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The definition of atmospheric entry is the process by which an object transitions from a planet's surface into outer space.
Answer: False
Explanation: The provided definition is inaccurate. Atmospheric entry is defined as the process by which an object moves from outer space *into* and through the gaseous envelope surrounding a celestial body, not from its surface into space.
Controlled atmospheric entry is characterized by the natural descent of astronomical objects such as meteors.
Answer: False
Explanation: Controlled atmospheric entry refers to the deliberate management of a spacecraft's descent, whereas the natural descent of astronomical objects like meteors is considered uncontrolled entry.
Objects entering Earth's atmosphere from low Earth orbit typically travel at speeds approximating 12.5 km/s.
Answer: False
Explanation: Objects entering Earth's atmosphere from low Earth orbit typically travel at speeds around 7.8 km/s. Speeds of 12.5 km/s are more characteristic of missions entering from higher energy trajectories.
Atmospheric entry on Mars is conventionally considered to begin at a higher altitude than on Earth.
Answer: False
Explanation: Conventional atmospheric entry altitudes differ: Earth is typically considered to begin at 100 km (Kármán line), Mars at approximately 80 km, and Venus at a higher altitude of about 250 km.
Objects typically enter atmospheres at hypersonic speeds, a consequence of sub-orbital, orbital, or unbounded trajectories.
Answer: True
Explanation: The high velocities associated with sub-orbital, orbital, or unbounded trajectories naturally result in objects entering planetary atmospheres at hypersonic speeds.
Entry, Descent, and Landing (EDL) refers only to the final touchdown phase of a spacecraft's journey.
Answer: False
Explanation: Entry, Descent, and Landing (EDL) encompasses the entire sequence from atmospheric interface through deceleration to final touchdown or splashdown.
Which characteristic is indicative of uncontrolled atmospheric entry?
Answer: Descent of astronomical objects or space debris.
Explanation: Uncontrolled atmospheric entry is typically associated with the natural descent of celestial bodies, meteoroids, or space debris, lacking any navigational or deceleration systems.
According to the provided information, at what approximate altitude does atmospheric entry conventionally begin for Earth?
Answer: 100 km
Explanation: Atmospheric entry for Earth is conventionally considered to commence at the Kármán line, which is approximately 100 kilometers above sea level.
On which celestial body does atmospheric entry conventionally begin at the highest altitude (approximately 250 km)?
Answer: Venus
Explanation: Conventional atmospheric entry begins at approximately 100 km for Earth, 80 km for Mars, and about 250 km for Venus.
What is the primary objective of Entry, Descent, and Landing (EDL) for a spacecraft?
Answer: To dissipate kinetic energy and reach a specific destination safely.
Explanation: The primary objective of EDL is to safely dissipate the spacecraft's immense kinetic energy during atmospheric transit and deceleration, ensuring a controlled touchdown at the intended destination.
Aerodynamic heating during atmospheric entry is primarily attributed to friction between the object's surface and atmospheric particles.
Answer: False
Explanation: Aerodynamic heating is predominantly caused by the compression of atmospheric gases ahead of the object, not primarily by friction with the surface.
Atmospheric entry forces can result in objects gaining mass through accretion.
Answer: False
Explanation: Atmospheric entry forces typically cause mass loss through ablation and disintegration, not mass gain via accretion.
High-altitude parachute jumps require heat shielding due to their involvement of very high entry velocities.
Answer: False
Explanation: High-altitude parachute jumps, typically initiated from near-stationary positions within or close to the atmosphere, do not achieve the high velocities necessary to generate significant atmospheric heating, thus negating the need for heat shielding.
A higher drag coefficient on an entry vehicle leads to a greater heat load on its surface.
Answer: False
Explanation: A higher drag coefficient, typically achieved with a blunter shape, results in a lower heat load on the vehicle because the shock wave and hot gas are pushed further away.
Convection is the dominant source of heating during atmospheric entry at extremely high velocities.
Answer: False
Explanation: At extremely high velocities during atmospheric entry, radiative heating becomes dominant due to the intense energy generated in the shock layer, surpassing convective heating.
Radio communication blackouts during reentry are caused by the spacecraft's engines interfering with radio signals.
Answer: False
Explanation: Radio communication blackouts are caused by the intense ionization of the air in the shock layer, which interferes with radio wave propagation, not by the spacecraft's engines.
The perfect gas model is accurate for reentry calculations even at temperatures exceeding 2,000 K.
Answer: False
Explanation: The perfect gas model becomes significantly inaccurate at temperatures exceeding approximately 2,000 K, where real gas effects such as dissociation and ionization become dominant.
The Fay-Riddell equation is used to model heat flux assuming the gas reaches chemical equilibrium at the stagnation point.
Answer: True
Explanation: The Fay-Riddell equation is a model for stagnation point heat flux that relies on the assumption of chemical equilibrium in the gas flow at that point.
The 'overshoot' trajectory primarily dictates the TPS material selection based on peak heat flux.
Answer: False
Explanation: The 'overshoot' trajectory (shallowest entry angle) primarily dictates the required *thickness* of the TPS due to higher heat load. The 'undershoot' trajectory (steepest entry angle) dictates TPS material selection based on peak heat flux and dynamic pressure.
Identify the principal mechanism responsible for aerodynamic heating during atmospheric entry.
Answer: Adiabatic compression of atmospheric gases ahead of the object.
Explanation: Aerodynamic heating is primarily caused by the adiabatic compression of atmospheric gases ahead of the entering object, which raises the gas temperature significantly. While friction and chemical reactions can contribute, compression is the dominant factor.
Explain the relationship between the heat load experienced by an entry vehicle and its drag coefficient.
Answer: Inversely proportional; higher drag coefficient means lower heat load.
Explanation: The heat load on an entry vehicle is inversely proportional to its drag coefficient. A higher drag coefficient, achieved through a blunter shape, pushes the shock wave and hot gas further from the vehicle, reducing heat transfer.
Identify the two primary sources of heat experienced during atmospheric entry.
Answer: Convection and radiation from the shock layer.
Explanation: The primary sources of heat during atmospheric entry are convective heat transfer from the hot gas flowing over the vehicle's surface and radiative heat transfer from the high-temperature plasma in the shock layer.
At very high speeds during atmospheric entry, which type of heating becomes dominant?
Answer: Radiative heating
Explanation: As entry velocity increases, radiative heating, which scales with velocity to a higher power than convective heating, becomes the dominant mechanism for heat transfer.
Explain what causes the 'radio-blackout' phenomenon during atmospheric entry.
Answer: The intense ionization of air in the shock layer interfering with signals.
Explanation: The high temperatures during reentry ionize the surrounding air, creating a plasma sheath that absorbs or reflects radio waves, causing a temporary communication blackout.
Under what condition does the 'perfect gas' model become significantly inaccurate for reentry calculations?
Answer: Temperatures above approximately 2,000 K
Explanation: The perfect gas model becomes significantly inaccurate at temperatures exceeding approximately 2,000 K, where real gas effects such as dissociation and ionization become dominant.
Which trajectory type primarily dictates the required *thickness* of the Thermal Protection System (TPS)?
Answer: Shallow trajectory ('overshoot')
Explanation: A shallow entry trajectory, often termed an 'overshoot,' results in a longer duration of atmospheric interaction and a higher cumulative heat load, thus primarily dictating the required thickness of the Thermal Protection System (TPS).
Explain the purpose of the 'radio-blackout' phenomenon during atmospheric entry.
Answer: It is an interference effect caused by ionized air, disrupting radio signals.
Explanation: The 'radio-blackout' phenomenon is not a purpose but a consequence: the ionized plasma sheath formed around a spacecraft during reentry interferes with radio wave propagation, disrupting communications.
Retrorockets are considered a highly efficient method for decelerating an entire spacecraft throughout the entire atmospheric reentry process.
Answer: False
Explanation: Retrorockets are generally impractical for decelerating an entire spacecraft throughout the entire reentry process due to the immense kinetic energy involved, making such an approach highly fuel-inefficient.
Crewed spacecraft must achieve subsonic speeds prior to the deployment of parachutes during reentry.
Answer: True
Explanation: For crewed space vehicles, it is essential to decelerate to subsonic velocities before parachutes or air brakes can be safely deployed to avoid structural failure.
Ballistic warheads are designed to slow down significantly during reentry to ensure a gentle landing.
Answer: False
Explanation: Ballistic warheads are designed to maintain high speeds during reentry, utilizing streamlined shapes for minimal deceleration, rather than slowing down for a gentle landing.
Buoyancy is a viable alternative method for controlled atmospheric entry on planets with very thin atmospheres.
Answer: False
Explanation: Buoyancy is most effective as a controlled entry method in planets with dense atmospheres or strong gravitational forces, not thin ones.
H. Julian Allen and A. J. Eggers Jr. discovered that sharp, pointed shapes were most effective for heat shielding during reentry.
Answer: False
Explanation: H. Julian Allen and A. J. Eggers Jr. discovered that blunt shapes, which create a detached shock wave and push hot gas away from the vehicle, are more effective for heat shielding during reentry.
The Apollo command module utilized its angle of attack and rolling maneuverability to control its landing site.
Answer: True
Explanation: By flying at a specific angle of attack and rolling, the Apollo command module could generate lift, directing its trajectory for controlled landing site selection.
A biconic shape offers a lower lift-to-drag ratio compared to a simple sphere-cone design.
Answer: False
Explanation: A biconic shape generally provides a significantly improved lift-to-drag ratio compared to a simple sphere-cone design, offering greater maneuverability.
The 'feathered configuration' used by SpaceShipOne dramatically decreases aerodynamic drag during reentry.
Answer: False
Explanation: The 'feathered configuration' of SpaceShipOne significantly *increases* aerodynamic drag, enabling deceleration at higher altitudes.
Inflatable heat shields significantly reduce the 'drag area' of an entry system, limiting payload capacity.
Answer: False
Explanation: Inflatable heat shields significantly *increase* the 'drag area' for deceleration, which can allow for greater payload capacity, not limit it.
Explain why retrorockets are generally considered impractical for decelerating an entire spacecraft throughout the entire reentry process.
Answer: Retrorockets require excessive amounts of fuel due to the high kinetic energy involved.
Explanation: The immense kinetic energy of a spacecraft during reentry necessitates an enormous amount of fuel for retrorockets to achieve significant deceleration, rendering this approach highly impractical and inefficient for the entire process.
What counterintuitive discovery concerning reentry vehicle shapes was made by H. Julian Allen and A. J. Eggers Jr.?
Answer: Blunt shapes push the shock wave and heated air away, acting as effective heat shields.
Explanation: Allen and Eggers discovered that blunt shapes, despite generating higher drag, are more effective heat shields because they displace the shock wave and the superheated air layer away from the vehicle's surface.
Identify the mechanism that enabled the Apollo command module to achieve cross-range control during reentry.
Answer: Adjusting its angle of attack and rolling along its axis.
Explanation: The Apollo command module, by flying at a specific angle of attack and rolling, generated aerodynamic lift that could be directed laterally, providing cross-range capability for landing site control.
Explain how the 'feathered configuration' employed by SpaceShipOne aids in reentry.
Answer: It increases aerodynamic drag significantly, slowing the vehicle at higher altitudes.
Explanation: The feathered configuration of SpaceShipOne dramatically increases its drag coefficient, causing significant deceleration at higher altitudes and reducing the peak thermal and dynamic loads experienced.
What advantage do inflatable heat shields offer for missions such as Mars sample returns?
Answer: They significantly increase the 'drag area' for deceleration, allowing for greater payload.
Explanation: Inflatable heat shields can dramatically enlarge the 'drag area' of an entry system, enhancing deceleration capabilities and thereby enabling the transport of larger payloads, which is advantageous for missions like Mars sample returns.
What type of trajectory do ballistic warheads typically follow during reentry?
Answer: A trajectory that maintains high speed using a streamlined shape.
Explanation: Ballistic warheads are designed with streamlined shapes to minimize drag and maintain high velocities throughout reentry, rather than employing deceleration strategies for gentle landing.
What is a key advantage of a biconic shape compared to a sphere-cone shape for entry vehicles?
Answer: Significantly improved lift-to-drag ratio.
Explanation: Biconic shapes offer a significantly improved lift-to-drag ratio over sphere-cone designs, enhancing maneuverability and control during atmospheric entry.
Ablative heat shields are designed to be reusable for multiple reentry missions.
Answer: False
Explanation: Ablative heat shields function by sacrificing material through charring, melting, or sublimation, making them non-reusable for subsequent missions.
PICA-X is a TPS material developed by NASA for its cost-effectiveness.
Answer: False
Explanation: PICA-X is an improved and more cost-effective version of PICA, developed by SpaceX, not NASA.
The Space Shuttle utilized tiles made of refractory insulation materials to keep heat contained within the outermost layer.
Answer: True
Explanation: The Space Shuttle employed refractory insulation tiles, which are characterized by high melting points and low thermal conductivity, to insulate the spacecraft's structure from external heat.
Actively cooled TPS relies on absorbing heat during reentry and radiating it away later.
Answer: False
Explanation: Actively cooled TPS uses circulating coolants to remove heat from the shield's surface. Absorbing and radiating heat is characteristic of passively cooled (radiative) TPS.
Describe how an ablative heat shield protects a spacecraft.
Answer: By charring, melting, or sublimating its surface material to carry heat away.
Explanation: Ablative heat shields protect spacecraft by undergoing controlled material degradation (charring, melting, sublimation), which absorbs heat and carries it away with the ejected gases, forming a cooler boundary layer.
Define PICA as a type of Thermal Protection System (TPS) material.
Answer: Phenolic-impregnated carbon ablator
Explanation: PICA stands for Phenolic-impregnated carbon ablator, a lightweight and effective ablative material used for thermal protection during atmospheric reentry.
Identify the TPS material utilized on the Space Shuttle's nose cone and wing leading edges, known for its high temperature resistance.
Answer: Reinforced Carbon-Carbon (RCC)
Explanation: Reinforced Carbon-Carbon (RCC) was employed on the Space Shuttle's nose cone and wing leading edges due to its exceptional resistance to the extremely high temperatures encountered during reentry.
Describe the main principle behind 'passively cooled' or 'radiatively cooled' TPS.
Answer: Using materials that absorb heat during entry and radiate it away afterward.
Explanation: Passively cooled TPS utilizes materials that absorb the heat flux during reentry and then dissipate this stored energy through radiation and convection after the peak heating phase.
Identify the TPS material described as an improved and more cost-effective version of PICA, developed by SpaceX.
Answer: PICA-X
Explanation: PICA-X is an advanced, cost-effective variant of the PICA (Phenolic-impregnated carbon ablator) material, developed by SpaceX for use in their spacecraft heat shields.
What is the primary function of refractory insulation TPS materials, such as those used on the Space Shuttle?
Answer: To keep heat contained within the outermost layer of the spacecraft's surface.
Explanation: Refractory insulation TPS materials, like the tiles on the Space Shuttle, function by minimizing heat conduction into the spacecraft structure, effectively containing the heat within the outermost layers.
Robert Goddard proposed the concept of an ablative heat shield in the early 20th century.
Answer: True
Explanation: Robert Goddard documented the concept of an ablative heat shield as early as 1920, drawing inspiration from the erosion experienced by meteors.
The development of reentry vehicles for ICBMs required less advanced heat shielding than that needed for medium-range missiles.
Answer: False
Explanation: The longer ranges and higher velocities of Intercontinental Ballistic Missiles (ICBMs) necessitated more advanced heat shielding and blunt vehicle designs compared to earlier medium-range missiles.
Dean R. Chapman proposed feathered reentry as a method for increasing speed during entry.
Answer: False
Explanation: Dean R. Chapman proposed feathered reentry as a method for *decreasing* speed during entry by increasing drag, not for increasing speed.
Robert Goddard's early reasoning for developing an ablative heat shield was inspired by:
Answer: The erosion experienced by meteors traveling at high speeds.
Explanation: Robert Goddard's concept for an ablative heat shield was motivated by observing the erosion experienced by meteors during their passage through Earth's atmosphere.
Approximately 50% to 70% of a satellite's mass typically survives reentry and reaches the Earth's surface.
Answer: False
Explanation: Typically, only a fraction of a satellite's mass, estimated between 10% and 40%, survives atmospheric reentry and reaches the Earth's surface.
The Soviet satellite Kosmos 954 scattered non-radioactive debris across Canada upon reentry.
Answer: False
Explanation: The Soviet satellite Kosmos 954 scattered *radioactive* debris across Canada upon its reentry in 1978.
The Skylab space station's reentry was successfully controlled by the Space Shuttle to ensure a safe landing zone.
Answer: False
Explanation: The Skylab space station's reentry in 1979 was uncontrolled. NASA had intended to use the Space Shuttle to manage its descent, but delays prevented this, and debris scattered across Australia.
The increasing number of satellites reentering the atmosphere contributes significantly to atmospheric pollution, potentially impacting the ozone layer.
Answer: True
Explanation: The cumulative effect of numerous satellites reentering the atmosphere introduces artificial aerosols into the atmosphere. These pollutants can react with atmospheric constituents and potentially negatively impact layers like the ozone layer.
'Atmosphere-blindness' refers to the practice of designing spacecraft to be completely immune to atmospheric effects.
Answer: False
Explanation: 'Atmosphere-blindness' describes the current focus on preventing uncontrolled reentry and space debris, while inadequately addressing the cumulative atmospheric pollution caused by routine de-orbiting.
What is the approximate percentage of a satellite's mass that typically survives atmospheric reentry and reaches the Earth's surface?
Answer: 10% to 40%
Explanation: Typically, only a fraction of a satellite's mass, estimated between 10% and 40%, survives the intense heat and forces of atmospheric reentry to reach the Earth's surface.
What is the main challenge addressed by the concept of 'atmosphere-blindness' in the context of space sustainability?
Answer: Managing the cumulative atmospheric pollution from reentering spacecraft.
Explanation: 'Atmosphere-blindness' highlights the challenge of addressing the environmental impact of atmospheric pollution caused by the increasing number of spacecraft reentering Earth's atmosphere.
What did the Soviet satellite Kosmos 954 scatter across Canada upon its reentry?
Answer: Radioactive debris
Explanation: The Soviet satellite Kosmos 954, which reentered in 1978, scattered radioactive debris across a significant area of Canada.