Comment by sd9
4 days ago
Minutes after launch they reached "ten thousand miles per hour". That's 2.78 miles per second. Nuts. No doubt the speeds go even higher later too.
I'm sure people here are already familiar with the speeds these things go, but that's the first time I've confronted a fact like that and it blew me away.
Escape velocity is 25,020 mph (6.95 mps), so not completely surprising.
Note that escape velocity applies to a situation without continued propulsion and also without air resistance, but still you can imagine that the order of magnitude is similar.
Not surprising if you know that. Pretty surprising to me who didn’t.
Maybe you’ll like this too: The Earth’s speed around the sun is around 67,000 mph. So it moves significantly faster than the rocket, though not orders of magnitude. The solar system itself moves at 43,000 mph relative to its local neighborhood.
But speed is always just relative to some frame of reference. Acceleration, on the other hand, is absolute, and so might be the more interesting thing to look at here.
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Thank you for that precision "without continued propulsion", because when talking about rockets, physics teachers always talk about escape velocity, as if it was an absolutely necessary condition to escape earth's gravity.
But can't you escape gravity slower, just by going higher and higher at lower speed? Like a plane? (ie not vertically, but at an angle)
If you don't accelerate, my understanding is that you will slow down. In other words, it takes more and more energy to escape orbit. Eventually, if you don't accelerate, your speed drops to zero and you "fall back down". Escape velocity is about how much energy you put into your motion, not the velocity as such.
No, the absolute minimum speed IS required. Anything below that and you’re just making your orbit elliptical.
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Exactly. Your rocket can escape the earth at the speed of a slow elevator if you burn the engines continuously and you can carry an infinite amount of fuel and your fuel weighs nothing.
Since those constraints are impossible to meet in the real world, we have to get going fast enough to coast most of the trip on inertia after the fuel runs out.
Artemis II won't fly by the moon until Day 6, but it only took Apollo 8 to Day 4 to get to the moon. Looking at the wiki for Apollo 8, it shows the moon was 218k miles at launch while they said the moon is currently 240k, so it still looks like Apollo was moving faster than Artemis.
Apollo put a lot more burden on the Service Module than Artemis plans to put on the Orion. Apollo put the CSM/LM into a low lunar orbit while Artemis plans to put Orion into a high lunar orbit and make the Starship carry a lot more delta-V to land from a much higher velocity (and then accelerate back up to that velocity when coming back).
On top of that there weren’t really solar panels in the 1960s so the Service Module had to carry tons of chemicals to produce electricity, as well as extra fuel for all of that weight. As a result it was massively overbuilt compared to anything we’d try today and even so had to take an expedited flight path to the moon of 3 days in order to conserve operational lifetime. Artemis does not have nearly as severe constraints on either the Orion or the future Starship and so can afford to take a more fuel efficient 5 day coast up to the Moon and make the design tradeoffs on Orion that that entails.
Admittedly, I let this launch sneak up on me, and I just haven't paid attention to the flight details. Thanks
My understanding is Artemis II orbits earth for 23.5 hours before heading to the moon while Apollo 8 did so for under 3 hours, so that accounts for some of the difference.
That would account for some of it. I was surprised the TLI burn wasn't until tomorrow, but I guess we didn't get the Apollo 2-7 tests of the system either, so maybe those are getting compressed into the additional time in earth orbit before TLI???
It's kind of said that we are having to do all of this repeated work just to get to where we've already been even if we are doing it on a much more accelerated schedule.
I knew someone who knew someone, so I got to see STS-133 from the VIP area.
Nine minutes after launch, it was in orbit.
Nine minutes.
Yup, that's how long it takes. There are a bunch of competing requirements and 9 minutes to orbit is the sweet spot, you can't change it much in either direction. If you go slower you waste all of your fuel just holding yourself up against gravity ("gravity drag" which is a bit of a tongue in cheek engineering term) If you go much faster you're accelerating too hard for your passengers or your structure.
To understand gravity drag think about the rocket firing just hard enough to hover 1 meter above the pad, you burn out all your fuel in 10 or 15 minutes and go nowhere...
In the other direction if you want to accelerate harder you need to make your structure stronger so you need to burn more fuel per second and have to displace some fuel in exchange for more structure and you keep doing that until you're so heavy you can't produce any more acceleration and you're all engine and structure and no fuel.
I get the physics and engineering intellectually, but it’s very different to be standing there, still watching the smoke clear, and hear the announcement.
Your comment inspired me to vibe code https://calcubest.com/other/shuttle to see how fast the space shuttle travels between world cities. Pretty darn fast.
(also my first time trying to vibe code with Gemini as opposed to Claude and I don't know if I noticed a big difference, which probably makes sense for such a simple project).
A Dodge Challenger SRT Demon can also reach 10,000mph in 4 minutes if it held its 0-60 acceleration over the whole span.
So yes, you can buy a car today that'll let you feel the G's like you're a space pilot.
The acceleration of a rocket is slower than a normal car at lift off. It's pulling about 1.2G, but 1G of that is fighting gravity, so effective acceleration is only 0.2G. Almost any car can do that at low speeds.
But a car's acceleration slows almost instantly. The rocket just keeps accelerating faster as the tank empties and it gets lighter. By main engine cut off it might be pulling 5G.
One fact that I found unintuitive (while we're at cars doing things they can't):
If you could drive your car straight up vertically, you'd have to cruise just for an hour or so at 100 km/h (<65 mph) until you reached space. It's not that far.
However space is not orbit. Space is easy, orbit is hard. https://what-if.xkcd.com/58/
ICBMs also have a similar speed at the terminal warhead stage — only the direction is different.
I’d prefer to cheer for something that’s primary objective isn’t killing people. So there’s that, too.
Just a friendly reminder that midterms are this year.
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NASA uses metric units even under Trump. So this is 16093 km/h or 4.474 km/s .
I was thinking the exact same thing when they announced the speed. I assume the top speed of Artemis will be at least double that too...
Well, notions of speed are a little tricky for spaceships, but yeah, Artemis's top speed is going to be right when it starts reentry: about 25,000 MPH.
It will be slower, eventually. The moon orbits at about 2300 mph, and as Artemis gets further from Earth, it will slow down to a similar speed.
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