The RS-68A also improves on the specific impulse, or fuel efficiency, of the RS-68.
Reconnaissance Office (NRO) to partner with the service on the RS-68 engine work, which isalready in progress. The NRO plans to develop an upgraded RS-68A variant for a mission. Fromthat variant, NASA would join with the Air Force to develop a common RS-68B version for use onboth the Ares V and the Delta IV, featuring upgrades required by NASA for operability andchanges planned by the Air Force for their Assured Access To Space program to improverobustness. Planned modifications to the current RS-68 are:1. Increased power level to 108 percent from the current 102 percent.2. Main injector changes to improve Isp to at least 414.2 seconds from the current 407.7.3. New bearing material to decrease stress corrosion susceptibility.4. Redesigned turbopump pump inlets to incorporate tip vortex suppression.5. Redesigned fuel turbopump second stage blisk to decrease susceptibility to cracks.6. Redesigned gas generator igniter that eliminates squib foreign object debns concern.7. Higher reliability oxidizer turbopump bearing chill sensor.8. Higher reliability hot gas sensdr.9. Redesigned oxidizer turbopump to reduce pre-start and operational helium usage.10. Modified engine start sequence/configurationto reduce free hydrogen on the padduring engine start.11. Redesigned ablative nozzle to accommodate the longer-duration Ares V missionprofile.The increased power level and main injector modifications are included in an engineupgrade program that PWR is implementing under a contract with United Launch Alliance for theRS-68A variant. Changes 3 through 8 are currently conducted under the Air Force AssuredAccess to Space Program. NASA will work with the Air Force to combine the AATS upgrades withchanges 9-11 above, required for Ares V, to produce a common RS-68 B engine variant.
Look at the Ares-V data for the performance expectations for this evolution.Those are the numbers NASA has been told to expect from this engine. The only real difference is one will include the necessary human-rating hardware, the other won't.Ross.
What might that human-rating modification be? If it improves the reliability of the engine, why wouldn't that equipment be cost effective as 'added insurance' towards preventing the loss of billion dollar defense oriented payloads? --- CHAS
What might that human-rating modification be? If it improves the reliability of the engine, why wouldn't that equipment be cost effective as 'added insurance' towards preventing the loss of billion dollar defense oriented payloads?
1) Additional redundancy on some parts; I'm talking backups for many of the smaller valves, actuators and other parts. This provides additional capability to continue to fly even if certain things fail. Designed to prevent both LOM & LOC situations.2) Additional Sensor Package and Health Monitoring Computers. This allows more extensive examination of the engine while in flight allowing for the detection of problems very early and provides the necessary data to the Launch Abort System to get out of Dodge a little bit quicker - ideally before the engine ever goes critical - i.e. "boom". Designed to prevent LOC in LOM situations.Current unmanned engines make the assumption that almost any significant engine failure is going to automatically result in the payload being inserted into the Ocean, and there is nothing which can be done to even try to save the payload if it happens. So health monitoring and extensive sensor packages are fairly minimal on cargo-only flights. This has to change for human flights.3) Software re-write. The current software used in the RS-68 is commercial-grade and is fairly minimal in capability. NASA will require the equivalent of mil-spec software, *really* extensive testing and multiple backups for in-flight engine controllers. These do not exist currently. Designed to prevent both LOM and LOC events.
3. There is no requirement for back up controllers. The SSME does not have them.
Quote from: Jim on 09/27/2008 06:44 pm3. There is no requirement for back up controllers. The SSME does not have them.Well I may be waaaaay off here, but if my memory isn't totally nuts STS-93 had problems with at least one primary and one secondary engine controller, and they continued the ascent using the backup-controllers.....Primary, secondary and backup means 3 controllers per SSME doesn't it??
Quote from: cb6785 on 09/28/2008 09:24 amQuote from: Jim on 09/27/2008 06:44 pm3. There is no requirement for back up controllers. The SSME does not have them.Well I may be waaaaay off here, but if my memory isn't totally nuts STS-93 had problems with at least one primary and one secondary engine controller, and they continued the ascent using the backup-controllers.....Primary, secondary and backup means 3 controllers per SSME doesn't it??Backup was the secondary and they are in the same box with the primary
Quote from: Jim on 09/28/2008 01:41 pmQuote from: cb6785 on 09/28/2008 09:24 amQuote from: Jim on 09/27/2008 06:44 pm3. There is no requirement for back up controllers. The SSME does not have them.Well I may be waaaaay off here, but if my memory isn't totally nuts STS-93 had problems with at least one primary and one secondary engine controller, and they continued the ascent using the backup-controllers.....Primary, secondary and backup means 3 controllers per SSME doesn't it??Backup was the secondary and they are in the same box with the primaryThanks for correcting. So backup in the definition you meant would mean a completely seperated system?
3) Software re-write. The current software used in the RS-68 is commercial-grade and is fairly minimal in capability. NASA will require the equivalent of mil-spec software, *really* extensive testing and multiple backups for in-flight engine controllers. These do not exist currently. Designed to prevent both LOM and LOC events.