Mining isn't an easy thing even here on Earth - a maintenance-prone task that runs through lots of consumables - let alone on Mars where you have to choose between horrible throughput for remote operation, or local operation with astronomical local labour costs. A number of Mars in-situ proposals have outright done away with the water side of the equation, opting to harvest CO2 from the atmosphere locally (splitting to CO and O2 in a SOFC, like MOXIE on Mars 2020), but shipping in the hydrogen to avoid the need for mining. Most of the mass of fuels like methane is the carbon, not the hydrogen.
That is not the best strategy. It is better to push forward, take risks, and fail fast. You learn more from your failures than from your successes.
Indeed. But part of the problem is that SpaceX wants to simultaneously be taken seriously as a reliable delivery service, and push the bounds for rapid, radical cost reduction. Even rockets blowing up on the test stand or failing during experimental landings comes across as bad press for them - even if they expect to have low odds of success. I've seen way too many comments and articles along the lines of "OMG, SpaceX crashed a landing, how can you think about sending up astronauts with a company that unreliable?", when the concept of "fail until you get it right" was always the plan with those landings.
If I were to start a rocket company it'd be in two parts. The first would be something like "Crazy Karen's Discount Rocket Emporium", and would go for a total Kerbal vibe, down to crudely spraypainted "This Way Up" notes on the side of stages, duct tape holding things in place on test stands, any interviews given in totally unprofessional clothing, etc. The sort of company that you'd be more surprised when things work than when they fail. The other would be your standard stuffy boring professional institution and would have a partnership with the kerbal-esque company, making clear that they acquire "promising but immature" technology from the other side, then invest their engineering resources on turning it into a refined and reliable experience for their launch service customers. All of the risky research efforts would be done by the first side.
It's effectively the same thing, but it'd make the delineation that all rocketry companies strive for explicit. You move fastest by taking risks rather than trying to avoid all failures, but you try to insulate the risk-taking side from the actual experience you offer paying consumers as much as you realistically can.
That's not what people were complaining about in the video. What people were complaining about was that they were landing right next to an exposed, filled propellant stage. You don't land a skyscraper-sized fireball-on-a-stick right next to a half billion dollar tank of fuel. That aspect was clearly stylized.
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.
Concerning Europa (remember that this was before the recent news):
The most significant opportunity for Juno to do Europa science would be to follow up on the plumes possibly detected by Hubble Space Telescope. Confirming Hubble's detection would be very scientifically valuable. Any information on the source location would be valuable. This science goal just may not be possible with the large distances from Juno to Europa, but we will look.
JunoCam or ASC can only detect plumes if they contain fine particles. The Hubble discovery (if real) only shows the presence of water vapor. We can predict by analogy to Enceladus that water vapor plumes will also contain particles. However, it is important to remember that the Hubble discovery was of gas, not particles. If the putative Europa plumes are Enceladus-like and do contain particles, they would not be as tall as Enceladus', because of Europa's higher gravity. Scaling for Europa’s gravity gives a maximum plume height of under 140 kilometers. To detect plumes, we need at least two pixels, so the image spatial scale would need to be better than 70 kilometers, at a relatively high phase angle where the particles would forward-scatter light to JunoCam and ASC.
To achieve resolutions better than 70 kilometers per pixel, UVS needs to be within 40,000 kilometers of Europa; JunoCam, 100,000 kilometers; and ASC, 170,000 kilometers. For the cameras, given the low expected height of the plumes, there is not much flexibility.
There are just four orbits that have Europa flybys that are closer than 300,000 km. Juno reaches the best available geometry in September 2017 as the rotation of the line of apsides brings Juno’s orbit close to Europa’s orbit:
2017-03-08 253,118 km 2017-09-19 264,043 km 2017-10-03 92,267 km 2017-10-17 204,654 km
The cause is not the same reason as with comets (sublimation), Europa isn't on a sungrazing elliptical orbit. It's also not impact related, as the impact flash would have been seen, and the plumes wouldn't have been this frequent / long lasting.
It's pretty limited what you can gather from individual grains captured at hypersonic velocities and analyzed with spacecraft-sized instruments. Certainly there was no "clear evidence of life" from Enceladus - although it showed us some very promising things about the potential habitability of its oceans.
Personally, I'm not a believer in the theory that wherever there's liquid water, there's life. First off, it'd make the Fermi paradox even worse, as water is bloody everywhere. Secondly, I think it's incredibly naive. The argument goes, wherever we find water on Earth, we find life, and whereever we don't, we don't, so we should expect that with the universe. But that says nothing about how life came about. Sure, LAWKI requires hydrogen, and water is the most convenient source of hydrogen, so obviously that's going to form the boundaries of where life has spread to. But where it's spread to says nothing about where it originated, or what it looked like when it did. We have no reason to think that the entire wet surface of Earth just spontaneously erupted into life; we certainly don't see anything resembling this in laboratory abiogenesis experiments. So what were the specific conditions that brought life about? I think it's a safe bet that they were rare. Quite likely no longer present on Earth, as Earth was a radically different place back then. And quite possibly rare in the universe as a whole. Little bursts of luck separated by great relativistic distances.
Indeed, bodies like Europa (and the many other bodies confirmed to or believed to have subsurface water in our solar system) should help answer these questions. I'm also exceedingly curious about what's gone on with alternative solvents and polymeric compounds, such as at the surface of Titan (I find the cyanide chemistry there fascinating, it seems to be extremely flexible).
Yeah, landing the booster right next to the refueling tanker seems little,eh... optimistic
The video is clearly stylized and not meant to be taken that literally. Unless you think the arrival of the spacecraft is supposed to make Mars spin until it develops oceans;)
That said, while there's much to like, there's one aspect of it that's really clawing at me... the fact that they plan to make it out of composites. Including the LOX tank. We've never succeeded (and failed multiple times) at making flight-intent LOX tanks for orbital rockets. And they want to make the first time be on what's by far the largest rocket ever built? Without a lining?
Is it worth mentioning that they just had an explosion somehow related to the only major carbon fiber component in the Falcon 9 in a LOX tank?
CF becomes brittle in LOX. It leaks. And most concerningly, it's impact / shock sensitive in LOX. At atmospheric pressure it usually won't do a self-sustained burn on impact, but it chars on impact, and even that alone would be bad. But they plan to have significant pressure as well. He mentions briefly that they expect this to be one of the biggest challenges, getting stable coatings and the like. I think that's an understatement.
I just don't want to see the largest rocket ever built turn into the largest flying fireball on Earth. I don't trust composites with LOX. Composite cryogenics tanks are an active research topic, and they're making progress, but it's not a solved problem.
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.
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.
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.
I think you're confused. Plumes means "in space". The whole benefit of plumes is that you don't need to go under the ice at all, you can do flybies to collect ice particles, or have a lander observe and sample the plumes at the surface. The key is that it means a recent connection between the depths and the surface, and that would be huge for simplifying exploration.
We're nowhere near to being able to launching an ice boring / swimming probe. If I recall correctly the last thing I read on the subject, however, the most promising means for communicating with such a probe on an affordable mass budget was.... not communicating with it. Aka, having it fully autonomous - melting its way down, sampling/observing the ocean, then re-melting its way back to the surface - then and only then transmitting. The waiting period with no data would be stressful (as if it failed you'd never know why), but it could potentially be used on almost any icy solid body regardless of the ice thickness.
It's also possible that there's liquid water much closer to the surface than the global ocean. There are some inferred lakes at a depth of only a few kilometers, which is potentially short enough for a probe to maintain a fiber connection with the surface. And after JUICE and Clipper, we may well have found locations that are even shallower.
Right. Because brief observations from an already present spacecraft that could help make critical design decisions about an upcoming multibillion dollar mission are an absurdity.
Look, we know Juno wasn't designed for this sort of mission and is not well equipped or positioned for it. But if researchers determine that its observations could help pinpoint more details of the plumes, then yes, they damn well should regardless of whether "tomhath at slashdot" considers that to be "real science" (apparently some vague category that he doesn't even feel the need to expand upon -- apparently planetary scientists have been working on "fake science" all these years, who knew?).
Look, I'm sorry but what sea-level Merlin does or doesn't achieve is totally irrelevant for Raptor - even for sea-level Raptor.
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?
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.
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.
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.
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.
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.
Chances are that even the sea-level version of Raptor will have its vacuum Isp in the 360-370 range anyway
"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.
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.
Slashdot Mirror
We really don't know if Mars' gravity is "enough" like Earth's to avoid wasting. We certainly hope it is, but we don't know that.
Venus on the other hand, at 0.9g....
Despite how Elon phrased it, "water" isn't abundant on Mars. Rock-hard, gritty, perchlorate-contaminated, hexavalent chromium-contaminated clay-brine permafrost ? Yes. "Water"? No.
Mining isn't an easy thing even here on Earth - a maintenance-prone task that runs through lots of consumables - let alone on Mars where you have to choose between horrible throughput for remote operation, or local operation with astronomical local labour costs. A number of Mars in-situ proposals have outright done away with the water side of the equation, opting to harvest CO2 from the atmosphere locally (splitting to CO and O2 in a SOFC, like MOXIE on Mars 2020), but shipping in the hydrogen to avoid the need for mining. Most of the mass of fuels like methane is the carbon, not the hydrogen.
If you're not onboard with SpaceX's not-at-all-secret long-term strategy, you shouldn't invest in SpaceX.
You just know that they're going to get to Mars and then, and only then, discover that they forgot to include a ladder ;)
Well, it's a bit dangerous, but the performance is indeed incredible...
Indeed. But part of the problem is that SpaceX wants to simultaneously be taken seriously as a reliable delivery service, and push the bounds for rapid, radical cost reduction. Even rockets blowing up on the test stand or failing during experimental landings comes across as bad press for them - even if they expect to have low odds of success. I've seen way too many comments and articles along the lines of "OMG, SpaceX crashed a landing, how can you think about sending up astronauts with a company that unreliable?", when the concept of "fail until you get it right" was always the plan with those landings.
If I were to start a rocket company it'd be in two parts. The first would be something like "Crazy Karen's Discount Rocket Emporium", and would go for a total Kerbal vibe, down to crudely spraypainted "This Way Up" notes on the side of stages, duct tape holding things in place on test stands, any interviews given in totally unprofessional clothing, etc. The sort of company that you'd be more surprised when things work than when they fail. The other would be your standard stuffy boring professional institution and would have a partnership with the kerbal-esque company, making clear that they acquire "promising but immature" technology from the other side, then invest their engineering resources on turning it into a refined and reliable experience for their launch service customers. All of the risky research efforts would be done by the first side.
It's effectively the same thing, but it'd make the delineation that all rocketry companies strive for explicit. You move fastest by taking risks rather than trying to avoid all failures, but you try to insulate the risk-taking side from the actual experience you offer paying consumers as much as you realistically can.
That's not what people were complaining about in the video. What people were complaining about was that they were landing right next to an exposed, filled propellant stage. You don't land a skyscraper-sized fireball-on-a-stick right next to a half billion dollar tank of fuel. That aspect was clearly stylized.
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.
This is not correct. Juno is planned to do some limited observation/a> of the Galilean moons. It's a side mission, not central to it's focus (and Juno is anything but optimized for it), but it's one of those cases where, if you're there and you have the hardware...
Concerning Europa (remember that this was before the recent news):
Yes. The thermal requirements are significant.
The cause is not the same reason as with comets (sublimation), Europa isn't on a sungrazing elliptical orbit. It's also not impact related, as the impact flash would have been seen, and the plumes wouldn't have been this frequent / long lasting.
It's pretty limited what you can gather from individual grains captured at hypersonic velocities and analyzed with spacecraft-sized instruments. Certainly there was no "clear evidence of life" from Enceladus - although it showed us some very promising things about the potential habitability of its oceans.
Personally, I'm not a believer in the theory that wherever there's liquid water, there's life. First off, it'd make the Fermi paradox even worse, as water is bloody everywhere. Secondly, I think it's incredibly naive. The argument goes, wherever we find water on Earth, we find life, and whereever we don't, we don't, so we should expect that with the universe. But that says nothing about how life came about. Sure, LAWKI requires hydrogen, and water is the most convenient source of hydrogen, so obviously that's going to form the boundaries of where life has spread to. But where it's spread to says nothing about where it originated, or what it looked like when it did. We have no reason to think that the entire wet surface of Earth just spontaneously erupted into life; we certainly don't see anything resembling this in laboratory abiogenesis experiments. So what were the specific conditions that brought life about? I think it's a safe bet that they were rare. Quite likely no longer present on Earth, as Earth was a radically different place back then. And quite possibly rare in the universe as a whole. Little bursts of luck separated by great relativistic distances.
Indeed, bodies like Europa (and the many other bodies confirmed to or believed to have subsurface water in our solar system) should help answer these questions. I'm also exceedingly curious about what's gone on with alternative solvents and polymeric compounds, such as at the surface of Titan (I find the cyanide chemistry there fascinating, it seems to be extremely flexible).
Since when does division by zero yield precisely zero?
The video is clearly stylized and not meant to be taken that literally. Unless you think the arrival of the spacecraft is supposed to make Mars spin until it develops oceans ;)
That said, while there's much to like, there's one aspect of it that's really clawing at me... the fact that they plan to make it out of composites. Including the LOX tank. We've never succeeded (and failed multiple times) at making flight-intent LOX tanks for orbital rockets. And they want to make the first time be on what's by far the largest rocket ever built? Without a lining?
Is it worth mentioning that they just had an explosion somehow related to the only major carbon fiber component in the Falcon 9 in a LOX tank?
CF becomes brittle in LOX. It leaks. And most concerningly, it's impact / shock sensitive in LOX. At atmospheric pressure it usually won't do a self-sustained burn on impact, but it chars on impact, and even that alone would be bad. But they plan to have significant pressure as well. He mentions briefly that they expect this to be one of the biggest challenges, getting stable coatings and the like. I think that's an understatement.
I just don't want to see the largest rocket ever built turn into the largest flying fireball on Earth. I don't trust composites with LOX. Composite cryogenics tanks are an active research topic, and they're making progress, but it's not a solved problem.
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.
I think you're confused. Plumes means "in space". The whole benefit of plumes is that you don't need to go under the ice at all, you can do flybies to collect ice particles, or have a lander observe and sample the plumes at the surface. The key is that it means a recent connection between the depths and the surface, and that would be huge for simplifying exploration.
We're nowhere near to being able to launching an ice boring / swimming probe. If I recall correctly the last thing I read on the subject, however, the most promising means for communicating with such a probe on an affordable mass budget was.... not communicating with it. Aka, having it fully autonomous - melting its way down, sampling/observing the ocean, then re-melting its way back to the surface - then and only then transmitting. The waiting period with no data would be stressful (as if it failed you'd never know why), but it could potentially be used on almost any icy solid body regardless of the ice thickness.
It's also possible that there's liquid water much closer to the surface than the global ocean. There are some inferred lakes at a depth of only a few kilometers, which is potentially short enough for a probe to maintain a fiber connection with the surface. And after JUICE and Clipper, we may well have found locations that are even shallower.
Right. Because brief observations from an already present spacecraft that could help make critical design decisions about an upcoming multibillion dollar mission are an absurdity.
Look, we know Juno wasn't designed for this sort of mission and is not well equipped or positioned for it. But if researchers determine that its observations could help pinpoint more details of the plumes, then yes, they damn well should regardless of whether "tomhath at slashdot" considers that to be "real science" (apparently some vague category that he doesn't even feel the need to expand upon -- apparently planetary scientists have been working on "fake science" all these years, who knew?).
They're already ahead of you :) Clipper will likely include the SUDA instrument for doing just that - roughly equivalent to Cassini's CDA
I don't disagree with a word that you wrote. :)
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.
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.
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.
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.
"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.
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.