The document of NASA is interesting in terms that those guys have considered the problem of collecting regolith and moving it to a central location. It is the same problem, and one of the tasks for tech seed on the moon surface, to collect regolith and deliver it to processing unit, thus it is interesting to see the difference in the approach of the methodology of doing so. Those are more like my comments for some of their statements and assumptions, where I see significant difference or find interesting.
My eye caught some sentences from a “Conceptual Design of a Fleet of Autonomous Regolith Throwing Devices for Rad” from NASA document from 1992(link, pdf), and I see it as an opportunity to make a comparison between approaches and highlight some significant differences design ideology. The difference is typical with other plans and concepts, and this paper is basically about moving regolith, which is also a key for IRSU and for Plan0 approach.
The main idea of them is:
- The project of the mechanical engineering design team is to develop a method to automatically cover a lunar habitat with the needed regolith. An example of such a method is a fleet of “robots” that independently “toss” regolith on the habitat.
Exactly what we need, an automatic fleet of robots which scrape and toss/unload the regolith in IRSU bucket.
Now we get to the interesting part, which caught my eye, Design Criteria.
- The design must have low mass.
- The design must have a long life.
- The device must be storable and compact
None of that applies to any transportation system which is the part of second generation tech seed or is a product of original tech seed. We do not need super lightweight systems because they have to be produced locally from materials available locally. It might require some limited mobility for initial means, in case of seed landed in an area where only the rocks in the reach, but a 30kg bucket on wheels might be enough to solve that initial problem.
It looks, at least for now, that a transporting craft mass of one tonne and which is capable to transport one tonne of regolith with speed of 1m/s is sufficient as transport for the whole system. And by using regolith from the upper layer, it seems that a typical second generation seed may occupy a surface of about 3 square km.
With such assumption, it seems sufficient if unit will travel 10-20 km distance during its life time and that will be sufficient for the system. So basically it should last for about less than a day. If it will last for twice more than that – very good, if it will last 3 times more than that – there is nothing more we could ask in regards to their durability.
- The rigors of the lunar surface include a near total vacuum, electrostatic dust, and intense radiation. The devices must be able to function and survive in this harsh environment.
Ok. Yes. I would add thrive in that environment.
- The lunar device needs to have a high efficiency. Fuel is difficult to obtain on the Moon The provided fuel must be used sparingly and not wasted. A low power consumption is vital for the lunar devices.
High efficiency and consumables. Efficiency for the growing system is one of the parameters which define the speed of the growth of the system, but it is not a most important parameter and not each efficiency is equally good for the increase of the growth speed. And as long as the whole system has to comply with the bill of moon materials, and materials which are the result of processing and extraction, mostly from lunar regolith. Thus resources are not such a big problem, or else the whole system can’t just function and grow. Thus consumables are not a concern, same as efficiency but building the system with the bill of moon materials in mind is an important factor.
- low power consumption reduces the mass of the required energy storage devices.
Not a concern for the system, because energy storages are very expensive energy wise to build so typical work cycle is – there is the sun we work, there is not enough sun, go sleep.
So important is not the to figure out a lightweight energy storage systems, or capacities of such systems, or how to build them in place, but build production and resource collection around the fact that half of the time there is no energy on the moon (until a bigger system is built, maybe some equatorial ring).
A day on the moon is about 15 earth days long, so it helps to the situation because it would be way more difficult to squeeze different technological processes which can’t be finished in short time. Having long days makes such decision easier. 15 earth days is plenty of time to finish a batch of something.
- The design must be robust to withstand and survive the lunar environment. The device must be stable to move around the lunar surface and fulfill its tasks without becoming inoperable, for example, by improper orientation for movement. If a device becomes momentarily inoperable, it must be able to right itself or it will no longer function.
As we do not rely on reliability and long life of devices, the constraint does not apply. It is good for a transporting unit to recover after a failure, but if it fails not a big problem as we rather rely on numbers of these devices, that there is many of them, thus failures of particular units are not so critical, especially transporting units.
- lubrication of moving surfaces is a large problem on the Moon. The near total vacuum removes the water vapor that acts as a lubricant on the Earth. In addition, without perfect sealing, any fluid lubricants will vaporize on the Moon.
As we do not rely on long service life and efficiency, we can allow having not lubricated parts, as long as it works. Use of ceramics will help in that both preventing cold welding of parts, and freeing from the need of lubricating parts. It still limits the field of available solutions, but it frees from seeking of some perfection in those devices.
Task specific criteria:
- The device must have a high reliability. Initially, astronauts will not be on the Moon to repair a broken device, so the units must have a low failure rate.
As we rely on numbers and do not rely on reliability and repair, but mostly on the production of those devices, it makes device design simpler.
- The design is to set up habitats before any humans are on the Moon. An automated device, reduces the problems seen with teleoperation from the Earth.
- lunar environment may be conducive to non-obvious design solutions and hostile to standard design solutions.
Yes, absolutely. A design should covert disadvantages into advantages.
- The temperatures on the Moon ranges from 102 K at lunar night to 384 K at lunar noon . Materials and equipment insensitive to these extreme conditions must be selected. Several problems are associated with extreme temperatures. High temperatures cause evaporation of materials and lubricants and low temperatures cause embrittlement of certain materials. Thermal gradients also cause large strains in most materials. All equipment reliant on lubrication must be carefully sealed so that the lubricant does not evaporate. To minimize thermal strains, materials with low coefficients of thermal expansion should be considered
This paragraph is interesting in terms of ideology. It is good and bad if we look at it from tech seed perspective. Not having lubricants and not caring about super efficiency and durability allow caring less about expansion and contraction of materials, because there is no such incentive to remove backlashes, to keep seals etc.
By not working at night means embrittlement of materials is less or no concern for the system or units. Working at day and higher temperature is basically a plus for the system considering that variety of available materials is not that high, especially at initial phases.
2.2.3 Micrometeorlte Impact:
- The device should be protected from micrometeorite impacts. … Micrometeorites between 1 to 10 mm are predicted to impact the lunar surface at a rate of 300/m^2 per year .
If we rely on cheap to replace units it is not a concern for the system.
- the acceleration of gravity on the Moon is about 1/6 of the gravity on Earth. This will cause objects on the Moon to weigh less than on the Earth.
Funny how few to say they have about that. Even didn’t describe it as an advantage, which it is, for the systems which carry/transport loads.
Lol. They have enough phantasy for jumping devices, why they do not have guts for broader problems?
- Lastly, a suitable, although extreme, solution is preliminary surface preparation. By removing all hazards, the device can be assured of safe movement. However, such preparation can be quite extensive. Craters need to be filled, slopes need to be leveled, and rocks need to be removed. These activities require long periods of extra-vehicular activity (EVA) which is expensive and dangerous for the astronauts. Surface preparation can be done autonomously. However, autonomous surface preparation has the same problems as the other methods, such as control and obstacle avoidance.
Guys, do that by teleoperating if you can’t do that autonomously.
- A third alternative is to have the lunar device store itself for protection from the cold. To do this the device is simply programmed to go to a heated shelter when a certain temperature is detected. A disadvantage of this alternative is that it prevents the device from operating during the lunar night. This means that the device will sit motionless for 14 Earth days.
Storing units is ok solution, why not. Anyway, production over night is reduced and add complexity to the system by introducing energy storage systems. Do your business when energy is available and cut batteries and complex energy system expenses.
- Transporting the shelter materials to the Moon adds more mass to the total system. In addition, building a shelter for the devices could prove to be a challenging design task.
Build it from slag bricks, not need to transport it.
Generally, Na+K mix used as heat carrier allows to use electricity to pre-heat the units, so shelter is not so much required.
- Several methods are considered for the removal of lunar dust. These methods consist of using electrostatics, vibrations, brushes, and fluids or compressed gas. Due to the electrostatic charge inherent in lunar dust particles, it is possible to charge a surface and repel the dust particles. However, high voltages are needed for repelling the dust. Voltages needed are on the order of 11 kV . With the power sources currently available for lunar use, it is not possible to directly create this voltage.
Use LMMHD (Liquid Metall MHD), it allows to create high voltages directly, or at least do not require massive transformation units, also electrostatic generator is simply mean to create a high voltage, if you have energy. Similarly to LMMHD, it is possible to combine electrostatic methods and moving liquid conductors with current in a magnetic field to create high voltage potential.
Note: One of the problems in their decisions making is that the device they talk about, should to work about 6-7 years, and that drives a lot of their selection in a different direction.
- The fourth alternative consists of using compressed gas, fluids, or gels to wash or blow off the lunar dust. A problem with this alternative is that these fluids or gels must be periodically replaced, as they are used by the lunar device.
When you produce tonnes of oxygen as a byproduct and do not know where to spend it, gas availability is not a problem.
- The design team did not select an optimum alternative for each function.
- Cost is another factor that needs to be addressed. However, limited information on the cost of each component prevented the design team from directly considering cost in the selection of the overall designs.
This is the result of too many options, a not system which helps to select between them, and too many unknowns.
The situation can be avoided, by designing the system in the way we can adapt it later to nuances of the moon environment while creating more complex systems there, but the initial system should work regardless of unknowns.
As we do not need the best solution, but one which works, it reduces the amount of work required to design such solution, by eliminating testing and design alternatives. We need a solution. The difference may be not so important at the initial phase, but it adds up when solutions get more detailed.
As the main option they inclined for throwing system and collecting system in one device, it is a result of their goal, to cover a habitat module to protect it from radiation and impactors and make it habitable/safe for humans.
And because and other decision factors they are forced to combine everything in one device with resulting problems of such device
But in terms of a system which just collects the regolith, and produces machinery required for that locally, mass is not a problems and separation of the task in two devices one for skimming the surface for regolith and another for transporting it is a better way to address some problems, and eliminate that throwing way of delivering to a destination.
Like the last page of the document, that time of typewriters, so sweet.