Rajan Wilcox
The external tank of a spacecraft, also known as the ET, is an essential component that provides fuel during the initial stages of a mission. Once the fuel is depleted, the tank is typically discarded through a process called separation. After separation, the tank usually falls back to Earth, with its fate depending on various factors such as its design, the presence of a heat shield, and the conditions of re-entry. In some cases, the tank may disintegrate in the atmosphere, while in others, it may reach the Earth's surface, typically landing in the ocean. While there have been proposals to reuse or repurpose external tanks, such as converting them into space habitats, implementing these ideas poses challenges due to weight constraints and the cost associated with recovery.
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What You'll Learn
External tanks disintegrate in the atmosphere before falling into the sea
External tanks typically disintegrate in the atmosphere before falling into the sea. During re-entry, the tank heats up and starts to break apart due to the lack of protection. The remaining fuel and oxidizer mix, resulting in rapid combustion, which breaks the tank into smaller pieces that burn up before reaching the Earth's surface. This combustion ensures that the tanks do not make it to Earth in one piece and typically fall into the Indian Ocean.
The tanks are not stable in orbit at main engine cut-off, and their recovery would be challenging and costly. The process would require a large, heavy heat shield and strengthening to ensure the tank's survival during re-entry and splashdown. The weight and cost associated with recovery make it impractical.
The external tanks are not reusable, and their remains fall into the ocean. The Space Shuttle Solid Rocket Boosters (SRB) are, however, reusable. These steel casings hit the water quite hard upon re-entry, creating a significant impact.
The disintegration of external tanks in the atmosphere is a well-documented phenomenon. The tanks are not designed to withstand the heat and stresses of re-entry, and their remains typically end up in the ocean. This process raises questions about the potential for reusing these tanks and the challenges of recovery.
The combustion and disintegration of external tanks during re-entry highlight the importance of understanding the behavior of these large structures as they return to Earth. The study of external tank behavior provides valuable insights into the design and recovery possibilities of such components, even though they are not currently reused.
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Residual fuel, oxidiser and heat cause combustion and tank break-up
During re-entry, the external tank is subject to intense heat, which causes residual fuel and oxidiser within to ignite and explode, resulting in the tank's disintegration. This phenomenon, known as rapid combustion, breaks the tank into smaller pieces that are typically incinerated before they can reach the Earth's surface. This process ensures that any falling debris is less likely to cause significant damage upon impact.
The external tank, a crucial component of the Space Shuttle system, is responsible for providing the necessary fuel for the shuttle's main engines during lift-off and ascent. It consists of two primary tanks containing liquid oxygen (LOX) and liquid hydrogen (LH2) fuels, separated by an intertank structure. During the critical phase of separation, the external tank is jettisoned to reduce weight and allow the shuttle to manoeuvre more efficiently in space.
However, the process of separation and re-entry exposes the external tank to extreme conditions. The tank is not designed for long-term orbit and experiences significant heating during re-entry. This heat causes any remaining fuel and oxidiser within the tank to ignite, leading to rapid combustion and the subsequent disintegration of the tank.
The combustion process is so intense that it breaks the tank into smaller fragments. These pieces are then subjected to even more extreme heat, causing them to incinerate before they can reach the Earth's surface. This natural process serves as a safety mechanism, reducing the potential impact and hazard of falling debris.
While the combustion and disintegration of the external tank mitigate the risks associated with falling debris, the tank itself is not the only source of potential hazards. The tank is covered in a layer of insulation foam, which helps maintain the fuel's temperature during the shuttle's ascent. However, this foam has been known to shed during flight, as observed in the Columbia disaster, where a piece of detached foam damaged the shuttle's wing, leading to its destruction during re-entry.
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Ice debris floats alongside the tank, mistaken for UFOs
The external fuel tank is an integral component of a spacecraft, providing the necessary fuel for propulsion and manoeuvring. However, once the fuel is depleted or the spacecraft reaches its intended orbit, the external tank becomes obsolete and is typically discarded. This separation of the external tank can sometimes lead to unique and unexpected phenomena, including the formation and presence of ice debris.
During the operation of the fuel tank, super-cooled liquid fuels and oxidisers are stored within. Even after separation, residual amounts of these cryogenic liquids can remain, and the extreme temperatures of space cause them to freeze rapidly. As a result, chunks of ice can form both inside and outside the tank. When the external tank re-enters the Earth's atmosphere, these chunks of ice may begin to melt or evaporate due to the increasing temperatures. This process can cause the ice to break apart, creating a trail of ice debris floating in space or even falling back towards Earth alongside the descending tank.
The ice debris, often in the form of small ice crystals or larger icy fragments, can reflect sunlight in peculiar ways. As the tank falls back towards Earth, the ice debris may appear to be floating alongside it, creating a unique visual spectacle. This phenomenon has, on occasion, caught the attention of people on the ground, leading to intriguing reports of unidentified flying objects (UFOs). The ice crystals, when struck by sunlight, can create a shimmering effect, resembling a moving, mysterious object rather than mere ice particles.
Additionally, the larger icy fragments may reflect sunlight in such a way that they appear to have structured, defined shapes, further fuelling speculation and curiosity. In some instances, these icy objects could even create a prism-like effect, refracting sunlight into a spectrum of colours akin to a rainbow. Such optical phenomena can be particularly intriguing and contribute to the perception of these icy fragments as something otherworldly or unexplained.
The mistaken identification of ice debris as UFOs is understandable, given the unique circumstances and visual illusions that can occur. However, it is essential to recognise that these occurrences are natural phenomena resulting from the separation and subsequent re-entry of external fuel tanks. While it may spark curiosity and intrigue, it highlights the importance of accurate identification and the need to consider the various factors contributing to such visual illusions in aerospace observations.
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External tanks are not recoverable or reusable
The cost and weight associated with making external tanks recoverable or reusable are also prohibitive. The tank would require a large, heavy heat shield and strengthening to ensure it survives re-entry and splashdown. Additionally, the shuttle's operating regime is not a stable height for stations, and potential customers looking to take advantage of the "free tanks" would have to ship up other components to make use of them.
The external tank is not in a stable orbit at main engine cutoff, so it re-enters the Earth's atmosphere and burns up, typically over the Indian Ocean. This is why external tanks always land in the ocean and not on land.
While the external tanks themselves are not recoverable or reusable, some have proposed ideas for reusing the tank in orbit. For example, NASA stated that they would be willing to take external tanks to orbit if a private company would use them. However, no private company ever stepped up to take advantage of this offer.
The inability to recover and reuse external tanks highlights the challenges and complexities of space exploration and the limitations of current technology. It also raises questions about the sustainability and long-term viability of space travel, given the significant resources and costs involved in constructing and launching these tanks.
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External tanks could be converted into space habitats
External fuel tanks, after separation, usually burn up in the atmosphere. However, these tanks could be converted into space habitats. The concept of using external fuel tanks as habitats is not new, with proposals dating back to the 1960s. NASA has funded plans to explore this idea further, partnering with companies like Bigelow Aerospace, Boeing, Lockheed Martin, and NanoRacks.
NanoRacks, in collaboration with Space Systems Loral and United Launch Alliance, aims to convert empty fuel tanks from upper-stage rockets into space habitats. These tanks have their own guidance systems, propulsion, attitude control systems, and large, lightweight propellant tanks capable of handling atmospheric pressure. By reusing these tanks, a significant cost saving of at least one launch vehicle can be achieved.
The process of converting a fuel tank into a habitable space involves installing bulkheads, airlocks, and cutting holes for access. The Ixion Team, for instance, proposes converting a Centaur rocket upper stage, attaching it to the International Space Station (ISS), and utilizing it as a proving ground for commercial activities in low Earth orbit.
The advantages of converting external fuel tanks into space habitats include cost savings, as it eliminates the need for a separate rocket to launch the habitat. Additionally, the strong walls, structural reinforcements, airtight sealing, and tubing of the fuel tanks can be reused as structural parts of a space station, such as habitats, greenhouses, or trusses.
Overall, the conversion of external fuel tanks into space habitats offers a revolutionary, low-cost solution for space exploration, providing additional space for various activities and potentially reducing the need for multiple launches.
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Frequently asked questions
The external fuel tank disintegrates in the atmosphere and falls into the sea. During re-entry, the tank heats up and breaks apart, resulting in rapid combustion which breaks the tank into smaller pieces that are easily burned up before reaching the surface.
The cost and weight associated with reusing the external fuel tank are too great to be permitted. The tank would require a large, heavy heat shield and strengthening to ensure it survives re-entry and splashdown.
The remains of the external fuel tank typically land in the Indian Ocean.
