Solar System Travel With Advanced Propulsion

To start with, an internal gravity of one g is desirable, if not actually mandatory. We easily solved that with a proper space habitat anywhere we want.  what that means is that point to point travel also needs to be at one g acceleration. and otherwise, have artificial gravity whenever we invent that.

We will want space habitats built to orbit every significant object out there and hte loads can be driven out there using a laser assist from perhaps the moon or moon orbit.  These can also be massive if needed using raw materail consumed for manufactures.

For human transport, we really want that one g thrust however done.  Not only is it human freindly, it provides short time haulage throughout the inner solar system  and still practical throughout the solar system.

Any space habitat can protect and maintain a large population and well over thusands and plausibly through a million.  The solar system can easily hold a million such habitats which impies a build though a billion folks while Earth itself will easily surpass 100 billion.  All this without worrying about a planetary surface where landing and lift off is expensive.

Solar System Travel With Advanced Propulsion

March 13, 2025 by Brian Wang

If we achieve advanced nuclear, antimatter propulsion or other advance propulsion it would be possible to achieve near constant acceleration. This would enable travel times to Mars in the 3-8 day range depending upon where Mars was in its orbit relative to Earth. This would be with constant 0.33G acceleration and deceleration.

What exactly is a Brachistochrone Orbital Transer?

A Hohmann orbit is the maximum transit time / minimum deltaV mission. Weak spacecraft use this because they do not have a lot of deltaV. All current space probes use Hohmann because currently there ain’t no such thing as a strong propulsion system.

A “Brachistochrone” is a minimum transit time / maximum deltaV mission. Torchships use this because they have lots of deltaV to spare.

A torchship is a spacecraft with more than 300 km/s total delta V and an acceleration greater than 0.01 g.

The most probable torchship designs proposed are nuclear pulse propulsion (e.g., Project Orion) and nuclear salt water rockets (NSWR). These leverage high thrust and exhaust velocity to achieve >300 km/s delta V and >0.01 g acceleration, enabling Brachistochrone transfers. Among nuclear rockets, those using nuclear fission, particularly Project Orion, are the most achievable with current technology due to their development in the 1960s and reliance on known physics. The NSWR is also fission-based and promising but less mature. Fusion-based propulsion (e.g., Daedalus) offers superior potential but awaits technological breakthroughs. Beamed power to ion drives or laser thermal rockets could work but demands advanced infrastructure, reducing near-term feasibility.

1. Nuclear Pulse Propulsion (e.g., Project Orion)

Description: This concept, developed in the 1950s and 1960s, uses nuclear explosions (typically fission bombs) detonated behind a spacecraft to propel it. A pusher plate absorbs the blast, transferring momentum to the vehicle.

Performance:

Exhaust velocity: Approximately 20–60 km/s, depending on the design (e.g., specific impulse of ~6,000 seconds yields ~59 km/s).

Thrust: Extremely high due to the explosive force, enabling accelerations well above 0.01 g (potentially up to 1 g or more, though typically lower for crew comfort).

Delta V: For interplanetary missions (e.g., Mars in 125 days), delta V is in the tens of km/s, but interstellar designs (e.g., Freeman Dyson’s analysis) suggest velocities up to 10% of light speed (30,000 km/s). With a mass ratio of ~160, a delta V of 300 km/s is feasible, though it requires significant propellant.

Fit for Torchship: Meets both criteria handily, supporting Brachistochrone trajectories (continuous acceleration to midpoint, then deceleration).

Status: Feasible with 1960s technology, making it one of the most developed proposals.

2. Nuclear Salt Water Rocket (NSWR)

Description: Proposed by Robert Zubrin, this system uses a solution of fissionable material (e.g., uranium salts) in water as propellant. The mixture undergoes a continuous nuclear reaction in a nozzle, producing a high-thrust exhaust.

Performance:

Exhaust velocity: Up to 4,725 km/s (based on theoretical estimates), far exceeding most fission systems.

Thrust: High, due to the continuous explosion-like reaction, supporting accelerations >0.01 g.

Delta V: With an exhaust velocity of 4,725 km/s, a delta V of 300 km/s requires a mass ratio of just ~1.065, meaning very little propellant is needed, easily surpassing the 300 km/s threshold.

Fit for Torchship: Exceptional efficiency and thrust make it a strong candidate for Brachistochrone missions.

Status: Conceptually sound but untested; engineering challenges (e.g., containment) remain.

Fusion-Based Propulsion (e.g., Project Daedalus)

Description: Uses fusion reactions, such as inertial confinement fusion (ICF), where small pellets of fusion fuel (e.g., deuterium-helium-3) are ignited by lasers or electron beams. Project Daedalus aimed for an interstellar mission to Barnard’s Star in 50 years.

Performance:

Exhaust velocity: Potentially 10,000 km/s or higher.

Thrust: High enough for significant acceleration, though dependent on pellet ignition rates.

Delta V: Could exceed 300 km/s with moderate mass ratios, aiming for velocities up to 12% of light speed (36,000 km/s).

Fit for Torchship: Meets the criteria, though interstellar focus might exceed typical interplanetary needs.

Status: Requires fusion technology breakthroughs, making it less achievable currently.

3. Beamed Power Propulsion (e.g., Laser Thermal Rocket)

Description: An external power source (e.g., a laser or microwave beam) provides energy to the spacecraft, either heating propellant (laser thermal) or powering ion thrusters (beamed ion drives).

Performance:

Laser Thermal: Exhaust velocity ~10–20 km/s; thrust can be massive (e.g., 700 MN per engine in speculative designs, yielding >2 m/s² for large ships).

Beamed Ion: High specific impulse (5,000–10,000 s, or 50–100 km/s exhaust velocity), but thrust is typically low unless scaled massively.

Delta V: Laser thermal could achieve >300 km/s; beamed ion might struggle with acceleration unless paired with enormous power input.

Fit for Torchship: Laser thermal fits well; traditional ion drives may fall short on acceleration.

Status: Requires advanced infrastructure (e.g., gigawatt-scale lasers – arrays of smaller lasers in the 100kw to megawatt class).

4. Plasma Magnet Ships (Dynamic Soaring Against Solar Wind)

Description: Uses magnetic fields to interact with the solar wind or interstellar medium, gaining velocity via dynamic soaring (exploiting velocity gradients, akin to how birds soar). You noted a potential 2% of light speed (6,000 km/s) using interstellar shock waves.

Performance:

Velocity: Could reach 6,000 km/s over time, but acceleration is likely low due to the diffuse nature of solar wind (thrust scales with particle density and field strength).

Delta V: Potentially high, but built gradually.

Acceleration: Estimated at <<0.01 g (e.g., ion thrusters achieve ~0.0001 m/s²), unless a novel high-thrust variant exists. Fit for Torchship: High velocity is promising, but low acceleration may disqualify it unless enhanced designs exist. Status: Speculative; lacks detailed engineering proposals for torchship-level thrust.