Chair Force Engineer

Thursday, February 08, 2007

The Danger of Diameters?

When NASA announced the initial specs for the Ares I rocket in late summer 2005, I was a bit perplexed by the 5.5 meter diameter of the Ares I upper stage. My cynical reaction was that they wanted to make the Orion capsule too wide to fit on the Delta IV, which is 5 meters wide. But that idea was quickly refuted when NASA shrank the Orion diameter to 5 meters while keeping Ares I at 5.5m.

My thoughts then turned to the Saturn I's S-IV stage. In some ways, the Ares I upper stage is similar, albeit much longer, especially due to the use of a single J-2 (like on the later S-IVB.) The use of six RL-10's on the S-IV was an idea that I feel should have been probed further by NASA for the Ares rockets, in order to eliminate the cost of J-2X development. The Ares I upper stage is looking even more like an S-IV or S-IVB, due to the recent change to a common propellant bulkhead.

Then I noticed that Ares I's upper stage had the same diameter as proposed Liquid Rocket Boosters for the shuttle, which were projected during the mid-80's. My assumption is that NASA's Michoud facility has the tooling for 5.5 meter diameter tankage.

I'm under the impression that there's a lot of neat tooling at the Michoud plant. For years we were told that "those NASA idiots destroyed the tooling for the Saturn V," only to find out recently that Michoud still has the tooling to build the 10m tankage that was used on the first and second stages of the Saturn V. I don't know what program would have paid for the 5.5 meter tooling, but apparently it exists. Perhaps they're reusing the jigs and such from the S-IV after all.

On the topic of rocket manufacuring facilities, I do see problems on the horizon. One big question is where NASA plans on building the Ares i and Ares V, and I haven't yet seen the details to ease my concerns.

For the Saturn 1B and Saturn V, four different facilities were employed to build four different rocket stages. The S-IB was built by Chrysler (I enjoy the thought that my car's manufacturer built rockets back in the good old days.) The S-IC was built by Boeing at NASA's Michoud plant (now operated by LockMart and used for building the Shuttle ET.) The S-II was built by North American Aviation in the government-owned factory at Seal Beach, CA (I believe this plant is now used by ULA for the Delta II.) Finally, the S-IVB was built by Douglas Aircraft at the Huntington Beach, CA plant. For the Ares I and Ares V, does NASA have a plan for spreading out the construction, or does it plan to do everything at Michoud?

I see challenges ahead if NASA plans on doing everything at Michoud--not because the flight rate is too high (only 2x Ares I + 2x Ares V are envisioned per year,) but because the variety of tankage is a challenge from a manufacturing point-of-view. The Michoud plant will have to crank out two 5.5m tanks, two 10m tanks, and two 8.38m tanks (reusing the Shuttle ET tooling for the Earth Departure Stage.) It should also be remembered that the 42m height of the S-IC was dictated by the ceiling height of the Michoud plant, and that costly mods to the plant would be necessary to grow any longer. I haven't seen the published numbers for the Ares V first stage, but it appears to be almost 60m long based on the published artwork! I've never seen this question asked, but I have no clue how NASA intends to build the Ares V. Perhaps they'll build it horizontally and never turn it vertically while in the building.

NASA may quickly get a rude lesson in the difficulties of large-scale manufacturing. Dreaming of a rocket is a challenge, demonstrating its feasibility is a challenge, and drafting it is a challenge. But the hardest challenge may very well be the transformation of an engineering drawing into real hardware. Even if a design is technically feasible, the question of manufacturability is left open.