A high-speed vertical lunar impact probe deorbiting and descent guidance scheme

Abstract

The patent of this invention, "A guidance scheme for the deorbiting and descent of a high-speed vertical impact lunar probe", belongs to the field of guidance technology of lunar exploration engineering. This guidance scheme enables the probe to deorbit from the lunar orbit, enter the descent trajectory, and finally vertically impact the moon at a specified speed and penetrate into the lunar soil. The guidance scheme is divided into three steps in chronological order: the main engine is turned on at the apogee of the probe's lunar orbit to provide thrust perpendicular to the tangent of the orbit, lowering the trajectory angle until it approaches negative ninety degrees, and the main engine is turned off; the probe falls freely under the action of gravity, and the speed continues to increase; at an appropriate time, the main engine is turned on for the second time and braked with full force until the probe vertically impacts the moon at the desired speed. The key to this scheme is the estimation of the time when the main engine is turned on for the second time. Using the sensors carried by the probe to collect and analyze data on the impact process, we can have a comprehensive and in-depth understanding of the physical and chemical properties of the lunar soil, which is of great significance for exploring the mysteries of the moon and its development and utilization.

Description

Technical Field

[0001] The present invention belongs to the field of guidance and control technology of lunar exploration projects, and in particular to a high-speed vertical lunar impact probe de-orbit descent guidance scheme. Background Art

[0002] There are three main types of lunar exploration by lunar probes: flyby, flyby, and landing. Among them, landing is divided into two types: soft landing and hard landing (impact). Among them, the guidance and control technology of soft landing has been studied more thoroughly, and although hard landing (impact) has been implemented many times, such as ESA's SMART-1 (launched in 2003), my country's Chang'e 1 (launched in 2007), India's "Chuhang 1" (launched in 2008), etc., the US LCROSS mission has a high-speed impact with the moon as its main mission goal. However, in these impact missions, the impact speed is extremely high, generally above 1000m / s. The probe itself has been damaged and there is no scientific payload on it. The high-speed impact causes the lunar soil to splash out for other probes to conduct further exploration and research. Therefore, these high-speed impact flights do not have strict requirements on the impact angle and speed. The article "Orbit Design of the Probe Hitting the Moon under Multiple Constraints" on pages 1-7 of the 2nd issue of "China Space Science and Technology" in 1997 studied the orbit of launching from the Earth directly into the Earth-Moon transfer orbit and hitting the Moon at 10km / s; the article "Design of the Flight Plan for the Subsequent Mission of Chang'e 2" on pages 26-40 of the "Proceedings of the 8th Annual Academic Conference of the Deep Space Exploration Technology Professional Committee of the Chinese Society of Astronautics" considered that after the probe entered the lunar gravitational influence sphere, it was considered that the probe's orbit relative to the Moon was a hyperbolic orbit. Using the two-body model, it was estimated that the impact speed when hitting the Moon was 2.6km / s. After such a high-speed collision with the Moon, the probe was completely destroyed, and it could only rely on other probes to detect and study the lunar surface ejected materials produced by the high-speed impact.

[0003] The scenario studied in this invention is that the probe separates from the lunar orbit, vertically hits the moon at a speed of hundreds of meters per second, and penetrates to a certain depth on the lunar surface, relying on the various sensors carried by the probe itself to detect and analyze the physical and chemical properties of the lunar soil. Therefore, it is required to accurately control the speed and direction of the probe during the deorbit and descent process. There is little public literature on this aspect so far. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a high-speed vertical lunar impact probe deorbiting and descent guidance scheme in view of the defects of the background technology. The present invention aims to propose a guidance technology scheme to ensure that the probe reaches the moon at a specified high speed and a nearly vertical angle of incidence to achieve the best lunar impact effect. The guidance technology scheme proposed by the present invention should also save the probe engine fuel consumption, reduce the probe's own weight, increase the payload, and maximize the benefits of lunar impact detection.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] The probe is operating in an elliptical orbit around the moon. The basic process of its deorbiting and descent guidance technology is as follows:

[0007] Step 1), Normal Guidance

[0008] When the probe reaches the apogee, the normal guidance is turned on. The attitude control system makes the nozzle direction of the probe's main engine perpendicular to the orbital tangent, and the engine works at maximum thrust, so that the probe's ballistic inclination angle increases from zero to the negative direction, that is, the probe's trajectory is lowered. The target value is -90°, that is, perpendicular to the local lunar surface and pointing to the center of the moon. The normal guidance law can be expressed as

[0009]

[0010] Among them, F n is the normal thrust provided by the main engine to the probe, F max is the maximum thrust value of the engine, γ is the instantaneous ballistic inclination of the detector, and ε is the pre-set allowable error tolerance.

[0011] Step 2), Tangentially guided free fall

[0012] When the detector's trajectory inclination enters the interval This indicates that its velocity direction is almost perpendicular to the local lunar surface, pointing to the center of the moon, and the normal guidance ends. The probe attitude control system makes the probe's main engine nozzle point downward, entering the tangential guidance phase. The tangential guidance is subdivided into the free fall phase and the full braking phase. In the free fall phase, the probe's main engine is shut down, and the probe falls freely and accelerates under the action of the moon's gravity. Until a pre-calculated time t s , the main engine is started and enters the full braking stage.

[0013] Step 3), full braking phase of tangential guidance

[0014] During this phase, the main engine nozzle is kept downward, the engine works at maximum thrust, and full braking is performed until the probe hits the moon. s (Right now Figure 1If the calculation of the time corresponding to point D in the figure is accurate, then the flight speed of the probe at the moment of impact with the moon will meet the predetermined value. The second start time of the main engine is t s The calculation is:

[0015]

[0016] Compared with the prior art, the present invention adopts the above technical solution and has the following beneficial effects:

[0017] 1. From the perspective of the engine working process, the guidance scheme provided by the present invention belongs to the "on-off-on" working mode, which is consistent with the control method with the lowest fuel consumption in the optimal control theory.

[0018] 2. This solution can save the probe's fuel consumption, reduce the probe's own weight, increase the payload, and improve the efficiency of lunar exploration while meeting the required impact speed and angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the probe's high-speed vertical impact with the moon and its descent into and out of orbit.

[0020] Figure 2 This is the schematic diagram of the high-speed vertical lunar impact guidance scheme for the probe.

[0021] Figure 3 Schematic diagram of the guidance and control integration of attitude control. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0023] The present invention can be implemented in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0024] The key to the guidance scheme proposed by the present invention is the secondary start-up time in the tangential guidance stage, i.e. Figure 1 The time t at point D s Determination of s The s in the lower right corner is the abbreviation of switch, which means "switch". s The calculation method of .

[0025] In the tangential guidance phase, the impactor descends at a speed nearly perpendicular to the local lunar surface, i.e., vertical downward one-dimensional motion. In addition, since the flight altitude of the impactor is much smaller than the lunar radius, the lunar gravitational acceleration can be regarded as a constant g (about 1 / 6 of the surface gravity acceleration). The following is an estimate of the impactor main engine secondary start-up time t under the assumption of constant gravity acceleration and vertical descent motion.s .

[0026] The first stage of vertical descent is free fall, and the equation of motion of the impactor is

[0027]

[0028] where v C ,y C The vertical descent starts at Figure 1 The flight speed and altitude of the impactor at point C.

[0029] Suppose at a certain time t s , the impactor's flight speed and altitude are v s ,y s , mass is m s , the main engine of the impactor is turned on and fully braked until it lands on the moon. During this stage, its flight dynamics equation is

[0030]

[0031] When studying the full braking section, we temporarily define the time when the main engine is started again as the zero time, and the time variable is τ to distinguish it from the time variable of the previous free fall section.

[0032] The third equation of equation (2) integrates the time variable τ and takes into account m s =m C , there are (3)

[0033]

[0034] Substituting equation (3) into the second equation of equation (2), we get

[0035]

[0036] Right now

[0037]

[0038] Right now

[0039]

[0040] Integrate both sides simultaneously

[0041]

[0042] have to

[0043]

[0044] Substituting equation (4) into the first equation of equation (2) and integrating it over time, we get

[0045]

[0046] The above integration process uses the indefinite integral formula

[0047] ∫lnxdx=xlnx-x+C

[0048] Formula (4) and (5) are the functional relationships between the flight altitude and speed of the impactor under full engine braking conditions and the time τ. Assume that at a certain time τ f , at a specified speed v fc The impactor hit the moon,

[0049]

[0050] Set t = t s Substituting into formula (1) we get

[0051]

[0052] Formula (6) and (7) are combined

[0053]

[0054] Formula (8) contains four unknowns, namely t s ,v s ,y s ,τ f , the problem is well-posed and has a unique solution, which can be solved quickly by numerical methods such as Newton's iteration method.

[0055] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0056] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-speed vertical lunar impact probe deorbiting and descent guidance scheme, characterized in that: The guidance scheme is divided into three stages in chronological order: normal guidance stage, free fall stage, and full braking stage; the steps of the scheme are as follows: Step S1, the probe starts normal guidance at the apogee of the elliptical orbit around the moon; the attitude control system makes the nozzle direction of the probe's main engine perpendicular to the orbit tangent, and the engine works at maximum thrust, so that the probe's ballistic inclination angle increases negatively from zero, that is, the probe's trajectory is lowered, and the target value is -90°, that is, perpendicular to the local lunar surface and pointing to the center of the moon; the normal guidance law is: In the formula, F n is the normal thrust provided by the main engine to the probe, F max is the maximum thrust value of the engine, γ is the instantaneous ballistic inclination of the detector, and ε is the preset allowable error tolerance; Step S2: When the instantaneous ballistic inclination angle γ of the detector falls into the interval After that, the probe attitude control system makes the probe's main engine nozzle point downward, and the probe enters the free fall stage; during this stage, the probe's main engine is shut down, and the probe falls freely and accelerates under the action of the moon's gravity until t s The main engine is started up again at any time; Step S3, t s The main engine is started again at this moment and enters the full braking stage. During this stage, the nozzle of the main engine is kept downward at the maximum thrust F max Work, braking with full force until the probe hits the moon.

2. According to the high-speed vertical lunar impact probe deorbiting and descent guidance scheme of claim 1, it is characterized in that: The main engine secondary start-up time t in step S3 s The calculation formula is: The unknown variable in the formula is t s ,v s ,y s ,τ f , respectively represent the second start-up time of the engine, the flight speed of the probe at the second start-up time, the flight altitude from the lunar surface, and the time taken for the full braking phase; the known parameters in the formula are: g is the lunar gravitational acceleration, F max is the maximum thrust of the probe's main engine, I sp is the specific impulse of the fuel, v C and C are the flight speed of the probe at the intersection of the normal guidance section and the free fall section and the flight altitude from the lunar surface, v fc is the specified moon landing speed.

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