New Mars Forums

Well, the Yellowstone news is actually only a few months old.  Until they found the hotspot was gone (this still needs to be confirmed, BTW), Yellowstone had remained a significant threat.  In fact, it could still erupt again - even though the hotspot is gone, there could be enough active lava to power another eruption.

Although I'm not a terribly big fan of modern media, I'm glad they error on the side of being too alarmist rather than too complacent.

I'm not saying that MEMS is useless - far from it.  However, it's taken about 15 years to even see the most basic applications start appearing and these are quite different from the applications that were originally thought up.

For example, the lab-on-a-chip stuff (I haven't messed with these, they're too expensive for anything but companies and the biggest academic labs still) have actually been commercialized for a few years now and show great promise but were only possible after people realized that the low Reynolds number flow regimes at those size scales make it impossible to make normal valves and pumps.  On the other hand, the same flow conditions make possible a whole host of extremely efficient filtration and pumping sustems that are radically different from what we are accustomed to.

As far as accelerometers, the MEMS stuff isn't very sensitive.  Those accelerometers are great for detecting whether you just wrapped your car around a telephone pole but not much good for detecting stuff like a degree per day rotation like the Hubble gyroscopes do.  (I don't understand why the Hubble doesn't use laser gyros - they're more accurate and don't wear out).  OTOH, for things like vibration detection and impact detection, MEMS sensors are great.  I'm assuming the hundreds of sensors they're installing in the Shuttle to watch for debris impact are going to be MEMS based.

Things like being able to dope single atoms with an STM tip and the like are nothing but dumb stunts.  It's a great way to make a computer if you don't mind waiting a few thousand years for it to be built.  Modern lithography can churn out thousands of chips a day.  A standard fab line can churn out literally several billion transistors a day.

In contrast, these manipulation techniques are lucky to be able to make a single transistor in several hours of work.  There is no way to parallelize this process, either.  The only way that nano is going to give us computers is with some sort of massive self-assembly technique.  The biological nanotech I'm working on is trying to expand on this approach but practical applications are still years off.

I agree that nano will give us some useful products in afew years but this is nothing new.  Photographic film is an applied nanotech system using silver halide nanoparticles.  Chinese rose-tinted pottery uses the quantum confinement effects of the plasmon absorption of nano-sized gold particles to generate it's distinctive color and that's been around for about 500 years.

The reason that bio people tend to be underawed by nanotech is that they have been working on studying a fully integrated nanotech system that naturally evolved 3.5 billion years ago.  The particle and wire stuff coming out of the labs these days is kinda silly in comparison.

My take is that nanotech will have a number of applications in the next 10 years.  Nanotech will start to ahve an impact on semiconductors in 10-30 years.  Nanotech will start to become commonplace with artificial living organisms in the 20-100 year timeframe.

OK, I ran some numbers for the ETP barge idea I had and the numbers are considerable less attractive than I originally thought.  The idea is plausible but probably only practical for cargo shipments - it's too slow for sending people. 

Taking data from the Tethers Unlimited proposal for a 100 km rotating kinetic energy boost tether and optimizing it for propulsive force generation using 16 times the power output of the original design, I get the following numbers:

100 km tether, composed of 10 - 10km segments.
16 - 80 km long copper force generating electrodes.
Solar cells capable of generating an average of 980 kW of electrical power.
Unlike the original design, this does not rotate, greatly simplifying the strength requirements and allowing for greater thrusting efficiencies.
All data taken from the original paper is linearly extrapolated, assuming that non-linearities in mass scaling will end up approximately evening out.  Note that the original numbers are taken from experimentally derived numbers and existing commercial subsystems.

The projected mass of the whole thing is about 40 metric tons.  Assuming a spacecraft that masses 140 metric tons, the amount of time to boost the spacecraft to the Near Escape orbit is about 4.8 months.  Too long for manned crews but not too bad for cargo.

Carrying the example to extremes, boosting the power capacity of the tether to 32 and 64 times the original power levels give tether masses of 73 and 141 metric tons and transit times to Near Escape orbit of 2.85 and 1.9 months respectively.

The idea I've got isn't a new one but I haven't seen it being discussed seriously with respect to Mars.

Electro tether propulsion.

Basically, is you have a conductive tether in Earth orbit and apply a current to it, you can generate a thrust against Earth's magnetic field - not unlike how an electric motor works.  So far, tether experiments have met with mixed results but it looks as if we're getting close to being able have working sytems.  right now, one of the more prominent tether companies is Tethers Unlimited - check out their website, they have some nice technical documentation.  NASA's been interested in using Electro Tether Propulsion (ETP) to keep the ISS orbit stable.  If they can get the system to work, ETP will use excess power from the ISS solar panels to keep the orbit boosted, saving over $2 billion in launch costs to keep lofting hydrazine to the station over its lifetime.  There's the additional benefit of getting softer thrust that is more compatible with long term microgravity experiments.

Tether Unlimited is somewhat enamored with the idea of rotating tethers flinging cargo up into higher orbits.  Personally, I'm dubious about the engineering practicalities and safety of this approach.  What I'd be more interested in is an ETP powered space tug.

Since ETP thrust is pretty much 100% efficient and requires no propellant, the size of your power source is the most important factor.  A very large photovoltaic array win combination with a large battery array could give decent amounts of thrust for boosting vehicles into high orbits that minimize the amount of fuel needed to get to Mars, vastly increasing the total amount of cargo that we can deliver or allowing the use of smaller Earth to LEO boosters, lowering the cost. 

Basically, loft cargo to LEO with a heavy booster and dock it with the ETP barge.  The barge can then so a series of perigree boosts that greatly reduce the amount of fuel needed for a Trans Martian Injection(TMI).  After releaseing the Mars mission, the barge uses ETP to bring its orbit back down to boost the next mission.  The boosting period would occur over a month or two.

I haven't looked at the power requirements for the barge yet but here's some numbers I crunched for how much of an advantage you get for getting mass to Mars.

I used numbers out of Case for Mars and did a very simplistic set of calculations.  Someone better versed in orbital mechanics than I should feel free to correct any mistakes I've made:

Delta V's:
LEO to Near Escape eliptical orbit: 3.1 km/s
LEO to TMI (for slow 270 day cargo transfer) 3.7 km/s
LEO to TMI (for faster 180 day crew transfer) 4.3 km/s
NE to TMI (cargo) 0.6 km/s
NE to TMI (crew) 1.2 km/s

ISPs:
H2/O2: 470
NTP: 900
NEP: 8000

(mass of spacecraft + mass of propellant)/mass of spacecraft = e^(delta V / engine exhaust speed)
Engine exhaust speed (km/s)  = 0.0098 * ISP

Crunching these numbers, I get figures quite a bit higher than what Zubrin quites in Case for Mars - I assume that means that he is not including the mass of the transfer engine and associated fuel tanks as part of the total Mass sent to Mars as it is not useful mass.  To get my figures to match with his, I've divided the tonnage by 1.36 for checical and 1.23 for nuclear propulsion.   The space barge figures basically assume that the velocity boost gained is 'free' since the barge doesn't use propellant and detatches from the spacecraft before it launches off for Mars.

Here are the figures for how much tonnage we can get to Mars orbit (the usable amount we can get to the surface of Mars is lower by about 1/2 and I don't have the necessary data to properly calculate it) assuing a 140 ton to LEO heavy booster.  (NE stand for Near Escape - the orbit the space barge will raise the spacecraft to for 'free')

.....................O2/H2.......NTP.........NEP
LEO to TMI
cargo.............46.1..........74.8........109.4
LEO to TMI
crew..............40.5..........74.8........108.6
NE to TMI
cargo.............90.4..........106.3.......112.9
NE to TMI
crew..............79.3..........99.3.........112.1

As you can see, the space barge allows one to greatly increase the mass to Mars - even with chemical rockets on the spacecraft.  In fact, it would seem that chemical propulsion is a fairly good competitor to NTP with the barge.  For cargo missions, the barge is especially effective. 

Alternately, instead of larger masses, we can get away with smaller heavy lift vehicles, greatly reducing the cost of getting to Mars.  With purely chemical propulsion, you can use a booster 1/2 the size compared to a booster without the use of the barge.  Therefore, Zubrin's Mars Direct plan could use 70 ton to LEO boosters and otherwise be identical.

NTP engines have the disadvantage of having a heavy nuclear reactor that is designed for heat, not power generation.  NEP engines suffer from a lack of thrust.  In both cases, the level of development of these engines is far lower than what you have with chemical engines.  Use of the ETP barge allows one to get enough power out of plain old chemical rockets to make large Mars expeditions possible.

I suppose that one could argue that ETP is even more of an untried system than either NEP or NTP and that would be correct.  However, the principles behind tether propulsion are very simple and if successful in boosting the ISS, we will have an ample amount of operational data to work from.

I'll try to come up with some good estimates of what sort of magnitude of thrust and barge mass we're looking at here.

Again, I hate to be a wet towel but this is something of an area of expertise for me.  (I work on biologically assembled nanotech in grad school) 

This is cool work but it is not going to create a molecular assembly factory in 5 years.  Nanotech has been rife with overoptimistic predictions of its progress rate that have consistently been wrong. 

Take for example MEMS - back in the early 90's, they started making gears and stuff with silicon fab technology and they predicted all of these marvellous micro-scale robots that would run aroud, cleaning and doing other stuff for us (sound familiar?)  Well, 10+ years later, there are a handful of useful applications for MEMS and none of them involve those little gears.  (tiny cantelievers are used as deaccelleration sensors for airbag deployment) 

So far nanotech has been great at making tiny junk - like wires and particles.  Unfortunately, the ability to wire these into something useful has basicaly been non-existent.  Partially, it's because there's no real science for self-assembly of these things and also, we have only a vauge idea of what sort of nanoscale structures will be useful once built.  My guess is, that like MEMS, the sorts of structures that we think will be useful and the sort of structures that will end up actually being useful are two completely different things.

I think that the general consensus is that although Mars cannot stably retain an atmosphere, the process of losing it is slow.  If we were to terraform Mars tomorrow, it would be millions of years before it lost that atmosphere.  Presumably, in a million years, if humanity still exists, we'll have figured something out to deal with the problem in a sustainable fashion.

You're right, all those X-numbers start getting mixed up in my head after a while.  I now vaugely recall something about the X-33 being started *before* the X-30 or something wierd like that.

I realize that you have to be going supersonic for a ram/scramjet to operate.  However, maglev or not, you have to get that velocity somehow (rockets or standard turbofans) and in that case, the horizontal velocity component of a maglev launcher wouldn't be wasted as it would with a standard rocket.

I was just reading last night about seismograph readings of the Aurora planes being tracked at mach 6.  Perhaps the DOD is further along with high speed aircraft than it is letting on?  If so, stuff like the X-30 might be realistic on a shorter time frame. 

I agree that VASMIR is still a ways out but it does have some promise.  A multimegawatt reactor is theoretically possible.  Normal nuclear generators on Earth are in the gigawatt+ range.  Therefore, it is possible to think of a space nuclear reactor that operates in the 100 MW regime being possible.  It would have to be lofted piecemeal on heavy boosters, though.  Such a beast would have to be used in a reusable capacity, though.  Sort of a high speed cargo interplanetary freight hauler. 

In lieu of that, there's always standard ion engines.  I was browsing a Boeing site (don't remember the URL now) that was talking about tests of the new next-gen ion engines.  It didn't mention thrust but the engine mouth was 30 cm which gives womething like a 10-fold increase over what Deep Space 1 had for thrust, assuming no increase in thrust per emitter area.  Also, the ISP is topping 8000 and the projected engine lifetime is something like 15,000 hours.

The Yellowstone caldera is a bit worrisome but it is unlikely to erupt in the near future.  In fact, some recent evidence seems to indicate that it might be going extinct. 

It has been assumed that the Yellowstone activity is due to a hot spot like the one under Hawaii and Iceland.  You can actually follow the North American plate's progress across this hotspot by following volcanic geological features out West.  The Snake river valley was basically formed when the N. American plate kinda melted like butter over a flame as it passed over the hotspot.  The huge basalt floods millions of years ago that repaved most of Eastern Washiington with 50 feet of volcanic rock were probably a result of this action as well.  You can even see a shift in the direction of the hotspot movement that corresponds to the crustal plates getting knocked out of whack when India hit Asia millions of years ago.  (The same dogleg is why the Hawaiian islands change directions as they receed back towards Alaska.  This includes older islands that have since receeded under the water)

However, a recent meta survey of seismological data reveals the locations of various hotspots.  (hotspots are basically the result of how the mantle convects from the heat it receives from the core.  Because of the particular physical conditions involved, the upwellings tend to occur in thin columns) The hotspot expected under Yellowstone was not found.  This might also explain why Yellowstone just has hot springs and the like instead of more aggregious volcanic activity.  Although it's nota clsoed case, Yellowstone doesn't appear to be a large threat.  ( a recent flurry of reports of increased geological activity appear to have been a hoax)  Although the US government might have information containment policies, I can't see the information being kept secret.  Too many of the researchers at Yellowstone are academics with grad students.  Keeping secrets in that environment is nearly impossible.

However, there has been increased activity in an ancient caldera in CAlifornia.  (can't remember the name of the volcano, though)  If it erupts again, it could be in the same order of magnitude as Yellowstone.

What's the relative efficiency of thermoacoustic refrigeration these days?  I was under the impression that is was significantly more power-hungry than a traditional refrigerant-based system.

I can see how the center of mass might be a problem.  However, the solid booster stage I was thinking of was something along the lines of looking like a flat tuna can on the bottom of the DC-X.  Alternately, I suppose that you could strap a set of SRBs to the outside of a DC-X so that the denter of gravity is minimally disturbed.

The advantages to solid rocket boosters is the extremely low  failure rate and low cost of manufacture.  The more complex reusable rocket engines would be in the DC-X upper stage.  Basically, you throw away an empty metal can when you jettison the 1st stage.

The primary disadvantages to the solid rocket booster is that the geometry involved would require multiple engines.  This adds the danger that there will be a thrust differential that would send the rocket off course.  However, given that 6 SRBs are used in the Delta IV which has the highest success rate of any booster in history, this is probably a moot concern.

However, regardless of TSTO or SSTO, I'm more interested in hammering out just how adventageous it is to employ the sort of low level boosting schemes that have been mentioned.  For example, just how much of an advantage do you have by setting up a maglev train booster? 

I'm personally dubious about the maglev booster since it can realistically only achieve about mach 1 and imparts mostly horizontal velocity rather than vertical velocity.  Gaining horizontal velicoty that low in the atmosphere might even be counterproductive since it means fighting much more atmospheric drag.  The only way I see this being advantageous is with some sort of scramjet boosted orbiter.

I hate to be the wet towel here but those 2 year estimates for attaining the required cable strengths are wildly optimistic.  In the next 2-10 years, we will see practical carbon nanotube fibers become a reality and start hitting specialized markets.  These fibers will have several times the strength of present high tensile strength materials like Kevlar and will revolutionize engineering. 

HOWEVER, I'm highly dubious about these 1st gen fibers being good enough for a space elevator.  IIRC, the theoretical strength of CNTs is something like 300 GPa and the strength needed for a apace elevator is something like 100 GPa.  Presently, we're just starting to push past 1GPa to 10 GPa with existing CNT cables.  The major problem is that the actual CNT's are only a few microns long and are held together by glue.  Therefore the bulk strength if the cable is largely determined by the glue strength and the strength of the glue-CNT bond which is weak since the graphene structure of CNT's is quite slippery.

There are proposals to chemically modify the CNT's so that they bond to the glue better and this will lead to a significant increase in the cable strength.  However, the glue still will remain a weak link.  Furthermore, the CNT's themselves will lose a LOT of strength due to the chemicla modifications done to them.  Threfore it is unlikely that composite nanotubes are capable of the kind of strength needed.

What will ultimately be the elevator material is a cable made of single-wall, defect-free CNTs that basically run the length of the cable.  Unfortunately, we have no idea how this might be done, much less used to makea 36,000+ km cable.  It *might* be possible at some point in the future to do this but probably on a time frame much longer than 10 years.

Actually, someone recently proposed a method for getting a probe to the Earth's core.  Basically, you take a year's worth of global iron production, heat it up to 10,000 degrees C, put some sort of super heat-shielded sensor package with cryogenic cooling and drop it.

The mass of iron is hot enough to melt through rock like butter and dense enough to sink most of the way to Earth's core.  Of course, there's about 1000 different reasons this wouldn't work but it is theoretically possible.