122 Sentences With "periapsis" | Random Sentence Generator

The point at which a moon and its planet come closest together, known as periapsis, is not constant.

On each of a moon's orbits, periapsis shifts a little farther around the planet until it eventually returns to where it was.

If the December 11th periapsis is also missed, it could become harder for Juno to execute all 36 flybys perfectly, owing to the slow degradation of its scientific instruments in Jupiter's intense radiation environment.

On October 19th, at its point of closest approach to Jupiter (called periapsis), the Juno spacecraft was scheduled to perform its final main engine burn, a "period reduction maneuver" that would narrow its orbit from 53.4 days to 2 weeks.

The longitude of periapsis is a compound angle, with part of it being measured in the plane of reference and the rest being measured in the plane of the orbit. Likewise, any angle derived from the longitude of periapsis (e.g., mean longitude and true longitude) will also be compound. Sometimes, the term longitude of periapsis is used to refer to ω, the angle between the ascending node and the periapsis.

At periapsis , so solving gives = . This puts the periapsis on 4 January 2000 at 00:11:41 while the actual periapsis is, according to results from the Multiyear Interactive Computer Almanac (abbreviated as MICA), on 3 January 2000 at 05:17:30. This large discrepancy happens because the difference between the orbital radius at the two locations is only 1 part in a million; in other words, radius is a very weak function of time near periapsis. As a practical matter this means that one cannot get a highly accurate result for the equation of time by using and adding the actual periapsis date for a given year.

Fig. 1: Diagram of orbital elements, including the argument of periapsis (ω). The argument of periapsis (also called argument of perifocus or argument of pericenter), symbolized as ω, is one of the orbital elements of an orbiting body. Parametrically, ω is the angle from the body's ascending node to its periapsis, measured in the direction of motion. For specific types of orbits, words such as perihelion (for heliocentric orbits), perigee (for geocentric orbits), periastron (for orbits around stars), and so on may replace the word periapsis.

Also, the argument of periapsis is undefined. Geostationary orbit is a geosynchronous example of an equatorial orbit.

Integrating the above energy equation is often unnecessary if the burn duration is short. Short burns of chemical rocket engines close to periapsis or elsewhere are usually mathematically modelled as impulsive burns, where the force of the engine dominates any other forces that might change the vehicle's energy over the burn. For example, as a vehicle falls towards periapsis in any orbit (closed or escape orbits) the velocity relative to the central body increases. Briefly burning the engine (an “impulsive burn”) prograde at periapsis increases the velocity by the same increment as at any other time (\Delta v).

In celestial mechanics, the argument of latitude ( u ) is an angular parameter that defines the position of a body moving along a Kepler orbit. It is the angle between the ascending node and the body. It is the sum of the more commonly used true anomaly and argument of periapsis. u = u + \omega where u is the argument of latitude, u the true anomaly, and \omega the argument of periapsis.

The apsides are the orbital points closest (periapsis) and farthest (apoapsis) from its primary body. The apsidal precession is the first time derivative of the argument of periapsis, one of the six main orbital elements of an orbit. Apsidal precession is considered positive when the orbit's axis rotates in the same direction as the orbital motion. An apsidal period is the time interval required for an orbit to precess through 360°.

The orbiter primary mission ended at the beginning of solar conjunction on October 5, 1976. The extended mission commenced on December 14, 1976 after solar conjunction. On December 20, 1976 the periapsis was lowered to 778 km and the inclination raised to 80 degrees. Operations included close approaches to Deimos in October 1977 and the periapsis was lowered to 300 km and the period changed to 24 hours on October 23, 1977.

These orbital variations cause the axial tilt (the angle between rotational and orbital axes) to vary between 0 and 0.33°. Ganymede participates in orbital resonances with Europa and Io: for every orbit of Ganymede, Europa orbits twice and Io orbits four times. Conjunctions (alignment on the same side of Jupiter) between Io and Europa occur when Io is at periapsis and Europa at apoapsis. Conjunctions between Europa and Ganymede occur when Europa is at periapsis.

Initially, Surveyor entered a highly elliptical orbit that took 45 hours to complete. The orbit had a periapsis of above the northern hemisphere, and an apoapsis of above the southern hemisphere.

A circular orbit is a special case, wherein the foci of the ellipse coincide. The point where the orbiting body is closest to Earth is called the perigee, and is called the periapsis (less properly, "perifocus" or "pericentron") when the orbit is about a body other than Earth. The point where the satellite is farthest from Earth is called the apogee, apoapsis, or sometimes apifocus or apocentron. A line drawn from periapsis to apoapsis is the line-of-apsides.

To serve as an example of how the gravity turn can be used for a powered landing, an Apollo type lander on an airless body will be assumed. The lander begins in a circular orbit docked to the command module. After separation from the command module the lander performs a retrograde burn to lower its periapsis to just above the surface. It then coasts to periapsis where the engine is restarted to perform the gravity turn descent.

As a result, as a planet approaches periapsis, the planet will increase in speed as its potential energy decreases; as a planet approaches apoapsis, its velocity will decrease as its potential energy increases.

Phobos-Grunt around Mars: (1) Arrival of Phobos-Grunt, (2) Insertion maneuver in orbit around Mars, (3) Drop of the Fregat stage and separation of the probe and Yinghuo-1, (4) Maneuver for to raise the periapsis, (5) Yinghuo 1 starts his mission on the first orbit, (6) Maneuver to place himself in an orbit close to that of Phobos; (A) Orbit of Phobos, (B) Orbit of insertion of Phobos-Grunt and Yinghuo-1, (C) Orbit with raised periapsis, (D) Quasi-synchronous orbit with Phobos.

In celestial mechanics, the eccentricity vector of a Kepler orbit is the dimensionless vector with direction pointing from apoapsis to periapsis and with magnitude equal to the orbit's scalar eccentricity. For Kepler orbits the eccentricity vector is a constant of motion. Its main use is in the analysis of almost circular orbits, as perturbing (non-Keplerian) forces on an actual orbit will cause the osculating eccentricity vector to change continuously. For the eccentricity and argument of periapsis parameters, eccentricity zero (circular orbit) corresponds to a singularity.

Thereafter, the periapsis was allowed to rise to a maximum of and then fall, to conserve fuel. In 1991, the Radar Mapper was reactivated to investigate previously inaccessible southern portions of the planet, in conjunction with the recently arrived Magellan spacecraft. In May 1992, Pioneer Venus began the final phase of its mission, in which the periapsis was held between , until the spacecraft's propellant was exhausted, after which the orbit decayed naturally. The spacecraft continued to return data until 8 October 1992, with the last signals being received at 19:22 UTC.

The estimated semi-major axis of the planet's orbit is 1.2 astronomical units (AU), which would give it a periapsis distance of 0.9 AU and an apoapsis distance of 1.5 AU. By comparison, the star has a radius of 0.07 AU.

A powered slingshot is the use of a rocket engine at or around closest approach to a body (periapsis). The use at this point multiplies up the effect of the delta-v, and gives a bigger effect than at other times.

Pallava Bagla, Science Magazine. 17 February 2017. The orbiter, depending on its final configuration, would have a science payload capability of approximately with 500 W available power. The initial elliptical orbit around Venus is expected to have at periapsis and at apoapsis.

First evaluation of the orbital insertion showed that the orbiter had reached its first milestone at Mars. The orbit was later adjusted by four more main engine firings to the desired 259 km × 11,560 km near-polar (86 degree inclination) orbit with a period of 7.5 hours. Near periapsis (nearest to Mars) the top deck is pointed down towards the Martian surface and near apoapsis (farthest from Mars in its orbit) the high gain antenna will be pointed towards Earth for uplink and downlink. After 100 days the apoapsis was lowered to 10,107 km and periapsis raised to 298 km to give an orbital period of 6.7 hours.

First, during its first five orbits of the planet (one Earth week), MRO used its thrusters to drop the periapsis of its orbit into aerobraking altitude. This altitude depends on the thickness of the atmosphere because Martian atmospheric density changes with its seasons. Second, while using its thrusters to make minor corrections to its periapsis altitude, MRO maintained aerobraking altitude for 445 planetary orbits (about five Earth months) to reduce the apoapsis of the orbit to . This was done in such a way so as to not heat the spacecraft too much, but also dip enough into the atmosphere to slow the spacecraft down.

If a body in circular orbit (or at the periapsis of an elliptical orbit) accelerates along its direction of travel to escape velocity, the point of acceleration will form the periapsis of the escape trajectory. The eventual direction of travel will be at 90 degrees to the direction at the point of acceleration. If the body accelerates to beyond escape velocity the eventual direction of travel will be at a smaller angle, and indicated by one of the asymptotes of the hyperbolic trajectory it is now taking. This means the timing of the acceleration is critical if the intention is to escape in a particular direction.

Despite heavy oscillation during ascent, Apollo 10 achieved orbit without incident, successfully docked the LM and CM, and achieved its translunar injection burn. Upon arriving in lunar orbit, Stafford and Cernan undocked in the LM and entered an elliptical orbit with a periapsis (the closest distance) of nine miles over the lunar surface. To provide reconnaissance, the periapsis coincided with the Sea of Tranquility, the intended landing site for Apollo 11. Upon ascent, the LM began turning rapidly from a misaligned switch on the Abort Guidance System; Stafford was able to regain control and conduct the burn to rendezvous with the CM. The LM docked with the CM to return the astronauts and was jettisoned.

The deorbit, coast, and possible reentry phase leading up to the beginning of the final landing burn. The vehicle begins by orienting for a retrograde burn to reduce its orbital velocity, lowering its point of periapsis to near the surface of the body to be landed on. If the craft is landing on a planet with an atmosphere such as Mars the deorbit burn will only lower periapsis into the upper layers of the atmosphere, rather than just above the surface as on an airless body. After the deorbit burn is complete the vehicle can either coast until it is nearer to its landing site or continue firing its engine while maintaining zero angle of attack.

Thus, a final controlled experiment was > designed to maximize mission return. This final, low altitude was necessary > to study the effects of a carbon dioxide atmosphere. The final OTM took the > periapsis to where the sensible drag on the spacecraft was very evident. The > solar panel temperatures rose to 126 deg.

So if a spacecraft is on a parabolic flyby of Jupiter with a periapsis velocity of 50 km/s and performs a 5 km/s burn, it turns out that the final velocity change at great distance is 22.9 km/s, giving a multiplication of the burn by 4.58 times.

A typical Titan encounter changed the spacecraft's velocity by 0.75 km/s, and the spacecraft made 127 Titan encounters. These encounters enabled an orbital tour with a wide range of periapsis and apoapsis distances, various alignments of the orbit with respect to the Sun, and orbital inclinations from 0° to 74°.

The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus, when they approach to within approximately 1400 km. Prometheus is itself a significant perturber of Atlas, with which it is in a 53:54 mean-longitude resonance.

The maximum height above the surface of the orbit is the length of the ellipse, minus R\,\\!, minus the part "below" the center of the Earth, hence twice the increase of a\,\\! minus the periapsis distance. At the top the potential energy is g times this height, and the kinetic energy is .

That usage of the term is especially common in discussions of binary stars and exoplanets."Format" in Sixth Catalog of Orbits of Visual Binary Stars , William I. Hartkopf & Brian D. Mason, U.S. Naval Observatory, Washington, D.C. Accessed on 10 January 2018. However, the angle ω is less ambiguously known as the argument of periapsis.

After the ε ring, the α and β rings are the brightest of Uranus's rings. Like the ε ring, they exhibit regular variations in brightness and width. They are brightest and widest 30° from the apoapsis and dimmest and narrowest 30° from the periapsis. The α and β rings have sizable orbital eccentricity and non- negligible inclination.

A given rocket burn always provides the same change in velocity (Δv), but the change in kinetic energy is proportional to the vehicle's velocity at the time of the burn. So to get the most kinetic energy from the burn, the burn must occur at the vehicle's maximum velocity, at periapsis. Oberth effect describes this technique in more detail.

In this instability region, solar perturbations at apoapse cause the moons in this region to acquire large eccentricities that lead to collisions or ejection over 10 million to a billion years. Margaret's periapsis precession period (Pw) is almost 1.6 million years long. Margaret itself may be ejected from the Uranian system in the far future. In 2010, Margaret's orbital eccentricity was 0.812.

A small radial impulse given to a body in orbit changes the eccentricity, but not the orbital period (to first order). A prograde or retrograde impulse (i.e. an impulse applied along the orbital motion) changes both the eccentricity and the orbital period. Notably, a prograde impulse at periapsis raises the altitude at apoapsis, and vice versa, and a retrograde impulse does the opposite.

The inner of the two Martian moons, Phobos, is in a subsynchronous orbit of Mars with an orbital period of only 0.32 days. The outer moon Deimos is in supersynchronous orbit around Mars. The Mars Orbiter Mission—currently orbiting Mars—is placed into highly elliptical supersynchronous orbit around Mars, with a period of 76.7 hours and a planned periapsis of and apoapsis of .

Here the centripetal force is the gravitational force, and the axis mentioned above is the line through the center of the central mass perpendicular to the plane of motion. In this case, not only the distance, but also the speed, angular speed, potential and kinetic energy are constant. There is no periapsis or apoapsis. This orbit has no radial version.

To avoid overly-redundant data at the highest and lowest latitudes, the Magellan probe alternated between a Northern-swath, a region designated as 90 degrees north latitude to 54 degrees south latitude, and a Southern-swath, designated as 76 degrees north latitude to 68 degrees south latitude. However, due to periapsis being 10 degrees north of the equatorial line, imaging the South Pole region was unlikely.

A despun dish antenna provided S and X band communication with Earth. A Star-24 solid rocket motor was integrated into the spacecraft to provide the thrust to enter orbit around Venus. From Venus orbit insertion to July 1980, periapsis was held between (at 17 degrees north latitude) to facilitate radar and ionospheric measurements. The spacecraft was in a 24-hour orbit with an apoapsis of .

Approximate Inspiration Mars Trajectory (not to scale) Artist's Concept of Inspiration Mars Capsule and Hab. Inspiration Mars Periapsis. They proposed a free return trajectory to allow the spacecraft to use the smallest possible amount of propellant to flyby Mars and return to Earth. They stated that the January 2018 launch window offered a rare orbit opportunity to travel to Mars and return to Earth in 501 days.

The telescope had an initial orbit of with a periapsis of , an apoapsis of , with inclination 98.0° and eccentricity 0.064048, giving it a period of 99.2 minutes. The orbit was sun-synchronous, and the attitude of the spacecraft could be controlled through reaction wheels. The momentum stored in the reaction wheels throughout the orbit was regularly dumped via magnetic coils that interacted with the Earth's magnetic field.

Thus, the angular rate is faster nearer periapsis and slower near apoapsis. The same is so for the Moon's orbit around the Earth. Because of these variations in angular rate, the actual time between lunations may vary from about 29.18 to about 29.93 days. The long-term average duration is daysCRC Handbook of Chemistry and Physics, page F-258 (29 d 12 h 44 m 2.8016 s).

The initial transfer orbit was at an inclination of 26.2 degrees. It had a periapsis of 171 km and an apoapsis of 3,524 km and an orbital period of 619 minutes.NASA Space Science Data Coordinated Archive The orbit was circularized at the operational geosynchronous altitude by a solid propellant apogee kick motor (AKM). The satellite's main body was 1.7 meters high by 2.7 meters in diameter and a hexagonal shape.

Methone's orbit is visibly affected by a perturbing 14:15 mean-longitude resonance with the much larger Mimas. This causes its osculating orbital elements to vary with an amplitude of about in semi-major axis, and 5° in longitude of its periapsis on a timescale of about 450 days. Its eccentricity also varies on different timescales between 0.0011 and 0.0037, and its inclination between about 0.003° and 0.020°.

2, p. 580 For a body in an elliptical orbit wishing to accelerate to an escape orbit the required speed will vary, and will be greatest at periapsis when the body is closest to the central body. However, the orbital speed of the body will also be at its highest at this point, and the change in velocity required will be at its lowest, as explained by the Oberth effect.

Lanzilotti's compositions are characterized by the frequent use of field recordings and extended techniques for strings. Lanzilotti creates soundscapes that invite the audience to engage with sound and listen carefully to the subtleties of resonance. She was the winner of the first Periapsis Emerging Artist Residency, and has been commissioned by The Noguchi Museum several times to write musical works. Lanzilotti was a guest composer at Thailand International Composers Festival in 2018.

The instruments of the orbiter consisted of two vidicon cameras for imaging (VIS), an infrared spectrometer for water vapor mapping (MAWD) and infrared radiometers for thermal mapping (IRTM). The orbiter primary mission ended at the beginning of solar conjunction on November 5, 1976. The extended mission commenced on December 14, 1976, after solar conjunction. Operations included close approaches to Phobos in February 1977. The periapsis was reduced to 300 km on March 11, 1977.

Altitude of Tiangong-1 during its final year of uncontrolled reentry. In orbital mechanics, decay is a gradual decrease of the distance between two orbiting bodies at their closest approach (the periapsis) over many orbital periods. These orbiting bodies can be a planet and its satellite, a star and any object orbiting it, or components of any binary system. Orbits do not decay without some friction-like mechanism which transfers energy from the orbital motion.

As of 6 August, AMC-14 orbit is vastly different. Figures for perigee (periapsis), apogee (apoapsis) and Inclination are given in the info box at the beginning of this article, Inclination has dropped to 17.7 and Eccentricity has decreased to 0.199. As of January 29, 2009, after more than 6 months of low-thrust maneuvering, AMC-14 had finally reached an inclined (13.1°) geosynchronous orbit at 34.8°East under US DoD ownership.

The Keplerian orbital elements An elliptical orbit in three dimensions is uniquely described by a set of six coordinates, called orbital elements. The traditional choice are the Keplerian elements, which consist of the eccentricity, semimajor axis, inclination, longitude of the ascending node, argument of periapsis, and true anomaly. In celestial mechanics calculations, it is common to use a set of orbital elements introduced in nineteenth century by Charles-Eugène Delaunay.Shevchenko 2017, p.

These variations are connected with the variations of the ring width, which is 19.7 km at the periapsis and 96.4 km at the apoapsis. As the ring becomes wider, the amount of shadowing between particles decreases and more of them come into view, leading to higher integrated brightness. The width variations were measured directly from Voyager 2 images, as the ε ring was one of only two rings resolved by Voyager's cameras.

Such behavior indicates that the ring is not optically thin. Indeed, occultation observations conducted from the ground and the spacecraft showed that its normal optical depth varies between 0.5 and 2.5, being highest near the periapsis. The equivalent depth of the ε ring is around 47 km and is invariant around the orbit. A close-up view of the (from top to bottom) δ, γ, η, β and α rings of Uranus.

The Delaunay orbital elements, commonly referred to as Delaunay variables, are action-angle coordinates consisting of the argument of periapsis, the mean anomaly and the longitude of the ascending node, along with their conjugate momenta. They are used to simplify perturbative calculations in celestial mechanics, for example while investigating the Kozai–Lidov oscillations in hierarchical triple systems. They were introduced by Charles-Eugène Delaunay during his study of the motion of the Moon.

If an orbit is about a planetary body with significant atmosphere, its orbit can decay because of drag. Particularly at each periapsis, the object experiences atmospheric drag, losing energy. Each time, the orbit grows less eccentric (more circular) because the object loses kinetic energy precisely when that energy is at its maximum. This is similar to the effect of slowing a pendulum at its lowest point; the highest point of the pendulum's swing becomes lower.

Another limitation is the atmosphere, if any, of the available planet. The closer the spacecraft can approach, the faster its periapsis speed as gravity accelerates the spacecraft, allowing for more kinetic energy to be gained from a rocket burn. However, if a spacecraft gets too deep into the atmosphere, the energy lost to drag can exceed that gained from the planet's gravity. On the other hand, the atmosphere can be used to accomplish aerobraking.

Ridges and grooves are also present on moon's surface. The orbit of Pandora appears to be chaotic, as a consequence of a series of four 118:121 mean-motion resonances with Prometheus. The most appreciable changes in their orbits occur approximately every 6.2 years, when the periapsis of Pandora lines up with the apoapsis of Prometheus and the moons approach to within about . Pandora also has a 3:2 mean-motion resonance with Mimas.

Simulated view of an object in an elliptic orbit, as seen from the focus of the orbit. The view rotates with the mean anomaly, so the object appears to oscillate back and forth across this mean position with the equation of the center. The object also appears to become smaller and larger as it moves farther away and nearer because of the eccentricity of the orbit. A marker (red) shows the position of the periapsis.

If the central body is the Earth, and the energy is only slightly larger than the potential energy at the surface of the Earth, then the orbit is elliptic with eccentricity close to 1 and one end of the ellipse just beyond the center of the Earth, and the other end just above the surface. Only a small part of the ellipse is applicable. If the horizontal speed is v\,\\!, then the periapsis distance is .

During its penultimate orbit on April 17, LADEE's periapsis took it within of the lunar surface. Contact with the spacecraft was lost around 04:30 UTC on April 18 when it moved behind the Moon. LADEE struck the Moon's far side surface some time between 04:30 and 05:22 at a speed of . The far side of the Moon was chosen to avoid the possibility of damaging historically important locations such as the Luna and Apollo landing sites.

A Broadband Imaging X-ray All-sky Survey, or ABRIXAS was a space-based German X-ray telescope. It was launched on 28 April 1999 in a Kosmos-3M launch vehicle from Kapustin Yar, Russia, into Earth orbit. The orbit had a periapsis of , an apoapsis of , an inclination of 48.0° and an eccentricity of 0.00352, giving it a period of 96 minutes. The telescope's battery was accidentally overcharged and destroyed three days after the mission started.

An important subtlety of performing an inclination change is that Keplerian orbital inclination is defined by the angle between ecliptic North and the vector normal to the orbit plane, (i.e. the angular momentum vector). This means that inclination is always positive and is entangled with other orbital elements primarily the argument of periapsis which is in turn connected to the longitude of the ascending node. This can result in two very different orbits with precisely the same inclination.

There were two models for its orbital period: one where it took about 31 days to orbit and the second transit was during a large data gap; and another where it took over 50 days to orbit. The latter scenario was considered unlikely, as K2-229d would need to have a very eccentric orbit to exhibit such a short transit duration – so eccentric that its periapsis would cross the orbit of K2-229c and destabilize the system. It has an equilibrium temperature of .

An artist's conception of aerobraking with the Mars Reconnaissance Orbiter An example of Aerobraking 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, and it requires less fuel than does the direct use of a rocket engine.

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. This method was originally planned for the Mars Odyssey orbiter, but the significant design impacts proved too costly.

In celestial mechanics, the mean anomaly is the fraction of an elliptical orbit's period that has elapsed since the orbiting body passed periapsis, expressed as an angle which can be used in calculating the position of that body in the classical two-body problem. It is the angular distance from the pericenter which a fictitious body would have if it moved in a circular orbit, with constant speed, in the same orbital period as the actual body in its elliptical orbit.

The Small Astronomy Satellite 2, also known also as SAS-2, SAS B or Explorer 48, was a NASA gamma ray telescope. It was launched on 15 November 1972 into the low Earth orbit with a periapsis of 443 km and an apoapsis of 632 km. It completed its observations on 8 June 1973. SAS 2 was the second in the series of small spacecraft designed to extend the astronomical studies in the X-ray, gamma-ray, ultraviolet, visible, and infrared regions.

A view from MESSENGER as it uses Earth as a gravitational slingshot to decelerate to allow insertion into an orbit around Mercury. Due to the reversibility of orbits, gravitational slingshots can also be used to reduce the speed of a spacecraft. Both Mariner 10 and MESSENGER performed this maneuver to reach Mercury. If even more speed is needed than available from gravity assist alone, the most economical way to utilize a rocket burn is to do it near the periapsis (closest approach).

The periapsis portion of the orbit would have allowed in-situ measurements of the thermosphere and lower exosphere and remote sensing of the lower atmosphere and surface. The more distant parts of the orbit would be for study of the ions and neutral gas escaping from Mars and their interactions with the solar wind. The nominal mission was planned for one martian year (approximately two Earth years). An extended mission might have allowed operation of the mission for three to five years.

However, a space based gravitational wave observatory like LISA will be able to detect EMRI events up to cosmological distances, leading to an expected detection rate somewhere between a few and a few thousand per year. Extreme mass ratio inspirals created in this way tend to have very large eccentricities (e > 0.9999). The initial, high eccentricity orbits may also be a source of gravitational waves, emitting a short burst as the compact object passes through periapsis. These gravitational wave signals are known as extreme mass ratio bursts.

On 11 October, the flight team performed a maneuver to raise the periapsis out of the atmosphere. This suspension of aerobraking was performed because air pressure from the atmosphere caused one of Surveyor's two solar panels to bend backward by a slight amount. The panel in question was slightly damaged shortly after launch in November 1996. Aerobraking was resumed on 7 November after flight team members concluded that aerobraking was safe, provided that it occurs at a more gentle pace than proposed by the original mission plan.

At periapsis, its variable thrusters were again fired in order to reduce its velocity, descending to above the Moon's surface. It hovered at this altitude, moving horizontally under its own guidance to avoid obstacles, before slowly descending to above the ground, at which point its engine was shut down for a free-fall onto the lunar surface. The landing sequence took about 12 minutes to complete. Topographic data from the Chang'e 1 and 2 orbiters were used to select a landing site for Chang'e 3.

Maximum (instantaneous) orbital speed occurs at periapsis (perigee, perihelion, etc.), while minimum speed for objects in closed orbits occurs at apoapsis (apogee, aphelion, etc.). In ideal two-body systems, objects in open orbits continue to slow down forever as their distance to the barycenter increases. When a system approximates a two-body system, instantaneous orbital speed at a given point of the orbit can be computed from its distance to the central body and the object's specific orbital energy, sometimes called "total energy". Specific orbital energy is constant and independent of position.

Minor orbit adjustments were done occasionally over the course of the mission, primarily to change the walk rate — the rate at which the areocentric longitude changed with each orbit, and the periapsis was raised to 357 km on July 20, 1979. On August 7, 1980, Viking 1 Orbiter was running low on attitude control gas and its orbit was raised from 357 × 33943 km to 320 × 56000 km to prevent impact with Mars and possible contamination until the year 2019. Operations were terminated on August 17, 1980, after 1485 orbits.

After the process was complete, MRO used its thrusters to move its periapsis out of the edge of the Martian atmosphere on August 30, 2006. In September 2006 MRO fired its thrusters twice more to fine-tune its final, nearly circular orbit to approximately above the Martian surface, with a period of about 112 minutes. The SHARAD radar antennas were deployed on September 16. All of the scientific instruments were tested and most were turned off prior to the solar conjunction that occurred from October 7 to November 6, 2006.

A close-up view of the ε ring of Uranus The ε ring is the brightest and densest part of the Uranian ring system, and is responsible for about two-thirds of the light reflected by the rings. While it is the most eccentric of the Uranian rings, it has negligible orbital inclination. The ring's eccentricity causes its brightness to vary over the course of its orbit. The radially integrated brightness of the ε ring is highest near apoapsis and lowest near periapsis. The maximum/minimum brightness ratio is about 2.5–3.0.

Venera 16 was launched on June 7, 1983, at 02:32:00 UTC and reached Venus' orbit on October 11, 1983. The spacecraft was inserted into Venus orbit a day apart from Venera 15, with its orbital plane shifted by an angle of approximately 4° relative to one another probe. This made it possible to reimage an area if necessary. The spacecraft was in a nearly polar orbit with a periapsis ~1000 km, at 62°N latitude, and apoapsis ~65000 km, with an inclination ~90°, the orbital period being ~24 hours.

The probe reached Mars on 12 February. At 14:44:25 the spacecraft's engines ignited to begin its orbit insertion burn, which successfully placed it into an Areocentric orbit with a periapsis of , an apoapsis of , and 35.3 degrees inclination. The spacecraft's pressurised instrument compartment began to leak as soon as the spacecraft entered orbit around Mars, which controllers believed to be the result of a micrometeoroid impact during orbital insertion. It ceased operations on 28 February, having returned 180 photographic frames, 43 of which were of usable quality.

Four to five (preferably five) days before arrival, the spacecraft was to release both Surface Stations to land at two separate sites in the northern hemisphere. After release, the spacecraft would perform a deflection maneuver to change the orbiter's trajectory to a fly-by path in preparation for orbit insertion. At the appropriate moment, with the main engine of the propulsion unit facing the direction of flight, the spacecraft would make a burn to slow down and enter Mars orbit. Initial Mars orbit would have a periapsis of 500 km, an apoapsis of about 52,000 km, with an orbital period of 43.09 hours.

23 August 2004 – At a distance of 9 million kilometers from Saturn, the last major firing of the main engine took place to adjust the next closest approach and avoid the particles in the ring system. The 51 minute burn increased the velocity of the probe by 325 meters per second, moving the orbital periapsis point about 300,000 km farther away from Saturn than its smallest distance during SOI. At the same time, the new course will bring Cassini very close to Titan on its next flyby. 14 September 2004 – Final checkout of the Huygens lander was completed successfully.

The pair share a close, elliptical orbit with a period of 4.55970 days. The orbital eccentricity is 0.277, which means that at the separation at closest approach, or periapsis, is only 57% of the distance at their greatest separation, or apoapsis. There is a third, more distant companion at an angular separation of around 1 arcsecond that may be orbiting the pair with a period of about 64 years. The pair that share the close orbit, Epsilon Lupi Aa and Epsilon Lupi Ab, have estimated masses of 13.24 and 11.46 times the mass of the Sun, respectively.

Completion of the orbital insertion placed the orbiter in a highly elliptical polar orbit with a period of approximately 35.5 hours. Shortly after insertion, the periapsis – the point in the orbit closest to Mars – was from the surface ( from the planet's center). The apoapsis – the point in the orbit farthest from Mars – was from the surface ( from the planet's center). When MRO entered orbit, it joined five other active spacecraft that were either in orbit or on the planet's surface: Mars Global Surveyor, Mars Express, 2001 Mars Odyssey, and the two Mars Exploration Rovers (Spirit and Opportunity).

The true anomaly of point P is the angle f. The center of the ellipse is point C, and the focus is point F. In celestial mechanics, true anomaly is an angular parameter that defines the position of a body moving along a Keplerian orbit. It is the angle between the direction of periapsis and the current position of the body, as seen from the main focus of the ellipse (the point around which the object orbits). The true anomaly is usually denoted by the Greek letters or , or the Latin letter , and is usually restricted to the range 0–360° (0–2π).

Flight profile of Venera 15 Venera 15 was launched on June 2, 1983, at 02:38:39 UTC and reached Venus' orbit on October 10, 1983. The spacecraft was inserted into Venus orbit a day apart from Venera 16, with its orbital plane shifted by an angle of approximately 4° relative to the other probe. This made it possible to reimage an area if necessary. The spacecraft was in a nearly polar orbit with a periapsis ~1000 km, at 62°N latitude, and apoapsis ~65000 km, with an inclination ~90°, the orbital period being ~24 hours.

Pulsars are rapidly rotating neutron stars which emit regular radio pulses as they rotate. As such they act as clocks which allow very precise monitoring of their orbital motions. Observations of pulsars in orbit around other stars have all demonstrated substantial periapsis precessions that cannot be accounted for classically but can be accounted for by using general relativity. For example, the Hulse–Taylor binary pulsar PSR B1913+16 (a pair of neutron stars in which one is detected as a pulsar) has an observed precession of over 4° of arc per year (periastron shift per orbit only about 10−6).

Instead, the new plan was to place the probe in a highly elliptical orbit with an apoapsis of a hundred thousand kilometers and a periapsis of a few thousand kilometers from Venus. Engineers planned for the alternate orbit to be prograde (in the direction of the atmospheric super- rotation) and lie in the orbital plane of Venus. The method and orbit were announced by JAXA in February 2015, with an orbit insertion date of 7 December 2015. The probe reached its most distant point from Venus on 3 October 2013 and had been approaching the planet since then.

Gamma Virginis is a binary star, consisting of two stars of nearly equal apparent magnitudes 3.65 and 3.56, and of spectral type F0V. With an orbital period of 168.93 years, it was an easy object for amateur astronomers until the beginning of the 1990s, but in 2011 the smaller apparent distance between the stars requires a larger telescope or special techniques such as speckle interferometry, adaptive optics or optical interferometry to resolve the individual components. The last time they were at periapsis was in 1836. The distance will again be wide enough in 2020 to view with a small telescope.

The transverse orbital speed is inversely proportional to the distance to the central body because of the law of conservation of angular momentum, or equivalently, Kepler's second law. This states that as a body moves around its orbit during a fixed amount of time, the line from the barycenter to the body sweeps a constant area of the orbital plane, regardless of which part of its orbit the body traces during that period of time. This law implies that the body moves slower near its apoapsis than near its periapsis, because at the smaller distance along the arc it needs to move faster to cover the same area.

The craft was launched on September 9, 1975. Following launch using a Titan/Centaur launch vehicle and a 333-day cruise to Mars, the Viking 2 Orbiter began returning global images of Mars prior to orbit insertion. The orbiter was inserted into a 1500 x 33,000 km, 24.6 h Mars orbit on August 7, 1976 and trimmed to a 27.3 h site certification orbit with a periapsis of 1499 km and an inclination of 55.2 degrees on August 9. Imaging of candidate sites was begun and the landing site was selected based on these pictures and the images returned by the Viking 1 Orbiter.

In some cases, it is even worth spending fuel on slowing the spacecraft into a gravity well to take advantage of the efficiencies of the Oberth effect. The maneuver and effect are named after the person who first described them in 1927, Hermann Oberth, an Austro-Hungarian-born German physicist and a founder of modern rocketry. The Oberth effect is strongest at a point in orbit known as the periapsis, where the gravitational potential is lowest, and the speed is highest. This is because firing a rocket engine at high speed causes a greater change in kinetic energy than when fired at lower speed.

This image taken by Mars Global Surveyor spans a region about across, showing gullies on the walls of Newton Basin in Sirenum Terra. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating. After orbital insertion, Surveyor performed a series of orbit changes to lower the periapsis of its orbit into the upper fringes of the Martian atmosphere at an altitude of about .

The Orbiter type was the 4MV, used also for Mars-3 and later Mars and Venera Probes. The orbiter engine performed a burn to put the spacecraft into a , 18-hour orbit about Mars with an inclination of 48.9 degrees. Scientific instruments were generally turned on for about 30 minutes near periapsis. The orbiter's primary scientific objectives were to image the Martian surface and clouds, determine the temperature on Mars, study the topography, composition and physical properties of the surface, measure properties of the atmosphere, monitor the solar wind and the interplanetary and Martian magnetic fields, and act as a communications relay to send signals from the landers to the Earth.

Extra fuel is required to compensate for the fact that the bursts take time; this is minimized by using high-thrust engines to minimize the duration of the bursts. For transfers in Earth orbit, the two burns are labelled the perigee burn and the apogee burn (or apogee kickJonathan McDowell, "Kick In the Apogee: 40 years of upper stage applications for solid rocket motors, 1957-1997", 33rd AIAA Joint Propulsion Conference, July 4, 1997. abstract. Retrieved 18 July 2017.); more generally, they are labelled periapsis and apoapsis burns. Alternately, the second burn to circularize the orbit may be referred to as a circularization burn.

HD 80606, a sun-like star in a binary system, orbits a common center of gravity with its partner, HD 80607; the two are separated by 1,200 AU on average. Research conducted in 2003 indicates that its sole planet, HD 80606 b is a future hot Jupiter, modeled to have evolved in a perpendicular orbit around 5 AU from its sun. The 4-Jupiter mass planet is projected to eventually move into a circular, more aligned orbit via the Kozai mechanism. However, it is currently on an incredibly eccentric orbit that ranges from approximately one astronomical unit at its apoapsis and six stellar radii at periapsis.

The S/C was launched from an American Lockheed L-1011-385-1-15 TriStar registered N140SC with a Pegasus-XL rocket from Gando Air Base in the Canary Islands the 21st of April 1997. It was successfully put on a near-circular close orbit of 585 km of apoapsis and 566 km of periapsis with and inclination of 151º (29º retrograde) and an orbital period of 96 minutes. After 5 years of successful operation, the satellite reentered the atmosphere on 14 February 2002. During its whole service life it was operated by INTA, who monitored the satellite from the Maspalomas Station (15º 37' 45” W, 27º 45' 49” N).

The ship reaches periapsis where tidal forces nearly pull Shaeffer apart anyway, but he manages to hold himself in the access space at the ship's center of mass and survives. After returning to We Made It, Shaeffer is hospitalized (he has received a sunburn by starlight blue-shifted into the ultraviolet) for observation at the Puppeteer's insistence. While explaining tidal forces to the Puppeteer, Schaeffer realizes the alien had no knowledge of tides, something that would be elementary for a sentient species living on a world with a moon. The Puppeteers are extremely cautious when dealing with other races, and keep all details about their homeworld secret.

Hohmann transfer orbit, 2, from an orbit (1) to a higher orbit (3) A Hohmann transfer orbit is the simplest maneuver which can be used to move a spacecraft from one altitude to another. Two burns are required: the first to send the craft into the elliptical transfer orbit, and a second to circularize the target orbit. To raise a circular orbit at v_1, the first posigrade burn raises velocity to the transfer orbit's periapsis velocity: :\Delta v_1\ = v_p - v_1 The second posigrade burn, made at apoapsis, raises velocity to the target orbit's velocity: :\Delta v_2\ = v_2 - v_a A maneuver to lower the orbit is the mirror image of the raise maneuver; both burns are made retrograde.

Puck, Miranda, Ariel, Umbriel, Titania, and Oberon The orbiter science phase would consist on the Uranus Science Orbit (USO) phase of approximately 2 years in a highly elliptic polar orbit to provide best gravimetry data, during which 36 Uranus orbits are performed. Subsequently, the orbiter will continue to the Moon Tour (MT) phase, which would last three years. During this phase, the periapsis would be raised, facilitating nine flybys of each of Uranus' five major moons: Miranda, Ariel, Umbriel, Titania, and Oberon. Because of the long distance from the Sun (20 AU on average), the orbiter would not be able to use solar panels, requiring instead four Advanced Stirling Radioisotope Generators (ASRGs) to be developed by ESA.

In astronautics and aerospace engineering, the bi-elliptic transfer is an orbital maneuver that moves a spacecraft from one orbit to another and may, in certain situations, require less delta-v than a Hohmann transfer maneuver. The bi-elliptic transfer consists of two half-elliptic orbits. From the initial orbit, a first burn expends delta-v to boost the spacecraft into the first transfer orbit with an apoapsis at some point r_b away from the central body. At this point a second burn sends the spacecraft into the second elliptical orbit with periapsis at the radius of the final desired orbit, where a third burn is performed, injecting the spacecraft into the desired orbit.

The Earth's apsidal precession slowly increases its argument of periapsis; it takes about years for the ellipse to revolve once relative to the fixed stars. The Earth's polar axis, and hence the solstices and equinoxes, precess with a period of about years in relation to the fixed stars. These two forms of 'precession' combine so that it takes between and years (and on average years) for the ellipse to revolve once relative to the vernal equinox, that is, for the perihelion to return to the same date (given a calendar that tracks the seasons perfectly). This interaction between the anomalistic and tropical cycle is important in the long-term climate variations on Earth, called the Milankovitch cycles.

Shaeffer, realizing he is trapped, agrees to fly the mission. The Skydiver reaches the neutron star, and the ship's autopilot puts the Skydiver into a hyperbolic orbit that will take 24 hours to reach periapsis with BVS-1, passing a mile above its surface. During the descent Schaeffer notices many unusual things: the stars ahead of him began to turn blue from Doppler shift as his speed increases enormously; the stars behind him, rather than being red-shifted, were blue too as their light accelerated with him into the gravity well of the neutron star. The nose of the ship is pulled towards the neutron star even when he tries to move the ship to view his surroundings.

As with other RR Lyrae-type variables, RR Lyrae itself has a low abundance of elements other than hydrogen and helium—what astronomers term its metallicity. It belongs to the Population II category of stars that formed during the early period of the Universe when there was a lower abundance of metals in star-forming regions. The trajectory of this star is carrying it along an orbit that is close to the plane of the Milky Way, taking it no more than above or below this plane. The orbit has a high eccentricity, bringing RR Lyrae as close as to the Galactic Center at periapsis, and taking it as far as at apapsis.

LunaH-Map's primary objective is to map the abundance of hydrogen down to one meter beneath the surface of the lunar south pole. It will be inserted into a polar orbit around the Moon, with its periapsis located near the lunar south pole, initially passing above Shackleton Crater. LunaH-Map will provide a high resolution map of the abundance and distribution of hydrogen rich compounds, like water, in this region of the Moon and expand on the less accurate maps made by previous missions. This information may then be used to improve scientific understanding of how water is created and spread throughout the Solar System or used by future manned missions for life support and fuel production.

Like Themisto and Valetudo, this moon seems to be the lone member of a unique class, which makes it particularly interesting. The orbital inclination of satellites such as this one is limited by the Kozai effect, discovered by Yoshihide Kozai in 1962. This effect induces a periodic exchange between the inclination and eccentricity of the orbit; if the inclination is large enough, the eccentricity can in turn grow so large that the periapsis of the satellite (called the perizene in the case of moons of Jupiter) would be in the immediate vicinity of the Galilean moons (Io, Europa, Ganymede and Callisto). The satellite would eventually collide with one of these, or a close encounter would eject it altogether from the Jovian system.

View video On August 24, 1993, Mars Observer would turn 180-degrees and ignite the bipropellant thrusters to slow the spacecraft, entering into a highly elliptical orbit. Over the next three months, subsequent "transfer to lower orbit" (TLO) maneuvers would be performed as the spacecraft reached periapsis, eventually resulting in an approximately circular, 118-minute orbit around Mars. The primary mission was to begin on November 23, 1993, collecting data during one Martian year (approximately 687 Earth days). The first global map was expected to be completed on December 16, followed by solar conjunction beginning on December 20, and lasting for nineteen days, ending on January 3, 1994; during this time, mission operations would be suspended as radio contact would not be possible.

For orbits that do not have an eccentricity close to zero, the rotation rate tends to become locked with the orbital speed when the body is at periapsis, which is the point of strongest tidal interaction between the two objects. If the orbiting object has a companion, this third body can cause the rotation rate of the parent object to vary in an oscillatory manner. This interaction can also drive an increase in orbital eccentricity of the orbiting object around the primary - an effect known as eccentricity pumping. In some cases where the orbit is eccentric and the tidal effect is relatively weak, the smaller body may end up in a so-called spin–orbit resonance, rather than being tidally locked.

However, the predictions of Newtonian gravity do not match the observations, as discovered in 1859 from observations of Mercury. If the potential energy between the two bodies is not exactly the 1/r potential of Newton's gravitational law but differs only slightly, then the ellipse of the orbit gradually rotates (among other possible effects). This apsidal precession is observed for all the planets orbiting the Sun, primarily due to the oblateness of the Sun (it is not perfectly spherical) and the attractions of the other planets to one another. The apsides are the two points of closest and furthest distance of the orbit (the periapsis and apoapsis, respectively); apsidal precession corresponds to the rotation of the line joining the apsides.

Bi- elliptic transfer from blue to red circular orbit In astronautics and aerospace engineering, the bi-elliptic transfer is an orbital maneuver that moves a spacecraft from one orbit to another and may, in certain situations, require less delta-v than a Hohmann transfer maneuver. The bi-elliptic transfer consists of two half elliptic orbits. From the initial orbit, a delta-v is applied boosting the spacecraft into the first transfer orbit with an apoapsis at some point r_b away from the central body. At this point, a second delta-v is applied sending the spacecraft into the second elliptical orbit with periapsis at the radius of the final desired orbit, where a third delta-v is performed, injecting the spacecraft into the desired orbit.

In astronautics, a powered flyby, or Oberth maneuver, is a maneuver in which a spacecraft falls into a gravitational well and then uses its engines to further accelerate as it is falling, thereby achieving additional speed. The resulting maneuver is a more efficient way to gain kinetic energy than applying the same impulse outside of a gravitational well. The gain in efficiency is explained by the Oberth effect, wherein the use of an engine at higher speeds generates greater mechanical energy than use at lower speeds. In practical terms, this means that the most energy-efficient method for a spacecraft to burn its engine is at the lowest possible orbital periapsis, when its orbital velocity (and so, its kinetic energy) is greatest.

The polar orbit ranged between over Venus. The periapsis was located almost above the North pole (80° North latitude), and it took 24 hours for the spacecraft to travel around the planet. Venus Express studied the Venusian atmosphere and clouds in detail, the plasma environment and the surface characteristics of Venus from orbit. It also made global maps of the Venusian surface temperatures. Its nominal mission was originally planned to last for 500 Earth days (approximately two Venusian sidereal days), but the mission was extended five times: first on 28 February 2007 until early May 2009; then on 4 February 2009 until 31 December 2009; and then on 7 October 2009 until 31 December 2012. On 22 November 2010, the mission was extended to 2014.

The satellite was part of the Soviet Union's RORSAT programme, a series of reconnaissance satellites which observed ocean traffic, including surface vessels and nuclear submarines, using active radar. It was assigned the Kosmos number 954 and was launched on 18 September 1977 at 13:55 UTC from the Baikonur Cosmodrome, on a Tsyklon-2 carrier rocket. With an orbital inclination of 65°, a periapsis of and apoapsis of , it orbited the Earth every 89.5 minutes. Powered by a liquid sodium–potassium thermionic converter driven by a nuclear reactor containing around of uranium-235, the satellite was intended for long-term on-orbit observation, but by December 1977 the satellite had deviated from its designed orbit and its flightpath was becoming increasingly erratic.

KH-8 GAMBIT-3 Photographic Payload Section KH-8 Photographic Payload Section The Camera Optics Module of KH-8 consists of four cameras. The main camera of KH-8B (introduced in 1971) with a focal length of is a single strip camera, designed to gather high-resolution images of ground targets. In the strip camera the ground image is reflected by a steerable flat mirror to a diameter stationary concave primary mirror. The primary mirror reflects the light through an opening in the flat mirror and through a Ross corrector. At periapsis altitude of 75 nautical miles, the main camera imaged a 6.3 km wide ground swath on a wide moving portion of film through a small slit aperture, resulting in an image scale of 28 meter / millimeter.

Because the vehicle remains near periapsis only for a short time, for the Oberth maneuver to be most effective the vehicle must be able to generate as much impulse as possible in the shortest possible time. As a result the Oberth maneuver is much more useful for high-thrust rocket engines like liquid-propellant rockets, and less useful for low-thrust reaction engines such as ion drives, which take a long time to gain speed. The Oberth effect also can be used to understand the behavior of multi-stage rockets: the upper stage can generate much more usable kinetic energy than the total chemical energy of the propellants it carries. The Oberth effect occurs because the propellant has more usable energy due to its kinetic energy in addition to its chemical potential energy.

Its Laplace orbital resonance with Europa and Ganymede maintains Io's eccentricity and prevents tidal dissipation within Io from circularizing its orbit. The eccentricity leads to vertical differences in Io's tidal bulge of as much as as Jupiter's gravitational pull varies between the periapsis and apoapsis points in Io's orbit. This varying tidal pull also produces friction in Io's interior, enough to cause significant tidal heating and melting. Unlike Earth, where most of its internal heat is released by conduction through the crust, on Io internal heat is released via volcanic activity and generates the satellite's high heat flow (global total: 0.6–1.6 W). Models of its orbit suggest that the amount of tidal heating within Io changes with time, and that the current heat flow is not representative of the long-term average.

The bi-elliptic transfer consists of two half-elliptic orbits. From the initial orbit, a first burn expends delta-v to boost the spacecraft into the first transfer orbit with an apoapsis at some point r_b away from the central body. At this point a second burn sends the spacecraft into the second elliptical orbit with periapsis at the radius of the final desired orbit, where a third burn is performed, injecting the spacecraft into the desired orbit. While they require one more engine burn than a Hohmann transfer and generally require a greater travel time, some bi-elliptic transfers require a lower amount of total delta-v than a Hohmann transfer when the ratio of final to initial semi-major axis is 11.94 or greater, depending on the intermediate semi-major axis chosen.

Magellan to Venus On August 10, 1990, Magellan encountered Venus and began the orbital insertion maneuver which placed the spacecraft into a three- hour, nine minute, elliptical orbit that brought the spacecraft 295-kilometers from the surface at about 10 degrees North during the periapsis and out to 7762-kilometers during apoapsis. During each orbit, the space probe captured radar data while the spacecraft was closest to the surface, and then transmit it back to Earth as it moved away from Venus. This maneuver required extensive use of the reaction wheels to rotate the spacecraft as it imaged the surface for 37-minutes and as it pointed toward Earth for two hours. The primary mission intended for the spacecraft to return images of at least 70 percent of the surface during one Venusian day, which lasts 243 Earth days as the planet slowly spins.

The calendar predicted the movement of the moon, the first time such considerations had been made in ancient China. This system marked the first appearance of the argument of periapsis, a means to calculate syzygy (the calculation between three celestial bodies), and a means of charting the moon through the seasons. His means of establishing the accuracy of the calendar was by the detection of eclipses. This system replaced one which had been used by the Han dynasty since 85 CE, and following the end of the Han dynasty and beginning of the Three Kingdoms period, it was adopted by the Eastern Wu state (229–280 CE) until China was re-unified under the Jin dynasty in 280 CE. In 179 CE, he was asked by the Imperial Secretariat to consider proposals made by a private scholar called Wang Han regarding lunar calendars, but did not support those proposals.

The technology needed to move a large asteroid into an arbitrary orbit does not yet exist; altering an asteroid's orbit around the Sun would require a large delta-v to be imparted to an object with a mass several orders of magnitude greater than existing spacecraft. Once an asteroid is on course to encounter a planet with an atmosphere, it is in principle possible to tweak its orbit so that it intercepts the planet's atmosphere, using aerobraking to slow the asteroid at periapsis by dumping some of its kinetic energy into the atmosphere - this technique has however never been used by spacecraft performing rendezvous manoeuvres with other planets such as Mars, but it would reduce the otherwise very large amount of fuel required to decelerate a spacecraft from a Sun- orbital velocity to a planet-orbital velocity. This technique is referred to as aerocapture.

The tidal forces experienced by Io are about 20,000 times stronger than the tidal forces Earth experience due to the moon, and the vertical differences in its tidal bulge, between the times Io is at periapsis and apoapsis in its orbit, could be as much as .Interplanetary Low Tide - NASA Science Mission Directorate The friction or tidal dissipation produced in Io's interior due to this varying tidal pull, which, without the resonant orbit, would have gone into circularizing Io's orbit instead, creates significant tidal heating within Io's interior, melting a significant amount of Io's mantle and core. The amount of energy produced is up to 200 times greater than that produced solely from radioactive decay. This heat is released in the form of volcanic activity, generating its observed high heat flow (global total: 0.6 to 1.6×1014 W). Models of its orbit suggest that the amount of tidal heating within Io changes with time; however, the current amount of tidal dissipation is consistent with the observed heat flow.

Astronomical timing as the basis for designating the temperate seasons dates back at least to the Julian calendar used by the ancient Romans. It continues to be used on many modern Gregorian calendars worldwide, although some countries like Australia, New Zealand, Pakistan and Russia prefer to use meteorological reckoning. The precise timing of the seasons is determined by the exact times of transit of the sun over the tropics of Cancer and Capricorn for the solstices and the times of the sun's transit over the equator for the equinoxes, or a traditional date close to these times. The following diagram shows the relation between the line of solstice and the line of apsides of Earth's elliptical orbit. The orbital ellipse (with eccentricity exaggerated for effect) goes through each of the six Earth images, which are sequentially the perihelion (periapsis—nearest point to the sun) on anywhere from 2 January to 5 January, the point of March equinox on 19, 20 or 21 March, the point of June solstice on 20 or 21 June, the aphelion (apoapsis—farthest point from the sun) on anywhere from 4 July to 7 July, the September equinox on 22 or 23 September, and the December solstice on 21 or 22 December.