A rocket (from Italian ‘rocket’ bobbin) is a missile, spacecraft, aircraft or other vehicle that gains propulsion from the rocket engine. The exhaust gas of the rocket engine is formed completely by the propellant contained in the rocket before use. The rocket engine works by action and reaction, and the rocket can only be advanced by expelling the exhaust at high speed in the opposite direction, so it can work in vacuum in space. In fact, rockets are more effective in the universe than in the atmosphere. Multistage rockets can achieve escape speed from the Earth, so you can achieve unlimited maximum height. Compared with the air breathing engine, the rocket is lightweight, strong and can generate large acceleration. In order to control their flight, rockets rely on momentum, airfoil, auxiliary reaction engine, universal joint thrust, momentum wheel, deflection of exhaust flow, propellant flow, rotation and / or gravity.
While nuclear thermal rockets seem the most immediately feasible nuclear rocket technology currently, there are several other promising nuclear propulsion technologies as well such as pulse fission, fusion rockets and nuclear ramjets. The technology for nuclear propulsion certainly has a long way to go and is very much unproven in comparison to chemical propulsion. Key challenges include cost of further development and testing as well ensuring a high enough level of reliability given the safety consequences of a nuclear rocket failing. However, the potential benefits are easy to see. Chemical propulsion is approaching its limitations in traveling to Mars. For travel to Mars to ever become commonplace, short travel time, mission flexibility and cost are enormously important factors, all of which can in theory be improved dramatically by nuclear propulsion.
A new, plasma-based rocket propulsion technology known as the VASIMR® rocket (Variable Specific Impulse Magnetoplasma Rocket) has been in development by NASA, along with the Department of Energy and the Oak Ridge National Laboratory, for several years now. This new technology is expected to reduce fuel consumption and enable long-term space missions in the future.
We often look to the past when we reach for the future. There have been significant advances in rocket technology in recent years and many more are on the horizon. In part one for this series on rocket technology, we focused on the existing heavy-lifting rockets available in 2018. In this part, we will focus on the technologies that are just around the corner and will become available in the next 5-10 years.
As we progress through the R&D phases of developing rockets for commercial space flight, additional applications to the rocket technology will be uncovered. One such application was recently announced by Elon Musk at a space industry conference.
A few months after they filed this application with the FCC, SpaceX flew — for the first time — a used rocket into space. It was a big step in the SpaceX “Master Plan,” part of which is to perfect the technology of rocket reusability such that a spacecraft can be landed and sent back into space within hours of releasing their payloads.
So to be clear on SpaceX and their reusable rocket technology: their Falcon 9 is a Two Stage to Orbit system (TSTO) . The rocket uses a conventional engine, where oxygen carried on-board is mixed with the fuel within a combustion chamber and burned to generate a high pressure gas, that is exhausted through the nozzle to generate the thrust. The 2nd stage, separates at about 80 km from launch and proceeds towards deployment of its payload.
Rockets can be throttled by controlling the propellant combustion rate (usually measured in kg/s or lb/s). In liquid and hybrid rockets, the propellant flow entering the chamber is controlled using valves, in solid rockets it is controlled by changing the area of propellant that is burning and this can be designed into the propellant grain (and hence cannot be controlled in real-time).
There are two main categories of rocket engines; liquid rockets and solid rockets. In a liquid rocket, the propellants, the fuel and the oxidizer, are stored separately as liquids and are pumped into the combustion chamber of the nozzle where burning occurs. In a solid rocket, the propellants are mixed together and packed into a solid cylinder. Under normal temperature conditions, the propellants do not burn; but they will burn when exposed to a source of heat provided by an igniter.
For chemical rockets the combustion chamber is typically just a cylinder, and flame holders are rarely used. The dimensions of the cylinder are such that the propellant is able to combust thoroughly; different rocket propellants require different combustion chamber sizes for this to occur.
A typical rocket engine consists of the nozzle, the combustion chamber, and the injector, as shown in Figure 1.4. The combustion chamber is where the burning of propellants takes place at high pressure. The chamber must be strong enough to contain the high pressure generated by, and the high temperature resulting from, the combustion process. Because of the high temperature and heat transfer, the chamber and nozzle are usually cooled.
Liquid-fueled rockets have higher specific impulse than solid rockets and are capable of being throttled, shut down, and restarted. Only the combustion chamber of a liquid-fueled rocket needs to withstand high combustion pressures and temperatures and they can be regeneratively cooled by the liquid propellant. On vehicles employing turbopumps, the propellant tanks are at very much lower pressure than the combustion chamber. For these reasons, most orbital launch vehicles use liquid propellants.
Liquid-fuelled rockets force separate fuel and oxidiser components into the combustion chamber, where they mix and burn. Hybrid rocket engines use a combination of solid and liquid or gaseous propellants. Both liquid and hybrid rockets use injectors to introduce the propellant into the chamber. These are often an array of simple jets – holes through which the propellant escapes under pressure; but sometimes may be more complex spray nozzles.
A liquid-propellant rocket or liquid rocket is a rocket engine that uses liquid propellants. Liquids are desirable because their reasonably high density allows the volume of the propellant tanks to be relatively low, and it is possible to use lightweight centrifugal turbopumps to pump the propellant from the tanks into the combustion chamber, which means that the propellants can be kept under low pressure.