Were the Lunar Rovers faked?

[JayUtah]

Here's a suggestion: work out how many scenarios cause cars here on Earth to end up traveling sideways, then work out how many of those could possibly transpire on the Moon.

Here's a suggestion...

I apologize: Jason points out I've misattributed his remark to anywho and demanded an explanation from him.  No explanation needed, obviously, and I regret the error.

[Jason Thompson]

No worries, Jay. Thanks for the correction.

[DataCable]

Hey, I just realized:
[...]
So all the EVAs are fake.

What, you think he wasn't building up to that?

Sorry - Dogs and bells.

<Eddie_Izzard>Pavlov's debunker: Day 1...</Eddie_Izzard>

[Noldi400]

Which is why cars are rolling over all across the streets and highways.

Heck, I rarely drive at under 6 MPH, even in a parking lot.  I have driven a bit less than 20 times that -- and on just a two-lane blacktop.

Your parking lot is not a very uneven surface with extremely low traction, nor are the streets and highways.

Now, I know you were hoping to lose the connections in the forest of uneeded detail, but your scenario requires the LRV -- a vehicle with a top speed of 15 MPH, typically driven at half that -- to be traveling SIDEWAYS at 2.5 MPH or more.  On a regular basis! 

Why on a regular basis? It only has to happen once to roll the vehicle therefore it only has to be a possibility before a rollcage and harness are needed.

And, on an uneven surface with an extremely low coefficient of traction it is not exactly an unforeseeable possibility, more likely a highly probable event.

Note that the calculation of the LRV's SSF that Jay provided is a good margin higher than any of the Earth vehicles.

Not with two astronauts sitting up high and weighing 800lbs, especially when the vehicle only weighs 460lbs.

And how will they end up sideways?

Here's a suggestion: work out how many scenarios cause cars here on Earth to end up traveling sideways, then work out how many of those could possibly transpire on the Moon.

One scenario is gong off road onto uneven terrain in slippery conditions, then it is very easy to end up sideways. If you are ever in that scenario you would be well advised to crawl along, even here on earth.

Can we all agree that scenario is very likely to happen on the moon? Or do you guys just want to relate your experiences in parking lots to the moon.

This really is mostly personal incredulity on your part, you know.

No, the LRV's frame wasn't tremendously strong.  Weight was a major consideration, along with the ability to fit into a small space for transport. It was made as strong as it needed to be (plus a safety margin) and no stronger. But it was strong enough for the planned task.

It wasn't terribly powerful. Again, as much as was needed and no more. The motor and steering were designed to provide sufficient power, with a maximum of reliability and maneuverability and a minimum of weight, to cart 121 kg around at an average 10 kph.  Making comparisons to earth vehicles is an unreliable comparison, but E-Z-Go of Georgia does make an all terrain utility vehicle called the Terrain 1000 which weighs 595 kg, has a cargo capacity of 450 kg, and a top speed of 26 kph. Its battery-powered electric drive motor is rated at 2.5 hp; it seems reasonable that 1 hp would be sufficient power in the lunar gravity.

Yes, the ultra-light LRV's traction on regolith was low enough that the rear end tended to break loose when turning.  But the designers weren't working in the dark; they had soil samples and data acquired from the first landings to go by.  They also had experienced test pilots, accustomed to and proficient at cautiously feeling out the handling characteristics of new vehicles, to operate their creation in the lunar environment.

It was built low and wide for stability. The astronauts weren't sitting "up high"; their seats were bare inches above the floor pan. Operating it with only one astronaut aboard did have some effect on the lateral stability -the Apollo 15 crew felt that "...  roll instability would be approached on the 15-degree slopes if the vehicle were traveling a contour line with one crewmember on the downhill side.  Except for the brief "Grand Prix" and short movements near the LM, the LRV was always occupied by both astronauts while in motion, so this wasn't a factor.

Actually, your "slide sideways and hit a  rock" scenario was almost realized at one point. In the same report quoted above the crew described it:

      "There was one instance of breakout and lateral skidding of the rear wheels into a crater approximately
       1/2 meter (1-112 feet) deep and 1-1/4 meters (4 feet) wide. This resulted in a rear wheel contacting
       the far wall of the crater and subsequent lateral bounce. There was no subsequent roll instability or
       tendency to turn over, even though visual motion cues indicated a roll instability
       might develop.*".

*[I think the phrase in blue is test-pilot speak for "I was afraid my butt was going to bite a hole in my pressure suit trying to grip the seat"]

They were well aware of the theoretical possibility of a rollover, but all three crews agreed that the vehicle did not show any noticeable tendency to roll. Although it was definitely something to be avoided, they didn't seem to regard the possibility as a catastrophic event; the Apollo 15 crew's main concern (in the event of a rollover) was how difficult it would be to release their seat belts so they could crawl out from under the 35 kg machine and turn it back over.

Exercising due caution was the obvious approach; As CDR Dave Scott put it, "It was just a matter of going slow when you had obstacles, and catching up on your rate when you had a clear field."

You make the statement that problems controlling the rovers is "not what we see in the video and photographic footage", which is just silly. What video footage we have of the LRVs being driven is during the "Grand Prix" runs which were deliberate speed runs done on familiar terrain near the LM and certainly not typical of operation during the long traverses.

You haven't presented a single piece of evidence that doesn't amount to "I don't believe this would work", which puts your premise on the level of a coffee house bull session, not intelligent discussion.

[Allan F]

Has it been established if it was the frame, the suspension or the wheels that was the load-limiting factor?

Also, I believe, the two-point seatbelts were velcro straps.

[ka9q]

Looking at the LRV Operations Handbook Performance Data (still available on the ALSJ site) I found a plot showing wheel deflection as a function of radial load. (Figure 2-8, document page A-11, pdf page 20). It was set so that on the moon it would be halfway through its range before hitting the bump stop. I think that makes it the limiting factor; on earth the wheels would have bottomed out, possibly damaging the inner frames. That's why you see the LRV up on blocks as the astronauts are fit-testing it on earth.

[armillary]

Hmm. I just realised I failed to account for the gyroscopic effect from the wheels. That's one effect that won't be gravity-related, but will relate directly (well, probably quadratically) with the vehicle's speed.

[ka9q]

They also had experienced test pilots, accustomed to and proficient at cautiously feeling out the handling characteristics of new vehicles, to operate their creation in the lunar environment.

And true to their nature, nearly all of them drove sports cars on earth, typically Chevy Corvettes. While they didn't always exhibit the same amount of skill driving them as they did test-piloting aircraft and flying spacecraft, they probably knew the basics of how to keep a car right-side up.

[Sus_pilot]

They also had experienced test pilots, accustomed to and proficient at cautiously feeling out the handling characteristics of new vehicles, to operate their creation in the lunar environment.

And true to their nature, nearly all of them drove sports cars on earth, typically Chevy Corvettes. While they didn't always exhibit the same amount of skill driving them as they did test-piloting aircraft and flying spacecraft, they probably knew the basics of how to keep a car right-side up.

Suggestion: if you and a test pilot are going anywhere by car, you drive.  Trust me on this - you'll thank me later (nothing like being anywhere near an airport with those guys when they're driving "Look - it's an F18!"  "No! You look at the semi cutting us off!!")

[gillianren]

Suggestion: if you and a test pilot are going anywhere by car, you drive.  Trust me on this - you'll thank me later (nothing like being anywhere near an airport with those guys when they're driving "Look - it's an F18!"  "No! You look at the semi cutting us off!!")

Personally, the person whose lifestyle does not involve taking insane risks strikes me as the better driver ninety-nine times out of a hundred.  In the hundredth time, you're probably not having fun either way.

[Peter B]

Here's another thing for anywho to consider, though still just a sideline really.

In a car on Earth if you roll it it flips quickly and you're strapped inside a metal box, powerless to stop physics from doing its thing. If the rover flipped, how quick would it be, and given that the astronauts are not confined within, wouldn't just sticking a leg outhave some effect in slowing the roll? Or maybe they could just jump off. Either way, rolling an open vehicle you're not strapped into at speeds lower than normal human walking speed hardly seems like a catastrophe....

Keep in mind that the astronauts had to wear seatbelts, so they couldn't just leap out if the rover started to roll.

However, if it started to roll, I suspect the driver would have had enough time to steer away from the lifted wheels, and thus bring the rover back down.

[Noldi400]

OK, this is me, "just asking a question".

I was wandering around in the ALSJ (I could get lost in there for days if I could find someone to bring me sandwiches) and I found a spot where Dave Scott, Apollo 15 CDR and first man to operate the LRV on the lunar surface, had some comments about the stability of the Rover and what it might take to cause a rollover. He and Eric Jones are talking about their (Scott and LMP James Irwin) return from Geo Station 2, driving downhill from Hadley Delta when the front wheels dug in and sent them into a sudden 180^o spin.

[Jones - "You remember the 180? Which way did the back end go?"]

[Scott - "I think to the right. I don't really recall, but I remember it was real quick, before you could do anything about it. As I said here, the front wheels dig in. We were trying to maneuver around stuff, and it just broke. It was over before we even knew it. That's why we're laughing. Tsuuuu! and around it went. And then we went uphill, turned around, and came back downhill. And I know that the people in the back row at the Control Center were probably all crossing their legs tight."]

[Jones - "And it was basically a really stable little vehicle."]

[Scott - "Very stable. There was never any feeling of maybe turning over, at all. That's why it (incidents like the 180) was interesting: even though the rear end broke out - several times - and you spin all the way around, you don't have any feeling that it's going to turn over. It's sliding"]

[Jones - "Gene said that on their third EVA, when they were doing a fair bit of cross-slope driving on the North Massif, they had the feeling that if the upslope wheels started bouncing that they were getting toward the margins of stability. Did you ever have that feeling?"]

[Scott - "Nope. Gee, it's hard to imagine. I think you'd have to go look at the c.g. (center-of-gravity) and it would be easy to calculate. 'Cause if you know the c.g. and you know the angle the Rover is driving, you know the difference between the center of gravity and the center of pressure and you can figure our how much force it would take to push it over. And I think'd be really difficult to turn over."]

[Jones - "You'd have to be well tilted and you'd really have to bounce the uphill wheels."]

[Scott - "And you don't get a lot of angular momentum from the force, because of the low g. It's just kinematics, freshman physics."]

[Jones - "Assume you're going along at some tilt angle and at some speed and you hit a crater which gives you a force."]

[Scott - "And your force would be a reactive force from the Rover, which is limited by the Rover mass. There's nobody pushing you, so it has to be a wheel going into a crater to create a reactive force. Boy, I think it would be hard to get enough reactive force, with the suspension system which damps out the force. Boy, tough to do, but it could probably be done. It'd be interesting. If you were going very fast, then you've got a lot of energy in the system and, you might translate the energy into an overturning moment. It would be a great little exercise for somebody at school."]

Would someone be so kind as to clarify the part of the conversation I've marked in red, especially the underlined sentence?  I get the general principles, but I'm not clear on what is meant by "reactive force" in this context and how it relates to the mass of the rover.

Thanks.

[Allan F]

The CoG is easy to find, with regards to sideways tilt. If it's correct what I've read, the LRV could stay on it's wheels up to 45 degrees sideways tilt. If you view the LRV from the front, draw a 45 degree angle with the ground, and the top at the bottom center of the wheels. Do this from both sides. Where the lines intersect at the center, you have the CoG. This cannot move outside the wheel, or the LRV would fall over. At any slope, draw a line from the CoG in the direction of gravity. That's the Center of Pressure. There is a drawing a couple of pages back.

Since the mass is much greater than the weight (about 6 times bigger) bumps wouldn't upset the LRV much. The momentum is proportional to weight on wheel, but the angular momentum would be proportional to mass. It's a little counter-intuitive, but if you divide the two events up, and look at them separatly, it's easier to understand.

The wheel presses on the surface, and the surface presses back with the same force. A bump will transfer momentum to the chassis in proportion to the pressure against it. No pressure - no force.

The momentum imparted by the bump will have an effect relative to the mass. And since the mass is much greater than the weight, you don't get much movement. On the other hand, the low weight would make the gravity-dampening effect slower.

[Noldi400]

The CoG is easy to find, with regards to sideways tilt. If it's correct what I've read, the LRV could stay on it's wheels up to 45 degrees sideways tilt. If you view the LRV from the front, draw a 45 degree angle with the ground, and the top at the bottom center of the wheels. Do this from both sides. Where the lines intersect at the center, you have the CoG. This cannot move outside the wheel, or the LRV would fall over. At any slope, draw a line from the CoG in the direction of gravity. That's the Center of Pressure. There is a drawing a couple of pages back.

No kidding. Go back and note who posted that diagram.

Since the mass is much greater than the weight (about 6 times bigger) bumps wouldn't upset the LRV much. The momentum is proportional to weight on wheel, but the angular momentum would be proportional to mass. It's a little counter-intuitive, but if you divide the two events up, and look at them separatly, it's easier to understand.

The wheel presses on the surface, and the surface presses back with the same force. A bump will transfer momentum to the chassis in proportion to the pressure against it. No pressure - no force.

The momentum imparted by the bump will have an effect relative to the mass. And since the mass is much greater than the weight, you don't get much movement. On the other hand, the low weight would make the gravity-dampening effect slower.

Sorry. That just confuses me. I don't understand your statement that "the mass is much greater than the weight". Mass is measured in kg and weight in newtons; you can't compare them directly, although they are directly proportional. I'm also not sure what you mean about a bump 'transferring' momentum to the chassis (assuming that by "bump" you mean an actual physical feature of the surface), since a bump has no velocity and therefore no momentum.

But. Hmmm. A bump could and does change the velocity vector of some of the vehicle's linear momentum to angular momentum, with the bottom of the opposite wheel as the center of rotation.  I'll crunch some numbers on that and see where they lead.

[Noldi400]

Also, I believe, the two-point seatbelts were velcro straps.

The seat belts were a textbook example of simplicity of design; a strap with a hook on it to hook over the side ingress handle:



This is one of the reasons I love hanging around engineers - the combination of complexity where required and simplicity where possible is positively elegant.

Engineering: The Art Of The Practical.