genebujold
18-August-2005, 10:12 PM
Source: http://news.yahoo.com/s/afp/20050818/sc_afp/usspaceshuttledelay
"From an overall standpoint we think really March 4 is the timeframe we are looking at," said NASA associate administrator for space operations Bill Gerstenmaier.
While the shuttle was still in orbit, I worte NASA, via website. Upon hearing no response, about three days after the shuttle landed, I wrote Mr. Gerstenmaier, via NASA, asking my letter be forwarded to him.
In it, I outlined two methods by which the foam on the orbiter's external tank could be stabilized enough to reduce or eliminate the problem of foam separation.
First, I proposed they use a hexagonal interlocking weave mesh which would be slipped over the external tank like a giant sock. It need not weight much, perhaps 50 lbs. Made out of a flexible carbon fiber string which is in turn made of hundreds of much thinner carbon fibers, this string would have an immense strength to weight ratio, five times stronger than steel. Because of the interlocking hexagonal weave, a break in any portion of the netting means that the rest of the netting would remain intact, resisting any tearing. An added benefit is that any fittings between the orbiter and the external tank can be made to fit through an ordinary pair of sheers. Because it's made of carbon fiber, any frictional heating due to its rapid assent would not affect it. Because it is a mesh, it's mostly open, but would provide enough pressure on the foam, not only to keep the foam in place, but also to keep the mesh netting in place. Finally, due to the fact that the boundary layer effect of the main tank is quite large, the any effects of the airstream flowing past the netting would be minimal.
The idea of using netting to protect foam from external stresses is nothing new, and we see it all the time in various applications raging from foam-insulated underwater lines to nylon-wrapped foam protection on children's playground equipment. It works very well.
In retrospect, I believe a more appropriate weave would be an interlocking, elongated diamond pattern, with the elongations parallelling the slipstream. However, to provide the necessary circumferantial compression, a horozontal cross-thread would be required across the middle of each diamond.
Second, I propose they imbed thin, long, multi-strand fibers in the foam as it's applied. The long fibers act as an anchoring system, much like embedding fiberglass in epoxy for superior strength, a technique long used in building boats and sailboats, surfboards, and composite aircraft, including Rutan's Starship 1. Because the foam is flexible, however, the fibers must be reasonably flexible as well, and the best fiber for the job is plain old very thin, braided nylon string, cut in lengths sufficient to provide the requisite holding power while short enough to allow many of them to be added to the foam, overlapping it in place. Monofiliment would not work, as it's too slippery. But a braided nylon might have sufficient surface area if the foam can penetrate deep enough into the fiber. Alternatively, pre-penetrating the foam via some form of foam "wash" might work as well.
A third technique I thought up in the meantime would be to use aerogel, covered with a high tear-resistance mono-coating polymer film. In it's least dense form, aerogel is the lightest material known on the planet, and excellent insulating qualities, but it's very fragile. Fortunately, it can also be made in densities sufficient to provide the requisite strength while maintaining very good insulative qualities, and the aerogel would not itself take much of the stress of the slipstream - that would be born by the mono-coating polymer film, which itself could be embedded with fibers to increase it's own strength.
A fourth technique I thought up involves a self-dissolving foam, one that, once it's no longer needed, such as during the ascent, would simply slew away from the orbiter in liquid form. There are several materials that can be foamed, but under stress revert nearly instantaneously to liquid form. There are many problems with this, however, such as how the super-cooled inner layer would responsd to the stress of flight through the air, how the liquid foam might affect the tiles if it ever touched them, and what effects strong wind would have on the foam.
It would be a sad day if 40-kt winds caused half the tanks foams to drip away!
Can anyone think of any other ways to improve the retainability of the external tank's foam?
"From an overall standpoint we think really March 4 is the timeframe we are looking at," said NASA associate administrator for space operations Bill Gerstenmaier.
While the shuttle was still in orbit, I worte NASA, via website. Upon hearing no response, about three days after the shuttle landed, I wrote Mr. Gerstenmaier, via NASA, asking my letter be forwarded to him.
In it, I outlined two methods by which the foam on the orbiter's external tank could be stabilized enough to reduce or eliminate the problem of foam separation.
First, I proposed they use a hexagonal interlocking weave mesh which would be slipped over the external tank like a giant sock. It need not weight much, perhaps 50 lbs. Made out of a flexible carbon fiber string which is in turn made of hundreds of much thinner carbon fibers, this string would have an immense strength to weight ratio, five times stronger than steel. Because of the interlocking hexagonal weave, a break in any portion of the netting means that the rest of the netting would remain intact, resisting any tearing. An added benefit is that any fittings between the orbiter and the external tank can be made to fit through an ordinary pair of sheers. Because it's made of carbon fiber, any frictional heating due to its rapid assent would not affect it. Because it is a mesh, it's mostly open, but would provide enough pressure on the foam, not only to keep the foam in place, but also to keep the mesh netting in place. Finally, due to the fact that the boundary layer effect of the main tank is quite large, the any effects of the airstream flowing past the netting would be minimal.
The idea of using netting to protect foam from external stresses is nothing new, and we see it all the time in various applications raging from foam-insulated underwater lines to nylon-wrapped foam protection on children's playground equipment. It works very well.
In retrospect, I believe a more appropriate weave would be an interlocking, elongated diamond pattern, with the elongations parallelling the slipstream. However, to provide the necessary circumferantial compression, a horozontal cross-thread would be required across the middle of each diamond.
Second, I propose they imbed thin, long, multi-strand fibers in the foam as it's applied. The long fibers act as an anchoring system, much like embedding fiberglass in epoxy for superior strength, a technique long used in building boats and sailboats, surfboards, and composite aircraft, including Rutan's Starship 1. Because the foam is flexible, however, the fibers must be reasonably flexible as well, and the best fiber for the job is plain old very thin, braided nylon string, cut in lengths sufficient to provide the requisite holding power while short enough to allow many of them to be added to the foam, overlapping it in place. Monofiliment would not work, as it's too slippery. But a braided nylon might have sufficient surface area if the foam can penetrate deep enough into the fiber. Alternatively, pre-penetrating the foam via some form of foam "wash" might work as well.
A third technique I thought up in the meantime would be to use aerogel, covered with a high tear-resistance mono-coating polymer film. In it's least dense form, aerogel is the lightest material known on the planet, and excellent insulating qualities, but it's very fragile. Fortunately, it can also be made in densities sufficient to provide the requisite strength while maintaining very good insulative qualities, and the aerogel would not itself take much of the stress of the slipstream - that would be born by the mono-coating polymer film, which itself could be embedded with fibers to increase it's own strength.
A fourth technique I thought up involves a self-dissolving foam, one that, once it's no longer needed, such as during the ascent, would simply slew away from the orbiter in liquid form. There are several materials that can be foamed, but under stress revert nearly instantaneously to liquid form. There are many problems with this, however, such as how the super-cooled inner layer would responsd to the stress of flight through the air, how the liquid foam might affect the tiles if it ever touched them, and what effects strong wind would have on the foam.
It would be a sad day if 40-kt winds caused half the tanks foams to drip away!
Can anyone think of any other ways to improve the retainability of the external tank's foam?