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Comment by isostatic | Hacker News Reader

Launch it from LA and land it in Florida for the test flight?

I don't think anybody is allowed to launch rockets from the United States where any part of the boost phase is over land.

Traditionally, rockets dropped their boosters. If they are no longer dropping large explosive things, such a requirement could go away.

Even if the intent is not to drop boosters, as long as there's some reasonable chance boosters will be dropped (accidentally), I can see that requirement sticking around.

> If they are no longer dropping large explosive things

If you were a rocket engineer, would you stake your life on it? Every single launch?

Are you afraid of jumbo jet engines falling out of the sky near airports?

Exactly, that's the end goal.

The energy output of a jumbo jet is four orders of magnitude less then that of a rocket. A jet engine is equivalent to a controlled fire. A rocket is equivalent to a controlled nuclear explosion.

There's almost as much energy stored in a BFR as there is in the nuclear bomb dropped on Hiroshima. This energy is released over 3 minutes.

Considering their long term plan involves building pads out in the ocean and doing suborbital hops between cities:

https://www.youtube.com/watch?v=zqE-ultsWt0

maybe

If you launch to the west this might be viable. The government wouldn't be particular thrilled about test flights over land (or any flight over land), but for a test flight you would want something longer than a jump across the continent anyway.

Rockets rarely launch at a retrograde (western) orbit because you have to overcome the earth’s rotation to reach orbital velocity, rather than the speed boost you get from launching with the earth’s rotation. IIRC, satellites launching from Vandenberg AFB in California take a polar orbit.

Even if they went all the way up to the ISS's orbit (which would be useless both because it's a test flight and because they would be going the wrong direction), the difference between going in a western or eastern orbit is a ~10% difference in delta-v requirements. Normally that's an enormous difference, but if you can just decrease the size of the test payload at will it shouldn't matter much beyond spending a few thousand dollars more on fuel.

It's not the height that counts, it's the sideways speed. Getting to 250 miles above sea level is relatively easy. Getting to 5 miles a second it far harder.

But if you're not aiming for orbital velocity the earth's rotational speed doesn't make any difference -- the relative speed of start and end points are the same. It doesn't take more fuel to travel west than east because of the rotation of the earth (jet stream sure, but if rockets are affected by the jet stream there's something seriously wrong)

Disclaimer: my entire picture of orbital dynamics comes from KSP

Check your orbital velocity at the surface. It's not 0. The direction you head does matter.

OTOH if they're just trying to get from California to Florida they don't need full orbital velocity.

If the rocket can be used without limit this almost makes perfect sense.

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