HOUSTONâ€”Franklin Chang-DÃaz bounds up a handful of stairs and peers through a porthole cut into the side of a silver, tanker-truck-sized vacuum chamber. Inside, a blueish-purple light shines, unchanging and constant, like a bright flashlight. â€œIt looks kind of boring,â€ Chang-DÃaz admits. â€œBut that plume is 3.5 million degrees. If you stuck your hand in that, it would be very bad.â€
Truth be told, the plume does not look impressive at all. And yet the engine firing within the vacuum chamber is potentially revolutionary for two simple reasons: first, unlike gas-guzzling conventional rocket engines, it requires little fuel. And second, this engine might one day push spacecraft to velocities sufficient enough to open the Solar System to human exploration.
This has long been the promise of Chang-DÃazâ€™s plasma-based rocket engine, Vasimr. From a theoretical physics standpoint, Vasimr has always seemed a reasonable proposition: generate a plasma, excite it, and then push it out a nozzle at high speed. But what about the real-world engineering of actually building such an engineâ€”managing the plasma and its thermal properties, then successfully firing it for a long period of time? That has proven challenging, and it has led many to doubt Vasimrâ€™s practicality.
Sure, the naysayers say, Chang-DÃaz is a wonderful fellow. Hard worker. Brilliant guy. And at a time when the national discourse assails the value of Spanish-speaking immigrants, his story offers a powerful counter to that narrative. Speaking almost no English at the time, he immigrated to the United States from Costa Rica in 1969 to finish high school. Chang-DÃaz then earned a doctoral degree in plasma physics from Massachusetts Institute of Technology. Later, as an astronaut, Chang-DÃaz flew seven Space Shuttle missions, tying Jerry Rossâ€™ record for most spaceflights by anyone, ever.
All the while, from his first days at Johnson Space Center when he installed an early Internet connection to work with data from his Boston-based plasma physics lab, Chang-DÃaz nurtured dreams of linking his science background with his career as a flier. Slowly, he developed the theory of a plasma rocket and began to build prototypes. All along, the critics whispered it just wasnâ€™t feasible.
Only, now it just might be. As part of a program to develop the next generation of in-space propulsion systems, NASA awarded Chang-DÃazâ€™s company, Ad Astra, a three-year, $9 million contract in 2015. This unlocked an opportunity long awaitedâ€”a chance to prove the doubters wrong. Naturally,Â it won’t be easy. Ad Astra must fire its plasma rocket for 100 hours, at a power level of 100 kilowatts, next year.
This February, the company has worked about halfway through that contract, and Ars has been keeping tabs on progress in the lab. So far, the immigrant from Costa Rica seems to be holding up his end of the bargain. NASA gave the company a sterling review after the first year of the agreement. Still, there is a ways to go.Â During a visit this month,Â the Vasimr engine fired at 100kW for 10 seconds and 50kW for one minute.
The rocket engine starts with a neutral gas as a feedstock for plasma, in this case argon. The first stage of the rocket ionizes the argon and turns it into a relatively â€œcoldâ€ plasma. The engine then injects the plasma into the second stage, the â€œbooster,â€ where it is subjected to a physics phenomenon known as ion cyclotron resonance heating. Essentially, the booster uses a radio frequency that excites the ions, swinging them back and forth.
As the ions resonate and gain more energy, they are spun up into a stream of superheated plasma. This stream then passes through a corkscrew-shaped nozzle and is accelerated out of the back of the rocket, producing a thrust.
Such an engine design offers a couple of key benefits over most existing propulsion technology. Perhaps most notably, unlike chemical rockets, Vasimr operates on electricity. As it flies through space, therefore, it does not need massive fuel tanks or a huge reservoir of liquid hydrogen and oxygen fuel. Instead, the rocket just needs some solar panels.
The Sun powers both the production of plasma and the booster exciting the plasma, andÂ the extent to which it does either can be shifted. When a spacecraft needs more thrust, more power can be put into making plasma. This process uses more propellant, but it provides theÂ thrust needed to moveÂ out of a gravity well, such as Earth orbit. Later, when the vehicle is moving quickly, more power can be shifted to the booster, providing a higher specific impulse and greater fuel economy.
â€œItâ€™s like shifting gears in a car,â€ Chang-DÃaz explained. â€œThe engine doesnâ€™t change. But if you want to climb a hill, you put more of your engine power into torque and less into rpm, so you climb the hill, slowly, but youâ€™re able to climb. And when youâ€™re going on a freeway, flat and straight, you upshift. Youâ€™re not going to go to Mars in first gear. Thatâ€™s the problem. Itâ€™s why we run out of gas going to Mars with a chemical engine.â€
Another benefit of Vasimr’s design is that the plasma remains confined within a magnetic field, inside the engine, throughout the burn. In practical terms, this should greatly reduce the wear and tear on the engineâ€”which is useful if youâ€™re designing a spacecraft to eventually fly people around the entire Solar System.
Listing image by Ad Astra Rocket Company
from Ars Technica http://ift.tt/2mbMPMW