Chair Force Engineer

Tuesday, October 02, 2007


NASA Spaceflight has an excellent overview of recent developments with the Orion capsule and Ares I launcher. Some are quite positive, while others are worrysome and demand the attention of NASA's best minds.

The Positive
--Ares I performance has improved. Perigee of the initial orbit has increased by 19 nautical miles (from -30 to -11,) and the insertion orbit has increased from 55 to 70 nautical miles.
--J-2XD performance is increasing to above 452 seconds, vs. the predicted 448 seconds. This is a bit confusing, as I had previously read that the interim J-2XD was being dropped, in favor of moving straight to the final J-2X configuration. Of all the current aspects in Project Constellation, J-2X development appears to be the most successful.
--The boost protective cover which connects the escape tower to Orion has assumed a bullet-like shape, as previously reported by Flight International. This improves the aerodynamics of the Ares I stack and reduced drag losses (increasing payload to orbit.)

The Negative
--Ares I has insufficient margins to lift the lunar-capable version of Orion without removing certain types of fault tolerance.
--The Orion design team has adopted the "Zero Baseline Vehicle" approach, which starts with a minimal amount of redundancy, then adds some redundancy back in as Ares I performance will permit.
--While the airbag trade study is not complete, there's a very good chance that airbags could be dropped in the middle of the current design cycle.

I like a lot of the effort that has been made towards getting the Ares-Orion system to work, especially in regards to the J-2X. However, I think that NASA has put itself in this bind because of poor systems engineering practices that were employed from the outset. Every spacecraft is designed to carry certain amounts of reserve mass at different points in its design evolution. While Ares I was capable of meeting the performance goals based on the mass targets, it quickly became clear that NASA had skimpy margins for Orion, which were quickly outgrown once the design for Orion became more detailed.

NASA's current choice is to meet the mass targets by removing safety, or by removing capabilities. Sadly, I feel the agency is making the dangerous decision to remove safety features before removing capabilities. Landing bags are probably the most glaring safety feature that may be thrown out, because they may be needed if the capsule has to abort over dry land. I would rather that NASA reduce the crew size or on-orbit lifetime for Orion before they take out the redundancy. The agency's wounded "safety culture" still has a long way to go before it's acceptable to our astronauts and to the taxpayers who make the missions possible.