Space Control with a Reusable Military Aircraft (SCREMAR)
The SCREMAR (Space Control with a REusable Military AiRcraft) is a transatmospheric vehicle that can provide flexible, reliable, routine, and readily available access to space well into the future for a variety of applications. It is a multiple-stage-to-orbit (MSTO) vehicle designed for integrated use with the SHAAFT. It is 66 feet long with a gross takeoff weight of 50,000 pounds, roughly the size of an F-15, and fits piggyback on the SHAAFT. The hypersonic capabilities of the SHAAFT are used to take the SCREMAR to mach 12 at 100,000 feet where the SCREMAR then separates. The SCREMAR then uses its two rocket engines to complete the remainder of the access-to-space mission in a similar fashion as the Space Shuttle, returning to a predetermined base for a horizontal landing on a conventional runway. Since SHAAFT produces a significant portion of the velocity change required to get the SCREMAR to orbit, the size of the SCREMAR can be greatly reduced while the payload increased.
The SCREMAR is a TAV/orbiter capable of carrying a 3,000 pound payload to a low-earth orbit. This payload will most likely be three 1,000-pound satellites, but there are also other options. The SCREMAR is not designed to replace the existing fleet of space launch vehicles. Rather, it is designed to fulfill a specific niche that current launch systems do not occupy. Specifically, the SCREMAR accomplishes the deployment and retrieval of satellites for a variety of scenarios (to include critical wartime replenishment), on-orbit support and repair of damaged satellites, and sophisticated ASAT warfare against vulnerable space assets of potential adversaries. Essentially, the SCREMAR can fulfill the essential mission requirements for spacelift, on-orbit support, and counterspace applications.
There are a variety of scenarios where an easily planned access-to-space mission is critical. The best means for accomplishing these missions is a reusable TAV/orbiter, for example, the SCREMAR. The most likely is a situation in which an adversary has managed to render a significant portion of a satellite constellation inoperable. In this situation, the SHAAFT/SCREMAR combination would be a means of quickly replenishing vital space capabilities. This would occur in two possible ways: the SCREMAR would take several new satellites to space to be deployed and replace damaged satellites or the SCREMAR could simply repair damaged satellites by docking with them in their orbit.
The role SCREMAR will play in helping the US maintain its space superiority status well into the future is crucial. In the past, and even present day, the US has enjoyed unopposed access to space, albeit at a very costly and time-consuming process. In the vastly changing political structures throughout the world, it is very likely potential adversaries will have the capabilities required to significantly hinder the missions we now accomplish from space through the use of satellites as well as our access-to-space capability. Due to its increasing importance, space is most likely to be the dominion of the modern battlefield.
The Need for Access to Space
The accelerated pace of the modern battlefield has dictated that the US become increasingly dependent upon their space assets. In fact, the success of the Army, Navy, and Air Force throughout Desert Shield and Desert Storm was due in large part to the advantages provided by global positioning system, communication, and intelligence satellites. The war was won in the air and on the ground because there was no contest in space; the United States maintained control of the ultimate high ground throughout the entire conflict. In the future, space power and control over the ultimate high ground will be critical to winning battles on the sea, in the air, and on land. The SCREMAR can maintain this control.
With the increasing importance on space assets, the US cannot afford to neglect the necessity of space superiority. Space has become a vital means of communication, intelligence, and navigation for the Army, Navy, and Air Force in all military operations. Already in place are large and small satellites of varying types arranged in constellations to perform these and many other specific functions. Most nations of concern do not possess an adequate space infrastructure, but they do, however, possess the ability to level the playing field against the US through the use of nuclear weapons in space. For example, Russia and China, with their formidable space infrastructure, have the capability of posing a serious threat to US space assets. With the assets the US currently has in place and the vital role they fulfill in all military operations, America cannot lose a significant portion of this infrastructure and still function as a modern-day military power.
Nations without a strong access-to-space infrastructure (e.g., Iraq and North Korea) could still significantly hinder the US space capabilities at low costs and with little effort. Consider this: Iraq possess an enormous Scud missile inventory and possibly the ability to procure nuclear warheads. This could be extremely dangerous to US interests abroad. Although the range of the Scud missile is very limited and nowhere close to being able to strike the US mainland, it is a ballistic missile with the capability of reaching the earth's upper atmosphere and lower regions of space if launched straight up. If fitted with a nuclear warhead, the electromagnetic pulse alone due to a nuclear detonation in the ionosphere could wipe out a significant portion of a satellite constellation's ability to operate effectively. Several detonations could make our satellite fleets inoperable.
Future concerns also include the possibility of a nation with notable space capabilities, such as Russia, performing sophisticated ASAT warfare. A resurgent ultranationalist Russia or a disgruntled China could either selectively engage and destroy our satellites as needed or use the previously mentioned method of random destruction depending on how many space assets they have in the area and if they can afford to lose them.
Satellites are extremely fragile spacecraft. This is due largely to the push for lower spacecraft weights (directly impacting lower launch costs) and the fact that no real threat exists in space to damage satellites other than the solar radiation damage (which we have made significant progress over the last few years in reducing) and the extremely unlikely and very rare event of the satellite being struck by a projectile of significant size, such as an asteroid or man-made object. The ability of a rogue nation with no legitimate space infrastructure being able to guide an object to impact a satellite in the vastness of space is an extremely difficult task.
However, with nuclear weapons, accuracy is not an issue. A nuclear detonation close to the earth's atmosphere in the lower regions of space would have enough energy alone to completely obliterate all satellites in the region overhead that are positioned in low-earth orbits. Although the exact effective region for such an explosion alone in space is unknown, it is estimated in the thousands of miles. Clearly accuracy is not a driving factor for an adversary wanting only to take out America's ability to look at them for several hours; they could clear out the entire region above them while they launch a surprise attack on allied forces.
The damage to US satellites extends far beyond just what is done from the impact of the explosion. There is also an electromagnetic pulse that is dispensed by the explosion, extending for thousands of miles beyond the area affected from the detonation forces, which could incapacitate satellites' sensitive sensors and circuits, although the satellites' structures themselves would not be significantly damaged. This electromagnetic disturbance also tends to linger over an affected area for extended periods of time (e.g. several days) that make operations over the infected area extremely difficult until the disturbance had degenerated.
Regardless of the duration of the electromagnetic disturbance, there would be a significant US interest to replace those satellites in the constellation which have been destroyed and repair those which have been damaged. Replaced and repaired satellites should be ready to become fully operational as soon as conditions permit or in as little as a couple of days. Although current technology uses "hot spares" (satellites that are already in the constellation, but not turned on) to cover for satellites that quit working for various reasons, these extra satellites would most likely also be damaged to some extent from the detonations. Using hot spare satellites that are in other orbital planes in order to reduce the impact of such an explosion is extremely difficult. Only if the satellite is in the same orbital plane does it have a chance of being effective in covering the area of responsibility for a destroyed or damaged satellite in an emergency situation. In the event that several nukes are set off at given intervals over an area, the effect of hot spares being able to restore previous capabilities is drastically reduced.
With flexible access to space through the use of a transatmospheric vehicle, (for example, the SCREMAR, the military would be able to replenish destroyed satellites and repair damaged ones in a substantially reduced time frame relative to what is required by today's launch systems. This restoration time would be measured in terms of hours in getting a spacecraft that is on alert status into orbit with its payload of new satellites and/or replacement parts and getting the new/repaired satellites operational. A specially configured TAV could also perform various aspects of sophisticated ASAT warfare again enemy space assets. Also of importance would be the development of a technology that would readily allow access to space on a regular basis during all phases of conflict: before, during, and after the war. Having easily obtainable access to space on a regularly repeated basis would greatly increase the United States' chances of maintaining overall combat effectiveness through such a situation as previously described. Space control would become as regular a mission as air superiority. There is a definite need for the US to develop some form of countermeasure to the diverse space threats in anticipation of maintaining space control throughout the duration of any battle.
General Mission Requirements
The success of the access-to-space mission is dependent on several key requirements. Although not all of the requirements mentioned in this section are critical, they are necessary in terms of getting the flexibility, reliability, responsiveness, and low costs desired in an access-to-space TAV/orbiter. Some of the more critical requirements include (1) ability to get a 3,000-pound to a LEO, (2) 50,000-pound gross weight, (3) release point from first stage at mach 12 at 100,000 feet, (4) launch-on-demand capability, (5) ease of mission planning, (6) small, flexible, highly trained ground crew, (7) build off of existing infrastructure as much as possible, (8) develop in conjunction with other hypersonic technologies, (9) rapid turnaround time, (10) horizontal takeoff and landing (HTOL), and (11) global reach from a suborbital flight path. These requirements are directly related to increasing flexibility and cost effectiveness. Other important requirements to be considered are manned and unmanned aircraft versions and modular cargo bay for ease of integration of various cargo and weapon systems.
The most critical requirement for a reusable military aircraft to fulfill the flexible access-to-space mission is the ability to take a sizable payload into a LEO. Having a military aircraft that is just designed to get to space without carrying any type of payload, as past programs have suggested, is virtually useless as a space control asset. The US' presence in space is based on the number of deployed and usable satellites.
Typical communication and intelligence satellites weigh in the neighborhood of 1,000 pounds or so and have dimensions roughly 6 feet x 6 feet x 6 feet when folded up. This is more or less the case for the newest constellation of satellites being deployed, the Iridium satellites, with expected reductions in size and weight in time with technology advances in materials and electronics. Having this capability would allow the SCREMAR to put approximately three satellites into a LEO (approximately 100 nm x 400 nm) in a single mission that can be planned and executed in a few days. Using today's technology, this would most likely take three separate missions with several weeks of planning in between each launch.
The benefits in terms of time and monetary costs can be seen from just this aspect while operational benefits extend even further. The SCREMAR could replenish an entire orbital plane of a satellite constellation with just three missions that could be accomplished in succession. The importance of the ability to plan and execute these missions in a short time as well as turn around the vehicle for subsequent missions quickly will be discussed in more detail later. Nevertheless, the importance of this capability can be seen in that satellites cannot be deployed (or repaired) if they (or the necessary tools) cannot be taken to orbit.
The requirement for a gross takeoff weight around 50,000 pounds is driven by several factors. First and foremost is that this is the maximum payload of the SHAAFT. Also of importance is the fact that the lighter the overall weight, less fuel will have to be used to get the required change in velocity to get such a spacecraft into orbit. This places less demands on the need for significant improvements in both fuel and rocket propulsion technology. This relationship can be seen from the following orbital velocity equation:
where g is the earth's gravitational acceleration, ISP is the specific impulse of the fuel, m0 is the initial mass, and mp is the mass of the propellant. Thus, costs savings are realized both in terms of cost to build and cost to launch/operate when existing fuel and propulsion technologies can be taken advantage of.
The constraints placed upon a final stage TAV/orbiter from the first stage, for example the SHAAFT are critical. Having a TAV/orbiter much greater than 50,000 pounds causes a significant impact on the ability for the SHAAFT to accelerate the SCREMAR to mach 12 at 100,000 feet. The rationale for needing to stage at mach 12 at 100,000 feet is explained later; however, it is important to realize that the issues of size, weight of dry structure, weight of payload, weight of fuel, and staging are all interrelated and have significant impacts on each other. Previous studies, such as Blackhorse,25 Beta,26 and Saenger,27 have concluded that a spacecraft roughly the size of an F-15 or F-16 would be the most beneficial configuration in terms of technology required to produce such a vehicle.
Another important consideration is the fact that attempting to produce such an orbiter that carries an equivalent payload, 3,000 pounds, that is much lighter than 50,000 pounds requires a significant breakthrough in structure materials. As it stands now, the proposed SCREMAR's total weight is nearly 75 percent fuel and the other 25 percent encompassing both the payload and dry structural weight. As can already be seen, this is going to require improvements in structural technology; however, it will not require a significant breakthrough, only the natural progression of technology with time.
As alluded to earlier, there is also a critical need for staging at mach 12 at 100,000 feet. Studies have shown that the altitude is not so much a factor as is the staging mach number. In order to reach a LEO, the required velocity is around 26,000 feet/s (30,000 feet/s considering losses due to losses from pressure, drag, etc.). Since the desired orbit is at least 100 nm, the effects on required velocity change of staging at 50,000 feet versus 100,000 feet versus 150,000 feet are nearly negligible versus staging mach number. The overriding factor is the change in velocity that the TAV/orbiter, SCREMAR, has to produce on its own. Staging at mach 12 versus mach 8 means a starting velocity difference of approximately 12,000 feet/s versus 8,000 feet/s. This is a difference of having nearly 40 percent of the required orbital velocity supplied by the first stage versus 27 percent. Similarly, the staging height of 50,000 ft versus 150,000 feet is only between 10-25 percent of the total height above the earth needed, but the same velocity change has to be produced.
Staging at a lower altitude requires a larger vehicle since more fuel will be required to achieve the additional height as well as overcome the effects of air density. This places more demands on the structure all over, including weights and TPS. Staging at a higher altitude is limited to the capabilities of the first stage, e.g. the SHAAFT, since it uses airbreathing engines. Either way, the same amount of total energy is required to put an object in orbit. The velocity of the TAV/orbiter that is required to get it to a specified orbit is given by:
where v1 is the tangential velocity at the minimum radius, r1 is the minimum radius, r2 is the maximum radius, and is the earth's gravitational constant. The only biggest difference is how much of this velocity is supplied by the first stage, the SHAAFT, and how much will have to be supplied by the final TAV/orbiter stage. The diagram for describing this orbital equation around earth is given below (note: the figure is not drawn to scale):
Using the LEO previously described, r1 would relate to the 100 nm part of the orbit and r2 would relate to the 400 nm part of the obit. However, this equation also takes into account the radius of earth, re, which is 3,443 nm (much greater than the 100 nm or 400 nm height above the earth's surface). For instance, r1 = re + 100 nm and r2 = re + 400 nm. Therefore, the real benefits in terms of the velocity change that would have to be produced by the TAV/orbiter considering staging at 150,000 feet versus 50,000 feet are less than 0.01 percent. Staging above 100,000 feet places other excessive demands on the SHAAFT since it is an airbreathing aircraft. Having a staging height somewhere below 100,000 ft means that more fuel will have to be burned to achieve the additional height, increasing operating costs. This would also mean that additional size would be needed to hold the additional fuel. In terms of benefits versus costs, 100,000 feet appears to be the optimum staging altitude. From this altitude, SCREMAR size increases significantly with a 50 percent decrease in staging height; but the size does not decrease significantly for a 50 percent increase in staging height.
The effects of staging velocity are even more critical. Using the two equations above and spreadsheets that varied the different parameters affecting the SCREMAR, relationships were determined between staging height, mach number, payload weight, gross total weight, and fuel weight. Various fuels with different densities and ISPs were used with staging heights between 50,000 feet and 150,000 feet and staging mach numbers between eight and 12. With height, the only amount of additional fuel required is that to achieve an extra 50,000 feet or so of altitude. However, the study showed that much more additional fuel is required to produce the extra required velocity from mach 8 than from mach 12 at every altitude than the amount of additional fuel required to produce the additional height from 50,000 feet to 150,000 feet at either mach 8 or mach 12. Thus, a TAV staging at mach 12 at 50,000 feet would be about half the size of a TAV staging at mach 8 at 150,000 feet. With the considerations mentioned before, the optimum staging conditions for the SCREMAR are mach 12 at 100,000 feet.
Also, developing the technology for the first stage to have the capability to stage at mach 12 will be less costly in the long run than trying to develop a TAV/orbiter of roughly the same size that overcomes greater velocity changes. The SCREMAR TAV/orbiter concept is already stretched in terms of existing technology for dry structural weight versus size. Having a staging point of mach 12 at 100,000 feet greatly reduces the amount of fuel needed to achieve the required velocity change, and thus the overall size of the TAV/orbiter. Also, 100,000 feet is a reasonable altitude in which the SHAAFT can operate with sufficient air and without the excessive drag penalties. This topic is also discussed in more detail in chapter 5.
The requirements for launch-on-demand capability, ease of mission planning, rapid turn-around time, and a small, flexible, highly trained ground crew go hand-in-hand. The requirement for launch-on-demand capability stems from the need for time-critical replenishment/repair of US satellites. Only by having the capability to replace damaged satellites in a short time can the US maintain the upperhand with space assets during a military operations. As previously mentioned, consider the case in which a majority of our space assets or a key satellite have been destroyed. Today's capabilities would require weeks to replace a single key asset, months or even years to replace a majority of a constellation. With the pace of the modern battlefield, the war could long be over before we could even get a single satellite on-line with today's launch systems. By having launch-on-demand capability, a mission to replace damaged or destroyed satellites could be underway within hours of the incapacitation of the satellites, thus getting the US back into the war with C3I in a matter of days.
Of course, getting three satellites into orbit in a matter of hours is great, but really means nothing if another mission cannot be launched for several weeks. Thus, the need for launch-on-demand is required in conjunction with the need for ease of mission planning and rapid turnaround time for vehicle missions. A given mission should be able to be identified and planned within a days time. The proposed time frame for turnaround time, six to eight hours, is enough to allow for two missions to be completed in a single day, allowing also for a four to six hour mission time. A normal orbital plane of a constellation usually consists of 5-15 satellites, depending on the orbital height and number of satellites required in a field-of-view (FOV). Having six satellites placed in an orbital plane would be enough in most situations to provide substantial coverage over any given area.
It is also important to realize that these two requirements of launch-on-demand and rapid turnaround can only be met with a small, flexible, highly trained ground crew. The more people involved, the more time required for everyone to communicate and agree upon the status of the vehicle and increased chances of breakdowns in communication. Also, having a small, highly trained ground crew reduces the operating costs by not having to use as many resources to maintain operability. A small, flexible crew would also be much easier to transport in the event that the SCREMAR has to divert to a remote base. Most importantly, it implicitly requires that everything be done in a relatively simple manner. The less complexity, the cheaper the costs, the easier to operate and maintain, and the less chance there is for a major catastrophe.
With the need for reducing the complexity of the overall system, there are a couple of complementary requirements: (1) develop critical technologies in conjunction with other hypersonic programs (for example, the SHAAFT and SHMAC) and (2) build off the existing infrastructure as much as possible. These requirements produce several key benefits to the program.
Savings in time and costs can also be realized by developing critical technologies, such as propulsion, fuels, TPS, and structural materials in conjunction with the other hypersonic programs of the SHAAFT and the SHMAC as well as extracting information and experience gained from vehicle and technology programs done and underway elsewhere. Since the technologies will be developed together, they will be cheaper in terms of the usefulness gained among the different systems (SCREMAR, SHAAFT, and SHMAC) rather than applying technology to only one. It will also make it easier to integrate the technologies among the three systems since they will be applicable to all systems. By building off of the existing infrastructure and developing hypersonic technologies together at one time, the SHAAFT/SCREMAR/SHMAC becomes a much lower-cost and less-complex integrated weapons system.
Building off of the existing infrastructure means several things. Considerable monetary savings can be realized by not having to develop and build and entirely new and different access-to-space infrastructure. Existing infrastructures for both space and general aviation can be utilized and combined. Also, facilities for handling the support of the SHAAFT and SCREMAR combination will be available worldwide, wherever, for example, the SCREMAR lands, providing greater flexibility to the SHAAFT/SCREMAR system. Only slight modifications to training and facilities would be required, reducing both costs and time to produce an operational infrastructure that is mission capable.
Building from the existing infrastructure has several advantages. First is the reduced costs associated with being able to redesign and utilize existing structures versus having to develop a completely new infrastructure. This is due primarily to the fact that almost everything needed to support operations is already in place and has already demonstrated the capability to support similar operations. Also, by combining assets from both the aero and space infrastructures, all US Air Force aircraft operations could be conducted from one multifunctional infrastructure rather than three separate ones. This is consistent with the Air Force's movements towards composite wings. It also increases the flexibility of the SHAAFT/SCREMAR system by expanding the number of bases from which it can operate. This is an extremely important factor in the storage of fuels. If a majority of bases do not possess the ability to store the fuels required by both the SHAAFT and the SCREMAR, the base is essentially useless unless the fuels can be transported in by a special aircraft, such as a modified KC-10. However, if this is not possible, then the SCREMAR can be transported to wherever the SHAAFT is located via a Boeing 747, similar to the Shuttle.
It is also necessary that the infrastructure be able to support both the SHAAFT/SCREMAR system. This is because the SHAAFT is required for SCREMAR operation. The SCREMAR is not designed to takeoff on its own. It must be loaded onto the SHAAFT in order to get off the ground. As designed, the SCREMAR is currently expected to fit on top of the SHAAFT. This could present some problems with bases having the capability to load the SCREMAR onto the SHAAFT in the situation where the SCREMAR must be diverted to a remote base. If a majority of bases do not have this capability, then they become useless. The means fitting the aircraft together, either to the SHAAFT or a 747, should either be transportable or extremely simple. The Beta concept of rolling the TAV/orbiter underneath the staging vehicle and then attaching it should be explored more.28 In any case, the SHAAFT should be able to get to any location of the SCREMAR and at least be able to return it to a staging base, if not launch another mission from where it is.
As previously mentioned, requirements dictate that rapid turnaround is a capability that should definitely be sought after. The ability for rapid turnaround extends primarily from the ability to perform maintenance and other ground operations. Normal maintenance and ground operations, such as refueling and reloading, should be able to be accomplished in the desired time to meet the six to eight hour turnaround time requirement on the ground. Other maintenance and ground tasks, such as cleaning and damage repair, should be able to be accomplished within reasonable times. A good criteria would be approximately the same time it takes to accomplish these with today's fighter aircraft. Also of importance here are members of the ground crew. They play an important role in accomplishing all of the maintenance and ground tasks. They should be highly trained and specialized in accomplishing all of the necessary functions that occur on the ground.
Current launch systems are not standardized in their configurations. There is a definite need for standardizing launch vehicles and payload interfaces. Having payloads that are interchangeable among different vehicles increases the flexibility of both the payload and the launch system. This standardization also reduces the complexity involved with having to put similar payloads on different spacecraft or a variety of different payloads upon a single spacecraft, such as the SCREMAR. It could be done simply by using modular cargo bays that can be added and removed depending upon mission requirements and payload. Thus making it easier to reload cargo onto another spacecraft in the event that a mission is aborted prior to takeoff. The ability for cargo to be placed on different airframes allows for easier transportation of cargo to different bases. In a way, it also inherently implies that subsequent space transport systems will be developed. Having standardized payload interfaces also allows for the vehicle and payload to be prepared in parallel. Today's systems often require that the payload be prepared and loaded only after the vehicle is in place or vice-versa. Using modular cargo bays, the SCREMAR would be able to be prepared for launch and already loaded onto the SHAAFT while the cargo is still being modified. The cargo could be loaded into the SCREMAR either before or after connection to the SHAAFT.
Because of SCREMAR's integration with the SHAAFT, there are two other important requirements: (1) the capability for horizontal takeoff and landing and (2) the capability for global reach from a suborbital flight path. Like previous requirements, these two also go hand in hand. The ability for horizontal takeoff will be provided by the SHAAFT. Having this capability allows for the SHAAFT/SCREMAR system to operate from any base with a sufficient support structure and a conventional Class A runway. This would be extremely important in the event that the enemy has taken out our current space facilities at Vandenberg AFB, California, and Cape Canaveral AFS, Florida. In the event of war, these bases would become primary targets for a nation trying to hinder our space control capability. This ability also provides for greater flexibility in the planning, timing, and versatility of access-to-space missions.
Likewise, the capability for horizontal landing provides similar advantages along with others and is characteristic for both the SCREMAR and SHAAFT as individual aircraft. First is the reduced weight since the TAV/orbiter will be able to glide to a landing in a similar manner as the Shuttle. The landing gear would only have to be designed to support the nearly empty weight of the TAV/orbiter since almost all of the fuel will be spent in achieving orbit. Landing vertically on rockets after reentering the earth's atmosphere not only presents a challenge but also requires that additional fuel be carried in order to provide significant thrust as the vehicle reaches the ground. Conversely, vertical landing would provide for the capability to land practically anywhere a concrete pad could be laid. Although already demonstrated through programs such as the DC-X, this technology need not be exploited since a little fuel will remain in the SCREMAR in order to ensure global reach from a suborbital flight path. Also, being able to land in the middle of nowhere does little good if the SCREMAR can not be efficiently transported back to a base where is can be mated with the SHAAFT and its zero stage. Nevertheless, the capabilities of global reach from a suborbital flight path would allow the SCREMAR to reach and land on any conventional runway in the world. Which is very essential if our current facilities are destroyed, especially if they are destroyed while the SCREMAR is accomplishing a mission.
The requirements mentioned throughout this section seem to be the most critical requirements driving the design of the SCREMAR TAV/orbiter concept; however, they are not the only factors to be considered. If the access-to-space mission is to truly ever become cheap, flexible, and reliable, there are millions of other considerations that need to be taken into account. A couple of the more important of these considerations seem to stand out. First is the potential to develop both piloted and unpiloted versions of the SCREMAR. The first step lends itself to the piloted version since real-time control and on-hands experience will be necessary in accomplishing the prescribed missions. However, with increases in technology, unpiloted versions will allow for the accomplishment of almost all of the prescribed missions (with the possible exception of only on-orbit support) while providing less risk of human casualties. Having less manpower to operate would also be a substantial benefit since the entire mission could be controlled by one person on the ground.
As alluded to earlier, another important consideration is a modular cargo bay with standardized cargo and weapon modules. This speeds up the turnaround time significantly since subsequent missions can already be preplanned and prepackaged before the TAV/orbiter even returns to the ground. It also reduces the costs of having to fit individual payloads to individual spacecraft cargo bays. A standardized system could be incorporated that could be applied to future spacecraft, reducing the need to continually redesign cargo.
The requirements, as defined throughout this section, play a critical role in determining the final design of the SCREMAR TAV/orbiter concept. Obviously, these are not the only factors involved in developing access-to-space technology, nor are they absolute. Although there are many factors to be considered, these consistently appear throughout various studies to be the most critical in developing ready, reliable, flexible access to space. Concentrating on these requirements yields the greatest possibility of developing an access-to-space vehicle that successfully accomplishes all of the missions previously presented in this study.
With the increasing importance being placed on space assets such as communication, intelligence, and GPS satellites, the US can not afford to overlook the drastic impact of having a significant portion of the existing satellite fleet wiped out. It takes dozens of satellites in a constellation just to make the constellation operational enough for practical applications. With today's launch capabilities, it normally takes months, or even years, to insert a satellite constellation into orbit. This is due to the inefficiencies of only being able to take up one or two satellites at a time with launch intervals that take months to be planned and executed.
With the future possibilities of threats that face space assets, the
US must have a viable means of maintaining control of space. As with maintaining
control over the air, there must be a space infrastructure designed to
provide Force Enhancement, Force Support, and Space Control. The most likely
solution to accomplishing these missions with a single system is Space
Control with a Reusable Military Aircraft. A TAV/orbiter (fig. 4-1) roughly
the size of an F-15 and capable of carrying a 3,000-pound payload to LEOs
could fill the major facets of these missions by accomplishing ready, reliable
spacelift and on-orbit support while also providing a platform for counterspace
operations. In fulfilling these multiple roles, the advantages of flexible
access to space with a single platform can be realized.
Figure 4-1. SCREMAR Performing Various On-Orbit Operations.
The three primary missions to be accomplished by the SCREMAR TAV/orbiter are (1) deployment/retrieval of satellites, (2) repair of damaged satellites on-orbit, and (3) antisatellite warfare against enemy space assets. These missions (fig. 1-3) help achieve the broader concepts of Force Enhancement with spacelift and replenishment of space assets, Force Support by providing on-orbit support, and Aerospace Control through counterspace and counterinformation tactics achieved with ASAT. However, with the capabilities of a small TAV/orbiter, other possible missions still exist. SCREMAR could also be used as weapons platform for launching key strikes from above (strategic attack) as well as reconnaissance platform to gain and disseminate tactical information and intelligence in real time (Information Operations and Combat Support). These missions could be accomplished by manned or unmanned versions of the SCREMAR.
Deployment/Retrieval of Satellites
The current successes enjoyed by US space operations are due primarily to the large, unopposed fleet of satellite constellations which has taken years to acquire. With an enemy capable of performing any of the various kinds of ASAT, these years and billions of dollars could become vain as the US would be unable to operate on the modern military battlefield. Having routine, easily accomplished access to space allows the effects of such a blow to be significantly reduced. This is best accomplished by the capability of ready, reliable deployment of satellites provided by a small TAV/orbiter. In a situation where the enemy has detonated a nuclear weapon, or a series of nuclear weapons, near satellite orbits, wiping out a majority of a constellation, the SCREMAR could be used to replenish destroyed satellites.
With a rapid turnaround mission time, the SCREMAR could deploy as many as six satellites within a single day. Time to get a complete satellite constellation on-line and operational could be reduced to just a few days. This limits the enemy's ability to downgrade our command, control, communication, and intelligence (C3I) operations for any significant period of time. Satellite replenishment could be used in any situation in which more satellites are desired, including the cases where an enemy has selectively destroyed several key satellites and just adding new constellations for various reasons. The TAV/orbiter could also be used to retrieve severely damaged satellites and return them to earth for repairs. Although the need for this mission is clear during war, it could also be accomplished during peacetime to aid in the normal deployment of satellites on a regular basis, also providing operational experience to the crews of the SHAAFT/SCREMAR platform so that they have the knowledge and understanding to accomplish the same missions during the accelerated pace of war.
Repair of Damaged Satellites
In the situations described previously, not all satellites will be destroyed. In some cases, it might be more cost and time efficient to have many of the damaged satellites repaired while in orbit. This is especially true if all of the satellites are in the same orbital plane. The SCREMAR TAV/orbiter could accomplish this by simply slowing down or speeding up within the orbital plane to dock with individual satellites and repair them real time. This significantly reduces the costs of an operation by not having to take as much of a payload into orbit (only the necessary tools and replacement parts) as well as the costs of not having to actually build replacement satellites. Time would be reduced in that the in-orbit satellites would not have to be positioned nor configured. As soon as they are repaired, they would be on-line and ready to go.
This mission could also be accomplished in conjunction with the deployment/retrieval of satellites for maximum effectiveness, for example, the SCREMAR would reach orbit with replacement satellites and deploy them, repair the slightly damaged satellites, and retrieve the severely damaged satellites, all in one mission. As previously mentioned, the missions of spacelift and on-orbit support could also be performed during peacetime as a means of maintaining a viable satellite fleet as well as providing practice for routine access to space during wartime situations. This would be an essential portion of the training the crews receive.
Another integral form in maintaining space control is space superiority. In a wartime situation, it is very plausible that our enemy will also have significant space assets. SCREMAR could be used to perform sophisticated ASAT to take out the enemy's "eyes" and "ears." Just as the destruction of our satellites could significantly hinder our C3I capabilities, so could the destruction of the enemy's satellites hinder theirs. Having the ability to gain an intelligence advantage over the enemy and to be able to communicate when they cannot provides a significant advantage, especially in the fast pace of the modern battlefield, as demonstrated in Desert Shield and Desert Storm.
This could be accomplished by fitting the SCREMAR TAV/orbiter with a weapons system capable of destroying satellites at varied ranges, perhaps a laser or other beam weapon. Also, the SCREMAR TAV/orbiter could simply "capture" the enemy's satellite, take it out of orbit, and bring it back to earth. The satellite could be dismantled and probed for valuable information with regards to the enemy. Another concept is to have the SCREMAR dock with the enemy satellite, similar to repairing operations (fig. 4-1), and "fix" the satellite so that it sends falsified information controlled by the US as a means of deceiving the enemy. This mission achieves several principles of war, including taking out the enemy's ability to see and communicate along with surprise by deception.
Although these missions alone are enough to provide the US with the ability to control and exploit space, the SCREMAR is not limited to just these. Once the technology for a TAV/orbiter is developed, variations of the SCREMAR could be developed to serve as a suborbital or space-based weapons platform (depending on the various treaty requirements) for attacking the enemy from overhead as part of a strategic attack or as a reconnaissance platform for gaining wartime intelligence in real time. The SCREMAR could serve as the ultimate standoff weapon by being able to attack well out of range of any enemy fighter or missile.
Possible weapon configurations include an extremely powerful laser for attacking pinpoint strategic locations and the capability to release either conventional or nuclear "brilliant" munitions from the cargo bay and guide them to their targets from a suborbital flight path. As a reconnaissance spacecraft, the SCREMAR could be used to direct a battle in real time by gaining valuable intelligence information from above and sending it to particular on-field commanders. The TAV/orbiter could also be used to gain information in a gap that working satellites do not cover.
Having a well-developed infrastructure does not mean just being able to provide maintenance to the SCREMAR while it is on the ground. The infrastructure must also have the necessary systems to allow the SHAAFT/SCREMAR to function operationally. This is in reference primarily to the control centers that communicate with, exchange information with, and direct operations of the SCREMAR. It is the operations of the SCREMAR that accomplish the missions, not the ground operations. Operationally, there are four phases of a mission that must be considered: (1) preflight, (2) takeoff/separation, (3) space operations, and (4) reentry/landing. Each is unique and presents its own challenges to the SCREMAR.
Preflight. The preflight phase includes all of the ground operations: mission planning, refueling, loading cargo, loading onto the SHAAFT, maintenance, etc. The importance of many of the factors to be considered during the preflight phase have already been addressed. The main focus in this phase is on the ability to have reliable and quick ground operations that allow for the SCREMAR to be launched on demand and accomplish successive missions rapidly. Of great importance is the ability to be able to reload the SCREMAR with cargo and onto the SHAAFT for a turnaround mission. It is in the other three phases where the SCREMAR as an operational vehicle will earn its money.
Takeoff/Separation. The takeoff/separation phase begins once the SHAAFT has started its takeoff roll and ends once the SCREMAR has successfully separated from the SHAAFT and is climbing to space under its own power. The SCREMAR will be loaded in a piggyback fashion aboard the SHAAFT. The SHAAFT will already be placed on its zero-stage flying wing. Essentially, the SCREMAR will take off by means of the SHAAFT's and zero-stage's engines as a multiple-stage-to-orbit (MSTO) vehicle. Upon departure, the SHAAFT will separate from its zero-stage around mach 3.5 at 60,000 feet, as previously described in chapter 2. The SHAAFT will then continue to accelerate and climb to its maximum velocity of mach 12 at 100,000 feet. Here, a pop-up maneuver will be performed in which the SCREMAR will detach from the SHAAFT. Once free and clear from the SHAAFT's wake, the SCREMAR will ignite its rocket engines and accelerate to orbit.
There are a couple of very important factors that need to be examined during this phase. First is the shock/shock interactions that would occur during separation and the impact they would have on both the SHAAFT and the SCREMAR. If they cause significant problems, then ways to reduce the problems need to be sought, such as releasing or ejecting the SCREMAR directly backwards. Another consideration is how the maneuver should be performed to release the SCREMAR or if any maneuver needs to be performed at all. This is the most critical phase of the entire mission. More things could go awry here than at any other time, with a likely exception being the landing phase. Nevertheless, separations at these high speeds have never been demonstrated before and must be studied extensively in order to quantify the effects and reduce the chance for mishap. Other possibilities for failure during this phase, such as rocket engines not igniting, the SCREMAR not separating, etc. need to be carefully examined to ensure successful completion of the stage.
Space Operations and Reentry/Landing. The next phase is where the mission accomplishment occurs, space operations. This phase, although complex, has already been demonstrated in some respects by the Shuttle and other space vehicles. Similarly, so has the reentry/landing phase. Important items to be considered in these two phases have already had extensive research in past programs. Particularly, these items include thrusters for maneuver in space, thermal protection systems and gliding to a landing from a suborbital flight path.
The SCREMAR will require a means to maneuver in space, especially if it is going to dock with several satellites for retrieval, repair, and ASAT. Of essential importance is how much latitude the SCREMAR will have while maneuvering in LEOs. It is an extremely difficult task with limited maneuverability because of the proximity to the earth's atmosphere. Nevertheless, it can be accomplished by placing small thrusters at various points on the SCREMAR. They will also assist in maneuvering the TAV/orbiter into the proper position for reentry.
Thermal protection systems have been studied extensively. The capability to use heat absorbent tiles for reentry has been successfully demonstrated with the Shuttle; although a similar concept might not be recommended for the SCREMAR. Nevertheless, a significant advancement in TPS would not need to be made for the SCREMAR to accomplish its mission other than what is required for the SHAAFT. This topic is also discussed further in chapter 5.
The ability to glide to a horizontal landing on a conventional runway has also been demonstrated by the Shuttle. The capability just needs to be improved so that global range to any conventional runway can be achieved from a suborbital flight path.
SCREMAR Vehicle Concepts
The design of the SCREMAR TAV/orbiter concept is driven primarily from
the environments it must endure as well as the multiple mission profiles
and the respective requirements. Increased cost benefits can be realized
by increasing the vehicle's flexibility for multiple missions, using common
logistics and operational procedures with other systems, using the existing
infrastructure for support, and designing critical technologies in conjunction
with other programs, such as the SHAAFT and SHMAC. A schematic of the SCREMAR
TAV/orbiter concept can be seen in figure 4-2.
Figure 4-2. Space Control with a Reusable Military Aircraft (SCREMAR).
The SCREMAR is aerothermodynamically designed as a TAV/orbiter that piggybacks aboard the SHAAFT to a release point of mach 12 at 100,000 feet where it then separates and uses two rocket engines to boost up to orbit. It can carry a 3,000-pound payload to orbit, roughly the size of three 6 feet x 6 feet x 6 feet, 1,000-pound satellites. The cargo bay is 6 feet x 18 feet x 6 feet. With a modular cargo bay integration, payloads could vary anywhere from tools to satellites to weapons systems. Upon returning to the atmosphere, the TAV/orbiter would have the ability to reach and land on any Class A conventional runway worldwide. The design is simple enough so all that needs to be done once it returns is loaded with the new prepackaged payload, refueled, and reloaded onto the SHAAFT for another mission. Of course, due to the changing needs, the US has in the operational space environment versions that could be developed for both piloted and unpiloted vehicles.
As previously mentioned, the SCREMAR TAV/orbiter concept is roughly the size of an F-15. It is 66 feet in length and a total wingspan of 40 feet. It has an inverse-cokebottle type of shape that is similar in some respects to that of a lifting body or waverider concept. The wings themselves are fairly short, being only seven feet long each with a slight anhedral but rounded underside to produce a detached shock wave during reentry. Other concepts could have the wings with a slight dihedral and keeping everything else the same. Studies would need to be conducted on which design would be the most beneficial in terms of heating during reentry to the atmosphere, which provides the better lift to drag ratio in order to ensure global range from a suborbital flight path, and which is easier to integrate with the SHAFFT. Studies may also need to be conducted as to whether having the SCREMAR piggyback on top of the SHAFFT (as considered for this report) or whether it might be more beneficial to have the SCREMAR stored inside or underneath the SHAAFT, similar to the Beta concept.29
Considering the vertical stabilizer component of the wings, then each wingspan could actually be considered to be 12 feet. This is due to the fact that the vertical fins are actually canted at roughly 50 from the edges of the wings themselves. The reasoning for placing these vertical stabilizers in such a manner is so that lateral-directional stability can be maintained throughout the high angles of attack that occur during reentry as well as help lower the q's. This is why the vertical stabilizer of the Shuttle had to be enlarged; it was not very effective at the high angles of attack the Shuttle encountered during reentry since it was directly blocked from the airflow by the body. Since there is no inlet for an airbreathing portion of the engine, the entire body configuration can be even more aerothermodynamically designed to support the mission.
There are two rocket engines that would provide enough thrust to get the spacecraft to orbit. There would also be various other thrusters along the body so that the SCREMAR TAV/orbiter could maneuver in orbit. Roughly 75 percent of the TAV/orbiters gross takeoff weight would consist of fuel which would be loaded throughout the entire body, maximizing the available volume. The only areas that would not contain fuel would be the cargo bay, cockpit, and the nose forward of the cockpit where all of the electronics would be placed. As previously mentioned, the density of the fuel as well as the ISP are critical in maintaining the ideal size and weight of the spacecraft. Studies as to which fuels are the most efficient in terms of both ISP and density are discussed further in chapter 5 as well as other important design considerations.
The SCREMAR TAV/orbiter concept has the capability to fulfill all of the tenets of aerospace power: Force Enhancement, Force Support, Aerospace Control, and Force Application. It can perform the missions of spacelift, on-orbit support, counterspace, and possibly strategic attack and reconnaissance. It provides a direct contribution to the missions of C3I operations and counterinformation operations which are accomplished by the satellites it deploys. Refinements may also be used as part of a strategic attack and combat support operations. The use of a small TAV/orbiter, such as SCREMAR, allows for responsive, reliable, flexible access to space in all situations that are crucial to controlling and exploiting space.
The technologies needed for the SCREMAR should be developed in conjunction with the SHAAFT and SHMAC and from other similar programs to reduce time and costs. The infrastructure for supporting the SCREMAR should be developed from existing infrastructures. Because of the integrated nature of the SCREMAR with the SHAAFT, an integrated infrastructure should also be developed. This is because the SCREMAR functions operationally by means of the SHAAFT. Maintenance and other ground operations should be able to be accomplished within the times of what is already required for today's fighters.
There is also a need for standardization among launch vehicles and payload interfaces. In reducing planning, preparation, and turnaround times, the payload and spacecraft should be able to be prepared in parallel. The infrastructure should be able to allow the SHAAFT/SCREMAR to be launched on demand from a quick-reaction alert status while also allowing for the use of the widest number of bases possible. The infrastructure should be designed so that the SHAAFT/SCREMAR can function operationally similarly to today's aircraft.
There is no doubt that space is going to be the battlefield of tomorrow. The SCREMAR TAV/orbiter concept is designed to fulfill a vital role in maintaining control over that battlefield. It is intended to build off of the technologies and infrastructures that already exist or are in the process of being developed. Because of the simplicity of the SCREMAR and the reliance on near-term technologies, a significant breakthrough in technological achievement will not be required. This makes the development costs cheaper and the development time shorter. The SCREMAR, or similar vehicle, is destined to become a mainstay in the fleet of the US Air Force's vehicles. It is the capabilities of such a vehicle that will ensure that the US is able to control and exploit space for years to come through reliable, flexible, routine access to space. This concept will enable the United States to Scream into the Future!
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