关于万户一号火箭推迟发射原因的说明

“万户一号”火箭项目,是我国业余火箭第一次以团队身份正式在公众面前亮相,得到了当地主管部门、媒体、学校和全国各地网友的大力支持,这是我国科技爱好界的一件大事。

KCSA广州课题组承担研发万户一型探空火箭的工作。初定的试验项目包括:多发动机并联的推力平衡控制,二级火箭的分离技术,多基站联合多普勒定位,惯性导航技术等。初定射高3千米,整备质量35千克。同时进行系统工程方面的学习和尝试。预订研发周期为90天。

由于技术跨度太大,预研中发现要在短期内解决多项关键技术存在困难,因此对试验项目进行了精简,降低了技术目标。即使如此,万户一号仍然是目前为止国内尺寸最大的业余火箭。

KCSA要求达到零地面风险的目标,即:即使火箭最大限度偏航,也不能落入有人区域。广州课题组为寻找就近的适当发射场地进行了艰苦努力,但是由于广州地区经济发达,就近地方没有大片农村和无人区,因此难以实现安全目标。为了降低对场地的要求,课题组多次修改极限射高参数,从3千米降低到1500米,又降低到500米,一二级在100米高度分离。但是这样的射高,虽然对偏航的概率进行了控制,但万一发生意外,最远可以散布到1千米左右范围,仍难以找到适当发射场地。

最终,课题组将射高设计为230米,场地就近选在大学城附近的空地。当地媒体根据这一决定,立即进行了跟踪报道,预告了发射地点和时间,引起了社会舆论的高度关注和支持。军队获悉后,专门打电话过问发射的详细情况,并再三叮嘱注意安全。

11月10日晚,KCSA广州课题组根据外弹道计算数据,对发射的地面安全性进行了最后论证,认为场地尺寸不足,地面人员清场难度较高,仍然难以满足零地面风险的要求。根据本质安全性的基本要求,决定推迟发射,另找场地。

11月11日,课题组向媒体通报了推迟发射的决定,同时陈述了军方过问的详细内容。当天,进行了地面点火试验,并向在场人员介绍了火箭发射的相关科技知识。由于地面装置较重不易搬运,试验场地选择在了距离中山大学的实验室不远处的一块空地,即广州电视台播出时所展现的场地位置。

我们注意到网上有很多责问空管局等有关部门的声音。我想说的事,这次试验活动,有关部门未给予任何阻挠,一直本着探讨的角度与课题组交流安全问题,他们已经做到了在现行航空管理体制内最大限度的支持。课题组会另选场地进行新的试验,仍然会按照零地面风险的要求进行安全管理。(文/刘虎)

初定方案发动机布置图

航电系统框图

火箭平台上引力蓝移现象的观测(英文)

本文受到学术造假质疑,KCSA可能从网站上撤销本文的发表,详情请见:http://bbs.kechuang.org/read-kc-tid-41784.html
火箭平台上引力蓝移现象的观测(英文)
李雨翀 广东广州
1. Abstract
An experimental verification of general relativity conception was made using an atomic maser in a rocket attaining an altitude of 1,800 metres.
The signal of the maser was monitored on the ground, so that the effect of gravitational potential on the frequency of the maser was measured.
The resulting data was processed through a careful prediction and elimination of the Doppler shift and other error resources, so that the gravitational blue shift is directly observed. The experiment is described including a consummate discussion of navigation algorithm applied in the processing procedure. The authors believe that this is a direct high accuracy test of the general relativistic phenomena using an airborne clock.
2.Introduction
A rocket is constructed and launched carrying an atomic frequency standard as the payload. The frequency of the signal from the atomic frequency standard is examined on the ground.
Another atomic frequency standard is used as a comparison to monitor the change in frequency of the received signal from the payload.
A group of variables that will influence the change are eliminated so that the resulting data, representing the relativistic shifts, are recovered andrecorded.
The objective of the experiment is to test general relativity concept by measuring directly the effect of gravitational potential on thefrequency of a proper clock, in this case the atomic frequency standard.
In this experiment, a gravitational effect amounting to 5.6e-13 was measured.

The predicted proportion change in frequency is expressed in equation [a].Where β is the velocity/c and r is the displacement of the rocket relative to theground base. ais the centrifugal acceleration of the ground station while ε represents thepropagation vector of the rocket-to-ground signal. Our knowledge of the relative velocityand displacement of the rocket is obtained from the flight data recorder installed in thepayload. As we chose the ground base as the navigation frame, the movement of the groundbase in the geographic frame was straightly eliminated in the
navigation system.
In equation [1], the first term is the gravitational blue shift, the second term expressesthe Doppler shift. The last term describes the effect of the rotation of the earth during thepropagation of the signal. In the elimination of the second and third terms, out knowledge ofthe rocket’s velocity and position are obtained from the FDR(Flight Data Recorder) while theknowledge of the velocity and position of the ground base is gained from the Earth Modeland GLarLng of the launching site.
The specific procedure is exhibited in the materials and methods section.

3. Materials and Methods

The data was first generated and collected after the hardware processing of ground base, which procedure is labeled as data
acquisition. The recorded data was then stored in the computer for further processing, labeled as Data processing.
Data acquisition
a) Algebra description
The frequency signal transmitted from the payload is fixed at f0 + △f.
△f was set to be 50mHz (Figure [d]).
The signal received on the ground base is labeled as f1. It is predicted to be

after the elimination of errors.
The ground station processed f1 with a standard signal of frequency f0 , which was generated by the atomic frequency standard.
Heterodyne-beat method was applied thus a signal with frequency f1 – f0  was sampled by a high speed analog to digital converter as f2 and processed by the digital signal processor. A standard signal of frequency△f is generated by atomic frequency standard and processed in the computer, a series of effects including doppler shift are taken into account.

The final signal, labeled △fR, is expressed by equation [2].
The frequency of f2 was estimated by 4-parameter estimation algorithm and recorded in the computer. The method of 4-parameter
estimation will be discussed later.

Therefore, the resulting data was obtained. The predicted behaviour of this final signal is shown in figure [6].

b) Technical details
A transmitter and a superheterodyne receiver were built specially for the experiment.
The signal from the on-board AFS(Atomic Frequency Standard) was directly amplified and transmitted. The output power of the amplifier was +38dBm and the frequency was 63.8978MHz.
The structure of the receiver is shown below.

The signal from the antenna at the ground base was filtered and directly amplified by a LNA(Low Noise Amplifier) and mixed with FS1 by mixer 1 to obtain an IF(Intermediate Frequency) with a frequency of 5MHz. The IF signal was processed by an AGC(Automatic Gain Control) circuit so that the amplitude was stabilized. This processed IF signal was mixed with FS2 by mixer 2 to obtain a 50mHz signal and was converted into digital signal by a high speed ADC. The exact frequency of the signal sampled by the ADC was estimated through 4-parameter estimation algorithm. FS1 and FS2 were generated by the AFS at the ground base.

1) The realization of heterodyne-beat method
The kernel of heterodyne-beat method is the shift of spectrum. As a result, a mixer is used to obtain the difference in frequency of two signals. In this application, two integrated mixer circuits AD831 were used.
The following images indicate a test result for the mixer circuit. The left image indicates the signal of RF input of the mixer and another one shows the local oscillation input of the mixer. They were generated by two DDS(Direct Digital Synthesis) circuits. The clock standard of the DDS circuits was connected to an AFS. The frequencies of them were 7MHz and 7.00001MHz.

The following image shows the output of the mixer which equals to the difference between two frequency signals connected to the local

oscillation input and the RF input. Here, the difference was 10Hz.

2) The design of AGC circuit

An AGC circuit was used to stabilize the amplitude of IF signal.
The input signal was demodulated and filtered into a voltage signal represents the strength of the signal. This voltage signal was used to

control the gain of a VGA(Variable Gain Amplifier).

In this case, the wave-detector was AD8307 and the VGA was AD603.
A test for the AGC module is shown below. Channel 1 was connected to the output of the AGC module, channel 2 was connected to the input. The input of the AGC module was connected to a function generator.

As the waveform shown on the oscilloscope, although the amplitude of the input signal to the AGC was changed, the amplitude of output signal of it remained the same.
A test result for the transmitter and the receiver is shown below.
The transmitter was placed 800 metres away from the receiver. The image on the left shows the output signal from the transmitter and another image shows the signal sampled from the output of LNA of the receiver.

The image below shows the signal sampled from the output of the AGC module, where frequency = IF = 5MHz.


2) Method of estimation of frequency
a) Definition of 4 parameters Assume the sampled signal S(t) is given by

Where A0′ is the ideal amplitude of the signal, ω0′ is the ideal frequency of the signal, C0′ is the ideal DC offset of the signal and θ0′ is the ideal phase of the signal.
The signal can be expressed by the equation

Where

Suppose the magnitude of the signal sampled during time tk(k = 0, 1, 2, …) is y(k), is given by

b) Method of 3-parameter estimation
Suppose the sampled voltage value of the signal at time tk is y(k), k = 1, 2, 3 …N-1. The amplitude of sine, amplitude of cosine and DC offset is defined as A,B and C. The RSS(Residual Sum of Squares) between the estimation value and actual value is given by

Where N is the length of samples, set

The solution for X is given by the least square solution below:
.  
c) 4-parameter estimation algorithm
The idea of successive approximation is applied in this algorithm. First, a rough frequency is given, 3-parameter estimation algorithm is applied to the sampled signal. The cosine amplitude, sine amplitude, DC offset and estimated RSS are obtained. The operation is repeated with
different frequencies so a serial of estimated RSS are obtained. One of those set of obtained result with minimum estimated RSS is the value of actual frequency. The detailed steps are shown below.
1) Determine the frequency of the signal roughly though DFT(Discrete Fourier Transform), label this frequency as f0.
2) Set the domain of iteration to be ωdl and ωdu, where ωdl is the lower boundary, given by ωdl = f0 – fclk / N. ωdu is the upper boundary, given by ωdu = f0 + fclk / N. fclk is the frequency of sampling clock and N is the length of DFT.
3) Set ω0 = ωdu – ωdl. 2M+1 points (M∈N*) are samples between ωdl and ωdu with equal intervals. 3-parameter estimation algorithm is used here to compute the RSS of this group of samples.
4) Find and record the minimum value of RSS of samples in step 3 This minimum value is corresponding to the actual frequency.
Repeat operations 2 to 4 until the precision of the estimation reaches the required level.
A picture of the receiver is shown below.

2) Data processing

a) Downlink signal

The navigation system provided data of dynamics with a sample rate of 1,200 samples per second. The data was given in terms of
angular velocity and acceleration in the on-board coordinate. The six groups of parameters are ωx, ωy, ωz, ax, ay and a–z, respectively where the X-axis if the mean axis of the rocket.
In the determination of change in angle, △θ and change in velocity, △V, the cubic spline function is adopted in curve fitting before integration. This method of Simpson’s rule provides six groups of data: △θx, △θy, △θz, △Vx, △Vy and △Vz. As a result, the behaviour of the rocket between samples are predicted and considered.

In the determination of attitude angle, the method of Quaternion is applied.
The quaternion numbers at time tm+1 are given in equation [9], where △θx, △θy and △θz are the output of change in angle and vector Φ

is the rotation vector, which is given by equation [9]

In equation [9] and [10], the angular velocity of the rocket is assumed to fit cubic function. However,  the actual angular velocity does not fit a cubic function.
Equations [9] and [10] do not achieve minimum shift of algorithm. After the parachute deployment, the rocket was suspended in the descending stage. Thus the rocket is likely to experience coning motion, which means that the rocket vibrate about the equilibrium position at small angles. The coning motion is the worst working environment for the SINS(Strapdown Inertial Navigation System) as it will cause serve shift of the Math Platform.

For optimization algorithms, the following improvements are made.
O-XYZ represents the reference frame R, which is the on-board frame when the rocket is in equilibrium.

Let b(tm-1) and b(tm) to be the instantaneous on-board frame at time tm-1 and tm.
According to Euler Theorem, O-XYZ can be regarded as a rotating transformation of b(tm) or b(tm-1) with rotating vector Q(t) given in equation [11].

The shift on-board frame can be regarded as a rotation transformation of the ideal on-board frame, which is the frame when the rocket is in equilibrium. The samples of △θ is grouped in three again.
In each group, the samples are labeled as .

Equation [12] is an improved  form of equation [3]. By selecting proper constant k1 and k2, the effect of the coning motion is minimised.
Here, the ideal values for k1 and k2 are 0.45 and 0.675.
Therefore, the attitude of the rocket is found through the optimized quaternion algorithm. The Eular angles are found by equation [13].

The quaternions are supposed to be standardized. However, resulting form calculation errors and other factors, the quaternion numbers gradually loses standability. The standardization of quaternion numbers is applied at the end of each period of attitude refreshment. The formula for standardization is given by equation [8].

Where  is the standardization value and  is the value after attitude refreshment.
So far, the discussion of the rocket’s dynamic is in the on-board coordinate. However, the final results have to be expressed in the navigation frame, which sets the ground base as the origin.

Equation [15] gives the coordinate transformation matrix (attitude matrix) from on-board frame to navigation frame in terms of quaternion.
The initial extraction quaternion numbers are thus given by the initial attitude matrix obtained in initial azimuth alignment.

The velocity of the rocket at time tm in the navigation frame, Vm, is given by equation [16], containing a series of error compensations.
Vm-1 is the velocity in the same frame at time tm-1. Cm-1 is the coordinate transformation matrix at time tm-1. Vm-1 is the compensation velocity caused by while△Vg/corm is the compensation velocity caused by the deleterious acceleration. △Vsfm is the compensation velocity caused by ecific force.

Where△Vm us the change in velocity during period [tm-1, tm].
△Vrotm is the compensation velocity caused by rotation effect.
△Vsculm is the compensation velocity caused by sculling motion.

Due to air current, gustiness and other factors, the rocket experiences vibrations during the flight. Those factors cause a highly dynamic working environment for the payload. Therefore, the velocity has to be compensated so that the sculling effect and the rotation effect are
eliminated. Otherwise, the calculation of velocity will involve serve errors. When it comes to position determination, there two error resources contribute to scroll errors. Here△Vrotm and△Vsculm represent the compensation velocities due to the rotation effect and the sculling effect
respectively. the rotation effect happens when the direction of linear velocity rotates in a three-dimensional coordinate. The sculling effect is caused by the angular vibration and linear vibration are in phase and of same frequency on the rocket. This is quite similar to the sculling motion: on one hand, the syrup vibrates periodically about the lateral axis of the boat. On the other hand, the boat forges ahead along the direct-axis in an intermittent behaviour.

The original expression for △Vrotm and △Vsculm are:

The optimized formula for △Vrotm and △Vsculm are

The optimized algorithm for sculling effect rotation effect, in velocity determination as well as the correction for conning motion in attitude determination make sure that the motion of the layload is precisely calculated in spite of the unstable motion of the rocket. Hence the cancelling of doppler effect and second-order general relativity conception shift are more reliable. The specific precision level is related in the discussion section.

The final expression for Vm is given by equation [22]:

Considering that all the compensation dosages have been taken into account the calculation of Vm and that the data is discrete with equal time internals, the data of displacement, is obtained through numerical integration.
As the dynamic data is determined, the following equations are substituted into
equation [2].

Where c is the velocity of light, Wen is the angular velocity of the earth in the navigation frame and  is the radius vector of the earth at the launching spot.
The frequency of this signal is plotted against time in Figure [5].
The navigation algorithm aims to calculate the velocity of the rocket in the navigation frame. However, the accelerometer does not tell deleterious acceleration and relative acceleration of the rocket. Therefore, the compensation velocity has to be estimated from the measure value.

Where g is the gravitational acceleration of the launch site.
In equation [24], the second term represents the centripetal force of the navigation frame, which rotates about the earth. The third term is the coloris acceleration due to the interference of the  and . The coloris acceleration is when the rocket experiences a relative velocity to the navigation frame, while the navigation frame rotates itself.
Substituting the data obtained from the FDR module, which are ωx, ωy, ωz, ax, ay and az during the flight into the equation [24], data of
velocity is obtained.
A compensated with the data of frequency monitored from the ground base, the dynamic data is applied in the following Doppler-
cancelling system.
The doppler shift is given by equation [25]

Theta is given by

In the former process, the dynamic data of each sample is recorded with its corresponding frequency monitored.
Thus doppler shift effect of  the downlink signal eliminated. Now this signal is sipposed to be given by the following equation

This is the pure relativistic shift of the downlink signal.

b) Comparison group

The data of the transmitter on the payload, was real time recorded, which is linearly related to the time standard on the payload. As the payload experiences a relative velocity to the navigation frame, the clock effect is considered. The following cancellation applies to the special Relativity Conception. For the time base, the original time interval between two pulses tm-1 and tm is △    t.

The data of the time base experienced former processing with the dynamic data, thus the actual transmitted signal is calculated from the corrected time base in the computer. This signal is labeled as fair. Fair is processed to predicted relativistic shift.

 

 
During the experiment, a series of error resources were introduced, which fall into two categories: the errors generated in the data acquisition process and Data processing progress.

4.Error of data acquisition

1) Time standard

a)Difference of the time standards    During the experiment, two sets of time standards were applied: one on the payload and the other in the ground base. The one on the payload generates the downlink signal and the comparison group. The one in the ground base is used in the first comparison with the downlink signal to generate the signal f1 – f0.    So the error caused by the difference between the two time standards were only introduced in the first order comparison.
During the pre-launch testing, the frequency of two time standards were adjusted. One of the zero beat was shown in figure .    b ) During the light time of downlink signal          i) Change in frequency of signal    When the EM wave travels in the troposphere(which covers the space within an altitude of 12 kilometres while the apogee of the rocket is within 2 kilometres), the velocity of light, c, is not a constant but a vector. It varies with graphic parameters.    Where n is the refractive index of the troposphere is given by equation [54]

Where T is the absolute temperature, p is the absolute pressure, ew is the absolute humidity(in terms of hPa)
Equation [53] is substituted into each sample, after this correction,  , is 5%.

ii) Path variation

The propagation vector in equation [1],  is assumed to be a straight line. However, due to the nonuniform variation of air particles, refraction take place. So the real propagation path of the downlink signal is a curve rater than a straight line. The actual path is given below.

Where rm is the displacement of the rocket from the centre of the earth, which is given
by  . Where  is the transformation matrix that map the navigation frame to the earth frame.

Where L and  are the longitude and latitude of the launch site.

After correction, the error in path determination can be ignored.

5.Error of frequency estimation

The received signal was discretized and the frequency of it was calculated though algorithms by digital circuits. During this process, errors are introduced. In this section, the error introduced by the frequency estimation algorithm will be discussed.
Assume the actual value of four parameters of the sample signal is ω0, A0, B0  and C0, the sampled value of the signal at time tk is y(k), the RSS of them is given by

△ω = ω – ω0
△A = A – A0
△B = B – B0
△C = C – C0
[60]

The difference in frequency between the estimation value and actual value is r(k) at time tk. The value of r(k) is given by

Substitute the equation [64] to the equation [63], equation [65] is obtained. This equation gives the error of this algorithm.

In this experiment, the sample rate was 120 million samples/s. The frequency was calculated per 10 second. The SNR of the signal was 50dB+. As a result, the accuracy of this algorithm reached a level of 1×10-12 Hz.

6.Conclusion

An experimental verification of the gravitational blueshift has been successfully achieved as a test of the general relativity conception.

作者简介:李雨翀,火箭爱好者,高中学生。初中时开始接触火箭制作,开发有RF系列火箭,已发射二十余次,是国内较早采用惯性导航技术的业余火箭之一。

业余火箭方面推荐的研究项目

 

业余火箭方面推荐的研究项目

拔刀斋/刘

小时候,我们拿鞭炮药做火箭发射——BOOM。
刚来科创,我们配制燃料、试燃,然后制作发动机、地面试车,最后制作火箭、发射。
今天,我们设计、制作、测试火箭的各个分系统,最后总装和发射。

高水平的火箭需要以下三方面的进步:
1,更精深的技术:从黑药到糖类燃料,再到高能的RAP推进剂;电子设备和控制系统从无到有。
2,更大的工作量:零部件的数量越来越多,个人完成整个系统的难度越来越大。
3,更高的可靠性:由于零部件数量增加,每个零部件需要更高的可靠性才能保证系统可靠性不下降。

这三方面的需求有一个共同的解决方法:对每个技术问题分别深入研究和测试,然后组合成系统设计。
问题细分之后,不仅可以研究的更透彻,合作的更灵活,还降低了研究的难度和危险性门槛。

新手也有机会发出高水平的精华文章!

以下是一些主要的研究问题(后续会不断添加):

基本分类:
资料文献、测试仿真、固体燃料、固体火箭、液体燃料、液体火箭、箭体、火工品、回收技术

资料文献:
与各个具体研究课题相关的资料文献,无论个人水平高低都适合参加资料收集,上传时应搭配简要的概述。

测试仿真:
火箭各部分的测试仿真技术、仪器、软件平台,包括但不限于以下主要课题:

测量与仪器:
发动机推力测量(推力计)——测力使用应变片(包括成品电子秤传感器),目前急缺试车台机械结构!
燃烧室压强测量(压力传感器)——可以用直喷管推力换算,或使用成品气体压力传感器。
固体燃料性能参数测量——使用发动机的压强时间曲线换算,或恒压燃烧装置,欢迎继续编写计算程序!
燃料性能的热力学计算——GUIPEP等软件,可计算任意燃料组合配方的理论比冲等性能。
液体燃料喷嘴雾化性能测量——PIV:高速摄影+图像处理?
液体发动机燃烧室声谐振测量——使用扬声器和麦克风(专业方法也这样做)。
火箭飞行状态参数的测量——使用加速度计、陀螺仪等惯性元件作姿态估计、多普勒测速等。
火箭发射视频的拍摄——包括摄像机的选取、位置布置等,新手也可成为摄影达人哦!

计算与仿真:
固体发动机内弹道特性的仿真——推力计算器、多段药柱优化等程序,已有一些计算程序作品,欢迎补充!
液体发动机内弹道特性的仿真——有一些热力学和流体力学的理【6158 0361】式,待整理编写计算程序!
火箭飞行外弹道特性的仿真——SpaceCAD、MATLAB Simulink的Aerospace工具箱,欢迎继续编写计算程序!
结构力学计算与有限元仿真——ANSYS软件的使用、发动机的结构应力分析等。
流体力学计算与CFD仿真——ANSYS/FLUENT软件的使用、空气阻力的计算、燃烧室和喷管的仿真等。

固体燃料:
常见的固体推进剂介绍:

黑火药BP——本版有详细教程、技术成熟、压制药柱费力并且药柱强度低,适合制作20mm以下的小火箭
(不建议使用)鞭炮火药、窜天猴笛音剂——含氯酸钾、极易爆轰
糖类推进剂(KNDX/KNSU/KNSB)——本版有详细教程、技术成熟可靠、热浇注。
AP类复合推进剂(RAP、聚氯乙烯-AP、HTPB-AP)——本版有部分教程、高性能、有爆轰危险、真空浇注。

推荐的研究课题:
糖类推进剂(KNDX/KNSU/KNSB)的配方、性能、燃烧试验——目前已经较为成熟。
糖类推进剂(KNDX/KNSU/KNSB)的批量制备工艺、产品品质一致性的改进、KNSB的推广使用。
AP类复合推进剂(RAP、聚氯乙烯-AP、HTPB-AP)的配方设计、理论性能计算、制备、燃烧性能测量。

固体火箭:
现有的固体发动机设计资料介绍:

推荐的研究课题:
固体火箭发动机的总体设计——从PVC发动机到金属发动机。
筒体、喷管、堵头等结构件的设计——材料、工艺、紧固件、防热技术,最好有定量的受力、传热计算。
固体火箭发动机的试车实验——测量详细的推力曲线等数据比单纯追求高性能、大规模更重要。

液体燃料:

常见的氧化剂介绍:
过氧化氢——易得、无污染、强腐蚀、易分解、可作为单组元推进剂、高浓度易分解爆炸、储存不很稳定。
液氧——高能、无污染、低温、不能长时间储存、不易购买和运输。
N2O——无腐蚀无污染、压缩液化气体(常温下蒸汽压约6MPa)、可作为单组元推进剂、易分解爆炸。
发烟硝酸——较为易得、易挥发、烟雾有毒、强腐蚀。
(不建议使用)红烟硝酸、四氧化二氮——用于长征火箭、极易挥发、气体剧毒、强腐蚀。
常见的燃料介绍:
燃油(汽油、煤油等)——易得、无污染、燃烧值高、需要火源点火。
醇类(甲醇、乙醇等)——易得、乙醇无污染、蒸发冷却燃烧室的效果较好、需要火源点火。
胺类(乙二胺、乙醇胺等)——易得、有毒但污染环境不严重、加入催化剂后与90%过氧化氢混合可以自燃点火。
(不建议使用)肼类——用于长征火箭、与硝酸或四氧化二氮混合可以自燃点火、有毒、致癌。

推荐的研究课题:
液体推进剂的制备——制备的原理、装置、流程、难获得原料的采购。
液体推进剂的化验——目前主要是过氧化氢浓度测量,包括化学滴定、密度法、PH法等。
液体推进剂与材料的相容性——推进剂接触、浸泡储存容器、管道、阀门等部件材料是否会发生分解或腐蚀材料。

KCSA广州研究组:造真火箭明日大学城发射升空

本站注:科创广州地区火箭爱好者历时三个月完成二级火箭万户一号的制作工作,原定于11月11日在广州发射。设计制作得到了国内火箭爱好者的大力支持。当地媒体进行了非常专业的报道,空管局领导提供了宝贵指导。发射前进行了严格的安全论证,因最终未能找到适当发射场地,达不到科创航天局提出的零地面风险要求,在10日晚决定推迟发射。预定发射日进行了全箭地面试车,采集发动机推力等关键参数,试验结果为后期进行性能和安全方面的改进提供了依据。

四“小毛孩”造真火箭明日大学城发射升空 

原载广州日报

  地点:番禺大学城中大与华师之间一空置地块

  流线型的箭体直指长空,黝黑的空心锥发动机喷嘴,飘逸的尾翼,除了比著名的长征火箭小几号,与真的几乎一模一样,这枚基本组装完成的火箭惊艳了所有见到它的人。

万户一号

  四个“90后”大学生,平均年龄只有19岁,所学专业也五花八门不完全对口,但他们在没有老师的指导下,自筹资金,历时3个多月,经历无数次失败造出这枚“真”火箭,并定于12日下午发射。

  文/记者李立志 图/记者黎旭阳

  “这算是一种探空火箭,比探空气球飞得高、比低轨道运行的人造地球卫星飞得低。探空火箭所获取的资料可用于天气预报、地球和天文物理研究,为弹道导弹、运载火箭、人造卫星、载人飞船等飞行器的研制提供必要的环境参数。”

将要装入探空火箭用于箭体回收的降落伞。

  “万户-I号”可以说是真火箭

  “在某种意义上可以说就是真火箭,因为每一个细节,包括小小的螺丝钉,箭体材料上头发丝大的小缝我们都要经过严格数据测试,它的细微的运行轨道变化都能监测到,可以一二级分离,有回收装置,也有视频监控。”这或许是中国科技含量最高的业余火箭,此次实验可能是国内第一次由在校本科大学生自行研发完成的探空项目,项目涉及物理、化学、机械、电子等专业,初次设计的飞行高度是640米。四个“90后”的大学生,平均年龄只有19岁,所学专业也五花八门,但他们在没有老师的指导下,自筹资金,历时3个多月,经历无数次失败造出真火箭。“我们给它取名万户一号,一旦加注好燃料组装完成,就能发射升空。”

大学生在组装探空火箭。

  三个月自筹经费造火箭

  昨日在中山大学的一间实验室里,记者见到这枚火箭的四位“研制者”。记者对他们的第一印象:四个“小毛孩”。不过他们却是相当牛的人:负责组织管理及箭体设计的胡振宇是一个狂热的化学迷,曾获得全国化学奥赛的三等奖。负责航电部分的罗澍曾经获得全国发明展金奖,为此还废寝忘食狂啃捷联惯导的理论和算法。负责发动机设计的张子林,常与国外业余火箭爱好者讨论技术改进,而黄德恩则负责场地的管理及制作。

用于制作探空火箭燃料的原料。

  “我们三个月前开始试制火箭,8000元经费完全是自己筹集。”胡振宇告诉记者,“这项实验是一次探索两级固体火箭技术的尝试,同时是一项科技爱好活动。为了纪念我国‘航天’的先驱万户,故火箭取名为万户-Ⅰ号。”他告诉记者:“这算是一种探空火箭,比探空气球飞得高、比低轨道运行的人造地球卫星飞得低。探空火箭所获取的资料可用于天气预报、地球和天文物理研究,为弹道导弹、运载火箭、人造卫星、载人飞船等飞行器的研制提供必要的环境参数。”

  自豪:业余领域研究方法国内最好

  胡振宇告诉记者,此次实验可能是国内第一次由在校大学生自行研发完成的探空项目,而且是跨学科、跨校合作,他们所用的方法是业余领域研究方法国内最好的,某些技术能媲美当今民用航空技术。

火箭的飞控电路板。

  整个火箭的制作,在缺少资金的情况下大家尽量自己动手,比如称重的称重仪,几个人自制芯片,将普通的电子秤改装成一台高灵敏度的测重仪。罗澍告诉记者:“就算现在民用航空领域,我们一些研究方法和技术都算是先进的。”成果还不只这些,为了跟踪降落的箭体,他们还设计两个简易的天线,如果要买,一个至少要上千元,但他们通过数据分析,只几十元就解决问题。“如果材料能更好一点的话,我们的航电监控技术或许比得上现在民用飞机上的技术。”

  火箭发射是否要备案?

  记者了解到,我国空域一直是严格管理的范围,直到现在并没有开放,目前我们对空间领域的法规所针对的只是有人驾驶的飞机。而对类似的航空模型,火箭之类的航空器,暂时没有明确规定。据悉,目前,国家已经在沈阳、广州试点对1000米以下的空域开放。

  如何保证降落时安全?

  记者了解到,一级火箭体脱离的高度约100米,按照多次测试及数据分析,不会飞离场地。

  二级箭体主要依靠降落伞保证降落,为了确保降落伞能打开,控制器专门设置了两重保护,确保打开。

  此外,四人小组还对火箭的降落安全进行特别设置,打开降落伞的控制器都是双重控制,以防不测。

  如何保证发射安全?

  发射当天选择的空地,在发射之前会做一些清场工作,保证场内没有人。万一发动机发生爆炸也没有关系,发动机爆炸的范围已经经过数据及实验测试控制在一定范围内,点火是用电子点火方式,有足够的安全距离。

  如何回收?

  会组织搜索队搜索降落箭体,搜索的仪器由灵敏度高的德国监测仪,以及两台自制的天线组成,能定位到几米的距离。

  艰辛的制作过程

  每颗螺丝钉都经测试

  虽然是业余,但按罗澍的话来说,他们是按照现在最先进的研究方法来设计的,技术上没有一点马虎。

  记者采访时,罗澍正埋头制作火箭最关键的航电监控芯片,他说:“火箭的每一个组成部分,用什么材料,长度重量大小都经过严格的数据测试,再通过软件进行不断测试,才得出最后的数据。”正在组装尾翼的胡振宇举了一个例子,固定尾翼的螺丝就不是乱选的,首先要计算它的承受力,如果螺丝的承受力不够,尾翼就会松动脱落,发射就可能失败。这些大量的数据可不是一天两天就能得来的。“经常做通宵的实验,困了就在行军床上睡会儿,有时做出成品,凌晨5时都会去做试验。”

  头发丝般的缝致爆炸

  因为资金不够,四个小伙子尽量找价格最便宜但又合乎数据要求的制造火箭的材料。在实验台上,记者见过好几个已经爆炸开裂的发动机。“这是因为隔热层有一个头发丝大小的缝隙,当固体燃料瞬间燃烧时,产生非常大的破坏力,将铝合金的发动机撕开一条缝,最后发动机就报销了。”随后他们经反复试验,终于找到正确的密封方法。

  20万元监测仪监控

  为了追求最大限度的仿真,“万户-I号”设计了复杂的航电技术和回收装置。制造过程中所应用的技术,部分是通过采集文献,借鉴国内外爱好者实验数据所获得,其余均由参与成员通过多年的实践经验积累,再通过知识整合,加以创造性思维自我创新。

  为了跟踪火箭的运行轨迹,并掌握火箭的飞行姿态,四位研制者运用了复杂的航天技术。负责航电技术的罗澍告诉记者,火箭总共有两个控制监测芯片,还安装有视频摄像头。此外,“一位科普专家专门提供一台尖端仪器,价值近20万元,通过火箭上的传感装置,能灵敏感受火箭的每一个细微动作,比如说降落伞不能打开,监测仪就能敏感感受飞行轨道的变化,我们就要启动第二重的保护装置。”

  “万户-Ⅰ号”两级火箭都设有降落回收装置,降落是通过降落伞来实现的,但别看它不起眼,它却“报废”了实验小组10余枚试验火箭。

  华南理工大二学生胡振宇,18岁,管理专业;

  中山大学大一学生罗澍,信息科技专业,不到19岁;

  华南师范大学大二学生张子林,物理专业,20岁;

  广州中医学院的黄德恩,有机化学专业,大二,20岁。

  “万户-Ⅰ”相关数据

  箭体总长:247cm

  一级长度:103cm

  二级长度:100cm

  头锥长度:40cm

  连接部分长度:4cm

  总重:11.793kg

  外壳材质:HD-PVC

  发动机壳体材质:6061-Al(铝合金)

  发动机喷口材质:45#钢

  燃料:改性KNDX(一种固体燃料)

  一级推力:288.4N;总冲:622.4N/s

  二级推力:188.6N;总冲:409.4N/s

  降落伞材质:尼龙-66

  仿真软件:MATLAB,Simulink,SRM,SpaceCAD,OpenRecket。

  设计射高:640m

  最大速度:100.4m/s

  最大加速度:3.32g

利用软件设计液体燃料火箭发动机

经过一段时间对文献的研究,我们整理出一些列公式,然后根据公式利用VB编写了一个小程序,该程序适用于液体发动机的理论设计。再次感谢拔刀斋版主提供的Guipep热力学计算权威软件。

下面请跟着我一步一步来通过软件计算设计一个液体发动机要件的基本尺寸结构。
STEP1——设计要求:设计一个以90%质量浓度的过氧化氢为氧化剂,甲醇+乙醇胺+氯化铜(可溶性催化剂)为燃料的液体发动机。发动机燃烧室压力2MPa,设计推力20Kg(约200N)。根据氧平衡和点火性能,得出燃料比例为75:12:12:1(本文不作详细说明)。
STEP2——下载以下两个软件(Guipep以及液机尺寸设计均为绿色免安装软件,前者对visita系统兼容不好)
GUIPEP.rar (295 K)

液机尺寸设计.rar (6 K)
注:由于本站的下载功能尚未完成,下载需注册科创论坛,诚致歉意。
STEP3——找到Guipep.exe文件,双击运行之(该软件的dos计算内核为NASA开发,计算结果可信度较高,尤其适用于燃烧产物固相含量很少的液体发动机),出现该界面,如下图。


STEP4——在Desciption下选择各种原料对应的英文名称,并在右边的Weight内输入质量,单位g,质量设置为0表示取消该原料选择。在右边Title框中输入这种燃料的命名(自定),在Operating Conditions栏目下输入燃料常温(单位K)、燃烧室设计压强(单位PSI)、当地大气压强(单位PSI)。我处气温20℃(293K)、燃烧室压强2MPa(2×145=290PSI)、当地大气压为0.85atm(0.85×14.7PSI=12.5PSI),设置好的参数如下图。


STEP5——在工具栏中找到Run—>Singel Run单击之或者按下组合键Ctrl+R,此时弹出如下dos视窗。


STEP6——在dos视窗中按回车键执行,打印出一个文本文档,里面的内容即是计算结果。如下图


STEP7——找到“******CHAMBER RESULTS FOLLOW    ******”下的燃烧室计算结果,以及“****PERFORMANCE: FROZEN ON FIRST LINE, SHIFTING ON SECOND LINE****”下的冻结流数据。如下图

这里,我们只对以下四个计算结果感兴趣。分别是:

燃烧温度T(K)=2401K;

产物气体比热比γ CP/CV=1.1952;

产物气体的平均分子量THE MOLECULAR WEIGHT OF THE MIXTURE=20.413;

以及冻结流理论比冲IMPULSE=222.6。

根据需要将这四个结果记录下来。
STEP8——找到“液机尺寸设计.exe”文件并运行之,弹出如下界面。(该软件系自行编写,没时间去修正bug,例如除数为0错误等,各位海涵)


STEP9——根据设计任务的要求,将各项数据输入到对应的框中。
这里的氧燃比定义为氧化剂总质量比上燃料总质量;
特征长度定于为燃烧室容积除以喉口面积,表征了燃料在燃烧室内驻留的时间也既是燃烧完全程度,一般根据反应物活性取值1.5-6;
径收敛比定义为燃烧室直径与喉口直径的比值,表征了燃烧室喷注面积的大小,一般取3-7。
填好后,点击“计算”按钮进行计算,得到的结果如下图。


根据计算结果:
1.可以根据氧化剂流量和供液压力确定需要的氧化剂喷嘴型号和数目
2.可以根据燃料流量和供液压力确定需要的燃料喷嘴型号和数目
3.可以根据喷管排气速度判定是否为超音速发动机,以及火箭是否能够超音速飞行
4.可以根据喉口直径和出口直径设计拉瓦尔喷管扩张段尺寸
5.可以根据扩张比和喉口直径,来计算不同扩张角下的出口直径
6.可以直接根据燃烧室内径和长度设计发动机内壁尺寸

适当说明一下:

关于特征长度,取决于采用的喷注结构、燃料的汽化热和反应的活性。例如气态氧和汽油,可以低于1.5m,而过氧化氢多一个分解的过程,故取值较高。

关于径收敛比,取决于喷注面大小,也就是喷注流达到完全混合时所需要的最小面积,喷嘴雾化角越大,收敛比越大。
关于拉瓦尔喷管,较优性能和加工便捷度的设计为收敛段半角60°,喉口长度等于0.7倍喉口直径,扩张半角15°,三个部分均为圆弧过渡,不允许留有台阶或较深的刀纹。
关于金属壁厚与耐压的设计,参见此贴http://bbs.kechuang.org/read-kc-tid-31380.html

至此,一个液体发动机的燃烧室关键尺寸就计算出来了,可以根据这个数据设计图样进行加工。关于喷注器、材料、冷却系统、加工等具体说明,请参见本人译著《液体火箭发动机设计与制作》,链接http://bbs.kechuang.org/read-kc-tid-37433.html

原著:ehco魏