Q: Why do scientists want to impact a comet?
Scientists expect significant changes in the material that makes up the comet as you go deeper into
the comet, just as the material of the Earth changes significantly the deeper you go underground.
Only an impact mission can study the interior of a comet below the evolved surface layer. Other
missions, such as ESA's Rosetta Mission, are being planned that will land on a comet and scratch
the surface. But the Deep Impact Mission is the only one that will excavate a large enough hole to
see the interior composition of the comet. Take a look at our science
Q: Who came up with the idea to impact a comet?
The idea of impacting a comet has been around for a long time and has been seriously discussed as
the ending scenario for orbiter missions. The idea dates back at least 30 years to the book 2001
written by Arthur C. Clarke. Mission teams from a variety of other missions have studied the concept,
including the team of the Comet Rendezvous Asteroid Flyby (CRAF) mission that was subsequently
cancelled by NASA in the mid 1990's and the team of the
Giotto mission (which
was flown by ESA to comet Halley). The Deep Impact project was first proposed in a somewhat
different form and rejected in 1996. In 1998 the team re-proposed the idea with a number of changes
and on the basis of this proposal was one of two Discovery missions ultimately selected in July
Q: Who is working on Deep Impact?
Project members are affiliated with numerous organizations. The science team includes members
from The University of Maryland and other universities, NASA/JPL (the Jet Propulsion Laboratory),
and Ball Aerospace & Technologies Corp. (BATC). You can learn more about the science
team and their specific roles on the Deep Impact mission here.
In addition to the scientists, there are many other people working on the mission. To learn more
about the different mission roles, take a look here.
Q: Will the Hubble Space Telescope (HST) be
involved in this project?
Yes. The HST will be imaging the encounter before, during and after the impact. It will be joined by several large and small
ground-based telescopes at various locations around the world.
Q: Will any ground-based telescopes be observing the impact?
The most spectacular images will come from the flyby spacecraft. But many ground-based
telescopes will be collecting data in the optical and other wavelengths to complement the data from
the flyby spacecraft. Details about the observing opportunities can be found
Q: Will I be able to see the impact?
We hope so! Unfortunately, one side of the earth will be facing away from the comet at the time of
impact so that side won't be able to see it directly. However, we plan on broadcasting the event on
television and on the internet so that everyone all over the world can see the impact. Details about
observing the comet can be found here.
Q: How will the data get from the spacecraft to the scientists?
The data gathered by the spacecraft is transmitted to the ground via X-band communication. The
data will go through NASA's Deep Space Network to JPL and then to Cornell University and the
University of Maryland. They then get distributed to the science team for analysis.
Q: When are launch and impact?
Launch was 12 January 2005. The impact is planned for 05:52 4 July 2005 UT. Take a look at the
mission timeline to see where we are in the schedule. To find out when the impact will
occur in local time, see our page of Questions About the Encounter.
Q: What tasks exist between 2000 and 2005, before the launch?
The flight systems will be built between March 2001 and October 2003. It is then delivered to Cape Canaveral at the end of
2004 for launch at the beginning of 2005. Meanwhile, the science team will continue observations of the
comet to better understand the environment that the spacecraft will encounter. Studies of cratering
processes, both lab simulations and computer models,
will continue. And the details of the observing sequence -- when to take images, when to take
spectra, and when to send data back -- for the mission will be designed. Be sure to watch our
timeline to see where we are in the mission.
Q: I gather we'll see the collision in full-motion video
(televised) because the event will be near enough. At what point is full-motion video no longer possible, i.e. at what distance
We will not be able to observe the impact in "full motion video" (ie., at a rate of 30 frames/sec) because of data rate limitations
both in the imaging cameras and in the data link from the spacecraft to Earth. The cameras are designed to make accurate
scientific measurements, not primarily to produce video. As such, the imaging detectors are read out relatively slowly in order
to keep the noise levels low, and the data are encoded to 14 bits to make the most accurate measurements possible. At their
full frame format (1024x1024 pixels), the cameras will output only one frame every 1.7s. At impact and for the following few
seconds, we plan to use subframe imaging modes (64x64 pixels in the Medium Resolution Instrument and 256x256 pixels
in the High Resolution Instrument). With these formats, the cameras can produce frames at rates of about 20/sec for the MRI
and 5/s for the HRI. So we will be able to reconstruct the impact itself with pretty good time resolution. Even if the cameras
could produce frames at 30/sec, the data link to Earth at the range of the comet at impact would not allow the data to be
returned to Earth fast enough to support full-motion video in real time. The maximum data rate that we expect to use given the
spacecraft telecommunications system capabilities and the receiving capabilities of the Deep Space Network stations on Earth
is about 300,000 bits/s, which is about 200 times slower than needed for full-motion digital video. The data link could support
full-motion video only at ranges less than about 10 million km.
Q: How precisely known will the time of the impact
be, and how soon will you know it?
Our targeted impact time is 05:52 4 July 2005 UT plus or minus 3 minutes. In late June, 2005, we should know within 1 minute. Two or
three days from the impact (July 2/3, 2005) we will know within 30 seconds. Five minutes away from impact we will know within 2.7
seconds. The web site will be updated with the time of impact as the event gets closer.
Q: How do you get all the data from the spacecraft
back to Earth?
Both the flyby and the impactor spacecraft will gather images and other data as they observe the comet - but what good is that if
we don't get it back to Earth? That's why the huge white antennas of NASA's Deep Space Network (DSN) are so important. They
are positioned about 120 degrees apart around the world in: Spain, Australia and in California, USA. From there, they
communicate with and listen to all our spacecraft. Not only will these antennas receive data, but they will send it on for distribution
to our scientists and engineers at Jet Propulsion Laboratory, University of Maryland and Cornell University. In addition to collecting
data, these dish-like structures serve as the communication path between the Deep Impact team on Earth giving instructions, and
the spacecraft replying back to the team. It's through this two-way communication that the team can confirm the health of the
spacecraft and give any changes needed in its flight. The DSN will be even more important in the 24 hours that the impactor aims
at and hits the comet. So much data will be coming down for the 14 minutes of primary science that the team will actually time the
collision to make sure they have overlapping coverage from 70-meter dishes in two locations in the world. This makes the DSN a
truly important partner to the Deep Impact project. The next time you think of spacecraft in space - remember the Deep Space
Q: Why does a mission have a "launch period" and
what does that mean?
The launch period is the number of days during which a mission can launch and still reach its target. The launch period is
determined by several factors such as the current position of the planetary body they need to reach combined with the power
of the launch vehicle. The launch period can be a number of days or weeks depending on the mission. Deep Impact had
a launch period of 21 days beginning 12 January 2005. A spacecraft can be ready, installed in its launch vehicle, and on
the launch pad and certain circumstances can put it on hold. Some of the factors are:
- Bad weather
- High winds
- A launch vehicle of the same type has problems on another mission
- The Deep Space Network antenna assigned for initial acquisition of the spacecraft has a problem and is not rated "green" and
ready to track.
- A possible problem with the spacecraft or launch vehicle during last testing
- A violation of the surrounding secured air, land or ocean space
- A breakdown in the communication system for the launch team
For many systems needed during launch, there are additional backup systems but they are very careful to assure the success
of a launch as much as possible before they proceed with the countdown.
Q: Are you using explosives to make the crater in
Comet Tempel 1?
There is no bomb nor explosives on our spacecraft. When the impactor hits the comet, it forms the crater simply from the
transfer of kinetic energy. For example, 2 cars traveling very
slowly only get crunched a little when they hit, but two cars traveling very fast can get demolished upon impact. Same thing
with Deep Impact's impactor and the comet, they are both traveling very fast (faster than cars, faster than bullets) so the
crunch they make is enough to carve out a good-sized crater on the comet without using explosives.