Matt Wilson wrote:
Suppose you have a setting like The Expanse, with hyper-efficient reaction drives.
I don't know The Expanse, but basically the more efficient a spaceship drive is the more horrifyingly devastating it is, and the more places you have trouble landing. Basically, the issue is that thrust is equal to mass flow rate times exhaust velocity, but the power in the exhaust stream is a half times the mass flow rate times the exhaust velocity squared
. The power/thrust ratio is half the effective exhaust velocity. To make an efficient spaceship drive you make exhaust velocity as high as possible so that you don't get caned by Tsiolkovsky's equation, but that means the exhaust power goes up
with efficiency. A lot more power (kinetic energy) goes into your exhaust stream than into your ship.
A while ago I generated at 3,000-ton survey frigate using the GURPS Spaceships rules
, and gave it a "limited superscience" antimatter plasma torch drive capable of 1 gee. Its fuel consumption implied an effective exhaust speed of 3.84 Mms-1
, about 1.28% of lightspeed. I calculated the power of the exhaust stream as 115 TW. Now, a kton TNT-equivalent is 4.2 TJ, so that exhaust is equivalent to 27 kilotons per second: 0.54 seconds' exposure to the exhaust is equivalent to the bomb that levelled Hiroshima.
The more efficient you make the drive, the worse it gets.
Are there worlds/moons where that drive would be problematic when trying to land?
For a start it would be a crime against Humanity to land it on an inhabitated world. Don't land spaceships. Land shuttles.
I seem to recall a Larry Niven story where someone uses a hot engine somewhere like Pluto and sets off some volatiles. But that was decades ago and I have no idea how accurate.
I remember it vaguely, too. It was something about the heat of the engine subliming frozen nitrogen, which re-condensed around the bell, gluing the bell to the ground. The bell then trapped the exhaust and exploded. That's plausible enough.