SPACE STATIONS USING THE SKYLON LAUNCH SYSTEM

IAC-10.B3.7.3 SPACE STATIONS USING THE SKYLON LAUNCH SYSTEM Mark Hempsell Reaction Engines Ltd Building D5,Culham Science Centre, Abingdon, Oxon, OX14 3DB United Kingdom mark.hempsell@reactionengines.co.uk After the International Space Station is decommissioned in 2020 or soon after, SKYLON will be an operating launch system and it is obvious means to launch any successor in orbit infrastructure. The study looked at establishing 14 stations of 7 different types located from Low Earth Orbit out to the Moon s surface with common elements all launched by SKYLON. The key reason for the study was to confirm that SKYLON could launch such an infrastructure, while the study s secondary objectives are to contribute to consideration of what should replace the ISS, and explore a multiple small station architecture. It was found that the total acquisition costs for LEO stations could be below $1 billion (2010) while stations beyond LEO were found to have total acquisition costs between $3 and $5 billion. No technical constraints on the SKYLON launch system were found that would prevent it launching all 14 stations in under 5 years. Keywords: SKYLON, space stations, multi role capsules, modular construction 1 INTRODUCTION The International Space Station (ISS) is likely to remain mankind s main in orbit facility until around 2020 and certainly it will not operate for more than few years past that date. Then it will be decommissioned and a replacement infrastructure will need to be established to continue the science work and extend in orbit operations in both scope and location. The SKYLON spaceplane is an aircraft like vehicle powered by SABRE engines which have two modes of operation; air-breathing and pure rocket. SKYLON can take off from a runaway and fly to over Mach 5 using SABRE engines in airbreathing mode. Then the SABRE engines switch to the pure rocket mode and power the vehicle into Low Earth Orbit (LEO). Once the mission is complete SKYLON can re-enter the Earth s atmosphere and glide back for a runway Fig. 1: SKYLON and the ISS landing. The system is designed for 200 flights per vehicle and will provide orders of magnitude improvements in cost, reliability and availability of access to space. It is planned to be operational in 2020 and so will interact with the ISS at the end of its life, a subject explored elsewhere [1] (Fig. 1), thus SKYLON is the obvious system to both 1

launch and support the ISS s successor systems. This paper reports a study to exploring a scenario for a complete in orbit infrastructure of space stations that could be implemented from the start of SKYLON service life i.e. from 2020. This Study had three objectives: i to further validate SKYLON payload provisions, ii to explore the early potential of SKYLON to expand the in orbit infrastructure, iii to explore the potential of the lego approach to infrastructure architecture. The first objective is primary justification for the investment in the Study. SKYLON s payload requirements are defined in Reference 2 and the detailed provisions are described in Reference 3. These have been derived from a combination of the needs of the current launch market and explorations of future applications. This study falls into the second category; exploring whether any feature in the provisions as currently defined would inhibit the introduction of such stations or whether there is any additional feature that if included would facilitate their construction. The second objective is to address the issue of how to sustain the capability that has been acquired beyond the ISS retirement date. Given that the current development times for such facilities are in the order of a decade, it was thought timely to explore the options for successor systems. The third objective looks at a specific infrastructure architecture. This uses many small (Mir class) specialist stations to obtain the total capability required rather than one big station. This architecture has been discussed previously [4] and shows promise as a superior strategy to in orbit infrastructure expansion for three reasons: i it centres on the reuse of standard module minimises development and allows learning curve factors to reduce overall costs, ii - the resulting architecture is more flexible in operation and more resilient to failure, iii - it allows the overall in space infrastructure to be extended to several locations without major new development programmes. These small stations would be constructed from a set of standard Core Modules; each module encapsulating specific functions that are required by all stations. These Core Modules are be assembled in different configurations and, when combined with appropriate specialist modules, form the various station types needed for a complete in orbit infrastructure. The study methodology was to produce concept designs for the Core and specialist modules, while establishing a scenario of the stations that would be built to make a complete infrastructure. The various station acquisition costs are then determined by simple parametric modelling, assuming the market in the study scenario. 2 ASSUMED INFRASTRUCTURE This section describes the assumptions regarding the systems that would be supporting the stations construction and operation. 2

2.1 SKYLON The use of SKYLON as the only launch system was determined from the study s prime objective; to explore aspect of SKYLON s payload provisions as defined in the Users Manual [3]. The elements of the stations were generally designed to be below 11 tonnes in mass (including the mass of the SOFI described below) which was the SKYLON performance to an ISS orbit. However some specialist elements could exceed 11 tonnes where the station was in a lower inclination orbit. The station elements all fitted within the payload bay which was 4.8 m diameter and 10 m long when the SOFI was installed. The scenario assumed these stations would start to be built in 2020 or soon after, that would be when SKYLON enters service and would charge entry in to service launch prices (approximately $80 million per launch) and would be complete around 2025 by which time it was expected the prices will be falling to the mature operation price (approximately $10 million). As the exact price point could not be established the station acquisition costs were determined for the full expected range of SKYLON launch prices. 2.2 SPLM and SOFI For most missions to in orbit facilities SKYLON required one of two items of airborne support equipment located in the payload bay. These were the SKYLON Personnel/Logistics Module (SPLM) which enabled crew and logistics to be carried in a pressurised cabin and the SKYLON Orbital Facility Interface (SOFI) which enabled SKYLON to dock or berth with an orbital facility when carrying. The study assumed the concept designs for these that are described in the SKYLON User s Manual [3] The SPLM (Fig.2) was mounted within the SKYLON payload bay throughout the flight. and was the means by which SKYLON could deliver people and pressurised cargo into space and deliver them to orbiting facilities. The SPLM was 9.5 m long with an internal cabin diameter of 4 metres and had an unloaded mass of 7800 kg. A docking system was incorporated into the SPLM roof to connect to the station. In the station support role it would normally carry 4 passengers and the station supplies, however when supporting a Space Hotel it could carry up to 24 passengers. Fig. 2 SKYLON Personnel/Logistics Module In the cost analysis the use of the SPLM was assumed to add $10 million to the basic price for a SKYLON flight [5]. The SOFI (Fig. 3) provided the means by which SKYLON can dock (or berth - as it had provision for both types of operation) with orbiting facilities. The SOFI had an installed mass of around 750 kg. It used the rear payload interface and occupied 3 metres of the bay so only 10 m was available to the payload that is carried with it. In the cost analysis it was assumed that the use of the SOFI would have a negligible impact on the SKYLON launch price. 3

Copyright 2010 by Reaction Engines Ltd. Published by the IAF with permission and released to the IAF to publish in all forms. 2.4 Multi-Role Capsule The in-orbit crew transport role was undertaken by a Multi-Role Capsule. For this Study it was assumed to be the Excalibur Multi-Role Capsule (Fig.5) [7]. This could carry 4 people and had a large orbit transfer capability including the ability to operating down to the lunar surface (with drop tanks) and thus it covered all the crew transportation roles within the infrastructure except Earth surface to orbit and return which was the role of the SPLM. Excalibur could return the crew to Earth although this capability would only be used in emergency. Fig. 3 SKYLON Orbital Facility Interface 2.3 Fluyt SKYLON was limited to payload delivery to LEO so it followed that to establish station beyond LEO would require an in orbit transportation system. The Study assumed this to be the Fluyt Stage [6]. The Fluyt stage was a space based rocket stage using oxygen / hydrogen propellants and two Vinci engines. It was capable of placing 15 tonnes into GEO and over 12 tonnes into Lunar orbit. In the cost analysis a Fluyt mission was assumed to cost $20 million to recover the stage and base costs. The SKYLON flights involved were separately accounted for but at $30 million a flight the total Fluyt launch cost would be around $180 million. Fige 5 Multi-Role Capsule In the cost model, Excaliburs were priced at $150 million each which was based on the assumption that 30 would be built. 2.5 Lunar Surface Logistics Vehicle The overall study architecture assumed that humans were delivered to the lunar surface using the Multi-Role Capsule, but this could not deliver significant supplies and other equipment so an unmanned Lunar Surface Logistics Vehicle was also required. A one way expendable stage launched by a single Figure 4: Fluyt Orbit Transfer Stage 4

SKYLON with an upper stage could deliver in the order of two tonnes which was adequate for the support of early Lunar operations. There was no work performed to produce any definition of the Lunar Surface Logistics Vehicle. In the Study Scenario the Lunar Surface Station delivers itself with an integral propulsion system so it was not necessary to know anything about this element other than it would exist to support the Surface Station operations after it had been established. It follows that it did not make any contribution to the Lunar Surface Station s acquisition costs. 3 THE CORE MODULES The Stations were all constructed from a series of eight Core Modules that together created a small station with a crew of four. Once the basic station was build from the Core Modules specialist modules were added to provide the functionality required to meet the specific application for which the station is intended. The assumption for all the modules was that technology in some cases the actual equipment (e.g. the manipulator and the equipment racks) are directly taken from the ISS. Apart from an inflatable structure for the Hotel Module no new technology was assumed above what is available and proven on the ISS Seven of the eight modules are shown in Figure 6 the missing module being the gravity version of the Node Module. They are shown exploded from a typical configuration although there are variations from this nominal layout. Each module is briefly described below in the nominal order they are flown in the construction sequence. Fig. 6: Core Modules 5

3.1 Multi-Role Capsule The Multi-Role Capsule was part of the supporting infrastructure but it was also an integral part of the Station as an operating systems. It was the only source of propulsion, it provides most of the backup systems, it is the escape system. The Capsule was the first element to be launched as the foundation stone for the stations construction. For LEO stations the Capsule was launched by SKYLON fully fuelled but without crew or logistics, a second SKYLON flight, with the SPLM followed which delivered the construction crew and logistics to the Capsule. For stations beyond LEO a Capsule with crew and supplies was delivered using a Fluyt stage to start the build process. The Capsule was also the main crew space transport system. If a Station s function required significant activity away from the Station by some of the crew then a second Capsule would have been required. 3.2 Quay Module The Quay Module was the main interface with the crew and supply transport systems, which was SKYLON in the case of LEO stations and was the Fluyt and Multi-Role Capsules in the case of stations located elsewhere. It had two docking and two berthing ports, the latter intended for temporary location of items such as the Logistics Module. Internally it was the station s main storage area which was sized to have in excess of twice the capability of the SPLM so a complete download and upload manifest could be stored at the same time enabling an SPLM to be emptied and then filled without the need for any temporary storage locations. The Quay Module was the second station element to be launched after the Multi-Role Capsule. This means it needed to be able to operate without other station services and to carry the equipment required for the subsequent build. It had a small solar panel to generate a few 100 watts continuous power to supplement the power from the Capsule and it had the control cupola and carried the manipulator arm for the location of the modules that follow. The location of the control cupola on the quay module was also logical for later operations, as it was the key tool in handing the joint operations with the transport systems. As there is no Manipulator system prior to the Quay Module arrival it followed it could not use the SOFI. This meant the Module could use the full 13 m available in SKYLON s payload bay. The deployment procedure was as follows; the crewed Capsule docked with the Quay Module s radial docking port while it was still in the payload bay and then, once connected, the two elements were ejected together using SKYLON s payload deployment system. 3.3 Node Module (Microgravity and Gravity) The Quay Module was followed by the Node module that is the key link between the other modules providing the main distribution hub for all the utilities (power, data air etc) and it contained the main environmental control systems. This module also had a large (4.6 m diameter by 6 m long) open hall area. The Node Module was the first of the station elements to be launched with the SOFI and, once the SKYLON/SOFI was docked to the Quay Module s axial docking port, the Node Module was removed from the SKYLON payload bay and permanently berthed to the other end of the Quay module using the 6

remote manipulator. This was the basic assembly technique employed on all subsequent modules. For the Lunar Surface Station and the Artificial Gravity Station a second variant on the Node Module was used which had an architecture and structure suitable to gravity applications. 3.4 Power Module After the Node Module the next element to be launched was the Power Module which generates electrical power for the Station. Once the power module was in place, the systems in the Node Module could be activated and the station s systems start to operate independently of the Capsule except for attitude control and communications. The Module had a one degree of freedom rotating bearing and power transfer adaptor to track the sun in one axis. Tracking the second axis, to enable the array to be orientated full onto the Sun, was achieved by rotating the station about the r axis generally the stations were gravity gradient stabilised. Each module had a deployable array of 300 square meter and 18 LiH batteries each with 2.8 kw total capacity used at 40% Depth of Discharge for LEO operations. Each module could provide 25 kw average electrical power in LEO, and 40 kw average electrical power in GEO. Except for the Lunar Surface Station and the Artificial Gravity Station, once completed, the stations had two of these Power Modules in their final configuration. 3.5 Habitation Module The Habitation Module followed the first power module in the assembly sequence. This Module contained an open loop life support system, galley, the main station control workstation, a workbench, a toilet and hygiene area, a medical station, a ward room and 4 crew rooms. The module had 100 kg/m 2 of shielding so the whole module could be used as a shelter in the event of solar storms. By having all the habitation functions shielded means the crew could stay within this Module for days if necessary. However the shielding meant that despite the small size (only 5 m long) it was a heavy module and could not be lifted in one SKYLON flight. A second outfitting flight using the Logistics Module to carry additional equipment and shielding was then conducted to make the module fully operational. It was the provision of a full storm shelter that was the key to using the Core Module suite to be used outside of LEO. 3.6 Logistics Module The outfitting flight for the Habitation Module used the Logistics Module which was very close in size and function to the Multi-Purpose Logistics Modules on the ISS. Apart from the use during assembly, LEO station would not normally use this Module, the logistics supply function being performed by the SPLM. In the study scenario this Module was primarily used to transfer logistics to the GEO and Lunar Orbit stations 3.7 EVA and Utilities Module The final module in the core station build up was the EVA and Utilities Module this contained an air lock, EVA work area and tool store, the attitude control reaction wheels, and the main communication equipment. 7

4 STATION TYPES The study scenario had a total of 14 stations of 7 different stations types. 4.1 Science Station The first stations to be launched were assumed to be those dedicated to science which has been the role of space stations since Saluyt and remains the main role of the ISS. The study scenario assumed five science stations to replace the ISS capability and expand it slightly (by approx 20%). To create the Science Station (Fig. 7) the standard core modules were enhanced with a pressurised Laboratory Module located near the Station s Centre of mass. This module was laid out along the same lines as the non- Russian laboratories with equipment racks mounted around the wall to create the sides, floor and ceiling of the work area. It could carry 47 equipment racks which was a little more capable than the Kibo module, the largest laboratory on the ISS. The Science Station also had an unpressurised experiment platform which is attached to the Laboratory Module. 4.2 Fluyt Support Station The Fluyt stage was assumed to be the transport system to GEO and Lunar orbit so before stations can be established there the Flute Support Stations need to be placed in LEO. The scenario assumed two Fluyt Stations one to support Lunar operations and the other to support operations in GEO including the two GEO Space station The Fluyt Support Station used the Core Modules but in a change to the normal build sequence a pressured spine around 18 m long was placed between the Quay and Node Modules. This spine s primary role was to provide the structure for the Fluyt support facilities but it also had four small temporary crew rooms for transit crews on their way to higher earth orbits. Once the remaining Core Modules were assembled, two combined hanger and propellant plants were attached either side of the spine, thus each base supported two Fluyt stages. The hydrogen and oxygen propellant were delivered in cartridges carrying 11 to 12 tonnes of propellant (dependent upon the bases orbit) and each facilities had connections for six cartridges. Once empty they were exchanged for full cartridges on the next SKYLON delivery flight. Fig. 7: The Science Station At maximum capacity it was be possible for the Base to fly 40 missions a year which corresponded to around 500 tonnes a year to geostationary and a little less to Lunar orbit. Since this exceeded the current total launch traffic from Earth it was thought unlikely this capability would be fully utilised in the near term and it certainly greatly exceeded what 8

would be required for the non-leo stations assumed in the study scenario. 4.3 Lunar Orbit Station The study scenario assumed one station in lunar orbit to support lunar surface operations. In addition to the core modules it had a facility for storing Excalibur drop tanks needed for lunar surface missions. It was also the location fore the assembly of the Lunar Surface Station. 4.4 Lunar Surface Station The Lunar Surface Station was composed of a habitation module a gravity Node and specialist pressurised and unpressurised facilities including power generation, communications and specialist airlock and laboratory. This assembly was integrated with four propulsion stages which used hydrazine and nitrogen tetroxide feeding a single engine of the type used on the Multi- Role Capsule. These stages then delivered the Station as an integrated whole on to the Moon s surface. The Study Scenario assumed only one surface Station would be constructed. This combined with the low utilisation of standard core module and that it used the Fluyt system to launch it made it the most expensive of the stations to acquire 4.5 GEO Station The GEO Station was assumed the starting point for human serviced megawatt communication and earth observation platforms. For the Study Scenario two of these stations were assumed each consisting of the core modules and three specialist modules (together with a mass of over 30 tonnes). 4.6 Space Hotel The Study Scenario assumed two Space Hotels servicing a public access market expected to be primarily tourism. The Space Hotels design used the Core Modules with two inflatable Hotel Modules which together provided accommodation for 20 people, which when the 4 staff are included matched the 24 maximum passenger capability of the SPLM. The two Hotel Modules were identical with regard to structure and systems but were differently outfitted; with one acting as a dormitory the other as an activity area including restaurant. Both had small independent power, attitude control and 84 person day open loop life support capability and so either module could act as a lifeboat for all the Station s inhabitants that would allow three days for an SPLM equipped SKYLON to rescue the passengers and crew and return them to Earth. 4.7 Artificial g Laboratory The Artificial g Laboratory had a Habitation module Gravity Node and Specialist Laboratory Module at the end of an 80 m pressurised arm. The Hub had another Gravity Node, a Quay with Multi-Role Capsule and a Power Module. The specialist counter balance had communications, additional power, attitude control and propulsion. As EVA was thought to be an unlikely requirement on this station the provisions in the Multi-Role Capsule would have been used in an emergency and so EVA and Utilities Module was not included in the station s configuration. 9

Station type Location No of stations Build flights per station Total flights SKYLON flights per build flight Total SKYLON flights Science LEO 5 11 55 1 55 Fluyt base LEO 2 12 24 1 24 Lunar Orbit Lunar orbit 1 10 f 10 5.2 52 Lunar Base Lunar Surface 1 9 f 9 5.2 47 GEO GEO 2 12 f 24 5.2 125 Hotel LEO 2 11 22 1 22 Artificial G LEO 1 12 12 1 12 TOTAL 14 337 f = Fluyt flight Table 1: The Study Scenario 5 THE STUDY SCENARIO Table 1 summaries the Study Scenario s assumptions regarding the numbers of each type and the impact on the launch infrastructure. It shows that a total of 337 SKYLON flights would be needed to construct the overall infrastructure and assuming 2 flights a week (well with the capability of a single vehicle) it would take 170 weeks; that is three and quarter years, so an conclusion it could take 5 years to build the infrastructure would be safe from the point of view of launch system availability. From the assumption of two SKYLON flights a week it followed a typical LEO station would be constructed in about 6 weeks and the stations requiring Fluyt stages around 30 weeks (but only 24 weeks for the assembly crew), both times were within capability of a single assembly crew. For the acquisition cost estimation it was assumed each module was a separate development making enough modules to full fill the Study Scenario plus an engineering module. The Modules were costed using the NASA Advanced Mission Cost Model (AMCM) was reported in Reference 8. This module is crude and may underestimate slightly but is adequate to reach the broad conclusions the study was looking for. SKYLON, SPLM, Multi-role Capsule and Fluyt stage costs were taken from previous work as discussed in Section 2. Station Acquisition Cost ($ Million 2010) 6000 5000 4000 3000 2000 1000 0 80 70 60 50 Figure 8 shows the per station acquisition costs of the various Station types plotted against the range of expected SKYLON launch prices from entry into service to mature operation. The Study Scenario covered a period from entry into service so the first stations were likely to be at the left side of this graph, how far the prices would have moved towards the mature operation prices in the 5 years assumed could not be 40 30 SKYLON Launch Price ($ Million 2010) 20 10 Lunar Surface GEO Lunar Orbit Artificial g Fig. 8 Station Acquisition Cost Vs SKYLON Launch Price LEO 10

determined but a price around $30 million was thought to be a safe assumption. At this point the cost of acquiring a LEO station (regardless of type) would be below $ 1 billion and the Lunar and GEO stations 3 to 4 times greater. The cost of stations located beyond LEO were more dependent upon the cost of the SKYLON launch as the launch of the Fluyt stage fuel means there were 5.2 SKYLON flights per mission instead of one and so their acquisition cost fell faster as the SKYLON launch price fells.. 6 CONCLUSIONS With regard to the primary study objective: none of the concept designs produced by the study required any alteration to the SKYLON payload provisions as defined in the User s Manual confirming the results of earlier studies and contributing to the validation of SKYLON s payload requirements The cost modelling showed than assuming mid-level SKYLON launch prices that LEO stations could be acquired for less than a billion dollars (2010) and cost less than $100 million a year to operate. The cost of stations beyond LEO with the same launch cost assumptions were between 3 or 4 times higher than LEO stations. The study found that there were no technical, cost or operational reasons preventing the establishing of the baseline in-orbit architecture by 2025 assuming a start in 2020 when SKYLON becomes operational. That was 100 people (half of whom are in privately funded in Space Hotels), on 14 stations, including stations on the Lunar surface and in Geostationary orbit. That is not to say this is scenario is the one that should be followed; demand drivers derived from public good and commercial considerations would determined the actual path of the development of the post ISS in orbit infrastructure. The study simply highlighted that, with the constraints inherent in the expendable launch system approach removed, the development of human spaceflight could progress as fast as the demand drivers dictated. The use of the Lego approach also proved attractive as a means to compliment the capability of SKYLON. Its cost advantage is the improving of the development versus production balance and action of the learning curve on comparatively long production runs. It also has the advantage of providing flexibility so new station types or the expansion of capability through construction of new stations of an existing types would be relatively easy and quick to acquire compared with starting from scratch as new capability requirements emerge. Although the Study Scenario was not an attempt to in anyway predict the future or to establish an optimum development path it does illustrate that the speed of development that could be possible once SKYLON is operational would be solely dependant upon the development and production of the station elements. The launch system constraints in terms of both cost and availability that have hampered the ISS assembly would be for all practical purposes removed. With acquisition cost an order of magnitude below existing space stations achieving a considerable expansion of the inorbit infrastructure in terms of size, function and location becomes simply a matter of vision and will. 11

References 1. M Hempsell, The Interaction Between SKYLON and the International Space Station, IAC-09.D2.3.8 presented at the 60 th International Astronautical Congress, Daejeon, October 2009. 2. SKYLON Requirement Specification, Dc-SEL- SP-0001, rev 1, Reaction Engines Ltd, August 2010 3. SKYLON Users Manual, SKY-REL-MA-0001, rev 1.1, Reaction Engines Ltd, January 2010. 4. Mark Hempsell, "The Cost Impact of Space Station Architectural Approaches", The Journal of Practical Applications in Space, Vol 3 No 3, Spring 1992. 5. M Hempsell, A Phased Approach to Orbital Public Access, Acta Astronautica 66 (2010) 1639 1644 6. S Feast, The Fluyt Stage: A Design for a Space Based Orbit Transfer Vehicle, IAC-10-D2.3.7 presented at the 61 th International Astronautical Congress, Prague, October 2009 7. M. Hempsell, Multi-Role Capsules: Fulfilling Their Potential, Journal of the British Interplanetary Society, 58, pp.347-356, 2005 8. W.J.Larson and L.K.Pranke, Human Spaceflight Mission Analysis and Design, MacGraw Hill. 12