DEVELOPMENT OF GEOSYNCHRONOUS SATELLITE SERVICING Andrew E. Turner Space Systems/Loral. Abstract

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1 DEVELOMENT OF GEOSYNCHRONOUS SATELLITE SERVICING Andrew E. Turner Space Systems/Loral Abstract Servicing of geosynchronous (GEO) spacecraft would permit removal of the large propellant tanks used for north-south stationkeeping (NSSK) and orbit-raising (OR), while avoiding the power and OR maneuver duration requirements for present-day electric propulsion. The propulsion subsystem is removed from the spacecraft except for a modest arrangement capable of performing east-west stationkeeping and momentum wheel unloading, permitting the spacecraft to be designed to maximize revenue. In a GEO communications spacecraft designed for on-orbit servicing, the revenuegenerating payload would be expanded to fill the volume formerly occupied by the propellant tanks. ayload mass, power, and heat rejection capability would also be expanded. Thus, payload capability to generate revenue increases, which provides the economic incentive for the development of on-orbit servicing. Reduction in spacecraft cost would also provide an incentive for servicing. It would appear that economic benefits result from introducing servicing for GEO spacecraft. Economic benefit is obtained as the spacecraft payload becomes power-limited in a GEO spacecraft optimized for on-orbit servicing. Any additional power capability obtained from increasing the size of the solar arrays or batteries is made available to the payload to maximize revenue. Any additional power that is made available by redesigning the power subsystem or by other means can be translated into additional revenue, creating an economic incentive to introduce servicing for GEO spacecraft. Electric propulsion for on-orbit stationkeeping, a possible alternative to on-orbit servicing, requires considerable power to operate and might not be competitive if additional power can be used to generate increased revenue. The development of spacecraft servicing from current GEO operations, which do not involve on-orbit servicing in any shape or form, is the topic of this paper. 1

2 1. OVERVIEW (sections of paper) Section Topic 2 Commercial Geosynchronous (GEO) Satellite Servicing Issues 3 Recent GEO developments that impact servicing 4 Benefits from Servicing: Revenue Up and Cost Down 5 Steps in evolution of servicing 6 Core Technologies to Enable GEO Servicing 7 Conclusions 8 Background 9 References 2. COMMERCIAL GEOSYNCHRONOUS (GEO) SATELLITE SERVICING SATELLITE ISSUES ro (Issues favoring GEO satellite servicing) Over 100 satellites in one orbital plane 1, therefore the servicing vehicle reach multiple satellites with V of a few meters per second All satellites in GEO require 50 m/s V annually for north-south station keeping, therefore an on-orbit use exists for propulsive servicing Orbit raising V following launch of m/s to reach GEO, therefore an orbit-raising use exists for propulsive servicing Advantageous to delete large tanks used for orbit-raising V, this frees up volume for payload Con (Issues not favoring GEO satellite serving Current GEO spacecraft operate reliably for 15 years 2 Long-term propellant storage, power, payload demonstrated Major effort in program is completed shortly after launch Some degradation near end of life is accepted Approaching an operating GEO spacecraft with a second spacecraft is not tolerated No price difference between launch of servicing supplies and launch of commercial satellite 2

3 3. RECENT GEO DEVELOMENTS THAT IMACT SERVICING ro (Developments favoring GEO satellite servicing) Scalable payload payload can generate a high number of tight spot beams as opposed to a few regional beams as K-, V-bands develop to expand satellite revenue more spot beams to individual ground sites are added when the spacecraft is designed and built Deployable thermal radiators increase heat rejection capability of spacecraft to enable payload growth Con (Developments not favoring GEO satellite servicing) Electric ropulsion (E) provides an alternative to propulsive servicing less than 10 kg per year of fuel power for E available because payload cannot use all of solar array power due to payload thermal dissipation limits Regulatory limits International and national regulatory bodies (ITU, FCC) ower Flux Density--cannot add power to payload and make it available on the ground due to interference issues 4. BENEFITS FROM SERVICING: REVENUE U AND COST DOWN Revenue increased by adding throughput to the payload by increasing the number of transponders, not increasing the power per channel Cost to build the satellite is not expected to be dramatically reduced by adding onorbit servicing--only minor cost items such as certain thrusters, tanks, and support structures are deleted Cost to build satellite would tend to increase if servicing were added because a considerably higher number of transponders would be installed, but revenue generating capability increases faster than cost Cost to launch satellite can be decreased by 25% if orbit-raising servicing is introduced and spacecraft is launched to a staging orbit Cost to launch satellite could remain the same if satellite is launched directly to GEO instead of performing its own orbit raising maneuvers Gain in revenue larger in magnitude than cost reduction/increase 3

4 5. STES IN EVOLUTION OF SERVICING These steps are evolutionary, not revolutionary (net present value at launch tends to increase with each step) re-servicing steps (see Figure 1) Step Description 1 Current GEO Satellite 2 Satellite propellant tanks are grouped near the anti-earth side of the satellite, providing more volume for the earth-facing payload, also lower within the satellite body as it sits on the launch vehicle so the center of mass is lower within the launch vehicle fairing, which is also advantageous 3 Satellite large propellant tanks are migrated to a separable apogee stage 4 Satellite without large propellant tanks can be efficiently launched on a vehicle with Direct Geosynchronous Injection (DGI) capability, see Table 1 Early servicing--one path: orbit-raising servicing (see Figure 1) Step Description 5 Satellite is launched without apogee stage, therefore a launch vehicle that could carry one satellite before can now carry two. Apogee stage is attached to satellite by a servicing vehicle in a staging orbit at km altitude (Figure 2), apogee stages launched on a medium-cost, medium-risk foreign launch vehicle like Ukrainian Zenit 3,4 or Chinese Long March 3,4 Economic considerations for the steps displayed above and later steps are displayed in Figure 3, including the net present value (NV) of a typical spacecraft at the time of launch. NV at launch tends to increase with each evolutionary step. 4

5 High Cost Launch High Cost Launch High Cost Launch Circular Staging Orbi t Rendezvous High Cost Launch Moderate-Cost launch for Apogee Stage Dual Launches Apogee Stage includes modest attitude and thermal control capability 1. Current GEO spacecraft 2. Spacecraf t with ropulsion Module (2005) 3. Spacecraft with detachabl e Apogee Stage (2007) 5. Spacecraft, apogee mated in staging orbit (Figure 2). Globalstar-derived space tug handles rendezvous & docking (2010) High Cost Launch 4. Direct GEO Insertio n (2007) No Apogee Stage Figure 1. re-servicing and Early Servicing Steps (Steps 1-5) 5

6 Geosynchronous Orbit (GEO) Transfer orbit apogee is in the plane of the equator, however due to inclination most points lie north and south GEO orbit is in the plane of the equator Staging Orbit 4. Separation S Staging Orbit 1. Launches 3. Orbit-Raising. Delta-V of 2400 m/s Transfer Orbit S A 2. Rendezvous A-S Apogee Van Allen Belts Geosynchronous Orbit A Disposal Orbit for Apogee Stage Geosynchronous Orbit Current spacecraft are launched into transfer orbit with apogee at geosynchronous altitude, km, and perigee at an altitude of about 200 km. The spacecraft performs maneuvers at apogee to circularize the orbit over a span of several days. This orbit is not appropriate for long-term use such as servicing missions due to perturbations that move apogee out of the plane of the equator, which causes an unacceptably large increase to the delta-v to reach GEO. Spacecraft (S) and Apogee Stage (A) are launched separately and are assembled in staging orbit. The apogee stage carries the spacecraft to a circular orbit 300 km above GEO and is then jettisoned. The spacecraft lowers altitude to GEO. The orbit raising operation takes a few days. In this case the primary task for servicing is to mate the apogee stage with the spacecraft in staging orbit. The apogee stage is launched on a medium-cost, medium-risk vehicle. Figure 2. Orbit Raising Strategies for current spacecraft (left) and using a staging orbit (right). 6

7 Second path to servicing: launch direct to GEO, then servicing on orbit Step Description 6 Captive-carry servicing for north-south station keeping (NSSK) 8 Refueling for NSSK 10 Captive-carry NSSK with new low-cost, high-risk fuel launch (Aquarius 5 ) 12 Refueling for NSSK with new low-cost, high-risk fuel launch 14 Refueling, on-orbit supply of fluid for massive heat sink Servicing: orbit-raising servicing and on-orbit servicing Step Description 7 Captive-carry servicing for north-south station keeping (NSSK) 9 Refueling for NSSK 11 Captive-carry NSSK with new low-cost, high-risk fuel launch (Aquarius 5 ) 13 Refueling for NSSK with new low-cost, high-risk fuel launch 15 Refueling, on-orbit supply of fluid for massive heat sink 7

8 Figure 3. Steps displayed here correspond to evolutionary steps in the development of servicing discussed on the preceding pages. Even numbered steps from 4 to 14 assume launch directly to GEO; odd-numbered steps from 5 to 15 assume launch to staging orbit and servicing to support orbit raising to GEO. Steps 1-4 occur before servicing develops. The assumptions made in support of this graph are presented on the following page. 8

9 Background to graph presented in Figure 3: Spacecraft baseline (no servicing) Dry mass: 1550 kg ropellant mass: 2100 kg (bi-prop: monomethyl hydrazine, nitrogen tetroxide), no electric propulsion 70 transponders, C- and Ku-band Cost: $150 M, Annual revenue: $100 M/year Launch cost: $100 M, insurance: 12% of sum of satellite and launch costs ayload mass is about one-third of total mass, cost is about half of total cost Assumptions for satellite modifications as dry mass can be increased Half of satellite dry mass increase is available to increase payload mass Revenue generating capability increases linearly with payload mass ayload cost increases at 60% of payload mass increase due to economy of scale Nearly all recurring cost increase for satellite is in the payload (development costs in the $5-15 M per satellite range added for some evolutionary steps) Satellite recurring cost percentage increase is 0.3 of revenue percentage increase, cost, revenue increases are percentages of $150 M cost and $100 M/year revenue Orbit raising servicing assumptions Apogee stage cost is $10 M Apogee stage launched in dual launch by medium-cost foreign launch 3,4 for $30 M On-orbit servicing assumptions 6,7 Service available for $6 M annually using medium cost foreign launch Service cost reduced to $4.5 M annually using low-cost high-risk Aquarius Addition of refueling capability to satellite increases cost by $10 M but lowers servicing cost by 12.5% from reducing station keeping fuel consumption Assumptions for financial accounting Assess net present value (NV) at launch of revenue and servicing cost Constant revenue and costs throughout 15-year on-orbit lifetime 30% discount rate for revenue NV (high end of commercial range) 8 10% discount rate for servicing cost NV (low end of commercial range) 8 Annual operating cost: $1 M/year, 10% discount rate since this is a cost Secondary benefits of servicing such as inspection of other satellites not capable of being serviced are ignored. Taxation and effort to raise capital also not included 9

10 6. CORE TECHNOLOGIES TO ENABLE GEO SERVICING Space Qualified umps Transfer of propellant, other fluids from one satellite to another Active thermal control on GEO satellites umped loops instead of passive heat pipes Eliminates thermal dissipation constraint on payload--payload becomes power-limited: any additional power available used to generate revenue ayload consumes power previously available for Electric ropulsion, and uses it for generating increase revenue umps are under development for Orbital Express (OE) Mission 9 Low-Cost, High-Risk Launch Launch propellant, other fluids, consumables at a lower cost than satellites High risk acceptable because consumables are low cost and replaceable Concept envisioned by Dr. David Whalen 10, former DARA technology manager, at the time when the Orbital Express 9 program was being initiated Aquarius 5 launch vehicle concept under development, effort funded by a California Space Grant Commercial programs, first step: medium-cost, medium-risk foreign vehicles Solar Orbit Transfer Vehicle (SOTV) 11,12,13 Transfer fluids, other items from low orbit to staging orbit or GEO Currently USAF-funded program for SOTV in work at Boeing-Seal Beach 4-year, $48 M program Solar thermal or solar electric propulsion envisioned Multiple month transfer time acceptable for fluids delivery, not for most commercial satellites Second generation vehicle might move satellites in days instead of months Tank technology for massive on-orbit heat sink Heat sink levels thermal load for GEO spacecraft, goal would be a 7-day span to take advantage of lower weekend business traffic Working fluid might be a slush of material in water that forms a solution at elevated temperature and absorbs heat while material is going into solution Working fluid loaded on-orbit, not carried in client satellite through launch (continued on the next page) 10

11 Core Technologies to Enable GEO Servicing (continued) Satellite Rendezvous and Docking Early development involves satellites where the payload is not in operation One evolutionary pathway leads to non-intrusive mechanical/electrical docking where the servicing vehicle docks with a satellite in which the payload is fully operational and the servicing vehicle performs station keeping for the client satellite via captive-carry maneuvers Another evolutionary pathway leads to simple fluid transfer where the client satellite is refueled annually, or at the beginning of its operational life When the technology is mature, tons of slush composite fluid may be transferred to satellites in GEO to serve as a heat sink. When this capability is developed the captive-carry maneuver technique described above might become obsolete--this could occur circa 2030 Rendezvous and docking technology is under development for the Orbital Express 9 7. CONCLUSIONS Net resent Value (NV) of satellites at launch improves with servicing primary benefit from increasing revenue, secondary benefit from reducing cost evolutionary steps possible where NV improves with each step GEO on-orbit servicing could begin circa 2015, orbit raising servicing could begin Core technologies for servicing require development if GEO servicing is to evolve: pumps, low-cost fuel launch, Solar Orbit Transfer Vehicle (SOTV), heat-sink U.S. Government (USG) can invest in capabilities to be adopted and sustained by commercial entities, these capabilities undergo evolution for commercial uses Commercial evolution of servicing permits leveraging of medium-cost, mediumrisk foreign launch vehicles not usable by USG for support. In time this capability will receive competition from a domestic low-cost, high-risk launch vehicle Orbital depots for storing consumables may not make sense for military missions to low orbit due to potential vulnerability of depots, but depots would be beneficial for GEO commercial and USG civilian and military missions can store supplies for more than a year--this permits slow, cost-effective resupply by SOTV GEO depots relatively invulnerable due to extreme altitude, over kilometers 11

12 8. BACKGROUND Table 1. Beginning of Life (BOL) and End of Life (EOL) capability for 5 LV families. BOL mass refers to spacecraft mass at beginning of operational lifetime in geosynchronous (GEO) orbit following orbit raising maneuvers performed using bi-propellant thrusters. A 100 kg LV adapter assumed for the 4 large LV families. Launch Vehicle BOL Capability for Direct GEO (GSO) Insertion (kg) Availability Date ROTON 14 K 1800 Currently available 2590/1990 ARIANE V Versatile /2810 DELTA IV M+ (5,4) 2583 August /2760 ATLAS 15 V /2620 ATLAS V /3010 ATLAS V /3350 ATLAS V /3640 Soyuz-Fregat 480 Currently available 700/540 Approximate GEO BOL/EOL capability if launch vehicle injects spacecraft into Geosynchronous Transfer Orbit and spacecraft performs orbit raising and station keeping using bi-propellant propulsion (kg) Mass capabilities for various LV families appear suitable for launching both large and small GEO spacecraft directly to GEO. Excess capability beyond the maximum spacecraft mass might be used to launch small, scalable fuel cans for refueling the servicing vehicle. 12

13 9. REFERENCES 1. Top 20 Satellite Service Operators, Space News, p. 6, vol. 12, no. 18, 7 May Owners View 15-Years as Limit for Satellite Lifetimes, Space News, p. 6, 23 April S. Isakowitz, et.al. International Reference Guide to Space Launch Systems, 3 rd Edition, AIAA, A. Turner, J. Wertz, Launch cost as a function of vehicle reliability, ISDC 2001 conference, 25 May A. Turner, Aquarius, AIAA , AIAA Space 2000 Conference, 21 September A. Turner, Orbit Dynamics of Cost Effective Spacecraft for Frequent Non-Intrusive Servicing, AAS , AAS Astrodynamics Conf., 31 July A. Turner, Cost-Effective Spacecraft Dependent Upon Frequent Non-Intrusive Servicing, AIAA , AIAA Space 2001 Conference, 28 August Collopy, Economic-Based Distributed-Optimal Design, AIAA , AIAA Space 2001 conference, 30 August entagon to Demonstrate On-orbit Refueling of Spacecraft, Space News, p. 17, 30 April D. Whalen presentation at plenary session, AIAA Space 1999 conference, 28 September T. Kessler, Solar Thermal OTV, IAF 99-V.2.04, 50 th IAF Astronautical Congress, October R. artch, Solar Orbit Transfer Vehicles, ISDC 2001 conference, 28 May Boeing to Build Orbital Transfer Vehicle, Space News, p. 3, 2-8 March roton mission planner s guide, International Launch Services, LKEB , Issue 1, Revision 4, March Atlas launch system mission planner s guide, Atlas V addendum, International Launch Services, Revision 8, December