Dr. Jer Chyi Liou

Jer Chyi Liou

Orbital Debris Program Manager

Learn more about Orbital Debris Program Manager Jer Chyi Liou.

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Points of Contact

For details on contacting an Orbital Debris Point of Contact (PoC), click below.

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NASA's Chief Scientist for Orbital Debris


Jer Chyi Liou

As NASA’s chief scientist for Orbital Debris (OD), Dr. Jer Chyi “J.-C.” Liou oversees OD interests for the agency, OD Program Office and Hypervelocity Impact Team (HVIT). He is responsible for interactions with other agencies and organizations, policy development, and NASA's strategic plans for the OD environment, debris mitigation, risk assessments and spacecraft protection.

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Objectives Hierarchy

The Office of Safety and Mission Assurance (OSMA) has introduced a new objectives-based approach to better support NASA’s increasingly complex missions in a changing design environment. By focusing on objectives, OSMA hopes that the new standards will be more flexible, agile and cost-effective, and will allow more ingenuity to achieve objectives. It will serve as a guide to help programs and projects plan how they will meet their objectives, instead of dictating what they must do to via prescriptive requirements. Read the article, “OSMA Introduces New Objectives-Based Strategies,” to learn more about objective hierarchies.

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In this series, Nick Johnson, NASA's former chief scientist for Orbital Debris (OD), discusses orbital debris work at NASA. Johnson explains what he sees as the future for the agency's OD work.

Orbital Debris: Future of Orbital Debris

Jul 11, 2019, 17:18 PM
Knowledge Byte
Vimeo video i ds:
Is public:
May 16, 2014, 04:00 AM

In this series, Nick Johnson, NASA's former chief scientist for Orbital Debris (OD), discusses orbital debris work at NASA. Johnson explains what he sees as the future for the agency's OD work.

Video classification:


SATERN Courses

Orbital Debris SMA-HQ-WBT-200

This course is designed to provide an overview of the Safety and Mission Assurance (SMA) community of the NASA Orbital Debris (OD) Program and the need for OD mitigation. It describes the work of the NASA OD Program Office and explains NASA’s process and requirements for limiting OD. It summarizes current U.S. space policy and government OD mitigation standard practices.

SMA-HQ-WBT-200 Details Launch SATERN 

Policy and Guidance


Policy Title Buttons Buttons
NPR 8715.6 NASA Procedural Requirements for Limiting Orbital Debris NPR 8715.6 Details See NPR 8715.6
NASA-STD-8719.14 Process for Limiting Orbital Debris NASA-STD-8719.14 Details See NASA-STD-8719.14
NASA-HDBK-8719.14 Handbook for Limiting Orbital Debris NASA-HDBK-8719.14 Details See NASA-HDBK-8719.14

Orbital Debris Quarterly News

Orbital Debris Quarterly News

Orbital Debris Quarterly News (ODQN) is a newsletter published by the Orbital Debris Program office containing relevant information on orbital debris events, research, statistics, projects, meeting reports and more.

Visit ODQN Home Page Subscribe to ODQN Emails 

Orbital Debris Workshop

The NASA Orbital Debris (OD) Workshop is a virtual workshop that provides an opportunity for the agency OD community to share knowledge, challenges and solutions regarding OD mitigation. The workshop is hosted by the Office of Safety and Mission Assurance.

Take a look at the 2017 agenda for workshop details and an outline of the presentations and presenters.

To watch videos of the 2013 and 2015 presentations and view the accompanying slides, check out the corresponding agenda pages.

See the 2017 Agenda See the 2015 Agenda See the 2013 Agenda

Frequently Asked Questions

  • All man-made objects in Earth’s orbit that no longer serve a useful purpose are considered OD.
  • Examples of OD include derelict spacecraft and upper stages of launch vehicles, carriers for multiple payloads, debris intentionally released during spacecraft separation from its launch vehicle or during mission operations, debris created as a result of spacecraft or upper-stage explosions or collisions, solid rocket motor effluents, and tiny flecks of paint released by thermal stress or small-particle impacts.
  • More than 21,000 pieces of OD larger than 10 centimeters are known to exist. The estimated population of particles between 1 and 10 centimeters in diameter is approximately 500,000. The number of particles smaller than 1 centimeter exceeds 100 million.
  • Large OD (greater than 10 centimeters) is tracked routinely by the U.S. Space Surveillance Network. Objects as small as 3 millimeters can be detected by ground-based radars, providing a basis for a statistical estimate of their numbers. Assessments of the population of OD smaller than 1 millimeter can be made by examining impact features on the surfaces of returned spacecraft, although this has been limited to spacecraft operating in altitudes below 600 kilometers.
  • Satellite explosions and collisions are the principal sources of large OD. Prior to 2007, OD was from explosions of old launch vehicle upper stages left in orbit with stored energy sources, (e.g., residual propellants and high-pressure fluids). The intentional destruction of the Fengyun-1C weather satellite by China in 2007 and the accidental collision of American and Russian communications satellites in 2009 greatly increased the amount of large debris in orbit and now represent one-third of all cataloged OD.
  • Most OD resides within 2,000 kilometers of the Earth's surface. Within this volume, the amount of debris varies significantly with altitude. The greatest concentrations of debris are found near 750-800 kilometers.
  • In low-Earth orbit (below 2,000 kilometers), OD circles the Earth at speeds of 7-8 kilometers per second. However, the average impact speed of OD with another space object will be approximately 10 kilometers per second. Consequently, collisions with even a small piece of debris will involve considerable energy.
  • The U.S. Space Surveillance Network regularly examines the trajectories of OD to identify possible close encounters. If another object is projected to come within a few kilometers of the ISS, it normally will maneuver away from the object if the chance of collision exceeds 1 in 10,000. This occurs infrequently — about once a year on average.
  • The ISS is the most heavily shielded spacecraft ever flown. Critical components, e.g., habitable compartments and high pressure tanks, will normally be able to withstand the impact of debris as large as 1 centimeter in diameter. The risk of a critical ISS component being struck by debris 1-10 centimeters in diameter is slight and ways to reduce this risk are being investigated.
  • Photographs of Mir's exterior show a large number of impacts from small OD and meteoroids. The most significant damage was to the large, fragile solar arrays that could not be protected from small particles. OD caused no loss of mission or capability on Mir.
  • Systems such as Iridium, Orbcomm and Globalstar do not represent unique debris problems. In fact, many of the systems are being deployed in ways designed to minimize OD generation. Often, upper stages and spacecraft are placed in lower-altitude orbits after their missions have been completed to accelerate their fall back to Earth.
  • The higher the altitude, the longer OD typically remains in Earth orbit. Debris left in orbits below 600 kilometers normally falls back to Earth within several years. At altitudes of 800 kilometers, the time for orbital decay is often measured in decades. Above 1,000 kilometers, OD normally continues circling the Earth for a century or more.
  • A significant amount of debris does not survive the severe heating that occurs during reentry. Components that do survive are most likely to fall into the oceans or other bodies of water or onto sparsely populated regions like the Canadian Tundra, the Australian Outback or Siberia in the Russian Federation. During the past 50 years, an average of one cataloged piece of debris fell back to Earth each day. No serious injury or significant property damage caused by reentering debris has been confirmed.
  • Our ability to detect OD at such heights is limited, but studies indicate that the OD population is probably less severe there than in low-Earth orbit. However, since the geostationary orbit is a special natural resource, many spacecraft operators boost their old spacecraft into higher disposal orbits at the end of their mission.
  • Operational spacecraft are struck by very small debris (and micrometeoroids) routinely with little or no effect. Debris shields also can protect spacecraft components from particles as large as 1 centimeter in diameter. The probability of two large objects (greater than 10 centimeters in diameter) accidentally colliding is very low. The worst such incident occurred on Feb. 10, 2009, when an operational U.S. Iridium satellite and a derelict Russian Cosmos satellite collided.
  • The most important action currently is to prevent the unnecessary creation of additional OD. This can be done through prudent vehicle design and operations. Cleaning up the environment remains a technical and economic challenge.
  • Since 1988, the official policy of the U.S. has been to minimize the creation of new OD. The most recent National Space Policy (June 28, 2010) addresses the importance of preserving the space environment, including OD mitigation. NASA and the Department of Defense also are directed to pursue research and development of technologies and techniques to mitigate and remove on-orbit debris, reduce hazards, and increase the understanding of the current and future debris environment.
    "Orbital debris poses a risk to continued reliable use of space-based services and operations and to the safety of persons and property in space and on Earth. The United States shall seek to minimize the creation of orbital debris by government and non-government operations in space in order to preserve the space environment for future generations."
  • NASA and the Department of Defense have issued requirements governing the design and operation of spacecraft and upper stages to mitigate the growth of the OD population. The Federal Aviation Administration, the National Oceanic and Atmospheric Administration, and the Federal Communications Commission also consider OD issues in the licensing process for spacecraft and upper stages under their auspices. A set of U.S. Government Orbital Debris Mitigation Standard Practices was developed in 1997 and approved in 2001.
  • Manufacturers and operators of U.S. spacecraft and upper stages are aware of the hazards of OD and the need to mitigate its growth. Many firms voluntarily adhere to measures designed to limit the growth of OD.
  • Yes, Russia, China, Japan, France and the European Space Agency have all issued OD mitigation guidelines.
  • No, but the leading space agencies of the world have formed the Inter-Agency Space Debris Coordination Committee (IADC) to address OD issues and to encourage operations in Earth orbit that limit the growth of OD. Since 1994 OD has been a topic of assessment and discussion in the Scientific and Technical Subcommittee of the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). Both IADC and COPUOS have published OD mitigation guidelines.
  • An excellent primer on the many aspects of OD is the Interagency Report on Orbital Debris. A more in depth summary can be found in Orbital Debris: A Technical Assessment. Also see the United Nations Technical Report on Space Debris.