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SpaceX Tests Its Raptor Engine For Future Mars Flights (techcrunch.com)
Thelasko writes: Elon Musk is preparing to unveil his plans to colonize Mars at the 67th annual International Astronautical Congress tomorrow. As a tease to his lecture, he has released some details about the Raptor engine on Twitter, including pictures. Mr. Musk states that, "Production Raptor coal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar." He goes on to note that the specific impulse spec is at Mars ambient pressure. The Raptor interplanetary engine is designed for use with Space X's Mars Colonial Transporter craft. Musk notes that the "chamber pressure runs three times what's present in the Merlin engine currently used to power Falcon 9," according to TechCrunch. "Merlin has specific impulse of 282 seconds (311 seconds in the vacuum of space), and a relatively paltry 654 kilonewton (0.6 MN) at sea level, or 716 kN (0.7 MN) in a vacuum. You can view a picture of the "Mach diamonds" here, which are visible in the engine's exhaust.
In before someone comments that they can't do R&D while simultaneously sorting out the recent problems with the Falcon 9.
People can multitask, companies even more so. If they were still blowing up every vehicle on the pad, then maybe they'd have a point, but their systems are certainly working better than other programs at their stage of evolution.
Trying to become famous by taking photos. Visit my homepage please.
What alternative do you suggest? ...
Using a few hundred thousand toy rockets, $10, each?
I guess from our persprctive it is best to leave rocket sciense to the rocket scientists
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
Before someone comments that we don't need humans on Mars if robots can do the same cheaper: that's beside the point. I mean, robots are no where near performing on the same level as humans when it comes to ingenuity and ability to come up with and implement ad hoc fixes to problems that no one could even imagine before launch of the mission. But putting that question aside, the problem with robotic missions is that they will never get the same sort of funding as human missions. A human mission automatically has to have a certain size, e.g. has to develop capabilities to land payloads in the ballpark of 10 tons or more on Mars. Once we have this capability, we can easily send lots of robotic and scientific payload along with humans -- it amounts to simply using the same payload delivery system that we are developing for humans anyway.
On the other side, if there is no ambition to fly humans to Mars, then no one will develop these capabilities. There is simply no funding for a system that delivers 10 tons of cargo onto the surface of Mars, unless it can also deliver humans, and bring them back safely. So we cannot send big robotic missions to Mars.
Human missions generate lots of excitement, lots of excitement leads to lots of funding. Robotic missions can never be on par with human missions in terms of how much excitement, and thus funding they can raise.
Because the United States so far has no decent engine worth speaking of?
Ezekiel 23:20
It's 382 in vacuum for the vacuum version of Raptor. Why mention the 311 s figure of Merlin with the 3 MN that the Merlin doesn't have?
Ezekiel 23:20
Even if you didn't go for Mars, this would still be a major item on the list of things you need to do in order to hurl big stuff into Earth's orbit more affordably. There are long waiting lists of customers for such capability.
Ezekiel 23:20
The article made a ridiculous comparison between the non-vacuum optimuzed Merlin and the (near) vacuum optimized raptor. The merlin 1d vacuum is 348 sec, not 311.
300 bar is pretty extreme for an engine. But SpaceX has so far had a good record with engines, so here's to hoping they can carry that forward :)
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
F-1 wasn't vacuum optimized. You're making the same mistake that TFA made when comparing Raptor with Merlin.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
this would still be a major item on the list of things you need to do in order to hurl big stuff into Earth's orbit more affordably. There are long waiting lists of customers for such capability.
There isn't a large pent-up demand for "big stuff" in orbit, at least nothing that anyone's willing to pay even $5000/kg for. The demand for launches of up to fifteen tonnes a lump is handled by the current fleet of rockets. Very occasionally the US spy industry wants to put a unitary big-mirror observation satellite up and that can run to 20-25 tonnes. In those cases the Delta Heavy is used, the only time it is ever launched as far as I know.
The human race has got very good at throwing up small lumps of stuff into orbit and putting them together there afterwards -- the ISS is over 400 tonnes of small lumps, none of them over ten tonnes in mass when they were on the ground. A heavy lifter is not really needed for day-to-day operations or even a blue-sky Manned Mars mission, it's achievable with today's hardware and without the cost overheads of developing new heavy launchers with little or no other commercial sales to pay for them.
Chances are that even the sea-level version of Raptor will have its vacuum Isp in the 360-370 range anyway, so a comparison is still in order, but the particular mention of Merlin's vacuum Isp that I was responding to was clearly a mix-up.
Ezekiel 23:20
So you're saying...what, that there's no interest in more capable scientific missions, or better remote sensing satellite with big (and heavy) optics, or GEO communication satellites with larger antennas and greater number of transponders (all requiring more power and propellants), or simply in slightly oversizing the LV so that hardware reuse could get easier?
Just because you don't need to lift 400 tonnes in one go doesn't mean that Shuttle's load of around twenty tonnes was anywhere close to optimal. A better launch vehicle is not an either-or proposition. And the ISS launch campaigns were crazy expensive. In part because of the piecemeal approach, in part because even using only Protons would still have been much, much cheaper.
Ezekiel 23:20
The recent Falcon 9 accident has been traced to a Helium COPV tank in the oxygen tank. It runs at more like 5,500 PSI, not 300 PSI. Delamination of COPV in cryogenic applications is a longstanding problem which they must have thought they'd conquered, having used them successfully so many times.
And this article is about an engine, not a composite helium tank. The engine runs on cryogenic methane, which is a new fuel for Spacex, replacing kerosene. They are running scaled tests during the design phase of their new engine - so not exactly building it faster now and hoping to get lucky that it doesn't blow up. The new engine is supposed to be much more efficient than current incarnations and is specifically tuned for use in a vacuum. Plus it has the advantage of using a fuel that can be harvested or manufactured from several locations around the solar system.
Considering that the US Congress is apparenly not unfriendly to the idea of sending people to Mars, provided that the cost is not crippling to the project, even in the absence of SpaceX-initiated colonization, there'd still be some interplanetary business to be done. It doesn't really matter what's going to happen in the future, we know a modern engine would come handy even today.
Ezekiel 23:20
This is all true if nothing changes.
But what happens if they build a reusable booster that can lift this sort of weight? If Spacex could lift 200mT to LEO for costs that are comparable to today's heavy launches, would new uses arise?
NASA is also building a heavy lift rocket - the SLS. So Spacex is not alone in thinking a big rocket is a good idea. Of course, NASA is responsible to Congress, not the owners of a private company, so that part is different.
""Production Raptor coal is specific impulse of 382 seconds and thrust of 3 MN"
That's impressive, considering they are using coal as the fuel!
Sure there's an interest in big launches, big-mirror observatories and the like. What there isn't are the bucks to pay for them and the need for multiple launches a year that would justify spending tens of billions to develop a 50-tonne class launcher which would only fly once a year, if that.
At the moment humanity is launching about ten to twelve vehicles a month -- December 2015 was a recent activity peak with eighteen launches, three of them within the same 24-hour period. The next large scientific payload I know of is the James Webb telescope which will fly on an Ariane V in 2018, and that's only 6.6 tonnes.
ESA are blowing the cobwebs off their own heavy-lifter, the ES variant of the Ariane V for a couple of missions to launch four Galileo satellites at a time but apart from its original purpose to fly the ATV resupply vehicles to the ISS nobody needing a 20-tonne unitary lift has been buying flights on it, while the regular ECA variant of Ariane (10 tonnes to GTO, usually two GEO satellites plus SYLDA carrier) and the smaller Vega have full order books.
Indeed. Part of the reason that satellites are so expensive is how light you have to make everything; there's a huge amount of engineering that has to be done in order to achieve mass goals, as well as make use of the most expensive materials on the planet. An example is the use of things like top-end Spectrolab multi-junction solar cells, which get the highest efficiencies, but since they're basically lab-scale production hardware they cost two orders of magnitude more than what slightly less efficient panels on Earth cost (about $400/W).
Beyond the simple cost effect on engineering, there's the size effect. Look at James Webb and the massive expense they had to try to make it "origami" itself to fit into smaller launch vehicles. Or how many parts ISS had to be built out of in space, dramatically escalating both ground engineering / production costs and in-space assembly costs (the latter costing nearly $10m per man-day). There are serious expenses to trying to compensate for a lack of space or payload capacity when you really need it.
Then there's the size of the market. As launch costs have been dropping, the number of companies looking to launch payloads has skyrocketed. The skyrocketing launch demand has been reducing average payload development costs, as designs get more reuse. Both of these trends will continue as costs continue to decline. Meanwhile, new markets will continue to open up. Space tourism has always been hindered by the absurdly high launch costs, limiting it to only the wealthiest individuals. While it will remain a "small" market for the forseeable future, it can expand by orders of magnitude with reduced launch costs. Which again makes more demand..
Lastly, there's economies of scale. It's generally recognized in the rocketry world that - at least up to a point - larger rockets get a better cost per kilogram than smaller rockets. So wherein you can launch a lot at once - multi-satellite launches, large geo launches, large interplanetary probes, fuel depots for tugs/boost stages, shielding mass for manned missions, etc - you tend to save a lot of money by going big rather than using multiple smaller launches. The caveat is that just simply going big is no guarantee of a price reduction. Just like you can make an absurdly-expensive smaller craft, you can also make an absurdly expensive large craft. And even a "moderately priced" large craft isn't generally a "win" - if you can sell payload space for $5k/kg on a 10 tonne payload rocket and for the same price per kilogram on a 100 tonne payload, the vast majority of customers will choose the former. But if you're a company like SpaceX that's been delivering cost reductions on the small scale, and you can carry it over to the large scale, it gives you the potential to take the cost reductions even further.
If you can pull it off.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
"Chances are" in no way that a sea-level version of a vacuum-optimized rocket with an Isp of 384 will have an Isp of 360-370. Merlin-1D vacuum has a vacuum ISP of 348, but the nearly identical Merlin-1D designed for atmospheric use (same thing, just without the nozzle extension) has a sea level Isp of 282 sec.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
To be fair, we don't know that it was a COPV failure (although that would be most likely) - all we know at this point is that the failure was in the helium system and was unrelated to the strut failure in CRS-7.
While technically you can also produce other fuels off-world methane is indeed the highest throughput and efficiency, as sabatier synthesis yield by far the highest mass fraction as methane, so you don't have to do a lot of recycling of the methane to try to get your desired fraction as an output. Yet the mass is still mostly carbon, which is much easier to get than hydrogen (to the point that even a lot of in-situ production concepts have still called for bringing the needed hydrogen from Earth (reliable/sustainable fuel cell decomposition of CO2 to CO and O2 is pretty much a solved problem; reliable/sustainable permafrost brine mining and purification in Mars conditions, not so much). Methane is also cleaner burning, aka less likely to clog up your injectors and the like. Its disadvantages compared to RP-1 are its cryogenic nature and much lower density (increasing rocket bulk/cross section/mass and decreasing thrust). The lower density does however have its advantages as well - by virtue of requiring bulkier launch vehicles, you inherently increase fairing diameters, which allows for bulkier payloads.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
The sea-level versions of advanced kerosene engines already have a vacuum Isp of ~340. Methane will be higher than that, especially at somewhat higher pressure than the RD-1xx line. The and prototype RD-0162 methane engine is already at 356 s of vacuum Isp at 17 MPa. What's so difficult to understand about it? The effect of the vacuum nozzle will be smaller for Raptor because the higher pressure allows for a higher expansion nozzle even for the sea-level version.
Ezekiel 23:20
A coal-LOX hybrid rocket would work, and the ISP wouldn't be too bad (though hydrogen-rich fuels would be better). It'd be an interesting challenge.. normally with hybrids you want the fuel to melt and whip up into droplets at the surface to increase their surface area, but I imagine with a coal hybrid you'd want it to break up into a dust. So maybe fine coal dust with a paraffin or polyethylene binder.... that'd actually probably have excellent thrust performance.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
You have stolen the words from my mouth. Exactly that. For the same money we could explore more and do more science than spending it to send a useless piece of meat with no embedded measurement capabilities to grab some knowledge from the worlds it explores.
First off, if we only send probes or only send humans that would be idiotic. There are things that each can do that the other cannot. For example it is basically impossible to study human or animal physiology away from Earth unless we send a human. Similarly there are some environments that are simply too hostile to life to send a human. Use the best tool for the job. Sometimes that a robot, occasionally it will be a human. It should never be a case of only one or only the other. We should be working towards both.
Second, there is no robot or probe that we could send that would be even a fraction as scientifically productive per unit of time as an on site human. We send robots solely because they are currently the only practical option available to us. That will remain the case for a while as we lack the technology to send a human safely to anywhere beyond the moon at this time. But once the technology to send a human is available there are a LOT of missions where it would be much preferable to send a human if that were a feasible option. A geologist on the surface of Mars would be far more scientifically productive than 100 probes. We just can't get one there safely or economically... yet.
Third, your argument that humans are "a useless piece of meat with no embedded measurement capabilities" is an idiotic statement. Humans are the most useful, flexible, and productive tool we have. Our probes and tools are crude mockeries of what humans can do given adequate resources. Yes humans are hard to keep alive in hostile environments. So what? We aren't designed to go sailing on or under the oceans and yet we figured that out. We aren't designed to go into space either but we've figured out that as well. It's going to take a while to figure out interplanetary travel but there is no objective reason why we shouldn't go there too eventually. We're not going to stop sending probes. They're terrifically useful. But it is short sighted to believe that there is no value in sending a human to explore space or that humans would be no value there. Sometimes the best tools are the most fragile ones. Sometimes what seems fragile is actually incredible robust.
If Spacex could lift 200mT to LEO for costs that are comparable to today's heavy launches, would new uses arise?
Such as? The only unitary large-lift mission I can think of is a single-mirror super-Hubble space observatory which has its own problems -- building a one-piece very large mirror, say five metres in diameter that could survive 3G-plus during launch, vibration etc. isn't going to be easy or light. The James Webb is using folding mirror segments and will have an effective diameter of 6.5 metres when deployed and it fits in a regular launcher fairing.
We've got better at doing things in space in the past fifty years, we don't have to go back into the Jet Age to justify Big Dumb Boosters.
As an aside, large amounts of stuff needed in orbit is actually fuel for satellite manoeuvering, deep-space probes, a future manned return to the Moon etc. A remarkable amount of the mass delivered into LEO and GEO today is cheap fuel at a delivery cost of $5000/kg. What I'd like to see Musk doing is working on a robot fuel production system based on, say, Ceres or other water and carbon rich asteroids, bringing back tankers full of fuel to Earth orbit. That way he could go to Mars without having to lift a thousand tonnes of fuel up from the ground in expensive boosters.
The sea level version of the aforementioned Merlin 1D is 311. Not "~340". We're comparing different nozzle versions of an otherwise identical engine. You don't lose a mere 15-25 sec ISP when losing your nozzle extension and operating at sea level. Period. That's just not reality. If you think for some reason that the Merlin-1D is a bad comparison, pick another engine with otherwise identical vacuum and sea level versions, and cite the vacuum ISP for the vacuum version and the sea level ISP for the sea level version. The sea level ISP will always be vastly lower, not a mere 15-25 sec. I strongly challege you to find a single engine where the difference even remotely approaches your figures.
And to be clear, Merlin 1D is already a fairly high pressure engine, 100 bar is no slouch. And it's not some sort of linear relation with pressure because a lot of the heat is from the internal energy difference between the high-pressure and low-pressure exhaust; it's not simple thermal expansion, as there's a change in the reaction equilibria and in some cases release of the latent heat of vaporization. Chamber pressure has a positive but fairly weak correlation with ISP; most people overestimate its influence.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
There isn't a large pent-up demand for "big stuff" in orbit, at least nothing that anyone's willing to pay even $5000/kg for.
What is your evidence that there is no demand for large objects in orbit? I'd imagine there is lots of demand if the price can be reduced to something that doesn't require the resources of a nation state. You have no idea what the actual demand for large satellites is because it's not presently economically feasible to get very large objects into space in a single piece. It's a chicken vs egg problem.
Very occasionally the US spy industry wants to put a unitary big-mirror observation satellite up and that can run to 20-25 tonnes. In those cases the Delta Heavy is used, the only time it is ever launched as far as I know.
That's a economic problem, not a technical one and certainly not an indicator of potential demand. It's like arguing that there is no demand for supercars because only the really rich can buy them today. Bring the price down to something affordable and there will be people doing all sorts of clever things you didn't begin to imagine.
The human race has got very good at throwing up small lumps of stuff into orbit and putting them together there afterwards -- the ISS is over 400 tonnes of small lumps, none of them over ten tonnes in mass when they were on the ground.
That's because we had no other options at the time we launched those components. Given a larger and economically viable launch vehicle and the ISS likely would have been designed differently and probably would have cost less to lob into orbit.
It didn't need to be since it never ran in true vacuum. The F-1 was actually optimised for reliability and not-killing-the-passengers hence its abysmal performance by today's standards. Even the SpaceX Merlin 1-D has a better Isp figure than the F-1.
F-1 - Isp (sea level) = 263 seconds.
Merlin 1-D Isp (sea level) = 282 seconds.
RD-180 Isp (sea level) = 311 seconds.
Look, I'm sorry but what sea-level Merlin does or doesn't achieve is totally irrelevant for Raptor - even for sea-level Raptor. The fact is that the 17 MPa LCH4/LOX sea-level RD-0162 is rated for 356 s of vacuum Isp, so the 30 MPa (+76%!) LCH4/LOX sea-level Raptor is definitely going to be in the 360+ s vacuum Isp territory. And that's including the assumption that the sea-level Raptor and vacuum Raptor are going to be identical units with different nozzles - the point is that the nozzles will be less dissimilar because the high-pressure sea-level engine already has a higher area ratio (M1D has only 16:1, but the RD-191 has 37:1 and Raptor will be even higher, even for the sea-level version).
And I was not the one to pick Merlin 1D for comparison; I actually pointed out how pulling it into the discussion makes no sense. I'm pointing it out again for you, in case you still haven't caught on.
Ezekiel 23:20
Even a 50-tonne-class launcher could be easily pretty busy for ten flights per year, especially if it can throw multiple GTO payloads in a single flight and/or use flexible upper stages. You yourself are mentioning the Ariane 5 which only differs in the upper stage option, so it's not like having the ES version requires a completely new production line. This is pretty much the same case. And the ECA version would be even busier if it could throw two heavy sats to GTO instead of one heavy and one lightweight (which was reported as difficult these days due to the lower demand for lightweight slots), which is straight in the territory for a launcher that can throw ~50 tonnes to LEO, plus a cheaper methane upper stage.
Ezekiel 23:20
F-1 would still have benefitted from improved vacuum Isp because even first stages operate at significantly decreased pressures for a substantial period of its burn. The problem with F-1 was that the nozzles were already too wide and improving vacuum Isp without worsening the overall size and sea-level Isp would have required significantly higher chamber pressures. Which is not to say that it was a bad engine - a modernized version could still be very handy today. It is the complexity of its hand-crafting that would make it a relic these days, not the raw performance figures.
Ezekiel 23:20
>scale ion thrusters or solar sails or Moon based laser push-beams
OK, and how many ounces is that going to push?
Dude, manned missions are HEAVY. You have the people, their air systems, food, water redundant everything to keep people alive.
Slow pushers like what you listed make the travel time a LOT longer (say 10x, if you're optimistic), meaning you need that much more food, water, oxygen, etc - making the whole payload mind-bogglingly heavy... meaning then the engine then won't get the job done at all.
Thank you. I stand corrected.
Religous speak to God. Insane are spoken to by God. When all shut up, one can finally hear Shostakovich in peace
Because pointing out the typical difference between vacuum and sea level performance in hydrocarbon engines is "totally irrelevant" in a discussion about the difference in vacuum and sea level performance in hydrocarbon engines?
I see your argument - all engines for a given propellant mixture are identical except for only one varying parameter (pressure). Why it's so simple, why didn't I think of that? ;) *snicker*
Meanwhile, back in the real world, performance varies widely between different engine families, and there are many factors that affect them. What you're doing is equivalent to saying "Because my gasoline hybrid engine is super efficient, then your non-hybrid gasoline pickup truck engine should be too!" If you want to compare the performance of vacuum engines to sea level engines, you need to compare for the same engine.
There is nothing magical about methane that makes it somehow, unlike all other fuels, have a tiny difference between ISPs in optimal vacuum vs. optimal sea level designs.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
I see your argument - all engines for a given propellant mixture are identical except for only one varying parameter (pressure). Why it's so simple, why didn't I think of that? ;) *snicker*
And that makes Merlin somehow more relevant?
Meanwhile, back in the real world, performance varies widely between different engine families, and there are many factors that affect them. What you're doing is equivalent to saying "Because my gasoline hybrid engine is super efficient, then your non-hybrid gasoline pickup truck engine should be too!" If you want to compare the performance of vacuum engines to sea level engines, you need to compare for the same engine.
The RD-0162 is the closest unit you can compare the Raptor with. It pushes all its propellant mass through the chamber. It uses the same propellant mixture. Therefore the real world vacuum performance of the sea-level version Raptor can be best guesstimated from the RD-0162 figures rather than by comparing it with dissimilar units.
Ezekiel 23:20
I don't disagree with a word that you wrote. :)
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
What I'd like to see Musk doing is working on a robot fuel production system based on, say, Ceres or other water and carbon rich asteroids, bringing back tankers full of fuel to Earth orbit.
Well, this is one of the more obvious use cases, too.
Ezekiel 23:20
My evidence is that there is actually, in reality, no demand for large objects in orbit
That my friend is the very definition of begging the question. Your premise assumes the conclusion.
SpaceX is a for profit business. If there were no demand or market for a heavy lift vehicle then why would they bother developing one? That's a huge expense if there is no expected ROI. I'm pretty sure they have a better feel for the market than either of us. Is it possible they are building a figurative bridge to nowhere? Maybe but that would be inconsistent with their prior behavior and economic sanity. Elon Musk has been accused of many things but stupidity has rarely been among them. It is difficult to gauge demand for very large objects in space until you have a realistic means of getting them there. Given that SLS is subject to the whims of congress and that SpaceX hasn't brought their heavy lifter to market yet why would anyone seriously plan a very large satellite today? Simple logic would dictate taking a wait and see approach. Once the lift vehicle is available then and only then should we expect to see very large objects getting designed.
A modernised version of the F-1 did exist, with much better Isp of 311 seconds at sea level and a greater thrust of 7.25MN at sea level. It could be throttled and pivoted, unlike the brute-force-and-ignorance of the fixed F-1. It's called the RD-171. It spawned a series of cut-down versions flying today such as the two-chamber Atlas RD-180 and the single-chamber Angara RD-191/Antares RD-151.
As for the Saturn V, the first stage spent 10% of its burn time and fuel just clearing the tower so vacuum performance was not really a mission-critical factor in the F-1's development and design. It was laid out in the early days of rocket development where "design" involved slide rules and large sheets of drafting parchment -- the idea of CAD, computer modelling, 3-D printing of engine parts, modern engineering materials etc. were science-fiction dreams whereas they had to bend metal then and there.
Why show how much sea level and vacuum ISPs vary in other hydrocarbon engines? Because they vary that much in all engine, even non-hydrocarbons (same sort of difference in LOX/LH and solids). Methane is not some sort of magical exception to the rule.
No, they cannot. You have no clue whatsoever how the efficiency of the RD-0162 compares to Raptor. Not in the slightest. Which makes it a pointless comparison.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
Yes, coats are a lousy fuel, they constantly tangle up the turbopumps.
thinks he'll be able to wring out some amazingly fat government subsidies
Exactly.
“SpaceX no doubt has some brilliant ideas about Mars. But who will pay?”
From the Ars Technica article:
“He’s made a lot of money from NASA over the years, and now he may be about to effectively tell NASA that they’ve had their head up their ass for a long time about how to go to Mars, that this is how we’re going to do it, and you’re going to pay. I don’t know how well that is going to be received.”
http://arstechnica.com/science...
My personal take is humans to Mars is a fantasy, perpetuated by an old dated Manifest Destiny. I see no huge landrush to the Gobi Desert even though it’s a thousand times easier to settle. Reason it is barren, inhospitable (except for a few hardened individuals). We romanticized about Mars because it is so far away (and will always be 20 years away from putting a man on Mars like fusion power is always 10 years away).
mfwright@batnet.com
> What alternative do you suggest?
Even if there is an 80% chance that the money is wasted, doing the development might be the smart choice in order to establish market share while the private space industry is in it's infancy. So I wouldn't *suggest* a change.
The other *option* they should consider finding and fixing the significant existing problems before investing so much in a new platform that will likely have the same problems again. Figure out how to build an pressure tank before you build an even bigger version, for example. Maybe one problem is the quality control of the materials that one of their subcontractors is using. Example, maybe the material lining their tanks has more impurities than specified. Find out and get a different, better source for the material before you build another rocket with the same substandard lining . Or figure out how to build a tank that still work with the lining material, maybe by making it twice as thick. But don't just build another rocket with the same type of lining, which have the same type of failure.
The F-1 was actually optimised for reliability and not-killing-the-passengers hence its abysmal performance by today's standards.
I believe GP was referring to aerostatic nozzle optimization, which every rocket needs to have. This type of optimization applies only to the nozzle, and not the rest of the rocket engine. (pumps, combustion chamber, etc.) A rocket with a nozzle designed for space will not perform well compared to the same rocket with a nozzle optimized for earth at sea level. This is because Earth's atmosphere plays a role in how the gases expand from the engine.
This phenomenon can be observed particularly well on the SpaceX webcasts. The exhaust gases from the engine are expelled directly behind the engine when the rocket is leaving the launch pad. Just before stage separation though, a significant portion of the exhaust gasses can be seen to the sides of the rocket. This is another of the many reasons multiple stages are used in rocketry.
Other trade offs are made between safety and performance, mainly in the combustion chamber and pumps. Experienced scientists and engineers can do some calculations to factor out nozzle optimization and get a more accurate comparison between different types of rockets.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
SpaceX will be streaming Elon Musk's presentation live on their website.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
As conventional fuels were in extremely short supply by late 1944, Lippisch proposed that the P.13a be powered by coal. Initially, it was proposed that a wire-mesh basket holding coal be mounted behind a nose air intake, protruding slightly into the airflow and ignited by a gas burner. Following wind-tunnel testing of the ramjet and the coal basket, modifications were incorporated to provide more efficient combustion..
The coal was to take the form of small granules instead of irregular lumps, to produce a controlled and even burn, and the basket was altered to a mesh drum revolving on a vertical axis at 60 rpm. A jet of flame from tanks of bottled gas would fire into the basket once the P.13a had reached operating speed (above 320 km/h), whether by using a rocket to assist takeoff or by being towed..
The air passing through the ramjet would take the fumes from the burning coal towards the rear where they would mix under high pressure with clean air taken from a separate intake. The resulting mixture of gas would then be directed out through a rear nozzle to provide thrust. A burner and drum were built and tested successfully in Vienna by the design team before the end of the war.
There are a number of launchers that burn the same engines from ground to true vacuum, indeed the Shuttle's engines burned from launch to orbit insertion (aided by the SRBs in the early part of the flight). Other examples include the Vulcain-2 on the Ariane V and the RS-68A central core stage of the Delta 4 Heavy. Notably all these long-duration burn motors are LH2/LOX which have even better Isp numbers than kerosene/LOX motors.
There are a number of launchers that burn the same engines from ground to true vacuum.
Trade offs were made. Those nozzles are only performing optimally at one altitude. I didn't say it can't be done, it's just not efficient.
One of our competitors trademarked the term "hypothesis". From now on, we will call them "boneheaded ideas".
But what happens if they build a reusable booster that can lift this sort of weight? If Spacex could lift 200mT to LEO for costs that are comparable to today's heavy launches, would new uses arise?
There is not so much demand for milli-tablespoon launches.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
3MN is pretty damned impressive. That's roughly half of what an F-1 engine produced.
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
LOX/LH2 motors have a good enough Isp figure that they can take the hit in performance -- the Vulcain 2 runs between about 360 at sea level and 420-odd in vacuum, comfortably outperforming vacuum-specific kerosene/LOX designs at all altitudes. The SpaceX Merlins are actually quite poor performers for kerosene/LOX but there may be other trade-offs in terms of construction costs and reusability. They can certainly do the job of getting modest amounts of materiel into orbit.
As for the Raptor engine I'll be interested to see where they go with it. Other people have tried methane/LOX in the past but reported problems. I've heard there is a fuel decomposition problem resulting in coking of the pumps as well as sulphur impurities in the methane causing problems too. What puzzles me is the mention of using a partially-cryogenic fuel mix as an interplanetary engine; LOX is not storable over any sort of a timescale even in space and even methane would require active refrigeration to stay liquid for weeks or months on end during a transfer orbit to, say, Mars.
It's almost impossible to predict the "killer app" for a technology before it becomes available. The PC was around as a hobbiest contraption for quite a few years before it became a serious business tool, the internet was around for a while before Google and Facebook learned that targeted advertising and data collection were the real cash cows (and became some of the largest corporations in the world)... nobody predicted in the early days of the internet that collecting user data would be so lucrative. They never imagined that something like a social network would become so significant or that a company like Facebook could become such a prominent corporation.
So, on some level, it's going to be a matter of lowering costs and building the infrastructure, and then waiting to see what crops up. Space tourism gets a lot of press, and it might be overstated, but I can say for a fact that if you get the cost low enough a huge market will emerge. At $100k/ticket, would you pay for a flight to orbit? Nah. At $10k? Maybe. At $1k? Hell yes.
So Musk is pulling out all the stops to drive that price/lb into the dirt and planning on the market to respond. But he's dumping his own cash into the business to do it, and in the short term, if you have 20 launches in the global market, and all of a sudden SpaceX does 10 of them for half the standard price, the net effect is that now there's 25% less global spending on the launch market. So the question is how fast the market will respond to the decreases in price, and if the increase in volume will be enough to offset the decrease in per-launch spending. Traditionally, that's how markets have worked, but if it ends up being a lot more lethargic, or less elastic, than Musk is projecting, he could run out of cash (or die of old age) before he succeeds in making space access routine and affordable.
Why show how much sea level and vacuum ISPs vary in other hydrocarbon engines? Because they vary that much in all engine, even non-hydrocarbons (same sort of difference in LOX/LH and solids). Methane is not some sort of magical exception to the rule.
Of course it is the case that even a single propellant mixture's performance varies depending on how it's used, but that does not make your comparison of a methane engine to Merlin any more relevant - less relevant, if that's even possible.
Well, well, well...would you look at that?? Sea-level Raptor at sea level has an Isp of 334 s, where the by-you-mentioned Merlin 1D has a sea-level performance of the sea-level version at 282 s, as you claim. And you still claim that the sea-level version of Raptor can't possibly have vacuum Isp in the 360 s range even thought the Raptor practically starts where the RD-17x/18x ends.
No, they cannot. You have no clue whatsoever how the efficiency of the RD-0162 compares to Raptor. Not in the slightest. Which makes it a pointless comparison.
If I can't compare it even to the RD-0162, being the closest performer, then I can't compare it to anything at all and your nonsensical blurb about Raptor not possibly being able to achieve this or that parameter is rendered even more naive.
Ezekiel 23:20
pick another engine with otherwise identical vacuum and sea level versions, and cite the vacuum ISP for the vacuum version and the sea level ISP for the sea level version. The sea level ISP will always be vastly lower, not a mere 15-25 sec.
You may have missed the part where I'm discussing the difference between vacuum Isps of the vacuum and the sea-level version of one engine (even in sea-level engines, the operation in diminished pressure is prolonged and therefore relevant), not between the sea-level Isp of the sea-level version and the vacuum Isp of the vacuum version. In case your comprehension is that bad, I'm spelling it out explicitly here. I've been trying to make it obvious by talking about vacuum Isp of sea-level engines explicitly the whole time but for some reason, you still haven't caught on.
The RD-191[V] engine has sea-level Isp of 311 s for the sea-level version, vacuum Isp of 338 for the sea-level version, and approximately 344 s for the vacuum extension version. It's quite obvious that the already-rather-high-expansion nozzle on the sea-level version of the RD-191 is responsible for the small-ish difference, and the Raptor actually has almost the same area ratio as the RD-191 (just 40:1 instead of 37:1). That makes the difference between the performance of sea-level and vacuum-optimized versions of a high-pressure engine significantly smaller than the difference between the sea-level version and vacuum-optimized version of a low-pressure engine like Raptor. That was the whole point of my reaction to your irrelevant remark. The Merlins are a "from 16:1 expansion to 150:1 expansion" case whereas the Raptors are a "from 40:1 expansion to 200:1 expansion" case. Given the quickly diminishing returns on increased expansion, it should come as no surprise to you that vacuum Raptor and sea-level Raptor are going to be much closer in performance than the sea-level Merlin and the vacuum Merlin, but for some reason, it does.
Ezekiel 23:20
Sorry, that should have read " of a low-pressure engine like Merlin"...obviously!
Ezekiel 23:20
Well would you look at that indeed! I argued for a loss of 348-282=66 sec in Merlin, and said that Raptor would be somewhat less of a difference but not much, as "chamber pressure has a positive but fairly weak correlation with ISP". You said 384 - "360-370" = 14-24 sec difference.
And the reality is... drumroll... the envelope please...
384-334 = 50 sec
I hope this has been a learning experience for you.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
VACUUM ISP. I really don't know at this point if you're trolling on purpose or if you've been simply cognitively challenged since birth. 334 s is a sea-level figure that has nothing to do with my claim about VACUUM ISP.
Ezekiel 23:20
Remember that the Hubble exists because US spy satellites existed. They looked suspiciously like a hubble telescope, except pointed in the other direction.
Why weren't they any bigger? Because they wouldn't fit on the launcher.
This launcher might be able to put a Keck-class scope in outer space. Think the CIA might find a use for something in that class? I know astronomers would.
If launch cost was a couple-hundred million, I'd say we could find the money to build the thing. The Hubble cost a lot more than that to launch.