Quote from: Elmar Moelzer on 04/01/2018 04:31 pmI think that the best argument for a BFS based SSTO with a small payload is for SpaceX to gather a lot of experience with it relatively quickly by using it to launch their Starlink constellation. It could potentially allow for a lot of launches in a relatively short time frame.Starlink polar orbit requires considerable more delta-v than just "barely reaching some orbit" which BFS might be able to do.No way BFS will reach starlink polar orbit without the booster, so could we stop polluting all threads with this BFS-SSTO nonsense, please.
I think that the best argument for a BFS based SSTO with a small payload is for SpaceX to gather a lot of experience with it relatively quickly by using it to launch their Starlink constellation. It could potentially allow for a lot of launches in a relatively short time frame.
Quote from: billh on 04/02/2018 05:47 pmQuote from: speedevil on 04/02/2018 05:13 pmQuote from: Ludus on 04/02/2018 05:06 pmWhat’s the business case for P2P on earth? If the per flight cost is $5M, which is fantastically low for space launch purposes and quite low enough for space tourism, it still doesn’t seem to fit P2P. It doesn't.The basis of P2P on earth is launch costs well under $1M, and lots of people fly.'Cheaper than economy air fare' - for around a thousand people, flying the airframe a dozen times a day, can really add up to a profitable vehicle.May it start out rather more expensive than this - likely.What this actually says to me is that BFR is probably oversized for an initial P2P suborbital passenger service. What you need is a fully reusable vehicle that can carry maybe 50-100 people at super premium fares. It will be cheaper to build, cheaper to operate, require cheaper infrastructure, and generate the same revenues as 1000 people paying an economy fare.No, building ANOTHER COMPLETELY DIFFERENT VEHICLE is not cheaper. It is much more expensive.And for super premium fares, the people also want to have super premium conditions. Lots of space/person.
Quote from: speedevil on 04/02/2018 05:13 pmQuote from: Ludus on 04/02/2018 05:06 pmWhat’s the business case for P2P on earth? If the per flight cost is $5M, which is fantastically low for space launch purposes and quite low enough for space tourism, it still doesn’t seem to fit P2P. It doesn't.The basis of P2P on earth is launch costs well under $1M, and lots of people fly.'Cheaper than economy air fare' - for around a thousand people, flying the airframe a dozen times a day, can really add up to a profitable vehicle.May it start out rather more expensive than this - likely.What this actually says to me is that BFR is probably oversized for an initial P2P suborbital passenger service. What you need is a fully reusable vehicle that can carry maybe 50-100 people at super premium fares. It will be cheaper to build, cheaper to operate, require cheaper infrastructure, and generate the same revenues as 1000 people paying an economy fare.
Quote from: Ludus on 04/02/2018 05:06 pmWhat’s the business case for P2P on earth? If the per flight cost is $5M, which is fantastically low for space launch purposes and quite low enough for space tourism, it still doesn’t seem to fit P2P. It doesn't.The basis of P2P on earth is launch costs well under $1M, and lots of people fly.'Cheaper than economy air fare' - for around a thousand people, flying the airframe a dozen times a day, can really add up to a profitable vehicle.May it start out rather more expensive than this - likely.
What’s the business case for P2P on earth? If the per flight cost is $5M, which is fantastically low for space launch purposes and quite low enough for space tourism, it still doesn’t seem to fit P2P.
"since you dump a bunch of reentry velocity using a heat shield."How is this possible? The entry angle from a minimum-energy ICBM trajectory is around 20 degrees.
"since you dump a bunch of reentry velocity using a heat shield."How is this possible? The entry angle from a minimum-energy ICBM trajectory is around 20 degrees. Mercury and Gemini entered at about 8 degrees at Mach 25 and subjected the astronauts to about 8g. At Mach 22 and 20 degrees the passengers will be smashed against the nose. If you use aerodynamic lift to shallow out the trajectory, the passengers will be smashed again the floor. Has Elon explained how he plans to deal with reentry?
Retro propulsion before you start reentry.
Quote from: Alkan on 04/02/2018 07:59 pmRetro propulsion before you start reentry.This is not required if you are doing near-orbital entries.The BFS gently settles into the atmosphere, its effective weight counteracted by lift until it's at around half or so of orbital speed.After this, it gradually sinks, all at fairly low G.
BFS will hold far more than 100 passengers. Also, remember that these flights are only 30-60 minutes in length. Individual passengers don’t require near as much niceties and space for very short haul flights. Think business class space on a regional jet.
What’s the business case for P2P on earth?
I get that there may be a theoretical break even with large numbers of passengers at relatively low prices. Say 500 at $5000 business class each gets to $2.5M, about halfway to $5M. It’s just not clear that there is that much demand for those tickets. How much more other inconvenience will a passenger tolerate for the convenience of a much shorter travel time? Different departure and arrival cities? Different travel day? In a sense it’s a bet on hub and spoke for long distance which didn’t work out well for the A380.
>As for size I'll note that people though Concorde was the smallest vehicle that was viable for this service (despite the French initially wanting to build it smaller). AIUI most "Concorde II" design studies have gone bigger thinking at least 300 passengers.
At what altitude would the noise of BFR flying over inhabited land be acceptable? I think once BFR/BFS is certified for commercial passenger service it should also be certified to fly over land, except for the noise.
Quote from: guckyfan on 04/05/2018 06:18 amAt what altitude would the noise of BFR flying over inhabited land be acceptable? I think once BFR/BFS is certified for commercial passenger service it should also be certified to fly over land, except for the noise.Overflight altitude is not so much a noise issue, launch and reentry are the loud parts. Only the area around the launch/landing site will have issues with noise.
Quote from: envy887 on 04/05/2018 01:05 pmQuote from: guckyfan on 04/05/2018 06:18 amAt what altitude would the noise of BFR flying over inhabited land be acceptable? I think once BFR/BFS is certified for commercial passenger service it should also be certified to fly over land, except for the noise.Overflight altitude is not so much a noise issue, launch and reentry are the loud parts. Only the area around the launch/landing site will have issues with noise.I am thinking of the launch phase where the engines are running and they are already quite high.Edit: Like launching from London and still suborbital over Scandinavia.
Quote from: guckyfan on 04/05/2018 02:29 pmQuote from: envy887 on 04/05/2018 01:05 pmQuote from: guckyfan on 04/05/2018 06:18 amAt what altitude would the noise of BFR flying over inhabited land be acceptable? I think once BFR/BFS is certified for commercial passenger service it should also be certified to fly over land, except for the noise.Overflight altitude is not so much a noise issue, launch and reentry are the loud parts. Only the area around the launch/landing site will have issues with noise.I am thinking of the launch phase where the engines are running and they are already quite high.Edit: Like launching from London and still suborbital over Scandinavia.BFR will typically leave the sensible atmosphere before it leaves the noise footprint of it's own launchpad. At that point, even if it's still suborbital, there is no real noise propogation to the surface.The only noise issue is the sonic boom along the entry corridors for the space ship and the booster, and launch noise immediately around the launch site.
Quote from: envy887 on 04/05/2018 03:39 pmBFR will typically leave the sensible atmosphere before it leaves the noise footprint of it's own launchpad. At that point, even if it's still suborbital, there is no real noise propogation to the surface.The only noise issue is the sonic boom along the entry corridors for the space ship and the booster, and launch noise immediately around the launch site.I thought a platform in the North Sea might have made a suitable launch site. It could probably be positioned sufficiently far away from land so as not to cause major problems during take-off, but the final stages of re-entry with sonic booms across Ireland and England would be a show stopper.
BFR will typically leave the sensible atmosphere before it leaves the noise footprint of it's own launchpad. At that point, even if it's still suborbital, there is no real noise propogation to the surface.The only noise issue is the sonic boom along the entry corridors for the space ship and the booster, and launch noise immediately around the launch site.