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A rocket a day keeps the high costs away (1993)

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Re: A rocket a day keeps the high costs away (1993)

#21

Post by wolfram74 »

flashback2199 wrote: post #20
lkbm wrote: post #17

Earlier quoted context omitted.

There are thousands of long-haul flights—and something like 100k flights overall—per day. If we're doing 10k+ rocket launches per day, then that's a huge problem. If we're doing 1 per day, it's a rounding error. This is premature optimization. (Either way, the solution, of course, is a carbon tax to price in the emissions.)

Edit: I messed up the math - didn't see 100k per day of flights...

one upside is many modern rockets use methane, synthesizing methane with pv/wind power would be much lower impact, depending on how much of the exhaust is actually at escape velocity it could be very slightly carbon negative, like new forged steel with ore prepped with clean hydrogen.

Re: A rocket a day keeps the high costs away (1993)

#22

Post by cma »

lkbm wrote: post #17
flashback2199 wrote: post #14

[flagged]

There are thousands of long-haul flights—and something like 100k flights overall—per day. If we're doing 10k+ rocket launches per day, then that's a huge problem. If we're doing 1 per day, it's a rounding error. This is premature optimization. (Either way, the solution, of course, is a carbon tax to price in the emissions.)

Elon said by 2028 they will be in active passenger service replacing long haul aviation for cheaper than a business class ticket.

Re: A rocket a day keeps the high costs away (1993)

#23

Post by wolfram74 »

joebig wrote: post #18
sabareesh wrote: post #15

Earlier quoted context omitted.

If we can generate Methane for example from CO2 in the atmosphere this could potentially solve this problem

Oxides are incredibly stable chemically. Any further conversion or sequestration process is guaranteed by thermodynamics to be very energy-intensive.

we know transitioning to pv/wind is going to lead to some months where we've got megawatt-hours coming out of our ears. If the only problem is energy cost, that won't be a problem long.

Re: A rocket a day keeps the high costs away (1993)

#24

Post by flashback2199 »

wolfram74 wrote: post #21
flashback2199 wrote: post #20

Earlier quoted context omitted.

Edit: I messed up the math - didn't see 100k per day of flights...

one upside is many modern rockets use methane, synthesizing methane with pv/wind power would be much lower impact, depending on how much of the exhaust is actually at escape velocity it could be very slightly carbon negative, like new forged steel with ore prepped with clean hydrogen.

Correct me if I'm wrong but I am under the impression that Starship does not use that, the least expensive fuels for rockets are highly CO2 emitting, and the least expensive fuels are what will get rolled out in mass numbers if SpaceX, Blue Origin, and others succeed in building a rocket transportation industry.

Re: A rocket a day keeps the high costs away (1993)

#25

Post by actinium226 »

flashback2199 wrote: post #14

[flagged]

These are not great comparison numbers. When rockets fly passengers it's ~4 people as compared to ~200 for a plane.

A modern 737 has a max fuel load of almost 30000L of jet fuel [1].

The density of jet fuel is 775-840 g/L [2]. Let's take 800g/L so that we can just multiply the lead numbers - that gives 24,000 kg of fuel.

According to spaceflight101 [3], the Falcon 9 uses 123,570 kg of RP-1 (similar to jet fuel) in the first stage and 32,300 kg of RP-1 in the second stage for a total of 155,870 kg, which is about 6.5x the total fuel load on the 737.

Falcon 9 launched 98 times last year (which includes some Falcon Heavy flights which have more fuel, but I don't think it changes the big picture here).

There are 5000 737's in active service [4]. Most of them are probably flying several times per day, but if we just assume once per day that's 1,825,000 flights. That's almost 3000x the amount of CO2 as produced by all those F9 flights. And that's just 737s.

1. https://en.wikipedia.org/wiki/Boeing_737#Specifications

2. https://en.wikipedia.org/wiki/Jet_fuel

3. https://spaceflight101.com/spacerockets/falcon-9-ft/

4. https://simpleflying.com/boeing-737-in-service-stored/

Re: A rocket a day keeps the high costs away (1993)

#26

Post by flashback2199 »

lkbm wrote: post #17
flashback2199 wrote: post #14

[flagged]

There are thousands of long-haul flights—and something like 100k flights overall—per day. If we're doing 10k+ rocket launches per day, then that's a huge problem. If we're doing 1 per day, it's a rounding error. This is premature optimization. (Either way, the solution, of course, is a carbon tax to price in the emissions.)

Just as 100k jet airplane flights per day would have been unimaginable in the ~50s when the jet airliner industry started, I actually can imagine a near future where many more than 10k rockets per day are launched, if the industry has it's way and succeeds in reducing costs dramatically.

Re: A rocket a day keeps the high costs away (1993)

#27

Post by flashback2199 »

actinium226 wrote: post #25
flashback2199 wrote: post #14

[flagged]

These are not great comparison numbers. When rockets fly passengers it's ~4 people as compared to ~200 for a plane. A modern 737 has a max fuel load of almost 30000L of jet fuel [1]. The density of jet fuel is 775-840 g/L [2]. Let's take 800g/L so that we can just multiply the lead numbers - that gives 24,000 kg of fuel. According to spaceflight101 [3], the Falcon 9 uses 123,570 kg of RP-1 (similar to jet fuel) in th…

Right, I think people are misunderstanding a key point here, which is that SpaceX, Blue Origin, etc would really like to see rockets be an alternative to airplanes, in which case we are talking about a dramatically increased number of launches.

Re: A rocket a day keeps the high costs away (1993)

#29

Post by LeifCarrotson »

cma wrote: post #22
lkbm wrote: post #17

Earlier quoted context omitted.

There are thousands of long-haul flights—and something like 100k flights overall—per day. If we're doing 10k+ rocket launches per day, then that's a huge problem. If we're doing 1 per day, it's a rounding error. This is premature optimization. (Either way, the solution, of course, is a carbon tax to price in the emissions.)

Elon said by 2028 they will be in active passenger service replacing long haul aviation for cheaper than a business class ticket.

That's not realistic simply because of the carbon requirements. Long haul aviation only burns a couple hundred kg of jet fuel per passenger. (I don't know how the top-level comment is calculating 1-3 tonnes of CO2 per passenger, Contrail effects? Construction of the plane? Altitude? Incomplete combustion? but a 250-passenger 787 doesn't carry 750,000 kg of fuel, it only fits 100,000 kg at most, plus plenty of reserve capacity). The flight only costs $100-$200 per person in fuel.

Rocketry is far less efficient than a modern high-bypass turbofan.

NASA can afford to buy 75,000 kg of methane per astronaut. Even if the rocket was amortized to zero over infinite flights, and had zero maintenance costs, even if crew cost nothing and airport/spaceport leases cost nothing, thermodynamics insists that you still have to buy $100,000 worth of RP-1 rocket fuel. A business class ticket cannot buy enough carbon to support 75,000 kg of emissions.

Re: A rocket a day keeps the high costs away (1993)

#30

Post by avhon1 »

flashback2199 wrote: post #24
wolfram74 wrote: post #21

Earlier quoted context omitted.

one upside is many modern rockets use methane, synthesizing methane with pv/wind power would be much lower impact, depending on how much of the exhaust is actually at escape velocity it could be very slightly carbon negative, like new forged steel with ore prepped with clean hydrogen.

Correct me if I'm wrong but I am under the impression that Starship does not use that, the least expensive fuels for rockets are highly CO2 emitting, and the least expensive fuels are what will get rolled out in mass numbers if SpaceX, Blue Origin, and others succeed in building a rocket transportation industry.

Starship, Blue Origin's upcoming heavy-lift rocket New Glenn, and United Launch Alliance's upcoming heavy-lift rocket Vulcan, are all powered by methane and oxygen.
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