It's ironic that 10 m tooling costs are said to be prohibitive, since the USA's successful Apollo program used a rocket with two stages having the 10 m diameter. But, development costs, schedule constraints, and political factors are outside my field of expertise.
Yes, the box that a LRB would have to fit to optimize performance during the first 120 seconds without breaking structural limits means that a higher ISP booster can burn longer than 120 sec while still having the same or very slightly better performance during the first 120 sec i.e. deltaV. A 311 ISP 3.4mlbf booster weighing 1.3mlb and burn time of ~145 sec would definitely system wise out perform a SRB. That first 120 sec is almost like it is set in stone. The more thrust an LRB booster has so that you can carry more propellant may increase the burn time more. There is a minimum thrust value for each ISP value that gives a SRB equivalent booster that burns 120 sec. By adding more thrust than that allows for carrying more propellant on the boosters allowing them to burn longer. Basically a 311 ISP booster would optimally be sized to burn at ~155 sec, thrust 3.6mlbf and 1.43mlb weight. A 280 ISP booster would be optimal for a burn time of ~138 sec, thrust 3.55mlbf and 1.39mlb weight (three 1.2mlbf Merlin 2 engines or 7 .5mlbf AJ-500’s). A 440 ISP booster would be optimal for a burn time of 218 sec, thrust 3.57mlbf and 1.4mlb weight. Because of the longer burn time they will deliver more overall performance i.e. payload than the SRB. Increasing the payload weight means an adjustment to the thrust or booster weight as well as burn time to optimize.The SLS core design is a poor compromise for an efficient booster. We see that the CCB approach delivers better performance as well as lower overall costs. Using three boosters for the first stage burning for duration of 180sec, then a large LH2 US will greatly outperform SLS than using the same boosters on an SLS.So if a LRB is designed and built, a tank stretch of the booster tanks, plus using 3 of them in line with a stretched SLS US would be about an equal performer to SLS. In fact a 5 engine 3 SLS core in line would work too, making the LRB’s a shortened core version of the SLS core itself or even the same length with crossfeed.
I'm told that the Michoud facility cannot handle a stage with a diameter greater than 10 m.
Quote from: Rocket22 on 10/05/2011 12:54 amIf SSME engines are to be used for the SLS core, why not just eliminate the solid rockets, expand the diameter of the first stage to about 33', and fit it with 10 SSME engines? Then, with 5 J2-type engines in a second stage and a single J2-type engine in a third stage, over 130 metric tons of payload could be delivered to low earth orbit with a tandem three-stage LOX/LH2 rocket weighing about 4.5 million lbs at liftoff. The large number of SSME engines needed in a heavy-lift program using this rocket should cause the unit cost of the engine to decrease significantly. From my limited perspective, I don't see how a rocket with two huge strap-on recoverable solid boosters could deliver more payload per dollar than an expendable LOX/LH2 three-stage rocket. I must be (and probably am) missing something.From what I've read and been told, they had very specific time, budget and contractual constraints from the budget act. So they specifically went to the lowest development risk path, namely, ET tank core, RS-25D engines, Ares I solids, Ares I avionics, etc. The specifically wanted the least amount of new developments possible. Apparently, the 10m tooling was a huge cost. But more importantly, a huge development and certification risk.I've seen a video, where they stated that a monolithic RP-1 first stage and H2/LOX second stage probably had the lowest operation cost, and best scalability. But the cost of development was big, but not ridiculous but they couldn't have anything flying before 2020.From my humble position, the 2009/2011 ridiculous situation at NASA was caused by years of suspending investment in the fundamentals (big thrust RP-1 first stage engines and H2/LOX upper stage engines), and then doing too big and moving specs programs (Ares I/V). Can you believe that Griffin, in the recent Hearing stated, with a straight face, that the logical thing was his "presidential budget proposal" where he had 14B just for the Constellation program from 2013 onwards?After that lesson, the ones that stayed at NASA learned the hard lesson and scoped programs for available budgets (around 3.5B of development money per year). Hence, the current SLS.
If SSME engines are to be used for the SLS core, why not just eliminate the solid rockets, expand the diameter of the first stage to about 33', and fit it with 10 SSME engines? Then, with 5 J2-type engines in a second stage and a single J2-type engine in a third stage, over 130 metric tons of payload could be delivered to low earth orbit with a tandem three-stage LOX/LH2 rocket weighing about 4.5 million lbs at liftoff. The large number of SSME engines needed in a heavy-lift program using this rocket should cause the unit cost of the engine to decrease significantly. From my limited perspective, I don't see how a rocket with two huge strap-on recoverable solid boosters could deliver more payload per dollar than an expendable LOX/LH2 three-stage rocket. I must be (and probably am) missing something.
Quote from: baldusi on 10/05/2011 01:58 pmQuote from: Rocket22 on 10/05/2011 12:54 amIf SSME engines are to be used for the SLS core, why not just eliminate the solid rockets, expand the diameter of the first stage to about 33', and fit it with 10 SSME engines? Then, with 5 J2-type engines in a second stage and a single J2-type engine in a third stage, over 130 metric tons of payload could be delivered to low earth orbit with a tandem three-stage LOX/LH2 rocket weighing about 4.5 million lbs at liftoff. The large number of SSME engines needed in a heavy-lift program using this rocket should cause the unit cost of the engine to decrease significantly. From my limited perspective, I don't see how a rocket with two huge strap-on recoverable solid boosters could deliver more payload per dollar than an expendable LOX/LH2 three-stage rocket. I must be (and probably am) missing something.From what I've read and been told, they had very specific time, budget and contractual constraints from the budget act. So they specifically went to the lowest development risk path, namely, ET tank core, RS-25D engines, Ares I solids, Ares I avionics, etc. The specifically wanted the least amount of new developments possible. Apparently, the 10m tooling was a huge cost. But more importantly, a huge development and certification risk.I've seen a video, where they stated that a monolithic RP-1 first stage and H2/LOX second stage probably had the lowest operation cost, and best scalability. But the cost of development was big, but not ridiculous but they couldn't have anything flying before 2020.From my humble position, the 2009/2011 ridiculous situation at NASA was caused by years of suspending investment in the fundamentals (big thrust RP-1 first stage engines and H2/LOX upper stage engines), and then doing too big and moving specs programs (Ares I/V). Can you believe that Griffin, in the recent Hearing stated, with a straight face, that the logical thing was his "presidential budget proposal" where he had 14B just for the Constellation program from 2013 onwards?After that lesson, the ones that stayed at NASA learned the hard lesson and scoped programs for available budgets (around 3.5B of development money per year). Hence, the current SLS.Is it a good idea to build a 10m core fully liquid fuelled rocket?I'm not so sure about these SRBs getting the SLS to 130mt. Are they saying it can because that was it says in the authorisation act?Are the costs of building new SRBs too high? I mean how much did the technology mature during the life of the shuttle?