Respectfully, I have to disagree. The F-1B is actually not an entry by Rocketdyne; it is an entry by Dynetics. Further, those solids are the poorest choice possible on every level, regardless of how many times Chris calls them the "favorite". They have the lowest Isp. They incur high weight on the crawler. They are toxic and place limitations on VAB operations. In case of an in flight abort, they cannot have the engines turned off, and if they have to be detonated they will spew pyrotechnic debris throughout the sky, debris that would be very dangerous to the parachutes. Though the upper end of the cylinder could be blown, NASA didn't do that on STS and likely wouldn't do so on SLS. ATK has already said they can't reach the 130 mT requirement without a 5th RS-25 on the core. That would require the LUS with J-2X of Block II. NASA has said they are not going to add that 5th RS-25. They seem to want DUUS as it can do circ., TLI, and LOI burns, or a TMI burn. The advanced solids just do not meet the requirements. (I know some here think they can do the calculations better than ATK and that Dark Knights can meet the specs. I find it highly doubtful that others are right and ATK's own engineers are wrong.)This competition needs to be decided on merit, not politics, and not by ATK playing a victim card of, "Oh poor us. Those guys have a monopoly, therefore you have to give this contract to us." That's balderdash.
I look at it this way. Where does the country's current top hands-on knowledge of high thrust kerosene/LOX rocket engines reside? The answer: not at Aerojet-Rocketdyne, but rather in the hands of some folks at Hawthorne and McGregor. Now a follow-up question. Who is more likely to succeed at developing a new super-high thrust kerosene/LOX engine? The folks who shut down their production years ago, or the folks who are building them, right now? - Ed Kyle
Heavy Lift is an absolute necessity for the beginning of any serious BEO exploration mission profile, but that vehicle won't see a reasonably consistent launch rate for many years to come, making it very expensive to build and use. But that level of expense can be brought down, provided the boosters chosen for it are LRBs, and those LRBs are designed to be able to function alone in combination with an upper stage as both a CLV and a general purpose LEO launch vehicle in their own right. As such they will fly far more often than the HLV they support, driving their cost per unit down and, as a result, driving down the cost of the HLV when that vehicle is employed.
Strapping 3 boosters together? Unlikely. Any potential HLV replacement would need a LOX/LH2 core and Kero/LOX or Meth/LOX boosters. The boosters need to be hydrocarbon-based for their raw power in the lower atmosphere where isp is not an issue and the core needs to be LH2/LOX because it will burn most/all the way to orbit where isp is very important, thrust not so much.
But again, we need to stop falling into the trap of optimizing for performance vs. optimizing for cost.
They do have the poorest ISP, but remember, these are boosters. ISP isn't all that big of a hit for short burn boosts like SRB's or LRB's would do. They are only burning for around 2 minutes or so, so thrust is the major driver for most of that boost...
It's not just the raw thrust; it's also the T/W (thrust to weight ratio). As I understand it, those SRBs are so heavy that most of their liftoff thrust goes into just lifting themselves, and not as much of the thrust is being transferred to the thrust beam. With the KeroLox boosters, while the Isp density is high, the pure volumetric density is not (if I understand correctly) as high as the solid propellant. This means the liquids are contributing more of their thrust to the thrust beam on the core.
Those advocating HydroLox boosters are forgetting one important factor: width of the VAB doors. Due to horizontal clearance, boosters are limited to 5.5 meters. The very low density of LH requires much more volume. To get the equivalent thrust that an RP-1 booster would give, you would need boosters as wide as or wider than the core. (I know you have proposed a 8.4 m common HydroLox core, but that won't work. The core can't even support its own weight at liftoff; it depends on the structural strength of the boosters to support it from the beam.) HydroLox boosters are just not possible on SLS because they would be far too large to fit through the doors. There's also the issue of what engine you'd put on them. Six or seven RS-25s for a two minute burn; I don't think so. Eight or nine RS-68-As? I don't want to even think about the complications of that.RP-1 is just the only fuel that makes sense for this application.
Something tells me ATK will win this easily. So with liquids (F-1B) you get..A new high-thrust kerolox engine program, 8000kn (!), that's 10x a Merlin.A new core which must be strong enough to transfer all this raw thrust to the upper attachement.4 additional liquid engines at launch which can fail.With AJ-1E6 you have 6 SC kerolox engines in addition to the 4 RS-25. So in total 10 engines without engine out capability (correct me if I'm wrong about that one).
Quote from: Oli on 09/03/2013 02:27 amSomething tells me ATK will win this easily. So with liquids (F-1B) you get..A new high-thrust kerolox engine program, 8000kn (!), that's 10x a Merlin.A new core which must be strong enough to transfer all this raw thrust to the upper attachement.4 additional liquid engines at launch which can fail.With AJ-1E6 you have 6 SC kerolox engines in addition to the 4 RS-25. So in total 10 engines without engine out capability (correct me if I'm wrong about that one).Well, if ATK wins, it will probably have more to do with cost than technical merit (or politics). IF ATK can make the composite casings cheaply, then the infrastructure to get the segments to KSC and assemble them there will already be in place. The SLS ML will already be set up for it.I don't know that engine count will be a big deal, unless SpaceX proposes a booster with 25 Merlin 1D's on it or something. Then they might start thinking that could be detrimental.I would think you -would- have engine out capability depending on where the engine fails. But that's the same as the stages on Saturn V, and on STS. Any engine failure too early one them would have caused a LOM abort.And as far as engine failures go, at least typically an engine failure of F-1B or AJ-1E6 would not be a catastrophic failure. But an SRB failure would be fully catastrophic failure. or a failure on the pad...or in the VAB....etc...I think LRB's probably have the advantage over SRB's in terms of overall safety. Dunno about reliability as F-1B, AJ-1E6, and advanced solids will all be new engines...so we won't really know until there's a track record.If reliability is the concern, then go with an engine already proven like RD-180 or RS-68.
Of course, if you actually look at the stats regarding the Shuttle's SRBs, they were only at fault in one instance in 135 flights. Once the O-ring issue was resolved I can't say I ever heard of another moment when the SRBs were ever a significant issue from a safety perspective. My guess is aside from ground handling safety, SRBs will be neck-and-neck with LRBs in terms of flight safety risk. They're certainly more proven, though obviously there is no engine shutdown option with solids unless you engineer something into the SRB. I get the feeling that will not happen with ATK emphasizing the low cost of their "Black Knights".
I think the SLS program is an opportunity for developing components for a new ELV. The RL-60 engine for example would be nice to have, I heard about NASA and air force cooperating on this one. So we have...F-1B engine for a first stage a la Falcon 9. Sounds interesting, although manufacturing such a huge engine could be expensive. With its low first stage ISP it would also require early staging and a relatively powerful second stage engine (e.g. Merlin).
AJ-1E6 as a RD-180 replacement. I think NASA does not want 6 SC kerolox engines on SLS, also manufacturing them in the US could be too expensive for an ELV.
An Ariane 6 style launcher with monolithic solids. ATK's SLS solids would share similarities with those developed for A6. Approx. the same diameter, composite casings and electrical TVC. Unfortunately the infrastructure for casting the solids would have to be set up in Vandenberg and at the Cape.
RS-68 with higher thrust. Potentially allows for getting rid of the solids on Delta IV (if that is a big cost factor). Requires a regen nozzle for SLS. Just a thought.
Edit: This may have been mentioned before in another thread, but what about adding 4 strengthened Falcon 9 cores as boosters? Does it have to be 2 boosters?
F-1B engine........manufacturing such a huge engine could be expensive.
This may have been mentioned before in another thread, but what about adding 4 strengthened Falcon 9 cores as boosters? Does it have to be 2 boosters?
Yes, it has to be 2 boosters due to the configuration of the thrust beam. 4 F9s are not enough thrust. Lobo had an entire thread about connecting 3 per side at the single attachment point using a strongback; that gets really complicated. You were just talking about too many engines. Now you're talking about 54 engines just on the boosters.
Quote from: Oli on 09/03/2013 01:35 pmThis may have been mentioned before in another thread, but what about adding 4 strengthened Falcon 9 cores as boosters? Does it have to be 2 boosters?Yes, it has to be 2 boosters due to the configuration of the thrust beam. 4 F9s are not enough thrust. Lobo had an entire thread about connecting 3 per side at the single attachment point using a strongback; that gets really complicated. You were just talking about too many engines. Now you're talking about 54 engines just on the boosters.