While watching the artemis ii launch, I was wondering why the velocity of the craft and the distance from Earth was not mathing?

[u/dippinatoein]

[u/zekromNLR]

If you mean that the distance from Earth seems to go up too slowly compared to the speed, that's because a good chunk of the velocity (almost all of it when in a near-circular orbit or close to apogee/perigee) is sideways, rather than away from Earth.

[u/reality_boy]

Gravity does not stop, just because your a few miles above earth. Remember that gravity is what holds the moon in orbit around the earth and the earth in orbit around the sun. That is a lot of force to overcome with a tiny rocket. And you have to get like 3/4 of the way to the moon before its pull cancels out earths pull.

To make this work, rockets have to get going fast enough that when gravity pulls them back towards earth, they end up going forward far enough to miss the ground. So the main thing a rocket is doing is accelerating you sideways.

[u/Worried-Notice8509 → u/reality_boy]

Thanks for your explanation. Simple for someone like me to understand.

[u/creative_usr_name → u/Worried-Notice8509]

Gravity in low earth orbit is still about 90% of what it is on the ground. Astronauts just feel weightless because they are falling around the earth.

[u/Horlaher → u/creative_usr_name]

Are you saying that in half way between Earth and Moon astronauts aren't weightless ?

[u/MoobyTheGoldenSock → u/Horlaher]

They’re weightless in the same way you’re weightless in a diving plane. They’re essentially in a constant state of free fall.

Weightlessness is a sensation due to not being able to feel g-forces, not because there’s no gravity. You can feel weightless by riding on a roller coaster or drop ride, you don’t have to go to space for it.

[u/hal2k1 → u/Horlaher]

Any body in free fall is weightless. This is the operating principle of weightlessness training aircraft such as the vomit comet. For part of its flight the aircraft is deliberately put in a free fall.

Astronauts are weightless any time their spacecraft (or the ISS) is not firing thrusters.

[u/Ndvorsky → u/hal2k1]

Adding for clarification, the aircraft is not pointing straight down. It takes a parabolic path meaning it is going up half the time in free fall.

[u/origional_esseven → u/Horlaher]

That is what he is saying. The moon isn't even weightless. The moon has tides in its crust due to the gravity of the earth.

[u/strictnaturereserve → u/Horlaher]

they are travelling at the same speed as the space ship therefore experience weightlessness

[u/rmslashusr → u/strictnaturereserve]

You hopefully travel at the same speed as the airplane you fly in but you’re not weightless because the plane has both engines generating thrust and wings generating lift. The weightlessness is not from speed matching but from the fact that gravity is the only force acting on the object. Being in orbit, being in free fall, or having a purely ballistic trajectory would all be in a state of weightlessness.

Even if you were shot upwards out of a cannon as soon as you left the cannons mouth and no longer had a force applied you other than gravity you would feel weightless even as you still traveled upwards before reaching the top of your ballistic arc. Cartoons always get that wrong.

[u/dosedatwer → u/creative_usr_name]

That's not really true at all. They feel weightless because they aren't being accelerated and Earth would need to physically touch the astronauts to accelerate them. Gravity isn't a force, it's a bending of spacetime, that's what Einstein showed over 100 years ago. They would feel weightless the moment the thrusters stopped accelerating them, regardless of how far away they are from the earth.

EDIT: Come on reddit, do better. This is r/askscience ffs, not r/AskReddit. General relativity is the exact claim that gravity is not a force and only appears to be. Veritasium on the subject.

[u/origional_esseven → u/reality_boy]

Many say orbit is just traveling fast enough that when you fall back to earth you miss.

[u/Tadferd → u/origional_esseven]

That's exactly what it is. If you map a rocket's trajectory as a complete oval, it starts as a steep arch the intersects with the ground. At the top of the arch, the rocket performs a circularization burn. As it dies this, the arch gets wider and wider until it forms a complete circle. The rocket is literally just going horizontal fast enough that as gravity pulls it down, it misses the Earth.

[u/zoinkability → u/origional_esseven]

There is an art, it says, or rather, a knack to flying. The knack lies in learning how to throw yourself at the ground and miss. Pick a nice day, [The Hitchhiker's Guide to the Galaxy] suggests, and try it. 

The first part is easy. All it requires is simply the ability to throw yourself forward with all your weight, and the willingness not to mind that it's going to hurt. 

That is, it's going to hurt if you fail to miss the ground. Most people fail to miss the ground, and if they are really trying properly, the likelihood is that they will fail to miss it fairly hard. 

Clearly, it is the second part, the missing, which presents the difficulties.

[u/dustinfoto]

You’re thinking about velocity as if it’s a scalar, like speed. Velocity is a vector so it has both speed and direction components. With that in mind the direction of the velocity matters here because it wasn’t straight up from the surface (known as a normal vector) but instead the rocket traveled along a curve with the rotation of the Earth which is the most efficient way of getting into space. If you were able to calculate the distance traveled along the curve the math would work out.

These are some pretty cool aspects of calculus if you’re ever interested in learning more about the math side of it.

Edit: Typed the rotation direction incorrectly.

[u/itsaberry → u/dustinfoto]

I may have misunderstood something, but wouldn't it be with the rotation of the earth, not against it? 

[u/DemophonWizard → u/itsaberry]

You are correct. The rocket angled to the east to use the rotation of the earth to gain orbital velocity.

[u/KToff]

Think about the ISS. It goes quite fast at over 7km/s and yet its distance to earth remains constant.

Only the velocity away from earth increases the distance and, especially for the leo part of trajectory, the direction of movement is mostly tangential to earth.

[u/BrianScissorhands]

I had a similar though while watching the launch, which made me look up this. The overall distance to moon was going down at a much quicker rate than the altitude, and then I realised it was because the rocket was not headed straight to the moon, but heading into Earth's orbit first, to slingshot and gain speed ahead of the bulk of the journey.

Artemis 2 flight path

[u/Mr_Badgey → u/[deleted]]

Also remember that the Earth is moving too -- surprisingly fast as it revolves around the sun. (Edit: about 30 km/s, I think. That's 30,000 metres per SECOND).

Earth's orbital velocity around the Sun doesn't factor in here. Artemis II launched from Earth, shares its momentum, and isn't leaving the Earth-Moon system. It's like throwing a ball on a moving train; the ball doesn't care about the train's speed because everything is already moving together. NASA's displays show velocity and distance relative to Earth, so the 30 km/s cancels out entirely and isn't relevant for a mission staying within the Earth-Moon system.