New Mars Forums

The latest results from Venus Aerospace.
https://www.nextbigfuture.com/2025/07/h … lanes.html

Impressive technology.  It is described as a ramjet engine, that uses a rocket to achieve an intial subsonic boost.  As airspeed increases into the Mach range, it transitions into a detonation engine.  At high Mach speeds, the velocity of incoming air will exceed the velocity of shockwaves travelling through air.  So detonations can provide useful thrust, as they can only travel backwards through the combustion chamber.  It isn't clear to me whether this is pulsed power or not.  Detonation requires premixed fuel air mixtures.  But if the incoming air is already hot, then combustion will naturally occur as increased speed.  But it cannot occur more rapidly than the rate of mixing.  Hydrogen is the natural fuel for such a detonation engine, because its high molecular speed allows for very rapid diffusion of fuel molecules into air.  It also supports a very high flame speed for the same reason.  Lighter molecules travel faster.

Vibration from these engines may be a stumbling block.  Detonation results in higher peak chamber pressures.  If it is pulsed, then vibration will severely shake the airframe.  Also, at Mach 10, the temperature and force acting on the compression inlet nozzles will be extreme.  This clearly isn't something that could make it all of the way to orbit in a single stage.  But it would be a very effective lower stage.  If it can exit the sensible atmosphere on a suborbital trajectory, then a second stage could be released from a paload bay.  If material and structural problems are sumountable.

Dissociation is not an easy problem to solve.  It happens when energetic molecules at the high end of the boltzmann tail break apart, usually into oppositely charged components.  There is a work function associated with dissociation, because it pulls apart counter electrically charged species.  You don't get the energy back without cooling the combustion products, which allows them to recombine.  That only occurs after the exhaust exits the engine.  Dissociation robs energy from the system.  But it does also reduce exhaust molecular weight.  But not enough to be useful.

All light water reactors are naturally load following.  Increased load reduces turbine speed.  This opens steam inlet valves on the turbine, resulting in a reduction of pressure in the boilers (PWR) or core (BWR).  Reduced pressure increases the rate of boiling, but also lowers the temperature of the coolant water by removing energy from it.  Water is also the moderator, so reducing its temperature also reduces the average speed on neutrons.  This adds reactivity to the core, increasing power.

This is a useful characteristic in LWRs.  But it becomes problematic during a loss of coolant accident.  During a LOCA, there is a sudden loss of pressure in the primary circuit.  This causes a power surge, because boiling reduces coolant water temperature.  LWRs have trip settings that scram the reactor if neutron detectors see a sudden surge in population.  Without out that, the power surge resulting from LOCA would cause fuel damage, because of the lag imposed by heat transfer into the coolant.  Delayed neutrons and the use of fixed neutron sources are both used to increase the average lifetime of neutrons.  This limits the gradient of a power surge, allowing active control systems time to respond.

I think we need to break the comets into smaller pieces before sending them into the inner solar system.  Tsar bombs are likely to fragment comets uncontrollably.  And the political issues with building them makes this idea unlikely to succeed.  It would violate the test ban treaty.  The fission rocket idea is possible, but I suspect it would strain the Earth's supply of fissile material if deployed on a large scale.  Fusion-fission hybrid propulsion using a mixture of DU and thorium may be more sustainable.  We use fusion to produce the neutrons needed for fast fission.

One for Void.
https://youtu.be/MDM1COWJ2Hc

Using the TARS system, rotational kinetic energy of a body can be recharged using radiation pressure from the sun.  This can then be used to accelerate spacecraft.

It is about the IVO quantum drive, that produces thrust without propellant.  Not a warp drive, but it could (if it works) allow acceleration to a large fraction of c.  So almost as good as warp drive.

The work done by GW Johnson has shown that at altitudes higher than 100,000' and speed greater than Mach 6, air breathing engines become ineffective.  The density of the air is too low to produce much thrust at any achievable compression ratio.  And shock heating becomes more of a problem the faster the vehicle travels.

This suggests to me that a space plane would work better as the lower part of a TSTO.  Imagine a plane that can carry an upper stage within a payload bay, which is released at 100,000'.  That altitute is only one tenth what is required for a stable orbit and velocity is only about 30% of orbital velocity.  But the relative velocity means that the upper stage engines have high propulsive efficiency and the vacuum at 100,000' allows efficient expansion.  So the upper stage should reach orbit with a good mass ratio, which is more conducive to reusability.

In the past few years, we have seen three interstellar comets entering the solar system.  One of these bodies is around 20km in diameter.  In the centuries ahead, humanity will perfect the technologies that allow colonisation of plutoids.  At that point, a large interstellar body passing through the solar system would be a colonisation option.  This provides a slow but steady way of colonising the galaxy.  The sun orbits the galaxy at a speed of 200km/s and takes about 200 million years to complete one orbit.  A rogue asteroid or comet will be doing much the same, but will follow a different trajectory.  Such a body will make numerous close passes of other planetary systems during its long journey through the galaxy.

A patient species could ride such a body, waiting for the opportunity when celestial mechanics brings them close enough to another world for a portion of their population to jump off.  Could a branch of humanity be so patient?  Living on a small world for millenia, far from any star, pursuing their own affairs and knowing that their distant descendants will leave when the time is right?

I think a dwarf planet would need to be quite close to a supernova to be seeded by its products in any substantial way.  For example, there are traces of Pu-244 in ocean sediments that may have arrived as Earth passed through a supernova shockwave.  But the quantities are really tiny, so small in fact that they are hard to detect spectroscopically.

One thing I have occasionally wondered about is whether interstellar comets could contain elements in different abundance to solar comets.  Could we find comets that are oddly enriched with uranium, or berylium or something equally strange?  These comets would have formed from a different nebula than our sun did.  Will we find interstellar comets and asteroids with really wacky compositions?  I think it is possible.  We seem to be seeing quite a few interstellar objects passing through our neck of the woods.  Patient observation could yield unexpected surprises.

I remember a while back there was discussion about developing smart shells.  These would be something like 30mm cannon shells with the ability to steer their trajectory.  Instead of having to fire a hundred rounds to hit something like a drone, the point defence system would fire a single round, which would steer towards the reflected monochromatic light which is used to illuminate the target.

Another option for drones is electrolasers.  A laser beam ionises the air creating a trail of ions, which provide a path for electric current.  Rather like a bolt of lightening.  This would cook the electronics within the drone.

Generally, the problem with railguns is that friction between the projectile and the barrel causes excessive wear.  This is especially the case if there is arcing that generates a plasma.  But this does depend upon the speed of the shell within the barrel.  Tank guns can reach muzzle velocity of 1.7km/s.  That isn't far short of the 2.38km/s needed for lunar escape.

A circumferential torus within an asteroid could be used to house a giant toroidal ring habitat.  Interestingly, the ring could transfer load to a maglev track mounted on the ceiling of the tunnel.  This would make construction of the ring habitat easier, as it would no longer need to withstand the hoop stress caused by rotation.  In theory, it wouldn't need to withstand pressure either, as the tunnel walls could absorb compressive stresses.  There are practical limitations on the size of habitats as tensile forces result in impractically thick pressure shells.  Using gravity as a counterbalancing force obviates this problem.  World sized habitats become possible.

I think this is an interesting idea.  The way to maximise the effectiveness of a nuclear device in changing the velocity of the comet, would be to drill a hole and bury it beneath the crust.  The bomb would vaporise a lot of ice, turning it into steam which would then blast lumps of ice into space as reaction mass.  The main body of the comet will then be deflected, assuming it doesn't disintegrate.

The problem is that it will be difficult to deflect the course of the comet accurately enough to hit Mars of any other body.  The problem is comparable to hitting a pinhead with another pinhead across the length of a football pitch.  We could use other nukes to trim its course, but each one would risk fissioning the comet.

A similar option that I looked at a couple of years back, involved placing mass drivers on Ceres or a similar icy asteroid.  These would fire small water ice payloads at a velocity that would result in their perogee crossing the Martian orbit.  They would explode in the upper atmosphere of Mars filling it with greenhouse inducing water vapour.  The problem with doing this is similar to deflecting a comet.  The mass driver would need to be extremely accurate to ensure that the majority of payloads reached the Martian atmosphere.

In short, deflecting comets and icy asteroids into Mars is a great idea, if we can do it.

Interesting.  The tangent launch does much the same thing as air launch.  The pegasus rocket was launched from an aircraft flying in the statosphere at a speed of ~Mach 0.8.  The tangent launch system does much the same thing, but at ground level.  The pegasus rockets were small and were carried under the wing of a carrier aircraft.  Payload capacity was also small because the carrier plane could only carry a small rocket under wing and this tended to result in a high cost per kg delivered to orbit.  This was aggrevated by the fact that each launch required a dedicated carrier plane, crew and fuel load.

But I wonder if it would be possible to modify the fuselage of a 747, such that it could carry dozens of air launch rockets that are then deployed through a launch system in its payload bay?  Each flight could then deliver dozens of payloads to orbit.  The rockets could be equipped with reentry heat shields allowing them to be recovered.  This would allow reusability.