Bushe and Shelley had visited Bechuanaland the previous year, but had got lost, and were arrested by the Transvaal authorities, who were apparently trying to stop others from visiting Lake Ngami. On the 1851 trip they were more successful.
The previous year, Bushe and Shelley's journey to Bechuanaland ended in arrest by the Transvaal authorities due to getting lost and being caught trying to visit Lake Ngami. However, they were able to successfully complete their trip in 1851.