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Mission: Hayabusa 2
pandaneko
post Sep 23 2018, 03:09 AM
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Something has been bothering me a lot. It is as follows.

If an asteroid is made of hard metal and somewhow it is covered with sands and pebbles and rocks and if someting collides with it very
hard resulting schock wave must be cataclysmic to shake them beyond escape velocity, leaving nothing but the metal asteroid.

Craters on Ryugu seem to suggest that Ryugu is like a metal, soft metal, soft enough to leave crater holes but hard enough not to break
up on impact. So, why are there regolith and boulders still left on Ryugu? Where did those boulders come from in the first place?

I am trying to persuade myself that those shaken off Ryugu travelled into deep space and came back to where they started from after
billions of years in the solar system. Am I going mad?

P
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Explorer1
post Sep 23 2018, 03:29 AM
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There's probably no metal at all in Ryugu, it's more of a 'rubble pile', of low density rocks (just like Itokawa), with many voids and empty spaces inside. I'd guess the inside is as broken and fractured as the surface the cameras can show us.
The craters we see are all very soft, with rounded edges, and every impact just breaks off more pieces, which either don't have enough velocity to escape and come back as boulders (I'd guess the enormous one at the pole is one), or, if they have enough velocity, fly off as separate bodies, permanently. The ones we see now were all probably part of the original body when it first broke off in turn from its parent body eons ago, and have just been broken up and reformed, probably many times since.

The impact projectile Hayabusa 2 is carrying is the perfect experiment to demonstrate this when they fire it at Ryugu. It should replicate the natural process on a smaller scale.
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wildespace
post Sep 23 2018, 06:22 AM
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QUOTE (Explorer1 @ Sep 23 2018, 04:29 AM) *
There's probably no metal at all in Ryugu, it's more of a 'rubble pile', of low density rocks (just like Itokawa), with many voids and empty spaces inside. I'd guess the inside is as broken and fractured as the surface the cameras can show us.
The craters we see are all very soft, with rounded edges, and every impact just breaks off more pieces, which either don't have enough velocity to escape and come back as boulders (I'd guess the enormous one at the pole is one), or, if they have enough velocity, fly off as separate bodies, permanently. The ones we see now were all probably part of the original body when it first broke off in turn from its parent body eons ago, and have just been broken up and reformed, probably many times since.

The impact projectile Hayabusa 2 is carrying is the perfect experiment to demonstrate this when they fire it at Ryugu. It should replicate the natural process on a smaller scale.

Ryugu's extremely low gravity probably corresponds to it being a rocky rubble pile. If it were a solid metal asteroid, it would have a much stronger density and gravity, right?


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OrbitrapInSpace
post Sep 23 2018, 10:28 AM
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QUOTE (pandaneko @ Sep 23 2018, 05:09 AM) *
If an asteroid is made of hard metal and somewhow it is covered with sands and pebbles and rocks and if someting collides with it very
hard resulting schock wave must be cataclysmic to shake them beyond escape velocity, leaving nothing but the metal asteroid.


the collision will result in huge fragmentation, generating a kind of cloud of material, which will collide each other and dissipate the energy, to the point their relative speed is reduced and accretion starts again.

close observation of Ryugu and its reaction to the impactor is hence part of the evaluation of the theoretical descriptions.

Patrick Michel is part of the Hayabusa scientific team, and he is an expert in simulation of such processes,

movies illustrating the various mechanisms here : simulations of asteroid collisions

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pandaneko
post Sep 23 2018, 11:51 AM
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QUOTE (OrbitrapInSpace @ Sep 23 2018, 07:28 PM) *
the collision will result in huge fragmentation, generating a kind of cloud of material, which will collide each other and dissipate the energy, to the point their relative speed is reduced and accretion starts again.

movies illustrating the various mechanisms here : simulations of asteroid collisions


OrbitrapInSpace , thank you for this. My thinking was too simplistic. I would have thought that all bits and pieces on the asteroid surface
will move in the same way upon impact, each with enough escape velocity. Mutual collisions in confusion after impact leading to energy
dissipation, no, never thought about it that way.

My guess is that they will then fall into an equilibrium state for some time, just like gas molecules in a container, forming, presumably
clouds around the asteroid, then eventually falling back down to its surface, making up regolith and boulders as we see now.

Yes, it makes sense.

P



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mcmcmc
post Yesterday, 07:44 AM
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QUOTE (dvandorn @ Sep 22 2018, 03:30 PM) *
Outstanding!

I have one thing about which I am curious. The final of the three images states it was taken while its rover was in mid-hop. I'm wondering why any hopping activity was occurring without any commands sent from Earth -- I didn't see any indication of pre-programmed hopping set up in the deployment and landing timelines

I don't remember which one, but one rover has an "automatic temperature-triggered hopping engine": every time it passes from light to shadow and viceversa, the mechanism is triggered and the rover bounces.
For ever, as it does not use any fuel but the sun.
It is one out of 4 or 5 different hopping mechanisms being tested.

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mcmcmc
post Yesterday, 07:58 AM
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QUOTE (mcmcmc @ Sep 24 2018, 07:44 AM) *
I don't remember which one

Looks like it's the "next one":
QUOTE
Yamagata University was in charge of one of the moving mechanisms installed in MINERVA-II-2. We devised and developed an "environmentally driven" moving mechanism using bimetal as an actuator, utilizing large temperature difference caused by the presence or absence of sunshine. Bimetal is a laminate of two types of alloy thin plates with different expansion coefficients, and it is a buckling type (mainly developed by Mineki Laboratory) that tends to bend due to temperature change and momentarily warps to the opposite side when exceeding the limit point , And a magnetic latch type which momentarily warps off the magnet (mainly developed by Tsumiki Laboratory). Even if the ambient temperature varies depending on the MINERUVA - II - 2 's dropping position and surrounding conditions, the possibility of either of which can be coped with is raised by setting the operating temperature to be shifted to the high temperature area and the low temperature area respectively. The rotation period of this asteroid is about 8 hours, and hopping in random directions every 4 hours corresponding to morning and evening.


http://mineta-lab.yz.yamagata-u.ac.jp/HAYABUSA2.html
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mcmcmc
post Yesterday, 09:05 AM
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I can't find anything about rovers "1", but quite a lot about rover "2".

Next rover (Minerva-II-2) hopping mechanisms which are going to be tested:

1) Eccentric motor, which consists of a brushless DC motor.
This actuator enables ROVER2 to micro-hop by the motor’s vibration force

2) Elastic cilia mechanism on the ROVER2 surface fosters micro-hopping capability, and thus this is expected to achieve precise locomotion in a micro-gravity asteroid. (by Kenji Nagaoka, Kazuya Yoshida)
Prof Kazuya Yoshida Facebook page (last post: 2014).

3) Magnetic permanent magnet mechanism using a DC brush-less motor.
This actuator consists of one movable magnet and two stationary magnets, and enables ROVER2 to hop by the impact force generated when the movable magnet sticks to the stationary magnet. This mechanism provides a large impact force in spite of low power consumption.

4) Metallic and thin leaf spring.
The actuator stores preliminarily the elastic energy of the spring by bending it. This enables ROVER2 to hop by the impact force generated when the bending energy releases. The stored bending energy is locked by “tegus” before its driving, and will be released all at once by burning off the tegus.
ROVER2 has two metallic springs. Each spring is non-reusable but is highly reliable in harsh space environment because of its simple mechanism.

5) Shape Memory Alloy (SMA).
The most advantage of this actuator is that it can work with a change of surrounding temperature. This enables ROVER2 to hop by the impact force generated when the SMA bends in a specific temperature condition. As for safety launch-lock, this is also locked by tegus so as not to drive in an unexpected situation. Unlike the third actuator using leaf springs, this actuator will be able to work semipermanently with temperature shift.

1A2-L08 Design of Environment Driven Rover for Asteroid(Space Engineering and Robotics and Mechatronics(1))
TSUMAKI Yuichi - Yamagata University
AKAIKE Takahiro - Yamagata University
MINETA Takashi - Yamagata University
TADAKUMA Riichiro - Yamagata University

2015.10.24 Mr. Minoda (Takashi Mineta?) gave a lecture on the MEMS device & Hayabusa 2 Jumping Actuator at the Yonezawa Industry Association Chiba Branch (Chiba City)

1P2-N02 Performance Evaluation of Ambient Temperature Driven Bimetall Buckling Actuator for Asteroid Exploration Rover (Space Robot)
Takashi Mine , Atsuhisa Sugai , Ryo Kazama , Yuichi Tsumaki


"Bimetallic actuator" = のバイメタルアクチュエ
"Hayabusa 2" = はやぶさ2

Google for のバイメタルアクチュエ はやぶさ2

5b) ROVER2 employs two different SMA mechanisms so that ROVER2 can move in different temperature ranges. Of particular note that the total weight of these four different types of actuators is just 88.1 g. The simplified system design of MINERVA-II2 enables to result in low cost missions.

Development of MINERVA-II2, a Micro-Robot for Asteroid Surface Exploration with Innovative Mobility
Nagaoka, K., Tohoku University
https://www.dlr.de/pf/Portaldata/6/Resource...t_Nagaoka_K.pdf


Minerva-II-2 paper (in Japanese) about camera:
http://www.kimura-lab.net/wp-content/uploa...S-2013-4744.pdf
Shinichi Kimura (Tokyo University of Science)

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mcmcmc
post Yesterday, 09:30 AM
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Highly detailed paper on interior mechanisms of 4th rover, MASCOT:
https://elib.dlr.de/104842/1/Bachelor%20The...%20Hass_red.pdf
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mcmcmc
post Yesterday, 09:46 AM
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Maybe found details about rovers II-1:

QUOTE
Some rover packages named MINERVA-II are proposed to install in Hayabusa2 spacecraft. Since the target asteroid parameters may be different from the previous target, the rover design has to be made from the beginning. Technical challenging matters are arisen from the point of the distance from the Sun as well as the surface cruel temperature of low-albedo body.

MINERVA in Hayabusa mission <previous mission, previous rover>has two actuators inside in order to move. One of them is used as a torque. By rotating the torque, a reaction force against the asteroid surface makes the rover hop with a significant horizontal velocity. After hopping into the free space, it moves ballistically. Based on this mechanism, by changing the magnitude of torque, the hopping speed can be altered, so as not to exceed over the escape velocity from the asteroid surface.

The primary rover <II-1 in Hayabusa 2?> of the packages has the totally same kind of the mobile system[/b]. This time two torquers are aligned orthogonally. By simultaneously rotating the torquers, both the hopping speed and direction are controlled. The hopping speed is basically dominated by the magnitude of torques, while the hopping direction is set by he ratio of two torquers.


Intelligent Rover with Hopping Mechanism for Asteroid Exploration
Takashi Kubota
Institute of Space and Astronautical Science
Japan Aerospace Exploration Agency - Sagamihara, Japan
Kubota@isas.jaxa.jp

Tetsuo Yoshimitsu
Institute of Space and Astronautical Science
Japan Aerospace Exploration Agency - Sagamihara, Japan
kikko@nnl.isas.jaxa.j
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mcmcmc
post Yesterday, 02:30 PM
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Hayabusa 3d/HD realtime simulator soon available? (maybe)
https://www.nhk.or.jp/corporateinfo/english...df/20180906.pdf


Next operations in schedule:
MASCOT operation: October 2 ~ 4 (MASCOT separation October 3)
Touchdown 1 rehearsal 2: mid-October
Touchdown 1: late-October

Press briefings:
Sept. 27, Thursday 15:30-16:30 JST (06:30-07:30 GMT)
Oct. 11, Thursday 15:30-16:30 (TBD)

http://global.jaxa.jp/projects/sat/hayabus...hayabusa2_e.pdf
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mcmcmc
post Yesterday, 02:35 PM
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3D Web Visualization Tool to support HAHAYBUSA2-MASCOT Landing Site Selection Process
Imagine if it was made available to the public! :-)
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