exploration systems architecture study

exploration systems architecture study

Yesterday NASA unveiled their roadmap for implementation of the first phase of the Moon, Mars and Beyond initiative. There are some good points to their new plan, which I will cover in this post.

They have separated cargo launches from personnel launches. This is as it should be, as the requirements for launching cargo and personnel are different. Cargo should be launched at as high an acceleration as possible (generally speaking, a higher acceleration through the atmosphere means a bigger payload delivered to orbit for the same price), but launching people requires accelerations that the human body can withstand.

They are abandoning the side-by-side configuration and are instead going to an inline launch system. This eliminates the debris problem that plagued the shuttle, and allows an escape tower at the top of the stack: if there is a problem during launch, the tower at the top can fire its small booster, separating the manned capsule from the rest of the rocket and allowing the crew to escape from a situation such as the one that killed the Challenger astronauts.

They are re-using existing technology, in particular the space shuttle main engines and the solid rocket boosters. The SSMEs are some of the most powerful rocket engines ever developed, and they are proven quantities. The SRBs are also proven technology, with the only modification being the addition of a fifth section to the stack (current SRBs have four sections). For the cargo launcher they are also keeping the existing diameter of tankage (although much longer) as is currently used for the space shuttle external tank, allowing existing tooling and production methods to make the fuel tank for the cargo.

They are not trying to recover the SSMEs on each launch, and would instead be building new ones every launch. At first glance, this might seem like an increased cost in comparasin to the shuttle, but that first glance would be wrong. The requirement to build a great many such engines means that production line methods can be brought to bear, decreasing the total per-unit cost. Furthermore, the current system of refurbishing engines with every launch means increased wear on each engine (reducing safety) without reducing cost, as each engine currently needs to be completely rebuilt by hand.

Finally, they do not have wings on the crew compartment. It will reenter the atmosphere much the same as the Mercury, Gemini, Apollo, and Soyuz craft: as a blunt wedge with a small heat shield. The shield will be consumed and jettisoned on each reentry, rather than trying to make a shield that can withstand multiple reentries and which must be carefully inspected and refurbished with each launch.

I will be writing about the drawbacks to the plan in a later post.

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