Patent Publication Number: US-2017373754-A1

Title: System and method for communicating with deep space spacecraft using spaced based communications system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 62/354,965, filed Jun. 27, 2016, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a space based communications system for communications with deep space spacecraft, and more particularly to a space based communication system using communication spacecraft placed at strategic locations to communicate with deep space spacecraft. 
     BACKGROUND OF THE INVENTION 
     According to conventional systems, deep space spacecraft communicate directly with large antennas located on Earth. The network that provides this communication for deep space missions from the United States is NASA&#39;s Deep Space Network (DSN), which is central to the communication and navigation of deep space missions. Europe and other countries have DSNs similar to NASA&#39;s DSN. DSNs provide a two-way communications link for human deep space flights and various unmanned interplanetary space probes to acquire images and other data from the probes. 
     NASA&#39;s DSN include three deep space communication facilities that are located approximately 120° apart from each other to enable consistent communication with deep space spacecraft as the Earth rotates. Each of these facilities includes a plurality of large parabolic antennas for receiving signals from deep space spacecraft. Since deep space spacecraft communicate from locations far from Earth, DSN antennas must have a large aperture in order to be able to receive sufficient energy from signals transmitted by the deep space spacecraft. For example, current DSNs include parabolic antennas as large as 70 meters in diameter. 
     While nominally supporting the requirements of the past and continuing deep space missions, the current DSN infrastructures are not agile enough to keep pace with the currently increasing number and complexity of civil and commercial deep space spacecraft. Adding to this problem is the return to human deep space flight. Due to the critical nature of human space flight, DSN assets will be dedicated to human space missions, further limiting the availability of the already oversubscribed DSN assets to other deep space spacecraft. 
     NASA&#39;s DSN is a prime example of the challenges Earth based DSN systems are facing. In the March 2015 Office of Inspector General (OIG) audit report on NASA&#39;s Management of the Deep Space Network, the OIG points to the challenges and cost of maintaining an aging infrastructure while dealing with the current economic realities of government budget cuts. Compounding this problem is the increasing system demand. According to their own data, NASA&#39;s DSN 34-meter High Efficiency (HEF) and Beam Waveguide (BWG) antennas are 20.7% oversubscribed for 2016-2019. To meet budget cuts, NASA is facing the closure of the three HEF antennas, which would create a 25.5% oversubscription. There is additional concern about even being able to continue the current level of service due to budget constraints preventing the needed long-term maintenance for the aging infrastructure. 
     Within the context of decreasing budgets, government agencies have sought out alternative methods for obtaining the data necessary to support their missions. One alternative method that has gained momentum in the past decade is commercial data buys. Space based communications systems according to the present invention support the commercial data buy framework. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a near-Earth space based communications system, deep-space space based communications system and space based deep space communication method that facilitates communication with deep space spacecraft without burdening the current DSN infrastructure. The space based communications systems and method uses communication satellites in Geosynchronous Earth Orbit (GEO) and High Elliptical Orbit (HEO) and deep-space spacecraft placed at strategic locations throughout the solar system having large, gimbaled/deployable RF antennas and gimbaled/deployable laser communications systems (lasercom) and/or x-ray communications systems (XCOM). The deep-space system spacecraft may be positioned at Sun to Earth Lagrange points, Earth to Moon Lagrange points, and any other Sun to planet Lagrange points for creating a communication backbone throughout the solar system. The system and method may also place the deep-space system spacecraft having deployable antennas at other strategic locations throughout the solar system and even into deeper areas of space, with the communications satellites being placed in geosynchronous Earth orbits, Equatorial orbits, Tundra or Molniya orbits, other High Elliptical Orbit (HEO), Medium Earth orbits (MEO), or low Earth orbits (LEO). 
     Near-Earth space based communications systems satellites (communications satellite) that communicate with deep space spacecraft may be provided in deep space stable-looking orbits around the Earth, or with deep-space space based communications systems spacecraft in strategic locations throughout the solar system to operate as relay stations between deep-space spacecraft and Earth. Both the satellite and spacecraft styles may include gimbaled/deployable antennas, gimbaled/deployable lasercom, and/or x-ray communication (XCOM), and other inclusive communications equipment, including, but not limited to separate low noise amplifiers (LNAs), transmitters, and receivers for communicating with one or more deep space spacecraft. By placing the antennas outside of Earth&#39;s atmosphere and being capable of performing long periods of communication contact, smaller communications antennas than those used on Earth in DSNs can be used. Signals received by the system specific spacecraft from the deep space spacecraft can be stored in the spacecraft&#39;s on-board storage system. Data from the signals received by the deep-space system spacecraft from a deep space spacecraft or deep-space system spacecraft can be stored in the spacecraft&#39;s on-board storage system. No processing would need to be performed on the received data before storage. When data is received from a deep space spacecraft or a deep-space system spacecraft (communications satellite) at a near-Earth or Earth-orbiting system satellite, the stored signals can then be wrapped in the communications satellite provider&#39;s currently used encoding scheme and be burst transmitted directly to existing ground based communications systems for distribution to the end user. 
     Data from deep space spacecraft can therefore be retrieved and downlinked for processing and storage without using a DSN. Thus, additional data from deep space spacecraft can be obtained while reducing the burden on DSNs. Consequently, this allows for a greater number of deep space missions and increases the retrieval of images and other data from deep space missions through increased contact periods outside those provided by ground antennas. Also, this allows for backward compatibility with older deep space spacecraft currently on-station or with new, low cost spacecraft that may normally operate at lower data rates or lower periods of contact to a DSN. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a sample of available orbits around the Earth. 
         FIG. 2  illustrates near-Earth space based communications system satellites (communications satellite) orbiting Earth communicating with deep space spacecraft and to Earth ground stations. 
         FIG. 3  illustrates deep-space space based communications system spacecraft placed at strategic locations throughout the solar system communicating with deep space spacecraft. 
         FIG. 4  illustrates a double gimbaled/deployable reflector antenna with multiple feeds, gimbaled/deployable lasercom and/or XCOM and associated hardware to communicate with a deep space spacecraft in a GEO or near-Earth orbit on a near-Earth space based communications system satellite. 
         FIG. 5  illustrates a double gimbaled/deployable reflector antenna with multiple feeds, gimbaled/deployable lasercom and/or XCOM and associated hardware to communicate with a deep space spacecraft placed at strategic locations throughout the solar system deep-space space based communications system spacecraft. 
         FIG. 6  illustrates a single deployable reflector with multiple feeds and associated hardware to communicate with a deep space spacecraft.  FIG. 6  also illustrates lasercom and XCOM and associated hardware to communicate with a deep space spacecraft. 
         FIG. 7  illustrates a method of receiving a communication from a deep space spacecraft and transmitting the communication to a satellite or ground terminal. 
         FIG. 8  illustrates locations for deep-space space based communications system spacecraft that communicate with deep space spacecraft from Earth-Moon Lagrange points. 
         FIG. 9  illustrates locations for deep-space space based communications system spacecraft that communicate with deep space spacecraft from Sun-Earth Lagrange points and from a deep-space space based communications system spacecraft in a Sun-centered, Earth leading heliocentric orbit that is relatively stationary with respect to Earth at approximately 18.3 Mkm from Earth. 
         FIG. 10  illustrates locations for deep-space space based communications system spacecraft that communicate with deep space spacecraft from Sun-Mars Lagrange points and from a deep-space space based communications system spacecraft in a Sun-centered, Mars leading heliocentric orbit that is relatively stationary with respect to Mars at approximately 24.5 Mkm from Mars. Sun-Mars L 4  and L 5  Lagrange points can be used with care since these points are known to contain Trojan asteroids. 
         FIG. 11  illustrates locations for deep-space space based communications system spacecraft that communicate with deep space spacecraft from Sun-Jupiter Lagrange points and from a deep-space space based communications system spacecraft in a Sun-centered, Jupiter leading heliocentric orbit that is relatively stationary with respect to Jupiter at approximately 59.2 Mkm from Jupiter. Sun-Jupiter L 4  and L 5  Lagrange points can be used with care since these points are known to contain Trojan asteroids. 
         FIG. 12  illustrates a halo orbit that would be used at the Sun-Earth L 1  or L 2  Lagrange points for a deep-space space based communications system spacecraft station keeping. 
         FIG. 13  illustrates a large amplitude halo orbit that would be used at the Sun-Earth L 3 , Sun-Mars or Sun-Jupiter L 1 , L 2  or L 3  Lagrange points for a deep-space space based communications system spacecraft station keeping. The large amplitude halo orbit may be larger than that shown depending on the specific location. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The present invention is directed to near-Earth space based communications system satellites in near-Earth, deep space stable-looking orbits and deep-space space based communications system spacecraft placed at strategic locations throughout the solar system to communicate with deep space spacecraft. Communications with a plurality of deep space spacecraft can be handled simultaneously by looking to various sections of deep space using a plurality of space based communications systems. 
       FIG. 1  illustrates a sample of available stable-looking orbits around the Earth  10 . The near-Earth space based communications system satellites can be disposed as a payload on a satellite in the Geosynchronous Earth orbit (GEO)  1  or Equatorial orbit. Alternatively, the near-Earth space based communications system satellite can be disposed in the Tundra  2  or Molniya  3  orbits. Medium Earth orbit (MEO)  4  and low Earth orbit (LEO)  5  are illustrated for completeness of various Earth orbits. The characteristics of these orbits are described below: 
     
       
         
           
               
               
               
             
               
                   
               
               
                 Orbit Definition 
                 Altitude Range, km 
                 Period, hrs. 
               
               
                   
               
             
            
               
                 Low Earth Orbit (LEO) 
                   150-1,000 
                 1.5-1.8 
               
               
                 Medium Earth Orbit (MEO) 
                 5,000-10,000 
                 3.5-6   
               
               
                 Geosynchronous Earth Orbit 
                 36,000 
                 24 
               
               
                 Inclined 
               
               
                 Geostationary Earth Orbit (GEO) 
               
            
           
           
               
               
               
               
            
               
                 High Elliptical Orbit 
                 Molniya 
                 Perigree: ~500 
                 12 
               
               
                 (HEO) 
                   
                 Apogee: ~40,000 
               
               
                   
                 Tundra 
                 Perigree: ~24,000 
                 24 
               
               
                   
                   
                 Apogee: ~48,000 
               
               
                   
               
            
           
         
       
     
     Deep space spacecraft  200  ( FIG. 2 ) can be communicated with using a near-Earth space based communications system satellite  100  ( FIG. 2 ) that has components including tunable receivers (receiver systems with pre-selector filters and variable LO ultra-stable frequency generators to achieve the proper IF frequency) and tunable transmitters, deep space oriented deployable antenna(s) with a plurality of antenna feeds. The near-Earth space based communications system satellite  100  may be located in a near-Earth  10  ( FIG. 2 ), deep space stable-looking orbit. The near-Earth space based communications system satellite  100  communicates with a deep space spacecraft  200 , stores the return (downlinked) telemetry transfer frames in existing on-board solid-state-recorders (for example) and communicates with specific receive infrastructure for distribution to an end user. The communication between the near-Earth space based communications system satellite  100  and different, multiple deep space spacecraft  200  can be performed by using tunable transmitters and receivers on different frequencies and/or by using polarization variation (switching from right-hand circular polarization (RHCP) to left-hand circular polarization (LHCP)) as required. 
     The near-Earth space based communications system satellite  100  location enables the allocation of the entire bandwidth of a space based communications system  100  to a deep space location of one or more deep space spacecraft  200 . This use philosophy can be applied to multiple near-Earth space based communications system satellites  100  in Earth  10  orbit. 
       FIG. 2  illustrates near-Earth spaced based communications systems satellite  100  communicating with deep space spacecraft  200 . The components of a near-Earth space based communications system satellite  100  can readily be interfaced with commercial communications satellites, leveraging existing infrastructure and providing a secondary revenue source to their original mission. As illustrated in  FIG. 2 , the near-Earth spaced based communications systems satellite  100  can conduct two-way communications with deep space spacecraft  200  and with GPS  300  and MEO/LEO commercial communication satellites  350  and ground terminals (GT)  400 . Since commercial communication satellites  300  and  350  are on a regular launch cycle, they provide continual upgrade opportunities to stay ahead of the increasing number and complexity of civil and commercial deep space spacecraft  200 . 
     The near-Earth space based communications system satellites  100  provide a number of benefits and advantages over current systems. Near-Earth space based communications system satellites  100  provide an offload benefit for deep space spacecraft  200  and DSN antennas, because deep space spacecraft  200  are capable of collecting and downloading more data than they currently do due to the scheduling and communication limits of DSNs. Currently, spacecraft operators coordinate their downlink schedule with the DSN based on DSN availability—not on the spacecraft&#39;s capability. Even with the restricted scheduling method of DSNs, they are oversubscribed for even collecting the minimum volume of required spacecraft data. Near-Earth space based communications system satellites  100  enable deep space spacecraft  200  operators to maximize their data collection and offload the oversubscribed DSNs. 
     Near-Earth space based communications system satellites  100  can be placed in orbits that support near continuous coverage of deep space locations, enabling the allocation of the entire bandwidth of a near-Earth space based communications system satellite  100  to a deep space location of one or more deep space spacecraft  200 . Deep space locations such as Mars, the Moon, and the Lagrange Points can be covered 24 hours per day from Equatorial, Tundra, and Molniya orbits. The Tundra and Molniya orbits are also strategic for the commercial communication satellite operators expanding their fleets to provide greater service to populations that are not near the equator. The components of a near-Earth space based communications system satellite  100  can readily interface with single or multi-purpose satellites, leveraging existing infrastructure and providing a secondary revenue source to their original mission. As illustrated in  FIG. 2 , near-Earth spaced based communications systems satellites  100  can conduct two-way communications with deep space spacecraft  200  and with commercial communication satellites  300  and  350 . 
       FIG. 3  illustrates deep-space spaced based communications systems spacecraft  600  placed at strategic locations throughout the solar system creating an internet-like system using relay spacecraft  600  as hubs for communication with deep space spacecraft  200  and Earth  10 , including along orbital paths between planets and at Lagrange points L 1 , L 2 , L 3 , L 4 , and L 5  between planets and the Sun  900 . The components of a deep-space spaced based communications system spacecraft  600  can readily interface with single or multi-purpose satellites, leveraging existing infrastructure and providing a secondary revenue source to their original mission. As illustrated in  FIG. 3 , the deep-space spaced based communications system spacecraft  600  can conduct two-way communications with deep space spacecraft  200  and with near-Earth spaced based communications systems satellite  100 . Deep-space spaced based communications system spacecraft  600  can also be strategically located between planetary orbits  550  ( FIG. 3  dashed line between Earth  10  and Mars  1004 ), offset from the inner planet pair and at the same velocity as the inner planet or at a slower velocity than the inner planet but able to withstand the gravitational pull of the Sun  900 . As planets move out of alignment, the range between them increases. These between planet deep-space spaced based communications systems spacecraft  600  or relay stations can ease the burden of requiring a high-power telecommunication subsystem on a deep space spacecraft  200  or assist in maintaining the highest data rate transmission possible back to Earth  10 . 
     Space based communications between a deep space spacecraft  200  and Earth  10  can be performed with as many intermediate deep-space spaced based communications systems spacecraft  600  as necessary to reach Earth  10  with the highest bandwidth as possible and the lowest data latency as possible. Current deep space spacecraft  200  use fixed size reflector antennas for communication with Earth  10  through the DSN, with the size of the reflector based on the size of the spacecraft and overall mission system capability. Reflector size, telecommunications hardware and range to Earth  10  effect available data rate, and thus contact time and data latency. Using multiple deep-space spaced based communications systems spacecraft  600  with large deployable antennas, data rates can be increased and data communicated to Earth  10  faster. Deep-space spaced based communications systems spacecraft  600  locations will be easily known, like Earth  10 , by being in relatively stable locations in the solar system respective to Earth  10  through on-board ephemeris files. 
     The near-Earth space based communication systems satellite  100  may include point-to-point radio frequency communication (RF), point-to-point laser communication (lasercom), or point-to-point x-ray communication (XCOM) to/from a deep space spacecraft  200  (deep space referring to any spacecraft outside of Geosynchronous orbit) to any of the following: (a) any Earth-based lasercom station, XCOM station, RF deep space network, e.g., NASA DSN, ESA DSN, JAXA DSN, ISRO DSN or communications satellite teleport  400  as shown in  FIG. 2 ; (b) A near-Earth space based communication system satellite  100  in near-Earth Orbit, e.g., GEO, HEO, Tundra or Molniya orbits as shown in  FIG. 1 ; (c) a deep-space spaced based communications system spacecraft  600  at Earth-Moon Lagrange Points (L 1 , L 2 , L 3 , L 4  or L 5 ) as shown in  FIG. 2 ,  FIG. 3 , and  FIG. 8 ; (d) a deep-space space based communications system spacecraft  600  at Sun-Earth Lagrange Points (L 1 , L 2 , L 3 , L 4  or L 5 ) as shown in  FIG. 3  and  FIG. 9  in a halo ( FIG. 12 ) or large amplitude Halo orbit (example  FIG. 13 ); (e) a deep-space space based communications system spacecraft  600  at Sun-Mars Lagrange Points (L 1 , L 2 , L 3 , L 4  or L 5 ) as shown in  FIG. 3  and  FIG. 10  in a large amplitude Halo orbit (example  FIG. 13 ); (f) a deep-space space based communications system spacecraft  600  at other solar system Sun-planetary Lagrange Points (L 1 , L 2 , L 3 , L 4  or L 5 ) as shown in  FIG. 3 ,  FIG. 11 , and  FIG. 13  for Jupiter and other inner/outer planet communication. 
     For planets from Earth  10  and outside of Earth  10  orbit, the system may include a deep-space spaced based communications systems spacecraft  600  in a leading or trailing Sun-centered heliocentric orbit at a stationary distance from the planet to avoid the solar corona (3.5° from the solar corona) for any necessary Earth  10  contact during solar conjunction where signal degradation or loss would occur, or to be used as a relay station for further distance spacecraft. 
     Caution should be used with all planetary L4 and L5 Lagrange points, as they are gravitationally stable, and dust and asteroids can settle at these locations. 
       FIG. 4  illustrates a functional concept for a near-Earth space based communications system GEO satellite  100 . Communications may be made through RF gimbaled/deployable antennas  101  and via lasercom/XCOM transmitter/receivers/detectors  102 . The RF antennas  101  and lasercom/XCOM receivers  102  can be directly or indirectly attached to a solar array drive  104 , which points a solar array  103  continually at the Sun  900 , allowing the antennas  101  and receivers  102  to continually point at the Sun-Earth L 1  or L 2 . This provides the link between the Sun-Earth L 1 /L 2  Lagrange points and Earth  10 . 
       FIG. 5  illustrates a functional concept for a deep-space space based communications system spacecraft  600  (relay spacecraft) placed at strategic locations throughout the solar system. Communications may be made thru RF gimbaled/deployable antennas  101  and lasercom/XCOM receivers  102 . The RF deployable antennas  101  may be independently gimbaled with one antenna pointing at Earth  10  and the other antenna pointing to a deep space spacecraft or another similar relay spacecraft. The lasercom/XCOM transmitters/receivers/detectors  102  on these spacecraft would be much larger than those described in  FIG. 4  to allow for better signal reception. This provides the link between any deep space spacecraft to the Sun-Earth L 1 /L 2  Lagrange points, near-Earth space based communications system satellites or directly to Earth  10 . As a note, the gimbal on a gimbaled antenna allows the antenna to track the RF signal on any moving spacecraft or body to maintain signal lock, maintain highest possible signal strength and maintain the telecom link for best possible data rate and low bit errors. 
       FIG. 6  illustrates a single deployable reflector with multiple antenna feeds  110  and associated hardware in a near-Earth space based communications system satellite  100  or a deep-space space based communications system spacecraft  600  to communicate with a deep space spacecraft  200 . The antenna feeds  110  may include, for example, an S-band feed, an X-band feed, a K-band feed, and a Ka-band feed. Each of these antenna feeds  110  may be connected to one or more wideband and/or low noise amplifiers  111 , which are connected to appropriate (e.g., S-band, X-band, K-band, and Ka-band) transmitter  113  and receiver assemblies  112 . The system may also include data storage and a controller connected to the transmitter and receiver assemblies, illustrated as part of the Avionics hardware  114 . This configuration can be duplicated for multiple reflectors. 
     Communication with deep space spacecraft  200  may be through transmitters and receivers, as shown in  FIG. 6 , that can be tuned to various channels as set forth by the International Telecommunication Union (ITU) for Category A (&lt;2 Mkm from Earth) near-Earth (although many organizations consider the moon and beyond deep space) and Category B (&gt;2 Mkm from Earth) deep space missions. As noted above, the system may include deployable antennas with multiple feeds that allow the transmission of the signal from the deep space spacecraft with the space based communications system. More than one antenna can be used at the same time to communicate with multiple spacecraft in the field of view as long as there is enough spectral bandwidth between frequencies. 
       FIG. 6  also illustrates laser communication and/or X-ray communication  115 . This illustration aligns with  FIGS. 4 and 5 . Lasercom or XCOM transmitter and receiver  115  are controlled by their own separate electronics assemblies  116  that are controlled by flight software commands through the Avionics Subsystem  114 . This set of hardware allows for very high data rate communication without any interference with RF communication bandwidth limitations. Hardware/components that may be used for the near-Earth space based communications system satellite will be of high TRL level and capable of interfacing to the communication satellite providers standard hardware, practices and interfaces with no or minimal modifications. Hardware/components that may be used for the deep-space space based communications system spacecraft  600  will be of high TRL level and capable of interfacing to the spacecraft providers standard hardware, practices and interfaces with no or minimal modifications. The goal is to achieve as close as possible to factory assembly-line integration. 
       FIG. 7  illustrates a method of receiving a communication from a deep space spacecraft  200  and transmitting the communication to a satellite  100  or ground terminal  400 . In step  701 , the near-Earth space based communications system satellite  100  may receive a signal from any type deep space spacecraft  200 . Alternatively, a near-Earth space based communications system satellite  100  can receive a signal from a near-Earth spacecraft. Orientation would not be an issue since the satellite  100  has gimbaled/deployable antennas. In particular, as shown in  FIG. 6 , an antenna of the near-Earth space based communications system satellite receives the signal and, via an appropriate antenna feed  110  based on the frequency of the signal, provides the received signal to an amplifier  111 . For lasercom or XCOM  115 , the signal from the detector may be provided to the electronics box  116 . In step  702 , the RF amplifier  111  amplifies the received signal and provides the amplified signal to an appropriate receiver assembly  112 . All data from either RF, lasercom or XCOM may be then provided as a digital signal to the spacecraft Avionics hardware  114 . 
     In step  703 , the processed data may be transmitted to an end user, either directly to a ground terminal  400  on Earth  10  or via a satellite  100  orbiting Earth  10  that transmits the data to a ground terminal  400 . Also, the amplified signal may be stored in the near-Earth space based communications system satellite&#39;s  100  data storage. Additionally, commands can be sent from the space based communications system satellite  100  to the deep space spacecraft  200  for start of data retrieval. 
     There may be provided a non-transitory computer-readable medium encoded with a computer program for communicating with deep space spacecraft. The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions for execution. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, a hard disk, magnetic tape, any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EPROM, any other memory chip or cartridge, and any other non-transitory medium from which a computer can read. 
       FIG. 8  illustrates locations of deep-space space based communications system spacecraft  600  that communicate with deep space spacecraft  200  from Earth-Moon Lagrange points. All five Lagrange points are shown with appropriate ranges from either the Earth  10  or the Moon  806 . It is noted that the L 1   801 , L 2   802 , and L 3   803  Lagrange points are metastable so objects around these points slowly drift away into their own orbits around the Sun unless they actively maintain their positions, for example by using small periodic reaction control thrust. L 4   804  and L 5   805  are gravitationally stable in that objects there will orbit L 4   804  and L 5   805  with no assistance. The distances relevant to the Earth-Moon Lagrange points are described below: 
     
       
         
           
               
             
               
                   
               
               
                 Distances to Lagrange Points 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Earth to Moon 
                 ≈384,300 km 
               
               
                   
                 Earth to L4/L5 - 
                 ≈384,300 km 
               
               
                   
                 804/805 
               
               
                   
                 Earth to L3 - 803 
                 ≈384,700 km 
               
               
                   
                 Earth to L1 - 801 
                 ≈326,200 km 
               
               
                   
                 Moon to L1 - 801 
                  ≈58,200 km 
               
               
                   
                 Moon to L2 - 802 
                  ≈64,700 km 
               
               
                   
                 Moon to L4/L5 - 
                 ≈384,300 km 
               
               
                   
                 804/805 
               
               
                   
                   
               
            
           
         
       
     
     Lagrange points L 1  and L 2  are based on the following simplified equation, where R=range between the two main objects, M 1  is the mass of the larger object and M 2  is the mass of the smaller object: 
     
       
         
           
             r 
             ≈ 
             
               
                 R 
                 3 
               
                
               
                 
                   
                     M 
                     1 
                   
                   
                     3 
                      
                     
                         
                     
                      
                     
                       M 
                       2 
                     
                   
                 
               
             
           
         
       
     
     Lagrange point L 3  is calculated based on the following simplified equation: 
     
       
         
           
             r 
             ≈ 
             
               R 
                
               
                 
                   7 
                    
                   
                       
                   
                    
                   
                     M 
                     2 
                   
                 
                 
                   12 
                    
                   
                       
                   
                    
                   
                     M 
                     1 
                   
                 
               
             
           
         
       
     
       FIG. 9  illustrates locations of deep-space space based communications system spacecraft  600  that communicate with deep space spacecraft  200  from Sun-Earth Lagrange points. All five Lagrange points are shown with appropriate ranges from the Earth  10 . It is noted that the L 1   901 , L 2   902 , and L 3   903  Lagrange points are metastable so objects around these points slowly drift away into their own orbits around the Sun  900  unless they actively maintain their positions, for example by using small periodic reaction control thrust. L 4   904  and L 5   905  are gravitationally stable in that objects there will orbit L 4   904  and L 5   905  with no assistance. At least one Trojan asteroid is at each Earth L 4   904  and L 5   905  Lagrange points and possibility more.  FIG. 9  also illustrates a deep-space space based communications system spacecraft  200  in a Sun-centered, Earth leading heliocentric orbit  906  that is relatively stationary at approximately 18.3 Mkm from Earth  10 . This range from Earth  10  allows communication with a spacecraft at the L 3  point  903  by having a line-of-sight angle of greater than 3.5° to limit any signal degradation due to the solar corona. The distances relevant to the Sun-Earth Lagrange points are described below, calculated in the same manner as described for the Earth-Moon Lagrange points above: 
     
       
         
           
               
             
               
                   
               
               
                 Distances to Lagrange Points 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Earth to L1 - 901 
                 ≈−1,503,475.5 
                 km 
               
               
                   
                 Earth to L2 - 902 
                 ≈1,503,475.5 
                 km 
               
               
                   
                 Earth to L3 - 903 
                 ≈−299,198,132.8 
                 km 
               
               
                   
                 Earth to L4/L5 - 
                 ≈149,597,870.7 
                 km 
               
               
                   
                 904/905 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 10  illustrates locations of deep-space space based communications system spacecraft  600  that communicate with deep space spacecraft  200  from Sun-Mars Lagrange points and from a space based communications system spacecraft  600  in a Sun-centered, Mars leading heliocentric orbit  1003  that is relatively stationary at approximately 24.5 Mkm  1003  from Mars  1004 . This range from Mars  1004  allows communication with a spacecraft  600  to the Earth  10  from the far side of the Sun  900  by having a line-of-sight angle of greater than 3.5° to limit any signal degradation due to the solar corona. Sun-Mars L 4   1005  and L 5   1006  Lagrange points should be used with care since these points are known to contain Trojan asteroids. The distances relevant to the Sun-Mars Lagrange points are described below, calculated in the same manner as described for the Earth-Moon Lagrange points above: 
     
       
         
           
               
             
               
                   
               
               
                 Distances to Lagrange Points 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Mars to L1 - 1001 
                 ≈−1,088,338 
                 km 
               
               
                   
                 Mars to L2 - 1002 
                 ≈1,088,338 
                 km 
               
               
                   
                 Mars to L4/L5 - 
                 ≈227,620,000 
                 km 
               
               
                   
                 1005/1006 
               
               
                   
                 Sun to L3 - 1003 
                 ≈−227,620,043 
                 km 
               
               
                   
                   
               
            
           
         
       
     
     The L 1   1001  and L 2   1002  orbit constellation of the  FIG. 10  Sun-Mars Lagrange Points would require only two deep-space space based communications system spacecraft  600  for a fully operational constellation (each spacecraft sees approximately half of Mars  1004  at all times). The Sun  900  would always be visible to both L 1   1001  and L 2   1002  satellites, greatly simplifying system power requirements. Lander and orbiter pointing requirements are simple, given that the deep-space space based communications system spacecraft  600  would always be at the same relative distance from the Sun-Mars line. Interference from the constant solar radiation along the Sun-Mars line (solar exclusion zone that would be disruptive to communications) and certain Earth  10  viewing geometries has been compensated for by using a high amplitude halo orbit. A minor overlap in planetary coverage allows for continuous coverage of a Mars  1004  asset. A deep-space space based communications system spacecraft  600  may be also located, for example, in a Sun center heliocentric leading orbit  1003  at a stationary distance from Mars  1004  for communication with the any deep space spacecraft  200  or space based communications system spacecraft  600  behind the Sun  900  to Earth  10 . The L 3   1003  system may be made available as a relay station for other satellites. 
       FIG. 11  illustrates locations of deep-space space based communications system spacecraft  600  that communicate with deep space spacecraft  200  from Sun-Jupiter Lagrange points and from a deep-space space based communications system spacecraft  600  in a Sun-centered, Jupiter leading heliocentric orbit that is relatively stationary at approximately 56.8 Mkm  1103  from Jupiter  1104 . This range from Jupiter  1104  allows communication with a spacecraft to the Earth  10  from the far side of the Sun  900  by having a line-of-sight angle of greater than 3.5° to limit any signal degradation due to the solar corona. Sun-Jupiter L 4   1105  and L 5   1106  Lagrange points should be used with care since these points are known to contain Trojan asteroids. The distances relevant to the Sun-Jupiter Lagrange points are described below, calculated in the same manner as described for the Earth-Moon Lagrange points above: 
     
       
         
           
               
             
               
                   
               
               
                 Distances to Lagrange Points 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Jupiter to L1 - 
                 ≈−53,295,971 
                 km 
               
               
                   
                 1101 
               
               
                   
                 Jupiter to L2 - 
                 ≈53,295,971 
                 km 
               
               
                   
                 1102 
               
               
                   
                 Jupiter to L4/L5 
                 ≈778,570,000 
                 km 
               
               
                   
                 1105/1106 
               
               
                   
                 Sun to L3 - 1103 
                 ≈−779,003,539 
                 km 
               
               
                   
                   
               
            
           
         
       
     
     The L 1   1101  and L 2   1102 , orbit constellation of the  FIG. 11  Sun  900  to Jupiter  1104  Lagrange Points requires only two deep-space space based communications system spacecraft  600  for a fully operational constellation (each spacecraft sees approximately half of Jupiter  1104  at all times). The Sun  900 , using a large amplitude halo orbit, would always be visible to both L 1   1101  and L 2   1102  deep-space space based communications system spacecraft  600 , greatly simplifying system power requirements. Orbiter pointing requirements are simple, given that the deep-space space based communications system spacecraft  600  would always be at the same relative distance from the Sun-Jupiter line. Interference from the constant solar radiation along the Sun-Jupiter line (solar exclusion zone that would be disruptive to communications) and certain Earth  10  viewing geometries have been compensated for by using a high amplitude halo orbit. A deep-space space based communications system spacecraft  600  may also be located, for example, in a sun center heliocentric leading orbit at a stationary distance from Jupiter  1104  for communication with the any deep space spacecraft or deep-space space based communications system spacecraft  600  offset from the Sun  900  to Earth  10  by 3.5°. The L 3   1103  system may be made available as a relay station for other satellites. The configuration may be also usable for other outer planets and can be extend out to the outer boundary of the solar system. 
       FIG. 12  illustrates a halo orbit  1202  that would be used at the Sun-Earth L 1  or L 2  Lagrange points  1201  for a space based communications system spacecraft  600  station keeping near Earth  10 . The illustration shown here is from the Genesis Mission. This figure would also be similar to the large amplitude halo orbit needed for other planet Lagrange points. 
       FIG. 13  illustrates a large amplitude halo orbit  1302  that would be used at the Sun-Earth L 3 , Sun-Mars or Sun-Jupiter L 1 , L 2  or L 3  Lagrange points  1301  for a space based communications system spacecraft  600  station keeping near a planet  1300 . This type of orbit would be relatively slow in spacecraft velocity, where one orbit may take one Earth year. This allows the orbiting spacecraft to appear as a stationary point to any other spacecraft in communication. The large amplitude halo orbit may be larger than that shown depending on the specific location.