5 ms·

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 peo

by sd9 6mo 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.

devilbunny 6mo ago
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.
- colechristensen 6mo ago
  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.
  - devilbunny 6mo ago
    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.
kypro 6mo ago
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...
- ryandrake 6mo ago
  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.
- CobrastanJorji 6mo ago
  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.
layer8 6mo ago
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.
- sd9 6mo ago
  Not surprising if you know that. Pretty surprising to me who didn’t.
  - layer8 6mo ago
    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.
    - lionkor 6mo ago
      Acceleration is change in speed, so it is, by its very nature, relative just like speed is. If I fall, I might accelerate at G meters per second, relative to the earth, but I don't absolutely accelerate. If the earth decelerates at the same time, I'm now both accelerating an decelerating. It's relative.
      - layer8 6mo ago
        It’s absolute in the sense that you can determine your acceleration without any external reference. You feel a certain force (like what you feel in an elevator). That’s your acceleration. You don’t accelerate relative to Earth, or relative to anything else. You accelerate relative to when you wouldn’t be accelerating (your inertial rest frame, a state of free fall). If you are in space accelerating and the Earth would decelerate (which is just an acceleration in the other direction), you would still feel exactly the same force (minus Earth’s gravity, to the small extent you’d still feel it), and people on the Earth would feel the Earth’s acceleration. (For them it would feel like “down” isn’t perpendicular to the Earth’s surface anymore, or as if the Earth’s surface was tilted.) When you sit on a chair on Earth, the pressure you feel on your butt is your acceleration upwards. If there was no chair and no ground (and no air), so that you’d be in free fall, that’s when you’d have zero acceleration. Your inertial rest frame is the trajectory you’d take in free fall. When you’re sitting on a chair, or lying in bed, or standing on the ground, you’re accelerating upwards relative to that rest frame, and that’s the pressure you feel on your butt, or on your body, or under your feet.
wpollock 6mo ago
[flagged]
WaterRun 6mo ago
ICBMs also have a similar speed at the terminal warhead stage — only the direction is different.
- hsbauauvhabzb 6mo ago
  I’d prefer to cheer for something that’s primary objective isn’t killing people. So there’s that, too.
  - justinator 6mo ago
    Just a friendly reminder that midterms are this year.
    - hsbauauvhabzb 6mo ago
      If we survive that long.
      - justinator 6mo ago
        We'll survive; not sure about our present voting rights.
dylan604 6mo ago
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.
- furyofantares 6mo ago
  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.
  - dylan604 6mo ago
    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.
- ls612 6mo ago
  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.
  - 6mo ago
casefields 6mo ago
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.
- FabHK 6mo ago
  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.
  - jve 6mo ago
    However space is not orbit. Space is easy, orbit is hard. https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/
- bryanlarsen 6mo ago
  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.
amai 6mo ago
NASA uses metric units even under Trump. So this is 16093 km/h or 4.474 km/s .
4887d30omd8 6mo ago
Your comment inspired me to vibe code https://calcubest.com/other/shuttle 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).
thecommakozzi 6mo ago
[dead]

by sd9 6mo ago

devilbunny 6mo ago

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.

colechristensen 6mo ago
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.
- devilbunny 6mo ago
  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.

kypro 6mo ago

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...

ryandrake 6mo ago
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.
CobrastanJorji 6mo ago
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.

layer8 6mo ago

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.

sd9 6mo ago
Not surprising if you know that. Pretty surprising to me who didn’t.
- layer8 6mo ago
  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.
  - lionkor 6mo ago
    Acceleration is change in speed, so it is, by its very nature, relative just like speed is. If I fall, I might accelerate at G meters per second, relative to the earth, but I don't absolutely accelerate. If the earth decelerates at the same time, I'm now both accelerating an decelerating. It's relative.
    - layer8 6mo ago
      It’s absolute in the sense that you can determine your acceleration without any external reference. You feel a certain force (like what you feel in an elevator). That’s your acceleration. You don’t accelerate relative to Earth, or relative to anything else. You accelerate relative to when you wouldn’t be accelerating (your inertial rest frame, a state of free fall). If you are in space accelerating and the Earth would decelerate (which is just an acceleration in the other direction), you would still feel exactly the same force (minus Earth’s gravity, to the small extent you’d still feel it), and people on the Earth would feel the Earth’s acceleration. (For them it would feel like “down” isn’t perpendicular to the Earth’s surface anymore, or as if the Earth’s surface was tilted.) When you sit on a chair on Earth, the pressure you feel on your butt is your acceleration upwards. If there was no chair and no ground (and no air), so that you’d be in free fall, that’s when you’d have zero acceleration. Your inertial rest frame is the trajectory you’d take in free fall. When you’re sitting on a chair, or lying in bed, or standing on the ground, you’re accelerating upwards relative to that rest frame, and that’s the pressure you feel on your butt, or on your body, or under your feet.

wpollock 6mo ago

[flagged]

WaterRun 6mo ago

ICBMs also have a similar speed at the terminal warhead stage — only the direction is different.

hsbauauvhabzb 6mo ago
I’d prefer to cheer for something that’s primary objective isn’t killing people. So there’s that, too.
- justinator 6mo ago
  Just a friendly reminder that midterms are this year.
  - hsbauauvhabzb 6mo ago
    If we survive that long.
    - justinator 6mo ago
      We'll survive; not sure about our present voting rights.

dylan604 6mo ago

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.

furyofantares 6mo ago
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.
- dylan604 6mo ago
  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.
ls612 6mo ago
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.
- 6mo ago

casefields 6mo ago

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.

FabHK 6mo ago
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.
- jve 6mo ago
  However space is not orbit. Space is easy, orbit is hard. https://what-if.xkcd.com/58/ https://what-if.xkcd.com/58/
bryanlarsen 6mo ago
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.

amai 6mo ago

NASA uses metric units even under Trump. So this is 16093 km/h or 4.474 km/s .

4887d30omd8 6mo ago

Your comment inspired me to vibe code https://calcubest.com/other/shuttle 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).

thecommakozzi 6mo ago

[dead]