Wall structure for rocket nozzle extension

An improved structural material for the wall of a rocket engine nozzle extension comprising a thin sheet-metal base 12 and a rib wall 16 comprising a grid of intersecting ribs 18 which form internal cavities 20. A surface of the base 12 is plated 14 with Cu and the rib wall 16 is bonded thereto so that each cavity 20 has an open end. The interior surfaces of the ribs 18, which form the cavities 20, are also plated with Cu.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to rocket-engine nozzle extensions and especially to 
wall structures for increasing the strength and thermal-radiation 
capability of rocket-engine nozzle extensions. 
2. Description of the Prior Art 
Many rocket engines are made with nozzle extensions, so that the engine 
length may be decreased for storage by retracting the nozzle extension and 
may be increased to its full length by extending the nozzle extension 
section. The nozzle extension provides the engine with greater thrust. 
Nozzle extensions are generally formed from sheet metal, such as Ti, 
stainless steel, columbium, etc.. The thin sheet metal is subject to 
vibration problems which can shatter the nozzle extension. Various 
expedients, such as circumferential thickening ribs known as hatbands, 
have been employed to increase structural stiffness, but other problems 
arise. The thermal conductivity of the ribs is different from that of the 
intermediate sheet metal areas and they expand at different rates, 
resulting in a warping of the shape of the nozzle extension. 
OBJECTS OF THE INVENTION 
An object of the invention is to increase the structural strength of the 
walls of a nozzle extension for a rocket engine. 
Another object is to improve the thermal radiation capability of the walls 
of a nozzle extension for a rocket engine. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawing. 
SUMMARY OF THE INVENTION 
The invention is an improved structure for the wall of a rocket-engine 
nozzle extension comprising a rib wall section bonded to a thin 
sheet-metal base. A surface of the base is plated with a metal having good 
thermal conductivity and a high melting point. The rib wall is bonded to 
the base surface. The rib wall comprises ribs of metal forming a grid 
which encloses a group of internal cavities. The walls of the internal 
cavities are also plated with a material having good thermal conductivity 
and a high melting point. The composite wall structure exhibits greater 
stiffness and greater heat radiative capability than the usual sheet metal 
from which nozzle extensions are built, provides greater resistance to 
vibrational damage, and permits the nozzle extension to operate at lower 
temperatures.

DETAILED DESCRIPTION OF THE INVENTION 
The invention comprises a wall structure 10, a portion of which is 
illustrated in the FIGURE. The wall structure 10 comprises a flat base 12 
which may be fabricated from a usual metal for a nozzle extension, such as 
inconel, incalloy, stainless steel, hastelloy, titanium, etc.. Instead of 
the conventional thickness of about 0.030", the thickness can be reduced 
to about 0.005", for example. 
The base 12 is coated by any suitable process with a thermally radiative 
plating 14 of about 0.002", for example. Copper is preferred, although any 
metal, such as Ni, with good thermal conductivity (e.g., approximately 40 
BTU/hour/foot/.degree.F. or higher) and a high melting point (above about 
1500.degree. F.) may be used. A rib wall section 16 is bonded to the 
copper plating 14. The ribs 18 may be of a structural material such as Ti, 
stainless steel, graphite, etc., and about 0.0025" thick, for example. The 
ribs 18 are configured in a grid so that they enclose cavities 20 reaching 
down to the copper plating 14 on the base 12 and open at the other end. 
These ribs 18 are bonded to or integral with base 12. The interior walls 
of the cavities 20 are also coated with a plating 22 of a good thermally 
conductive material, such as copper. The plating material should also have 
a good radiation emissivity characteristic, i.e., in the range of 0.7 to 
0.95. Oxidized copper will exhibit a value within this range. 
The ribs could be formed from a metal plate of about 0.2-0.5" in thickness 
by electro-discharge machining or electro-chemical etching or single sheet 
honeycomb material, for example. If the cavities 20 are square in the 
area, the height-to-width ratio should be approximately between 1 and 2. 
If the height is too small, the rib wall will not provide sufficient 
stiffening and if the height is too deep, the radiation capability will 
drop. The transverse cross-section of the cavities 20 can have other 
shapes, e.g., hexagonal or rectangular, as long as the dimensions provide 
good radiative and structural characteristics. 
The wall structure described provides increased structural strength and 
stiffness for the wall of a rocket nozzle extension and provides excellent 
thermal radiation, permitting the nozzle extension to run cooler during 
operation of the engine. Cooler operation also improves the thermal 
fatique characteristics of the nozzle extension. 
The invention would also be useful with refractory metal bases (e.g., Mo, 
Co, Ta, W) at very high operating temperatures). 
Obviously, many modifications and variations in the present invention are 
possible in light of the above teachings. It is therefore to be understood 
that, within the scope of the appended claims, the invention may be 
practiced otherwise than as specifically described.