CN113978767B - A method for probe ballistic lift type Mars entry - Google Patents

Abstract

The invention relates to a method for entering a detector ballistic lift type Mars, which comprises the following steps: s1, offsetting the centroid of the landing patrol instrument before launching; s2, starting to descend the rail according to a preset flight time sequence; s3, after descending the rail, the detector slides along the entering rail; s4, the landing patrol device continues to slide along the entering track, and the landing patrol device maneuvers to a stable posture of three separated sliding shafts; s5, the landing patrol instrument is adjusted to the entering posture until the landing patrol instrument enters the Mars atmosphere, and the landing patrol instrument enters the attack angle balancing stage; s6, the landing patrol device keeps the stable attitude of the three sliding shafts to continue flying, and then the landing patrol device enters a lift force control stage; s7, in the lift force control stage, controlling the roll angle of the landing patrol instrument, and adjusting the direction of the lift force to enable the landing patrol instrument to track the preset nominal trajectory flight; s8, the landing patrol device pops up a leveling wing, and the aerodynamic force of the landing patrol device gradually enables the attack angle of the landing patrol device to return to 0 degree; and S9, the landing patrol device pops up the parachute, and the speed of the landing patrol device is reduced to subsonic speed.

Description

A method for probe ballistic lift type Mars entry

technical field

The invention relates to a ballistic lift-type Mars entry method of a probe, which is suitable for Mars landing and patrol detection tasks, and belongs to the technical field of spacecraft EDL.

Background technique

1) How to enter the atmosphere of Mars

Based on the current technical capabilities, there are two main ways of entering the Martian atmosphere: ballistic and ballistic lift. Different entry methods directly affect the design status of the entry system in many aspects, such as function, configuration, overload, heat protection, parachute opening height, and drop point accuracy.

Ballistic: After entering the Martian atmosphere, the entrant only generates drag, not lift, and the lift-drag ratio is 0.

Ballistic lift type: On the basis of ballistic entry, by configuring the center of mass method, the enterer can generate a trim angle of attack when entering the Martian atmosphere, thereby generating a certain lift, and the lift-drag ratio is generally not more than 0.5.

2) Martian atmospheric conditions

The atmospheric conditions of Mars mainly include atmospheric density, temperature, wind speed, light depth, dust storm, Martian dust, etc. The parameters that mainly affect the process of atmospheric entry are atmospheric density, temperature and wind speed. Due to the characteristics of Mars itself and the lack of human understanding of Mars, the atmospheric conditions of Mars are still subject to great uncertainty.

The Martian atmosphere is very thin, mainly composed of: carbon dioxide (95.3%), nitrogen (2.7%), argon (1.6%) and very small amounts of oxygen (1.5%) and water (0.03%). The average air pressure on the surface of Mars is about 640Pa, which is less than 1% of Earth's air pressure. Mars' thin atmosphere produces a weak greenhouse effect, raising its surface temperature by only 5K, which is less than Venus's 500K and Earth's 33K. According to the statistics of previous Mars exploration missions, the estimated deviation of the Martian atmospheric density is about ±10% to ±75%, and the estimated deviation of the Martian atmospheric temperature is about -15K to +18K.

Winds on the Martian surface are highly variable, determined in part by conventional atmospheric circulation (and thus with seasonal and local climate variability), while being primarily controlled by regional and local environments, including the effects of topography, albedo, and thermal inertia.

3) Existing ballistic lift entry scheme

Judging from the successful Mars landing missions abroad, the MPF, MER and Phoenix missions all adopted ballistic entry methods.

Viking, MSL and Perseverance use the "ballistic-lift" entry method, but there are essential differences between the two. Viking has no guidance, and does not control and utilize the magnitude and direction of lift. Its lift configuration is due to the fact that it is the first Mars landing mission in the United States, based on reducing mission risks, making the entry trajectory smooth, reducing the peak heat flux density, etc. to improve survivability, But the price is that the landing accuracy is greatly reduced. MSL is the world's first Mars rover that adopts "ballistic lift" entry and control, and achieves high landing accuracy by controlling the inclination angle. Perseverance is similar to the MSL entry method, except that Perseverance uses image matching guidance.

The main events of MSL's EDL process are as follows:

(1) Cruise stage separation

At 05:14:34 (UTC) on August 6, 2012, the probe separated from the cruise stage 10 minutes before entering the atmosphere.

(2) Prepare to enter the Martian atmosphere

Nine minutes before entry, the thrusters on the back cover were ignited to establish the atmospheric entry attitude.

(3) Release the counterweight for the first time

When the atmospheric entry attitude is established, the back cover separates two solid tungsten alloy counterweights, each weighing 75kg, so that the center of mass of the enterer deviates from the axis of symmetry, so that the enterer generates a trim angle of attack when entering the atmosphere.

(4) Guided atmospheric entry

MSL adopts a linear entry guidance law, which is based on EPTC (Entry Terminal Point Controller) to formulate a reference trajectory for dual-segment constant inclination angle guidance, tracks drag acceleration and altitude change rate, and adjusts the angle of attack by changing the lift vector through the attitude control system. MSL motion and attitude analysis are shown in Figure 1. Before entering the Martian atmosphere, MSL obtains the initial navigation parameters through the ground measurement and control station, and uses the cruise-level star sensor to obtain the inertial attitude to provide initial values for inertial navigation. After entering the atmosphere, the GNC subsystem obtains the current lander's speed and resistance acceleration through the inertial measurement unit, and the expected value of the target value, determines the target tilt angle, completes the reference trajectory tracking, and adjusts the traverse through the inversion of the tilt angle. Entry segment guidance is divided into two segments: including range control and lateral control. When the entry resistance acceleration reaches 0.2g, the entry guidance process is carried out to correct the voyage error, and at the same time, the necessary roll angle reversal is performed by monitoring the change of the yaw error.

The peak heat flow occurs about 80s after entering the atmosphere. At this time, the extreme high temperature generated on the outsole is about 2100℃, the flight altitude is 27km, the distance from the landing point is 230km, the flight Mach number is 24, and the speed is 4690m/s. After 10s, the acceleration reached a peak value of 11.4g. It was 19km away from the surface of Mars and 200km away from the landing site. The flight Mach number was 19 and the flight speed was 3600m/s.

(5) The second release of the counterweight

When the probe ends the guidance and enters the maneuver, a few seconds before the parachute is opened, the back cover releases another set of counterweights, a total of 6, each weighing 25kg, so that the center of mass of the enterer is transferred to the rear of the symmetry axis, and the trim angle of attack is reset. becomes 0°.

(6) Supersonic parachuting and parachuting

The parachute opened 255s after entering. At this time, the height of the probe was 11km and the speed was about 405m/s. After 20s, the outsole is separated. At this time, the height is 8km and the speed is about 125m/s. The Mars Landing Camera began photographing the surface of Mars below the rover. Lower the sensor at the end and start measuring relative speed and altitude.

(7) Lower engine ignition

The back cover connected with the parachute is separated from the descending stage and the rover after the outsole is separated for 97s. After the back cover is released, the descending stage and the rover accelerate for 0.8s in an approximate free fall manner to ensure a safe distance from the back cover. At this time, the height of the entrant is 1.4 km, and the speed is 80 m/s. Eight engines on the descending stage start firing during the braking descent stage.

(8) The aerial crane descends the rover

After the descending segment, at a height of 18.6m, the GNC system switches to aerial crane mode. The crane and the rover are connected by three nylon ropes and the center of mass is arranged side by side to limit external interference to the greatest extent. During the suspension process of the aerial crane, it continued to descend at a vertical speed of 0.75m/s. After the crane was separated from the rover for 7s, the nylon rope was fully expanded to a length of 7.5m and stopped descending to achieve hovering, followed by a final touch of 2s. ground attitude correction. After 9s of separation, the touchdown process starts, and it still descends at a speed of 0.75m/s to the final touchdown. After the final touchdown of the Mars rover is determined, the crane ignites and blows the rope, and the crane begins to fly away. It also acts as a landing gear and bounces off before touching the ground, and the rover successfully achieves a soft landing, as shown in Figure 2. (9) Crane flying away

When the crane is disconnected from the rover, the crane will automatically search for a landing point and activate the flyaway mode. The crane will hover first, waiting for the rope wire and the rover to completely detach and no longer affect each other. After hovering, the crane will adjust two of the engines to 100% working state, and the other two will be adjusted to lower than 100% working state, so that the crane will have an inclination angle of 45° in the vertical direction. All are adjusted to 100% working state, and the crane flies away from the landing site of the rover. After the fuel was exhausted, the crane moved freely and finally crashed to the surface of Mars 150m away from the rover.

SUMMARY OF THE INVENTION

The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, to provide a ballistic lift-type Mars entry method of a probe, and to improve the adaptability of the Mars atmosphere entry process to the deviation of atmospheric parameters by utilizing a very small weight cost.

The technical solution of the present invention is: a method for a probe ballistic lift type Mars entry, the probe includes an orbiter and a landing rover, and the method includes the following steps:

S1. Offset the center of mass of the landing rover before launch, so that the landing rover generates the expected trim angle of attack during the entry of the Martian atmosphere;

S2. Send the probe into the orbit of Mars, the probe will fly around Mars, and start to de-orbit according to the preset flight sequence;

S3. After descending the orbit, the detector slides along the entry orbit, and under the control of the ground remote control command, the orbiter is separated from the landing patrol;

S4. After the orbiter is separated from the landing rover, the orbiter lifts its orbit back to the parking track, maneuvers to the relay communication attitude, establishes a relay communication link between the ground and the landing rover, and the landing rover continues to glide along the entry track , maneuvering to the three-axis stable attitude of separation and sliding;

S5. Before entering the Martian atmosphere, the landing rover is adjusted to the entry attitude. The entry attitude rotates around the Y-axis of the landing rover's main system on the basis of the three-axis stable attitude of separation and taxiing, so that the landing rover can keep the expected trim angle of attack and fly. , until the landing rover enters the Martian atmosphere, and the landing rover enters the angle of attack trim stage;

S6. In the trim phase of the angle of attack, the landing rover maintains the stable three-axis taxiing attitude in step S6 and continues to fly, and enters the Martian atmosphere until the aerodynamic drag acceleration is greater than the preset threshold, and the landing rover enters the lift control phase;

S7. In the lift control stage, control the inclination angle of the landing patrol and adjust the direction of lift, so that the landing patrol follows the preset nominal ballistic flight;

S8. When the Mach number of the landing patrol is less than the first preset threshold, the landing patrol pops out the trim wing. After the trim wing pops up, the trim angle of attack returns to 0° through the trim wing, and the aerodynamic force of the landing patrol gradually makes the landing patrol The angle of attack returns to 0°;

S9. When the Mach number of the landing patroller is less than the second preset threshold, the landing patroller ejects the parachute and rapidly reduces the speed of the landing patroller to subsonic speed.

Preferably, the expected trim angle of attack is -10°.

Preferably, the orbital period of the Mars orbit is 2 Martian days. When the probe reaches the perigee point, it just passes over the landing point. In order to ensure the accuracy of entering the orbit, the perigee point of the orbit should not be higher than 300km.

Preferably, the deorbiting time is 5.5 hours to 6.5 hours before the detector reaches the near-fire point.

Preferably, the preset threshold in step S6 is 2m/s ² .

Preferably, the first preset threshold is 2.35˜3.25.

Preferably, the second preset threshold is 1.5˜2.1.

Preferably, the three-axis stable attitude of separation and sliding means that the coordinate system of the body coordinate system of the landing rover-X axis points to the direction of Mars in the orbital plane of the entry point, and the included angle with the speed direction of the entry point is -40°, and the coordinate system of the body coordinate system +Y The axis is in the direction of the entry point orbit normal.

Preferably, in the steps S2 to S4, in the non-orbit control or separation process, the Mars probe uses orbital dynamics to perform position and velocity navigation, and in the orbit control and separation process, the measurement results of the accelerometer are introduced, and the orbital dynamics are used. On the basis of the six-degree-of-freedom dynamic integration, the position and velocity navigation is completed.

Preferably, in the steps S5-S7, the landing rover introduces the measurement result of the plus meter, and performs a six-degree-of-freedom dynamic integration on the basis of the orbital dynamics, so as to complete the position and speed navigation.

The beneficial effects of the present invention compared with the prior art are:

(1) The present invention biases the probe into the center of mass of the cabin before launching, so that it generates the expected trim angle of attack during the entry of the Martian atmosphere, and adjusts the lift direction by controlling the inclination angle of the entering cabin, which can adapt to a larger initial value of navigation Deviation, atmospheric parameter deviation and aerodynamic parameter deviation, unfold the trim wing before opening the parachute, so that the entering cabin trim angle of attack returns to zero, and meets the angle of attack control requirements of the aerodynamic deceleration section with the angle of attack and the zero angle of attack before the parachute opening;

(2) In the present invention, before entering the Martian atmosphere and not during the orbital control period of the probe, the landing rover does not introduce accelerometer measurement data, and only uses orbital dynamics for position navigation to improve navigation accuracy.

(3) The design of the de-orbit strategy of the present invention takes the nominal values of longitude, latitude, and entry angle of the landing rover when the landing rover reaches a height of 125 km on the surface of Mars.

Description of drawings

Fig. 1 is the schematic diagram of entering attitude in the EDL process of MSL;

Figure 2 is a schematic diagram of the soft landing of MSL's aerial crane;

Fig. 3 is the aerodynamic shape of the entry cabin of the landing rover according to the embodiment of the present invention;

FIG. 4 is a flowchart of a method for a probe ballistic lift-type Mars entry according to an embodiment of the present invention;

FIG. 5 is the unfolded state of the trim wing according to the embodiment of the present invention.

Detailed ways

The present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments of the description.

The present invention provides a method for a probe ballistic lift type Mars entry. The probe includes an orbiter and a landing rover. As shown in FIG. 4 , the method includes the following steps:

S1. Offset the center of mass of the landing rover before launch, so that the landing rover generates the expected trim angle of attack during the entry of the Martian atmosphere;

For a certain aerodynamic shape, flying with different angles of attack will generate different lift. The larger the angle of attack, the greater the lift and the stronger the control ability, but the lower the deceleration performance. Based on the landing accuracy requirements and deceleration performance requirements of the Mars exploration mission, the trim angle of attack of the landing rover is determined to be -10°.

/力矩

令质心在端部坐标系下的坐标矢量为

则通过解方程

得到质心位置。The position of the center of mass determines the size of the trim attack angle. The design process of the center of mass position is as follows: According to the results of the aerodynamic shape design, the optimal trim attack angle is determined; according to the aerodynamic/moment analysis, the end force when the attack angle is ɑ is obtained.

/torque

Let the coordinate vector of the centroid in the end coordinate system be

then by solving the equation

Get the centroid position.

In a specific embodiment of the present invention, the aerodynamic shape of the entry cabin of the landing patrol vehicle is shown in FIG. 3 .

S2. Send the probe into the orbit of Mars, the probe will fly around Mars, and start to de-orbit according to the preset flight sequence;

The orbital period of the Mars orbit is 2 Martian days. When the probe reaches the perigee point, it just passes over the landing point. In order to ensure the accuracy of entering the orbit, the perigee point of the orbit should not be higher than 300km.

De-orbit timing selection is constrained by the degree of orbit error divergence and ground flight control decision-making time. De-orbiting too early will lead to excessive entry point error, and de-orbiting too late will lead to insufficient time for decision-making on ground state interpretation after de-orbit.

The derailment time of the present invention is determined according to the following principles:

The leading edge at the time of de-orbiting should meet the requirements of the entry point after the degree of error divergence after de-orbiting, and the trailing edge at the time of de-orbiting should meet the requirements of the entry point after de-orbiting. Considering the signal propagation time, there should be at least 40 minutes on the ground for judging the state and decision-making on the ground. time. In summary, the deorbiting time is 5.5 hours to 6.5 hours before the probe reaches the near fire point.

In a specific embodiment of the present invention, 30 minutes before the detector descends the orbit, the orbit measurement results on the ground are used to extrapolate the position and speed information 10 minutes before the orbit descend, which is used as the initial navigation value and injected into the detector. The specific form of the initial navigation value is (trv), where t is the epoch time corresponding to the initial navigation value, r is the position vector of the probe at time t, described in the Mars J2000 inertial system, and v is the speed of the probe at time t Vector, described in the Mars J2000 inertial frame.

10 minutes before de-orbiting, use the position and velocity information on the landing rover, combine the attitude and acceleration measurement results of the star sensor and IMU, that is, the three-axis acceleration of the landing rover, start the navigation extrapolation, and obtain the landing rover Current real-time attitude, position and velocity. In order to improve the navigation accuracy, when the probe does not execute the jet command, the measurement results of the accelerometer are not introduced, and only orbital dynamics are used for position navigation. This mode lasts until the first 10 s of its entry into the atmosphere.

S3. After descending the orbit, the detector slides along the entry orbit, and under the control of the ground remote control command, the orbiter is separated from the landing patrol;

S4. After the orbiter is separated from the landing rover, the orbiter lifts its orbit back to the parking track, maneuvers to the relay communication attitude, establishes a relay communication link between the ground and the landing rover, and the landing rover continues to glide along the entry track , maneuvering to the three-axis stable attitude of separation and sliding.

In this step, the detector separation conditions include that the single device of the detector is normal, the parameters of the navigation track meet the requirements of the entry point, and the like. After de-orbiting, the probe establishes a separation attitude. After the ground judges that the probe meets the separation conditions according to the telemetry data, the ground sends an instruction to allow the separation of the landing rover and the orbiter to realize the separation of the orbiter and the landing rover.

At this time, the landing rover considers thermal control and sensor field of view constraints, and maintains the three-axis stable attitude of separation and taxiing. The three-axis stable attitude of separation and taxiing refers to the coordinate system of the landing rover body - the X axis points to Mars in the orbital plane of the entry point direction, and the included angle with the speed direction of the entry point is -40°, and the +Y axis of the body coordinate system is along the normal direction of the track of the entry point.

S5. Before entering the Martian atmosphere, the landing rover is adjusted to the entry attitude. The entry attitude rotates around the Y-axis of the landing rover's main system on the basis of the three-axis stable attitude of separation and taxiing, so that the landing rover can keep the expected trim angle of attack and fly. , until the landing rover enters the Martian atmosphere, and the landing rover enters the angle of attack trim stage;

In a specific embodiment of the present invention, 10s before the entry of the atmosphere, the entry cabin adjusts the entry attitude so that it satisfies the -10° angle of attack and maintains it, and at the same time, the instrument starts to unconditionally introduce the addition measurement results. In order to prevent errors in the measurement data of the star sensor after the atmosphere enters, the star sensor is automatically turned off on the device, and the real-time attitude is determined by the gyro integral.

The altitude from the reference Martian surface ranges from about 125km to about 60km. The atmosphere is thin. According to the aerodynamic characteristics of the entry cabin, the drag coefficient increases rapidly with the increase of altitude above 80km, the lift-to-drag ratio decreases rapidly, and the static stability margin decreases rapidly, and appears above 95km. statically unstable. Therefore, the segment performs the taxiing three-axis stabilized attitude control to maintain the entering attitude.

S6. In the trim phase of the angle of attack, the landing rover maintains the stable three-axis taxiing attitude of step S6 and continues to fly, and enters the Martian atmosphere until the aerodynamic drag acceleration is greater than the preset threshold, and the landing rover enters the lift control phase; the preset threshold is 2m/s ² .

S7. In the lift control stage, the direction of lift is adjusted by controlling the inclination angle of the landing rover, so that the landing rover tracks the preset nominal ballistic flight;

At this stage, the height from the reference Mars surface is from about 60km to about 11.3km. The aerodynamic resistance in this section increases, and the lift control effect is gradually significant. The lift direction is adjusted by adjusting the inclination angle of the entry cabin to ensure that the entry trajectory and parachute opening point meet the requirements for use.

The main constraints on the entry trajectory include total heating constraints, peak heat flux density constraints, trim wing deployment dynamic pressure constraints, parachute height constraints, and parachute dynamic pressure constraints. Under the Martian environmental conditions, the entry process satisfies the above constraints.

S8. When the Mach number of the landing patrol is less than the first preset threshold, the landing patrol pops out the trim wing. After the trim wing pops up, the trim angle of attack returns to 0° through the trim wing, and the aerodynamic force of the landing patrol gradually makes the landing patrol The angle of attack returns to 0°; the first preset threshold is 2.35-3.25.

The trim wing satisfies the following aerodynamic characteristics: after the trim wing is deployed, the aerodynamic force center of the landing rover changes. The line connecting the center of mass of the landing rover is parallel to the X-axis of the landing rover's own system.

As shown in FIG. 5 , in a specific embodiment of the present invention, the trim wing includes a wing plate, a deployment arm, a connecting rod assembly, a screw transmission device, a damping device, an air source device, a pressing and releasing device, and the like. The wing plate is an isosceles trapezoid structure, which is connected with the deployment arm at the root of the wing plate; the deployment arm is a supporting structure composed of two C-shaped arms, the two arms are connected by a square connecting plate, and the root of the arm is connected by a bearing. And the base is installed on the side wall structure of the Mars probe entering the cabin, the wing plate and the unfolding arm assembly can be rotated relative to the entering cabin side wall, and the wing plate is pressed by the pressing and releasing device when the trim wing is retracted; the damping device and the screw transmission device It is installed horizontally on the mounting bracket provided by the entry cabin. The damping device provides linear motion, and its output shaft is connected with the screw rod of the screw transmission device, so that the linear motion of the damping device is converted into the rotation of the screw pair through the screw rod of the screw transmission device; The connecting rod mechanism is connected with the output shaft of the screw transmission device. The connecting rod assembly is composed of connecting rod A, connecting rod B and a hinge. The connecting rod A and connecting rod B are connected by a hinge, and the hinge has the function of rotating and locking; , Connecting rod assembly connecting rod B, wing plate and deployment arm C-shaped arm rod together constitute a crank rocker mechanism; the air source device is installed on the entry cabin structure, and the air source device consists of a gas cylinder, a gas filling and exhaust valve (2 pcs) , Electric explosion valve (one upstream and downstream pipelines) and pipelines, the gas source components and the damping device are connected by pipelines, and the gas cylinders are pre-filled with a certain pressure of gas (helium, nitrogen, etc.).

When the Mars rover is launched, the trim wing is in a retracted state, and the wing plate is pressed against the side wall of the entering cabin by the compression release device; during the probe entry process, the compression release device is first unlocked, and then the electric explosion valve of the air source device is opened ( As long as one of the two electric explosion valves is open), the pipeline between the gas cylinder and the damping device is connected, and the high-pressure gas stored in the gas cylinder enters the damping device, which drives the piston rod of the damping device to move, and the piston rod of the damping device pulls the screw drive. The screw rod of the device moves in a straight line, and the screw sleeve matching the screw rod rotates, and the rotation is transmitted to the connecting rod assembly through the output shaft. The connecting rod assembly drives the wing plate and the unfolding arm assembly to rotate relative to the unfolding arm base. During the movement, the damping device can effectively reduce the impact load when the trim wing is unfolded and locked; after the wing plate is flattened, the linkage assembly hinge is locked. After the wing plate is deployed, the link A and the link B of the link assembly move to the dead center position and lock. The wing plate, the deployment arm, and the link assembly form a stable structure, which can withstand the aerodynamic load of the probe during the process of entering the Martian atmosphere. And through the aerodynamic load to achieve the control of the entering cabin into the angle of attack.

In order to ensure that the trim wing deployment conditions meet the operating conditions, similar to the previous Earth return missions, the acceleration, altitude, and pressure triggers could not meet the trim wing deployment requirements in the Martian environment. . In combination with the parachute opening conditions, in a specific implementation of the present invention, when the navigation Mach number is less than 2.8, the trim wing deployment command is sent on the device. Before opening the parachute, by unfolding the trim wing, the aerodynamic pressure center of entering the cabin is changed, so that the connection line between the aerodynamic pressure center and the center of mass is parallel to the axis of the cabin body, so that the trim angle of attack of entering the cabin can be returned to zero. The deployed state of the trim wing is shown in Figure 2.

S9. When the Mach number of the landing patroller is less than the second preset threshold, the landing patroller ejects the parachute and rapidly reduces the speed of the landing patroller to subsonic speed. The second preset threshold is 1.5˜2.1.

In the above steps S2-S4, during the non-orbit control or separation process, the landing rover uses the orbital dynamics to carry out position and velocity navigation. Dynamic integration of degrees of freedom to complete position-velocity navigation.

In the above-mentioned steps S5-S7, the landing rover introduces the measurement result of the plus meter, and performs the six-degree-of-freedom dynamic integration on the basis of the orbital dynamics to complete the position and speed navigation.

In order to ensure that the parachute deployment conditions meet the working conditions, similar to the acceleration, altitude, and pressure triggers in the previous Earth return missions, they could not meet the trim wing deployment requirements in the Martian environment. A parachute deployment strategy based on the navigation Mach number was designed.

The main constraints on the selection of the parachute opening threshold include the parachute opening load, the parachute descent time after the bottom is thrown, and the steady descent speed.

In a specific embodiment of the present invention, when the navigation Mach number is less than 1.8, the parachute signal is triggered, the parachute is ejected, and the cabin enters the parachute drop section.

To sum up, the present invention has the following features:

(1) Based on the trim wing to realize the zero return of the trim angle of attack

The entry capsule is a revolving body, and the centroid of the entry capsule is offset before launch to produce the expected trim angle of attack during the entry into the Martian atmosphere. Before opening the parachute, by unfolding the trim wing, the trim angle of attack of the entry cabin can be returned to zero.

(2) Use the navigation Mach number as the trigger condition for trim wing deployment

In order to ensure that the trim wing deployment conditions meet the operating conditions, similar to the previous Earth return missions, the acceleration, altitude, and pressure triggers could not meet the trim wing deployment requirements in the Martian environment. .

(3) The trim section of the angle of attack adopts the three-axis stable attitude control to maintain the entry attitude

The altitude from the reference Martian surface ranges from about 125km to about 60km. The atmosphere is thin. According to the aerodynamic characteristics of the entry cabin, the drag coefficient increases rapidly with the increase of altitude above 80km, the lift-to-drag ratio decreases rapidly, and the static stability margin decreases rapidly, and appears above 95km. statically unstable. This stage does not have the conditions to use the aerodynamic force to maintain a stable attitude, so this stage performs three-axis stable attitude control to maintain the entering attitude.

(4) The lift control section adopts the nominal ballistic tracking control strategy

At this stage, the height from the reference Mars surface is from about 60km to about 11.3km. The aerodynamic resistance increases in this section, and the lift control effect is gradually significant. Adjust the lift direction by adjusting the inclination angle of the entry cabin, track the nominal ballistic trajectory, and ensure the entry trajectory and parachute opening point. meet the usage requirements.

(5) Use the drag acceleration ≥ 0.2g as the switching condition between the attack angle trim section and the lift control section

The density of the upper atmosphere of Mars has a large uncertainty, and there is a large error in the division of the trim section and the lift control section with altitude alone, which may affect the aerodynamic stability or lift control efficiency of the entry cabin, and then affect the parachute opening conditions. Using the drag acceleration as the switching condition can better avoid the influence of atmospheric density fluctuations on the control. According to the entry condition of the landing rover, when it reaches 60km, the plus measurement result is about 2m/s ² . Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can use the methods and technical contents disclosed above to improve the present invention without departing from the spirit and scope of the present invention. The technical solutions are subject to possible changes and modifications. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solutions of the present invention belong to the technical solutions of the present invention. protected range.

Claims (10)

1. a method for probe ballistic lift type Mars to enter, described probe comprises surround device and landing patrol device, it is characterized in that comprising the steps: S1. Offset the center of mass of the landing rover before launch, so that the landing rover generates the expected trim angle of attack during the entry of the Martian atmosphere; S2. Send the probe into the orbit of Mars, the probe will fly around Mars, and start to de-orbit according to the preset flight sequence; S3. After descending the orbit, the detector slides along the entry orbit, and under the control of the ground remote control command, the orbiter is separated from the landing patrol; S4. After the orbiter is separated from the landing rover, the orbiter lifts its orbit back to the parking track, maneuvers to the relay communication attitude, establishes a relay communication link between the ground and the landing rover, and the landing rover continues to glide along the entry track , maneuvering to the three-axis stable attitude of separation and sliding; S5. Before entering the Martian atmosphere, the landing rover is adjusted to the entry attitude. The entry attitude rotates around the Y-axis of the landing rover's main system on the basis of the three-axis stable attitude of separation and taxiing, so that the landing rover can keep the expected trim angle of attack and fly. , until the landing rover enters the Martian atmosphere, and the landing rover enters the angle of attack trim stage; S6. In the angle of attack trim stage, the landing rover maintains the three-axis stable attitude of separation and taxiing in step S4 and continues to fly, and enters the Martian atmosphere until the aerodynamic drag acceleration is greater than the preset threshold, and the landing rover enters the lift control stage; S7. In the lift control stage, control the inclination angle of the landing patrol and adjust the direction of lift, so that the landing patrol follows the preset nominal ballistic flight; S8. When the Mach number of the landing patrol is less than the first preset threshold, the landing patrol pops out the trim wing. After the trim wing pops up, the trim angle of attack returns to 0° through the trim wing, and the aerodynamic force of the landing patrol gradually makes the landing patrol The angle of attack returns to 0°; S9. When the Mach number of the landing patroller is less than the second preset threshold, the landing patroller ejects the parachute and rapidly reduces the speed of the landing patroller to subsonic speed. 2 . The method for probe ballistic lift type Mars entry according to claim 1 , wherein the expected trim angle of attack is -10°. 3 . 3. the method that a kind of probe ballistic lift type Mars enters according to claim 1, it is characterized in that the orbital period of described Mars orbit is 2 Martian days, when probe reaches near fire point, just passes through landing Above the point, in order to ensure the accuracy of entering the descending orbit, the surrounding orbit near the fire point should not be higher than 300km. 4 . The method for probe ballistic lift type Mars entry according to claim 1 , wherein the orbit down time is 5.5 hours to 6.5 hours before the probe reaches the near fire point. 5 . 5 . The method for probe ballistic lift type Mars entry according to claim 1 , wherein the preset threshold in the step S6 is 2 m/s ² . 6 . 6 . The method for probe ballistic lift type Mars entry according to claim 1 , wherein the first preset threshold is 2.35˜3.25. 7 . 7 . The method for probe ballistic lift type Mars entry according to claim 1 , wherein the second preset threshold is 1.5˜2.1. 8 . 8. The method for a probe ballistic lift type Mars entry according to claim 1, wherein the three-axis stable attitude of separation and sliding refers to the coordinate system-X axis of the landing rover body pointing in the entry point orbital plane. The direction of Mars, and the included angle with the speed direction of the entry point is -40°, and the +Y axis of the body coordinate system is along the normal direction of the orbit of the entry point. 9. A method for probe ballistic lift type Mars entry according to claim 1, characterized in that in the steps S2-S4, in the non-orbital control or separation process, the Mars probe utilizes orbital dynamics to carry out the position velocity For navigation, in the process of orbit control and separation, the measurement results of the accelerometer are introduced, and the six-degree-of-freedom dynamic integration is carried out on the basis of orbit dynamics to complete the position and velocity navigation. 10. A method for probe ballistic lift type Mars entry according to claim 1, characterized in that in the steps S5-S7, the landing rover introduces accelerometer measurement results, and carries out six degrees of freedom on the basis of orbital dynamics Dynamic integration to complete position and velocity navigation.

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