Were the Lunar Rovers faked?

[nomuse]

Once again, anywho, look at the graph and the testing regime. At 0% slip they have defined a 0% pull coefficient. They are NOT testing the ability of the wheel to get the mass of the rover moving, they are testing the abilities of the wheel once steady state has been reached, i.e. at a constant speed over a level surface, and making it slip deliberately to see what it could do on a slope where it does have to pull its weight (not mass) against gravity. At this point the rover does not have to pull its mass in the way you are describing.

The only thing that test tells us about the rovers ability to get moving is that if you started to spin the wheels at that speed the rover would likely slip and not make a clean start in its motion. Well so what? Cars do the same thing. You get round that by using a slow initial acceleration to give the wheels a chance to grip and get the mass of the vehicle moving.

You're taking a test that is designed to assess one aspect of performance and applying it to the one you think it should be testing, just as you did with the footage of the rover going over the test bed.

Heh.  He's saying that since I could burn rubber in second gear in my old Mustang (boy, I miss that car!) it is obviously impossible for me to drive.  Especially since I was already "losing" traction in the most perfect conditions (according to him); no slope to speak of, and essentially no forward velocity either.  Heck, and not the slightest hint of turning forces either (I never left donuts.  They are for the uncultured).

[smartcooky]

For simplicities sake we will use a 600lb vehicle, and all measurements in lbs, and ignore rolling
resistance.

A 600lb vehicle on earth weighs 600lbs and has a mass of 600lbs, on the moon it weighs 100lbs but still has a mass of 600lbs. Each wheel on earth has 150lbs of weight on it, and on the moon each wheel has 25lbs of weight on it.

In both cases the same mass has to be moved horizontally, and the forces needed to accelerate the vehicle horizontally are the same in both cases ("x" for smartcooky), but relative to the weight on the wheels it is not the same.

Aha!! I think I see what you are trying to say, and where you are making your mistake.

Are you saying that the 25lbs of weight on each wheel is not enough weight to give it the friction it needs to gain traction to move 150 kg of mass horizontally?

If you are, then you are making a fundamental error and approaching the issue too simplistically. Weight on the wheel is not the only thing involved in this process, There are other factors, such as the composition and texture of the surface, the shape, texture and composition of the wheel surfaces, contaminants at the interface of the surface and the wheel, and the relative motion of loose components of the tractive surfaces.

[gwiz]

A 600lb vehicle on earth weighs 600lbs and has a mass of 600lbs, on the moon it weighs 100lbs but still has a mass of 600lbs. Each wheel on earth has 150lbs of weight on it, and on the moon each wheel has 25lbs of weight on it.

So for a given surface, you only have one sixth of the traction force on the moon that you have on earth.    All that means is that the maximum acceleration you can get on the moon is one sixth you can get on earth.  So you have a low-acceleration vehicle, but you aren't trying to do high-speed manoeuvres or heavy breaking, so why does it matter?

[smartcooky]

A 600lb vehicle on earth weighs 600lbs and has a mass of 600lbs, on the moon it weighs 100lbs but still has a mass of 600lbs. Each wheel on earth has 150lbs of weight on it, and on the moon each wheel has 25lbs of weight on it.

So for a given surface, you only have one sixth of the traction force on the moon that you have on earth.    All that means is that the maximum acceleration you can get on the moon is one sixth you can get on earth.  So you have a low-acceleration vehicle, but you aren't trying to do high-speed manoeuvres or heavy breaking, so why does it matter?

I believe anywho mistakenly believes that the lack of traction will cause the vehicle's wheels to spin continuously and the vehicle to remain stationary, and if so, then that is his mistake.

Even if his 600lb vehicle had smooth steel wheels and the lunar surface was perfectly flat ice, there would still be some traction and therefore, some acceleration.

[Jason Thompson]

In both cases the same mass has to be moved horizontally, and the forces needed to accelerate the vehicle horizontally are the same in both cases

No. Any force can accelerate any mass. If you want to accelerate the mass at the same rate on both Earth and the Moon you need the same force, but nowhere is that requirement specified.

In the test they lost usable traction at 50 to 60% over what it takes to drive the weight of the wheel, but on the moon the need enough traction to pull an additional 500% more than the weight of the wheel, or a "pull coefficient" of 5, not .5 like they got.

Check out this page:

http://en.wikipedia.org/wiki/Pushback

Note the section where it says a typical tractor used to move an airliner has a weight of about 120,000 lb and a drawbar pull of about 75,000 lb. Now explain how a vehicle with those specifications is able to move an airliner weighing in excess of 200,000 lb in addition to itself, using the same 'logic' you just applied to the rover wheel test.

[anywho]

Once again, anywho, look at the graph and the testing regime. At 0% slip they have defined a 0% pull coefficient. They are NOT testing the ability of the wheel to get the mass of the rover moving, they are testing the abilities of the wheel once steady state has been reached, i.e. at a constant speed over a level surface, and making it slip deliberately to see what it could do on a slope where it does have to pull its weight (not mass) against gravity. At this point the rover does not have to pull its mass in the way you are describing.

The only thing that test tells us about the rovers ability to get moving is that if you started to spin the wheels at that speed the rover would likely slip and not make a clean start in its motion. Well so what? Cars do the same thing. You get round that by using a slow initial acceleration to give the wheels a chance to grip and get the mass of the vehicle moving.

0% slip and 0% pull coefficient just means that the wheel is driving the weight on it (and no more) without slip

II will have a more comprehensive answer to this post in a day or two when I have time to muddle through the testing they dd in more detail, but one thing I will say now is in relation to the comment "The only thing that test tells us about the rovers ability to get moving is that if you started to spin the wheels at that speed the rover would likely slip and not make a clean start in its motion."

The tests performed got nowhere near showing that the rovers could operate on the moon at all, the wheel failed way before it reached the necessary drawbar pull. That test was done at 2.5 ft/s or a very leisurely walking pace, they gradually added the load and the traction started failing too much at about .5 drawbar pull.

http://en.wikipedia.org/wiki/Pushback

Note the section where it says a typical tractor used to move an airliner has a weight of about 120,000 lb and a drawbar pull of about 75,000 lb. Now explain how a vehicle with those specifications is able to move an airliner weighing in excess of 200,000 lb in addition to itself, using the same 'logic' you just applied to the rover wheel test.

That drawbar pull will certainly be pertaining to power and not traction, it is worked out on a set speed, so as long as they go slow enough and have enough traction they can do it.

From your source:

For sufficient traction, the tractor must be heavy, and most models can have extra ballast added.

[anywho]

Aha!! I think I see what you are trying to say, and where you are making your mistake.

Are you saying that the 25lbs of weight on each wheel is not enough weight to give it the friction it needs to gain traction to move 150 kg of mass horizontally?

If you are, then you are making a fundamental error and approaching the issue too simplistically. Weight on the wheel is not the only thing involved in this process, There are other factors, such as the composition and texture of the surface, the shape, texture and composition of the wheel surfaces, contaminants at the interface of the surface and the wheel, and the relative motion of loose components of the tractive surfaces.

Every "factor" you raise was dealt with in the test, they used the same wheels and a simulated soil.

[anywho]

Even if his 600lb vehicle had smooth steel wheels and the lunar surface was perfectly flat ice, there would still be some traction and therefore, some acceleration.

Good luck

In the test they say:

Pull/load increased rapidly with increasing slip to a near maximum at 15 to 25% slip for all wheels, then increased slowly with Increasing wheel  slip to 100% sllp. This behavior suggests that the operation of a vehicle at slips higher than 25% for protracted periods would result in immobilizing the vehlcle,

http://www.hq.nasa.gov/alsj/PerfBoeingLRVWheelsRpt1.pdf

[Andromeda]

Anywho, you still haven't shown us how you resolve your contradiction.

You say that the videos prove that the rover could not move, based on the way the lunar soil looks when the rover moves on it.  Can you not see the problem with that?

[Jason Thompson]

0% slip and 0% pull coefficient just means that the wheel is driving the weight on it (and no more) without slip

So according to your interpretation of that graph the pull of the vehicle goes up with increasing slip?!

The numbers for 'pull coefficient' on the y-axis of that graph, as I have already pointed out, represent the proportion of the weight of the vehicle that is acting downslope at those angles, also on the y-axis, i.e. that would be acting to actively oppose the forward motion of the vehicle.

The tests performed got nowhere near showing that the rovers could operate on the moon at all, the wheel failed way before it reached the necessary drawbar pull.

No, it did not.

That drawbar pull will certainly be pertaining to power and not traction, it is worked out on a set speed, so as long as they go slow enough and have enough traction they can do it.

From your source:

For sufficient traction, the tractor must be heavy, and most models can have extra ballast added.

[/quote]

Doesn't matter. The drawbar pull/weight ratio of the tractor is 75,000/120,000, which is about 0.34. That, according to you, means that vehicle can pull its own mass plus 34% more. An airliner is waaaaay above that, so according to you it should not be able to pull that airliner.

You're not even being consistent with your own arguments.

[RAF]

The tests performed got nowhere near showing that the rovers could operate on the moon at all, the wheel failed way before it reached the necessary drawbar pull.

Are you saying that NASA performed tests that proved that it was impossible for the rovers to operate on the Moon?

If not, what does the above quote mean??

[Echnaton]

The tests performed got nowhere near showing that the rovers could operate on the moon at all,

Then why do you think that physicist and engineers have not detailed this lack of performance before, over the past 40+ years?  If some have please provide the results of your lit search.  Why has it been left to you Anywho, some anonymous guy on the internet who dodges questions that are basic to establishing a case?

[anywho]

So according to your interpretation of that graph the pull of the vehicle goes up with increasing slip?!

It's not just my interpretation, it is the interpretation of the authors also, although you do seem to have put the cart before the horse.

The slip increases with increased load, they both go up happily together until the slip gets to around 25% at which point the slip increases dramatically for very little rise in load.

Pull/load increased rapidly with increasing slip to a near maximum at 15 to 25% slip for all wheels, then increased slowly with Increasing wheel slip to 100% sllp. This behavior suggests that the operation of a vehicle at slips higher than 25% for protracted periods would result in immobilizing the vehlcle,

http://www.hq.nasa.gov/alsj/PerfBoeingLRVWheelsRpt1.pdf

Doesn't matter. The drawbar pull/weight ratio of the tractor is 75,000/120,000, which is about 0.34. That, according to you, means that vehicle can pull its own mass plus 34% more. An airliner is waaaaay above that, so according to you it should not be able to pull that airliner.

You're not even being consistent with your own arguments.

Or .625

It's apples and oranges, that drawbar pull relates to power, not traction.

The tests performed got nowhere near showing that the rovers could operate on the moon at all, the wheel failed way before it reached the necessary drawbar pull.

Are you saying that NASA performed tests that proved that it was impossible for the rovers to operate on the Moon?

If not, what does the above quote mean??

Yes, although technically the army conducted the test, for NASA.

[Jason Thompson]

It's apples and oranges, that drawbar pull relates to power, not traction.

Prove it. Calculation of drawbar pull requires the use of the coefficient of traction between the wheels and the surface. You can't ignore it because the whole point of drawbar pull is how much it can pull forward, and to do that it has to move its wheels, and to move it forward they have to have traction. How much traction they get determines the drawbar pull. Since the operation of that vehicle is restricted to one type of surface, why would that number not be valid for the traction it gets in its normal operating environment?

With a drawbar pull of 75,000 lb, a tractor like that can pull an airliner with a mass well above that. In fact you'll find various sources that tell you drawbar pull is a fraction of the maximum load the vehicle can pull, because any mass can be accelerated with any force. A vehicle does not have to be able to exert a force greater than the weight of the load it is pulling in order to move it, unless it is moving it upwards.

[Jason Thompson]

Or .625

Quite right, I stand corrected. However, the vehicle can still clearly pull itself and a great deal more than that.