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Light-weight and Low Cost Composite Cryotank



PROPOSALS ACCEPTED: Phase I and DP2. Please see the 16.2 DoD Program Solicitation and the DARPA 16.2 Direct to Phase II Instructions for DP2 requirements and proposal instructions.

TECHNOLOGY AREA(S): Air Platform, Space Platforms

OBJECTIVE: Develop high-performance, lightweight composite cryogenic propellant tanks suitable for use on expendable and reusable space access vehicles and hypersonic aircraft.

DESCRIPTION: While advancements in composite pressure-vessel technology have allowed the fabrication of composite cryogenic propellant tanks, the state of the art falls far short of what is currently possible with propellant tanks in terms of performance and reusability.

Existing graphite-fiber composite-pressure vessels can safely operate without leaks with multi-axis strain levels in excess of 15,000 microstrain, however conventional graphite-fiber composite cryotanks tend to operate at less than 5,000 microstrain [Ref 1]. This means that these cryotanks tend to be three times heavier than a pressure vessel designed for the same operating pressure. Achieving 15,000 microstrain in a graphite-fiber composite cryotank would offer the capability to achieve tank weight/volume that is far less than the metal cryotanks currently in use in space launch vehicles [Ref 2], enabling improved vehicle performance and payload delivery.

In this effort, DARPA seeks very low-cost and lightweight composite cryotanks that offer substantially better cost and weight/volume than state-of-the-art tanks. The target performance is to achieve a recurring production cost of less than $1,000/ft3 internal volume and less than 0.50 lbm/ft3 (weight of tank/volume of tank) performance in a reference cryotank that is 6 ft. in diameter with a volume of 350 ft3, assuming a minimum burst of 120 psi, not including structural load bearing skirt extensions. The cryotank needs to remain leak-tight after repeated cryogenic temperature and pressure cycles, with a minimum threshold of 25 combined cycles and a goal of more than 1,000 combined cycles. The cryotank must be capable of operating with common rocket propellants, with a minimum threshold of liquid oxygen (LOX), RP-1 and liquid methane containment capability and a goal of liquid hydrogen capability.

PHASE I: Experimentally demonstrate the capability of a thin graphite-fiber composite laminate to remain leak-tight when subjected to repeated multi-axis strain and thermal cycles. Specifically, the testing would need to demonstrate leak-tight capability after at least ten combined thermal (less than LOX temperature) and multi-axis strain (greater than 15,000 microstrain) cycles. Using test results, develop a conceptual design of a cryotank that would demonstrate the weight/volume goal for the reference tank requirements. Show how the cryotank could be adapted to include structural load-bearing capability and assess the performance impact.

PHASE II: Design, analyze and fabricate cryotanks that meet the reference tank requirements. Test the cryotank to verify that it achieves the weight/volume goal and remains leak-tight after more than the threshold number of combined thermal (at liquid nitrogen (LN2) temperature) and pressure cycles (design operating pressure).

PHASE III DUAL USE APPLICATIONS: Achieving the composite cryotank cost and weight/volume performance goals cited in phase 2 and 3 above offers the means to reduce launch vehicle mass and increase launch vehicle payload while reducing cost. Achieving the combined cycle goal would provide this performance advantage to reusable vehicles, thereby reducing launch costs. The technology is directly applicable to follow on reusable vehicles to DARPA’s Experimental Spaceplane (XS-1) program, as well as next-generation global reach and advanced hypersonic aircraft.

This technology would support a wide range of commercial launch vehicles being pursued today, both expendable and even a few reusable vehicle concepts. The technology would also support advanced hypersonic aircraft and airborne laser systems as well as liquefied natural gas transportation systems.


  • Stokes, E., “Hydrogen Permeability of a Polymer Based Composite Tank Material Under Tetra-Axial Strain,” 5th Conference on Aerospace Materials, Processes, and Environmental Technology (AMPET), September 16 -18, 2002
  • Sleight, D, et al, “Structural Design and Sizing of a Metallic Cryotank Concept,” 54th AIAA/ASME/ASCE/AHS/ASC, Structures, Structural Dynamics, and Materials Conference; April 8-11, 2013

KEYWORDS: Additive Manufacturing, Liquid Rocket Engines, Launch Vehicle, Spacecraft Propulsion

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