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Commercial and US Government Launch Vehicles => ULA - Delta, Atlas, Vulcan => Topic started by: Chris Bergin on 09/25/2008 09:19 pm

Title: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Chris Bergin on 09/25/2008 09:19 pm
ULA PAO Mike (who's very good) will be sending a photo in about an hour.

United Launch Alliance First RS-68A Hot-Fire Engine Test a Success

Denver, Colo., (Sept. 25, 2008) - United Launch Alliance today announced
the successful first hot-firing of the new Pratt & Whitney Rocketdyne
RS-68A engine that will be used to power a future upgraded version of
the Delta IV Heavy Lift launch vehicle.  The hot-fire test was conducted
3:16 p.m. CDT, at NASA's John C. Stennis Space Center, Miss., today.
Stennis is the home of America's largest rocket engine test facility.
The RS-68A engine, an upgraded version of the current RS-68 liquid
hydrogen-liquid oxygen engine used on Delta IV, will allow the Delta IV
Heavy vehicle to boost heavier payloads into orbit. Currently, the RS-68
engine can deliver more than 660,000 pounds of sea level thrust and the
upgraded RS-68A will increase this to more than 700,000 pounds.  The
RS-68A also improves on the specific impulse, or fuel efficiency, of the
RS-68.  The Delta IV Heavy is comprised of three Delta IV core boosters.
With the new RS-68A engines, the Delta IV Heavy's thrust will increase
by more than 100,000 pounds.
The hot-fire test lasted the full planned duration of approximately 40
seconds and the test team will spend the next several days evaluating
data to characterize engine performance and to clear the engine for
future tests.  This initial test was on the first of three engines that
will be used during an extensive engine test program.  The test program
will continue during the next twelve months, leading to certification of
the new engine in mid-2010 and initial launch capability of the upgraded
Delta IV Heavy in early 2011.
"We congratulate Pratt & Whitney Rocketdyne and the entire RS-68A engine
team for this successful first step in making the most powerful liquid
hydrogen-liquid oxygen engine in the world even more capable," said Jim
Sponnick, ULA Vice President, Delta Product Line.  "The RS-68A upgrade
is a critical element in upgrading the Delta IV Heavy allowing ULA to
meet evolving needs of our government customers with even greater
reliability and performance than achieved in the past, while keeping
mission success our top priority." 
ULA program management, engineering, test and mission support functions
are headquartered in Denver, Colo.  Manufacturing, assembly and
integration operations are located in Decatur, Ala., Harlingen, Tex.,
San Diego, Calif., and Denver, Colo.  Launch operations are located at
Cape Canaveral Air Force Station, Fla., and Vandenberg Air Force Base,
Calif.
For more information on the ULA joint venture, visit the ULA Web site at
www.ulalaunch.com,
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Chris Bergin on 09/25/2008 11:57 pm
NASA's Stennis Space Center, Miss. - The successful first
40-second hot-fire test of the new Pratt & Whitney Rocketdyne RS-68A
engine that will be used to power a future upgraded version of the
United Launch Alliance Delta IV Heavy Lift launch vehicle was conducted
at 3:16 p.m. CDT, here today.
The RS-68A engine, an upgraded version of the current RS-68
liquid hydrogen-liquid oxygen engine used on Delta IV is the most
powerful engine of its kind in the world.  The upgraded RS-68A will
allow the Delta IV Heavy vehicle to boost heavier payloads into orbit.
Currently, the RS-68 engine can deliver more than 660,000 pounds of sea
level thrust and the upgraded RS-68A will increase this to more than
700,000 pounds.  (Photo courtesy of Pratt & Whitney Rocketdyne)
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Antares on 09/26/2008 03:58 am
Godspeed that the data analysis is more fruitful than that of the first RS-68 tests back in 98.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: kraisee on 09/26/2008 05:21 am
Great stuff from PWR!

Seems like it was only yesterday that the project was in PDR!   They've been flying through the effort so far.

Actually, there's a question:   Could someone provide the correct dates for the SRR, PDR and CDR for this development program?

Ross.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Nick L. on 09/26/2008 12:33 pm
Oh, very, very cool!

Congrats and here's hoping for a nice trouble-free certification!
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Stephan on 09/26/2008 08:05 pm
The RS-68A also improves on the specific impulse, or fuel efficiency, of the RS-68.
What will be the ISP of the RS-68A ?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: pm1823 on 09/26/2008 09:53 pm
Expected ISP 365/415 sec or better.

Quote
Reconnaissance Office (NRO) to partner with the service on the RS-68 engine work, which is
already in progress. The NRO plans to develop an upgraded RS-68A variant for a mission. From
that variant, NASA would join with the Air Force to develop a common RS-68B version for use on
both the Ares V and the Delta IV, featuring upgrades required by NASA for operability and
changes planned by the Air Force for their Assured Access To Space program to improve
robustness. 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/configuration
to reduce free hydrogen on the pad
during engine start.
11. Redesigned ablative nozzle to accommodate the longer-duration Ares V mission
profile.
The increased power level and main injector modifications are included in an engine
upgrade program that PWR is implementing under a contract with United Launch Alliance for the
RS-68A variant. Changes 3 through 8 are currently conducted under the Air Force Assured
Access to Space Program. NASA will work with the Air Force to combine the AATS upgrades with
changes 9-11 above, required for Ares V, to produce a common RS-68 B engine variant.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: kraisee on 09/27/2008 02:18 am
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.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: HIPAR on 09/27/2008 01:20 pm
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
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: kevin-rf on 09/27/2008 04:32 pm

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

Human rating means it may not fail in a way that will result in a LOC, it may still fail and any failure on a Delta IV is a LOM.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: siatwork on 09/27/2008 05:21 pm
LOC can only be mitigated via a launch escape system.  For that an engine needs health monitoring instrumentation such as sensors, LES activation logic.  Nothing to do with engine reliability/production quality.  DOD/NRO/Science don't want to skimp on that either.  Both EELVs engines were just fine for the OSP program under O'Keefe as long as engine health monitoring system was implemented.  Then came ESAS... and made up a ruse to exclude them for launching crews, while pushing "human rated" "safe" Ares-1 solids which embarassingly can't now meet ESAS own human rating reqs (due to TO).
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: kraisee on 09/27/2008 05:53 pm
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,
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; 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.

4) Finally, more testing.   A lot more testing will be required for NASA to get confidence.   The testing which has been done so far is good, if not excellent, and the handful of flown engines are even better.   But NASA will want to know this engine inside and out.   They will want to also know precisely where its limits are - and no RS-68 has so far ever been pushed to its absolute limits.   They're run a bunch up to their maximum required tollerances and even beyond, but none has so far ever been pushed to its destruct point.   I'd guess that NASA will probably want to *know* precisely where that point is for a human-rated engine - and that is going to be quite a spectacular test to witness, IMHO.   Designed to prevent both LOM and LOC events.


A Human Rating package could be developed for the existing RS-68 first, with the intention to move it over to the new RS-68A.

There are more changes which can be done to improve the engine as well, which aren't specifically Human Rating requirements - and most of those are already being implemented in the RS-68A development work at the core of this thread.   These include changes to reduce the "flame-ball" on engine ignition, and a change to tighten up the bearing tolerances so the engine can use less Helium during start-up too.   And there are internal changes to improve performance also.   But while those are all desirable, none of those are explicitly "required" for human-rating to succeed.

Ross.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 09/27/2008 06:44 pm

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.


Ross, you are way off base

1. The SSME doesn't even have have this.   It doesn't have redundant valves or actuators.   The SSME only has pneumatic backup to shut down valves, something not needed in a non reusable engine. Margins are what keeps an engine burning not redundancy.

2.  There is no difference in the placement of sensors for an unmanned or manned engine.  Only the numbers for redundancy.  Unmanned missions still need the same info used in LAS activation for anomaly resolution and margin analysis.  The health monitoring system is on the LV vs the engine.  The items needs to monitored are few and not extensive. Among them is turbopump RPM, turbine EGT, inlet and outlet pressures, combustion chamber pressure and temp. 

3.  There is no requirement for back up controllers.  The SSME does not have them.  NASA would not require mil-spec software.

 None of these is in the manrating spec
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Antares on 09/28/2008 04:13 am
Eh, Ross is closer than Jim gives him credit for, just a little loose with terminology.  Pneumatic back-up is not exactly redundancy, but that's probably what he was referring to.  The current sensors would need to go into an LVHM system, which they don't now of course.  And, one could make the argument for additional real-time sensors for that LVHM suite - ones that could be derived from existing sensors when they are post-processed now, but would be needed real time for LVHM.  SSME has at least 3 control strings in the engine, no?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: cb6785 on 09/28/2008 09:24 am
3.  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??
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 09/28/2008 01:41 pm
3.  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
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: cb6785 on 09/28/2008 01:52 pm
3.  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
Thanks for correcting. So backup in the definition you meant would mean a completely seperated system?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 09/28/2008 02:09 pm
3.  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
Thanks for correcting. So backup in the definition you meant would mean a completely seperated system?

The point is whether redundancy or to what level.  the manrating document doesn't require a certain level, it is up to the "program manager"
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Ron Carlson on 07/25/2009 09:11 am

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.


What software language does/will NASA use for the RS-68 family of engines?

Ron Carlson
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Nick L. on 07/25/2009 10:41 am
Ada? (no idea, just throwing that out there)
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Antares on 07/25/2009 02:57 pm
Just to clarify, NASA doesn't do that.  PWR does.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: GraphGuy on 07/30/2009 10:57 pm
Ada? (no idea, just throwing that out there)

Ada or C, don't really know.  Hopefully C as Ada is basically a dead language.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: iamlucky13 on 08/01/2009 07:10 am
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?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mikes on 08/01/2009 08:48 am
Ada? (no idea, just throwing that out there)

Ada or C, don't really know.  Hopefully C as Ada is basically a dead language.

Hopefully not C!

I've never used Ada as I'm not in the military or aerospace industries, but I've been programming in C for just shy of 30 years. It's a wonderfully flexible language, that gives you plenty of rope to hang yourself with. I can certainly admire the design goals of Ada to provide a highly formal language with efficient run-time checking of the commonest programming errors (buffer overrun, array bounds, fencepost).

Just because it's been around for a while and may not be well suited to general-purpose progamming does not make Ada a "dead language". People have been saying that about COBOL forever, but you can still make a good living from it. Fortran has been declared dead repeatedy, but there are plenty of people writing new code in it. Yes, there are newer tools, possibly better suited, but a good craftsman with old tools that s/he knows well can outperform the latest hot stuff in the hands of someone less experienced.

So, does anyone actually know what's used in the RS-68(A), rather than conjecturing?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mmeijeri on 08/01/2009 08:56 am
I'm hoping the answer is something cool and old like Lisp or Forth, but somehow I don't think so...
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 08/01/2009 12:12 pm
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?

It is on another thread.  Looking for it
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: DGH on 08/01/2009 02:11 pm
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?

Not sure how this is going to look


From 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 deg
in lbs base 102% and 106%
Medium       9.4 klbs   9.9 klbs    10.5 klbs
4,2              13.1 klbs 13.8 klbs    14.0 klbs
5,2              10.3 klbs 10.9 klbs    11.3 klbs
5,4              14.1 klbs  14.9 klbs    15.1 klbs

Heavy  just lists 2  current and 106%
Current 28.4 klbs 32.1 klbs
Sorry no figures for other orbits.
Pages 10-14 to 10-17  have great upgrade information
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Danny Dot on 08/01/2009 07:19 pm
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,
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;

snip

Ross.

Is it OK on factor of safety?  What is it designed to?

Danny Deger
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Nick L. on 08/02/2009 11:51 am
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?

Not sure how this is going to look


From 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 deg
in lbs base 102% and 106%
Medium       9.4 klbs   9.9 klbs    10.5 klbs
4,2              13.1 klbs 13.8 klbs    14.0 klbs
5,2              10.3 klbs 10.9 klbs    11.3 klbs
5,4              14.1 klbs  14.9 klbs    15.1 klbs

Heavy  just lists 2  current and 106%
Current 28.4 klbs 32.1 klbs
Sorry no figures for other orbits.
Pages 10-14 to 10-17  have great upgrade information


And the reason that they provide both 102% and 106% is because running them at 106% might require more requalification and testing. 102% would reduce those (and hence the time to launch).
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Antares on 08/02/2009 09:07 pm
Minimum factor of safety is 1.25 (so not OK on NASA STD 5001, but neither is Ares 1), but then there is proprietary fuzz on that.  It never goes below 1.25, but it's not textbook simple either.  IIUC, the same methods are in use on SSME, but to 1.4.

This thread is kind of going into Delta IV Q&A territory.
http://forum.nasaspaceflight.com/index.php?topic=9350.0
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: iamlucky13 on 08/05/2009 09:40 pm
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?

Not sure how this is going to look


From 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 deg
in lbs base 102% and 106%
Medium       9.4 klbs   9.9 klbs    10.5 klbs
4,2              13.1 klbs 13.8 klbs    14.0 klbs
5,2              10.3 klbs 10.9 klbs    11.3 klbs
5,4              14.1 klbs  14.9 klbs    15.1 klbs

Heavy  just lists 2  current and 106%
Current 28.4 klbs 32.1 klbs
Sorry no figures for other orbits.
Pages 10-14 to 10-17  have great upgrade information


Thanks, I just looked up the guide and found those pages. So 10-13% increase. That seems quite respectable.

Following up on Nick's post, the guide also explains the potential requalification or even modification would be structural. Reading his post I thought he was referring to additional engine testing.

I also noticed the section about possibly adding more GEM-60's, and most interestingly, using GEM-60's on the Heavy configuration. I was unaware of such proposals existing. Very interesting.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Antares on 08/07/2009 03:08 pm
I'm hoping the answer is something cool and old like Lisp or Forth, but somehow I don't think so...

C and assembly.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mmeijeri on 08/07/2009 03:13 pm
Ah, that's more like it!
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Targeteer on 08/07/2009 08:07 pm
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.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mmeijeri on 08/07/2009 08:08 pm
Lower gravity losses I think.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: NASAJim on 08/07/2009 08:14 pm
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.

Gravity losses are reduced with higher thrust. The amount thrust your engines produce to overcome the gravitational forces on the rocket don't do anything to accelerate the rocket into orbit. So if your Thrust/Weight ratio at liftoff is only 1.0, you could have an ISP of a million seconds and you still wouldn't go anywhere. Higher thrust allows you to spend less time fighting gravity during the launch, particularly in the early part of flight just after liftoff.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 08/07/2009 09:14 pm
but I haven't seen any discussion of stretching the Delta IV tanks

There are infrastructure constraints preventing this.  Adding SRM's and uprating engines is easier
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Targeteer on 08/08/2009 07:50 pm
Thanks for the responses. My Physics and orbital mechanics background are really rusty and incomplete.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: JosephB on 08/09/2009 02:30 pm
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!
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Nomadd on 08/09/2009 03:18 pm
Thanks for the responses. My Physics and orbital mechanics background are really rusty and incomplete.

 It just takes a little logic. (The basis of all physics outside of some advanced forums) Think of all the fuel you expend just to support your own weight. The faster you get up, the less time you hang around burning that fuel.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Nick L. on 08/09/2009 05:02 pm
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!

Yes, the 2007 one is the latest.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: ugordan on 08/11/2009 05:56 pm
Reading this presentation (http://www.ulalaunch.com/docs/publications/BoosterInnovationJPC2009.pdf), 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, optimized for max performance)?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 08/11/2009 05:59 pm
Reading this presentation (http://www.ulalaunch.com/docs/publications/BoosterInnovationJPC2009.pdf), 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 would think so.  Also it means the forward adapter would be field installed or a late factory installation.
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mmeijeri on 08/11/2009 06:09 pm
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)?

Can you explain the differences between the cores and how they help performance?
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: Jim on 08/11/2009 06:13 pm
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)?

Can you explain the differences between the cores and how they help performance?

I did it months/years ago in another thread

http://forum.nasaspaceflight.com/index.php?topic=15541.msg357064#msg357064
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: mmeijeri on 08/11/2009 06:16 pm
Thanks!
Title: Re: United Launch Alliance First RS-68A Hot-Fire Engine Test a Success
Post by: sdsds on 09/21/2009 06:31 am
Hadn't seen this before:

http://www.ssc.nasa.gov/sirs/movies/propulsion/mpeg/low/rs-68.mp4

NTRS describes it as an RS-68 test firing conducted April 6, 2009, on the B-1 stand at Stennis.  Was this an RS-68A test?