Is there a way to scramble the GPS signal
GPS satellites transmit several signals. The lowest power and least accurate signal, the C-code, is unencrypted. It is the one used by civilian GPS receivers. Just before he left office in 2000, Bill Clinton set up the Presidential Commission on GPS (I forget the exact name, but you get the idea.) One of the first actions of the commission was to remove the "military error" from the C-code. They also issued a statement to the effect that the U.S. would "never" introduce error or deny access to the C-code. George Bush shut down the commission shortly after assuming office, but the damage had been done. The U.S. considered scrambling the C-code during Operation Enduring Freedom, but decided against doing so.
The C-code uses less bandwidth and is inherently less accurate than the wider bandwidth and more powerful encrypted military signals. In addition errors were deliberately added to decrease the accuracy.
The original premise for the unencrypted c-code was that it would always be less accurate than inertial navigation, and would therefore never provide an adversary any military utility. Clinton was apparently indifferent to such considerations. The existing C-code is reliable and accurate enough for worldwide free access for end users. It costs the U.S. about a billion dollars a year to maintain, which works out to about a penny a day per person. Your welcome. The GPS system was so perfectly worked out and implemented that is has discouraged serious imitation. The initial investment is about 20 billion dollars in sunken costs, to duplicate what is already available.