Marc RaymanJul 30, 2013

Dawn Journal: Craving Power

Dear Megalodawniacs,


Xenon-powered Ion Engine
Xenon-powered Ion Engine An ion engine powered with xenon is demonstrated here inside a test chamber at the Jet Propulsion Laboratory. This engine is used on NASA's Dawn mission and a larger version is envisioned for use on the proposed Asteroid Retrieval Mission.Image: The Planetary Society


We crave power!!








Over the course of the exercise, the arrays were positioned at five angles, each for an hour, and the main computer recorded their output power and other pertinent measurements. Initially, when the wings were pointing directly at the sun, a glowing orb 2.48 AU (371 million kilometers, or 230 million miles) away, together they could generate more than two kilowatts. The ion propulsion system then was thrusting at level 53, consuming 1,368 watts. When the arrays were tipped to their maximum angle of 47 degrees, the insolation was the same as it would be at 3.00 AU (449 million kilometers, or 279 million miles), and the system yielded more than 1,300 watts. By then, the program engineers had stored onboard had throttled the ion drive down to level 24, where it drew 753 watts, and the spacecraft autonomously reduced it still further. When the activity was finished, the wings were turned back to their usual orientation, facing the distant sun so they could generate the maximum power possible, and the Brobdingnagian dragonfly could resume its normal flight pattern.

The calibration will be repeated occasionally as Dawn proceeds on its deep-space trek. Engineers will use the resulting data to continue to refine their plans for reaching Ceres and for maneuvering in orbit once there. Yet this is just one of the myriad details that must be worked out with exquisite care to ensure that the exploration of that enigmatic world is as richly productive, as tremendously rewarding, as outstandingly successful as the investigation of Vesta.

Dawn's position as of July 30, 2013
Dawn's position as of July 30, 2013 Image: NASA / JPL (Gregory J. Whiffen)

It is thanks to the extraordinary scrupulousness of their work that Dawn's human counterparts are able to accomplish this ambitious adventure. And although they are responsible for ensuring that the craft achieves its objectives, this endeavor extends far beyond the members of the team. This is a mission of humankind. Everyone who ever gazes in wonder at the night sky is part of it. Everyone who is curious about nature and about the reality of the universe is part of it. Everyone who hungers for knowledge and insight is part of it. Everyone who feels the passion for pursuing bold dreams and the exhilaration of discovery is part of it. Everyone who feels the lure of the unknown is part of it. Everyone who appreciates the great challenges and the great rewards of aiming beyond the horizon is part of it. So as Dawn continues its audacious exploits, anyone can be part of it.

Dawn is 18 million kilometers (11 million miles) from Vesta and 50 million kilometers (31 million miles) from Ceres. It is also 3.47 AU (519 million kilometers or 322 million miles) from Earth, or 1,310 times as far as the moon and 3.42 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 58 minutes to make the round trip. 

Dr. Marc D. Rayman
4:00 p.m. PDT July 29, 2013