Space Elevators Could Be Lethal

Maggie McKee writes, "A new study reports that passengers on space elevators of current design could be killed by radiation. Even traveling at 200 kilometers per hour, passengers would spend several days in the Van Allen radiation belts, long enough to kill them." Looks like the elevator scientists will get this one solved before liftoff.

The two rubs

[LotsOfPhil]

This hasn't been an issue before because most astronauts don't get in the way of the van Allen belts. The Apollo astronauts went through super fast (escape velocity is 40,000 km/hr).

"For a space elevator travelling at the current proposed speed of 200 kilometres per hour, however, passengers might spend half a week in the belts. That would hit them with 200 times the radiation experienced by the Apollo astronauts."

The article says that you may not want to add shielding because of the added mass. Wikipedia [wikipedia.org] says that "an object satellite shielded by 3 mm of aluminum will receive about 2500 rem (25 Sv) per year." I don't know how this would translate for people going through the area, but 3 mm of aluminum doesn't weigh much.

Re:Aqua viva

[maxume]

Radiation does bad things to dna. It mostly just heats water. Ooooh, scary, somewhat warmer water.

Re:Oh, the horror!

[Vraylle]

I was neither serious, nor trolling. I believe in many cultures my original statement would be considered "a joke". Typically goes well with a sense of humor.

Re:Oh, the horror!

[A beautiful mind]

Well contrary to the popular opinion, scientists aren't idiots, so they thought about the Van Allen radiation belts [wikipedia.org] long before any sensationalist headline came up with it.

Re:The two rubs

[InterGuru]

2500 rem a year is about 6.8 rem/day. While occupational regulations are complex and depend on what type of radiation, they are the equivalent of 5 rem/year. See [state.ny.us] as an example. This means the occupants could not spend too much time in the Van Allen Belt.

Re:I've always wondered ...

[NEOGEOman]

It's the high-speed rotation and length of the cable that keeps it upright and taut. If you don't anchor the bottom of the elevator the entire thing will go flinging off into space. Fun for a while, but eventually someone will get upset about it.

Hybrid solution

[Fonce]

Given that gravity won't be nearly as much of an issue at that altitude, a combination of shielding including water or metal (likely both) and increased speed seems to me to be the simplest route. All things being equal, that's probably the better solution.

We've made it through the Van Allens before, we'll figure out how to do it again.

And, anything can kill you, really, so long as it's an action. Space elevators aren't lethal in and of themselves. Organ failure due to blunt trauma, rapid depressurization, radiation poisoning; these can kill you. An elevator cannot. It's an inanimate object. Well, unless you're on acid. Then you're on your own, kid.

Re:space elevator - environmental impact

[InfiniteWisdom]

http://en.wikipedia.org/wiki/Space_Elevator#In_the _event_of_failure [wikipedia.org]

No significant difference

[Stealth Potato]

While there might be some small benefit, it would not be as large as you think. Gravitational acceleration is still very significant at 500km up.

Acceleration toward an object due to gravity is given by g = GM/r^2, where G = 6.67e-11 is the gravitational constant, M is the mass of the object, and r is the distance from the center of mass of the object. The mass of the earth is about 5.97e24 kilograms, and its mean radius is about 6.37e6 meters. Thus, the acceleration due to gravity at the planet's surface is approximately (6.67e-11 * 5.97e24) / (6.37e6^2) = 9.81 m/s^2.

Go up another measly 500 kilometers, and your new acceleration is approximately (6.67e-11 * 5.97e24) / (6.87e6^2) = 8.44 m/s^2. That's only a 14% difference; a very noticeable reduction, but not enough to have significant savings. Your rocket fuel wouldn't go much farther at all, at least when the goal of the space elevator is to reduce cargo costs by orders of magnitude.

Re:I smell problems

[spun]

The cable needs to stretch beyond geosynchronous orbit. The center of mass of the cable will be in geosynchronous orbit. As for the sheilding, the article simply says what you say: we will need some. Three centimeters of aluminum should do it. This is absolutely not news to anyone who has seriously looked into space elevator technology.

Re:The two rubs

[Compholio]

While occupational regulations are complex and depend on what type of radiation, they are the equivalent of 5 rem/year.

Either your information is out of date or is for a specific state (in which case it is trumped by the federal limit). The federal limit is 100 mrem (1 mSev) per year [anl.gov] (not the actual legislation but references the federal limit, I believe the number was last changed in 1998). If you know anything about radiation then you know that the federally imposed limit is absolutely ridiculous, it is equivalent to approximately how much radiation you are exposed to by sleeping with your significant other over the course of a year [iem-inc.com].

Re:Jeez

[Cadallin]

The difficulty is that while a space elevator can reduce the cost of moving freight to orbit by a factor of hundred or so (easily enough to be worthwhile) That's still a hugely long way from being "free" like you describe. Even at a cost of $10 to $50 per kilogram (I'm very unsure of the actual speculated values), adding a metric tonne or two of shielding would still increase the cost to get people people (and non-rad resistant items) into orbit immensely. This is why a space elevator, while still a very good idea is not a magic bullet solution to space flight.

Realistically, some kind of reusable passenger rocket or space plane is still desirable in order to get passengers and sensitive kinds of freight through the Van Allen Belts to a Space Station (probably the one at the top of the elevator) in a rapid manner, so as to side step the issue entirely.

None of this is to say that a Space Elevator is a bad idea, FAR from it, but it may not necessarily to sensible to expect the same infrastructure to be able to accomodate both passengers and freight. I would argue that this is actually one of the major problems with the Space Shuttle's design. Being committed to a Freight and Passenger vehicle resulted in having to do a Saturn V scale launch just to get anybody into orbit, in addition to the limits this placed on any number of satellites launched with the shuttle. Had we designed a smaller, simpler vehicle, specifically for passengers (as the did the Russians) launches would have been MUCH cheaper, on a Saturn I or a modern Atlas scale. Additionally we would have been able to achieve significantly higher orbits (What if we didn't have to worry about Hubble's orbit decaying? Among any number of other advantages) Reliance on a Space Elevator for all our Space travel also gives a rather significant single point of failure.

Re:Math error?

[stunt_penguin]

If it just lets people off, they're going to fall straight back down to earth unless they have some way of accelerating to an extra 20,000km/h fairly quicky.

Re:C'mon, COMMON SENSE!

[Jeremi]

Stuff had damn well better come down the cable, or the thing will deorbit itself.

I don't think you've thought it through. Of course angular momentum isn't free, but that doesn't mean that you have to send things down the cable to keep the elevator from deorbiting. Once a unit of payload mass is lifted past the center of gravity of the cable, it effectively becomes part of the counterweight, increasing the amount of mass the space elevator is capable of lifting from then on (up to the point where the increased tension would cause the cable to snap, anyway).

So where does the "non-free" angular momentum come from? From the angular momentum of the Earth, of course... every time something goes up the elevator, the Earth spins a tiny bit slower -- similar to how an ice skater spins more slowly after she extends her arms. Fortunately, the Earth is massive enough compared to us humans that we'd never conceivably make a noticeable dent in Earth's momentum reserves (famous last words? ;^))

That said, a second parallel "down" elevator near the "up" elevator might be useful at some point, for more efficient round trips. But that's for later, the first task is to get a one-way elevator working.

Re:Math error?

[Cecil]

Actually, the giant counterweight at the top of it would be actually beyond geosynchronous orbit, and the center of mass of the cable would be in geosynchronous orbit, but the cable itself would not be in any kind of orbit.

Saying the cable is in geosynchronous orbit is analogous to saying that the cables on a suspension bridge are "flying".