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NASA's Deep Impact Moved Into Cruise Phase
karvind writes "NASA is reporting that the Deep Impact spacecraft has completed the commissioning phase of the mission and has moved into the cruise phase. Deep Impact mission planners have separated the spacecraft's flight operations into five mission phases. Cruise phase will continue until about 60 days before the encounter with comet Tempel 1 on July 4, 2005. Deep Impact has been covered on slashdot before"
Not the fastest, as Sandia National Laboratories have used one of their railguns to propel a .1 gram object at 16,000 m/s (nearly 36000 miles per hour). A spacecraft is certainly larger than that though, so perhaps the greatest kinetic energy of any such collision?
uhhh, the reason for the wide range in their estimates is because the composition of the comet is largly unknown. They won't know what its made of until they smash into it and attempt to get some readings from the core of the comet. So it nearly impossible for them to attempt to calculate a reasonable size for this impact since the size of the impact will be determined by the comets composition. Thats the whole point of the mission; to find out what the comet is made of. Since the comet was made during the begining of the our solar system's creation it will give us a good insight into how our solar system was created and what type of materials are most abundant.
Kinetic energy is 0.5*m.v*v. I guess that the probe is at least 370Kg (3700000 more than your bullet). So to reach the same kinetic energy they only need roughly 0.0005 of the velocity, that is 8 m/s-1. I tried a quick search and found it it is 370 kilos but could not find out what the speed is, but due to relative velocity difference you can bet it is faaaar more than your bullet in KE.
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wouldn't it be easier to just drill a core sample from the comet?
No.
In the solar system frame, the comet is approaching very fast. Its aphelion is just inside Jupiter's orbit. Our probe is poking along at an Earthlike velocity in a roughly Earthlike orbit- it's the comet that's going to crash into the probe, really, not the other way around.
To get your Black & Decker to it in one piece, you'd have to accelerate to 0 mph relative to the comet. That alone requires gravity assists off other planets. Then you need to design robotics to move around on an object with almost no gravity and a surface that can't be surveyed very well from Earth (thanks to the bright coma). You'd have to drill a hole into a material of unknown composition, in a process lasting minutes to hours rather than microseconds. That means you'll have to make decisions at certain points during the operation, requiring bug-prone programming or impractical communication links to ground-based controllers.
Simply allowing the comet to crash into something and taking pictures of the explosion from a distance is much cheaper and more likely to work.
In addition to millionthmonkey's reply, I want to add that they're expecting a very deep hole covering a large area (potential up to 150 feet deep). There simply has been no low gravity, remote deep drilling techniques or devices developed. This will hopefully give the scientists a look at any strata that may exist within the comet, as deep as whatever is blown out. Also, the size of the crater should allow help them figure out how well bound together comets are and they will see particles blown out from a large area of the comet's surface, not just the diameter of a drill.
A lander mission has it's own advantages, which is why some scientists want to land on a comet, as well. There's definitely an advantage in getting a lens or a sprectrograph right up against the item of interest and looking at the microscopic instead of macroscopic picture. It's also much more expensive and probably cuts down the number of reasonable targets, since you've got to match orbits with the comet.
The asteroid landing mission another poster mentioned was easier because asteroids generally have less eccentric orbits, which means their velocity in the inner solar system will be closer to that of earth. The landing was actually a bonus feature the science team decided to try after the primary mission of orbiting, photographing and mapping the asteroid was completed, just because they thought it might work. Thanks to the low gravity, the crash/landing actually did work. Theoretically, the probe is still in good condition on the surface and can continue to return images and data, although I don't think there will be another time when it simultaneously faces the earth (for radio contact) and the sun (for power) for several years.
This will hopefully bring to fruition the hard work of Jana and Audrey and all those other Honolulu-based astrobiology folks for whom I sometimes point this scope at comets.
Now I just have to remember to ask way far ahead of time to be running the scope around then. Or... maybe not. Maybe I should just drive up to the visitor station and kick back with their 16-inch Meade and some popcorn.
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