Space Shuttle Solid Rocket Booster: 250 ISP 2,500 meters per second.
Liquid oxygen-liquid hydrogen: 450 ISP 4,400 meters per second.
Ion thruster: 3000 ISP 29,000 meters per second.
New Lithium-ion drive: 50000 ISP 480,000 meters per second (1.07 million mph).
Positron Dynamics catalyzed fusion: 100000 ISP 980,000 meters per second (2.1 million mph).
Advanced catalyzed fusion: 1000000 ISP 9,800,000 meters per second. (21 million mph)
JPL (Jet Propulsion Lab) will be testing a 50000 ISP lithium ion thruster within 4 months. This is part of a NASA NIAC phase 2 study to use lasers to beam 10 megawatts of power to new ion drives.
Many people are not aware of the recent progress with more powerful lasers. The US military is developing arrays of lasers that can produce 100 kilowatts within the next 2 years. The military should have megawatt laser arrays by around 2025.
Laser beam powered lithium-ion drives ten times faster than any previous ion drive. A spacecraft with this system would take less than a year to get to Pluto.
JPL is building and proving out the various components of this system. The sail and the ion drives are coming together. The hard part is the phased array lasers.
They are boosting the testing voltage up to 6000 volts so the lithium ion drives can be directly driven. Direct drive eliminates the need for a lot of heavy electronics which would kill the performance.
The power density will be one hundred times more than sun based solar power. They will reduce system size by using a laser wavelength of 300 nanometers instead of 1063 nanometers.
The multi-megawatt lithium-ion drive has technical challenges. However, a well-funded project can be successful before 2040.