BFR concepts and ideas thread.

[mikegarrison]

We already talked about this. Here's why it won't work:

Way too expensive. Musk keeps going on about how gloriously cheep it will be if it's fully reusable, but guess what is already fully reusable? Airplanes. He would have to get the per trip costs down to something close to what current airplane tickets cost.

People will pay for speed, which is they take airplanes and not boats, but they won't pay all that much for speed, which is why there are no supersonic airliners anymore.

[Rakaydos]

16 minutes ago, mikegarrison said:

We already talked about this. Here's why it won't work:

Way too expensive. Musk keeps going on about how gloriously cheep it will be if it's fully reusable, but guess what is already fully reusable? Airplanes. He would have to get the per trip costs down to something close to what current airplane tickets cost.

People will pay for speed, which is they take airplanes and not boats, but they won't pay all that much for speed, which is why there are no supersonic airliners anymore.

That explains why BFR will never replace regional airlines, but that says nothing about intercontenental flights. The fuel to keep a plane in the air for 10-14 hours despite air resistance is more expensive than the fuel needed to boost BFS into a suborbital hop, which means all else being equal the BFR is actually cheaper.

Edited September 10, 2018 by Rakaydos

[mikegarrison]

1 minute ago, Rakaydos said:

That explains why BFR will never replace regional airlines, but that says nothing about intercontenental flights. The fuel to keep a plane in the air for 10-14 hours despite air resistance is more expensive than the fuel needed to boost BFS into a suborbital hop, which means all else being equal the FR is actually cheaper.

No it's not. That's just ridiculous. A full fuel load on an A380 is 570,000 lb. A Falcon F9 first stage has 270,000 lb of kerosene. Are you saying that BFR is going to have no more than twice as much fuel as an F9? Sure, I know it's liquid methane rather than kerosene, but still.

[Rakaydos]

5 minutes ago, mikegarrison said:

No it's not. That's just ridiculous. A full fuel load on an A380 is 570,000 lb. A Falcon F9 first stage has 270,000 lb of kerosene. Are you saying that BFR is going to have no more than twice as much fuel as an F9? Sure, I know it's liquid methane rather than kerosene, but still.

https://www.eia.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm

3.81 dollars per Thousand Cubic Feet, industrial pricing, for Natural Gas. (methane)

https://www.eia.gov/dnav/pet/PET_SUM_MKT_A_EPPK_PTG_DPGAL_M.htm

3.292 dollars per GALLON for Kerosene.

 

[Mad Rocket Scientist]

Economically, it may not work. But physically, I can't come up with any reason it wouldn't work. By launching from barges, and the way sonic booms work when you're travelling vertically, it shouldn't be too loud, and it has such large margins that you could probably keep it full enough with fuel that it could do a gentler and safer hover landing instead of a suicide burn.

I'm not sure about reliability, but I can't see any clear reasons rocket engines couldn't be made as safe as jet engines, even if you had to add some weight to do it.

Economically, it all depends on how many times you can refly BFR+BFS before they need refurbishment or replacement. Fuel costs would definitely be better, but if you have to build a new one every 100 flights it won't matter. I also suspect that beyond a certain point people will start to pay for speed again, although I don't know where that point is. Plus, if there's any money in space tourism people might be willing to fly in it just for that.

[cubinator]

I think it can work, and it will be tried, but it will be a while before that point.

[RedKraken]

Point-to-point BFR will not use a full load of fuel.....

....a half load of fuel (1500t in the booster+500t in the ship) will get 30t payload (250 people and luggage?) most places on the planet (9700 m/s)

Estimate dry masses are 208t for the booster and 85t for the ship.

[mikegarrison]

52 minutes ago, Rakaydos said:

https://www.eia.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm

3.81 dollars per Thousand Cubic Feet, industrial pricing, for Natural Gas. (methane)

https://www.eia.gov/dnav/pet/PET_SUM_MKT_A_EPPK_PTG_DPGAL_M.htm

3.292 dollars per GALLON for Kerosene.

 

You are comparing the cost per volume of a gas and a liquid? What's the cost per pound?

[Xd the great]

The cost of a orbiral flight is 7 million for the bfr. For suborbital hops the heat shield can probably be swapped for something cheaper and lighter, so i say 6.5 million per hop. Still, there is the concern of aborting in flight, but whatever. 

Then, you have to worry about the payload. The orbital payload is somewhere like 145t, so for suborbital it will be higher. Assuming a passenger with luggage, supplies(snacks and water), and his/her chair is 100kg, you get 1500 passengers per hop. Cost per ticket will be about $4300. Quite expensive.

As for suicide burns, the bfr can probably be able to land at 1.3g if necessary, which is probably what you experience on a rollercoaster.

[mikegarrison]

Let's put is another way. SpaceX themselves said the cost of a launch will be $7M. Let's say it held 350 people (like a 777). That's $20,000/passenger.

[tater]

1 hour ago, Rakaydos said:

3.81 dollars per Thousand Cubic Feet, industrial pricing, for Natural Gas. (methane)

 

12 minutes ago, mikegarrison said:

You are comparing the cost per volume of a gas and a liquid? What's the cost per pound?

It's roughly 12 gallons per 1000 cubic feet of natural gas, apparently. So that is ~$0.32/gallon.

I see that LNG costs ~$3 per "Diesel Gallon Equivalent" which is 2.894 kg of LNG. So that's ~$1/kg. LOX is pennies per kg (15 cents?).

The total prop loading estimate was done on NSF at some point, and it's pretty cheap, several hundred grand.

[mikegarrison]

3 minutes ago, Xd the great said:

Assuming a passenger with luggage, supplies(snacks and water), and his/her chair is 100kg, you get 1500 passengers per hop.

No no no. Each passenger (plus luggage) on a plane today is on average over 100kg. That does not count for any cabin furnishings.

And 1500 per flight? Airlines seriously struggle to fill A380s with 500 people. More than half of those 500 are flying economy and their ticket price is maybe $2000 for anywhere in the world.

[Mad Rocket Scientist]

17 minutes ago, mikegarrison said:

You are comparing the cost per volume of a gas and a liquid? What's the cost per pound?

A thousand cubic feet of compressed natural gas weighs 3630kg, a thousand cubic feet of methane gas weighs 15.69kg. One gallon of kerosene weighs 3.03kg. I'm not sure if the original source for cost was compressed methane or not. Either way, it's cheaper. I don't know how expensive liquid oxygen is, but I imagine it would get much cheaper if it was used as much as SpaceX plans to use it.

[Rakaydos]

4 minutes ago, mikegarrison said:

Let's put is another way. SpaceX themselves said the cost of a launch will be $7M. Let's say it held 350 people (like a 777). That's $20,000/passenger.

Fuel costs for BFR are only 200,000 per flight. it has 40 rooms that can handle up to 6 passangers each. 480 people, gives a price under $500 per ticket.

The long distance plane ticket is $700.

[tater]

4 minutes ago, mikegarrison said:

Let's put is another way. SpaceX themselves said the cost of a launch will be $7M. Let's say it held 350 people (like a 777). That's $20,000/passenger.

That's an orbital launch.

Presumably wear and tear is different suborbital vs orbital, so the number of flights to amortize the vehicle cost changes (which is most of the launch cost).

I'm certainly not sanguine about P2P being a thing, BTW.

Shotwell said the cost per ticket was someplace between premium economy and business class, so call it 2-3 grand. You'd think that such a model would charge a premium for window seats, so make those full bore first class prices (north of 10k).

Still, the math has always seemed hinky to me. I did it and it worked out when the seats were a maxed out economy A380 (800 seats), lol. Short of that it seems unlikely to make ends meet.

 

3 minutes ago, Rakaydos said:

The long distance plane ticket is $700.

I think the baseliune number they are using is last minute, full cost premium economy. So NYC or LA to Sydney is more like $1500.

[sh1pman]

1 minute ago, Rakaydos said:

Fuel costs for BFR are only 200,000 per flight. it has 40 rooms that can handle up to 6 passangers each. 480 people, gives a price under $500 per ticket.

The long distance plane ticket is $700.

And what about the BFR deprecation? Operations cost? Maintenance? 

[Rakaydos]

Just now, sh1pman said:

And what about the BFR deprecation? Operations cost? Maintenance? 

There's a significant per-seat price delta. It can come out of that and still be cheaper.

[mikegarrison]

9 minutes ago, tater said:

That's an orbital launch.

Presumably wear and tear is different suborbital vs orbital, so the number of flights to amortize the vehicle cost changes (which is most of the launch cost).

If you (and SpaceX) are going play in this realm, you need to start thinking about cycles. One flight = one cycle. It's not going to be significantly different no matter how far you fly (Mars versus Hong Kong). Long distance airplanes are good for something like 30,000-40,000 cycles. That's how many trips the capital cost is amortized over. The most ambitious numbers I've seen for BFR is 1000 cycles. So the airplane gets 30-40 times as many trips to pay for itself.

[tater]

The original ITS concept gave a lifespan for boosters at 1000 flights, and the spaceship at something like 12 (for BLEO ops), I want to say it was 100 for LEO.

If the whole thing was optimized for suborbital, presumably they could get the 1000 for both stages. (I'm being hyper-optimistic to see if it's even possible in that case, lol).

Total cost for the 2 was supposed to be ~230 million.

That's 230k/flight.

Shotwell has not said 500 or 800 people, but more like 100 people on a flight, and they would make multiple flights in a day to beat a larger plane per day.

I can't see how that math works out. Heck, it doesn't seem to work out even if the vehicle cost was $0/flight.

 

 

1 minute ago, mikegarrison said:

If you (and SpaceX) are going play in this realm, you need to start thinking about cycles. One flight = one cycle. It's not going to be significantly different no matter how far you fly (Mars versus Hong Kong). Long distance airplanes are good for something like 30,000-40,000 cycles. That's how many trips the capital cost is amortized over. The most ambitious numbers I've seen for BFR is 1000 cycles. So the airplane gets 30-40 times as many trips to pay for itself.

Exactly. I'm spitballing best possible cases, I'm with you in thinking the math doesn't work.

In short, unless the thing has many hundreds of seats, I don't see how it could even come close to breaking even.

[Mad Rocket Scientist]

A couple of possibilities:

SpaceX has much more optimistic internal targets for reuse cycles.

SpaceX expects to make a much more durable (but heavier) version of BFR for e2e.

SpaceX expects that once they are mass producing BFR/BFS, they will become as cheap or cheaper than airplanes to produce.

SpaceX thinks they can drop operations costs massively over airplanes.

SpaceX expects people to pay much, much more for a flight than on a jet, at least in the beginning. I think this is the most likely case, either due to speed or due to taking a flight on a spaceship. I know I'd pay more for either, I just couldn't afford it. At least at the start, I expect tickets to be over $1 million.

[K^2]

5 hours ago, magnemoe said:

I saw it on an New Shepard video, space sickness would not be an issue, Vomit comet to lots of violent turns 

There are some high altitude, nearly sub-orbital aircraft proposals for which space sickness isn't an issue. BFR as transport will have to be ballistic. Ballistic suborbital trajectories, by necessity, include extended coasting times in which passengers experience microgravity. You're going to get at least half an hour of free fall, which is more than enough to develop space sickness in susceptible individuals. It's not as bad as start-and-go of vomit comets, but it is longer duration. A significant fraction of passengers will require medication, at very least, to avoid losing their previous meals.

[Vanamonde]

Overlapping BFR threads have been merged. 

[tater]

Somehow I skipped this post:

15 hours ago, mikegarrison said:

We already talked about this. Here's why it won't work:

Way too expensive. Musk keeps going on about how gloriously cheep it will be if it's fully reusable, but guess what is already fully reusable? Airplanes. He would have to get the per trip costs down to something close to what current airplane tickets cost.

Yeah, WRT the (now merged) thread about P2P,  I just can't see the numbers working. I'd pay a premium for speed (and space travel!), but as a "regular" person, any more than business class would be impossible. Note that the speed premium would be only for long haul flights to places like US to Asia, or LA-->Europe/Africa (LAX is closer to me than the East coast by a lot). I've done the Asia thing enough to hate it (I can't sleep sitting up, ever).

Shotwell said something less than business class, and clearly she has done the math, but it seems utterly impossible to me unless operating costs (including the airframes) are similar to aircraft.

Quote

People will pay for speed, which is they take airplanes and not boats, but they won't pay all that much for speed, which is why there are no supersonic airliners anymore.

Yeah, but it was a matter of how much they'd pay, I suppose.

In 2018 dollars, a Concorde flight was ~$16,000 (RT). That's nearly twice the current price for First Class. (NYC-London)

There's clearly a market for 1st and business class, it's just a matter of how many seats per route, per day. If I was trying to make this round peg fit into the square hole of reality, I'd be looking at those numbers, given the small number of seats they're talking about (100-something).

Edited September 11, 2018 by tater

[Cassel]

10 hours ago, Ultimate Steve said:

I can't imagine liquid hydrogen being used to fuel fighters and bombers any time soon.

This is because you do not understand the military way of thinking, the range is more important than anything that seems important to you.

https://www.quora.com/What-was-the-thinking-behind-the-external-fuel-tanks-on-the-T-34

[kerbiloid]

Just the internal fuel tank was kept small, enough for a battle itself, to keep te armored hull as small and light as possible.. 
While all additional fuel was outside.