Sunday, September 23, 2007

Cruising around the Solar System

We have this idea that the Solar System is a vast place, and when we hear that Pluto is about 3 billion miles away or that the probe currently making its way to Pluto will arrive in 2015, our suspicions are confirmed. Even proposed manned missions to Mars talk about a 7 month transit time.

But that's more a reflection of how we choose to go. Currently, almost all(*1) of our probe propulsion is chemical... we typically accelerate in one big WOOSH (technical rocketry term) and then coast the rest of the way. You often see terms like 'Hohmann transfer orbit' - which sounds cool, but it's really just a minimum energy trajectory. Think 'slow'. Yes, the probe to Pluto has been coasting for years and will coast for many more years(*2).

There are two performance numbers of interest for a rocket, roughly sortakinda analogous to gas mileage and top speed for a car.(*3).

Here's the big 'a-ha': If we got better 'gas mileage' with our rockets, we wouldn't *have* to use minimum-energy trajectories! And the trips wouldn't take nearly so long.

In the future we'll travel using continuous-thrust propulsion. And we don't even need much thrust. If we could thrust at a continuous .03g (that is 3% of the gravitational pull you feel right now), Pluto is just over 2 months away! Talk about shrinking the size of the Solar System!
But .03g would really be quite a futuristic feat. I'd love to see a manned vehicle capable of even .0001g, which would be interesting just as a proof-of-concept; it's too wimpy to actually get us anywhere.

Things start to get fun around .001g. If we had a manned vehicle capable of .001g, we could start thinking about a 7-month trip to Europa rather than Mars. A while back I wrote a sci-fi story(*4) about the first manned mission to Ceres, and in that story, the crew ship was capable of .001g acceleration.

A century from now 'Hohmann transfer orbit' will be a quaint olde term. All manned trips will be continuous-thrust, we'll use spiral trajectories, etc. The Solar System will effectively shrink in size just like the Earth has shrunk over the last century due to telecommunications.

(*1) We have used Ion engines on one or two probe missions, everything else is chemical.
(*2) With the exception of minor course corrections. We may have (I don't know) done a burn while passing Jupiter, it is an efficient way to add speed; accelerating during a gravitational slingshot.
(*3) The analogous numbers are Isp and maximum sustained acceleration. Isp is the Specific Impulse of the rocket; measured in how long (in seconds) a pound of fuel can produce a pound of thrust. Today's chemical rockets are in the 300s - 450s range. Ion engines are over 20,000s - but today, we can't take off from Earth with Ion engines. Even if we could we probably wouldn't choose to since the exhaust is dangerous.
(*4) Since I wrote it I have come across some writings on the web that make me painfully aware I can't write worth a hoot!

Johannes Kepler. The man, the myth, the enigma!

And now a quick word about Johannes Kepler - the rennaissance scientist I borrowed my moniker from. Even though he was a recluse and a bit of a mystic, I've always been a big fan.

Kepler was born in 1571 and died in 1630 and hung out mostly in Germany, Austria, and Denmark. He was a contemporary of Galileo (though they didn't have much more than a passing familiarity with each other, probably mostly due to religious differences (Catholic vs. Protestant)). You may read a detailed bio here:

He is on the *very* short list of scientists who, if he didn't do what he did, it wouldn't have been done for a long time. Einstein is probably also on the list... Euler... Chandreshekar, a few others. (But not Newton. Not Darwin. Not Hawking. Not almost anyone you've heard of.) But he developed his three laws of orbital motion almost a century before they 'should' have been discovered.(*)

Kepler was positively obsessed with planetary orbits - working on them for years, obtaining crucial orbital elements from Tycho Brahe (Kep's eyesight was poor while Brahe's was excellent and he was a skilled observational astronomer). In Kepler's time, no one was all that sure what shape the planetary orbits made. - they just knew that whatever it was, it wasn't a circle. He cranked on the observational data until he discovered what is now known as Kepler's First Law:

The shape of a planetary orbit is an ellipse with the Sun at one focus.

He then tried to quantify orbital speed for a planet, which led to his 2nd law:
A line drawn from the Sun to a Planet sweeps out equal areas in equal time. [This is conservation-of-angular-momemtum, but no one knew it then.]

Then he related the orbital speed of one planet to another via his 3rd law:

The cube of the semimajor axis of the orbit is proportional to the square of the period.

An amazing accomplishment. No one else was wrestling with this stuff during Kepler's time.
Kepler even predicted a transit of Venus (where, from Earth's point of view, Venus moves across the face of the Sun) in 1639 or so, but unfortunately for him he died years before it happened(*2). For you, however, you'll have the chance to see one in 2012! Which is cool, they are rare. Many people never have the chance to see one during their lifetimes. After 2012, it'll happen again in 2117 when we're all well into the dirtnap.

I'll close with a quote about Kepler from Bruce Stephenson (which I believe is from his book Kepler's_Physical_Astronomy),

"It can be said of Kepler, as of few great scientists, that what he accomplished would never have been done had he himself not done it. The discovery from the examination of naked-eye observational reports that planets move on ellipses, and according to the area law, is so exceedingly improbable - and Kepler's manner of arriving at it was so decidedly personal - that it lies outside the course of any inevitable development."

Johannes Kepler. Rock star.

(*) 2 of Kep's 3 laws could have been figured out by Newton by the time Newton published the Principia Mathematica in 1687. But even the 3rd Law would IMHO have eluded him... perhaps Euler would have later caught it. It's now an undergrad problem in Physics to derive Kep's 3 laws given Newton's law of gravitation, and it is very cumbersome to derive Newton's law given Kep's three (I don't know how to do it without some simplifying assumptions). You can argue Newton's Laws 'should' have been discovered first then Kepler's - but that's not how it happened.
(*2) Kepler died in 1630. Word of Kepler's calculations reached a young Astronomy student in England named Horrocks, who was almost definitely the first person ever on the planet to knowingly observe it. Kep actually predicted a transit in 1631 and a near miss in 1639, but Horrocks found the error in Kep's calculations, and he and friend William Crabtree made the observation. It's a cool story:

Cruising Around The Solar System

In part 1,
I said I'd love to see a manned vehicle capable of an acceleration of even .001g - which if I live to a ripe old age(*1) I may see at the end of my lifetime.

The only problem with this spaceship is it can't take off from Earth and it can't (safely) land on anything too big. Details, details!

Takeoff isn't a big problem, we do that with booster rockets today. Hopefully in a couple of decades we'll have a space elevator going... but we don't truly need it. Either way, takeoff is do-able.

But .001g puts some constraints on where we can go... they're not likely to have space elevators anywhere but the Moon! The problem is we couldn't land or take off from anywhere with a gravitational pull more than .001g - one thousandth the pull you're feeling now. (Assuming you're near the surface of the Earth!).

OK - so now how big is too big? Somewhere around 25 miles in diameter(*2) a body starts to have more self-gravity than .001g. This, unfortunately, rules out all the planets, the interesting moons, and some of the asteroids.

What's left?

Earth-crossing asteroids! Almost all of them are way smaller than this (there's only one that isn't). So of we had the Ronco .001g Spaceship we should and could visit a small hunk of rock nearby. This mission is do-able today & I'd love to see it done.

While we're at it, we should start focusing on is asteroid detection and deflection. We're not bad on the detection side; it would be extremely unlikely for anything 1/2 km in diameter or larger to get close without our knowing it. But even a half-kilometer rock hitting in the "right" place (unlikely, but possible) (and by 'right', I mean 'wrong'!) could kill tens or hundreds of millions of people.

And, it would be nice to detect them well in advance of them hitting us... you know that hunk of rock that we recently thought could hit us in 2029? Turns out it'll miss, but even if we found it would hit, we have the time to do something about it. The real concern is finding one that'll hit in, say, 3 weeks. All we could try to do is evacuate the impact area (if it hit land).

So - we need to experiment with deflection techniques. There are a few ideas out there & it would be great to test-drive them before we need them.

Remember, the dinosaurs died out because they didn't have a space program!

(*1) Which may happen - both of my grandfathers are alive today at ages 94 and 97 & they're both going strong for 100!
(*2) I assumed a density of 2 for this calculation - typical for an asteroid.

Newsweek and Global Warming part 2

The more I read this week’s cover article the more I see just how weak it is. The article doesn’t even differentiate between ‘deniers of global warming’ (I’ve yet to meet anyone who denies the Earth is in a recent warming trend) and folks who think evidence is lacking that humans are a major cause. All doubters are part of the vast evil industry-funded ‘denial machine’ while proponents of anthropogenic global warming (AGW) are Right and True, fighting the Good Fight.

Humans *might* be causing it (though I currently think it is unlikely) but at this point the jury is still out. AGW proponents seem to be in a politically-motivated rush to judgment that is hardly scientific. To beat a well-worn drum, AGW proponents need to address the following:

* From 1940 to 1975, why is it that CO2 emissions were high but the Earth cooled slightly?

* Why did the original IPCC report intentionally alter their data to skew results in favor of AGW? Intentionally altering data is terrible - a scientist should have a reverence toward actual data. Theories should be altered to fit data, not the other way around.

* Why is Mars warming?

* We can’t predict weather a week out - why should we trust models looking out a century? Aren’t we, in the words of Peter Huber, just multiplying the infinitesimal by the infinite to reach any desired conclusion?

* The Earth’s climate has always changed - why are we trying to fight it?

* Why do existing climate models fail to predict the known past? What was the cause of the medieval warming period from 900-1300? Why did it start? Why did it stop?

* Humans produce about .00001% of the dominant global-warming gas, H2O, and about 5% of the CO2 released to the environment each year. Why do we think our relatively small contribution has such a large effect? Where are the data to support that?

* Why have we decreed that RIGHT NOW is the magic point where Earth's climate is practically perfect in every way (movie quote alert)? How do we know that slightly-warmer is worse than slightly cooler?

* Why aren't AGW activists major proponants of nuclear power?

* If CO2 causes global temps to increase, why hasn’t this ever happened before? Why don’t we see it in ice-core-sample records to correspond to major volcanic eruptions?

I’m not saying we should ignore the environment and pollute away - far from it. As humanity’s population and environmental impact grows it behooves us to ensure that impact is as slight as possible. We are the first species on Earth able to respond to future predictions and so one is hopeful we can avoid the binge-and-purge population lessons of the past. But climate-change alarmism should never be confused with intelligent impact management.

The Earth has been far warmer and far colder than it is right now. CO2 concentrations in the atmosphere have risen and fallen. Shorelines have moved in & out. Clearly change is the only constant.
The one thing we know for sure about the Earth’s climate in a century? It will be different.

Saturday, September 22, 2007

Throwing my weight around

Let’s say the impossible happens and *I* get to control 50 mil of NASA’s bloated budget. (less than 1/300 of the total!)

I’d do two things:

First) I’ve blogged before about the dirt-cheap Mars sample-return plan: Perform a major search for bits of Mars that are already here. The easiest place to look is Antarctica - that's how we found ALH84001(*3). There are only a few known Martian meteorites, a program like this could easily double that number. And one of the new finds could be the Holy Grail (definite proof of life) we're looking for.

Just to start the ball rolling - we could send out Antarctic explorers for 50K per explorer per year (we‘d be turning away volunteers by the tens of thousands!). So it would be possible to send a crew of 100 for 5 mil per year. I think we’d turn up something interesting!

Second) Start actual R&D with tethers. (Browse that website - *very* cool and there are even other Tether companies out there. But IMHO this is the best). A tether consists of a central mass and a long rope - say 10 or 20 miles. The tether and payload are in orbit around Earth, spinning around each other like a gigantic bolo. It has one massive side and one small side (the payload). By letting go of the payload at the right time, the tether is able to throw a payload on ballistic trajectories anywhere in the inner Solar System. The max payload is about a tenth of the central tether mass.

I'd love to put one around Earth, then launch a tether to the Moon, then they could start playing catch with a small "ball" (which could be as low-tech as a bucket of rocks and a radio transmitter). We'd learn a ton from a year's worth of experiments like this. After playing catch for a while, we could even practice soft-landing the ball on the Moon & picking it up again. If we lose it, no biggie, they’re practically disposable. In fact, the bulk of the tether mass could be spare ‘balls’!

The round-trip time for the ball would be about a week, and then the tethers would take time to restore their orbits. We would also need to practice tossing a payload from the end of the tether to the central tether mass.

All this seems doable for ~40 mil - so I’d spend 10 mil looking for rocks and 40 mil on tethers.

This idea is hardly original with me - it is basically wrapping a mission around and

It is a brilliant idea to explore... getting outside the stupid LOG function in the Rocket Equation [ ] is absolutely key to exploration of the inner Solar System for far less fuel/cost/mass than otherwise. Until viable fusion rockets are available (50-100 years), this seems like the optimal solution.

Once the tethers are in place, all the miles are free. Let’s say we get the central mass of the Earth tether up to 25,000 kg - this could be spent fuel tanks from the Shuttle, buckets of rocks - anything really!

Now we could deposit 2500 kg on the Lunar surface for the cost of getting it to LEO.

Now, the fun part to consider is - if we were really able to deposit 2500 kg on the Lunar surface for (almost) free - what sort of infrastructure could we build up over time? Obviously, this type of capacity could be used to resupply a (nonexistent) Lunar base with food/water - but could we do other things?

Here's a list:

1) Tell top American colleges that if they design a rover, we'll park it on the Moon. Solicit proposals, take the top 5, give the top5 schools 200K in development money, and a year later, launch the rovers. We'd have to hitch a ride to LEO & that's it. The only requirements: the rover must be mobile, capable of teleoperation, include a videocamera, and be < 2500 kg. (*2). Total mission cost: $1 mil to develop the rovers, 5 - 50 mil to launch them. We could even partner with a TV network to run a 12 week weekly show, 1 intro, 5 rover builds, 5 rover launch/landings, 1 wrapup. Put it on prime-time, and I'd bet people would watch - plus, it would establish an entertainment link to a real space mission.

2) Set a rover (maybe even one of the above 5) down at the poles, check out the water ice that is almost definitely there.

3) Land a small electric-powered bulldozer/rover near one of the water-ice (?) sites at the poles. Dig a trench. Land a second one, dig more... If the trench were (say) 8 feet deep, 8 feet across, and 30 feet long, it would be suitable for low-tech human occupation. A small dozer or two could dig this, given enough time. If the trench were near the poles, the Sun would never appear overhead - so most of the trench would be in the shade all the time and we wouldn't need to cover the roof to avoid solar radiation. The dozers could dig until 2/3 of the battery capacity were exhausted, then climb out, maybe climb a small hill, and position themselves for solar recharge - which could take as long as a couple of weeks, but we've got time. When the trench is completed, we could try sending up an inflatable hab that would fit in the trench and be light enough for the tethers to throw. Would this work? No idea! But if it did, it is even possible we could do a quick manned mission with the tethers. Send up some food & water, a couple of space suits, some kind of heater. Send up some scuba air tanks on a separate trip & use them to inflate the hab. Another nice advantage of tethers is that they can be tested repeatedly prior to actual use - obviously, we would take advantage of this prior to anything risky.

Since the Moon has no atmosphere, in theory the tether can set payloads gently right on the surface.

4) Land a rover near the Apollo 11 landing site, check it out.

5) Sample return - tethers optimize this beautifully. In fact, we should and could use this for the Mars sample-return mission. It would be very useful to install a Mars tether during the course of something we were going to do anyway.


(*1): The first referenced PDF file shows 85 days for the tether exactly as defined in the paper. Obviously, if we change key parameters (mass of the system, length of the tether), we change this figure also.

(*2): Getting our payload to LEO will cost some, but no more than $20,000,000. (the current price for launching a person to the ISS) Or - as long as we're into tethers - check out , we could do it with a high-altitude plane launch.

(*3) This is the Mars meteorite announced by NASA in '95 or so to contain proof of Martian life. The 'proof' is a bit lacking; the jury is still out. We know it's from Mars from the analysis of gases trapped in tiny bubbles in the rock. They're like nothing on Earth and they are very similar to what we know is on Mars

Part 2 - the D+He3 fusion reactor

A Deuterium-Helium3 fusion reaction will be our next step. It may well be our last step, since the D-He3 fusion reaction produces the most energy per unit mass of *any* possible reaction. [except for matter-antimatter - but antimatter does not occur naturally around here.]
The fusion reaction we'll use is:

D + He3 -> He4 + H

This is a *great* equation - the reaction produces no neutrons! In the D-T reactor discussed previously we had these pesky neutrons flying out of our containment trap since (being neutrally charged) we were unable to contain them. We made a virtue out of this fact by utilizing the speedy neutrons as best we could... but still it would be better if they weren't there at all.
If everything is charged it (hopefully!) stays in the trap. Better yet, we can extract energy from a fast He4 and H by electromagnetically braking them, converting their speed into energy with ~95% efficiency. Back in the D-T days, we turned speed into energy with efficiencies more like 35%.

And H and He4 aren't dangerous gases, they can be vented to the environment without issue.

It's all good!

We have the key concepts in place to grok any kind of fusion... we have a Bunsen Burner to heat the reaction chamber to 100 million degrees and we have a magnetic trap good enough to hold a small reaction chamber under high pressure so fusion can take place. We're good to go with D-He3... except for three little nagging details:

* All magnetic reaction chambers leak. If they leak too much, they can't sustain the pressure/temperature we need. Currently, the best magnetic traps in the world are just barely able to contain the D-T reaction and they are not good enough to contain D-He3. They need to be roughly 100 times better. This sounds like a big problem... but over the last 50 years we have improved our magnetic reaction chambers by a factor of over 10000. There is nothing fundamental about making them better still, we "just" need to do what we're doing, only better. So we should have it figured out by 2020.

* A magnetic trap good enough to contain a D-He3 fusion reaction will also permit D-D fusion. Without going into details, a bit of D-D fusion will be occuring in the magnetic trap, right alongside D-He3. And unfortunately, D-D makes fast neutrons. We will probably solve this problem by ignoring it.

* He3 doesn't exist on the Earth and it is energy-inefficient to manufacture it. But the Sun very kindly planted a small amount of it on the Moon. We could go fetch it. Cherei had a good blog post discussing the details here:

The Moon has enough He3 to power our civilization at current rates for about 1000 years. By then we'll be able to get it from the Mother Lode: The gas giant planets!

Kepler's stuff - my 'greatest hits' from 360

Fusion - The Power Generation Technique of the Future - Part 1

One way to categorize various techniques for generating eletrical power is:

1) Mechanical. This covers hydro power, wind power, and some funky variants like ocean-wave power and ocean-current power. All these use some natural phenomena to turn a permanent magnet in a coil, which generates electrical energy. The source can be continuous (like today's hydro) or intermittant.

2) Chemical. This is IMHO the most environmentally damaging... coal, natural gas, internal combustion engines., etc. In terms of the mass involved, it is a step up from mechanical power. That is, it requires far less mass to generate the same amount of power, as compared to mechanical power generation systems.

3) Nuclear fission. It turns out if we split certain atoms in the right way, energy is released. If that energy is harnessed, we get nice stable electric power. This is a step up from chemical power - meaning it doesn't take much mass at all. If done properly it generates very little waste.

4) Nuclear fusion. It doesn't exist... yet. But Any Day Now, Real Soon it will.

Fusion is slamming the right kinds of atoms together fast enough that the nucleii fuse and form a new kind of atom. (this is how the Sun makes energy) Sometimes (depending on the fusion reaction) energy is released also, and sometimes that energy can be usefully harnessed.

The problem is that atomic nucleii are positively charged - they repel each other, so they don't normally collide. But if they are heated to a sweltering 100 million degrees (Celcius, though at this point it hardly matters!) and held in a confined area, the nucleii will be zipping (technical nuclear physics term) around fast enough they'll sometimes collide.

Cool - so all we need it a container capable of holding a hundred million degrees (ouch!) under high pressure!

It doesn't exist, it *can't* exist. Bummer. [as a side note, this is why there was so much excitement over the bogus 'cold fusion' announcement in the 1980s... if fusion could occur at temps and pressures we consider normal, we'd be home free]

But wait - it doesn't have to be a physical container. Because the nucleii are charged, they can be affected by magnetic fields. So if we make a really really really really really really strong magnetic field we can confine the nucleii... this is actually possible with today's technology, even at a temp of 100 mil. Yeaaa, we're home free!

Well, not quite.

Most of today's experimental fusion research programs are trying to achieve the easiest useful fusion reaction involving the fusion of deuterium (hydrogen with an 'extra' neutron in its nucleus) and tritium (hydrogen + 2 extra neutrons).

D(euterium) is found in seawater and we know how to extract it.

T(ritium) is radioactive with a half-life of 12.33 years. So it's not found naturally, but we can (and do) know how to manufacture it.

The nuclear reaction is:

D+T -> He4 + n

The He4 nucleus is positively charged, so it will stay in our magnetic trap, smashing into other nucleii there & helping to heat them.

The n)eutron isn't charged, it won't even see the magnetic trap & it will zip (nuclear physics term) right out at a high rate of speed (about 1/6 the speed of light!) in some (essentially) random direction and smash into the first thing it sees. It's nice if that isn't you or me! It is commonly a lithium 'blanket' used to capture speeding neutrons. The blanket will probably absorb most of the energy of the speeding neutron, getting really hot. Using a lithium blanket does two useful things:

1) It will usually absorb the neutron, generating some Tritium as a possible result. So a D-T reactor can breed its own fuel.

2) Because it absorbs the speeding neutrons it gets hot. Hot enough we can wrap some steam pipes around it and run them to a turbine, creating power while cooling the blanket.

Sadly, we can't guarantee the blanket will capture all the neutrons. The metal of the reactor is bound to capture some as is the metal of the steam pipes. Depending on how exactly the capture occurs, radoiactive by-products will be formed.

So although a D-T fusion reactor doesn't directly create radioactive by-products, they are formed by the practical realities of building such a reactor. The energy created is on the order of 100 times more than the already-good nuclear fission reactor, and the waste is on the order of 100 times less. A D-T fusion reactor that produced as much energy as it cost (to maintain the magnetic fields) was first demonstrated in 1997 at the European JET Tokamak. It's all good... but it can be even better.

Coming next: Part 2, the D-He3 fusion reactor. Watch me get my geek on!