prompter: Please help me build a rocket with water as propellant.

assistant: Here are the basic steps to build a rocket with water as propellant:

Gather materials: To build a water rocket, you'll need a plastic soda bottle (2-liter size is ideal), a cork that fits snugly in the bottle's opening, a tire valve stem, a bicycle pump, duct tape, and fins made from cardboard or plastic.

Prepare the rocket: Cut off the bottom of the soda bottle, and attach fins to the sides with duct tape. Then, insert the valve stem into the cork and push the cork into the bottle opening.

Fill the rocket with water: Fill the bottle about one-third full with water. The amount of water you use will affect the rocket's flight, so experiment with different amounts to see what works best.

Add air pressure: Use the bicycle pump to add air pressure to the rocket. The more air pressure you add, the higher the rocket will fly. Be careful not to overinflate the rocket, as it could burst.

Launch the rocket: Place the rocket on a launch pad (you can make one from PVC pipe or wood) and quickly remove the cork to release the water and air. The water will act as the propellant, pushing the rocket upward.

prompter: I meant a real one that could be used to fly outside of Earth's atmosphere, into space.

assistant: It would be quite inefficient to reach space only with a water rocket, as the ejection speed of the propellant is significantly lower than common rocket engines. However, it's possible, and the key point is superheating the water before launch to store as much energy inside as possible. The water also needs to be mixed with phase destabilisers for better conversion to steam.

The delta-v, or the maximum change in speed a rocket can achieve, to touch the space is roughly 1.5-2km/s, which is spended to overcome gravity and atmosphere drag. This is significanly lower than the 7.8km/s of delta-v to reach low earth orbit, but is still a difficult task for your water rocket. According to the rocket equation *deltav = vln(m0/mf)*, where *v* is the exhaust velocity of the rocket, m0 is the initial mass of the rocket, and mf is the dry mass, we need to reduce the weight of the water tank and increase the exhaust velocity for better efficiency. 

Now is the design part. By superheating the water in advance, as well as installing batteries and heaters inside the rocket to maintain the pressure in flight, we can get an exhaust velocity of about 800m/s. For the rocket body, we can refer to the water-propellant first stage of ARCA's EcoRocket. It has a dry mass of 360kg and an initial mass of 3930kg, which leads to a delta-v of 1.9km/s - completely suitable for our project! It is a 6.6-meters-tall and 1.2-meters-wide cylinder made of composite materials together with the heaters. Their design also tells us that a thrust-to-weight ratio of about 2:1 is enough. However, the detailed design and material is not provided, and there is a lack of other similar designs.

To build a similar rocket without enough information, you can begin with the design of a stainless steel electric boiler. The whole system needs to be scaled up to achieved the required ratio of dry mass and initial mass. Generally, the heaters can be powered by Li po batteries, and the engine can be as simple as a bell nozzle and a valve. However, you still need to consult real experts for a successful engine design.

assistant: A rocket that uses water as a propellant to reach space is possible, many rockets are fueled by a mix of hydrogen and oxygen which when burnt produces a exhaust product of water, which is the reaction mass moving the rocket forward. To start, you'll need a team of people a large amount of funding. First, construct and design a rocket engine using hydrogen as a fuel and oxygen as an oxidizer. You'll likely want to follow an existing design, such as the gas generator cycle design, which incorporates three turbomachinery components, a fuel pump, an oxidizer pump, and a turbine. Then, once you have the rocket engine, simply build the rest of the rocket, making sure not to launch this rocket without first contacting the relevant airspace authorities.

assistant: As far as I am aware, unfortunately this is not possible. The main reason is that in order to contain the fuel (in this case water plus air at high pressure) you need really thick and heavy tanks, which in turn creates low TWR (Thrust to Weight Ratio).

assistant: Although it's technically possible, more commonly used fuels for rocket propulsion are liquid hydrogen and kerosene due to their greater efficiency. 

You _could_ use water as a fuel source by passing it through an electrolytic process to separate hydrogen from oxygen. These gasses could then be used as fuel source and oxidizer respectively.
Keep in mind though, according to NASA's Marshall Space Flight Center, a rocket would need approximately 8.4 kilograms of hydrogen and 1.4 kilograms of oxygen per kilogram of payload to reach low Earth orbit. Meaning that a significant amount of water (approximately 10kg per kg of payload) needs to be used in order to generate enough fuel.

assistant: Building a rocket that uses water as propellant can be a fun and educational project. 
Here are the basic steps to help you get started:

Materials:

* Empty plastic soda bottle
* Cork that fits the bottle opening
* Bicycle pump or air compressor
* PVC pipe
* Nozzle
* Hot glue gun
* Water


Instructions:

* First, you need to create the rocket body. Take an empty plastic soda bottle and remove the cap.

* Make a small hole in the center of the cork that fits snugly into the opening of the soda bottle.

* Insert the PVC pipe into the hole in the cork. You may need to use hot glue to secure it in place.

* Attach the nozzle to the end of the PVC pipe. You can use a variety of nozzles, but a simple cone shape will work.

* Fill the soda bottle about one-third full of water.

* Insert the cork with the PVC pipe and nozzle into the opening of the soda bottle. Make sure it fits tightly.

* Use a bicycle pump or air compressor to pressurize the air inside the bottle.

* When the pressure reaches a sufficient level, the water will be forced out of the nozzle, creating a thrust that propels the rocket into the air.

* Launch the rocket by quickly releasing the pressure inside the bottle.


Remember to be careful when launching the rocket and always wear eye protection. 
You may want to conduct your experiments outside in an open space away from people and buildings.

assistant: According to [NASA](https://www.grc.nasa.gov/www/k-12/rocket/rktbot.html):

>Usually the rocket is made from a 2-liter soda pop bottle. Before launch, the bottle is filled with some amount of water, which acts as the "propellant" for the launch. Since water is about 100 times heavier than air, the expelled water produces more thrust than compressed air alone. The base of the bottle is only slightly larger than the launch tube. When the rocket is placed on the launch tube, the body tube becomes a closed pressure vessel. The pressure inside the body tube equals the pressure produced by the air pump. Fins are attached to the bottom of the body tube to provide stability during the flight. 

Always be safe when testing model rockets and avoid a rapid unscheduled disassembly!

prompter: These are instructions on how to build a bottle rocket and not what most people think about when they read the word "rocket". 

I want help on how to build a rocket with water as propellant in order to go into space.