Solutions for Large-Scale and Low-Cost Access to Space in the Future

LU Yu,DONG Xiaolin,WANG Xiaowei,ZHANG Feng

China Academy of Launch Vehicle Technology,Beijing 100076

Abstract:The objective of this study is to identify the requirements of access to space for the future,the required methodology,key technologies and international cooperation mode.Firstly,the mission requirements and the challenges of current technologies to access to space are analyzed and summarized.The solutions and related key technologies to realize large-scale and low-cost access to space (L2AS) are presented here,including the low-cost design of expendable launch vehicles and a reusable space transportation system,interface standardization,and new conceptual launchers.The mission modes based on launch vehicles to realize L2AS and three future international collaboration modes are presented.Lastly,the relevant conclusions and suggestions are given.

Key words:large-scale,low-cost,access to space,solution

1 INTRODUCTION

With the social development of humankind,the demands on each type of space mission become increasingly higher,space activities become more and more frequent and the scale of access to space becomes larger and larger,prompting an intense demand for low-cost access to space.

The level of the space transportation system represents the capability of free access to space.During the early period of developing a space transportation system,most space countries ignored the cost in order to ensure the success of launch and flight.With the further development of space technology,each space country begins to seriously consider the launch cost.The research on large-scale and low-cost access to space (L2AS)must be significant to meet the demand for large-scale access to space in the future,support the development of the space tourism industry and lead and promote the development of science and technology.

2 MISSION REQUIREMENT ANALYSIS FOR ACCESS TO SPACE

2.1 LEO Small Satellite Constellation

A satellite with a mass of lower than 500 kg is called small satellite with features of low-cost,simpler design and manufacture,flexible maneuverability,convenient operation and management.The development of new technologies in micro mechanics,microelectronics and new materials promote an increasing improvement in the single satellite’s function,increased maneuverability and on-orbit service life.

With the increasing requirements for remote-sensing data from the commercial users,the emerging commercial remote-sensing companies will continue to operate their present constellations and start the deployment of new small satellite remote-sensing constellations in order to promote the continuous prosperity of the Earth observation market.The traditional space companies are also making a strong push into the small satellite Earth imagery market.Similarly,the fast-growing requirements for global internet connectivity is fueling the flourishing development of LEO communications constellations.Projects with huge-scale constellations consisting hundreds,thousands or even tens of thousands of satellites have emerged in quick succession.Thus,the development of LEO constellations for internet will be accelerated.

China Aerospace Science and Technology Corporation(CASC) proposed Hongyan Constellation project,which aims to construct a global communications system based on LEO satellite constellation.China Aerospace Science and Industry Corporation (CASIC) also announced its Rainbow Cloud project,based on the construction a global mobile broadband network using a satellite constellation.The main recent global constellation plans are summarized in Table 1.

2.2 LEO Commercial Human Spaceflight

With the increasingly mature technology of the construction and deployment of large-scale facilities and long-term human residence in near space,accompanied with the rapid development of reusable technology of launch vehicles,it enables the commercialization and industrialization of human spaceflight.In the private sector,led by American companies like SpaceX and Northrop Grumman,they have realized regular cargo transportation to low-Earth orbit.SpaceX has also realized LEO commercial crew transportation services in May 2020,and space tourism products and services proposed by Blue Origin and Virgin Galactic are planned to be coming soon.In addition,the U.S.government has proposed a commercial space station plan and is actively expanding the business mode of exploration beyond the moon.

2.3 Robotics Deep Space Mission

In the future,deep space exploration activities will continue to thrive,with targets being the moon,Mars and small celestial bodies,as well as those in other solar systems.The mission types will be more complicated,moving towards manned exploration at the same time.International cooperation and commercialization will become two major ways to achieve deepspace exploration development.

Table 1 Main global constellation plans in recent years [4]-[9]

China has completed several lunar missions including circumlunar exploration,lunar soft-landing,auto-survey on the moon surface and lunar sampling return,and will undertake explorations of the polar area of the moon and a lunar station mission in the future.Meanwhile,China launched the Mars exploration and landing probe in 2020 and plans to complete a Mars sampling &returning mission by 2030.In addition,China plans to start asteroid exploration before 2022 and Jupiter exploration before 2029

The US and Europe have established ambitious strategic exploration plans that cover major celestial bodies in the solar system.Recently,they both announced that they will conduct robotic lunar exploration and exploration of Mars to lay the technical foundation and provide data for the development of subsequent manned exploration missions.Russia has also previously explored Mars as part of its cooperation with Europe and plans to launch several lunar exploration missions over the next ten years. Russia also plans to carry out explorations of other celestial bodies.Japan plans to continue on small celestial body exploration programs and plans in the future to carry out a lunar landing mission and sample return mission to the Martian moons.India has announced its intent to conduct further lunar and Mars explorations.In addition,emerging space countries such as the United Arab Emirates has conducted a Mars exploration mission.Deep space exploration has become an important space field where major space nations are competing in development.

2.4 Human Deep Space Mission

It is reasonable for human space exploration to develop from conducting near-Earth activities to deep space activities.According to the current plans,the US human deep space missions will be realized by around 2024,beginning with building a lunar orbital station,then conducting human lunar missions.The lunar orbital station will be established as a stable base supporting missions to the lunar surface.A human lunar base will be built through international cooperation.By around 2030s,it is expected a self-sufficient lunar base capable of stable operation will be completed.It will be routine to conduct human lunar missions.At the same time,the human Mars mission will commence.

2.5 Construction of Space Infrastructure and On-orbit Service

With the development of space technology,the demand for large-scale space infrastructure is continuing to grow,particularly for space power stations,space factories,and on-orbit depots.ESA has proposed a Moon Village while the US is pushing for a Lunar Orbital Platform-Gateway (LOP-G).The US,Japan and other space powers are actively conducting research in the area of solar power stations and proposing a preliminary plan for solar power stations of the scale of tens of thousands tons.The International Academy of Astronautics (IAA) research shows that the scale demand for space power stations will be more than 130 thousand tons by 2050In addition,there are many other space infrastructure transportation demands coming up in the future,such as nuclear materials disposal,sun shaders at L-1 point.

The future on-orbit service and maintenance systems will provide comprehensive space services.Looking outward,the systems will not only help large spacecraft to conduct deep space maneuvers,but also looking inward for the removal of space debris and de-orbit disabled spacecraft.At the same time,the life of space assets can be extended through on-orbit refuel and maintenance,and the performance and flexibility of space assets can be enhanced through on-orbit assembly,maintenance and upgrades.According to the plans of the US government and US private companies,space tugs will be produced,capable of moving from low orbit to high orbit,so large-diameter and large-scale space systems can be built up through on-orbit assembly by around 2045.

Table 2 Future space launch demand [14]

2.6 Space Tourism

The space tourism market is also becoming more and more popular,with the US,Russia,ESA,China,Japan and other space powers and organizations conducting research and tests in this area.The suborbital vehicle of Virgin Galactic,Blue Origin and XCOR Space Expedition are still at the testing stage although more than 800 tourist tickets have already been sold.The suborbital space tourism tickets also promoted by Taobao were quickly sold out in China once they were released on the line.ChinaRocket Co.,Ltd.published a three-step plan for space tourism in 2016.In addition,the commercial lunar tourism offered by SpaceX was attractive and a private contract was signed in September 2018.

3 CHALLENGES TO CURRENT TECHNOLOGIES OF ACCESS TO SPACE

According to the task demand analysis,for access to space in the future,there are still some limitations due to the current technology,meaning that today we cannot meet the demand for access to space.

1) The carrying capability of current launch vehicles is insufficient to meet the requirements of large-scale access to space in the future,which requires higher carrying capability beyond that of current launch vehicles.

2) There are many exclusive characteristics required of current launch vehicles,thus the launch adaptability and flexibility need to be improved.Due to the exclusive nature of launch missions,the carrying capability of existing launch vehicles is not fully utilized,or they have to be matched with the appropriate payloads to be launched.This has creates a certain amount of waste in transport resources.

3) Launch preparation time is too long to meet the needs of future launch vehicles.The launch preparation time of general expendable launch vehicles is currently more than 2 weeks,and even extends up to 2 months.

4) The launch price is high and there is a need to reduce costs.From the view of current international space development,the launch price of mainstream launch vehicles is over 100 million US dollars for the commercial space launch market.

4 TECHNICAL SOLUTIONS AND KEY TECHNOLOGIES FOR LARGE-SCALE AND LOW-COST ACCESS TO SPACE

To enable L2AS in the future,a space transportation revolution is necessary.The era of space transportation revolution is coming,with the following characteristics:multiplied carrying capability,greatly reduced cost (1/5-1/10),intelligence,airline flight mode for launching,flexibility and responsiveness,industrialization,thus providing a deep impact on the society and people’s life.

Three technical approaches for L2AS are proposed including a low-cost design of expendable launch vehicles,and a reusable space transportation system,interface standardization,and new concepts of launchers.The new concept launchers include propellant depot,electromagnetic propulsion launch vehicle,nuclear propulsion launch vehicle and space elevator.

4.1 Expendable Launch Vehicle

4.1.1 Solution and mission mode

To meet the market demand for commercial satellites and reduce cost,reasonable planning of carrying capacity,overall configuration using modular design,unity of product status,system design scheme simplification,mature technologies,product-scaled manufacture,rapid test and launch and disruptive technologies should be adopted for the expendable launch vehicle.

1) Multiple satellites launch with one rocket

Multiple satellites launch with one rocket is to send 2 or more satellites to the same or different orbits on one rocket to utilize the payload capacity and reduce launch cost.The countries that have mastered this technology include the US,Russia,ESA,China,Japan and India.This solution depends on the application of interface standardization.

Taking the launch of 104 satellites on one rocket from India for example,India introduced a standard multi-satellite distributor to solve the interface adaptation problems between the hundreds of nano-sats and launch vehicle while also improving the separation of upper stage and attitude control performance.

2) Piggyback

Multi-payload piggyback is quite common and mature internationally.The US,Russia and ESA have a solid technological foundation and engineering experience with the separation of multi-payload launch.

The China Space Express service is a good example of piggyback.China Academy of Launch Vehicle Technology (CALT)is mainly responsible for the research and launch services of the Long March series launch vehicle.CALT coordinates margin for each launch,and now offers a“Space Ride”service.

3) Exclusive small launch vehicle

The small launch vehicle has two purposes.One is to meet the commercial launch requirements and be profitable.The other is to meet the emergent launch requirements.To launch in 48 even 24 hours,multiple disciplines must all come together to enable the fast response.In parallel,it also requires to be low-cost with high reliability.

The LM-11 launch vehicle of CASC and the KZ series launch vehicle of CASIC are representative small launch vehicles.The LM-11 launch vehicle is capable of sending a 400 kg payload into a 700 km SSO orbit.The KZ series consists of KZ-1,KZ-2,KZ-1A,and KZ-11.The SSO payload capacity of KZ-11 can reach up to 1 ton and the cost of launching 1 kilogram into orbit can be achieved for about 5000 US dollars.

4.1.2 Key technology

1) The design configuration of a low-cost launch vehicle

The solid booster has the advantages of being a simple structure with few moving parts,a short development cycle,relatively low development cost,high reliability,and simple maintenance.Combining the advantages of solid motors and liquid engines,the overall configuration of a hybrid launch vehicle can be more feasible in terms of technology and cost,while boosting the development of the liquid and solid rocket engine technology.

Moreover,serialized launch vehicle configurations based on modular design can be developed to conduct different missions.Future launch vehicles should adopt an universal core stage using an envelop design,which can both satisfy various launch requirements and achieve volume production,thereby reducing the production and assembly cost.

2) Design of an integrated high-reliability electrical system

To achieve a high reliable electrical system integrated design technology,an integrated power supply,distribution,and modular design electrical system are needed.

During the design process of an integrated power supply and distribution,the designers mainly consider the factors such as high reliability,simplified vehicle/ground interface,optimized system composition and simplified launch flow.

Modular design technology for an electrical system means to use programmable logic devices to realize module miniaturization;module integration and optimization through electrical system integration design;redundancy and reconstitution of vital modules and unit equipment to enhance system reliability.

3) COTS based high-reliability electrical products and testing

With the rapid development of technology,the performance and function of current civil-use products is up to and even exceeds space standards,hence makes it possible for several vital space products to be realized based on civil-use technology and products.The only requirement necessary is to match special technology for space missions with civil-use technology or products,thus reducing the development cost and shortening the development period.Hence,adopting Commercial-Off-The-Shelf (COTS) technology to develop onboard and ground test products for the space transport system has become an important trend.The key technologies need to be mastered include device procurement and screening control technology,application of mechanical,electrical and thermal design technology,COTS device error-detection and fault-tolerance technology,and reliability analysis,demonstration and assessment.

4) Multivariate launch

Multivariate launch includes air launch and sea launch.An air launch rocket is launched from an aircraft after it has reached a certain altitude.Compared with a land launch rocket,it is more flexible,rapid and low cost.The relevant key technologies for air launch include a multi-disciplinary optimized design for the rocket,a mechanical design taking into account the delivery/separation concept,research on the rocket/aircraft separation dynamic aerodynamic characteristics and the large angle of attack aerodynamic characteristics,along with an air launch rocket rapid test launching ability.

Sea launch rockets,such as Sea Launch Zenith manufactured by Sea Launch Corporation,China’s LM-11 launch vehicle and the Russian submarine launched rocket,are launched from sea launch pads.Compared with traditional land launch,sea launch is more flexible,safe and efficient.The relevant key technologies and associated design must take account of the sea conditions,a new test and launching procedure,along with an adopted propellant filling mode.

5) Others

There are also other key associated technologies,such as the modular structure design and manufacturing technology,additive manufacturing,remote distributed rapid test and launch technology.

4.2 Reusable Space Transportation System

4.2.1 Solution and mission mode

The traditional mode to access space is hard to meet the increasing commercial requirements due to limitations including the long preparation cycle and fixed launch time.In the future,a novel airline type of flight mode to access space would provide a flexible,frequent,rapid response,and safe service to meet batch-oriented and customized requirements.A reusable space transportation system would be the proper choice.

Reusable technology is a vital approach to greatly reduce the cost of access to space and also the main approach enabling an airline type flight mode to access space in the future.In view of requirements of L2AS,an airline type flight mode in space transportation will come true.

In addition,the mission modes for multi-satellite and piggyback launch can also adopted to the reusable space transportation system as well.

4.2.2 Key technology

The reusable space transportation system revolves traditional axisymmetric reusable space transportation systems and lifting body configuration reusable transportation systems.

1) Traditional axisymmetric reusable space system

The traditional axisymmetric reusable space system includes parachute-landing reusable launch vehicles and vertical takeoff and landing reusable rockets.For the parachute-landing reusable launch vehicle,it is necessary to pay attention to the multi-parachute system design,large buffering airbag design and supersonic parachute-opening.

For the vertical take-off and landing reusable rocket,highly accurate vertical return control technology ensures the rocket to return to a preset landing area along a steady preset trajectory.Landing support is the last step of the vertical return,which is the key to success.

2) Lifting body configurable reusable launch vehicle

? Rocket engine based reusable launch vehicle (RERLV)

The optimization of overall design of the reusable space system in a rocket powered reusable space vehicle involves many aspects such as the overall design,aerodynamics,trajectory,heat proof,structure,power,guidance,navigation and control.The reusable space system aerodynamic configuration and aerodynamic characteristic design is also a problem and can be solved by using hypersonic aerodynamic principles to determine the aerodynamic configuration of a reusable suborbital vehicle.A reusable space vehicle naturally has high requirements for operation and maintenance.Safety,reliability,cost-effectiveness and fault management and maintenance should be considered to ensure critical maintenance and status monitoring of key components and subsystems.Research on the in-orbit flight performance of a reusable vehicle and reentry flight characteristics is conducted to ensure an integrated design for guidance,navigation and control technology.Development in the areas of guidance,navigation and control systems for different phases of flight along with the comprehensive performance optimization for the overall flight tasks is required.

? Combined cycle propulsion reusable launch vehicle

For the combined cycle propulsion reusable launch vehicle,the system design focuses on multi-coupling and the narrow feasible region that limits the system concept.The multi-coupling problem mainly reflects on the mutual restriction between the aerodynamic configuration,propulsion system,structural thermal protection,inner loading space,flight trajectory and control-stability.

The combined propulsion reusable launch vehicle requires combined propulsion.The flight profile is large and the environment changes extremely.The problem is how to model combined power performance accurately and how to take advantages of combined power to make sure the vehicle operates stably during the change of the combined power to optimize performance.

4.3 Interface Standardisation

Serial standard joining and separating devices for launch vehicle have been designed according to satellite configuration,mass,envelope,joining and separating mode.This satisfies the requirements of different satellite launch tasks and solves the problems regarding a lack of standard satellite-launching interface,a large difference in joining and separating devices,often unique and long development cycle,high cost,satellite deployment and so on.According to the components and characteristics of the spacecraft and the payload,the mechanical interface,power interface,data interface and thermal interface should follow a standardised design.

4.4 Propellant Depot [21-23]

As a part of the future space transportation infrastructure,a depot can be parked in different orbits to support different missions.The architectural concept based on a depot for future routine space missions is shown in Figure 1.On one hand,the adoption of a propellant depot enables an enhanced carrying capability for launch vehicles by several times and thus greatly widens the mission scale.On the other hand,for a given mission scale,the propellant depot enables the reduction of the launch scale of launch vehicles,which results in a cost reduction.

Figure 1 The architectural concept based on a depot for future routine space missions [22]

Figure 2 Electromagnetic propulsion launch vehicle system [24]

For a propellant depot,the key technologies include inspace propellant transfer,cryogenic propellant long-term storage in orbit,on-orbit propellant transfer,cryogenic tank pressure control,assembly attitude control for propellant refueling and mass property identification during refueling.

4.5 Electromagnetic Propulsion Launch Vehicle

As an innovative launch vehicle technology,the electromagnetic propulsion launch vehicle system(Figure 2) is able to provide a large thrust and generate a high velocity for the launch vehicle to increase the launching capability and will become a new space launch technology.The launching cost for a GTO payload with an expendable launch vehicle is about 10,000?20,000 US dollars per kilogram,which will be reduced to 200 US dollars by using electromagnetic propulsion launching technology.Thus,it would be an appropriate solution to enable largescale low-cost access to space in the future.

For the electromagnetic launch vehicle,the key technologies include system design,adaptive design technology for large payloads,aerodynamic influence analysis of the electromagnetic launcher,accurate takeoff control,pulse linear motor technology and the emitter.

4.6 Nuclear Propulsion Vehicle

With its development,nuclear propulsion technology will be much safer in the future and may be applied to launch vehicles for orbit transfer missions,which will greatly improve the efficiency of the orbit injection and the orbit transfer.It has great significance for supporting large-scale space exploration and the implementation of space power stations.

For the nuclear propulsion vehicle(Figure 3),the key technologies include system design,nuclear thermal engine,nuclear reactor design,nuclear radiation protection,and controllable nuclear fusion.

Figure 3 The crew nuclear propulsion vehicle

4.7 Space Elevator [23-27]

A space elevator is a system for lifting payloads,and eventually people,from the Earth to space,as shown in Figure 4.The cost of space elevator transportation for a GEO payload unit should be several hundred-dollars per kilogram,an order of magnitude of 2 less compared with current launchers.A space elevator can enable a 24/7 hours of uninterrupted,normal transport,the weekly delivery of hundreds of tons of payloads to space becomes possible.

Figure 4 Space elevator system [14]

For the space elevator,the key technologies include system parameter optimization and design,dynamic design and analysis,tether material design,tether deployment control,climber system optimization design,power system optimization design,anchor design and terrestrial and in-orbit verification &test.

5 INTERNATIONAL COOPERATION AND INNOVATION MODE FOR L2AS IN THE FUTURE

With the globalized economy and associated development in science and technology,each country is actively promoting international space cooperation,continuously expanding channels and fields of cooperation,and evaluating the effectiveness of cooperation.At present,the trend in international cooperation in space indicates the level of cooperation will be further improved.The main theme of cooperation is expanding towards diversification,but with the constant expansion of cooperation there is a gradual increase in non-binding cooperation.The cooperation mode for the large-scale and low-cost access to space could be more flexible in the fields of space science and technology,space utilization and exploitation,space environment and maintenance and space law.Particularly the modes of cooperation,such as project-leader designation,negotiation-exchange,and deep-interaction,could be adopted.

6 CONCLUSIONS AND SUGGESTIONS

1) Commercial space continues to grow and the quantity of payloads entering space will continue to increase rapidly year by year,large-scale and low-cost access to space is not only a necessity in development,but also now being demanded by the global commercial space market.

2) The four major issues for current expendable launchers to meet the mission demands for L2AS include limited payload capabilities,inadequate adaptability and flexibility,long launch cycle,and high cost.Three technical solutions for L2AS are proposed including low-cost design of expendable launch vehicles and RLV,interface standardization,and new concept launchers.The technical development for low-cost access to space needs to be vigorously promoted.

3) The mission modes based on launch vehicles to realize L2AS include multi-satellite launch with a single mission,piggyback launch,and a dedicated launch.An airline type flight mode for access to space needs to be developed in the future.

4) Three modes for future international L2AS collaboration can include project-leader designation,negotiation-exchange,and deep-interaction.It is recommended that international organizations such as UN should coordinate relevant legal restrictions to ensure harmonious adoption.

The era of space transportation revolution is coming.It features multiplying carrying capability,a magnitude-lower cost(1/5-1/10),intelligence,airline flight mode,flexibility and responsiveness,industrialization,providing a significant positive impact on society and daily life.