The thread for space cadets!

[Winner]

VASIMR takes a lot less propellant.

At the cost of thrust. In the (paraphrased) words of the first speaker in the video I linked, if someone told you: "I'll give you a car that can drive a million kilometres per litre of fuel, but it will take you a week to get out of the parking lot", would you buy that car? I guess not.

In most proposals for a piloted VASIMR ship to Mars I've seen, they ended up with space monstrosities with the overall mass of thousands of tonnes which can still deliver the same payload as a much lighter chemical or even lighter nuclear-thermal powered systems. In other words, totally impractical if the goal is to have a fast, fuel-efficient way of moving humans between Earth and Mars.

I can imagine a Mars cargo ship based on a viable combo of ultralight solar panels and electric propulsion. Such a ship would be hopefully reasonably reusable, use relatively little propellant and thus reduce the cost of supplying materials for a piloted Mars mission which would use more conventional means of propulsion. Since it would be automated and transporting only durable cargo, it wouldn't matter that it needed months to climb out of the Earth's gravity well and something over a year to get to Mars and insert itself into a reasonable orbit around it.

That's the kind of a job VASIMR can excel in, the others I've already listed. Thus, I am not anti-VASIMR, I just want people to understand the limitations and guard themselves against hype. Yes, it has a nice ISp and the thrust is better than in other electric propulsion systems, but there are very significant trade-offs

I haven't been keeping up with the SKYLON. That's the SSTO ramjet spaceplane, right?

It's neither ramjet or scramjet. They have a summary at the Reaction Engines Ltd. webpage.

As much as the purist in me wants to be skeptical, I must admit it's a tempting, almost brilliant idea.

Yup, definitely one of the most developed ones. It would definitely change the way we go to space, probably driving most medium-lift expendable launchers out of business.

 

[hobbsyoyo]

@Bugwar - I just don't see a space elevator being technically viable within 50 years. But yes, space races do tend to push the technological envelope outward quite a bit.

It'll also be a political issue as much as a technological issue. Space Elevators need to be on the equator (no country on the equator could build one themselves, so some bargaining will be necessary). Also, the Red/Blue/Green Mars books show how disasterous a space elevator failure would be.

Also, if you use an asteroid as the anchor, well. People aren't going to be happy with moving one into orbit.

Happy to see this thread has some traction!

 

[holy king]

Yup, exactly. That is, Earth space elevators are hard as hell. Lunar space elevator we could build right now, using a simple kevlar or steel cable. There even are commercial projects to demonstrate that.

hm, last time i checked there werent all that many people on the moon that could use such an elevator...

i mean i'm sure it makes sense, i just dont get it...

 

[Winner]

hm, last time i checked there werent all that many people on the moon that could use such an elevator...

i mean i'm sure it makes sense, i just dont get it...

Well, obviously it is meant as a way to get stuff (maybe even humans, thought that's not the primary objective) to and from the Moon very cheaply.

You see, the stuff we want from the Moon is water (and perhaps some easily extractable minerals/metals). If we can mine water, process it into propellant, and get it back to low-Earth orbit (LEO) cheaply, it would be a huuuuuge enabler for all kinds of missions in space. As it goes, 90%+ of the mass of any manned mission to Mars, asteroids, or anywhere else is propellant. Therefore, if you can get it cheaply from the Moon instead of hauling it to LEO from Earth surface in mega-expensive expendable heavy-lift rockets, you've just made your mission 5-10 times cheaper without changing anything in its design.

That's an attractive thought, and a possible venue for commercial subjects to explore, if there is government stimulus in terms of... you know, doing something in space.

 

[Winner]

It'll also be a political issue as much as a technological issue. Space Elevators need to be on the equator (no country on the equator could build one themselves, so some bargaining will be necessary). Also, the Red/Blue/Green Mars books show how disasterous a space elevator failure would be.

Actually, they don't have to be on the equator (I thought that too, but apparently I was mistaken). It's probably preferable to have them anchored as close as possible, but it's not necessary.

And yes, the elevator episode in Red Mars is one of my favourites

 

[holy king]

i see.

but space corporations? every dystopian sf story starts with them. i'm not sure we should go there.

 

[Winner]

i see.

but space corporations? every dystopian sf story starts with them. i'm not sure we should go there.

Yeah, they've got a bad rep, but we're not there yet. Blue space indians can rest easy... for now.

 

[hobbsyoyo]

but space corporations? every dystopian sf story starts with them. i'm not sure we should go there.

The quest for profits will push us further off this planet than government intentions in the long run. For good or bad

 

[Crezth]

At the cost of thrust... <snip>

That's the kind of a job VASIMR can excel in, the others I've already listed. Thus, I am not anti-VASIMR, I just want people to understand the limitations and guard themselves against hype. Yes, it has a nice ISp and the thrust is better than in other electric propulsion systems, but there are very significant trade-offs

Noted. Keep in mind that a (highly theoretical) 200 megawatt VASIMR could get to Mars in 40 days. Yeah, it isn't feasible right now, and waving around the Fantasy Science wand (antimatter! fusion!) doesn't actually do anything, but this is what I am primarily touting when I refer to it as the future.

That having been said, maybe I shouldn't have hyped anyone up on the premise of a technology that only works with fantasy power sources.

It's neither ramjet or scramjet. They have a summary at the Reaction Engines Ltd. webpage.

Yup, definitely one of the most developed ones. It would definitely change the way we go to space, probably driving most medium-lift expendable launchers out of business.

A quick glance tells me I'll definitely need to unpack this in detail later. Woah. O_o

 

[bugwar]

i see.

but space corporations? every dystopian sf story starts with them. i'm not sure we should go there.

Dystopian?
Yea, when doing an emo SF story, they make better bad guys than Space Nazi's.

However, if you aren't part of the 'doom and gloom' is the future crowd, check out tales like 'Pandora's Star'. Humanity manages to do well even with mega-corps.

 

[SouthernKing]

I don't know enough about materials science to say.

The most important thing to look at here here is breaking length, which is the longest a long strand of a material can be suspended without tearing. The strongest metals have breaking lengths in tens of kilometers. Carbon fibers, kevlar, and such have breaking lengths in the hundreds of km. Right now, the strongest materials in tensile strength, carbon nanotubes and graphene ribbons, have breaking lengths in the thousands of km, but that's still an order of magnitude too weak for an elevator cable from surface to geosynchronous orbit. Nevertheless, they are not only the strongest tensile strength wise, they also conduct electricity, meaning that theoretically (although a power source on the elevator 'car' would work better) one could power the elevator through the 'cable' alone.

And the lunar one: There is already an American firm trying to kickstart a lunar space elevator construction. An elevator from the lunar surface to either L1 or L2 could be done with current materials and tech (Kevlar is possible, and another fiber called M5, which is the least brittle carbon fiber yet developed, has been touted)

My knowledge on the subject makes me believe that space elevators (and whatever comes out of them) are a far better and more promising solution to further space exploration than surface launches, and that it's an important first step before further exploration and colonization. My interest in space has always been more scientific (and astronomy-oriented) than engineering, and you probably know better than me how this works.

On a different subject, is there any recent word about that one idea that was going around a while back to send an unmanned spacecraft to try and drill through the ice on Europa?

 

[uppi]

Right now, the strongest materials in tensile strength, carbon nanotubes and graphene ribbons, have breaking lengths in the thousands of km, but that's still an order of magnitude too weak for an elevator cable from surface to geosynchronous orbit. Nevertheless, they are not only the strongest tensile strength wise, they also conduct electricity, meaning that theoretically (although a power source on the elevator 'car' would work better) one could power the elevator through the 'cable' alone.

Having a material that has the required strength is one thing. Being able to actually make a long cable from it is another thing. Nanostructures tend to be small and not ten thousands of kilometers long.

 

[SouthernKing]

Having a material that has the required strength is one thing. Being able to actually make a long cable from it is another thing. Nanostructures tend to be small and not ten thousands of kilometers long.

True, that's the other problem. But carbon nanotubes have been created that have a length-diameter ratio of over a hundred million to one, and its definitely a step in the right direction.

 

[uppi]

True, that's the other problem. But carbon nanotubes have been created that have a length-diameter ratio of over a hundred million to one, and its definitely a step in the right direction.

And that's still just a centimeter...

Well it does suggest that in theory infinitely long nanotubes could be possible, but it remains to be seen if there is a realistic method to produce them that long.

 

[hobbsyoyo]

There was not, nor are there, any funds for a Europa ice mission. There is research on the subject, but no plans on the books. I also think there is a desire to wait until the lake Vostok drilling is complete to see what lessons can be learned.

 

[Winner]

My knowledge on the subject makes me believe that space elevators (and whatever comes out of them) are a far better and more promising solution to further space exploration than surface launches, and that it's an important first step before further exploration and colonization. My interest in space has always been more scientific (and astronomy-oriented) than engineering, and you probably know better than me how this works.

As much as I like the idea, I don't think that they're "far better and more promising" than surface launches nor "an important first step for further explorations". If we waited for a space elevator on Earth, we'd probably have to delay everything by 50 years or more.

Also, to build a space elevator, one kind of has to have some infrastructure in space already, which isn't very feasible without having a decent ability to send stuff to space by more conventional means.

Lastly, SSTO spaceplanes are potentially more flexible in terms of transporting passengers. A launch to LEO on something like Skylon would take minutes. A climb on the space elevator to GEO would take days, and you'd still end up somewhere else then where you wanted to be.

Space elevators definitely have a future ahead of them, but I doubt they'll come before SSTO spaceplanes and play a key role in the near-term exploration of the Solar System.

On a different subject, is there any recent word about that one idea that was going around a while back to send an unmanned spacecraft to try and drill through the ice on Europa?

Way too difficult for now.

 

[SouthernKing]

That's true, there are short-term disadvantages, but in the long-term space elevators are a far cheaper, more efficient, and better alternative to anything else.

I'm just not convinced on spaceplanes at all as a truly long-term solution, even if they are SSTO. While it may be cheaper compared to current launch vehicles (I.e. the giant waste that was the space shuttle) the problem lies in that there's issues regarding propellant vs. weight, which severely limits cargo weight. That being said, if somebody can get one working, I do see a bright future for SSTOs.

 

[Winner]

That's true, there are short-term disadvantages, but in the long-term space elevators are a far cheaper, more efficient, and better alternative to anything else.

I'm just not convinced on spaceplanes at all as a truly long-term solution, even if they are SSTO. While it may be cheaper compared to current launch vehicles (I.e. the giant waste that was the space shuttle) the problem lies in that there's issues regarding propellant vs. weight, which severely limits cargo weight. That being said, if somebody can get one working, I do see a bright future for SSTOs.

Sure, but I mentioned passengers specifically. SSTO spaceplanes, if available, have the benefit of speed and flexibility (in terms of points of departure) comparable to the difference between trains and airplanes on Earth. Trains are more efficient, can carry much more cargo, but they're slower and limited to existing rail networks. Airplanes have an advantage over long distances even though they're more expensive and far less fuel-efficient.

In the end, I believe space elevators will be used mostly for cargo and lower-class passengers moving out of Earth for good. Tourists and business people travelling to LEO will find spaceplanes more convenient. (Geez, this sounds as if it was written in the 1960s )

 

[SouthernKing]

Sure, but I mentioned passengers specifically. SSTO spaceplanes, if available, have the benefit of speed and flexibility (in terms of points of departure) comparable to the difference between trains and airplanes on Earth. Trains are more efficient, can carry much more cargo, but they're slower and limited to existing rail networks. Airplanes have an advantage over long distances even though they're more expensive and far less fuel-efficient.

In the end, I believe space elevators will be used mostly for cargo and lower-class passengers moving out of Earth for good. Tourists and business people travelling to LEO will find spaceplanes more convenient. (Geez, this sounds as if it was written in the 1960s )

Makes sense. As long as it works well, I'm fine with it.
Hey, at least you didn't mention Pan Am flights to space

 

[hobbsyoyo]

Actually, they don't have to be on the equator (I thought that too, but apparently I was mistaken). It's probably preferable to have them anchored as close as possible, but it's not necessary.

And yes, the elevator episode in Red Mars is one of my favourites

Missed this before. How far off the equator can they go? I suspect it's not far enough off it to make a difference. The further off it you go, doesn't that impose massive penalties in the required material strength, expense, tether length, etc?