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Comment by lkbm | Hacker News Reader

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.)

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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.

At such scale it would be a different (and in some cases potentially much more dangerous :D) technology - huge hydrolox SSTOs, launch loops, rotovators, nuclear lightbulb SSTOs, maybe even orbital elevators.

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.

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.

starship uses methalox, a combination of methane and oxygen. I'm far from an expert, but my understanding is the methane comes from refining LNG.

That's generally where methane comes from today, but in time it may come from captured CO₂, e.g. see https://terraformindustries.com/ (disclaimer: I am a minor investor).

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.

Starship has the size to carry about 400 passengers. Both stages together carry about 5,000t of propellant. But over 3/4 of that is liquid oxygen, and most of that is the first stage. The second stage alone with 1200t of propellant can't put humans into orbit, but it does have a range comparable to that of a 787. So 300t of liquid methane will get 400 passengers about as far as a 787 can get 250 passengers with 100t of kerosene.

A starship ticket could theoretically cost <3x the price of an airline ticket.

A rocket may be less efficient than a turbofan but it gains it back by coasting through space for all but 3 minutes rather than pushing through air for the entire flight.

Starship has nowhere near the capacity to carry 400 passengers - people are not sardines you can just stuff into the rocket like you can satellites. You need plenty of equipment per person for manned spaceflight. Much more so if you want to compete with business class flying.

Also, the total travel time would be horrible, since you can't have a rocket launch/landing facility anywhere near a city, and loading and unloading a rocket is an immensely time consuming process. Plus, you never ever load people into a an already fuelled rocket.

It's not as if 40,000 feet is survivable without a flight suit and parachute, yet airliners don't provide those. And 400 people per starship is much more spacious than the area you get in economy class.

Travel time is the main reason to use Starship. It might add 30 minutes extra on either end, but if it saves 10 hours of flight tine...

Loading people into an already fueled rocket is standard operating procedure for every rocket except Falcon.

It doesn't gain anything back, what are you on. Before landing it has to shed all the speed it gained that was needed for the ballistic trajectory. That energy is lost. Orbital or suborbital flights will never, ever be competitive to flying with regards to required energy expended.

It gains efficiency compared with an airplane by spending most its trajectory outside of atmosphere with no air resistance.

No it does not, because thanks to atmosphere wings on an airplane generate lift. And they do it more efficient than any kind of engine known to the mankind

Yes, an airplane can climb much more efficiently than a rocket. So on a 300km flight where all it is doing is climbing and descending it's way more efficient than a rocket.

But for a 10,000km flight the airplane expends almost all of its fuel coasting rather than climbing.

Luckily we don't have to rely on assertions. If I'm wrong, there should be an obvious error in my math (which is trivial) or facts (which is on Wikipedia). Please point it out.

You think an airplane doesn't need lift when in a level flight? :) Thanks to the atmosphere an airplane doesn't need to carry its own oxidizer, either. I'll leave to you to check how much oxidizer a Falcon rocket needs to carry for every ton of fuel.

We don't have to wait long to prove you wrong. Starship using just ~1200t of Methane and 150t of payload capacity will fly East (the long way) from Texas to Hawaii in 90 minutes. That's 8x as much payload 3x as far as a 787 can do with its 100t of fuel.

1.5 hour trips to Hawaii from the US would be crazy fun.

That's 1.5 hours going the long way around. It'd be under 30 going west rather than east.

That's more efficient if most of your trips require you to go 90% of the way around the planet (maybe?). Or for sure if you coast twenty times around the planet.

But half the circumference of earth is not that far.

Airliners with extended range tanks are much less efficient than normal airliners, since they both decrease capacity and increase consumption. That's the range where Starship becomes competitive, basically trans-Pacific or further.

I estimate to hit the 2028 in active passenger service timeframe they would have probably have needed at least thousands of flights by now demonstrating safety with a perfect track record.

There are also other benefits - avoiding weather along the route, taking a straight road where an airplane needs to take a longer route for political or safety reasons, etc.

Elon says many things, but this is one of the silliest ideas.

The experience of such a flight would be horrible. It all starts some weeks or months before with an extremely thorough physical check-up to make sure you are still able to withstand a rocket launch. On the day, you drive/sail to the middle of nowhere, at least an houror two out from any major city. Then, you get dressed into a used space suit - this takes experienced astronauts a good 10 minutes. You then board the rocket. Once everyone else is boarded and some pre-flight checks are successful, the fuelling starts. It will take a few hours, so hopefully they have good on-board entertainment.

Then, finally the rocket is ready to launch, and you get shot up into the atmosphere at an acceleration that is likely to make you pass out. Of course, this all happens with extremely tight noise canceling headphones to prevent your eardrums from bursting. But it's OK, you'll only wear them for an hour or so, and they may even allow you to take them off for a few minutes while you're coasting in the upper atmosphere. Then the deceleration will be just as enjoyable on the way down, of course. After you disembark and off the suit, you're now just a few short hours away from your actual destination.

There is 0 chance this will ever be allowed as a service for consumers, or that it would ever compete with business flights. It might make a cool tourism experience, but probably just up and down at the same place, no point in actually moving around.

If I had a list of "Elon said by x we will have y"...

When did he say that? That might be when they’re planning a demonstration, but it ain’t gonna be regular airline service then, purely for regulatory reasons if not the fact you’d need like 100,000 Starship launches to prove it’ll be safe enough.

I think most people familiar with space stuff, even ardent Musk supporters, don't really see that panning out. Even putting aside the pollution, there are too many logistical issues when it comes to spreading out all those launch sites and resupplying them.

The rocket transport service they're working on with the DoD is the only thing that we might see demonstrated by then but not really used since there aren't many things so valuable as to need it. That too only because the DoD will probably be willing to pay for the Starship to be scrapped after landing, as unless they build up the infrastructure to fuel and launch the rocket, it's stuck there.

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