Yes. So it looks like Blue Origin might be the first to go orbital in a truly "privately funded" enterprise that didn't have some kind of Gov't funding source.
Quote from: HMXHMX on 12/16/2016 04:28 pmToday, turbopumps are getting ridiculously cheap, so there is little reason to go pressure-fed. If I was to embark upon another LV project, it'd be pump-fed.Spacex spent at least $1m - probably significantly more - on their first Barber Nichols turbopump for Falcon 1. I think that is quite cheap at that scale but what if you wanted to build a real turbopump for a 22kn engine like Rocket Lab but not electrical? What would you consider reasonable for that, and is there really anything off the shelf? It's still an r&d project with the usual fixed costs.
Today, turbopumps are getting ridiculously cheap, so there is little reason to go pressure-fed. If I was to embark upon another LV project, it'd be pump-fed.
Quote from: Kabloona on 12/17/2016 03:39 amYes. So it looks like Blue Origin might be the first to go orbital in a truly "privately funded" enterprise that didn't have some kind of Gov't funding source.Blue Origin has a contract with NASA right now to provide a suborbital research platform. Earlier on Blue Origin received $22 million from NASA for a pusher escape system in CCDev2. Matthew
Quote from: matthewkantar on 12/18/2016 01:04 amQuote from: Kabloona on 12/17/2016 03:39 amYes. So it looks like Blue Origin might be the first to go orbital in a truly "privately funded" enterprise that didn't have some kind of Gov't funding source.Blue Origin has a contract with NASA right now to provide a suborbital research platform. Earlier on Blue Origin received $22 million from NASA for a pusher escape system in CCDev2. MatthewNot just that, but they actually got paid for BE-3 milestones from NASA as well.I don't get this obsession with avoiding any government help whatsoever. Did you avoid highways as well? It's a dumb contest when taken to extremes.
And yet the "Sea Dragon" concepts were all (AFAIK) pressure fed. OTRAG was a victim of Russian disinformation.I'm guessing Von Braun went with turbo pumps to side step issues with triggering combustion instability caused by (potential) pressure fluctuations of positive displacement pumps. Which John Whiteheads groups reckon are the best option up to about 5 Klbs. Today a turbine can be CNC machined in 19 hours, as is done for the turbochargers on Mack trucks. AMROC died on the death of it's CEO basically. His advice on buying parts IE buy what's on the spec, don't insist on mods when buying from aerospace parts houses, is part of what drove SX into mfg in house. Ablative cooling sounds like a good idea for a single use engine but IRL only solids are really fired once. All others are fired at least twice for testing and that makes ensuring the state of the ablative char inside the rocket after that firing critical. That is there's still enough left for the launch and that it does not go on cooking after the test fire. I think this was the single worst idea Boeing had for the engine on the Delta IV.For anyone worried about coking they should consider that LO2 cooling of a 40 000lb combustion chamber was done 25 years ago by NASA, including deliberate holes in the wall to make the LO2 leak into the chamber during firing. It did not sustain any further damage. It's time the fear of LO2 cooling was put to bed. Both HTP and NTO have been used as coolants on other rockets (IIRC because amines have a tendency to explode in cooling channels).
And yet the "Sea Dragon" concepts were all (AFAIK) pressure fed.
But small engines below certain scale are impossible to regenertive cooling , since the ratio of surface area / volume rise too high at small scale.
"Pressure fed" appears to be one of the concepts of rocketry that sounds oh so much simpler in theory than it is in practice. (like hybrid rockets) And none of the Sea Dragon concepts got anywhere close to reality.It may also be one of the technologies that just doesn't scale well.
Solids OTOH are very deceptive. They truly look simple (who can't set off a firewwork?) but have as much trouble as liquids with combustion stability, plus the large quantity of explosive you have packed in one place. They also can be prone to deflagration-to-detonation transition, when the whole lump goes up in one go.
Quote from: Katana on 12/18/2016 03:35 amBut small engines below certain scale are impossible to regenertive cooling , since the ratio of surface area / volume rise too high at small scale.The 10 kN Ausroc I kerolox engine used regenerative cooling, so that places an upper limit. That engine was pretty small.
Ablative cooling sounds like a good idea for a single use engine but IRL only solids are really fired once. All others are fired at least twice for testing and that makes ensuring the state of the ablative char inside the rocket after that firing critical. That is there's still enough left for the launch and that it does not go on cooking after the test fire. I think this was the single worst idea Boeing had for the engine on the Delta IV.
1. The issues with pressure fed is the tank weight and perceived loss of performance. It's real benefit (cheapness) has not, in reality, been a key design driver for any government space programme. 2. Military systems prize absolute performance and storability. Solids and toxic hypergols are the best in these areas. For civilian (and especially human rated) systems they should not be used. There benefits simply don't outweigh their downsides, which are substantial. those benefits are simply not relevant to the priority of a civilian and / or commercial programme.
1. Yes, it has. See the original Delta. And also see the EELV-S.2. Wrong again. You are overstating the issues with hypergols. And the fact that every GSO comsat, along with many others, uses them proves that the benefits outweigh downsides. Not to mention that most are commercial and Dragon, CST-100, Cygnus, etc are civilian
Quote from: Lars-J on 12/18/2016 04:12 am"Pressure fed" appears to be one of the concepts of rocketry that sounds oh so much simpler in theory than it is in practice. (like hybrid rockets) And none of the Sea Dragon concepts got anywhere close to reality.It may also be one of the technologies that just doesn't scale well.A number of upper stages are pressure fed, typically with hypergols. It eliminates the turbopump and ignition system.The issues with pressure fed is the tank weight and perceived loss of performance. It's real benefit (cheapness) has not, in reality, been a key design driver for any government space programme. Project cost was what drove Sea Dragon. it's strategy was cut the $/lb by making a huge lump of payload available in one go.Which is the SLS and ITS strategy as well.Solids OTOH are very deceptive. They truly look simple (who can't set off a firewwork?) but have as much trouble as liquids with combustion stability, plus the large quantity of explosive you have packed in one place. They also can be prone to deflagration-to-detonation transition, when the whole lump goes up in one go. Military systems prize absolute performance and storability. Solids and toxic hypergols are the best in these areas. For civilian (and especially human rated) systems they should not be used. There benefits simply don't outweigh their downsides, which are substantial. those benefits are simply not relevant to the priority of a civilian and / or commercial programme.
Pressure feds use insane amount of helium or require complicated pressurization when pressure goes beyond upperstage level 0.8--1MPa.
Solids are really easier with modern polymer binders.
And ISS, which is even routinely refueled with the stuff! - Ed Kyle
Wrong takeaways again1. Yes, it has. See the original Delta. And also see the EELV-S.
2. Wrong again. You are overstating the issues with hypergols. And the fact that every GSO comsat, along with many others, uses them proves that the benefits outweigh downsides. Not to mention that most are commercial and Dragon, CST-100, Cygnus, etc are civilian
Going the solid motor route served Pegasus and Taurus well in terms of short development schedules and relatively low development cost. And although Orbital opted to go liquid on Antares, they still chose a solid third stage for "Block 1" because it was a shorter development cycle and lower schedule risk.
And if you want to talk about "large quantities of explosives," the most recent "large explosions" I can remember have involved by SpaceX helium bottles, an Antares liquid engine failure, and a fatal nitrous oxide tank explosion. None of which involved composite solid propellants, whose safety record in recent years has been quite good.
But please let's not rehash the eternal "which is better/safer" argument. I merely observe that solids "can" be a safe, short-development cycle, and cost-effective option for small and medium LV's, as demonstrated by Pegasus and Taurus.