Delta 4 Should Be Replaced by New Delta 5

[envy887]

Please forgive me, envy887. I made a typo when inputting the ISP for MB-60. It should have been 466.7 and not 266.9.

When you said, "use the AVERAGE specific impulse," are you referring to the specific impulse at sea level?

No, I mean the average specific impulse over the entire burn. A SL engine's specific impulse continuously increases from liftoff to burnout, while a vacuum engine operates at near constant specific impulse.

To get the exact average you need to integrate the I_sp vs time curve for a specific launch profile and divide by duration, but for these purposes a simple average of SL and Vac I_sp is typically close enough. For an SSME the average is around 410 to 415 seconds. For a SRB more like 250 seconds.

[AncientU]

So the goal is to keep flying RS-25 engines?

Is that a worthy (or worthwhile) goal?

Their thrust-to-weight ratio is pretty terrible (sea level, 418klbf/7.7klb=54), so using them on a reusable rocket might be a fatal flaw.  Of course, if you add 6-8 solids -- there went reusability -- you can drag an under-powered hydrolox core stage to orbit.

[Chasm]

Just trying to find out what the goal of this exercise is.

One of my recent pet projects was reshuffling the Delta tanks for Methalox and sticking BE-4s on it. Does not really work out on the silverbird calculator though.
I would love a tool where it is easier to change existing vehicles, without finding parameters and then retyping everything. Bonus points for an ensemble of results based on a parameter change.

[clongton]

My answer to the title question is no. ULA already has its hands full trying to create Vulcan. If the ULA leadership tried to do this the BOD would fire the lot of them on the spot.

Rocket Lego is a fun game for a Saturday night and a bottle of Crown Royal.

[Oli]

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

[clongton]

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible in the sense you are talking. That needs to be part of the fundamental base design.

[Lars-J]

This thread should be renamed "RS-25 or bust"... 

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible. That needs to be part of the fundamental base design.

I know people are huge fans of the SSME, but it is by now a pretty ancient design compared to newer engines. It is very expensive. And despite its great efficiency, it is not well suited for a reusable vehicle.  Newer engines that are built with reusability in mind - M1D, BE-4, Raptor - are better choices for new rocket stages.  Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

[spacenut]

What about 5-7 BE-3's on the Delta 5m core, with a BE-3 vacuum upper stage ACES?  That would be an all hydrolox vehicle, 1st stage may be able to land. 

[Space Ghost 1962]

This thread should be renamed "RS-25 or bust"... 

Agreed!!

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible. That needs to be part of the fundamental base design.

I know people are huge fans of the SSME, but it is by now a pretty ancient design compared to newer engines. It is very expensive.

Boy and howdy!

It's a wonderfully compact ground start engine, perfect for a spaceplane! If you wanted to do a 1/3 scale carbon composite Shuttle variant, it would be the perfect technology base to start from.

And despite its great efficiency, it is not well suited for a reusable vehicle.

Stage you mean. As in powered landing meaning restart. Agreed. Would work great for reuse on a flyback where you don't restart.

Newer engines that are built with reusability in mind - M1D, BE-4, Raptor - are better choices for new rocket stages.  Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

Agree with the highlight I've done.

FWIW, the only way I could see RS-25E derivative used would be with either an air launched/started or ground launched/started (with side boost) spaceplane concept (unlike Shuttle by having integral LH/LOX tanks).

add:
For a rapid deploy & recovery spaceplane single engine use *only*, there are some redesign/additive mfr/materials changes that could exploit hydrolox propulsion as originally intended for a vehicle in the capability class of the HL20. You could push it then well beyond the 108% thrust level.

The only advantage for such a vehicle might be a more rapidly reusable crew transport to LEO turnaround than Dreamchaser/Dragon/Starliner/derivative NS capsule.

[envy887]

What about 5-7 BE-3's on the Delta 5m core, with a BE-3 vacuum upper stage ACES?  That would be an all hydrolox vehicle, 1st stage may be able to land.

OTOH hydrolox is a poor booster fuel. Apparently RL-10 can run on methane and can throttle. Might be a worthwhile landing engine for the Vulcan booster. Or maybe the Broadsword engine?

BE-3 would make a better upper stage engine - more thrust can push a bigger stage, and probably a lot cheaper than throwing away RL-10s.

[Chasm]

Have weight and ISP of the BE-3 been released to the public? I can't find them.
The external customers obviously know.

[robert_d]

OK.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.
That should be a cheaper path to keeping a hydrolox booster in production.

[Lars-J]

OK.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.
That should be a cheaper path to keeping a hydrolox booster in production.

RS-68 is still very expensive. And not reusable. Just because they ran one engine for 700s does not mean that this provides enough margin if it is used again. The ablative liner(s) in the nozzle would have to be refurbished for every flight. It would seem like perhaps 7-9 BE-3's would be an option if you wanted a reusable stage.

[ulm_atms]

Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

Only when NASA does...

LOL...sorry, I kid, I kid...just couldn't help it. 

But question.  Is there ever a good reason to do hydrolox for the first stage?  And what I mean is that it seems kerolox is both cheaper (hardware and GSE requirements....hydrogen always seemed to have more requirements/issues for handling, loading, storage, etc...) and better performance pound per pound for a first stage booster. (we will see about methane...should be...but no hard numbers yet that I know of)  Also, hydrolox first stages always seems to need solids to actually get going (has there ever been a Delta IV without solids attached?)

I guess I am just wondering, if thinking reusable and/or cheap, that hydrolox would ever be a good first stage booster?  All of it's glory seems to be in the void of space where it shines supreme on the performance meter.

[MATTBLAK]

Sadly, the RS-25 will never again be used on a reusable spacecraft.  It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

[Patchouli]

Sadly, the RS-25 will never again be used on a reusable spacecraft.  It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

Yah it's kinda a shame as the RS-25 is up to the task of powering a SSTO.
A simplified RS-68 with a regen nozzle might be a lot cheaper.
Ironically the Ares V design probably would be workable with regen RS-68s.

[RocketmanUS]

OK.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.
That should be a cheaper path to keeping a hydrolox booster in production.

Why keep a hydrolox 1st stage?
Why keep Delta IV with modifications? Just how long would it take to get to first launch if this concept were possible?

ULA is going with Vulcan with ACES ( with tanker and in-space refueling ).
Blue Origin is going with New Glenn ( 2 and 3 stage version ).
These should have no problem being cheaper than any Delta IV with greater payload mass to orbit.
They will both be using the same 1st stage engine.

[envy887]

... Also, hydrolox first stages always seems to need solids to actually get going (has there ever been a Delta IV without solids attached?)

Uh... All the Heavies?

[Thorny]

(has there ever been a Delta IV without solids attached?)

Three, not counting the -Heavies:

Delta 296 (DSCS-III A3)
Delta 301 (DCSC-III B6)
Delta 320 (DMSP-F17)

[Lars-J]

Sadly, the RS-25 will never again be used on a reusable spacecraft.  It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

But not any cheaper than the Delta IV (which is VERY expensive), so I'm not sure I understand the point?