

#### Dissemination

Slingshot’s data products are disseminated in minutes from collection for use by government agencies and commercial operators servicing a range of missions. Space operations involve the integration of numerous systems — both terrestrial and spaceborne, civilian and military, domestic and international — and the ability to share and use data across these systems is key to our customers' success.

### Overcoming Traditional Optical Tracking Challenges

#### LEO Tracking at Scale

Slingshot's sensors are tracking high-priority objects in Low Earth Orbit (LEO), but the need for large-scale LEO tracking is growing alongside the LEO population. As such, Slingshot has developed the first uncued commercial optical fence that can simultaneously detect and track all transiting LEO objects of cubesat size or larger. Unlike gimbaled optical systems and commercial radars, each optical fence system persistently monitors the entire horizon. This scalable system enables a two-tiered approach to LEO space surveillance:

1. Slingshot’s optical fence systems track the majority of LEO payloads in a completely uncued fashion.
2. Slingshot’s gimbaled telescope systems monitor high-priority satellites, detecting smaller objects and collecting more information on each satellite pass to further increase accuracy.

Learn more about our LEO-focused Slingshot Global Sensor Network expansion here.

#### Daytime Observation

Daylight-capable optical systems provide, on average, 400% more observable LEO passes than night-only equivalents. This improvement to observation frequency enhances each daytime-equipped sensor's value, maintaining custody of objects with more regular observations and cataloging.

Slingshot’s patented daytime optical capability provides a passive EO option for tracking LEO objects in heavily populated sun-synchronous orbits (SSO). Nighttime-only optical systems can only monitor LEO near dawn and dusk when satellites are still sunlit, which is limited. In contrast, Slingshot’s daytime-capable systems can regularly observe satellites in these SSO configurations.

#### Weather-Related Outages

Slingshot’s 150+ sensors at 20+ sites globally create a resilient, distributed network that mitigates weather outages and provides redundant observation opportunities. Each site is chosen following an analysis of historical weather patterns to maximize network viewing regularity. When local weather outages occur, Slingshot’s optimization software reallocates tasking across the network.

### Advantages of Slingshot’s Global Sensor Network

#### Improved Custody Through High Revisit Rates

High revisit rates are core to space domain awareness and represent a critical component in space object custody. The Slingshot Global Sensor Network combines technical attributes to create a mesh network providing superior revisit rates compared to other sensing modalities:

1. **Distributed Global Network:** 20+ strategically chosen global sites increase total observation opportunities.
2. **Patented Daytime Observation Capabilities:** Daytime sensors allow for 5x the number of observation opportunities compared to night-only systems.
3. **Multiple Sensor Types:** The combination of gimbaled telescopes and ultra-wide-field-of-view staring arrays improves overall revisit rates.

For more details on how Slingshot benchmarks its revisit rates, email info@slingshot.space.

#### Superior LEO State Estimate Accuracy Through ‘Dirt-to-Dirt’ Tracking

Gimbaled telescope systems allow Slingshot to track a given satellite from horizon to horizon, improving orbital state accuracy. The majority of LEO satellite passes exceed 1-2 minutes in duration. Slingshot’s MFAST software uses these observations to generate precise orbital state estimates.

#### Actionable Insights Through Photometric Observations

Photometric observations are produced by optical sensors to detect changes in satellite behavior or to characterize aspects of a satellite’s structure. Slingshot has developed a proprietary AI/ML-based photometry prediction model that helps in rapid identification of on-orbit anomalies.

#### Multi-Regime Tracking

Slingshot’s multiple optical sensor types work together to provide coverage from LEO to xGEO, allowing tracking regardless of orbital regime. If urgent need arises for more data in any of these orbits, Slingshot can rapidly reallocate resources as needed.

### Ease of Deployment and Network Resiliency

Passive EO sensors require fewer resources to deploy compared to active radar systems. This low power requirement allows for rapid development of large-scale, distributed optical networks, resulting in over 500 million vetted observations used operationally by both government and commercial entities around the globe.

### Autonomous and Passive Optical Detection Capabilities

The passive optical measurements derived from Slingshot's global autonomous network provide resilience against non-cooperative satellites, eliminating the possibility of them evading sensing opportunities.

### Slingshot’s SDA Solutions

Slingshot Vantage is the world’s only day and night LEO-to-GEO optical tracking and monitoring service, distributing millions of observations per month to government and commercial customers for mission-critical insights.

Email info@slingshot.space to learn more about Slingshot’s SDA capabilities.