Synchronized Position, Hold, Engage, Reorient, Experimental Satellites-Universal Docking Port (SPHERES-UDP) - 12.13.17

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
The addition of the Docking Ports is a critical upgrade to the Synchronized Position Hold, Engage, Reorient Experimental Satellites (SPHERES) facility aboard the International Space Station (ISS). With the new ability to dock and undock, SPHERES provides a test bed to address many of the challenges of combining autonomous spacecraft. Mated spacecraft can assemble complex systems in orbit or combine sensors and actuators for satellite servicing and repurposing missions. The Synchronized Position, Hold, Engage, Reorient, Experimental Satellites-Universal Docking Port (SPHERES-UDP) enables testing of complex tasks through optimal and adaptive control, autonomous decision-making processes, and real-time image processing.
Science Results for Everyone
Information Pending

The following content was provided by Alvar Saenz-Otero, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: SPHERES Docking Port

Principal Investigator(s)
Alvar Saenz-Otero, Ph.D., Massachusetts Institute of Technology, Cambridge, MA, United States

David W. Miller, Ph.D., Massachusetts Institute of Technology, Cambridge, MA, United States

NASA Ames Research Center, Moffett Field, CA, United States
Massachusetts Institute of Technology, Cambridge, MA, United States
Aurora Flight Sciences Corporation, Cambridge, MA, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
Technology Demonstration Office (TDO)

Research Benefits
Space Exploration, Scientific Discovery, Earth Benefits

ISS Expedition Duration
March 2015 - March 2016; March 2016 - September 2017

Expeditions Assigned

Previous Missions
- Synchronized Position Hold, Engage, Reorient Experimental Satellites (SPHERES). - Self-assembling Wireless Autonomous and Reconfigurable Modules (SWARM). - Agile Reconfigurable Modules with Autonomous Docking for Assembly and Servicing (ARMADAS) – MIT flat floor demonstration.

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Experiment Description

Research Overview

  • The SPHERES Universal Docking Ports enable SPHERES satellites to dock and undock to each other autonomously. They provide a necessary technology demonstration in order to explore and study the complex scenarios involved during on-orbit servicing and robotic assembly missions.
  • The science enabled by the addition of the SPHERES Universal Docking Ports is directly traceable to the DARPA Robotic Servicing of Geostationary Satellites project and future missions requiring in orbit assembly of complex systems. The intent of DARPA RSGS is to harvest subsystems from a defunct satellite and assemble a new spacecraft on-orbit. This requires bore-sight visual docking, and precise characterization and control of the mated spacecraft. The SPHERES Universal Docking Ports are a strategic risk-reducing technology demonstration to validate the multi-agent control procedures and autonomous docking processes proposed for DARPA RSGS and next generation satellites.
  • Controlling the new system dynamics of the docked vehicles is particularly challenging, and not something that can be easily tested on the ground. All satellites, especially those being serviced, are constrained by hard deadlines, tight resources and low risk maneuvering. The Docking Ports will be able to validate these higher risk, end-to-end docking scenarios in a zero-gravity environment.
  • After proven technology demonstration of operational capability, the intent is for the SPHERES Universal Docking Port to become part of the current SPHERES Facility suite of hardware, thus expanding to the science community the research capabilities of SPHERES. Therefore, the current planned test sessions of the SPHERES Universal Docking Ports are to test hardware functionality and demonstrate the technologies relevant to robotic satellite servicing missions.


There has been a growing interest in recent years to repurpose retired or defunct satellites, as exemplified by the DARPA Phoenix and RSGS missions. A robotic servicing mission typically involves four high-risk tasks: rendezvous in orbit, close proximity operations, servicer-target berthing or docking, and target manipulation and repurposing. The software and hardware required for these operations have few precedents in space, and as such, the SPHERES facility provides a long-duration microgravity test bed to develop such technologies in a low-risk environment that affords risk reduction capabilities. Additionally, the addition of autonomous rendezvous and docking capabilities to the SPHERES facility will enable early testing of key technologies for in orbit assembly of future complex space systems.
Therefore, the addition of SPHERES Universal Docking Ports is motivated by the goal of enabling such technology development. The objective of the Docking Ports is to provide a mechanism for rigidly docking and holding two SPHERES satellites together. These satellites may be moving relative to one another initially, so the docking mechanism must be able to maintain rigid capture despite forces and torques acting on and across the docking interface. The interface itself must be rigid so that it does not add additional dynamics to the system. Furthermore, the Docking Port must provide a capture cone for docking two SPHERES satellites together. This cone allows for slight misalignment in the orientation of two SPHERES satellites approaching docking while still locking into a set position.
While both SPHERES satellites have global metrology, the Docking Port provides direct sensing between the two docking interfaces. This capability, provided by an onboard camera and visual references, allows the SPHERES satellites to assess their relative pose in the approach phase prior to docking. Using relative sensing to supplement global metrology for docking, replicates the approach a robotic servicer would take and provides a more realistic testing scenario. Furthermore, the VERTIGO Avionics Box through which the Docking Port is attached blocks four of the Position and Attitude Determination System (PADS) ultrasound sensors. The Docking Port replaces these blocked sensors to maintain maximum global metrology capability.
Through the docking of multiple SPHERES, many critical issues related to robotic servicing are addressed. Among these issues is the need to respond successfully to changing dynamics and control. As multiple vehicles of similar mass dock, the system dynamics change to reflect the coupled structure. A servicer must adequately characterize and respond to the combined system, and the control of the docked vehicles must be reconfigured to reflect the new system dynamics. This characterization and reconfiguration poses a challenge for robotic servicing operations that are addressed in the context of the docking and undocking of SPHERES.

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Space Applications
Robotic satellite servicing poses many technical challenges. Among those challenges is the change in system dynamics which occurs when the robot is docked to the satellite being serviced. With the development of a docking capability using SPHERES, various techniques for reconfigurable control and response to changing system dynamics are addressed. DARPA is developing a variety of robotics technologies to address key on-orbit mission needs, including assembly, repair, asset life extension, and refueling in the harsh environment of space. Development activities include the maturation of robotic arms and multiple generic and mission-specific tools. These technologies are expected to be integral on future robotic assembly platform.

Earth Applications
Underwater vehicles operate in environments similar to space. Current underwater servicing technology is limited by hard deadlines, tight resources, and low risk maneuvers. Development of robotic servicing in space can be applied on Earth, such as in missions to an uncharted ocean floor or the construction and repair of seabed pipelines.

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Operational Requirements and Protocols

The SPHERES facility is allocated a certain number of test sessions per ISS Increment. As the facility lead, NASA Ames determines specific test session scheduling based on ongoing planning and research results.

A typical SPHERES Universal Docking Port test session consists of ground control sending up algorithms one week before the test session. SPHERES batteries are charged prior to each test session. The crew member unstows and configures SPHERES facility satellites and clears the work area. The SPHERES VERTIGO Avionics Stack is attached to each satellite, followed by attachment and configuration of the SPHERES Universal Docking Ports. Maneuvering algorithms are loaded onto the SPHERES through the communication system. Software programs are loaded to the VERTIGO Avionics Stacks by Ethernet cable connected to the ISS ELC laptop. A crew member initiates individual tests using the ISS laptop. After completion of all tests, data are downlinked to ground operation center for post-session assessment. Once the data is analyzed, algorithms are revised and the next test session is scheduled.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites
MIT SPHERES Universal Docking Port Project portal
Massachusetts Institute of Technology

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image SPHERES Universal Docking Port. (Image courtesy of MIT)
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image SPHERES Assembly with Universal Docking Port attached. (Image courtesy of MIT)
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image An early Docking Port prototype showing the internal cams locking mechanism (center) driven by a micro gearmotor (right) and the onboard camera to control docking maneuvers (left). (Image courtesy of MIT)
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image Docking Demonstration of Ground Units. (Image courtesy of MIT)
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