Laser ride

ToughSF finds a good 'un, from David Appell: shooting cargo to Mars in 45 days. Or to Venus in rather less time - although, this is a game of averages, dependent on departure-time and porkchop. McGill University's plan is to use Earth-orbiting lasers to hit the propellant tank; to which, I could add the Moon as an Earth orbiter or maybe TLL4/5. Like me, ToughSf likes his lightcraft.

This is for a tonne at a time per target, which target unfortunately might include the propellant, but hey - high exhaust-velocity. Higher I_sp even than NERVA and, since the heat-source is external, no (radioactive) heating-unit on board. Off the rocket rockets at 17 km/s. 16 km/s when it gets to Mars (probably more than 17 km/s if at Venus).

I do wonder about how that chamber is staying cool and/or shielding its chassis from the tens of thousands of Kelvin involved.

The other question is how, at the destination, to SLOW this monster. We could have another laser orbiting Mars (better: Venus) but not on our first trip out there. Appell sez: aerobraking. I am sold for Venus, if we have some acid-protexion. Unsold for Mars.

My thought - if Marsbound - is that this is exactly what Deimos is for: a laser (and battery of power-cells) to shoot at incoming cargo (which must include some leftover propellant). Admittedly it might not work. So Marsbound freight should plan on a backup. Once we get to human freight, they'll need a nuclear reactor to heat that propellant in case the laser doesn't work (and if it does work, woohoo, Deimos has a new reactor).