Launching a rocket into space from Earth is an expensive and complex process. It requires a lot of dedication and team work.
There are many methods to accelerate spacecraft and artificial satellites into the space. Each has its own advantages and drawbacks. However, nowadays, most rockets are propelled by forcing a gas from the rear of the vehicle at very high speed via a supersonic de Laval nozzle, known as rocket or spacecraft engine.
Unlike air-breathing jets, rockets cannot stream atmospheric gases to create motion because at high altitude the atmosphere becomes thin. A rocket engine must propel off its own exhaust fluid in order to get thrust. Looks quite simple, but technical issues involved in this process makes it extremely difficult. Today, we are presenting a few conceptual spacecraft propulsion techniques that may expand the horizons of humanity.
Table of Contents
14. Synergistic Turbojet
Image credit: wikimedia
This is a new concept of hybrid rocket engine that uses single-stage-to-orbit approach and doesn’t rely on jettisoning hardware to reach orbital altitude. Instead, it would use atmospheric air to feed the engine’s burning reaction. This will avoid carrying the extra oxidizer and thus decrease weight.
The concept is developed by British company Reaction Engine Limited to propel the proposed Skylon spaceplane to low Earth orbit.
The air-breathing mode integrates a turbo compressor with a lightweight air precooler which is located just behind the inlet cone of the rocket. As the name suggests, precooler cools the hot, compressed air leading to a high pressure ratio within the engine. The compressed air continuously passes into the combustion chamber where it is ignited with liquid hydrogen. The high pressure ratio in engine gives high thrust at high altitudes. The precooler doesn’t liquefies air, letting the engine run more efficiently.
13. Electromagnetic Coilgun Launcher
An electromagnetic coilgun accelerates its payload with pulsed magnetic fields, without direct electrical contacts that generates arcing. A coilgun works by inductive forces, and made up of a series of solenoidal coils that are powered at the appropriate time which is controlled by computer.
A large coil with high electric power can produce a strong magnetic field capable enough to thrust a spacecraft or payload at high-speed across miles of railroad. However, to achieve enough momentum, the track should be of several miles long and this would cost tens of billions of dollars. According to its inventor, it’s a small price to pay for the future.
Image credit: Adrian Mann
The Vacuum to Antimatter Rocket Interstellar Explorer System (VARIES) is an advanced space propulsion concept introduced by Richard Obousy, president of Icarus Interstellar Inc. It would use giant solar arrays to create power for high density lasers. These lasers would take advantage of quantum effect called Schwinger pair production to generate particles of antimatter. These particles could be stored and used as fuel.
This sounds simple, but there would be a lot of engineering hurdles. Along with building a solar power system and lasers, the starship would need magnetic bottles to store the antimatter. A tiny mistake would vaporize the whole ship in a flash of gamma rays. In addition to this, magnetic nozzles, radiation shielding and all the other precautions would be necessary to protect a craft while flying through interstellar space.
If all of these obstacles can be overcome, the VARIES concept can be used to accelerate the ship to a fraction of the speed of light.
11. Nuclear Thermal Rocket
Bimodal Nuclear Thermal Rocket in Low Earth Orbit
In nuclear thermal rocket, hydrogen is heated to a high temperature in a nuclear reactor, and then expands through a rocket nozzle, creating thrust. It creates a superior effective exhaust velocity, and thus a superior propulsive efficiency, with specific impulses in the order of twice of chemical engines.
Rosatom (Russian State Corporation) is building a nuclear rocket engine that would take 45 days to travel from Earth to Mars. Conventional rockets that are used at present, take 18 months.
This type of rockets can be grouped by the construction of its reactor, which can be solid, liquid or gas. The most efficient designs require the highest temperature possible, and this is typically limited by the properties of materials.
10. Ducted Rocket
Ducted Rocket uses the supersonic exhaust to further compress air collected by ram effect. This results into higher thrust power for any given amount of fuel as compared to the rocket or ramjet alone. It gives useful thrust form zero speed, and capable to operate outside the atmosphere.
Usual solid rockets have a specific impulse of about 260 seconds, while using the same fuel in ducted rocket design can improvise this to over 500 seconds – even the best oxygen or hydrogen engine can’t match this figure.
However, the intakes of high-speed engines are quite difficult to develop and they can’t be located anywhere on the airframe easily. Entire airframe needs to be developed around the intake design. Moreover, the air will eventually run out, so the amount of additional thrust would be limited by how fast the rocket climbs.
9. Stellar Windjammer
Sun constantly spouts charged particles – a storm of high speed electrons and protons. Such radiation pressure can be pushed against magnetic field in order to generate thrust. Further, the direction of thrust can be adjusted by altering the sail according to the solar wind.
Andrews Zubrin magsail uses a superconductor loop to generate a magnetic field that catches and diverts the stellar wind of plasma. As the magnetic field entirely surrounds the ship, any payload is completely protected from alpha and beta radiation. However, it is not protected from gamma radiation, neutrons and x-rays.
NASA plans to deploy a solar sail in 2018 during the flyby survey of Asteroid Scout.
8. Nested-Channel Hall Thrusters
The X2 nested channel Hall thruster with both channel firing
Nested-Channel Hall Thrusters were developed to improve upon the thruster system power per unit mass of traditional single channel Hall thrusters. The aim is to study the plume characteristics of different nested thruster configurations to enhance understanding of discharge channel interactions, and also study high-thrust and high-Isp operation modes.
Nesting discharge channels could reduce the footprint area and decrease thruster mass of a high-power Hall thruster. Furthermore, the nested-channel configuration features the ability to alter the exit area via selective activation of available channels. Use of various combinations of discharge channels provides a secondary method of throttling and permits multiple design points for the overall thruster.
7. Antimatter Rocket
Image credit: NASA/Marshall Space Flight Center
Antimatter is exactly opposite of normal matter. The sub-atomic particles of antimatter have properties opposite to those of normal matter. The electric charge of those particles is reversed. When both twins interact, they annihilate each other and creates a lot of energy. Scientists want to make use of this power to boost rocket engines into the space.
The antimatter rockets would have a far higher energy density and specific impulse as compared to any other proposed class of rocket. 100 milligrams of antimatter is enough to send a rocket from Earth to Mars, while a chemical rocket would need tons of propellant.
However, this power comes with a price. Some antimatter reactions create blasts of high energy gamma rays, which penetrate matter and break apart molecules in cells. They can make the engines radioactive. The NIAC (NASA Institute for Advanced Concepts) is currently working on a new design for an antimatter-powered spacecraft that avoids this brutal side effects.
6. External Pulsed Plasma Propulsion
Image source: NASA
External Pulsed Plasma Propulsion uses nuclear explosions for thrust, first developed as Project Orion by DARPA. The design effort was carried out at General Atomics in the late 1950s. The momentum transfer was increased by efficient directional explosives, leading specific impulses to 6,000 seconds. It is around thirteen times than that of the space shuttle main engine. Theoretically, with further improvements and refinements, maximum of 100,000 seconds specific impulse is possible.
Various engineering issues were found and solved over the course of Project Orion. Most of them were related to pusher-plate lifetime and crew shielding. In 1965, the system appeared to be entirely workable, but the project was shut down because of the Partial Test Ban Treaty.
5. Project Daedalus
Project Daedalus was a study conducted for 5 years in 1970s by the British Interplanetary Society. The aim was to design an efficient unmanned interstellar spacecraft using existing or near-future technology, that can reach Barnard’s Star (5.9 light years away) in 50 years.
It was to be a 2 stage spacecraft. The first 2-year-stage would accelerate the spacecraft to 7.1 percent of the speed of light, and the second stage would take it to 12 percent of light speed, before being shut down for a 46 year cruise period.
Because of extreme temperature conditions (from absolute zero to 1600 K), the whole structure plus engine would be made of molybdenum alloyed with Carbon, Zirconium and Titanium. The spacecraft was going to use Friedwardt Winterberg’s inertial confinement fusion drive concept, which initiates nuclear fusion reaction by heating and compressing a fuel target in the form of pellet, containing a mixture of tritium and deuterium.
4. Cubesat Ambipolar Thruster (CAT)
The Cubeset Ambipolar Thruster is a new plasma propulsion system that is designed to push small spacecraft around in orbit or far beyond the Earth. Cubesats are a kind of nano-satellite that cost thousand times less to develop and launch as compared to conventional satellites. They are powered by a novel DC to RF oscillator with air-core inductors.
The plasma is created continuously by a Radio Frequency antenna to launch a Helicon wave. The wave heats the electrons that are insulated from the walls of the plasma liner by a magnetic field created by rare Earth magnets. The electrons drag ions with them by streaming out of the plasma liner via magnetic nozzle. The thermal energy of the electron is converted to kinetic energy in the ions to create thrust.
CAT is designed to fit in 1U or 3U cubesat. Currently, they hitch a ride on larger rockets, and once they are in space, they drift around Earth. However, this will change soon, as CAT technology will help us send these small spacecraft to the asteroids, moon, Mars and beyond.
3. Nanoparticle Micropropulsion
The NanoFET (Nanoparticle Field Extraction Thruster) electrostatically charges and accelerates nano and micro particles to create thrust. It provides a high propulsive envelope capable of accomplishing numerous missions that are not currently possible with single propulsion system. Generalized nano-particles accelerators are also used in environmental remediation, material processing and biomedicine.
The Evolutionary Xenon Thruster (NEXT) project tested the ion engine for more than five and a half years. They found that ion propulsion engines can minimize the bulkiness of fuel. Over the course, NEXT consumed 860 kilograms of fuel, while a conventional rocket took 10,000 kilograms to generate the same momentum.
2. Photonic Laser Thruster
Image credit: wikimedia
Dr. K. Bae designed a concept of space driver that wouldn’t need to carry fuel tanks. The principle is generating thrust directly from the momentum of a photon from a laser reflected from a mirror. Unlike laser propulsion and solar sail, an amplification process is used. In this process incident beam reflected by a stationary mirror is re-used, with an amplification phase at each reflection.
10,000 times recycling of photos with 15 kW input laser power would create 1 N of photon thrust – the same amount of thrust generated by a 100 kW solar panel. Along with high-precision and high-speed maneuver of small rocket, it can be used for beaming thrust of expensive, lightweight mission vehicle, similar to aerial refueling.
1. Alcubierre Warp Drive
A Mexican physicist Miguel Alcubierre proposed an idea based on a solution of Einstein’s field equations in general relativity – A spacecraft could achieve speed faster than light if a configurable energy density is lower than that of vacuum (less than zero mass) could be created.
Objects cannot move at the speed of light within normal spacetime. What Alcubierre suggested is shift the space around an object so that the object would arrive at its destination faster than light in normal space without violating any physics laws.
Alcubierre Drive stretches spacetime in a wave – the fabric of space ahead of spacecraft contracts and the space behind the spacecraft expands. The ship can ride the wave to accelerate to high speeds and time travel.