國際低傾角中小衛(wèi)星發(fā)射服務(wù)方案設(shè)計和發(fā)展建議

尚 輝，王清揚，孟 翔，白志富

（中國運載火箭技術(shù)研究院，北京，100076）

0 Introduction

The development of small satellite technology and its business application brings lots of market requirements of launch service for medium and small satellites. Their launch service has become an important subdivided market. Besides the launch requirements from conventional orbits such as Sun synchronous orbits, more and more launch requirements to low inclination orbits for medium and small satellites emerge in global market.

1 Low Inclination Orbits

1.1 Definition and Classification of Low Inclination Orbits

The low inclination orbits conventionally refer to the orbits with an angel less than 30° between the planes of satellite orbit and Earth equator, and is also divided into low, medium and high orbits by the altitude ranges of 100～2000 km, 2000～20 000 km and above 20 000 km.Currently, the launch requirements mainly concentrate on the low inclination low orbits and the low inclination high orbits. The low inclination orbits with orbit inclination less than 15° are also called near equatorial orbits.

1.2 Low Inclination Low Orbits and Characteristics of Their Launch Services

When the satellites operating on low inclination low orbits, the track of sub-satellite points locate in the low latitude area between 30° N～30° S, where about half of the world population are living and is rich in agricultural, fishery, mineral and forestry resources.Many world class transportation paths are also in this area.Meanwhile, it is one of the regions where developing nations converged, whose infrastructures are under-developed. Great demands on satellite application,such as communication, remote sensing and so on, are emerging in the area.

Compared with the satellites operating on conventional orbits such as SSO, for same satellite number and same single-satellite service capacity adopted,by operating on low inclination low orbits, the satellites realize more converged and higher efficiency services to the nations and regains in low latitude area, such as communication, remote sensing and so on.

Due to the great cost of energy during orbit plane transfer, the launch point of low inclination low orbit should be located at or near the sub-satellite points. Only if the latitude of launch point is greater than orbit inclination, the satellite can be launch into orbit without loss of launch capacity caused by orbit plane transfer.When the latitude of launch point is larger than the orbit inclination, during reducing a dozen degree of inclination by orbit plane transfer, it usually costs more than 90%launch capacity of the launch vehicle. Considering these,in order to conduct low inclination low orbit launch, the launch point should be located in low latitude area.

1.3 Low Inclination High Orbit and Characteristics of Their Launch Services

Low inclination high orbits are represented by Geosynchronous Earth Orbit (GEO) that is a circular orbit on Earth equatorial plane (0° inclination) with altitude of about 36 000 km. The satellite with GEO as operational orbit is conventionally sent by launch vehicle to a Geosynchronous Transfer Orbit (GTO) that is also a low inclination high orbit. GEO and GTO are among the low inclination orbits that utilized earliest and most frequently, as well as the low inclination high orbit launch service.

During past 10 years, as the GEO orbital position and frequency resource is becoming constrained, high compression ratio communication technology are developed and operation duration of existed satellites are extended, launch requirements from newly built conventional big scale high orbit telecommunication satellites have reduced significantly. Meanwhile, as the application of miniaturization and electric propulsion in high orbit communication satellites, the develop and commercial utilization of small scale high orbit communication (also named “Small GEO”) have become more and more popular, which can meet the requirements from small or medium enterprises especially the newcomers of satellite operation, as well as the requirements from mature satellite communication operator such as the gap filling based on existing orbital position and the occupying of orbit position and frequency resource. Furthermore, on-orbit mission extension service for high orbit satellites based on medium and small spacecraft have been emerged, which provides services including propellant fueling, attitude and orbit control taking over and so on, to make full use of existed GEO satellites. These spacecraft have been evaluated in flight mission. Their launch services bring new low inclination high orbit launch requirements of medium and small satellites to launch service market.

Most launch sites in the world locate at the locations with latitudes greater than 0°, from where the satellites are sent to a GTO with an inclination greater than 0°.After that, multiple satellite propulsion system operations are needed to conduct orbit transfer, in order to conduct orbit inclination reduction and circulation that make satellites enter into GEO, their final orbit on equatorial plane. Due to the high orbit altitude, compared with the low inclination low orbits, a low inclination high orbit needs less velocity variant for orbit inclination reduction and allow the propulsion systems of launch vehicle and satellite to conduct orbit maneuver with longer duration and smaller thrust. Therefore low latitude of launch point is not the crucial factor for whether such launch mission is feasible, but is still benefit for enhancing the payload capacity, reducing energy and time consumed during orbit transfer. It is good for reducing duration and risk of satellite deployment, and the propellant of satellite saved can be used for future orbit and position keeping, and so extending the operating life of spacecraft.

2 Market Status of Launch Service for Low Inclination Medium and Small Satellites

2.1 Status of Launch Service for Low Inclination Low Orbit Medium and Small Satellites

Most of the launch sites in the world locate at middle latitude areas. Few launch sites have latitudes less than 30°. Only 2 near equator launch sites including Guiana Space Center and Sriharikota Launch Site have latitudes less than 15° that has a high efficiency for launch of near equatorial low orbit mission.

The launch vehicles for low orbit missions operating in these 2 launch sites are including Soyuz-ST, VEGA and PSLV, whose launch capacity is in the class of several tons (their launch capacities respectively: LEO 8 t / SSO 4.9 t, SSO 1.395 t, LEO 3 t / SSO 1.105 t). Their main missions are targeted to SSO and they have little chance for low inclination low orbit launch. Considering the less than 1 t mass on 1 orbit plane for each mission from most launch requirements, piggyback launch or multi-satellite combination launch between multiple customers is needed but normally causes a long waiting duration and lots of coordination among different customers.

Another way to meet the requirements for low latitude of launch point is mobile launch by which the launch vehicle and its launching system are transferred to low latitude area and conducting the launch. Besides sea launched LM-11H launch vehicle, in current international market, it is reported by media that commercial launch services basing on mobile launch are also including the Launcher One of Virgin Orbit from USA and the sea launch vehicle of S7 Corporation from Russia. The Launcher One failed in maiden flight at the beginning of 2020 and succeeded in its 2nd flight test in February,2021 (shown in Fig. 1). The S7 Corporation acquired the assets of International Sea Launch including launch platform and so on and released launch service business plan basing on it, which had no progress reported till now.

Fig. 1 Air Launch of Launcher One

2.2 Status of Launch Service for Low Inclination High Orbit Medium and Small Satellites

The launch masses of medium scale high orbit communication satellites are around 1～2 t, which are 1/5～1/3 of conventional high orbit communication satellites, while the launch masses of small scale high orbit communication satellite are at the class of 100 kg to several hundred kg. Among the international market, for the launch requirements of these low inclination high orbit medium and small satellites, launch services are mainly provided by multi-satellite combination launch based on conventional launch vehicles for dedicated launch of high orbit satellites. Several low inclination high orbit medium and small satellites are accomplished by multi-satellite launch of Arian 5, Proton M and so on.

3 International Market Exploration of Low Inclination Medium and Small Satellite Launch Service of China

3.1 International Market Exploration of Low Inclination Low Orbit Medium and Small Satellite Launch Service

Aiming at the international market chance on field of low inclination low orbit launch service, explorations have been conducted, focusing on the low inclination launch requirements from international customers.

Stimulated by these market requirements, LM-11H sea launched launch vehicle was developed. Its maiden flight was in Jun, 2019 from the Yellow Sea (shown in Fig. 2) while the 2nd flight was in Sep, 2020, also was the 1st application flight and marked the starting of its commercial operation. LM-11H and its launching system have the ability to ship to low latitude sea areas for conducting low inclination low orbit launch service. A good foundation has been set for the low inclination low orbit launch service for international market.

Fig. 2 Sea Launch of LM-11H

3.2 International Market Exploration of Low Inclination High Orbit Medium and Small Satellite Launch Service

Low inclination high orbit medium and small satellite launch requirements from international customers have been receiving by launch providers in China during the past years, and many launch requirement analyses have been conducted. On Oct. 24th,2014, Luxspace-4M moon mission spacecraft, which was a low inclination high orbit small satellite, was successfully launched by LM-3C (shown in Fig. 3).

Fig. 3 Luxspace-4M Moon Mission

Meanwhile, dealing with the international market competition in the field of high orbit satellite communication, the “Small GEO” solution is provided and marketed by China space industry basing on DFH-3E satellite platform. To meet the launch requirements from these Small GEO satellites, the launch services have been put forward which is represented by LM-2C.

4 Analysis on Launch Service Solution for Low Inclination Medium and Small Satellites

In order to meet the market requirements of low inclination launch services, launch service solution for low inclination medium and small satellites are analyzed in terms of the following aspects.

4.1 Launch Mode Selection

4.1.1 Fixed Launch or Mobile Launch

The fixed launch is a conventional way of launching,by which the launch vehicle is launched based on a fixed launch pad or platform that confined the launch point to a fixed location. The launch missions in the 4 main launch sites of China adopt this mode. It is a mature way of launch for large scale launch vehicle, which can conduct launch missions frequently and continuously. If the fixed launch is used to a new selected launch point, it is needed to finish the infrastructure construction and equipment installation, which needs a long duration.

The mobile launch refers to the way of launching with launch point that can be freely moved in wide geographical area according to mission requirement.Compared with the fixed launch, the mobile launch is a new application for commercial launch service, by which the launch vehicle and its launching system are movable that makes the selection of launch points freely. The launch operation of mobile launch is not based on fixed infrastructures, so it has low demand on local infrastructure at launch point. 1 type of launch vehicle and 1 set of its launching system can be used in multiple launch locations for different types of launch missions,and the launch vehicle and its launch system can be withdraw or redeployed to other locations if needed.

When the launch location can be selected at mature launch sites, the fixed launch is the first choice, as it can take maximum avail of current resources. When the launch point locates at other locations, to have launch ability quickly, the mobile launch is the first choice.

4.1.2 Mode Selection for Mobile Launch

The usual modes of mobile launch include land mobile launch, air mobile launch and sea mobile launch.

The land mobile launch is based on a launching vehicle or a mobile launch platform, as well as their mobile ground equipments, which is suitable to conduct launch mission from the launch point on open ground.When launching from a newly selected launch point located at land area without constructed launch sites,compared with the fixed launch basing on constructing launch site infrastructure, the land mobile launch mode can quickly initiate a first launch from this location.

The air mobile launch is conducted with aircraft and airborne launch vehicle. The maneuver to the launch point of airborne launch vehicles can be conducted quickly and freely while the aircraft can partly act as the first stage of the launch vehicle by giving it an initial altitude and a velocity that enhance its launch capacity.Confined by the lift capacity and volume of aircraft, the 500 km SSO launch capacity of airborne launch vehicle in current global market (e.g. Launcher One, Pegasus) is not greater than 300 kg class according to public reports.

The sea mobile launch is basing on watercraft including ships and marine platforms. Comparatively,watercrafts have lower maneuver speeds, but greater carry capacities and fewer costs, so the lift-off mass and operation space of the launch vehicles are not limited by watercrafts and have great potential for launch capacity enhancement. On the other hand, China has a good industrial foundation in ship and marine platform building and the sea launch vehicle, such as LM-11H, has already accomplished development and put into launch service operation.

Comprehensively considered, the sea launch is currently the best mobile launch mode for launch service.

4.1.3 Vehicle Propellant Selection between Liquid and Solid

Liquid propellants have higher efficiency for their greater specific impulses, especially when used to the last stages of launch vehicles for high orbit missions. When a launch mission can be conducted from a conventional launch site where there is a mature liquid propellant launch vehicle with suitable launch capacity, the launch solution based on liquid propellant launch vehicle is prior.

Solid propellant launch vehicles need no equipment for propellant storage, fueling and processing during launch operation. There is no risk of marine pollution from toxic conventional liquid propellants when adopted to sea launch, while there are no problem from marine storage and utilization of cryogenic and explosive propellant represented by liquid hydrogen. So although having less specific impulse than liquid, with more simple launching system, safe and convenient launch operation, the solid propellant is priority for sea launch.

4.2 Launch Vehicle Selection

4.2.1 Launch Vehicle Selection for Low Inclination Low Orbit

In order to meet the launch requirements for low inclination low orbit, the dedicated launch by small scale launch vehicle of single or multiple satellites can be selected, as well as the piggyback launch based on launch missions for big scale low inclination satellites with residual launch capacities.

When an LM-11 or LM-11H conducts low inclination low orbit launch, the launch capacity for the 500 km low inclination circular orbits is not less than 600 kg, which is a suitable capacity for single launch of 1 medium scale satellite or combined launch of multiple small satellites. The LM-11 and LM-11H have accomplished 11 launch missions including 2 from the sea which established the launch capacity for low inclination low orbits.

Smart Dragon 1 (SD-1) launch vehicle who accomplished maiden flight on Aug. 17th, 2019 (shown in figure 4) is also a solid launch vehicle with mobile launch ability by land or sea launch, but has a smaller launch capacity than LM-11. When SD-1 launched from low latitude locations for low inclination low orbit missions,its launch capacity for 500 km low inclination circular orbit is not less than 200 kg, which is suitable for dedicated launch of 1 or several small satellites.

Fig. 4 Maiden Flight of SD-1

LM-8 launch vehicle, which accomplished its maiden flight on Dec. 22nd, 2020 (see figure 5), can launch satellites into low inclination low orbits from Wenchang Space Launch Center (WSLC), with launch capacity for 500 km low inclination circular orbit greater than 5000 kg that is suitable for large scale satellites.During these missions, LM-8 can conduct piggyback launch service for low inclination low orbit medium and small satellites.

Fig.5 Maiden Flight of LM-8

4.2.2 Launch Vehicle Selection for Low Inclination High Orbit

The dedicated launch solution basing on mature LM-2C launch vehicle is selected to provide launch service to low inclination high orbit medium satellites,represented by the Small GEO, with launch mass of 1～1.5 t, and is also available for combined launch of multiple small high orbit satellites. This LM-2C launch solution has 2 modes including the “2 stage launch vehicle + satellite propulsion module” mode and the 3 stage launch vehicle mode. When LM-2C launched from Xichang Satellite Launch Center (XSLC) has the maximum launch capacity, the orbit inclination is 28.5°,so more propellant consumption from propulsion system of launch vehicle and satellite is needed for entering into a final operation orbit with inclination 0°.

LM-7A and LM-5 launch vehicle, as well as the LM-8, can launch the high orbit satellites into a target orbit with 18.5° or lower inclinations from WSLC with the benefit of the lowest inclination among 4 land launch centers of China. During these missions, medium or small satellites can be launch into low inclination high orbits by dedicated launch with multiple satellite combination or by piggyback launch basing on residual launch capacity of another planned launch missions.

The launch service solutions basing on sea launch from equatorial sea area are also feasible, in which the dedicated launch provided by new sea launch medium scale launch vehicles are expected. By these launch service solutions, the low latitude advantage of equatorial area is taken to maximum the launch capacity while the satellite is directly sent into GTO with 0° inclination that makes the satellite enter into GEO without inclination variation maneuver and corresponding propulsion consumption, while the deployment duration can be shortened and the satellite platform can be simplified.

4.3 Launch Point Location Selection

Low latitude launch point is the key to low inclination low orbit launch services while a great advantage for high orbit launch services on their launch capacity. So the location selection of launch point is requested for low inclination launch service.

4.3.1 Launch Point Locations in China

Basing on integrated infrastructures established and the location with latitudes of 28.5° and 19.5°, XSLC and WSLC are available for low inclination high orbit missions, as well as for the low inclination low orbit missions with inclination around 19.5～30°.

In territory of China, in order to efficiently conduct launch service to an orbit with inclination lower than 19.5° or to send medium and small satellites into GTOs with lower inclination that is more closed to the equatorial plane，it is suggested to conduct sea or land mobile launch from launch point located in the sea area or islands to the south of the Hainan island.

4.3.2 Launch Point Locations outside China

Compared with those from launch points located in China territory, the launch mission conducted from a launch point outside normally has a longer transportation journey and duration, as well as more coordination among correspondent parties. But it is available to reach equatorial locations with lower latitude by launching outside China, which benefits low inclination missions,especially low inclination low orbit missions. The cooperative launch operation is also expected to be a new mode for international space cooperation.

The sea launch for low inclination launch is suggested to be utilized with the launch point selected from the locations in international waters in equatorial region, or sea area besides low latitude countries basing on international cooperation. Land mobile launch basing on international cooperation with low latitude countries are also expected.

5 Proposals of Developing Low Inclination Launch Service for International Medium and Small Satellites

In order to meet the market requirements from the field of low inclination low orbits and low inclination high orbits of medium and small satellites, it is proposed that the low inclination launch service should be further developed.

a) Serving to both domestic and abroad satellites.

The low inclination launch service can be provided to satellites of the in-orbit-delivery business of China.While cooperating with customers from the countries in low latitude area to conduct the low inclination launch service to their self-developed satellites also has good market prospect.

b) Launching from both domestic and abroad locations.

According to target orbit, customer cooperation mode and conducting timing of the launch service project,the launch point can be selected from both domestic and abroad locations. It is suggested that the low inclination launch service should start from the missions that can be conducted from territorial water and the near sea areas.Then the low orbit mission with lower inclination can be carried out from international waters outside China. After that, if demanded and invited by customers, the launch service can conducted from territorial water or land of customer countries.

c) Focusing on both high and low orbit satellite market.

Focusing on low orbit launch requirements from medium and small satellite, the ability of LM-11H and SD-1 sea launch service should be further enhanced to be the key to promote low inclination low orbit international launch service to medium and small satellite market.

Meanwhile, following the development and business application of Small GEO communication satellites,besides the combined launch or piggyback launch basing on existing launch vehicles, new types of sea launched launch vehicles are suggested to be developed to meet the requirements, which can conduct high orbit launch from equatorial sea area. This will establish a new business noted “Small GEO + equatorial sea launch” and introduce the sea launch capacity of China into the market field of high orbit launch service.

6 Conclusion

As the development and implication of space technology all over the world extending to the low latitude countries and regions, more and more requirement of low inclination satellites have raised while the market for low inclination launch service is promising.By business practice, a good foundation on this field has been set. Basing on it, international low inclination launch service should be developed, which will bring well-beings to more people on broader area of the world.