Atlas V Alternatives

[edkyle99]

For those who've wondered about alternative engines, here are a couple of alternatives to Atlas 5-401 with equivalent performance to GTO.  One uses six Merlin 1D engines (as an example of gas generator state of art) and a 19% tank stretch.  Another uses three 154 inch diameter composite case solid motors topped by a Centaur.  The latter produces a surprising result for some - less GLOW for the same payload.

 - Ed Kyle

[cmj9808]

A 19% stretch? The weight of CCB seems only 9% increase according to your GLOW figure.

[edkyle99]

A 19% stretch? The weight of CCB seems only 9% increase according to your GLOW figure.

Propellant load increases 19%, thus the tank stretch.  Some dry mass reduction is provided by use of the "Merlins".    Also, GLOW includes the Centaur, which does not change.

 - Ed Kyle

[cmj9808]

A 19% stretch? The weight of CCB seems only 9% increase according to your GLOW figure.

Propellant load increases 19%, thus the tank stretch.  Some dry mass reduction is provided by use of the "Merlins".    Also, GLOW includes the Centaur, which does not change.

 - Ed Kyle

Thanks for clarification. I did exclude the Centaur. The GLOW increase (27t) comes solely from CCB, which leads to 332t CCB/Merlin vs 305t CCB/RD-180, a 9% increase.

[baldusi]

Which Merlin 1D did you used? The first version or the Full Thrust?

[spacenut]

Wouldn't 5 full thrust Merlin's do the same? 

[edkyle99]

Which Merlin 1D did you used? The first version or the Full Thrust?

I assumed "Full Thrust".  Of course this is only an exercise to demonstrate what is possible with state-of-the-art gas generator engines.

 - Ed Kyle

[edkyle99]

Wouldn't 5 full thrust Merlin's do the same? 

They would only give a 1.07 T/W ratio at liftoff.  Five engines would each need to produce more than 86 tonnes (190 Klbf) sea level thrust to give a 1.2 T/W ratio.

 - Ed Kyle

[spacenut]

Thanks, I asked that question somewhere else, and got shot down.  A stretched Atlas using Merlin engines is doable.  It seems it would be a much cheaper solution that totally getting rid of Atlas V.  Maybe with 6 Merlins, they could call it Atlas VI.  SpaceX doesn't like solids strapped on their rockets, thus they are stretched to the max and use the 9 engines.  At least they wouldn't have the problem of the Russian engines.  It wouldn't give us a variety of choices though.  Right now we do have Delta IV, Atlas V, Falcon 9(when they get back to launching).  I do like the Vulcan rocket, with it's larger diameter. 

The Merlin seems to be a very good engine.  I think they have only had one fail, but they had engine out and the satellite made orbit. 

[edkyle99]

Thanks, I asked that question somewhere else, and got shot down.  A stretched Atlas using Merlin engines is doable.  It seems it would be a much cheaper solution that totally getting rid of Atlas V.  ...

The only problem, of course, is that SpaceX would never sell a Merlin to a competitor.  ULA would have to develop (or have someone develop) its own gas generator engine.  Presumably this would be easier and less costly than developing a staged combustion engine (like AR-1), but it would still take time and money.  Also, as you can see, the stage itself would have to be redesigned with stretched or fattened tanks and a new thrust section. 

Of course in the end ULA decided to develop a big new stage and new engine burning new propellants regardless - a full-bore clean-sheet approach.  I wonder how close they came to going kerosene gas-generator instead.

 - Ed Kyle

[Jim]

Thanks, I asked that question somewhere else, and got shot down.  A stretched Atlas using Merlin engines is doable. 

And rightly so.  This thread has just stated the tank size and #of engines required to replace the RD-180.  It does not state that the configuration is "doable".  It does not go into the thrust section modifications and whether it would be compatible with the existing MLP or handling GSE.  Nor does it look at the facility impacts due to the additional height.

And what does Spacex not liking solids have to do with a thread about Atlas?    It isn't a Spacex rocket and so solids can be used.

Aside from the technical aspects, it is politically not "doable".  Spacex is not going to be an engine supplier.

This is a perfect example of the axiom that "Rockets are not Legos"

[Zed_Noir]

How about replacing the RD-180 with 2 RD-181. Never mind that it is not doable politically. But theoretically how close in performance to the Atlas V 401?


@spacenut
OP ask for alternate with Atlas V 401 performance to GTO. Presume with as little new development as possible with the existing tooling & GSE.

[edkyle99]

How about replacing the RD-180 with 2 RD-181. Never mind that it is not doable politically. But theoretically how close in performance to the Atlas V 401?

@spacenut
OP ask for alternate with Atlas V 401 performance to GTO. Presume with as little new development as possible with the existing tooling & GSE.

If it were possible to buy RD-181 at the RD-191 (Angara) thrust level, then RD-180 performance could be closely approximated.  Orbital ATK appears to be receiving engines with a reduced thrust level (about 5%, but I'm assuming last year's reporting was accurate), which would limit Atlas 5 capability if used in the same configuration.  Two RD-181s might even weigh a bit less than one RD-180, but might also have a tic  lower ISP.

 - Ed Kyle

[notsorandom]

Assuming a return to GG RP-1 engines for the Atlas what does the old stage and a half trick do for the rocket? A Merlin type engine would be more efficient both is mass and ISP than the old RS-58. Would the performance increase be worth the hassle of going that route?

[Prober]

The Merlin seems to be a very good engine.  I think they have only had one fail, but they had engine out and the satellite made orbit.

small point about the Merlin under "failure".   Note that SpaceX has redefined this before congress.  The loss of CRS-7 is the loss of 10 Merlins.  From :Mr. Jeff Thornburg
Senior Director of Propulsion Engineering, Space Exploration Technologies Corporation

http://docs.house.gov/meetings/AS/AS29/20150626/103668/HHRG-114-AS29-Wstate-ThornburgJ-20150626.pdf

"Most relevant to today’s hearing, SpaceX manufactures our launch vehicles and spacecraft—including
propulsion systems—entirely in the United States. Our Merlin 1D engine, manufactured at our
Hawthorne, CA headquarters, has flown to space more than any other boost-phase rocket engine involved
in the EELV Program today, including the Russian RD-180 used on the Atlas V and the RS-68 and RS-
68A used on the Delta IV. This is a little appreciated fact borne of the reality that each Falcon 9 flies 10
engines per flight. So, each launch of the Falcon 9 provides rapid and discernible heritage for the Merlin
1D engine, which has now surpassed the RD-180. It also bears noting that SpaceX currently produces
more liquid rocket engines than any other private company in the world."

The amazing peoples might not agree with this now, but SpaceX redefined this before Congress, it bites them now

[edkyle99]

The Merlin seems to be a very good engine.  I think they have only had one fail, but they had engine out and the satellite made orbit.

small point about the Merlin under "failure".   Note that SpaceX has redefined this before congress.  The loss of CRS-7 is the loss of 10 Merlins.  From :Mr. Jeff Thornburg
Senior Director of Propulsion Engineering, Space Exploration Technologies Corporation

http://docs.house.gov/meetings/AS/AS29/20150626/103668/HHRG-114-AS29-Wstate-ThornburgJ-20150626.pdf

The referenced document doesn't say anything about counting CRS-7 as a failure of 10 Merlins.  The CRS-7 flight did not involve a Merlin engine failure.  If they follow traditional practice, they would register the flight as a "no test" for the Merlin engines involved, since none of them had a chance to perform full duration burns.

 - Ed Kyle

[edkyle99]

Assuming a return to GG RP-1 engines for the Atlas what does the old stage and a half trick do for the rocket? A Merlin type engine would be more efficient both is mass and ISP than the old RS-58. Would the performance increase be worth the hassle of going that route?

I think it would be more trouble than it is worth at this point.  Atlas used it successfully primarily thanks to the ultra-low dry mass of the balloon tank sustainer stage (and the low dry mass of the sustainer engine).  CBC dispensed with the balloon, so the advantage would likely be reduced.

Here's a comparison that shows ULA's planned Vulcan (at least as I guess it will look, though there are hints that it might end up taller than Atlas 5) and a slightly fattened Atlas (to 165 inches from current 150 inches) that could carry the extra propellant needed for gas generator engines while still matching the current Atlas height. 

Maybe its just me, but that 165 inch diameter Atlas looks like an easier change than going to Vulcan.  Then again, I'm not taking into account the plan to go to a single-core Heavy using Vulcan, which drives ULA toward a bigger rocket.

 - Ed Kyle

[kevin-rf]

Did they state somewhere common bulkhead on Vulcan?

[savuporo]

The only problem, of course, is that SpaceX would never sell a Merlin to a competitor. 

Maybe while we are doing a lego excercise, try with this :
http://www.yuzhnoye.com/en/technique/rocket-engines/marching/rd-801/

[Steven Pietrobon]

Did they state somewhere common bulkhead on Vulcan?

I don't remember if they said they are using common bulkhead, but the launch animations only show a thin frost free layer between the tanks, which presumably is due to using a common bulkhead.