Patent Grant
7055435
The present invention generally relates to spacecraft ordnance systems and test methods for spacecraft ordnance systems and, more particularly, to an improved spacecraft ordnance system that enables automatic testing of a spacecraft ordnance harness and a method for self-testing of a spacecraft ordnance system.
Spacecraft ordnance systems are explosive release systems that can be used for a variety of pyrotechnic applications such as release systems for antenna tie downs, spacecraft separation devices, mechanism launch locks, and propulsion valves. Spacecraft ordnance systems currently used by Government and industry rely on relatively high electric current to activate these initiators, which require many safeguards to avoid accidentally setting off the initiations.
A typical prior art spacecraft ordnance system 10 is shown in a simplified block diagram in FIG. 1. The spacecraft ordnance system 10 comprises an electrical bridgewire initiation system. For example, a standard initiator 11 (hereafter called “squib”) is connected to a driver unit 13 via a dedicated harness cable 14 comprising a shielded twisted pair of cables. The harness cable 14 is wired to a harness connector 15 providing easy connection between the output of driver unit 13 and the squib 11. Only two squibs, squib 11 and squib 12, are shown in
Since proper squib firing is absolutely critical to mission success, verification of proper installation of the squib harness cables 14 and 141 in the spacecraft test is also critical. Currently, testing of the spacecraft ordnance system is done manually using a specially designed low current, low range ohmmeter. Test points, for example test points 17, 18 and 19, which allow access to the actual harness wires, are located inside the driver unit 13. To test the continuity of squib 11, for example, the ohmmeter probes are placed on test point 17 and 19. A resistance reading is taken and then manually compared with given pass/fail limits. This resistance measurement process needs to be repeated for each squib circuit. Furthermore, the entire test needs to be repeated several times during the space vehicle integration and test process.
This manual verification process for testing a spacecraft ordnance harness has several disadvantages. It is not possible to unambiguously verify that the proper output of driver unit 13 is wired to the proper squib in the proper location by applying the described test procedure. This can result in squib circuits being swapped or miswired by human error, which can lead to severe on-orbit problems at the point when deployments or propulsion system initializations are performed. Further, the testing of a spacecraft ordnance harness as described above is manual measurement-intensive, and therefore requires a considerable amount of time causing increased cycle time and test cost. Since tests are performed manually, they cannot be performed after the spacecraft is closed out prior to shipment to launch site. The described test for a spacecraft ordnance system also requires specialized test equipment, such as a low-range ohmmeter. Further, the test procedure directly exposes live squibs to potential electrostatic discharge sources, which represents a potential personnel safety hazard. This potential personnel safety hazard is traditionally mitigated by operators wearing ESD grounding protection, but this approach is not foolproof. Also the manual verification process requires the driver unit 13 to be placed outside of the spacecraft for test access purpose exposing the driver unit 13 to a severe environment. If placed inside a spacecraft, the driver unit 13 requires a heavy shielded test access harness, which must fly with the spacecraft, even though the driver unit 13 is only used during testing.
Prior art describes several methods to guarantee that the proper output of a driver unit is connected to the proper squib. For example, color-coding of the squib and the mating harness connector was employed, but this method relies on human judgment and has proven to be ineffective. This method also requires a visual inspection of each mating harness connector; which is not possible after a certain stage in spacecraft-level integration. Pin programming of each squib (i.e. giving each squib its own jumper wire programmed address) was disclosed, but this approach is impractical because it requires the driver unit to interrogate many programming wires from each squib, greatly increasing the wire harness complexity, weight, and cost. Further, mechanical keying of each squib connector was proposed. This is also impractical because it requires a modification to the existing NASA Standard Initiator and therefore increases the cost, requires stocking up to 100 different types of squibs, each with a different key, along with 100 different types of mating connectors, and requires the wire harness designer to have a priori knowledge of the specific key used for each squib at each location. This adds to schedule cycle time and cost. Finally, proposals were made for “intelligent” squibs containing active electronics, in which the squib reports its identity back to the driver unit via a simple digital interface. In addition to being relatively costly, this approach is impractical because of the extremely harsh temperature and radiation environment at many squib locations on the spacecraft. Traditional active electronics are not capable of withstanding these environmental conditions.
There has, therefore, arisen a need for the development of a method for testing of a spacecraft ordnance harness that makes it possible to unambiguously verify that the proper output of the driver unit is wired to the proper squib in the proper location. There has further arisen a need to specify the squibs to allow determination of correct harness routing eliminating the chance of human error. There has also arisen a need to modify the driver unit of the spacecraft ordnance system to enable automatic testing of a spacecraft ordnance harness, to reduce cycle time and test cost, to eliminate the need for specialized test equipment, and to eliminate the potential personnel safety hazard, as connected with manual testing. There has still further arisen a need for the development of an improved spacecraft ordnance system that enables automatic testing of the spacecraft ordnance harness allowing the driver unit to be placed inside the spacecraft where it may be protected from the relatively harsh temperature and radiation environment outside of the spacecraft and allowing the spacecraft ordnance system to be tested at any time during the spacecraft integration and test process, up to and including launch.
As can be seen, there is a need for an improved spacecraft ordnance system that enables automatic testing of a spacecraft ordnance harness and eliminates manual work and human error. Also, there is a need for specification of each squib that allows the determination of correct harness routing. Moreover, there is a need for a method for self-testing of a spacecraft ordnance system providing cost-effective and unambiguous verification that the proper output of the driver unit is wired to the proper squib in the proper location at any time during spacecraft integration, up to and including launch.
The present invention provides an improved spacecraft ordnance system including a driver unit with added built-in test circuitry suitable for, but not limited to, automatic testing of a spacecraft ordnance harness. The present invention also provides a squib having a resistor of a squib unique resistance value attached for determination of correct harness routing. The present invention further provides a method for self-testing of a spacecraft ordnance system enabling unambiguous verification of correct connection of an output of the driver unit and a squib.
In one aspect of the present invention, a spacecraft ordnance system comprises a standard squib, a resistor, a driver line having an output, a driver unit, and test circuitry built into the driver unit that enables verification of correct connection of the standard squib with the output of the driver unit. The resistor has a unique resistance value, and has a first end and a second end, wherein the second end of the resistors is connected to ground and the first end of the resistor is connected with the standard squib. The driver line has a first end and a second end, the first end of the driver line is connected with the standard squib and the second end is connected with an output of the driver unit. The combination of the driver line, the resistor, and the standard squib forms an extended squib having a unique resistance value.
In another aspect of the present invention, a built-in test system for automatic testing of a spacecraft ordnance system comprises a standard squib, a driver unit having an output and a telemetry interface, a driver line, test circuitry built into the driver unit, and a resistor having a unique resistance value and being connected with the standard squib. The driver line connects the output of the driver unit with the standard squib.
In still another aspect of the present invention, an EMI (electromagnetic interference)-tight adapter comprises an adapter case having a first end and a second end, a resistor having a unique resistance value and being placed inside of the adapter, a pair of connector sockets located at the first end of the adapter case for mating with a standard squib, and a pair of connector pins at the second end of the adapter case for mating with an ordnance harness connector.
In a further aspect of the present invention, a spacecraft ordnance system comprises a standard squib, a resistor having a unique resistance value, and wherein the resistor is connected with the standard squib, an EMI-tight adapter, wherein the resistor is placed inside of the EMI-tight adapter, a driver line, wherein the driver line is connected with the standard squib, a driver unit having an output and a telemetry interface, wherein the output of the driver unit is connected with the driver line, and test circuitry built into the driver unit that enables verification of correct connection of the standard squib with the output of the driver unit. The test circuitry built into the driver unit includes a low-impedance multiplexer that selects the driver line for monitoring, a precision current source that provides a current to the selected driver line and produces a voltage proportional to the total resistance between the selected driver line and ground, and an analog/digital converter that digitizes the voltage and reports the voltage to a computer for comparison to predicted values using the telemetry interface of the driver unit identifying the standard squib.
In yet another aspect of the present invention, a method for self-testing of a spacecraft ordnance system includes the steps of: providing a spacecraft ordnance system to be tested, providing a built-in test system including test circuitry and a resistor having a unique resistance value, incorporating the test circuitry including a low-impedance multiplexer, a precision current source, and an analog/digital converter into the driver unit of the spacecraft ordnance system, attaching the resistor to the standard squib, selecting the standard squib for monitoring with the low-impedance multiplexer, providing a current to the output of the driver unit using the precision current source and producing a voltage proportional to the total resistance between the ordnance harness cable and ground, digitizing the voltage with the analog/digital converter, reporting the voltage to a computer, and comparing the voltage to predicted values identifying the selected standard squib.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.
The present invention provides an improved spacecraft ordnance system including a driver unit with added built-in test circuitry suitable for automatic testing of a spacecraft ordnance harness. The present invention also provides a squib having a resistor of a squib unique resistance value attached for determination of correct harness routing. The present invention further provides a method for self-testing of a spacecraft ordnance system enabling unambiguous verification of a correct connection of an output of the driver unit and a squib.
The spacecraft ordnance system of the present invention may be used for automatic testing of an ordnance harness of a spacecraft, missile or other vehicle, that use NASA Standard Initiators or other commercially available initiators as squibs. Since NASA Standard Initiators or other commercially available initiators are used in the present invention and built-in test circuitry of the present invention is added to an existing prior art driver unit of a spacecraft ordnance system, the need for special measuring equipment has been eliminated and a cost-effective method for unambiguous verification of the proper connection between an output of driver unit and a squib at a certain location has been introduced.
In one embodiment, the present invention provides a spacecraft ordnance system including a modified driver unit with added built-in test circuitry. By providing built-in test circuitry, the value of a squib-specific resistor that is connected with a squib can be sensed and then be reported to a computer for analysis using an existing telemetry interface. Consequently, the squib can be unambiguously verified. The computer may be part of the existing system test equipment and therefore external to the spacecraft or the computer may be part of the existing spacecraft data handling system and therefore on board the spacecraft, not adding to the system cost. By incorporating the built-in test circuitry of the present invention into a standard spacecraft ordnance system the need for manual testing can be eliminated, saving cost and cycle time during spacecraft integration and test. Further, the use of the built-in test circuitry does not impact the existing tools and procedures used to design, route, manufacture, and install the ordnance wire harness.
In one embodiment, the present invention provides a spacecraft ordnance system including squibs that are connected with a resistor, wherein a first end of the resistor is connected with a standard squib and a second end of the resistor is connected to ground. Each squib has a resistor with a squib unique resistance value assigned. Since modifying an existing squib, such as a NASA Standard Initiator or other commercially available initiator would be impractical and expensive, a small, cylindrical, EMI (electromagnetic interference)-tight adapter including the squib-specific resistor has been developed. The EMI-tight adapter of the present invention includes a resistor with a squib unique resistance value and connects the existing squib with the ordnance harness. In order to be able to unambiguously verify that the proper output of the driver unit is connected to the proper squib at the proper location, the adapter including the squib-specific resistor should be permanently attached to the existing squib before installation of the squib. A bonding material for attaching the adapter to an existing squib should be of such nature that it is difficult but not impossible to remove the adapter from the squib. By using the EMI-tight adapter of the present invention, the range safety or EMI integrity of the ordnance system is not compromised, and the existing squibs, such as NASA Standard Initiators or other commercially available initiators, do not have to be modified which is cost and time saving.
Since the improved spacecraft ordnance system of the present invention allows the ordnance harness of a spacecraft to be automatically tested, there would no longer be a requirement to locate the driver unit of the spacecraft ordnance system on the outside of the spacecraft to provide test access. The driver unit could now be placed inside the spacecraft or other vehicle along with other spacecraft bus electronics. This has several benefits. The driver unit could be placed closer to many of the squibs it is controlling, thereby reducing the length of the ordnance harness and thus the harness weight. The lower radiation environment within the spacecraft would allow the driver unit to use less shielding, reducing the unit weight. Finally, placing the driver unit inside the spacecraft would make it possible to combine the squib driver function with other spacecraft electronics in the same box, reducing total recurring cost and weight and therefore simplifying the spacecraft integration.
Referring now to
The driver unit 23 provides the switching and the current drive necessary to individually fire the squibs, for example squib 21 and squib 22. The driver unit 23 is designed having multiple switches (switches 230, 231, 232, and 233) such that no fewer than three failures can result in an inadvertent squib firing. In normal operation, an enable switch 230 is first to be closed, followed by the appropriate arm switch, for example arm switch 231 activates squib 21, arm switch 232 activates squib 22, etc. The fire switch 233 is then closed, allowing a relatively high current (for example 5 to 6 amperes) to flow through the selected squib (squib 21 or squib 22), causing a relatively small explosive reaction. This in turn allows the mechanism to which the squib is attached (bolt cutter, pin puller, tie down, etc.) to actuate.
Since proper squib firing is absolutely critical to mission success, verification of proper installation of the squib harness cables 24 in the spacecraft test is also critical. To enable unambiguous verification that the proper output of driver unit 23 is connected to the proper squib at the proper location and to enable automatic built-in testing of a spacecraft ordnance harness, the driver unit 23 of the spacecraft ordnance system 20 may further include built-in test circuitry 27, as shown in FIG. 2. The built-in test circuitry 27 may include a low-impedance multiplexer 270, a precision current source 271, and an analog/digital converter 272. The output 274 of the multiplexer 270 is connected to the precision current source 271 and to the input 279 of the analog/digital converter 272. The following example for unambiguous identification of squib 21 is used to illustrate the operation of the built-in test circuitry 27. The built-in test circuitry 27 of the current invention can be used to automatically test and verify all squibs installed on a large spacecraft individually.
The low-impedance multiplexer 270 may be used to select one of the driver lines for monitoring. When driver line 241 is selected, driver line 241 is connected to output 274 of multiplexer 270, as shown in FIG. 2. Consequently, the precision current source 271 provides a relatively low current Itest 275 via output 274 of the multiplexer 270 to the selected driver line 241. This produces a voltage Vtest 276 at the input 279 of the analog/digital converter 272. This voltage Vtest 276 is then digitized by the analog/digital converter 272 and reported via an existing telemetry interface 28 to a computer 29 for comparison to predicted values. The computer 29 may be either external to the spacecraft such as being part of the already existing system test equipment or may be on board of the spacecraft such as being part of the already existing spacecraft data handling system. Therefore, the built-in test circuitry 27 is able to sense the unique resistance value of the squib unique resistor 210 and to report the resistance value via the existing telemetry interface 28 to the computer 29 for analysis. Consequently, the squib 21 can be unambiguously verified.
Referring now to
Referring now to
It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4068556 | Foley | Jan 1978 | A |
| 6300764 | Kelley | Oct 2001 | B1 |
| 6386108 | Brooks et al. | May 2002 | B1 |
| Number | Date | Country |
|---|---|---|
| 2 571 843 | Apr 1986 | FR |
| Number | Date | Country | |
|---|---|---|---|
| 20040231545 A1 | Nov 2004 | US |
