Pogo can happen without solids, as in Saturn V early on, but solids can be really good at provoking it. That Ares 1 "stick" configuration was really bad for pogo problems, because (1) 100% of the liftoff thrust was solid, (2) it was a long narrow structure subject to pogo, and (3) the stretched 5-segment shuttle SRB design proved to be really hard to tame, as regards combustion instabilities.
This was in spite of being 20% aluminized, which is about the max tolerable metal content. Metals usually help damp the instability tendencies. That kind of periodic thrust oscillation simply wasn't tolerated in tactical solid designs, and we at the plant where I once worked would never let a product like that out the door. Our stuff burned "smooth", only random combustion noise, not organized oscillations.
Aluminized, non-metallized, we just did the job right in development testing and redesign. Expensive up front, but well worth it in the longer run. Part of our better-than-1/million failure rates, sometimes far better.
GW
]]>NGIS highlights advantages of their Air Force contract win with OmegA
The Omega rocket is meant to be a replacement for the Antares rocket and Delta II.
Meanwhile, ATK (which then became Orbital-ATK and then Northrop Grumman Innovation Systems) had already been working on a heavy-lift solid/liquid propellant rocket with Liberty.
Of course none of this would have happened if we had not seen the RD-180 was from Russia.....
]]>The Ares 1B makes a lot of sense from a design perspective
I think this is still moving forward under Northern Gruman and would do well with cargo shots to LEO
]]>Actually, I didn't see such capacity for cultural change in any of the giant defense contractors, but ULA has proven me wrong. Their Atlas-V is pretty competitive with Spacex's Falcon-9, in spite of being defense conglomerates, which Spacex is not. So it can be done. (One can always argue about how it was done, because things are easy to hide in a giant conglomerate.)
As for the Frankenstein-design of Liberty: there's nothing wrong with using older technologies to do a job, as long as they serve well. There's nothing wrong with bastardizing-together a mish-mosh of things to do a job, as long as it works well. You're corresponding with a guy who would have no qualms at all about pulling a steam locomotive out of mothballs to pull long freights up steep grades faster, or to put sails on ocean-going tankers and freighters to save fuel.
A big solid right off the pad makes a lot of sense, because thrust, not Isp, is the real issue in the first several km going up. Solids do that in spades, and much better than liquids, in part because of the high molecular weight in the exhaust, and in part because the typical throat to casing diameter ratio is just far higher (frontal thrust density achievable). You do have to address extreme reliability if men are to ride, because they cannot be turned off once lit. In that respect, I think the hybrid might be a better deal.
Putting a liquid upper stage on a solid lower stage also makes a lot of sense. This is particularly true if you can generate Isp in the higher range of liquid capabilities, combined with precision thrust control and termination, something solids completely lack. The Ariane upper stage on Liberty has all of these qualities. Restart capability is the most important, personally I don't know if the Ariane stage has that. For Liberty to be really viable, upper stage restart is a critical capability.
That is an awfully long and slender stack, though. There are many possible modes of structural oscillation, most of them dangerous. The most slender vehicles I remember were Scout and Vanguard. They did OK structurally (Vanguard had other problems). Liberty looks worse to me. I think I would have proposed it as a side-by-side cluster of 3 or 4 smaller solids from the strap-on stable, not stretched shuttle SRB technology.
GW
]]>ATK is just trying to pitch NASA a Frankenstein launch vehicle composed entirely of existing parts most of which are from other contractors, half of which aren't even American. Do they really think all these other contractors will just sell them this stuff at marginal cost so they can stick everyone else with the development costs, sure NASA fell for that with the 5 segment Ares I SRB, but I don't think all the rest of these contractors are that dumb. I don't see how ATK could purchase let alone integrate all this stuff into a competitive CCiCap bid, I think their just gambling that a Republican President & Congress will steer business towards them via their DoD connections so long as they can put together a semblance of a vehicle that flies while deliberately low-balling their price quote. Then after the competition is killed off they can have 'unanticipated cost-overruns' till the cows come home which will be blamed on foreign providers justifying yet more money be spent for them to recreate this stuff in house.
]]>Re-insulating the case is not all that big a deal, although in that size, it isn't trivial, either. The insulation is sheets of fiber-reinforced rubber compound wrapped around a bladder inserted into the segment. You pressurize the bladder, which compresses the sheeting against the primed case segment, and you cook it while pressurized to cure the rubber, preferably in vacuum, for best quality control.
Casting propellant isn't all that big a deal, although not trivial in that size. For one thing, it requires a huge mix of propellant. That's a giant facility. OK, there's cast tooling emplaced in the primed/insulated motor case segment to form the finished surface of the propellant. Depending upon the effective viscosity of the propellant (this stuff is thixotropic/non-Newtonian, like concrete, but worse), you gravity or pressure cast this stuff into the segment, under high vacuum. Then you cook it with tooling in place for a few days to cure the propellant. Typical AP-Al-composite, HTPB binder, etc. Just huge.
What baffles me is how they expect to support all of this with a population about the size of a small town instead of the major city they used during shuttle. You have to count all the vendors and subcontractors in that population. Spacex does it mostly in-house, and with a very small population, that's how they do liquid-propellant launch so cheaply. How you do that with giant solids, I'm not so sure, but I am sure that it can be done: because that's what we do making small solid motors for tactical weapons.
GW
"It's all in the cultural change"
]]>"The thrust Oscillation was talked about quite a bit when the Ares was still in developement mode under Constellation and was resolved by isolation of the upper stage by shock obsorbers in the interchange section."
Using shock absorbers to attenuate thrust oscillations means the oscillations are still there in the motor, where they really are dangerous, because they are evidence of combustion instability. As I said in some earlier post, the 5-segment design is known to have those problems in horizontal ground tests. It has never flown. This kind of thing can be solved, but my guess is they need to keyhole-slot the propellant grain in the segment closest to the nozzle. That would reduce the peak bore velocity (while preserving burn surface neutrality), which should reduce or possibly even eliminate the tendency to oscillate.
No forward-segment slots, though. That's how they (ATK, formerly Hercules) blew up AFRPL's test stand about 20 years ago. Cost them a billion dollar write-off, it did. They need to talk to their tactical guys about doing a combined thermo-structural / fluid dynamical interior ballistic analysis. Tactical guys do that all the time, the big motor guys do not. But they should. That same kind of inattention to adequate design analysis is what sunk the Titanic.
They don't need that crappy 3-O-ring joint either. That's still a disaster waiting to happen, just like the original 2-O-ring joint was before it (Challenger, 1986). One O-ring will do just fine. If it leak checks OK at 5 psi, it'll hold all the way to case burst. You just need one, and you DO NOT put goo in the insulation joints "upstream" of it: that guarantees an O-ring burn-through (no matter how many you have). The static gas column in the bent space approaching the O-ring is better than any insulator we can build. The only thing you don't want is a straight line-of-sight path for radiant heating from the fire in the motor.
Yeah, it can be solved and made to fly just fine. The tougher problem is corporate cultural change. How do you build it and operate it with a small logistical tail instead of a large one (like the one supporting shuttle SRB's)? That's the real secret to lower launch costs. Spacex is the example that proves it.
GW
]]>Based on NASA’s 15-ft.-dia. Multipurpose Logistics Module for the space shuttle, the Liberty Logistics Module (LLM) will be capable of transporting up to 5,100 lb. of pressurized cargo. Liberty is based on a combination of hardware from NASA’s defunct Constellation program, including the five-segment solid-rocket booster developed for the Ares 1 rocket and a composite space capsule based on the Orion Multipurpose Crew Vehicle. Astrium Space Transportation is providing the Liberty second stage based on the liquid-fueled cryogenic core of the Ariane 5.
]]>GW
]]>On the other hand, whether ATK/EADS can compete economically with Spacex depends upon a massive change in corporate vision. It can be done, but few do it. The support per launch has to be trimmed from the population of major city to that of a small town. I include subcontractors and vendors in that assessment.
With its 3 vehicles, Spacex has been establishing a trend of payload cost to LEO vs max payload weight to LEO that is lower than all comers except perhaps ULA's Atlas-5 at its 551/552 configuration only. Maybe. Depends upon exactly how you plot the data.
The way I plot it, ULA Atlas-5 comes off a tad higher than Spacex, and Delta-4 much higher. These are built by giant corporations, used to doing things the NASA way, or at least the DOD way. Both customers are a bit bloated, NASA more so, these later decades.
ATK and EADS fall in that same giant corporation category, used to working on bloated things for government space or defense stuff. If they make the same paradigm shift that Spacex did, they can compete in commercial launch. So could Boeing and Lockheed-Martin, except I really don't see them making that paradigm change, unless forced to do so.
For now, I'd rather see what Spacex can really do, as it will drive paradigm change in its competitors, and break this bloated, expensive impasse we have suffered since the beginning of manned spaceflight.
The Russians did the same launch support model, just within a different economic system: a huge population supported every single launch. That can never be cheap.
Dark horses might include the Skylon thing, or orbital outgrowths of the suborbital spaceplane folks. As organizations, they have the right idea: keep the support team size per launch very small or it'll never be cheap. We'll see.
GW
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