Qualification Other integration issues were requested. The expert stated that they were mainly "paper issues" 1. Vehicle has proof and burst pressure qualifications: proof pressure - 1.2 x max operating pressure burst pressure - 1.5 x max operating pressure example: valve has 1000 psi max operating pressure proof = 1200 psi burst = 1500 psi now new standards are made: 1.5 x max for proof 2.5 X max for burst Expert states that if the other components are still at 1.2 and 1.5 that the new standard makes no sense. The engine was tested with EMA on one valve and pneumatic on others: 48 hot firings with 2 aborts. The aborts were for a specific reason. Computer modeling showed good valve timing. Overall, there was little impact on the entire vehicle caused by the changes to the engine. The systems are well modularized. 1. Torch igniter fits where current igniters were. Exciters also fit. 2. Electrical actuators caused some changes. The engine qualified as a component Qualification To qualify the engine, must show 10 times mission lights and 10 times mission burn time: 2 firings/mission - 20 firings to qualify 400 sec firing time/mission - 4000 seconds to qualify. Looked at variations in temperatures between fast starts and slow starts Fast starts - hotter engine - faster start Slow start - colder engine Qualification - vibrational qualification 1. Main booster probably puts the worst loads on Centaur 2. Vibrational loads at various locations 3. Explosive charge to separate stages 6-8 gs 12-14 gs transient Qualification 1. Impose worst cases all at once 2. Impose worst realistic cases Reliability models - historical data is run - models come up with probabilities. Changes are need driven - don't perturb properly working components. Try to improve reliability by minimizing parts - it is generally a good idea to minimize parts but counter examples exist: Eliminate shutoff valve for oxidizer pump Shutdown - close oxidizer valve, pump spins down Shutdown - close flow control valve Inlet to fuel pump - inducer - higher pressure, higher performance Qualification Testing again Vibration during mission is a function of: 1.Vibration level (amplitude) in Gs 2. Frequency of vibration A component may be more suceptible to failure due to low frequency vibration than because of high frequency vibration. Digression upgrading takes out design margin Try to look at actual worst case Battery power requirements - EMAs and Electronic engine controller 5 EMAs using 5 amps each 5 x 5 = 25 amps Realistically, not all of the EMAs will use current at once. realistically perhaps 15 amps is max required. Envelope - all worst case for vibration, load and heat. Bill concept - wants a new design with more margin. At present new designs have less margin but they always upgrade and always push limits. Specific impulse is high for RL-10 450 sec New design max is to be 470 sec NASA Plum Brook Station Simulate coast in space in cold vacuum chamber, then fire engines. 1. Pump chamber to low pressure (hard vacuum where Centaur goes) 2. Centaur is placed inside 3. Lamp heaters used to simulate solar heating 4. Engines are placed in duct opening into water spray. In this chamber, beneath the craft, vaporized water is vented as steam to simulate firing into a vacuum. 5. The pressure from the exhaust gases are vented to simulate fire in space. Qualification Test cycles - qualify the full system - propulsion system, etc. A valve may have to operate 1000 times in 400 sec firing. Cycles- - x10 qualifying considered excessive now - x10 duration being considered Qualification of: 1. Mechanical systems are no big deal - steady state operation not a problem 2. Electrical systems are more difficult to get to qualify. Duration x10 is more difficult, e.g., battery more difficult to get to x10 adds weight. Qualification - number of tests is an issue 2 firings - qualify to 20 firings. Tradeoff - 1. don't want to redesign and qualify too often because the process is so expensive. 2. Don't want to save up too many changes, make them all at once because unanticipated interactions may occur. If too many changes are made, a previously stable system may be made unstable. Vacuum conditions - if it will operate in a vacuum, try to test in a vacuum. Plum Brook Station is an example.