A method for measuring optical depth on the surface of Mars

Abstract

The present invention provides a method for measuring the optical depth of the Martian surface, comprising the following steps: step 1, assuming that Mars has no atmosphere and without considering the optical depth, determining the ideal power generation power; step 2, obtaining the voltage and current telemetry data of the solar panel of the Mars rover, and determining the actual power generation power according to the voltage and current telemetry data of the solar panel; step 3, obtaining the analog coefficient C through the actual power generation value and the ideal power generation value; step 4, determining the atmospheric optical depth τ according to the analog coefficient C, the solar altitude angle θ and the albedo A. In the present invention, the optical depth value of the Martian surface can be determined according to the telemetry data on the Mars rover without the need for optical image information, thereby reducing the load of the Mars rover and extending the patrol and exploration mission cycle of the Mars rover.

Description

Technical Field

[0001] The invention belongs to the technical field of space exploration, and in particular relates to a method for measuring optical depth of the surface of Mars. Background Art

[0002] China's first Mars rover, Zhurong, safely left the landing platform and arrived at the surface of Mars for patrol and exploration on May 22, 2021. During the illumination period, it used the photovoltaic effect of solar cells to convert sunlight into electrical energy, and powered the rover through a power controller.

[0003] According to the light quality, the sunlight reaching the surface of Mars can be divided into direct light, scattered light and reflected light. Among them, the direct sunlight and scattered light are mainly related to the energy and thermal control design of the Mars rover. The atmospheric movement on the surface of Mars sweeps dust into the air, and the atmospheric dust environment formed will cause a certain degree of shielding of sunlight. The concept of light depth is usually used to describe the shielding effect of the Martian atmosphere (including dust) on light. Light depth is used to indicate the attenuation degree of light with an intensity of F0 when it passes through the atmosphere at a certain incident angle. As a basis for judging the degree of environmental dust, when the light depth is not greater than 0.8, the Mars rover completes the established standby / charging, solar wing movement, perception, movement, detection and other normal work items according to the ground plan; when the light depth is greater than 0.8, the Mars rover autonomously enters the minimum working mode or sleep mode according to the severe sand and dust conditions. Therefore, inverting the light depth of the Mars surface based on the information on the instrument is of great significance for the planning of the Mars rover patrol exploration mission. Summary of the invention

[0004] In order to overcome the deficiencies in the prior art, the inventor has conducted intensive research and provided a method for measuring the optical depth of the Martian surface, which inverts the optical depth value of the Martian surface based on the onboard telemetry data of the Mars rover (such as the voltage and current telemetry data of the battery panels), and provides basic input information for onboard energy management and behavior planning. Thus, the present invention is completed.

[0005] The technical solution provided by the present invention is as follows:

[0006] A method for measuring optical depth of the Martian surface comprises the following steps:

[0007] Step 1, assuming that Mars has no atmosphere and ignoring the light depth, determine the ideal power generation;

[0008] Step 2, obtaining the voltage and current telemetry data of the solar panels of the Mars rover, and determining the actual power generation according to the voltage and current telemetry data of the solar panels;

[0009] Step 3, obtain the analogy coefficient C through the actual power generation value and the ideal power generation value;

[0010] Step 4, determine the atmospheric optical depth τ according to the analogy coefficient C, the solar altitude angle θ and the albedo A;

[0011]

[0012] Where f(θ, τ, A) is the normalized net heat flow function, q is the light efficiency of direct light participating in the power generation of the battery array, and k is the light efficiency of scattered light participating in the power generation of the battery array.

[0013] Furthermore, in step 1, the step of determining the ideal power generation includes the following sub-steps:

[0014] Step 1.1, determine the solar incident angle α of the solar wing zya ;

[0015] Step 1.2, according to the solar incident angle α of the solar wing zya 、The power generation power of the solar wingspan during normal operation P zya0 and power generation efficiency Y MPPT , determine the ideal power generation power P of the solar wing zya_lx , P zya_lx =P zya0 ×cos(α zya )×Y MPPT .

[0016] Furthermore, in step 1.1, the solar incident angle α of the solar wing is determined zya The steps include the following sub-steps:

[0017] Step 1.1.1, determine the position of Mars in the heliocentric ecliptic coordinate system, and then convert it through the international astronomical reference coordinate system, the Mars fixed coordinate system, the Mars surface celestial northeast coordinate system, the Mars surface northeast coordinate system, and the Mars rover control body coordinate system to obtain the unit azimuth vector r from Mars to the sun in the Mars rover control body coordinate system sb ;

[0018] Step 1.1.2: Determine the direction vector r of the normal line of the battery surface in the coordinate system of the Mars rover control body s1 , according to the direction vector r of the normal line of the battery surface in the coordinate system of the Mars rover control body s1 and the unit azimuth vector r from Mars to the Sun sb , get the solar incident angle α of the solar wing zya .

[0019] Furthermore, in step 2, the actual value of the power generated by the solar wing is:

[0020] P ya_sj =U mx ×I1

[0021] Where U mx and I1 are the +Y solar wing A panel voltage and current telemetry data respectively.

[0022] Furthermore, in step 3, the actual power P ya_sj and ideal power P zya_lx The analogy coefficient C is obtained:

[0023] C=P ya_sj / P zya_lx .

[0024] Furthermore, in step 4, q is taken as 1 and k is taken as 0.5.

[0025] A method for measuring optical depth of the Martian surface provided by the present invention has the following beneficial effects:

[0026] The present invention provides a method for measuring the optical depth of the Martian surface. In the present invention, the optical depth value of the Martian surface can be determined based on telemetry data on a Mars rover without the need for optical image information, thereby reducing the load of the Mars rover and extending the Mars rover's patrol and exploration mission cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the solar wing of the Mars rover of the present invention. DETAILED DESCRIPTION

[0028] The following detailed description of the present invention will make the features and advantages of the present invention more clear and explicit.

[0029] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0030] The present invention provides a method for measuring optical depth of the surface of Mars, comprising the following steps:

[0031] Step 1, assuming that Mars has no atmosphere and ignoring the light depth, determine the ideal power generation;

[0032] Step 2: Get the rover's battery panel voltage U mx and current I1 telemetry data, and determine the actual power generation according to the voltage and current telemetry data of the solar panel;

[0033] Step 3: derive the analogy coefficient C by dividing the actual power generation value by the ideal power generation value, C = P ya_sj / P zya_lx ;

[0034] Step 4: Determine the atmospheric optical depth τ based on the analogy coefficient C, the solar altitude angle θ and the albedo A.

[0035] The following uses the Zhurong Mars rover as an example to illustrate: Figure 1 As shown in the figure, the Mars rover has a total of 5 solar panels: each of the ±Y sides of the vehicle body is provided with an A panel that can be rotated to orient to the sun, a B panel that is unfolded and locked at one time, and a body-mounted top plate with a battery circuit. The telemetry data of the +Y side solar wing A is used as an example to illustrate the numerical determination of the optical depth. Before calculating the optical depth value, the +Y solar wing A must be rotated first, and then returned to its original position. The bionic superhydrophobic structure of the glass cover of the Mars rover's solar array makes the surface of the solar wing have good self-cleaning performance. During the rotation process, the dust on the surface of the solar wing will fall to the surface of Mars under the action of gravity, eliminating the influence of the surface Martian dust on the calculation results. The rotation axis of the solar wing on the ±Y side of the Mars rover is parallel to the X axis of the vehicle body.

[0036] (1) Determine the ideal power generation

[0037] Assuming that Mars has no atmosphere and without considering the light depth, the ideal power generation is determined, including the following steps:

[0038] 1.1 Determine the solar incident angle of +Y solar wing A

[0039] In expression (1), rs_angle_solve is the incident angle function of the solar wing. According to the time (t), the longitude and latitude (θ lon ,θ lat ), Mars rover attitude (θ yaw ,θ pitch ,θ roll ), +Y solar wing A deployment angle θ zya , we can get the solar incident angle α of the solar wing zya .

[0040] α zya =rs_angle_solve(t,θ lon ,θ lat ,θ yaw ,θ pitch ,θ roll ,θ zya ) (1)

[0041] 1.1.1 Unit azimuth vector from Mars to the Sun in the rover control body coordinate system

[0042] First, the position of Mars is obtained in the heliocentric ecliptic coordinate system, and then through a series of coordinate transformations (heliocentric ecliptic coordinate system → international astronomical reference coordinate system → Mars fixed coordinate system → northeast coordinate system on the surface of Mars → northeast coordinate system on the surface of Mars → Mars rover control body coordinate system), the unit azimuth vector from Mars to the Sun in the Mars rover control body coordinate system is obtained.

[0043] 1.1.1.1 Determination of the position of Mars in the heliocentric ecliptic coordinate system

[0044] In expression (2), position_solve is the position function of Mars in the heliocentric ecliptic coordinate system at time t. According to time (t), Mars orbit parameters The position of Mars (x,y,z) can be solved.

[0045]

[0046] For the planets in the solar system, the semi-major axis a0, orbital eccentricity e0, orbital inclination i0, ascending node right ascension Ω0, perihelion longitude at J2000.0 are known. Average longitude L0, average rate of change The number of orbital elements at time t is determined as follows:

[0047] ΔT={[JED(T0)-JED(2000.0_UTC)]+t / 24 / 3600} / cy (3)

[0048] ΔT is in Julian century, JED represents Julian calendar day, T0 is zero time on the instrument

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055] Perihelion argument ω:

[0056]

[0057] Mean anomaly angle M:

[0058]

[0059] The mean anomaly angle M and the eccentric anomaly angle E satisfy the following relationship (this is only true when the angle unit in formulas (12) and (13) is radians. The angle needs to be converted to radians first and then converted to degrees after the solution is completed):

[0060] M = M × π / 180, the unit is converted to radians;

[0061] M=Ee×sinE (12)

[0062] Use the following approximate series calculation formula:

[0063]

[0064] E = E × 180 / π, the unit is converted to degree;

[0065] True anomaly f:

[0066]

[0067] Track wheelbase r:

[0068]

[0069] In the solar orbital plane coordinate system, the position coordinates of Mars are:

[0070]

[0071] In the heliocentric ecliptic coordinate system, the position coordinates of Mars are:

[0072]

[0073] 1.1.1.2 Coordinate Conversion

[0074] Determine the Mars position vector according to the position coordinates of Mars, and record the Mars position vector as:

[0075]

[0076] In the formula, x m ,y m 、z m are the position coordinates of Mars in the heliocentric ecliptic coordinate system;

[0077] Orthogonalize it to get the unit azimuth vector from the sun to Mars:

[0078]

[0079] The unit azimuth vector from Mars to the Sun is:

[0080] r m_s_N =-r s_m_N (20)

[0081] The unit azimuth vector r from Mars to the Sun m_s_N Transform from the heliocentric ecliptic coordinate system to the International Astronomical Reference Coordinate System (ICRF):

[0082] r m_s_N_1 =R x (-is_e )·r m_s_N (twenty one)

[0083] In the formula, i s_e is the obliquity of the ecliptic at J2000.0;

[0084] The unit azimuth vector r from Mars to the Sun m_s_N_1 Transform from the International Astronomical Reference Frame (ICRF) to the Mars Fixed Frame:

[0085] r m_s_N_2 =R z (W _mars )·R x (90-δ 0_mars )·R z (90+α 0_mars )·r m_s_N_1 (twenty two)

[0086] Where W _mars is the distance from the intersection of the orbit and the standard equator to the 0° longitude; δ 0_mars is the declination of the North Pole of Mars in ICRF; α 0_mars is the right ascension of the North Pole of Mars in ICRF;

[0087] The unit azimuth vector r from Mars to the Sun m_s_N_2 Transform from the Mars fixed system to the celestial northeast coordinate system on the surface of Mars:

[0088] r m_s_N_3 =R y (-θ lat )·R z (θ lon )·r m_s_N_2 (twenty three)

[0089] In the formula, θ lon ,θ lat are the longitude and latitude of the Martian surface where the rover is located;

[0090] The unit azimuth vector r from Mars to the Sun m_s_N_3 Transform from the celestial northeast coordinate system on the surface of Mars to the terrestrial northeast coordinate system on the surface of Mars:

[0091] r m_s_N_4 =R y (-90)·r m_s_N_3 (twenty four)

[0092] The unit azimuth vector r from Mars to the Sun m_s_N_4 Convert from the north-east coordinate system on the surface of Mars to the coordinate system of the Mars rover control body:

[0093] r sb =Rx (θ roll )·R y (θ pitch )·R z (θ yaw )·r m_s_N_4 (25)

[0094] In the formula, θ yaw ,θ pitch ,θ roll They are the rover's yaw angle, pitch angle, and roll angle respectively.

[0095] 1.1.2 Determination of solar incident angle of solar wing

[0096] When the solar panel is at zero position (including ± solar panel A, ± solar panel B, and body-mounted solar panel), the normal vector of the solar panel surface is expressed in the coordinate system of the Mars rover control body as follows:

[0097]

[0098] The rotation axis of the solar wing is parallel to the X axis of the vehicle body. zya When (±Y solar wing B, the deployment angle of the body-mounted solar wing is considered to be 180°), the direction vector of the normal line of the battery surface in the Mars rover control body coordinate system is expressed as:

[0099] r s1 =R x (-θ zya )·r s0 (27)

[0100] Then the angle between the normal line of the solar panel and the sunlight (incident angle) α zya for:

[0101] α zya =arccos(r s1 T ·r sb ) (28)

[0102] 1.2 Determination of the power generation of +Y solar wing A

[0103] P zya_lx =P zya0 ×cos(α zya )×Y MPPT (29)

[0104] Where P zya0 is the power generated by the solar wing at normal speed, Y MPPT For power generation efficiency.

[0105] (2) Determine the actual power generation

[0106] Collect the Mars rover telemetry data and calculate the actual power generation. The actual value of the power generation of +Y solar wing A is:

[0107] P ya_sj =U mx ×I1 (30)

[0108] Where U mx and I1 are the +Y solar wing A panel voltage and current telemetry data respectively.

[0109] (3) Determine the analogy coefficient C

[0110] The analogy coefficient C can be obtained from the actual power and the ideal power:

[0111] C=P ya_sj / P zya_lx (31)

[0112] (4) Determine the optical depth τ

[0113] 4.1 The relationship between light depth τ and direct sunlight irradiance is as follows:

[0114]

[0115] Where F0 is the solar irradiance on the surface of the Martian atmosphere, θ is the solar altitude angle, τ is the atmospheric light depth, and F dir is the direct solar irradiance on the surface of Mars.

[0116] The relationship between light depth and solar scattered irradiance is as follows:

[0117]

[0118] In the formula, F diff is the solar diffuse irradiance on the Martian surface, f(θ, τ, A) is the normalized net heat flow function, and A is the albedo.

[0119] 4.2 Analogy coefficient C and optical depth τ

[0120]

[0121] Where q is the light efficiency of direct light participating in the power generation of the battery array, and k is the light efficiency of scattered light participating in the power generation of the battery array.

[0122] It is known from the ground test that 100% of the direct light and 50% of the scattered light participate in the power generation of the battery array, that is, q is 1 and k is 0.5.

[0123] 4.3 Determination of optical depth τ

[0124] The analog coefficient C is obtained. When θ and A are known, the optical depth τ can be iteratively obtained by expression (34). Table 1 shows the optical depth τ under different combinations of C and θ when A = 0.1.

[0125] Table 1 Optical depth τ value table (A = 0.1)

[0126]

[0127] The present invention has been described in detail above in conjunction with specific implementations and exemplary examples, but these descriptions cannot be understood as limiting the present invention. Those skilled in the art understand that, without departing from the spirit and scope of the present invention, a variety of equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its implementation methods, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be subject to the attached claims.

[0128] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A method for measuring optical depth on the surface of Mars, characterized in that: The steps include: Step 1, assuming that Mars has no atmosphere and ignoring the light depth, determine the ideal power generation; Step 2, obtaining the voltage and current telemetry data of the solar panels of the Mars rover, and determining the actual power generation according to the voltage and current telemetry data of the solar panels; Step 3, obtain the analogy coefficient C through the actual power generation value and the ideal power generation value; Step 4, determine the atmospheric optical depth τ according to the analogy coefficient C, the solar altitude angle θ and the albedo A; Where f(θ, τ, A) is the normalized net heat flow function, q is the light efficiency of direct light participating in the power generation of the battery array, and k is the light efficiency of scattered light participating in the power generation of the battery array; It is characterized in that, in step 1, the step of determining the ideal power generation comprises the following sub-steps: Step 1.1, determine the solar incident angle α of the solar wing zya ; Step 1.2, according to the solar incident angle α of the solar wing zya 、The power generation power of the solar wingspan during normal operation P zya0 and power generation efficiency Y MPPT , determine the ideal power generation power P of the solar wing zya_lx , P zya_lx =P zya0 ×cos(α zya )×Y MPPT ; It is characterized in that, in step 1.1, the solar incident angle α of the solar wing is determined zya The steps include the following sub-steps: Step 1.1.1, determine the position of Mars in the heliocentric ecliptic coordinate system, and then convert it through the international astronomical reference coordinate system, the Mars fixed coordinate system, the Mars surface celestial northeast coordinate system, the Mars surface northeast coordinate system, and the Mars rover control body coordinate system to obtain the unit azimuth vector r from Mars to the sun in the Mars rover control body coordinate system sb ; Step 1.1.2: Determine the direction vector r of the normal line of the battery surface in the coordinate system of the Mars rover control body s1 , according to the direction vector r of the normal line of the battery surface in the coordinate system of the Mars rover control body s1 and the unit azimuth vector r from Mars to the Sun sb , get the solar incident angle α of the solar wing zya ; It is characterized in that, in step 1.1.1, the position of Mars in the heliocentric ecliptic coordinate system is determined by: According to the orbital semi-major axis a0, orbital eccentricity e0, orbital inclination i0, ascending node right ascension Ω0, perigee longitude at J2000.0 Average longitude L0, average rate of change Determine the number of orbital elements at time t: ΔT={[JED(T0)-JED(2000.0_UTC)]+t / 24 / 3600} / cy The unit of ΔT is Julian century, JED represents Julian calendar day, T0 is instrumental zero time; Perihelion argument ω: Mean anomaly angle M: The mean anomaly angle M and the eccentric anomaly angle E satisfy the following relationship: M = M × π / 180, the unit is converted to radians; M=Ee×sinE Use the following approximate series calculation formula: E = E × 180 / π, the unit is converted to degree; True anomaly f: Track wheelbase r: In the solar orbital plane coordinate system, the position coordinates of Mars are: In the heliocentric ecliptic coordinate system, the position coordinates of Mars are:

2. The method for measuring the optical depth of the Martian surface according to claim 1, characterized in that: In step 1.1.1, the unit azimuth vector r from Mars to the Sun in the rover control body coordinate system is obtained through coordinate transformation sb The process is as follows; Determine the Mars position vector according to the position coordinates of Mars, and record the Mars position vector as: In the formula, x m ,y m 、z m are the position coordinates of Mars in the heliocentric ecliptic coordinate system; Orthogonalize it to get the unit azimuth vector from the sun to Mars: The unit azimuth vector from Mars to the Sun is: r m_s_N ＝-r s_m_N The unit azimuth vector r from Mars to the Sun m_s_N Transform from the heliocentric ecliptic coordinate system to the International Astronomical Reference Coordinate System (ICRF): r m_s_N_1 =R x (-i s_e )·r m_s_N In the formula, i s_e is the obliquity of the ecliptic at J2000.0; The unit azimuth vector r from Mars to the Sun m_s_N_1 Transform from the International Astronomical Reference Frame (ICRF) to the Mars Fixed Frame: r m_s_N_2 =R z (W _mars )·R x (90-d 0_mars )·R z (90+a 0_mars )·r m_s_N_1 Where W _mars is the distance from the intersection of the orbit and the standard equator to the 0° longitude; δ 0_mars is the declination of the North Pole of Mars in ICRF; α 0_mars is the right ascension of the North Pole of Mars in ICRF; The unit azimuth vector r from Mars to the Sun m_s_N_2 Transform from the Mars fixed system to the celestial northeast coordinate system on the surface of Mars: r m_s_N_3 =R y (-θ lat )·R z (i lon )·r m_s_N_2 In the formula, θ lon ,θ lat are the longitude and latitude of the Martian surface where the rover is located; The unit azimuth vector r from Mars to the Sun m_s_N_3 Transform from the celestial northeast coordinate system on the surface of Mars to the terrestrial northeast coordinate system on the surface of Mars: r m_s_N_4 ＝R y (-90)·r m_s_N_3 The unit azimuth vector r from Mars to the Sun m_s_N_4 Convert from the north-east coordinate system on the surface of Mars to the coordinate system of the Mars rover control body: r sb =R x (i roll )·R y (i pitch )·R z (i yaw )·r m_s_N_4 In the formula, θ yaw ,θ pitch ,θ roll They are the rover's yaw angle, pitch angle, and roll angle respectively.

3. The method for measuring the optical depth of the Martian surface according to claim 1, characterized in that: In step 1.1.2, the solar incident angle α of the solar wing zya , determined by: Solar wing unfoldedθ zya When , the direction vector of the normal line of the battery surface in the coordinate system of the Mars rover control body is expressed as: r s1 =R x (-θ zya )·r s0 In the formula, r s0 is the normal vector of the battery surface when the solar panel is at zero position in the coordinate system of the Mars rover control body; The angle between the normal line of the solar wing cell surface and the sunlight is the solar incident angle α of the solar wing. zya for: a zya =arccos(r s1 T ·r sb )。 4. The method for measuring the optical depth of the Martian surface according to claim 1, characterized in that: In step 2, the actual value of the power generated by the solar wing is: P ya_sj =U mx ×I1 Where U mx and I1 are the +Y solar wing A panel voltage and current telemetry data respectively.

5. The method for measuring the optical depth of the Martian surface according to claim 1, characterized in that: In step 3, the actual power P ya_sj and ideal power P zya_lx The analogy coefficient C is obtained: C=P ya_sj / P zya_lx 。 6. The method for measuring the optical depth of the Martian surface according to claim 1, characterized in that: In step 4, q is set to 1 and k is set to 0.5.

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