The other problem is that the BFR would carry 10 kt of fuel. Even a very small chance of that much fuel exploding anywhere near a major city is too much risk, so you'd have to put them well away from population centers. So you can tack on a couple hours to the spaceport on each end.

SpaceX's vision was a 30 min ride on a high speed catamaran. Depending on details that probably puts the landing pad something like 15-20 miles out in the ocean.

Do you think that that is unreasonable?

Well, something to consider is that Little Boy (the hiroshima bomb) had a yield of roughly 15kt. Obviously a nuke has different characteristics from a fuel-air explosion, most of which I haven't considered and would not qualified to comment on anyway, but the comparison doesn't make me very comfortable with 15 miles. It probably wouldn't be within the blast radius (depending on how the burning fuel propagated), at least, but the the amount of radiant heat generated would be nothing to sneeze at. I could certainly be overestimating the issue - I'm guessing the rapidity of a nuclear explosion vs. a fuel air explosion affects its pound for pound destructiveness significantly.

Sibling comment has a good point that hyperloop could make spaceports at safe distances more accessible.

Hiroshima was total destruction within 1 mile, the farthest away that glass broke was 12 miles, no damage past that.

So 15 miles is definitely out of the blast radius. What about the fireball?

Google told me the following. 15 miles is roughly 24 km. The mass of air is 1.2 kg per cubic meter. The volume of a sphere is 4/3 pi r^3. The energy of a kt is about 4.184e9 joules. It takes about 1 joule to increase the temperature of air by 1 C. When I put all of that together I calculate that a 15kt explosion has enough energy to raise the temperature of a 15 mile ball of air by about 0.9 C.

Please double check my figures and calculation, but I think that your average city can survive that. :-)

Ha! Thanks for running through the numbers, very interesting. The air in that 15 mile ball is almost transparent to infrared, though, so I'd probably assume that the surface area of the sphere would receive the lion's share, rather than the volume within it. So the energy delivered should fall off roughly with the square of the radius rather than the cube. Might be enough to give a sunburn, if nothing else.

Edit: On my phone I'm getting ~5.8 joules per square meter. Google seems to be mangling the units, though, so I can't be sure it's not dropping or adding in a factor of 1,000, though.

Edit 2: assuming that figure is correct, unless it's released in <1/200 of a second, it's not competitive with the sun at the equator (>1,000 Watts/Joules per m^2 per second)

I think that there are some decimal places missing. But that said, I'd expect a chemical explosion to deliver itself mostly as a shockwave and a ball of hot gas, with relatively little delivered by light. Because the part exploding is surrounded by smoke and chemicals that absorb light.

Yeah, I was going for worst case assumptions, where all of the energy turned into infrared, which is definitely not going to be the case.

Here's the math, if you want to double check: (10 x 4.184 x (10^9 joules))/(4 x pi x (24000 meters)^2)

Atmosphere is only transparent to infrared in 7-13 mkm window. Yet I expect the fireball to producing heat at above 500 C that gives peak of radiation below 4 mkm.

Thanks, good to know. I was going for worst case calculations, assuming complete transparency. Even that doesn't seem bad.

Lenghty travel to spaceport would tie in nicely with the hyperloop.

Good point, that might make it more feasible. I hope we see some successful deployments.

This is lower, however, when you're strapped into your seat. In the vomit comet, you're free to move about, which drastically increases the likelihood of nausea.

The F9 makes a pretty disgusting triple boom on landing so I can't see the bfr being better in that respect.

Per SpaceX's plans, the landing would be some miles away from people.

A supersonic jet makes a sonic boom on the ground over its whole trajectory. That's what makes it undesirable for overland travel.

What? Surely you mean perpendicular to the path? Or does path mean something different from trajectory..?

I do mean perpendicular, sorry.

I really want it to happen, but I'll believe it when I see it.