But as to my previous quandry, can there simply be a scaled up Delta IV? Rather than a 3-stage rocket? Can you have a 10m core (or maybe 11 or 12m?) with seven RS-68A's (Assume for this they can be thermally protected enough to not fail), with say three or four RL-60's on an upper stage that also does a BLEO burn, just as the DCSS does on Delta IV now? Or when the rocket is scaled up, does it need 3 stages? I would think a single core Super-Delta would be more mass efficient than 7 Delta IV's, so it should at least be able to match the performance of 7 Delta IV's with just the two stages I would think. (But I am no rocket engineer so I might be way off on that assumption. :-) )
I took a stab at this by starting with a six times scale up of Delta IV Medium. I've assumed the Delta IV mass fractions (for the heavier RS-68A version), which is likely conservative. The results provide a couple of clues for why I don't tend to end up with this result given the limitations of the VAB and the mission.
The six times scale up obviously needs six RS-68A first stage engines and six RL10B-2 second stage engines. In reality, it isn't possible as I understand it to actually cluster that many RL10B-2 engines due to the size of the nozzle extensions, but lets not worry about that detail right away, shall we? This gives us the Delta IV liftoff T/W ratio of a bit more than 1.2 with a second stage T/W ratio of about 0.42 at engine start.
We get about 20 tonnes to escape velocity. For LEO missions, second stage propellant must be offloaded to keep T/W2 >= 0.42, which is what also happens with Delta IV Medium. This results in a 200 km x 28.7 deg payload of about 55 tonnes. These payload numbers are also roughly six times larger than Delta IV Medium. To get SLS Block 1 equivalent performance then would require a 10 times scale up of Delta IV Medium, which is going to present a size problem.You are right that a 10 meter first stage is required to fit the thing in the VAB. - Ed Kyle
Yout think the core needs strengthened, but why? The 5-seg SRB will have about 3.5Mlbs of thrust at liftoff each. How much will Pyrios have? About 3.6Mlbs. That's very similar.
Quote from: Lobo on 10/08/2013 11:38 pm Yout think the core needs strengthened, but why? The 5-seg SRB will have about 3.5Mlbs of thrust at liftoff each. How much will Pyrios have? About 3.6Mlbs. That's very similar.But that's not what matters. The Pyrios will be much lighter and therefore have much more usable thrust, i.e. a higher thrust/weight ratio. Most of the thrust in that 5 segment will be just to lift its own self and not much more acceleration will be transferred to the core. The issue that comes out of this is something you did touch on further down in your post, that T/W means higher G loads on the core. In any case, however, these loads are applied at the thrust beam, so instead of buckling the core, they actually pull on the core and keep the cylindrical shape more true. Think about a thin Aluminum soda can. If you get the cylinder just a little out of true, you can easily crush it with your hands. OTOH, how likely is it you could take the two ends of that can in your hands and pull/rip it apart? You can't. A pulling force (which is what that thrust beam does to the core) must be much greater (for thin Aluminum at least) than a pushing force to malform the cylinder. The tensile strength of the Al is greater than its resistance to flex or compression forces.
Ed,There's a Boeing AIAA paper out as of about a month ago."The Space Launch System Capabilities with a New Large Upper Stage"I can't post it as it was shared with be with the instructions not to post it.But, I did list some performances above (I'm hoping that is ok. :-) )It lists performance for Block 1, and the three Block 1B configurations, four RL-10's, two MB-60's, and one J2X.I notice your numbers for Block 1, and Block 1B with four RL-10's to LEO and escape in your drawing.Per the Boeing paper?LEO: Block 1: LEO: 70mt TLI: 24mtBlock 1B (with four RL-10's) LEO: 93.1mtTLI: 39.1mtThose are a little less than you are showing for Block 1 and 1B to LEO and Escape. I think Escape is usually less mass than TLI?Just just thought I'd mention that. Are your numbers for Block 1 and 1B a little high? (I have no idea myself)
My drawing showed a high number for Block 1/ICPS Escape. I've now retroactively fixed that. The higher number was likely for a different stage, ICPS obviously being the limiting factor. Block 1B performance depends on the size of the second stage, which varies from Boeing paper to Boeing paper. My numbers came from last year's Boeing paper! Pardon my skepticism, but since this paper presumably supports a J-2X powered Large Upper Stage, the authors would have no incentive to show the maximum possible for a DUUS.
Block 1 LEO is given as 70 tonnes in the contract, so that's simply the end of the discussion even though much more is possible. (That Boeing paper looks like a managerial level overview, so it'll show the contract number.) The fact is that Block 1 will during its brief life never lift even 70 tonnes and never to LEO. It is going to fly twice on cis-lunar tests with a 31+tonne ICPS and a 24.2-ish something tonne MPCV. They will be injected initially into an elliptical orbit, so LEO specifically is a useless number for this configuration. - Ed Kyle
And finally here is an F-1B based core option. Again I've optimized these for Escape missions and made them with only two stages, EELV style. A two-stage core can roughly do the SLS Block 1 mission. Switching to an RP core solves the VAB height constraint. Adding F-1B boosters gets the machine to Block 2 capability. As far as I'm concerned, the Block 1 rocket could run any space program. - Ed Kyle
Lobo, could you post the exact specifications from the document about burnout mass and propellant mass for the SLS core? Knowing that would be a great help in the payload to LEO discussion.Edit: Also, this thread has turned into a bit of a "show off your concepts" thread. I suck at paint, are pencil drawings allowed too?
The core would be 8.4m in diameter and about 50 meters high. It carries 1785.6 tons of propellant and has an empty mass of 134.4 tons, with a PMF of 0.93. Instead of F-1, I thought it would be a better idea to fuel it with something similar to the AJ-1E6, because of higher efficiency. It uses 5 of them. It can use large strap on boosters which use 3 AJ-1E6 engines, carry 742 tons of propellant and have a burnout mass of 76 tons. The second stage is based on the Boeing proposed LUS designed for SLS, but uses an RS-68A instead of J-2X, for lower cost and higher thrust. It can also use a modified DUUS, with 2 or 4 RL-60 engines, either for BEO missions or some extra oompf for LEO. The base vehicle without boosters or DUUS can bring 70 tons into LEO, the complete vehicle with boosters and DUUS can lift 150 tons to LEO.
I think that would be the least of our concerns in the development of such a vehicle. It could probably be modified to be air-started fairly easily.
Lobo, could you post the exact specifications from the document about burnout mass and propellant mass for the SLS core? Knowing that would be a great help in the payload to LEO discussion.
I posted some info here on it.http://forum.nasaspaceflight.com/index.php?topic=32035.msg1108031#msg1108031Block 1 core at 220.6klbs (100.062mt) and Block 1B core at 222.0klbs (100.7mt)So almost idenitcal for the. Unfortunatley it doesn't list the burnout mass, just the dry mass. Although it also gives the following:Usable prop: 2116.9klbsstartup prop 18.6klbsnon-usable: 30.9klbsSo maybe burnout is dry mass plus non-usable?The DUUS info here:they list the DUUS (they call the LUS) total mass of 264.2klbs (119.8mt), with 231.5klbs (105mt) of usable propellant, and a dry mass of 27.6klbs (12.5mt). That dry mass is with the single J2X version of the DUUS. The J2X weighs 5,450lbsThe RL-10 weighs 664lbs each (2,656lbs for four) So that DUUS weighs 262.75klbs fully fueled. I thinkt he MB-60's weigh about 1300klbs, so two of them weight about the same as four RL-10's, give or take.
Ed, Any chance of you running the numbers for a compartive LV using like 7 or 8 RD-180's instead of the four F-1's?Then with RL/MB-60 upper stage engines as well as your concept above?
Quote from: Lobo on 10/16/2013 06:58 pmEd, Any chance of you running the numbers for a compartive LV using like 7 or 8 RD-180's instead of the four F-1's?Then with RL/MB-60 upper stage engines as well as your concept above?Sure. Give me a day or so. In the mean time I can point to ESAS 5.1 "Evolved Atlas", which was an 8.4 meter diameter two-stager powered by five RD-180s and four J-2S second stage engines listed for 78 tonnes to a 28.5 deg LEO. ESAS rules seem to have required higher second stage T/W than we've seen in subsequent studies, likely for crew escape requirements. - Ed Kyle