21st Century Spaceplanes and Space Expeditionary Forces: Pivotal Capability for a Third Offset Strategy A White Paper February 2017 Executive Summary. Reusable spaceplanes offer a third offset strategy to the U.S. that builds on the first and second offsets of nuclear weapons followed by precision navigation, munitions and stealth. Military space systems today are satellites that are large, expensive, and typically take many years to develop, launch and employ. They are also very effective at their intended function; however, that effectiveness is also destabilizing in that it is motivating foreign nations to develop and potentially employ anti-satellite (ASAT) systems that would deny the U.S. the advantage of its space systems. Today, the U.S. is heavily dependent on space capabilities, as is the U.S. public, even as foreign threats to U.S. space systems have grown precipitously. Reusable spaceplanes are stabilizing in that they can responsively and routinely replenish satellites to any orbit, while also enabling rapid access to any part of the world – capabilities seminal to the Air Force vision of Global Vigilance…Global Reach…Global Power.

Spaceplane attributes like launch on demand, routine space access and low flight costs enable many options for global reach, whether via “aircraft-like” sorties of spaceplanes with sensor suites or by launching satellites into constellations. Sorties with fully reusable spaceplanes enable overflight in a manner akin to past SR-71 flights, except they enable global reach at four nautical miles (nm) per second while accessing any point on earth, and most geographic locations in less than an hour. Moreover, spaceplanes are generally invulnerable to anti-ballistic missile, ASAT, and other anti-access and area-denial (A2/AD) systems. Spaceplanes, even those employing an expendable upper stage, can rapidly replace space assets, faster and cheaper than a near-peer can realistically destroy them. With aircraft-like sortie rates, spaceplanes can rapidly reconstitute our space asset losses and deliver new and tailored capabilities to theater commanders. An intriguing option for spaceplanes is the ability to launch recoverable and reusable satellites on demand, within hours or days of a crisis, and recover them after the crisis is over for refurbishment, upgrade, and reuse.

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This white paper describes how spaceplanes can provide commanders with battle management command, control, communications, computers and intelligence (BMC4I) gathering capabilities. This third offset harkens back to the thoughts of early advocates of air power, except spaceplanes take airpower and power projection one-step further by offering flexible and rapid global reach not limited by the range and speed of conventional aircraft. Spaceplanes can potentially fly with impunity from the continental U.S., create effects globally without refueling or even the need to suppress air defenses, and render massive foreign military investments obsolete.

Emerging spaceplane entrepreneurs. Today’s military space systems are large and expensive to both develop, launch and operate. It typically takes many years to develop and deploy new systems, which then must survive autonomously on orbit for years, often decades, further driving cost as well as spacecraft obsolescence. The emergence of partially and eventually fully reusable “spaceplanes” in the commercial and military sectors offers many new opportunities for more effective and efficient air and space operations. A key driver is space entrepreneurs who are rapidly changing the way the U.S. will access and employ space systems including billionaire’s Elon Musk at SpaceX, Jeff Bezos at Blue Origin, Paul Allen at Vulcan Aerospace, and large corporations backing DARPA’s Experimental Spaceplane One – XS-1. As illustrated in Figure 1, the coming spaceplanes don’t always look like traditional aircraft; however, they will earn the name with “aircraft-like” attributes including on-demand flight, high tempo operability, maintainability, reusability, reliability, rapid turn-around and low recurring flight costs. This paper will offer several concepts for employing spaceplanes to support military missions; however, the focus will be on Global Reach…Global ISR capabilities. Separate papers will address future options, which could enable new missions including conventional prompt global strike and space-based missile and space defenses.

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Figure 1 – Today’s spaceplane’s offer the promise of “aircraft-like” operability

Reusable space access. The emergence of reusable spaceplanes opens new approaches for executing traditional air and space missions, as well as enabling fundamentally new capabilities. Mature flight systems will enable both global reach sortie aircraft as well as rapid launch of payloads to orbit. The speed of orbital flight at over 4 nm/sec enables very rapid access to any location on earth. Figure 2 highlights the speed at which a reusable spaceplane can overfly or access any part of the earth from the continental United States. Most locations are accessible within an hour although some may take longer depending on the direction of flight and the distance (due west retrograde flight has more severe thermal environments).

Figure 2 – Spaceplane global reach times from Holloman AFB

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Today’s aircraft are most useful when complemented by a suite of weapon systems whether a target tracking and surveillance pod or a precision guided munition. Spaceplanes also require complementary assets: a small expendable stage for inserting payloads to their final orbit, a common aero vehicle for reentry and delivery of payloads to terrestrial locations, and a recoverable and reusable upper stage. For example, spaceplanes can use an expendable upper stage to launch conventional long life satellites, but they also incentivize a new class of spacecraft. Namely, satellites specifically designed for rapid launch and employment, followed by deorbit, reentry and land for refurbishment, upgrade, and reuse. As part of an overall operational concept for reusable spaceplanes, a Reusable Flyback (ReFLY) satellite was proposed in the 1990’s. ReFLY was a small, unmanned reusable upper stage, in essence a maneuverable and recoverable satellite bus or Space Maneuver Vehicle (SMV), enabling high ops tempo deployment and recovery of the satellite sensors/payload. The SMV has the potential capability to perform numerous satellite type missions where recovery of the payload is important. An early high cost, low ops tempo version of an SMV designed to launch on expendable launch vehicles (ELVs) was flight tested in the Air Force X-40 program and subsequently developed into the X-37 orbital test vehicle. However, ELVs are very expensive and they do not support high ops tempo flight for rapid emplacement of operational constellations. Today, as illustrated in Figure 3, several SMV concepts exist ranging from the use of capsules to the use of simple fabric heat shields. The key common feature is using these SMVs as components in reusable space architectures comprised of emerging commercial and/or military spaceplanes, and thereby taking advantage of low cost and high ops tempo launch.

Figure 3 – Space Maneuver Vehicle’s enable on-orbit maneuver & recovery

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Although it does perform missions like a satellite, the SMV’s strength is in its extreme maneuver, direct recovery to ground and reuse. This offers additional military flexibility to the warfighter supporting a variety of missions. Maneuverability in particular offers on-orbit ∆V for orbit changes, deorbit and survivability. It is very hard to kill systems flying at over four nm/sec and maneuvering. Two of the Figure 3 concepts also offer the potential for low unit costs, the capsule on the left and the upper stage/satellite on the right. The latter has a high temperature fabric surrounding the upper stage/satellite that deploys like an inverted umbrella for reentry resulting in low heating, a slow terminal velocity and a simple vertical landing. Combined with the reusable space access systems identified earlier, an SMV provides another flexible option for supporting rapid deployment of tailored space forces, including a space expeditionary force. Their on-orbit maneuverability makes them less susceptible to anti-satellite threats, while their ability to recover, upgrade, refuel and refly promises both more effective and efficient military capabilities tailored to warfighter needs. Perhaps more to the point, rapid and routine replenishment of space capabilities, will likely deter foreign nations from employing ASATs in the first place. This is likely true whether employing traditional satellites, SMVs or the spaceplanes themselves to deliver that capability.

High-tempo spaceplane operations. The operability characteristics of commercial and military spaceplanes promise a boon to the prospects for space-based systems. Spaceplanes can deploy satellites reliably, quickly and on-demand. Space assets often take decades to develop, test and employ, and once launched their operating life is limited. Spaceplanes can break this cost equation via on-demand and routine space access. The ability of aircraft to “fly- fix-fly” enables easy and rapid upgrades, especially when compared to space systems which often taken decades and many billions of dollars to field. A good example is Synthetic Aperture Radar (SAR) systems that flew routinely on the SR-71 two decades before SAR ever flew in space. Spaceplanes and reusable satellites can provide similar on-orbit test and rapid recovery for sensor upgrades.

A small, high ops tempo spaceplane able to launch a few thousand pounds to orbit could rapidly deploy satellites or SMVs with tailored payloads. The inclusion of SMVs in space architectures introduces further flexibility including maneuver to enhance resilience as well as

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periodic recovery for refurbishment, critical component and software upgrades, and relaunch. Similarly, commercial heavy lift spaceplanes currently in development at SpaceX and Blue Origin could deploy multiple SMVs, rapidly filling an orbital constellation. Such deployment scenarios will allow rapid and flexible employment of space-based assets.

One of the new and unique characteristics spaceplanes can introduce is aircraft-like operations; particularly launch on-demand and launch from alert status. Another feature that requires some equipment and facilitation is the ability to operate from bare-bases with small ground crews. As an example, the XS-1 program plans to demonstrate military flight tempos with a goal of 10 flights in 10 days using a small ground support team. These rapid turnaround times enable call-up times of 4 hours, with the eventual goal of driving call-up time down to under 2 hours. SpaceX’s Elon Musk has even talked publicly about eventually achieving one- hour turnaround times for his vertical take-off and landing “spaceplane.”

XS-1 will also demonstrate a clean-pad operations concept. This concept, combined with transportable ground equipment, could point the way to future bare-base operations akin to military aircraft at forward operating locations. Even operating from U.S. dispersed interior sites vs coastal sites will be possible as reusability and flight test validate the reliability of the reusable stages and allow overflight of the continental U.S. Spaceplane architectures will enable lower launch costs, launch on demand, higher reliability, maintenance and upgrade of space assets, potential recovery of forces after a crisis, and, with the introduction of fully reusable spaceplanes, flight from secure interior U.S. operating bases.

A fully reusable spaceplane flying sortie missions can support many spaceplane missions; however, some missions do require satellites for persistence. An SMV answers that need, and provides an effective platform for everything from persistent theater ISR to locating and tracking mobile missiles. Launching into an orbital inclination approximately equal to a theater’s latitude enables six passes over a theater each day for each SMV – two within approximately 500 nm of a target point and four within 200 nm. Figure 4 illustrates this point for one spacecraft in a 32 degree inclined low earth orbit over the Persian Gulf region. Given that a single SMV provides theater coverage approximately every 1.5 hours for 7.5 hours, and

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three SMV s provide continuous coverage every 1.5 hours, it is possible to envision a constellation that provides regional and persistent coverage for any satellite mission, and specifically for ISR and communication missions. Moreover, depending on the number of assets deployed, theater revisit rates range from minutes to a few hours.

6 Passes per 24 hour

9 10 30 N 8 11 12 7

15 N

20 E 40 E 60 E 80 E 100 E

Figure 4 – Each SMV provides six passes every 24 hours

XS-1 and variants of proposed SpaceX and Blue Origin reusable launch vehicles are opening a path to evolved spaceplanes offering the capability to rapidly launch constellations tailored to a theater commander’s needs. This is especially true in a high threat A2AD theater or field of operation. A small squadron of spaceplanes can launch on demand and surge as required to directly overfly or populate constellations specifically tailored to match a theater commander’s requirements. If advanced surface to air threats deny use of JSTARS, AWACS, and Global Hawk/U-2, then spaceplanes can supplement or replace those assets and provide the theater commander with similar BMC4I capabilities. The addendum at the back of this document is a requirements matrix for an operational spaceplane system notionally evolved from commercial systems or DARPA’s XS-1 program. Depending on fleet size, this gives some idea of the rapidity spaceplanes offer for emplacement of one or more assets over a theater, whether global reach spaceplanes, traditional satellites or SMVs.

Space Expeditionary Forces. Time Phased Force Deployment Data Lists (TPFDDLs) and expeditionary forces are used by the military to deploy combat ready assets and weapons to theaters in support of combatant commanders. In USAFE (USAF Europe), combat wings go a

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step further storing their weapon loads sequentially in order to facilitate removal and employment during the initial phases of a conflict. These pre-loads enable rapid attack of preselected targets during the initial phases of a conflict without the delay caused by waiting for a slow developing BMC4I picture of theater activities and operations. Similar preloads for satellites could speed up availability of BMC4I assets to theater commanders. Properly designed, these satellites could also provide responsive protection against counter space efforts such as jamming and kinetic and directed energy ASAT weapons. For communication and ISR missions the satellites employed could leverage the emerging commercial Low Earth Orbit (LEO) satellite constellations. These commercial satellites typically target costs in the $0.5M range. Military variants may be a bit more expensive due to more robust packaging for survivability in an Electronic Attack (EA) environment. For example, to fight in a congested and contested battlespace, satellites may require robust construction for operation in an EA environment, additional propellant for maneuver, crosslinks for reliability and redundancy, compatibility with current BMC4I systems, and the ability to operate autonomously where current assets are at risk from aggressor threats. Development of these satellites needs to balance military utility against cost to prevent gold plating. The goal should be to minimize incremental costs greater than commercial assets.

Employing these assets as part of a pre-planned TPFDDL is only possible due to the launch on demand and routine launch capability of spaceplanes. A logical order of battle for employing such assets in an emerging theater of operations is: 1) battle management communications satellites, 2) low altitude EO/IR/hyperspectral ISR satellites, and 3) low altitude SAR/GMTI/AMTI, recoverable and reusable satellites (SMVs). For each of these cases, this paper identifies satellite constellations providing a responsive capability to the theater commander. The approach selected was to launch these satellites into orbits where the theater latitude equals the orbital inclination; this maximizes coverage of the theater. Other constellations are possible; however, this approach suffices to make the points advocated in this paper. In all cases, and at the theater commander’s request, the planes can be filled in an order that maximizes early theater coverage, and the constellations could be augmented with additional satellites to decrease the time between coverage events.

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Communications constellation. At the start of any crisis, the most pressing need of a theater commander is communications dedicated to the theater and interoperable with current ground, air and space assets. Because of the A2AD environment, these satellites will likely employ long life, robust, high-powered communications payloads with steerable antennae, data link capability, and robust anti-jam features. They also must be interoperable with theater systems such as the Theater Air Control System and future CONUS-based systems with TACS capatilities. All should provide critical battle management capabilities early in hostile environments. The 1,000 nm altitude selected for these assets is well suited for LEO communications, but is a little high for typical ISR assets. Nonetheless, where limited resolution is acceptable, the spacecraft could include an ISR sensor suite.

After adjusting many parameters, Satellite Tool Kit (STK) analysis derived the constellation coverage shown in Figure 5. Communications coverage is essentially horizon-to- horizon while ISR passes occur approximately every 20 minutes. ISR coverage is less because the sensor look angles are smaller than the broad coverage provided by a communications antenna. The high altitude will limit ISR resolution, but still provide a useful capability. Estimated satellite mass is in the 1,000 to 2,000 lb range, larger than equivalent commercial satellites, but designed to operate and survive in a more challenging environment.

Note that this constellation provides excellent continuous coverage for the target theater as well as most of the world’s populated areas, with a few temporary holes at high and low latitudes and near the equator. In the event a commander required more coverage or additional bandwidth, more spacecraft can be launched into the constellation. Our example constellation provides middle-eastern coverage at ~36° North latitude.

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Figure 5 – Communications constellation of 12 satellites (2 planes at 36°, 1,000 nm altitude)

ISR Constellation. Besides communications, theater commanders will need dedicated EO/IR, and possibly hyperspectral, coverage early in the crisis. Using STK analysis, an optimized ISR constellation, illustrated in Figure 6, was formulated with 24 satellites in 4 planes of 6 satellites each. This yields a dedicated look at the theater/target area averaging every 17 minutes with a duration averaging 3.7 minutes. Similar to the communications satellites, ISR satellites will likely leverage the commercial sector analog with additional robustness, maneuver, and redundant high bandwidth crosslink and downlink capabilities for transmitting imagery data. An altitude of 400 nm offers a good compromise between optics size, resolution and coverage on the ground. The assumed field of view was 45 degrees left and right of ground-track, highlighted by the red circles in the figure. Although it depends on the requirements, based on similar commercial assets a reasonable mass estimate for these satellites is in the 500 to 1,000 lb range. Again, if more persistence is required the user can request deployment of additional satellites in either existing or new planes. The optimum way to augment a constellation will vary depending on theater needs. A Weapon School guide on the physics of constellation building choices would prove valuable to future space users.

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Figure 6 – ISR constellation of 24 satellites (4 Planes of 6, 36° Inclination, 400 nm altitude)

For clarity, Figure 7 shows an image of a single plane of 6 satellites with the same altitude and inclination as the constellation above that makes coverage a little easier to envision. The interaction between the four planes shown above fills in the gaps. If a single plane of 6 satellites is filled first, there would be approximately 6 hours of coverage, followed by 18 hours of no coverage as the earth rotates below the plane’s satellites. 24 hour coverage could be obtained by putting one satellite in each of the four planes, but the gaps in coverage would be much longer. Constellation building with rapid launch capability is something the U.S. currently cannot do. In the future, theater commanders and national requirements, will dictate how constellations are filled.

Figure 7 – ISR constellation in a single plane of 6 satellites

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Synthetic Aperture Radar (SAR). By far the most challenging constellation considered was space-based radar. It is important to note this analysis extrapolates the use of conventional state-of-the-art SAR systems and did not consider advanced techniques such as bi- static or multi-static radars. To support the analysis, constellations enabling both continuous Ground Moving Target Indicator (GMTI) and Air Moving Target Indicator (AMTI) coverage weredeveloped. To accomplish this, the analysis baselined a relatively low altitude of 300 nm due to the r4 factor driving radar size, weight and power requirements (the radar beam must travel to the target and back).

Extrapolating based on today’s SAR technology used on fighters yields a satellite mass of around 3,000 lbs. Moreover, the cost and number of satellites will likely drive the need for a recoverable satellite system; i.e., placing the SAR payload on some kind of SMV which will increase the net payload mass that must be launched. Nonetheless, these weights seem reasonable given the state-of-the-art. For example, Northrop-Grumman is planning to adapt a fighter Active Electronically Scanned Array (AESA) for its concept on the E-8C JSTARS replacement program. This modern AESA will have both GMTI and SAR modes and is supposed to be small enough to fit on a much smaller executive jet size platform, much smaller than the current Boeing 707 based JSTARS aircraft. Additionally, Northrop-Grumman has developed a smaller version of the updated JSTARS radar, the AN/ZPY, to fit on the Global Hawk. The AN/ZPY radar will also have GMTI and SAR capability. Given the advancements in AESA radars with constantly changing frequency, pulse width, antenna pattern, and pulse repetition frequency, a 3,000 lb SAR spacecraft providing SAR, GMTI and AMTI capability seems reasonable. If technology improvements allow higher altitudes for the radar, the coverage problem becomes less of an issue. Doubling the altitude of a satellite doubles the coverage circle diameter (although the search area then increases by the square of the radius adding to the challenge).

Trying to provide continuous coverage for AMTI to supplement or replace AWACS capability takes a very large number of assets from a 300 nm altitude, which will likely drive the need for recoverable SMV basing. GMTI is not as critical for continuous coverage because of the low velocity of the vehicles being tracked, and short gaps would still provide very useful

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information if combined with target movement prediction software. Conversely, AMTI requires continuous coverage because of the much higher velocity and g capability of aircraft, which can rapidly change direction and altitude. Realistically, a small constellation of spacecraft can provide the theater commander with an excellent SAR imaging capability, but has large gaps in coverage for both GMTI and AMTI. These gaps are not an issue for SAR, where specific targets are identified and scanned, but are a significant issue for GMTI and a huge issue for AMTI.

STK analysis illustrates that an effective GMTI capability is enabled with a constellation of 96 satellites at 300 nm altitudes (6 planes of 16 satellites each) as illustrated in Figure 3 below. That capability yields 3 minutes of coverage followed by 3 minutes of no coverage. For GMTI’s low velocities using moving extrapolation software, that is a very useful capability. Conversely, to get continuous AMTI coverage at 300 nm altitude, 192 satellites are required, assuming addition of 16 satellites to each plane shown in Figure 8. If technology improvements enable doubling the altitude to 600 nm, the coverage gaps effectively goes to zero for both GMTI and AMTI. It should be noted that even a limited GMTI/AMTI constellation would provide valuable information on target areas and lines of communication beyond the range of JSTARS/Global Hawk and AWACS assets. MTI data could also be used to cue SAR and EO/IR/hyperspectral assets to warn of impending force movements towards friendly forces.

Figure 8 – GMTI/AMTI Constellation (6 Planes of 16, 36° inclination, 300 nm)

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Summary. Today’s military space systems are large and expensive to both develop and operate. It typically takes many years to develop and deploy new systems, which then must survive autonomously on orbit for years, often decades, further driving cost and spacecraft obsolescence. Moreover, emerging foreign ASAT threats are potentially destabilizing in that they may well motivate nations to engage in space warfare. For example, the loss of an unmanned air vehicle is typically not a big concern, are unmanned spacecraft any different? The “Maginot Line” of large unmanned spacecraft may well prove too tempting to any nation trying to undercut the U.S. technological edge. Conversely, rapid, routine and low cost access to space minimizes and perhaps eliminates the motivation for space warfare.

The coming era of aircraft-like space access enables many military applications and helps to deter future space warfare. Spaceplanes can rapidly launch both traditional spacecraft and recoverable SMVs into constellations providing regional coverage, eventually enabling space expeditionary forces for support of future crisis. An intriguing spin-off of this commercial and military technology could give the United States Air Force new capability options which it has sought since its birth; namely, Global Reach…Global ISR aircraft based in the continental United States. Such aircraft require no aerial refueling and their speed allows overflight of regional threats largely with impunity. Even with the loss of today’s large spacecraft, such a capability would fill critical gaps essential to both theater commanders and national needs.

Fielding of low cost commercial and high ops tempo military spaceplane systems is in its early stages of development. However, just as the 20th century ushered in many new aircraft, the 21st century will likely see the introduction of many new spaceplanes. The operability characteristics needed to enable spaceplane missions, although synergistic with the commercial sector, primarily support near term military needs. Spaceplanes are not a panacea but their low cost and potential for reliable, high ops tempo flight promise to enable new military, political and policy options. In particular, spaceplane capabilities offer a commercially based and potent third offset strategy to the United States, which will be very difficult for other nations to follow.

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The United States should leverage its technological edge and the emerging private sector by incentivizing commercial spaceplane ventures, and developing a Global Reach…Global ISR…Global Vigilance capability suitable for the 21st Century. In parallel, the U.S. should fully explore other defensive missions and capabilities required to protect the nation and deter war in the 21st century. The alternative is to walk away from the promise of spaceplanes just as the U.S. military walked away from airpower in 1908. The result a century ago was to export overseas the aviation industry invented in the United States. It took 30 years and a world war to bring that industry and air power back to the United States. The U.S. stands at a similar crossroads today, let us hope we make the right decisions.

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Addendum: Requirements Matrix

REQUIREMENTS MATRIX FOR A FULLY REUSABLE, ORBIT-CAPABLE SPACEPLANE Requirement Threshold Objective • Sortie Utilization Rates Peacetime sustained 0.10 sortie/day 0.20 sortie/day War/exercise sustained (30 days) 0.33 sortie/day 0.50 sortie/day War/exercise surge (7 days) 0.50 sortie/day 1.00 sortie/day Emergency surge (1 day) 3 sorties in 24 hours 4 sorties in 24 hours • Turn Times Peacetime sustained 2 days 1 day War/exercise sustained (30 days) 18 hours 12 hours War/exercise surge (7 days) 12 hours 8 hours Emergency surge (1 day) 8 hours 2 hours • System Availability Mission capable rate 80 percent 95 percent • Flight and Ground Environments Visibility 0 ft 0 ft Ceiling 0 ft 0 ft Crosswind component 25 knots 35 knots Total wind 40 knots 50 knots Icing light rime icing moderate rime icing Absolute humidity 30 gms/m3 45 gms/m3 Upper level winds 95th percentile shear all shear conditions Outside temperature -20° to 120°F -45° to 130°F Precipitation Light Moderate • Space Environment (On-Orbit Spaceplane) Radiation equivalent level in circular orbit 300 nm 500 nm • Flight Safety Risk to friendly population <1 x 10-6 <1 x 10-7 Flight segment loss <1 loss/2000 sorties <1 loss/5000 sorties Reliability 0.9995 0.9998 • Performance Boost 3000 lb payload polar orbit retrograde orbit (360°/180° azimuth) (270° azimuth) • Cross Range Downrange booster landing cross range @ 1000 nm 250 nm 400 nm Orbiter cross range 1200 nm 2400 nm • On-Orbit Maneuver (On-Orbit Spaceplane) Excess ∆V (at expense of payload) 300 fps 600 fps Pointing accuracy 15 milliradians 10 milliradians • Mission Duration (On-Orbit Spaceplane) On-orbit time 3 orbits/~5 hours 72 hours Emergency extension on-orbit 12 orbits/~18 hours 24 hours • Call-Up Time Mission Capable to Launch Initiation 6 hours 2.5 hours

• Alert Hold Hold Mission Capable 15 days 30 days Mission Capable to Alert 2-Hour Status 4 hours 2 hours Hold Alert 2-Hour Status 3 days 7 days Hold Alert 15-Minute Status 12 hours 24 hours Alert 15 Minute to Launch 15 minutes 5 minutes

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Requirement Threshold Objective • Design Life Primary structure 250 sorties 500 sorties Time between major overhauls 100 sorties 250 sorties Engine life 100 sorties 250 sorties Time between engine overhauls 50 sorties 100 sorties Subsystem life 100 sorties 250 sorties • Take-off and Landing Runway size 10,000 ft x 150 ft 8,000 ft x 150 ft Runway load bearing S65 S45 Vertical landing accuracy 25 ft 1 ft • Payload Bay (If fitted) Size 300 ft³ 15’x8’x6’ Weight capacity 6,000 lb 8,000 lb • External Payload or Payload Container Carriage capacity 8,000 lb 12,000 lb Time to load external payloads 1 hour 30 minutes • Payload Capability Direct orbital polar, requirement (360° or 180° azimuth) 3000 lb 4000 lb Direct orbital east, derived (090° azimuth) 4000 lb 6000 lb Once around east with payload kick stage, derived 5500 lb 8000 lb • Maintenance and Support Maintenance man hours/sortie 100 hours 50 hours R&R engine 8 hours 4 hours

Note: All requirements apply to a single spaceplane

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