Cuddihy's Cut

Cuddihy's Cut on the events of the day....


Monday, May 15, 2006

Comments are hosed again

Sorry, I was fiddling with the template and seem to have screwed up comments. I'll try and get this resolved tonight...

Fake but accurate? and, LH2 vs RP-1.

NASAWatch posted the official cancellation of the reusable RS-25 for the CaLV. Presumably, this means that NASA is indeed going to the RS-68 with a 10 m rocket body, as originally reported in a now retracted article.

It seems like the RS-68 is indeed the new choice for the 'SDLV', which, as others have now pointed out, has very little left that is 'shuttle derived.'

In fact, as Chairforce Engineer has stated, the SDLV now bears more in common with the Saturn V rocket than the Shuttle. All that's left, in my opinion, is to shift from the absurdity of a LH2 powered first stage to a Kerosene (RP-1) first stage. Then, at last, we would be back to where we started. Von Braun proven right again.

Lately it's become pretty clear to me that using LH2 for a lower stage is pretty much a fool's errand. I recently had to run some launch numbers for class (capstone) project that required launching multiple heavy satellites to a high LEO orbit (500 km and 1000 km). The only two launchers I was allowed to consider were the Atlas V and Delta IV. Imagine my shock when I discovered just how bad the Delta is for LEO launch. It's so bad that Boeing doesn't even publish true launch curves for LEO in the the payload user's guide. I had to reconstruct them from published launch capacity to 185 km circ, estimated LEO launch mass, Is, and mass fraction.

I calculated the following numbers for payload to LEO(metric tons)*:



Rocketpayload to 500km(circ)payload to 1000km (circ)
Atlas V 40210.3t9.1t
Atlas V 52213.5t12.0t
Atlas V 55215.8t14.0t
Delta IV 5,25.6t5.1t
Delta IV 5,48.1t7.2t
Delta IV Heavy17.4t16.2t

* these numbers included an inclination penalty to launch into a 64.3 degree orbit from the Cape, if anybody's looking at the actual payload curves.


Amazing, isn't it? the smallest Atlas V (402), with no solids on it, demolishes all but the Heavy, three core Delta IV. Which makes it all the more curious that the DOD still has contracts for Boeing to launch satellites to LEO with medium Deltas. WTF?

The Delta doesn't really gain any advantage until you start looking at higher altitudes. This is entirely due to the higher Isp RL-10B-2 (Isp 462s) vs. the RL-10A-4 (Isp 450s). It has nothing to do with the first stage.

Virtually any introductory course to rocketry will stress that higher ISP is 'better'. Most people liken it to miles per gallon in an automobile, an especially inapt comparison IMHO. By that measure, the first stage of the Delta IV, boasting the Isp 420s RS-68, should destroy the 'wasteful' Atlas V, w/ Isp 311s RD-180. The RD-180 has higher thrust to weight (70 for RD-180 vs 40 for RS-68) and overall thrust. But, of course, RP-1 weighs a lot more than LH2.

So what explains the discrepancy? The big problem as I understand it s that the Delta IV is thrust limited. In other words, the RS-68 has to limit its thrust while in the atmosphere to keep from structurally damaging the rocket itself. This has the effect of dramatically increasing the burn time of the first stage engine. As the Ambivalent Engineer makes clear in an excellent discussion on staging, more burn time for the first stage means higher gravity losses incurred for the same total impulse. So basically, Boeing developed this super-whamodyne LH2/LOX common core booster with a big honkin RS-68, for perceived higher efficiency, only to have to use it suboptimally because--oops, the first stage has to go through the atmosphere. It's a bit like dropping a high-torque truck engine into a small racecar, but forgetting that all that torgue goes to waste if the low-gear transmission and 10 inch wheels can't deal with it.

The Atlas V, on the other hand, with a much heavier mass at takeoff, is structurally stronger to begin with and runs at nearly its full thrust rating for the entire first stage burn. It incurs smaller gravity losses and the first stage is able to add a higher velocity increment as a result, which increases the payload on the second stage, despite having a lower 'efficiency' engine than the Delta IV.

Add to that the difficulty and expense of working with LH2, and the massive amounts of it you need on a lower stage, it makes one wonder--why use it on the CaLV lower stage at all?

Monday, May 08, 2006

Enough Already

One of my pet peeves about the blogosphere is the instant piling on that takes place whenever somebody makes a 'politically incorrect' statement in public.
*I don't in any way condone* what Peter Diamandis said, and the very fact that I have to state that to keep from receiving angry links or comments is exactly what I'm talking about.
There is a certain element in the blogosphere that takes extreme delight in calling attention to any and all slips of the tongue, inappropriate wording, and mistakes. It's a gotcha mentality that represents all the worst of reporting and the relative anonymity of being behind a keyboard.

NASAwatch does this all the time--a significant percentage of the postings are gotchas about this or that NASA release that doesn't exactly match up with an internal document, or two Griffen statements at different events that appear to contradict--more the point, often completely irrelevant to any major issue dealing with NASA.

The real joy, I guess, is in intimating that someone else has not done their homework or done their job right or some aspect of their job.

But personally, I'm just sick of the whole atmosphere. Our society should be secure enough that we don't have to go demanding self-flagellation whenever someone makes a slip of the tongue.

Accuracy in metaphors

Among the visionaries of the new frontier at the ISDC conference 2006, I'm sure it's tough to find naysayers about our (meaning humanity's) progress towards actually becoming a spacefaring civilization. Without a doubt, most of the speakers are preaching to the choir. I'm afraid that I mostly agree with Jeffrey Bell of UH (Hawaii). Jeff wrote this article a few years ago-- I read it at the time and agree with most of its major points. If you're going to use a historical analogy, better use it appropriately, and accept the positives AND negatives.

I saw it again tonight when I was trolling usenet--somebody reposted it. Probably the part of Bell's thesis that's most distressing to alt.space types is the contention that our technology level is currently too low. Here, I'll quote:
I think we are in the same position with respect to space flight that the Norsemen were in respect to colonizing Canada. Our chemical rockets are just as inadequate as the Viking longboats. Our spacesuits are as clumsy as chainmail armor. Our means of defense from solar and cosmic radiation are as ineffective
as the Viking spears and axes were against the Indians. Our ideas for using local resources are as primitive as the farming and mining techniques of 1000 A.D.
Say that at ISDC, or worse, Space Access, and visionaries and alt.space geeks will fall all over themselves telling you that it's not true, that the technology exists today and just needs to be 'done right.'

I'd say that's a category I fell into until I got to school and started studying the actual physics and engineering required to get off-planet. TANSTAAFL is an excellent motto to keep in mind. Want higher performance engines? Be prepared to pay a hefty price. Reusable engines? Be prepared to pay a performance penalty. You have a completely new way of doing things? Be prepared for it to take 3 times as long, 4 times as much money, and 5 times as many failures as you initially budget for.

I do think there's one big hole in Bell's perspective of NASA as our society's version of Cheng Ho's journeys to nowhere: Cheng Ho's journeys may not have been able to challenge western technology, but as Bell himself stated, that was because Ming dynasty China could not compete with the real advances taking place in the West. The fact is, we ARE the West. The outward expansion begun in Prince Henry the navigator's day may be confined to our humble planet at the time, but the rational mind and the scientific method are alive and well. The cause of the technological advances that gave Western Europe the advantage over other cultures (for a time at least), is still currently in motion. Given enough time, we will develop more powerful engines, better ISRU techniques, and sufficient political will to really colonize space.
The real question is whether our society will stick around that long or lapse into decline because of ever-falling birthrates.

Thursday, May 04, 2006

A rational solution to immigration

OK, I get tired of hearing the pundits of both sides argue about turning illegal immigrants into felons or about another amnesty that would encourage more law breaking.
First, a disclaimer: although I am a legal native-born American, my grandfather, Thomas Long, illegally entered the US from Canada after immigrating there from Ireland. He worked on the docks in NY as a longshoreman for several years until he saved enough money to go back to Ireland, immigrate legally, and then fought in WWII shortly after receiving his legalization status. I don't condone my ancestor for working here illegally, but he desperately wanted to be a real American, so he rectified the situation as soon as he had sufficient means to do so.

I would submit that there are several truths that both sides can agree on:

There's no practical possibility of deporting 11 million illegals, if the number really is that high. It's just not possible. Every single one of those people pretty much gets a hearing. As if the federal courts aren't clogged enough as it is, dumping an extra 11 million cases on their hands is just not feasible, especially as they would be heavily concentrated in the border districts. That doesn't mention the likely effect this would have on the economy, as the cheap labor is suddenly taken off the market. That fact alone would make the INS's job even more unworkable than it already is, with politicians from both sides screaming about specific enforcement efforts killing their constituents.

Encouraging future lawbreaking is not desirable. However, there has to be some answer to the current rampant lawlessness with regard to immigration laws. Any solution has to take into account not only the specific cause of current lawbreaking but the concerns of a labor market producing more jobs than native-born Americans can fill.

So what is the cause of current law breaking? As this graph from a study done at Mizzou shows, the numbers of immigrants coming into the United States peaked around 1900 at close to 1 million/year, then dropped sharply, and has only recently come back to that level. But how many of those are legal? In 2003, only 463,000 people were made legal residents of the United States. Less than half the number of people immigrating(Legally!) in 1890. Keep in mind that the US population in 1890 was somewhere between 62-65 million. In other words, legal immigration was 2-3% of the total population per year. I think most Americans today would agree that that worked out pretty well in the long run. In contrast, in 2003, there were somewhere around 278 million Americans, and yet we only allowed short of 500,000 to join us in the greatest nation on Earth. That's 0.001% of our population. What the hell is wrong with us? Are we really that scared that 88 million Mexicans are going to overwhelm us 280 million Americans? Have math skills decayed that badly?

What, is the cause of the lack of assilimation that plagues many Mexican immigrants, especially in California? Conservatives like to blame the problem on liberal multi-culteral philosophy that is entrenched in our education system. Perhaps that plays a role. But I would argue that the main cause is the fact that so many of our immigrants are here illegally, never given the opportunity to raise their right hand and swear allegiance to this country and our consitution, is the main factor. When did our society lose the concept that words are important, even to those who barely understand what they are speaking? Keeping a noticeable percentage of the population restricted to the barrio, where they can hide safely in their illegal identity, is NOT a solution, and only perpetuates a 'seperate' identity. Granting amnesty to those already enmired in the current proto-slavery of illegal immigration would only perpetuate the current seperation in that population.

I would challenge conservatives who say that the problem is 'not immigrants, but "illegal" immigrants,' to put their money where their mouth is and start calling for drastically increased LEGAL immigration. I mean where the only requirement to immigrate and obtain a green card, beyond health issues, should be the ability to show up at a US port of entry and not be on a terrorist watch list.

This one stroke would solve a LOT of immigration problems. Illegals already in Amercia would find themselves competing against legals with the same hard work ethic, but much better prospects, raising immigrant wages. Many would be forced to go back to a port of entry and enter legally, or go home altogether. The very act of reentering the United States at a port of entry will act to break the 'barrio' mindset of many of these immigrants. Ceremonies and words have important effects on the human psyche.

Couple increased legal immigration with slightly stronger enforcement, especially on the payroll tax side, and suddenly the agricultural and meatpacking industries that rely so heavily on illegal labor, would have little reason to continue to do so.

There is no need to condone past illegal behavior, but there are ways to discourage future illegal behavior without throwing our economy under the Homeland Security bus.