Published September 27, 2017
One of Japan's most popular science fiction television series has inspired researchers to develop a new technique in order to protect spacecraft from the intense heat of atmospheric re-entry.
The experimental re-entry method utilizes an aeroshell that acts like a parachute, similar to the ones featured in the 1985 science fiction television show "Mobile Suit Z Gundam," according to The Asahi Shimbun newspaper.
The test took nearly three months to complete but was proven successful as a small micro-satellite using the research team's aeroshell device made its return to Earth late last month.
While the Earth's atmosphere is essential for protecting and supporting life on the planet, it acts as major obstacle for both crewed and uncrewed spacecraft as they return from orbit.
Typical low Earth orbit re-entry speeds can reach nearly 17,500 mph, according to NASA. A hypersonic descent through the atmosphere subjects spacecraft to intense atmospheric drag and aerodynamic heating as it plunges back to Earth.
"All of the energy expended to get to orbit dissipates on the way back to Earth, usually in the form of extreme heating," according to a NASA report.
"In addition to the aerodynamic concerns of high-speed flight, there are serious thermodynamic issues with a 17,500-mph plunge through Earth’s atmosphere," the report states.
For example, temperatures nearing 3,000 degrees Fahrenheit have been measured during the re-entry of NASA's Space Shuttle Orbiter.
In the Gundam anime, the "mobile suits" employ a hemispherical device similar called a "ballute," which acts as a heat shield and slows the decent of these robotic vehicles through the extreme conditions of Earth's atmosphere. Researchers used this as inspiration in their design, according to the Asahi Shimbun.
The balloon-like, "ballute" devices featured in the television show were critical in the military operations of both the AEUG resistance group and the tyrannical Titans, which used them to transition from space to terrestrial combat during the events of the Zeta Gundam series.
"The chief characteristic of re-entry aerodynamics is that the temperature of the flow is so great that the chemical bonds of the diatomic molecules of the air are broken," according to NASA. "The molecules break apart producing an electrically charged plasma around the aircraft."
By slowing the plunge to Earth with decelerating speeds through the use of the aeroshell, spacecraft protected by the device would encounter less air resistance, which could help prevent overheating and simplify the design of heat-shielding for future spacecraft.
The research team was able to replicate the Gundam-like deceleration method when testing their heat-shielded aeroshell on the EGG micro-satellite as it entered Earth's atmosphere from low Earth orbit, according to The Asahi Shimbun.
University of Tokyo's team designed EGG, short for "re-Entry satellite with Gossamer aeroshell and Gps/Iridium" as a miniature, 34 cm, cube-shaped satellite.
The micro-satellite was then deployed from the International Space Station in January to test the re-entry method. As the small spacecraft fell to Earth, the aeroshell inflated like a parachute, slowing its speed and protecting it from aerodynamic heating.
The aeroshell itself was around 80 cm in size and made out of a material similar to fireproof clothing, according to the report. At around 95 km altitude, the aeroshell burned up over the Pacific in May as planned.
Allowing a heat shield to burn up during re-entry is part of the design in thermal protection systems used on other spacecraft.
These ablative, or burning, heat shields have been used for the Russian Soyuz, the Chinese Shenzhou and all of the early Apollo, Gemini and Mercury spacecraft missions, according to NASA.
After nearly three months of falling, the EGG finally made its return to Earth, proving the experiment successful on June 23.
“The EGG would be useful for bringing samples from space as well as exploring atmospheric planets such as Mars,” aerospace engineer Kojiro Suzuki told reporters with the Asahi Shimbun.
In the future, this technology may be able to help reduce the risk to spacecraft and crew and make for a safer return to Earth.