First Delta IV Heavy launch

[LunarOrbit]

Great news! I, of course, missed the launch. Doh.

[Jirnsum]

I saw it on the news this morning. Impressive!

[Ottawan]

That's one BIG booster

Reminded me a bit of the show put on by a Saturn V.

[Satanic Mechanic]

They did have some problems though.  I read on Space.com that the test sattelites did not make orbit but the Delta Heavy was successful.

[Satanic Mechanic]

That's one BIG booster

Reminded me a bit of the show put on by a Saturn V.

I was looking at the Boeing site pictures and I most definately agree on the Delta Heavy being big.  Hell, the Delta Heavy is nothing but three regular Deltas hooked together with an upper stage.

[Ottawan]

What was the line from "From the Earth to the Moon" . . .  "multiple engines in multiple configurations"?

It reminded me of THAT too.

What I look forward to most is manned lunar missions, and I think this vehicle could be a major part of that endeavour.

[Bob B.]

Sorry for bringing up this old thread, but I just added Delta IV specifications to my Web page for anyone who is interested:

http://www.braeunig.us/space/specs/delta.htm

I also added the Atlas V:

http://www.braeunig.us/space/specs/atlas.htm


Sources:
Encyclopedia Astronautica
Delta IV Payload Planner's Guide
Delta IV Technical Summary
Atlas Launch System Mission Planner's Guide

[SpaceChem]

Wow, the Delta IV is impressive!  Can we say new manned launch vehicle?

[Bob B.]

Wow, the Delta IV is impressive! Can we say new manned launch vehicle?

It does look like a monster vehicle, but this is somewhat deceiving.  Since it is fueled entirely with liquid hydrogen, the tanks are enormous due the fuel's very low density.  Nonetheless, it does seem to have the lift capacity to launch the CEV.  I have a feeling though the Delta IV will never be man-rated.

What does seem to me like a viable possibility is using the RS-68 engines on the Shuttle-derived Heavy Launch Vehicle.  This heavy launcher will use 5 SSMEs, but it is my understanding these are very expensive engines.  The SSME are built for multiple use and are man-rated, but the heavy launcher is for cargo and the SSMEs will be expended each launch.  This seems rather wasteful to me.  I've heard the RS-68 was designed specifically to have a low production cost, and three of them have almost exactly the same thrust as five SSMEs.  So why not replace the five SSMEs with three RS-68s?

Although the RS-68 and SSME have almost exactly the same specific impulse at sea level (365 s and 361 s respectively), the RS-68 does have a lower specific impulse at altitude (410 s versus 452 s).  This means some loss of performance for the RS-68 that would have to be made up for with more propellant.  This could potentially cancel out the cost savings from using the cheaper engine.  I'm sure NASA has already thought of all this.

[skyjim]

The other issue is that the RS-68 is pretty heavy compared to the SSME on a thrust/weight basis - SSME is at 73:1 vs RS-68 at only 54:1.  Three RS-68s would mass about 43700 lbs, while 5 SSME are about 38900 lbs, with a 42 second Isp advantage in vacuum to boot.  The RS-68 has a 2 second Isp advantage at sea  level.  Pretty big performance handicap, though I imagine you might save a bit of mass on ducting and thrust structure for three vs five engines.

One big mass reduction for RS-68 would be to go to a lighter regeneratively cooled nozzle rather than the heavy ablative piece now used - selected expressly to lower cost.  While you were at it you could increase the area ratio of the RS-68 to gain a bit more Isp at altitude - but it's still never going to achive SSME Isp or thrust/weight numbers.

Last charts I saw indicated that the 5 SSMEs on the cargo booster were to be recovered and reflown.  That throws in  another wrinkle - how much mass for recovery systems?

Jim

[Bob B.]

Three RS-68s would mass about 43700 lbs, while 5 SSME are about 38900 lbs

I wasn't aware the RS-68 was that much heavier.  (That’ll teach me for not doing my research.)

While you were at it you could increase the area ratio of the RS-68 to gain a bit more Isp at altitude - but it's still never going to achive SSME Isp or thrust/weight numbers.

I though of this, but although it increases the vacuum Isp, it decreases the sea level Isp.  The R-68 has an expansion ratio of 21.5:1.  If we were to increase this to, say 40:1, then we gain about 3% on vacuum Isp, but we lose about 9% on sea level Isp.  This may still be a good tradeoff since the RS-68 will do most of its work at high altitude, and most of the liftoff thrust is provided by the SRBs.

Last charts I saw indicated that the 5 SSMEs on the cargo booster were to be recovered and reflown. That throws in another wrinkle - how much mass for recovery systems?

I wasn’t aware of this; I hadn’t previously seen anything to suggest the SSMEs would be recoverable.  This largely removes my objection to their use.  I’m surprised they can survive a reentry from such a high altitude and velocity.

[Simkid]

I wasn’t aware of this; I hadn’t previously seen anything to suggest the SSMEs would be recoverable.  This largely removes my objection to their use.  I’m surprised they can survive a reentry from such a high altitude and velocity.

The recovery equipment to let them survive shouldn't be that complicated (just a heat shield and parachutes), the question really is, how much mass does it add?

[Johno]

The recovery equipment to let them survive shouldn't be that complicated (just a heat shield and parachutes), the question really is, how much mass does it add?

Maybe, but "shouldn't be" and "isn't" are two VERY different concepts!

Of course, there are other possibilities that should be examined - perhaps soft airbags in the sea?

[SpaceChem]

Thanks for the technical data on the Delta's engines.  It does make man-rating much more difficult.  See what you learn being part of this forum - Fantastic!

[snake river rufus]

Wow, the Delta IV is impressive!  Can we say new manned launch vehicle?

That information is not in the public domain as far as I know.