
Hayabusa 2 rovers send new images from Ryugu surface - DanBC
https://www.bbc.co.uk/news/science-environment-45667350
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cheeko1234
"Gravity on the surface of Ryugu is very weak, so a rover propelled by normal
wheels or crawlers would float upwards as soon as it started to move,"
officials with the Japan Aerospace Exploration Agency (JAXA) wrote in a
description of MINERVA-II1A and MINERVA-II1B.

So, the robots — each of which measures 7 inches wide by 2.8 inches tall (18
by 7 centimeters) and weighs 2.4 lbs. (1.1 kilograms) — hop instead. They do
this by moving a "torquer" in their interior, which rests atop a disk-shaped
turntable.

By rotating the torquer, a reaction force against the asteroid surface makes
the rover hop with a significant horizontal velocity," a team of researchers
led by JAXA's Tetsuo Yoshimitsu wrote in a 2012 study outlining the concept.
"After hopp[ing] into the free space, it moves ballistically. With this
mechanism, by changing the magnitude of torque, the hopping speed can be
altered, so as not to exceed … the escape velocity from the asteroid surface.

Src: [https://www.space.com/41941-hayabusa2-asteroid-rovers-
hoppin...](https://www.space.com/41941-hayabusa2-asteroid-rovers-hopping-
tech.html)

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mc32
Wonder if they could use some sort of rather slow mechanical deformation to
provide movement with pump mechanisms. I guess that still would rely on
significant gravity or other anchoring ti avoid slippage.

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GlenTheMachine
Problem with that is you're relying on the surface properties of the material
you're pushing against. If it's too soft, you get no motion. If it's too hard
you get too much. The nice thing about using internal reaction wheels is that
the torque you get is entirely independent of the surface you're resting on.

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mc32
Oh those are very observations. Thanks for pointung them out.

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black_puppydog
I love that they opted for color cameras. Not much color to be seen, but the
flares, together with the motion blur (while falling and hopping!) make the
pictures look really dynamic. :)

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joemi
I'm not entirely sure that's motion blur. The images shown in the article make
it look like it's just lens distortion. It's probably a fairly wide angle
lens, and that's why things look stretched out the further from the center of
the image they are. (I think.)

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black_puppydog
Some of it definitely is, they even mention it here:
[http://www.hayabusa2.jaxa.jp/en/topics/20180922e/](http://www.hayabusa2.jaxa.jp/en/topics/20180922e/)

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chuckledog
すごいよ Sugoiyo! Super! Cool! Wow! Awesome achievement Japan.

I really admire that its means of propulsion doesn’t involve wheels (since the
gravity is so low)

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joering2
Just came back from Europe. Everyone knows about this and all media reported
on it. Surprisingly so little is said in American media. Its not new that
Americans do not like other nations succeed in space! If these were US-based
rovers, each network will give it 10 minutes cover. Same sad story about
Chinese Moon landing. Most American friends laughed at me when I told them
China landed rover on moon. Some even question Wiki article as conspiracy
theory.

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z2
Consider literal competitions--it was similarly appalling to watch recent
Olympics in the US. 95% or more of the coverage was of Americans winning. If a
particular day had fewer wins, they would replay earlier footage rather than
dare show any other country succeeding at non-American dominant areas. One
saving grace is that the NBC app had all the footage they didn't deem worthy
of broadcasting.

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maxxxxx
I can't watch the Olympics on US TV. Hours of stories about the upbringing of
the US athletes interviewing moms and grandparents. Then a little actual sport
if you are lucky. And certainly nothing where there isn't a US athlete/team at
the front. It's unbearable.

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justtopost
I cannot agree more. I remember growing up it was just raw footage of events
without break, and often with little or no commentary. We would sit for hours
and watch the pinnicale of human physical ability. Now its 95% pomp and
commentary, and you find yourself just looking up the events you wanted to
watch the next day on a video hosting site. This just fits into the larger
context of broadcasting digging their own grave in the glow of the internet.
Even though their offerings are still often technically and artistically
superior, the are bound outside like writhing beasts to their business model
and it kills them by forced exposure (nessitating constant 'content'). Youtube
is now doing the same by deranking channels that fail to release videos on a
regular, if not frantic, schedule. Patreon is helping, but just enough to
defer actually dealing with the huge problem. Its a vicious cycle.

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walrus01
Considering their very tiny size, I'm curious about three things... What sort
of software/watchdog timer these mini rovers have set up for charging their
batteries, the size and type of the batteries (in Wh, chemistry, etc), and how
often they wake up and take photos and temperature measurements.

The size of the surface area exposed to the sun with high-efficiency PV cells
is not very large, since they are so tiny. I'm assuming the cells are triple-
junction GaAs for the greatest Wh per square cm per day.

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tychomaz
What compression protocol is used to send images?

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JoeAltmaier
The pictures are thrilling! The rock looks stratified - which might imply they
were created under gravity? Or is it just the camera angle...

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sandworm101
Less gravity, more radiation/light. There is lots of water/ice involved, and
the rock varies in distance from the sun. So the layered effect is probably
the result of different temperatures at various depths, and the resulting
sublimation (or not) of water ice. Imho it is akin to the layered effect in
soil during a hard frost.

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sytelus
Stupid question: why does these images look so low res and over/under exposed.
Sometime I feel iPhone camera tend to do much better job than those million
dollar cameras on these missions. I am obviously missing some key details.

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dekhn
One of my personal wishes is that we covered as much surface area of asteroids
and other interesting bodies in the solar system; one wonders, if we sample
enough, what unexpected things we will find?

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yazr
How does one "land" on an asteroid which is spinning too fast ?

Is it at all possible to match the spin of a smallish android from orbit ?

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tychomaz
They have an open websocket to an Asteroid Landing five-layer Neural Network.
The lander sends images back in real time and the earth-borne NN sends it
telemetry adjustments in BSON.

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gchokov
Sadly, no diamonds on the surface. Or gold. Would love to see how "the market"
will react to that ;)

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skykooler
Diamonds are unlikely to be found on asteroids, because they require immense
pressures to form, and the gravity on asteroids is so weak that even at the
core the pressure is less than sea level air pressure on Earth.

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narag
Except if the asteroid is a piece from a bigger body that got teared apart.

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rhcom2
Just fantastic.

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21
I'm sure it's a very complicated problem, but I would have expected a 5 year
old rover to have a better camera.

I am a bit shocked at the potatoness of it.

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rwmj
I'm pretty sure it's not a poor camera because they couldn't afford it. It'll
be because of weight considerations. If you have a higher resolution camera,
everything has to be bigger and heavier - larger camera, more local storage,
more processing power, bigger antenna (these have to be sent using lossless
compression for science), etc. Each robot has a mass of 1.1 kg, lighter than
my laptop - and it has to do other science and return a sample to earth!

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withinrafael
I suspect that too, but am looking for data to support this. We have tiny
miracles in our cell phones today, are they really any heavier than what's on
that vehicle? (I understand a cell phone camera isn't Space Ready™.) Does it
require, perhaps, additional hardware that wouldn't be needed otherwise with
today's on-board solution? And what's up with the severe lens distortion?

Cool topic I hope to dig into a bit to get those answers.

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Rebelgecko
A few factors I can think of:

The rovers launched in 2014, and they were designed well before that. I
wouldn't be surprised if the camera hardware was decided on in 2010

A normal camera in space is going to have problems. I'm not any sort of camera
expert, but I can imagine there's a _lot_ of electronics in one. There's the
sensor. That sensor may be hooked up to an analog to digital converter, which
might be hooked up to a processor that converts whatever the sensor reads into
a compressed image. Someone who is familiar with how cameras work can probably
think of a dozen bits I'm missing :)

All of those bits of silicon are going to get bombarded with radiation, so
they need to be radiation hardened. Smaller transistors are especially
susceptible to radiation, so your radiation hardened chips are going to be
bigger, more power hungry, and generally not as good as more up to date ones.
From looking around online, it looks like the best rad-hard cameras _today_
are only a couple megapixels.

I'm not sure about this case, but often times cameras not a priority for a
mission. They're great for generating PR and excitement, but in terms of
scientific value there's lots of other instruments that may have higher
priority (both in terms of the design, and in terms of available bandwidth for
returning data). If the cameras are just there to make sure the rover doesn't
crash into something, they're probably using a wide angle lens which helps
with navigation but can cause distortions.

