Debris Removal

Optical Measurement

NASA

Researchers using NASA’s LEGEND debris model found that even without launching any new spacecraft, collisions among existing objects would generate more debris faster than natural processes like atmospheric drag could remove it. This shows that merely avoiding new debris isn’t enough to secure long-term orbital stability.

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2005 study by LEGEND:

1. LEGEND stands for the LEO-to-GEO Environment Debris model. It is an advanced numerical simulation tool developed by NASA’s Orbital Debris Program Office that predicts both the past and future behavior of the orbital debris environment around Earth. 

2. LEGEND reconstructs the debris environment from the start of the space age (around 1957) up to the present. It does this by adding objects from actual launch records (satellites, rocket bodies, mission-released hardware) and simulating known breakup events to create debris fragments down to about 1 mm in size.

3. The model uses Monte Carlo simulation methods — essentially many randomized “what-if” runs — to forecast how debris populations might evolve over time under different scenarios, including future launches and possible breakups. It uses a pair-wise collision probability algorithm to capture how objects might encounter and fragment in orbit as debris levels change.

4. Three-Dimensional: Unlike some earlier debris models (like EVOLVE, which used simpler one-dimensional descriptions by altitude), LEGEND tracks debris in three dimensions (altitude, latitude, longitude) to better represent spatial variations in debris density and movement.

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How it works:

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1. It combines multiple source processes (launch traffic, mission-related releases, breakup fragments) and sink processes (natural orbital decay and atmospheric drag) to simulate debris over time.

2. In the historical part, the model uses actual launch and breakup data to “replay” how the debris environment developed.

3. For the future projection, LEGEND performs repeated Monte Carlo runs with statistically sampled collision and explosion events to see how debris populations might grow or shrink under different assumptions.

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Challenges: technical feasibility, the technology must be capable of safely removing debris from LOE; economic affordability, cost must be reasonable relative to the benefits; political and international acceptance, because shared is shared globally, debris removal must be coordinated in ways acceptable to multiple nations; activities must also avoid creating hazards on earth, such as debris surviving and reentry that could threaten people or property.

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Debris remediation by re-entry:

“Debris reentry” refers to the return of human-made space objects from orbit back into Earth’s atmosphere. These objects can include defunct satellites, upper stages of rockets, and fragments from breakups. The reentry can happen:

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• Uncontrolled: orbit decays over time due to atmospheric drag,

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• Controlled: the spacecraft is deliberately steered into a specific path toward the atmosphere. 

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As orbital debris and defunct spacecraft accumulate, space agencies use reentry as a form of end-of-life disposal to remove objects from orbit and reduce collision risk. However, bringing an object back through the atmosphere involves structural breakup and heating, which affects whether pieces survive to reach the ground. 

Natural (Uncontrolled) reentry

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• Over time, atmospheric drag lowers a spacecraft’s orbit until it reenters the atmosphere.

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• Because this process isn’t steered, the location where fragments might reach Earth cannot be precisely controlled. 

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Controlled reentry

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• With active propulsion, spacecraft can target a specific reentry path so that surviving debris will fall in uninhabited areas (e.g., remote ocean regions).

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• This is often done for large spacecraft that otherwise could pose more risk to people or property if debris landed in populated areas.

Space X (Starlink)