Air Chief Marshall Mike Wigston said space is now a "contested war-fighting domain" with enemy missiles able to cause a "disastrous effect on day-to-day lives".
He issued the stark warning as Boris Johnson's chief adviser Dominic Cummings wields the axe over an upcoming defence review.
Speaking at RAF Waddington in Lincoln, the air chief said: "Space is now a contested war-fighting domain.
"Today we can no longer assume the unchallenged access to air or space that we have enjoyed for the last three decades, nor can we ignore the threat of air, ballistic and cruise missile attack.
"Our access to space is fundamental to national security and any loss or disruption to our satellite services would have a disastrous effect on day-to-day lives."
Millions of pounds are expected to be poured into defending British assets in space in the major review.
Russia has been accused of ignoring British pleas for all countries not to engage in space warfare by firing a missile-like projectile into outer space.
Mr Cummings recently entered Downing Street for a Cabinet meeting holding a 1986 letter for a review of defence spending for President Ronald Reagan by former US air force general Bernard Schriever.
The general was backed "the wise and timely application of technology to provide qualitatively superior weapons".
Defence Secretary Ben Wallace has also spoken about the importance of technological innovation.