Method for measuring rocket plume obscuration angle based on optical interpretation

Abstract

The application discloses a rocket plume shadowing angle measurement method based on optical interpretation, and belongs to the field of rocket plume shadowing angle measurement. First, it is assumed that the rocket central axis is parallel to the optical lens plane, rocket imaging in the optical image is used to analyze and calculate the shadowing angle, and the shadowing angle is calculated based on the parallel condition in the case that the rocket central axis is not parallel to the optical lens plane. Through analysis, it is known that the change of the length-diameter ratio of the rocket in the optical image represents the change of the angle between the rocket central axis and the lens plane. The length-diameter ratio of the rocket in the optical image is obtained through optical interpretation, the angle ω between the rocket central axis and the lens plane is obtained by combining the actual length-diameter ratio of the rocket, the shadowing angle image value θ' is judged by using the optical interpretation method, and finally the actual rocket plume shadowing angle is calculated. The application has simple principle, is easy to realize, has strong operability, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of rocket exhaust plume obscuration angle measurement, specifically referring to a rocket exhaust plume obscuration angle measurement method based on optical interpretation. Background Technology

[0002] In solid-fuel rocket launches, the solid fuel burns at the rocket's tail, creating a large exhaust plume. The intense chemical reactions within this plume generate a large number of positive and negative ions, effectively turning it into a plasma zone. During telemetry signal propagation, signals passing through the exhaust plume are attenuated due to resonance with these ions. Since telemetry antennas are typically mounted at the front of the rocket, and the exhaust plume diameter of a solid-fuel rocket is significantly larger than the rocket's diameter, the exhaust plume creates a noticeable shielding angle for telemetry signals transmitted tail-wise. This frequently causes signal interruptions when ground-based telemetry equipment tracks and receives target telemetry signals tail-wise. Consequently, the command and control center cannot properly process and display telemetry parameters and curves, and on-site experts cannot promptly assess the rocket's flight status.

[0003] Based on theoretical trajectories, the angle between the rocket's tail and the ground equipment's measurement baseline during flight can be calculated in advance before the mission. However, in the past, due to the lack of specialized measurement equipment and methods for measuring the plume size, it was difficult to calculate the shielding angle and determine the time period when the ground equipment's measurement baseline entered the shielding angle. Therefore, it was difficult to predict the plume decay period before the mission, and it was also difficult to conduct in-depth analysis of the plume decay after the mission, resulting in only qualitative conclusions.

[0004] In existing technologies, there are several methods for obtaining the exhaust plume shielding angle, including experimental data back-calculation and solid fuel simulation. The experimental data back-calculation method involves using post-processed rocket flight trajectory and attitude data to calculate the change in the β angle of ground equipment in the rocket's coordinate system, and combining this with the actual interrupted segments to obtain the β angles at the start and end points of the interruption as an approximate shielding angle. This method yields a shielding angle with significant errors. The solid fuel simulation method obtains the flame range by simulating the combustion process of solid fuel. This method requires a large amount of input information, and different rocket fuels have different characteristics. The simulation algorithm is complex, and its operability and timeliness are poor.

[0005] Therefore, the measurement and calculation of the exhaust plume obscuration angle has become a technical bottleneck in the analysis of exhaust plume attenuation. Accurate measurement and calculation of the exhaust plume obscuration angle is a necessary task for analyzing the exhaust plume attenuation of telemetry signals and evaluating the total attenuation. It is of great significance and urgent. Summary of the Invention

[0006] This invention aims to find useful information from optical images to calculate the tail flame shielding angle. It proposes a method for measuring the tail flame shielding angle based on optical interpretation and attempts to study the reverse calculation of the shielding angle using experimental measurement data, providing a means of verification for the method of calculating the shielding angle based on optical interpretation.

[0007] The specific steps of the method for measuring the rocket exhaust plume shielding angle based on optical interpretation are as follows:

[0008] For optical images, the rocket exhaust plume shielding angle is precisely measured by analyzing two cases: when the rocket's central axis is parallel to the plane of the deployed optical lens and when they are not parallel. This is used to analyze the exhaust plume attenuation of telemetry signals and to evaluate the total attenuation.

[0009] Step 1: Assuming the rocket's central axis is parallel to the plane of the deployed optical lenses, the obscuring angle is calculated using the rocket image from the optical image.

[0010] In the optical image, the length of the vertical section of the rocket is *a*, and its diameter is *b*. The telemetry antenna is mounted at point A on the outer surface of the vertical section of the rocket, and the distance between point A and the bottom is *c*. Assume the exhaust plume is frustoconical, with a single-sided angle γ between the edge of the exhaust plume and the vertical surface of the rocket, a double-sided angle of 2γ, a side length of the exhaust plume of *d*, and the angle (shielding angle) at which the telemetry antenna is obscured by the exhaust plume is θ.

[0011] Methods for calculating the occlusion angle θ using image interpretation include:

[0012] (1) Direct Judgment Method:

[0013] First, determine the outline of the rocket's outer side with the telemetry antenna installed in the rocket image, and then determine the installation point A of the telemetry antenna according to the scale.

[0014] The outline length is a, and the installation point A is at position c / a.

[0015] Then, determine the tangent and tangent point between the telemetry antenna mounting point A and the outermost edge of the tail flame on the same side.

[0016] Finally, the angle between the tangent and the outer contour of the rocket body is determined, which is the shielding angle θ of the tail flame on the telemetry signal.

[0017] (2) Indirect folding method:

[0018] Step 101: Determine the outline of the outer side of the rocket with the telemetry antenna installed in the rocket imaging, as well as the outline of the corresponding side exhaust plume.

[0019] Step 102: The angle between the tail flame profile and the rocket profile is the angle γ between the tail flame edge and the rocket's central axis on one side.

[0020] Step 103: Obtain the installation point of the telemetry antenna on the rocket outline according to the c / a ratio, and connect it with the outermost tangent point of the tail flame outline to form the tangent line.

[0021] Step 104: The distance between the outermost tangent point of the exhaust plume contour and the tail of the rocket is the length of the exhaust plume contour.

[0022] Step 105: The shielding angle θ is obtained by using the sine and cosine laws.

[0023] Let A be the installation point of the telemetry antenna, B be the lowest point of the rocket's outline, and C be the outermost point of tangency of the exhaust plume's outline, forming triangle △ABC. Here, the length of line segment AB is c, and the length of exhaust plume segment BC is d. Then, according to the law of cosines, the length of line segment AC is:

[0024] AC 2 =c 2 +d 2 -2cdcos(180°-γ)=c 2 +d 2 +2cdcosγ

[0025] Calculate the blocking angle θ using the law of sines:

[0026]

[0027] Step 2: When the rocket's central axis is not parallel to the optical lens plane, the shielding angle when they are parallel is corrected to obtain the actual shielding angle when they are not parallel.

[0028] Step 201: Based on the optical image data of the rocket's central axis and the lens plane under parallel and non-parallel conditions, calculate the angle between the rocket's central axis and the lens plane when they are not parallel.

[0029] In optical images, the change in rocket length depends on both distance and the angle between the rocket's central axis and the lens plane; the change in rocket diameter depends only on distance and is independent of the angle between the rocket's central axis and the lens plane; the change in the ratio of rocket length to diameter depends only on the angle between the rocket's central axis and the lens plane and is independent of distance. Therefore, the change in the ratio of rocket length to diameter in optical images represents the change in the angle between the rocket's central axis and the lens plane.

[0030] Assuming the rocket's central axis is parallel to the lens plane, the rocket's length in the optical image is L, and its diameter is... Therefore, the ratio of the rocket's actual length to its diameter is consistent with the ratio of its length to its diameter in the optical image. When the rocket's central axis is not parallel to the lens plane, the rocket's length in the optical image is L', and its diameter is... When the distance between the rocket and the lens remains constant, and only the central axis of the rocket is not parallel to the plane of the lens. L' < L; at this point, the ratio of the rocket's length to its diameter in the optical image is... ω is the angle between the rocket's central axis and the lens plane; the other chord values ​​are:

[0031]

[0032]

[0033] Step 202: When the rocket's central axis is not parallel to the lens plane, establish triangle AXY with telemetry antenna mounting point A as the vertex and the actual shielding angle θ of the tail flame on the telemetry antenna as the apex angle; establish triangle A'XY with the projection A' of the telemetry antenna mounting point on the lens plane as the vertex and the projection angle θ' of the shielding angle on the lens plane as the apex angle; determine whether one side of angle θ is parallel to the rocket's central axis, that is, determine whether the intersection line XY of one side AX or AY of angle θ is perpendicular to the intersection line XY of plane AXY-plane A'XY. If yes, proceed to the calculation process in step 203; otherwise, proceed to the calculation process in step 204.

[0034] △A'XY is the projection of △AXY onto the lens plane. The plane containing △AXY is the plane containing the vertical section of the rocket that is projected onto the lens plane. △A'XY is the lens plane, and XY is the intersection of plane A'XY and plane AXY.

[0035] Step 203, when one side of angle θ is parallel to the rocket's central axis, the calculation process for θ is as follows:

[0036] AY⊥XY, A'Y⊥XY, cotθ=AY / XY, cotθ'=A'Y / XY, cosω=A'Y / AY;

[0037]

[0038] tanθ=tanθ′cosω (3)

[0039] Therefore, by using optical interpretation to determine the occlusion angle image value θ', and then combining it with the ω angle, the actual occlusion angle θ can be calculated.

[0040] Step 204, when one side AY of angle θ is not parallel to the rocket's central axis, the calculation process for θ is as follows:

[0041] In triangle AXY, AY and AX are not parallel to the rocket's central axis. Draw a line AD parallel to the rocket's central axis through the vertex A of angle θ, dividing angle θ into θ1 and θ2. Their projections on the lens plane are θ1' and θ2', respectively. Then AD⊥XY and A'D⊥XY.

[0042] Based on the analysis above:

[0043] tanθ1=tanθ1′cosω

[0044] tanθ2=tanθ2′cosω

[0045]

[0046] When θ1 = θ2:

[0047]

[0048] Therefore, when one side of angle θ is not parallel to the rocket's central axis, θ' is divided into θ1' and θ2' using optical interpretation methods, and then determined separately. Combined with the measurement results of angle ω, the tail flame shielding angle θ is calculated.

[0049] Step 3: Use the actual exhaust plume shielding angle to analyze the exhaust plume attenuation of the telemetry signal and to evaluate the total attenuation.

[0050] The advantages and beneficial effects of this invention are as follows:

[0051] This invention explores the feasibility of measuring and calculating the exhaust plume obscuration angle using optical interpretation methods. Useful information for calculating the exhaust plume obscuration angle is sought from optical images. The angle between the rocket's central axis and the lens plane is calculated by interpreting changes in the rocket's aspect ratio. The obscuration angle projection is then interpreted and combined with the aforementioned angle to calculate the actual obscuration angle. This method is simple in principle, easy to implement, highly operable, and suitable for widespread application. Furthermore, with the continuous development of optical measurement technology, image processing technology, and optical interpretation technology, the measurement accuracy of this method will be further improved. Attached Figure Description

[0052] Figure 1 A schematic diagram of a solid rocket and its exhaust plume.

[0053] Figure 2 This is a schematic diagram showing the tail flame shielding angle and the relative position of the telemetry antenna.

[0054] Figure 3 This is a schematic diagram illustrating the relationship between rocket length, diameter, image quality, distance, and included angle; where, Figure 3 a represents a close-up image of the rocket when it is parallel. Figure 3 b represents a distant image of the rocket when it is parallel. Figure 3 c represents a close-up image of the rocket when it is not parallel. Figure 3 d represents the distant view of the rocket when it is not parallel;

[0055] Figure 4 This is a schematic diagram showing the angle between the rocket's vertical cross-section and the lens plane.

[0056] Figure 5 A diagram showing the relationship between angles θ, θ', and ω when one side of angle θ is parallel to the central axis of the rocket.

[0057] Figure 6 A diagram showing the relationship between angle θ, angle θ', and angle ω when one side of angle θ is not parallel to the central axis of the rocket.

[0058] Figure 7 This is an optical image of a rocket launch during a specific mission, as shown in the example. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0060] This invention starts with the interpretation data of optical measurement images in the initial stage, analyzes the characteristics of rocket imaging, studies the interpretation and calculation method of the tail flame shielding angle, so as to obtain the accurate tail flame shielding angle of solid rockets, and explores the verification with experimental data, providing feasibility for quantitative analysis and prediction of tail flame attenuation of telemetry signals.

[0061] In space launch and missile flight test missions, optical measurement is an indispensable measurement method. Each mission deploys numerous optical devices in the launch area, flight path, and landing area to acquire a large amount of rocket launch and flight image measurement results. Optical devices not only provide image measurements but also provide measurements of rocket drift during the initial launch phase, infrared target characteristics during missile flight, and target attitude measurements during the terminal phase. During rocket launch, the exhaust plume creates a shielding angle on telemetry signals. This shielding angle can also be optically imaged and interpreted to obtain the imaging angle, but this angle needs to be converted into the true shielding angle through certain calculations. For optical images, by analyzing the cases where the rocket's central axis is parallel to and not parallel to the deployed optical lens plane, the rocket exhaust plume shielding angle is precisely measured to analyze telemetry signal exhaust attenuation and assess total attenuation.

[0062] The following section, in conjunction with the accompanying drawings and embodiments, further explores the methods for interpreting and calculating the shading angle.

[0063] The specific steps of the method for measuring the rocket exhaust plume shielding angle based on optical interpretation are as follows:

[0064] Step 1: Assuming the rocket's central axis is parallel to the plane of the deployed optical lenses, the obscuring angle is calculated using the rocket image from the optical image.

[0065] Assuming the rocket's central axis is parallel to the plane of the optical lens, the dimensions of the rocket, exhaust plume, and other parts are proportionally scaled in the optical image, and all angles are consistent with the actual angles. Therefore, the occlusion angle can be analyzed and calculated using the rocket image in the optical image.

[0066] like Figure 1 As shown, the length of the vertical section of the rocket is *a*, and its diameter is *b*. The telemetry antenna is mounted at point A on the rocket's surface, and the distance between point A and the bottom is *c*. Assume the exhaust plume is frustum-shaped, with the angle between the edge of the exhaust plume and the rocket's central axis on one side being γ and the angle on both sides being 2γ. The length of the exhaust plume is *d*, and the angle (shielding angle) at which the telemetry antenna is obscured by the exhaust plume is θ. There are two methods for calculating this angle:

[0067] (1) Direct Interpretation Method: Determine the occlusion angle θ using image interpretation methods, then perform secant compensation on the occlusion angle θ to restore it to the true occlusion angle. The following principles should be followed during interpretation:

[0068] ① First, determine the outline (straight line) of the outer side of the rocket (the side where the telemetry antenna is installed).

[0069] ②Then determine the installation position A of the telemetry antenna on the rocket body: on the outer edge of the rocket, according to the scale, at position c / a of the total length of the rocket when viewed from the tail towards the arrowhead.

[0070] ③ Then determine the tangent line and tangent point between the telemetry antenna installation point and the outermost side of the tail flame (on the same side as the telemetry antenna).

[0071] ④ Next, determine the angle between the above tangent and the outer contour line of the rocket body, which is the shielding angle θ of the tail flame on the telemetry signal.

[0072] (2) Indirect calculation method: First, use image interpretation to determine the angle γ between the edge of the tail flame and the rocket's central axis on one side, and the tail flame length d. Then, combine this with the installation position of the telemetry antenna and use the sine theorem, cosine theorem, etc. to calculate the shielding angle θ.

[0073] The following principles should be followed when interpreting:

[0074] ① First, determine the outline (straight line) of the outer side of the rocket (the side where the telemetry antenna is installed).

[0075] ②Then determine the outer contour line of the tail flame near the tail of the rocket.

[0076] ③Then determine the angle between the tail flame outline and the rocket outline, which is the angle γ between the tail flame edge and the rocket's central axis on one side.

[0077] ④ Next, determine the installation position A of the telemetry antenna on the rocket body: on the outer edge of the rocket, according to the scale, at position c / a of the total length of the rocket when viewed from the tail towards the arrowhead.

[0078] ⑤ Then determine the tangent line and tangent point between the telemetry antenna installation point and the outermost side of the tail flame (on the same side as the telemetry antenna).

[0079] ⑥ Then determine the distance from the tangent point to the tail of the rocket, which is the tail flame length d.

[0080] like Figure 2 As shown, let the telemetry antenna installation point be A, the closest point on the rocket's bottom to the telemetry antenna be B, and the point of tangency between the telemetry antenna installation point and the outermost part of the exhaust plume (on the same side as the telemetry antenna) be C. Let the length of line segment AB be c, and the length of exhaust plume segment BC be d. Then, in the triangle △ABC formed by the above three points:

[0081] According to the Law of Cosines:

[0082] AC 2 =c 2 +d 2 -2cdcos(180°-γ)=c 2+d 2 +2cdcosγ

[0083] According to the Law of Sines:

[0084]

[0085] Step 2: When the rocket's central axis is not parallel to the optical lens plane, the shielding angle when they are parallel is corrected to obtain the actual shielding angle when they are not parallel.

[0086] The analysis and calculations in step one are performed under the assumption that the rocket's central axis is parallel to the optical lens plane. During rocket flight, its flight attitude and relative position to ground equipment constantly change, making it extremely rare for the rocket's central axis to be parallel to the optical lens plane. When the rocket's central axis is not parallel to the optical lens plane, the shielding angle obtained through optical interpretation is not the true shielding angle θ of the exhaust plume on the telemetry antenna, but merely the projection of the actual shielding angle onto the lens plane. Correcting θ yields the actual shielding angle θ' under the non-parallel condition.

[0087] The specific correction process is as follows:

[0088] Step 201: Based on the optical image data of the rocket's central axis and the lens plane under parallel and non-parallel conditions, analyze the relationship between the length-to-diameter ratio of the rocket image and the angle between the rocket's central axis and the lens plane.

[0089] like Figure 3 In the four images shown, when the rocket's central axis is parallel to the lens plane, the close-up view of the rocket in the optical lens when the rocket is directly facing the lens is as follows: Figure 3 As shown in Figure a, when the rocket is directly facing the optical lens, the distant view formed by the rocket in the optical lens is as follows: Figure 3 As shown in b; when the rocket's central axis is not parallel to the lens plane, but the included angle is constant, the close-up image of the rocket in the optical lens when the rocket is angled towards the lens is as follows: Figure 3 As shown in Figure c, when the rocket is angled towards the optical lens, the distant view formed by the rocket in the optical lens is as follows: Figure 3 As shown in d.

[0090] Let the length of the rocket be L and the diameter be... Given that both length and diameter are known, then the ratio of length to diameter is... Let n be a constant.

[0091] From the four figures above, let Figure 3 The dimensions of rocket a are consistent with the actual dimensions, with a length of L and a diameter of [missing information]. It can be seen that:

[0092] Figure 3 b and Figure 3 A comparison shows that when the rocket is directly facing the optical lens but far away from it... Figure 3 In shot b, the rocket is shown in the length L direction and diameter... The imaging length in both directions is affected by the change in distance between the rocket and the lens, and the length L direction and the diameter are both affected by the change in distance between the rocket and the lens. The direction is reduced proportionally, and L is reduced to L1. Shrink to The length-to-diameter ratio remains constant.

[0093] Figure 3 c and Figure 3 A comparison shows that when the rocket is angled towards the optical lens (at a constant angle) and not far from the lens, Figure 3 In the lens c, the image length of the rocket in the length L direction is reduced from L to L' due to the angle between the rocket's central axis and the lens plane, but the diameter... The imaging length in the direction remains unchanged, still being... The ratio of length to diameter becomes Let it be n'.

[0094] Figure 3 d and Figure 3 Comparison with c shows that when the rocket is angled towards the camera (the angle is...) Figure 3 (c) when it is consistent and far from the camera. Figure 3 In d, the rocket length and diameter imaging length are affected by two factors: the distance and angle between the rocket and the lens. Figure 3 Based on c, the length is reduced proportionally from L' to L1', and the diameter is reduced from... Shrink to Length to diameter ratio

[0095] Based on the above analysis, in optical images, the change in rocket length is related to both the change in distance and the change in the angle between the rocket's central axis and the lens plane; the change in diameter is only related to the change in distance and is independent of the change in the angle between the rocket's central axis and the lens plane; the change in the ratio of rocket length to diameter is only related to the change in the angle between the rocket's central axis and the lens plane and is independent of the change in distance. Therefore, the change in the ratio of rocket length to diameter can be used to represent the change in the angle between the rocket's central axis and the lens plane.

[0096] Step 202: Calculate the angle between the rocket's central axis and the lens plane when they are not parallel by using the ratio of the rocket's length to its diameter in the optical image;

[0097] When the rocket's central axis is parallel to the lens plane, the ratio of the rocket's length to its diameter in the optical image is the same as the actual ratio of the rocket's length to its diameter.

[0098] When the rocket's central axis is not parallel to the lens plane, the rocket's length in the optical image is L', and its diameter is... When the distance between the rocket and the lens remains constant, and only the central axis is not parallel to the lens plane... L' < L; at this point, the ratio of the rocket's length to its diameter in the optical image is...

[0099] like Figure 4 As shown, polygon MBOPQ is the vertical cross-section of the rocket passing through its central axis, and polygon M'BOP'Q' is the image of the rocket's vertical cross-section on the lens plane. Angle ω is the angle between the rocket's vertical cross-section MBOPQ and the lens plane M'BOP'Q', which is the angle between the rocket's central axis and the lens plane.

[0100] In triangle MBM', the corresponding values ​​are MB = L and M'B = L'. ∠MBM'=ω, ∠MM'B=90°.

[0101]

[0102]

[0103] Where n is a known condition, which can also be obtained using optical interpretation methods; while n' can only be obtained using optical interpretation methods.

[0104] Therefore, by using a combination of optical interpretation and calculation, the angle between the rocket's central axis and the lens plane can be obtained.

[0105] The following principles should be followed when interpreting n or n':

[0106] ① Obtain L by interpreting the image directly. Oblique image interpretation yields L',

[0107] ② First, determine the outer contour line of the rocket;

[0108] ③ Next, determine the length in the length direction;

[0109] ④ Finally, determine the length of the diameter direction, which is perpendicular to the length direction.

[0110] ⑤ Interpretation yields L, With L', back:

[0111]

[0112]

[0113] Step 203: When the rocket's central axis is not parallel to the lens plane, establish triangle AXY with telemetry antenna mounting point A as the vertex and the actual shielding angle θ of the tail flame on the telemetry antenna as the apex angle; establish triangle A'XY with the projection A' of the telemetry antenna mounting point on the lens plane as the vertex and the projection angle θ' of the shielding angle on the lens plane as the apex angle; determine whether one side of angle θ is parallel to the rocket's central axis, that is, determine whether the intersection line XY of one side AX or AY of angle θ is perpendicular to the intersection line XY of plane AXY-plane A'XY. If yes, proceed to the calculation process in step 204; otherwise, proceed to the calculation process in step 205.

[0114] Step 204, when one side of angle θ is parallel to the rocket's central axis, the calculation process for θ is as follows:

[0115] like Figure 5 As shown, angle θ is parallel to the rocket's central axis on one side AY. Plane A'XY is the lens plane, plane AXY is the plane containing the rocket's vertical cross-section projected onto the lens plane, △A'XY is the projection of △AXY onto the lens plane, and XY is the intersection of plane A'XY and plane AXY. The actual exhaust plume shielding angle is θ, and its image value on the lens plane is θ'.

[0116] but:

[0117] AY⊥XY, A'Y⊥XY, cotθ=AY / XY, cotθ'=A'Y / XY, cosω=A'Y / AY;

[0118]

[0119] tanθ=tanθ′cosω (5)

[0120] Therefore, by using optical interpretation to determine the occlusion angle image value θ', and then combining it with the ω angle, the occlusion angle θ can be calculated.

[0121] Step 205, when one side AY of angle θ is not parallel to the rocket's central axis, the calculation process for θ is as follows:

[0122] When one side of angle θ is not parallel to the rocket's central axis, the relationship between angle θ, angle θ', and angle ω is as follows: Figure 6 As shown in the diagram, AY and AX are not parallel to the rocket's central axis. Draw a line AD parallel to the rocket's central axis through the vertex A of angle θ, dividing angle θ into θ1 and θ2. Their projections onto the base are θ1' and θ2', respectively. Then AD⊥XY and A'D⊥XY.

[0123] Based on the analysis above:

[0124] tanθ1=tanθ1′cosω

[0125] tanθ2=tanθ2′cosω

[0126]

[0127] When θ1 = θ2:

[0128]

[0129] Therefore, when one side of angle θ is not parallel to the rocket's central axis, θ' can be divided into θ1' and θ2' using optical interpretation methods, and then the angle θ can be calculated by combining the measurement results of angle ω.

[0130] The typical exhaust plume shielding angle θ and its projection θ' are both based on the outer contour line of the rocket and its projection as one side. Since the outer contour line of the rocket is parallel to the central axis of the rocket, the method in step 204 is suitable for determining the typical exhaust plume shielding angle.

[0131] Step 3: Use the actual exhaust plume shielding angle to analyze the exhaust plume attenuation of the telemetry signal and to evaluate the total attenuation.

[0132] Example

[0133] In previous space launch missions, optical measurement systems have repeatedly obtained images of the rocket's exhaust plume during launch. An image of a rocket launch taken in one instance, along with its length-to-diameter ratio and exhaust plume obscuration angle, is shown below. Figure 7 As shown, the aspect ratio of the rocket image and the size of the exhaust plume obscuration angle can be easily determined from the image.

[0134] The interpretation and calculation steps are as follows:

[0135] ① Based on the known actual length L and diameter of the rocket Alternatively, the rocket's length L and diameter can be determined by interpreting an image of the rocket facing the camera. Calculate the actual length-to-diameter ratio n of the rocket using Equation 3;

[0136] ②The length L' and diameter of the rocket are obtained by interpreting the image of the rocket at an angle to the camera. The length-to-diameter ratio n' of the rocket image was calculated using Equation 4.

[0137] ③ Using the above-calculated n' and n, calculate the angle ω between the rocket's central axis and the lens plane, and the cosine value cosω, using Equation 2;

[0138] ④ The image value θ' of the tail flame shielding angle is obtained by interpreting the image of the rocket at an angle to the camera;

[0139] ⑤ Using the calculated cosω and the interpreted θ', calculate the tail flame shielding angle θ using Equation 5:

[0140]

[0141]

[0142] For example, suppose the rocket is actually 8m long and 1m in diameter. From the optical image, the rocket's image length L' = 2cm and its diameter... If the tail flame shielding angle image θ' = 10°, then according to Equations 3, 4 and 8, we can obtain:

[0143]

[0144]

[0145]

[0146] That is, the actual tail flame shielding angle θ is 5.03837°.

Claims

1. A method for measuring the obscuration angle of rocket exhaust plume based on optical interpretation, characterized in that, The specific steps are as follows: For optical images, the rocket exhaust plume shielding angle is precisely measured by analyzing two cases: when the rocket's central axis is parallel to the plane of the deployed optical lens and when they are not parallel. This is used to analyze the exhaust plume attenuation of telemetry signals and to evaluate the total attenuation. Step 1: For the case where the rocket's central axis is parallel to the plane of the deployed optical lenses, the obscuring angle is calculated using the rocket image from the optical image. In the optical image, the length of the vertical part of the rocket is a, the diameter is b, the telemetry antenna is installed at point A on the outer surface of the vertical part of the rocket, and the distance between point A and the bottom is c; the tail flame is truncated cone-shaped, the angle between the edge of the tail flame and the vertical surface of the rocket is γ on one side and 2γ on both sides, the length of the side of the tail flame is d, and the shielding angle is θ. Methods for calculating the occlusion angle θ in image interpretation using indirect folding algorithms include: Step 101: Determine the outline of the outer side of the rocket with the telemetry antenna installed in the rocket imaging, as well as the outline of the corresponding side exhaust plume. Step 102: The angle between the exhaust plume contour line and the rocket contour line is the angle γ between the exhaust plume edge and the rocket's central axis on one side. Step 103: Obtain the installation point of the telemetry antenna on the rocket outline according to the c / a ratio, and connect it with the outermost tangent point of the tail flame outline to form the tangent line. Step 104: The distance between the outermost tangent point of the exhaust plume contour and the tail of the rocket is the length of the exhaust plume contour. Step 105: The shielding angle θ is obtained by using the sine and cosine laws. Step 2: For cases where the rocket's central axis is not parallel to the optical lens plane, the shielding angle when they are parallel is corrected to obtain the actual shielding angle when they are not parallel. Specifically: Step 201: Based on the optical image data of the rocket's central axis and the lens plane under parallel and non-parallel conditions, calculate the angle between the rocket's central axis and the lens plane when they are not parallel. The change in the ratio of rocket length to diameter in optical images represents the change in the angle between the rocket's central axis and the lens plane; Assuming the rocket's central axis is parallel to the lens plane, the rocket's length in the optical image is L, and its diameter is... Therefore, the ratio of the rocket's actual length to its diameter is consistent with the ratio of its length to its diameter in the optical image. When the rocket's central axis is not parallel to the lens plane, the rocket's length in the optical image is L', and its diameter is... When the distance between the rocket and the lens remains constant, and only the central axis of the rocket is not parallel to the plane of the lens. L' < L; at this point, the ratio of the rocket's length to its diameter in the optical image is... ω is the angle between the rocket's central axis and the lens plane; the other chord values ​​are: Step 202: When the rocket's central axis is not parallel to the lens plane, establish triangle AXY with telemetry antenna mounting point A as the vertex and the actual shielding angle θ of the tail flame on the telemetry antenna as the apex angle; establish triangle A'XY with the projection A' of the telemetry antenna mounting point on the lens plane as the vertex and the projection angle θ' of the shielding angle on the lens plane as the apex angle; determine whether one side of angle θ is parallel to the rocket's central axis, that is, determine whether the intersection line XY of one side AX or AY of angle θ is perpendicular to the intersection line XY of plane AXY-plane A'XY. If yes, proceed to the calculation process in step 203; otherwise, proceed to the calculation process in step 204. Step 203, when one side of angle θ is parallel to the rocket's central axis, the calculation process for θ is as follows: AY⊥XY, A'Y⊥XY, cotθ=AY / XY, cotθ'=A'Y / XY, cosω=A'Y / AY; tanθ=tanθ′cosω Therefore, the occlusion angle image value θ' is determined by optical interpretation, and then the actual occlusion angle θ is calculated by combining it with the ω angle. Step 204, when one side AY of angle θ is not parallel to the rocket's central axis, the calculation process for θ is as follows: In △AXY, AY and AX are not parallel to the rocket's central axis. Draw a line AD parallel to the rocket's central axis through the vertex A of angle θ, dividing angle θ into θ1 and θ2. Their projections on the lens plane are θ1' and θ2', respectively. Then AD⊥XY and A'D⊥XY. Based on the analysis above: tanθ1=tanθ1′cosω tanθ2=tanθ2′cosω Therefore, when one side of angle θ is not parallel to the rocket's central axis, θ' is divided into θ1' and θ2' using optical interpretation, and the angle values ​​are determined separately. Then, combined with the measurement results of angle ω, the tail flame shielding angle θ is calculated. Step 3: Use the actual exhaust plume shielding angle to analyze the exhaust plume attenuation of the telemetry signal and to evaluate the total attenuation.

2. The method for measuring the rocket exhaust plume obscuration angle based on optical interpretation according to claim 1, characterized in that, The calculation process of the indirect folding algorithm described in step one is as follows: Let A be the installation point of the telemetry antenna, B be the lowest point of the rocket's outline, and C be the outermost point of tangency of the exhaust plume's outline, forming triangle △ABC. Here, the length of line segment AB is c, and the length of exhaust plume segment BC is d. Then, according to the law of cosines, the length of line segment AC is: AC 2 =c 2 +d 2 -2cdcos(180°-γ)=c 2 +d 2 +2cdcosγ Calculate the blocking angle θ using the law of sines:

3. The method for measuring the rocket exhaust plume obscuration angle based on optical interpretation according to claim 1, characterized in that, The method for calculating the occlusion angle θ by image interpretation in step one also includes a direct judgment method, specifically: First, determine the outline of the rocket's outer side with the telemetry antenna installed in the rocket image, and then determine the installation point A of the telemetry antenna according to the scale. The outline length is a, and the installation point A is located at position c / a. Then, determine the tangent and tangent point between the telemetry antenna mounting point A and the outermost edge of the tail flame on the same side; Finally, the angle between the tangent and the outer contour of the rocket body is determined, which is the shielding angle θ of the tail flame on the telemetry signal.

4. The method for measuring the rocket exhaust plume obscuration angle based on optical interpretation according to claim 1, characterized in that, In step 204, when θ1 and θ2 satisfy θ1=θ2, the occlusion angle θ is:

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