Space Maneuvering Vehicle Control Thruster

This invention relates to the control of maneuvering vehicles that operate in space and specifically relates to new and improved thrusters for such devices.

A space maneuvering vehicle is a specialized spacecraft, sometimes referred to as an orbit maneuvering vehicle (OMV), with propulsion capacity that is capable of retrieving other spacecraft, for servicing by a space shuttle orbiter or space station in low earth orbit, of placement of spacecraft into low earth orbits but at altitudes higher than the space shuttle orbiter is capable of reaching, and of docking of spacecraft in order to accomplish servicing tasks; all by remote control or through fully automated techniques.

To accomplish this, maneuvers in close proximity to spacecraft, including closing maneuvers and docking, the vehicle will be controlled by low level thrusters operating in conjunction with the vehicle's guidance and navigation system, under control of an operator situated at a ground based or space based control situation. For full control (6.degree. of freedom) a total of 24 thrusters are required located on the vehicle in the geometry approximately as depicted in FIG. 1; FIG. 1 being simply a parallelpiped representing the vehicle with groups of three thrusters, 12 fanning out from the eight corners of the vehicle.

However, there are complicating factors that can cause the requirement for thrusters to go up by a factor of three, to a possible total of 72.

First, for remote control of the maneuvering vehicle by a shuttle or earth-stationed operator, ie., manual control, a high level of thrust is desired in order that maneuvers can be accomplished in reasonable periods of time. This thrust level may be, for example 15 lbs per thruster. Second, however, when the maneuvering vehicle operates autonomously, ie, automatically, significant fuel savings can be effected if the control thrusters operate at a lower level, for example, 5 lbs of thrust per thruster. Normally, automated operations can take longer using less to accomplish than those that are under manual control. The importance of saving fuel is recognized due to the high cost of transportation to earth orbit; on the order of $1000 per pound. So propellant conservation is the resultant benefit from operating at a lower thrust level.

Lastly, when a maneuvering vehicle operates in close proximity to a spacecraft, the exhaust plume from the control thrusters is a source of contamination or possible damage to sensitive parts or to surfaces. It is therefore desirable to use an inert gas for thrusting when in close proximity to spacecraft.

So for these three possible modes of operation of a teleoperator, the following requirement arises for control thrusters:

Therefore, an object of this invention is to eliminate the need for a large number of control thrusters on a maneuvering vehicle yet maintain the performance capability thereof. More specifically, it is an object of this invention to reduce the requirement of control thrusters on a maneuvering vehicle from a possible 72 to a total of 24.

Still another object of this invention is to provide control thrusters for the vehicle which are easily removable from the vehicle and replaceable, to make the vehicle easily maintainable.

The foregoing object of the invention is accomplished by expanding the capability of a single thruster so that it can operate at various levels. The control thruster of this invention is capable of operating at two thrust levels when chemically fueled and at a third level when fueled with an inert gas. In one embodiment, the control thrusters are in a "plug-in" package by which the control thrusters can be easily removed from and replaced in a vehicle for easy maintenance of the vehicle.

FIG. 1 illustrates, as described above, the geometric arrangement of thrusters on a maneuvering vehicle;

FIG. 2 is a perspective view of a reaction control thruster for a maneuvering vehicle constructed in accordance with the teachings of this invention;

FIG. 3 is a schematic diagram of a series redundant solenoid actuated fluid valve forming part of the thruster of FIG. 2;

FIG. 4 is a schematic illustration of the control and distribution of fuel in the thruster; and

FIG. 5 is a perspective view of an arrangement of a package of three thrusters used at each corner of the geometric arrangement of FIG. 1.

As mentioned before, FIG. 1 illustrates the location of the control thrusters 12 on a maneuvering vehicle 10 represented by a parallelpiped.

Turning now to FIG. 2, there is illustrated one control thruster 12 constructed according to this invention and comprising a three-lobed valve housing 14, connected via a thruster support (brackets) 16 to a catalytic thrust chamber 18 and thrust exhaust cone 20. The three-lobed valve housing 14 is provided with an inlet pipe 22 for connection to a supply of hydrazine and a second inlet pipe 24 for connection to a supply of inert gas and three outlet pipes 26 which are connected to a manifold 28 of the catalytic thrust chamber.

The three-lobed valve housing 14 is actually formed of lobed triads containing fluid passages and valving in each lobe for the three separate modes of operation of the thruster. Thus, the housing end is a first solenoid triad 30 separated by a valve seat wafer 32, from a second solenoid triad 34 and capped by a second valve seat wafer 36 to which the above mentioned thruster support 16 is connected and from which the outlet pipes 26 extend. The details of the series connected solenoid actuated valves in one lobe is illustrated in FIG. 3 to which attention is now directed.

The schematic diagram comprising FIG. 3 shows that the first solenoid triad 30 encloses a solenoid 40 and its core 42 in a counterbore 44 forming an enlargement of a centerbore 46 which contains a slideable poppet 48 which is urged toward a valve seat 50 by a spring 52 thus forming a normally closed valve in a valve chamber 54. The triad is also provided with a fluid passage 56 connected at one end to one of the fluid inlets 22 or 24 that is to hydrazine or the inert gas and which opens into the valve chamber 54 normally closed by the valve poppet. In contact with the solenoid triad 30 is the valve seat wafer 32 which is bored to contain the valve seat 50 shown extending into the valve chamber 54 and which is provided with an outlet passage 58 which connects to a fluid passage 56 in the second solenoid triad 34. The function of the components of the second solenoid triad 34 and valve seat wafer 36 are similar to the function of the components of the first solenoid and valve seat triad and wafer and are thus given the same reference numerals except that the valve chamber 54 of the second solenoid triad 34 opens into the fluid outlet pipe 26 for connecting the fluid to manifold 28.

Thus, within each lobe of the valve housing are two solenoid operating valves arranged to operate in series as a redundancy for the purpose of assuring thruster shut downs in the event of valve failure. The inert gas, which may be nitrogen or helium, but usually nitrogen, is directed to the inlet port 24 of one of the lobes, while hydrazine is directed to the ports of the other two lobes. The exit of each lobe leaves via the outlet pipes 26 to the inlet manifold 28. One of the outlet pipes is orificed (restricted) as at 60 in or before the manifold to control the flow of hydrazine from one of the lobes so that the thruster will operate at either one or two thrust levels depending upon which lobe is activated by the system controls. The inert gas solenoids for the flow of inert gas are operated only when the hydrazine solenoids are deactivated as would be the case for spacecraft proximity maneuvering. This is illustrated schematically in FIG. 4. This figure also shows the electrical connections 62 between the solenoid valves and the electronic controls.

While the redundant solenoid valves, as such, are old in the catalytic thruster art, it is their arrangement in a three-lobed housing and the logic of their operation for three level thrust operation which provides the means by which the number of control thrusters for a maneuvering vehicle can be reduced to one third, resulting in large cost savings and improved reliability.

Turning now to FIG. 5, there is shown a "plug-in" type of package 70 with a cluster of three control thrusters 12. This package permits the three control thrusters located at each corner of the maneuvering vehicle 10, such as shown in FIG. 1, to be easily removed and replaced, either manually or by robotics for easy maintenance of the vehicle. The package comprises a housing 72 with three walls 74 on which the three thrusters 12 are mounted at the desired angle. At the side opposite the thrusters, there is a locking sleeve 76 which encloses a hydrazine disconnect coupling 22a, a gaseous coupling 24a, and an electrical disconnect coupling 62a by which the fuel and electrical connections for the thrusters are attached and detached from, for example, a mounting post 80 which contains the fuel and electrical lines and which is attached to the vehicle. One or more of the walls of the housing 72 are, of course, removable for access to the fuel and electrical lines within the housing.