[meteorite-list] Beyond Deep Impact: Possible Targets After Fireworks

[Ron Baalke]

http://www.space.com/businesstechnology/050629_deep_impact_beyond.html

Beyond Deep Impact: Possible Targets After Fireworks
By Leonard David 
space.com
29 June 2005

BOULDER, Colorado -- Deep Impact's scheduled run-in with a comet this
holiday weekend may not be a one hit wonder. Scientists are studying
other potential targets after the spacecraft completes its dramatic
mission at Comet Tempel 1.

The main mission for the NASA craft 
is to create celestial fireworks early Monday morning (late Sunday in
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 kinetic energy of the
collision is expected to create a crater the size of a football field
and propel material from the comet's nucleus into space.

>From its vantage point several hundred miles away, the Flyby spacecraft
will use its telescopes, cameras and spectrometer to monitor the impact,
all in an effort to study what's underneath the comet's icy surface.

Then the Flyby spacecraft might be retargeted to another faraway comet.

High-tech checkup

"We've been working on an extended mission," said Monte Henderson,
Deputy Director of Programs in Civil Space Systems for Ball Aerospace &
Technologies Corporation 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/no-go decision can be made to send it on
a 3.5 year cruise to Comet Boethin.

That object orbits the Sun every 11 years. It was discovered on January
4, 1975 during a routine comet-hunting session carried out by the now
deceased Reverend Leo Boethin of the Philippines.

Henderson told SPACE.com that shortly after Deep Impact's slam-dunk with
Comet Tempel 1, engineers will give the Flyby spacecraft a high-tech
checkup. Particular attention will be paid to how much dust and debris
that spews out from the comet has hit the Flyby craft.

Will instruments onboard the Flyby spacecraft remain in tip-top shape?
Or have their optics been sandblasted?

Potential damage

The Flyby spacecraft -- nearly as large as a Volkswagen Beetle --
carries two of the three primary instruments, the High Resolution
Instrument (HRI) and the Medium Resolution Instrument (MRI), for
imaging, infrared spectroscopy, and optical navigation.

Debris shielding is a key part of the Flyby spacecraft's design.

As the spacecraft passes through the inner coma of Comet Tempel 1 it is
in danger of being struck by small particles that could damage the
control, imaging and communication systems.

To minimize this potential damage the Flyby spacecraft is rotated before
it passes through the inner coma. That debris shielding should provide,
it is hoped, complete protection to the flyby spacecraft and its
instruments.

The spacecraft's main deck serves as a back wall and an aluminum shield
protects the Flyby spacecraft.

Fuel budget

"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 to put
it on a 3.5-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 (JPL) in Pasadena, California of trying out
autonomous navigation software, Henderson said.

Additionally, Deep Impact's Principal Investigator, Michael A'Hearn at
the University of Maryland, is also 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 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 has a problem.

Focus anomaly

Deep Impact's high resolution telescope has experienced a "focus
anomaly," Henderson explained. "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.

If all this sound's a bit familiar, think Hubble Space Telescope. It too
was initially focus-challenged. Eventually, the Earth orbiting
observatory was outfitted with corrective optics thanks to a space
shuttle servicing crew. For Deep Impact, there's no chance for any
on-the-spot, hands-on help.

Gee-whiz factor

Experts at the Hubble Space Telescope Science Institute, however, had
computer based algorithms - 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.

And as the $333 million Deep Impact mission closes in on its prey,
Henderson said the team is ready for action.

"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."