Thirty years ago, the United States launched the first space shuttle mission from Kennedy Space Center. It marked a new era of American leadership in space and showed that Americans would be committed to being first in space and on the cutting edge of scientific progress to improve our lives.

This week, President Obama will attend the launch of the Space Shuttle Endeavour's last mission. While it is an opportunity to celebrate Endeavour's history and the brave people who have made it a proud one, it is also a bittersweet occasion. The president's space policy is jeopardizing America's longstanding commitment to manned space exploration. This has serious consequences for Florida.

The Constellation program's cancellation will close off what has been our most reliable path to low-earth orbit, endanger thousands of jobs and force us to rely on the Russian Soyuz vehicle to continue our work on the International Space Station. Although America once led the way to the moon, we now face the unacceptable prospect of limited options to simply get a human into space.

By failing to develop a heavy-lift rocket and crew vehicle to replace the space shuttle program, America will fall behind in the space race. China, India and Russia are all committed to establishing a pre-eminent position in space and have invested in manned space exploration to fulfill their ambitions.

Facing growing international competition, Congress must ensure that the president adheres to the NASA Authorization Act of 2010 by not undermining America's next generation of manned space vehicles. Doing so would relinquish a half-century of space leadership as well as the resulting benefits in the areas of science and technology.

And by not having our own capabilities to transport Americans into space, our reliance on foreign countries for manned space exploration will jeopardize many of the national security functions that have made NASA's work so vital.

In writing this, I fully recognize that our nation faces a debt crisis because politicians in both parties have spent recklessly for many decades. Solving this will require policies to grow the economy, cut spending and put us on a credible path to fiscal responsibility. It will require Washington to finally live within its means and for leaders to make tough choices about what our nation's priorities are. NASA is no exception.

Unfortunately, the Obama administration's 2012 budget cuts $1.2 billion for the next generation heavy-lift rocket program and multipurpose crew vehicle that were included in the law he signed in December. This will prevent NASA from meeting its congressional goal of fielding an operational heavy-lift rocket and capsule by 2016. The bottom-line impact of the president's space agenda is a full retreat from America's long-standing commitment to space exploration.

Some doubt the necessity of funding manned space exploration, especially in this period of record deficits and debt. I believe they ignore the central mission NASA plays in advancing vital national security and scientific imperatives.

For example, satellite technologies developed and improved by NASA now connect the world in unprecedented ways, support our military's reconnaissance efforts, and facilitate travel through GPS devices.

For decades, Americans have taken risks, and even lost their lives, in pushing the limits of space exploration. But until now, America has never recoiled from pushing further in fulfillment of NASA's mission.

On Friday, Americans will proudly watch as Endeavour is expected to take off for its last flight, with Commander Mark Kelly, Rep. Gabrielle Giffords' husband, leading the mission. It will be a poignant opportunity to recall Endeavour's history and all that has been achieved in the more than 50 years of NASA's existence.

It will also remind us why the U.S. space program has always been about far more than rockets and astronauts. Our trailblazing space program reflects all the things that make America exceptional — courage, ingenuity and ambition. As Florida's senator, I don't want us to lose that by giving up on manned space exploration.

Marco Rubio is a Republican U.S. senator from West Miami.