What's Up With Hayabusa? (fka Muses-c) Options

[alan]

Everyone seems to agree that Itokawa is a rubble pile. I've been wondering about this. All asteroids form as rubble piles. How does an asteroid become something other than a rubble pile? Do the individual pieces fuse after it reaches a certain size? How large would it have to be for this to happen? Is internal heating or radioactive decay involed?

[Ames]

pdf file - can't read the words but has some images of Minerva departing.

http://www.isas.jaxa.jp/j/snews/2005/1113_minerva.pdf

Nick

[djellison]

Very bad google from that PDF and two images from it.
Inquiry robot " Minerva ", at the time of the 2nd rehearsal November 12th, " is quick the ぶ ", empty separation The れ it increased. When separating as for the probe the thruster injection in order to compensate gravity repeatedly difficult to be, meet on Because separation is executed at the point in time when it had degree of speeding up, regrettable as for the る thing which drops " Minerva " to the I To matte surface it is the pattern which it is not possible. Furthermore as for details it is in the midst of investigating. After the separating, " Minerva " while turning, with the process which keeps being discharged, " is quick the ぶ ", the color photographing stripe it is to do. (Data? 1) In the picture, " it is quick the ぶ ", ()" the metallic parts of panel B-1 spreading/displaying opening delay mechanism of the + Y surface side solar panel of the probe (the hook)" with, the electrical instrumentation line of reverse side of the solar array board is photographed. フッ As for ク, (data? 2) It is inside 0 on the plan, as for this electrical instrumentation line being something of the same solar array, (resources charge? 3) It is possible to collating & to verify with the photograph which is in the midst of servicing before the launching. In addition, (data? 4) " It is quick the ぶ ", after the empty separating it was photographed with the wide angular navigation camera 212 seconds later, the object which is thought " ミ Nerva " is shown. " Minerva " after the separating thinks rise was continued from the I To matte slowly, but " it is quick the ぶ ", With communication, 18 hours continuing, to be guaranteed in stability, at this time, temperature and power source voltage the inside " Minerva ", The photodiode which shows the attitude of the inquiry robot (the simple sun sensor) output and the like is transmitted to the probe, " It is quick the ぶ ", it has succeeded in transmitting to the ground via. (Data? 5) The う of the data which is obtained Furthermore as for the ち temperature data after the separating the for the sake of rises, receives the thermal radiation from the I To matte surface thought And others the れ, there is a possibility the measurement which has meaning even scientifically being possible. 18 hours later, direction of antenna There is a possibility communication becoming impossible with problem of direction, but furthermore continuing, the plan which tries the contact Is. In addition, " it is quick the ぶ ", concerning the order to of empty " Minerva ", change of function the communication which is ordered is done normally, it is verified that also the operation which receives that is executed appropriately. The data which " Minerva " transmitted, 1) status (working condition in the midst of hopping and in the midst of et cetera standing still), 2) the Ha mortar keeping data (), 3) measurement data such as power source voltage of the electric double layer condenser and the memory capacity which is recorded (photodiode output and the temperature sensor), 4) is the graphics data. ("Minerva ", 6 photodiodes and 10 temperature sensors (inside 4, outside 6) has loaded 3 cameras.)

The point where voltage has fallen separated point in time (the changing to " Minerva " side supply) the signal from photodiode (shows the fact that the attitude " of Minerva " is turning from the inquiry field.) C) the temperature rise which leads separation " is quick the ぶ ", it is thought the for the sake of because it approaches to the asteroid the rose ンス of heat balance changes with thermal radiation from the surface.

Attached thumbnail(s)

 

[deglr6328]

I don't understand. Is it in orbit then? why would temperature level off like that if we weren't? The paper seems to say that temperature rise is due to increased light being reflected from the surface.

[Phil Stooke]

Alan, all asteroids - as we see them now - don't form as rubble piles. Going way back to the period of planetesimal accretion, they may have begun as rubble accreting into larger objects. But two processes act to change that. Impact (kinetic) energy itself from each accretion event , and (very important indeed) the decay of Aluminum 26 and other short-lived isotopes. They put heat into the growing planetesimals, more effectively as things get bigger. So after a few tens of millions of years many of the small rubbly planetesimals have grown large enough to be melted inside. They differentiate into silicate (and/or ice/silicate) mantles and iron cores. An early version of the adteroid belt might have contained hundreds of small differentiated worlds like this, a few hundred km across.

Then Jupiter and other lesser influences start stirring it up. Many are ejected from the solar system or collide with other planets. Many more hit each other. A handful survive to today - Vesta, Ceres, presumably Juno... remnants of that early population. The ones which hit each other produce the current observed population of asteroids... essentially monolithic fragments, irregular in shape, some from the silicate mantles, some from the iron cores. They still get hit, so some are shattered and reassemble as rubble piles - Itokawa may be one of these. Others fracture inside but remain basically monoliths, with pore space and open fractures reducing the bulk density. Eros, Gaspra and Ida would be examples of these. Linear grooves on the surface are evidence of the deeper fractures. Our current understanding of the rocky asteroids is that they are not primordial, they have evolved considerably. What I describe here may not apply so much to the very dark asteroids from the outer belt, as the degree to which they have been processed is less clear. Mathilde may be one of these.

It would be practically impossible for a rubble pile to survive 4 billion years. Itokawa must be much younger if it's truly just rubble.

Phil

[Rakhir]

Suzuka posted on space.com the transcript of the press conference held at 8:00PM November 12 concerning the rehearsal descent.

http://uplink.space.com/showflat.php?Cat=&...&fpart=all&vc=1

He also summarized the comments of Kawaguch Project Manager concerning Minerva.

"1. The speed of Minerva is 8.3cm/s in an infinite distance.

2. The rise stops in 6-7 days if it is early because the deceleration by the sun radiation pressure is 1.4cm/s/day. And, it falls aiming at ITOKAWA spending the same time.

3. And, when Minerva returns to the position of ITOKAWA, Minerva collides with ITOKAWA if ITOKAWA is near.

4. If Minerva passes the neighborhood of ITOKAWA, it never returns to ITOKAWA according to the sun radiation pressure.

Therefore, ISAS/JAXA seems to monitor the signal from MINERVA continuously. Minerva will return at the time of landing on just November 25."

If I understand well, Minerva was departing from Itokawa at 8.3 cm/s but because of the sun radiation pressure, it will "fall back" and arrive in the vicinity of Itokawa on November 25.
And if by chance, Itokawa is on its trajectory, it could eventually collide (and perhaps land).

But they don't know if the power supply of Minerva can last such a long time.

BTW, the link between Minerva and Hayabusa was lost after 18h of communication, but it could be due to a bad orientation of the antenna. They are trying to re-establish contact.

Rakhir

[Bob Shaw]

If you go to :

http://uplink.space.com/showflat.php?Cat=&...&fpart=all&vc=1

You'll find an image from MINERVA itself, plus two more of it in flight (as a distant blob). The MINERVA picture appears to be of the back of one of Hayabusa's solar panels.

Bob Shaw

[Guest_BruceMoomaw_*]

Regarding rubble piles: yeah. What Phil said. Except that Pallas is certainly also one of the original surviving protoplanets, given its large size. (But a mystery: how the hell did it get walloped into an orbit tilted 30 degrees to the ecliptic without shattering? Or did it make a very close flyby of something very large that tilted it into that orbit, with its flyby companion getting catapulted into some other part of the Solar System altogether, or even into interstellar space?) Also, adaptive-optics photos of Juno show it to have a highly irregular shape, suggesting that it too may be a piece of a larger original body. (One of the biggest puzzles about asteroids in general is why most of the original bodies have been smashed to bits, but there are a few stubborn survivors like Ceres and Vesta -- with Vesta apparently even retaining the basaltic lava flows on its surface that it acquired shortly after its original formation.)

Also: a couple of LPSC abstracts have pointed out that -- for the still-small number of asteroids for which we have density data -- the C types seem to be consistently lower-density than the S-types, confirming that their softer rock gets more easily fractured by impacts. (But Psyche remains a mystery: recent spectral and radar measurements continue to indicate that -- unlike some other supposed M-types -- it really does have a lot of iron-nickel in it, but its density measurements are incredibly low, indicating that if it's iron-nickel it must be 75% empty space! Something isn't being properly measured or interpreted here.)

Finally: Hayabusa's density data on Itokawa show it to be about 2.3 g/cc -- distinctly lighter than Eros (2.67), which is assumed to be a fractured S-type. The fact that an object as small as Itokawa has such a low density is another puzzle, and the possibility has been raised -- given its odd shape -- that it's actually a contact binary, with a lot of loose debris piled up to cover the junction point.

[dilo]

2. The rise stops in 6-7 days if it is early because the deceleration by the sun radiation pressure is 1.4cm/s/day. And, it falls aiming at ITOKAWA spending the same time.

Radiation pressure should be slightly lower than this (see Jaxa article) but figures are correct.
Sad to say, even if batteries will survive and radio link will be re-established, soft impact onto Itokawa is highly improbable because there are other effects deviating trajectory... in particular, while rotating, the small probe re-irradiate thermal IR radiation in a direction different from the Sun-Itokawa direction, escaping from this ideal line.

[Guest_BruceMoomaw_*]

One other very important side note: as one abstract at LPSC pointed out (I'll have to look it up, but I have a copy sitting in my notes): without all that highly radioactive aluminum-26 melting and softening the rocky debris early in the Solar System's history, that debris would have had a harder time sticking together to make protoplanets in the inner System. And that Al-26, in turn existed in such large amounts in our original planetary nebula only because a supernova happened to go off nearby while the System was first forming. Since this doesn't happen very often, this raises the grim possibility that few other solar systems may have inner rocky planets at all -- most solar systems may consist of giant planets and asteroid belts, period (with the asteroid belt extending all the way in where the terrestrial planets exist in our system).

[Guest_BruceMoomaw_*]

Here's the abstract: http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1886.pdf . I don't, of course, know remotely enough to judge its validity.

[The Messenger]

Here's the abstract: http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1886.pdf .  I don't, of course, know remotely enough to judge its validity.

I was tempted to say, "At least it is a starting point", but since there is such puzzling diversity in planet, moon, comet and asteriod compositions, a lot of less- definitive rewrite is needed.

But Psyche remains a mystery: recent spectral and radar measurements continue to indicate that -- unlike some other supposed M-types -- it really does have a lot of iron-nickel in it, but its density measurements are incredibly low, indicating that if it's iron-nickel it must be 75% empty space! Something isn't being properly measured or interpreted here.

****

Meanwhile, back on topic, - It was not reasonable to rely on Human judgement 15 light-minutes away to determine when Minerva should be released: The problem here is not the software or engineering, but a control-freak mentality.

[Guest_BruceMoomaw_*]

At a minimum, the damn fools should have included a simple software command prohibiting the computer from releasing Minerva in response to the ground command if Hayabusa happened to be going UP at the time. They could then have solved the problem simply by transmitting the ground command several times. At the risk of setting Doug off again, I continue to regard Japan's space program (unlike the ESA's) as a joke, and not a very good one.

[The Messenger]

I - We - were involve in a tech exchange with Japan a little over a decade ago. There were certain things we were restricted by IOTA and other constraints from sharing. We knew some of the Japanese designs were likely to fail, and there would be some trial-and-error learning curves.

It is a bittersweet experience - on one hand, I hate to see the failures, on the other, technology transfers inevitably mean less foreign payloads for U.S. missions, fewer U.S. satellites, and less for me to do....

[Guest_Sedna_*]

At a minimum, the damn fools should have included a simple software command prohibiting the computer from releasing Minerva in response to the ground command if Hayabusa happened to be going UP at the time.  They could then have solved the problem simply by transmitting the ground command several times.  At the risk of setting Doug off again, I continue to regard Japan's space program (unlike the ESA's) as a joke, and not a very good one.

Completely in agreement with that...