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An error in any of the orbital math may have seen them flung out into space with no chance of recovery.

by pictureofabear 5mo ago

gct 5mo ago
Orbits do not work that way
- ggm 5mo ago
  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.
  - 420official 5mo ago
    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.
    - dgfl 5mo ago
      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.
      - 420official 5mo ago
        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
        dgfl 5mo ago
        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.
        WalterBright 5mo ago
        The lumpiness of the moon's gravity is not well mapped out.
        accrual 5mo ago
        It is now better mapped after the GRAIL mission: https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_Laboratory https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_...
        WalterBright 5mo ago
        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.
- numpad0 5mo ago
  Anyone who has had hit period key once too many during Munar free-return in KSP knows it's exactly how orbits work...
- SV_BubbleTime 5mo ago
  Hilarious the the intellectual forum downvoted you for being absolutely right. Artemis II never escaped Earth’s pull. That video that NASA put out where the craft did a sling shop around the moon is extremely deceptive. The pull of the moon had very little effect. If they had missed, they would have eventually crashed back to earth in the worst case, and best case just re-adjusted and returned a little bummed.
  - pdonis 5mo ago
    > The pull of the moon had very little effect. No, it had a very significant effect: it's what made possible the free return trajectory while observing the far side of the moon.
    - SV_BubbleTime 5mo ago
      Ok, but no not really. This is incorrect, the “free return” would have happened if they launched entirely in the wrong direction. Like I said, the gif you saw makes it look that way. Here is a link that explains it very well. https://youtu.be/MF8IbYbVIA0?t=269 https://youtu.be/MF8IbYbVIA0?t=269 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.
      - pdonis 5mo ago
        > This is incorrect 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.
        SV_BubbleTime 5mo ago
        I’m sorry that you feel so strongly about a position that is incorrect. I provided a source to help explain it to you.

An error in any of the orbital math may have seen them flung out into space with no chance of recovery.

gct 5mo ago

Orbits do not work that way

ggm 5mo ago
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.
- 420official 5mo ago
  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.
  - dgfl 5mo ago
    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.
    - 420official 5mo ago
      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
      - dgfl 5mo ago
        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.
        WalterBright 5mo ago
        The lumpiness of the moon's gravity is not well mapped out.
        accrual 5mo ago
        It is now better mapped after the GRAIL mission: https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_Laboratory https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_...
      - WalterBright 5mo ago
        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.
numpad0 5mo ago
Anyone who has had hit period key once too many during Munar free-return in KSP knows it's exactly how orbits work...
SV_BubbleTime 5mo ago
Hilarious the the intellectual forum downvoted you for being absolutely right. Artemis II never escaped Earth’s pull. That video that NASA put out where the craft did a sling shop around the moon is extremely deceptive. The pull of the moon had very little effect. If they had missed, they would have eventually crashed back to earth in the worst case, and best case just re-adjusted and returned a little bummed.
- pdonis 5mo ago
  > The pull of the moon had very little effect. No, it had a very significant effect: it's what made possible the free return trajectory while observing the far side of the moon.
  - SV_BubbleTime 5mo ago
    Ok, but no not really. This is incorrect, the “free return” would have happened if they launched entirely in the wrong direction. Like I said, the gif you saw makes it look that way. Here is a link that explains it very well. https://youtu.be/MF8IbYbVIA0?t=269 https://youtu.be/MF8IbYbVIA0?t=269 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.
    - pdonis 5mo ago
      > This is incorrect 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.
      - SV_BubbleTime 5mo ago
        I’m sorry that you feel so strongly about a position that is incorrect. I provided a source to help explain it to you.