He said the heat shield ablates for Mars trips but not Earth trips (not sure why). If so then propellant should be the only important consumable.

Of course this level of reusability and reliability has never been achieved before, but the whole thing depends on it.

> He said the heat shield ablates for Mars trips but not Earth trips (not sure why)

Falcon 9 presently lands completely without any heat shield, because it just uses it's engines to reduce velocity until they are not needed. In principle, you can always replace heat shields with fuel like this.

Mars trips need to bleed velocity aerodynamically because the craft cannot bring enough fuel. Presumably a sub-orbital hop on Earth can save enough fuel to act as the brakes.

Falcon 9 has a heat shield around the engines. Since they are going into the atmosphere engines-first it's going to be hot there. The engine bells sticking out from there don't care (much, since the entry burn reduces speed enough). Most of the speed reduction for the landing happens via aerobraking, not by using the engines.

The first stage of a Falcon 9 also flies much slower than a ship arriving to Mars or coming back to earth from orbit. It just needs to slow down a bit with engines when entering the thickest part of the atmosphere.

The shield ablates on Mars trips because the ship is using the atmosphere to slow itself down, it will pass threw many times and bleed of speed.

On earth you just need to survive, the speed is primarily reduced with the engines.

> the heat shield ablates for Mars trips but not Earth trips (not sure why).

I suppose the reentry speed on mars is much higher, since it happens at the end of an interplanetary trip.

For E2E routes, the rocket doesn't have to be given as much kinetic energy - it doesn't have to escape Earth's gravity well.

Dragon 1 has already gone through a couple of iterations of heat shields. Mars entry is expected to be hotter, that's straightforward math.

I imagine they can fit 400 passengers though. No need for those cabins or even a need to give passengers drinks.

Actually, an A380 can hold 853, so BFR could probably hold the same.

If he can get the cost down to US $10 million per trip, that's US $12K per person.

For 30 minute trips you barely even need toilets.

I'd just shit my pants on liftoff.

That's really on spot but maybe it won't be your case. Many people don't like accelerations. Braking and turning a car a little harder than usual is much less that 1 g but some people don't feel comfortable with it, even when there is no danger. Remember motion sickness and the puke bags on planes. Lifting off with a rocket is always going to be higher g than with a plane. Furthermore it's probably going to require some amount of fitness. Too young or too old: fly on a plane. In the middle: it depends.

That's where the vacuum of space will clean up.

Free adult diapers for all passengers!

I think personally I'd keep my seat belt on regardless even if there were restrooms

You kidding? There's no way I'm staying in my seat during zero gravity. I might pay more to do a couple of extra orbits and play around before coming down.

I reckon everyone would be out of their seats as soon as boost is done. Getting everyone back into their seats in time for re-entry might be the issue ("take the nearest available").

Earth to earth flights would be sub-orbital though, so no opportunity for extra orbits.

I'm gonna miss the ding of the seatbelt sign.