Scientists can study recovered debris more closely as more and more enters Earth’s atmosphere for reentry. Reentry requires complex tracking and monitoring tools.
The primary goal is to maintain equilibrium between dynamic pressure and velocity so that the spacecraft can gradually descend to Earth on an accurately calculated trajectory. To accomplish this task, thermal energy conversion occurs.
Heat shields
Reentry is one of the hottest parts of space travel, where temperatures and forces strain materials and technology to their limit. To prevent its spacecraft from burning up during reentry, heat shields must be present onboard.
Insulating tiles designed specifically to cover vulnerable parts of a vehicle are available and their effectiveness depends on their emissivity (how well they reflect or absorb thermal heat).
Spacecraft reentering Earth’s atmosphere experience extreme heat from atmospheric friction, which can melt metals. To protect itself against this searing heat – which can reach 2900 degrees Fahrenheit – TPS materials of the Space Shuttle provide thermal protection.
NASA’s ablative ceramic tiles have proven themselves as one of the best heat shields, used on Soyuz and Shenzhou vehicles as well as Apollo, Gemini, and Mercury spacecraft. Unfortunately these heavy tiles cannot be reused since they’re attached directly to spacecraft.
Ablators
As soon as a spacecraft enters Earth’s atmosphere, it generates enormous heat that could potentially damage or even dismantle it.
Engineers use ablators to reduce the likelihood of this happening; these materials help carry excess thermal energy away from spacecraft by burning away or vaporizing.
Ablative materials also aid reentry spacecraft cooling by being located on its backside (leeward side) where temperatures tend to transfer at a much lower rate compared to windward.
Ablator materials typically consist of glass, ceramics or composites containing both organic and inorganic material, and they can be formed into different shapes and sizes to meet different purposes. Beyond atmospheric reentry applications, ablators may also be used for cooling rocket engine nozzles that have been exposed to extreme temperatures during launch and atmospheric reentry.
Orbiter reentry
Spacecraft with low reentry velocity such as the space shuttle or Crew Dragon depend heavily on thermal protection to slow their descent and land safely. While these craft have earned themselves an outstanding safety record, even small damage could trigger catastrophic failure during reentry if ignored; for this reason it’s essential that they undergo thorough inspection every orbit. On their second day of flight two crew members perform a detailed scan of reinforced carbon-carbon wings leading edges and nose caps, looking out for any damage which might cause problems during reentry.
Damage to the heat shield is the most frequently occurring issue during reentry. As it heats up during reentry, it absorbs atmospheric gases before radiating them back out again – increasing atmospheric pressure over wide areas and thus slowing the spacecraft down while potentially increasing risk as its speed converts to thermal energy that could potentially burn its crewmembers.
Breakup
Dependent upon its materials, anywhere between 10-40 percent of a spacecraft may survive reentry. This is likely due to differences in melting points and structural properties; stainless steel and titanium tend to have higher melting points than aluminum, meaning much of such satellites will disintegrate upon reentry and eventually burn up during their descent into earth’s atmosphere.
Fragmentation can also occur due to shock-layer heating, which causes gas molecules to undergo chemical dissociation and absorb heat. Direct friction also contributes to shock-layer heating; however, it may not be its main source.
Timing of reentry is also vital; an error of even one minute in timing could alter footprint locations by hundreds of miles.