Wednesday, September 09, 2009

Apollo +50: Big Joe 1

I am not back to blogging. I have scheduled this post in advance.

I am writing a series of posts celebrating the 50th anniversary of Apollo. 50 years ago today what is considered the second launch of the Manned Space Program took place.

I think that the greatest relevance of the manned space program in the 1960s is as an excellent example of the scientific method. Engineers built something, they tested it, they looked for material causes for the effects that they saw, they made adjustments consistent with those theories, they tested again, they modified their theories.

In less than 10 years, this process carred us from the failed mission of Little Joe 1 on August 21, 1959, to the first lunar landing on July 16-24 1969.

Big Joe 1 was intended to test the heat shield on a Mercury capsule. The Big Joe rocket (a modified Atlas intercontinental ballistic missile) was supposed to launch a Mercury capsule to a height of 100 miles, then drop it back to the Earth, to see how well it would survive re-entry.

Its purpose was to test one of two competing theories for how to deal with the heat of re-entry.

One competing method was the "heat sink" method. This involved using a thick plate of beryllium, which could hold onto a great deal of heat.

The other method was the "ablation" method. This involved using a resin that effectively 'boiled off' during re-entry. The heat of re-entry was to be consumed in turning the solid resin into a gas, then the gas would simply fly away (taking the heat energy with it).

This mission was meant to test whether the ablation method would actually work. Would it allow a human occupant to survive the heat of re-entry?

Naturally, this was an unmanned mission.

It is important to note that the rocket being used was the same type of rocket to be used to deliver Mercury astronauts into orbit. (The sub-orbital missions were to use a Redstone rocket, which could put an astronaut into space but not with enough speed to keep him there.)

This is important because the Atlas rocket malfunctioned.

The Atlas rocket used a pair of booster engines during the first two minutes of launch. Unlike the two solid rocket boosters that we see on the Shuttle, the two booster engines on the Atlas were just that. They were just engines. They fed from the same fuel tank as the main engine but, after helping to provide initial thrust to get the rocket moving, they dropped off. One engine remained to do the rest of the work.

Well, with Big Joe 1, the booster engines did not come off. This meant that remaining engine had to carry that extra weight. As a result, the Atlas rocket did not go as high or as fast as it was supposed to go.

Furthermore, as a result of this malfunction the capsule did not spash down anywhere near where it was expected. There was some fear for a while that the capsule was lost, and the whole experiment was a failure.

However, the Navy found the capsule.

When the experts examined the heat shield they discovered that it was in very good shape. Furthermore, the capsule was subjected to enough heat on re-entry to answer the question that the researchers wanted to answer. The ablation method was an effective method of dealing with the heat of re-entry. The resin was lighter than beryllium in a field where weight is important.

Each extra pound of weight requires that the rocket use more fuel to get that weight into orbit. That extra fuel has weight, requiring even more fuel, which adds even more weight. There are many and strong reasons to keep the weight down as low as possible.

As a result of this method, NASA adopted the ablation method, and the heat-sink method was dropped.

However, there was still the problem of getting a reliable rocket that can actually put a capsule (with or without somebody inside of it) into orbit.

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