Engine Shuts Off and Wont Start Again During Landing Ksp

Spacecraft launch or descent maneuver

A gravity turn or zero-lift turn is a maneuver used in launching a spacecraft into, or descending from, an orbit around a celestial trunk such as a planet or a moon. It is a trajectory optimization that uses gravity to steer the vehicle onto its desired trajectory. It offers two main advantages over a trajectory controlled solely through the vehicle'due south own thrust. Kickoff, the thrust is non used to change the spacecraft's direction, so more of it is used to accelerate the vehicle into orbit. Second, and more chiefly, during the initial rising stage the vehicle can maintain low or even null angle of attack. This minimizes transverse aerodynamic stress on the launch vehicle, assuasive for a lighter launch vehicle.^{[1] [2]}

The term gravity turn tin can too refer to the utilise of a planet's gravity to change a spacecraft'south direction in situations other than entering or leaving the orbit.^[3] When used in this context, it is like to a gravitational slingshot; the divergence is that a gravitational slingshot often increases or decreases spacecraft velocity and changes direction, while the gravity turn merely changes management.

Launch procedure [edit]

Vertical climb [edit]

A diagram showing the velocity vectors for times ${\displaystyle t}$ and ${\displaystyle t+one}$ during the vertical climb phase. The launch vehicle's new velocity is the vector sum of its quondam velocity, the acceleration from thrust, and the acceleration of gravity. More formally ${\displaystyle V_{t+i}=V_{t}+(a_{\text{thrust}}+a_{\text{gravity}})\cdot \Delta t}$

A gravity turn is normally used with rocket powered vehicles that launch vertically, similar the Space Shuttle. The rocket begins past flying straight upwardly, gaining both vertical speed and altitude. During this portion of the launch, gravity acts directly against the thrust of the rocket, lowering its vertical acceleration. Losses associated with this slowing are known equally gravity drag, and tin can be minimized past executing the next phase of the launch, the pitchover maneuver, equally soon as possible. The pitchover should besides be carried out while the vertical velocity is small-scale to avoid large aerodynamic loads on the vehicle during the maneuver.^[1]

The pitchover maneuver consists of the rocket gimbaling its engine slightly to direct some of its thrust to ane side. This strength creates a net torque on the ship, turning information technology so that it no longer points vertically. The pitchover bending varies with the launch vehicle and is included in the rocket's inertial guidance system.^[i] For some vehicles information technology is only a few degrees, while other vehicles use relatively large angles (a few tens of degrees). After the pitchover is complete, the engines are reset to signal straight downwards the axis of the rocket again. This small steering maneuver is the only time during an ideal gravity plow ascension that thrust must exist used for purposes of steering. The pitchover maneuver serves two purposes. Showtime, information technology turns the rocket slightly so that its flight path is no longer vertical, and second, it places the rocket on the right heading for its ascent to orbit. Later the pitchover, the rocket's angle of attack is adjusted to zero for the remainder of its climb to orbit. This zeroing of the angle of attack reduces lateral aerodynamic loads and produces negligible lift force during the rise.^[1]

Downrange acceleration [edit]

A diagram showing the velocity vectors for times ${\displaystyle t}$ and ${\displaystyle t+1}$ during the downrange acceleration stage. Every bit earlier, the launch vehicle'south new velocity is the vector sum of its old velocity, the acceleration from thrust, and the acceleration of gravity. Because gravity acts straight down, the new velocity vector is closer to existence level with the horizon; gravity has "turned" the trajectory downwardly.

After the pitchover, the rocket'due south flight path is no longer completely vertical, and then gravity acts to turn the flying path back towards the footing. If the rocket were non producing thrust, the flight path would be a simple ellipse like a thrown ball (it's a common mistake to think it is a parabola: this is only true if it is assumed that the Earth is flat, and gravity always points in the same direction, which is a adept approximation for short distances), leveling off and and so falling dorsum to the ground. The rocket is producing thrust though, and rather than leveling off and so descending again, by the fourth dimension the rocket levels off, it has gained sufficient distance and velocity to place information technology in a stable orbit.

If the rocket is a multi-stage system where stages burn down sequentially, the rocket's ascent burn may non be continuous. Some fourth dimension must be allowed for stage separation and engine ignition between each successive stage, but some rocket designs call for extra gratis-flight fourth dimension between stages. This is particularly useful in very high thrust rockets, where if the engines were fired continuously, the rocket would run out of fuel earlier leveling off and reaching a stable orbit above the temper.^[2] The technique is also useful when launching from a planet with a thick atmosphere, such every bit the Globe. Because gravity turns the flying path during free flight, the rocket can use a smaller initial pitchover angle, giving it higher vertical velocity, and taking information technology out of the temper more than quickly. This reduces both aerodynamic elevate as well as aerodynamic stress during launch. Then later on during the flight the rocket coasts betwixt stage firings, allowing it to level off above the atmosphere, and then when the engine fires over again, at zilch angle of attack, the thrust accelerates the ship horizontally, inserting it into orbit.

Descent and landing procedure [edit]

Because rut shields and parachutes cannot be used to land on an airless body such as the Moon, a powered descent with a gravity turn is a good alternative. The Apollo Lunar Module used a slightly modified gravity plow to land from lunar orbit. This was essentially a launch in reverse except that a landing spacecraft is lightest at the surface while a spacecraft being launched is heaviest at the surface. A computer programme called Lander that imitation gravity turn landings applied this concept by simulating a gravity plow launch with a negative mass flow rate, i.e. the propellant tanks filled during the rocket burn.^[four] The idea of using a gravity plow maneuver to country a vehicle was originally developed for the Lunar Surveyor landings, although Surveyor fabricated a straight approach to the surface without first going into lunar orbit.^[v]

Deorbit and entry [edit]

The deorbit, coast, and possible entry stage 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 bespeak of periapsis to near the surface of the body to be landed on. If the craft is landing on a planet with an temper such as Mars the deorbit burn will only lower periapsis into the upper layers of the atmosphere, rather than but above the surface as on an airless body. After the deorbit burn is complete the vehicle tin can either declension until information technology is nearer to its landing site or continue firing its engine while maintaining null bending of attack. For a planet with an atmosphere the declension portion of the trip includes entry through the temper equally well.

After the coast and possible entry the vehicle jettisons any no longer necessary heat shields and/or parachutes in preparation for the final landing burn. If the atmosphere is thick enough it can be used to slow the vehicle a considerable amount, thus saving on fuel. In this case a gravity plow is not the optimal entry trajectory just information technology does allow for approximation of the true delta-v required.^[6] In the case where there is no atmosphere however, the landing vehicle must provide the total delta-v necessary to state safely on the surface.

Landing [edit]

The final arroyo and landing portion of the descent. The vehicle loses horizontal speed while transitioning to a vertical hover, allowing information technology to settle down on the surface.

If it is non already properly oriented, the vehicle lines upward its engines to fire directly opposite its current surface velocity vector, which at this point is either parallel to the footing or just slightly vertical, every bit shown to the left. The vehicle and so fires its landing engine to wearisome down for landing. As the vehicle loses horizontal velocity the gravity of the body to exist landed on will begin pulling the trajectory closer and closer to a vertical descent. In an ideal maneuver on a perfectly spherical trunk the vehicle could reach zero horizontal velocity, zero vertical velocity, and zero distance all at the same moment, landing safely on the surface (if the body is not rotating; else the horizontal velocity shall be made equal to the one of the body at the considered latitude). However, due to rocks and uneven surface terrain the vehicle usually picks up a few degrees of angle of attack almost the end of the maneuver to naught its horizontal velocity just above the surface. This process is the mirror image of the pitch over maneuver used in the launch process and allows the vehicle to hover straight downwardly, landing gently on the surface.

Guidance and control [edit]

The steering of a rocket's course during its flying is divided into two dissever components; control, the ability to bespeak the rocket in a desired direction, and guidance, the decision of what direction a rocket should be pointed to reach a given target. The desired target can either be a location on the ground, as in the case of a ballistic missile, or a particular orbit, equally in the case of a launch vehicle.

Launch [edit]

The gravity turn trajectory is virtually commonly used during early rise. The guidance programme is a precalculated lookup tabular array of pitch vs time. Control is washed with engine gimballing and/or aerodynamic control surfaces. The pitch program maintains a zero angle of attack (the definition of a gravity plough) until the vacuum of space is reached, thus minimizing lateral aerodynamic loads on the vehicle. (Excessive aerodynamic loads can rapidly destroy the vehicle.) Although the preprogrammed pitch schedule is adequate for some applications, an adaptive inertial guidance system that determines location, orientation and velocity with accelerometers and gyroscopes, is almost always employed on modern rockets. The British satellite launcher Black Pointer was an example of a rocket that flew a preprogrammed pitch schedule, making no attempt to correct for errors in its trajectory, while the Apollo-Saturn rockets used "closed loop" inertial guidance after the gravity turn through the atmosphere.^[seven]

The initial pitch program is an open up-loop system field of study to errors from winds, thrust variations, etc. To maintain nil bending of attack during atmospheric flying, these errors are not corrected until reaching space.^[8] And so a more sophisticated closed-loop guidance programme tin can take over to right trajectory deviations and attain the desired orbit. In the Apollo missions, the transition to closed-loop guidance took place early on in second stage flight after maintaining a fixed inertial attitude while jettisoning the first stage and interstage ring.^[8] Because the upper stages of a rocket operate in a almost vacuum, fins are ineffective. Steering relies entirely on engine gimballing and a reaction control organisation.

Landing [edit]

To serve as an example of how the gravity plow can exist used for a powered landing, an Apollo type lander on an airless trunk volition be causeless. The lander begins in a round orbit docked to the command module. After separation from the control module the lander performs a retrograde fire to lower its periapsis to merely higher up the surface. It so coasts to periapsis where the engine is restarted to perform the gravity turn descent. It has been shown that in this state of affairs guidance can be accomplished by maintaining a constant bending between the thrust vector and the line of sight to the orbiting command module.^[9] This simple guidance algorithm builds on a previous study which investigated the apply of diverse visual guidance cues including the uprange horizon, the downrange horizon, the desired landing site, and the orbiting control module.^[x] The written report concluded that using the control module provides the best visual reference, as it maintains a well-nigh constant visual separation from an ideal gravity turn until the landing is nigh complete. Because the vehicle is landing in a vacuum, aerodynamic control surfaces are useless. Therefore, a arrangement such as a gimballing main engine, a reaction control system, or possibly a command moment gyroscope must exist used for attitude control.

Limitations [edit]

Although gravity turn trajectories use minimal steering thrust they are not always the most efficient possible launch or landing procedure. Several things can touch the gravity plow process making it less efficient or fifty-fifty impossible due to the design limitations of the launch vehicle. A brief summary of factors affecting the plow is given below.

• Atmosphere — In club to minimize gravity drag the vehicle should begin gaining horizontal speed every bit soon as possible. On an airless body such as the Moon this presents no problem, still on a planet with a dense atmosphere this is not possible. A merchandise-off exists between flying college earlier starting downrange dispatch, thus increasing gravity elevate losses; or starting downrange acceleration earlier, reducing gravity drag but increasing the aerodynamic drag experienced during launch.
• Maximum dynamic pressure — Some other effect related to the planet'due south atmosphere is the maximum dynamic pressure exerted on the launch vehicle during the launch. Dynamic pressure level is related to both the atmospheric density and the vehicle's speed through the atmosphere. But after liftoff the vehicle is gaining speed and increasing dynamic pressure faster than the reduction in atmospheric density tin decrease the dynamic force per unit area. This causes the dynamic force per unit area exerted on the vehicle to increment until the two rates are equal. This is known as the point of maximum dynamic force per unit area (abbreviated "max Q"), and the launch vehicle must be congenital to withstand this amount of stress during launch. As earlier a trade off exists betwixt gravity drag from flying higher first to avoid the thicker temper when accelerating; or accelerating more than at lower altitude, resulting in a heavier launch vehicle because of a college maximum dynamic pressure experienced on launch.
• Maximum engine thrust — The maximum thrust the rocket engine can produce affects several aspects of the gravity turn process. Firstly, before the pitch over maneuver the vehicle must be capable of non only overcoming the strength of gravity but accelerating upwards. The more dispatch the vehicle has beyond the acceleration of gravity the quicker vertical speed tin be obtained assuasive for lower gravity drag in the initial launch stage. When the pitch over is executed the vehicle begins its downrange dispatch phase; engine thrust affects this phase too. College thrust allows for a faster dispatch to orbital velocity likewise. Past reducing this time the rocket can level off sooner; further reducing gravity drag losses. Although higher thrust tin can make the launch more efficient, accelerating besides much depression in the atmosphere increases the maximum dynamic pressure. This can be alleviated by throttling the engines back during the offset of downrange dispatch until the vehicle has climbed higher. However, with solid fuel rockets this may not exist possible.
• Maximum tolerable payload acceleration — Another limitation related to engine thrust is the maximum acceleration that tin can be safely sustained by the crew and/or the payload. Nearly primary engine cut off (MECO), when the launch vehicle has consumed most of its fuel, the vehicle will be much lighter than information technology was at launch. If the engines are however producing the aforementioned amount of thrust, the acceleration will grow equally a result of the decreasing vehicle mass. If this acceleration is non kept in check by throttling back the engines, injury to the crew or damage to the payload could occur. This forces the vehicle to spend more time gaining horizontal velocity, increasing gravity drag.

Use in orbital redirection [edit]

For spacecraft missions where large changes in the direction of flight are necessary, direct propulsion by the spacecraft may not be feasible due to the large delta-5 requirement. In these cases it may be possible to perform a flyby of a nearby planet or moon, using its gravitational allure to alter the send'due south direction of flight. Although this maneuver is very similar to the gravitational slingshot it differs in that a slingshot often implies a modify in both speed and direction whereas the gravity turn simply changes the direction of flying.

A variant of this maneuver, the complimentary return trajectory allows the spacecraft to depart from a planet, circle another planet once, and render to the starting planet using propulsion simply during the initial departure burn. Although in theory it is possible to execute a perfect free return trajectory, in practice small correction burns are frequently necessary during the flight. Even though it does not require a burn for the return trip, other return trajectory types, such as an aerodynamic turn, can result in a lower total delta-five for the mission.^[three]

Use in spaceflight [edit]

Many spaceflight missions have utilized the gravity turn, either directly or in a modified class, to conduct out their missions. What follows is a short list of various mission that accept used this procedure.

• Surveyor program — A precursor to the Apollo Program, the Surveyor Plan's principal mission objective was to develop the ability to perform soft landings on the surface of the moon, through the use of an automated descent and landing programme built into the lander.^[11] Although the landing procedure tin be classified as a gravity plow descent, it differs from the technique most commonly employed in that information technology was shot from the Earth directly to the lunar surface, rather than first orbiting the moon as the Apollo landers did. Because of this the descent path was virtually vertical, although some "turning" was done past gravity during the landing.^{[ commendation needed ]}
• Apollo program — Launches of the Saturn V rocket during the Apollo program were carried out using a gravity turn in lodge to minimize lateral stress on the rocket. At the other end of their journey, the lunar landers utilized a gravity turn landing and rise from the Moon.

Mathematical description [edit]

The simplest instance of the gravity turn trajectory is that which describes a point mass vehicle, in a uniform gravitational field, neglecting air resistance. The thrust forcefulness ${\displaystyle {\vec {F}}}$ is a vector whose magnitude is a role of time and whose management tin can exist varied at will. Nether these assumptions the differential equation of motion is given past:

${\displaystyle chiliad{\frac {d{\vec {v}}}{dt}}={\vec {F}}-mg{\hat {yard}}\;.}$

Here ${\displaystyle {\hat {one thousand}}}$ is a unit of measurement vector in the vertical direction and ${\displaystyle grand}$ is the instantaneous vehicle mass. By constraining the thrust vector to indicate parallel to the velocity and separating the equation of motion into components parallel to ${\displaystyle {\vec {v}}}$ and those perpendicular to ${\displaystyle {\vec {five}}}$ we arrive at the post-obit organisation:^[12]

${\displaystyle {\begin{aligned}{\dot {v}}&=g(n-\cos {\beta })\;,\\five{\dot {\beta }}&=thousand\sin {\beta }\;.\\\end{aligned}}}$

Hither the current thrust to weight ratio has been denoted by ${\displaystyle n=F/mg}$ and the current angle between the velocity vector and the vertical by ${\displaystyle \beta =\arccos {({\vec {\tau _{ane}}}\cdot {\chapeau {grand}})}}$ . This results in a coupled system of equations which tin be integrated to obtain the trajectory. Still, for all but the simplest instance of abiding ${\displaystyle n}$ over the entire flight, the equations cannot be solved analytically and must exist integrated numerically.

References [edit]

1. ^ ^{a b c d} Glasstone, Samuel (1965). Sourcebook on the Infinite Sciences. D. Van Nostrand Visitor, Inc. pp. 209 or §4.97.
2. ^ ^{a b} Callaway, David W. (March 2004). "Coplanar Air Launch with Gravity-Turn Launch Trajectories" (PDF). Masters Thesis. Archived from the original (PDF) on 2007-eleven-28.
3. ^ ^{a b} Luidens, Roger Due west. (1964). "Mars Nonstop Round-Trip Trajectories". American Institute of Aeronautics and Astronautics. ii (2): 368–370. Bibcode:1964AIAAJ...two..368L. doi:10.2514/3.2330. hdl:2060/19640008410.
4. ^ Eagle Engineering, Inc (September thirty, 1988). "Lander Programme Manual". NASA Contract Number NAS9-17878. EEI Report 88-195. hdl:2060/19890005786.
5. ^ "Boeing Satellite Development: Surveyor Mission Overview". boeing.com. Boeing. Archived from the original on 7 February 2010. Retrieved 31 March 2010.
6. ^ Braun, Robert D.; Manning, Robert Yard. (2006). Mars Exploration Entry, Descent and Landing Challenges (PDF). IEEE Aerospace Conference. p. 1. doi:x.1109/AERO.2006.1655790. ISBN0-7803-9545-X. Archived from the original (PDF) on September 3, 2006.
7. ^ "Launch vehicle handbook. Compilation of launch vehicle performance and weight information for preliminary planning purposes". NASA Technical Memorandum. TM 74948. September 1961.
8. ^ ^{a b} "Apollo systems clarification. Volume ii - Saturn launch vehicles". NASA Technical Memorandum. TM Ten-881. February 1964. hdl:2060/19710065502.
9. ^ Barker, L. Keith (December 1964). "Application of a Lunar Landing Technique for Landing from an Elliptic Orbit Established by a Hohmann Transfer". NASA Technical Annotation. TN D-2520. hdl:2060/19650002270.
10. ^ Barker, L. Keith; Queijo, M. J. (June 1964). "A Technique for Thrust-Vector Orientation During Manual Control of Lunar Landings from a Synchronous Orbit". NASA Technical Note. TN D-2298. hdl:2060/19640013320.
11. ^ Thurman, Sam W. (Feb 2004). Surveyor Spacecraft Automatic Landing System. 27th Annual AAS Guidance and Control Briefing. Archived from the original on 2008-02-27.
12. ^ Culler, Glen J.; Fried, Burton D. (June 1957). "Universal Gravity Plow Trajectories". Journal of Practical Physics. 28 (6): 672–676. Bibcode:1957JAP....28..672C. doi:10.1063/1.1722828.

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Source: https://en.wikipedia.org/wiki/Gravity_turn

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