1. it is NOT UNUSUAL for technologies from SCIENCE FICTION to JOIN THE REAL WORLD, WITH EXAMPLES RANGING FROM video phones, VIA artificial intelligence, TO self-driving cars.

2. The ION [ˈaɪən] drive IS ANOTHER SUCH.

3. Ion drives PURPORTEDLY PROPELLED the

4. REAL ION DRIVES now REPOSITION satellites and send SPACE PROBEs ON INTERPLANETARY journeys.

5. they may have an EARTHLY role, too.

6. an AEROPLANE has FLOWN powered by an ion drive.

7. THE REASON FOR SURPRISE IS THAT an ion drive DELIVERS only A TINY AMOUNT OF THRUST.

the propulsive force of a jet or rocket engine.

8. IN THE VACUUM OF space,

9. because WITHOUT FRICTION TO HOLD a spacecraft BACK, SPEED BUILDS UP GRADUALLY TO A DECENT RATE.

Synonyms of build up: accelerate, accumulate

10. ON EARTH, however, iT HAD LONG BEEN ASSUMED THAT the atmosphere is too DENSE for an aircraft USING an ion drive to GET OFF THE GROUND.

11. the FIVE-METRE-WINGSPAN model aircraft

12. FLEW WITH an ion drive was launched WITH THE AID OF a BUNGEE [ˈbʌndʒi] 跳簧.

13. it successfully TRAVERSED a 60-metre INDOOR SPORTS TRACK.

14. This distance IS COMPARABLE to that

15. contains NO MOVING PROPULSION PARTS IN THE FORM OF PROPELLERS or JET ENGINES.

16. It can fly silently and without DIRECT EMISSIONS FROM BURNING FOSSIL [ˈfɑ:sl] FUELS.

17. It works by using electrodes to IONISE ['aɪənaɪz] A GAS IN SUCH A WAY THAT the resulting ions [ˈaɪən] CREATE THRUST.

18. In space, the gas to be ionised, usually xenon [ˈzenɑ:n], has to be carried BY THE CRAFT.

19. The MIT aircraft, however, ionises nitrogen from the air.

20. STRIPS OF parallel electrodes SUSPENDED IN A RACK below the craft’s wing.

21. These electrodes are powered by A PACK OF lithium-ion batteries. [ˈlɪθiəm]

22. The nitrogen ions generated INTERACT WITH neutral molecules in the air TO FORM WHAT IS KNOWN AS AN IONIC WIND.

23. The direction of this wind depends on the ARRANGEMENT of the electrodes.

24. meaning that NEWTON’S THIRD LAW OF MOTION (to every action there is an equal and opposite reaction) CARRIES THE CRAFT FORWARD—and, crucially, DOES SO AT A SPEED SUFFICIENT FOR ITS WINGS TO PROVIDE LIFT.

25. Scaling the design up will, ADMITTEDLY, be TRICKY.

26. Though the LEVEL of thrust generated is SUFFICIENT to fly Dr Barrett’s 2.5kg prototype, it is less than 1% of what would be required to KEEP AN AIRLINER AIRBORNE.

27. There are, though, other sorts of aircraft which, WITH FURTHER DEVELOPMENT, ion drives might POWER.

28. UNMANNED drones

29. high-altitude research craft.

30. Although the test model used a conventional TAIL PLANE to provide STABILITY AND STEERING, Dr Barrett thinks future designs COULD DO WITHOUT IT.

31. Instead, the electrodes would SHAPE THE IONISING ELECTRIC FIELDS in different ways, to control the direction of flight.

32. Moreover, he ADDS, it might be possible to INCORPORATE the ELECTRODES INTO the skin of the aircraft so that there appears to be no DISTINCTIVE power system.

33. a bit like a SAUCER, which could hover silently or ZIP THROUGH the air.

[zip through something] to deal with or complete something very quickly

34. Then ANOTHER PIECE OF SCIENCE FICTION would become SCIENCE FACT.