Wednesday, December 29, 2010

My 2010 Review

I started this year thinking the Augustine committee had nailed the Moon shut. Considering that I was a proponent of Constellation before the Augustine committee, that's pretty significant. If I go back to that time and see what I was saying to people, most of it was explaining the flexible path as an alternative to sitting on the ground waiting for a booster and a capsule and a lander to be developed by NASA.

I end this year thinking that the Moon isn't nailed shut. SpaceX has demonstrated that making a capsule and booster need not be expensive. Armadillo Aerospace and the other contractor's work on Project M (now Project Morpheus) demonstrated to me that going to the Moon need not be expensive. Tim Pickens and the Rocket City Space Pioneers have successfully restored my faith that the Google Lunar X-Prize will be won. Paul Spudis has actually become a robotic exploration advocate! In a few years time it won't be absurd to suggest that a commercial effort could send a rover to characterize the polar ice, make money by selling data to NASA, and later start selling lunar derived propellant in orbit.

I don't mean to suggest this negates the need for heavy lift. Actually, quite the opposite. I mean this to demonstrate that my belief that lunar exploration was necessarily expensive is slowly going away. With that frame of reference, I have to admit that maybe my belief that heavy lift is also necessarily expensive may have to go away. SpaceX have suggested they can do 130t to LEO for $2.5B in development costs and $300M per flight.

But the other problem with heavy lift is that it's a gate keeper. The advocates are perfectly happy to say that the Moon (or any beyond Earth target really) is off limits without heavy lift. This is simply wrong. We don't need heavy lift to send rovers to Mars so I think it is pretty clear that we don't need heavy lift to send rovers to the Moon.

Humans weigh less than rovers.

The problem is the can't-do attitude.

Monday, December 20, 2010

Soonest Space Solar Power

Space Solar Power has a bad rap, caused predominately by advocates who can't separate the exciting long term vision from the short term facts. In his recent paper, Al Globus has tried to rectify this by investigating what can be done with demonstrated launch vehicles, solar collectors and power beaming (and without on-orbit assembly, manned outposts, lunar materials, etc). His conclusion is that it appears space solar power is now ready for niche markets, such as forward military bases, where the price of power can be as much as $1/kWh.

The low cost launch vehicle of choice is, of course, SpaceX's Falcon 9. High specific power solar collection is achieved using thin-film heliogyros as demonstrated by the Japanese Ikaros satellite. The power beaming technology is infrared laser with custom solar panel receivers, as demonstrated by LaserMotive in their win at the Space Elevator Games last year.

A minor improvement in Globus' architecture is apparent. The mass of the spacecraft was estimated based on the throw capability of the Falcon 9 to geostationary transfer orbit (GTO), presumably because a solar sail style flight is expected to circularize the orbit, and solar sails can't start from low earth orbit (LEO). This is an implicit trade over a solar electric style flight from LEO, which I'm guessing is intended to utilize the solar collector for double duty in order to avoid additional mass. I'm not sure this trade wins. Even with a SMART-1 performance thruster, starting from LEO places 7751kg in GEO, 3.2 tons more than the estimated mass in the paper. If a NEXT thruster is available, the improvement goes up to 5.2 tons. However, this improvement only doubles the performance of the system, perhaps halving the price of power at the meter, which still doesn't make it competitive with the grid.

The problem is scale. Globus should be commended for describing a space solar power system that is achievable with current technology and could even make a profit in some niche markets, but let's think just a little bit further ahead for a moment. LaserMotive continues to improve the performance of their laser power beaming systems, so the 8% efficiency suggested may soon be on-par with the often quoted 10% efficiency of microwave power transmission. The paper suggests that SpaceX could reduce their prices by a factor of 3.6 if one ordered 1000 launches, but this claim is a few years old now. A more recent claim by SpaceX is that a super heavy lift vehicle could be built that delivers 130t to LEO for $300M per flight, a factor of just 2.3 - but the improved logistics of a single launch may offset that.

It should come as no surprise that reducing launch costs makes space solar power more feasible. What does surprise me is that sufficient specific power improvements in solar collection has been demonstrated which makes it reasonable to choose a lower efficiency beaming technique, with the resulting effect on the mass of the spacecraft making it launchable on existing boosters. This is a revolutionary idea which not only makes sense right now but defines a path for future work that will bring space solar power to the meter.

Thursday, December 16, 2010

Non-Rotating Artifical Gravity

If you put a long boom on a satellite, it will align to the "local vertical". This was first demonstrated on the GOES 3 probe in 1978. It works because the forces of gravity and the "centrifugal force" balance at the center of mass.

Today, long life space tethers are available, using existing materials they are light enough for long lengths to be launched on a cheap launch vehicle like SpaceX's Falcon 9. A length of 500 km, with a lifetime of 10 years, would have mass of just 1275 kg. The tether would stretch from the altitude of the International Space Station (~340 km) up past the altitude of the Hubble Space Telescope (~595 km), out to where the polar orbiting satellites do their job (~700 km+). Within equal masses on each end of the tether, a force of 0.1g would be experienced, with no rotation of the structure required.

Of course, this only works while in orbit around a planetary body. Around the Sun, say for generating artificial gravity for a trip to Mars, a much longer tether would be required and it quickly becomes infeasible. So what good is it? Currently, we have very little data on how the human body responds to partial gravity. Sure, we know lots about how it responds to 1g, and we have some ideas about how it responds to "zero g", but we don't have any data at all about anything in-between. 0.1g is just enough gravity for a human to stand upright and walk around (although Joe Carroll recently suggested that 0.06g was sufficient). If we could put some astronauts on a station with this level of partial gravity for a few months it would give us some vital data for determining whether people can actually live on the Moon or Mars or even asteroids for long periods of time without serious health issues.

Having the low end of the tether at the same orbit as the ISS, and having it not rotating around at high speed would make getting to the experiment very convenient. The high end of the tether could simply be the upper stage of the launch vehicle. SpaceX has already demonstrated that their second stage can be relighted, and flying to a circular orbit of 800km seems well within their capabilities. A 500km tether reel could fit in the trunk of the Dragon, which can remain connected to the second stage after separation.

Considering the availability and low cost of the hardware, the low risk of non-spinning artificial gravity, and the massive scientific payoff, NASA should be pursing this.. now.

Wednesday, December 08, 2010

A New Sputnik Moment?

Stephen Smith has an post over at his blog questioning President Obama's rhetoric that the down tick in the economy is having the same effect today as Sputnik had on the USA in the 50s and 60s. He's not convinced and neither am I, but near the middle he asks an interesting question: What would be the equivalent of a "Sputnik moment" in today's world?

The shock in the US caused by Sputnik was not so much that it was a military threat - although it was - but that it was a significant technical feat achieved by what most of the western world considered a backwater of scientific thought. Today, there are many technologies that are slowly being developed around the world which are primed for a breakthrough. Earlier this year North Korea claimed a fusion power breakthrough which certainly would have been a Sputnik moment if it hadn't turned out to just be a claim about fusion bombs, not fusion power.

This highlights a very important part of the Sputnik formula: how does the protagonist country dramatically demonstrate their technological achievement so there's no misunderstanding and no way to refute it? Sputnik did this fabulously by broadcasting an unmistakable signal that could be confirmed by amateurs and professionals alike. Any attempt to put the genie back in the bottle with Sputnik would be met with howls from the populous.

Suppose some manufacturing backwater suddenly started turning out superb jet engines, or even a whole new fighter plane. Just as a matter of competitive interest, other manufacturers would no doubt arrange to get their hands on a few samples and check out their quality. I expect that more than a few "national security" inquiries would also be made. What they discover blows their mind: the fan blades, the compressor, the combustion chambers, even the cowling, are all made from materials they've never seen before. Parts of the combustion chambers even appear to be made of perfectly shaped diamond.

By releasing these products onto the market, the protagonist has demonstrated a highly functional molecular nanotechnology manufacturing system. This is a massive breakthrough, and it would be completely unexpected. The current state of the art in molecular nanotechnology is basically: designing stuff we can't actually build. Here's some examples done with the open source nanotechnology CAD tool NanoEngineer-1:

There has also been some interesting work done by Ralph Merkle and Robert Freitas Jr. into making a "tool set" that might some day be usable to slowly make small objects in single quantities using hydrogen and carbon.

If some backwater country was to demonstrate that they had a molecular manufacturing system that could build anything they can design, using a handful of atoms - aka, not "just" a hydrocarbon metabolism - and do so on the macro scale, it would instantly make them a super power and set the stage for a worldwide scramble to duplicate their efforts and come up with some reasonable defense. I could imagine immediate calls for non-proliferation of the technology, etc.

That would be the equivalent of a "Sputnik moment" in today's world.

Friday, December 03, 2010

Apollo 8 Solo

In 1927 Charles Lindbergh flew non-stop from Long Island to Paris. He was catapulted to instant fame by doing so and won the Orteig Prize. He didn't have a co-pilot. He didn't have an army of engineers monitoring his plane or a flight surgeon monitoring his heart rate, it was just him and his trusty single-engine monoplane, the Spirit of St. Louis. His achievement is heralded today as kick-starting the commercial aviation industry and opening up the skies to the everyman.

But what of space? Could a modern Lindbergh fly an impossible journey and change the way we look at spaceflight forever? I think it can be done, and for cheaper than you might imagine.

In 1968 the first humans left the vicinity of Earth, flew 6 days and nearly a million miles to the Moon and back. Their mission not only was the first, it also proved the feasibility of the missions to follow. Apollo 8 would have been much easier to achieve had they only wanted to swing-by the Moon, and still a significant achievement. Instead, they entered lunar orbit, circling it 10 times before returning home.

If the flight is to be attempted today, the cheapest available launcher is the Falcon 9 from SpaceX. It can put 10,450kg into LEO. The Dragon capsule is also available - they say the crew configuration is not much different from the cargo configuration - and after removing the 310kg Common Berthing Mechanism, and another 60kg of miscellaneous mass savings, a dry mass of 1926kg is achievable.

For a single crew member, assumed to be less than 90kg, the consumables requirements for one week are: 11.839kg cabin air and pressurization, 25.83kg oxygen candles, 52.71kg LiHo CO2 scrubbers, 45kg food and water. Adding this to the dry mass gives a final mass to run the rocket equation on: 2152kg.

The delta-v required to leave Earth orbit and head towards the Moon is a whopping 3107m/s. Entering low Lunar orbit requires another 837m/s, and returning home requires another 837m/s. So we need a grand total of 4781m/s.

All the propulsive maneuvers are achieved using the Draco thrusters on the Dragon capsule, which I estimate to have a specific impulse of 309 seconds. dv = 9.8 * 309 * ln(10450 / 2152) gives us an uncomfortable 4m/s of margin. :) [edit: it occurs to me that the Dragon dry mass already includes a life support system, and a 78.54kg reduction in mass has a massive effect on delta-v. So this is more like 115m/s of margin, which should make anyone happy.]

In order to win the Orteig, Lindbergh had the Spirit built custom for his needs. Benjamin Mahoney is said to have built it for cost. Perhaps Elon Musk could be similarly persuaded, but at current prices it'll cost around $130M.