Successful tests of an all-composite cryogenic fuel tank for space launch vehicles hold promise for lower-cost access to space, perhaps before the decade is out.
A small composite fuel tank fabricated bywith funding from the “game-changing” program of ’s Space Technology Mission Directorate contained 2,091 gal. of liquid hydrogen through a series of shifts in its internal pressure and three temperature cycles ranging from ambient down to minus 423F.
The June 25 test atwith a 2.4-meter-dia. composite fuel tank paves the way for more tests next spring. That test will subject a 5.5-meter tank to flight-like mechanical loads as well as temperature and pressure cycles.
So far it appears the project is achieving its goal of reducing the cost of building tanks by at least 25% from that of conventional aluminum-lithium tanks, while cutting the weight of tanks made from the lightweight aluminum alloy by at least 30%.
“This is a very difficult problem,” says Mike Gazarik, associate administrator for space technology. “Composites and cryos don’t work well together, and these guys have done incredible work in figuring out how to design and how to fabricate these tanks.”
During the day-long test the Boeing-built subscale tank went through 20 pressure cycles from zero to 135 psi, without leaking and with strain-gauge measurements meeting expectations.
“It performed nominally, and nominally is a very good thing for us,” said John Vickers, project manager on the composite cryogenic tank technology demonstration project at Marshall.
Next up for testing will be a 5.5-meter-dia. tank already in fabrication at the Boeing Advanced Development Center in Tukwila, Wash.
Both test tanks are built up with thin-ply composites that don’t require a pressurized autoclave for curing. The out-of-autoclave fabrication helps hold the cost down, says Dan Rivera, Boeing’s project manager on the tanks, while the thin-ply approach, already in use on satellite structures and other Boeing products, prevents microcracking that causes leaks.
“It’s been known theoretically that thin plies could reduce permeability of the hydrogen through the laminate,” Vickers says. “But the work we’ve done recently has been quite comprehensive and has shown that not only can it reduce permeability through the laminate, but it can eliminate it completely.”
Boeing halved the 5.5-mil plies used previously, adopting plies weighing 70 grams per square meter instead of 145, Rivera says. In the 5.5-meter tank, the design will also tackle the honeycomb substructure that is believed to have contributed to the X-33 tank failure by substituting a “fluted” core structure.
“It varies significantly from honeycomb in that the core of that structure is essentially a hollow tube,” Rivera says. “So if you do have any escape of gases they’re very easily vented or purged through that hollow structure.”
The test at Marshall came a short distance from the test structure where’s X-33 single-stage-to-orbit testbed came to an ignominious — and expensive — end in November 1999 when its composite hydrogen tank delaminated after it was filled. Vickers says the new composite tanks can be retrofitted into existing launch vehicles, passing the weight savings along directly to increase payload capacity.
That is attracting attention in the launch-vehicle industry as new players likeand Blue Origin crank up the competition.
“There is a lot of excitement about this technology,” Vickers says. “We are being approached by other organizations, both government and industry, to transition this technology to their products.”