Put simply, the original Japanese version of the anime states it's (supposedly) one million kilometers long (a little over 621 thousand miles), while the English translations state that it's (again supposedly) ten thousand miles (a little over 16 thousand kilometers).
I'm rather curious if there's any documented reason for this huge discrepancy in the stated length, especially since the Japanese version makes Goku seem absurdly super-human (doing the math and accounting for him having to restart part way through, he still ran at a speed of more than 200 kph (or about 125 mph), which is about 5.5 times the typical sustained top speed for a well trained human distance runner), while the English version makes him sound honestly pathetic (same math there works out to about 3 kph (or about 2 mph), which is a leisurely walk even for most lazy humans).
A quick search online has turned up nothing, and I honestly wouldn't be surprised if it's just another case of the questionable translation quality that was the norm at the time for a majority of anime series. However, there are a couple of other cases in the series where questionable original translations (such as using 'spirit bomb' for both the soukidon and the geki-dama) have documented reasons (usually stupid translators) and this one doesn't seem to fit the usual 'stupid Americans' excuse that most of the other cases both in DBZ and other anime from that time do.
