Really at every landing site. And given the wide distribution of terrain and minerals I would be very surprised if there weren’t many sites that different countries or even teams have their eye on.
That is a damn clever solution for one off landing pads. I wonder if a man portable "pad gun" could use the same idea, without throwing the human off the surface, to make a more permanent pad.
It'll be pretty expensive no matter what the construction material is if you have to ship it from Earth, since transportation costs will dwarf any costs for the actual materials.
Little to none as it's injected into the nozzle. Engines are designed to extract maximum energy from the propellant, so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion. When you see a rocket taking off wth a plume bigger than the nozzle, that's lost energy, but unavoidable due to the changing pressure of the atmosphere. Once you're in orbit, you can use vacuum-designed engines. Youd' inject these into the nozzle further enough down that they go directly down and out, not to the sides. You don't need to inject them with very much force at all, just enough to keep it away from the injector and near wall. You can design it so that virtually none of the material ever hits the nozzle walls.
> so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion.
Exactly the opposite. The gasses will INFINITELY expand as the atmospheric pressure on the Moon is for all intents and purposes exactly zero.
> Engines are designed to extract maximum energy from the propellant, so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion.
Engines are NOT designed to extract maximum energy. Engines are designed for COMPROMISE between extracting maximum energy and other parameters like mass of the rocket.
For example, the engine could extract more energy from the propellant if the bell was larger. But that would make it also heavier and would reduce the performance of the rocket as a system.
Another example, part of the fuel is wasted to create screen to protect the engine from overheating. It is injected on the sides of the engine and does not burn. This waste is a planned compromise because better cooling mechanism would be much heavier and so wasting a little bit of fuel is best way to improve total performance of the rocket.
> Youd' inject these into the nozzle further enough down that they go directly down and out, not to the sides. (...) You can design it so that virtually none of the material ever hits the nozzle walls
No, you can't.
You mister, need to learn some physics.
The way engine works is by creating pressure. That pressure acts on the bell (the sides) and transfers to the rocket.
The "sides" aren't there to ornament the rocket, they serve a very important purpose as they are the surfaces which direct the exhaust back and on which the pressure of the gasses act to propel the rocket.
None of these two important roles can be fulfilled without the gasses actually pressing on them.
The vacuum regime isn't any different. There is positive pressure within the bell and this propels the rocket forward as the gasses expand backwards.
If you injected (ejected) fuel directly down and out you would get pitiful thrust the likes of your bottle of coke gets when a mint is dropped in it.
There are engines that do what you describe (ion engines) but they work in a very different way.
This is as a response to absolute bonkers explanation to how a rocket engine works.
I tried to keep good ratio of actual factual explanation to "swipes", which I think was fully deserved. Sometimes, somebody needs to at least hint you you are telling complete and utter rubbish (ideally backed by some explanation).
Now, I don't want to say everybody has to know physics or how an engine works.
But if you are starting to explain to people on HN, be ready to get fact-checked. You need to learn some.
You can't take that kind of potshot at people regardless of how bonkers their explanation was or you feel it was.
Aggression in your reply is much more significant than inaccuracy in the other comment. This is a big deal, because everyone underestimates the negativity of their own comments by (let's say) 10x and overestimates the negativity in other people's comments by another 10x. That makes for a 100x perception gap. This causes people who aren't being careful to blast bile into the the ecosystem here—something that, long term, leads to its destruction. Therefore we all need to be careful. Maybe you don't owe people who know less physics than you better, or don't feel you do, but you owe this community better if you're participating in it.
Here's what to do instead: if someone else is wrong, and you know more than they do, then patiently provide correct information. Otherwise don't post; or, alternatively, chalk it up to someone being wrong on the internet and just don't post. Punishing the other person, or strutting your stuff superciliously, does not engage curiosity, and isn't conducive to learning nor to curious conversation.
I said nothing incorrect, you misunderstood what I was talking about, presumably due to not reading the article we're commenting on. Do you really think I'm wrong saying that fuel is burned and directed out an exhaust nozzle to impart force in the opposite direction of the flow? Am I wrong that the bell is designed to capture as much energy as possible (within constraints) by directing the flow in a single direction?
I have absolutely no problem being corrected, but please don't be wrong in your correction, and don't do it with such attitude. You're agressively wrong here.
Oooooook... So we start off with misinformation and insults. The problem here is you think I don't know what I'm talking about, and that's not a good assumption. And you're being overly pedantic in order to find flaws in what should be an ordinary conversation.
1. Yes, the gas will expand indefinitely eventually. That doesn't change anything about the way nozzle's are designed.
2. Obviously everything has cost constraints. That doesn't change the fact that within financial and material limits, you want to extract all the energy possible. A larger bell does not equal mor energy in all cases. In fact, once you have your exhaust in a non-expanding perpendicular flow, there's nothing left to extract. Alfo, fuel is run through tubing around the bell to cool it down, it's not generally wasted to be coolant, you use pumps to run it through tubes in the bell to cool the bell, heat up the fuel, and that adds pressure to the fuel as it then cycles back up and exists into the reaction chamber.
3. Yes, you 100% can design your injector to not make the material not impact the bell. I said sides to indicate where I'm talking about, no need to mock a simple word choice, I never said they were ther for ornamentation, so you're just being rude.
4. Just because exhaust has a presure doesn't mean every particle impacts the bell, or you'd have a ring of exhaust flow with nothing in the center. You can inject your material so that it flows down the center. Note, I'm talking about the ceramic material injected into the flow as described in the article, NOT THE FUEL. I think you think I'm talking about fuel this entire time, which is not correct.
6. Yes, you just explained how a rocket works in the same way I did after trying to tell me how stupid I am.
7. I was talking abut the ceramic material injected into the flow, not the engines. Nothing I described applies to ion engines. Please mke sure you understand the comment before you rup into someone.
> After the base layer is deposited, alumina particles of approximately 0.024 millimeters in diameter would be required to heat up and liquify as they pass through the engine.... The pad would then require 2.5 seconds to cool before the vehicle touches down for a safe landing.
That's really, really fast solidification. I'd be worried about inadvertently sinking in or brazing the landing legs into the pad and making takeoff impossible. On investigation, though, a 6 meter diameter disc has a surface area of 28 square meters. Building that disc with 186 kg of alumina, which has a density of about 4 g/cm^3, would give you a plate with a thickness of only about 1.6 mm.
I think this is just a one-time-use landing pad, not a landing-and-takeoff pad. Its purpose is to prevent lander damage and contamination of the research area by ejecta.
The tech is still cool, don't get me wrong, but I guess I imagined something more like a spaceport runway with a massive slab of steel-reinforced concrete. This is more like dropping a Nomex blanket to land on than what I had in my head when I read "landing pad".
There will not (initially) be a steel-reinforced concrete structure on the moon. The best that can be done in the short term would be e.g. a covering blanket, or a application of (solar?) heat to fuse the surface.
Drop a small Wall-E with solar powered laser sinter few days before big landing.
On a general note - a Dr. Evil can make Moon much less accessible just by kicking some amount of dust into low Moon orbit. One can imagine future fight tactic in an environment like this.
Holding that foil in a well-focused lens shape, and keeping it focused on one spot on the surface while in orbit around the moon, would be pretty tough.
Even though a mirror surface can be like 90% efficient, I think you'd have a better chance of putting down more energy by collecting the energy with 30% efficient solar panels, and transmitting it with a tightly collimated, easily focused, easily aimed laser that may only be 30% efficient. That's only 9% of your incident energy output to do useful work, but I doubt you could be as successful with a foil mirror.
And when you've got those constraints, why would you not land it on the surface as a rover and work from a meter away instead of working in orbit many kilometers above the surface? The latter saves some landing energy and rover mechanisms at the cost of collimation requirements. It gains you the freedom to put your landing pad anywhere on the surface instead of having to drive there, but I don't think we need that yet.
I was wondering how they'd handle the 2.5 seconds without landing, given that the engine plume is going to heat it back up again. Are the particles being released from a much higher point than the pictures suggest? Otherwise you'd think it would drop into the still molten pad after less than a second, right?
Imagine one of those drivable bridges the army has for fording rivers where there is no bridge. Make it radially symmetrical instead and use maneuvering thrusters instead of wheels.
It’s going to float on the regolith, instead of water.
Myself, when I saw this, I imagined that instead of this "spraying" approach, you could build a very flat lander, basically a large metal disk with some propulsion and support structure beneath it, and drop it just ahead of your "real" lander. Then you'd get a firm platform to land on mere tens of seconds later.
Oh I like this very much. The previous idea I read about was a crawler that had essentially a giant microwave antenna pointed down that would "pave" where it drove by melting regolith under the antenna and then letting is cool.
Of course that required landing the paver near where you wanted your payload to land, and then it had to finish before you lander came in. This is, I suspect, the "$120M" solution they alluded to on that web page.
I wonder if the problem is as big as they are painting it.
There is no atmosphere and very little gravity.
The exhaust gasses expand out in a hurry and any particles should not be spending time in any kind of vortices -- should travel outward in a straight line along with the exhaust.
It could technically be possible for things to maybe rebound (maybe if there are rocks nearby) and come back at the pad?
The dust was a serious problem in Apollo and they were landing in isolated areas. It obscures landing sites and approaches that just let dust billow disturb the local regolith, meaning you kick up more dust than you might otherwise have during your mission. Future missions are almost surely going to involve landing near to existing equipment that must work for longer than the 3 days and change of Apollo 17's surface excursion, making dust management that much more important.
You could, theoretically, always make your landings happen away from equipment but at 1/6th gravity with no atmosphere those sites would need to be quite far away to avoid kicking the seriously, seriously sharp dust into your equipment. But if you take that you also have to solve a hard transportation issue.
> those sites would need to be quite far away to avoid kicking the seriously, seriously sharp dust into your equipment.
The dust will trail off with distance, but on the moon, there is no 100% safe distance. Literally anywhere on the surface of the moon is within range to some extent. In orbit around the moon could also be in range.
There was an interesting paper (poster linked below[1]) about the unique risks that are posed by high velocity lunar regolith. The amount of exhaust mass you need to decelerate a lander is proportional to that lander's mass. Since you can either eject more mass more slowly, or less mass more quickly (momentum being simply mass times velocity), to save mass for the payload you want to get your exhaust velocity high.
However, when that exhaust collides with the lunar regolith it transfers its momentum there. Further, given the low gravity of the Moon, you run the risk of accelerating dust and rocks so much that they actually go into an elliptical orbit with the lander at the perigee of that orbit.
If that happens, you touch down and anywhere from 20 to 35 minutes later a rock you kicked up comes right back at you from the other direction!
Perhaps worse, that rock hits a satellite or support module that is currently in orbit. In any case its not a good thing and something that was avoided in the Apollo program because the landers had relatively low mass (< 10 tons).
> If that happens, you touch down and anywhere from 20 to 35 minutes later a rock you kicked up comes right back at you from the other direction!
It is not simple as that, it is actually more interesting:)
On a spherical ideal body it is impossible for the rock to do this. That is because the only orbit that does not intersect the ground must be exactly parallel to the ground at the landing site. So not only it can't hit the landing pad, it can't even hit the rocket sticking way above the ground.
Now, there is couple of interesting reasons I can figure out why this is at all possible on Moon, but I am too lazy or in some cases incapable to estimate which ones are significant.
1. Moon rotates. If the landing happened anywhere but the poles, by the time the projectile completes orbit the surface has shifted (but just a tiny bit since Moon rotates so slowly). If the projectile was shot parallel to the ground in the right direction, it does not need to complete entire orbit to hit the landing pad or the rocket.
2. Moon has lumpy gravity. It is not an ideal spherical body and it is known to have huge gravitational anomalies. The anomaly is so large that satellites around Moon need regular boosts because otherwise their orbit would degrade.
3. Moon has atmosphere. It is as good as vacuum in most circumstances but it might possibly be significant for particles of dust traveling at thousands of meters per second. For those interested, the entire atmosphere of Moon is estimated to weigh around 10t. So don't count on using it Watney-style for anything practical.
4. Solar wind. Very small particles may be significantly shifted in their orbit due to interaction with energetic particles traveling in particular direction (like solar wind).
5. Particles skipping off of Lunar surface? I think it could maybe be possible for a particle being close to complete its orbit to hit something at really extremely small cross section that rather than vaporize it would just deflect it by couple arc seconds and hit the rocket.
Of course this is just thought experiment. Dust flooding other structures on the Moon, satellites, orbits around Moon and Earth is reason enough to try to find a solution.
Agreed, it is never simple! What was most interesting to me was the non-intuitiveness of being able to throw a rock into orbit (I know tumang[1] prejudice), with the right conditions the NASA paper suggests some could escape the Moon's gravity completely!
The ejecta travel so far that there is no 100% clear distance anywhere on the moon. Some will escape the moon entirely.
> The paths of these particles travel all the way around the Moon with a significant fraction traveling higher than the Lunar
Gateway orbit, as shown in Fig. 4. This ejecta sheet
slowly evolves for days or weeks.
40 comments
[ 3.4 ms ] story [ 94.0 ms ] threadA little like pouring concrete, you'd pour molten aluminum (or molten steel?) into a prepared area or crater and let it settle and cool.
As anyone that has ever had to work with sandblasters will tell you, running powder through things has its own challenges.
I hope they keep winning (and keep their mojo) in the growing space race.
Exactly the opposite. The gasses will INFINITELY expand as the atmospheric pressure on the Moon is for all intents and purposes exactly zero.
> Engines are designed to extract maximum energy from the propellant, so the expansion curve of the nozzile is made to direct exhaust directly aft with no further expansion.
Engines are NOT designed to extract maximum energy. Engines are designed for COMPROMISE between extracting maximum energy and other parameters like mass of the rocket.
For example, the engine could extract more energy from the propellant if the bell was larger. But that would make it also heavier and would reduce the performance of the rocket as a system.
Another example, part of the fuel is wasted to create screen to protect the engine from overheating. It is injected on the sides of the engine and does not burn. This waste is a planned compromise because better cooling mechanism would be much heavier and so wasting a little bit of fuel is best way to improve total performance of the rocket.
> Youd' inject these into the nozzle further enough down that they go directly down and out, not to the sides. (...) You can design it so that virtually none of the material ever hits the nozzle walls
No, you can't.
You mister, need to learn some physics.
The way engine works is by creating pressure. That pressure acts on the bell (the sides) and transfers to the rocket.
The "sides" aren't there to ornament the rocket, they serve a very important purpose as they are the surfaces which direct the exhaust back and on which the pressure of the gasses act to propel the rocket.
None of these two important roles can be fulfilled without the gasses actually pressing on them.
The vacuum regime isn't any different. There is positive pressure within the bell and this propels the rocket forward as the gasses expand backwards.
If you injected (ejected) fuel directly down and out you would get pitiful thrust the likes of your bottle of coke gets when a mint is dropped in it.
There are engines that do what you describe (ion engines) but they work in a very different way.
Please edit personal swipes out of your comments here. It's not what this site is for, and it destroys what it is for.
If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.
I tried to keep good ratio of actual factual explanation to "swipes", which I think was fully deserved. Sometimes, somebody needs to at least hint you you are telling complete and utter rubbish (ideally backed by some explanation).
Now, I don't want to say everybody has to know physics or how an engine works.
But if you are starting to explain to people on HN, be ready to get fact-checked. You need to learn some.
Aggression in your reply is much more significant than inaccuracy in the other comment. This is a big deal, because everyone underestimates the negativity of their own comments by (let's say) 10x and overestimates the negativity in other people's comments by another 10x. That makes for a 100x perception gap. This causes people who aren't being careful to blast bile into the the ecosystem here—something that, long term, leads to its destruction. Therefore we all need to be careful. Maybe you don't owe people who know less physics than you better, or don't feel you do, but you owe this community better if you're participating in it.
Here's what to do instead: if someone else is wrong, and you know more than they do, then patiently provide correct information. Otherwise don't post; or, alternatively, chalk it up to someone being wrong on the internet and just don't post. Punishing the other person, or strutting your stuff superciliously, does not engage curiosity, and isn't conducive to learning nor to curious conversation.
https://news.ycombinator.com/newsguidelines.html
Here's a 5 year old youtube video deascribing it the exact same way: https://youtu.be/l5l3CHWoHSI?t=32
I have absolutely no problem being corrected, but please don't be wrong in your correction, and don't do it with such attitude. You're agressively wrong here.
1. Yes, the gas will expand indefinitely eventually. That doesn't change anything about the way nozzle's are designed.
2. Obviously everything has cost constraints. That doesn't change the fact that within financial and material limits, you want to extract all the energy possible. A larger bell does not equal mor energy in all cases. In fact, once you have your exhaust in a non-expanding perpendicular flow, there's nothing left to extract. Alfo, fuel is run through tubing around the bell to cool it down, it's not generally wasted to be coolant, you use pumps to run it through tubes in the bell to cool the bell, heat up the fuel, and that adds pressure to the fuel as it then cycles back up and exists into the reaction chamber.
3. Yes, you 100% can design your injector to not make the material not impact the bell. I said sides to indicate where I'm talking about, no need to mock a simple word choice, I never said they were ther for ornamentation, so you're just being rude.
4. Just because exhaust has a presure doesn't mean every particle impacts the bell, or you'd have a ring of exhaust flow with nothing in the center. You can inject your material so that it flows down the center. Note, I'm talking about the ceramic material injected into the flow as described in the article, NOT THE FUEL. I think you think I'm talking about fuel this entire time, which is not correct.
6. Yes, you just explained how a rocket works in the same way I did after trying to tell me how stupid I am.
7. I was talking abut the ceramic material injected into the flow, not the engines. Nothing I described applies to ion engines. Please mke sure you understand the comment before you rup into someone.
That's really, really fast solidification. I'd be worried about inadvertently sinking in or brazing the landing legs into the pad and making takeoff impossible. On investigation, though, a 6 meter diameter disc has a surface area of 28 square meters. Building that disc with 186 kg of alumina, which has a density of about 4 g/cm^3, would give you a plate with a thickness of only about 1.6 mm.
I think this is just a one-time-use landing pad, not a landing-and-takeoff pad. Its purpose is to prevent lander damage and contamination of the research area by ejecta.
The tech is still cool, don't get me wrong, but I guess I imagined something more like a spaceport runway with a massive slab of steel-reinforced concrete. This is more like dropping a Nomex blanket to land on than what I had in my head when I read "landing pad".
There will not (initially) be a steel-reinforced concrete structure on the moon. The best that can be done in the short term would be e.g. a covering blanket, or a application of (solar?) heat to fuse the surface.
On a general note - a Dr. Evil can make Moon much less accessible just by kicking some amount of dust into low Moon orbit. One can imagine future fight tactic in an environment like this.
Even though a mirror surface can be like 90% efficient, I think you'd have a better chance of putting down more energy by collecting the energy with 30% efficient solar panels, and transmitting it with a tightly collimated, easily focused, easily aimed laser that may only be 30% efficient. That's only 9% of your incident energy output to do useful work, but I doubt you could be as successful with a foil mirror.
And when you've got those constraints, why would you not land it on the surface as a rover and work from a meter away instead of working in orbit many kilometers above the surface? The latter saves some landing energy and rover mechanisms at the cost of collimation requirements. It gains you the freedom to put your landing pad anywhere on the surface instead of having to drive there, but I don't think we need that yet.
Complicated solutions are a dime a dozen...
It’s going to float on the regolith, instead of water.
Of course that required landing the paver near where you wanted your payload to land, and then it had to finish before you lander came in. This is, I suspect, the "$120M" solution they alluded to on that web page.
There is no atmosphere and very little gravity.
The exhaust gasses expand out in a hurry and any particles should not be spending time in any kind of vortices -- should travel outward in a straight line along with the exhaust.
It could technically be possible for things to maybe rebound (maybe if there are rocks nearby) and come back at the pad?
You could, theoretically, always make your landings happen away from equipment but at 1/6th gravity with no atmosphere those sites would need to be quite far away to avoid kicking the seriously, seriously sharp dust into your equipment. But if you take that you also have to solve a hard transportation issue.
The dust will trail off with distance, but on the moon, there is no 100% safe distance. Literally anywhere on the surface of the moon is within range to some extent. In orbit around the moon could also be in range.
https://www.theverge.com/2019/7/17/18663203/apollo-11-annive...
https://www.hou.usra.edu/meetings/lunardust2020/pdf/5040.pdf
However, when that exhaust collides with the lunar regolith it transfers its momentum there. Further, given the low gravity of the Moon, you run the risk of accelerating dust and rocks so much that they actually go into an elliptical orbit with the lander at the perigee of that orbit.
If that happens, you touch down and anywhere from 20 to 35 minutes later a rock you kicked up comes right back at you from the other direction!
Perhaps worse, that rock hits a satellite or support module that is currently in orbit. In any case its not a good thing and something that was avoided in the Apollo program because the landers had relatively low mass (< 10 tons).
[1] https://ntrs.nasa.gov/api/citations/20205007525/downloads/Hi...
It is not simple as that, it is actually more interesting:)
On a spherical ideal body it is impossible for the rock to do this. That is because the only orbit that does not intersect the ground must be exactly parallel to the ground at the landing site. So not only it can't hit the landing pad, it can't even hit the rocket sticking way above the ground.
Now, there is couple of interesting reasons I can figure out why this is at all possible on Moon, but I am too lazy or in some cases incapable to estimate which ones are significant.
1. Moon rotates. If the landing happened anywhere but the poles, by the time the projectile completes orbit the surface has shifted (but just a tiny bit since Moon rotates so slowly). If the projectile was shot parallel to the ground in the right direction, it does not need to complete entire orbit to hit the landing pad or the rocket.
2. Moon has lumpy gravity. It is not an ideal spherical body and it is known to have huge gravitational anomalies. The anomaly is so large that satellites around Moon need regular boosts because otherwise their orbit would degrade.
3. Moon has atmosphere. It is as good as vacuum in most circumstances but it might possibly be significant for particles of dust traveling at thousands of meters per second. For those interested, the entire atmosphere of Moon is estimated to weigh around 10t. So don't count on using it Watney-style for anything practical.
4. Solar wind. Very small particles may be significantly shifted in their orbit due to interaction with energetic particles traveling in particular direction (like solar wind).
5. Particles skipping off of Lunar surface? I think it could maybe be possible for a particle being close to complete its orbit to hit something at really extremely small cross section that rather than vaporize it would just deflect it by couple arc seconds and hit the rocket.
Of course this is just thought experiment. Dust flooding other structures on the Moon, satellites, orbits around Moon and Earth is reason enough to try to find a solution.
[1] Belter word for someone who lives on Earth.
it's a known problem, has been publicised before:
https://www.theverge.com/2019/7/17/18663203/apollo-11-annive...
> It could ruin a spacecraft in orbit around the Moon
https://www.hou.usra.edu/meetings/lunardust2020/pdf/5040.pdf
The ejecta travel so far that there is no 100% clear distance anywhere on the moon. Some will escape the moon entirely.
> The paths of these particles travel all the way around the Moon with a significant fraction traveling higher than the Lunar Gateway orbit, as shown in Fig. 4. This ejecta sheet slowly evolves for days or weeks.
https://www.thespaceresource.com/news/2019/2/the-importance-...