Future Spacecrafts for Interstellar Space Travel

Our ancestors were migrated out of Africa and started to explore the Earth thousands of  years ago. A new human fossil discovered in Israel is found be 177,000 to 194,000 years old. So, modern humans are explorers from the beginning of their history itself. Now, we are in the similar mind set to migrate out of our home planet and exploring other planets and galaxies. Our curiosity for space travel has enormously grown recently. 

(Picture of Orion Nebula taken using Hubble Telescope. Photo Courtesy: NASA/ESA)

We need faster spacecrafts to travel to other planets and to travel beyond our solar system.  Currently, NASA’s Juno space probe of Jupiter mission is the fastest man-made spacecraft. It was traveled at the maximum speed of 265,000 km/h (165,000 mph) in 2016, thanks to the Jupiter’s gravitational pull. Juno uses LEROS 1b chemical rocket engine which utilize hydrazine and nitrogen tetroxide as propellant. 

Previously, New Horizons space probe was launched at the record speed of 58,536 km/h (36,373 mph) in 2006. Saturn V SA-505 rocket of Apollo 10 mission was traveled at the highest speed of 39,897 km/h (24,791 mph) relative to Earth on May 18, 1969. Saturn V rocket used kerosene, liquid oxygen and liquid hydrogen as fuel.  

The chemical rockets are slow even for travelling to nearby planets. NASA’s Mariner probe took 128 days to reach Mars. A key factor in space travel is speed of the spacecrafts. Increasing speed of the spacecrafts help us to reach the planets faster and also to travel beyond our solar family.  NASA and SpaceX are planned to take humans to Mars using Space Launch System (SLS) rocket and BFR rocket respectively. Even though these are advanced rockets, NASA and other companies are planning to develop more faster spacecrafts which can reduce the travel time. Such spacecrafts are mainly based on ion and plasma thrusters. 

Ion Thruster

Physicists are developing electrically-powered propulsion system which could reduce Mars travel time from few months to few weeks. As an electrical propulsion system, ion thruster uses ions which are created by colliding electrons with propellant such as xenon to create thrust. The following YouTube video explains about how an ion thruster works;

Ion Thruster Introduction

Fuel efficiency of ion thrusters are more than 90%; while fuel efficiency of chemical rockets is just up to 35%. So, ion thrusters need very less fuel than conventional chemical rocket engines. One of the drawbacks of using ion thrusters is erosion caused by ions. The ion mediated erosion limits the lifetime of this engine. NASA and other space agencies are working on to reduce such erosion to increase the lifetime of the ion thrusters. 

Hall thruster is an ion thruster and have been used since 1971 for satellites and space probes. French physicists are improving Hall thruster to travel at the speed of 72,420 km/h (45,000 mph). It is proposed to use 100 million times less fuel than the chemical rockets. Currently, Hall thruster can work up to 10,000 hours (1.1 year). 

Another promising ion propulsion technology is NASA’s Evolutionary Xenon Thruster (NEXT). It can fly at the speed of 90,000 mph. NASA has tested it over 48,000 hours (5.5 years). In the test, NEXT used 860 kg of xenon, while chemical rocket requires 10,000kg of propellant to show the same momentum.  To know how NASA’s ion propulsion thruster work, see the below video.

Gridded Iron Thruster 

Former NASA astronaut Franklin Chang Díaz is working on plasma rocket since 1973. He has founded Ad Astra Rocket Company in Houston to develop his VASIMR / Variable Specific Impulse Magnetoplasma rocket. VASIMR uses hydrogen, xenon or argon gases as propellant which is ionized and heated by radio waves to produce plasma. The plasma is accelerated by a magnetic field to create thrust. Unlike ion thrusters, VASIMR engine is electrodeless and shielded by magnetic field which increases its lifetime. VASIMR electric thruster needs electricity. For near-Earth missions, the electricity can be generated using solar panels and for planetary missions, the electricity can be generated using nuclear reactors.   He has proposed that his spaceship can travel at 180,000 km/h (112,000 mph) and reach Mars in 39 days. 

(VASIMR Engine)

Apart from the conventional chemical rockets and electric propulsion engines, several physicists have hypothesized some future spacecraft technologies. They have proposed that those future spacecrafts can travel at few fractions of light speed. Some of those hypothesized spacecrafts would use nuclear reactor as the fuel. Because of the safety reasons, they have recommended to build nuclear powered spacecrafts in space as like we had built ISS. No need to mention that building such spacecrafts in space require enormous amount of money. Now we can see about few hypothesized future spacecraft technologies.

Project Daedalus

In 1970s, British Interplanetary Society proposed an unmanned interstellar spacecraft called Daedalus. This spaceship was proposed to use nuclear fusion rocket to fly to Barnard’s Star, 5.9 light years away from the Earth. This spaceship would be weighed 54,000 tones and would travel at the speed of 12% of light speed. It would take 50 years to reach the Barnard’s Star. 

Project Icarus

Motivated by Project Daedalus, British Interplanetary Society and Tau Zero Foundation designed and launched the Project Icarus in 2009. Icarus Interstellar Inc. is currently managing this project. Icarus probe is also proposed to use nuclear fusion rocket. It is aimed to travel within 22 light years of Earth. 

Antimatter Rockets

Dr. Ryan Weed of Positron Dynamics is working on antimatter-based rockets that can reach speed of 72 million mph which will take humans to Mars in weeks-time and to Alpha Centuari in 40 years-time. Antimatter can be generated by particle accelerators and radioactive decay. It is very expensive to generate antimatter. Generating one gram of positrons needs $25 billion and one gram of antihydrogen costs $62.5 trillion. But,  antimatter may be an efficient fuel and spacecrafts need only few milligrams of antimatter when comparing to tons of chemical fuel. 

Warp Drive

Warp drive is the most fascinating hypothesis regarding the interstellar space travel. It is portrayed in many science fiction literatures and movies including Star Trek. Alcubierre warp drive is proposed by Miguel Alcubierre, a Mexican theoretical physicist. He has proposed that a spacecraft would travel faster than light by contracting space in front of it and expanding space behind it. This type of spacecraft needs ‘exotic matter’ to operate. Below video explains how a warp drive would work.

Science of warp drive 

EM Drive

British inventor Roger Shawyer proposed a microwave technology based electromagnetic thruster called EMDrive. The microwaves moving back and forth inside a chamber could produce thrust. Thus, they call this as a reactionless drive. It won’t expel propellant like traditional rockets and therefore violating Newton’s third law and conservation of momentum. Recently, NASA has tested this type of thruster and published a paper on this technology. China’s China Academy of Space Technology has also declared that they have successfully created a working prototype of EMDrive last year. Next to ion propulsion thrusters, few physicists are interested in developing EMDrive.

These are some of the future spacecraft technologies which may help mankind to explore the space.