Google wants to usher in the world of wireless broadband so much that it is willing to spend vast sums to make it happen. It bid more than $4.6 billion in the recent FCC spectrum auctions (which it ended up not having to pay because it lost to Verizon), is backing the WiFi 2.0 initiative, and today it announced that it plunked down $500 million to shore up the new Clearwire-Sprint WiMax business.

Google is very clear about why it invested—to ensure that the resulting broadband network is as open as possible and accepts Android handsets and devices. It also sounds like Google may also be the default search engine on devices connected to the network.

This morning, it explains all of this on the Official Google Blog:

In addition to our $500 million contribution as part of the investment group, we will provide search and applications to the network’s users, and will work with Clearwire to offer additional services and applications. This will include jointly creating an open Internet protocol to work with mobile broadband devices (including Android-powered devices) and implementing other open network practices and policies.

We believe that the new network will provide wireless consumers with real choices for the software applications, content and handsets that they desire. Such freedom will mirror the openness principles underlying the Internet and enable users to get the most out of their wireless broadband experience. As we’ve supported open standards for spectrum and wireless handsets, we’re especially excited that Clearwire intends to build and maintain a network that will embrace important openness features. In particular, the network will: (1) expand advanced high speed wireless Internet access in the U.S., (2) allow consumers to utilize any lawful applications, content and devices without blocking, degrading or impairing Internet traffic and (3) engage in reasonable and competitively-neutral network management.

Google desperately wants access to future wireless broadband networks of all stripes and sizes,but it wants to avoid having to build and operate its own. Deals like this show that it is willing to pay to play. If Clearwire should ever go bust, though, that’s $500 million down the drain.