Chair Force Engineer

Saturday, April 22, 2006

Not invented here

NASA's silly insistence on throwaway Space Shuttle Main engines for their Ares 5 is yielding to the reality that these engines are just too expensive to throw away. The RS-68 is under consideration, but it brings many drawbacks to the table, like inferior Isp and about twice the mass of the SSME.

If NASA is open to international cooperation in the lunar return mission, they could ask the Russians to build the Ares 5's engines. The engine NASA is really looking for is RD-0120, built by RPO-Energomash for the defunct Energia rocket that flew in 1987-8.

When the US announced its space shuttle program in 1972, the typical Soviet reaction was that they needed one, too. Never mind the fact that the US shuttle was designed around a polar orbit mission that was never performed when the shuttle went operational.

The Soviets did make a few major changes to the basic shuttle design, based on their inexperience in certain fields of rocket propulsion. The most significant was the use of four LOX-Kerosene boosters instead of the two solids, because they had never built large solid rockets before. Also, the Russians had no experience building large, hydrogen-burning rockets. The Soviets felt that it would be more realistic to build throwaway main engines instead of reusable ones. It was decided that the Buran space shuttle would not carry the main propulsion system on the orbiter, but on the "Energia" rocket that the orbiter mated to.

The Energia's RD-0120 main engines have slightly less thrust and slightly less Isp than the SSME. However, they are only marginally heavier than the SSME. As far as weight and Isp concerns, they beat the pants off the RS-68. Key to the weight savings and good Isp is the chamber wall design. Cooling was provided by milling coolant channels around the nozzle, then affixing a thin metal jacket over the nozzle to seal the coolant channels. As an added benefit, RD-0120 was tested with methane replacing hydrogen as the fuel; this would be excellent if NASA allows methane back onto the lunar return mission.

Two real obstacles exist to implementing the RD-0120 in the Ares 5. The first is a very real concern, which is the ability of Russia to produce the engines. How much of the tooling for the engines still exists? The Energia factory has supposedly been turned into a plant for consumer products, including baby formula. Then again, a lack of tooling hasn't stopped NASA from calling for the resurrection of the J-2 engine from the Saturn rockets.

The other concern is one of national pride. Will NASA be able to swallow their pride and accept an engine that's "not invented here"? Lockheed Martin had no problems accepting the RD-180 for the Atlas III&V. However, some people suspect (and I have no info to corroborate this) that the defense department is not launching critical satellites on the Atlas because it's concerned about having to rely on the Russians for national security.

The big-picture view is that RD-0120 is the right engine for the Ares 5. With Ares 5, NASA is essentially trying to replace Energia using American components. Perhaps NASA should open high-level discussions with Rossaviakosmos and try to leverage as much of the Energia assets as possible--especially the RD-0120 engines.