Sep 19 2006, 02:54 PM
As plans to explore the Moon move forward, I wondered about the possible success of MER-like rovers sent to the Moon. There are a number of contrasts with Mars:
The same "drive train", in half of martian gravity, could easily carry a much larger set of instruments.
Communications would be almost instantaneous.
Rovers on the lunar near-side would ALWAYS be in radio contact with Earth. No relays necessary.
The lunar sol is 14 days.
Combine those last three points, and you could imagine HUGE (by MER standards) drives performed in a single sol. Or a large number of IDD explorations in a modest-sized area.
The rover would have to survive a lunar night. Some of the mass advantage could be put into heaters.
(Apparently) no issue with dust covering the solar panels.
No seasons. No winter.
Twice the solar power, all things being equal.
MER fans ought to drool. Downside, of course: the Moon may not be as interesting for you as Mars. But there's still plenty there to study.
Operations wise, imagine two "packs" of rovers (a pack could be as small as one rover) sent to different latitudes but the same longitude. Send one pack to someplace near the eastern limb and somewhere near the western limb, so that the fraction of the time that one pack would be in in daylight would approach unity. Have three or four teams on Earth that operate 8 hour shifts to keep each rover in constant action throughout the lunar day. When night falls on one pack, it would not be long until the other pack experienced dawn.
Without the delta-v requirements of interplanetary cruise, it should easily best the cost of MERs. For the launch cost of a New Frontiers mission, two pairs of rovers could be launched to support this kind of exploration, and could last seemingly indefinitely. Four sites with very long drives at each could explore a great variety of the lunar service.
Sep 19 2006, 06:58 PM
Honestly, as much as I would *really* love to see some robotic lunar exploration in the pipeline, I don't think that robotic rovers are the best investment for what we need from the Moon at this point, scientifically.
What would be most useful in terms of unraveling the remaining mysteries of the Moon, IMHO, would be a fleet of small sample return missions. Something like the Luna 16 plan -- able to pull a core up from next to the lander and return it to Earth.
I think the most valuable science you could do at the Moon right now would be to get more samples back here that you could date. We need to be able to pin down the extent of the Late Heavy Bombardment and the range of ages of the maria, and while we have some decent ballpark figures, we don't know very well when all the various basins were emplaced. That information, and data on how long the Moon was volcanically active, can only really be derived from dating of samples. And since the current technology doesn't really let you date the samples in situ, we need to bring them back here.
Now, from an engineering standpoint, rovers make good sense. If you're planning on building a lunar base (or a lunar resort hotel), it would be great to send a bunch of robotic surveyors (small 's'). But except for the thrill of exploration, I don't see any other reasons to send rovers at present... *sigh*...
-the other Doug
Sep 20 2006, 03:38 PM
QUOTE (helvick @ Sep 19 2006, 05:18 PM)
Does anyone have a back of the envelope mass budget estimate for landing material on the Moon? Roughly what sort of launcher do we need to get a few hundred kg softly onto the lunar surface? And once there how expensive is the remote comms likely to be?
My back of an envelope. Assumptions first:
- LEO is obtained by off-the-shelf launchers (= cheap)
- All fuels are hypergolics with an ISP ~310 (= reliable, storable, cheap, old technology)
- Stage 1 does both the TLI and LOI burns, for a total delta-v of 3.9 km/s.
- Stage 1's dry mass is equal to the fuelled mass of Stage 2.
- Stage 2 is a lander from LLO to the lunar surface, capable of delta-v 2.2 km/s.
- Stage 2 has a dry mass of which 20% is the payload.
Regarding this thread on current boosters
and their capabilities for LEO, you can land 1 MER as payload on the Moon, drawing on the above assumptions
, using a Zenit 2. Titan III gets you 200kg of payload on the Moon. Proton, Delta IV Heavy and Titan IV are around the 290kg mark. The Atlas V HL tops the list at 336kg.
Going down the scale, a Soyuz gets 98 kg safely down, and the humble Pagasus XL could
(aye, right!) land 5.7 kg of useful payload on the Moon. 5.7kg?? = "Half a Sojourner"
Not wishing to hijack the thread, I'd be keen to have input on the above assumptions...
Sep 20 2006, 07:50 PM
QUOTE (Phil Stooke @ Sep 20 2006, 08:23 AM)
The Surveyors descended most of the way to the surface braked by a rocket engine underneath the frame. In the final stage of descent the engine and its associated equipment were dropped and the spacecraft continued its descent balanced on three small "vernier" thrusters. The descent stage fell nearby. None of the landers imaged their descent stages, but they might possibly be seen by LRO. Anyway, that accounts for quite a lot of the weight difference.
You also have to remember that the Surveyors used a solid-fuel rocket engine as the main braking engine. I'm not sure, but I'd bet that there are higher-performance fuels out there that would give you more Isp for the weight than the solid fuel they used. (IIRC, they used the solid motors because it was far easier, and more mass-effective, to simply drop the motor and its casing out of the Surveyor structure after it burned out than it would have been to build tanks, piping, valves, etc., to feed liquid fuels into a braking rocket.)
The motor, again IIRC, was only abotut the size of a basketball (albeit with a nozzle attached). I have something of a hard time believing that this engine was more than 500 kg in weight -- they must have used quite a bit of fuel to power the final-stage descent thrusters, which were completely useless in terms of doing the major braking. So, I guess the solid fuel system did end up saving enough weight to make the landings possible...
-the other Doug
Sep 23 2006, 10:31 AM
As I've commented before, one of the most valuable "experiments" on later Apollo missions was a bucket-rake. This was shaped sort of like a dustpan, and could be dragged through the regolith to scoop it's way through a cubic foot or several of "dirt". After a good shake, it would contain some number of "walnut sized" rocks.
Those rocks are small enough you can collect a LOT of them
They're large enough that they are a statistically good minerologically complete sample of all but the coarsest grained rocks.
Given the local and regional and global "monte-carlo" nature of ejecta being tossed every which way, rake samples contain a lot of "very local" rocks, some "regional unit" rocks, and scattered random "from somewhere else" rocks.
A rover, traversing several hundred km of selected terrain, complete with multispectal visual and infrared imaging, and x-ray/gamma/neutron spectrometers, would collect an incredibly comprehensive traverse sample for return to Earth and future study.
Sep 25 2006, 06:54 AM
QUOTE (DDAVIS @ Sep 25 2006, 03:14 AM)
I would place a digital HD camera on the rover, if not two for stereo. They would be 1080 P video 30 FPS with time lapse capability, using less compression. The camera(s) would be on during approach and landing. One thing to watch for would be possible levitating dust activity along the terminator, something the high frame rate would be useful in capturing. A dedicated low light video camera of NTSC resolution might also be justifiable for this line of study. Besides panoramas with fewer images one could do time lapse studies of the scenery under differing lighting characteristics and catch the occassional eclipse above and around the rover.
Why send a video camera to the Moon with NTSC resolution when a camera with PAL resolution would surely be ever so much better?
QUOTE (DDAVIS @ Sep 25 2006, 03:14 AM)
Such a rover should probably be a fresh design, with or without a sample return capability. A hi def video camera on an orbiter with a daringly low orbital minimum height would also be a great source of inspiring fresh Lunar images.
A fresh design and/or a sample return capability would surely increase the cost of the mission, which in turn would make it less likely to be funded, especially with the first Orion mission to the Moon probably then only a few short years away.
A sample return capability on a mission which was expected to traverse "several hundred km" also seems rather pointless unless the rover also had the capability to not merely collect but store samples along the way; and that would surely mean a capability to store dozens if not hundreds of samples over that "several hundred km" traverse.
Oct 23 2006, 01:48 AM
Why do we need an unmanned lunar rovers? It's really simple.. we need them to test out their possibilities.
The greatest asset of an unmanned vehicle is that it doesn't eat, sleep or breath, and can be remotely programmed and operated from an armchair on good old Earth.
As far as feasibility, I think that the Russians proved that in 1970 with Lunokhod 1, and 1973 with Lunokhod 2. We have progressed significantly since then in almost all aspects needed to create an unmanned lunar rover.
Newer lightweight carbon composite materials can stand temperature extremes from -250 to 1500 degrees fehrenheit. Not only are they lighter in weight, they are less likely to deform over the temperature extremes, and can be developed into almost any use that is needed (relatively friction-free bearings, housings, tires and wheels, etc.). Lunokhod 1 weighed just slightly less that 2000 poounds, while the Mars rovers only weighed 387 pounds, had a lot more going for them, and are still operating after two years.
In addition to newer micro processing and communications capabilities, sensor and camera technology have also advanced. If we can communicate with the rovers on Mars, and get back great pictures, we can darn sure talk to one on the Moon, and almost in real time: approximately 20 minutes for Mars as opposed to 2 seconds for the Moon.
But is it necessary to confine Lunar rovers to simply exploration? The answer is NO. What we really need to develope is a series of rovers capable of performing Lunaforming. I would like to see a series of rovers capable of constructing a permanent landing site and ready a colony on the Moon, without the necessity of placing a single astronaut in peril. In other words, not even sending an astronaut until the majority of the heavy work is completed.
Imagine a Lunar rover that can build a Solar Panel array. The University of Houston has already tested one that may perform this function (http://www.newscientist.com, "Lunar Power", 24 June 2000). Why solar power? It's relatively cheap, and basically maintenance free (no atmosphere on the Moon; no clouds, no dust: which was one of the problems with the Mars rovers). The problem with solar power is that it only works in sunlight.
So why not nuclear power? New research into nuclear batteries (http://www.livescience.com, "Personal Nuclear Power; New Battery Lasts 12 Years", 13 May 2005, and other sources), suggests that a tritium gas impregnated wafer material can produce 10 times the power of current nuclear battery technology, last for 10 years, and does not require excessive shielding. Tritium gas is a normal by-product of radioactive decay of heavier elements, and as such is realitively inexpensive. We have to get rid of it anyway, so put it to use. They envision a battery approximately the same size as the current laptop battery producing approximately the same amount of current within five years. What this may mean is that a larger battery (say the size of an automobile battery) would have more than enough energy to power a Lunar rover, without the necessity of reliance on Solar power, meaning that the rover could operate continuously throughout the entire lunar cycle.
Before I talk any more about the various unmanned rovers needed to do the actual construction, I would like to discuss the unmanned Rover Lander Module. Since there is no need of an Orbiter module, the lander module can be that much greater in size and complexity. Since it doesn't need to be aerodynamic, and need never return to orbit, it may be preferable to have the main descent solid rocket pack jettisonable just prior to landing so that there is actually nothing beneath the flat bottomed final descent module. The three final descent vernier rockets could be gymbol mounted in a position above the bottom of the lander, between the tripod landing legs, which would extend outward and downward just prior to final descent. Once grounded and stabilized, the landing legs would be retracted and the lander would rest flat upon the Lunar surface. It really doesn't have to have a floor or walls, just a tubular framework and a method of placing or simply dropping the rovers onto the Lunar surface, possibly only a matter of inches. Additionally, it would be not be necessary or desirable (weight wise) for each rover to be able to comunicate directly with the Earth, but simply with the lander. The majority of computing capability and communications would reside in the lander, with the rovers as drones to the lander's computer and communications system. The lander could also be the base for sample analysis and storage.
A seperate type of lander, if desired, could be an actual remotely operated repair facility, equipped with mechanical arms with extractors, welders, etc., for repair of the various unmanned rovers. It should be capable of lifting and manouvering a rover to facilitate such work. If the various rovers could all be designed with essentially the same "plug and play" batteries, sensors, servomotors, communications and computer boards, etc., this lander could be supplied with the needed replacements parts. If for instance one of the rovers had a failed sensor, simply return the rover to the lander repair module and replace the sensor from stock.
So, what is the first step? Nothing more than placing landing site transponders to allow future landers to home in and land on, which need not be more than microwave emitting sources. Think of it as putting hooks on the wall behind your workbench, so that all your tools are in one place. No guesswork, all your preliminary landers are in one place. Put a simple receiver in them so that the lander can shut off or change the signal of the transponder to indicate that particular site is already in use.
So, the first actual construction lander and rover need do nothing more than simple clear site surveying and placing transponders. Multiple transponder packages would be stored in the lander until deployed by the rover. This rover is really a simple thing; a mobile imaging and delivery system. This first lander need not be more complex than a couple of cameras, and an articulating arm. It grabs a transponder package from the lander, finds a suitable lander site to drop it, and goes back to the lander for another package.
The next major thing is the construction of a permanent Lunar landing pad. What kind of pad do you want? I believe that I would construct a landing pad that is higher than the surrounding surface. Why? Because it would be easier to maintain and keep free of debris. How much higher? I guess that it would depend on the size of the pad, the type of landing approach that will be utilized, and the surrounding topography. I think a a fairly large, circular landing pad is preferable to any other design, because a circular pad would be non-reliant on the actual direction of orbital insertion; ie., it doesn't matter which orbital direction you're coming in from. For safety sake, I would make the pad approximately 10 kilometers wide. This should leave sufficient room for error. If you can center the lander on the pad approach beacon, you've got five kilometers to each side and ten kilometers length to work with. Sounds really big, huh? But remember, we're talking building it with rovers, multiple, capable of operating 24 hours a day, seven days a week, 365 days a year.
I know, the proposed 10 kilometer landing site may some day be discovered to have contained the only traces of the venerable Lunar Bogart Molecule that contains all the answers to the the really big universal question of what if! Tough luck, we destroyed it.
Now, on with the Rovers.
Construction Rover 1: the Lunadozer:
I envision a rover that can perform the same function as as a bulldozer does here on Earth, moving Lunar soil to create a flattened, obstacle free Lunar landing site. Lets call it the Lunadozer. It could also double as a survey instrument. By this I don't mean running all over collecting rock samples, I mean the same type of surveying required to lay out and construct a flat road here on Earth.
The only problem I see is one of engineering and design. We have the engineering, and there is no doubt in my mind that someone can come up with a feasible design.
I even have some ideas along this line. Make a rover that is basically a big, deep, empty box. Form the bottom of the box so that it is a V-shape. Either give it a movable door on the bottom of the V, or a screw type system so that it can be emptied when necessary like an earthmover. Give it a beefy suspension system, power train, and deep fin-type catapiller tracks. Put a bulldozer-type blade on one end, and a conveyor-type accessory on the other. Put some mechanical arms on it with appropriate cutting tools; drill, saw, laser, jackhammer, etc. It would of necessity need extensible stabilization pads of some sort. Equip each rover with all the necessary sensors, lander communications system and minimal computer capabilities. If the Soviets could land 2000 pounds of rover, plus 4000 pounds of lander on the Moon in 1970, we should be able to do the same thing, possibly landing three 600 pound LunaDozers with each lander.
This is the way it works.
1. Land the lander for the LunaDozers on the Moon. I won't go into the technicalities of a trans Earth - Luna landing. We know that we can do this. For crying out loud, both we and the Russians did it back in 1970. Find a nice large relatively flat initial landing site, preferably in the middle of one of the equitorial mares, facing the Earth, or with a permanent line-of-site communication capability with the Earth. Why an equitorial landing site? I'm not really certain about this, but I believe it would be easier to land at an equitorial site than it is at one that is not on the equator due to orbital considerations. Also, it would be much easier to construct a linear launch facility at an equitorial site. I think a good site would be about where Apollo 11 landed.
2. Move the LunaDozers from the lander to the surface of the Moon, and perform the required pre-survey. In other words, find a fairly good initial landing pad site. This could actually be done simply by using the cameras, and performing a general survey.
3. Perform the pre-construction survey. The LunaDozers should be able to do this simply by moving over the terrain, communicating to the lander not only distances, but depth, obstacle, and soil variances as they are encountered during the each rover's movement. At this point, they could also collect rock and soil samples if desired. The computer aboard the lander would send this data back to Earth where a really good topographical site map could be created, and interesting samples could be recorded for later analysis. Better yet, these samples could be taken back to the lander for storage and retrieval at a future date if desired, or an analysis facility could be incorporated in the lander.
4. Start the actual construction by first filling the hopper of each LunaDozer with fine soil using the conveyor attachment. This will not only add stability to the rover, but increase its lunar weight. It must be remembered that although a 60 pound object on the Earth only weighs 6 pounds on the Moon, it will still have 60 pounds of linear inertia. So in order to push a 100 pound (lunar weight) rock, you must have a minimum of 600 pounds of traction and inertia. So, the 600 pound (Earth weight) LunaDozer only weighs 100 pounds on the moon, and the actual dozing becomes a question of traction. So, if you fill the hopper with 500 pounds (lunar weight) of soil, now your LunaDozer has 600 pounds (lunar weight) of traction, and 3600 pounds of inertia. Now it's fairly easy to move that 100 pound rock.
5. The next step would be the removal of debris in the area of the landing pad. Hopefully, your survey would have eliminated the need to move any really large objects. Still, some of the debris will have to be broken into manageable pieces. Using the appropriate tools on the LunaDozer, start chopping, cutting, or moving the larger pieces of debris. Use this debris to fill in any low lying areas of the landing pad.
6. Now you start the actual leveling process. It's really kind of simple. Find the lowest part of the terrain and empty your hoppers. Move the LunaDozer outside the area of construction. Refill the hopper. With the hopper full, return to the place where the first load was dumped, and level the soil that was previously dumped. Repeat as necessary. Actually, if three LunaDozers are operational, one could be left with a full hopper to do the leveling, while the other two did the actual hauling and dumping.
7. Once the initial leveling process is completed, it would be necessary to overlayer it with a consistant fine particle layer, again dumping and leveling this out. The reason for this fine particle layer is to facilitate surfacing the site.
You've got the landing pad area level, and it's time to think about surfacing it. Why? Because a dirt road is just a dirt road until you pave it, and it is easier to land and move a vehicle on a smooth surface, and easier to keep that surface free of debris. Just because it's the Moon doesn't mean that you have to blow dust everywhere.
Yes, you heard me right, I said move. Future passenger landers are going to have to be capable of movement while they are on the Lunar surface (either by means of cable and wench system, or a self propelled landing gear system). This means tires of some kind, with at least one capable of swivel movement (easier to take the horse to the barn than the barn to the horse). The barn, in this case, would be a hangar just slightly larger than the lander, capable of being sealed so that it could be either pressurized or evacuated as needed. It would also contain a debarkation tube, refueling station, and maintenance/repair facilities.
Of the two systems of lander movement, the cable and wench system would be the most practical. The wench cable could be as much as 200 meters in length. Once landed, a lunar technician in a self contained wench truck would pull up to the lander and remotely attach the wench cable to the lander's swivel wheel. He would then pay out the wench cable while driving to the most appropriate surface imbedded power/latch point. Again, remotely, he would connect the the wench truck to the power/latch point and control the wench to move the lander in the direction of that point. When appropriate, he would cease wenching, detach from the power/latch point and again playing out cable move to the next appropriate point. This operation would be repeated until the lander had reached its desired hangar location.
So how do you surface the landing pad? This actuallly necessitates the need for a different type of rover, which I'll designate the LunaPaver.
Construction Rover 2, the LunaPaver:
The LunaPaver is really much less complex than the LunaDozer. The whole purpose of the LunaPaver is to melt the fine particle surface layer using focussed solar power, and forcably lay it back down while still in a molten state. Since the majority of the Lunar soil is silicate in nature, it would basically be laying out spun glass behind it.
In order do this, the LunaPaver would have to be able to couple to the LunaDozer. It would then be able to utilize the LunaDozer's conveyor, hopper, and hopper emptying system to replenish its own hopper. In addition, the two hooked in tandom should prove more stable and better capable of keeping a straight-line course. Ideally, the second LunaDozer would connect to the side of the first LunaPaver, and the third LunaDozer Connect to the side of the second LunaPaver, etc. The completed paver system would then consist of three connected staggered pairs, possibly laying out a nine to twelve meter width of glass on each traverse.
Naturally, the more of these Dozer/Paver pairs that can be attached to the paver system, the wider and more consistant a path that could be deposited at each pass. For instance, six staggered connected pairs would give a 24 meter pass.
The consistancy and thickness of the glass would be determined by the speed of the tandom rovers, the actual make-up of the fine particle layer, and the size and type of nozzles used to lay the melted glass back down (round nozzles, spray nozzles, ribbon nozzles, etc.). It may be possible to apply layers of melted glass that is 2 to 3 inched thick.
So, the paver system crosses the landing pad laying down the ribbons of spun glass for the ten kilometer width of the landing pad, assuming that they started at a line directly through the landing pad's center. Reaching the end, they make a wide turn and reverse course, choosing one side or the other of the completed strip and head back the other direction. Since they started on a line through the center of the of the landing pad, the distance to be covered on each consecutive pass out from center would get geometrically shorter.
A single layer over the whole surface of the pad won't be enough to create a surface that will withstand repeated landings. Multiple layering will be required, which means that the dozers will have to haul another fine soil layer layer over the top of the first glass layer and repeat the paver process. This layering must be done as many times as deemed structurally necessary. Consecutive layers should not be applied in the same linear direction as the previous layer.
To prevent deterioration and cracking due to temperature fluctuations during the lunar cycle it will be necessary to leave expansion gaps in the glass not only between each ribbon and linear gaps in each ribbon, but between each layer of ribbon. This expansion gap will consist of unmelted fine particle soil. Not only will this allow horizontal expansion and contraction, but also allow expansion slippage between each layer. The soil between each layer should also allow some degree of insulation as well as helping to distribute weight between the layers. It may be necessary to repeat the layering process twenty to thirty times. The entire effect should resemble a large woven fiberglass sheet prior to adding resin.
This completes the landing pad. The addition of power/latch points and other niceties (landing lights, etc.) in the pad will have to be done probably by an astronaut/technician at a later date.
I have been working on this dialogue now for about nine hours, so I,ll quit for now and return at a later date.
Oct 23 2006, 05:45 PM
Yes, you're right, it was a long post, but sometimes you have to stir things up and look in other directions for the answers.
Many people keep thinking along the paths of building Lunar habitats out of Earth materials, sending up sufficient aluminum panelling, structural members, etc., to build some grand Lunar habitat. That's the pipe dream. Expense wise and in every other way this is a ludicrous idea. We could never send up and safely land sufficient materials to build even a small sized Lunar habitat, whether publically or privately funded.
We have to look outside the box and think along the lines of using strictly Lunar materials in their natural environment, which without fanfare means using whats available on the Moon. We may even, at some future date have to consider salvaging the materials of the landers and rovers that we have already sent, regardless of their historic value.
We need to envision manufacturing techniques that are may be possible not just now, but in the future. Actually looking along the lines of constructing Lunar foundries using Lunar materials and resources. Using a Lunar still to melt soil and form it into useable shapes. Instead of using an aluminum panel, using formed glass panels and girders manufactured on the Moon. It may sound Sci-Fi, but consider Jules Verne's atomic submarine.
I may be a romantic, but to me human life is precious. I would never send a human being into a dangerous situation that could be handled more efficiently by a robotic device. So we need Lunar rovers and robotic devices capable of operating in that environment to perform routine manufacturing functions. It may be as simple as sending up a single lunar module that accepts lunar soil on one end and spits out glass panels and girders on the other. This to me seems a lot more feasible than sending up load after load of Earth materials.