I find it truly amazing that New Horizons was able to take photos of a 20 mile object whilst flying past at ~8 miles/sec - that’s an incredibly small space and time window within which to capture the images. Does anyone know how NASA manages to pilot spacecraft with this level of precision? What kind of engineering processes do you need to enable this?
Actually doing the fly-by is less impressive (the fly-by was planned and programmed a while ago) than the fact that we were able to line up Horizons to an object like this at all!
I find it more impressive and awe inspiring that stuff in space is so predictable that we can actually program the fly by such a long time in advance and get such a high degree of accuracy.
I also find this somewhere between impressive and amazing. However...
...after watching the Dragon/ISS docking manoeuvre for quite a bit longer than I probably should have, I think I now understand this precision better. When we think of "flying" including flying in space, we automatically have an image of something that's a bit unstable, always being buffeted a little, because that's how all the flying we are familiar with is.
Actually seeing that docking manoeuvre, you get a feel for just how stable things are in space. When the Dragon is parked in its relative position (10m?) it is just there, rock solid, as if attached with steel beams. No, better, as if both parts are part of a single piece of granite. No quivering, nothing.
Of course this is intellectually clear/obvious, but seeing it in practice is something different.
Yup. And if you've ever done maneuvers manually in KSP, you know that a tiny error in your nudge early on - e.g. hamfisting the throttle, or being a little too late in mid-maneuver staging - leads to a huge difference farther out, which you then have to correct, wasting precious ∆v :).
I'm very much impressed by the control precision of real-life space probes.
Wow, I actually had no idea; how is this all pre-planned, does somebody at NASA just put "67-P/Churyumov" into a "Orbital Maneuver Planner" and let some computers crunch the possible paths out? Or does someone actually sit down and come up with the possible sequence of orbital assits (to later verify with a computer) with a pencil and paper?
It's a combination of both. They have tools that help worth the trajectory calculations, but they have to manually decide on the basic layout of the path to take.
There is a very interesting interview with Pablo Munoz from the Bepi Colombo team about flight dynamics on the Omega Tau podcast that explains this: http://omegataupodcast.net/295-bepicolombo/
The other interviews on the same episode are also worth listening to. In fact, the entire podcast is great.
Common orbits are solutions to the two body problem, but Shane Ross has a few videos on youtube about chaotic solutions to the three body problem, allowing objects to move in very complex orbits with very little fuel. This has been used for a few missions as I understand it, the math is WAY above my head, but the video is still quite watchable with lots of cool orbit animations:
I think everyone with an interest in spaceflight should play Kerbal Space Program. It gives you a sense of scale, both of space and time (luckily you can fast-forward to 100.000x), and also teaches you the basics of making orbital trajectories and correcting them, landing on planets/moons with different gravity... I'm really glad to have played it!
> photos of a 20 mile object whilst flying past at ~8 miles/sec
Not to detract at all from the astonishing technical achievement, but that's the wrong comparison. You can see the ISS with your naked eye, and it's a <1 mile object flying past at 4.8 miles/sec. The right comparison is with the distance at which this photo was taken: 18,000 miles, or about half an hour from closest approach.
Actually, the right comparison is of the closest approach distance (~2000 miles) with the distance from earth (4,000,000,000 miles). That's like launching a missile from Los Angeles to New York and hitting your target to within a meter.
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.
No, 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, 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.
I 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.
Pulsars can be used to arrive at celestial positioning accurate to ±5 km. There is a test rig on the ISS that has validated this. No need to build human made beacons when the universe has so graciously provided us with them.
They plan to get within 1km, which is quite impressive for one system alone. Thanks for the pointer (after reading it, I remember having read about NICER, but didn't remember the precision they got)
Id 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.
Not 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.
Actually, in the case of New Horizons, it is. Mission navigators use LORRI images of known objects relative to the background stars to calibrate their position.
Brain 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.
"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.
> The right comparison is with the distance at which this photo was taken: 18,000 miles, or about half an hour from closest approach.
Implicit in this statement: the camera was pointing close to the direction of travel and the target wasn't moving much within the field of view. Hugely easier than trying to image from the side at closest approach, which at best would have given a smeared image and at worst a complete miss.
It's still impressive and awesome. But always try to skew the odds of success in your favor when dealing with stuff like this. You have one pass and then the opportunity is gone.
the development of double precision floating point, and the kalman algorithm, were two major improvements. Basically there is a computer at JPL that, given a location in the solar system and a current location of a ship, will give you instructions on when to burn. After you burn fuel to move, you update based on visual locations of known stars, fit a model, and do incremental burns until convergence.
The book Digital Apollo touches on a wide range of issues associated with building systems that can do this.
New Horizons is a mere few billion miles/km away, while financial matters these days sometimes involve trillions. Plus extra digits for cents and fractions thereof, of course.
“There are 10^11 stars in the galaxy. That used to be a huge number. But it’s only a hundred billion. It’s less than the national deficit! We used to call them astronomical numbers. Now we should call them economical numbers.” - Richard Feynman
i know you're joking but it's really the precision at large numbers that makes doubles so valuable. Typically when somebody is steering a spacecraft to a remote location, the large distance as well as the fine precision needs to be represented. I am not aware of people working with very large sums of money who also need penny-level precision (and even then, floats aren't the right solution).
JPL also has PhD applied mathematicians on staff to ensure numerical stability of their algorithms at double precision. Most developers do not have the ability to do that sort of non-trivial analysis. They are not just blindly saying "a double is good enough."
The problem with floating point for money is that simple calculations can give different answers than you would like because of how numbers are represented. E.g in a JS console:
> 0.1 * 0.1
<- 0.010000000000000002
This matters whenever you do things where the error might be allowed to accumulate and you're not careful to control for it. The general advice to avoid floating point for money is not because it's impossible to do correctly, but because it's very easy to get wrong in ways that are hard to discover with testing, and doing it with money is one of those areas where it's easy to get it wrong in ways that people will care about (because you're suddenly paying the wrong amount of tax, for example).
I don't know about you, but I don't trust myself to get this right, much less developers who often don't understand the issues involved.
It’s good enough for dollars and cents if you put thought into it, but you can’t just represent money as double-precision dollars and expect to get the results you need.
floating point was designed for scientific and numerical/math applications (written by people with numerical analysis skills), not money. There are decimal data types which are much better for money management.
I searched for "New Horizons GNC" and this link came up [1]. "The AOCS/GNC (Attitude and Orbital Control System / Guidance Navigation and Control) subsystem takes care that a spacecraft points to a specific point in space, determines the s/c attitude, and does trajectory corrections."
They actually managed to predict the bi-lobed shape by keeping track of when the shadow of the object swept different points on the Earth’s surface. Amazing.
I watched that video and when the pictures finally came out i was completely floored by how accurately they were able to predict the shape. An incredible problem solving strategy that seems very simple in hindsight.
Re: able to take photos of a 20 mile object whilst flying past at ~8 miles/sec...Does anyone know how NASA manages to pilot spacecraft with this level of precision?
I cannot speak for this probe, but other probes have made the probe itself or camera boom move slightly to compensate for the target moving relative to the probe. It's kind of like moving your head back and forth to follow a tennis match if your eyes alone have difficulty tracking.
The object looks like BB-8. We'll get even better pics in the coming weeks.
In the press conference they said that the spacecraft tried to take one megapixel image of Ultima Thule one hour after this image. Interesting to see it in couple months.
Kind of sucks that this is the big first picture that is being published. The LORRI, while an impressive piece of hardware in and of itself, is not built for high detail, close-in shots (although it was used some for the Pluto flyby closeups). That's the job of the Ralph telescope on-board the spacecraft.
It's a neat picture, but I fear that any subsequent pictures will have less impact on the public, as many laymen will say "Meh, saw that the other day on <insert_news_site>. Old news".
I'm really looking forward to the spectacular shots we will get from the close-in imager. New Horizons will be MUCH closer to this object than it was Pluto, so it should really get some fantastic shots of the surface features.
For comparison, just check out the wikipedia pages. They show a pretty solid contrast of the capabilities/uses of the two devices:
"The team says that the two spheres likely joined as early as 99 percent of the way back to the formation of the solar system, colliding no faster than two cars in a fender-bender."
Welded together by gravity, i'm really in awe seeing the, by far, weakest power so lovely at work.
So, two masses were close enough in relative velocity and vector, that one of them didn't careen off the other one, and instead, allowed the weakest of all known forces to bond them together as they hurtled at high velocity through space.
This object(s) seem statistically unlikely to me. I'm not saying it's artificial. That would be even more unlikely, by orders of magnitude. Just saying "Wow!".
Contact binaries are fairly common. Expected to make up about 10-15% of NEOs. My layman's understanding of how Kuiper object contact binaries develop is mutual capture during the early life of the solar system and angular momentum decay until they come into contact.
Can you say more about how angular momentum decays in orbital mechanics? I understand that, because the Earth rotates faster than the moon orbits, our tidal bulge will be ahead of the sublunar point, and will accelerate the moon in its orbit. Are there any other ways to get rid of angular momentum?
Tidal forces are one way - either between the two binary components, or from a close encounter with a third, larger body.
Another is the "YORP Effect". Sunlight falling on an asteroid produces a slight thermal radiation pressure (push). If, due to asymmetries in asteroid shape/albedo, the net radiation pressure force is not aligned with the asteroid's center of mass, it will produce a torquing force which will cause the asteroid to spin faster (or slower) over time. Applying the idea of YORP Effect to binary asteroids yields the "BYORP [Binary YORP] Effect", by which the orbital dynamics of the binary system are modified by this asymmetric radiation pressure over time, in a way that either pushes them together into a contact binary or apart into two unbound asteroids.
It's even hypothesized that some asteroids may be in a binary/contact-binary cycle on long timescales! There are solutions to the above in which the BYORP effect causes a loss of angular momentum in a binary pair, causing them to merge into a contact binary - but the contact binary may settle into a state where the YORP Effect actually causes the newly merged asteroid to spin faster, eventually flinging them apart due to centripetal forces... back into a binary state where the BYORP Effect may again cause them to merge someday.
> This object(s) seem statistically unlikely to me.
At this mass these bodies are at, they aren't going to crush together from gravity to form a single round body.
However, if you've got two bodies in very similar orbits around the Sun, in close proximity, it doesn't seem incredible to me that they might eventually collide and stick.
When you think about the vastness of space (even in our own star system), as well as the incredible amount of time involved since the formation of our system, many things that seem statistically unlikely probably become very likely. How many objects are in orbit around the Sun in this system? We probably only know a small fraction of them, since we can't see ones this small very well from this distance, and there could be many more that are even more distant. So really unlikely objects like this could be more common than you think.
In the vastness of a universe as large as ours, polka dotted unicorns are probably very likely. But it's still unlikely to actually encounter one ... you know, because they're polka dotted unicorns and because the universe is so big...
What I mean is, your argument doesn't make any sense. Just because the universe is big, doesn't make unlikely events more likely to be stumbled upon.
If a center of mass begins to aggregate in an area of space, smaller objects may get captured and will move in an elliptical orbit with the forming object at one of the foci of an ellipse. Because the other foci of the ellipse is also fairly stable, it is also a likely point for smaller objects to aggregate into another larger object. Objects forming in pairs can reinforce each other. Over time when the small objects around the two foci have all aggregated, the objects at the foci will fall together due to gravity.
It doesn’t seem unlikely to me. There are many many approach paths that would result in two similar sized objects ending up orbiting each other.
Once they are orbiting each other then it’s just a matter of time for the orbits to decay. In the final, they would be spinning very very fast but would be inching towards each other until they touch.
Given the slower speeds in the outer solar system, especially since they will be rotating in the same direction, so the relative speed will be less, I would imagine that contact binaries would be fairly common. And since they are primarily made of ices, the actual contact event should melt the ice, which will then re-solidify since the impact speed is so little.
I don't know if this is how it actually happens, but it gives a mechanism for this being fairly common. The only information I could find was a short wikipedia article:
What's exciting to me is, both the first interstellar object we've observed visiting our solar system (Oumuamua) and the first Kuiper Belt Object we've visited have been "unusual". That strongly suggests to me that the unusual is more usual than we would have suspected, which means there's probably a great deal of opportunity to increase our understanding of the universe!
Oumuamua was literally the only extra-solar object known. There was nothing to be picked.
Similarly for Ultima Thule. They may have been able to find a different target, but it was very difficult to find any target at all in the first place (lots of Kuiper belt objects are known; the difficulty was finding one that could be reached by New Horizons). See this Twitter thread that was linked elsewhere: https://twitter.com/Alex_Parker/status/1077986070128668674
At least in the case of Oumuamua though, being non-spheroid wasn't really the weird thing about it. It was that it exhibited comet-like acceleration, without any visible off-gassing, and without breaking up as it passed the sun, as a comet would be expected to do. Also the fact that from our current understanding, it is much more likely for a comet to be ejected from a solar system than an asteroid, so it's surprising (not impossible, certainly, but unlikely) that the first interstellar object was more like an asteroid.
Pluto may be a KBO also. Further, it's possible some moons of the gas-giant planets are captured KBO's.
The unusual thing about Ultima Thule is that it's in a nearly circular and "flat" orbit, which many experts interpret to mean it's mostly undisturbed from its point of origin. It's a prime "fossil".
Pluto has a "disturbed" orbit such that its origin is currently unknown. Same for gas-giant moons. Pluto has also been turned inside-out, perhaps multiple times, by a still unidentified force. Ultima Thule is probably mostly as-is since formation.
> Pluto has also been turned inside-out, perhaps multiple times, by a still unidentified force.
Whoa, come again? How do we know this? What does it mean for a planet-like object to be turned inside out?
Inside out just means that the local equivalent of Earth's geologic plates seem to be subducting below the surface and fresh geologic plate equivalents are abducting back up. You can estimate how long a planetary surface has been exposed to the elements by the statistical distribution of number and size of craters. We have a reasonable idea of the likelihood of objects impacting Pluto, and it should have a lot of craters. Pluto's moon Charon has many more visible craters but Pluto has large areas with no large craters, so some sort of geologic process must be going on that's recycling areas of the landscape and covering or subducting the craters.
Given lack of fast erosion from liquid water or significant wind (in a very thin atmosphere), whatever geologic process is smoothing out Pluto is happening quickly compared to other points of reference we have.
I use the example of Earth's geologic plates, but that's only one possible explanation. There's also speculation about freeze/thaw cycles of the planetary material and atmosphere (since it has an irregular orbit), movement of water-ice mountains, cryovolcanos, and other theories.
"hi-res" is relative - this is still about 5 times the feature size that was actually captured by the LORRI camera. Going to have to wait at least a few days for the glorious 30m/pixel version.
Pluto's flyby generated about 8GB of data and it took about 16 months to get all of it downloaded [1], and this data includes more than just the images, and i read somewhere that the Ultima Thule flyby will generate about 6GB of data.
I think the images are the first thing that get downloaded, so it should not take more than a week to get all high res images.
Each line is the same star viewed from a different point on Earth. They arranged for telescopes in a long line North to South to all observe UT at the same time, just as it was predicted to pass in front of the star. Then they precisely timed the apparent blinks of the star. The North-South offset meant the star bisected UT across different sections for each telescope.
Then they just worked out the parallax difference and mapped out the blink times on a chart to see the silhouette.
Those streaks in that pic are the path of a star that UT passed. Given they know the velocity, if they time the period where the light from the star is occluded, they get a measure of how wide the object is at that elevation.
I've been getting most of my updates for this from /r/space personally, but I think that's the main attraction of HN for me. I don't need to curate my own list of subreddits to get links to content that interests me, because it's all (mostly) likeminded people on here that are on average interested by the same kind of stuff as me. I find more new interests on here than I ever could on reddit looking through my preconceived list of interests.
Whenever I see these updates, I am reminded of the three body problem trilogy and its contemplations on space exploration (the parts I enjoyed the most).
Then I get sad because things just take so incredibly long on a stellar scale, and a human life is so short.
I agree. However, the people that are paying for this mission still use imperial units. Those of them that are paying the most attention would probably agree with us though.
US customary units are not imperial units. Many people don't realize, for instance, that MPG is not comparable between the US and the UK because gallons are substantially different.
It's pretty common. Based on radar data about 10-15% of Near Earth asteroids (larger than 200 meters) are contact binaries (or contact-binary shaped at least). We don't have enough data on main belt asteroids, trojan asteroids, and especially TNOs/KBOs to say what the percentages look like for those populations but it's a fair likelihood that the proportions are at least as high if not higher among KBOs.
14 missions to comets, 20 to asteroids, and around 50 planetary small moons imaged well enough to see their shapes. Under a hundred miles in diameter many have irregular shapes. I would guess this shape only occurs a few percent of the time.
Wednesdays news conference speculated UT shape is primordial, while the others may have been carved through four billion years of planetary evolution.
The new images — taken from as close as 17,000 miles (27,000 kilometers) on approach — revealed Ultima Thule as a "contact binary," consisting of two connected spheres.
Are these common in the asteroid belt or as smaller moons of the outer planets?
I highly recommend reading the book Chasing New Horizons by Alan Stern[0]. It is a great insight into years of work it takes to get a mission like New Horizons going. It is a very well written book and I could not put it down until finished.
This is still nowhere near full resolution - it's at 140 meters per pixel, whereas the camera got 30 meters per pixel. It's going to take a few days to download the full images at 1kbps though.
No, "baud" counts number of signal changes per second, which would equal number of bits per second in the old past (one bit encoded by one signal change). Ever since modems changed to e.g. quadrature encoding the number of bits per second would be higher than the baudrate. When somebody talks about bitrate these days then bps (bits per second) is what they should be using, not baud.
Can't help to mention that several round stones stacked in balance is so artificial that is an 'universal' sign to mark the path in wild remote areas. A typical I was here sign.
No, this photo was taken before the closest approach (note the very high sun angle, there's basically no shadows, so the probe was still inside the orbit of UT when the photo was taken). It's going to be another month before we see the closest/highest resolution photos (and years before all the data is downloaded)
Modeling it as two spheres, one 16 km across the other 12 km, with a density the same as water, its total mass would be about 3*10^15 kg. At a distance of 8 km from the center of mass, the escape velocity [0] would be about 7 meters/second or 16 miles/hour.
But the asymmetry of Ultima Thule means that its gravitational field would be weird. Not like a sphere at all. So the acceleration of gravity and escape velocity would vary a lot from place to place.
Probably not, from the approximate sizes noted in the article it sounds like Ultima Thule is a bit bigger than Diemos, which XCKD says you could escape with a bicycle and a ramp.
And just for fun, I also worked out a best guess for the force between the two "lobes": 1.5 x 10^13 N (assuming Ultima Thule is the same density as our Moon), which is about equal to the (Earth) weight of all the ships in the world. [0]
