LiftPort Staff Blog

(This post is my personal opinion, and does not reflect official LiftPort policy. I apologize for the length of this post.)

I have only made this letter longer because I have not had the time to make it shorter.

Blaise Pascal

Brad Edwards posted some commentary on LiftPort’s recently released technical roapmap to space elevator development. While I appreciate feedback, and we did ask for suggestions on how to improve the roadmap, I prefer the feedback not be wrapped in ad hominem attacks.

That being said, I will address Edwards’ technical concerns, and then I’ll get to his personal attacks.

Technical Concerns

When writing up the roadmap, I was torn between including every single last detail that went into it, and trying to keep it relatively brief. We decided to go for the shorter, summary version. In retrospect, we probably should have included more details, a mistake for which I accept blame. And it seems that I must have failed to explain things clearly in the summary version, given Edwards’ misunderstandings. I will try to clarify things below. Let’s take the technical arguments in order.

Edwards first references a Los Alamos announcement about high-strength carbon nanotube-based material. The strength claim is made in a single sentence, and the rest of the release talks about a partnership between Los Alamos and CNT Technologies. There are two points to be made. First, there is no mention of a peer-reviewed journal publication documenting the fibers’ properties. I, along with the rest of the industrialized world, am eager to see proof of these claims.

More importantly, the timeline in the roadmap is unaffected by quicker development of high strength fibers. Edwards says:

Liftport has this material strength milestone at the year 2020 and this drives much of their roadmap.

Apparently he missed this quote about material advances from page two of the roadmap:

earlier availability will not particularly speed up development of the space elevator.

While the Gantt chart is easier to understand when it can be manipulated inside MS Project instead of viewed as a static PDF document, it turns out that pushing all the material strength advances up as far as you wish does not significantly affect the final completion date projected in the roadmap. In other words, if a material that had all the required properties (not just strength, but lack of creep, resistant to mechanical & thermal fatigue, etc.) were to magically appear in bulk quantities tomorrow, the space elevator would still not begin commercial operations (by our estimates) until roughly 2031. There’s too much other work to do.

Second, he refers to laser experiments from 1995 at the Starfire Range in New Mexico. While tracking a moving target (such as was done at Starfire) is an important advance, it does not fulfill all the requirements for power beaming to a lifter vehicle (e.g., a continuous wave, high-power laser at the proposed light frequency, with the required pointing accuracy and beam divergence, with a system efficiency which matches predictions). In his NIAC final report, Edwards himself states that the Starfire tests were not a complete systems test. But again, perhaps I should have spelled out the test elements in more detail. The roadmap says:

a retired satellite will be used to test tracking and focus of laser power beaming from the ground.

In the phrase “power beaming” we of course include the requirement that there must be useful, predictable conversion of the laser beam into electrical power at the satellite, something which was not (as far as I can tell) part of the Starfire experiments.

Third is a reference to finite element analysis (FEA). I know that Edwards has worked with David Lang, so I don’t understand how Edwards could characterize Lang’s excellent FEA work as nearly complete. While Lang has done much to study ribbon dynamics, he himself admits that there is much more work to be done. For example, he has not yet included some factors (such as changes due to thermal cycling as the ribbon goes in and out of Earth’s shadow, and as the ribbon itself twists and changes from being face on to the sun to being edge on), and other parts of his work need to be extended (e.g., deployment instabilities). His papers for ISDC 2006 made a number of simplifying assumptions that were necessary for a first pass at analyzing the factors he did study, but they must be refined for future work. Lang has done some excellent work, but it is nowhere near being finished.

Fourth is a discussion of balloon-lofted tether-climbing experiments. One point that I did not make clear enough in the first draft of the roadmap was that LiftPort does not expect to perform all of the experiments and system demonstrations ourselves. There have been a number of groups working on space tether experiments, for example, and I would not be surprised to see one of them attempt something resembling our proposed 200km test before we do. And we are the first to admit that our balloon tests are only the first tiniest baby steps on the long road to building a space elevator.

Edwards says that we ignored the Elevator:2010 competition, when we did no such thing. If an entrant in the competition produces a working system which demonstrates power beaming to a vehicle which can carry cargo equal to or greater than the vehicle’s weight while climbing a ribbon of an appropriate cross-section design (i.e., an aspect ratio, curvature, and material properties close to what is expected for the final SE ribbon) to a height of 10km (or preferably 30km), and reports back on how the ribbon performs when exposed to varying winds and weather conditions for months at a time, then there would be no need to duplicate those efforts. Of course Elevator:2010′s goals do not encompass all of those elements, but the competition certainly has the potential to demonstrate many of them. But we at LiftPort are not counting any chickens before they hatch. This roadmap outlines what we expect needs to be done and by what time; it does not talk about who will be doing it, nor does it attempt to predict the outcome of the Elevator:2010 competition.

Fifth is the issue of orbital tether experiments. Again, a piece of text that I now see should be spelled out in greater detail is what we meant by “debris dodging ability” as part of the experiments. Because the space elevator ribbon will not be able to take advantage of ground-based “steering” ability until it is, in fact, anchored to the ground, demonstrating the ability to dodge debris during deployment is critical to securing the necessary permits for the final space elevator. The shorter tests will include multiple systems (presumably both electrodynamic tethers as well as some form of electric propulsion) for testing system response and fuel usage. The longer test will be roughly one-third the full length of the SE and will be within a few hundred kilometers of a ‘belt’ of satellites. By using simulated debris objects under varying conditions (e.g., reduced warning time), the tether system can be tested for robustness and to demonstrate the required capabilities, in order to gain the needed legal & political support.

The sixth technical issue is the orbital environment test. NASA’s LDEF experiment did study many materials, but it didn’t study carbon nanotubes because they hadn’t been discovered yet. And while we are aware that the velocity of such a satellite in LEO will not be a great analogue for atomic oxygen, it will be useful to study a section of CNT ribbon under stress in an environment that combines atomic oxygen, radiation, and micrometeor debris. Many of those components can and will be studied separately in labs on the ground, but studying them together may be easier in orbit.

Note that the combination of tests and demonstrations we’ve proposed may not, in fact, be enough. The hardest part of the SE to test in advance is the section above the atmosphere and below ~10,000km. Deployment and environmental effects on the system need to be extremely well understood before the SE is built, but the LEO regime is difficult (at best) to do geostationary tests in.

Finally, Edwards says that we make no mention of various component & system studies and designs which need to be done (in direct contrast to his earlier assertion that most such studies have already been completed). He must not have looked at our schematic roadmap diagram or the Gantt chart, since that kind of design work is mentioned in both places.

Engineering, or Science?

Edwards’ comments reflect a scientist’s contempt for engineering. Whether it’s laser tests, finite element analyses, or orbital material exposure experiments, he seems to mistake proof-of-concept tests and initial scientific explorations for final engineering system demonstrations. If he does believe that intermediate orbital tether tests are truly unwarranted, then I fear he may be following the path of NASA’s historical method of trying to jump from an advanced concept to a final product without the requisite intermediate engineering steps, only to end in failure (e.g., NASP and the X-33).

Worse, Edwards’ disregard for the need to demonstrate functionality of space elevator components totally ignores the process of acquiring the needed regulatory approvals that he himself mentions. The system demonstrations we outline in our roadmap are directly focused at securing the diverse legal and political authority needed to build a space elevator, the largest engineering project humanity has ever undertaken.

Personal Issues

Although I am hesitant to get involved in Edwards’ ad hominem attacks, I feel there are a few points which demand a response.

Part of his attack on the roadmap focuses on third parties who provided useful feedback to us. He attempts to discredit them in two ways. First he says that they “have extremely limited involvement in the space elevator development.” Edwards seems to not appreciate that the entire point of getting independent feedback is to get a fresh perspective, not to have biases confirmed by the echo chamber effect. Second, he points out that the third parties “have their own competing concepts.” By questioning their biases, is he indirectly accusing these independent parties of unprofessional behavior? Or does he mean that anyone who is not a True Believer in the SE should not be consulted? The worst part, in my opinion, is how he seems to view people who are pursuing alternative concepts as “competitors.” We want to build a system to enable low-cost, safe, reliable and large capacity transportation to Earth orbit. Whether that comes with a space elevator or some other system is less important than that it happens. Reducing orbital access costs will enable broad activities in space, regardless of how the costs are reduced. And who knows, perhaps a rocket + rotovator system (as has been studied by multiple groups) would be a stepping stone to the space elevator?

Another part of Edwards’ attack focuses on me. He says that I am a “recent graduate.” I’m not sure how finishing my undergraduate work in 1993 and my master’s degree in 1999 qualifies me as a “recent” graduate. (Maybe I don’t look like I’m really 34 years old?) But the innuendo in how he uses the phrase “recent graduate” suggests that anyone with “recent” degrees are not worthy of respect. How does he reconcile such disdain with the fact that many of the entrants in the Elevator:2010 competition have not graduated yet? He is, after all, on the board of of the competition, and he promotes it as a useful project (which it is). It would behoove us all to remember that the bulk of the work on the space elevator will be done by those who are currently in college or have only recently graduated. LiftPort has repeatedly reached out to this group, rather than dismissing their contributions.

In two separate instances, Edwards comments on space elevator expertise. First he says that I have “limited experience on the space elevator.” He also claims that we “had no input from technical experts on the space elevator” while working on the roadmap. Edwards deserves respect for the work he did for NIAC which revived interest in the space elevator by showing the world that it really should be possible to build one. Such accolades do not, however, make him the sole arbiter of who qualifies as a space elevator expert.

I won’t comment specifically on the remainder of the personal attacks and inconsistencies, other than to request more professional behavior by Dr. Edwards in the future.

LiftPort: Open to All

To conclude, I want to point out that LiftPort policy is to be as open to the world as possible, whether it be blogging our successes and failures, or seeking international inclusion, or presenting in front of numerous groups. Our SE questions database is open to the world. We invite everyone to participate, whether through research, discussing the idea on our forums, advocating for research funds to advance the numerous fields discussed above, or simply publicizing the concept to friends and family.

Written by Tom Nugent and posted on Monday, October 9th, 2006 at 8:56 pm and is filed under 1.2. Technology, LiftPort Group. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.