HALO jumps are used to enter hostile territory undetected when threats to both Airmen and aircraft are expected.
The Logistics of Getting Man to Mars
No one knows how many billions of dollars a human mission to Mars will eventually cost, and the enormous financial burden will have to be shared by other nations. The epic endeavor will be far more dangerous and technically difficult to accomplish than it was when we sent men to the Moon over three decades ago. The Moon was only a short hop of 240,000 mi. compared to a 47-million-mi. voyage to Mars. If an Apollo 13–type disaster were to befall them, the astronauts wouldn't be able to return again to Earth. Read more at http://www.infoplease.com/ipa/A0778174.html#ixzz24ThhGJPy