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Can the Deep Impact spacecraft return to Tempel 1 and look at the impact site? No, but the Stardust spacecraft can!

This question came up immediately after impact. The question went to Bill Blume and the JPL mission design team.

Bill replies:

As we expected, there was no chance to get back to Tempel 1 until the next perihelion (5.5 years later), but we were surprised that there really was a viable trajectory to get back to the comet:

• First Earth Flyby (Jan 2008) - Gravity assist from 1.5-year orbit to a 1-year orbit
• Second Earth Flyby (Jan 2009) - Gravity assist from a 1-year orbit to a Tempel 1 intercept trajectory
• Tempel 1 Flyby (Jan 2011)

This was found by our trajectory expert Dr. Chen-wan Yen shortly after the July 4th encounter. The delta-V for this mission wasn't impossible (about 136 m/s vs. 85-100 m/s for Boethin), but there were a number of sticky issues and we were suddenly in a time crunch to make a decision. This was because the operations staff was rapidly moving off to other projects and a maneuver needed to be executed fairly quickly to target an Earth flyby to enable an extended mission.

The PI, Mike A'Hearn, decided that an attempted return to Tempel 1 too risky because of the following factors:

The return required two more years in flight, which substantially increases both cost and risk to spacecraft performance.

There is a long period when the spacecraft is behind the sun as viewed from Earth, which hampers navigation.

At this encounter, the range to Earth would be 2.3 AU (compared to 0.9 AU at the July 4th impact), which results in lower data rates and more use of the largest 70-m tracking antennas.

The geometry of approach is such that in the imaging attitude the IR spectrometer would be warm and its performance would be seriously degraded.

When weighed against the possibility of studying another comet in the 1-4.8 micron spectral region, the option to target the spacecraft to Comet Boethin was chosen and the Earth-return targeting maneuver was executed on July 20th.

So the Deep Impact spacecraft cannot return to Tempel 1.

The Stardust spacecraft, which successfully sent back comet particles to Earth in 2006 proposes to go to Tempel 1 and look at the crater and changes to the comet after the Deep Impact encounter. The Deep Impact spacecraft proposes to visit and observe a different comet in the future.