While the space station is the most visible sign of the superpowers' collaboration, it is the loss of the RD-180 engines that will really hurt, according to space commentator Brian Harvey, who has reported on the Russian space programme since the 1970s.
"For the Americans not to take RD-180s any more would probably be quite disruptive of their space programme in the medium-term," he says. This is because of the time it would take to develop a replacement.
"Most people don't realise just how advanced and powerful Russian rocket engines are," says Harvey.
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