[Spaceships] Martian “Gas” Station

[AlexanderHowl]

Deimos and Phobos are the natural sites for such a well. They have a good delta-v compared to other sources of ice (including Mars), and they may be 20% ice. Lifting gases are unlikely to matter on Mars until you get a Thin atmosphere, and you might as well use water if you are using methane. By avoiding the delta-v associated with landing on Mars, you also end up saving a lot of time and money.

[DaltonS]

I was thinking more in terms of a "Domed Mars" type setting (Chapter 4 of GURPS Classic: Mars) as the core of a small Martian community, but the idea of a "grounded" space station on Phobos or Deimos has some merit (although I hadn't heard of them having that much ice). As for hydrogen as a lifting gas, it could be useful sooner than you think.

Airships and balloons can make use of the fact that Mars’ atmosphere, though tenuous, is composed of relatively heavy gases like carbon dioxide and argon. A cubic foot of hydrogen has a lifting power of 0.0004 lbs. on Mars. That may not sound like much, but recall that the entire weight of the airship is reduced by the lower Martian gravity. The cost of lifting gas is also lower: the amount of hydrogen required to fill 1 cubic foot at Earth atmospheric pressure can fill 30 cubic feet on Mars. That being said, it still takes a pretty big balloon to carry a useful payload on Mars – at least 20,000 cubic feet just to lift the gasbag. Because of the reduced efficiency of airscrews, in some circumstances airships may be rocket-powered!

GURPS Mars, page 37

Or a Fission Air-Ram (SS7 p. 10) might be useful. Also, hydrogen is safer to use as a lifting gas on Mars: no combustion hazard. Terraforming might actually make airships less useful as the mean molecular weight of the atmosphere went down. I discussed the topic rather extensively in my "Homebrew: Expanding on Gasbags" thread 3½ years ago and really don't have anything to add at this point (at least until I re-read and understand it ;D ).

Dalton “who may have an inflated opinion of himself” Spence

[AlexanderHowl]

Since the volumetric lifting power of hydrogen increases proportionally with the density of the atmosphere, the denser the atmosphere the better the lifting power.

[DaltonS]

And the density of a gas at given temperature and pressure is dependent on its molecular weight. Since temperature and pressure are the same both inside and out of an unheated balloon only the difference in mean molecular weights matters when calculating lift.

Dalton “see my "Homebrew: Expanding on Gasbags" thread for details” Spence

[AlexanderHowl]

That is lifting power by mass. Lifting power by volume depends on the density of the atmosphere. A cubic meter of hydrogen has a lot more lift on Earth than on Mars.

[DaltonS]

Yes, by volume this may be true (see my quote from GURPS Mars above) but I expect hydrogen would be sold by mass, not volume. It's up to the user to have a gasbag big enough to provide the necessary lift.

Dalton “who decided not to make a political comment” Spence

[Agemegos]

Originally Posted by DaltonS

Yes, by volume this may be true (see my quote from GURPS Mars above) but I expect hydrogen would be sold by mass, not volume. It's up to the user to have a gasbag big enough to provide the necessary lift.

Dalton “who decided not to make a political comment” Spence

The mass and cost of the gasbag envelope go with volume. Where the air is very thin you would need a vast, massive, costly envelope, perhaps impractical or uneconomic.

[Fred Brackin]

Originally Posted by AlexanderHowl

Deimos and Phobos are the natural sites for such a well.

Refueling stations for hard science space ships make the most sense at actual destinations. Perhaps if there were a beanstalk at Deimos you could ride down to the Martian surface the numbers would crunch the right way.

Otherwise, if you're going to Mars, go there directly and refuel after you get there. You might ship fuel to the asteroids from the moons of Mars rather than the planet itself. It'd depend on how high the start-up and manintence costs were.

[TGLS]

Originally Posted by Fred Brackin

Refueling stations for hard science space ships make the most sense at actual destinations. Perhaps if there were a beanstalk at Deimos you could ride down to the Martian surface the numbers would crunch the right way.

Otherwise, if you're going to Mars, go there directly and refuel after you get there. You might ship fuel to the asteroids from the moons of Mars rather than the planet itself. It'd depend on how high the start-up and manintence costs were.

It depends if the rocket has enough thrust to do a landing or not, as well as how efficient the rocket is. High efficiency rockets with low thrust could make good use of water available from Deimos, which hardly takes any thrust to land on. Low efficiency rockets could plausibly "island hop" from space rock to space rock, as adding more propellant to a rocket has declining gains.

[johndallman]

Originally Posted by TGLS

Low efficiency rockets could plausibly "island hop" from space rock to space rock, as adding more propellant to a rocket has declining gains.

Err, no. This is the classical mistake when comparing space travel to sea travel. To land on a rock and pick up fuel, your craft has to burn fuel to slow down, and then to speed back up again. This usually ends up wasting time on the journey as compared to coasting the whole way.