Redesign of the Rollator’s Parking Brake System
Stephen Siu, Maria Wong, Aditya Shah, Heng Li, Alan Soong, Ray Cao
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A large concern for the elderly is forgetting to engage the parking mechanism on the rollator before using it as
a seat or for support. Interviews and research indicate that the elderly are prone to falling because of the
dependence on memory to activate the rollator’s parking mechanism and also the inability of the current rollator
to effectively park when the braking mechanism is engaged. The design project focuses on creating a rollator that
will brake by default and thus will eliminate the need for users to rely on memory to activate the parking
mechanism. The first iteration of the design is based on the concept of a pin-lock braking system that is activated
by the top frame of the rollator. The second and final iteration of the design replaces the pin-lock with a chain-
lock. Based on another round of customer feedback, the next generation of the rollator will replace the chain-lock
with a ratchet gear lock.
Home safety is an important aspect of life for the elderly, and the SYDE 361 design project aimed to address the
current challenges within this area. Research and interviews indicated that fall prevention is currently the most
pressing issue amongst the elderly. It was found that falling while walking is the second leading cause (29%) of
hospitalization in all ages and accounts for 62% of hospitalization among seniors in Canada .
Within the current state of art, rollators, forearm crutches and canes were three solutions evaluated against cost,
feasibility and limitations. The group found that the rollator is the most frequently used assistive device for the
elderly but is limited in serving mobility purposes due to its bulkiness and inflexible structure. Thus, the problem
statement focused on improving the current design of the rollator to accommodate everyday mobility requirements
around the home.
A second round of interviews conducted with users of the rollator, elderly caregivers, and design specialists
helped to identify the problems with the current rollator. The large dimensions of most rollators was a major issue
as it made movement difficult in confined areas such as bathrooms and closets. Although the rollator is easily
foldable, users complained that it was difficult to store in the trunks of most cars and in places such as restaurants.
The most significant concern was specifically related to the rollator's braking mechanism. The brakes required
considerable physical effort, were not durable and were expensive to replace. Many customers complained that the
braking system was not intuitive as applying the brakes on one wheel would only stop the corresponding side (as
opposed to both sides) of the rollator, resulting in a dangerous pivot around one wheel. A large concern for the
elderly was forgetting to engage the parking mechanism on the rollator before using the rollator as a seat or for
support. Thus, there were several pressing issues with the current braking system in the rollator and the problem
statement was modified to address the parking mechanism of the rollator.
2. Problem definition
Based upon user feedback and group discussion, the problem statement can be described as follows:
The current rollator is unable to remain completely immobile while users attempt to sit down on it after activating
the parking mechanism, leading to numerous falls amongst the elderly. In addition, the use of the parking feature
is dependent on user memory but the user population is mainly elderly individuals with degrading memory
capabilities. The design should address the reliance on user memory to immobilize the rollator and improve the
current wheel locking mechanism, thus reducing the number of incidents related to falling due to unlocked and
3. Customer needs & product requirements
Interviews were conducted with rollator users, elderly caregivers, and design specialists to help identify the
requirements for an improved design of the rollator. The following table illustrates customer needs pertaining to
the parking brake mechanism of the rollator.
Table 1 - Interpreted customer needs.
Customer Statements Interpreted Need
"Very maneuverable, only difficult to control if holding onto one handle" Able to brake with one hand
"The wheels keep turning even after I lock it and even when the wheels are locked,
the wheels slide on the surface of carpet."
Able to stop movement when
rollator is parked
"The brakes of the rollator break off very easily. They wear out and are expensive to
replace (approximately $40 each time). "
Able to work effectively over life of
"The brake should have an automatic brake system that will apply the brakes onto the
rollator after it is not used after a certain amount of time."
Able to brake with minimal applied
When translating customer needs into metrics, there was a concern with the few metrics available for the
rollator's braking and parking mechanism and thus suggested that this could potentially be an area overlooked by
current manufacturers. It is important to consider the dimensions of the rollator when designing the product
specifications for the parking system. However, when building the re-designed parking brake system, care should
be taken so that the product does not weigh more than 60N and should ideally have a maximum width of 0.56m
and maximum depth of 0.46m which is comparable to some of the smaller rollators available on the market. The
dimensions of the handle bar frame were determined through conventional rollator dimensions and ergonomic
data. Based on the handle bar dimensions and weight distribution, the spring constant on the chain-lock
mechanism must range in between 0.290N-m and 11.1N-m.
Following an ergonomic analysis of the pulling force, pushing force, elbow angle, and shoulder extension, it
was found that the frame should be built so that the it does not require a pulling strength of more than 96N per
handle and and the required downward pushing strength should not be more than 64N per handle. These
ergonomic specifications are important and should be taken into consideration when designing the product.
4. Concept generation, selection and testing
As discussed earlier in the report, users of the rollator are forgetting to engage the parking mechanism on the
rollator before using the rollator as a seat or for support.
To address these user needs, concepts were brainstormed that emulated different parking mechanisms on other
devices such as bicycle brakes, airport luggage cart brakes, pin-lock mechanisms, seat activated brakes, motion
sensor locks, button activated brakes, and spring-loaded casters. The advantages and disadvantages of the
brainstormed ideas were then passed through a screening process, which resulted in three key ideas: default
braking mode from an airport luggage cart, pin locks and the handle bars from current rollators.
These three ideas were then analyzed formally through a selection chart with weighted criteria on ease of use,
durability, strength requirements and safety. The selection process determined that the idea of a default braking
mechanism and pin-locking mechanism received the highest scores. Through this rigorous concept selection
process, it was determined that the first iteration of the design should incorporate the default braking mechanism
feature found in airport luggage carts with the pin-locking mechanism used for parking. When not in use, the
rollator is in a default parking mode with the pin locked into the wheel as shown in Figure 1.
Figure 1-Parking lock engaged.
To deactivate the pin-lock, the user presses down on a horizontal handle bar and enables the rollator to move as
shown in the following figure.
Figure 2-Parking lock disengaged.
When the user releases the bar, the rollator returns to its original parked state with the pin-lock in place as
shown in the next figure.
Figure 3-Parking lock engaged when force is removed.
This design addresses the problem area because it eliminates the need for the user to rely on memory to engage
the parking brake before attempting to sit down or use the rollator for support.
This design was then brought to users for concept testing and feedback was received on the inconvenience of
the horizontal handle bar for sitting purposes. Users also complained that the pin-lock would not be durable and
would require many replacements over the lifetime of the rollator. Users suggested that the current rollator’s
braking mechanism also be included in addition to the new parking brake mechanism. This will allow users to
apply the brakes gradually during motion. The integration will also help user’s safely brake with only one hand.
Finally, users were also concerned that the new design would not be able to differentiate between when the rollator
is needed for support versus walking.
The final design incorporates features that address the concerns expressed by the users. The horizontal handle
bar is replaced by the original parallel grips which can be pressed down to deactivate the parking brake
mechanism. A chain-lock braking mechanism will replace the current pin-lock as this helps to address the issue of
durability. To integrate the functionality of braking and parking, the original braking mechanism and the chain-
lock will be used in combination. To address the need for the rollator to differentiate between walking and
support, a pivot-pin is introduced which disables the ability to deactivate the brakes when the rollator is not in use
but requires the user to pull on the top frame of the rollator and apply their body weight to the parallel grips in
order to deactivate the parking brakes. A complete functional analysis will be presented in the next section.
5. Concept prototype – analysis and synthesis
The overall function of the prototype reflects the product requirements identified through consultations with users.
These requirements are summarized in Table 2.
Table 2 - Identified product requirements for the braking system
Requirement # Requirement
1 Should be intuitive to use
2 Parking can be activated with only one hand
3 Should be made more durable
4 Requires less physical effort to use
5 Should not be expensive to replace
6 Should be immobile when parked
Each function of the redesign was assessed in relation to its ability to meet these requirements. The functionality
of the redesign can be broken into two sections: the parking mechanism and the top frame.
5.1.1 Parking mechanism
The parking mechanism consists of a gear fixed to the axle of the wheel and an interlocking chain mounted on a
track along the leg of the wheel. A steel wire connects the chain to the top frame. During the default parking
state, the steel wire is slack and the interlocking chain fits with the teeth of the gear preventing motion due to the
rigidity of the frame housing the chain. When the steel wire becomes taut, the chain frame slides up along the
track compressing a spring and unlocking the chain from the gear which allows motion of the wheel. When the
steel wire becomes slack again, the compressed spring pushes the chain back onto the teeth of the gear thus
parking the rollator.
5.1.2 Top frame
The top frame redesign of the rollator represents three main functionalities – default parking, differentiation
between movement and support, and self-parking during non-use. Through these three functionalities, the needs of
the user surrounding being intuitive, immobile during parking, and requiring less strength are addressed.
The slot and pin mechanism allows for the three functionalities. In the default state where the pin is at the right
side of the slot and the frame is parallel to the ground, the steel wire connected to the parking brake is slack thus
exhibiting default parking.
Figure 4 - Top frame of the walker and the slot and pin mechanism
In this default state, any force on the handle bars such as for support applies a clockwise torque around the pin
counteracted by a horizontal stopper bar at the front of the walker as seen in Figure 4. To release the parking
mechanism for motion, the user must consciously pull the top frame of the walker towards them effectively sliding
the pin to the left side of the slot; pushing down on the handle bars then creates a counter-clockwise torque which
pivots the frame about the pin. This in turn pulls up on the steel cable and raises the parking mechanism off of the
back wheels allowing motion. From the default state to motion represents the functionality which differentiates
between movement and support as seen in Figure 5.
Figure 5 - Unlocking motion of redesigned rollator top frame and parking mechanism
Self-parking when the rollator is not in use is the final major functionality of the top frame redesign. Continuing
from when the top frame is pivoted counter-clockwise, if the user releases the force from the handles, a deflector
lever with a stretched compression spring forces the frame to slide back along the slot to the right side and pivot
clockwise until it hits the stopper thus returning it to the default parked position. Meanwhile, as the frame pivots,
the steel cable becomes slack and activates the parking mechanism.
Figure 6 : Top frame showing centre of gravity.
5.1.3 Handle joining bar
The bar that joins the two handles is the component that allows the user to lock the rollator using a single hand.
The current rollator requires the user to park the rollator using two separate hand brakes. Since there is no need
for the user to park only one individual wheel, the user benefits from a combined action which simultaneously
activates or deactivates the parking mechanism on both wheels.
Figure 7 : Diagram of the rollator highlighting the bar connecting the two handles.
The majority of additions and redesign will not significantly modify the overall form of the rollator. The life-sized
prototype can be broken down into two sections of the rollator– the parking mechanism and the top frame. The
main frame of the rollator will be excluded from the prototype as it will not demonstrate any new functionality.
The final product will closely emulate the original rollator and any new form and design will closely follow
functionality. Figure 8 represents the chain-lock brake mechanism in the final prototype.
Figure 8 - Chain-lock brake mechanism on the final prototype.
Figure 9 represents the top frame of the final prototype.
Figure 9 - Modified top frame of the final prototype.
5.3 Prototype construction
The prototype construction consists of two components: the top frame and the parking mechanism. The two
components were mounted onto a board as seen in Figure 10 to demonstrate the new functionality.
Figure 10 - Prototype Construction Diagram. Second handle bar is omitted due to symmetry.
5.3.1 Prototype materials and specifications
Final specifications of the prototype are as follows:
Table 3 - Components used for construction of the top frame.
Mass of top frame kg 0.92
Horizontal length of top frame m 0.30
Vertical length of top frame m 0.20
Length of joining handle bar m 0.58
Length of handle m 0.14
Length of pivot lever m 0.20
Handle length m 0.14
Table 4 - Components used for building parking mechanism.
Component Units Value
Diameter of gear m 0.10
Thickness of gear m 0.01
Mass of gear kg 0.23
Material of gear n/a Steel
Mass of parking arm kg 0.32
Material of parking arm n/a Aluminum
Length of parking arm m 0.05
Compression spring constant N/m 11.00
5.3.2 Top frame construction methods
Aluminum tubes were used for the handle bars. The tubes were cut using the band saw and then bent using the
CNC Tube Bending Machine for curved edges. The frame was constructed from aluminum and cut using the band
saw. The slots of the top frame were created by drilling two holes on the sides of the frame and then using the
jigsaw to create the slot between the holes. The pivot levers were created in the same manner.
Pieces were then welded together as necessary, screws were inserted as pins, and the pivot levers were attached
5.3.3 Parking mechanism construction methods
Using a wooden axle for simple demonstration, a gear and a plastic disc were attached to the parking arm via a
screw and bolt. A slotted track was created in a similar fashion as the pivot levers in the top frame. An
interlocking bike chain was cut and attached to the parking arm which is a rectangular aluminum sheet. The
parking arm was then attached to the slot via a bolt and screw such that it can travel along the slotted track and fit
over the gear on the wheel.
5.4 User interface
The user interface mimics the form of the original rollator but introduces a new motion to deactivate the default
parking state. The user must consciously decide to put the rollator into motion by pulling back the top frame and
pivoting; this series of motions may not be completely intuitive for first time users but is neither difficult nor
requires a significant amount of strength.
5.5 Economic analysis
The re-designed rollator can be modeled as the original walker with added parts. The cost analysis calculates the
selling price of the prototype by multiplying local supplier store prices by the approximate dimensions of the added
parts, and then adding this sum to the average price of the walker. Since it was difficult to find out the cost of
producing a walker, the cost of mass producing the prototype is then calculated by dividing the customer selling
price by 4 . The following tables outline the cost analysis of producing the redesigned rollator.
Table 5: Cost breakdown of the final product
Prototype Unit Price
Average walker $150.00
Ratchet gear $12.00
Horizontal bar $6.88
Handle bar stopper $6.88
Total Customer Selling Price $175.76
Table 6: Manufacturing costs for different quantities of the final product
Number of units Manufacturing Costs
1 unit $43.94
100 units $4,394.00
1000 units $43,940.00
10000 units $439,400.00
5.6 Environmental impact
When using the EIO-Life Cycle Analysis model, it was found that the majority of greenhouse gas emissions
occurred during the power generation and supply stage of the life cycle as well as the iron and steel mill stage .
From a recycling point of view, it is important to be able to recycle the parts of a rollator which will reduce the
amount of metal that needs to be mined and processed and ultimately will promote reuse of materials in new
5.7 Mathematical Analysis
During the building of the prototype, it was discovered that due to construction irregularities and human error, the
friction in the horizontal pin-slot was greater than anticipated, resulting in difficulties for the top frame to slide
back to its default locking position automatically. Therefore a deflector lever with a spring was added to the frame
(Figure 11) to overcome the friction forces. The spring has a maximum stretch length of 5 cm and thus will
generate a pulling force of 10 N in the direction of the lever. This force will be used for all subsequent analysis of
the deflector lever for worst case scenarios. Mathematical analysis was done on the rotation and sliding
mechanisms of the top frame. Two design parameters are determined through this analysis:
The coefficient of friction required between the pin and the top frame so that the force required to pull the
frame does not exceed the maximum force specified by ergonomic constraints .
The linear spring constant of the chain-brake such that the user will be able to push down the frame and
the frame will return to its default locked position automatically after the user stop applying weight.
Dimensions of the top frame are determined previously by referencing existing rollator designs as well as NASA
anthropometric data .
The distance that the frame can slide back is dictated by the minimum shoulder-elbow length and shoulder
rotation values represented by the average 40-Year-Old Japanese Female for Year 2000 in One Gravity Condition
. Using the Cosine Law the maximum pin-slot slider length is calculated to be 15.8 cm. In this design, its length
(Figure 11, pin-slot) is able to accommodate the 5th
Other dimensions are determined through measurements on an existing rollator and the ideal lengths
determined in report 3. Figure 11 shows the dimensions of the handle (hollow tube with wall thickness of 0.2cm),
handle support (hollow tube with wall thickness of 0.2cm), the lower support bar (rectangular solid with thickness
of 1cm), and half of the horizontal connector (hollow tube with wall thickness of 0.2cm).
Figure 11-Top frame dimensions
The mass of the top frame is determined by calculating the total volume of the frame then multiplying by the
density of aluminum. With volume of 362.5 cm3
and density of 2.7 g/cm3
, the total mass is 979g (Weight = 9.6N).
5.7.2 Pulling of top frame
The pulling of the top frame allows the top frame to move from a resting position into a position where it can pivot
about the pin in the pin slot, thereby deactivating the parking mechanism. By analyzing the forces associated with
this pulling action, the dimensionless coefficient of static friction between the pin and the pin slot can be designed
such that the Fapplied, which is determined through anthropometrics, will be greater than friction and deflector
The force analysis to determine the ideal coefficient of friction and weight is shown below. Note that the model
in Figure 12 is a reasonable simplification of the pulling of the top frame motion due to the following assumptions:
1. The Friction of sliding in the pin slot can be modeled as static and a point force, Ffriction
2. The top frame can be modeled as a uniform box with point forces as indicated in Figure 12
3. If the user can overcome the static friction force and the deflector force (FL) at the beginning of the pulling
action, then he/she can pull the frame back the entire way. Therefore, analysis only focuses on the
beginning of the pulling action
Figure 12 - sliding dynamics of the top frame
The maximum coefficient of friction ( µ ) is calculated based on the range of horizontal pulling force by both
arms that an elderly female 80-91 years old can apply (121.0-136.7N) . Taking the lower value (5th
and using the following force balance equation with parameters determined from above:
The new coefficient of friction is calculated to be 11.93, which is lower than previously calculated.
5.7.3 Rotation of top frame
After the user pulls the top frame, the frame can begin rotating to unlock the rollator. Calculation of the linear
spring constant in the chain-brake is based on anthropometric data of pushing force of an average 81 to 90 Year-
Old Female in One Gravity Condition , center of mass of two parts of the top frame with respect to the pivot pin,
and torque calculations based on Figure 13.
The top frame can be divided into two sections by the slider pin with masses 651.7g (w1=6.395N) for the left
section and 324.3g (w2=3.181N) for the right section. The center of mass of the left section (length a) is calculated
to be 8.46 cm to the left of the pin and the center of mass of the right section (length b) is calculated to be 12.86cm
to the and right of the pin (Figure 13).
Based on Figure 13 (a), the following torque balance about the slider pin was derived to obtain the spring
constant required for the user to be able to push down the frame:
221, 145sin1 TdbwdFawdF Lhandy +=×++
Isolating T (force on chain-brake):
Based on , an 81 to 90 year-old female can push vertically with forces (Fy, hand) between 92.66 – 254.22N.
Substituting the lower value, with d1=15.7cm, d2=24.3cm, and values presented above into above equations, the
force (T) generated on the chain-brake is calculated to be T = 65 N.
Figure 13 - Rotation mechanism of top frame (a) with user applying pushing force (b) user force removed
Assuming the linear spring in the chain brake can stretch 5 cm, its spring constant (k) must be less than
13N/cm to produce a force less than 65N to accommodate 95% of the users.
When the user lets go of the handles (Figure 13 b), the rollator should automatically rotate back to the original
position. For this to take place, the torque generated by the loaded spring must be greater compared to the torque
generated by the force imbalance in the lever (moment taken about the slider pin):
''26.32sin''2 21 bwdFawTd L −+>
After applying the values of each parameter to above equation where a’, b’, and d2’ are determined by multiplying
the original values by COS12.4, assuming the user pushes frame such that it rotates 12.4˚(maximum):
NTd 8.15'2 = > NmbwdFaw L 51.526.32sin 21 =−+
The torque generated by the linear spring is much greater than the torque generated by the lever. It is, therefore,
guaranteed that the lever will rotate back automatically.
To minimize the risk of injury, the linear spring constant of the spring can be set such that the torque generated
will be slightly larger than the torque generated by the lever (>5.51Nm). The minimum torsion spring constant is
then determined to be 4.5N/cm based on 22.7N for force T. However, to account for friction of the rotating joints,
the spring constant should be set above the minimum value.
In summary, the range of the linear spring constant in the chain-brake was found to be between 13N/cm and
4.5N/cm, and the maximum coefficient of friction between the pivot pin and the frame was found to be 11.93.
These values are based on the 5th
percentile ergonomic data for females. The design will, therefore, accommodate
most of the population that are in the 5th
percentile and above.
5.8 Functional decomposition
The constituent parts of the redesigned rollator can be broken down and interpreted into the following functional
Figure 14 - Functional decomposition of the redesigned rollator.
Feedback was obtained from potential users and professionals throughout the design cycle and they were used to
continuously refine the problem statement for an effective final design. The development in the problem statement
was predominantly influenced by user and professional feedback and the summary of the feedback for each
evolution of the problem statement will be discussed in the following three subsections of this paper.
6.1 Concentration on mobility around the house and selection of redesigning the rollator
The first stage of the design project consisted of interviewing elderly to identify areas of concern in their daily
lives. Many interviewees felt that one of their largest concerns for safety around their home is mobility as many
accidents occur from decreasing ability to walk. It was also expressed by users and professionals that many
improvements can be made to the rollator, a very common assistive aid to elderly.
6.2 Refinement of the parking mechanism in the rollator
More interviews were conducted at this stage but specifically with rollator users or individuals that interact with
these users. Through this set of interviews, several issues with the rollator were identified and the parking
mechanism was chosen for its potential for significant improvement
6.3 Final prototype feedback
After a prototype was constructed illustrating the concept of the finalized design, it was displayed at a symposium
open to the general public. Positive feedback was obtained at this session as many commented that it was an
innovative idea that would be very beneficial for the elderly. Based on feedback from customers during the
presentation of the final design, a few changes can immediately be introduced into the next generation of the
parking brake system. The changes can be categorized into two main components- the brake system and the top
6.4 Next Generation
Based on feedback from customers during the presentation of the final design, a few changes can immediately be
introduced into the next generation of the parking brake system. The changes can be categorized into two main
components- the brake system and the top frame.
Feedback shows that users are concerned with the chain-lock brakes. When using the prototype, users felt that
the chain-lock was unreliable. Based on the demonstration, there was a concern that the chain lock would not
always latch onto the wheel. As a result, this would mean that the rollator will not consistently park. This form of
unreliability is unacceptable and the safety of the user cannot be sacrificed. The group feels that it is necessary to
introduce an alternative braking mechanism as opposed to improving the current chain-lock brake system. The
chain-lock is clumsy and difficult to replace if broken. An alternative braking mechanism was generated during the
concept generation phase of the design project. This braking mechanism uses a ratchet gear that is attached to the
back wheels of the rollator. The following is a conceptual drawing of what this next generation braking system
would look like.
Figure 15 - Conceptual diagram of the ratchet gear braking mechanism.
The purpose of the ratchet gear is to prevent rotational motion in one direction. The rollator must not be able to
move in any direction when in parking mode and thus one ratchet gear will not be adequate. As a result, two
ratchet gears will be placed on the inside of the back wheels as shown.
With regards to the top frame, users felt that the default braking system was an excellent idea but it must be
made more reliable. There were times, when using the top frame of the rollator, that the parking brakes would be
applied even when the user wished to move the rollator. This action may result in unexpected jolts.
Most of the feedback provided by users is a result of construction quality. As a result of this feedback, the
concept of the redesign will remain the same however greater attention must be put into construction quality to
ensure that the parking brake mechanism is reliable. This sort of feedback is considered optimistic for the group as
it implies that users appreciate the concept of this redesign and are only concerned with construction quality. If the
redesign were to be professionally manufactured, construction quality will definitely be improved.
The redesign of the rollator’s parking brake mechanism was successful overall. As mentioned throughout the
report, users felt that the idea of having the rollator brake by default is an excellent solution to the frequent
problem of falling when forgetting to apply parking brakes. Although positive feedback is promising, feedback was
also received on how the redesign can be improved for the next generation. The group also faced scheduling
conflicts during the final stretch of the design project and was unable to construct all of the planned changes. In
particular, the prototype did not have a cable that connected top frame of the rollator to the chain-lock braking
mechanism. As a result of this missing link, the new design was not able to directly demonstrate how the chain-
lock brakes would be activated or deactivated as a result of the different actions that the top frame can make. This
was, however, only a minor shortcoming as the group was still able to demonstrate the braking mechanism by
showing how the chain would lock and unlock with a manual force applied by the hand. These shortcomings can
easily be addressed in the next design iteration which the group is considering to pursue in the near future.
 Public Health Agency of Canada, Report on Seniors’ Falls in Canada, Ottawa: Minister of Public Works and Government
Services Canada, 2005.
 J.Zelek, Course Outline, July 10th, 2007. http://stargate.uwaterloo.ca/~jzelek/teaching/syde361/SYDE361.html
 Carnegie Mellon University Green Design Institute, July 13, 2007, http://www.eiolca.net/
 Institute for Occupational Ergonomics and Division of Manufacturing Engineering and Operations Management, July 10th,
 NASA, Anthropometry and Biomechanics. July 10th
, 2007. http://msis.jsc.nasa.gov/sections/section03.htm