Skylon

SpaceX Discussion Thread

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Nothing is built yet.

Due to the nature of spaceflight it'll always be less safe than atmospheric flight, higher pressure, higher fuel flow, more fuel, less stable structures and all. Gas turbines spool 10.000s of hours without failures before they are exchanged (and still working !), rocket engines have only demonstrated minutes, 10s of minutes in case of the Merlin so far. I am cool :-)

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1 hour ago, StarStreak2109 said:

There's one more thing. Well granted, on a long distance flight, it doesn't really matter but still, it is an inconvenience: You have to get to and from the point where your BFR flight takes off from and lands. I mean given how loud an F9 is, I imagine that the BFR is still a bit louder. You won't have that landing near any populated area (well not only from noise considerations, range safety as well, I guess). And I am not even taking about the effects of NIMBY-ism. So lets figure there is one place in Europe, three in the US, maybe four in Asia, one in the Gulf region and one in Australia. That still means that you first of all have to travel to whichever Airport is close to the launch site, then travel to the launchsite, have your 30min flight to wherever, and then travel to the nearest airport to fly to your ultimate destination. Whereas now you maybe have a feeder flight and then can relax on board your long distance flight. Granted it takes a bit longer, but I would guess with all the to and fro involving the BFR, your grand total travel time will not be that much shorter. No way that thing is landing anywhere near any city...

Yeah, this is the killer for both P2P passenger transport and P2P cargo transport. Getting to and from the transit point will take far longer than your actual flight, so where are the time savings, exactly?

I used to know a guy in the jewelry business who could get diamonds from a hub France overnight. No idea how, but he could do it. Supply chain management is an extremely detailed and refined area of business. If the supply chain can get diamonds across the Atlantic overnight, it's hard to imagine beating it for cargo with a couple of rockets.

Doing a single-stage BFS P2P system helps a little bit, but it's still got a long way to come.

1 hour ago, StarStreak2109 said:

BTW, if compared to regular airline travel, whats the CO2 footprint of a BFR taking off and landing? Also a consideration to take into account...

I think I've seen speculation about using solar and Sabatier to fuel the BFRs, at least partially...

5 hours ago, tater said:

Still, space tourism, unlike any other possible human spaceflight suggestion could actually make money. I used to think it was silly, but what else is there? In the 1950s and 60s, the idea of a von Braun S-1, with hundreds of crew seemed reasonable, because you need workers. Heck, you probably needed astrogators with punch cards and slide rules to work out the trajectories to the Moon base, lol. People are less needed now, and will only become even more superfluous for getting any work done.

Tourism is the killer app.

You just need someone who will lay out the dough for a destination in LEO.

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41 minutes ago, Green Baron said:

Outch.

Bad, very bad. Like 3 magnitudes higher than a B747 or A380 ? But there is no reliable data on bfr yet, could be 2.9 magnitudes ;-)

 

Elon said the CO2 and other stuff exhaust will be sucked up again because they use the atmosphere to generate the fuel or something.

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5 minutes ago, NSEP said:

Elon said the CO2 and other stuff exhaust will be sucked up again because they use the atmosphere to generate the fuel or something.

Yeah, he probably wants to test a hypothetical Mars fuel station thingy. We'll yet have to see, until then it can be doubted he extracts 3000tons of fuel from the atmosphere when he can just buy it around the corner ;-)

Edit: is anyone thinking about drawing fuel out of the atmosphere for classic applications, like cars or planes ? I mean, if that was running, i'd believe Elon's words ...

Edited by Green Baron

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13 minutes ago, Green Baron said:

Yeah, he probably wants to test a hypothetical Mars fuel station thingy. We'll yet have to see, until then it can be doubted he extracts 3000tons of fuel from the atmosphere when he can just buy it around the corner ;-)

Edit: is anyone thinking about drawing fuel out of the atmosphere for classic applications, like cars or planes ? I mean, if that was running, i'd believe Elon's words ...

You can get CHthat way, but it's very difficult to get larger hydrocarbons like octane synthetically. And cars won't run on pure octane anyway. Diesel is king, really, and there's no way to synthesize diesel.

But you can use atmospheric CO2 to get methane. I believe there are some plans to do that, backed by Gates....

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2 hours ago, StarStreak2109 said:

 

BTW, if compared to regular airline travel, whats the CO2 footprint of a BFR taking off and landing? Also a consideration to take into account...

I hate rubbish wifi. Not rewriting my whole post.

Does anyone know the fuelox ratio for methylox?

I think that the soot and related organics from f9 looked far nastier than any CO2 emission problem. Sure all kerolox rockets, but I've never seen the engjnes spewing out crap in such HD before. So I'll blame spacex :wink:

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27 minutes ago, sevenperforce said:

... and there's no way to synthesize diesel.

Sure there is. Fischer Tropsch conversion does it.

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44 minutes ago, sevenperforce said:

You just need someone who will lay out the dough for a destination in LEO.

Yeah, like I said, it requires serious cost reduction. I don;t think it's going to happen soon, mind you, I'm just saying it's the only case I can think of for having significant numbers of humans in space that makes any economic sense.

45 minutes ago, sevenperforce said:

Yeah, this is the killer for both P2P passenger transport and P2P cargo transport. Getting to and from the transit point will take far longer than your actual flight, so where are the time savings, exactly?

Have you ever flown across the Pacific? 30 min or an hour on each side of the trip on a boat is pretty small compared to the time in the metal tube right now. It's awful (unless you have a gajillion $ to spend on first class). Not that I think P2P is going to happen, mind you. They'd have to fly 1000s of times to get as much safety data as a fraction of a single day of airline traffic.

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39 minutes ago, sevenperforce said:

You can get CHthat way, but it's very difficult to get larger hydrocarbons like octane synthetically. And cars won't run on pure octane anyway. Diesel is king, really, and there's no way to synthesize diesel.

But you can use atmospheric CO2 to get methane. I believe there are some plans to do that, backed by Gates....

We've had the tech to synthesize diesel since the 40s at least...

Fischer Tropsch process can do it. Germany did it during WWII due to lack of oil, but they had plenty of coal to turn into fuels. Of course it only provided about 9% of their fuels during the war, but it's an old process.

Edited by Bill Phil

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1 hour ago, StarStreak2109 said:

Cause where they are going to launch from Boca Chica, which sits about 60 miles from the 3rd largest reserve of natural gas in the country. Natural gas currently is selling for $2.35 per MMBTU (27.096 cubic meters), they are burning off gas in the gulf of Mexico right now. A cubic meter has 16 grams/mole * 1000 liters/22.4 moles per liter  of gas, that translates to 0.714 * 27.096 = 19.075kg or $0.12 per kilogram. Thats equivilent to about $0.7 per gallon of gasoline or about 1/3 the price of kerosene. Of course natural gas is not pure methane, so they will have to scrub it. In addition its ISP is 9% higher than RP1 for two equivalent performance engines, this is due to ~1.5 additional C-H bonds relative to kerosene. So in total methane is going to cost them 1/3rd to 1/4th the price. Liquid methane is less dense than RP1 and has a higher storage pressure, so that they will need stronger storage vessels and a wider or taller spacecraft.

 


 

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32 minutes ago, Antstar said:

Does anyone know the fuelox ratio for methylox?

3.8.

Quote

I think that the soot and related organics from f9 looked far nastier than any CO2 emission problem. Sure all kerolox rockets, but I've never seen the engjnes spewing out crap in such HD before. So I'll blame spacex :wink:

What you're seeing is CO2 and a little bit of carbon-carbon. Basically graphite.

26 minutes ago, Green Baron said:
55 minutes ago, sevenperforce said:

...and there's no way to synthesize diesel.

Sure there is. Fischer Tropsch conversion does it.

Well color me an idiot.

23 minutes ago, tater said:

Yeah, like I said, it requires serious cost reduction. I don;t think it's going to happen soon, mind you, I'm just saying it's the only case I can think of for having significant numbers of humans in space that makes any economic sense.

I'm just saying that even with cost reduction for access to LEO, you still need a destination before tourism becomes a thing.

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In my mind E2E transport is a sales gimmick, sort of like that attachment that comes with your shop vacuum that you never use because you never figured out what its really for.

While Natural gas is available everywhere, if you are liquefying it from point sources off the coast, that's an awful lot of gas for any local pipeline.

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17 minutes ago, sevenperforce said:

Well color me an idiot.

Not at all, mate !

You helped me out with a basic physics error before ...

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41 minutes ago, sevenperforce said:

3.8.

What you're seeing is CO2 and a little bit of carbon-carbon. Basically graphite.

Thanks. So yeah, gonna be fuel rich.

I'm a chemist, but not a rocket scientist. I'd expect little CO. It should have time to disproportionate.  But wouldn't you get a lot of that microparticulate carbon they are blaming on modern efficient diesels and saying cause all kinds of bad lung things?

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44 minutes ago, sevenperforce said:

I'm just saying that even with cost reduction for access to LEO, you still need a destination before tourism becomes a thing.

Absolutely. Every single place for humans to go in space that we know of is someplace we build ahead of time (I’m looking at you, Mars, sorry). No place exists people can just show up to. 

Orbital tourism would be best served by a hab that rotates to provide some small effective gravity. Health is not an issue for short stays, the issue is eating, bathroom use, etc (easier for tourists without training). Not to mention 50% of astronauts get sick, which is not a good bet for a holiday. A zero-g area at the hub can allow as much of that as they like.

The Moon works for tourism eventually as well, I think.

Still, cost and safety matter a lot.

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9 minutes ago, tater said:

Orbital tourism would be best served by a hab that rotates to provide some small effective gravity. Health is not an issue for short stays, the issue is eating, bathroom use, etc (easier for tourists without training). Not to mention 50% of astronauts get sick, which is not a good bet for a holiday. A zero-g area at the hub can allow as much of that as they like.

The Moon works for tourism eventually as well, I think.

I would think spin-up and spin-down would be a better way to handle effective gravity. You'll have to do it for docking, anyway, and that will allow you to use a tumbling pigeon approach rather than a wheel.

Who's your target demographic?

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People who want a once in a lifetime experience. 

 

BTW the launch this week is now NET March 1 (Thursday).

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1 hour ago, tater said:

50% of astronauts get sick

As part of the package have them spend a week on a Schooner in the Caribbean.

Spirit_of_Bermuda.jpg

Problem solved. Of course for the Boca Chica you could contract out with the local shrimp boats and charter fishermen that run out of Isabel and SPI and pretty much the same effect.

 

 

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I'm told that it's hard to predict who will get sick, though people who get seasick might be more likely to have an issue. Even the guys I talked to who got sick said it was still awesome. Senator Garn told me when I asked if it was really cool, he said it was awesome, and also sort of sad. He said, "Imagine that you had your first experience with a woman, and someone afterwards says, 'Glad you liked that, you can never do it again.'" (and he got so sick up there they made a unit of space sickness where the worst possible space sickness was "1 Garn").

So even with sickness it has some allure.

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3 hours ago, PB666 said:

Cause where they are going to launch from Boca Chica, which sits about 60 miles from the 3rd largest reserve of natural gas in the country. 

Except that fuel (and presumably oxidizer) accounts for .1% of the price of Falcon 9 launch (but presumably more of a Falcon Heavy as it shouldn't cost 3 times as much as a Falcon 9, but use nearly 3 times as much fuel).  I'd expect that needing that much less carbon fiber fuel tanks thanks to methane's efficiency will be much more important than the price of methane.

Spacex has removed the biggest single cost of going into space, the price to manufacture a booster.  Fairing reuse was presumably an even lower level fruit.  I'd expect them to spend a great deal of time reducing launch costs, while fuel costs remain a non-issue (although it might make good PR: Elon has already tweeted about mass fractions).

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On the subject of hypervelocity crew and cargo transport....

If there was a market for high-speed P2P transport of the sort that the BFR is supposed to offer, wouldn't we have seen that niche being filled by some sort of airbreather by now?

Also on the topic of SpaceX:

DW-uWAhW4AAAoCK.jpg:large

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14 minutes ago, sevenperforce said:

On the subject of hypervelocity crew and cargo transport....

If there was a market for high-speed P2P transport of the sort that the BFR is supposed to offer, wouldn't we have seen that niche being filled by some sort of airbreather by now?

 

The reason BFR competes with long range transport but not short range is because air breathers need air, and air resistance is a female dog. Try making a KSP aircraft to reach the other launch center (not the island, the other crawlerway) in a reasonable amout of time. Then do it with a rocket.

Edited by Rakaydos

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35 minutes ago, sevenperforce said:

If there was a market for high-speed P2P transport of the sort that the BFR is supposed to offer, wouldn't we have seen that niche being filled by some sort of airbreather by now?

There used to be Concorde, at least. The short answer, is yes, it seems like people would pay for much more rapid transport, though to be honest, while faster, it's not 30 minutes to anywhere fast :D .

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