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.
Ada? (no idea, just throwing that out there)
Quote from: Nick L. on 07/25/2009 10:41 amAda? (no idea, just throwing that out there)Ada or C, don't really know. Hopefully C as Ada is basically a dead language.
The press release says specifically the RS-68A will be used on the Delta IV Heavy, but I presume they mean all Delta IV's, not just the heavy?Does anyone know what the expected lift capability will be with the upgraded engines?
Quote from: HIPAR on 09/27/2008 01:20 pmWhat 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,PWR/MSFC looked at RS-68 "as is" and determined that there were over 200 things which needed changing on the engine to meet human-rating standards. If it were to be flown without those changes, that would require a "waiver" for each of those 200+ things. Every one of those issues will have to be addressed before any human will ever use that engine. Each waiver will either have to be fixed, or that specific waiver will have to be justified, rationalized and accepted.The issues will range from lots of very simple fixes which can be implemented quickly and cheaply to a handful of complicated ones requiring extensive & costly development work. But almost all of the issues fit into four main categories:-1) Additional redundancy on some parts; snipRoss.
Quote from: iamlucky13 on 08/01/2009 07:10 amThe press release says specifically the RS-68A will be used on the Delta IV Heavy, but I presume they mean all Delta IV's, not just the heavy?Does anyone know what the expected lift capability will be with the upgraded engines?Not sure how this is going to lookFrom the recent Delta IV payload guide page 10-14 GTO Orbit: 35,786 km x 185 km minimum (19,323 nmi x 100 nmi minimum) at 27.0 degin lbs base 102% and 106%Medium 9.4 klbs 9.9 klbs 10.5 klbs4,2 13.1 klbs 13.8 klbs 14.0 klbs5,2 10.3 klbs 10.9 klbs 11.3 klbs 5,4 14.1 klbs 14.9 klbs 15.1 klbsHeavy just lists 2 current and 106%Current 28.4 klbs 32.1 klbsSorry no figures for other orbits.Pages 10-14 to 10-17 have great upgrade information
I'm hoping the answer is something cool and old like Lisp or Forth, but somehow I don't think so...
My apologies in advance for what may be a dumb question (for this audience) but how does just increasing the thrust at takeoff increase payload performance to orbit? I realize fuel is being burned faster so the stack gets lighter and accelerates faster but the amount of energy in the fuel tanks is fixed (I would think) so an increase in fuel capacity (bigger tanks) allowed by the increased thrust seems required. Increasing the ISP (ie fuel burn efficiency) may be the explanation but I haven't seen any discussion of stretching the Delta IV tanks so that's why I'm asking the question.
but I haven't seen any discussion of stretching the Delta IV tanks
Thanks for the responses. My Physics and orbital mechanics background are really rusty and incomplete.
Is the Sept 2007 Delta IV Payload Guide in L2 the latest & greatest?If there is an updated one does anyone have the thread? Also, this pdf is all I have on Delta growth options. Would anyone have something more detailed? Thanks!
Reading this presentation, there's mention (slide 9) of a standardized Delta IV CBC based on M+(5,4) booster after RS-68A is fielded. I presume this only means all Medium CBCs will be identical (as in Atlas), but the Heavy cores will not be common (mirror-images and such)?
I presume this only means all Medium CBCs will be identical (as in Atlas), but the Heavy cores will not be common (mirror-images, optimized for max performance)?
Quote from: ugordan on 08/11/2009 05:56 pmI presume this only means all Medium CBCs will be identical (as in Atlas), but the Heavy cores will not be common (mirror-images, optimized for max performance)?Can you explain the differences between the cores and how they help performance?