Solar electric propulsion engines are said to be the future of space travel. Solar electric propulsion can be combined with other space technologies to charter and explore deep space they will even play a role in one day colonising Mars.
Solar electric propulsion engines are the financially efficient answer to exploring the inner solar system, advancements in the technological fields of solar electric propulsion have the ability to open up commercial activities in space. NASA are particularly excited about the possibilities of solar electric propulsion and are focusing some of their efforts on developing technologies more rapidly and combining them with offer technologies such as plasma propulsion engines . This will allow NASA and other space organisations to access Mars and nearby asteroids for a reasonable cost and within a practical timescale. A solar electric propulsion engine uses one tenth of the propellant than its equivalent chemical propulsion counterpart. This frees up lots of mass for solar electric propulsion spacecraft as they do not need to carry as much propellant. This creates the opportunity for sending cargo, robots and people to more far-flung destinations than previously possible.
NASA's solar electric propulsion project is lead by its Glenn Research Center located in Cleveland. It aims to launch a system-level flight demonstration by the end of the decade. This solar electric propulsion project is to develop and exhibit; advanced solar arrays, high-voltage power management and distribution, power processing units and high-power Hall thrusters.
The solar electric propulsion project started out with the development of solar arrays that are large, flexible and capture vast amounts of solar energy, whilst also being lightweight, cost-effective, radiation resistant and have the ability to fold up into a small package during launch. NASA's solar electric propulsion project worked alongside ATK Aerospace and Deployable Space Systems Inc. to create two different designs of solar array, both are durable, radiation resistant, lightweight and flexible. One of the designs is the ATK MegaFlex is a solar array that folds out like a fan, the other design is the DSS Mega-ROSA and this solar array design rolls out like a window shade. A pair of either of these solar arrays provide up to around 50 kilowatts of electricity.
With the solar arrays decided upon for the solar electric propulsion project the next step was to decide upon the propulsion. The solar electric propulsion project will use several Hall effect thrusters combined with a magnetic shielding. The Hall effect thrusters use the electricity generated from the solar arrays to generate mild but constant thrust. The Hall effect thrusters trap electrons in a magnetic field then use them to ionise the xenon gas, this gas turns into plasma and is then forced out of the engine generating thrust. A new high-power 13 kilowatt Hall effect engine was recently tested at NASA's Glenn Research Centre this shows huge promise, demonstrating the readiness of solar electric propulsion systems for space travel.
The solar electric propulsion project's mission to demonstrate the capabilities of solar electric propulsion technologies was intended to The Asteroid Redirect Mission. This mission was to use a robotic spacecraft equip with a high power solar electric propulsion system to visit a large near Earth asteroid gather a large sample and place it within an orbit around the moon. Astronauts would then be sent to the sample, explore it and bring back pieces for further study. Unfortunately it was announced earlier this year that The Asteroid Redirect Mission will no longer be going ahead due to NASA being unable to receive funding from the US Government, however all technologies attained thus far will prove useful for any future missions.
Hayabusa translates literally as Peregrine Falcon, it was a unmanned spacecraft created by JAXA (Japan Aerospace Exploration Agency). The Hayabusa successfully used solar electric propulsion technologies to aid it with its mission of travelling to the near Earth asteroid 25143 Itokawa, gathering a sample and returning to Earth. The 25143 Itokawa is the smallest asteroid ever visited and photographed by a spacecraft measuring around 350m in diameter. Hayabusa lauched in May 2003, approached close to 25143 Itokawa in September 2005, in November the spacecraft landed but failed to collect a sample, five days later Hayabusa landed for a second time and successfully gathered a dust sample and before finally landing back on Earth in June 2010.
Deep Space 1 was the first mission by NASA that used spacecraft propelled with ion propulsion . The solar electric propulsion involved a set of solar arrays connected to NASA's NSTAR engine which uses high-voltage electrodes to accelerate ions. The Deep Space 1 launched in October 1998, its purpose was to carry out a flyby of the asteroid 9969 Braille. Deep Space 1 flew within 26km of the asteroid in 1999, but due to a malfunction with its ultraviolet spectrometer the images captured were indistinct to say the least. The Deep Space 1 mission was extended to include an encounter in September 2001, with the comet 19P/Borrelly, the images received from this flyby were of much better quality even though systems were still malfunctioning.
Dawn is a space probe that was launched in September 2007 by NASA to research the protoplanets Vesta and Ceres within the asteroid belt. It had three Hall thrusters with 10 kilowatts of power produced from its solar arrays, the solar electric propulsion system is able to produce 90 millinewtons of thrust. Dawn arrived at Vesta, its first target in July 2011 where it remained in orbit for 14 months. Whilst at Vesta the probe surveyed the entire protoplanet taking detailed photographs of the surface. The probe left Vesta in towards the end of 2012 and arrived at Ceres in March 2015. Dawn is currently within orbit of Ceres, which is where it has been since 2015. NASA have considered sending the probe to the third protoplanet of the asteroid belt but have decided against it. Dawn will instead remain in orbit of Ceres until it runs out of fuel. The Dawn space probe uses ion propulsion within its solar electric propulsion system this is what has allowed the probe to visit multiple targets. It is the first spacecraft to ever obit two separate bodies in space.
The Deep Space Gateway is a joint venture between NASA and Roscosmos. It involves a new space station to be placed into orbit around the moon, construction is scheduled to begin in the 2020s. The Deep Space Gateway will be used to aid deep space travel and to support any lunar surface missions. The Deep Space Gateway will be propelled with a combination of chemical propulsion and solar electric propulsion technologies. The deep space conditions near the moon will provide valuable deep space experience for humans. Robotics can be tested and perfected on the moon's surface before they are deployed to further away destinations such as Mars. The Deep Space Gateway ultimately will allow mankind to learn the skills we need to push deeper into the solar system.