Straybow
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In order to liquify, the latent heat of condensation must be removed from the gas. It is 14GJ/ton, which is an order of magnitude or so larger than the heat extracted to cool H2 by 300 K.
Spaceship Landing
- Thread starter BackworldTraveller
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AnotherDilbert
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Latent heat of hydrogen is about 461 kJ/kg.
Specific heat is about 14.3 kJ/kgK.
Condensating the hydrogen would release as much heat as cooling the gas by 461 / 14.3 [ (kJ/kg) / (kJ/kgK) ] = 32.2 [K]?
Condensating a ton of hydrogen would release 461 kJ/kg × 1000 kg = 461 MJ heat?
Either way the latent heat seems pretty marginal.
It still has nothing to do with the kinetic energy of the gas relative the ship?
AnotherDilbert
SOC-14 1K
OK, I have never looked at that in detail, so I will take you word for it.
Its pretty ironic that we're worrying about how to land spaceships when Elon Musk does it just fine. Before SpaceX Starship and Falcon, the sci fi convention was that spaceships land on their bellies, whereas Elon has demonstrated that spaceships can land on their tails. Now belly landers come in two varieties, those that need runways, and those that can land vertically. Now runway landers are useless on vacuum worlds, yet Starship can land on its tail just fine on the Moon.
Proneutron
SOC-13
CT didn't address this so I did from day 1. IMTU ships have always used a Grav drive. So if you have a 1 G drive and you are on a 1 G planet I just made it that you could (over rev) by 10% long enough to either reach orbit or to hover down from orbit at a slow pace. No aerodynamics used. Otherwise you cannot land or take off from 1G very thin or no atmosphere worlds.
Proneutron
SOC-13
EE Doc's Lensmen series of the 1940's had the ships land tail down like space X.
Timerover51
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So did the 1950 movie, "Destination Moon", landing on its tail on both the Moon and Earth. Robert Heinlein was heavily involved in that movie.
Yep, tail lander's were the stuff of 1950s and 1960s movies, and then Star Wars came around, and suddenly all the spaceships tried to imitate airplanes, and we've had the bias towards airplane like spaceships ever since in science fiction. Usually with the main engines in the back and the landing gear underneath. Remember the Flash Gordon cartoon? The SpaceX Starship looks sort of like that spaceship built by Doctor Zarkov which flew Flash, Dale, and himself to the planet Mongo, and for some strange reason, the missile like spaceship landed on its side, and it didn't look like a spaceship that was supposed to land on its side, it launched just once from its tail and for ever afterwards it was always taking off and landing on its side, if you tried that with the SpaceX Starship, you wouldn't be using it again that's for sure.
One thing I liked about some of the 1950s movies, is they often tried to get the science right, as much as their budgets could afford anyway. Rockets launched just the way they saw real rockets launch, and they landed on their tails because they didn't get the airplane analogy, that was George Lucas' idea.
One thing I liked about some of the 1950s movies, is they often tried to get the science right, as much as their budgets could afford anyway. Rockets launched just the way they saw real rockets launch, and they landed on their tails because they didn't get the airplane analogy, that was George Lucas' idea.
Actually the Star Trek TOS Shuttlecraft was a belly-lander, and the ships of Space 1999 were a mix of both tail and belly types. Both of those series predate Star Wars.
Proneutron
SOC-13
Yes, reaction drives tend to be made into belly landers. Star Treks drives (warp & Impulse) are not reaction drives. Star Wars had anti-grav lifters for low power movement. At least that is how it was depicted visually with the X-wings floating across the hanger floor, et al.
Let's see:
Star Trek Galileo (Shuttle): 1967
Star Wars: 1977
NASA Shuttle Enterprise (test landings): 1977-1978
NASA Shuttle Columbia (first flight): 1981
So both fiction and RL had bellylanders in the era, starting in the late '60s.
On the other hand, the only RL tail-landing ship I recall from the era was the LEM, on the moon (1969-1972). Most spaceships splashed down, in the ocean (USA) or on land (USSR). Fictional ships? 2001's moon landing comes to mind, but none others. And they also used a (Pan-Am) Space plane for the Earth-orbit leg.
Proneutron
SOC-13
Space 1999 in the 70's had belly landing moon ships
Condottiere
SOC-14 5K
Spheres would be tailsitters.
Anti-gravity is a recurring concept in science fiction, particularly in the context of spacecraft propulsion. Examples are the gravity blocking substance "Cavorite" in H. G. Wells's The First Men in the Moon and the Spindizzy machines in James Blish's Cities in Flight.
"Anti-gravity" is often used to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by moving air with electromagnetic fields.[1][2]
One assumes flying saucers would be belly landers.
Anti-gravity is a recurring concept in science fiction, particularly in the context of spacecraft propulsion. Examples are the gravity blocking substance "Cavorite" in H. G. Wells's The First Men in the Moon and the Spindizzy machines in James Blish's Cities in Flight.
"Anti-gravity" is often used to refer to devices that look as if they reverse gravity even though they operate through other means, such as lifters, which fly in the air by moving air with electromagnetic fields.[1][2]
One assumes flying saucers would be belly landers.
The thing about reaction engines is they look more impressive in movie theaters, reactionless engines look lame, they just float around and maybe make a slight humming sound or a warbling sound like a flying saucer in a 1960s movie. Now in the Star Wars era you have reaction engines that are pointed at right angles to the way they land, so they don't end up looking like a 1950s V2 style spaceship landing on its tail, but I think those 1950s movies got more right despite the cheezy special effects than Star Wars did as to what a real laudable spaceship would look like. Landing on one's tail makes sense because that is the way the primary reaction drive, the drive that produces the most trust is pointed, if you have some antigravity device to perform landings while the reaction drive is pointed sideways, like a jet airplane on a runway, then what is the reaction drive for anyway, to make a lot of noise?
Drakon
SOC-14 1K
My thought too. How does one distinguish, for spheres and saucers, tail vs. belly? Only by the orientation of floors? (Assuming that all the floors are parallel . . .)
Anti-gravity/gravity control allows lots more possibilities. Pre-gravitics, I'd think tail-sitters would be the default, simply because standing and sitting "work" with tail-sitting. And cargo, say, doesn't want to slide to the back wall of every compartment and cargo bay. But, with gravitics, the advantages of belly landing are more accessible: literally--ramps into the cargo bay, etc.
ETA: and then there's the possibility of non-parallel floors. (Remember the scene in 2001 where the attendant walks around the cylinder--using Velcro in zero-g, but the principle is the floors are not all the same way.) Opens up a whole :CoW:.
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Saucers fly like Frisbee through space, sometimes spinning, sometimes not, but a realistic flying saucer shaped spaceship would fly through space like a pie plate thrown at someone's face, it would basically be a vertically flattened missile. In the movie Forbidden Planet, the had a saucer shaped space ship, but it flew through space edge on, as if there was wind resistance in space to overcome.
Depending on how old your Sci Fi is, there might actually be "wind resistance". E. E. Smith had it in the Lensman books, for example.
