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Alternate Sled Track Braking Mechanism



OBJECTIVE: Develop a replacement sled braking mechanism for Supersonic Naval Ordnance Research Tracking (SNORT) that requires less setup time, and does not have the associated regulatory compliance and recurring cost issues as the existing SNORT water brake system. 

DESCRIPTION: The water braking system used at the SNORT currently includes a diesel-powered water pump that delivers water to approximately the midpoint of the track. The water then flows downhill and recirculates back into the 600,000-gallon storage pond at the north end of the track. Baffles and dams, placed manually in the concrete foundation trough between the rails, slow the water down and increase the water height. Rocket sleds typically have a probe or scoop incorporated into their structure to interface with the water. The length of the probe is set to start contacting the water as the rocket motor propulsion is tailing off. Most sleds with water brake probes are stopped on the track and reused. Occasionally, the water braking system only provides separation between sled stages resulting in all sleds destroyed at the end of the track. Maintaining, calibrating, and operating the existing water braking system is costly and has several areas requiring regulatory compliance. The diesel engine driven water pump is located in an underground vault which is designated a confined space. The confined space requires constant monitoring for hazardous atmospheric conditions such as the presence of Carbon Monoxide or low Oxygen levels. Annual calibration and maintenance costs are approximately $5,000. The engine requires an air permit to operate and the underground storage tank requires a permit. Inspectors must regularly log, and report on these permits, requiring escort of inspectors which is time consuming and costly. Annual permit and inspection costs are approximately $5,000. Certified inspectors are required to perform repairs, adding additional cost and complexity. Calibration and checkout of the water brake system is very time consuming because of the lag time between taking measurements, adjusting water flow rate, and waiting for the new flow rate to propagate through the two miles of track. This cycle takes approximately 2 hours. Water-profile adjustment costs are approximately $2,000 per year. Adjusting the water profile is difficult and has led to most changes being made to the sled probe or scoop and using the standard water profile. This approach can cause sub-optimal design constraints on the sled design or velocity/acceleration profile of the sled. Usually the result is high braking loads incorporated into the sled design adding weight, cost, and complexity. The goal is to design a new innovative braking mechanism without the drawbacks described above. The braking mechanism should meet the following requirements: a) Be a passive system with no outside inputs. Electricity, water, fuel, or coolant. b) Maximum of 21,600 feet of braking length. c) Equal or lower weight and drag penalties on the sled-side of the braking mechanism compared to existing probe designs. Spade brake example; 45 lbs. brake weight, 0.85 drag coefficient, 41,000 lbs. maximum braking force. High speed brake example; 110 lbs. brake weight, 0.85 drag coefficient, 95,000 lbs. maximum braking force. Detailed specifications will be provided to Phase I performers. d) Fit into or around the existing track foundation for the trackside portion of the braking mechanism. The concrete foundation trough is nominally 41.625” wide, 26” deep (measured from top of rail), and has 6” 45 degree chamfers on both bottom corners. e) Operate in desert climate without severe (greater than 10%) performance penalties. Direct sunlight, high winds, blowing dust, occasional rain, with ambient temperature ranging from 10°F to 120°F f) Adjustments to braking profile made without precision equipment (alignment lasers, surveying equipment). Simple gauge bars or lightweight alignment fixtures are allowable. g) Adjustments to braking profile completed by two personnel in under 2 hours per each mile of braking length. h) Consumables (if any) costing less than $1,000 per use. i) Reinstallation of consumables (if any) completed by two personnel in under 1 hour per each mile of braking length. j) Consumables (if any) may not damage the track or introduce hazardous waste cleanup requirements. k) Deceleration requirement; decelerate from velocities ranging from 1 to 3,000ft/s over a maximum distance of 10,000 feet l) Braking force requirement; maximum of 100,000 lbs reaction load on sled tailorable from 100% down to 10% over the entire braking distance. 

PHASE I: Design, develop, and demonstrate feasibility of replacement braking mechanism for SNORT as outlined in the Description. Characterize climate dependent performance penalties if any. Develop software model to simulate braking performance. The Phase I effort will include prototype plans to be developed under Phase II. 

PHASE II: Finalize, test, and demonstrate a full-scale prototype of the replacement braking mechanism. Test braking capability with representative sleds as well as adjustment, maintenance, and repair time. Develop the testing campaign in coordination with the Government. Incorporate braking simulation into the Government’s sled-velocity calculation software. 

PHASE III: Transition technology to platforms/industry after verifying the system meets program specific requirements and all the performance requirements as outlined in the Description. Braking technologies have applications in the transportation and entertainment sectors. Transportation uses include various forms of rail transit systems. Entertainment uses are roller coasters and other rides that need braking. 


1. Army Engineer Waterways Experiment Station Vicksburg MS Structures Lab. Condition Evaluation of Supersonic Naval Ordnance Research Track (SNORT). Vicksburg: Defense Technical Information Center, 1984.

KEYWORDS: Eddy Current; Sled; Sled Track; Rails; Braking; Deceleration 

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