Lunar Vehicle Impact and Debris

[tparvel]

As I sit here thinking about making a new base on the moon one thing struck me.
The proximity of landing pads and the actual base structures.
I have worked around airplanes at one time or another and FOD (foreign object debris) is a major concern.

Now comparing the thrust levels from a space craft compared to an airplane and then adding in the lower gravity FOD could do some serious damage to structures and spacecraft.

Any permanent outpost would need a barrier and or distance to keep the risk levels down.

And while I am thinking about it what would be a good material for a tarmac say on the moon that would put up with constant abuse ?

I did find this white paper it makes for some interesting reading.
http://research.nianet.org/~rtolson/theses/Zaleski_LunarOutpostDebrisHazard.pdf

If this has been discussed before then sorry for the re-post.

 

[statickid]

So it looks like even though you wouldn't have runways, there may be a directional ingress/egress protocol in place to protect the base.

 

[Urwumpe]

Remember that there is no atmosphere on the moon, so all objects during landing are only moved by the rocket exhaust. And the force of that exhaust is only high exactly during landing. Also, the exhaust is not uniformly moving at the exhaust velocity, as often simplified in aerospace engineering. in reality, the peak exhaust velocity is at the center of the nozzle and drops off towards the edges of the exhaust flow.

Also, after leaving the area of effect of the exhaust, the FOD will travel on an ballistic arc.

The flow of the exhaust when landing in vacuum would make a nice numerical simulation... I could draw, what I would expect to see, but I am sure, there could be some interesting effects, that I can't even imagine.

 

[tparvel]

I did play around with the runway on the moon.
Entirely possible to land on a runway and it was interesting.
Alignment was actually fairly easy when you treat your craft like a helicopter.
But not very practical.
So that would leave landing pads with no fly zones and definite approach vectors for any base within certain altitudes.

Yes with no air it is all about the thrust and not intakes, the white paper is all about the ballistics of any item stirred up by the thrust.
It basically comes down to the most practical solution would be a barrier not to stop particles but simply direct them up and over the base.
Or the inverse which would be to direct the particles into a ground catch.

 

[Artlav]

What about debris falling off the lander during the powered approach?
It would still have it's significant suborbital velocity, and is heading roughly the right way.

Could be loose bolts, could be nozzle heat cover shedding, could be some liquids leaking, etc - all going towards the base at significant velocity.

 

[statickid]

a simplified idea sketch. perhaps a wall to shield the base from dust and gravel blown out from rocket blasts. The receiving bay might be very heavy and bunker-like, with a transport tunnel to the base rather than an exposed route. The traffic zone may extend outwards for many kilometers.

 

[tparvel]

What about debris falling off the lander during the powered approach?
It would still have it's significant suborbital velocity, and is heading roughly the right way.

Could be loose bolts, could be nozzle heat cover shedding, could be some liquids leaking, etc - all going towards the base at significant velocity.

Yes and like any approach vector it would probably be alt and distance from base before final so any items would fall on that vector before the base.
And if something did fall off in this manner I would think you would be having a very bad day.

 

[Urwumpe]

..., the white paper is all about the ballistics of any item stirred up by the thrust.

No, the white paper is exclusively about impact debris external ballistics and the debris population and distribution to be expected. This includes impacts of spacecraft during landing and guidance strategies for limiting the danger of such impacts to an existing base on different celestial bodies.

---------- Post added at 11:12 PM ---------- Previous post was at 11:06 PM ----------

What about debris falling off the lander during the powered approach?
It would still have it's significant suborbital velocity, and is heading roughly the right way.

Could be loose bolts, could be nozzle heat cover shedding, could be some liquids leaking, etc - all going towards the base at significant velocity.

Yes, but I think the debris kicked up during lift-off will be far more dangerous.

During landing, the increasing intensity of the wall velocity at the surface of the landing pad will remove debris from the landing pad at low peak speeds and shallow ballistic arcs. shortly before landing, only few dense debris objects will be left, while the landing area is in a dust cloud.

During lift-off, any debris objects already on the area will be instantly subject to high wall velocities and high exhaust density. Deflected exhaust flow could even carry heavy particles on steep ballistic arcs.

 

[tparvel]

I found some more links of interest.

http://www.nasa.gov/centers/kennedy/home/lunar_landing_pads.html
 "When the Apollo lunar modules reached the 30-meter point (about 100 feet), the dust was like a fog making it difficult to see their landing site. Similarly, photographs show there were some rocks and dust kicked up by the rocket engines on the sky-crane lowering the Curiosity lander onto the Martian surface.” 

"Our best estimates indicate that descent engines of the Apollo landers were ejecting up to one-and-a-half tons of rocks and soil," said Dr. Phil Metzger, a research physicist in Kennedy's Granular Mechanics and Regolith Operations Laboratory. "It will be even more challenging when we land humans on Mars. The rocket exhaust will dig a deep hole under the lander and fluidize the soil. We don't know any way to make this safe without landing pads."

http://www.iaarc.org/publications/fulltext/S28-4.pdf

 

[Keatah]

I don't suppose there's any data from the apollo landings that would help in modeling material behavior here?

 

[MaverickSawyer]

I think that the stock Brighton Beach pads have a sort of "lip" around them. If porperly designed, these should deflect the debris into the "air" at a specific range of angles, depending on the situation. Perhaps certain pads would be set aside for vehicles with higher "footprints"?

Also, a proper FOD walk will eliminate ALL debris before arrival, before departure, and after departure. Three FOD walks around airliners is SOP for many airlines. That way, you have to have been REALLY blind to miss a hazard! :lol:

 

[Andy44]

Maybe you could build a grate over top of a well for a landing pad, with the well being a flame bucket that directs the jet wash into a culvert a safe distance away from the pad? Something like the blast deflection systems used on terrestrial launch pads.

The grating would have to be made of some sort of metal that can handle high temperature for short periods of time, as well as the extreme temperature of the local day/night cycles.

 

[Artlav]

During landing, the increasing intensity of the wall velocity at the surface of the landing pad will remove debris from the landing pad at low peak speeds and shallow ballistic arcs. shortly before landing, only few dense debris objects will be left, while the landing area is in a dust cloud.

Yes, but i meant the debris falling off the lander when it just broke orbit and began decelerating - pieces moving at near orbital velocity towards the base.

 

[statickid]

Yes, but i meant the debris falling off the lander when it just broke orbit and began decelerating - pieces moving at near orbital velocity towards the base.

maybe that could be avoided by a purposefully 1-ish degree "off-course" deorbit. It would cost a little more fuel but that's easier to fix than the base.

Although, retrospectively these are probably some of the reasons that lunar bases have been described as needing to be subterr-... er... sublunarian.

 

[Urwumpe]

Yes, but i meant the debris falling off the lander when it just broke orbit and began decelerating - pieces moving at near orbital velocity towards the base.

When the spacecraft just started decelerating, the debris should be in the same orbit as the lander in that instant. And not be moving towards the base, unless you want to waste fuel and do this intentionally (increase eccentricity without slowing down = turn trajectory on base).

Until shortly before landing, the ballistic free fall trajectory should impact behind the base from the view of the spacecraft: You want to land as shallow as possible so you reduce gravity losses. Passing over the base would actually be safer - at least until you are so low and slow that an explosion could permit debris to hit the base.

 

[Izack]

maybe that could be avoided by a purposefully 1-ish degree "off-course" deorbit. It would cost a little more fuel but that's easier to fix than the base.

Although, retrospectively these are probably some of the reasons that lunar bases have been described as needing to be subterr-... er... sublunarian.

You could also try building the base into the side of a shielding escarpment in the direction most vehicles are likely to land. Say, if most lunar orbiters would be in retrograde orbits for easier cislunar transportation, then have some natural or artificial shield on the spinward end of the base, blocking its line of sight with the direction most spacecraft will descend from. It could be anything from a metallic shield to a structure made of heaped regolith, or concrete produced on-site.

 

[Hlynkacg]

I actually gave this a lot of thought a while back but a computer crash wiped most of the data and I didn't have the patience to go back and rebuild it.

One thing that's always bugged me about brighton is that tower. Really it should just be the 6 pads and a small tram station with the mail structure at the OTHER end of the tram line.

---------- Post added at 13:56 ---------- Previous post was at 13:37 ----------

As an aside, I imagine that the first permenant lunar settlment will use some form of Marsden Matting to help mitigate FOD issues. Unless of course someone figures out a way to efficiently manufacture concrete or something similar using local resources.