The spacecraft might be a wingless electromagnetic air vehicle (WEAV) which gets its lift by ionizing the surrounding air and gaining lift. Details here and it's not everyday the citation is to the Scientific American about a flying saucer.
The saucer will hover and propel itself using electrodes that cover its surface to ionize the surrounding air into plasma. Gases (such as air, which has an equal number of positive and negative charges) become plasma when energy (such as heat or electricity) causes some of the gas's atoms to lose their negatively charged electrons, creating atoms with a positive charge, or positive ions, surrounded by the newly detached electrons. Using an onboard source of energy (such as a battery, ultracapacitor, solar panel or any combination thereof), the electrodes will send an electrical current into the plasma, causing the plasma to push against the neutral (noncharged) air surrounding the craft, theoretically generating enough force for liftoff and movement in different directions (depending on where on the craft's surface you direct the electrical current).
Fortunately the single-stage spacecraft is a far-future vehicle with possible matter-antimatter power system because that solves this problem with WEAV. Therefore, it is reasonable to assume that the practical problems of using antimatter as a power source have been solved. This vehicle is operating in the far-future after all.
The biggest hurdle to building a WEAV large enough to carry passengers would be making the craft light, yet powerful enough to lift its cargo and energy source.
A similar magnetohydrodynamic (MHD) vehicle was described in an article "How To Design A Flying Saucer" by Dr Richard J Rosa published in Analog and reprinted in The Analog Science Fact Reader (1974) edited by Ben Bova. That suggested that this type of craft could produce large volumes of low-speed ionized air for travelling slowly and hovering, but narrow its air intake to generate smaller volumes of high-speed ionized air to accelerate to high velocities. Rosa's proposed MHD vehicle could land and take-off VTOL style, so it wouldn't need extensive infrastructure.
A WEAV-type spacecraft could accelerate through the air and once it reached the upper atmosphere use its matter-antimatter power system to ionize reaction mass such as water stored in propellent tanks to attain orbital velocities to rendezvous with the space-station.
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A single-stage spacecraft with a matter-antimatter power source can effectively boost itself to whatever speed its operators desire. This will be more than sufficient to power itself during a WEAV flight mode. The WEAV flight modes will be for powered in the atmosphere during descent and ascent. Landings and take-offs will be VTOL.
With a matter-antimatter power source this will generate considerably more energy than needed to attain orbital velocity. Using direct mass annihilation of matter and antimatter for propulsion would produce large amounts of gamma radiation. This is not good. However, it could easily be used to drive a powerful rocket propulsion system.
There are two types of reaction mass the vehicle can use. One, as suggested above is water. Two, is liquid air. The liquid air could be produced while the spacecraft is landed. This assures the vehicle will be lighter during its planetary descent. Water might also be collected from the planet's surface. Otherwise it would have to be carried in the vehicle's fuel tanks.
Whichever type of fuel is for reaction mass, the procedure is the same. using the power output from its matter-antimatter system the reaction mass is totally ionized and accelerated via powerful magnetohydrodynamic accelerators. Instead of an exhaust velocity of 4 km/s from chemical rocket propulsion MHD accelerated ionized reaction mass could have an exhaust of 100 km/s. This means the vehicle will consume far less reaction mass than a chemical rocket system.
The vehicle will also be able to regulate its rate of acceleration, so even untrained personnel could fly this type of vehicle without too much discomfort or distress. This could be an acceleration that keeps itself to no more than two gravities during the rocket propulsion phase. However, with engines as powerful as these it would be easily possible to attain far greater rates of acceleration. But the for the sake of its personnel the acceleration can be kept within safe limits.
The MHD rocket mode would be used for approaches to take-offs and landings from and on to a planet. Either decelerating from or accelerating up to orbital velocity, for travel either from or to the space-station the vehicle could use a plasma propulsion system with an acceleration of about one centimetre per second squared.
This version of a single-stage spacecraft is designed to fully exploit the power capacity of matter-antimatter generator. It has three flight and propulsion modes: (1) WEAV plasma-lift technology for flight in atmospheres during ascent and descent. (2) A high-impulse fully ionized reaction mass rocket propulsion system enhanced by MHD accelerators with an exhaust velocity of around 100 km/s. (3) A plasma propulsion system for interplanetary travel at an acceleration of one centimetre per second squared. It also operates at levels of g-forces that are safe for regular untrained personnel.