An ion propulsion engine hurtled Dawn along the circuitous path between Earth and Vesta, and will again between Vesta and Ceres. The ion engine functions as follows (explanation courtesy NASA):
The thrusters work by using an electrical charge to accelerate ions from xenon fuel to a speed 10 times that of chemical engines. The electrical level and xenon fuel feed can be adjusted to throttle each engine up or down. The engines are thrifty with fuel, using only about 3.25 milligrams of xenon per second (about 10 ounces over 24 hours) at maximum thrust. The Dawn spacecraft carries 425 kilograms (937 pounds) of xenon propellant.
At maximum thrust, each engine produces a total of 91 millinewtons -- about the amount of force involved in holding a single piece of notebook paper in your hand. You would not want to use ion propulsion to get on a freeway -- at maximum throttle, it would take Dawn's system four days to accelerate from 0 to 60 miles per hour.
Ion Propulsion Engine, credit: NASA/JPL
As slight as that might seem, over the course of the mission the total change in velocity from ion propulsion will be comparable to the push provided by the Delta II rocket that carried it into space -- all nine solid-fuel boosters, plus the Delta's first, second and third stages. This is because the ion propulsion system will operate for thousands of days, instead of the minutes during which the Delta performs.
So, Dawn’s got this wildly, insanely cool engine, like some Buck Rogers, Lost In Space, Star Wars, Back To The Future but better interplanetary -- heck, intergalactic if you want -- propulsion system. And how are we proud citizens of planet Earth celebrating this mind-blowing technical achievement. I don’t know. We don’t seem to be celebrating at all.
And what about the asteroids, Vesta and Ceres that Dawn is expected to study? Here’s some more facts (courtesy of NASA, again):
Ceres and Vesta are the two most massive residents of the asteroid belt. Vesta is a rocky body, while Ceres is believed to contain large quantities of ice. The profound differences in geology between these two protoplanets that formed and evolved so close to each other form a bridge from the rocky bodies of the inner solar system to the icy bodies, all of which lay beyond in the outer solar system. ...
--Discovered: March 29, 1807 by Heinrich Wilhelm Olbers of Germany (fourth asteroid discovered)
--Dimensions: About 578 by 560 by 458 kilometers (359 by 348 by 285 miles)
--Shape: Nearly spheroid, with a massive chunk out of the south pole
--Rotation: Once every 5 hours, 20 minutes
The asteroid's official name is "4 Vesta" because it was the fourth asteroid discovered. About the length of Arizona, it appears to have a surface of basaltic rock -- frozen lava -- which oozed out of the asteroid's presumably hot interior shortly after its formation 4.5 billion years ago, and has remained largely intact ever since. Telescopic observations reveal mineralogical variations across its surface.
Vesta has a unique surface feature which scientists look forward to peering into. At the asteroid's south pole is a giant crater - 460 kilometers (285 miles) across and 13 kilometers (8 miles) deep. The massive collision that created this crater gouged out one percent of the asteroid's volume, blasting over one-half million cubic miles of rock into space.
What happened to the one percent that was propelled from its Vesta home? The debris, ranging in size from sand and gravel to boulder and mountain, was ejected into space where it began its own journey through the solar system. Scientist believe that about 5 percent of all meteorites we find on Earth are a result of this single ancient crash in deep space. ...
--Discovered: January 1,1801 by Giuseppe Piazzi of Italy (first asteroid/dwarf planet discovered)
--Size: 975 by 909 kilometers (606 by 565 miles)
--Rotation: Once every 9 hours, 4.5 minutes
The object is known by astronomers as "1 Ceres" because it was the very first minor planet discovered. As big across as Texas, Ceres' nearly spherical body has a differentiated interior - meaning that, like Earth, it has denser material at the core and lighter minerals near the surface. Astronomers believe that water ice may be buried under Ceres' crust because its density is less than that of the Earth's crust, and because the dust-covered surface bears spectral evidence of water-bearing minerals. Ceres could even boast frost-covered polar caps.
Astronomers estimate that if Ceres were composed of 25 percent water, it may have more water than all the fresh water on Earth. Ceres' water, unlike Earth’s, is expected to be in the form of water ice located in its mantle.OK, so NASA built Dawn, launched it into orbit around Earth, started up its ion propulsion engine, and sent it whizzing off to Vesta, a really big rock, a long, long way away. What’s the big deal?
The spacecraft will follow a series of circular near-polar orbits allowing it to study nearly the entire surface of the asteroid. These different orbits will be varied in altitude and orientation relative to the sun to achieve the best positioning for the various observations planned. At Vesta, the highest orbit will be roughly 2,500 kilometers (1,550 miles) in altitude, providing a nice vantage point to obtain a global view of the rocky world. The lowest orbit will be at an altitude of less than 200 kilometers (125 miles).Dawn will hang around in orbit for about nine months, and then, once again, fire up its ion thrusters, break free of Vesta’s gravity, and slip off toward a distant rendezvous with Ceres, the second largest asteroid, or dwarf planet in our solar system. Three years will go by before, about eighty-five days out from Ceres, Dawn begins its approach and deceleration into orbit around Ceres. Once in orbit, Dawn will do the same sorts of observations that it made of Vesta.
(NASA press release, “Dawn Launch, Mission to Vesta and Ceres”)
Dawn will beam all of the information it collects from Vesta and Ceres back to Earth, via its little, low-power radio and dish antenna, and down to NASA’s Deep Space Network stations in California’s Mojave desert; outside Madrid, Spain; and near Canberra, Australia. These stations mostly use 34-meter antennas, but occasionally make use of larger 70-meter monsters for mission-critical communications. This is like the ultimate long-range WiFi, but one that can never, ever fail.
After all that, according to NASA:
Dawn’s prime mission is scheduled to end in July 2015. At that time, the spacecraft will be in a “quarantine” orbit around Ceres at an altitude of about 700 kilometers (435 miles). This orbit ensures that the by-then-decommissioned spacecraft will not impact Ceres for more than half a century.But it will -- to use NASA’s bland term -- “impact” Ceres eventually. Meaning, it slowly spirals down toward the surface, where it finally, irrevocably wipes out in the sands of Ceres. That’s life.
Dawn is indisputably a big deal. Before the advent of spacecraft, humanity never before finessed so many subtle, graceful, elegant technologies into performing so long a succession of almost magical feats, so reliably. What NASA, and all of the people downstream have accomplished with Dawn, and any of their spacecraft for that matter, make a Swiss watch look like a chimpanzee’s Play-Doh art. Not to offend the Swiss, or any watchmaker, but getting a spacecraft from point A to point B, is insanely difficult. Not just the technical hurdles -- which are always surmountable with enough time and money (and there is never enough of either) -- but the logistical and quality control hurdles, too. Remember, thousands of intricate little parts, from hundreds of manufacturers need to fit together perfectly -- or as near to perfection as humanly possible -- but then all those interlocking pieces are required to function exactly as they were designed, for years and years with no possibility of tweaking, or reboots, or a smack upside the metaphorical head. An old engineer once told me, "As complexity approaches infinity, mean time between failure approaches zero." That is where the quality control comes in. If you have ever worked in a place that designs and manufactures products to military specifications, you will know what I am talking about: endless testing, endless documentation, endless record keeping for traceability of every single constituent component. Oh, and don’t charge too much either, or the politicians will have their knives out and cut, cut, cut the project to ribbons.
And after all that effort, we take the thing, this pinnacle of human technical achievement, and we lob it into space like we would toss an empty champagne bottle over the side of ship. Done. Gone. Never to be seen again. Thanks, it’s been fun, but so long. Now that comes from a cool, and uniquely human philosophy: to expend so much effort on something so ephemeral, which offers such ineffable immediate returns. That takes the courage of one’s convictions, especially when surrounded by screaming mobs of naysayers (benighted, insensate, narrow-minded politicians and TV talking heads) who insist that your efforts are criminally wasteful and self-indulgent. They are not.
Besides, there are short-term gains for a multitude of private contractors. That should please the bean-counting, campaign-contribution-grubbing politicians. All those contractors develop new technologies, or leverage old ones, and then immediately use those technologies to design and assemble spacecraft components to the very high standards demanded by NASA. These contractors make money and employ many, many people to do this. And the technology they create -- at least the stuff they tell us about -- is either available to license from NASA, or offered up by NASA in the public domain for anyone to use. The point of this is to get the technology out in the open, where entrepreneurs can apply it in as many new, yet unimagined pursuits as possible. This creates a multiplier effect that offsets the upfront investment by taxpayers for the spacecraft. (I don’t have the data on domestic economic activity initiated through tech transfers, but I’m sure it is out there. Contact NASA if you don’t trust my multiplier assertion.)
Another good reason to create and launch interplanetary spacecraft is that such projects offer engineers the opportunity to develop what would otherwise be “blue-sky” innovations, which in private industry are typically off limits due to cost and timing constraints. The chain of “Eureka!” moments such “blue-sky” ventures provoke can not be priced, but trust me, the effort is priceless for developing the expertise required to innovate. The 3M Company recognizes this (at least they did the last time I checked). They require their staff to invest at least 30% of their time in their own hair-brained schemes just to see what comes of it. Ever used a Post-It®? There you go.
|credit: NY Times|
If we have that between us, especially now on this imperiled, shrinking Earth -- our one and only safe harbor in the universe -- than we have hope. Not made-up-by-politicians-empty-rhetoric-hope, but real, meaningful, justifiable, actionable, save-the-world hope. And that’s what Dawn gently, gracefully, modestly extends to us as she circles silently around that gray stone a 120 million miles away. We should be awestruck and proud -- not as Americans, but as humans.
Thanks, NASA, and thanks to all the folks who make NASA tick.
|photo: Australian Aboriginal Astronomy|