Overview - Safety First!

While the goal of the competition is to land the rocket in "Goddard’s circle" 30 meters down range, we seek to impress upon participants the motto “design with safety in mind”. The competition will be held at a large field at WPI, and the competition rules and safety requirements are intended to limit the kind of water rocketry practiced in the competition in such a way as to make the safety considerations comparable to those in the game of baseball.

The foremost concern of competition staff is to ensure that the competition be as safe as possible for participants and spectators, while remaining exciting and fun. Launch inspectors will verify compliance with the safety rules by inspecting the rockets and launch pads, checking launch pressures, and observing launch procedures. Inspectors may require a team to make procedural or equipment adjustments, and will disqualify a team that fails to comply completely with all of the safety requirements.


Launch And Landing Areas

Teams will setup their launch pads in designated adjoining areas in the baseball infield and launch their rockets toward “Goddard’s Circle” located in the outfield. Team members participating in launch will find themselves in close proximity to their neighbor’s launch areas, and should be cognizant of their own safety as well as that of their neighbor’s. Each participant, while standing in the launch area must, at all times during periods of active pressurization and launching, wear safety goggles as a minimum. A full-face shield is recommended. Spectators must maintain a minimum distance of approximately 30 feet from the launch and landing areas, and will be restricted to the bleachers behind the backstop, and to the area behind the fence which lines the baseball field to the south (the north end of the football field and track). At no time will spectators be allowed to enter the launch and landing areas.

Launch Coordination

Launches will be coordinated by a Launch Director. To begin, a team will raise a “pressurization in progress” flag and will fuel and pressurize their rocket, allowing a Launch Inspector to verify launch pressure if requested. When a team is ready to launch, they will raise a “ready to launch” flag and, if required, a team member will notify the Launch Director in person. When the director gives permission to launch, the team will raise a “launch” flag, announce the launch to all present (spectators, participants, and staff), either by sounding a horn or calling out a launch sequence, e.g., “Launching in T minus 5, 4, 3, …”, and proceed to launch. Launch announcements must be loud enough to be heard by the Field Judges, who will be located in the outfield in the vicinity of Goddard’s Circle.

Launch Pad

The Launch pad must be of sufficiently sturdy construction to ensure a repeatable, predictable launch direction. The pad may optionally include a blast shield that disperses the rocket exhaust, a high velocity column of water, into a harmless spray, to protect participants and spectators and to prevent mud splatter from the dirt surface of the infield. Use of a launch guide pole is required to help launch the rocket in the intended direction. The launch pad may NOT be secured to the ground with spikes driven into the ground. This restriction is made to protect the baseball field’s underground sprinkler irrigation system. However, small diameter rods (wooden dowels or metal rods) which serve as guide poles may be pressed into the ground by hand, up to several inches deep.

Launch Method

A long string or other mechanism must be used that allows launch personnel to stand at least 10 feet away from the launch pad during launch. The rocket must be launched at an elevation angle of no less than 30 degrees, to avoid a low “line-drive” trajectory, and to limit water “slosh” inside the fuel tank during launch. Slosh can cause wobble and consequent unpredictability in launch direction.

General Design Criteria

Participants may design their own water rockets and launch pads, or purchase commercial water rocket kits and launch pads, and adapt these for use in the competition. The water rocket and launch pad should be designed with safety in mind. The following rules address many well-known safety issues of water rockets, but are not expected to cover all design possibilities. The designers should give thought to their designs and use common sense, and be aware that competition staff will inspect and assess rockets for compliance with the safety requirements on the day of the competition. Designers are strongly encouraged to consult one or more of the many resources available on the web that discuss rocket design.

Rocket Materials, Mass And Density

The mass of the empty rocket (withfuel tank empty) must not exceed 0.5 kilograms (1.1 pounds weight). The rocket shall be made of low-density materials such as paper, plastic, duct tape, and glue. Metal, ceramics, and other high-density materials may not be used. No exceptions will be made. The rocket should not be too compact, that is, the overall density of the rocket (ratio of total mass to total volume) should be low in order that the rocket should “float down” slightly on descent. While designing a rocket to achieve accuracy in landing, designers should strive for safety by building the rocket “larger and lighter” rather than “smaller and heavier”.


A rocket must be designed for stable flight, that is, it must have stabilizing fins in the rear of sufficient size to place the Center of Drag (COD) behind the Center of Mass (COM), also called the Center of Gravity (COG). One way to test stability is to swing the empty rocket (with fuel tank empty) around in a circle using a string tied to the rocket’s COM. If the rocket is aerodynamically stable, it will automatically orient itself nose-first in its motion. The stabilizing fins must be firmly attached to the rocket and must not have sharp edges and tips.

Rocket Nose Shape

While a sharper nose improves aerodynamics and accuracy, for safety the nose must be somewhat rounded and made of a soft, flexible material. The nose must definitely not form a sharp, hard point. It should not break a windshield or injure a judge!

Fuel Tank

The water-fuel tank must be a plastic soda-bottle, not a water bottle, with a maximum size of 2 liters. A soda bottle makes an ideal fuel tank for a water rocket; the bottle is strong, light-weight, and designed to be pressurized (a water bottle is not designed to be pressurized). The soda-bottle must be in pristine condition, with no cracks, dents, crinkles, scratches, in short, must have no defects that could compromise the bottle’s strength and lead to bottle burst during pressurization and launch. Although not absolutely required, participants should consider wrapping the bottle in duct tape or similar, or encasing the bottle, for example, in a cardboard tube, to inhibit fragmentation and limit scatter in the event of burst.


The rocket fuel must be water, driven by pressurized air to produce thrust. Water and air are non-toxic and non-combustible, and readily available. Air pressure must not exceed 60 psi, roughly 1/2 of the burst pressure of soda-bottles. Some soda-bottles are tougher than others, being made of heavier gauge plastic. Participants should choose a soda-bottle for its apparent toughness, and prior to the event, test the bottle at pressures, not to exceed to 60 psi, as required to achieve a 30 meter range of flight.

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