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ORS-5 (Operationally Responsive Space-5) / SensorSat

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The USAF (U.S. Air Force) officials have approved the ORS-5 bridging mission for launch in 2017 to monitor satellite traffic in geosynchronous orbit, tasking the MIT/LL (Massachusetts Institute of Technology /Lincoln Laboratory) to design and build a small space surveillance satellite. The ORS-5 mission, also known as SensorSat, is managed under the auspices of the USAF /ORSO (Operationally Responsive Space Office) based at Kirtland Air Force Base, N.M. 1) 2)

The Air Force's space surveillance network incorporates data from ground-based radars, SBSS (Space-Based Surveillance System) and other assets to keep tabs on more than 23,000 objects in orbit. The ORS-5 program will demonstrate a low-cost small satellite launch capability and aspects of autonomous operations via the existing Multi-Mission Space Operations Center ground architecture.

The overall objective of ORS-5 is to continue the SBSS satellite program’s mission to detect, track, and identify objects in deep space. These capabilities are needed to give satellite operators actionable knowledge and the ability to leverage U.S. and allied space capabilities to protect space assets and counter any potential hostile space activities. The ORS-5 mission is to answer a JFC (Joint Force Commander) need for SSA (Space Situational Awareness) of the geosynchronous (GEO) belt. The goal of the ORS-5 program is to demonstrate technologies that could prove "good enough" for geosynchronous SSA, create risk reduction opportunities to a future program of record, and develop and demonstrate ORS enablers and principles. 3)

In addition, the ORS-5 mission will act as a pathfinder for technologies to be used in a follow-on to the current SBSS-1 (Space Based Space Surveillance-1) satellite. ORS-5 provides risk reduction for cutting-edge technologies to be transitioned to the SBSS Follow-On program. ORSO will execute a technology transfer strategy, seeking opportunities for early industry involvement through requests for information and a near-term industry day.

The ORS-5 approach combines a streamlined commercial launch acquisition strategy, combined with a tailored systems architecting and mission assurance process for faster development outcomes in both ground and space segments. The ORS-5 mission is an “operational demonstration” that will provide continuous observation of the geosynchronous earth orbit (GEO) belt for the purposes of SSA. Highly unique to the mission is use of low-earth orbit, equatorial small satellite viewing of the GEO belt with a flight geometry and sensor arrangement that allows uninterrupted observations throughout its nominal 104 minute synodic orbit. 4) 5)


The ORS-5 integrated space vehicle is being designed, built, integrated and tested by MIT Lincoln Laboratory (MIT/LL). Lincoln’s history of developing visible CCD (Charge Coupled Device) sensors with high sensitivity was the primary driver for the award as well as the “urgent need” nature of the program. The vehicle design is a highly integrated package with a mass of ~140 kg and a length of 1.5 meters, whereby vehicle components and actuators are placed optimally around the stray light baffle, lens assembly, camera system that comprise the vehicles sensor. The most highly unique attribute of SensorSat is the combined use of the TDI (Time Delay Integration) technique in the sensor’s camera system and a flight geometry, that when combined, allow a continuous imaging and readout of the sensor for non-stop imaging of the GEO belt.

The space vehicle components are all commercial space vendor supplied except for the sensor’s CEB (Camera Electronics Board ) which is solely Lincoln Laboratory designed and built. MIT/LL designed all spacecraft bus structural panels, sensor optics, stray light baffle, CCD mount/camera assembly and camera radiator assembly. The EDU (Engineering Development Unit) components were either built or acquired for every space vehicle component and the EDU space vehicle is key to Lincoln’s functional, performance and environmental stress screening risk reduction ahead of final flight vehicle build and test.

SCD (System Capability Demonstrations): Key attributes applied to the ORS-5 program are the use of SCDs, “just in time” development of engineering drawings and assembly/test procedures and the high use of EDU vehicle components. Identified as part of the acquisition strategy, SCDs are part of developing the program’s functional architecture and planned as risk reduction events using both hardware and simulations to show progress and likelihood of success for key ORS-5 attributes. SCDs enabled a much lower level of formal “insight/oversight” activities more typical of other military operational programs (Figure 1).


Figure 1: ORS-5 SCDs (Systems Capabilities Demonstrations), image credit: USAF /ORSO)

SCD-1 was completed successfully in January 2015 and was aimed at demonstrating MIT Lincoln Laboratory’s preliminary designs of critical and enabling system elements could meet system functional and performance requirements for preliminary avionics control system and image processing chain including sensor-in-the-loop-control. Using emulated system sensors, actuators, and a high-fidelity physical models the demonstration used representative hardware to the maximum extent possible, along with derived characterizations of actual hardware to help validate preliminary system models. It provided insight potential system weaknesses and performance margins on system components, both hardware.

SCD-2 was used as a primary risk reduction test for the sensor subsystem, testing functional prototypes to provide feedback to EDU/Flight design efforts and serve as a preliminary design vector check between PDR (Preliminary Design Review) and CDR (Critical Design Review). The primary objectives of SCD-2, successfully completed in May 2014 were to validate optical performance of the OTA (Optical Telescope Assembly) to include optical throughput, focal plane distortion, ensquared energy at the focal plane, a-thermal performance, and structural integrity verification. Additional objectives included validating stray light performance against ray tracing analysis, demonstrating the end-to-end photon to digital chain and affirming the design maturity of a prototype optical telescope, stray light baffle and functional prototype camera electronics.

SCD-3 was an integrated system (Flat Sat) demonstration to validate the SensorSat FSW (Flight SoftWare) and GNC software functions and interactions with the complete complement of EDU hardware sensors and actuators. SCD-3 was successfully completed in August 2015 and demonstrated end-to-end performance of image-based pointing control loop, as well as real-time execution of algorithms on flight processor hardware. SCD-3 further demonstrated compatibility of hardware to software GNC interfaces (Full I/O set), the ability of the GNC hardware and software to respond appropriately to a simulated tumble to stabilize the SensorSat in Coarse Pointing, the ability of the GNC hardware and software to maintain stable SensorSat pointing with sensor-in-the-loop Fine Pointing and the ability of the flight software and firmware to process sensor image data.

MA (Mission Assurance): Mission assurance for ORS-5 given the small program size and budget relies on point application of subject matter expertise against early identified areas of risk or questions. Aerospace Corporation, Space Dynamics Laboratory, MITRE, Applied Physics Laboratory, all part of a ORS developed FFRDC/UARC (Federally Funded Research and Development Centers/University Affiliated Research Centers) consortium are called upon to witness key events such as SCD-3’s for independent insight to system development activities. Also key to the MA roles is the use of ORS program office “embedded” presence at vendor facilities, most notably at MIT Lincoln Laboratory. ORS-5 has the promise to radically change the way future GEO belt space situational awareness is conducted. The ORS-5 system design is currently being discussed as the governments “reference design” for the follow-on program to SBSS program of record. The unique TDI technique and the optimized flight geometry attributes combine to allow low-cost, relatively simple, non-propulsive small satellites to fulfill a key SSA mission. ORS-5 success will further to establish ORS principles as viable alternatives to traditional space mission fulfillment.


Figure 2: ORS-5, also known as SensorSat, is a single satellite constellation with a primary mission to provide space situational awareness. It measures about 1.5 m long, two and a 15 cm wide with a mass of 113 kg. It will operate from a low, zero inclination orbit approximately 372 miles above the earth to aid the U.S. military's tracking of other satellites and space debris in geosynchronous orbit, 22,236 miles (35,786 km) above the equator, commonly used by defense-related communications satellites, television broadcasting stations, and international space platforms (image credit: MIT LL)

Development status:

• August 21, 2017: With a Flight Readiness Review successfully concluded August 17, the ORS-5 satellite is now ready for its journey to equatorial orbit. 6)

- ORS-5/SensorSat was encapsulated August 11 at the Astrotech Space Operations Florida processing facility in preparation for its upcoming launch. Encapsulation of ORS-5 marked the satellite’s completion of all major testing prior to transfer to LC-46. The stacking of the Minotaur IV launch vehicle and integration events on the launch pad with the payload are significant milestones in ORS-5’s launch progress.

- ORS-5 will deliver space situational awareness capabilities at a significantly reduced cost compared to larger, more complex satellites, and serves as a gap filler mission for the Space-Based Space Surveillance (SBSS) Block 10 mission, originally launched in 2010. A successor SBSS mission is not expected to launch before 2021.

- Air Force Space Command's Space and Missile Systems Center (SMC), located at Los Angeles Air Force Base, California, is the U.S. Air Force's center of acquisition excellence for acquiring and developing military space systems. Its portfolio includes the Global Positioning System, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control networks, space based infrared systems and space situational awareness capabilities.

Launch: The ORS-5 spacecraft was launched on August 26, 2017 (06:04 UTC), corresponding to 2:04 p.m. EDT on Aug. 26). The launch vehicle for ORS-5 was the Minotaur-4 vehicle. The launch site was the Cape Canaveral Air Force Station, SLC-46 (Space Launch Complex-46), which is operated under license by Space Florida, Cape Canaveral, FL. 7) 8) 9)

In July 2015, Orbital ATK was awarded a contract from the USAF to launch ORS-5 in 2017. 10) The ORS-5 mission marks the first launch of a Minotaur-4 rocket (a five-stage vehicle) from Cape Canaveral and the first use of SLC-46 since 1999. 11)

Orbit: Circular equatorial orbit, altitude of 600 km, inclination = 0º.


Figure 3: Launch sequence of the ORS-5 spacecraft on the Minotaur-4 launch vehicle (image credit: Orbital ATK) 12) 13)

Flying in an Earth-centered fix (ECF) attitude at what is known as the “magic angle,” the ORS-5 vehicle images at a rate at which celestial objects are fixed and can be discerned from RSOs (Resident Space Objects) at geosynchronous altitude. Re-imaging of the entire GEO belt from an altitude of 600 km each 104 minute orbit allows a high awareness of change activity in the belt. The non-propulsive space vehicle is designed to use “sensor in the loop” as part of its fine pointing capability and the vehicle attitude over its lifetime will be adjusted to maintain the “magic angle” as a function of orbit altitude.


Figure 4: The ORS-5 mission concept (image credit: USAF /ORSO)

Mission status:

• October 9, 2019: The Operationally Responsive Space (ORS)-5 satellite, also known as SensorSat, will reach Full Operational Capability declaration later this year. Marking a significant milestone of success for the Air Force Space Command’s Space and Missile Systems Center and the 18th Space Control Squadron, ORS-5 will continue to expand Space Domain Awareness. — ORS-5 launched Aug. 26, 2017, and reached Operational Acceptance and Initial Operational Capability May 31, 2018. 14)

Enhancing orbital observation

- ORS-5 is part of the U.S.’s Space Surveillance Network, which is the responsibility of the Combined Space Force Component Command (CFSCC) through the 18th Space Control Squadron. It detects, tracks and catalogs man-made objects orbiting Earth such as active and inactive satellites, spent rocket parts and fragmentation debris, informing military, civil and commercial space operators if tracked objects may interfere with the satellites on orbit.

- “The diverse viewing geometries enabled by sensors in different orbit regimes, combined with ORS-5 data, have greatly increased the reliability, responsiveness, and accuracy of the space catalog,” said Maj. Gen. Stephen Whiting, Commander, CFSCC and 14th Air Force.

- Data obtained from ORS-5 is also used in predicting when and where decaying space objects are located and where they may re-enter the Earth's atmosphere.

- “ORS-5 has become the largest contributor of data to the Space Surveillance Network and has greatly exceeded performance expectations,” said Capt. Jacqueline Salas, ORS-5 Program Manager.

Going fast to maintain superiority

- Rapid innovation has always been the goal for ORS-5 during its development, and now its employment.

- “ORS-5 is a prime example of what SMC can achieve: the boldness and energy of a successful program that meets with ultimate success due to the exceptional efforts of our team,” said Col. Stephen Purdy, Special Programs Director.

- The ORS-5 development team, comprised of the Air Force’s Operationally Responsive Space Office, the precursor organization to the Space Rapid Capabilities Office, and SMC’s Directorate of Special Programs, exceeded all expectations by taking a new approach to risk and mission assurance in order to rapidly deploy capabilities to meet U.S. and Allied warfighter needs across the entire spectrum of operations from peacetime through conflict.

- “U.S. Strategic Command asked us to go fast, and we did,” said Purdy. “ORS-5 is the perfect embodiment of SMC’s rapid reaction and technology tenets and what we can do when we apply its principles.” - The operational impact and increased effectiveness of ORS-5 is noteworthy despite several initial inherent challenges.

- SMC made some choices that proved innovative and cost effective to ORS-5’s successful outcome. For example, choosing MIT/Lincoln Labs as its partner and the use of the SMC Development Corps’ Directorate of Innovation and Prototyping Multi-Mission Space Operations Center 2.1’s existing ground structure provided a high degree of autonomy, which made it possible to achieve a low-cost framework. Developing a small launch vehicle and miniaturized satellite systems contributed to its goal of reduced satellite operations manpower through automation, while also leveraging standard off-the-shelf spacecraft components.

- SMC continues to collaborate with the national and international communities on future Space Domain Awareness spacecraft, leveraging original components from the ORS-5 design.

- “It speaks volumes to the high level of expertise from our entire team of operators, engineers and sustainers. It has also shown us that rapid development and successful deployment is not only achievable, but is now the expectation in future projects. ORS-5’s success has already factored into our current and next-generation SMC portfolio,” said Salas.

• November 29, 2017: In the weeks that SensorSat has been in orbit, it has undergone a complete checkout process, opened the cover of its optical system, and collected the first imagery of objects in the geosynchronous belt. The quality of the initial images has demonstrated that SensorSat utilizes a highly capable optical system that is able to conduct its required mission. 15)

• September 28, 2017: The AFSC (Air Force Space Command) and the DGS (Diego Garcia tracking Station) are using the DISN (Defense Information Systems Network) Converged Access (DCA) Lite Network to communicate with the ORS-5 (Operationally Responsive Space-5), a space surveillance satellite that launched on August 26. 16)

- The network relies on a telemetry downlink upgraded with greater bandwidth to communicate between the tracking station and the satellite. The upgraded downlink, currently running at the highest rate of all satellites supported by the AFSCN (Air Force Satellite Control Network), allows data to be transmitted faster.

- DISA first deployed network equipment at Diego Garcia in the Indian Ocean; Okinawa, Japan; and Singapore to begin the process of sunsetting its DISN Asynchronous Transfer Mode System—a legacy transport network designed to exchange information between facilities, bases, and land masses.

- The DCA Lite Network was officially commissioned by the DISA Pacific Field Command on April 18, 2017.

Sensor complement

The SensorSat payload will circle the planet in LEO (Low Earth Orbit) to scan the valuable region of space 35,786 km high — the geosynchronous orbital belt — to spot debris and warn against collisions. GEO (Geosynchronous Earth Orbit) is where communications satellites, weather observatories and key reconnaissance platforms reside because that altitude allows the craft to fly continuously above the same part of the globe. 17)

Many of the details about ORS-5 remain classified. But SensorSat will test technologies and reduce the risk for future SSA (Space Situational Awareness) missions.

MIT/LL (Massachusetts Institute of Technology/Lincoln Laboratory) developed systems to detect, track, and identify man-made satellites; collects orbital-debris detection data to support spaceflight safety; performs satellite mission and payload assessment; and investigates technology to improve monitoring of the space environment, including space weather and atmospheric and ionospheric effects. The technology emphasis is the application of new components and algorithms to enable sensors with greatly enhanced capabilities and to support the development of net-centric processing and decision support systems. 18)


Figure 5: Flight-like hardware subsystems for SensorSat were integrated and tested as part of a system capability demonstration. Seen here is the imaging system, which consists of a Lincoln Laboratory–developed CCD imager, camera electronics, a custom lens cell, and a state-of-the-art lightweight baffle (image credit: MIT/LL)

The optical sensor provides continuous, un-cued, rapid GEO belt search to detect changes and provide precise regional awareness.


Figure 6: Photo of the ORS-5/SensorSat spacecraft with the optical payload during testing at MIT/LL (image credit: MIT/LL)

Ground segment:

The ORS-5 mission is designed for 3-years on orbit and will undergo a rapid launch and early operations (LEO) checkout before transitioning into operational transition/”trial period.” Operations of the system will initialize at the Kirtland AFB, RDT&E (Research, Development, Test and Evaluation) Support Center for the launch and early orbit “checkout” portion of on-orbit operations and then will transition to Schriever AFB for operational capability thereafter.

Operations of the ORS-5 vehicle will be conducted using the MMSOC (Multi-Mission Space Operations Center) ,version 2.1, located at 1st Space Operations Squadron and employing the use of Lincoln Laboratory developed mission unique software on the “Neptune” common ground architecture operation system. Lincoln Laboratory is responsible for mission data processing and will use an ORS-5 specific update of their previously developed OPAL (Optical Processing Architecture at Lincoln) software.

Command and control of ORS-5 will be done in both developmental and operational phase’s on-orbit through the AFSCN (Air Force Satellite Control Network ). Due the unique nature of a low Earth, equatorial orbit, only 3 AFSCN stations are geometrically in line-of-sight to the ORS-5 satellite. Guam and Diego Garcia AFSCN locations are primary and backup ground stations with Hawaii’s station having very limited capability as a backup in the case of lost contact with the primary station.

1) Stephen Clark, “Air Force satellite to continue tracking of space traffic,” Spaceflight Now, Sept. 3, 2014, URL:

2) “New Mission Selected for Operationally Responsive Space Office,” Los Angeles Air Force Base, July 30, 2014, URL:

3) Thomas M. Davis, ”Operationally Responsive Space – The Way Forward,” Proceedings of the 29th Annual AIAA/USU Conference on Small Satellites, Logan, Utah, USA, August 8-13, 2015, paper: SSC15-VII-4, URL:

4) Thomas M. Davis, Peter J. Thomas, Darrell B. Story, ”Sall satellites for operationally responsive space,” Proceedings of the 4S (Small Satellites, System & Services) Symposium, Valletta, Malta, May 30-June 3, 2016, URL:

5) ”ORS-5 SensorSat demonstration,” URL:

6) ”Air Force's SensorSat is Stacked to Track Satellites and Space Junk,” Satnews Daily, Aug. 21, 2017, URL:

7) ”45th Space Wing supports successful Minotaur IV ORS-5 launch,” Space Daily, Aug. 26, 2017, URL:

8) ”Orbital ATK Successfully Launches Minotaur IV Rocket Carrying ORS-5 Satellite for the US Air Force,” Orbital ATK Press Release, 26 August 2017, URL;

9) ”Orbital ATK Set to Launch U.S.A.F.'s ORS-5 Satellite to Monitor Satellites and Space Garbage,” Satnews Daily, Aug. 24, 2017, URL:

10) Mike Gruss, ”Orbital ATK Chosen To Launch U.S. Air Force’s ORS-5 Satellite,” Space News, July 3, 2015, URL:

11) Ken Kremer, ”Threat Tracking USAF Satellite Launching Nighttime Aug 25 on Cape Debut of Retired ICBM Minotaur Rocket,” Universe Today, 24 Aug. 2017, URL:

12) ”Mission Update: Minotaur IV ORS-5 Launch,” Orbital ATK, 2017, URL:

13) ”Minotaur-4 Fact Sheet,” URL:

14) ”SMC sets new standard of success for acquisition and operations of SensorSat,” SMC Public Affairs Office News Release, 9 October 2019, URL:

15) Dorothy Ryan, ”Monitoring activity in the geosynchronous belt,” MIT News, 29 November 2017, URL:

16) ”U.S. Air Force Uses DISA-Managed Network to Communicate with ORS-5,” Satnews Daily, 28, Sept. 2017, URL:

17) Justin Ray, ”Teams practice for Cape Canaveral’s first launch of Minotaur 4 rocket,” Spaceflight Now, Feb. 12, 2017, URL:

18) ”Space Control,” MIT/LL, URL:

The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (

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