DL Space Mountain, Part 2

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In this multi-part series, former Imagineer George McGinnis

and Bill Watkins share their memories of the design and construction of

Disneyland’s Space Mountain. To start from the beginning, see Part 1 (link),

and to see the conclusion, continue with Part 3 (link).

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In April 1975, a few months after Space Mountain opened

at Walt Disney World and proved to be popular, it was decided that there

would be a Space Mountain at Disneyland. Because of space limitations

at Disneyland, an entirely new design would be required and it had to

fit in a 200-foot diameter building that would be less than half the volume

of the WDW version.

For a popular ride such as Space Mountain was certain to be, the ride

capacity needs to be 2,000 passengers per hour or more. With room for

only one track instead of the two-track system at WDW, a larger vehicle

would be required. So instead of the WDW type vehicle, which has tandem

seating, a new, larger vehicle with side-by-side seating was indicated.

With two-car trains in each case, this increased the seating from eight

to 12 passengers for each dispatch. It also allowed the use of lap bars

instead of seat belts and eliminated the need for two people to share

the same seat, a real problem when strangers are involved and resulting,

in the extreme case, in some trains being dispatched with as few as four

passengers onboard. So, with a 20-second dispatch interval, the theoretical

hourly capacity (THC) would be 2,160 as opposed to 2,400 at WDW. But the

actual ride capacity would be more nearly the same due to the improved

seating arrangement.

This engineering model of Space Mountain shows an early track configuration.

Photo courtesy of Bill Watkins.

A wealth of data was gained from the Walt Disney World experience which

was useful for the new design. As I discussed in George’s article about

WDW’s ride system (link), the goal for a

ride with a space theme is that it be smooth and flowing; thus proper

curve banking and smooth transitions from level to fully banked is essential.

We found at WDW that some of the transitions had roll rates that were

a little severe, so we set a new standard for Disneyland that was only

half that of the WDW worst case (we also went back and altered the WDW

track.)

Next, we designed and built a prototype vehicle and a test track because

the track design is dependent on vehicle performance. We decided to use

nylon wheels with ball bearings rather than the polyurethane wheels with

roller bearings that had been used on the Matterhorn and WDW Space Mountain

because they have lower and more consistent rolling resistance. Step one

was to run the vehicle and measure such factors as rolling resistance,

bearing and seal drag, wheel skidding, and aerodynamic drag so that new

data could be plugged into the track design program that we had developed

for the WDW project. Step two was to run endurance tests to detect any

structural problems with the vehicle or track.

This track model (currently on display at Disneyland’s Main Street Opera

House as part of the historic display for Disneyland’s 50th birthday)

was created to illustrate, in three dimensions, the available space for

show effects and structural supports. Photo by Mark Goldhaber.

On to track design. This isn’t rocket science; it may be more complicated

than that. Once a rocket leaves the Earth’s atmosphere, there is little

drag to contend with. Sure, there are some issues with gravity from the

various planets and moons but, hey, they don’t have to worry about getting

a Mickey Mouse hat caught in their wheels. And furthermore, they have

little vernier rockets attached that can make corrections, whereas we,

who are trying to design a pure gravity ride, can make no corrections.

It’s the difference between a guided missile and a ballistic one.

Now for a little physics (those of you who hated Physics in high school

may want to skip the next three paragraphs; if, in fact, you’ve read this

far.) Gravity rides are all about potential energy vs. kinetic energy.

As a vehicle goes downhill, it is trading its “head” (or elevation)

for speed. The speed (in feet per second) as the train leaves the lift

is proportional to the square root of the decrease in head (in feet) multiplied

by a gravitational force of 2G (about 64.4 feet per second squared), plus

a little bit more because of the speed of the lift. As the trains go uphill

they give back speed to gain head. That’s the simple part. The complicating

factor is the various drag factors. If we didn’t have drag our Space Mountain

train, which starts at a height of 68 feet, we would be going about 45

mph when it returned to the station. But we do have drag, and it

is the job of the designer to manage that drag so that the head losses

will be about equal to the height of the lift.

This view of the track model shows the second lift (blue tunnel) and signage

indicating the speed of the coaster train at that point on the track.

Photo by Mark Goldhaber.

We like to return to the station at about five feet per second, which

is the same speed as the train was moving on the lift when we started

out. So that means we have to lose the entire 68 feet. We know from past

studies that, on the average, as we travel along a length of track, we

will lose head equal to about three percent of that length due to the

several drag factors. We don’t know exactly how much until we do our calculations

because some losses are dependent on track configuration, others on speed,

yet others on weight and some on all three. But we now can estimate that

we have to squeeze about 2,267 feet of track (68/.03) plus lifts, station,

and storage into a 200-foot-diameter building.

We also know that track crossovers have to be a minimum of 9.5 feet center-to-center

so that passengers won’t bump their heads, that banked curves will not

have a G-force of more than 2.5, and that there will not be negative Gs

at crests that will raise passengers off their seats. Further we need

to have braking stations at elevated positions less than 20 seconds apart

(remember the dispatch interval?) and satisfy George by zooming past the

queue line (part of this is to let people know what they are in for so

that the “chickens” will take the next exit out). And, as an

aside, about that Mickey Mouse hat. If something slows a train down so

that it does not get out of its zone in time, brakes will close so that

the following train will not hit it.

So the fun begins, and it is fun if you like puzzles. Track routings

are laid out on paper and checked on the computer to make sure that the

speeds, the timing, and the G factors are all within limits. There is

a lot of trial and error involved and the layout drawings—with all

the erasures—are not very pretty when they’re done. It takes a few

months before the track data can be sent to the shop for fabrication and

to the structural engineers to design the supports.

Another view of the track model shows how the ride’s track wraps around

itself. Photo by Mark Goldhaber.

Next comes installation and then Test & Adjust (T&A). First, we send

empty trains. The biggest worry is that an empty train will stall at the

top of some hill and the only solution would be to make expensive track

changes or to add one of those dreaded “energy wheels” (see

the earlier story linked above), thus violating the pure gravity ride

concept. Fortunately, the train came back without incident. Then there

are a few runs with sandbags and finally with the designer on board so

that he can assess the ride quality (and get his picture in the company

newspaper).

At this point I have to confess that, at the end of the ride in the reentry

tunnel, there are a series of devices that could be called “energy

wheels” although we call them “retarders.” I submit that

this does not violate the pure gravity ride principle because we are now

down (nearly) at station level and it’s important to fine-tune the vehicle

speed before it enters the station. The heavily loaded vehicles will approach

faster than the light ones. After a break-in period it became clear that

the loaded vehicles were approaching the retarders at about twice the

desired speed and the retarders were overloaded. Understand here that

doubling the speed from five to ten feet per second represents just a

few inches of head loss, a small percentage of the 68-foot drop. So, what

to do about it? We ran a series of tests with cast members on board, and

replaced some of the nylon wheels with more and more of the softer polyurethane

wheels until we got the reentry speed down to a level that the retarders

could handle.

This view of the track model gives a view of how the track circles the

“geodesic satellite.” Photo by Mark Goldhaber.

With all these cast members exposed to these tests, the rumors were flying.

One day on the way to Disneyland, I stopped at the Red Cross in Los Angeles

to donate blood. One of the nurses asked me what I did at Disney and I

told her. “Well”, she said, “Why are you slowing down the

ride?” The rumor seemed to be that the ride was too wild and that

we had to tame it down. The fact is—and you can see it if you study

the formula above for speed as a function of head—that although we

cut the reentry speed in half, the speed in the fastest parts of the ride

would drop by less than three percent, which is not noticeable.

Disneyland’s Space Mountain opened on May 28, 1977 and was reproduced

at Tokyo and, recently, Hong Kong. During those same years and later (1969

to 1986), we also designed the Big Thunder Railway (working title) rides

at Walt Disney World, Disneyland, Tokyo Disneyland, and Euro Disneyland

using the same principles and techniques. The Disneyland Space Mountain

was recently reopened with a new, but identical, track. 171 million people

had ridden on the old track, a total of more than 8 million miles.