Virgin Orbit (VORB.O), part-owned by billionaire Richard Branson, plans to launch nine satellites from a LauncherOne rocket attached under the wing of a modified Boeing 747, to be flown from a new spaceport in Cornwall on Monday.
Barring delays, it will be the first time a satellite has departed from western European soil.
For now the focus is on commercial payloads from companies such as Space Forge, which is developing in-orbit manufacturing.
But the launch is also seen by many as a blueprint for quicker launches of limited satellite capacity for tactical military purposes, in what planners call "Responsive Launch".
"Ukraine woke up the world in a lot of ways," Virgin Orbit Chief Executive Dan Hart told a news conference in southwest England on Sunday.
"Clearly there is a hope of a pan-European, as well as a U.S. collaboration ... and that we have responsiveness so that if something happens in the world, we can get assets there right away," he told the pre-launch briefing, monitored online.
Virgin Orbit said last year Britain's Royal Air Force was doing exercises to demonstrate the value of "Responsive Launch".
Britain had a brief foray into space launch activities in the late 1960s and early 1970s, when its Black Arrow rocket was cancelled after just one successful mission.
The rocket's four launches took place in Australia in an era when commercial satellites barely existed.
Now, constellations of miniaturised satellites are heading an explosion of commercial activity in low Earth orbit.
Lobbing small satellites into low orbit at short notice would do little more than fill temporary gaps in coverage from large spy satellites, but experts say the technology has some dual civil and military potential and could spread costs.
"It gives you greater resilience or redundancy or duality of systems, whether that's for position, navigation and timing or quicker access ... as we've seen in Ukraine," Ian Annett, deputy chief executive of the UK Space Agency, told Sunday's briefing.
"It's a natural transition that helps us develop security capabilities, but also, for government, keeps costs down whilst providing commercial opportunities as well."
Elon Musk's SpaceX activated its Starlink constellation over Ukraine after Russia's invasion last February. Its communication links have been used by civilians and by Ukraine's military.
Luxembourg said in October it had signed a letter of intent with Virgin Orbit to develop a "rapid and flexible response to different threats", for NATO and other allies.
Its defence ministry has called for "new, more flexible and agile satellite launch procedures and techniques from Europe".
Britain's own 2022-25 space roadmap calls for dual-use capabilities in Earth Observation and Space Domain Awareness.
Virgin Orbit is also talking to Japan and Australia.
Questions remain, however, over how quickly the mobile launch concept could work its way into actual budgets, which are dwarfed by U.S. spending on space.
"Everyone is playing up military space as the next big thing," said UK-based defence analyst Francis Tusa. "But ministries of defence have eyes larger than their stomachs."
The system's liquid propellant and final rocket assembly also require some local infrastructure, and Europe's crowded airspace has thrown up significant regulatory obstacles.
"At the moment, it's a bit bigger on the commercial side, but we see the defence and national security side growing so I think in this steady state, it'll probably end up being 50/50," Hart told Reuters.