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A comment on The Damage to Lunar Orbiting Spacecraft Caused by the Ejecta of Lunar Landers. Parent comment

Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by azernik on Tuesday May 23, 2023 @01:45PM (#36047982)
Landers don't impact hard - they fire rocket engines down, which may be much more efficient at kicking up dust than an impact.

(I still think this is overblowing the problem, because any lander that causes this big of an ejecta problem would also badly damage itself. All the designs will put a LOT of engineering work into minimizing debris, eg Starship putting separate landing engines high up on the vehicle.)

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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by Sharlin on Tuesday May 23, 2023 @02:27PM (#36048681)
> because any lander that causes this big of an ejecta problem would also badly damage itself

Not necessarily because the relative speeds will be very slow. Not so in low lunar orbit, where an orbiting spacecraft will slam into the ejecta curtain at x km/s.

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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by azernik on Tuesday May 23, 2023 @02:57PM (#36049087)
The paper estimates that if there's LLO debris, it'll be starting out with about 1.6km/s of surface-relative velocity. Not something you want to get even a small percentage of on your landing gear.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by sneak on Tuesday May 23, 2023 @03:58PM (#36050049)
My first time encountering this acronym. I can't wait until it's in common use and we have cities and communication satellites in and around the moon.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by cubefox on Tuesday May 23, 2023 @04:48PM (#36050667)
I guess you really like 1950s sci-fi.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by Sharlin on Tuesday May 23, 2023 @04:02PM (#36050109)
Oh, that's a good point.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by LorenPechtel on Tuesday May 23, 2023 @02:37PM (#36048828)
The ejecta would go out to the side and not harm the lander. I'm just amazed that the ejecta is being thrown hard enough to be a threat at orbital altitude.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by adastra22 on Tuesday May 23, 2023 @02:57PM (#36049086)
It’s a combination of the moon’s orbital velocity being low and the exhaust velocity being high.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by LorenPechtel on Wednesday May 24, 2023 @12:45PM (#36060729)
I'm still surprised that it can impart that much velocity, though.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by adastra22 on Thursday May 25, 2023 @04:35AM (#36068346)
Well is it not intuitive that something being blown by a moving fluid approaches speeds equal to the speed of the fluid?
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by azernik on Tuesday May 23, 2023 @02:58PM (#36049113)
That's a simplifying assumption (per the paper). In reality it would be a distribution, with a lot less going up than to the sides.

Plus then you're dealing with damage to your hopefully-smooth landing site.

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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by icodestuff on Tuesday May 23, 2023 @03:45PM (#36049867)
That doesn't bode super well for Blue Origin's lander then, since its engines are on the bottom.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by azernik on Tuesday May 23, 2023 @03:59PM (#36050059)
They're not going to get far without some other method of reducing ejecta, doing so is in the NASA requirements.
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by _joel on Tuesday May 23, 2023 @06:14PM (#36051511)
yet they've just been awarded a tender for HLS
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Re:The Damage to Lunar Orbiting Spacecraft Caused by the Eje... by azernik on Tuesday May 23, 2023 @08:59PM (#36052714)
Which means NASA is satisfied that they have some other solution
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