Check out this video that goes into a very deep technical explanation about how the satellites can be used as a Synthetic Aperature Radar to build a realtime representation of the entire globe at meters of resolution: https://youtube.com/watch?v=jbp3kdJZ1_A
The craft has aerodynamics and speed. It might be figuratively true "unrecoverable" but if it takes e.g. 2 weeks to complete a return, their oxygen and food and batteries ran out. Alternatively if it enters too fast they return ... in pieces.
I think you're being a pedant, if your point is a grazing entry causing rebound skip ultimately returns to some orbital path downward.
You seem to intentionally be ignoring the original quote that any error may have caused them to be flung into space. This is patently false unless the one math error is pumping in hundreds of pounds more propellant and burning far longer than the scheduled burns. NASA would need to make a significant series of mistakes beyond orbital math for the "flung out into space" statement to be true.
They certainly could've gotten the return wrong but with a perigee of 119 miles they arent even in a stable orbit and likely could deorbit themselves using only rcs thrusters at apogee, or by just waiting a few orbits.
This is underselling the risks. On top of the many trajectories which push them into unrecoverable situations, leaving them stranded in orbit, there can be trajectories where the moon gives a gravity assist strong enough to fling the spacecraft into escape velocity, fulfilling the OP.
In fact, the trajectory they chose for this mission exploited the opposite effect to yield a free return without propellant expense.
In the modern day, the chance of a math error being the root cause behind this failure mode are vanishingly small, but minor burn execution mistakes that do not require hundreds of extra pounds of propellant are definitely plausible. They were extremely common in the early days of spaceflight and plagued most of the very first moon exploration attempts. Again, with modern RCS this is unlikely. But reentry is still incredibly tight and dangerous. Apollo famously had a +-1° safe entry corridor, and Orion is way heavier and coming in even faster. If their perigee was off they could’ve easily burned up or doubled their mission time, which they may not have been able to survive.
The amount of things that would have to go wrong for the craft to get an accidental gravity boost and be ejected would be significant.
I feel like the original claim paints the whole thing as on a knife edge and barely achieved by virtue of not making a single mistake. In today's age with so many moon landing deniers and worse I feel like we should be specific about where the actual dangers challenges and unknowns there were here. In reality, the orbital mechanics are one of the simplest parts of the entire problem, at least when we're talking about a moon flyby
Yes, this is a fair point. I agree that orbital mechanics is trivially easy compared to everything else. The chances of a math mistake in particular are null, these trajectories have all been calculated years in advance.
The moon's gravity turns out to be "lumpy" because its density is not constant. This was detected by the Apollo missions and caused them to make errors in orbit calculations. This source of error could have influenced the flyby.
I’ll agree, it seems crazy that it left earth, made it to the moon, and never really left earth orbit at all. That the furthest we’ve been away is still destined to return on its own.
Watch the NASA video carefully. It's clear that, even before the "loop" begins, Artemis is slowed down and is soon going to reverse direction relative to Earth. Which of course it would anyway, as you say--because, as the video you linked to points out, it doesn't have Earth escape velocity. The TLI burn gave it just enough velocity to reach the Moon's orbit with a little extra speed left over to get it about 4000 miles further.
But what would not happen without the Moon there is the "backwards" part of the loop--the part that took Artemis around the far side of the Moon. The Moon's gravity is what did that. In the Moon-centered frame in the video, yes, it looks like just a slight deflection--because that frame is moving with the Moon, whereas Artemis was moving backwards--in the opposite direction from the Moon in the Earth-centered frame.
Without the Moon there, Artemis would never have moved backwards, relative to the Moon's orbit, at all. Its trajectory in the Earth centered frame would have been a simple ellipse, with a maximum altitude from Earth a little higher than what it actually achieved (since the Moon's gravity did pull it back a little bit).
No, it's not. You aren't responding to what I actually said. See below.
> the “free return” would have happened if they launched entirely in the wrong direction.
But it would not have been a free return that let them see the far side of the moon, which is what I said. The Moon's gravity is what made that possible. And that was very significant.
I'm sorry that you disagree with the correct things I've said. Your "source" is a YouTube video--hardly a rigorous scientific or engineering treatment. And I posted upthread in another response about the limitations of the viewpoint the video takes. Have a nice day.
Hmm. Maximum speed attained by Artemis II when they left their initial orbit was about 11.1 km/s IIRC. While this is somewhat less than true escape velocity from Earth (11.2 km/s) and you are technically correct, it is also enough of a speed that if you fly away in any random direction (and not a carefully calculated one), perturbances from the Sun and other massive objects will probably prevent you from reaching any sort of stable orbit around the Earth, and you will start bouncing around the inner Solar System in an erratic way.
I certainly wouldn't like to model that trajectory for months or years.
The sun’s pull on the ship at the outside limit at the moon, is obviously negligible compared to the pull of the Earth. This should be obvious, because otherwise the moon would have left long ago.
Why is this so difficult to understand? Honestly I think that misleading NASA graphic did a lot of damage.
You throw in acceleration, which I never mentioned and doesn’t matter. The Artemis II never left Earth’s gravitional pull, the original issue was effectively what if it missed - and the answer is no big deal.
I'd like to hear more about the synthetic part of these three spaces, because S2 works exactly as you say, embedding the 2-sphere in three (cartesian) dimensions. S2 points are always three dimensional.
S2 projects a 2-sphere onto a topologically homeomorphic 2-surface designed to play nicely with discrete representations. It is not a 3-space any more than a 2-sphere is. Most software uses three coordinates organized by a 2-surface DGGS.
DGGS that use 3-space embeddings are topologically 3-dimensional i.e. purely volumetric. They do not interpret the Earth as a 2-surface. In addition to polar coordinates, you must provide a volumetric model of the Earth to compute the DGGS cell. The shard distributions look very different between a 2-surface and a 3-surface. The latter has significantly better properties for large analytical data models but requires more sophisticated storage architectures.
The synthetic 3-space is optimized for two things. You want maximally efficient mapping function from the typical WGS84 geometry into it. Tidy math, basically. Since it is purely internal, the user will never see it, and it doesn't map to anything real, you have latitude to design it to satisfy software engineering objectives as long as it works. Second, the 3-space references are naturally less compact than 2-surface references at the same resolution even though you'll end up with roughly the same number of shards. A lot of effort goes to schemes to compress out the sparseness so that the storage requirements are similar to 2-surface DGGS e.g. how often do you need to represent geometry 1000 km below the Earth's surface?
These DGGS also have the low-key advantage that they natively represent and understand 3-space, not just surface geometry, if you move beyond making flat maps.
I'd be curious to hear more about how you do the 2 -> 3 embedding there. In S2 it uses cartesian three space, but points are constrained to be unit magnitude. This has advantage and disadvantages obviously.
You can do this with [S2](https://s2geometry.io/) as well which has the very nice property that parent cells do indeed always contain their children, and sorting the cell ids puts them into in-order order.
The Box is very frustrating, especially when there's no one handling the other things, yet you're still not allowed to do them because it'd make the wrong people look bad.
