GB2095336A

GB2095336A - Electrothermal gas thrust unit

Info

Publication number: GB2095336A
Application number: GB8206380A
Authority: GB
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1981-03-19
Filing date: 1982-03-04
Publication date: 1982-09-29
Also published as: GB2095336B

Abstract

Hydrazine is prevented from premature vapourisation by being introduced into the thrust chamber 10 via an injector tube 16 and an extension tube 15, the unit having a heat conducting diaphragm 18 attached adjacent the junction of the injector tube and the extension tube. <IMAGE>

Description

SPECIFICATION Electrothermal gas thrust units The present invention relates to electrothermal gas thrust units as used for the attitude control of space vehicles.

In a typical electrothermal gas thrust unit hydrazine is supplied through an injector tube to a thrust chamber where heat is added. The hydrazine vaporises, decomposes and dissociates into ammonia, nitrogen and hydrogen, with the production of more heat. The resultant hot gases are discharged through a nozzle to produce thrust.

The availability of thrust means constitutes one of the limiting factors of useful life of. a space vehicle, so the efficient use of the available hydrazine in a hydrazine thrust unit is essential. As attitude changes of a space vehicle only require small impulses each thrust unit pulse will be of only short duration (of the order of 5 milliseconds) so that transients at the start of a pulse will seriously affect the efficiency of the thrust unit. Transients occur due to heat from the thrust chamber raising the tempera- ture of the thrust chamber to injector tube junction and causing vaporisation of hydrazine in the injector tube. This inhibits flow through the injector tube and can also cause premature decomposition in the tube with a consequent large reduction in thrust and severe thermal cycling and stressing of the injector tube.

According to the present invention an electrothermal gas thrust unit includes a thrust chamber, an extension tube leading into the chamber, an injectortube leading into the extension tube, and a diaphragm member attached to the extension tube adjacent an injector tube to extension tube junction, the diaphragm being formed of a material having good thermal conductivity.

In one form of the invention the diaphragm is spoked and serves as a support member, being mounted on structure which forms part of the means by which the thrust unit is secured to a space vehicle.

A similar spoked diaphragm can be used as a mounting between structure and, for example, a thrust nozzle outlet.

One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing, which shows in section an elevation of a hydrazine thrust unit.

An electrothermal gas thrust unit has a thrust chamber 10 defined by a cylindrical casing 11 surrounded by an electrical heating element 12. The thrust chamber 10 contains a heat exchanger 13 of known type, and has a downstream end terminating in a convergent divergent thrust nozzle 14. The construction of a heat exchanger 13 and operation of the chamber 10 and associated equipmentforvaporising decomposing, and dissociating hydrazine and discharging the resultant gases are described in UK Patent No 1,534,601, do not form part of the present invention, and will not be described herein.

At an upstream end of the thrust chamber 10 the casing 11 tapers to join a cylindrical extension tube 15 which has an end cap 26. An injector tube 16 leads into the extension tube 15 from a flow control valve 17 which is connected to a hydrazine supply (not shown).

A thermally conducting spoked diaphragm 18 connects the downstream end of the extension tube to a thermally conducting or radiating outer support cylinder 19, and a spoked diaphragm 20 connects the extremity of the thrust nozzle 14 to the support cylinder 19. The diaphragms 18, 20 support the casing 11 within the support cylinder 19, and heat radiation from the casing 11 is reduced by insulating material 21 packed between casing 11, cylinder 19 and diaphragms 18, 20. The support cylinder 19 is mounted on an end plate 22 secured to the flow controy valve 17. The diaphragms 18, 20 and support cylinder 19 might be formed from, for example, titanium, titanium alloy or stainless steel. They need not all be of the same material.

In operation, when the control system of a space vehicle in which the thrust unit is installed requires the unit to operate, the flow control valve 17 releases a pulse of hydrazine. The hydrazine flows down the injector tube 16 into the extension tube 15 and hence into the thrust chamber 10. In the chamber 10 heat from the heating element 12 vaporises the hydrazine which then decomposes and dissociates with the release of heat. The resultant gases exit through the thrust nozzle 14 providing thrust which alters the attitude of the space vehicle.

Heat from the thrust chamber 10, which has a typical temperature of 6û0 to 900 C, inevitably passes along the casing 11 to the extension tube 15 and towards the junction between this tube and the injectortube 16. By suitable design of the diaphragm 18 and support structure sufficient heat is conducted along the diaphragm 18 to the support cylinder 19 and hence to the end plate 22, flow control valve 17, and space vehicle structure (not shown) to keep the junction between the injector tube 16 and extension tube 15, through end cap 26, below the temperature, approximately 300"C, at which hydrazine vaporises.

This minimises transient effects at the start of each pulse improving the efficiency of hydrazine utilisation and preventing thermal cycling and stressing of the injectortube 16.

1. An electrothermal gas thrust unit including a thrust chamber, an extension tube leading into the chamber, an injector tube leading into the extension tube, and a diaphragm member attached to the extension tube adjacent an injector tube to extension tube junction, the diaphragm being formed of a material of known thermal conductivity.

2. Athrust unit as claimed in claim 1 wherein the diaphragm is spoked.

3. A thrust unit as claimed in claim 1 or in claim 2 wherein the diaphragm serves as a support member, being mounted on structure which forms part of means by which the unit is secured to a space vehicle.

4. Athrust unit as claimed in claim 3 wherein the structure is constructed of material which is a good heat conductor.

5. A thrust unit as claimed in claim 3 wherein the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electrothermal gas thrust units The present invention relates to electrothermal gas thrust units as used for the attitude control of space vehicles. In a typical electrothermal gas thrust unit hydrazine is supplied through an injector tube to a thrust chamber where heat is added. The hydrazine vaporises, decomposes and dissociates into ammonia, nitrogen and hydrogen, with the production of more heat. The resultant hot gases are discharged through a nozzle to produce thrust. The availability of thrust means constitutes one of the limiting factors of useful life of. a space vehicle, so the efficient use of the available hydrazine in a hydrazine thrust unit is essential. As attitude changes of a space vehicle only require small impulses each thrust unit pulse will be of only short duration (of the order of 5 milliseconds) so that transients at the start of a pulse will seriously affect the efficiency of the thrust unit. Transients occur due to heat from the thrust chamber raising the tempera- ture of the thrust chamber to injector tube junction and causing vaporisation of hydrazine in the injector tube. This inhibits flow through the injector tube and can also cause premature decomposition in the tube with a consequent large reduction in thrust and severe thermal cycling and stressing of the injector tube. According to the present invention an electrothermal gas thrust unit includes a thrust chamber, an extension tube leading into the chamber, an injectortube leading into the extension tube, and a diaphragm member attached to the extension tube adjacent an injector tube to extension tube junction, the diaphragm being formed of a material having good thermal conductivity. In one form of the invention the diaphragm is spoked and serves as a support member, being mounted on structure which forms part of the means by which the thrust unit is secured to a space vehicle. A similar spoked diaphragm can be used as a mounting between structure and, for example, a thrust nozzle outlet. One embodiment of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawing, which shows in section an elevation of a hydrazine thrust unit. An electrothermal gas thrust unit has a thrust chamber 10 defined by a cylindrical casing 11 surrounded by an electrical heating element 12. The thrust chamber 10 contains a heat exchanger 13 of known type, and has a downstream end terminating in a convergent divergent thrust nozzle 14. The construction of a heat exchanger 13 and operation of the chamber 10 and associated equipmentforvaporising decomposing, and dissociating hydrazine and discharging the resultant gases are described in UK Patent No 1,534,601, do not form part of the present invention, and will not be described herein. At an upstream end of the thrust chamber 10 the casing 11 tapers to join a cylindrical extension tube 15 which has an end cap 26. An injector tube 16 leads into the extension tube 15 from a flow control valve 17 which is connected to a hydrazine supply (not shown). A thermally conducting spoked diaphragm 18 connects the downstream end of the extension tube to a thermally conducting or radiating outer support cylinder 19, and a spoked diaphragm 20 connects the extremity of the thrust nozzle 14 to the support cylinder 19. The diaphragms 18, 20 support the casing 11 within the support cylinder 19, and heat radiation from the casing 11 is reduced by insulating material 21 packed between casing 11, cylinder 19 and diaphragms 18, 20. The support cylinder 19 is mounted on an end plate 22 secured to the flow controy valve 17. The diaphragms 18, 20 and support cylinder 19 might be formed from, for example, titanium, titanium alloy or stainless steel. They need not all be of the same material. In operation, when the control system of a space vehicle in which the thrust unit is installed requires the unit to operate, the flow control valve 17 releases a pulse of hydrazine. The hydrazine flows down the injector tube 16 into the extension tube 15 and hence into the thrust chamber 10. In the chamber 10 heat from the heating element 12 vaporises the hydrazine which then decomposes and dissociates with the release of heat. The resultant gases exit through the thrust nozzle 14 providing thrust which alters the attitude of the space vehicle. Heat from the thrust chamber 10, which has a typical temperature of 6û0 to 900 C, inevitably passes along the casing 11 to the extension tube 15 and towards the junction between this tube and the injectortube 16. By suitable design of the diaphragm 18 and support structure sufficient heat is conducted along the diaphragm 18 to the support cylinder 19 and hence to the end plate 22, flow control valve 17, and space vehicle structure (not shown) to keep the junction between the injector tube 16 and extension tube 15, through end cap 26, below the temperature, approximately 300"C, at which hydrazine vaporises. This minimises transient effects at the start of each pulse improving the efficiency of hydrazine utilisation and preventing thermal cycling and stressing of the injectortube 16. CLAIMS

2. Athrust unit as claimed in claim 1 wherein the diaphragm is spoked.

5. A thrust unit as claimed in claim 3 wherein the structure is constructed of material which is a good heat radiator.

6. A thrust unit as claimed in any one of claims 1 to 5 wherein the diaphragm is formed of titanium.

7. A thrust unit as claimed in any one of claims 1 to 5 wherein the diaphragm is formed of a titanium alloy.

8. Athrust unit as claimed in any one of claims 1 to 5 wherein the diaphragm is formed of stainless steel.

9. A thrust unit substantially as herein described with reference to the accompanying d-.awings.

10. A space vehicle having at least one thrust unit as claimed in any one of claims 1 to 9.

11. A space vehicle as claimed in claim 10 wherein the thrust unit is fuelled by hydrazine.

12. A space vehicle as claimed in claim 11 wherein the junction between the injector tube and the extension tube is kept at a temperature below 300"C.