How the idea for the Deep Impact mission developed
Staff Consultant and Engineer
at Ball Aerospace & Technologies Corp.
B.Eng. in electrical engineering 1995, University of Liverpool
Several projects and proposals laid the groundwork for Alan
Delamere and his science colleagues to arrive at the precise
idea for the Deep Impact mission. Beginning in 1978,
Delamere and Mike Belton, then at the National Optical
Observatory in Tucson, collaborated on a project involving
"We got Halley data and investigated it and found the comet
was far blacker than we had imagined, blacker than coal. So
we asked ourselves: how could this happen?" Delamere said.
"There were many comet models, such as the dirty snowball
concept, and we became increasingly curious as to just how
this black layer accumulated. We suspect that as the comet's ice
dissipates, dust is left which becomes a loose, outer crust
insulating the trapped, inner comet.
"In 1996 Belton and I decided to submit a proposal to explore
the exterior of a dead comet, Phaethon, using an impactor. At
this point Mike A'Hearn, now Principal Investigator for Deep
Impact, joined our team. We proposed to the NASA Discovery
Program using a large mass hitting the comet at about 38 km/sec.
We found a way to hit the comet and observe the crater
development. However, the proposal wasn't funded because the
science panel was not convinced that Phaethon was a comet and
they did not believe we could hit it.
"But the idea evolved and in 1998 Mike A'Hearn took over the team
leadership and proposed to hit an active comet, Tempel 1. We added
a fine guidance system to the impactor. This approach convinced
reviewers we could hit the comet.
"I'm looking forward to finding out a lot about the nature of
inner cometary material as well as the crust. Deep Impact is
letting us gather a great deal of information about these little-known
"The biggest challenge of the mission is making sure we have
a very stable flyby spacecraft that is able to track the event as
the impactor reaches the comet. We'll have 800 seconds or
so to gather high fidelity images and data. All this makes the
flyby spacecraft critical because it will be traveling through a
hazardous area filled with cometary material. Moreover, it
needs to safely pass through the orbital plane of the comet where
there are cometary fragments that could destroy the spacecraft.
We've planned to cross the orbital plane as late and as far away as
possible while still maintaining a distance that will allow us to get
high resolution images."