NASA, as an aerospace research and development agency, sponsors and conducts flight missions to obtain data in furtherance of its objectives. In NASA's Science Mission Directorate (SMD), flight missions range from suborbital projects—including balloons, sounding rockets, and airplanes—to interplanetary probes and flagship observatories. All investigations and missions selected and flown must respond to Agency goals and strategic objectives. Mission opportunities are open to all proposers, within fixed rules, via public announcement, and selections are based primarily on scientific and technical merit as evaluated by independent peer review. Foreign partners are frequent and valued participants in joint missions. The partnerships are generally conducted on a cooperative, no-exchange-of-funds basis. NASA also works closely with a number of other Federal agencies to implement and support our flight missions.