The Realities of Space Travel... This Ain't Star Trek

[ArcticFox]

Artificial gravity doesn't bother me either, again, as long as they make no attempt to go into detail on how it works. Normally we just accept it because frankly, a television format would be ludicrously expensive to portray a 0g environment and it would also be harder fir audiences to relate to.

Star Trek:Enterprise did a nice job in one particular episode of acknowledging the tech without being stupid about it when Captain Archer defeated a Gorn by suddenly cranking up the artificial gravity on the deckplates it was standing on.

Also deserving of honorable mention is Babylon 5, in which Humans are the only race that has yet to develop artificial gravity, so Human spacecraft and installations (Including the B5 station itself) use rotation to simulate gravity while ships without this feature always show cremembers in 0g or having to buckle themselves into their couches.

Star Trek, like all popular speculative fiction, adds in the sound effects in space because people just plain like it. The new BSG doesn't eliminate sound in space altogether, it just muffles it as a sort of compromise between realism and rule of cool. And let's be honest... sound effects in space are cool, and it's jarring when they're missing. 2001: A Space Odyssey got this right, too, but they pull it off because it's used to build tension, or to contrast the silence outside with, say, Poole's panicked breathing inside his helmet as he tumbles away into space...

[brandon1984]

I don't want to flash my nerd cred, but I used to work at NASA.

Wow, cool! I considered applying to the aerospace medicine program and becoming a flight surgeon or something. But, I think i'd miss out on my true passion -- research into disease pathology -- so i had to drop this idea.

Artificial gravity doesn't bother me either, again, as long as they make no attempt to go into detail on how it works.

It always involves a crystal. Crystal power I tell you!

Star Trek, like all popular speculative fiction, adds in the sound effects in space because people just plain like it.

Agreed, it does make it more enjoyable, unless you're unable to take focus off of the scientific accuracy of the movie (scumbag brain).

[ArcticFox]

I guess everyone has their own threshold for how much they can take before they can't suspend disbelief anymore. I tend to be more aware of scientific shenanigans these days but unless it impacts the plot in a meaningful way, I let it be. It's like in Star Trek when starships engage in combat while in planetary orbit... I'm just thinking.... no.... it does NOT work that way.

Here's what I mean.

When an object is orbting a planet, and in a STABLE orbit, it does at a specific altitude and speed that cause centripetal force and the force of gravity to balance. If the ship moves lower, or slows down, gravity will be greater than centripetal force. If it speeds up or moves to a higher orbit, centripetal force wins out.

Also, the path of the orbit must be such that it is orbiting the planet's exact centre of mass. It's why in space you can never see planets that have rings running parallel to each other... only concentric rings (I'm looking at you, Pitch Black.) By the same token two ships cannot be in stable orbits and be running side by side with respect to their orbital path. One would have to be in front of the other at the same altitude.

So the idea of two ships manoeuvring around, circling, dodging, firing at each other... all while supposedly in orbit...

No.

BUT

Usually that isn't a big deal. It isn't that two ships can't fight in orbit, it just wouldn't happen the way we see it onscreen. Does the difference hurt the plot? Generally no, so I ignore it.

[ArcticFox]

So I was watching an episode of Star Trek: The Next Generation over the weekend. In this episode, Enterprise encounters the plot device for the week and is disabled. Several crewmembers are trapped in various parts of the ship.

Geordi LaForge and Dr. Crusher are stuck in a cargo bay and there's a plasma fire emitting radiation. They decide the best way to put the fire out is to open the bay door, shut off the forcefield, and vent the bay to space...

...while they're still in it.

This is where a lot of sci-fi really boogers things up but Star Trek actually got more right than wrong. The only really grievous mistake was that, in preparing to expose themselves to vacuum, they discuss what to do and Crusher advise Geordi to take a deep breath and hold it. This would actually resulting massive trauma to the lungs and ensured Geordi's death. (Here's a tip: If you're ever exposed to hard vacuum, blow all the air out of your lungs.)

But the characters didn't explode, they didn't freeze, none of that fancy stuff that sometimes gets depicted in Sci-fi. The physiological damage would have been far greater in reality, but overall the scene wasn't too badly done.

[ArchAngel]

In this episode, Enterprise encounters the plot device for the week and is disabled.

Oh, I think I saw that episode, too.

The only really grievous mistake was that, in preparing to expose themselves to vacuum, they discuss what to do and Crusher advise Geordi to take a deep breath and hold it. This would actually resulting massive trauma to the lungs and ensured Geordi's death. (Here's a tip: If you're ever exposed to hard vacuum, blow all the air out of your lungs.)

But the characters didn't explode, they didn't freeze, none of that fancy stuff that sometimes gets depicted in Sci-fi.

Yup. Depressurization is one of the biggest things that will get you, and it'd be incredibly painful. Your blood boils up, etc.
I believe you'd actually suffocate before you freeze, since you're in a vacuum and even if it is slightly above absolute zero, there is little room for transference of heat. Your body would not lose heat by conduction or convection, but only by the slow process of radiation.
All in all, I think it's lack of pressure that would kill first. Being that it may, space is just not friendly to human beings.


The point you made a couple posts ago about orbits and space combat and it had me visualizing large starships locked in combat in orbit around a planet, with some queues from the old naval battles. You'd still be able to get some fancy maneuvers since motion is relative and you'd have mostly a full range of motion in relation to orbit, but I never thought about it before and it's a cool concept.

[ArcticFox]

Actually not to nitpick, but your blood wouldn't boil, either. Human skin would do a reasonable job of keeping the blood pressurized enough not to allow it to reach the boiling point. You're absolutely right about heat loss being from radiation, and not from conduction or convection. (Hearkening back to an earlier post about how the Apollo 13 spacecraft was not insulated against cold because it didn't need to be, and even through radiation of heat after power was completely shut off they only lost 30 or 40 degrees over 3 days.)

I've toyed with the idea of writing a sort of thought experiment work on the basics of space combat tactics, especially as they relate to combat in orbit. It occurred to me that one tactic might be to try and force your opponent to run out of fuel before you do, by making them fire thrusters constantly to maintain orbit. One way to do that might be to use kinetic energy/ballistic weapons to make use of the Conservation of Momentum to force them to make corrections. The problem, of course, is that unless those weapons are self-propelled you'll be adding the exact same amount of momentum to your ship as you're trying to add to theirs, which makes it a battle of attrition.

I think, in the future, if ships are going to start fighting each other, then they'll have no choice but to leave orbit before the engagement begins. Anything that throws a ship's orbit off is a death sentence if the ship subsequently becomes disabled. Too risky. Life pods would have to be able to insert themselves into a stable orbit or be able to survive re-entry under unknown conditions of velocity, angle and altitude.

Bad mojo.

[ArchAngel]

Ahh, good point on the skin and not boiling. It'd be a excruciating case of the bends, but I didn't know about the boiling point.

I suppose most of the space battles might occur in orbit, at least high orbit, due to necessity (protecting/assaulting planets and moons). The exception might be over resources in asteroid fields or space stations in orbit around the sun.

[ArcticFox]

Ok so this one isn't about Space Travel, but it is heavy Sci-Fi.

It's from the new Total Recall.

This isn't really a spoiler, since it describes a technology that's shown in the opening moments of the film, so if yuo haven't seen it yet, no biggie.

It describes a form of mass transit, called The Fall. It's a large car, of sorts, that drops into a tunnel that goes from London to somewhere in Australia, and uses gravity and momentum to get it to its destination.

The problem:

The characters board the vehicle, sitting in upright seats. Safety devices, similar to what you see on a roller coaster, drop down to hold them in place. The Fall is released, and they drop. As they pass the Earth's core, gravity suddenly goes to 0, and the entire compartment rotates 180 degrees so that when they come up in Australia, they will still be upright... A few moments after this rotation, gravity reasserts itself and they ride the rest of the way. The entire trip takes 17 minutes.

Now, hypothetical mass transit methods like this have been speculated about for some time, and aren't entirely unrealistic. There are some issues though, in how they are portrayed in this movie.

-Gravity. If you're sitting in this device and it's dropped down into the Earth, you will be in a state of 0g the entire way, not just in the middle. The reason for this is that you're in freefall... You drop at the same rate as the vehicle around you. Astronauts in the space station experience 0g for the same reason. Technically an orbit is just freefall where you keep missing the ground. As you pass the midpoint of the trip and the vehicle starts to slow down because it's now rising toward the surface instead of falling, gravity and momentum would still affect your body in the same way as the vehicle, so you'd experience 0g all the way to the end of the trip.

-Speed. I'm not sure whether 17 minutes is a realistic time for such a trip, but it MIGHT be. The rate of acceleration when the vehicle leaves, if it's heading straight down, would be 9.8 meters per second per second. That's pretty fast. The rate of acceleration would slow as the vehicle went deeper, because in a spherical shape like a planet, only the mass closer to the center of the sphere than you actually exerts gravitational force upon you. (I've seen the calculus that proves this in my high school AP Physics class, but I won't replicate it here.) As you drop further and further toward the core, less and less mass is pulling on you, so the rate of acceleration from gravity would approach 0. As you reach the core, it would be 0 so your acceleration would cease for that instant. As you start to leave the core, more and more mass is closer to the core than you, so the force of gravity would gradually increase. Ignoring friction and assuming the point of departure and the destination were both at the same elevation, the acceleration from gravity would be back to 9.8 meters per second per second, but pulling you down. Your momentum would thus bleed off the entire time you're rising and ideally, would reach 0 at the same moment you reach the station at the far end.

-Wind. In one scene in the movie, somebody opens a hatch that exposes the inside to the outside atmosphere. In the movie, it's just wind rushing by really, really fast. In reality... No. If that tunnel has air in it at all, it would be rushing by at thousands of miles per hour at the point of peak velocity. That's much, much faster than any aircraft man has ever built. The heat from the air ahead of it being compressed would be enough to vaporize the vehicle. That's why we have heat shields on spacecraft. (Contrary to popular belief, it isn't the friction of the atmosphere. The heat of re-entry is mainly from the compression of the air in front of the falling spacecraft.)

Not that it should be a problem, because...

-Vacuum. For a system like this to work, the tunnel would have to be completely depressurized and be in a vacuum. This would eliminate problems from wind resistance which would not only fix the aforementioned heating problem, but also eliminate friction from air which would deplete the vehicle's kinetic energy long before it reached the surface.

-Friction. Not only would wind resistance be a problem, but the vehicle would have to travel along some kind of frictionless rails. Maglift trains use a technology that could be of use in a system like this. The movie didn't address this either way, so all is well there.

-The Core. This is the biggest issue I had with the movie. The Earth's crust is only about 30 - 40 mi thick on average, so a system like this would go all the way through that and then be into the Mantle... Which is a hot, gooey magma mess that can't simply be tunneled through. Depending on the path of The Fall, it would also have to pass through the Outer Core which is even worse. The Movie suggested that The Fall took a course that curved around the Inner Core, but still... The film implied that only a short part of the trip was through a zone of really hot rock.

In theory, a system like this would work fine between any two points on the Earth, not just on opposite sides. A Fall could be constructed to connect, say, Denver to Baltimore. It wouldn't go as fast, but all the principles would be the same.

[ArchAngel]

Lol, really? That's really part of that movie?
I mean, they don't go mars and now this?

[ScotchRobbins]

I love these stiff physics required in interstellar and interplanetary travel.

[ArcticFox]

I need some new Sci-Fi to pick on. Any suggestions?

[ArchAngel]

How about one of those mars movies? Like Mission to Mars or Red Planet?

Man... Mission to Mars. *shivers*

[ArcticFox]

Fertile ground.

I remember watching Mission to Mars and thinking: "This movie looks like it would be pretty realistic, right up until you start thinking about it."

Some of the more cringeworthy moments...

-Liquids in Space

When the micrometeorites start punching holes in the ship, some of those holes are punched into the fuel tank. The fuel starts to escape the tank, but immediately freezes, turning into sort of stalactites as they freeze solid, then pop off as more fuel pushes them away. The same thing happens later when holes in the hull are discovered by someone squeezing a drink bag and watching to see where the fluid goes to find the source of the air leak. Liquid doesn't freeze in space. Most liquids remain in liquid form in a pressurized environment. When the pressure is too low, they boil away. It's why water boils at a lower temperature on the stove in Denver than it does in Baltimore. Lower pressure = lower boiling point. In space, there's no pressure, so guess what water will do? And no, the cold doesn't flash freeze it too quickly for that to happen, because space isn't cold.

-Look ma, no helmet!

We sort of talked about this one before, but when Woody takes his space helmet off, he wouldn't die instantly, freezing. Woody's death would have been much slower than that, and pretty unpleasant to witness.

-Conservation of B.S.

Meanwhile, while Woody is drifting, his wife uses her suit thrusters to try and reach him. She burns her fuel to maintain her movement toward him, and reluctantly cuts the thrusters at about the halfway point since if she goes any further, she won't have enough fuel to propel herself all the way back...

...except that isn't how it works. Applying a thrust would cause her to accelerate, and cutting the thruster would stop the acceleration. Meanwhile, her momentum would keep her going at the same speed. All she really had to do was to get to a speed faster than Woody was moving, overtake him, use the thrusters to brake, then fire them to start back. As long as their orbit didn't decay too fast, they'd be able to get back just fine.

-In space, nobody can watch you burn

When the damaged ship is about to fire its engines, some of that frozen fuel has managed to drift in front of the engine nozzles. When the engine fires, BOOM! Half the ship blown away...

...except no. I don't know what kind of fuel this was supposed to be, but when thinking about rocket fuel, you need to think about how it burns. To make something burn, you need 3 things: fire, fuel and air. This is not negotiable. Even the Space Shuttle's engines needed these 3 things. Know what was inside that big orange tank? 2 smaller tanks. One had liquid hydrogen, the other had liquid oxygen. The two would get mixed in the engines and burned there. (Interesting trivia: The result of burning oxygen and hydrogen? Water. That was the exhaust product of the Space Shuttle's main engines... Water. Probably the cleanest burning engines ever used in the United States.) The Solid Rocket Boosters ran on a solid propellant where the fuel and oxygen were pre-mixed. To light the rockets, you just had to add some fire. It's why once those boosters started burning, it was impossible to stop them until they ran out of fuel. In a car engine, same deal. Fuel and air are mixed in the intake manifold and ignited by the spark plugs inside the combustion chamber.

With that in mind, consider the frozen fuel in front of the ship's engines. There was fire, there was fuel...

... no air. The fuel wouldn't have burned.

And even if it did.... it was obviously a very small amount, with engine thrust vectoring it away from the ship, in a non-sealed environment. There would have been no explosion of any significant size even if this was special fuel with premixed oxygen in it.

The one that bugged me the most was the part where the guy made a rotating DNA model out of M&Ms. Consider each individual M&M. In this model, it would be following a curved path. Objects in a 0g environment do not follow any path but a straight line unless affected by some outside force like gravity. What force was making these M&Ms follow a nonlinear trajectory?

Building a stationary model of DNA in a 0g environment out of M&Ms: Possible. Making it rotate: Impossible.

What makes me sad is that it was, overall, a decent movie and it would have been so easy to get these things right without altering the story. Don't make the M&Ms rotate. Let the micrometeorites damage the main engine itself in such away as to cause it to explode, rather than that ridiculous, contrived fuel leak. Have Woody irretrievable because nobody else had a thruster to reach him at all. Same story... but believable.

[ArchAngel]

You remember more of it than I do! I just remember first seeing it and the freezing scenes bother me. I'm not sure if it's this movie, but I remember one scene where a guy was in his spacecraft at "10% atmosphere" and he was just holding his breathe.
Just completely forgot what a zero/ultra-low pressure environment does.

To make a small correction, space is cold. There is very little thermal energy density. You won't "feel" as cold in space because you won't lose heat by conduction or convection, as we do here on earth, it'd be just by radiation. You wouldn't freeze to death in space, there are plenty of other things to kill you first.

[ArcticFox]

You remember more of it than I do! I just remember first seeing it and the freezing scenes bother me. I'm not sure if it's this movie, but I remember one scene where a guy was in his spacecraft at "10% atmosphere" and he was just holding his breathe.
Just completely forgot what a zero/ultra-low pressure environment does.

Yeah that was after the micrometeorites hit. The air in the ship was venting to space and a computer voice was counting off the atmosphere as a percentile. The thing that irked me was that several things should have been happening (or not happening)

-The hole wasn't that big, yo!

The holes were maybe, in total a couple inches in diameter if all in the same place. The internal volume of the spacecraft was huge. It should have taken a lot longer to vent out. Furthermore, the pressurization system should have been able to compensate. (As an example for comparison... If you were in a 737 at 35,000 feet, and one of the windows came completely out, the aircraft would still be able to keep the inside of the cabin pressurized at 1 atm.)

-Why are you talking so slow?

As the air pressure dropped, the computer voice started... to... speak... more... slowly... Why? Why would the computer be affected? The only auditory change as the cabin pressure vented would be that sound doesn't propagate as well in thinner air as it would in thick air, so the volume would seem to go down...

-Brrrrrrr?

As the cabin pressure dropped, it would get colder. Not because of space, but because temperature drops as pressure is vented. It's why an aerosol can gets cold in your hand as you spray it. The highly pressurized liquid inside is venting through the nozzle and leaving the pressure in the can lower, which drops its temperature. After a few moments the heat will be at equilibrium again as the outside air warms the can.

To make a small correction, space is cold. There is very little thermal energy density. You won't "feel" as cold in space because you won't lose heat by conduction or convection, as we do here on earth, it'd be just by radiation. You wouldn't freeze to death in space, there are plenty of other things to kill you first.

True what you said about the radiation of heat, but technically space isn't "cold" and neither is it warm... It just isn't anything because a vacuum doesn't have a temperature at all, high or low. We associate space with cold because things in space become cold as their heat radiates away.