4 ms·

Small and medium meteorites smack into the moon's surface all the time, being it has no atmosphere. I find it hard to believe that human-built landers have near

by tabtab 3y ago

Small and medium meteorites smack into the moon's surface all the time, being it has no atmosphere. I find it hard to believe that human-built landers have nearly as much impact on low-orbit grit than these meteor impacts.

dr_orpheus 3y ago
Some of the data from LADEE and Lunar Dust Experiment (LDEX) instrument might point to this being the case, but it was more along the lines of human-built landers do not have nearly as much of an impact as meteor showers themselves (not necessarily the impact and resulting dust). "if LADEE did encounter any lunar soil particles thrown up by the final descent of Chang'e 3, they would have been lost in the background of Geminid-produced events." [0] That said, the Chang'e 3 is an order of magnitude (or close to two) smaller than the lunar landers they are talking about in the study. Also my own speculation is that the more continuous thrust of a lander may get particles to higher velocities due to the additional time for acceleration in the wake of the thrust as compared to the single impact of the meteor. I struggle to compare exactly how bad the lunar dust ejection is though. Most Micrometeoroid and Orbital Debris (MMOD) curves are specified as a Flux by particle size (velocity is sort of irrelevant, as you assume most of the velocity is from the spcecraft itself and most hits are in the direction of travel of spacecraft, the ram direction). My suspicion is that MMOD flux in a LEO orbit is still going to be far far worse. [0] https://www.nasa.gov/ames/ladee-project-scientist-update-milestones-maneuvers-and-moisture/ https://www.nasa.gov/ames/ladee-project-scientist-update-mil... Edit: The paper talks about flux of particles 10 um and smaller of about 10,000 impacts/m^2 during the passes. If we assume that this is a sphere of iron (new MMOD fluxes are specified in mass, not size) its ~5e-9g. In LEO at 400 km altitude (a little above the ISS) the flux of particle this size is ~1000 impacts/m^2/year. But the paper says smaller than <10 um. And at smaller masses the flux increases exponentially to 10^7 particles/m^2/year at a particle mass of 10^-18 g. So I believe my suspicion is correct that most LEO orbits are still worse, but its hard to compare apples to apples.
azernik 3y ago
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.)
- Sharlin 3y ago
  > 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 >1 km/s.
  - azernik 3y ago
    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.
    - sneak 3y ago
      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.
      - cubefox 3y ago
        I guess you really like 1950s sci-fi.
    - Sharlin 3y ago
      Oh, that's a good point.
- LorenPechtel 3y ago
  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.
  - azernik 3y ago
    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.
fnordpiglet 3y ago
I would expect it’s the sustained thrust prior to landing and at take off that is the difference.
sandworm101 3y ago
Impacts are impacts. Rockets are more like leaf blowers. Drop a massive rock into a pile of leaves and few leaves even move. Point a leaf blower at the pile and leaves will scatter everywhere.
- moffkalast 3y ago
  Yeah but throw a car sized boulder into a pile of leaves at a few km/s and they'll scatter all the same.

by tabtab 3y ago

dr_orpheus 3y ago

Some of the data from LADEE and Lunar Dust Experiment (LDEX) instrument might point to this being the case, but it was more along the lines of human-built landers do not have nearly as much of an impact as meteor showers themselves (not necessarily the impact and resulting dust). "if LADEE did encounter any lunar soil particles thrown up by the final descent of Chang'e 3, they would have been lost in the background of Geminid-produced events." [0] That said, the Chang'e 3 is an order of magnitude (or close to two) smaller than the lunar landers they are talking about in the study. Also my own speculation is that the more continuous thrust of a lander may get particles to higher velocities due to the additional time for acceleration in the wake of the thrust as compared to the single impact of the meteor. I struggle to compare exactly how bad the lunar dust ejection is though. Most Micrometeoroid and Orbital Debris (MMOD) curves are specified as a Flux by particle size (velocity is sort of irrelevant, as you assume most of the velocity is from the spcecraft itself and most hits are in the direction of travel of spacecraft, the ram direction). My suspicion is that MMOD flux in a LEO orbit is still going to be far far worse. [0] https://www.nasa.gov/ames/ladee-project-scientist-update-milestones-maneuvers-and-moisture/ https://www.nasa.gov/ames/ladee-project-scientist-update-mil... Edit: The paper talks about flux of particles 10 um and smaller of about 10,000 impacts/m^2 during the passes. If we assume that this is a sphere of iron (new MMOD fluxes are specified in mass, not size) its ~5e-9g. In LEO at 400 km altitude (a little above the ISS) the flux of particle this size is ~1000 impacts/m^2/year. But the paper says smaller than <10 um. And at smaller masses the flux increases exponentially to 10^7 particles/m^2/year at a particle mass of 10^-18 g. So I believe my suspicion is correct that most LEO orbits are still worse, but its hard to compare apples to apples.

azernik 3y ago

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.)

Sharlin 3y ago
> 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 >1 km/s.
- azernik 3y ago
  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.
  - sneak 3y ago
    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.
    - cubefox 3y ago
      I guess you really like 1950s sci-fi.
  - Sharlin 3y ago
    Oh, that's a good point.
LorenPechtel 3y ago
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.
- azernik 3y ago
  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.

fnordpiglet 3y ago

I would expect it’s the sustained thrust prior to landing and at take off that is the difference.

sandworm101 3y ago

Impacts are impacts. Rockets are more like leaf blowers. Drop a massive rock into a pile of leaves and few leaves even move. Point a leaf blower at the pile and leaves will scatter everywhere.

moffkalast 3y ago
Yeah but throw a car sized boulder into a pile of leaves at a few km/s and they'll scatter all the same.