The primary function of the space propulsion system is to provide thrust, which helps in the functioning of the launch vehicle or satellite. In propulsion systems, the fluid (either solid, liquid, or electric) reacts to initiate acceleration and provide force in the system.
An ion thruster is a form of electric propulsion used for spacecraft propulsion. It creates thrust by accelerating ions with electricity. As the ionised particles escape from the aircraft, they generate a force moving in the other direction. Power supplies for ion thrusters are usually electric solar panels, but at sufficiently large distances from the sun, nuclear power is used.
Generally, an ion thruster has a few advantages over a chemical-powered rocket. Ion thruster can drive a spacecraft to speeds of up to 40 kilometers per second; its chemical counterpart can only manage 5 kilometers per second. Secondly, an ion thruster has ten times more fuel efficiency which is ideal for space travel. Chemical rockets need to bring their fuel supply for the whole journey and that load means more mass and additional fuel requirement for take-off..
Ion thrusters are being designed for a wide variety of missions—from keeping communications satellites in the proper position (station-keeping) to propelling spacecraft throughout our solar system. “Ion propulsion is even considered to be mission enabling for some cases where sufficient chemical propellant cannot be carried on the spacecraft to accomplish the desired mission,” says NASA. The technology could be used to power a return trip to Mars without refuelling, and use recycled space junk for the fuel. Ion thrusters will be used in the European Space Agency’s (ESA) mission to Mercury. The BepiColombo will launch in 2017, fly by Venus in 2019 and 2020, and be captured by Mercury’s gravity in 2024.
However Ion thrust engines create small thrust levels (the thrust of Deep Space 1 is approximately equal to the weight of one sheet of paper ) compared to conventional chemical rockets. They are practical only in the vacuum of space and cannot take vehicles through the atmosphere because ion engines do not work in the presence of ions outside the engine. Besides, the engine’s minuscule thrust would not matter when air resistance comes into play.
Michael Patterson, senior technologist for NASA’s In-Space Propulsion Technologies Program compared ion and chemical propulsion with “Tortoise and the Hare”. “The hare is a chemical propulsion system and a mission where you might fire the main engine for 30 minutes or an hour and then for most of the mission you coast.” “With electric propulsion, it’s like the tortoise, in that you go very slow in the initial spacecraft velocity but you continuously thrust over a very long duration — many thousands of hours — and then the spacecraft ends up picking up a very large delta to velocity.”
NASA has been investigating the Hybrid transportation system as a potential vehicle for a sustainable human Mars campaign. Hybrid Transportation System which utilizes both solar electric propulsion and chemical propulsion. The Hybrid propulsion system utilizes chemical propulsion to perform high thrust maneuvers, where the delta-V is most optimal when applied to save time and to leverage the Oberth effect. It then utilizes solar electric propulsion to augment the chemical burns throughout the interplanetary trajectory. This eliminates the need for the development of two separate vehicles for crew and cargo missions.
Hybrid propulsion is also been considered for Stand-alone interplanetary CubeSats primary propulsion systems for orbit maneuvering and precise trajectory control. There is growing demand for in-space propulsion systems that enable small satellites to achieve attitude and orbit control, orbital transfers, and end-of-life deorbiting. This is particularly important for the slew of LEO and MEO constellations currently being developed, as constellation control will be an important factor in the success of these ventures.
The current work focuses on the design and performance characterization of the combined chemical–electric propulsion systems that shall enable a stand-alone 16U CubeSat mission on a hybrid high-thrust–low-thrust trajectory from a supersynchronous geostationary transfer orbit to a circular orbit about Mars. The high-thrust chemical propulsion is used to escape Earth and to initiate stabilization at Mars. The low-thrust electric propulsion is used in heliocentric transfer, ballistic capture, and circularization.
Aerojet Rocketdyne Delivers DART Spacecraft Propulsion Systems Ahead of 2021 Asteroid Impact Mission
The dual chemical and electric propulsion systems for NASA’s Double Asteroid Redirection Test (DART) were recently delivered by Aerojet Rocketdyne to the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. The chemical propulsion system and the electric propulsion Xenon feed system have been undergoing assembly and integration onto the spacecraft structure at Aerojet Rocketdyne’s facility in Redmond, Washington, since August 2019. APL – designing, building and managing the mission for NASA – will now begin integration of the rest of the subsystems and final test of the spacecraft ahead of next year’s launch for the mission.
Propelled by Aerojet Rocketdyne propulsion, the DART spacecraft will be the first demonstration of a kinetic impactor: a spacecraft deliberately targeted to strike an asteroid at high speed in order to change the asteroid’s motion in space. The asteroid target is Didymos, a binary near-Earth asteroid that consists of Didymos A and a smaller asteroid orbiting it called Didymos B. After launch, DART will fly to Didymos and use an onboard targeting system to aim and impact itself on Didymos B. Earth-based telescopes will then measure the change in orbit of Didymos B around Didymos A.
DART is set to launch in late July 2021 from Vandenberg Air Force Base, California, intercepting Didymos’ secondary body in late September 2022. The spacecraft’s chemical propulsion system is comprised of 12 MR-103G hydrazine thrusters, each with 0.2 pounds of thrust. The system will conduct a number of trajectory correction maneuvers during the spacecraft’s roughly 14-month cruise to Didymos, controlling its speed and direction. As the DART spacecraft closes in on the asteroid, its chemical propulsion system will conduct last minute direction changes to ensure it accurately impacts its target.
In addition to providing the chemical propulsion system for the spacecraft, Aerojet Rocketdyne’s NEXT-C (NASA Evolutionary Xenon Thruster – Commercial) system will also be demonstrated on the mission. NEXT-C is a next-generation solar electric propulsion system designed and built by Aerojet Rocketdyne based on mission-proven technology developed at NASA’s Glenn Research Center. “DART plays an important role in understanding if it is possible to deflect asteroids and change their orbits,” said Eileen Drake, president and CEO of Aerojet Rocketdyne. “Our chemical propulsion system will help the spacecraft reach its destination and impact its target, while our electric propulsion system will demonstrate its capability for future applications.”
The NEXT-C system completed acceptance and integration testing at NASA Glenn in February. With a successful in-flight test of this next generation of ion engine technology, DART will demonstrate its potential for application to future NASA missions and may make use of NEXT-C for two of the planned spacecraft trajectory correction maneuvers.
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