Nov. 4th held a real treat: NASA’s EPOXI mission made a very successful close encounter with a comet known as Hartley 2. In fact this encounter is the closest a man-made object has ever come to any comet – coming within 435 miles/700 km. This is only the fifth time a spacecraft has “visited” a comet in this way. Many may recall the “Deep Impact” mission which launched in 2005 and aimed to rendezvouz with comet Tempel 1. It did just that on July 4th, 2005. That mission involved the spectacular release of a washing machine-size probe, known as the “impactor,” which collided with the comet, releasing material which was imaged by the Deep Impact spacecraft (which is, in comparison approx the size of a VW beetle).
Scientists used the data and spectra they observed as a means of better understanding the nature and composition of the comet. Although the Deep Impact spacecraft had completed its mission, NASA scientists saw potential for continuing to use the still functioning craft and set about determining a new scientific adventure for the probe. After realizing that a new mission could be accomplished using the same imaging equipment, scientists decided on a new target – the comet Hartley 2.
Hence the EPOXI mission was born. Same spacecraft, different set of of targets – which is why you may be hearing the term “Deep Impact” frequently when listening to coverage of the mission. EPOXI is actually a combination of two scientific investigations. The new mission name “EPOXI” comes from combining two scientific investigations being undertaken by the spacecraft:
EPOCH: Extrasolar Planet Observation and CHaracterization
DIXI: the Deep Impact eXtended Investigation of comets
So it came to be that the original $252 million dollar spacecraft was to fly an additional 2.9 billion miles (4.6 billion Km) to hunt down Hartley 2 arriving 5 years later on Nov. 4th 2010. During it’s time cruising between these comets, the Deep Impact spacecraft completed the Extrasolar Planet Observation and Characterization part of it’s mission objective: primarily a search and study of extrasolar planets and moons.
Catching comet Hartley 2 was to be significantly more challenging than the approach to Tempel-1 because it is about a seventh of the size at roughly 1.25 miles across (2 km) and yet still releases about the same amount of material into space. This makes the comet “flit around the sky” according to mission navigator Shyam Bhaskaran of NASA’s Jet Propulsion Laboratory. In fact the comet moves so much that three maneuvers were needed to adjust the spacecraft’s course – the latest last minute maneuver was 2 days ago!
Finally, yesterday at 10:10am EDT, the EPOXI spacecraft reached it’s goal, flying past Hartley 2 at a distance of 435 miles. The comet came by the EPOXI craft at 12.3 km/s or more than 27, 000 miles per hour.
The flyby went off without a hitch and within an hour 5 spectacular high resolution images arrived at Earth:
Expect more- much more in the coming months. Today’s flyby and the approach leading up to it have already provided a mountain of data for scientists and by Thanksgiving when EPOXI will shift it’s gaze from Hartley 2, scientists expect around 120,000 comet images to have been downloaded to the scientists computers.
NASA scientists have said that they feel that by reusing the Deep Impact spacecraft in this extended mission they have succeeded in getting a very good deal. Although extending the mission into EPOXI has cost an additional $45 million, Ed Weiler, associate administrator at NASA’s Science Mission Directorate has said that this amounts to about 10 percent of what it would have cost to launch a whole new mission. In his words: ”The spacecraft has provided the most extensive observations of a comet in history.” “Scientists and engineers have successfully squeezed world class science from a re-purposed spacecraft at a fraction of the cost to taxpayers of a new science project.”
So what is next for Deep Impact and EPOXI? Sadly the Deep Impact spacecraft is running out of fuel, so whether it will remain as a stationary observing platform or set it’s sights on another comet is unknown at this time. As for comet Hartley 2, its days are numbered too. Although it will continue to zip around the Sun for a while longer, (it orbits the Sun once every 6.5 years) it seems the sun is “cooking” 3 to 5 feet (1 to 1.5 meters) of material off the comet’s surface on each orbit. With its smallest side measuring about 1650 feet (500 m), Hartley 2 will not be around for very much longer.
Whatever the future holds the Deep Space/EPOXI mission has certainly shown us a new way to think about “recycling”, NASA style. Rethinking and repurposing missions to get the most science for our buck – that’s something I think we can all get behind.