Hypography X Prize Entry

[Pyrotex]

but there is some method to my madness in wanting to recharge the rovers at the base. In a word, moondust. The moon is covered with very fine, dust that gets into and onto everything.

Okay, have your "base". But instead of the base supplying electrical power, why not have it be a "car wash". Like, a light cylindical brush with fine soft hairs -- the rover rolls under it, the brush starts rotating and lowers down upon the rover's solar cell arrays -- and the rover drives off, clean as a whistle.

[CraigD]

Okay, have your "base". But instead of the base supplying electrical power, why not have it be a "car wash". Like, a light cylindical brush with fine soft hairs -- the rover rolls under it, the brush starts rotating and lowers down upon the rover's solar cell arrays -- and the rover drives off, clean as a whistle.

I suspect something more than rotating brush would be needed. Moon dust is very fine – 50% < [math]5 \times 10^{-5}[/math] m grain diameter, much of it < [math]1 \times 10^{-5}[/math], smoke-size. It’s also very sharp, not chemically and mechanically eroded like terrestrial dust and smoke, making it terribly scratchy. A bit of Apollo program trivia is that the vacuum seals on the “special environment sample containers” intended to protect some of the lunar rock and dust samples from atmospheric contamination never worked properly, due to damage from the scratchy dust. (Source: NASA - Apollo Chronicles: The Smell of Moondust).

 

In vacuum, bombarded by solar wind, moon dust has a lot of static charge, making it cling to fabric and surfaces. It also contains an unusual (by terrestrial standards) amount of [ce]FeO[/ce], leading some to propose a solution to the “lunar dust problem” involving “magnetic filters” (source: http://www.lpi.usra.edu/meetings/resource2000/pdf/7004.pdf).

 

Though an effective cleaning system would be a great invention, I suspect it wouldn’t be easy to design. I think the “keep the solar cells away from dust” solution is the most reliable.

[Turtle]

Happened on this Hypography while lurking :)

 

http://hypography.com/forums/space/511-mobile-lunar-base.html

 

... Another advantage of mobile moon habitats is that they will be able to move out of the lunar landing zone, which could be hazardous. "The landing zone poses the problem that once a habitat lands on the moon, it is not prudent to land another vehicle within several kilometers because of safety concerns from ejecta in a normal landing, and in case of an explosive failure on impact," Cohen said.

 

Cohen suggests that mobile habitats must have robust radiation shielding for them to be practical. "Radiation protection remains a challenge and a potential showstopper, as it does for all lunar base and rover concepts," Cohen said. However, there are potential shielding concepts that may well be reasonable, according to Cohen.

 

 

...

[CraigD]

Apologies in advance for this rant/brainstormish post. I have the impression that this thread is still in the brainstorming phase.

 

The more I consider the possibility of actually building a Google X Prize entry, the more I’m impressed with the need to take not only planning but physical first steps. This impression is likely a manifestation of a professional trait of mine - some of my best computer programming successes have come from following a “prototype before anyone can object” approach – but in this case, we’re talking not about a commitment of keystrokes, but of physical procurement, building, and testing. As I suspect most of our neighbors would object to even a small static test of a hydrazine rocket motor :), first tangible steps seem to me best focused on the rover system.

 

I propose a first step that’s actually fun, and an excuse to spend a few US$100s on a nice Spektrum RC kit and 802.11-based webcam, or possibly skip the COTS RC and do everything via 802.11 and some sort of PC-ish control system. Put everything together into a wheeled chassis close to one of our actual lunar rovers, and have fun driving it around on video, rather than the usual direct sight, with drive gears that make it much slower than any usual recreational or competitive RC vehicle.

 

That exercise in COTS engineering done, it remains to be seen how it would do on the moon. Since the rovers are planned to be fairly small, a fairly small vacuum chamber and pump should be sufficient to static test the rover. Even small high-ish ([math]< 10^{-5} [/math] atm) vacuum systems are pretty pricey ($2000+) new, and unlike radios and RC car chassis and radios, have limited fun potential, so are hard to justify as potential personal toys, leading me to think the best course to do this testing is to beg access to a school’s or private lab’s.

 

I’m terribly curious to know how an ordinary, toy RC vehicle, which is made mostly of injection molded plastic, fares in hard vacuum. An obvious failure point is its drive motor, which produces a lot of heat, exhausted either from the motor’s metal case, or a small attached heat sink, neither of which would be effective in vacuum. Many of these are small enough to fit inside the small bell-jar vacuum systems to be found in nearly all high school or better labs, and, even thick glass being radio transparent, could be tested without any special antenna trickery.

 

I’m also curious to know if any COTS wifi devices are vacuum capable. My suspicion is that anything with any sort of heat sink – visible or otherwise – is doomed. Vacuum = no convective cooling, so any component that gets even warm when powered on will, in vacuum, have to get hot and glow to reach thermal equilibrium. In my experience, glowing with heat is a dire sign with commodity electronic and electromechanical things.

 

So, can anyone suggest a parts list to the end of making a slow-moving, all-terrain, cam-carrying RC vehicle with a reasonable chance of being able to withstand a vacuum test? Better yet, does anyone already have an RC vehicle close to this spec, needing perhaps just a transmission change (most out-of-the-box RC vehicles are much too fast). Does anyone have access to even a small vacuum chamber/pump system?

[Roadam]

One comment to heat problem:

Will there even be such problem, becouse in vacum such as on moon, everything on sunside gets a lot of heat, and the other side is basically frezzing. So rover would have to have a good insulation which is not a problem becouse there arent many heat sources on the rover, even tho motor wouldt be such a problem becouse it is quite effifient and it would even turn slowly becouse we dont need much power.

[TheBigDog]

Nice post, Craig. I am right on board with you about actually building something. My plan is to start with a good RC toy, and then essentially rebuild the thing using aluminum in place of plastic. But before I make that switch I am going to work on the speed and duration aspects with payload including working cameras and data upload. I imagine having a very low power PC with accessories connected by USB. Everything is low power.

 

As far as dealing with heat, it is an obvious engineering challenge, but we just need to find out how it was solved previously.

 

Bill

[TheBigDog]

Another note on the testing...

 

Not only do we need to test in a vacuum, we need to have top down lights that heat the rover to nearly 100C. We need the exposed areas to withstand that punishment. I wonder if a coating of moondust acts as a decent insulator from solar rays?

 

Bill

[Turtle]

...As far as dealing with heat, it is an obvious engineering challenge, but we just need to find out how it was solved previously.

 

Bill

 

Here's some technical info on how the Mars rovers handle heating/cooling and other space environment challenges for machines. >> Mars Exploration Rover Mission: Technology

 

...Batteries and other components that are not designed to survive cold martian nights reside in the warm electronics box. Nighttime temperatures may fall as low as minus 105 Celsius (minus 157 Fahrenheit). The batteries need to be kept above minus 20 Celsius (minus 4 Fahrenheit) for when they are supplying power, and above 0 Celsius (32 Fahrenheit) when being recharged. Heat inside the warm electronics box comes from a combination of electrical heaters, eight radioisotope heater units and heat given off by electronics components.

 

...

 

Here's the Mars rover home page; there's a lot here. >> Mars Exploration Rover Mission: Home

 

I'd like to mention again that putting motors or other vacuum sensitive parts inside a pressurized enclosure is one proven way to avoid having to make/acquire parts that work in a vacuum. Then you only have to control temperature.

 

Up up and away, B)

[GAHD]

for testing to 100C, A large oven (such as found in pizzerias) would certainly do the trick. anything down to -40C will soon be testable by myself just by walking out my back door.

 

A parts list to withstand vacuum assuming central motor & transmission:

• +3* solid wheel, preferably a die-cast & machined unit
  
• 1* fluid less transmission (unless normal tranny fluid is replaced with something that won't boil-off in vacuum, mercury perhaps)?
  
• 1* fluid less differential (unless subbed as above)
  
• 2* RC boards & antennas (controller & vehicle)
  
• +1* battery pack(s)(which can always be made up pretty quickly)
  
• ?* bolts & other fasteners
  
• 1* basic chassis
  

Any part requiring lubrication probably won't work too well when it's lube boils off in the vacuum, so high-precision machining is our best if not only option if we go a mechanical route. Can you imagine trying to seal the system in such an environment? standard gaskets would freeze/cook and explode in next to no time.

[Jay-qu]

How can we precisely machine parts when they are going to be in a range of -40-100 degrees? wont thermal expansion make that impossible?

[TheBigDog]

anything down to -40C will soon be testable by myself just by walking out my back door.

Road trip to Winnipeg!

 

Any volunteers for engineering or locating a vacuum chamber for testing rovers? It will be easier to relocate the rovers than the chamber, so where should we look for locating it? I like the idea of having it in an environment that will provide good cold weather testing.

 

Bill

[Turtle]

...Any part requiring lubrication probably won't work too well when it's lube boils off in the vacuum, so high-precision machining is our best if not only option if we go a mechanical route. Can you imagine trying to seal the system in such an environment? standard gaskets would freeze/cook and explode in next to no time.

 

I think we need a library of sources on the pertinent topics so we don't unnecessarily reproduce work already done. Searching 'hazards of vacuum to space vehicles' I found this book for sale and some samples of chapters. Coinkydinkilly, the section quoted is on lubricants. :hihi:

 

Space Vehicle Mechanisms: Elements ... - Google Book Search

[GAHD]

I've started a thread dedicated to a specific design of rover. Those with the will come join TEAM SOLID STATE.

 

The Goal: NO mechanically connected moving parts.

 

 

I think we need a library of sources on the pertinent topics so we don't unnecessarily reproduce work already done...

Great Idea! I stole it...

[Roadam]

Does one really need a transmission? Electrical motor can be mounted directly, speed can be changed with voltage/current. As for steering, I think that it too can be made without use of direct contract, but that fits into team solid state thread...

[Turtle]

How can we precisely machine parts when they are going to be in a range of -40-100 degrees? wont thermal expansion make that impossible?

 

Not at all. We could do worse than research what metal(material) NASA used for their mobile machines. :doh:

 

A point I have yet seen mentioned that is bothering me a bit is whether or not we intend to leave an orbiter circling the Moon and acting as a relay for our data signals??? :hihi: I see most Mars rover signals go this route and the Apollo missions did as well? :doh:

 

Here's a nice bit for our Library titled Apollo TV and Communications Documentationhttp://history.nasa.gov/alsj/AWST690526Art.pdf

 

An article from the above link on the first color television signal sent to Earth from space. >> http://history.nasa.gov/alsj/AWST690526Art.pdf

[TheBigDog]

A point I have yet seen mentioned that is bothering me a bit is whether or not we intend to leave an orbiter circling the Moon and acting as a relay for our data signals??? :hihi: I see most Mars rover signals go this route and the Apollo missions did as well? :doh:

I was not planning on orbiting the moon, or leaving an orbiting satellite. I figured we land on the moon so that our Lander is always visible to the earth. Even the low powered conversations between the rovers and the lander should be easily snooped on by earth based listening stations. The Lander will be intended for two way conversations with the earth directly, and relay of data to the rovers.

 

But it brings me to a question that I was holding for later when we get to the landing phase of the mission: what is the reason for entering lunar orbit as opposed to going straight to the surface of the moon?

 

Bill

[Turtle]

I was not planning on orbiting the moon, or leaving an orbiting satellite. I figured we land on the moon so that our Lander is always visible to the earth. Even the low powered conversations between the rovers and the lander should be easily snooped on by earth based listening stations. The Lander will be intended for two way conversations with the earth directly, and relay of data to the rovers.

 

But it brings me to a question that I was holding for later when we get to the landing phase of the mission: what is the reason for entering lunar orbit as opposed to going straight to the surface of the moon?

 

Bill

 

On the boldened, I don't get this impression that it is "easy", but I think this is going to depend on the specifics of our radio equipment. I will be careful drawing parallels to Mars rovers and our Lunar project given the Moon's "close" proximity.

 

I'm not sure of any reason to orbit if we don't plan on leaving an orbiter. We better ask a rocket scientist. :) Maybe so we can line up our shot? :doh:

 

Ok; on to some specific ideas for the rover drive. I was thinking we could possibly adapt the rings-on-a-piston-in-a-cylinder used in internal combustion engines as an axle bearing. Works in a broad range of temperatures and pressures, and tolerates abrasive contaminants; proven technology and simple.

 

To expand on that I envision a single motor internal to our pressurized black box & driving a flywheel whose bottom bearing is as above and whose shaft projects below and outside the rover. The wheels, rather than having high tolerance machined axles and bearings are "sloppy" fit, like the old erector sets. Motive force to the wheels is drawn from the protruding flywheel axle by "loose" fit belts or chains. :hihi: :doh: