Scramjet A scramjet ( supersonic combustion ramjet ) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow . As in ramjets , a scramjet relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion ( hence " ram " jet ) , but whereas a ramjet decelerates the air to subsonic velocities before combustion , airflow in a scramjet is supersonic throughout the entire engine . This allows the scramjet to operate efficiently at extremely high speeds : theoretical projections place the top speed of a scramjet between and . The scramjet is composed of three basic components : a converging inlet , where incoming air is compressed and decelerated ; a combustor , where gaseous fuel is burned with atmospheric oxygen to produce heat ; and a diverging nozzle , where the heated air is accelerated to produce thrust . Unlike a typical jet engine , such as a turbojet or turbofan engine , a scramjet does not use rotating , fan - like components to compress the air ; rather , the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet . As such , no moving parts are needed in a scramjet . In comparison , typical turbojet engines require inlet fans , multiple stages of rotating compressor fans , and multiple rotating turbine stages , all of which add weight , complexity , and a greater number of failure points to the engine . Due to the nature of their design , scramjet operation is limited to near - hypersonic velocities . As they lack mechanical compressors , scramjets require the high kinetic energy of a hypersonic flow to compress the incoming air to operational conditions . Thus , a scramjet - powered vehicle must be accelerated to the required velocity by some other means of propulsion , such as turbojet , railgun , or rocket engines . In the flight of the experimental scramjet - powered Boeing X - 51A , the test craft was lifted to flight altitude by a Boeing B - 52 Stratofortress before being released and accelerated by a detachable rocket to near Mach 4 . 5 . In May 2013 , another flight achieved an increased speed of Mach 5 . 1 . While scramjets are conceptually simple , actual implementation is limited by extreme technical challenges . Hypersonic flight within the atmosphere generates immense drag , and temperatures found on the aircraft and within the engine can be much greater than that of the surrounding air . Maintaining combustion in the supersonic flow presents additional challenges , as the fuel must be injected , mixed , ignited , and burned within milliseconds . While scramjet technology has been under development since the 1950s , only very recently have scramjets successfully achieved powered flight . History . During World War II , a tremendous amount of time and effort were put into researching high - speed jet - and rocket - powered aircraft , predominantly by the Germans . After the war , the US and UK took in several German scientists and military technologies through Operation Paperclip to begin putting more emphasis on their own weapons development , including jet engines . The Bell X - 1 attained supersonic flight in 1947 and , by the early 1960s , rapid progress towards faster aircraft suggested that operational aircraft would be flying at " hypersonic " speeds within a few years . Except for specialized rocket research vehicles like the North American X - 15 and other rocket - powered spacecraft , aircraft top speeds have remained level , generally in the range of Mach 1 to Mach 3 . In the 1950s and 1960s a variety of experimental scramjet engines were built and ground tested in the US and the UK . In 1964 , Dr . Frederick S . Billig and Dr . Gordon L . Dugger submitted a patent application for a supersonic combustion ramjet based on Billig ’ s Ph . D . thesis . This patent was issued in 1981 following the removal of an order of secrecy . In 1981 tests were made in Australia under the guidance of Professor Ray Stalker in the T3 ground test facility at ANU . The first successful flight test of a Scramjet was performed by Russia in 1991 . It was an axisymmetric hydrogen - fueled dual - mode scramjet developed by Central Institute of Aviation Motors ( CIAM ) , Moscow in the late 1970s . The scramjet ﬂight was ﬂown captive - carry atop the SA - 5 surface - to - air missile that included an experiment ﬂight support unit known as the " Hypersonic Flying Laboratory " ( HFL ) , “ Kholod ” . Then from 1992 to 1998 an additional 6 flight tests of the axisymmetric high - speed scramjet - demonstrator were conducted by CIAM together with France and then with NASA , USA . Maximum flight velocity greater than Mach 6 . 4 was achieved and Scramjet operation during 77 seconds was demonstrated . These flight test series also provided insight into autonomous hypersonic flight controls . Progress in the 2000s . In the 2000s , significant progress was made in the development of hypersonic technology , particularly in the field of scramjet engines . US efforts are probably the best funded , and the Hyper - X team claimed the first flight of a thrust - producing scramjet - powered vehicle with full aerodynamic maneuvering surfaces in 2004 with the X - 43A . However , the first group to demonstrate a scramjet working in an atmospheric test was a project by a joint British and Australian team from UK defense company QinetiQ and the University of Queensland . The HyShot project demonstrated scramjet combustion on July 30 , 2002 . The scramjet engine worked effectively and demonstrated supersonic combustion in action . However , the engine was not designed to provide thrust to propel a craft . It was designed more or less as a technology demonstrator . On Friday , June 15 , 2007 , the US Defense Advanced Research Project Agency ( DARPA ) , in cooperation with the Australian Defence Science and Technology Organization ( DSTO ) , announced a successful scramjet flight at Mach 10 using rocket engines to boost the test vehicle to hypersonic speeds . A series of scramjet ground test were completed at NASA Langley Arc - Heated Scramjet Test Facility ( AHSTF ) at simulated Mach 8 flight conditions . These experiments were used to support HIFiRE flight 2 . On May 22 , 2009 , Woomera hosted the first successful test flight of a hypersonic aircraft in HIFiRE . The launch was one of 10 planned test flights . The series of up to 10 planned hypersonic flight experiments are part of a joint research program between the Defence Science and Technology Organisation and the US Air Force , designated as the Hypersonic International Flight Research Experimentation ( HIFiRE ) . HIFiRE is investigating hypersonics technology ( the study of flight exceeding five times the speed of sound ) and its application to advanced scramjet - powered space launch vehicles — the objective is to support the new Boeing X - 51 scramjet demonstrator while also building a strong base of flight test data for quick - reaction space launch development and hypersonic " quick - strike " weapons . On 22 and 23 March 2010 , Australian and American defence scientists successfully tested a ( HIFiRE ) hypersonic rocket . It reached an atmospheric velocity of " more than 5 , 000 kilometres per hour " after taking off from the Woomera Test Range in outback South Australia . On May 27 , 2010 , NASA and the United States Air Force successfully flew the X - 51A Waverider for approximately 200 seconds at Mach 5 , setting a new world record hypersonic airspeed . The Waverider flew autonomously before losing acceleration for an unknown reason and destroying itself as planned . The test was declared a success . The X - 51A was carried aboard a B - 52 , accelerated to Mach 4 . 5 via a solid rocket booster , and then ignited the Pratt & Whitney Rocketdyne scramjet engine to reach Mach 5 at 70 , 000 feet . However , a second flight June 13 , 2011 was ended prematurely when the engine lit briefly on ethylene but failed to transition to its primary JP7 fuel , failing to reach full power . On 16 November 2010 , Australian scientists successfully demonstrated that the high - speed flow in a naturally non - burning scramjet engine can be ignited using a pulsed laser source . A further X - 51A Waverider test failed on August 15 , 2012 . The attempt to fly the Scramjet , carried by a B - 52 for a prolonged period at Mach 6 was cut short when , only 15 seconds into the unmanned flight , the X - 51A craft lost control and broke apart , falling into the Pacific Ocean north - west of Los Angeles . The cause of the failure was blamed on a faulty control fin . In May 2013 an unmanned X - 51A WaveRider reached 4828 km / h ( Mach 5 . 1 ) during a three - minute flight under scramjet power . The WaveRider was dropped at 50 , 000 feet from a B - 52 bomber , and then accelerated to Mach 4 . 8 by a solid rocket booster which then separated before the WaveRider ' s scramjet engine came into effect . Design principles . Scramjet engines are a type of jet engine , and rely on the combustion of fuel and an oxidizer to produce thrust . Similar to conventional jet engines , scramjet - powered aircraft carry the fuel on board , and obtain the oxidizer by the ingestion of atmospheric oxygen ( as compared to rockets , which carry both fuel and an oxidizing agent ) . This requirement limits scramjets to suborbital atmospheric flight , where the oxygen content of the air is sufficient to maintain combustion . Basic principles . Scramjets are designed to operate in the hypersonic flight engine , beyond the reach of turbojet engines , and , along with ramjets , fill the gap between the high efficiency of turbojets and the high speed of rocket engines . Turbomachinery - based engines , while highly efficient at subsonic speeds , become increasingly inefficient at transonic speeds , as the compressor fans found in turbojet engines require subsonic speeds to operate . While the flow from transonic to low supersonic speeds can be decelerated to these conditions , doing so at supersonic speeds results in a tremendous increase in temperature and a loss in the total pressure of the flow . Around Mach 3 – 4 , turbomachinery is no longer useful , and ram - style compression becomes the preferred method . Ramjets utilize high - speed characteristics of air to literally ' ram ' air through an inlet nozzle into the combustor . At transonic and supersonic flight speeds , the air upstream of the nozzle is not able to move out of the way quickly enough , and is compressed within the nozzle before being diffused into the combustor . Combustion in a ramjet takes place at subsonic velocities , similar to turbojets , but the combustion products are then accelerated through a convergent - divergent nozzle to supersonic speeds . As they have no mechanical means of compression , ramjets cannot start from a standstill , and generally do not achieve sufficient compression until supersonic flight . The lack of intricate turbomachinery allows ramjets to deal with the temperature rise associated with decelerating a supersonic flow to subsonic speeds , but this only goes so far : at near - hypersonic velocities , the temperature rise and inefficiencies discourage decelerating the flow to the magnitude found in ramjet engines . Scramjet engines operate on the same principles as ramjets , but do not decelerate the flow to subsonic velocities . Rather , a scramjet combustor is supersonic : the inlet decelerates the flow to a lower Mach number for combustion , after which it is accelerated to an even higher Mach number through the nozzle . By limiting the amount of deceleration , temperatures within the engine are kept at a tolerable level , from both a material and combustive standpoint . Even so , current scramjet technology requires the use of high - energy fuels and active cooling schemes to maintain sustained operation , often using hydrogen and regenerative cooling techniques . Theory . All scramjet engines have an intake which compresses the incoming air , fuel injectors , a combustion chamber , and a divergent thrust nozzle . Sometimes engines also include a region which acts as a flame holder , although the high stagnation temperature s mean that an area of focused waves may be used , rather than a discrete engine part as seen in turbine engines . Other engines use pyrophoric fuel additives , such as silane , to avoid such issues . An isolator between the inlet and combustion chamber is often included to improve the homogeneity of the flow in the combustor and to extend the operating range of the engine . A scramjet is reminiscent of a ramjet . In a typical ramjet , the supersonic inflow of the engine is decelerated at the inlet to subsonic speeds and then reaccelerated through a nozzle to supersonic speeds to produce thrust . This deceleration , which is produced by a normal shock , creates a total pressure loss which limits the upper operating point of a ramjet engine . For a scramjet , the kinetic energy of the freestream air entering the scramjet engine is large comparable to the energy released by the reaction of the oxygen content of the air with a fuel ( say hydrogen ) . Thus the heat released from combustion at Mach 25 is around 10 % of the total enthalpy of the working fluid . Depending on the fuel , the kinetic energy of the air and the potential combustion heat release will be equal at around Mach 8 . Thus the design of a scramjet engine is as much about minimizing drag as maximizing thrust . This high speed makes the control of the flow within the combustion chamber more difficult . Since the flow is supersonic , no downstream influence propagates within the freestream of the combustion chamber . Thus throttling of the entrance to the thrust nozzle is not a usable control technique . In effect , a block of gas entering the combustion chamber must mix with fuel and have sufficient time for initiation and reaction , all the while traveling supersonically through the combustion chamber , before the burned gas is expanded through the thrust nozzle . This places stringent requirements on the pressure and temperature of the flow , and requires that the fuel injection and mixing be extremely efficient . Usable dynamic pressure s lie in the range , where where To keep the combustion rate of the fuel constant , the pressure and temperature in the engine must also be constant . This is problematic because the airflow control systems that would facilitate this are not physically possible in a scramjet launch vehicle due to the large speed and altitude range involved , meaning that it must travel at an altitude specific to its speed . Because air density reduces at higher altitudes , a scramjet must climb at a specific rate as it accelerates to maintain a constant air pressure at the intake . This optimal climb / descent profile is called a " constant dynamic pressure path " . It is thought that scramjets might be operable up to an altitude of 75 km . Fuel injection and management is also potentially complex . One possibility would be that the fuel be pressurized to 100 bar by a turbo pump , heated by the fuselage , sent through the turbine and accelerated to higher speeds than the air by a nozzle . The air and fuel stream are crossed in a comb like structure , which generates a large interface . Turbulence due to the higher speed of the fuel leads to additional mixing . Complex fuels like kerosene need a long engine to complete combustion . The minimum Mach number at which a scramjet can operate is limited by the fact that the compressed flow must be hot enough to burn the fuel , and have pressure high enough that the reaction be finished before the air moves out the back of the engine . Additionally , in order to be called a scramjet , the compressed flow must still be supersonic after combustion . Here two limits must be observed : Firstly , since when a supersonic flow is compressed it slows down , the level of compression must be low enough ( or the initial speed high enough ) not to slow the gas below Mach 1 . If the gas within a scramjet goes below Mach 1 the engine will " choke " , transitioning to subsonic flow in the combustion chamber . This effect is well known amongst experimenters on scramjets since the waves caused by choking are easily observable . Additionally , the sudden increase in pressure and temperature in the engine can lead to an acceleration of the combustion , leading to the combustion chamber exploding . Secondly , the heating of the gas by combustion causes the speed of sound in the gas to increase ( and the Mach number to decrease ) even though the gas is still travelling at the same speed . Forcing the speed of air flow in the combustion chamber under Mach 1 in this way is called " thermal choking " . It is clear that a pure scramjet can operate at Mach numbers of 6 - 8 , but in the lower limit , it depends on the definition of a scramjet . Certainly there are designs where a ramjet transforms into a scramjet over the Mach 3 - 6 range ( Dual - mode scramjets ) . In this range however , the engine is still receiving significant thrust from subsonic combustion of " ramjet " type . The high cost of flight testing and the unavailability of ground facilities have hindered scramjet development . A large amount of the experimental work on scramjets has been undertaken in cryogenic facilities , direct - connect tests , or burners , each of which simulates one aspect of the engine operation . Further , vitiated facilities , storage heated facilities , arc facilities and the various types of shock tunnels each have limitations which have prevented perfect simulation of scramjet operation . The HyShot flight test showed the relevance of the 1 : 1 simulation of conditions in the T4 and HEG shock tunnels , despite having cold models and a short test time . The NASA - CIAM tests provided similar verification for CIAM ' s C - 16 V / K facility and the Hyper - X project is expected to provide similar verification for the Langley AHSTF , CHSTF and HTT . Computational fluid dynamics has only recently reached a position to make reasonable computations in solving scramjet operation problems . Boundary layer modeling , turbulent mixing , two - phase flow , flow separation , and real - gas aerothermodynamics continue to be problems on the cutting edge of CFD . Additionally , the modeling of kinetic - limited combustion with very fast - reacting species such as hydrogen makes severe demands on computing resources . Reaction schemes are numerically stiff requiring reduced reaction schemes . Much of scramjet experimentation remains classified . Several groups , including the US Navy with the SCRAM engine between 1968 and 1974 , and the Hyper - X program with the X - 43A , have claimed successful demonstrations of scramjet technology . Since these results have not been published openly , they remain unverified and a final design method of scramjet engines still does not exist . The final application of a scramjet engine is likely to be in conjunction with engines which can operate outside the scramjet ' s operating range . Dual - mode scramjets combine subsonic combustion with supersonic combustion for operation at lower speeds , and rocket - based combined cycle ( RBCC ) engines supplement a traditional rocket ' s propulsion with a scramjet , allowing for additional oxidizer to be added to the scramjet flow . RBCCs offer a possibility to extend a scramjet ' s operating range to higher speeds or lower intake dynamic pressures than would otherwise be possible . Advantages and disadvantages of scramjets . Special cooling and materials . Unlike a rocket that quickly passes mostly vertically through the atmosphere or a turbojet or ramjet that flies at much lower speeds , a hypersonic airbreathing vehicle optimally flies a " depressed trajectory " , staying within the atmosphere at hypersonic speeds . Because scramjets have only mediocre thrust - to - weight ratios , acceleration would be limited . Therefore time in the atmosphere at hypersonic speed would be considerable , possibly 15 – 30 minutes . Similar to a reentering space vehicle , heat insulation would be a formidable task . The time in the atmosphere would be greater than that for a typical space capsule , but less than that of the space shuttle . New materials offer good insulation at high temperature , but they often sacrifice themselves in the process . Therefore studies often plan on " active cooling " , where coolant circulating throughout the vehicle skin prevents it from disintegrating . Often the coolant is the fuel itself , in much the same way that modern rockets use their own fuel and oxidizer as coolant for their engines . All cooling systems add weight and complexity to a launch system . The cooling of scramjets in this way may result in greater efficiency , as heat is added to the fuel prior to entry into the engine , but result in increased complexity and weight which ultimately could outweigh any performance gains . Vehicle performance . The performance of a launch system is complex and depends greatly on its weight . Normally craft are designed to maximise range ( formula _ 2 ) , orbital radius ( formula _ 2 ) or payload mass fraction ( formula _ 4 ) for a given engine and fuel . This results in tradeoffs between the efficiency of the engine ( takeoff fuel weight ) and the complexity of the engine ( takeoff dry weight ) , which can be expressed by the following : Where : A scramjet increases the mass of the engine formula _ 9 over a rocket , and decreases the mass of the fuel formula _ 10 . It can be difficult to decide whether this will result in an increased formula _ 4 ( which would be an increased payload delivered to a destination for a constant vehicle takeoff weight ) . The logic behind efforts driving a scramjet is ( for example ) that the reduction in fuel decreases the total mass by 30 % , while the increased engine weight adds 10 % to the vehicle total mass . Unfortunately the uncertainty in the calculation of any mass or efficiency changes in a vehicle is so great that slightly different assumptions for engine efficiency or mass can provide equally good arguments for or against scramjet powered vehicles . Additionally , the drag of the new configuration must be considered . The drag of the total configuration can be considered as the sum of the vehicle drag ( formula _ 12 ) and the engine installation drag ( formula _ 13 ) . The installation drag traditionally results from the pylons and the coupled flow due to the engine jet , and is a function of the throttle setting . Thus it is often written as : formula _ 14 Where : For an engine strongly integrated into the aerodynamic body , it may be more convenient to think of ( formula _ 13 ) as the difference in drag from a known base configuration . The overall engine efficiency can be represented as a value between 0 and 1 ( formula _ 18 ) , in terms of the specific impulse of the engine : Where : Specific impulse is often used as the unit of efficiency for rockets , since in the case of the rocket , there is a direct relation between specific impulse , specific fuel consumption and exhaust velocity . This direct relation is not generally present for airbreathing engines , and so specific impulse is less used in the literature . Note that for an airbreathing engine , both formula _ 18 and formula _ 22 are a function of velocity . The specific impulse of a rocket engine is independent of velocity , and common values are between 200 and 600 seconds ( 450s for the space shuttle main engines ) . The specific impulse of a scramjet varies with velocity , reducing at higher speeds , starting at about 1200s , although values in the literature vary . For the simple case of a single stage vehicle , the fuel mass fraction can be expressed as : Where this can be expressed for single stage transfer to orbit as : or for level atmospheric flight from air launch ( missile flight ) : Where formula _ 2 is the range , and the calculation can be expressed in the form of the Breguet range formula : Where : This extremely simple formulation , used for the purposes of discussion assumes : However they are true generally for all engines . Initial propulsion requirements . A scramjet cannot produce efficient thrust unless boosted to high speed , around Mach 5 , although depending on the design it could act as a ramjet at low speeds . A horizontal take - off aircraft would need conventional turbofan or rocket engines to take off , sufficiently large to move a heavy craft . Also needed would be fuel for those engines , plus all engine - associated mounting structure and control systems . Turbofan engines are heavy and cannot easily exceed about Mach 2 - 3 , so another propulsion method would be needed to reach scramjet operating speed . That could be ramjets or rocket s . Those would also need their own separate fuel supply , structure , and systems . Many proposals instead call for a first stage of droppable solid rocket booster s , which greatly simplifies the design . Testing difficulties . Unlike jet or rocket propulsion systems facilities which can be tested on the ground , testing scramjet designs use extremely expensive hypersonic test chambers or expensive launch vehicles , both of which lead to high instrumentation costs . Tests using launched test vehicles very typically end with destruction of the test item and instrumentation . Advantages and disadvantages for orbital vehicles . Propellant . An advantage of a hypersonic airbreathing ( typically scramjet ) vehicle like the X - 30 is avoiding or at least reducing the need for carrying oxidizer . For example the space shuttle external tank holds 616 , 432 kg of liquid oxygen ( LOX ) and 103 , 000 kg of liquid hydrogen ( LH2 ) while having an empty weight of 30 , 000 kg . The orbiter gross weight is 109 , 000 kg with a maximum payload of about 25 , 000 kg and to get the assembly off the launch pad the shuttle uses two very powerful solid rocket boosters with a weight of 590 , 000 kg each . If the oxygen could be eliminated , the vehicle could be lighter at liftoff and maybe carry more payload . That would be an advantage , but the central motivation in pursuing hypersonic airbreathing vehicles would be to reduce cost . On the other hand , scramjets spend more time in the atmosphere and require more hydrogen fuel to deal with aerodynamic drag . Whereas liquid oxygen is quite a dense fluid , liquid hydrogen has much lower density and takes up much more volume . This means that the vehicle using this fuel becomes much bigger and gives even more drag . Thrust - to - weight ratio . One issue is that scramjet engines are predicted to have exceptionally poor thrust - to - weight ratio , when installed in a launch vehicle , of around 2 . A rocket has the advantage that its engines have " very " high thrust - weight ratios ( ~ 100 : 1 ) , while the tank to hold the liquid oxygen approaches a tankage ratio of ~ 100 : 1 also . Thus a rocket can achieve a very high mass fraction , which improves performance . By way of contrast the projected thrust / weight ratio of scramjet engines of about 2 mean a very much larger percentage of the takeoff mass is engine ( ignoring that this fraction increases anyway by a factor of about four due to the lack of onboard oxidiser ) . In addition the vehicle ' s lower thrust does not necessarily avoid the need for the expensive , bulky , and failure prone high performance turbopumps found in conventional liquid - fuelled rocket engines , since most scramjet designs seem to be incapable of orbital speeds in airbreathing mode , and hence extra rocket engines are needed . Need for additional propulsion to reach orbit . Scramjets might be able to accelerate from approximately Mach 5 - 7 to around somewhere between half of orbital velocity and orbital velocity ( X - 30 research suggested that Mach 17 might be the limit compared to an orbital speed of Mach 25 , and other studies put the upper speed limit for a pure scramjet engine between Mach 10 and 25 , depending on the assumptions made ) . Generally , another propulsion system ( very typically , a rocket is proposed ) is expected to be needed for the final acceleration into orbit . Since the delta - V is moderate and the payload fraction of scramjets high , lower performance rockets such as solids , hypergolics , or simple liquid fueled boosters might be acceptable . Reentry . The scramjet ' s heat - resistant underside potentially doubles as its reentry system if a single - stage - to - orbit vehicle using non - ablative , non - active cooling is visualised . If an ablative shielding is used on the engine it will probably not be usable after ascent to orbit . If active cooling is used with the fuel as coolant , the loss of all fuel during the burn to orbit will also mean the loss of all cooling for the thermal protection system . Costs . Reducing the amount of fuel and oxidizer does not necessarily improve costs as rocket propellants are comparatively very cheap . Indeed , the unit cost of the vehicle can be expected to end up far higher , since aerospace hardware cost is about two orders of magnitude higher than liquid oxygen , fuel and tankage , and scramjet hardware seems to be much heavier than rockets for any given payload . Still , if scramjets enable reusable vehicles , this could theoretically be a cost benefit . Whether equipment subject to the extreme conditions of a scramjet can be reused sufficiently many times is unclear ; all flown scramjet tests only survive for short periods and have never been designed to survive a flight to date . The eventual cost of such a vehicle is the subject of intense debate since even the best estimates disagree whether a scramjet vehicle would be advantageous . It is likely that a scramjet vehicle would need to lift more load than a rocket of equal takeoff weight in order to be equally as cost efficient ( if the scramjet is a non - reusable vehicle ) . Issues . Space launch vehicles may or may not benefit from having a scramjet stage . A scramjet stage of a launch vehicle theoretically provides a specific impulse of 1000 to 4000 s whereas a rocket provides less than 450 s while in the atmosphere , potentially permitting much cheaper access to space . A scramjet ' s specific impulse decreases rapidly with speed , however , and the vehicle would suffer from a relatively low lift to drag ratio . The installed thrust to weight ratio of scramjets compares very unfavorably with the 50 - 100 of a typical rocket engine . This is compensated for in scramjets partly because the weight of the vehicle would be carried by aerodynamic lift rather than pure rocket power ( giving reduced ' gravity losses ' ) , but scramjets would take much longer to get to orbit due to lower thrust which greatly offsets the advantage . The takeoff weight of a scramjet vehicle is significantly reduced over that of a rocket , due to the lack of onboard oxidiser , but increased by the structural requirements of the larger and heavier engines . Whether this vehicle would be reusable or not is still a subject of debate and research . Applications . An aircraft using this type of jet engine could dramatically reduce the time it takes to travel from one place to another , potentially putting any place on Earth within a 90 - minute flight . However , there are questions about whether such a vehicle could carry enough fuel to make useful length trips , and there are issues with sonic booms . Scramjet vehicle has been proposed for a single stage to tether vehicle , where a Mach 12 spinning orbital tether would pick up a payload from a vehicle at around 100 km and carry it to orbit . References . Notes Bibliography