Solar Power Satellites and Spaceplanes. The SKYLON Initiative

Solar Power Satellites and Spaceplanes The SKYLON Initiative Reaction Engines Limited September 2008 1 of 29

Title Confidentiality, copyright and reproduction File reference Solar Power Satellites and Spaceplanes The SKYLON Initiative Copyright Reaction Engines Ltd. Distributed only on the basis of strict confidentiality. Confidentiality to be maintained. Enquiries about copyright and reproduction should be addressed to the Managing Director, Reaction Engines Ltd. My Documents/tony_martin/ssp/ssp_skylon_ver2 Report status Issue 1 Reaction Engines Ltd. D5 Culham Science Centre Abingdon Oxfordshire OX14 3DB United Kingdom Telephone 01865 408314 Facsimile 01865 408301 Name Signature Date Edited by Tony Martin (signed) A. R. Martin 11 Sept. 2008 Reviewed by Richard Varvill (signed) R. A. Varvill 11/9/2008 Approved by Alan Bond (signed) Alan Bond 11 Sept 2008 2 of 29

TABLE OF CONTENTS Executive Summary...4 1. Introduction...6 2. A Brief History of Solar Power Satellites...10 3. Baseline Scenario Launch Infrastructure (2007 NSSO study)...14 4. SKYLON Scenario Launch Infrastructure...18 5. Spaceplanes in a Solar Power Satellite Environment...22 6. Conclusions...26 References...28 Cover image: NASA 3 of 29

Executive Summary The issues of energy and the environment are critical for the future development and welfare of the world. The continuing availability of power and the generation of it in a way that does not cause unacceptable damage to the environment is a major concern. The need for increasing amounts of energy as world populations rise and aspirations for economic prosperity grow could also lead to increased competition for sources, increased levels of political tension and decreased levels of national security. Reserves of fossil fuels are limited, the effects on the global climate are becoming more apparent, and the levels of demand are leading to very high prices. The utilisation of nuclear energy will be an essential component of future power provision, but has problems associated with it that will preclude it meeting all energy needs. The use of renewable energy cannot contribute on a large scale, because of the diffuse nature of the sources. A further source of energy that has been proposed is space based solar power (SBSP). A solar power satellite (SPS) collects sunlight and transforms it into electrical energy. This is electromagnetically beamed back to Earth where it is collected by a large array of receivers. The energy can be used as baseload power by feeding it directly into the existing electrical grid. Alternatively, the energy can be used to manufacture synthetic hydrocarbon fuels, using hydrogen from water and carbon monoxide from carbon dioxide, resulting in a carbon neutral source of fuel for transportation. The US Department of Energy and NASA carried out a first major study in the 1970 s. In the 1990 s NASA carried out a Fresh Look study to re-examine the concept in the light of the more advanced technological state then applying. It was found that technical advances had made SPS an attractive prospect but the economic case could not be made in comparison with other alternatives. In 2007 the US Department of Defence s National Security Space Office (SBSP Study Group) returned to the concept of SPS in response to concerns not only over energy but also space, economic, environmental and national security. Among the findings and conclusions of the Study Group were that space based solar power offers: an attractive route to increased energy security and assurance a viable and attractive route to decrease reliance on fossil fuels a potential global alternative to wider proliferation of nuclear materials a long-term route to alleviate the security challenges of energy scarcity a path to avert possible wars and conflicts a potential path for long-term carbon mitigation a unique range of ancillary benefits and transformational capabilities. The Study Group also found, in agreement with all other studies of the solar power satellite concept, that the development of space based solar power would have a transforming effect on space access. Solar power satellites cannot be constructed without safe, frequent, affordable 4 of 29

and reliable access to space. The volume and number of flights required represent a revolution in spaceflight. These launch requirements cannot be satisfied by expendable rockets and fully re-usable spaceplanes must be developed. By lowering the cost to orbit so substantially, and by providing safe and routine access, entirely new industries and possibilities open up. SKYLON is a reusable single stage to orbit winged spaceplane designed to give routine low cost access to space. Combining air breathing propulsion and pure rocket mode the vehicle is capable of take off and landing on conventional runways on its own undercarriage. When in orbit the payload is deployed from the large payload bay. The system operates unmanned, but a passenger module can be placed in the payload bay. SKYLON s performance has been achieved employing near-term technology and materials without reliance on favourable new developments. The engine combustion and turbomachinery components are well within established technology. Heat exchangers are used to cool the incoming airflow. The characteristics of SKYLON are very similar to the required capabilities for a spaceplane set out by the SBSP Study Group. The Study Group envisaged a solar power satellite with a mass of 3,000 tonnes producing a power of 1 GW e (1,000 MW electrical). Each GW installed in space would require about 300 SKYLON flights. A programme of 10,000 flights per year enables the installation of 33.3 GW. To put this in context, the UK has an installed electricity generation capacity of ~75 GW, while the EU as a whole has a capacity of ~650 GW. Total world generation capacity is ~4,000 GW. With two launch sites operational at any one time (out of three available) a programme of 10,000 flights implies 5,000 flights per site per year. If there are 250 flight days per year, then this equates to 20 flights per site per day. This is comparable to operations at a regional airport. As an example Inverness Dalcross, the gateway to the Highlands and Islands of Scotland, handles about 20,000 commercial air transport movements (takeoffs and landings) per year. Over the next 20 years the EU is expected to increase capacity by about 250 GW to a total installed electricity generation capacity of 900 GW. Hypothetically, if this new capacity was supplied by SBSP and launched by SKYLON the total cost of launch into LEO orbit would be $225,000 million (0.3% of EU GDP). For comparison the existing construction program of new power plants is estimated by the International Energy Agency to cost $530,000 million from 2000 to 2030. The installation of new SBSP power stations would help address Europe s vulnerability to its high level of energy imports (currently 50% and expected to rise to 70% by 2030). The total cost of launch into orbit using current expendable launch vehicles would be about 50-100 times higher. The launch costs with a TSTO reusable rocket system (such as the Gen 1.5) would be about 5 times higher than SKYLON and in addition multi-stage vehicles cannot achieve the necessary flight rates. The development of a reusable spaceplane, on the other hand, enables solar power satellites to be a viable, economic alternative source of energy for the future. 5 of 29

1. Introduction The issues of energy and the environment are critical for the future development and welfare of the world. The continuing availability of power (in all of its forms) and the generation of it in a way that does not cause unacceptable damage to the environment is a major concern to all. The need for increasing amounts of energy as world populations rise and aspirations for economic prosperity grow could also lead to increased competition for sources, increased levels of political tension and decreased levels of national security. Figure 1 shows World energy consumption since 1965 (BP, 2008) indicating that consumption has increased by a factor of 2.9 over a 42 year period (2.5% per annum) driven by rising World population and increased living standards. World energy consumption (1965 to 2007) 12000.0 10000.0 MTOE (million tonne oil equivalent) 8000.0 6000.0 4000.0 2000.0 0.0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Figure 1. World energy consumption since 1965 Figure 2 shows World population since 1750 with a projection to 2150. The population has more than doubled over the last 50 years. The projected growth is expected to flatten due to the increased fraction of young people (below puberty) and United Nations sex education programs. Year World population statistics 12000 10000 Projected 8000 Millions 6000 4000 2000 0 1700 1750 1800 1850 1900 1950 2000 2050 2100 2150 2200 Year Figure 2. World population since 1750 6 of 29

Figure 3 is a breakdown of current consumption by source indicating that 88% is derived from fossil fuel. Reserves of fossil fuels (coal, oil, gas) are limited, the effects of their use on the global climate are becoming more apparent, and the levels of demand are leading to very high prices in the world market. The utilisation of nuclear energy (fission and, perhaps in the future, fusion) will be an essential component of future power provision, but has problems associated with it that will preclude it meeting all energy needs (such as limited availability of fissile material). The use of conventional renewable energy (wind, wave, hydro) cannot contribute on a large scale, because of the diffuse and temporal nature of the sources (wind and wave) and the limited number of suitable sites (hydro). World energy consumption by source (2007) Total 11099.3 million tonnes oil equivalent Nuclear Energy 6% Hydro electric 6% Oil 35% Coal 29% Natural Gas 24% Figure 3 Current World energy consumption breakdown by source A further proposed source of energy is that of space based solar power (SBSP). In concept SBSP is straightforward (Figure 4). A solar power satellite (SPS) collects sunlight and transforms it into electrical energy. This is then electromagnetically beamed back to Earth where it is collected by a large array of receivers. The energy can then be used as baseload power by feeding it directly into the existing electrical grid. Alternatively, the energy can be used to manufacture synthetic hydrocarbon fuels, using hydrogen from water and carbon from carbon dioxide, resulting in a carbon neutral source of fuel for transportation. The potential advantages of SBSP are: access to virtually unlimited quantities of energy (a 1km band at geostationary orbit intercepts nearly as much energy as the entire World oil reserves) inexhaustible for as long as the Earth is habitable (about 1 billion years) non polluting (no CO 2 emission or radioactive waste) suitable for baseload power (availability > 99%) rapid energy payback (about 1-2 years including the launch propellant). 7 of 29

Figure 4. Space based solar power (SBSP) concept. First suggested in detail in 1968 (Glaser, 1968), a major study was carried out by the US Department of Energy and NASA in the 1970 s (DOE/NASA, 1978). This showed the scientific feasibility of the concept, and a reference design for a SPS rated at 5 gigawatts was drawn up. However, at that time the technology was such that a very large SPS was necessary, and the associated costs of this (including launch) were not economic when set against the lower cost energy alternatives then available. In the 1990 s NASA carried out a Fresh Look study to re-examine the concept in the light of the more advanced technological state then applying (Mankins, 1997). It was found that technical advances has indeed made SPS a more attractive prospect but, again, the economic case could not be made in comparison with other alternatives. In 2007 the US Department of Defence s National Security Space Office returned to the concept of SPS in response to concerns not only over energy but also space, economic, environmental and national security (SBSP Study Group, 2007). The Study Group found that, in the situation of the world today, space based solar power presents a strategic opportunity 8 of 29

that could significantly advance US and partner security, capability, and freedom of action and merits significant further attention on the part of both the US Government and the private sector. Among the findings and conclusions of the Study Group were that space based solar power offers: an attractive route to increased energy security and assurance a viable and attractive route to decrease reliance on fossil fuels a potential global alternative to wider proliferation of nuclear materials a long-term route to alleviate the security challenges of energy scarcity a path to avert possible wars and conflicts a potential path for long-term carbon mitigation a unique range of ancillary benefits and transformational capabilities. The Study Group also found, in agreement with all other studies of the solar power satellite concept, that the development of space based solar power would have a transforming effect on space access. Solar power satellites cannot be constructed without safe, frequent, affordable and reliable access to space. The volume and number of flights required represent a revolution in spaceflight. These launch requirements cannot be satisfied by expendable rockets and fully re-usable spaceplanes must be developed. By lowering the cost to orbit so substantially, and by providing safe and routine access, entirely new industries and possibilities open up. This conclusion is supported by preliminary analysis at Reaction Engines which suggests that if economical space transport is developed the costs of SBSP derived electricity are comparable to the costs from existing fossil fuel and nuclear power stations. Previous studies have examined the questions associated with this access to space, setting out ways and means of implementing the necessary transport. The Study Group has also set out a spacefaring logistics infrastructure to ensure safe and routine operations. This paper contrasts the requirements of this proposed infrastructure for accessing low Earth orbit to that which would be the case if the SKYLON spaceplane (Bond et al, 2003; Varvill and Bond, 2004) were to be used instead. 9 of 29

2. A Brief History of Solar Power Satellites In the space based solar power (SBSP) concept a solar power satellite (SPS) collects sunlight and transforms that into electrical energy. This is then electromagnetically beamed back to Earth where it is collected by a large array of receivers. The energy can then be used as baseload power by feeding it directly into the existing electrical grid. Alternatively, the energy can be used to manufacture synthetic hydrocarbon fuels, using hydrogen from water and carbon monoxide from carbon dioxide, resulting in a carbon neutral source of fuel for transportation. First suggested in detail in 1968 (Glaser, 1968), a major study was carried out by the US Department of Energy and NASA in the 1970 s (DOE/NASA, 1978). This showed the scientific feasibility of the concept, and a reference design for a SPS rated at 5 gigawatts was drawn up (Figure 5). Figure 5. Reference solar power satellite (SPS) and rectenna 10 of 29

There are a number of options for the design of a SPS. The satellite could be located in geostationary Earth orbit (GEO), medium Earth orbit (MEO) or low Earth orbit (LEO). The energy could be collected by photovoltaic solar arrays or by solar dynamics methods. The power could be beamed back down to Earth using either microwave techniques or lasers. The reference design SPS was located in geostationary Earth orbit, in almost continuous sunlight. The low efficiency of solar cells in converting sunlight to electricity (10-12%) meant that the design required a very large (10 km x 5 km) solar array to collect the desired power. This determined the size and mass of the in-space segment. It was recognised that such systems were only feasible if an affordable low cost method of placing mass into orbit was available. The use of expendable launch vehicles would result in a prohibitive cost for the project and reusable vehicles would be essential. The method of transmitting the power back to Earth was chosen to be via a microwave beam. The practicalities of microwave transmission meant that a large (10 km x 13.2 km) receiving antenna (rectenna) was required on the ground, thus determining the size of the ground segment. However, as the microwave power density is low (230 W/m 2 ) and the rectenna is largely transparent, the ground under it could be used for farming and agricultural purposes. The reference SPS were envisioned to be deployed through the use of a massive, unique infrastructure. This included a fully reusable two stage to orbit transportation system as well as a massive construction facility in LEO that would have required hundreds of astronauts to work continuously in space for several decades. The reference design was assessed to be technically feasible. However, at that time the technology dictated that such a large in-space segment was necessary, and the associated costs of this were not economic when set against the lower cost energy alternatives then available. In the 1990 s NASA carried out a Fresh Look study to re-examine the concept in the light of the more advanced technological state then applying (Mankins, 1997). Several innovative concepts were defined and a variety of new technology applications were considered. A key feature in achieving initial cost goals was to avoid wherever possible the costs associated with SPS-unique infrastructure. A variety of key technical advances had been made involving key technological areas and diverse new systems concepts. Although systems-level validation of key technologies, such as power conversion and large scale wireless power transmission had not occurred, componentlevel progress had been significant. Three architectures in particular were identified as promising. These were a sun-synchronous low Earth orbit constellation, a middle Earth orbit multiple-inclination constellation and one or more stand-alone geostationary Earth orbit SPS serving single, dedicated sites. A typical system was the SunTower concept (Figure 6). This was a constellation of medium-scale, gravity gradient stabilised, radio frequency transmitting space solar power 11 of 29

Figure 6. SunTower solar power satellite (SPS) concept systems. Each satellite resembled a large, Earth-pointing sunflower in which the face of the flower was the transmitter array, and the leaves on the stalk were solar collectors. The concept was assumed to transmit from an initial operational orbit of 1,000 km, sunsynchronous, at a transmitted power level of about 200 MW. The nominal ground receiver for the concept was a 4 km diameter site with direct electrical feed into the commercial power utilities interface. Multiple ground stations would be required to achieve reasonable utilisation of capacity. The study revalidated the technical feasibility of the concept and demonstrated that it was far more feasible than had been the case several decades earlier. Again, it was found that the primary driver of acceptable low initial capital costs was the cost to orbit, requiring reusable launchers. It was found that technical advances had indeed made SPS a more attractive prospect but it was still the case that the economic case could not be made in comparison with other alternatives. In 2007 the US Department of Defence s National Security Space Office returned to the concept of SPS in response to concerns not only over energy cost but also space, economic, environmental and national security (SBSP Study Group, 2007). Long term energy security was seen as a key factor in the world strategic security environment. 12 of 29

Significant advances in relevant areas have been made in the decades since the reference system study. Solar photovoltaic efficiencies had improved from 10% to 40%, with the possibility of almost 50%. Wireless power transmission efficiency had climbed from 20% to 80 90%, and mechanical pointing of transmitting antennae had been replaced by electronic beam steering. Power management requirements had been eased by the move from very high voltages (50,000 V) to much lower voltage (1,000 V) systems. The development of autonomous or tele-supervised robotics with multiple degrees of freedom allowed in-space assembly, removing the need for a large number of astronauts and a large space factory in orbit. While these advances will result in less massive and costly systems it was noted that solar power satellites would nevertheless require substantially greater lift and in-space transportation than has previously been attempted (about 2 orders of magnitude). Consequently, they will also require a significantly expanded supporting infrastructure. A necessary pre-requisite for the technical and economic viability of space based solar power was seen to be inexpensive and reliable access to orbit. A logistics infrastructure based on the use of expendable launch vehicles could not handle the volume or reach the necessary cost efficiencies to support a cost-effective SBSP system. It was concluded that space based solar power was more technically executable than ever before and that current technological trends promise to further improve its viability. The question of whether or not such a system was affordable was now not only a matter of economics, but also had to consider issues relating to strategic security needs for a nation and the world. 13 of 29

3. Baseline Scenario Launch Infrastructure (2007 NSSO study) The SBSP Study Group set out a suggested route for establishing routine access to low Earth orbit. The report and associated fact sheets and other materials (SBSP Study Group, 2007; Snead, 2006; Snead, 2007 pp) provide a convenient benchmark to compare alternative approaches. The Spacefaring logistics infrastructure envisaged the development of a series of systems. The Aerospaceplane (Gen 1), shown in Figure 7, is to transport passengers and cargo with aircraft-like safety and operability. It is a fully-re-usable, two stage to orbit (TSTO) booster-orbiter system, rocket-propelled and using vertical takeoff and horizontal landing. Cargo is carried in an external container mounted on the second stage orbiter and can be returned to Earth in the container. It is envisaged that two design-independent types are deployed for assured space access. A limited number of units are produced (four operational systems per type) pending upgrade of the system, as described below. A relatively low flight rate of 20 per year is seen. The system operates unmanned, but development of a ten-passenger spaceplane carried in place of the cargo container is envisaged. The spaceplane is deployed into low Earth orbit where the passengers transfer to space facilities, and the spaceplane then returns to Earth on its own. Figure 7. Generation 1 (Gen 1) aerospaceplane 14 of 29

The Aerospaceplane (Gen 1.5), shown in Figure 8, is a block update to the Generation 1 aerospaceplane, optimised for SBSP component delivery. The booster is updated to reduce weight, add increased-life engines and incorporate design changes to reduce recurring costs and increase inspection intervals. The orbiter is redesigned to reduce weight, add increasedlife engines, incorporate design changes to reduce recurring costs, increase time between inspections, and to change the payload carriage from external mounting to an internal configuration. Again, it is envisioned that two design-independent types are employed, with both Gen 1 variants being upgraded. Ten operational systems per type are produced, giving a total fleet complement of 20 vehicles. The annual flight rate is seen as increasing to 80 per vehicle. After the safety of the system has been demonstrated, a passenger transport module would be carried in the payload bay or a separate version of the orbiter produced with an integrated passenger compartment. The capabilities and costs of these vehicles are summarised in Table 1. Figure 8. Generation 1.5 (Gen 1.5) aerospaceplane 15 of 29

Table 1. NSSO study illustrative launch vehicles Configuration Gen 1 Aerospaceplane Two-stage, fully reusable rocket. External cargo container or passenger module. Gen 1.5 Aerospaceplane Block upgrade to the Gen 1 system, optimised for SBSP payloads. Internal payload bay. Gross Take Off Weight (GTOW) Technology Readiness Level (TRL) Net payload weight 1332 tonnes 1364 tonnes 6-9 5 9 13.2 tonnes to 28.5 o at 500km or 10 passengers. 13.6 22.7 tonnes to 28.5 o at 500km Deployment Annual fleet launch rate Two design-independent types for assured space access; 3 operational vehicles per type for 6 total vehicles. ~20 per vehicle; ~160 for fleet Two design-independent types for assured space access; 10 operational vehicles per type for 20 total vehicles ~80 per vehicle; ~1600 for fleet Operating bases Kennedy Space Centre; Vandenberg Air Force Base 5 or more sites worldwide Turnaround time 14 days (FOC) 3 days (FOC) Initial Operational Capability 2018 (nominal with 2009 start); 2016 (accelerated) Development cost $31,000M per system (40% reduction over BAU) Total $62,000M 2023 (nominal); 2020 (accelerated) $6,500M per system (40% reduction over BAU). Total $13,000M Production cost $1,800M per vehicle $740M per vehicle Recurring cost Cargo $26M (FOC) Passengers $36M Cargo $8M (FOC) 16 of 29

This Baseline Scenario Launch Infrastructure is described in the SBSP report as only illustrative and meant to depict systems and capabilities that industry should be capable of providing. Nevertheless, several aspects and assumptions can be commented upon. Most obviously, the plan to develop two design-independent systems in parallel to achieve assured space access implies a lack of confidence in US launch vehicle technology. This leads to a doubling of the development costs and results in a very large total system implementation cost. The suggested development of separate cargo and passenger modules also adds significantly to the costs. Issues related to design feasibility and integration of all required roles into a single vehicle should have been resolved prior to the commencement of a development programme. The costings were carried out using TRANSCOST (Koelle, 2003), a model used worldwide for preparing early programme cost estimates. The costs listed in Table 1 represent a 40% reduction on the baseline costs produced by the model. This is justified on the grounds that cost engineering reduction will be achieved via the use of current or derivative subsystems and manufacturing technologies with a technology readiness level of 6 9 and of existing or derivative engines. The baseline development cost of the Gen 1 aerospaceplane is $99B. While alternative design approaches are briefly considered only a two-stage system using primarily rocket propulsion is considered a near-term design with TRL 6 9 enabling technologies. This disqualifies an alternative approach (single stage to orbit, combined cycle) that has slightly lower technological maturity but is more reliable and much cheaper. Both the number of systems deployed and the annual fleet capacity are very low in the context of the required flight rate for solar power satellite construction. Fleet numbers and capacities of the order of airline traffic models will be more appropriate. High flight rates and fast turnaround times, together with high reliability and low maintenance, are the keys to achieving low cost per unit mass of payload delivered to orbit. Overall the Scenario presented is, as noted, illustrative and shows a design-from-scratch approach that does not take account of developments that have taken place, and are being progressed, elsewhere. It can be asked whether there is an existing alternative that satisfies the characteristics required for the vehicles considered above and leads to a more economic approach. 17 of 29

4. SKYLON Scenario Launch Infrastructure SKYLON is a reusable single stage to orbit (SSTO) winged spaceplane designed to give routine low cost access to space. Combining air breathing and rocket propulsion the vehicle is capable of take off and landing on conventional runways on its own undercarriage. When in orbit the payload is deployed from the large payload bay (Figure 9). The system operates unmanned, but a passenger module can be placed in the payload bay. The vehicle transitions from air breathing to rocket mode at around 26 kilometres altitude, after which the vehicle climbs steeply out of the atmosphere to minimise drag losses. The resulting ascent trajectory is relatively benign to both engine and airframe. SKYLON s performance has been achieved employing near-term technology and materials without reliance on favourable new developments. The engine combustion and turbomachinery components are well within established technology. Heat exchangers are used to cool the incoming airflow. The manufacturing requirements for this are beyond state of the art, but experimental work has alleviated concerns in this area. The capabilities of SKYLON are summarised, and compared with the SBSP capabilities, in Table 2. Figure 9. The SKYLON spaceplane 18 of 29

Table 2. SKYLON capabilities (Initial Operational Capability) contrasted to NSSO Gen 1 aerospaceplane Configuration Gross Take Off Weight (GTOW) Technology Readiness Level (TRL) Net payload weight Gen 1 Aerospaceplane Two-stage, fully reusable rocket. External cargo container or passenger module. 1332 tonnes 275 tonnes 6-9 4-9 13.2 tonnes to 28.5 o at 500km or 10 passengers. SKYLON Single stage, fullyreusable, air breathing and rocket powered. Internal payload bay with optional passenger module. 12 tonnes to 0 o at 300 km or 30 passengers. Deployment Annual fleet launch rate Two design-independent types for assured space access; 3 operational vehicles per type for 6 total vehicles. ~20 per vehicle; ~160 for fleet One design sufficient for assured space access; initial market estimate of 30 vehicles ~100 or more Operating bases Kennedy Space Centre; Vandenberg Air Force Base Kourou Space Centre (Centre Spatial Guyanais) Turnaround time 14 days (FOC) 2 days (IOC) Initial Operational Capability 2018 (nominal with 2009 start); 2016 (accelerated) 2020 Development cost $31,000M per system (40% reduction over BAU) Total $62,000M Vehicle $16,500M Passenger module $3,200M Production cost $1,800M per vehicle $450M per vehicle Recurring cost Cargo $37M (IOC) Cargo $26M (FOC) Passengers $36M (FOC) $10.4M (IOC) 19 of 29

SKYLON capabilities (Full Operational Capability) contrasted to NSSO Gen 1.5 aerospaceplane Configuration Gen 1.5 Aerospaceplane Block upgrade to the Gen 1 system, optimised for SBSP payloads. Internal payload bay. SKYLON Configuration as above. Enhanced performance through in-service development. Gross Take Off Weight (GTOW) Technology Readiness Level (TRL) Net payload weight 1364 tonnes 275 tonnes 5 9 4-9 13.6 22.7 tonnes to 28.5 o at 500km 15 tonnes to 0 o at 300 km Deployment Annual fleet launch rate Operating bases Two design-independent types for assured space access; 10 operational vehicles per type for 20 total vehicles ~80 per vehicle; ~1600 for fleet 5 or more sites worldwide Worldwide fleet 100 vehicles. ~10,000 3 equatorial sites worldwide Turnaround time 3 days (FOC) 12 hours Initial Operational Capability 2023 (nominal); 2020 (accelerated) 2025 Development cost $6,500M per system (40% reduction over BAU). Total $13B $2,000M (approx) Production cost $740M per vehicle $292M per vehicle Recurring cost Cargo $8M (FOC) $1.5M 20 of 29

From the data in Table 2 it can be seen that the performance characteristics of SKYLON are very similar to the capabilities set out by the SBSP Study Group. Only one system is developed, rather than two design-independent systems. The development and production costs were derived using Reaction Engines internal costing models which give similar estimates to TRANSCOST, and are baseline costs without assuming any reduction for cost engineering. The total SKYLON development cost ($21,700M) is much lower than the SBSP Study Group Gen 1 and 1.5 systems ($75,000M). The production cost per vehicle is also much lower (40%). A properly implemented SKYLON launch infrastructure is capable of at least 10,000 flights per year with a worldwide fleet of 100 vehicles. This implies an average vehicle turnaround time of 3.65 days, which when combined with the Initial Operational Capability of 2 days, leaves ample downtime for maintenance, etc. These figures are very modest compared to typical airline models. 21 of 29

5. Spaceplanes in a Solar Power Satellite Environment The SBSP Study Group envisaged a solar power satellite with a mass of 3,000 tonnes producing a power of 1 GW e (1,000 MW electrical). Consideration of the LEO to GEO transfer requirement and SPS assembly suggests that the total number of flights to LEO will be about 1.5 times the number of flights to launch the bare SPS hardware into LEO. Therefore each GW installed in GEO will require about 4500 tonnes launched to LEO. The flight rate of ~1600 for the Gen 1.5 aerospaceplane is suggested for the SBSP programme and would be capable of installing about 8.2 GW per annum., However this power level is rather low compared to the energy needs of the industrialised West. It is useful, therefore, to extrapolate to the case where there is a very high flight rate, and to estimate the capacity of such a programme and the long term launch costs. This has been done using an economic model for SKYLON, and some details are given below: The Initial Operational Capability of 100 worldwide flights for SKYLON simply represents replacement of the current worldwide traffic carried by expendables. It does not represent the maximum potential flight rate that the system is capable of and is too low for a solar power satellite programme. A future scenario with ~10,000 worldwide flights annually is more appropriate and entirely feasible due to the low costs and turnaround times achievable with a single stage to orbit vehicle. Through in service development it is assumed that the SKYLON vehicle life has increased to 500 flights and the payload has risen to 15 tonnes. 10,000 worldwide flights per year would place 150,000 tonnes into LEO, equivalent to about 33.3 GW installed per year. This will require a vehicle production rate of 20 vehicles per year to maintain the fleet size. In principle a single vehicle could fly twice a day to an equatorial space station from an equatorial launch site. This would require streamlined payload handling (probably containerised) and automated checkout systems. At this flight rate a vehicle would last about one year giving roughly 250 flight days and 115 maintenance days. Therefore, in principle, only 20 vehicles could supply the worldwide flight rate. In practice the worldwide fleet would probably be rather larger (say 100) to give more time for post flight inspections and maintenance. The full costs of development and production are included in the economic model, together with all the costs associated with spaceport operations, vehicle operations, consumables and replacement parts, insurance, operator profit and financing. That is, a true commercial model is used to develop the costings. Using the currently estimated development and production costs and reasonable values for all other costs (based upon current spaceport and airport practice and aeroplane charges) the specific launch price in $/kg as a function of annual flight rate is shown in Figure 10. For 10,000 flights the specific launch price is $200/kg. This is in contrast to the $10,000-20,000/kg for a typical current expendable launcher, demonstrating the necessity to develop reusable SSTO spaceplanes in support of a solar power satellite programme. 22 of 29

10000.0 REACTION ENGINES Baseline Specific launch price ($/kg) 1000.0 100.0 10.0 100 1000 10000 100000 1000000 Flight rate per year Figure 10. SKYLON specific launch price as a function of flight rate The distribution of costs for the 10,000 flights per year case is shown in Figure 11. It can be seen that the largest costs are those associated with vehicle repayment, fuel and parts and maintenance. The SBSP Study assumed a national, government programme. That is, the development and production costs were written off. The costs charged to the programme were only those relating to support costs, booster engine and orbiter engine replacement, and spares and propellants. This leads to a specific launch cost of $3,250/kg for initial operational capability of the Gen 1 vehicle, and $435/kg for full operational capability of the Gen 1.5 system. The case for SKYLON under similar assumptions is shown in Figure 12. If development and production costs are written off then the specific launch price falls to $120/kg. If only the development costs are written off then there is very little difference between this case and the case for all costs being recovered (the baseline case). This is a result of the development costs being small compared with production and operating costs. To put these numbers in context, for the SKYLON case where all costs are being recovered, the cost of launching 150,000 tonnes into orbit at $200/kg is $30,000 million per year. This compares with a cost of about $3 trillion per year ($3,000,000 million) if expendable launch vehicles were to be used (although this flight rate is unachievable with expendable rockets). This clearly illustrates the point that a reusable spaceplane system is an essential, enabling part of implementing a solar power satellite infrastructure. 23 of 29

10,000 flights per year Abort surcharge ( M) 2% Vehicle Insurance [3] ( M) 6% Parts & Maintenance ( M) 17% Operator profit ( M) 10% Vehicle repayment ( M) 38% Vehicle repayment ( M) Spaceport charges ( M) Operator fixed costs ( M) Launch operations ( M) Fuel ( M) Parts & Maintenance ( M) Vehicle Insurance [3] ( M) Abort surcharge ( M) Operator profit ( M) Fuel ( M) 15% Spaceport charges ( M) 2% Operator fixed costs ( M) 3% Launch operations ( M) 7% Figure 11. Distribution of costs for 10,000 flights per year 10000 Specific launch price ($/kg) 1000 100 All Costs Recovered Development and Production Costs Written Off Development Costs Written Off 10 100 1000 10000 100000 1000000 Flight rate per year Figure 12. SKYLON flight costs versus flight rate 24 of 29

With two launch sites operational at any one time (out of three available) a programme of 10,000 flights implies 5,000 flights per site per year. If there are 250 flight days per year, then this equates to 20 flights per site per day. This is comparable to operations at a regional airport. As an example Inverness Dalcross, the gateway to the Highlands and Islands of Scotland, handles about 20,000 commercial air transport movements (takeoffs and landings) per year. This programme of 10,000 flights per year enables the installation of about 33.3 GW. To put this in context, the UK has an installed electricity generation capacity of ~75 GW, while the EU as a whole has a capacity of ~650 GW. Total world generation capacity is ~4,000 GW. Over the next 20 years the EU is expected to increase capacity by about 250 GW to a total installed electricity generation capacity of 900 GW. Hypothetically, if this new capacity was supplied by SBSP the required launch rate would be 12.5 GW per year costing about $11,250 million. The total cost of launch into LEO orbit would be $225,000 million (0.3% of EU GDP). For comparison the existing construction programme of new power plants is estimated to cost $530,000 million from 2000 to 2030 (International Energy Agency, 2002). The installation of new SBSP power stations would help address Europe s vulnerability to its high level of energy imports (currently 50% and expected to rise to 70% by 2030). The total cost of launch into orbit using current expendable launch vehicles would be about 50-100 times higher. This cost would rule out space based solar power as an option for fulfilling future energy needs. The launch costs with a TSTO reusable rocket system (such as the Gen 1.5) would be about 5 times higher than SKYLON. However it is probably impractical for a TSTO system to achieve the necessary flight rates for SBSP due to their labour intensive and cumbersome launch preparation procedures (e.g. the Space Shuttle). The development of a reusable SSTO spaceplane, on the other hand, enables solar power satellites to be a viable, economic alternative source of energy for the future. 25 of 29

6. Conclusions The issues of energy and the environment are critical for the future development and welfare of the world. The continuing availability of power and the generation of it in a way that does not cause unacceptable damage to the environment is a major concern. The need for increasing amounts of energy as world populations rise and aspirations for economic prosperity grow could also lead to increased competition for sources, increased levels of political tension and decreased levels of national security. A future source of energy that has been proposed is space based solar power (SBSP). A solar power satellite (SPS) collects sunlight and transforms it into electrical energy. This is electromagnetically beamed back to Earth where it is collected by a large array of receivers. Space based solar power offers: virtually unlimited quantities of energy for about 1 billion years non polluting (no CO 2 emission or radioactive waste) suitable for baseload power (availability > 99%) rapid energy payback (1-2 years) alternative to fossil fuels reduced nuclear materials proliferation alleviation of the security challenges of energy scarcity. The development of space based solar power would have a transforming effect on space access. Solar power satellites cannot be constructed without safe, frequent, affordable and reliable access to space. The volume and number of flights required represent a revolution in spaceflight. These launch requirements cannot be satisfied by expendable rockets and fully reusable spaceplanes must be developed. By lowering the cost to orbit so substantially, and by providing safe and routine access, entirely new industries and possibilities open up. SKYLON is a reusable single stage to orbit winged spaceplane designed to give routine low cost access to space. Combining air breathing propulsion and pure rocket mode the vehicle is capable of take off and landing on conventional runways on its own undercarriage. When in orbit the payload is deployed from its large payload bay. The system operates unmanned, but a passenger module can be placed in the payload bay. SKYLON is the world s most advanced and viable spaceplane design, having been studied for 30 years with supporting experimental investigations. Its user friendly operations and low maintenance requirements give it the lowest recurring cost and highest flight rate potential of any proposed launch system in the world. The NSSO study proposed a solar power satellite with a mass of 3,000 tonnes which would produce a power of 1 GW e (1,000 MW electrical). Thus each GW installed in space would require about 300 SKYLON flights. A programme of 10,000 flights per year enables the installation of 33.3 GW. To put this in context, the UK has an installed electricity generation capacity of ~75 GW, while the EU as a whole has a capacity of ~650 GW. Total world generation capacity is ~4,000 GW. 26 of 29

With two equatorial launch sites operational at any one time (out of three available) a programme of 10,000 flights implies 5,000 flights per site per year. If there are 250 flight days per year, then this equates to 20 flights per site per day. This is comparable to operations at a regional airport. As an example Inverness Dalcross, the gateway to the Highlands and Islands of Scotland, handles about 20,000 commercial air transport movements (takeoffs and landings) per year. Over the next 20 years the EU is expected to increase capacity by about 250 GW to a total installed electricity generation capacity of 900 GW. Hypothetically, if this new capacity was supplied by SBSP and launched by SKYLON the total cost of launch into LEO orbit would be $225,000 million (0.3% of EU GDP). For comparison the existing construction program of new power plants is estimated to cost $530,000 million from 2000 to 2030 (International Energy Agency, 2002). The installation of new SBSP power stations would help address Europe s vulnerability to its high level of energy imports (currently 50% and expected to rise to 70% by 2030). The total cost of launch into orbit using current expendable launch vehicles would be about 50-100 times higher. The launch costs with a TSTO reusable rocket system (such as the Gen 1.5) would be about 5 times higher than SKYLON and in addition multi-stage vehicles cannot achieve the necessary flight rates. The development of a reusable spaceplane, on the other hand, enables solar power satellites to be a viable, economic alternative source of energy for the future. Given the above conclusions SBSP deserves more detailed study. To properly evaluate its potential requires an in-depth system study of the technology, economics and launch requirements carried out by an industry-wide working party. 27 of 29

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Snead, M., Spacefaring logistics infrastructure fact sheet; System cost estimate: Aerospaceplane (Gen 1), August 2007. http://mikesnead.net/resources/spacefaring/fact-sheet-aerospaceplane-gen-1-cost-estimate- 20070807.pdf Snead, M., Spacefaring logistics infrastructure fact sheet; System name: Aerospaceplane (Gen 1.5), August 2007. http://mikesnead.net/resources/spacefaring/fact-sheet-aerospaceplane-gen-1-5-20070803.pdf Snead, M., Spacefaring logistics infrastructure fact sheet; System cost estimate: Aerospaceplane (Gen 1.5), August 2007. http://mikesnead.net/resources/spacefaring/fact-sheet-aerospaceplane-gen-1-5-cost-estimate- 20070808.pdf Varvill, R. and A. Bond, The SKYLON spaceplane, JBIS, 57, pp. 22-32, 2004. http://www.reactionengines.co.uk/downloads/jbis_v57_22-32.pdf 29 of 29