The row between Donald Trump and Elon Musk over a major spending bill has exacerbated uncertainty over the future of Nasa's budget, which is facing deep cuts, BBC reported.
The space agency has published its budget request to Congress, which would see funding for science projects cut by nearly a half.
Forty science missions, which are in development or in space already, are in line to be stood down.
The president has threatened to withdraw federal contracts with Musk's company, Space X. Nasa relies on the firm's Falcon 9 rocket fleet to resupply the International Space Station with crew and supplies. The space agency also expects to use its Starship rocket to send astronauts to the Moon and eventually to Mars once it has been developed.
Dr Simeon Barber, a space scientist at the Open University said that the uncertainty was having a "chilling impact" on the human space programme, according to BBC.
