Were the Lunar Rovers faked?

[Count Zero]

To everyone who wants to use a locomotive, or a tugboat, or an airport tractor, please consider that none of these can get bogged, none of these are indented into the surface before they even try moving (apart from the tug lol). This, along with the low traction of a loose surface, is why a loose surface is such an easy one to get stuck on, as most of us have probably experienced.

I have towed a truck that was stuck on a loose surface with a 4wd, but that was with the truck using whatever traction it could muster as well, if the truck was in neutral forget it, it was also a very good surface which is why the driver though he could make it.

Do you really think a 4wd on a loose surface can act like a locomotive and pull many other 4wds?

A locomotive's wheels are indented into the surface.  The rail is deflected downward by the weight on the axle.   

And - needless to say - a boat indents the surface it is on, and has to overcome the drag caused by trying to move horizontally in that indent.

[ka9q]

To be fair they understand the principle of shock loading... they just cant quite understand why, if they weigh 100Kg, they need an anchor sling with a far higher capacity.

To compute the shock loading, don't you also have to know something about the spring constant of the line and its hardware, not to mention that of your body? If there's no elasticity in the system then the peak force when you fall could be arbitrarily high, and even if your line can withstand it this shock could also hurt you.

I suppose you could say that there's no point in having a line with a load rating higher than the maximum force your body could withstand so it might as well break. But somehow that doesn't seem right.

[ka9q]

On the flat I don't have to exert any force to stop it moving because its weight won't make it move anyway. I can therefore apply any force to it and still move it, provided I can overcome the friction or rolling resistance.

Just to be rigorously complete, because the rolling resistance depends on weight (the downward force of gravity), it too depends on the slope. While the tractive force required to overcome gravity on a slope varies with the sine of the slope (from horizontal), the rolling resistance varies as the cosine of the slope because that sets the force of gravity normal to the ground.

Because the coefficient of rolling resistance is usually much less than 1, and because the sine of a small angle increases much more rapidly than its cosine decreases this is usually a small effect, but I mention it for completeness. 'anywho' may not have any rigor whatsoever in his analyses, but it's still good for us...

[Count Zero]

...when I start talking to non-scientific minded people about the moon and Apollo, they understand when I tell them that a 60 kg object only weighs 10 kg on the moon because the moon's gravity is only 1/6th that of earth, and that is why the astronauts walked funny on the moon.

Actually, this is not correct.  My son weighs 1/6th what I do (yes, I need to lose weight), but our walking-gait is essentially the same.  This is because the kinesthetics of the gait is dictated by the downward acceleration, not by weight. 

When you walk, the ankle joint of your left leg is rotating forward.   Your center-of-gravity is shifting forward (and gains some momentum as it does so). When it is so far forward that it is no longer over your foot, you are falling forward.  Meanwhile your other leg is swinging forward.  The downward pull of gravity brings your right heel into contact with the ground just as your center-of-gravity moves over it.  Your CoG continues forward, over your right foot as you pick-up your left leg and let it swing forward.  In 1g, your CoG will be moving forward and your legs will be swinging to stay under it so that it feels natural to move at ~2-3mph.

On the Moon, the CoG shifts forward, and you swing your leg to get your foot under it, but gravity is not pulling your heel down fast enough to make contact with the ground.  Your CoG keeps moving forward over the unplanted foot and you're trying to get the other leg forward to get it underneath... and a simple walk turns into a skipping-lope.  That is why the astronauts "walk funny".

[ka9q]

When you walk, the ankle joint of your left leg is rotating forward.   Your center-of-gravity is shifting forward (and gains some momentum as it does so). When it is so far forward that it is no longer over your foot, you are falling forward.  Meanwhile your other leg is swinging forward.  The downward pull of gravity brings your right heel into contact with the ground just as your center-of-gravity moves over it.

I think the term is "inverted pendulum", and like any pendulum its natural period depends on length and the acceleration of gravity.

and a simple walk turns into a skipping-lope.  That is why the astronauts "walk funny".

Here's how I like to think about it. Because a bipedal walker is an inverted pendulum, and every pendulum has a natural rate, there's a natural speed limit on how fast we can walk.

Above that limit, we can no longer keep a foot on the ground at all times because we simply can't fall fast enough. So we transition to running, defined as no longer having at least one foot on the ground at all times. The much lower gravity on the moon forces this walk-to-run transition to happen at an unusually slow speed, well below the speed you'd often like to move and which your metabolic rate can easily support.

So the totally natural thing to do is to "run" at walking speed -- and that's exactly what the loping stride we see in Apollo lunar EVAs really is.

Everyone who has done it says it's totally natural, even people who have only experienced lunar gravity on an airplane without much time to think or adapt. At the end of my favorite segment of that wonderful Mythbusters episode on the Apollo hoax, Adam Savage said that the 1/6g Apollo lope instantly felt totally natural to him.

We humans are extremely familiar with walking, and because it is so profoundly affected by gravity it is virtually impossible to convincingly fake lunar walking in 1g. If I had to pick a single compelling argument for the Apollo lunar EVA footage being real, this would be it.

[geo7863]

To be fair they understand the principle of shock loading... they just cant quite understand why, if they weigh 100Kg, they need an anchor sling with a far higher capacity.

To compute the shock loading, don't you also have to know something about the spring constant of the line and its hardware, not to mention that of your body? If there's no elasticity in the system then the peak force when you fall could be arbitrarily high, and even if your line can withstand it this shock could also hurt you.

I suppose you could say that there's no point in having a line with a load rating higher than the maximum force your body could withstand so it might as well break. But somehow that doesn't seem right.

Under EN (European Standards) Fall Arrest Harnesses must limit the force on the body to a maximum of 600kgf. For Fall arrest you must have a shock absorber, usually a webbing or rope line with a compact concertina of webbing straps stitched in a pouch with strategic stitches so that it deploys 'in sequence'.

This shock absorber needs more than 200kgf to deploy and before use,with its webbing or rope line, can be no longer than 2m in length from anchorage point to where it is connected on the harness (between the shoulder blades- 'dorsal' or over the chest- 'breast') although in practice this can be lengthened slightly if an anchor sling is used between the shock absorber line and the anchorage (not specified as long as you be sensible about it).

Currently in Europe harnesses shock absorber lines and anchorages are tested to 15kN but many components are far stronger (some karabiners for example can be rated to 45kN, and some slings as high as 70kN). The regulations are being looked at to increase this to 22kN. If you use proprietary equipment the only thing you need to ensure is that your anchorage point is strong enough, Currently 12kN for fall arrest, 15kN for rope access work (the nutters (my personal opinion  ) who abseil down the sides of buildings whilst at work!)

What this all means is that in a Factor 2 fall, usually where your anchor point is at foot level, you can fall the length of your connector rope from anchorage to where it is connected on your harness (maximum of 2m) and then the full length of the connector (maximum 2m) then you have to fall a further 1.2-1.5m as the shock absorber deploys, you will exert maximum force on the system.... the shock absorber, stretch in lines and harness, and the design of the harness mean that the force on your body is progressively reduced and you should not receive more than 600kgf (which should be spread fairly evenly across the thighs waist and torso).

However much the maximum loading experienced overall is, obviously you want your anchor point to be stronger than the potential maximum loading, which the systems designers currently rate at 1200kgf in a classic fall from height at work. (sorry everyone for being so off topic!)

[VQ]

To compute the shock loading, don't you also have to know something about the spring constant of the line and its hardware, not to mention that of your body? If there's no elasticity in the system then the peak force when you fall could be arbitrarily high, and even if your line can withstand it this shock could also hurt you.

I suppose you could say that there's no point in having a line with a load rating higher than the maximum force your body could withstand so it might as well break. But somehow that doesn't seem right.

Not could hurt you, but would definitely hurt you. IIRC, a fall stopped by an arrest system missing a shock absorbing device is fatal from a shorter height than an unarrested fall.

...However much the maximum loading experienced overall is, obviously you want your anchor point to be stronger than the potential maximum loading, which the systems designers currently rate at 1200kgf in a classic fall from height at work. (sorry everyone for being so off topic!)

At my work in the USA, we design "generic" (can be installed as required) fall arrest anchorages for 5000 lb static load - pretty similar to your 1200kgf rating. Application-specific designs that get field verified individually have lower safety factors, but its not my department and I couldn't tell you how much lower.

[onebigmonkey]

In Larry Niven & Jerry Pournelle's sci-fi Novel "The mote in God's eye", human walking is described as a 'controlled fall', which I always liked. Kind of apt here.

[Noldi400]

In Larry Niven & Jerry Pournelle's sci-fi Novel "The mote in God's eye", human walking is described as a 'controlled fall', which I always liked. Kind of apt here.

I never read that one, but the same authors used that same description in "Footfall".

The description was from the POV of alien invaders who were built very much like Terran elephants and for whom watching human locomotion was unsettling and a little queasy-making.

[onebigmonkey]

In Larry Niven & Jerry Pournelle's sci-fi Novel "The mote in God's eye", human walking is described as a 'controlled fall', which I always liked. Kind of apt here.

I never read that one, but the same authors used that same description in "Footfall".

The description was from the POV of alien invaders who were built very much like Terran elephants and for whom watching human locomotion was unsettling and a little queasy-making.

Aah that's the one - apologies. I couldn't remember the title, googled and 'Mote..' was the one I recognised.

Both good reads

[anywho]

To everyone who wants to use a locomotive, or a tugboat, or an airport tractor, please consider...

No, all those putative objections have their proper analogues in the problem you're purporting to study ...

No, the are just an attempt to divert away from the subject matter, which is an army test which shows the rover cannot get enough traction to operate in 1/6g.

What a train on tracks , and a tugboat can pull (news flash, tugboats don't have wheels), does nothing to prove a 4wd on a loose surface can tow 5 times its own weight.

If only someone would do an actual test with a rover wheel and a simulated soil so we could look at those results instead of relying on trains and tugboats and pushbacks.

However (and this is the point you seem to be consistently missing), the amount of force needed to pull 30 lb increases depending on the angle you wish to pull it at relative to the horizontal/vertical.

The drawbar pull required to drive up the hill is roughly equvalent to the tangent of the slope

All the wheel performance plots shown herein reflect the assumption that the pull coefficient measured at a given slip on a level surface with a slngle wheel is roughly equivalent to the tangent of the angle of the slope that a vehicle equipped with similar wheels can climb.

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

Accordingly, on this basis the maximum slope climbing capability of the 50 percent chevron covered wire-mesh GM wheel is estimated to be of the order of 20 deg.

So we have the rover wheel that is tested in a simulated lunar soil and it can only muster enough traction to drive up a 20 degree slope before traction becomes too problematic. That means traction is at its designated limit when the wheel has to sustain a pull of a little more than 1/3 of its own weight, there is a safety margin in that figure so lets round it up to a 27 degree slope where it has to pull 50% more than its own weight.

So a sustained pull of 0.5 times the weight on the wheel is the traction limit. Don't forget, these tests were done on a level pit and then extrapolated to find the slope climbing ability, therefore the pull limits are based on a level pull.

To accelerate the rover has to find enough traction to sustain a pull of 5 times its own weight, and that is undeniable.

The test shows a 50% drawbar pull coefficient is possible with the available traction, basic physics say a 500% coefficient is needed for acceleration.

BTW, the silence is deafening wrt anyone claiming the army test proves the rover could operate on the moon, it seems like the best tactic is to shift the discussion away from the test to tug boats lol.

 

[Allan F]

To accelerate the rover has to find enough traction to sustain a pull of 5 times its own weight, and that is undeniable.

So when my car is on black ice, where the friction coefficient is around 0.01, it cannot move? My car weight 1700 kilos, and according to you, it has to be able exert a pulling force of 6.5 tonnes? Is that right?

[Andromeda]

Anywho, you have been shown, multiple times, how to apply the physics you spout using a number of examples - and given reasons for those examples.  You have also been shown your errors.  Your only response is to refuse to accept facts as presented to you.

I still want to know how you can claim that a video showing the rover moving well on the lunar surface somehow disproves that the rover could do so.

If only someone would do an actual test with a rover wheel and a simulated soil so we could look at those results instead of relying on trains and tugboats and pushbacks.

Or.... they could drive it on the moon.  As the video you linked to shows them doing!

There is no need to rely on any other proof using "simulated" anything.  The rover is clearly seen working on the moon.

[RAF]

If only someone would do an actual test with a rover wheel and a simulated soil so we could look at those results instead of relying on trains and tugboats and pushbacks.

No need for further testing, as the rovers performed fine on the Moon.

If you believe differently, then present actual evidence that the rovers were faked...this "Army report garbage" combined with your woeful lack of physics knowledge leads you to the wrong conclusions...and as evidence, it is not convincing.

[RAF]

No, the are just an attempt to divert away from the subject matter, which is an army test which shows the rover cannot get enough traction to operate in 1/6g.

So the Army test "proved" the rovers could not operate on the Moon, and in the over 40+ years since that test, you are the very first person to "see" it?

Is that really what you are saying?, because if you are, then there is no need to debunk you...you've debunked yourself.