An even older document noted that configurability with common components has certain advantages that can outweigh the penalty of suboptimality in less-stressed configurations (for instance, a core designed for four engines and a 100-tonne payload is overbuilt for three engines and 75 tonnes, but it's still worth it to not have to design, qualify and maintain two distinct cores).
Quote from: 93143 on 02/06/2012 05:05 amAn even older document noted that configurability with common components has certain advantages that can outweigh the penalty of suboptimality in less-stressed configurations (for instance, a core designed for four engines and a 100-tonne payload is overbuilt for three engines and 75 tonnes, but it's still worth it to not have to design, qualify and maintain two distinct cores). Good points but to be fair, the core still needs to be designed to fly in two configurations, which is a more challenging design task than designing for a single configuration. Arguably, it would be easier to design two different cores than to design a single core that meets both requirements. Next, the cost to flight-qualify (e.g. by a test flight) seems to be paid per-configuration, not per-design. So there doesn't look to be much savings there. But your final point about maintaining a system that uses only one core, versus maintaining a system that uses two distinct cores, is super important and easily overlooked or under-estimated. USAF introduced the aeronautic terminology of "white tail" cores in the context of NASA and DoD sharing EELV manufacturing infrastructure.I certainly hope the SLS cores coming off the line at Michoud are going to be "white tail" in the sense that any of them could be flown in any of the vehicle's configurations.
I think if there were only 3 RS25's, they can't drain a full core by disposal orbit, even at full thrust.
The "70 tonne" rocket was the four segment booster plus smaller core with three RS-25 engines (the "4/3") that is not being developed. The "70 tonne" language is left over from "4/3", but there is no currently planned rocket design actually fits the description - unless the plan is to build a big core, under power it with only three engines, and fly it with partially empty tanks.
Quote from: Lobo on 02/06/2012 04:09 pmI think if there were only 3 RS25's, they can't drain a full core by disposal orbit, even at full thrust. If they use only three RS-25 engines, they can't launch a full core. It would be too heavy at booster burnout.Four RS-25 engines works, but that creates a rocket that lifts 95-100 tonnes to the injection orbit with five-segment boosters. The "70 tonne" rocket was the four segment booster plus smaller core with three RS-25 engines (the "4/3") that is not being developed. The "70 tonne" language is left over from "4/3", but there is no currently planned rocket design actually fits the description - unless the plan is to build a big core, under power it with only three engines, and fly it with partially empty tanks.95-100 tonnes is a lot of mass. It seems to me that once such a rocket is flying, there will be little need for improvement for many years, if ever. That's why I wonder about the "Phase 1b, Phase 2", etc. ideas. - Ed Kyle
Quote from: Lobo on 02/06/2012 04:09 pmI think if there were only 3 RS25's, they can't drain a full core by disposal orbit, even at full thrust. If they use only three RS-25 engines, they can't launch a full core. It would be too heavy at booster burnout.
Quote from: edkyle99 on 02/06/2012 10:34 pmQuote from: Lobo on 02/06/2012 04:09 pmI think if there were only 3 RS25's, they can't drain a full core by disposal orbit, even at full thrust. If they use only three RS-25 engines, they can't launch a full core. It would be too heavy at booster burnout.Depends on how long the booster burn is. If you're running the 120 seconds of the ATK SRB's, you'd be right. If you're running the 200 seconds of the ULA derived LRB, now the 3-engine core is no longer too heavy at booster burnout, and would in fact outperform the 4-engine SRB design as a result.
Quote from: Downix on 02/08/2012 07:15 pmQuote from: edkyle99 on 02/06/2012 10:34 pmQuote from: Lobo on 02/06/2012 04:09 pmI think if there were only 3 RS25's, they can't drain a full core by disposal orbit, even at full thrust. If they use only three RS-25 engines, they can't launch a full core. It would be too heavy at booster burnout.Depends on how long the booster burn is. If you're running the 120 seconds of the ATK SRB's, you'd be right. If you're running the 200 seconds of the ULA derived LRB, now the 3-engine core is no longer too heavy at booster burnout, and would in fact outperform the 4-engine SRB design as a result.Makes for a good argument to restart those SLI engine projects like the RS-84 and TR-107 the Bush Administration so foolishly axed.
Quote from: Patchouli on 02/08/2012 10:12 pmMakes for a good argument to restart those SLI engine projects like the RS-84 and TR-107 the Bush Administration so foolishly axed.Hindsight is always 20/20
Makes for a good argument to restart those SLI engine projects like the RS-84 and TR-107 the Bush Administration so foolishly axed.
Quote from: woods170 on 02/09/2012 06:41 amQuote from: Patchouli on 02/08/2012 10:12 pmMakes for a good argument to restart those SLI engine projects like the RS-84 and TR-107 the Bush Administration so foolishly axed.Hindsight is always 20/20I think that rather than hindsight is one of strategy. Doing the evolution in decoupled programs is better than monolithic ones. On the other hand, the RS-84 and TR-107 where designed to be reusable, thus, very heavy and expensive for disposable use. A strategy of one reusable and one disposable engine would have covered the bases better. Yet, now most studies are leaning on methane for reusable vehicles.
Forgetting sunk costs, would there be any advantages to redesigning the system to use 4-6 smaller solid boosters (since the SLS is no longer restricted to having just two srbs to acommodate the orbiter)?Is the ET design made simpler or more complicated by having two massive boosters, compared to other designs with srbs?
Quote from: gin455res on 02/10/2012 07:32 amForgetting sunk costs, would there be any advantages to redesigning the system to use 4-6 smaller solid boosters (since the SLS is no longer restricted to having just two srbs to acommodate the orbiter)?Is the ET design made simpler or more complicated by having two massive boosters, compared to other designs with srbs?I'm sure others have mentioned this. The core is designed to be "picked up" from the intertank section by the boosters. As a result, the big LH2 tank is not designed to take the full booster propulsion loads. That is why Block 1A SLS boosters have to be designed to apply their forces in the same manner as SRBs. Multiple small strap-on boosters or multiple liquid boosters are not an option for these and other reasons. Liquids are also limited to 5.5 meters diameter by VAB clearances, and the launch platforms, flame trench, and flame ducts limit where the boosters can be located, etc. Composite HTPB solids are going to be tough to beat. A strong argument could be made that existing 5-segment steel case PBAN boosters could serve just fine for more than a few launches too. - Ed Kyle
So in summary, the core would have to be redesigned from scratch to take the thrust of 4-6 smaller solids from lower down, is that right?Just out of curiosity, would this be a more complicated core design than the current design, or a simpler one (ignoring the complication of it's non-existence in comparison to the ET)?