Aerobraking is a spaceflight maneuver that reduces the high point of an elliptical orbit (apoapsis) by flying the vehicle through the atmosphere at the low point of the orbit (periapsis). The resulting drag slows the spacecraft. Aerobraking is used when a spacecraft requires a low orbit after arriving at a body with an atmosphere, as it requires less fuel than using propulsion to slow down.
When an interplanetary vehicle arrives at its destination, it must reduce its velocity to achieve orbit or to land. To reach a low, near-circular orbit around a body with substantial gravity (as is required for many scientific studies), the required velocity changes can be on the order of kilometers per second. Using propulsion, the rocket equation dictates that a large fraction of the spacecraft mass must consist of fuel. This reduces the science payload and/or requires a large and expensive rocket. Provided the target body has an atmosphere, aerobraking can be used to reduce fuel requirements. The use of a relatively small burn allows the spacecraft to enter an elongated elliptic orbit. Aerobraking then shortens the orbit into a circle. If the atmosphere is thick enough, a single pass can be sufficient to adjust the orbit. However, aerobraking typically requires multiple orbits higher in the atmosphere. This reduces the effects of frictional heating, unpredictable turbulence effects, atmospheric composition, and temperature.
Aerobraking done this way allows sufficient time after each pass to measure the velocity change and make corrections for the next pass. Achieving the final orbit may take over six months for Mars, and may require hundreds of passes through the atmosphere. After the last pass, if the spacecraft shall stay in orbit, it must be given more kinetic energy via rocket engines in order to raise the periapsis above the atmosphere. If the craft shall land, it must lose kinetic energy, also via rocket engines.
The kinetic energy dissipated by aerobraking is converted to heat, meaning that spacecraft must dissipate this heat. The spacecraft must have sufficient surface area and structural strength to produce and survive the required drag, The temperatures and pressures associated with aerobraking are not as severe as those of atmospheric reentry or aerocapture. Simulations of the Mars Reconnaissance Orbiter aerobraking use a force limit of 0.35 N per square meter with a spacecraft cross section of about 37 m2, equate to a maximum drag force of about 7.4 N, and a maximum expected temperature as 170 °C. [1] The force density (i.e. pressure), roughly 0.2 N per square meter, [2] that was exerted on the Mars Observer during aerobraking is comparable to the aerodynamic resistance of moving at 0.6 m/s (2.16 km/h) at sea level on Earth, approximately the amount experienced when walking slowly. [3]
Regarding spacecraft navigation, Moriba Jah was the first to demonstrate the ability to process Inertial Measurement Unit (IMU) data collected on board the spacecraft, during aerobraking, using an unscented Kalman Filter to statistically infer the spacecraft's trajectory independent of ground-based measurement data. Jah did this using actual IMU data from Mars Odyssey and Mars Reconnaissance Orbiter . Moreover, this was the first use of an unscented Kalman Filter to determine the orbit of an anthropogenic space object about another planet. [4] This method, which could be used to automate aerobraking navigation, is called Inertial Measurements for Aeroassisted Navigation (IMAN) [5] and Jah won a NASA Space Act Award for this work.
Many spacecraft use solar panels to power their operations. The panels can be used to refine aerobraking to reduce the number of required orbits. The panels rotate according to an AI-powered algorithm to increase/reduce drag and can reduce arrival times from months to weeks. [6]
Aerocapture is a related but more extreme method in which no initial orbit-injection burn is performed. Instead, the spacecraft plunges deeply into the atmosphere without an initial insertion burn, and emerges from this single pass in the atmosphere with an apoapsis near that of the desired orbit. Several small correction burns are then used to raise the periapsis and perform final adjustments. [7]
This method was originally planned for the Mars Odyssey orbiter, [8] but the significant design impacts proved too costly. [7]
Another related technique is that of aerogravity assist, in which the spacecraft flies through the upper atmosphere and uses aerodynamic lift instead of drag at the point of closest approach. If correctly oriented, this can increase the deflection angle above that of a pure gravity assist, resulting in a larger delta-v. [9]
Although the theory of aerobraking is well developed, using the technique is difficult because a very detailed knowledge of the character of the target planet's atmosphere is needed in order to plan the maneuver correctly. Currently, the deceleration is monitored during each maneuver and plans are modified accordingly. Since no spacecraft can yet aerobrake safely on its own, this requires constant attention from both human controllers and the Deep Space Network. This is particularly true near the end of the process, when the drag passes are relatively close together (only about 2 hours apart for Mars).[ citation needed ] NASA has used aerobraking four times to modify a spacecraft's orbit to one with lower energy, reduced apoapsis altitude, and smaller orbit. [10]
On 19 March 1991, aerobraking was demonstrated by the Hiten spacecraft. This was the first aerobraking maneuver by a deep space probe. [11] Hiten (a.k.a. MUSES-A) was launched by the Institute of Space and Astronautical Science (ISAS) of Japan. [12] Hiten flew by the Earth at an altitude of 125.5 km over the Pacific at 11.0 km/s. Atmospheric drag lowered the velocity by 1.712 m/s and the apogee altitude by 8665 km. [13] Another aerobraking maneuver was conducted on 30 March.
In May 1993, aerobraking was used during the extended Venusian mission of the Magellan spacecraft. [14] It was used to circularize the orbit of the spacecraft in order to increase the precision of the measurement of the gravity field. The entire gravity field was mapped from the circular orbit during a 243-day cycle of the extended mission. During the termination phase of the mission, a "windmill experiment" was performed: Atmospheric molecular pressure exerts a torque via the windmill-sail-like oriented solar cell wings, the necessary counter-torque to keep the probe from spinning is measured. [15]
In 1997, the Mars Global Surveyor (MGS) orbiter was the first spacecraft to use aerobraking as the main planned technique of orbit adjustment. The MGS used the data gathered from the Magellan mission to Venus to plan its aerobraking technique. The spacecraft used its solar panels as "wings" to control its passage through the tenuous upper atmosphere of Mars and lower the apoapsis of its orbit over the course of many months. Unfortunately, a structural failure shortly after launch severely damaged one of the MGS's solar panels and necessitated a higher aerobraking altitude (and hence one third the force) than originally planned, significantly extending the time required to attain the desired orbit. More recently, aerobraking was used by the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft, in both cases without incident.
In 2014, an aerobraking experiment was successfully performed on a test basis near the end of the mission of the ESA probe Venus Express . [16] [17]
In 2017–2018, the ESA ExoMars Trace Gas Orbiter performed aerobraking at Mars to reduce the apocentre of the orbit, being the first operational aerobraking for a European mission. [18]
Mars Orbiter Mission 2 is a future mission by ISRO, which is proposed to use aerobraking to reduce its apoapsis. [19]
In Robert A. Heinlein's 1948 novel Space Cadet , aerobraking is used to save fuel while slowing the spacecraft Aes Triplex for an unplanned extended mission and landing on Venus, during a transit from the Asteroid Belt to Earth. [20]
The spacecraft Cosmonaut Alexei Leonov in Arthur C. Clarke's 1982 novel 2010: Odyssey Two and its 1984 film adaptation uses aerobraking in the upper layers of Jupiter's atmosphere to establish itself at the L1 Lagrangian point of the Jupiter – Io system.
In the 2004 TV series Space Odyssey: Voyage to the Planets the crew of the international spacecraft Pegasus perform an aerobraking manoeuvre in Jupiter's upper atmosphere to slow them down enough to enter Jovian orbit.
In the fourth episode of Stargate Universe , the Ancient ship Destiny suffers an almost complete loss of power and must use aerobraking to change course. The 2009 episode ends in a cliffhanger with Destiny headed directly toward a star.
In the space simulation sandbox game Kerbal Space Program , this is a common method of reducing a craft's orbital speed. It is sometimes humorously referred to as "aerobreaking", because the high drag sometimes causes large crafts to split in several parts.
In Kim Stanley Robinson's Mars trilogy, the Ares spaceship carrying the first hundred humans to arrive on Mars uses aerobraking to enter into orbit around the planet. Later in the books, as an effort to thicken the atmosphere, scientists bring an asteroid into aerobraking in order to vaporize it and release its contents into the atmosphere.
In the 2014 film Interstellar , astronaut pilot Cooper uses aerobraking to save fuel and slow the spacecraft Ranger upon exiting the wormhole to arrive in orbit above the first planet.
Aerodynamic braking is a method used in landing aircraft to assist the wheel brakes in stopping the plane. It is often used for short runway landings or when conditions are wet, icy or slippery. Aerodynamic braking is performed immediately after the rear wheels (main mounts) touch down, but before the nose wheel drops. The pilot begins to pull back on the stick, applying elevator pressure to hold the nose high. The nose-high attitude exposes more of the craft's surface-area to the flow of air, which produces greater drag, helping to slow the plane. The raised elevators also cause air to push down on the rear of the craft, forcing the rear wheels harder against the ground, which aids the wheel brakes by helping to prevent skidding. The pilot will usually continue to hold back on the stick even after the elevators lose their authority, and the nose wheel drops, to keep added pressure on the rear wheels.
Aerodynamic braking is a common braking technique during landing, which can also help to protect the wheel brakes and tires from excess wear, or from locking up and sending the craft sliding out of control. It is often used by private pilots, commercial planes, fighter aircraft, and was used by the Space Shuttles during landings. [21] [22] [23]
Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric entry.
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: uncontrolled entry, such as the entry of astronomical objects, space debris, or bolides; and controlled entry of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric entry, descent, and landing of spacecraft are collectively termed as EDL.
A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.
Mars Express is a space exploration mission being conducted by the European Space Agency (ESA). The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was designed and built. However, "Express" also describes the spacecraft's relatively short interplanetary voyage, a result of being launched when the orbits of Earth and Mars brought them closer than they had been in about 60,000 years.
Mars Global Surveyor (MGS) was an American robotic space probe developed by NASA's Jet Propulsion Laboratory and launched November 1996. MGS was a global mapping mission that examined the entire planet, from the ionosphere down through the atmosphere to the surface. As part of the larger Mars Exploration Program, Mars Global Surveyor performed atmospheric monitoring for sister orbiters during aerobraking, and helped Mars rovers and lander missions by identifying potential landing sites and relaying surface telemetry.
Mars 96 was a failed Mars mission launched in 1996 to investigate Mars by the Russian Space Forces and not directly related to the Soviet Mars probe program of the same name. After failure of the second fourth-stage burn, the probe assembly re-entered the Earth's atmosphere, breaking up over a 320 km (200 mi) long portion of the Pacific Ocean, Chile, and Bolivia. The Mars 96 spacecraft was based on the Phobos probes launched to Mars in 1988. They were of a new design at the time and both ultimately failed. For the Mars 96 mission the designers believed they had corrected the flaws of the Phobos probes, but the value of their improvements was never demonstrated due to the destruction of the probe during the launch phase.
Lithobraking is a whimsical "crash landing" euphemism used by spacecraft engineers to refer to a spacecraft impacting the surface of a planet or moon. The word was coined by analogy with "aerobraking", slowing a spacecraft by intersecting the atmosphere, with "lithos" substituted to indicate the spacecraft is intersecting the planet's solid lithosphere rather than merely its gaseous atmosphere.
Venus Express (VEX) was the first Venus exploration mission of the European Space Agency (ESA). Launched in November 2005, it arrived at Venus in April 2006 and began continuously sending back science data from its polar orbit around Venus. Equipped with seven scientific instruments, the main objective of the mission was the long term observation of the Venusian atmosphere. The observation over such long periods of time had never been done in previous missions to Venus, and was key to a better understanding of the atmospheric dynamics. ESA concluded the mission in December 2014.
In astrodynamics and aerospace, a delta-v budget is an estimate of the total change in velocity (delta-v) required for a space mission. It is calculated as the sum of the delta-v required to perform each propulsive maneuver needed during the mission. As input to the Tsiolkovsky rocket equation, it determines how much propellant is required for a vehicle of given empty mass and propulsion system.
Orbital inclination change is an orbital maneuver aimed at changing the inclination of an orbiting body's orbit. This maneuver is also known as an orbital plane change as the plane of the orbit is tipped. This maneuver requires a change in the orbital velocity vector (delta-v) at the orbital nodes.
The Aurora programme was a human spaceflight programme of the European Space Agency (ESA) established in 2001. The objective was to formulate and then to implement a European long-term plan for exploration of the Solar System using robotic spacecraft and human spaceflight to investigate bodies holding promise for traces of life beyond the Earth.
The ballute is a parachute-like braking device optimized for use at high altitudes and supersonic velocities.
The Hiten spacecraft, given the English name Celestial Maiden and known before launch as MUSES-A, part of the MUSES Program, was built by the Institute of Space and Astronautical Science of Japan and launched on January 24, 1990. It was Japan's first lunar probe, the first robotic lunar probe since the Soviet Union's Luna 24 in 1976, and the first lunar probe launched by a country other than the Soviet Union or the United States. The spacecraft was named after flying heavenly beings in Buddhism.
Aerocapture is an orbital transfer maneuver in which a spacecraft uses aerodynamic drag force from a single pass through a planetary atmosphere to decelerate and achieve orbit insertion.
In spaceflight an orbit insertion is an orbital maneuver which adjusts a spacecraft’s trajectory, allowing entry into an orbit around a planet, moon, or other celestial body. An orbit insertion maneuver involves either deceleration from a speed in excess of the respective body’s escape velocity, or acceleration to it from a lower speed.
Timeline for the Mars Reconnaissance Orbiter (MRO) lists the significant events of the launch, aerobraking, and transition phases as well as subsequent significant operational mission events; by date and brief description.
An aeroshell is a rigid heat-shielded shell that helps decelerate and protects a spacecraft vehicle from pressure, heat, and possible debris created by drag during atmospheric entry. Its main components consist of a heat shield and a back shell. The heat shield absorbs heat caused by air compression in front of the spacecraft during its atmospheric entry. The back shell carries the load being delivered, along with important components such as a parachute, rocket engines, and monitoring electronics like an inertial measurement unit that monitors the orientation of the shell during parachute-slowed descent.
The ExoMars Trace Gas Orbiter is a collaborative project between the European Space Agency (ESA) and the Russian Roscosmos agency that sent an atmospheric research orbiter and the Schiaparelli demonstration lander to Mars in 2016 as part of the European-led ExoMars programme.
Mars atmospheric entry is the entry into the atmosphere of Mars. High velocity entry into Martian air creates a CO2-N2 plasma, as opposed to O2-N2 for Earth air. Mars entry is affected by the radiative effects of hot CO2 gas and Martian dust suspended in the air. Flight regimes for entry, descent, and landing systems include aerocapture, hypersonic, supersonic, and subsonic.
Moriba Kemessia Jah CorrFRSE is an American space scientist and aerospace engineer who describes himself as a "space environmentalist", specializing in orbit determination and prediction, especially as related to space situational awareness and space traffic monitoring. He is currently an associate professor of Aerospace Engineering and Engineering Mechanics at the University of Texas at Austin. Jah previously worked as a spacecraft navigator at the NASA Jet Propulsion Laboratory, where he was a navigator for the Mars Global Surveyor, Mars Odyssey, Mars Express, Mars Exploration Rover, and his last mission was the Mars Reconnaissance Orbiter. He is a Fellow of the American Astronautical Society, the Air Force Research Laboratory, the International Association for the Advancement of Space Safety and, the Royal Astronomical Society. Jah was also selected into the 10th anniversary class of TED Fellows and was named a MacArthur Fellow in 2022. He also was selected into the AIAA class of Fellows and Honorary Fellows in the year of the 50th Anniversary of Apollo 11. The AIAA "confers the distinction of Fellow upon individuals in recognition of their notable and valuable contributions to the arts, sciences or technology of aeronautics and astronautics."
