February 08, 2003
Gregory Benford: Beyond the Shuttle
Science fiction writer and physics professor Gregory Benford has an excellent article up about NASA and the future of manned space flight.
Perhaps the only good thing about this disaster is that it will prompt NASA to rethink the design of manned spacecraft from first principles. Foremost is that the more complex a spacecraft is, the more things can go wrong.
The safest manned descent module was also the simplest: the Soviet "sharik" descent capsule, which was used by Vostok and Voskhod craft, and also in many unmanned missions since. It was just a sphere with the center of gravity on the side with the thickest ablative thermal shielding, so it was self-stabilizing. Even if the retrorockets failed to separate, it could re-enter safely. Simple ballistic craft that do not fly are also (relatively) simple.
With a spaceplane like the shuttle, however, you are not only committed to a complex shape, you are also committed to using brittle ceramic materials for thermal shielding. The first item on NASA's agenda will be to revisit the tiles issue.
There is the old KISS principle of engineering: Keep It Simple Stupid. NASA's Shuttle design violates that principle in a big way and the result is an expensive, unreliable, and unsafe spacecraft. Benford argues for inherently more reliable designs that do not rely on so many things to go right in order to work.
Benford argues for the development of a centrifuge in space because it is needed for human health during extended periods in zero gravity. That seems like the wrong solution to the problem. It makes much more sense to fund basic research into how muscle and bone growth is regulated. If control could be achieved over those processes then humans could be adapted to zero gravity living. This would be beneficial for more than just zero gravity conditions. As Benford points out, Mars has only 0.377 of Earth's gravity. But the problem of insufficient gravity for human health is even worse for a Moon base with the Moon having only 0.166 of Earth's gravity. Plus, a space hotel at the L1 Earth-Moon Lagrange point would be cheaper to build and operate if it didn't have to be a large centrifuge.
An even more compelling reason to solve the human gravity problem with a biological approach is that the research would surely produce valuable information for the treatment of osteoporosis as well as for healing bone and tissue injuries. For years one justification offered up for space exploration is that it will yield valuable technological spin-offs that will benefit us down here on Earth. A biological approach to solving the gravity problem would produce medically valuable research results.
Benford also argues for developing a closed biosphere. Certainly permanent Moon and Mars bases should have the ability to grow their own food. This problem also would best be solved in biological research. Tissue engineering techniques could be used to develop cell lines that can grow edible steak meat and chicken meat. Plant and animal cell lines could be developed to produce optimal quantities of vitamins and other nutrients. This is another avenue of research that could be pursued to enable space exploration that would generate technological spin-offs with commercially valuable Earth-bound applications.
Biotechnological approaches could address many other problems that would need to be solved in order to maintain human populations on permanent Moon and Mars bases. One problem is medical. One could take as much of each type of drug as might conceivably be needed. But there are too many drugs and it would be difficult to predict needs. One approach to solving this problem would be to genetically engineer strains of bacteria, yeast or other organisms to produce a large variety of drugs. One would need to take along frozen samples of each strain of bacteria that produced a given type of drug. Then when the need for a drug arose that bacteria could rapidly be cultured to grow and produce the needed quantity.
We should not rush to make a trip to Mars. We should instead identify all the technological problems that need to be solved in order to make a Mars trip and permanent establishment of a Mars base safe and affordable. We should not push out into space using barely adequate technology. We should put technology development first. Nuclear propulsion for much faster interplanetary travel, biological techniques to adapt to zero gravity, and biological technologies for growth of food and drugs, are just a few of the areas that a forward thinking space program would fund.
I think you are a bit overoptimistic about bio-engineering's ability to deal with the negative health aspects of space flight (zero-gee, and not mentioned was high radiation levels).
The human body's complexity and kludgery makes the space shuttle seem elegant by comparison. There is a huge problem with complexity here... the very large number of complex organic chemicals, all potentially interacting, in a living organism with a complex physical structure.
We need to proceed on both the space medicine path and other approaches. We are more likely to get centrifugal space structures going before we solve the physiological engineering problems. Likewise, we need high impulse nuclear rockets to keep us from spending as much time getting to where we want to go - helping with both zero-gee and radiation problems. Ideally, systems could maintain acceleration of significant fractions of 1 g. Since nobody is talking about this, I suspect there are extremely hard or insurmountable engineering challenges to doing this: getting enough plasma to a high enough velocity to get an extreme specific impulse.
Just a couple of weeks ago, the rumours were flying that Bush was going to announce a trip to Mars using nuclear propulsion. I wonder what happened to that?
John, I realize that I'm arguing for working on problems that are hard to solve. But we need the solutions for lots of reasons. I see the centrifuge approach as an on-going expense. Whereas while the biological approach is expensive at the research stage once the answers are found they will be cheap to apply and will also help us down here. We really ought to approach more problems with a goal of making an advance as a way to solve them rather than just go with an approach that is workable but not ideal today. If we want to go into space in a big way then we need those big advances and lots of them.
I think the space program should be approached in a way that provides big tangible benefits for humanity.
The biological approach is a better more general solution even for space purposes. How can people live and do a lot of work on Mars or the Moon if they have to spend much of each day in a centrifuge?
I made a post about the nuclear propulsion proposal about a week ago. If you look at the bottom of the post where I added updates you'll see what was going on there.
I guess we are looking at different time horizons. The centrifuge approach is doable today, meaning we can go ahead and think about long trips now. None of this means we should stop the other research, but I suspect that some of the biological engineering stuff could take 50 years. We need a viable space program NOW!
As far as nuclear propulsion (and you post is indeed quite informative)... There are two basic approaches:
1) Use a reactor to generate heat. This is basically a standard rocket with more efficient fuel. It gets higher specific impulse, but not enough to be really revolutionary.
2) Use a reactor to produce electrical power, which is then used to accelerate ions. Ion engines can have a very high specific impulse because the ion's can achieve near-relativistic velocities, as opposed to 3000K thermal velocities of the first approach. But, I have never seen #2 suggested for main propulsion. I can only guess that the approach doesn't scale up well or something. I hope to hear more about this from someone who knows more about it.
And then there are the far out approaches - thermonuclear engines including Bussard ramjets.
John, I am guessing that you haven't been reading my blog for all that long. My biggest themes are biotech and the ways its going to change a great many things. Biological engineering in various forms is going to happen a lot sooner than 50 years and even sooner than 30 years. See my Biotech Advance Rates category archive. Also, see some of my other bio category archives. The rate of advance in biotech is accelerating.
We are not going to get a viable space program now. I think the key technology for a trip to Mars is a nuclear propulsion system that could speed the trip. NASA hasn't started working on that yet. I do not expect NASA to be ready to go to Mars in the next 15 years and possibly not until 20 or 25 years from now.
We certainly could figure out how osteocyte activity and other relevant biological activity involving muscle and bone maintenance is regulated and how to intervene pharmaceutically well before a Mars mission was ready to depart. Scientists could identity all the relevant proteins and figure out they work in 10 or 15 years tops. They could start developing compounds that will intervene in their regulatory systems well before understanding all the systems in detail.
My guess is that if the Mars mission doesn't happen before 2020 that by then the pharmaceutical industry will have treatments developed for anti-aging and wound healing that will be useful for astronauts. But NASA could accelerate the progress in this area by funding it.
While we obviously need to work on better launchers and better propulsion systems for travel between the planets we really need biological advances just as much in order to explore the solar system. We need genetically engineered organisms to grow food, medicine, and even structural materials. We need advances in our understanding and ability to manipulate how the human body responds to space.
I don't think we should go to Mars with the minimum amount of technology needed to make the trip. We should not repeat the Apollo experience. We should put technology development first. We should focus on the development of technologies that will allow us to sustain our presence in locations. Apollo was a stunt. It did not enable a follow-on step. We need to build a firmer base for moving into space and spend less on missions and more on developing technological capabilities.
I want to address a comment you made that Randall did not answer directly in his reply. We already have a viable space program--it just involves everything except the shuttle and the ISS.
We use that space program every time we make a long-distance phone call or watch HBO or play with one of those cool GPS devices. Granted the shuttle put many of the involved satellites in space, but the shuttle is the optional part of that equation.
When one factors in the cost of two shuttles and fourteen lives, I doubt the shuttle is all that cost-effective compared to the unmanned ballistic alternatives predating it by a decade or more.
Heck, just think of all the decommissioned ICBM's we could have used instead.
We rushed headlong into killing humans by the sevens; we don't need to rush headlong into killing humans by the dozens or the scores. Manned missions and permanent colonization can wait until we have better enabling technologies. Attempting it now would be like Europe trying to colonize America by canoe.
Theoretically, the canoe has an adequate propulsion system and--with a bit of luck--some of the expeditions would succeed.