Asked by Jeremy Hardwick
The power of any rocket is usually measured by the heaviest payload it can take into certain types of orbit. Using either low-Earth orbit (LEO – the position of the International Space Station) or the higher geostationary transfer orbit (GTO – the position of most communications and GPS satellites), Delta IV rockets win over Soyuz rockets by a large amount. The Delta IV Heavy (the most powerful type of Delta IV rocket) can take a payload four times heavier than Soyuz rockets can manage up to LEO, and a payload five times heavier up to GTO.
Even the least powerful Delta IV rocket (the Delta IV-M) can take heavier payloads than Soyuz rockets to both LEO and GTO. Soyuz rockets do have one major advantage over Delta IV rockets, though, as they can carry manned spacecraft, and so they are currently the only available method to take astronauts to and from the ISS. This may change in the next few years as private companies such as SpaceX are looking to develop their own manned spacecraft and hire seats to government space agencies.
Answered by Megan Whewell from the National Space Centre>
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