Jon Goff has an interesting post (if you’re into rocket propulsion) on a technology that’s been lying fallow for decades. But this post isn’t about that concept per se, but a more general one:

I stumbled on this while trying to track down some old Aerojet papers about a sort of forced flow separation control technique that they researched back in the late 50s. I had noticed that most of the papers that cited the research talked about how Aerojet’s had concluded that the approach didn’t yield any net benefit, however the way they discussed it made me somewhat suspicious of their conclusion. You can sometimes get a sort of telephone effect with academic citations–where someone will read someone else’s review of some obscure and hard to locate article, and instead of reading it themselves, they’ll just summarize the summary, and before long who knows what the original article said. To make a long story short, I had good reason to be suspicious that there was something of that sort going on with this paper (especially since the two abstracts I was able to find online for their research seemed to directly contradict all the claims I’ve seen in citations of their work elsewhere).

Assuming that it was the case here, this happens more than you might think, and more than it should. This kind of thing, in fact, is the source of a lot of false mythology about space technology (e.g., highest vehicle performance is achieved with LOX/hydrogen, air breathers are the key to low launch cost, etc.). Many “rules of thumb” and conventional wisdom are based on a limited analysis, and used by people unfamiliar with their origin, or the underlying assumptions. I’ve written about an example of this before from my own early career:

Back when I worked at the Aerospace Corporation, a couple decades ago, I was fresh out of school, and sitting in a meeting with more senior people, discussing a conceptual design for a new military geostationary satellite. The subject was how to provide orientation. The two traditional choices were spin stabilization (many of the Hughes communications satellites used this technique) and active reaction control, which was more accurate, but limited the lifetime, due to depletion of propellant.

I (or someone, but I think it was me) suggested using gravity gradient stabilization (that is, taking advantage of the fact that a non-spherical satellite will naturally orient itself in the local vertical position, due to differential tidal forces between the line of the orbit and the small distances of the appendages from that line). The response of one of the supposedly experienced engineers was, “There’s no gravity gradient at geosynchronous altitude.”

I was a little surprised. “Oh, you mean there’s not enough to do the job?” (I was thinking that perhaps he’d already considered it, and run the numbers.)

“No, there is no gravity gradient effect that high–it only applies in LEO.”

Note that he wasn’t making a quantitative argument, he was making a qualitative one. Low orbits had gravity gradient, high ones did not.

…What happened? Sometimes even engineers don’t always apply good scientific principles. In this case, I suspect that he was an airplane guy who’d migrated into the space business (as often was the case in the beginning decades in the space industry), and had never really learned the fundamentals of orbital mechanics, or the underlying principles. Instead, he’d probably taken a space systems design course, and been given a lot of engineering rules of thumb, one of which was, no doubt, that gravity gradient can be used in LEO, but not in GEO.

And that’s not a bad rule of thumb, as long as you understand where it comes from. Gravity gradient is indeed much less at twenty thousand miles altitude than at two hundred miles, and for most satellites could be considered, for practical purposes, to be non-existent. But we weren’t talking about most satellites–we were looking at a new concept, much larger than anything previously deployed in GEO, with long booms and appendages that might, in fact be used for G-G stabilization. But because he didn’t understand the physics, he mistook a rule of thumb for natural law, even though the law of gravitation says that the earth’s gravity extends out to infinity, though it drops off as the square of the distance.

Often someone will perform an analysis, and people in a hurry will simply look at the bottom line, while ignoring the assumptions that went into it, which, if altered, might completely change the conclusion. Worse yet, sometimes the author hides the assumptions, making it even more pernicious (this, to me, is one of the primary reasons that we make so little progress in advancing a useful space policy–there are too many hidden assumptions on the parts of debaters, and everyone assumes that they’re shared, when they’re often not).

This is why it’s important to properly document a trade analysis–so that when the assumptions change, it’s easy to go back and determine whether or not the trade conclusion has, or whether or not it has to be redone. This is also why it’s important to perform sensitivity analyses in the course of the trade–to make it easy later to determine, perhaps at a glance, whether an assumption change is critical or not.

I don’t know whether or not the augmented thrust technology that Jon unearthed will find its way into future vehicles, but I’ll bet that the original authors of the study didn’t consider all of the potential applications for it when they published it–they were probably working on an engine for a specific vehicle concept. XCOR has been doing a lot of this kind of archaelogy of the early space age, and (at least it’s my understanding) have found it a rich ore of untried but promising concepts. When one considers how much money was spent on the development of space technology in the early days (and how chaotic and largely undirected the vehicle development process has been over the last few decades), it would be surprising to me if there aren’t a lot of old tricks in there that can find applicability in the twenty-first century. But one has to read carefully, and hope that the papers were documented properly. And when documenting our own results now, we should think of those who may be reading them in the future.

Looks like a lot of interesting stuff at The Space Review today. I’ve only gotten to this one, so far, by Mary Lynne Dittmar, on selling NASA to the general public. I was pretty familiar with most of this analysis, and it hasn’t changed much since I was looking over public opinion data that we were doing at Rockwell in the early nineties, in terms of the public’s ignorance of the size of the NASA budget. But she identifies the real problem at the end:

…the second category of responses that emerged when asked about how NASA could become more relevant was that NASA could do so by actually engaging in activities that are perceived to be of value [Gee, what a concept…–rs]. This response may be difficult to understand at first. It also may provoke a defensive reaction among those who already believe NASA

Jon Goff has a must-read post on what we know and don’t know about reusable launchers, based on some insightful commentary by Jorge Frank.

The real mistake of the space shuttle was not that of attempting a reusable vehicle, nor a winged vehicle, nor a parallel-staged vehicle. The real mistake is that we attempted to build an “operational” vehicle before we had any real idea of what “operability” means in a space vehicle. The alternative – the real “road not taken” – would have been to build small experimental vehicles, starting from suborbital and working our way up, that explore all the different “corners” of the design trade space resulting from this multi-variable problem, and learning, one painful step at a time, what works and what doesn’t. Since these experimental vehicles would neither have carried payloads nor flown operational missions, there would be no attachment to them; they would have flown for a few years each and then retired and replaced with the next X-vehicle, just as happened with all the previous X-vehicles up to and including the X-15.

That approach may or may not have resulted in a truly economical launch vehicle by 2007, but it would surely by now have given us a better picture of what works and what doesn’t than the road we chose. By attempting an “operational” reusable vehicle that by definition would have to replace all the existing “operational” expendable vehicles, we locked ourselves into a path that was difficult to reverse and was expensive enough that we could not afford to replace it in parallel with flying it, necessitating another long and painful gap in our experience base.

And because that one vehicle represents the whole of our operational experience for the last generation, its failure has led many to overgeneralize. The space shuttle is a (partially) reusable, winged vehicle with parallel staging using a cryogenic propellant tank. And it failed to meet its cost, schedule, and reliability goals. Therefore, the reasoning goes, all reusable vehicles are bad, all winged vehicles are bad, all parallel-staged vehicles are bad, all cryogenically fueled vehicles are bad. This is nonsense. Were the emotionally charged names to be replaced with faceless variable names, any competent mathematics professor would reject this logic as faulty, and rightly so.

The latter is a point that I make often in response to the clueless and logic-challenged who think that Shuttle (or X-33) teach us that reusable vehicles aren’t possible.

Jorge’s comments are also a useful insight into what a kludgy compromise the Shuttle design was, and how many of the design choices were driven by other design choices, which were in turn driven by unrealistic requirements, both in terms of performance, and development budget.

As Clark Lindsey points out, we are going to be learning a lot of lessons from the suborbital business and rocket racing that will be directly applicable to orbital vehicles down the road. It’s a tragedy that it’s taken us so long to start this long process. But as long as the process might seem, at least we’re now going in the right direction (that is, to try a lot of different directions, and finally find out what works, and what doesn’t).

When I hear about NASA adding a fifth segment to the SRB, somehow it reminds me of this:

Over the summer of 1930, the R101 lay in the Number 1 shed at Cardington undergoing extensive modifications, which were needed following on from her 1929 and early 1930 trial flights. It was already known that both the R100 and R101 were lacking in the disposable lift originally planned at the outset of the Imperial Airship Scheme in 1925. Those involved in the scheme had already learnt that the R100 and R101 would not be viable for full commercial operations to Canada and India, and these intentions were later to be passed on to the new ship, the R102 class. To achieve the additional lift, R101 had a new central bay and gas bag installed.

It was expected that the new gas bag would give her another nine tons of disposable lift bringing her up to some 50 tons. The alterations were completed by Friday the 26th September and the R101 was gassed up and floated in the shed. The “new” ship, R101c, had disposable lift calculated at 49.36 tons, an improvement of 14.5 tons over the original configuration. Pressure was on for the ship to leave for Karachi on 26th September to carry the Air Minister, Lord Thompson of Cardington. Although the target date was on course to be met, wind was to keep the modified R101 in the shed until the morning of 1st October.

Not sure why, though.

Actually, I think that “Sliderule” should be required reading for every NASA employee.

I finally just got around to reading the report that Colonel “Coyote” Smith (that’s Michael Valentine Smith–no kidding) and company came up with on Space Based Solar Power, and will be commenting on it, but I should note for now that the January issue of Popular Mechanics has this as its cover story. I haven’t read it yet, but may post some thoughts after I do.

On a related note, while a ten buck per ton carbon tax on coal probably would be good for the nuclear industry, as Randall Parker notes, it wouldn’t hurt SBSP, either.

[Update a few minutes later]

OK, not much to the Pop Mechanics piece. I think it’s quite an overstatement to say that powersats are “all the rage” at either the Pentagon or in private industry. I would think that something that was “all the rage” would be getting significant funding, and so far the amount that’s been appropriated to this recently is…zero. In fact, one of the significant things about the Pentagon report was that it was done with no DoD budget, entirely by volunteers, other than the Colonel’s time. It might be a useful model for future such studies that have trouble otherwise finding government champions, but it hardly justifies the notion that this is now a major priority, either within the five-sided building, or in the government in general.

As for the article itself, my only quibble is to note that the seventies studies were jointly by DoE and NASA, not just DoE. It’s been noted many times in the past (and Coyote’s report notes as well) that one of the reasons that this concept has had trouble getting acceptance and ownership within the government is that it’s had no natural home. DoE thinks it’s a space program, and NASA thinks it’s an energy program, and both agencies consider it to be outside their charters. I do like the idea of the establishment of a quango, perhaps using COMSAT as a model, to provide a government-blessed (and at least initially, funded) focus for this.

[Update a couple hours later]

I see from his comments that Monte Davis now has a blog, which I’ll be adding to the sidebar.

Jesse Londin has a nice roundup of space links. She also notes the other legislative barrier to space entrepreneurs–not ITAR, but SOX. I’m working with a company that has been chased off shore by this.

Alan Boyle has a story and link roundup about the the Rocket Racing League, X-Racer, and Xerus.

Tim Oren has a wrap up of the DARPA Urban Challenge, about which he’s been reporting (go to the November archive page and scroll down to early in the month for earlier reports). Here’s hoping that Red Whittaker can be as successful on the lunar prize.

From Ferris Valyn, whose laptop I almost accidentally stole at the X-Prize Cup (I briefly mistook his rollaway case for mine). Fortunately, he pointed it out to me before I got far.

This post has been up at Space Politics for over a week now, and this is the first time I’ve linked to it, but there’s a lot of interesting commentary from “anonymous” in the comments section. I think that the analysis of Griffin and the origins of (and continuing support of) ESAS is right on.