Hi Senthil,
Spacewalk and Satellite both are from RedHat but the difference is that Spacewalk is a project where changes will occur very frequently. Spacewalk is free to download and its tested and supported by community users. There is no pay for support for Spacewalk, and its not supported by the Red Hat Global Support Services.
Satellite is a stable product available from Red Hat Network and its not free even the support.
For more information visit: http://spacewalk.redhat.com/faq.html
