Leonard David's INSIDE OUTER SPACE

Credit: CORDS/The Aerospace Corporation

What is the overall impact of the tons of human-made orbital debris, solid and liquid propellant discharges, and other space age substances that reenter the Earth’s atmosphere?

There’s a toss away line in use over the years – indeed, today — that spacecraft refuse “burns up” – but that is far from accurate. The chemistry from high heating of spacecraft materials – including beryllium, aluminum, etc. – is worthy of investigation, specifically the impact of these materials on the atmosphere – top to bottom.

What are the consequences from human-made materials reentering Earth’s fragile atmospheric cocoon?

New research

New research into this area has been done by Laura Ratliff of The Space Policy Institute at the George Washington University Elliott School of International Affairs.

Last month, her paper — “Space Debris Reentry: Inadvertent Geoengineering?” – won the Thacher Prize for Outstanding Publication in Space Policy.

Density of Human-made Objects by Altitude. From Pardini and Anselmo (2021) used in Laura Ratliff paper

“The potential atmospheric effects of satellite hardware reentering from low Earth orbit (LEO) megaconstellations have been largely unstudied to date,” the paper explains. “While researchers have raised concerns about the potential for megaconstellations to pollute LEO, they have largely accepted deorbiting of dead satellites without considering the potential atmospheric pollution from routine burning of various carbon compounds and aerosolization of metal components.”

Host of different materials

As Ratliff points out spacecraft contain a host of different materials that could have varied effects on the atmosphere:

• Aluminum: Commonly used for structural elements and radiation/impact shielding. It accounts for a large percent of the total mass for structures in which it is used.
• Carbon Composites: Either carbon fibers or woven fabric are combined with an epoxy to generate a rigid material which can be used for structural elements in combination with, or replacing, aluminum. Carbon fibers are also used in the construction of propellant tanks.
• Titanium: Useful for propellant tanks and engine components due to its high strength-to-weight ratio. Its thermal resistance and stability also make it useful for optical instruments, where it can thermally isolate cold detectors, and for casings and other supporting structures.
• Steel: A combination of iron and carbon, it is the most common material for fasteners (screws) and reaction wheels.
• Ceramics: Used in solar cells and thermal protection, can be a combination of silicon and other materials.
• Copper: Most commonly used in wiring.

Paucity of data

“The paucity of data available to quantify the effects of debris reentry make it challenging to establish whether there is any current or future danger of significant atmospheric damage,” Ratliff notes in the paper. “Yet, the technical basis upon which estimates of harm rest does suggest there may be cause for concern as reentry rates increase.”

Credit: The Aerospace Corporation/CORDS

Ratliff tells Inside Outer Space: “Starting to characterize the unknowns in the climate system and commercial satellite industry was a daunting task because the gaps in our knowledge are so great and many of the missing pieces interrelate in complex ways.”

With so many unknowns, Ratliff adds, “building an accurate model to predict future climate effects would be quite an undertaking, but doing so might be important to prevent us from committing to satellite disposal practices which we’ll later regret.”

This topic seems ripe for further study by an interdisciplinary group including atmospheric scientists, materials scientists, thermodynamicists, and engineers, Ratliff suggests to Inside Outer Space.

Logical first step

“Cries of “More Research!” can often be heard when policymakers don’t want to act on an issue, but this classic non-solution is actually fairly useful for the issue at hand,” Ratliff says in the paper. “With many fundamental pieces of knowledge unknown and yet knowable, building up a better understanding of the potential inputs into the atmosphere and their interaction within current global climate models would provide a much more solid foundation upon which future policy could be built.”

Credit: NASA

Given the current levels of uncertainty across the board, Ratliff concludes, investing in focused research on the interaction of spacecraft-based aerosols with the atmosphere is the most logical first step.

“This can inform next steps, such as reducing the mass entering the atmosphere, changing the materials used, or mitigating post-aerosolization. While we do not know whether these actions will become necessary in the next decade, next century, or ever, taking steps now to assess the situation in more detail and develop a proactive plan will likely benefit policymakers, citizens, and the environment,” Ratliff suggests in the paper.

To read the winning research paper — “Space Debris Reentry: Inadvertent Geoengineering?” – go to:

https://spi.elliott.gwu.edu/files/2019/08/Ratliff-Debris-Reentry-Final-reformat.pdf