It has been alleged that environmental regulations have undone the Space Shuttle. That's because a freon-based foam adheres better to the tank than a non-freon-based one.
Environmental requirements requiring removal of freon from the process for spraying the foam insulation onto the tank. NASA has said that the freon-free application method resulted in foam that initially did not adhere to the tank as well, but changes were later made to strengthen the bond of the environmentally friendly foam.
Let's see if this is true. First, a diagram from the Columbia investigation of the various insulation types.
Now a diagram from NASA showing where the failure occurred on Discovery. More detailed pictures to be found at California Yankee.
The foam that failed is NCFI 24-124. Again from the Columbia report.
Most of the External Tank is insulated with three types of spray-on foam. NCFI 24-124, a polyisocyanurate foam applied with blowing agent HCFC 141b hydrochlorofluorocarbon, is used on most areas of the liquid oxygen and liquid hydrogen tanks. NCFI 24-57, another polyisocyanurate foam applied with blowing agent HCFC 141b hydrochlorofluorocarbon, is used on the lower liquid hydrogen tank dome. BX-250, a polyurethane foam applied with CFC-11 chlorofluorocarbon, was used on domes, ramps, and areas where the foam is applied by hand. The foam types changed on External Tanks built after External Tank 93, which was used on STS-107, but these changes are beyond the scope of this section.
So, what's BX-250 and HCFC 141b? Let's ask NASA.
Environmental Protection Agency
In 1987, the United States and 45 other nations adopted the "Montreal Protocol on Substances that Deplete the Ozone Layer." Under the Protocol, class I ozone depleting compounds, such as chlorofluorocarbon 11 known as CFC 11 -- the Freon-based blowing agent used in the production of the External Tank's foam -- was to be phased out of production by the end of 1995. Production of these compounds after 1995 is allowed only by "Essential Use Exemption" and must have Montreal Protocol approval.
After extensive testing the External Tank project proposed hydro chlorofluorocarbon HCFC 141b as the CFC 11 replacement. HCFC 141b is a blowing agent more environmental regulation compliant. At the same time, the Environmental Protection Agency allowed the External Tank program to continue use of stockpiled supplies of CFC 11until HCFC 141b was certified for use on the Space Shuttle and phased in.
However, in 1999, the EPA proposed to expand its regulations by implementing a ban on nonessential products that release class I ozone-depleting substances under section 610 of the Clean Air Act. Under the proposed rule, sale and distribution of BX 250, used to insulate part of the External Tank, would have been banned because it contains CFC 11. NASA asked the EPA to revise the proposed rule to provide an exemption for BX 250 and other foam containing CFC 11 used in applications associated with space vehicles.
The EPA allowed the exemption but limited it to the Thermal Protection System of the Shuttle's External Tank and only allowed the use of CFC 11 as a blowing agent when no other chlorofluorocarbons are used in the foam product.
The "new" foam containing HCFC 141b was first used on the liquid hydrogen tank aft dome of ET-82 and flew on STS-79 in 1996. The foam was implemented on the tank's acreage, or its larger portions, beginning with ET-88, which flew on STS-86 in 1997. In December 2001, BX-265, which contains HCFC 141b, first flew as a replacement of BX-250. However BX250 continued to be flown as BX-265 was implemented step wise through the manufacturing process.
So, the freon-based BX-250 has replaced by the non-freon-based HCFC 141b. Is NASA passing the buck or did the EPA actually do what they said? NASA's summary is accurate, here's the EPA report.
EPA received a comment from the National Aeronautics and Space Administration (NASA) regarding the use of specific plastic foam products for the space shuttle. NASA identified one particular product, BX-250, a foam which is part of the thermal protection system of the Space Shuttle External Tank and which uses CFC-11 as a blowing agent. NASA stated that ``although extensive efforts have been made and continue to be made to replace this material, no viable alternative has been identified.'' NASA requested that EPA revise the proposed rule to provide an exemption for CFC-blown foam products in applications that are associated with space vehicles. NASA suggested that EPA consider using the same language that EPA has previously adopted under 40 CFR part 63, subpart GG (40 CFR 63.742) for the National Emissions Standards for Hazardous Air Pollutants (NESHAPs) program. NASA provided EPA with additional information concerning its proactive pursuit of potential alternative blowing agents.
Since human space flight safety is of paramount importance to NASA, prior to implementing any new material, that material must undergo a rigorous development and qualification program for which no suitable substitute has yet been identified. NASA requested that EPA consider using the language at 40 CFR 63.742:
Space vehicle means a man-made device, either manned or unmanned, designed for operation beyond earth's atmosphere. This definition includes integral equipment such as models, mock-ups, prototypes, molds, jigs, tooling, hardware jackets, and test coupons. Also included is auxiliary equipment associated with test, transport, and storage, which through contamination can compromise the space vehicle performance.
EPA agrees that an exception is necessary, but EPA disagrees with NASA's proposed language. This language is far broader than what EPA concludes is actually necessary based on an evaluation of the information NASA presented. If EPA were to simply exempt all foams used for any applications associated with space vehicles EPA could be exempting products where there are already suitable substitutes. NASA only provided information concerning one particular type of foam used in applications associated with the Space Shuttle External Tank.
Therefore, based on that information, through this action, EPA will modify Sec. 82.66(c) to provide an exemption for foam products manufactured with or containing Class I substances that are used as part of the thermal protection system of external tanks for space vehicles and will add the definition of space vehicles found at Sec. 63.742 to Sec. 82.62. The exemption will be limited to the use of CFC-11 as a blowing agent and where no other CFCs are contained in the foam product. Although EPA did not propose this exemption or the additional definition, they are logical outgrowths of the comment submitted by NASA and thus it is appropriate to proceed to final action without providing any additional proposal or opportunity for further comment.
Thanks EPA for killing our astronauts.