Hypersonic vehicle design consideration Notes | EduRev

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: Hypersonic vehicle design consideration Notes | EduRev

 Page 1


NPTEL – Aerospace 
Module-8: Hypersonic vehicle design consideration 
Lecture: 39: Hypersonic vehicle cooling strategies 
39.1. Design Considerations of Hypersonic Vehicles 
39.1.1. Major concerns of hypersonic flight 
The design of a typical hypersonic vehicle can be undertaken by a successful 
experimental test in a ground based facility. However, design criteria of any flight 
vehicle are governed by the regime of the flow, which the vehicle is going to 
encounter. ‘Streamlined body’ is the criterion for design of a subsonic vehicle while 
‘reduction of wave drag’ is the criterion for design of a supersonic vehicle. Earlier 
civil or fighter aircraft and missiles designed all over the globe were based on these 
themes. Excessive heating is the greatest concern in the design of ballistic missiles 
and spacecraft, since it could melt their surface. Temperature at the nose of the 
hypersonic vehicles, flying with the Apollo reentry speed, will be around 11,000 K. 
Hence, design of hypersonic vehicle is dominated by aerodynamic surface heating 
where ‘reduction of heat transfer rate’ plays an important role. Allen Julian showed 
that stagnation point aerodynamic heating varies inversely to the square root of the 
nose radius. This means the aerodynamic drag coefficient is inversely proportional to 
the heat load. Therefore, the blunt body configuration, which has a detached shock 
wave, experiences less heating than the traditional shape with its attached shock wave, 
is the choice of the hypersonic vehicle. Spacecrafts for the Mercury, Gemini, and 
Apollo programs were designed using this concept. However the maximum 
temperature that a space vehicle experiences in its hypersonic flight is far above the 
maximum sustainable temperature of any material. Hence, a proper heat shield should 
be designed to withstand the heating loads. Consequently nose bluntness increase the 
aerodynamic drag experienced by the body.  Increase in wave drag is useful during 
reentry of the spacecraft for aero breaking. Moreover, it is disadvantageous during the 
ascent stage for a vehicle since increased wave drag demands for more fuel. 
Therefore, different heat transfer and drag reduction techniques are devised for safer 
and cheaper hypersonic flight.  
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 12 
Page 2


NPTEL – Aerospace 
Module-8: Hypersonic vehicle design consideration 
Lecture: 39: Hypersonic vehicle cooling strategies 
39.1. Design Considerations of Hypersonic Vehicles 
39.1.1. Major concerns of hypersonic flight 
The design of a typical hypersonic vehicle can be undertaken by a successful 
experimental test in a ground based facility. However, design criteria of any flight 
vehicle are governed by the regime of the flow, which the vehicle is going to 
encounter. ‘Streamlined body’ is the criterion for design of a subsonic vehicle while 
‘reduction of wave drag’ is the criterion for design of a supersonic vehicle. Earlier 
civil or fighter aircraft and missiles designed all over the globe were based on these 
themes. Excessive heating is the greatest concern in the design of ballistic missiles 
and spacecraft, since it could melt their surface. Temperature at the nose of the 
hypersonic vehicles, flying with the Apollo reentry speed, will be around 11,000 K. 
Hence, design of hypersonic vehicle is dominated by aerodynamic surface heating 
where ‘reduction of heat transfer rate’ plays an important role. Allen Julian showed 
that stagnation point aerodynamic heating varies inversely to the square root of the 
nose radius. This means the aerodynamic drag coefficient is inversely proportional to 
the heat load. Therefore, the blunt body configuration, which has a detached shock 
wave, experiences less heating than the traditional shape with its attached shock wave, 
is the choice of the hypersonic vehicle. Spacecrafts for the Mercury, Gemini, and 
Apollo programs were designed using this concept. However the maximum 
temperature that a space vehicle experiences in its hypersonic flight is far above the 
maximum sustainable temperature of any material. Hence, a proper heat shield should 
be designed to withstand the heating loads. Consequently nose bluntness increase the 
aerodynamic drag experienced by the body.  Increase in wave drag is useful during 
reentry of the spacecraft for aero breaking. Moreover, it is disadvantageous during the 
ascent stage for a vehicle since increased wave drag demands for more fuel. 
Therefore, different heat transfer and drag reduction techniques are devised for safer 
and cheaper hypersonic flight.  
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 12 
NPTEL – Aerospace 
39.2 Cooling techniques 
The cooling techniques to remove thermal energy from the surface of spacecraft are 
broadly classified into two categories such as active cooling and passive cooling 
techniques. ‘Radiative shielding’ (e.g. Molybdenum and Zirconium) and ‘Insulation’ 
(e.g. Dynaquartz) cooling are the most widely used techniques in the area of passive 
cooling. A schematic of these techniques is shown in Fig. 39.1 Fig. 39.2 respectively. 
These techniques are used to avoid the oncoming heat to the vehicle and therefore 
they are called passive cooling techniques. ‘Convective cooling’, ‘ablative cooling’, 
‘transpiration cooling’ and ‘film cooling’ are classified as ‘active cooling techniques’.  
These techniques are directly used to cool the vehicle surface.  
 
 
     
Fig.39.1 Typical Radiative cooling system. 
 
 
    
Fig.39.2 Typical insulation cooling system. 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 12 
Page 3


NPTEL – Aerospace 
Module-8: Hypersonic vehicle design consideration 
Lecture: 39: Hypersonic vehicle cooling strategies 
39.1. Design Considerations of Hypersonic Vehicles 
39.1.1. Major concerns of hypersonic flight 
The design of a typical hypersonic vehicle can be undertaken by a successful 
experimental test in a ground based facility. However, design criteria of any flight 
vehicle are governed by the regime of the flow, which the vehicle is going to 
encounter. ‘Streamlined body’ is the criterion for design of a subsonic vehicle while 
‘reduction of wave drag’ is the criterion for design of a supersonic vehicle. Earlier 
civil or fighter aircraft and missiles designed all over the globe were based on these 
themes. Excessive heating is the greatest concern in the design of ballistic missiles 
and spacecraft, since it could melt their surface. Temperature at the nose of the 
hypersonic vehicles, flying with the Apollo reentry speed, will be around 11,000 K. 
Hence, design of hypersonic vehicle is dominated by aerodynamic surface heating 
where ‘reduction of heat transfer rate’ plays an important role. Allen Julian showed 
that stagnation point aerodynamic heating varies inversely to the square root of the 
nose radius. This means the aerodynamic drag coefficient is inversely proportional to 
the heat load. Therefore, the blunt body configuration, which has a detached shock 
wave, experiences less heating than the traditional shape with its attached shock wave, 
is the choice of the hypersonic vehicle. Spacecrafts for the Mercury, Gemini, and 
Apollo programs were designed using this concept. However the maximum 
temperature that a space vehicle experiences in its hypersonic flight is far above the 
maximum sustainable temperature of any material. Hence, a proper heat shield should 
be designed to withstand the heating loads. Consequently nose bluntness increase the 
aerodynamic drag experienced by the body.  Increase in wave drag is useful during 
reentry of the spacecraft for aero breaking. Moreover, it is disadvantageous during the 
ascent stage for a vehicle since increased wave drag demands for more fuel. 
Therefore, different heat transfer and drag reduction techniques are devised for safer 
and cheaper hypersonic flight.  
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 12 
NPTEL – Aerospace 
39.2 Cooling techniques 
The cooling techniques to remove thermal energy from the surface of spacecraft are 
broadly classified into two categories such as active cooling and passive cooling 
techniques. ‘Radiative shielding’ (e.g. Molybdenum and Zirconium) and ‘Insulation’ 
(e.g. Dynaquartz) cooling are the most widely used techniques in the area of passive 
cooling. A schematic of these techniques is shown in Fig. 39.1 Fig. 39.2 respectively. 
These techniques are used to avoid the oncoming heat to the vehicle and therefore 
they are called passive cooling techniques. ‘Convective cooling’, ‘ablative cooling’, 
‘transpiration cooling’ and ‘film cooling’ are classified as ‘active cooling techniques’.  
These techniques are directly used to cool the vehicle surface.  
 
 
     
Fig.39.1 Typical Radiative cooling system. 
 
 
    
Fig.39.2 Typical insulation cooling system. 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 12 
NPTEL – Aerospace 
The ‘convective cooling’ can be further divided into ‘direct convective cooling’ and 
‘indirect convective cooling’. In both the techniques, the heat absorbed by the coolant 
is used to raise its sensible heat or to change coolants phase. Typical convective 
cooling technique is shown schematically in the Fig. 39.3. In the direct convective 
cooling, the coolant is passed directly through the surface which needs to be cooled, 
while in the indirect convective cooling, one or many heat transfer loops are 
incorporated.  
 
 
Fig. 39.3. Typical Convective cooling system. 
 
In ‘ablation’ type active cooling, a layer of ablative material is coated over the surface 
to be protected. The protective layer melts and vaporizes due to heat load absorbing 
large amount of thermal energy. A typical ‘ablation cooling’ system is shown in Fig. 
39.4. Graphite and phenolic materials are currently popular ones for ablative 
materials. It is also found that the vehicle can be cooled efficiently by transferring 
coolant mass in the boundary layer from its surface.  
 
 
Fig. 39.4 Ablation cooling system. 
Hot gas
Solid
Q 
Convection
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 12 
Page 4


NPTEL – Aerospace 
Module-8: Hypersonic vehicle design consideration 
Lecture: 39: Hypersonic vehicle cooling strategies 
39.1. Design Considerations of Hypersonic Vehicles 
39.1.1. Major concerns of hypersonic flight 
The design of a typical hypersonic vehicle can be undertaken by a successful 
experimental test in a ground based facility. However, design criteria of any flight 
vehicle are governed by the regime of the flow, which the vehicle is going to 
encounter. ‘Streamlined body’ is the criterion for design of a subsonic vehicle while 
‘reduction of wave drag’ is the criterion for design of a supersonic vehicle. Earlier 
civil or fighter aircraft and missiles designed all over the globe were based on these 
themes. Excessive heating is the greatest concern in the design of ballistic missiles 
and spacecraft, since it could melt their surface. Temperature at the nose of the 
hypersonic vehicles, flying with the Apollo reentry speed, will be around 11,000 K. 
Hence, design of hypersonic vehicle is dominated by aerodynamic surface heating 
where ‘reduction of heat transfer rate’ plays an important role. Allen Julian showed 
that stagnation point aerodynamic heating varies inversely to the square root of the 
nose radius. This means the aerodynamic drag coefficient is inversely proportional to 
the heat load. Therefore, the blunt body configuration, which has a detached shock 
wave, experiences less heating than the traditional shape with its attached shock wave, 
is the choice of the hypersonic vehicle. Spacecrafts for the Mercury, Gemini, and 
Apollo programs were designed using this concept. However the maximum 
temperature that a space vehicle experiences in its hypersonic flight is far above the 
maximum sustainable temperature of any material. Hence, a proper heat shield should 
be designed to withstand the heating loads. Consequently nose bluntness increase the 
aerodynamic drag experienced by the body.  Increase in wave drag is useful during 
reentry of the spacecraft for aero breaking. Moreover, it is disadvantageous during the 
ascent stage for a vehicle since increased wave drag demands for more fuel. 
Therefore, different heat transfer and drag reduction techniques are devised for safer 
and cheaper hypersonic flight.  
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 12 
NPTEL – Aerospace 
39.2 Cooling techniques 
The cooling techniques to remove thermal energy from the surface of spacecraft are 
broadly classified into two categories such as active cooling and passive cooling 
techniques. ‘Radiative shielding’ (e.g. Molybdenum and Zirconium) and ‘Insulation’ 
(e.g. Dynaquartz) cooling are the most widely used techniques in the area of passive 
cooling. A schematic of these techniques is shown in Fig. 39.1 Fig. 39.2 respectively. 
These techniques are used to avoid the oncoming heat to the vehicle and therefore 
they are called passive cooling techniques. ‘Convective cooling’, ‘ablative cooling’, 
‘transpiration cooling’ and ‘film cooling’ are classified as ‘active cooling techniques’.  
These techniques are directly used to cool the vehicle surface.  
 
 
     
Fig.39.1 Typical Radiative cooling system. 
 
 
    
Fig.39.2 Typical insulation cooling system. 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 12 
NPTEL – Aerospace 
The ‘convective cooling’ can be further divided into ‘direct convective cooling’ and 
‘indirect convective cooling’. In both the techniques, the heat absorbed by the coolant 
is used to raise its sensible heat or to change coolants phase. Typical convective 
cooling technique is shown schematically in the Fig. 39.3. In the direct convective 
cooling, the coolant is passed directly through the surface which needs to be cooled, 
while in the indirect convective cooling, one or many heat transfer loops are 
incorporated.  
 
 
Fig. 39.3. Typical Convective cooling system. 
 
In ‘ablation’ type active cooling, a layer of ablative material is coated over the surface 
to be protected. The protective layer melts and vaporizes due to heat load absorbing 
large amount of thermal energy. A typical ‘ablation cooling’ system is shown in Fig. 
39.4. Graphite and phenolic materials are currently popular ones for ablative 
materials. It is also found that the vehicle can be cooled efficiently by transferring 
coolant mass in the boundary layer from its surface.  
 
 
Fig. 39.4 Ablation cooling system. 
Hot gas
Solid
Q 
Convection
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 12 
NPTEL – Aerospace 
Mass transfer cooling is an evolving solution to the aerodynamic heating problem. 
Mass transfer cooling is a type of active cooling technique. The field of mass transfer 
cooling can be further classified into ‘transpiration cooling’ and ‘film cooling’. In 
transpiration cooling, coolant mass is injected into the boundary layer from a porous 
surface of the vehicle so that the coolant comes out as a continuous mass steam and 
not as an individual jet. Typical transpiration cooling method is shown in the Fig. 
39.5. The film cooling technique uses discrete hole injection of coolant to come out of 
a large number of jets, as shown in Fig. 39.6. Liquid, chemically inert or active gas 
can be used as coolant in the case of mass transfer cooling. Liquids are generally not 
preferred due to formation of blockages. Light molecular weight inert gas like helium 
is most preferred for mass transfer cooling. 
 
 
Fig.39.5 Transpiration cooling system.  
 
 
Fig.39.6 Film cooling system. 
 
 
 
 
 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 4 of 12 
Page 5


NPTEL – Aerospace 
Module-8: Hypersonic vehicle design consideration 
Lecture: 39: Hypersonic vehicle cooling strategies 
39.1. Design Considerations of Hypersonic Vehicles 
39.1.1. Major concerns of hypersonic flight 
The design of a typical hypersonic vehicle can be undertaken by a successful 
experimental test in a ground based facility. However, design criteria of any flight 
vehicle are governed by the regime of the flow, which the vehicle is going to 
encounter. ‘Streamlined body’ is the criterion for design of a subsonic vehicle while 
‘reduction of wave drag’ is the criterion for design of a supersonic vehicle. Earlier 
civil or fighter aircraft and missiles designed all over the globe were based on these 
themes. Excessive heating is the greatest concern in the design of ballistic missiles 
and spacecraft, since it could melt their surface. Temperature at the nose of the 
hypersonic vehicles, flying with the Apollo reentry speed, will be around 11,000 K. 
Hence, design of hypersonic vehicle is dominated by aerodynamic surface heating 
where ‘reduction of heat transfer rate’ plays an important role. Allen Julian showed 
that stagnation point aerodynamic heating varies inversely to the square root of the 
nose radius. This means the aerodynamic drag coefficient is inversely proportional to 
the heat load. Therefore, the blunt body configuration, which has a detached shock 
wave, experiences less heating than the traditional shape with its attached shock wave, 
is the choice of the hypersonic vehicle. Spacecrafts for the Mercury, Gemini, and 
Apollo programs were designed using this concept. However the maximum 
temperature that a space vehicle experiences in its hypersonic flight is far above the 
maximum sustainable temperature of any material. Hence, a proper heat shield should 
be designed to withstand the heating loads. Consequently nose bluntness increase the 
aerodynamic drag experienced by the body.  Increase in wave drag is useful during 
reentry of the spacecraft for aero breaking. Moreover, it is disadvantageous during the 
ascent stage for a vehicle since increased wave drag demands for more fuel. 
Therefore, different heat transfer and drag reduction techniques are devised for safer 
and cheaper hypersonic flight.  
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 1 of 12 
NPTEL – Aerospace 
39.2 Cooling techniques 
The cooling techniques to remove thermal energy from the surface of spacecraft are 
broadly classified into two categories such as active cooling and passive cooling 
techniques. ‘Radiative shielding’ (e.g. Molybdenum and Zirconium) and ‘Insulation’ 
(e.g. Dynaquartz) cooling are the most widely used techniques in the area of passive 
cooling. A schematic of these techniques is shown in Fig. 39.1 Fig. 39.2 respectively. 
These techniques are used to avoid the oncoming heat to the vehicle and therefore 
they are called passive cooling techniques. ‘Convective cooling’, ‘ablative cooling’, 
‘transpiration cooling’ and ‘film cooling’ are classified as ‘active cooling techniques’.  
These techniques are directly used to cool the vehicle surface.  
 
 
     
Fig.39.1 Typical Radiative cooling system. 
 
 
    
Fig.39.2 Typical insulation cooling system. 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 2 of 12 
NPTEL – Aerospace 
The ‘convective cooling’ can be further divided into ‘direct convective cooling’ and 
‘indirect convective cooling’. In both the techniques, the heat absorbed by the coolant 
is used to raise its sensible heat or to change coolants phase. Typical convective 
cooling technique is shown schematically in the Fig. 39.3. In the direct convective 
cooling, the coolant is passed directly through the surface which needs to be cooled, 
while in the indirect convective cooling, one or many heat transfer loops are 
incorporated.  
 
 
Fig. 39.3. Typical Convective cooling system. 
 
In ‘ablation’ type active cooling, a layer of ablative material is coated over the surface 
to be protected. The protective layer melts and vaporizes due to heat load absorbing 
large amount of thermal energy. A typical ‘ablation cooling’ system is shown in Fig. 
39.4. Graphite and phenolic materials are currently popular ones for ablative 
materials. It is also found that the vehicle can be cooled efficiently by transferring 
coolant mass in the boundary layer from its surface.  
 
 
Fig. 39.4 Ablation cooling system. 
Hot gas
Solid
Q 
Convection
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 3 of 12 
NPTEL – Aerospace 
Mass transfer cooling is an evolving solution to the aerodynamic heating problem. 
Mass transfer cooling is a type of active cooling technique. The field of mass transfer 
cooling can be further classified into ‘transpiration cooling’ and ‘film cooling’. In 
transpiration cooling, coolant mass is injected into the boundary layer from a porous 
surface of the vehicle so that the coolant comes out as a continuous mass steam and 
not as an individual jet. Typical transpiration cooling method is shown in the Fig. 
39.5. The film cooling technique uses discrete hole injection of coolant to come out of 
a large number of jets, as shown in Fig. 39.6. Liquid, chemically inert or active gas 
can be used as coolant in the case of mass transfer cooling. Liquids are generally not 
preferred due to formation of blockages. Light molecular weight inert gas like helium 
is most preferred for mass transfer cooling. 
 
 
Fig.39.5 Transpiration cooling system.  
 
 
Fig.39.6 Film cooling system. 
 
 
 
 
 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 4 of 12 
NPTEL – Aerospace 
Lecture: 40: Drag reduction methods 
40.1 Drag reduction techniques 
Imposed bluntness at the nose of the hypersonic vehicle is necessary to alleviate the 
oncoming heat load. However, increased wave drag is the immediate consequence of 
the forced bluntness. The required fuel of the propulsive vehicle increases due to a 
large drag force. It is also observed that a, marginal change in the drag force produces 
drastic change in the range of the missile or payload of the vehicle. Therefore, 
numerous wave drag reduction techniques are devised. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Joint initiative of IITs and IISc – Funded by MHRD                                                            Page 5 of 12 
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