Hacker News Reader

Comment by jgrahamc | Hacker News Reader

"In the case of the latest Star Trek movie, the trailer clearly shows the construction of the Enterprise – on earth. This is the source of Nerd Rage for many who will not-so-calmly explain that a Constitution-class starship could not possibly be built on earth because it is too large to escape the earth’s gravity."

Wha?

So when the Enterprise comes near to the Earth what happens? It just can't escape the Earth's gravity, or does it only get stuck when it's near the Earth's surface? It's not the moon you know; it has engines.

NCC-1701-D is supposed to weigh about 400,000 tonnes. Leaving the Earth's surface to reach LEO requires a delta-v of 10km/s so you've got to accelerate 400,000 tonnes to 10km/s. The Space Shuttle does this and it weighs around 2,000 tonnes. So are we really expected to think that a vehicle 200x the size of the Space Shuttle could not be launched into orbit?

View on HN

I'm having trouble understanding your problem with the original statement. To me, it clearly means that with the facilities available (no enormous rockets, for example) it can't easily start from the Earth's surface and get into orbit.

Approaching the Earth is a completely different issue, and I don't understand why you mention it. It simply isn't a problem if you're already in space because you make sure you go into some sort of orbit (elliptical, parabolic or hyperbolic - any will do). You easily have enough speed to do this because you're falling into the gravitational well, and you simply need to deflect your path to one side, miss the atmosphere, and you're on a hyperbolic orbit. Slow a little and you're in a large elliptical orbit. Slingshot properly around the Lagrange points (including "bouncing off" the unstable ones) and you can convert to a "standard orbit" with very little effort.

Launching from the Earth's surface requires a huge amount of energy, and it's been stated that it wasn't done.

Now, what was your question?

"Launching from the Earth's surface requires a huge amount of energy, and it's been stated that it wasn't done."

This appears to be the key to the nerd rage. If Starfleet didn't build the craft on Earth then showing them in the new movie being built on Earth is a mistake. But it's not a question of physics.

Yes, I agree completely. The first part of my post was expressing why I found the question about approaching Earth misguided, irrelevant, or inappropriate. Clearly the Nerd Rage is just about the inconsistency with the "earlier" episodes.

The comments about the physics also sparked a conversation about escape velocity here in the office. It's easy to compute that orbital velocity at grazing altitude is about 8 km/s. People confuse that with escape velocity, which is sqrt(2) faster, or about 11.3 km/s.

The real confusion arises in that a craft never needs to reach escape velocity to escape. You can happily escape without ever travelling faster than 6km/hr - walking pace.

If this confuses you, it's fun to work out why. And how. And why NASA doesn't do that. The sums are fairly easy, it's the conceptualisation that's hard.

The statement that it wasn't done apparently applies to a different canon; there's apparently quite a lot that's changed in this one. However, the amount of energy is trivial compared to what starships in the Trek universe must be capable of. Impulse engines are supposed to be able to drive the ship to some respectable fraction of the speed of light, so no matter how they work, they should be able to get the ship off the surface of the Earth. I think the fact that the Trek universe has artificial gravity solves all of the handwavy problems, though, even apart from that, so there's no canonical technical problem here.

The ~10km/s figure refers to the speed an unpropelled object needs at the Earth's surface in order to escape gravity, so it doesn't apply to rockets and shuttles. Assuming it could keep the engine running, the shuttle could go into orbit at 1km/h.

Sorry to nitpick, but I couldn't resist as I used to have the same misconception.

Reply on news.ycombinator.com