Unmanned space missions are those using remote-controlled spacecraft.
NASA does, however, often use launch satellites and spacecraft on vehicles developed by private companies.
Yet hard-headed science fiction writers constantly use faster-than-light spacecraft.
The President also called for a major national and international program to use spacecraft for seeking solutions to environmental problems.
The program's guidelines call for missions using spacecraft that will cost no more than $150 million to develop, build and prepare for launching.
Using spacecraft, scientists have only twice viewed close-up images of comet nuclei.
This is not the first search using spacecraft to look for gravity waves.
Space-based solar power, is the concept using spacecraft in space for Earth power.
Cargo is the name people give to goods which they transport, using a ship, airplane, lorry (truck), train or spacecraft.
Scientific experimentation in space can be safer and more cost effective using long-duration remote controlled orbital spacecraft.