Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video] • Hacker News Board

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#11

Post by csl » Mon, Apr 23, 2018, 6:16 PM UTC

Semirhage wrote: post #5

What would be the environmental impact of ubiquitous rocket launches for business travel?

The BFR runs on a mix of liquid oxygen and methane, according to Wikipedia.

Ignoring obvious scalability problems, wouldn’t it be possible to manufacture that with a pretty decent environmental footprint from various carbon neutral bio sources?

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#12

Post by DiThi » Mon, Apr 23, 2018, 6:17 PM UTC

Semirhage wrote: post #5

What would be the environmental impact of ubiquitous rocket launches for business travel?

It will eventually be very low, much lower than planes. The same technology that is being developed to make propellant on Mars can be used on Earth to extract CO2 from the air and/or sea water. A few squared km of solar panels on floating structures can produce enough propellant for one BFR trip a day.

The same propellant (methane) can also be used on planes, eventually, so BFR will bring many technologies advances independently of the outcome of the project.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#13

Post by InclinedPlane » Mon, Apr 23, 2018, 6:20 PM UTC

Semirhage wrote: post #5

What would be the environmental impact of ubiquitous rocket launches for business travel?

Pretty similar to the environmental impact of jumbo jets. A 777-200LR burns around 145.5 tonnes of jet fuel to transport around 300 people 15,800 km. That's 31 grams of fuel per passenger-km, about 86% of the fuel is Carbon so that's roughly 27 grams of Carbon emissions per passenger-km. A BFR/BFS contains about 3,240 tonnes of propellant and allegedly will be able to transport around 850 passengers up to 20,000 km. The oxidizer to fuel ratio of the Raptor engine is currently unknown but it's likely it's around 3:1, meaning that 1/4 of the total propellant is Methane while 3/4 is liquid Oxygen, giving 810 of Methane per trip, give or take. Methane is 75% Carbon so a BFR flight should produce roughly 608 tonnes of Carbon emissions, or 36 grams per passenger-km (30% more than a conventional flight, seemingly).

However, it's possible to generate Methane fairly easily using solar power, so such launches have the potential to be nominally carbon neutral with some investment.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#14

Post by bmcusick » Mon, Apr 23, 2018, 6:28 PM UTC

The main thing I'm thinking of is noise pollution. You think living near an airport is loud? I cannot even imagine what living near a BFR spaceport would be like. For coastal cities maybe it would be worth it to build a landing pad on an ocean platform some miles out to sea, but what about for cities like Atlanta or Beijing? There's nowhere around them to build that isn't already a suburb.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#15

Post by mkirklions » Mon, Apr 23, 2018, 6:29 PM UTC

SpaceX is promising something that is feasibly decades away?

Do people still believe in Elon? Or have we figured out these are advertisements.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#16

Post by Retric » Mon, Apr 23, 2018, 6:35 PM UTC

btcindivist wrote: post #7

Semirhage wrote: post #5

What would be the environmental impact of ubiquitous rocket launches for business travel?

Depends on how many. Flying airplanes is around 1-2% of our total CO2 footprint. Of course, for an individual, doing 1 intercontinental flight with a full plane is equivalent to months if not a year of driving a car to work every day, but in total, not many people fly. Depending on the efficiency of the rocket and the reduced number of people doing this, the numbers shouldn't be that much higher.

That's not really the case. Per passenger mile commercial aircraft get ~70MPG with longer flights tending to have better fuel economy. The trend is really interesting: http://www.slate.com/content/dam/slate/articles/business/the...

So, they are actually very efficient transportation for long trips. Absolute worst case flying around the world is 24,901 mi which uses the same fuel per person as a 35 MPG car commuting 26 miles each way for one year.

PS: You can double check this by considering ~1/3 of the cost of a seat as being spent on fuel.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#17

Post by randyrand » Mon, Apr 23, 2018, 6:36 PM UTC

mkirklions wrote: post #15

SpaceX is promising something that is feasibly decades away? Do people still believe in Elon? Or have we figured out these are advertisements.

He's not promising it. Despite the optimistic language, its a somewhat-realistic dream that he'd like to do and plans to work on. At least that seems obvious to me.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#18

Post by larrydag » Mon, Apr 23, 2018, 6:41 PM UTC

As a business model I think SpaceX should be a manufacturer and not in the transportation business akin to Boeing or Airbus. There is a ton of logistics involved in transporting people globally. Of course there is the safety issues as well.

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#19

Post by wcoenen » Mon, Apr 23, 2018, 6:42 PM UTC

csl wrote: post #11

Semirhage wrote: post #5

What would be the environmental impact of ubiquitous rocket launches for business travel?

The BFR runs on a mix of liquid oxygen and methane, according to Wikipedia. Ignoring obvious scalability problems, wouldn’t it be possible to manufacture that with a pretty decent environmental footprint from various carbon neutral bio sources?

SpaceX plans to refuel the BFR on Mars with methane and oxygen produced via the Sabatier process and electrolysis [1]. They might do the same thing on Earth, even if only for the bragging rights of being carbon neutral.

[1] https://en.wikipedia.org/wiki/Sabatier_reaction#Manufacturin...

Re: Gwynne Shotwell: SpaceX's Plan to Fly You Across the Globe in 30 Minutes [video]

#20

Post by et2o » Mon, Apr 23, 2018, 6:43 PM UTC

byw wrote: post #10

Symmetry wrote: post #8

Earlier quoted context omitted.

Not too huge. This person[1] did some math and found that a BFR trip across the world should take 40% to 240% as much carbon as a regular plane flight. For short trips this would be worse, though, because a plane's range goes up almost linearly with fuel use while a rocket's goes up much faster than linearly. Rockets that use solid boosters like the Space Shuttle, SLS, or Atlas V do a good amount of ozone damage as t…

Also I'm not sure where SpaceX gets its methane from. If it's from above-surface sources wouldn't its net carbon contribution essentially be zero?

Did a little googling. Methane is primarily obtained from natural gas fields which are below ground. Atmospheric concentrations are relatively low (on order of parts per billion) although it is still an important greenhouse gas (30x more potent than CO2 per ton). There's a lot of ongoing research into generating CH4 from CO2 using renewable energy but it's relatively energy intensive to date.