4 ms·
To be fair, while that's an accurate representation of the distances, it's not accurate of the difficulty. They don't have to deal with unpredictable atmosphere
by jdmichal 8y ago
To be fair, while that's an accurate representation of the distances, it's not accurate of the difficulty. They don't have to deal with unpredictable atmosphere. There's reasons laser-guided missiles are about 1-2 meters-ish of accuracy with constant guidance, while we can basically fire-and-forget spacecraft to 4 billion miles away.
- Retric 8y agoSpacecraft also do some corse corrections. You can also measure where your going very accurately averaging over a few hours.
- dwaltrip 8y agoThey do have to deal with accurately determining the target destination, especially so in this case.
- lisper 8y agoNo, that's actually not true. Hitting Ultima-Thule is much harder. For starters, just figuring out where U-T actually is is very difficult. The observations we have only constrain two of its three degrees of orbital freedom. The third has to be inferred via orbital mechanics. Likewise, figuring out where the spacecraft is is also non-trivial. By way of contrast, figuring out where you are relative to New York to within a meter of accuracy is, nowadays, a simple matter of switching on your GPS receiver. (Even without GPS, all you need is inertial guidance that is stable for half an hour or so. That's much easier to achieve.) Finally, there are unpredictable orbital disturbances. N-H uses thrusters for attitude control, whose effect on the trajectory is not entirely predictable. (c.f. https://en.wikipedia.org/wiki/Pioneer_anomaly https://en.wikipedia.org/wiki/Pioneer_anomaly, which was only detectable because, although Pioneer had thrusters, they were turned off for long periods of time). I know these things because I used to work at JPL. There are entire teams dedicated to spacecraft navigation. The stuff they do will blow your mind.
- rbanffy 8y agoI wonder how much would it cost to build a GPS-like network for the whole solar-system... The good thing is that, for such a thing to be really useful, we'd have to invent better propulsion systems which would, in turn, make the network much cheaper to build.
- thereisnospork 8y agoId guess it could be done for not that much, assuming accuracy can go from a few meters to few thousands of miles. (Someone more versed might be able to give a better oom on accuracy). Just need to launch 4(+) satalites, 2 up and 2 down relative to the orbital plane. So long as a ship isn't hiding behind a planet/sun it should have LOS to all 4 for triangulation.
- garmaine 8y agoWe have one--stellar navigation. It's what they use.
- lisper 8y agoNot exactly. You can use star location to determine a spacecraft's orientation (and they do), but its location is determined by measuring the doppler shift of the carrier signal sent from the spacecraft back to earth and running those results through some pretty hairy math. GPS works by having a network of beacons in known locations transmitting signals with known timing. I just learned from a sibling comment in this thread that they're working on using pulsars as the beacons. But building an artificial GPS system for the solar system would require sending out a network of satellites into solar orbit. That might be technically feasible, but not economically feasible.
- raattgift 8y ago> two of its three degrees of orbital freedom Three? > I know these things because I used to work at JPL Ok, I don't. What are the three DoFs and how do they relate to 6DoFs or six Keplerian elements? Some background-fixing?
- lisper 8y agoBrain wedgie. I meant six. And direct observations give you four of the six. I guess I was just thinking about 3-d location and just forgot about the time derivatives. Sorry.
- deleted 8y ago[deleted]
- kzrdude 8y agoThanks for the link, didn't know the pioneer anomaly had a conclusion.
- kamaal 8y ago>>I know these things because I used to work at JPL. There are entire teams dedicated to spacecraft navigation. The stuff they do will blow your mind. How do we get to work with these teams, if even possible? (Though it should be impossible for me(given I'm an Indian), still how do someone who could work there go about joining them)
- lisper 8y agoStart here: https://www.jpl.nasa.gov/opportunities/ https://www.jpl.nasa.gov/opportunities/ (BTW, in this day and age if you can't figure out the answer to a question like that on your own, you're not ready.)
- jameshart 8y ago"They don't have to deal with unpredictable atmosphere" Well, no, but they do have to deal with an atmosphere that has, until they get to it, only been theorized about, never observed - which is not the case for the atmosphere above New York. There have been precisely four spacecraft that have gone anywhere near so far out as New Horizons, and they are between them the source for the majority of data we have about the atmosphere in the outer solar system. One of them discovered an anomalous acceleration effect that confused scientists for decades (and which, while it turns out not to have been externally caused, certainly left scientists wondering for a while whether their model for the solar wind was accurate). Of those that we believe have passed through the termination shock of the solar atmosphere, none have yet returned much accurate information, so we actually don't know much about the conditions there. I don't mean to say that these effects have meaningfully impacted navigation for deep space probes, but more these are genuine voyages of discovery - where they're going is predictable but until they get there we really don't necessarily know whether our predictions will be accurate.
- perl4ever 8y agoI believe New Horizons did course corrections, even fairly late.