Alaska's junior U.S. senator, Dan Sullivan, isn't surprised by the latest missile launch from North Korea -- but is worried that the threat is now "at our doorstep" with the use of longer-range missiles.

North Korea launched three short-range missiles Friday. Military officials determined that these missiles did not pose a threat to North America or Guam. U.S. Pacific Command officials say one missile appears to have blown up almost immediately after or during launch, telling CBS News that the other two flew about 155 miles.

When asked Friday whether North Korea could hit Alaska with a missile armed with a nuclear warhead, Sullivan told KTVA, "I think the estimates are 'not yet.' But they're making a lot of progress, and the estimates on that are 'soon' -- and not just Alaska, but the Lower 48."

Sullivan is currently working on legislation to bolster U.S. missile defense capabilities.

"My bill would do a number of things," Sullivan said. "It would significantly increase our capacity. By the end of the year there's going to be 44 ground-based missile interceptors at Fort Greely. My bill calls for at least 28 more."

Sullivan also says there's a study by the Pentagon on fielding up to 100 missile interceptors. He's hoping the missile defense bill will pass relatively soon.