Some time next year, the rocket-powered Lockheed Martin X-33 lifting-body demonstrator is due to make its first flight from Edwards Air Force Base (AFB). A few miles away, Boeing engineers will be working on the Future-X prototype at Palmdale. Both these programs, at the cutting edge of high-speed aerodynamic and material technology, are sponsored by the NASA Marshall Space Flight Center and are ostensibly intended to foster the development of civil and scientific spaceflight.
Few people realize that they are also prototypes for a military spaceplane which the US Air Force's (USAF's) scientific advisors believe could be under full-scale development within three years. It would provide the USAF with the means to perform reconnaissance, space control and strike missions from orbit.
Dozens of projects - black, white and grey - for military spaceplanes have been proposed since the late 1950s. The technical snags were severe, but the fundamental problem was always the absence of a clear military need, combined with the reluctance of civilian leaders to 'militarize' space. That situation may be changing.
A quiet revolution in military affairs has taken place since the 1990-91 Gulf War. That conflict saw the first extensive use of satellite systems for communications, warning and navigation. Today, military operations without them are almost impossible to contemplate.
A National Missile Defense system will likewise depend entirely on space-based warning and communications systems. The US intelligence community relies on imaging and electronic surveillance satellites, and even air-breathing platforms rely on high-bandwidth satellite communications.
The implications of this change are ominous and not widely recognized. In fact, former US military leaders have charged that current administration policy is hampering changes that are critically needed for preventing that revolution from directly endangering US military capabilities in the future.
Space systems reside in a medium where the US has no exclusive access and no direct defense against attack. "If the DSCS satellites or the MILSTAR satellites went out of commission, even some of them, we'd be devastated," former Air Combat Command chief General Mike Loh remarked at a roundtable organized last year by the Washington-based Center for Security Policy. "We depend on space communications to knit together a theater battle management system that all of the services will use. It is dependent on space. There is no more 'belt-and-suspenders'." Loh went on to note that he knows of no current weapons-delivery or guidance system that does not rely on GPS (Global Positioning System).
At the same meeting, former vice-Chief of Naval Operations Admiral Stan Arthur commented: "I was fortunate enough to participate in an Air Force war game recently - Global Engagement '97, played in 2012 - where we were working a problem with a near peer who had the ability to influence events in space - and utter chaos ensued." These officers and others see a widening gap between the US military's dependence on space and its ability to secure its position outside the atmosphere.
USAF Space Command's present leader, Gen Richard Myers, and his predecessor, Gen Howell Estes, have made no secret of their view that the USAF must fill that gap. To protect US military and commercial assets, to prevent adversaries from using space-based systems against US interests, and - eventually - to permit US space-based systems to strike ground targets, the USAF needs to dominate and control space as it dominates the air today.
Space Command's ambitions have gathered support within the USAF as the problems of projecting air power with a smaller number of forward bases become apparent. Events such as the Saudi restriction on the use of its air bases to launch strikes against Iraq, and the bombing of the Khobar Towers and US embassies in Africa, have underlined the difficulties of maintaining forward bases and the imprudence of relying upon them. Space-based systems are assuming increasing importance in the USAF's new doctrine of 'global engagement'.
However, this doctrine and Space Command's long-term plans run counter to the policy of the US administration, which remains committed to avoiding the militarization of space. The USAF is permitted to study needs for future military space systems, and to develop some of the technology for them, but is neither authorized nor funded to deploy them or conduct large-scale demonstrations.
This anomalous position has created a new alliance. After a long period in which the US government had three distinct communities in space - NASA, the USAF's 'white' side, and the 'black' world of intelligence operations - the different groups are collaborating as never before.
In the USAF view, the key to future space operations is better access to space. Better does not only mean cheaper (the Evolved Expendable Launch Vehicle meets that need), but also more responsive, so that payloads can be launched at shorter notice. The USAF wants the ability to maneuver outside the atmosphere - giving its systems greater freedom of movement than those of its adversaries - and to place systems in orbit that can be recovered and reused. NASA is also interested in improved access to space, because launch cost drives the cost of its civilian and scientific programs.
In February 1997, NASA and the USAF Space Command formed a partnership council to harmonize their future spaceflight plans and needs. The National Reconnaissance Office - responsible for intelligence-gathering spacecraft - joined this council in December. A subgroup of this council, the Space Technology Alliance, oversees cooperation in space vehicle technology.
Space Command, with technical support from the USAF's Phillips Laboratory, has drafted a concept of operations for an Aerospace Operations Vehicle (AOV), the first step to defining a requirement for such a vehicle. The AOV (also called the Space Operations Vehicle, SOV) is the successor to the Military Spaceplane, which was due to start in Fiscal Year (FY) 1998 but was terminated by the Clinton administration's line-item veto. This has since been ruled unconstitutional. As currently defined, the AOV is a two-stage-to-orbit system comprising a reusable booster and a mission-specific upper stage. The booster would follow a 'pop-up' flight profile, carrying about 5.5 tonnes of payload to a speed of M15-17 and an altitude of 300,000ft.
In a report published in November, the USAF Scientific Advisory Board recommended that the USAF should develop technology for the AOV, so that it would be ready for a full-scale go-ahead in 2002. In line with this recommendation, NASA and Space Command are collaborating on at least two dual-use programs, and the USAF is working on technologies with purely military applications.
Probably the leading candidate for the AOV booster would be a design based on Lockheed Martin's X-33 reusable launch vehicle technology demonstrator. The launch of this program in September 1996 represented a new start in USAF/NASA collaboration, because it drew technology from previously classified USAF programs.
The X-33's primary goal is to demonstrate technology for the VentureStar single-stage-to-orbit heavy launch vehicle. The first flight was originally scheduled for July, but may now slip for almost a year. It was first delayed until December this year, due to problems with building the linear aerospike rocket engine. Then, in January, one of the composite liquid hydrogen tanks suffered major damage while stabilizing patches were being cured in place. This is likely to delay the flight until mid-2000.
The most important new technologies to be demonstrated on the X-33 are the engine, the thermal protection system (TPS), and the stability and control of a lifting-body vehicle under re-entry conditions. The performance of the linear aerospike engine will be affected by the airflow around the vehicle, and flight test is the only way to confirm computer predictions of these effects. The TPS and other structural features are drawn from black USAF programs of the 1980s, aimed at creating a military spaceplane, and it is speculated that other, still-classified precursor projects may have proven other X-33 technologies, such as the engine - which, officially, has never been fired in flight.
A NASA experimental program, in which a linear aerospike engine was to be tested at transonic speeds on an SR-71, was terminated in November without firing the engine, adding weight to the speculation that the engine has been flown before.
The X-33 may be more likely to lead to an AOV than to a commercial launcher, because the AOV booster is a less risky departure from the X-33 than VentureStar. It is smaller and suborbital, so that it can accomplish its goals even if it has a higher structural weight fraction or a less efficient engine than the VentureStar.
The X-33 is not the only possible solution. Boeing, working on reusable booster concepts, is leaning towards a horizontal-landing solution with a blended wing-body configuration, based on its Boeing and Rockwell heritage, rather than a vertical take-off, vertical landing type similar to the McDonnell Douglas Delta Clipper. Moreover, there are commercial programs that could be suited to the AOV role. Space Access, for example, is proposing a two-stage horizontal-take-off/horizontal landing launch system with air-breathing ejector ramjet engines. The company claims that it could be fully operational in 2003.
The most important goal for an AOV booster can be described as 'aircraft-like operations'. This means being able to launch at short notice, to operate in all conditions from a variety of launch sites, and to recover the vehicle and ready it quickly for another mission. Rapid launch implies the use of non-toxic, easily handled fuels such as LOX/kerosene or LOX/ hydrogen. The key to being able to use many launch sites is reliability - avoiding the necessity for an over-water trajectory. A pre-requisite for the ability to launch in all conditions is that the vehicle is recoverable.
The AOV's sub-orbital trajectory covers a ground distance of 2,200km, so a launch from the continental US means a recovery elsewhere in the US, probably at Malmstrom AFB or one of the other northern-tier bomber bases. This requires a reliable all-weather automatic landing system, and a means of returning the vehicle to its launch point. The NASA/Orbital Sciences X-34 program is aimed at demonstrating technology to deal with these issues.
Development work is also under way on three optional upper stages for the AOV. The most sophisticated of these is the Space Maneuver Vehicle (SMV), designed to provide the USAF with a new level of flexibility in space operations. Today's spacecraft are limited in their ability to change their orbital paths. Any maneuver eats into the vehicle's finite fuel supply, and hence its lifetime. The SMV is a small spacecraft that carries a relatively large fuel supply, and when its fuel is used it can be recovered and refueled.
The SMV has a wide variety of uses. As a reconnaissance system, it can provide much faster response to a commander's needs than the National Reconnaissance Office's spacecraft, and can perform rapid orbital changes to approach a target at an unexpected time. In the space control mission, it uses its agility to perform a co-orbital maneuver or a fly-by, using multiple sensors to examine a suspicious spacecraft at close range. The logical extension of this role is to equip the SMV with the means to put a spacecraft out of action if it appears to be hostile.
The SMV is inexpensive enough to be used as a substitute or supplement for conventional satellites. With its own solar arrays and batteries, it has an endurance of up to 12 months. This would mean that SMVs could be stationed on-orbit as short-notice gap-fillers for LEO (low Earth orbit) satellite constellations.
NASA and the USAF are developing and building an SMV demonstrator. In December, NASA selected Boeing to build the first of a series of Future-X prototypes: the Boeing Advanced Technology Vehicle (ATV), which is expected to carry the designation X-37. Designed by the former Rockwell unit at Seal Beach, California, the ATV is based on a 1993 concept called Refly, which was being pursued under USAF funding before the NASA contract was awarded. Last August, a low-speed test vehicle, designated X-40A, was released from a helicopter at 9,000ft above Holloman AFB in New Mexico, and glided safely to an autonomous landing.
Boeing will design and build the ATV at Palmdale, California. The 7.8m long vehicle will have a wingspan of 4.5m, an empty weight of 1,680kg, and a loaded weight of 5,350kg, including a 540kg payload in a 1.2 x 1.2 x 2.1m bay. It will be powered by a Rocketdyne AR-4 rocket engine burning RP-1 (kerosene) and hydrogen peroxide. The primary structure will comprise high-temperature graphite/bismaleimide composites, and will be protected by an advanced tile and blanket TPS.
The onboard electronics will use an open systems architecture and will provide the same support for the payload as a spacecraft 'bus'. The basic NASA program calls for the vehicle to use battery power on orbit, but it is designed to include solar-electric panels in the payload bay doors.
The first step in the ATV program will be to upgrade the X-40A so that it can be released at M0.8 and 40,000ft from NASA's NB-52. The ATV itself will be air-launched for about 30 envelope-expansion test flights, starting in early 2001. As currently planned, this will lead to a Shuttle-launched orbital flight in late 2001 or early 2002, supporting the Scientific Advisory Board's recommended decision date for a full-scale AOV program.
The second upper stage for the AOV is the Modular Insertion Stage (MIS), a small expendable rocket designed to orbit a payload of 900-1,800kg. The principal goal for MIS is low cost: the USAF is looking at a price tag of US$600,000 or less. Technologies under development for MIS include low-cost composite fuel tanks; uncooled, ablative nozzles; and a pressure-fed propulsion system using kerosene and either LOX or hydrogen peroxide.
The third (and potentially most controversial) upper stage for the AOV is the Common Aero Vehicle (CAV). The CAV is a lifting-body boost-glide vehicle designed to attack time-sensitive ground targets. Launched by an AOV booster, the CAV would re-enter the atmosphere in a hypersonic glide, descending to a speed and altitude where it could dispense conventional, aircraft-type precision-guided munitions. Plans and documents suggest that the CAV would have a range of about 14,000km and would weigh between 700-1,100kg. A CAV demonstration program has been identified by the USAF as the X-41.
The USAF plans to launch the CAV with both the AOV and a conventional ballistic missile (CBM). The USAF is already conducting an Advanced Concept Technology Demonstration (ACTD) for the CBM. Textron Systems is developing a GPS-guided re-entry vehicle with a non-nuclear hard-target warhead. It will be mated to a surplus Minuteman II Inter-Continental Ballistic Missile booster and guidance bus, and a flight test from Vandenberg AFB to Kwajalein Missile Range is planned for FY01. Unlike most ACTDs, this program will not result in the deployment of operational systems, but the USAF expects this to lead to the development of a CAV-armed CBM, possibly with a new booster.
These are not 'on-orbit' weapons, so they technically avoid the US administration's ban on placing weapons in orbit. However, the fact that the AOV is potentially a strike system runs counter to the belief that space should be free from weapons.
The same kind of sensitivity applies to the invisible boundary in space control, between 'surveillance' and 'negation'. One program in this area is the XSS-10 'microsat', being jointly explored by Space Command and NASA. This 20kg spacecraft is designed to autonomously acquire and track targets in space, rendezvous with them and perform an imaging inspection. Formerly called Clementine II, the project was halted in late 1997 by the same (now reversed) line-item veto, as the AOV. The first XSS-10 will be ready for launch aboard the Shuttle in April 2000. Future microsats could be launched by the AOV/MIS combination.
The next US administration is going to have to tackle the question of space warfare, and the AOV will be the most visible symbol of what may be an energetic controversy. The rights and wrongs of an increased military presence in space may be debated, but there is no disputing that the technical means to establish such a presence are closer to reality today than they have been in decades.
