LOADING...

Orbital Debris

Orbital Debris

› Partnerships Home

The Johnson Space Center conducts a full range of research activities to limit the growth of orbital debris. NASA produces many products that can be used by spacecraft and mission designers to ensure that their missions are compliant with standards and best practices which protect the earth orbital environment from unacceptable growth of human-made orbital debris.

Mitigation and Modeling

Orbital Debris Model around Earth
Orbital Debris Model around Earth
Photo credit: NASA

Controlling the growth of the orbital debris population is a high priority for NASA, the United States, and the major space-faring nations of the world to preserve near-Earth space for future generations.

The Johnson Space Center conducts a full range of research activities to limit the growth of orbital debris. NASA produces many products that can be used by spacecraft and mission designers to ensure that their missions are compliant with standards and best practices which protect the earth orbital environment from unacceptable growth of human-made orbital debris.

Measurements of the current environment

As much as possible, estimates of the current orbital debris environment are based on measurements. This emphasis on data driven modeling helps ensure that model results have a solid, reality based, starting point.
Measurements of near-Earth orbital debris are accomplished by conducting ground-based and space-based observations of the orbital debris environment. Data is acquired using ground-based radars and optical telescopes, space-based telescopes, and analysis of spacecraft surfaces returned from space. Some important data sources have been the U.S. Space Surveillance Network, the Haystack X-Band Radar, and returned surfaces from the Solar Max, the Long Duration Exposure Facility (LDEF), the Hubble Space Telescope (HST) and the Space Shuttle spacecraft. The data provide validation for the environment models and identify the presence of new sources.

Modeling of the future environment

NASA scientists continue to develop and upgrade orbital debris models to describe and characterize the current and future debris environment. Engineering models, such as ORDEM2000, can be used for debris impact risk assessments for spacecraft and satellites, including the International Space Station and the Space Shuttle. This engineering model is available to any user at the Orbital Debris Website, http://orbitaldebris.jsc.nasa.gov.

Evolutionary models, such as LEGEND, are designed to predict the future debris environment. They are reliable tools to study how the future debris environment reacts to various mitigation practices, including scenarios involving active debris removal. The operation of LEGEND requires special training and elaborate databases and is not available to other users.

Mitigation Orbital debris damage seen during Hubble Space Telescope repairsOrbital debris damage seen during Hubble Space Telescope repairs.
Photo credit: NASA

Mitigation measures can take the form of curtailing or preventing the creation of new debris, designing satellites to withstand impacts by small debris, and implementing operational procedures such as using orbital regimes with less debris, adopting specific spacecraft attitudes, and even maneuvering to avoid collisions with debris.

NASA has developed a software suite specifically designed to allow spacecraft and mission planners assess compliance with NASA-STD 8719.14, Process for Limiting Orbital Debris. Although specifically designed for meeting the NASA mitigation standards, the tool, NASA Debris Assessment Software (DAS) can be useful for other agencies or commercial users. DAS is also available to all on the NASA Orbital Debris website.

Reentry Survivability

Due to the increasing number of objects in space, NASA and the international aerospace community have adopted guidelines and assessment procedures to reduce the number of non-operational spacecraft and spent rocket upper stages orbiting the Earth. One method of post-mission disposal is to allow the reentry of these spacecraft, either from natural orbital decay (uncontrolled) or controlled entry. One way to accelerate orbital decay is to lower the perigee altitude so that atmospheric drag will cause the spacecraft to enter the earth's atmosphere more rapidly. However, in such cases the surviving debris impact footprint cannot be guaranteed to avoid inhabited landmasses. Controlled entry normally is achieved by using more propellant with a larger propulsion system to cause the spacecraft to enter the atmosphere at a steeper flight path angle. The vehicle will then enter the atmosphere at a more precise latitude and longitude, and the debris footprint can be positioned over an uninhabited region, generally located in the ocean.

After spacecraft (or parent body) breakup, individual components, or fragments, will continue to lose altitude and receive aeroheating until they either demise or survive to impact the Earth. Spacecraft components that are made of low melting-point materials (e.g., aluminum) will generally demise at higher altitudes than objects that are made of materials with higher melting points (e.g., titanium, stainless steel, beryllium, carbon-carbon). If an object is contained inside of a housing, the housing must demise before the internal object receives significant heating. Many objects have a very high melt temperature such that they do not demise, but some can be so light (e.g., tungsten shims) that they impact with a very low velocity. As a result, the kinetic energy at impact is sometimes under 15 J, a threshold below which the probability of human casualty is very low.

There are two NASA methods to compute the reentry survivability of spacecraft components. DAS includes a conservative, easy-to-use tool. However, if the DAS tool indicates possible non-compliance with human casualty risks, the Object Reentry Survival Analysis Tool (ORSAT) provides a more accurate, higher fidelity model.

On 21 January 2001, a Delta 2 third stage, known as a PAM-D (Payload Assist Module - Delta), reentered the atmosphere over the Middle East. The titanium motor casing of the PAM-D, weighing about 70 kg, landed in Saudi Arabia about 240 km from the capital of Riyadh. On 21 January 2001, a Delta 2 third stage, known as a PAM-D (Payload Assist Module - Delta), reentered the atmosphere over the Middle East. The titanium motor casing of the PAM-D, weighing about 70 kg, landed in Saudi Arabia about 240 km from the capital of Riyadh.
Photo credit: NASA
The ORSAT code uses integrated trajectory, atmospheric, aerodynamic, aerothermodynamic, and thermal/ablation models to perform a complete satellite or launch vehicle upper stage component analysis in determining the impact risk. A three-degrees-of-freedom trajectory is used with the 1976 U.S. standard atmosphere, MSISe-90 atmosphere, or the GRAM-99 atmosphere to model various types of object shapes in either spinning or tumbling modes. Drag coefficients of these objects are considered from hypersonic to subsonic speeds to obtain the kinetic energy of objects at ground impact. Stagnation point continuum heating rates are obtained for spherical objects and are adjusted for other bodies and for rarefied flow regimes. Both lumped mass and 1-D heat conduction models may be used to compute the surface temperature. The object is considered to demise when its absorbed heat reaches the material heat of ablation.

Thermal properties for 80 materials are included in a database in ORSAT, with temperature-varying properties listed for thermal conductivity, specific heat, and surface emissivity. For objects that are on the threshold of demise or survival, parameters such as oxidation efficiency, initial temperature, surface emissivity, number of layers, dimensions, or breakup altitude may be varied in a single run to obtain the critical demise/survival point of a component. Good engineering judgment is applied in the parametric analysis to compute the best predicted total debris casualty area. The impact risk is then calculated to determine whether the satellite or upper stage is compliant with the NASA Standard 8719.14. Similar to LEGEND, ORSAT requires operator expertise and training and is not available to outside users.

 


Hypervelocity Impact Testing

HVIT geometry model

International Space Station MMOD shield locations (HVIT geometry model); each color represents a different level of impact risk. A red color indicates high impact risk from MMOD, and blue color indicates low impact risk. Based on impact analysis results, heavier/more capable MMOD shielding is used in red areas, and lighter/less capable shielding in blue areas.
Photo credit: NASA

The Johnson Space Center and the NASA White Sands Test Facility's Remote Hypervelocity Test Laboratory (RHTL) compose a team dedicated to evaluating the environmental effects from micrometeoroid and orbital debris (MMOD) impacts on orbiting spacecraft. This team has the in-house ability to prepare and plan hypervelocity impact tests, perform post-test damage analysis, conduct computer impact simulations and spacecraft risk assessments. The team designs and tests turnkey solutions for mitigating MMOD impact effects on spacecraft.

The Problem

The near-Earth space environment is cluttered with manmade orbital debris and naturally occurring meteoroid particles. Most of the debris particles are very small; however, they are moving at velocities averaging up to 15 kilometers per second and can pose significant impact hazard for orbiting spacecraft and personnel. Although some of these particles eventually fall back to Earth and burn up in the atmosphere, new debris particles are frequently added to the environment by such sources as exploding spacecraft and discharged spacecraft waste. The overall trend is that the near Earth orbital debris environment is gradually getting worse.

The Solution

Engineers and technicians design, test, and analyze spacecraft systems to reduce the risk from MMOD particle impact. The team has performed thousands of hypervelocity impact tests that have yielded numerous efficient and effective shielding designs, as well as detailed data on the effect of MMOD impact on various spacecraft components. The team applies state-of-the-art computer codes to improve the design of spacecraft MMOD protection systems and develop operational guidelines to reduce MMOD damage.

Capablilites

  • MMOD shielding design
  • Hypervelocity impact testing
  • Hypervelocity impact computer simulation
  • MMOD shield ballistic limit determination
  • MMOD impact/penetration risk assessment

› Partnerships Home

Page Last Updated: January 10th, 2014
Page Editor: Raymond Mitchell