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abalone
Posted on: Mar 7 2019, 12:27 PM


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QUOTE (Paolo @ Mar 7 2019, 06:55 PM) *
one question comes to my mind after seeing the video, that I have not seen addressed: are all of the flying debris still gravitationally bound to Ryugu? will they fall back on it? will they end up in orbit? are we witnessing the birth of a mini-moon? or, finally, will they end in separate solar orbit?

Almost all of the fragments will either have escape velocity and disappear or not quite enough and settle back on the surface. A single kick from the surface can put an object into orbit but this orbit will have a perigee that is the same as the point it was kick off the surface. To go into a stable orbit it needs a second kick at some altitude above the surface to raise it perigee off the asteroids surface. The escape velocity is about 0.38m/s or about 1.35 km/h. This is one of the reasons why a cannon shell can not be fired into a stable orbit.

QUOTE (pandaneko @ Mar 7 2019, 11:20 PM) *
Why is it that the same fragments look shiny and then dark as they fly up rotating?

P

Id say some are sun illuminated and some in shadow
  Forum: Hayabusa2 · Post Preview: #244183 · Replies: 710 · Views: 249101

abalone
Posted on: Jan 24 2019, 11:04 PM


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I get the impression that its possibly evidence of been put together like a hailstone accretion and the lines and lumpy appearance might be an artifact of that. https://upload.wikimedia.org/wikipedia/comm.../94/Granizo.jpg Could also be the reason for the 'hamburger' shape if the individual lobe were slowly rotating during the accretion process before coming together.
  Forum: New Horizons · Post Preview: #243552 · Replies: 127 · Views: 44125

abalone
Posted on: Dec 13 2018, 01:10 AM


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QUOTE (nprev @ Dec 13 2018, 10:56 AM) *
Thanks, Propguy. smile.gif

Quick question re the WTS: How much is it expected to reduce the amount of temperature variation?

I imagine that the soil covered by the WTS will provide some extra heat capacity that will stabilize the temp variation somewhat more than the air temperature
  Forum: InSight · Post Preview: #242550 · Replies: 530 · Views: 102500

abalone
Posted on: Oct 11 2018, 08:48 PM


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Japan delays touchdown of Hayabusa2 probe on asteroid: official
http://www.spacedaily.com/m/reports/Japan_...ficial_999.html

JAXA project manager Yuichi Tsuda said they needed more time to prepare the landing as the latest data showed the asteroid surface was more rugged than expected.
  Forum: Hayabusa2 · Post Preview: #241429 · Replies: 710 · Views: 249101

abalone
Posted on: Sep 22 2018, 02:08 PM


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http://www.hayabusa2.jaxa.jp/topics/20180922/
Surface images
https://pbs.twimg.com/card_img/104347041706...mp;name=600x314
  Forum: Hayabusa2 · Post Preview: #241081 · Replies: 75 · Views: 10272

abalone
Posted on: Jul 20 2017, 12:34 PM


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QUOTE (nprev @ Jul 20 2017, 03:07 AM) *
Amazing! The animated gif in the article clearly shows a gradual dimming and brightening...surely a demonstration of how small (and how slowly orbiting) MU69 really is given that it took observable time to occult an exceedingly small stellar disc.

Remarkable achievement, Alan, as per you & your team's usual. smile.gif

Great news, 5 occultations, so the obvious questions are why didn't any of the scopes detect it on 3rd June and what are the Sofia results?
  Forum: New Horizons · Post Preview: #236636 · Replies: 552 · Views: 301413

abalone
Posted on: Oct 20 2016, 09:44 AM


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"Schiaparelli Mars probe's parachute 'jettisoned too early'"
QUOTE
Europe's Schiaparelli lander did not behave as expected as it headed down to the surface of Mars on Wednesday.

QUOTE
But it is at the end of this parachute phase that the data indicates unusual behaviour. Not only is the chute jettisoned earlier than called for in the predicted timeline, but the retrorockets that were due to switch on immediately afterwards, fire for just three or four seconds. They were expected to fire for a good 30 seconds.

In the downlinked telemetry, Schiaparelli is seen to continue transmitting a radio signal for 19 seconds after the apparent thruster shutoff.



http://www.bbc.com/news/science-environment-37715202
  Forum: ExoMars Program · Post Preview: #233046 · Replies: 174 · Views: 66903

abalone
Posted on: Feb 12 2016, 11:09 AM


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Time-lapse: The Assembly of the James Webb Space Telescope Primary Mirror
https://www.youtube.com/watch?v=1d1sHLkmNQI
  Forum: Telescopic Observations · Post Preview: #229512 · Replies: 84 · Views: 99798

abalone
Posted on: Oct 24 2015, 12:08 PM


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NASA's New Horizons spacecraft has carried out the first in a series of four initial targeting maneuvers designed to send it toward 2014 MU69 - a small Kuiper Belt object about a billion miles beyond Pluto, which the spacecraft historically explored in July.

The maneuver, which started at approximately 1:50 p.m. EDT on Oct. 22, used two of the spacecraft's small hydrazine-fueled thrusters, lasted approximately 16 minutes and changed the spacecraft's trajectory by about 10 meters per second.
The remaining three KBO targeting maneuvers are scheduled for Oct. 25, Oct. 28 and Nov. 4.
http://www.spacedaily.com/reports/Maneuver...Target_999.html
  Forum: New Horizons · Post Preview: #227577 · Replies: 552 · Views: 301413

abalone
Posted on: Oct 15 2015, 12:20 PM


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Any news yet on when the first burn is due?
  Forum: New Horizons · Post Preview: #227294 · Replies: 552 · Views: 301413

abalone
Posted on: Jul 16 2015, 12:46 PM


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QUOTE (climber @ Jul 16 2015, 04:50 AM) *
Another answer, 100m delta V:

That's a bit confusing 100m/s, what does that include?
  Forum: New Horizons · Post Preview: #223750 · Replies: 552 · Views: 301413

abalone
Posted on: Jul 15 2015, 12:59 PM


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QUOTE (Paolo @ Jul 15 2015, 11:41 PM) *
this paper should answer most of your questions:
http://www.hou.usra.edu/meetings/lpsc2015/pdf/1301.pdf

Thanx
  Forum: New Horizons · Post Preview: #223492 · Replies: 552 · Views: 301413

abalone
Posted on: Jul 15 2015, 11:32 AM


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Just out of interest, what delta V do each of the candidates need compared to the delta V still in the tank? or What is NH's the cone of reachability and how close is each to the edge?

Have any followup observations been done or are planed by Hubble to identify any further targets now that the search area is smaller?
  Forum: New Horizons · Post Preview: #223488 · Replies: 552 · Views: 301413

abalone
Posted on: Jul 14 2015, 03:40 AM


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Looks like some of the dark areas are elevated terrain
Release Date: July 13, 2015
http://pluto.jhuapl.edu/Multimedia/Science...JHUAPL-SWRI.png
  Forum: New Horizons · Post Preview: #223180 · Replies: 1286 · Views: 450926

abalone
Posted on: Jul 13 2015, 01:53 AM


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New Horizons’ newest images reveal Pluto’s largest moon Charon to be a world of chasms and craters.
http://www.nasa.gov/feature/charon-s-chasms-and-craters
  Forum: New Horizons · Post Preview: #222977 · Replies: 729 · Views: 296985

abalone
Posted on: Apr 20 2015, 02:39 PM


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Rosetta's comet throws out big jet

http://www.bbc.com/news/science-environment-32380793
  Forum: Rosetta · Post Preview: #219666 · Replies: 390 · Views: 204170

abalone
Posted on: Nov 3 2012, 11:01 PM


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Just had a good look at the self-portrait and am a little disturbed by the large number of dents on the wheels. I know its been commented on and dismissed just after landing but we have only gone 400m and they look a little battered. Its especially visible on the center port wheel in the Hi-res in this picture. We dont see that kind of wear on Opportunity and its gone 35km. Are they really up to the job, MSL could well go 50km, will the wheels fall off before then???
http://www.nasa.gov/images/content/703574m...121101_full.jpg
  Forum: MSL · Post Preview: #194094 · Replies: 520 · Views: 283360

abalone
Posted on: Oct 3 2012, 03:17 AM


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An interesting paper
http://online.liebertpub.com/doi/pdfplus/1...9/ast.2011.0660
Liquid water could be stable as little as 100-200m below the surface
and
"At temperatures below 0C, liquid water can exist as either
a thin film or a brine with a freezing point < 0C. Including
salts to estimate ‘‘average Mars salinity water’’ expands the
regions where liquid water can occur. Modeling by Mellon
and Phillips (2001) showed that a concentration of 15–40% of
salts (sulfates, chlorides, bromides, carbonates, and nitrates)
is sufficient to allow the melting of ground ice (or to maintain
liquid water) in the top few meters of soil."
  Forum: MSL · Post Preview: #192692 · Replies: 150 · Views: 77159

abalone
Posted on: Oct 2 2012, 07:46 AM


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What would also be interesting is the depth below ground where the temperature is constantly above Zero and what the pressure would be at this depth. Its possible that only 100s of metres below the surface any water could be permanently liquid. Does anyone have any data in this?
  Forum: MSL · Post Preview: #192591 · Replies: 150 · Views: 77159

abalone
Posted on: Sep 25 2012, 10:50 AM


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Pleasure to give, donation made!
  Forum: Forum News · Post Preview: #192071 · Replies: 59 · Views: 46600

abalone
Posted on: Oct 15 2009, 12:49 PM


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QUOTE (djellison @ Oct 15 2009, 01:55 AM) *
We don't know what form it's in. It may be in a form that's hard to liberate. Furthermore - hydrogen on its own, isn't that useful* It's incredibly light so it's not much of a burden for space flight (consider the Mars Direct ISRU numbers). You tend to need something heavy (oxygen) to do something with it. If it's vast swathes of actual ice down there - then we have rocket fuel, air and water for future crews. If it's just hydrogen, you've still got to take 7/8ths the mass with you.

* apart from filling balloons - but that's not too useful on the moon smile.gif

Ill try to repeat my original post and see if it get through this time

Hydrogen used as a propellant in a fission rocket has a much higher impulse than when you waste it by burning it with oxygen. Designs for these do exist, you would only have to carry a couple of tens of kgs of uranium and it does not have the same emotive radiation hazard that it would have if launched from Earth. Even at 6.8% water there would be plenty to drink and breathe

And would like to add in support

"Usually, with hydrogen propellant the solid-core design is expected to deliver specific impulses (Isp) on the order of 800 to 900 seconds, about twice that of liquid hydrogen-oxygen designs such as the Space Shuttle main engine."
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket
  Forum: LRO & LCROSS · Post Preview: #148049 · Replies: 245 · Views: 70379

abalone
Posted on: Oct 15 2009, 12:31 PM


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QUOTE (abalone @ Oct 15 2009, 10:16 PM) *
Entire post of blue-sky engineering culled. See rules. - ADMIN

I cant understand why this post has been culled, fission engines using hydrogen as a working fluid were in the design stage in both the USA and Soviet Union in the 1950s and 60s. the Russians even tested one. If this is blue-sky then someone is lacking a bit of faith that any progress is going to be made
Seems to me there is more blue-sky engineering in harvesting water from the lunar poles than building these engines

"A nuclear engine was considered for some time as a replacement for the J-2 used on the S-II and S-IVB stages on the Saturn V and Saturn I rockets. Originally "drop-in" replacements were considered for higher performance, but a larger replacement for the S-IVB stage was later studied for missions to Mars and other high-load profiles, known as the S-N. Likewise the Soviets studied nuclear engines for their own moon rockets, notably upper stages of the N-1. However, neither design had progressed to the point where they were ready to test before the space race was ostensibly over.

To date, no nuclear thermal rocket has flown, or even reached a stage of development where it could be. The Russian nuclear thermal rocket RD-0410 went through a series of tests on the nuclear test site"
http://en.wikipedia.org/wiki/Nuclear_thermal_rocket
  Forum: LRO & LCROSS · Post Preview: #148048 · Replies: 245 · Views: 70379

abalone
Posted on: Oct 15 2009, 12:16 PM


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Entire post of blue-sky engineering culled. See rules. - ADMIN
  Forum: LRO & LCROSS · Post Preview: #148043 · Replies: 245 · Views: 70379

abalone
Posted on: Feb 17 2008, 01:30 PM


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QUOTE (Aussie @ Feb 17 2008, 10:08 PM) *
Volcanism + liquid water = acid - no matter what the orbital radius.

Yes but its the amounts that I'm referring to. In the inner solar system the amounts of acid and salt is relatively small and capable of being regulated by the large amount of rock and metal and as we move outwards they increase in concentration start to get out of the range that we know of as being capable of sustaining life.
My point is that the Earths iron core removes most of the free sulfur from the surface system and therefore limits the amount of salt produced.

  Forum: Opportunity · Post Preview: #109487 · Replies: 71 · Views: 35931

abalone
Posted on: Feb 17 2008, 01:18 PM


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QUOTE (Stephen @ Feb 17 2008, 06:17 PM) *
Where would Venus fit into that theory? Isn't there sulphuric acid in those Venusian clouds?

======
Stephen

Yes but the amount I assume is relatively small on a planetary scale and I also that most of Venus sulfur is also locked up in its core. The temp of Venus changes the equilibrium. Dont forget we are talking salt as well and on Venus there is not much opportunity for the acid to react with the basaltic rock.
  Forum: Opportunity · Post Preview: #109486 · Replies: 71 · Views: 35931

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