In this recent week of class, we covered the Kessler Syndrome. The concept arose in our course reading — Dr Space Junk Vs The Universe by Alice Gorman — and briefly appeared in our lecture notes. The Kessler Syndrome describes an extreme theoretical scenario where space debris collisions reach the point of self-replication, which jeopardizes or cuts off space activities (Whitt 2022). Learning about this theory prompted an investigation into the current issue of space debris and mitigation efforts. 

The present pace of the Space industry’s expansion is unsustainable and dangerous. There have grown to be 170 million pieces of space debris in orbit (Khlystov 2023). These “pieces” consist of small and large sections of dead satellites, flecks of paint, bolts, spent rocket bodies, and more (Khlystov 2023). The vast majority of space debris is small and untrackable due to technological limits in the U.S. Space Surveillance Network (Khlystov 2023). Space debris in LEO (Low Earth Orbit) travels roughly 17,000 mph, making any collision with space technology extremely detrimental (Khlystov 2023). These collisions produce more fragments, which exponentially worsens debris congestion. The Kessler Syndrome is a growing possibility. 

Space debris mitigation is categorized into short-term and long-term strategies. Short-term techniques address immediate risks, while long-term techniques reduce the total amount of mass and kinetic energy in orbit (Press 2023). Long-term strategies are therefore the most effective for preventing Kessler Syndrome. Some long-term strategies include deorbiting or lifetime reduction, using disposal orbits, and active in-orbit debris removals (Press 2023). 

Deorbiting involves retrograde propulsion, while lifetime reduction involves drag augmentation devices (Press 2023). Retrograde propulsion entails small rocket thrusters that direct spacecraft out of debris (Figure 1) (Press 2023). The spacecraft may be guided to a predetermined location on Earth or an orbit of a shorter lifetime (Press 2023). The latter is followed by an uncontrolled reentry and burn-up (Press 2023). Drag augmentation involves using devices, like inflatable balloons, to increase the surface area and thus drag of a spacecraft (Press 2023). Increasing drag accelerates orbital decay, which reduces orbital altitude (The Physics Teacher). The object may then reenter the Earth’s atmosphere and burn up.

Figure 1. A depiction of the mechanism behind rocket maneuvering thrusters. Photograph by F. Barbir.

Disposal orbits are regions that do not contain direct collisional hazards for spacecraft (Press 2023). Spacecraft often reorbit into disposal orbits at the end of their functional lifetime (Press 2023). Reorbitting uses two propulsive burns — similar to retrograde propulsion — to steer the spacecraft into a disposal orbit (Press 2023). 

Various schemes of active in-orbit removal technology have been devised. However, these propositions are too costly for practical implementation (Press 2023). One proposal was a “debris sweeper” with foam balls or braking foils that sift through debris to deorbit them (Press 2023). Another proposal was “space-based laser evaporation” (Figure 2) of debris material (Press 2023). Further discussion among space experts could produce more cost-efficient and feasible strategies. 

Figure 2. A schematic depiction of a space-based laser in function. Photograph by Alexander Rubenchik, Michail Fedoruk, and Sergei Turistyn.

While long-term mitigation techniques have been developed, their impact on the high concentration of space debris seems limited. Deorbiting, lifetime reduction, and using disposal orbits protect spacecraft by relocating them away from hazardous debris conditions and preventing additional debris generation. However, only in-orbit removal technology directly decreases the amount of existing debris. This technology is not currently viable. Consequently, space debris and the Kessler Syndrome are enduring threats. 

Additional Content:

Garcia, Marisa.  December 2, 2023.  “Airbus Detumbler for Satellite End of Life Addresses

Space Junk Crisis.” Forbes. https://www.forbes.com/sites/marisagarcia/2023/12/01/airbus-detumbler-for-satellite-end-of-life-addresses-space-junk-crisis/?sh=7016e4153462.  

Young, Chris.  November 24, 2023.  “11 Organizations Tackling the Space Debris Problem.”

Interesting Engineering. https://interestingengineering.com/lists/11-organizations-space-debris-problem.  

Reference List:

Barbir, F.  December 3, 2023  “Spacecraft Propulsion.” ScienceDirect Topics.

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/spacecraft-propulsion.

Fiolhais, Miguel. Gonzalez-Urbina, Luis. Milewski, Tomasz. Chapparo, Carlos. Ferroglia,

Andrea.  December 3, 2023.  “Orbital Decay in the Classroom.” Pubs.Aip.Org. https://pubs.aip.org/aapt/pte/article/61/3/182/2869907/Orbital-Decay-in-the-Classroom. 

Khlystov, Nikolai.  December 3, 2023.  “We Have a Space Debris Problem. Here’s How to

Solve It.” World Economic Forum. https://www.weforum.org/agenda/2018/04/we-have-a-space-debris-problem-heres-how-to-solve-it/.  

Press, National Academy.  December 3, 2023.  “7 Techniques to Reduce the Future Debris

Hazard.” The National Academies Press. https://nap.nationalacademies.org/read/4765/chapter/10.

Rubenchik, Alexander. Fedoruk, Michail. Turistyn, Sergei.  April 11, 2014  “The Effect of

Self-Focusing on Laser Space-Debris Cleaning.” Nature News. https://www.nature.com/articles/lsa201440.  

Whitt, Kelly.  September 20, 2022.  “Kessler Syndrome of Colliding Satellites Could Make

Low-Earth Orbit Unusable.” EarthSky. https://earthsky.org/human-world/kessler-syndrome-colliding-satellites/. 

In this recent week of class, we discussed early human techniques and their evolution in constructing various stone tools. We reviewed the types of percussion and hammering, and the four innovations in stone knapping: The Oldowan, Acheulian, Levallois, and Blade Technology techniques. These methods occurred alongside cognitive development in early humans. For instance, spatial awareness allowed for precise strikes and removal of flakes from a core stone. Goal-setting enabled the visualization of a final tool and a method to complete that end. Early humans exhibited significant creativity in devising stone tool techniques. Hence, it is hard to believe that the archaeological record was limited to four construction techniques. Early human ingenuity must have resulted in other methods of tool manufacturing. 

Upon investigation, I discovered that ancient craftsmen employed heat treatment to temper their tools. Archaeological research from South Africa dates the earliest use of heat treatment to 45,000-70,000 years ago… stone tools were heated to roughly 600 degrees and likely buried under fire to make the stone easier to shape (Fountain). After heat treatment, less force was needed to flake a core. Percussion could be done with greater control and precision. Experimental archaeology was applied to validate these claims of heat treatment. Archaeologists matched the color of uncovered silcrete blades on the South African Coast by heating and flaking silcrete themselves (Fountain). 

A silcrete nodule showing experimental changes in texture and color resulting from exposure to heat.

Photo Credit: Science/AAAS

Heat treatment was a prevalent practice. According to Mary Louise Kelly from All Things Considered on NPR, “Scientists say it [heat treatment] may have actually happened much earlier – 300,000 years ago. That’s based on a study of rock shards in the Middle East.” Further, “heat treatment first occurred in Europe about 25,000 years ago” (Fountain). Evidently, heat treatment was integral to the survival of different early human communities; it was an intercontinental and enduring innovation.  

The adoption of heat treatment also transpired with growth in the cognition of early humans. Several skills were developed to produce tempered crafts. Sophisticated, controlled use of fire building was one adaptation (Early Humans Used). An understanding of careful planning and multi-tasking was another adaptation, as explained by Wadley and Prinsloo, “the making of compound adhesives involve[d] not only careful planning, but also multi-tasking…The artisan need[ed] to simultaneously mix ingredients, control fire temperature, and mentally rotate stone tools to create the desired composite product.” The archaeological record dispels ignorant notions of early humans being primitive. In actuality, they exhibited cognitive complexity and adeptly utilized their resources for survival. 

The photo shows heated artifacts in silcrete made by Homo sapiens at Klipdrift Shelter, South Africa. Photo: Katja Douze, University of the Witwatersrand

Photo Credit: (Humans Used Fire)

Several other early human misconceptions are challenged by the discovery of heat treatment. First, early humans did not manufacture stone tools through only knapping and flaking. Second, fire was not only used for protection, cooking, and warmth. Third and lastly, heat treatment existed long before archaeologists’ first discovery of it in Europe, which was dated to 25,000 years ago (Fountain). Ultimately, heat treatment exemplifies transformative, early human adaptability and has clarified contemporary misperceptions of their capabilities. 

Reference List

“Early Humans Used Innovative Heating Techniques to Make Stone Blades.” ScienceDaily,

 October 20, 2016. https://www.sciencedaily.com/releases/2016/10/161020092107.htm. 

Fountain, Henry. “Early Humans Used Heat to Shape Their Tools.” The New York Times, August

 13, 2009. https://www.nytimes.com/2009/08/18/science/18obfire.html. 

“Humans Used Fire Earlier than Previously Known.” University of Bergen. Accessed October 1,

 2023. https://www.uib.no/en/news/101760/humans-used-fire-earlier-previously-known.  

“Scientists Find Proof Early Humans Could Control Fire Temperature in Tempering Tools.” NPR,

 October 6, 2020. https://www.npr.org/2020/10/06/920859196/scientists-find-proof-early-humans-could-control-fire-temperature-in-tempering-tv.  

Wadley, L., Prinsloo, C. Linda. “Experimental Heat Treatment of Silcrete Implies Analogical

 Reasoning in the Middle Stone Age.” Journal of Human Evolution, April 5, 2014. https://www.sciencedirect.com/science/article/pii/S0047248414000621#:~:text=Heat%20treatment%20of%20rocks%20is,an%20attribute%20of%20complex%20cognition.  

Additional Readings:

Delagnes, Anne, Patrick Schmidt, Katja Douze, Sarah Wurz, Ludovic Bellot-Gurlet, Nicholas J

 Conard, Klaus G Nickel, Karen L van Niekerk, and Christopher S Henshilwood. “Early Evidence for the Extensive Heat Treatment of Silcrete in the Howiesons Poort at Klipdrift Shelter (Layer PBD, 65 Ka), South Africa.” PloS one, October 19, 2016. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5070848/. 

Stolarczyk, Regine E, and Patrick Schmidt. “Is Early Silcrete Heat Treatment a New Behavioural 

Proxy in the Middle Stone Age?” PloS one, October 1, 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6166942/.