posted 09-27-2018 05:25 PM               

The heat shield is fabricated of a special stainless steel honeycomb sandwich manufactured by the Aeronca Co., Middletown, Ohio, and serves as the outer structure of the vehicle.

The shield is assembled from 40 individual panels produced by means of a special electric-blanket brazing process.

The brazing material used to join the steel skins to the honeycomb is a silver-copper-lithium alloy in a nickel matrix. Each panel is subjected to X-ray inspection after brazing to assure quality.

From R.W. Messlers's book "Joining of Advanced Materials"

Blanket Brazing simply uses a resistance-heated blanket to transfer heat to the brazement by a combination of radiation and conduction. The process is good for contoured parts.

posted 09-27-2018 08:50 PM               

One of the most important innovations was an induction brazing method in which a small unit can be moved as far as 600 feet away from its bulky generator. The small unit is used to join stainless steel fluid system components in remote and relatively inaccessible areas of the spacecraft.

In the portable brazing tool, a radio frequency current flows through coils and produces a highfrequency magnetic field around the work piece. This magnetic field produces the induction heating (up to 2,000 degrees) needed for brazing. The brazing substance is a gold alloy inside the sleeve which joins the two ends of a conduit.

Most of the spacecraft plumbing joints are induction-brazed stainless steel. This successful joining process offers a number of advantages. The joints are light (compared with mechanical joints). strong, and low cost. X-ray examinations have determined that more than 97 percent of these braze joints are acceptable. In addition, this system permits joining of tube stubs having widely different wall thickness.

This film also details the ablative section manufacture and shows the original nose cone design forward heat shield.

posted 09-30-2018 02:09 AM               

What is unfortunate is that I can not find an equivalent in French of the term "electric-blanket brazing process." I can not imagine what it's all about.

Nobody would have an industrial photo of the process? Thank in advance

oly, you said "The film was shot prior to the decision to omit the painting of the ablative material and the adoption of a boost protective cover."

posted 09-30-2018 08:25 AM               

quote:

---

Originally posted by Apolloman:
Okay, but are you sure about that?

---

After completion of these operations, the main ablator is checked for moisture content. A layer of thin, epoxy-based pore sealer and a moisture-protective plastic coating then are applied to the surface to ensure sealing of the porous ablator.

After this operation, the final weight and center-of-gravity measurements are made, and the heat-shield subassemblies are returned to NR for installation on the spacecraft. Before the CM is shipped from the prime contractor site to the NASA John F. Kennedy Space Center (KSC), the plastic coating is stripped off and the thermal-control coating with an adhesive backing is attached to the CM.

The Kapton tape highly reflective surface provided a better radiant heat protection than the painted surface and was considered an acceptable moisture protection to replace the paint.

The decision to use tape instead of paint and tape, was done for weight saving. The silver tape rejected up to 100 degrees F more heat than the painted surface.

posted 09-30-2018 09:21 PM               

The boost protective cover was a hand made structure that held a significant weight [around 700 lbs] and was repeatedly reviewed as a potential weight saving. At the same time, the Command module was developed and changes introduced.

Engineers finally decided that the BPC was the best available option. Apollo 1 had both the full BPC and the grey paint finish.

The Block 2 spacecraft weight reduction included the removal of the paint finish, as by this time it was understood that the Kapton tape was an acceptable alternative for a moisture seal.

I do not know when the Kapton tape was invented or when if first became a subject for use on the spacecraft, however the decision to use the tape as an alternate was done so due to the reflective thermal control properties over the painted surface, and was done so late in the program.

The whole procedure was an evolution over time. Questions were still being asked regarding the final configuration of the BPC layout, and weight reductions were still being sought.

Simple relocation of antennas from the CM to the SM meant modifications to the BPC, and the post Apollo 1 fire investigation wanted an alternate design consideration for the BPC. Each modification to the BPC would potentially require a flight test, and the engineering teams worked hard to finalise the system.

The Apollo Spacecraft Thermal Protection Summary details the reasoning for the paint deletion and other weight reductions found within the thermal protection system.

Early Little Joe II pad abort tests used a boilerplate spacecraft and the tope cone of the BPC attached to the LES tower. Later test flights trailed to lower BPC sections, and can be observed breaking away during the failed abort system test launch.

I have been trying to find images or drawings of the complete BPC and how it was assembled. From photos it can be determined that the lower parts were segments that could be removed individually for servicing. I think the BPC did not jettison in one piece but cannot find information on this easily.