Here’s how orbital dynamics wizardry helped save NASA’s next Mars mission
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L2 is metastable and it takes only small amounts of impulse to keep from heading down-gradient.
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But ESCAPADE isn't stopping at L2, right? It's just orbiting about that point.
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You’re always just orbiting a Lagrange point. There’s too much inhomogeneity to ever find “the” point. When L4 and L5 are stable, for instance, it’s because coriolis forces maintain the object in orbit around the point, and not because they push the object back to the exact point.
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Sorry, I meant, ESCAPADE is executing a free-return trajectory about L2 rather than orbiting.
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Oh, yeah… I should have realized that.
And you’re obviously right that the exact stability of orbits at L2 is rather moot in this case.
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Perhaps an odd question, but what exactly is the volume of space that makes up various "L" points? Obviously it isn't a precise place in space where only one orbital object sits as if on a gravity throne, but more similar to a Sargasso or pool of semi-stable gravity.
The question then is how many bodies could take advantage of that area safely?
The question then is how many bodies could take advantage of that area safely?
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To give a sense, JWST orbits the Earth-Sun L2 at a distance varying between 250,000 and 850,000 km from L2 and completes a little over two of those orbits a year. Its orbit is vertical to the ecliptic, though. Basically it stays much closer than those distances to the sphere described by the orange circle in the below diagram.
L1 and L3 are somewhat similar to L2, and the usefully stable regions around L4 and L5 are orders of magnitude larger.
EDIT: One good way to think of the JWST orbit is that it’s a big oval with the Earth’s shadow in the middle.
EDIT: Feel like I didn’t do a good job trying to describe JWST’s orbit. The following diagrams are from NASA. The first shows the orbit you were looking along the plane of the ecliptic. The second is looking from above, similarly to the diagram above, but closer. The circle in the second represents the Moon’s orbit.
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Thinking about it, the extra solar exposure isn't the only hazard ESCAPADE is going to face while waiting for departure in space. The volumes around the Lagrange points are more populated with rocks than the spaces between planets. JWST has taken at least one bad ding to its primary. It's not a high chance that ESCAPADE is going to get smacked by a rock, but it's higher than if it sat in climate-controlled storage.
Of course, the odds of cancellation while in storage are enormously high, so I guess NASA decided this was the lower risk path.
Of course, the odds of cancellation while in storage are enormously high, so I guess NASA decided this was the lower risk path.
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Maybe kaboom today? Their site now says, "...no earlier than Wednesday, November 12, due to forecasted weather and sea state conditions. We worked with the FAA and range to select a launch window from 2:50 PM – 4:17 PM EST / 19:50 – 21:17 UTC."
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Thanks for posting this. I wonder why the bow shock is tilted below the ecliptic plane.
(I understand why it's tilted along the plane.) I presume this is for solar wind particles?
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I would expect that to produce equal/symmetric pattern above and below the plane though.
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Why? The earth's magnetic field is tilted to the ecliptic. If it's summer/winter I'd expect a variation above/below. If it's spring/fall, I'd expect one side-to-sside.
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Okay, that makes sense if it's depicting a specific instant in time. I had been thinking the graph was a year-round average, but apparently that's not the case.
Thanks.
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They're waiting for the solar storm before launching, so this is gonna slide.
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Bill Swallow
Ars Centurion
Confirmed. No ESCAPADE launch today due to solar storm. No new launch time/date announced yet as of this writing.
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Another way to look at it is LESS than a quarter per US citizen. It works out to ~21 cents per person. The US has a population of ~380 million. $80 million mission cost.
I don't want to just be throwing away my pocket change, but I think there are bigger wastes that can be addressed, such as what it is costing us on the ballroom bribe, direct bribes to US Senators from the US treasury (see recent budget "deal"), general waste and abuse injected into the government from DOGE and ongoing OMB efforts to flip the table. Renaming the department of defense to super alpha department of war, Etc.
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L2 isn’t believed to be a particularly higher-risk micrometeoroid environment than the rest of nearby interplanetary space. As a metastable point, it doesn’t build up much of a captured micrometeoroid population, and what is temporarily captured will be traveling at much lower velocities than the transient stuff.
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Thank you for those JWST orbit figures! I had envisioned the "oval with Earth's shadow in the middle", though it's a much bigger orbit than I'd expected. But why is the orbit tilted with respect to the ecliptic? I thought the effective restoring force was all "toward the shadow", but that a spacecraft that got either closer to the earth or further away than L2 would fall away from it.
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They do want JWST to fall slightly towards Earth over time. The station keeping thrusters are on the Sun-side of the sunshield, so the observatory cannot thrust towards the Sun. If the orbit were exactly centered on L2, instead of being centered a little towards the Earth/Sun side of L2, there would be a chance to start drifting away from the Sun, with no way to thrust back towards L2.
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Nasa.gov has some good animations explaining how this actually works. This was the one that made it much more clear to me: https://svs.gsfc.nasa.gov/14915#media_group_379047
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Yeah, that was a cool launch and landing to watch. The tracking shots were really cool, and the landing was thrilling. I thought for sure it was going to land in the water on the side and then the view refreshes and it's standing upright in the middle of the barge. And then a few of the landing legs sparked with what I assume was the energetic welding holding the legs down to the deck of the barge.
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Right, of course, I missed that logic. IANAL, I didn't think of all the angles, just thought that based on NASA's past contracting history in general there might have been room for improvement. I guess not though, sorry for wasting time. Anyway, what's great is the design of the probes was able to handle the long propellant storage for the wait, and that the launch has now gone off without a hitch!You can’t know that without having been there. Since NASA is getting a great price, maybe … just maybe … that meant not having things like penalties for missing timelines. And trying to get those things, then, would have probably meant paying a lot more. It’s not clear why you think getting an historically low price for taking the risk the launch vehicle won’t be ready means that you also get to take no risk on the new launch vehicle not being ready.
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