Maiden Flight of Smart Dragon 1—The Smallest Launch Vehicle in China

GONG Min,ZHANG Yiguo,GAO Feng,REN Xinyu,ZHANG Dong

China Academy of Launch Vehicle Technology,Beijing 100076

Abstract:The Smart Dragon 1 (SD-1) launch vehicle is the first commercial rocket developed by China Academy of Launch Vehicle Technology (CALT),targeting to the international launch market for small satellites.As the smallest launch vehicle in China at present,SD-1 is one of the most efficient solid boost rockets nationwide in terms of launch capacity.Compared with current domestic rockets,it provides remarkable access to space with a faster response,higher orbit-injection accuracy and better payload accommodation at a lower cost.On August 17,2019,SD-1 completed its maiden flight and delivered three satellites into the desired Sun Synchronous Orbit (SSO) of 550 km accurately.In this article,a technical review of SD-1 is presented detailing the design concept and the use of state of the art technology throughout its development.

Key words:SD-1,smallest launch vehicle,cost control,commercial launch market

1 INTRODUCTION

With the rapid growth of the small satellite industry,meeting the needs for the commercial launch market has become an increasingly prominent task for rocket manufactures and providers.Small satellites require more frequent delivery missions and a more customized launch service at reasonable prices,which is hardly fulfilled by the existing mainstream rockets of large and medium scale.Therefore,in recent years,space companies worldwide have been working towards the development of compact and low-cost launch vehicles for pursuing the rising demand.The China Academy of Launch Vehicle Technology(CALT),the largest research and development enterprise for launch vehicles in China,has actively reformed and innovated to join the competition of commercial aerospace market.Thus the academy officially initiated the Smart Dragon 1 (SD-1) project in February 2018,intending to seize the surging demand for launch services of the flourishing satellite industry.

On August 17,2019,SD-1 performed its maiden launch from the Jiuquan Satellite Launch Center,as shown in Figure 1.Three satellites were accurately delivered into the scheduled orbit,indicating that the first flight mission of SD-1 had been successfully completed.The mission witnesses a new brand of Chinese carrier rocket has been launched.

2 SYSTEM DESIGN

Figure 1 The maiden flight was successfully performed

SD-1 is a four-stage solid rocket with total length 19.5 m and maximum diameter of 1.2 m,as shown in Figure 2.The liftoff weight is about 23 t,allowing the rocket to deliver payload up to 200 kg into a 500 km SSO.As a result of using a specialized mobile truck,SD-1 can be launched over a wide area with the preparation time less than 24 h,ensuring outstanding operational flexibility.

Throughout the development of SD-1,consistent contribution has been made towards cost control by employing advanced approaches such as product strategy and integrated design,along with efficient management concepts such as a project responsibility system and a flat management structure.As a result,the delivery time and total cost have been greatly reduced.The research and development process was accomplished within just 18 months,and the launch expenditure is lower than that of most small-sized rockets in the world.

Figure 2 SD-1 Y1 rocket before launching

Figure 3 Typical flight sequences for SD-1

2.1 Typical Flight Sequence

The four solid boost motors of SD-1 rocket are all setup to naturally cut off by burn-out,which extends the rocket’s ability to its maximum.In terms of staging,five separations take place sequentially during the flight,i.e.S-1/ S-2 stage separation,fairing jettison,S-2/ S-3 stage separation,S-3/ S-4 stage separation and satellite release,as shown in Figure 3 and listed in Table 1.

2.2 Vehicle Structural System

As shown in Figure 4,the vehicle structurally consists of six parts：the trailing segment,the first inter-stage segment,the second inter-stage segment,the satellite module,the attitude control capsule and the fairing.The payload capsule is located between the third and the fourth stage motors to obtain an intact and stable room for the onboard satellites,which is remarkably different from any other launch vehicle.In terms of material used onboard,a few composites with outstanding excellent properties have been adopted.For instance,the payload capsule uses a very light honeycomb sandwich structure,which reduces the weight significantly,and the materials for the attitude control capsule and satellite adapter use the carbon fiber composite,which also makes the rocket light and strong.

Table 1 Typical flight sequences for SD-1

2.3 Control System

The control system is mainly comprised of the navigation system,guidance system and attitude control system.The navigation and guidance system adopts a system based on a combination of gyroscope strap-down IMU and satellite navigation,which significantly reduces the cost of IMU while realizing great injection accuracy.The digital control system with three channels is optimized by multidisciplinary methods to simplify the actuators onboard,which in return lowers the cost.Consequently,the rocket is stabilized without thrust vector devices usually used by other rockets.

2.4 Electronic System

The low-cost,high-integrated electronic subsystem is designed for the commercial launch.There are only two core processing devices onboard.The first one is the upper-stage controller which provides control,navigation and measurement functions covering the whole flight of SD-1.The other one is the first-stage controller,which guides the first-stage debris to a desired impact point and provides timing control before the ignition of the second-stage motor.In terms of communications,a multibus architecture has been adopted on board,which consists of 1553B bus,RS-422 bus,I2C bus and Ethernet.This framework ensures different kinds of devices communicate stably.

3 INNOVATIVE ASPECTS

SD-1 is dedicated to the establishment of a space-access platform with the leading level of reliability,cost performance,response speed and payload accommodation.With a number of specified technical innovations synthesized in following four aspects,it is fully capable of satisfying the constraints carried out by small satellites for rapid launch and customized service.

3.1 Maximization of Payload Mass

Just as what is indicated by the name,SD-1 is designed to be of great agility which provides enhanced mobility during transportation and shortened launch preparation time,also making the rocket to be the smallest and lightest in China.However,the launching capability of SD-1 is relatively powerful considering its scale.Benefiting from the innovative utilization of a compact body arrangement,integrated electrical system,high-performance solid boost motor and light-weight composite material,the rocket's launching coefficient reaches an advanced level worldwide,which is superior to most of the existing solid boost rockets.Based on Jiuquan Satellite Launch Center,the launching capacity of SD-1 into different orbits is shown in Table 2 and Figure 5.

3.2 Intelligent Test and Flight

The engineers of SD-1 have made the rocket functionally intelligent through several cutting edge applications in automated aerospace system.For instance,the equipment for the on-board intelligent test system is able to realize a one-button test followed by automatic processing of test data and even intelligent analysis,reducing the time consumption to manual operation by 50% and eliminating the test errors caused by human factors.In addition,intelligent optimization algorithms are applied in the design for the guidance system,which provides a fault diagnosis function and online decision-making mechanism,improving the rocket's robustness.

3.3 Quick Response

The quick response of SD-1 can be summarized in two aspects.Firstly,the launch preparation is efficient.In addition to the intelligent test system aforementioned,several techniques are combined to reduce the work load during launch preparation.Pre-packaged liquid propellant is used in the attitude control system,releasing the need for any filling on site.The specialized launch truck of SD-1 (shown in Figure 6) is capable of autonomous positioning and orientation with reduced time consumption.On the other hand,the production cycle of SD-1's manufacture is simplified.Since a large number of productized items and well-developed techniques are employed owing to the commercialized design concept,the baseline performance of SD-1 is guaranteed with high-reliability,while the production process time is achieved in less than six months.

3.4 Payload Acommodation

In order to satisfy the diverse requirements for multi-satellite networking,a standardized launch adaptor and modularized control device for multi-releases are applied in the payload capsule of SD-1,allowing different types of separation controlled simultaneously.To mitigate the environmental stress exerted on the payload,the mass distribution and engine thrust are optimized for all stages so that the flight overload of SD-1 is acceptable for most small satellites.The accommodation space for satellites is elaborated using a spatial algorithm,providing the satellites with an intact envelope of φ1.1 m×1.5 m (shown in Figure 7),which is also designed to enable sound insulation.In return,the maiden flight indicates that the noise and vibration exerted on the satellites turned to be at a comparative order of magnitude as those of conventional liquid rockets.In addition,the shell allows radiowave transmission,enabling communication with the on-board satellites possible.During ground transportation and launch preparation,a special air-conditioning system is functional in the capsule to keep the temperature and humidity in a predetermined range,which guarantees a clean and mild storage environment.

Figure 6 SD-1’s off-road mobile vehicle

Figure 7 Capsule envelope

4 COST CONTROL

To enhance the rocket’s competitiveness in the market,a number of methods to accelerate the development and control the cost were applied.Through the breakthrough in design concepts and the application of new technologies,the cost reduction and efficiency of rocket development has been realized.

4.1 Application of Overall Integrated Design Method

In the development process,SD-1 proposed the engineering application of the overall integrated design method,along with the structural/process collaborative design,electrical/structure integration design and digital design to improve overall work efficiency.In the collaborative design process,multi-disciplinary optimization was carried out through unified digital models,saving conventional multiple 2D drawing conversion processes,reducing design iterations and greatly shortening the development cycle.As a result of the optimized design,SD-1 adopted for the first time the strategy of a satellite inversion configuration nationwide,which enables the rocket to minimize the control actuators on board.

4.2 Generalization/Modularization/Product Design Ideas

During the development process of SD-1,designers firmly implemented the product design routine,aiming to achieve optimal cost performance.For instance,designers optimized for streamlined designs of several major parts on the rocket,removed unnecessary components and used more commercial off-the-shelf products as possible.In the design of the electrical system,the open standard interface was applied,and the traditional single-machine function was modularized,which improves the adaptability and replaceability of the rocket electrical system thus reducing the cost of product development.In the design of the structural system,all of the mechanical interfaces,bolts and igniters have been unified.There is only one type of mechanical interface,two types of docking screws,and one type of igniter onboard,which significantly reduces product procurement and management costs.

4.3 Application of Virtual Experiment Technology

SD-1 fully utilized the professional competence of related concepts and advanced simulation methods to reduce time-consuming ground tests,achieving a significant reduction in test costs and period.For example,in the area of the aerodynamic experiment phase,SD-1 replaced ten traditional wind tunnel tests with CFD numerical simulation,saving nearly 7 million RMB in test cost and reducing the development period by nearly 4 months.In addition,the modal test cost was reduced by nearly 10 million RMB by using modal parameter prediction technology based on the finite element analysis and so test period was reduced by nearly half a year.In addition,in the electromagnetic compatibility test,structural statics test,thermal environmental test and instrument vibration test,virtual tests were also widely used,which effectively controlled the research cost and improved the development efficiency.

5 FUTURE DEVELOPMENT

In the subsequent development of SD-1,a three-phased strategy is scheduled.In phase I (from 2018 to 2019),the primary goal was to successfully accomplish the maiden flight,as well as achieve key breakthrough in the R&D and management modes.In phase II (from 2019 to 2020),the main objective is to complete five commercial launch missions,while finishing the development of the satellite capsule with a larger envelope space upgraded to φ1.3 m × 2.0 m,which fulfills the space requirement of overwhelming majority of small satellites within China.In phase III (2021 and on),the rocket production is expected to stabilize on a batch production rate,targeting to produce 10 rockets every six months.In detail,during the phase II and phase III,the following aspects will be addressed at the same time.

5.1 More Payload Mass

Variations of SD-1：The baseline SD-1 can be optimized by replacement of the current first stage engine with a larger one with 1.4-meters diameter,which is a well-developed product used in existing rockets.This replacement will increase the payload mass of SD-1 up to 270 kg of 500 km SSO,as shown in Figure 8.

5.2 Larger Envelope Space for Payload

The development of a larger modular and replaceable satellite capsule is in progress,which will provide the satellite with a larger envelope space of φ1.3 m × 1.7 m (shown in Figure 9)and allows more satellites on board.

Figure 8 SSO launching capacity of the SD-1 series

5.3 Better Payload Accommodation

In the further development,effort will be paid consistently to improve payload accommodation.For satellite connection and separation,the SD-1 rocket will provide various standard vehicle separation devices(shown in Figure 10),such as straps,point connections,cubic star release mechanisms,light straps and so on.In terms of the vibration environment for the payloads,energy absorption materials and structures will be developed to minimize the vibration response.

5.4 Continued Innovation

As the first commercial launch vehicle of CALT,SD-1 is not only a space-access option,but also a platform for technological innovation and technical communication.In the near future,in addition to the commercial launch mission,SD-1 will also be used as a space test platform to verify new exploration ideas and developments originating from universities and private enterprises around the world.Candidate techniques such as laser pyrotechnics,wireless electrical systems and Terahertz communications system are already scheduled at present.As an open platform,interested organizations around the world are warmly invited to cooperate on SD-1.

6 CONCLUSIONS

SD-1 is the first commercial launch vehicle developed by the Chinese“national team”.The presence of SD-1 not only demonstrates the resourceful technology potential of CALT,but also indicates its strong will to keep up with the evolution of the aerospace industry.The success of SD-1 will actively inspire a new era of Chinese launch service market for small satellite.With the leading level of reliability,cost performance and response agility,SD-1 will also become a competitive player on the international stage for commercial launch services.