The above image comes from a 600-kilogram, refrigerator-sized robot travelling at about 15 miles per second, around 170 million miles from Earth. They can be glad that the asteroid is also around 170 million miles from earth, travelling at 15 miles per second and this even in the same direction.
Relative motion is smaller though:
The gravitational force between the probe (660kg) and asteroid (4.5 * 10^11kg) is just 0.1 N. The probe has therefore to be circling the asteroid with about 0.25m/s or just 1km/h (0.57 mph for american readers).
And how else could it be: the asteroid was assumed to be a point mass and the probe in a circular orbit of 450m around it.
The hayabusa spacecraft is not in orbit about the asteroid. It's in orbit about the Sun, in an orbit very, very close to the orbit the asteroid is in, so they stay close to each other for a long time (about a year and a half IIRC).
The disclaimer was meant to say that it's just an idealized system of two masses at a given distance. I picked these values to show what speed an object orbiting around a 'light' object like an asteroid approximately has.
So sorry: it's not in that orbit. I should have made that clear instead of talking about the probe, circling, ... which sounds pretty concrete.
(The asteroid is not spherical or homogenous and is even supposed to be a "rubble pile" with large holes inside which makes it highly questionable at best to treat it as point mass (you could if the probe were far enough away from it ... which it is not at all), but hey ... ¯\_(ツ)_/¯)
I assume you calculated the average force and relative velocity experienced in the 450m circular orbit. At the perigee of the polar orbit (when the picture was taken) the force and the relative speed should be bigger. Also due to the small size of the asteroid the gravity should be quite uneven during the approach.
Hayabusa2 is such a cool mission! A veritable space Swiss Army Knife with tantalum bullets, deployable free-floating cameras, four small rovers that hopped around the asteroid in super low-G, and a 1.5kg kinetic impactor that blew a crater.
I went poking around Wikpedia. Ryugu's surface is mostly carbon. It's also a "rubble pile" and about 50% of its volume is empty space. There could even be large voids within because the force of friction between pieces is greater than the force of gravity holding it together.
I would guess even operating the RCS system could launch some of those loose looking rocks to escape velocity. Imagine blowing on a rock that's been in place for thousands of years and watching it drift into space.
It's hard to get a sense of how big these features are. 30 feet is damn close, but it's still hard to say. How big is that big chunk of rock (?) near the bottom-right, casting a blocky shadow?
Insane Contrast ratio - ultra bright sunlight when the sun gets in the frame (no atmosphere to diffuse light) plus ultra dark hard shadows as the light source is millions of miles away, and again no atmosphere to diffuse the light.
Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
And incredible motion, the spacecraft is whipping by the asteroid quickly.. so you'd need a fast shutter speed to get sharp detail. Which is made difficult by the lighting conditions.
No human photographer on the shutter button. Way too far away for that.
> And incredible motion, the spacecraft is whipping by the asteroid quickly
No it's not. The whole point of the Hayabusa2 mission is to go to the asteroid and stay there. In fact it landed on it and grabbed a sample back in March.
Could the spacecraft—just in theory—introduce an atmosphere? Maybe not this spacecraft, but if we’re riding around in the starship Enterprise and want to get better snaps of asteroids, would it be a good idea to just send out a big pair of glass hemispheres, encapsulate the asteroid with them, pump them full of air, and then take a picture of the asteroid-capsule system?
Alternately, could you stick something really good at diffusing light—like a big block of aerogel—between the sun and the asteroid?
> Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
Is it so dark? IIUC the asteroids is almost at the same distance from the Sun than Earth (something like a 50% more) so the illumination should be similar (about a half, but a glass that blocks half the light looks totally transparent at sight, it's weird to measure it experimentally). Is the soil of the asteroid too dark? Like what? Grounded coffee?
The camera was not a priority for this mission. The small monitor camera was built and installed on the spacecraft thanks to public donations. This mission is about chemical and physical properties of the asteroid. Having a camera on it is mainly for publicity. NASA did a similar thing with the Juno spacecraft, letting people vote on where to point the camera while the main mission was to map out Jupiter's magnetic and radiation fields.
Indeed, none of these cameras need to be super crisp, although DCAM-3 (the deployable camera) is both a navigational tool and expected to provide some scientific insight. It was used to monitor the impact from the crater they created for the next sample, while Hayabusa 2 was safely on the other side of the asteroid: https://twitter.com/haya2e_jaxa/status/1114112619844005889?l.... That thread also has a shot from one of their navigation cameras, which apparently has a flash.
I love how many deployable objects this spacecraft is carrying, the target markers included. The number of moving parts must be staggering! (I wonder if they charge over USB? :b). JAXA has really amazed me with how resilient their missions have been. (The first Hayabusa limped back with a sample after a bunch of engine failures; their Venus probe failed to enter Venus's orbit, spent 5 years orbiting the sun, then tried again and worked). There's clearly a mountain of potential over there, so it's a treat to see this one go so perfectly smoothly :)
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Relative motion is smaller though: The gravitational force between the probe (660kg) and asteroid (4.5 * 10^11kg) is just 0.1 N. The probe has therefore to be circling the asteroid with about 0.25m/s or just 1km/h (0.57 mph for american readers).
And how else could it be: the asteroid was assumed to be a point mass and the probe in a circular orbit of 450m around it.
So sorry: it's not in that orbit. I should have made that clear instead of talking about the probe, circling, ... which sounds pretty concrete.
(The asteroid is not spherical or homogenous and is even supposed to be a "rubble pile" with large holes inside which makes it highly questionable at best to treat it as point mass (you could if the probe were far enough away from it ... which it is not at all), but hey ... ¯\_(ツ)_/¯)
TFA called it a cannonball, which is really quite amusing.
Yup, and you break my ability to zoom in or right click and view image on mobile.
Welcome to the future.
[0]https://www.cnet.com/videos/japans-hayabusa2-space-probe-fir...
Again ultra dark, so the camera needs to have an incredibly sensitive sensor.
And incredible motion, the spacecraft is whipping by the asteroid quickly.. so you'd need a fast shutter speed to get sharp detail. Which is made difficult by the lighting conditions.
No human photographer on the shutter button. Way too far away for that.
Incredibly challenging photographic environment.
No it's not. The whole point of the Hayabusa2 mission is to go to the asteroid and stay there. In fact it landed on it and grabbed a sample back in March.
Could the spacecraft—just in theory—introduce an atmosphere? Maybe not this spacecraft, but if we’re riding around in the starship Enterprise and want to get better snaps of asteroids, would it be a good idea to just send out a big pair of glass hemispheres, encapsulate the asteroid with them, pump them full of air, and then take a picture of the asteroid-capsule system?
Alternately, could you stick something really good at diffusing light—like a big block of aerogel—between the sun and the asteroid?
Is it so dark? IIUC the asteroids is almost at the same distance from the Sun than Earth (something like a 50% more) so the illumination should be similar (about a half, but a glass that blocks half the light looks totally transparent at sight, it's weird to measure it experimentally). Is the soil of the asteroid too dark? Like what? Grounded coffee?
I love how many deployable objects this spacecraft is carrying, the target markers included. The number of moving parts must be staggering! (I wonder if they charge over USB? :b). JAXA has really amazed me with how resilient their missions have been. (The first Hayabusa limped back with a sample after a bunch of engine failures; their Venus probe failed to enter Venus's orbit, spent 5 years orbiting the sun, then tried again and worked). There's clearly a mountain of potential over there, so it's a treat to see this one go so perfectly smoothly :)
Edit: Thank you to all the other posters who wrote way better answers with more information!