Abstract:
A launch vehicle is deployed from an aircraft using gravity extraction of the launch vehicle with the aid of a small parachute which assists the extraction and damps the yaw and pitch of the launch vehicle. The launch vehicle is supported on two rows of tires which are rotatably mounted to the aircraft. Gravity and the drag force of the parachute causes the launch vehicle to roll on the tires along the load deck and out of the aircraft. Because the extraction forces are dominated by gravity, the launch vehicle acquires a rotation in the pitch axis as the launch vehicle leaves the aircraft. After the launch vehicle clears the aircraft, the launch vehicle rotates in the pitch plane, and is damped in the pitch plane by the parachute to a pitch attitude which is 70-80° and the vehicle engine is ignited, detaching the drag parachute.

Description:
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
   This invention was made with Government support under Agreement No. HR0011-04-9-4072 awarded by DARPA. The Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   Many designs have been considered for launching an orbital launch vehicle from a carrier aircraft. The designs which have been considered include carrying the launch vehicle on top of the carrier aircraft, on the bottom of the aircraft, under the aircraft wing, towing the launch vehicle behind the aircraft, and carrying the launch vehicle within the cargo area inside the aircraft. Launching a launch vehicle from a carrier aircraft, while having some limitations in terms of maximum gross weight of the launch vehicle, has many operational advantages. Launching from a carrier aircraft avoids the costs and limitations associated with ground-based launch ranges. Ranges may have restrictions limiting the number of launches which can be performed in a given time frame. At a typical rocket range, launches will be limited with respect to the launch azimuth which can be flown by the necessity of avoiding overflight of densely populated areas. A launch vehicle which is launched from a carrier aircraft, on the other hand, can be based anywhere where the carrier aircraft can be based. A carrier aircraft also has the advantage that it can be used to avoid unfavorable weather by flying around or over a weather system. For low-cost launch systems, the cost of using a national range in the United States can exceed 30 percent of total costs associated with a particular launch. The limitations associated with fixed ranges have caused at least one supplier of launch services to fly vehicle launches from a floating ocean platform, and another supplier of launch services to use a carrier aircraft where the launch vehicle is attached beneath the carrier aircraft or beneath the carrier wing. 
   Air launch can also provide a performance benefit based on the velocity of the carrier aircraft which is imparted to the launch vehicle at the time of separation from the carrier aircraft. Performance benefit is also gained by reduction in aerodynamic drag. Such drag can be substantially decreased by operating the launch vehicle at an initial starting altitude which is above one half to three quarters of the atmosphere. Reduced atmospheric pressure can increase performance of the first stage engine by allowing a greater area ratio between the rocket engine throat and the expansion bell. Reduced atmospheric pressure also allows the use of a lower engine chamber pressure, which, particularly in the case of a pressure fed vehicle, can result in substantially decreased structural weight for the propellant tanks. 
   In the past large airborne payloads, including in one case, a test missile, have generally been extracted from the air cargo bay along with a cradle on which the payload rests, by parachutes released into the air stream behind the carrier aircraft. This known approach has several disadvantages including high loadings caused by the substantial extraction loads, and the need to expend or recover the extraction cradle. Furthermore, the extraction parachutes, followed by orientation parachutes, substantially eliminate the forward velocity of the launch vehicle, thus limiting the benefit which is gained from the air launch. What is needed is an apparatus and method for dropping a launch vehicle from a carrier craft which minimizes loads on the launch vehicle and which minimizes loss of forward velocity, and which eliminates the need for a drop cradle. 
   SUMMARY OF THE INVENTION 
   The launch vehicle air launch method and apparatus of this invention employs gravity extraction of the launch vehicle assisted by a small drag parachute which assists the extraction and damps yaw and pitch of the launch vehicle. A carrier aircraft is pitched up 3-15 preferably 5-7 degrees so the load deck of the carrier has an upward slope. The launch vehicle is supported on two rows of tires which are rotatably mounted to the aircraft. The tires are arranged in groups of two opposed tires which ride against the outer circumference of the launch vehicle. The opposed tires are positioned about 41 degrees along the circumference on either side of the low point of the vehicle circumference. When the carrier aircraft pitches upward the launch vehicle is released for movement with respect to the aircraft along a track created by the supporting rows of tires and the launch vehicle begins to exit the aircraft under the influence of gravity assisted by the small drag parachute. Gravity and the drag force of the parachute causes the launch vehicle to roll on the tires along the load deck and out of the carrier aircraft. Because the extraction forces are dominated by gravity, the launch vehicle acquires a rotation in the pitch plane as the launch vehicle leaves the aircraft. The rotation in the pitch plane is produced when the center of gravity of the launch vehicle passes over the last tires of the rows of tires and gravity causes the vehicle to tip, i.e. to rotate in the pitch plane. 
   After the launch vehicle clears the carrier aircraft it continues to rotate in the pitch plane, but is simultaneously damped in the pitch plane by the extraction parachute which is attached to the first stage engine bell. Within a few seconds of leaving the carrier aircraft the nose of the launch vehicle has pitched upwardly to an attitude which is greater than about 60° from the horizontal plane due to the rotation of the launch vehicle in the pitch plane. The first stage is then ignited and burns through the riser lines to the parachute, thus releasing the drag parachute. The carrier aircraft continues in level flight, and turns away from the flight path to increase separation between carrier aircraft and the launch vehicle. The launch vehicle, following first stage engine ignition, overcomes downward velocity caused by gravity and is controlled to a vertical flight path and begins its ascent to orbit, crossing the altitude of the carrier aircraft behind and substantially spaced from the carrier aircraft. 
   To minimize the load on any single tire pair, a greater number of tires are arranged at the end of the track formed by the pairs of tires where the vehicle tips as it exits the carrier aircraft. The last three tire groups utilize four tires arranged circumferentially with pairs of tires on each sides of the launch vehicle. The four tires making up the first group of the last three tire groups tires are arranged slightly above of the level of the groups of all the previously transited groups of two opposed tires which ride against the outer circumference of the launch vehicle. The four tires making up the second to last tire group are arranged above the level of the previously transited groups of two opposed tires and lower than the tires in the first group of the last three tires groups. The four tires making up the last group of tires are arranged below the level of the previously transited groups of two opposed tires. By adjusting the relative height of the last three groups it is possible to reduce the maximum load on any one group of tires. 
   It is an object of the present invention to provide a method of air launching a launch vehicle which maximizes the payload performance of the dropped vehicle. 
   It is a further object of the present invention to provide a method of launching a launch vehicle which minimizes the amount of equipment which falls away from the launch vehicle. 
   It is a yet further object of the present invention to provide an apparatus from which a launch vehicle can be gravity extracted from the cargo compartment of a carrier aircraft. 
   It is another object of the present invention to provide an apparatus for limiting the line load applied to the loading ramp of a carrier aircraft as a launch vehicle exits the aircraft. 
   It is yet another object of the present invention to provide an apparatus and method for bringing the launch vehicle to a near vertical orientation while minimizing hardware and loss of forward velocity. 
   Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side elevational fragmentary view of the launch vehicle, the carrier aircraft, and the storage and launch carrier of this invention. 
       FIG. 2  is a schematic side elevational fragmentary view of the launch vehicle being gravity extracted from the carrier aircraft along the launch carrier of this invention. 
       FIG. 3  is a schematic side elevational view of the orientation and relative position of the launch vehicle of  FIG. 1  vis-à-vis the carrier aircraft. 
       FIG. 4  is a schematic top view of the shroud lines of the apparatus of  FIG. 1 . 
       FIG. 5  is a schematic side elevational view of the shroud lines of the apparatus of  FIG. 1 . 
       FIG. 6  is a front elevational view of the launch vehicle, launch carrier and vertical restraint system of  FIG. 1 . 
       FIG. 7  is an isometric view of the vertical restraint system of  FIG. 6 . 
       FIG. 8  is a back elevational view of the rearmost tires on the launch carrier of  FIG. 1 . 
       FIG. 9  is fragmentary side elevational view of the loading ramp mounted portion of the launcher showing the tipping rolls of  FIG. 1 . 
       FIG. 10  is a schematic fragmentary top view of a tie down arrangement for stabilizing the launch vehicle of  FIG. 1 . 
       FIG. 11  is a side elevational view of the tie down system for the vertical restraint system of  FIG. 6 . 
       FIGS. 12A-12D  are isometric views of a release mechanism shown for releasing the tie down chains of  FIG. 10 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring more particularly to  FIGS. 1-11 , wherein like numbers refer to similar parts, a carrier aircraft  20 , for example a C-17, is shown in  FIGS. 1 and 2 . The carrier aircraft  20  has an internal cargo bay  22 , which opens to the rear  24  of the aircraft so that cargo can be air dropped. The cargo bay  22  has a loading ramp  26  with an end  27  over which air cargo is dropped. The loading ramp  26  can function as one half of the rearwardly facing cargo door  28  as shown in  FIG. 1 . A launch vehicle  30  rests on a carrier and drop system  32  which has two parts, a carrier part  34 , which mounts to the cargo deck  36  within the cargo bay  22 , and a vehicle drop portion  38  which includes three final banks of rolls  44  which make up a teeter section. The drop portion  38  is mounted to the loading ramp  26 . 
   As shown in  FIG. 6 , the carrier and drop system  32  supports the external cylindrical shell  40  of the launch vehicle  30  on pairs of pneumatic tires  42 . As shown in  FIG. 1 , the launch vehicle  30  is arranged within the aircraft cargo bay  22  with the payload end  45  of the launch vehicle pointed towards the front of the aircraft, so that the end  47  of the launch vehicle having the rocket engine  71  faces the rear of the aircraft and the cargo door  28 . The tires  42  are general aviation, pneumatic tires such as front landing gear tires which are designed to withstand the low pressure of the drop altitude and withstand a significant amount of heating. The tires in the illustrated design have an air pressure in a range between about 100 and about 135 psi, and have a diameter of about 17.5 inches where the cylindrical shell has a diameter of 87 inches. The pneumatic tires  42  support the cylindrical launch vehicle  30  in a way that limits point loads and provides vibration damping. The load supported by any tire is limited by the tire pressure and the area of the tire in contact with the launch vehicle&#39;s cylindrical shell  40 . Loading any one tire causes the tire to compress, which naturally means adjacent tires begin to take on more load. As shown in  FIG. 6 , the tires  42  are rotatably mounted by stub shafts  48  to I beams  46 . The I beam structures  46  uniformly distribute the load to the carrier aircraft&#39;s conveyors rollers  49  forming a part of the cargo deck  36 . These rollers  49  shown in  FIG. 9  are part of the cargo handling system of the cargo aircraft such as the C-17. The tire support structures are tied together with standard dual rail airdrop system side rails and roller pads  51 . The pairs of tires  42  are symmetrically located at an angle α of about 41 degrees along the shell  40  on either side of the point  50 , closest to the cargo deck  36  on the cylindrical shell  40 . 
   The launch vehicle  30  is positioned on the vehicle carrier part  34  of the carrier and drop system  32  before the air drop. To withstand the negative loads required for aircraft safety, a retention fixture  52  may be used if necessary as shown in  FIGS. 6 ,  7 , and,  11 , extends across the center of gravity (CG)  54  of the vehicle  30 . A band  56  which forms a part of the retention fixture  52  extends across the top of the vehicle  30  and has four spaced apart wheels  58  which engage the external shell  40  of the launch vehicle  30 , which keep the band  56  from jamming against the external cylindrical shell  40  when the launch vehicle  30  is deployed along the pneumatic tires of the carrier and drop system  32 . Any thing carried on an aircraft must meet certain loads for safety reasons. As shown in  FIG. 1 , tie down straps  60  serve to distribute to the carrier part  34  or the cargo deck  36  negative g loads which the vehicle  30  could during an emergency apply to the retention fixture  52 . 
   Once the carrier aircraft  20  is in flight and attains the desired launch position, the launch vehicle  30  is deployed an extraction parachute  55  of relatively small diameter which is deployed into the wake of the carrier aircraft  20 , then trimming the carrier aircraft so that the cargo deck  36  slopes toward the rear of the aircraft at an angle of 4 to 7 degrees and pulling a pneumatically actuated pin  61 . As shown in  FIGS. 12A-12D  the pin  61  attaches a load plate  64  to which fore and aft loading chains  62  are fixed by pear shaped rings  63  which are mounted to the load plate  64 . The load plate  64  is supported on a lower attachment plate  57  and is attached by the pin  61  to an upper attachment plate  59 . Pulling the pin  61  causes the load plate  64  to separate in the sequence illustrated in  FIGS. 12A-12D . As illustrated in  FIG. 10  the load plates  64  are attached on either side of the CG  54  of the launch vehicle  30 . With the release of the loading chains  62  which tied the vehicle  30  to the cargo deck  36 , and which restrained the vehicle in the forward and aft directions, the vehicle begins to move down and rearward on the tires  42  of the carrier and drop system  32 . Motion of the vehicle rearward is also augmented by the extraction parachute  55  of relatively small diameter which is deployed into the wake of the carrier aircraft  20  before deploying the launch vehicle  30 . An applying load of 5,000 to 11,000 pounds by a parachute  55  having an open diameter of 6-8 feet is suitable for a launch vehicle weighing about 72,000 lb. 
   In order to prevent a parachute riser  66  from rubbing against the rear  24  of the aircraft  20  it is advantageous if the parachute riser is held as low as possible with respect to the loading ramp end  27 . As shown in  FIGS. 1 and 4 , the single riser  66  connected to the parachute  55  can have two riser lines  74  which diverge and are connected to the engine  71  near the bottom of the engine bell  70 . The two riser lines initially pass beneath the top member of a T-shaped bar  72 , shown in  FIGS. 4 ,  5 , and  8 . The T-shaped bar  72  is fixed to the last crossbeam  88  of the carrier drop portion  38 , and extends beneath the level of the cylindrical shell  40  so as not to obstruct the passage of the launch vehicle. The cross-member of the T-shaped bar has two outboard ends  76  which extend sidewardly. Early on in the deployment of the parachute, the two riser lines are close together, and are thus restrained beneath the bar  72 . As the launch vehicle moves towards the rear of the aircraft, the distance in a sideward direction between the two riser lines increases. The two risers lines  74  are nevertheless still restrained in a horizontal plane by the bar  72  until such time as the distance between the riser lines  74  is greater than the distance between the outboard ends  76  of the T-shaped bar. At that point, as shown in  FIG. 5 , the two riser lines are no longer restrained by the T-shaped bar, and the parachute extends directly from the engine. 
   The drop portion  38  of the carrier  32  mounted to the loading ramp  26  has pairs of tires  42  similar to those used on the carrier part  34  of the carrier and drop system  32 . In addition to the pairs of tires  42 , the carrier drop portion  38  has the three final sets of tires  44 , each set of tires consisting of four individual pneumatic tires  42 , which form a tipoff section of the drop portion  38 . The four tires  80  used in the roller sets  44  are substantially the same as the rest of the tires  42  used on the carrier and drop system. The tires are arranged in opposed pairs  82 . As shown in  FIGS. 8 and 9 , the pairs of tires  82  are mounted to a common shaft  84  which is mounted between triangular support members  86 . The triangular support members  86  bridge two crossbeams  88  distributing the tire  80  loads to the crossbeams. A shaft support beam  90  mounted between the two crossbeams  88  supports one end of the common shaft  84 . The shaft support beam  90  and crossbeams  88  are joined together by transverse shafts  92 . As the center of gravity (CG) of the launch vehicle  30  reaches the end  94  of the drop portion  38 , the vehicle tips off the drop portion  38  as shown in  FIG. 2 . 
   By adjusting in the design, the height of the last three sets of tires  44  relative to each other and to the height of the other tires  42 , a free variable is introduced in to the design which allows spreading the maximum load due to tipping the launch vehicle over the three sets of tires  44  rather than only the last set of tires  96 . For example as shown in  FIG. 9  the first set  98  of tires is raised half an inch above the height of the other tires  42 , the second set of tires  100  is raised 2/10 inches above the height of the other tires  42 , and the third or last set of tires  96  is positioned 1 inch below the height of the other tires  42 . A possibly better arrangement is +0.2 or +0.1, 0.0, −1.0 inches. The height of the tires is measured along radial lines  102  as illustrated in  FIG. 6 . The drop portion  38  is mounted to conveyer rolls  49  forming part of the loading ramp  26 . By adjusting the height of the last three sets of tires  44  the load on the conveyer rolls  49  can be limited to those allowable, for example for a 72,000 lb launch vehicle the load on any roller  49  is limited to about 3,000 lbs for only about one second. 
   As shown in  FIGS. 2 and 3 , the launch vehicle  30  is extracted by gravity and assisted and stabilized by the parachute  55  or other type of aerodynamic decelerator. The parachute  55  exerts an extraction force which is about 30 percent of the total extraction force due to gravity and the parachute. As the launch vehicle  30  tips on the tire sets  44 , the vehicle acquires a rotation in the pitch plane i.e. the vertical plane containing the pitch motion of the vehicle axis  79 , of for example 5 rpm or 30° per second, and leaves the carrier aircraft with a pitch up angle of approximately 8° at about T-3 seconds i.e., 3 seconds before engine ignition. As the launch vehicle falls away from the airplane, its initial pitch rate decreases rapidly from about 30° per second to a few degrees per second as the vehicle pitch angle reaches about 75°. The riser  66  of the parachute  55  produces a counter pitch torque with a moment arm that increases as the sine of the pitch angle. As pitch angle increases counter pitch torque increases, bringing the pitch rotation to near zero when the launch vehicle has a pitch up angle of about 70 and 80°. 
   The launch vehicle  30  has two aerodynamic chines  65  which are spaced apart circumferentially by approximately 90 degrees and which are arranged to make the vehicle  30  weakly aerodynamic stable as the vehicle moves with its long dimension substantially perpendicular to the local air-flow i.e. at a high angle. The aerodynamic chines  65  also served to dampen the roll about the axis of the launch vehicle. The aerodynamic chines may be arranged as 8 inch diameter pipes one of which functions to transport propellants, and one of which functions as a storage container for high-pressure gas bottles to operate the engine thrust vector control system (not shown). At T-0 seconds the engine is ignited and burns through the parachute risers  74  releasing the parachute  55 . As shown in  FIG. 3 , the engine comes up to full thrust and stops the downward descent of the vehicle at T+6 seconds, at T+12 seconds the launch vehicle  30  crosses the altitude of the carrier aircraft  20  at a separation from the aircraft of about 1,300 feet. The launch vehicle  30  retains a substantial portion of the carrier aircraft&#39;s velocity, as illustrated by the horizontal component of the velocity vectors  104  in  FIG. 3 . The horizontal velocity vector is about 550 fps when the vehicle leaves the carrier aircraft  20  and provides an overall benefit in reduced velocity necessary to achieve orbit and greater payload. 
   It should be understood that the carrier aircraft  20  can be any suitable aircraft, for example a C-141, C-5B, An-124, or a cargo plane which is specially constructed or a modification of an existing aircraft. The weight of the launch vehicle must be less than the payload capacity of the carrier aircraft. A launch vehicle of around 50,000 lbs or so can have a useful orbit payload of 500 to 2000 lbs. As the weight of the launch vehicle falls below some minimum, for example less than 5,000 to 10,000 lbs, achieving orbit becomes impractical because of the increased drag losses and minimum weights for equipment such as actuators and electronic. However air launch, by reducing drag, does allow a smaller minimum launch weight than a ground launched vehicle. 
   In a test performed with a dummy 50,000 pound launch vehicle where the launch vehicle was dropped from the C-17 retention fixture  52 , shown in  FIG. 6  and  FIG. 7  as well as the T-bar arrangement shown in  FIGS. 4-5 , and  8  were not used and thus were not found to be necessary. However they may be useful depending on the particulars of a the carrier and drop system. The drop test, as reported in  Aviation Week and Space Technology , Oct. 24, 2005 pages 56-59 which is incorporated herein by reference demonstrated the release, separation and orientation of the dummy launch vehicle. 
   To load the launch vehicle onto the C-17 aircraft, the aircraft rear ramp is set to a horizontal orientation and the launch vehicle mounted to the carrier part  34  was, means of a winch pulled into the aircraft from a trailer which was raised to the level of the aircraft rear ramp. The carrier part  34  was then secured to the cargo deck  36  within the cargo bay  22 . After the carrier part  34  was mounted to the cargo deck  36 , the vehicle drop portion  38  of the carrier and drop system  32 , was mounted to the loading ramp  26 . Although the aircraft has a set of guide rollers  49  for sliding airdrop packages out the back these are not used for dropping the launch vehicle rather it is the wheels mounted to the carrier and drop system  32 . 
   It should be understood that the parachute  55  may be any type of aerodynamic decelerator, and can be mounted to the engine bell  70  or other parts of the launch vehicle end  47  to which the engine  71  is mounted. The aerodynamic decelerator  55  can be detached from the launch vehicle  30  by the action of the hot gases produced by the engine  71  by burning through the riser lines  74 . Alternatively, an electrically controlled three ring release or pyrotechnic cutter can be used to release the riser lines  74 . 
   It should be understood that while the tires  42 ,  80  are preferably pneumatic, the tires could be wheels of any type. It should also be understood that a principal difference between the launch vehicle  30  of this invention and other types of air launched vehicles is that the vehicle uses kinematics and a drag device spaced from the launch vehicle by a line to orient the launch vehicle in the selected launch attitude, preferably between 70 and 80° from the horizontal. Typically air dropped launch vehicles use aerodynamic surfaces such as wings, or drag devices alone to orient the launch vehicle. 
   It should be understood that the launch vehicle  30  of this invention may be any suitable launch vehicle, and that the vehicle may be orbital or suborbital. In particular, the air launch system of this invention is particularly advantageous for vehicles having at least a first stage propellant which is pressure fed, for example by compressed gases or by the vapor pressure of the propellant of the propellants themselves. Propellants such as liquid oxygen and liquid propane may readily be conditioned to have vapor pressures sufficient to feed the propellants at a selected pressure into the rocket chamber of the first stage engine. For a pressure fed stage, weight of the stage is nearly proportional to the required chamber pressure. The air launching of the launch vehicle  30 , if carried out above a significant portion of the atmosphere, permits an engine chamber pressure which is substantially reduced from the pressure required by a ground launched vehicle of the same performance. 
   It is understood that the invention is not limited to the particular construction and arrangement of parts herein illustrated and described, but embraces all such modified forms thereof as come within the scope of the following claims.