Bo hiya
We have been using the same propellant system for rockets since around 1000 A.D. in volleys of bo hiya at the siege of Yuzhan.
While expanding gases in bamboo rockets work well enough; the hollow tube method has seldom passed the flash and bang weapon stage. Although, with enough fuel and fire in a sealed tube, you can break free from the gravitational bonds of Earth.
From gunpowder to liquid fuels to solid rocket boosters and, a few trials of nuclear fuel, only rocket size, volume, and chemistry have changed for over a thousand years.
Propulsion systems such as ion engines and solar sails are all suitable options once the bonds of Earth have been broken, but are not viable as launch systems directly from Earth. Magnetic rail guns or space elevators may be possible but are not even at the functional prototype stage. Nuclear rockets work but have horrible tail-pipe and fail issues.
We propose a new paradigm using old methods: Keep the chemistry, drop the booster, hide the nuclear fuel, and add a balloon lift / Solar sail.
It takes energy for lift, and more energetic systems generate more lift. The downside is, as you move up the periodic table, the tail-pipe waste products become more toxic.
Our popular fantasy T.V. and movies all have some unspecified, powerful propulsion system that can easily break a gravity well to propel ships to outer space. In spite of all of the (fantasy) literature on the subject, none of them are readily accessible, and they are still a dream in our very real world.
Sure, dilithium crystals are wonderful, and the 'boop-boop-boop' of the Jetson's car is bound to be a vast source of cheap, safe, unlimited power, someday, in some future time, maybe.
We have the materials available now to bring cheap, effective access to space for more than the rich or lucky.
Hydrogen, Helium, and Methane are all common molecules that are lighter than air. Hot air is used to fill recreational balloons, but for the past 200 years, the only lighter-than-air commercial ships have used Hydrogen or Helium.
You can float to a neutral point in the sky using any of the lighter-than-air gases, with some obvious limitations: When the gas pressure is above the tensile strength of the shell, the balloon bursts, and the device plummets to Earth.
With a few modifications, such as nano-particle bonded spider web fabric, we can take a balloon launch system to the next level.
Of course, this is a radical, untested system, but if it works, it could open up space flight to the rest of the world. We can then start mining the dilithium crystals our movies tell us will replace all other propulsion systems.