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Digital Firing Device


RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Air Platforms; Electronics; Weapons

OBJECTIVE: Design, develop, and demonstrate an innovative digital firing device that will be used as a form, fit, and function interchangeable replacement for the airborne rocket launcher.

DESCRIPTION: The Navy is currently using an intervalometer, which fits inside launchers such as the LAU-68 or LAU-131. The device allows pilots to fire individual rocket tubes in sequential order or ripple-fire an entire launcher within seconds. With limited space, the current design seeks enhancement of power, while accounting for the controlling voltage losses due to ambient circuit resistance to ensure sufficient firing current. The only time power is applied to the circuit is when the pilot pulls the trigger. The desired design needs to use innovative circuit designs to overcome the lack of power needed to maintain the current firing state of the intervalometer when the trigger is released. The lack of power can be overcome by storing information during the power cycle or by other means such as, but not limited to, energy harvesting to provide supplemental power.

The Navy would like to steer away from the current analog device and move to something digital. The Navy is looking for a form, fit, and function innovative replacement that can be used interchangeably with the existing intervalometer and launchers, except that the functionality is expected to be achieved via a digital circuit board design (vice the current analog design). The device should be roughly the size of a small (roughly 8”L x 2”W x 2”H) handheld flashlight. The current device uses a rotating dial, but another means of allowing user input (LOAD/ARM, rocket selection) may be used such as, but not limited to, rotary encoders.

General operation of the intervalometer should provide rocket firing current outputs including, but not limited to,:

a) input power of 20.0 to 31.5 volts direct current (Vdc), otherwise, in accordance with the dc normal operation characteristics of MIL-STD-704 [Ref 1], is supplied through a 5.0 ohm ±10 percent resistor;

b) control and apply rocket firing current to output pins sequentially;

c) each rocket firing output pins should be tested using a 4 ohm ±10 percent resistor;

d) rocket firing current pulse measured at each pin should be not less than 1.5 amperes (amps), with the load specified for not less than 10 milliseconds (ms).

e) interruptions of this power, as a result of any type of contact bounce or switch chatter of 4.0 +/- 0.4 ms duration, should not interfere with the performance of the intervalometer;

f) the single and ripple modes are controlled by an electrical switch located on the launcher structure; and

g) interface with the single/ripple switch and identify firing mode prior to operation.

The operation of the digital firing device should be defined in two modes: single mode operation and ripple mode operation. In single mode operation, the intervalometer should apply rocket firing current to only one output pin in sequence with each application of power, and be capable of not less than 12 firings per second. In ripple mode operation the intervalometer ripple rate should be self-generating in such a manner as to apply rocket firing current to output pins in sequential order. The overall firing time in the ripple mode should fire rockets with a minimum delay of 5 ms and a maximum delay of 30 ms with at least a 10 ms dwell time and an output between firing pulses of a minimum 35 ms and a maximum of 45 ms.

Setting the intervalometer to the LOAD position should internally ground all output circuits and prevent the intervalometer from being electrically sequenced upon the application of power. The internal grounding should be accomplished by means of the ground circuit. Upon completion of the last rocket firing, the intervalometer output should sequence to the LOAD position and not sequence any further (i.e., should not return to first rocket) upon the application of power. The arm circuit should provide the ground circuit to all outputs, but should also allow for electrical sequencing upon the application of power. The intervalometer should be manually switched from the LOAD position to the ARM position to provide positive arming of the intervalometer. 

The intervalometer should provide a grounding circuit through the intervalometer to ensure safety during loading and preparation. The ground circuit should ground all output pins when the intervalometer is in the LOAD or ARM position. As the intervalometer is electrically advancing through its sequence, the ground circuit should ground each output pin except those being fired. The ground circuit should ground the output pin with a resistance of not greater than 0.1 ohm. If the intervalometer is manually advanced through firing positions to the LOAD or ARM position, all output pins should remain grounded.

The intervalometer should have a settable firing sequence to maintain launcher center of gravity during firing. In the event of a short circuit to ground or an open circuit on the output pins during rocket firing current application, the intervalometer should be fault tolerant and be capable of continuing operation without damage.

PHASE I: Design, develop, and determine feasibility of a proof of concept for the digital firing device. Ensure to account for tube slipping, handling, and manufacturing plans. The Phase I effort will include prototype plans to be developed under Phase II.

PHASE II: Develop a prototype digital firing device, and demonstrate its application in a test rocket launcher (provided as Government furnished equipment (GFE)). If available, demonstrate the capability on existing platform and/or platform representative examples.

PHASE III DUAL USE APPLICATIONS: Perform final development and testing to include conformance testing to applicable MIL-STDs [Refs 1, 2]. Support final system application testing onboard aircraft with full system test, in coordination with NAVAIR Test and Evaluation.

The intervalometer has a potential commercial use in the fireworks industry to sequence the launching of multiple fireworks with a determined time interval. In addition to this commercial use, these intervalometer can be sold to foreign militaries.


  1. “MIL-STD-704F w/CHANGE 1: Department of Defense interface standard: aircraft electric power characteristics.” Naval Air Systems Command, Naval Air Warfare Aircraft Division, Lakehurst, December 5, 2016.  
  2. “MIL-STD-3018 w/CHANGE 2: Department of Defense standard practice parts management. Department of Defense, Defense Logistics Agency Land and Maritime, June 2, 2015.
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