The last supply mission to the International Space Station was with the Russian Progress M-27M spacecraft. The launch was successful, but after entering low Earth orbit it became unresponsive to commands. It now appears to be tumbling in a non-stable orbit and will experience an unplanned re-entry.
There are many questions to consider, here are a few.
Of course everyone knows it's difficult to operate things in orbit. You plan for a re-supply mission but bad things sometimes happen. Fortunately the ISS has enough supplies to make it until the next scheduled mission. But what about coffee? Yes, astronauts have a special cup that allows them to drink coffee in zero-g.
It's not so simple. If you had an object in a circular orbit around the Earth, you would think the object would just stay there forever. This would be true if the object's motion was governed only by the gravitational force. However, even at the orbit altitude of the ISS there is a tiny bit of air. Well, maybe it would be wrong to call it air but either way there is a drag force on the ISS and other spacecraft that would eventually slow them down. In fact, the ISS will often use the left over fuel from supply craft to reboost the orbit (increase speed) in order to keep it stable.
People like to think about the trip to the ISS like it was a trip to Disney World, but it's not. Disney World stays in place while you are traveling there. Also, you can take many different paths to reach your land-based destination. Oh, well then it must be like trying to catch up to a moving ship, right? No, it's much more difficult than that also. Here is my orbit rendezvous analogy. Suppose there is a boat that is driving by a dock and you want to jump on.
If you miss that first pier, you have to run to the second one before the boat gets there. Maneuvering in orbit is similar to running on the dock. You can only go on certain paths. For more details about orbital rendezvous, check out this post I wrote for the European Space Agency.
This isn't such an easy question. Current estimates are that it will re-enter the Earth's atmosphere possibly very early on May 8 (03:00 - 05:00 UTC) SpaceFlight101.com keeps track of predictions for you.
In order to get a very accurate re-entry prediction, you would need two things. First, you would need a very accurate trajectory of the spacecraft right now. This isn't so difficult since engineers can use ground-based radar to determine position and velocity. The other thing you need to know is the weather. As the weather on Earth changes, the atmosphere can expand and interact with the spacecraft earlier than you would expect. On top of that, the density of the atmosphere can increase from almost nothing to something significant fairly quickly. This means that with a lower atmosphere, the Progress can maintain its speed and travel much farther to a location where the atmosphere is again different.
Since you don't know WHEN the Progress spacecraft will re-enter the atmosphere, you don't know WHERE it will enter. The spacecraft is traveling with a speed over 7,000 m/s. If it is delayed in it's re-entry by just 1 second, it could go 7 km further. With a re-entry window of +/- 24 hours, it's difficult to say where it will land.
It is very likely that parts of the spacecraft will make it to the surface of the Earth. As it moves into the Earth's thicker atmosphere, it compresses the air in front of it which heats up both the air and the spacecraft. Many objects that re-enter in this manner just get completely obliterated from the high temperatures. However, big things aren't the same as small things (I know that seems obvious). Let me show the difference for two spherical objects entering the atmosphere. Sphere B has a radius twice that of sphere A.
Let's assume that most of the heating of the object comes from the front surface of the object and this goes into increasing the thermal energy of the whole thing. The surface area is proportional to the square of the radius, but the mass is proportional to the radius cubed. So, by doubling the size (doubling the radius) you increase the surface area by a factor of 4 but you increase the volume (and mass) by a factor of 8. This means that bigger objects won't increase in temperature quite as much and be more likely to make it to the ground.
Of course the Progress spacecraft isn't actually a solid object. It will still likely break up on re-entry. However, it still has some larger pieces that are dense enough to possibly survive all the way to the surface.
As bonus reading material, you should check out Randall Munroe's What If? blog where he looks at compressive heating for a steak during re-entry.
Absolutely. If the re-entry happens near you, it should appear as a brilliant streak of light in the sky. The compressed air during re-entry gets hot enough to create a plasma trail that can be seen from the surface. But how can you track the spacecraft? I think the best way is to use a site like heavens-above.com. Just enter your location and the site will give you times and locations in the sky in which you can view all sorts of things. You can get details about the next time the ISS passes over (which you should see at least once because it's awesome) or when you can see the Progress M-27M.
It's been a while, so you might not remember, but someone tried this before. In 2001, Taco Bell put a big target in the Pacific Ocean in an attempt to have the Mir space station hit it on re-entry. If the Mir hit the target, Taco Bell would give everyone in the USA a free taco. Of course, the space station missed the target. No free tacos.
