The Deep Impact mission to propel a projectile into Comet Tempel 1 may not be a one-hit wonder. NASA scientists are studying other potential targets for the main spacecraft to study once its dramatic initial mission is completed.
The main mission is to create some celestial fireworks early July 4 (It will be late July 3 in the western United States). A Flyby vehicle will deploy an Impactor probe for the hit-and-run encounter. The Impactor that thumps into Comet Tempel 1 is likely to vaporize upon impact. The collision is expected to create a 120-meter crater and propel material from the comet’s nucleus into space.
From its vantage point several hundred kilometers away, the Flyby spacecraft will use its telescopes, cameras and spectrometer to monitor the impact, all in an effort to study what lies beneath the comet’s icy surface.
Then the Flyby spacecraft might be retargeted to another faraway comet.
“We’ve been working on an extended mission,” said Monte Henderson, deputy director of Programs in Civil Space Systems for Ball Aerospace & Technologies Corp. here. The company designed and built the two-part spacecraft specifically for the Deep Impact mission.
Depending on the overall health of Deep Impact’s Flyby spacecraft after monitoring Comet Tempel 1, a “go” or “no-go” decision can be made to send it on a three-and-a-half year cruise to Comet Boethin.
That comet, which orbits the Sun every 11 years, was discovered Jan. 4, 1975, during a routine comet-hunting session carried out by the now deceased Rev. Leo Boethin of the Philippines.
Henderson said particular attention will be paid during the high tech checkup to how much dust and debris has hit the Flyby spacecraft after the impactor strikes.
The Flyby spacecraft, which is about the size of a a Volkswagen Beetle, carries two of the three primary instruments for imaging, infrared spectroscopy and optical navigation: the High Resolution Instrument and the Medium Resolution Instrument .
As the spacecraft passes through Comet Tempel 1’s inner coma — the cloud of gas that surrounds a comet’s solid nucleus — it risks being struck by small particles that could damage the control, imaging and communication systems.
Debris shielding is a key part of the Flyby spacecraft’s design to minimize such potential damage . Before passing through the inner coma, the spacecraft is rotated, which should provide it complete protection .
The spacecraft’s main deck serves as a back wall, and an aluminum shield protects the Flyby spacecraft.
“After the encounter, we’ll do a mini-commissioning of the Flyby spacecraft,” Henderson said. If the reassessment is positive, a good portion of the remaining fuel on the Flyby vehicle will be used for a three-and-a-half -year jaunt to reach Comet Boethin. The redirecting maneuver would need to occur sometime before July 24, he said.
“If we don’t have good solid science instruments to use at Comet Boethin, we probably wouldn’t want to expend our entire fuel budget. It would be more prudent to step back and figure out what else can we do,” Henderson said.
Given a healthy Flyby spacecraft, there is discussion at the Jet Propulsion Laboratory in Pasadena, Calif., of trying out autonomous navigation software, Henderson said.
Additionally, Deep Impact’s Principal Investigator, Michael A’Hearn at the University of Maryland, College Park, also is considering a request for proposals from the scientific community. Ideas will be welcomed, Henderson added, as to what other observations could be done with the Flyby spacecraft en route to zipping by Comet Boethin.
Big sweaty palms
Henderson admitted that it has been difficult to focus on an extended mission. There are many challenges facing the dual spacecraft encounter with Comet Tempel 1.
The “big sweaty palms” for the $333 million Deep Impact mission is getting the Impactor on its own, Henderson said. “We’ve been able to test it via the umbilical through the Flyby spacecraft, but the Impactor has never flown by itself.”
Then there’s the issue of the high-resolution telescope that’s onboard the Flyby spacecraft. It is the largest telescope to fly in deep space and will record the details of the collision – but it has a problem.
Deep Impact’s high-resolution telescope has experienced a “focus anomaly,” Henderson said . “It’s an engineering accident and it is unfortunate.”
Engineers found after Deep Impact’s launch that a reference flat used to calibrate the high-resolution telescope’s mirror on the ground did not accurately represent what cold temperatures the mirror would experience in space. “After a lot of analysis with that mirror, we essentially redefined what flat is for high-resolution telescopes,” Henderson noted.
This problem has frustrated scientists before with the Hubble Space Telescope, which initially also was focus-challenged. Eventually, the Earth-orbiting observatory was outfitted with corrective optics thanks to a space shuttle servicing crew — but that is not an option for Deep Impact.
Experts at the Hubble Space Telescope Science Institute, however, had a way to de-blur and sharpen up Deep Impact images using a technique called deconvolution. Henderson said through this process, Deep Impact’s picture taking can be “massaged and tweaked” on the ground to greatly overcome the out-of-focus problem.
“We’ve done test … done everything we can be ready for,” Henderson concluded. “This is a one-time exciting event. It has been an engineering challenge, but also has a gee-whiz factor that seems to have captured a lot of public attention.”