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The BBC News article Hayabusa-2: Japanese probe set to 'bomb' an asteroid says:

The charge is carried on the Small Carry-On Impactor (SCI) device.

This is a 14kg conical container attached to Hayabusa-2 and packed with plastic explosive.

The SCI is due to separate from Hayabusa-2 at 01:56 GMT on Friday at an altitude of 500m above the surface of Ryugu. That will kick off a 40-minute countdown to detonation. When the device explodes, it is expected to punch a 10m-wide hole in the asteroid.

In the meantime, Hayabusa-2 should have manoeuvred itself to hide away on the other side of the asteroid, shielding the spacecraft from any flying debris.

The answer to How far will the debris cloud from Hayabusa-2's touch-and-go sample recovery travel around Ryugu? Will any have escaped to heliocentric orbit? makes it clear that even low-velocity projectiles produced near Ryugu's surface could travel in Ryugu-centric as well as heliocentric orbits. Of course since the Ryugu-centric (elliptical) orbits intersect the surface at one point, they'll intersect somewhere else as well, and either come gently to rest or scatter secondary additional projectiles.

So just because Hayabusa-2 will move to the other side doesn't mean it can't get hit by something.

I'm curious what kinds of debris Hayabusa-2 mission-planners at JAXA might have thought about ahead of time, so I'd like to ask: How far did Hayabusa-2 back off before the "bomb" went off?


Lower volume before playing video because it contains an Earth-shattering kaboom!!

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  • $\begingroup$ "So just because Hayabusa-2 will move to the other side doesn't mean it can't get hit by something." Are you sure about this? Escape velocity is like 30cm/s and orbit is 26cm/s and just intuitively, I'd wager that debris thrown up by the explosion is either 1. Fast enough to escape Ryugu gravity. 2. Not fast enough to escape but thrown so elliptically that it won't return for a long time. 3. Slow enough to enter orbit but not cause spacecraft damage if it hit. $\endgroup$ – Dragongeek Jun 13 at 13:23
  • $\begingroup$ @Dragongeek see answer(s) to Could ejecta from asteroid Bennu enter into temporary orbit around it? If so, how? I can't speak to the damage as a function of velocity though... $\endgroup$ – uhoh Jun 13 at 15:07
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The answer is that the Hayabusa-2 was 4.61 km from the SCI when it detonated.

The link provides a mission status briefing from JAXA which describes the entire sequence of events, including positions. Slide 10 has the relevant mission data laid out on a grid.

http://www.hayabusa2.jaxa.jp/en/enjoy/material/press/Hayabusa2_Press20190411_ver10_en.pdf

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Before the bomb went off, I’m interpreting to mean explosive release of the copper impactor.

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In a sense, another bomb went off again when the copper impactor struck Ryugu 500 M below the SCI. The answer for that is 4.12 km.

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    $\begingroup$ Updated. Having a blast, thanks for keeping me sharp. $\endgroup$ – Anthony Stevens Jun 15 at 13:20
  • $\begingroup$ "Before the bomb went off, I’m interpreting to mean explosive release of the copper impactor" well I'm interpreting it as the moment when the "14kg conical container attached to Hayabusa-2 and packed with plastic explosive" which exploded after the "40-minute countdown to detonation" which was "expected to punch a 10m-wide hole in the asteroid." I'm not convinced that your answer talk about this exact explosion. $\endgroup$ – uhoh Jun 16 at 9:07
  • $\begingroup$ Well, you go on to talk about debris. There’s no chance of the impactor accidentally hitting Hayabusa-2. The real danger to the craft was something getting ejected from the surface, damaging the craft and ending the sample return mission. That would have been devastating. $\endgroup$ – Anthony Stevens Jun 16 at 10:43
  • $\begingroup$ I don't see an answer to my question yet then. When the impactor detonated, and presumably punched a hole in the asteroid, how far was Hayabusa-2 from Ryugu? Can you address that and clearly indicate your answer? Thank you! $\endgroup$ – uhoh Jun 17 at 0:34

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