After a voyage of 173 days and 431 million km, Nasa's Deep Impact spacecraft will get up-close and personal with comet Tempel 1 on July 4. The first of its kind, hyper-spped impact between space borne iceberg and copper fortified probe is scheduled for approximately 1.52 am on July 3. The potentially spectacular collision will be observed by the Deep Impact spacecraft, and ground and space-based observatories.