Some SpaceX Commentary

Well, I've noticed that my blogging has been getting rarer, snarkier, and of less substance than it used to be. Part of that is due to all the time we've been spending testing engines, killing the gremlins that like to inhabit our test trailer occasionally, and recovering from trips to our remote test site. Part of that is due to the work schedule, especially now that we're getting structural pieces in for our vehicle. If any of you have ever had a kid, or nephew, or brother (or yourself) who got an Erector Set, Legos, Constructs, or anything similar for Christmas, you can imagine what our office looked like tonight. Just imagine that instead of three little kids, its three lovable, not-so-juvenile deliquents....

Part of my lack of bloggyness has also been due to getting sick several times (and having Tiff and little Jonny get sick too). Part of it has been due to the fact that I really, really don't want to start blogging about politics or foreign policy, or crap like that. And part of it is because for some strange reason, I can't seem to blog while the "dishwasher" is going....

Anyhow, with that irrelavent personal stuff out of the way, now for some good ol' fashioned space punditry--because if you can't actually report new information, at least you can try to look really smart by commenting on what everyone else has been commenting on, and put your own snarky spin on it.

Pintles
I want to start by briefly mention something interesting that I think I've figured out about SpaceX's pintle woes. I think that most of their engine related problems are interrelated, and that they have to do with the combination of using a high chamber pressure engine design with a pintle-injector and an ablatively cooled chamber wall. First I'll give a couple of the reported facts, then a little explanation about why I think they fit together:

• Back about a year ago, SpaceX first mentioned that they had missed the performance goals for their Merlin-1 by a few percent, in spite of having very encouraging initial results.


• SpaceX runs with a fuel-centered pintle, and Elon mentioned that most of those performance losses were related to having to tune the pintle to get wall cooling right.


• Back in the fall (as discussed here and elsewhere), SpaceX had a chamber failure where the chamber lost structural integrity causing the nozzle to tear off.

[Note: For the next section, the picture to the right should help make what I'm saying a little clearer.]

One of the major drawbacks of a pintle injector design stems from the same thing that gives it most of its benefits--its unusual flow fields. Unlike in a normal rocket engine where the propellant mix, burn, and then accelerate in a nearly axial manner moving from the head-end to the nozzle, fluid flows in a pintle take a more complex path on their way out the thruster thingo. If you look at the picture, you can see that when the two propellant sheets mix, they form a cone shaped spray fan. That fan shape creates two donut-shaped vortexes, one between the fan and the head end, and the other between the fan and the throat. These two vortices have a lot to do with the stability and throttleability of the pintle engines.

Unfortunately, when you have this spray fan hitting the wall, by the time it gets there it is hot flamey stuff, which causes a localized area of higher-than-normal heat flux. Most rocket engines have only one area of really high heat-flux, the throat, like the figure on the right shows (I think this was scanned in by someone from Sutton's Rocket Propulsion Elements).

There are good canonical ways for designing an ablative chamber to deal with the higher heat flux at the throat. Since you have a large reduction in chamber diameter at that point, you can go with a much thicker wall and eat some throat area erosion over time. Or you can put in a graphite or carbon-carbon insert in the actual throat section.

Dealing with the second high heat flux area is more problematic though, particularly for ablatively cooled engines. For a regen engine, especially a chamber-saddle-jacket or milled-wall type, you can just make the flow passages a little narrower in that section to up the amount of heat transfer rate into the cooling jacket. But for an ablative you have a bit of a quandry. The spray fan impingement point is often at a very inconvenient place--on part of the flat sections of the wall, or on the converging section of the nozzle. In both of those places it's hard to put a graphite insert, but it's also hard to deal with large erosion over time. It's much easier to custom tailor the local heat transfer rates in a regen cooled engine than with an ablative engine. With an ablative engine, you really only can vary a few things: matrix material (ablator), reinforcement material, thickness, wrapping pattern, or adding inserts. And none of those are particularly easy to do, particularly away from the nozzle.

So, the canonical solution with pintles has been to have the fuel coming down the inside of the pintle (and shooting out radially), and to adjust the injection velocity to have some of the fuel punch all the way through the annular oxidizer sheet, impinge the wall, and create some fuel cooling. The problem is that any fuel that is used for wall cooling, by definition isn't participating with the reaction, and causes a reduction in performance. Most of the previous pintle injectors were also used for engines operating at much lower pressures (100psi for the engines used on the LEM for example), so the amount of fuel film cooling needed was relatively small. I think though that SpaceX had to go with a lot higher amount of film cooling due to the much higher chamber pressures. Heat flux is related quite strongly to density which is related to pressure. Doubling the pressure usually doubles the heat flux.

I think the nozzle failure event was also related to this. According to Elon, this failure happened while they were doing some intentionally off-nominal tests (to verify that their engine could function at off-nominal mixture ratios and pressures), and I think what happened is that they were running the engine lean enough that the fuel jets were no longer reaching the wall well enough to keep the impingement zone fuel cooled. That would square pretty well with the failure seen.

So in summary, I think there's a strong case that SpaceX's engine problems haven't so much been because ablative engines are inherently bad, or because pintle injectors are bad/overhyped, but because combining the two in a high pressure engine is a bad mix. Which is why Elon's comment in a Q&A that Clark Lindsey linked to is so encouraging:

Ablative was chosen because we thought, incorrectly, that it would have a lower development cost. All future engines will be regen and we will be coming out with a version of Merlin 1 that is regen.

I think this will be a real win for them. Using a regen engine will allow them to get back quite a bit of performance on the Merlin-1, and should make the engine both more robust and more reusable.

Anyhow, that's about all I can comment on this morning (as I have an industrial sized Erector Set that I'm getting payed to go play with, that's calling my name), but I figured I'd share some of my insights with the rest of you.

Shafted

It's kind of amusing to note (as several others on the blogosphere have now) that the supposedly "safe, simple, soon" Crew Launch Vehicle is turning out to be as difficult to pull off as many of us have been saying all along. The fact that modifying an SSME for airstart would be extremely difficulty if not impossible is hardly news. I don't have an exact number on how many SSME's were destroyed trying to get its startup sequence worked out, but it was a disturbingly high number. And that was with a slow, ground-launched startup sequence. As a friend of mine quipped, "every blip or jiggle in the SSME startup sequence has at least one trashed engine proving its neccesity."

But don't worry folks, so what if there really is no off-the-shelf hardware on this vehicle, NASA says that this will have about a 2000:1 odds of blowing up on any given launch. They're so smart that they knew the reliability to four significant figures before they even figured out how many segments the SRB was really going to need, or which engine was going to be used on the upper stage. Impressive.

I have to say that what NASA is doing with its COTS program, with Centennial Challenges, and with the money it's setting aside for microgravity research, is actually pretty darned good. It's just sad that the percentage of NASA's budget over the next five years that is going to stuff that has a potential of opening up the space frontier for the rest of us is such a small percentage of the money getting blown on the Space Shuttle, and on legalized graft like the Shaft.

Michael and several others like to point out that the Shaft and finishing up ISS with the Shuttle is more or less the price we have to pay for things like COTS, but it still doesn't make it any less galling to see so much money being thrown down such an obviously useless hole like this.

I still think that if the Shaft is supposed to be such a great deal, such a superior space launch vehicle, that NASA should require ATK to come up with all but $1B of the funding, and use the rest of that money saved on actually promoting a thriving commercial space transportation infrastructure. Why should the nation have to foot the bill when ATK pulls the good ol' bait-and-switch on us?

I feel Shafted.

MSS July-Now Update

I finally managed to write up a bit about what we've been doing at MSS over the past several months. We should have some more pictures, videos, and information to post in the coming weeks. Unfortunately, being this busy means that I won't be able to go to the ACES workshop this week, but Michael Mealling will be there, so maybe we can get him to post some updates on Rocketforge. Blogging may also continue to be light, but I'll try to put in my two cents here and there.

Busy, Busy, Busy

I was going to blog yesterday, but figured I needed to get some comments in on that AST Human Spaceflight NPRM before time runs out next month. Most of the phrasing in the actual regulation seemed to be common sense stuff that you'd want to do anyway if you weren't running some sort of rinky-dink fly-by-night space tourism shop anyway. There were a few areas I figured I'd comment on, including sticking my neck out and trying to make an attempt at a rational argument for why gun bans might not be the best way to protect crew and the public from hijackers/terrorists. I probably should have left that one alone, but couldn't resist.

It's kinda amusing reading all of the rather rude and clueless comments so far. I actually agree with at least some of the sentiments expressed there. I truly wish we were in a clean-slate situation where a more market-based instead of regulatory situation could be tried out. I think that if the FAA existed, that a market based solution to protecting third parties could probably be found that was less burdensome and maybe even safer overall. That said, we live in this world, and in this reality the FAA exists. AST has been given Congressional authority. If you disagree with that, try to get it changed by statute. But insulting the guys at AST and telling them that you spit on their proposals is immature as heck. It's times like these where I can see why most people think that libertarians are a bunch of nut jobs.

Changing tack a little bit, it's funny to mention that my coworker Ian thinks he's finally figured out what the government is doing to actively impede the progress of commercial space development. He said that all they had to do was distract all the alt.space engineers from actually doing engineering by getting them so wrapped up in debating politics and government on their blogs and reading silly political satires about cows, and doing other things other than actually building stuff. I still don't see what he had against the cows humor...

Anyhow, I really think I'll actually be in a position to blog some more about space stuff in the near future. We've now got most of the long lead-time items ordered in for our XA-0.1 demonstrator, and we'll probably have a rocket vehicle skeleton assembled and in our shop within the next week or two. And that should be cool.

Stay tuned, and Ken, keep up the good work!

[Update: Dan over at Space Pragmatism added a few space related cow jokes. What with the Philippines reference in my blog's name, I'm tempted to crack a joke about Space Balut, but that would just be fowl.]

So whose assumptions are ya gonna trust more?

byline: Ken

Well, Mr. Bonin's second part is out, and golly if he doesn't cover a lot of stuff I had in the post. But if it makes sense, then it's going to sound similar, isn't it?

Mr. Mark Whittington, who can sometimes be found hanging out here in the Selenian Boondocks, notes over at the Curmudgeons Corner:

"Grant Bonin concludes his polemic against heavy lift and his case is, alas, unpersuasive. As to why it is, just count the number of times he uses the words "assume" or "assumption" in his piece. Economic analysis based on back of the envelope calculations based on assumptions tend to fall down on close examination.

For a somewhat more rigorous cost justification for ESAS, based on some rather sophesticated [sic] cost modeling systems used by both NASA and the Air Force, download the PDF file on Costs."


Thing is, Mr. Whittington (Mark) is treading on thin ice. I checked the Bonin piece and variations on assume were in there 8 or 9 times. I then went to the Cost section of the ESAS report and found it over 50 times in the 42 pages. This is of course Section 12 of the report, which itself had a whole section (Section 3) on Ground Rules and Assumptions.

I'm actually kind of interested reading through it, though more than a little bit annoyed. There's really no good cost numbers for this poor investment analyst to dig through other than some projected (i.e. assumed) performance figures for the beknighted (sorry, I mean chosen. I've been reading Mark's stuff too long ;-) launch vehicles. If there are numbers for $ then they aren't noted or quantified as such, which I seem to recall is what got MPL in trouble. Are those $Bn, $Mn, $M? (thousands for you non-financial types out there, also $m (for mille), as $M is sometimes used for million)

The Ground Rules and Assumptions section is a little more lively, and quite a bit more interesting.
-We find the long sought after source of Human Rating - NASA Procedural Requirements (NPR) 8705.2, "Human-Rating Requirements for Space Systems".
-aborts from the Lunar surface will take no longer than 5 days for return, independent of orbital alignment.
-CEV will deliver crew to ISS till 2016
-CEV will deliver cargo to ISS till 2016
-CEV ground ops will be at KSC
(In the cost section they note that Sytems Engineering and Integration is estimated at 7% of total cost with staffing cap at 2,000 persons as compared with 1,000 to 1,500 in prior crewed programs)
-JSC gets the space ops part

***************************************************
-The Study will utilize the "Mars Design Reference Mission (DRM) known as DRM 3.0, 'Reference Mission Version 3.0 Addendum to the Human Exploration of Mars: The Reference Mission of the NASA Mars Exploration Study Team EX13-98-036, June 1998'"
***************************************************

(I believe that's the document found here. It's where the 85 metric tonne [m.t., ESAS uses mT] lift requirement comes from, and since the Moon architecture is supposed to be extensible to the Mars architecture, well, might as well start out big)

-the architecture supports global Lunar access. This will be done via EOR-LOR as is noted later.
-the architecture will support a permanent human presence on the Moon (but is it sustainable, not just supportable?)
-In-space EVA assembly will not be required [!?!]
-Human-rated EELVs will require new dedicated launch pads

Assuming that we're going to use the same shuttle launch facilities and equipment, maintained, gives your assumed HLLV a huge head start if the EELV automatically has to build a new facility. I've seen those crawlers they use. Those things are decrepit and the massive tread pieces are cracking. There's no way to tell from the numbers presented if new crawlers are priced into the cost of the system but I'm guessing no.

Another interesting tidbit: Foreign assets utilized in LV configurations in this study will be assumed to be licensed and produced in the U.S. (Again, is the cost of establishing those facilities for producing the "Foreign assets" baked into the equation?)

The Summary also informs us that "Initial analyses eliminated libration point staging and direct return [lunar surface direct to Earth surface, I assume] mission options". The Lunar Surface Activities section doesn't really tell us a whole lot about Lunar surface -activities-.

There's a lot of stuff to chew on in the report and I recommend strolling on over to SpaceRef.com to check it out for your self. Please note some of the .pdfs are pretty big. It's kind of fun to read through and see where they don't really want to talk about something because they use the same phrases like 'too demanding' or 'too complicated'.

I'll be back in a little while after I've had a chance to digest it a bit more. I'm wondering about some of the delta-V figures, and why in the Summary they bend over backwards talking about LOI and TEI delta-Vs, as well as plane changes, but not the delta-V for TLI, nor the delta-V to/from the Lunar surface. I'm also working on a future piece about the assumptions underlying Direct Trajectory, which itself underlies a lot of choices in the space field.

On Bonin's 'The case for smaller launch vehicles in human space exploration (part 1)'

Howdy All, Ken here. I just decided to weigh in a bit on an interesting article today. (and provide a bit more grist for Jon's mill)

Over at the The Space Review, Mr. Grant Bonin visits the question "are heavy-lift launch vehicles the best technology for opening space to humankind?". While I personally feel the question should have been something more along the lines of 'Are HLLVs the right technology right now for opening space to all of humankind?', I'm not going to pick nits. ;-)

M. Bonin then sets out two goals:
1) to dispel the belief that HLLV is an economic necessity for human spaceflight; and
2) to demonstrate the feasibility (both technically and economically) of undertaking human space exploration beyond low Earth orbit using existing, more modest launch systems.

This is quite a chore, and he gives himself two parts to answer it, so we'll see what unfolds next week.

In this week's part, he jumps right in to the the ideas of Payload Fraction (payload as total % of mass of vehicle) and mass-to-orbit (where it's generally assumed in spite of decades of miniaturization and industrial advances that it will nevertheless require hundreds of tonnes to do anything [ which is true to some extent, but...]).

In both cases the larger lifts seem to carry the day. But that's only on a very superficial and first blush basis. Luckily, this is why we have folks like trained investment bankers, who look at things from an entirely different perspective from aerospace engineers. M. Bonin cites Ed Wright's [not an investment banker] Ad Astra article and one of its contentions, that optimizing mass-fraction alone does not necessarily lead to a more cost effective system, as most of the lift-off weight is propellant, and fixed infrastructure and labor-hours are what really chew up the budget. It would require far more than two launches per year to even come close to making an argument that an HLLV is cost-effective. He (Mr. Bonin) also notes that the complexity of the big honkin' rockets makes them harder to get off the ground in the first place. I'm not so sure about the analogy with the model rockets. I seem to remember an earlier post about how many Falcons, Atlases and Deltas could be flown before the first HLLV gets off the ground, and the huge amount of mass that would already be in orbit before the first Longfellow flew..

I've long been an advocate of high volume to orbit, but in conjunction with high frequency. Getting 100 tonnes to orbit at one time hasn't been conclusively proven to me to be the most strategically effective way of doing it. What if the materials scientists and private consortiums need access to orbit more than twice a year? How is this thing going to serve access to the ISS?

(Answer: It's not supposed to. It's supposed to be a disposable means of conveying a few NASAnauts to the Moon to do a couple of practice runs for Mars. When I say a couple I do not mean a lot. Maybe 3)

M. Bonin also makes note of the learning effect. When someone does something a lot they tend to get very good at it, and figure out the thumbnail rules and shortcuts (oops, I mean procedural efficiencies...yeah, that's it). This helps to bring overall costs down, and makes for a better overall launch experience.

While citing some economic arguments, M. Bonin fails, as so often do aerospace engineer economists, to take the economic and financial considerations deeper and start applying them to what companies actually face out in the real world. Other things than your standard cost-of-capital and value-to-shareholder buzzwords.

Look at the insurance. There's no way to gather the risk pool sufficient to cover all of the small payloads of small companies that would be aggregated into such a behemoth. Even on larger payloads, like Bigelow's Nautilus balloons, there's no way anyone would launch four at the same time. This means you still need freight aggregation services to get full use out of the payload capability. Again, you run into the problem of gathering a sufficient risk pool to cover the potential losses in event of a failure.

And there will be failure. Just because a rocket is as big and complex as the Saturn V does not mean it will have the flight record of the Saturn V. It is, however, doable to get a risk pool together for a single EELV launch or some kind of RLV.

The whole point is mass production. Whether that mass number of flights is done by a boatload of cheap disposable rockets (and they will be cheap once we start using them in number) or by a whole bunch of RLV flights is something to which I'm indifferent. If the RLV guys can come up with something I'll get behind them (and I'm more optimistic than I used to be), but I know we've got a bunch of 20 mt to ISS lift capability that is desperate to be used.

If NASA uses the same launch systems as everyone else, then each successive launch will be cheaper for everyone. If NASA continues to be supplied with its own private launch system, then the taxpayers will continue to have to foot the bill for inefficient and ultimately ineffective access to orbit. Besides, if NASA uses the same rockets as everyone else then when a rocket goes boom (which it will) who do you think is going to get blamed? NASA? No way, it'll be the launch vehicle manufacturer. There's a benefit if I ever saw one.

There's also the question of launch risk. Is it really risk effective to put all of one's eggs in a single basket? Business teaches us no, it's not. It is better to spread the risk amongst a number of launches so that any individual failure does not compromise the entire investment. Business is more likely to go with the 11th launch with a 9 out of 10 success record (and only lofting 20mt of assets), than the 3rd launch of a 2 for 2 vehicle hauling 100mt of assets.

Also, I don't understand why there seems to be an assumption that any launches to the Moon require a free-space rendezvous and direct return from Lunar orbit. This seems to have a built-in implicit assumption that the proposed ESAS HLLV will really have nothing to do with the ISS, nor the ISS anything to do with a return to our Moon. To me this is silly as we have a space platform with at least one robotic arm (I'm not sure what ever happened with the German one). With a facility in orbit you have less of a sense of urgency of getting everything together to go quick, and one can re-think the launch sequence as well as double and triple check all systems post-launch (THE single most traumatic period of any payload's life).

We need to get lots of skilled people into space to do skilled-people things like make better products (materials science) or increase the efficiency (combustion science) of stuff here on Earth.

Hypothetical question: What if every single rotary machine on Earth used perfectly spherical, space produced ball bearings? What would be the decrease in energy required to operate each machine? What would be the aggregate of that? And the corresponding intangible benefit of less pollution from energy production?

This is of course complete fantasy, but the point is that there is so much unknown business opportunity in space it's mind-boggling, and this is the kind of opportunity that used to excite the American spirit. Tumlinson's "Return to the Moon" attempts to be a manifesto in this regard, but falls a bit short, I feel. It is in the right spirit, though, and this is important for our country.

Nevertheless, the idea of commerce and industry in space, fields in which the U.S. has a competitive advantage, needs wider acceptance. Investing our nation's capital and resources in a private launch vehicle for NASA, which serves no other interests, is in my view a dead end for NASA and a dead end for the American space industry. We can't afford this kind of investment right now, but we can afford to do it in small bite-size pieces. If we've got three launch vehicles and each can launch 4x per year, then we have a launch per month, and 240 mt in orbit per year. (Wait, but that's what the HLLV is going to do 8 years from now...)

That's not half-bad, and we know we can scale up from there. The Boeing facility is supposed to be capable of something like 40 cores per year or 14 launches just of the D-IV. The Falcon's supposed to be cheap and easy so we should be able to launch water or expendable cargo at least once a month on that one. Give Atlas half a dozen per year and you're talking about 30 launches per year, or 600mt to orbit per year at full speed. 2 or 3 launches per month is not a burdensome task for a smaller rocket, especially if different facilities are used.

Isakowitz doesn't really give us any insight into the launch costs of the vehicles (prices negotiable), but I'll assume $250Mn for the D4, $200Mn for the A5, and $25Mn for the F9. That's (14x250)+(6x200)+(12x25)=3,500+1,200+300 = $5.0Bn for 600mt. There's no way HLLV is going to be cheaper than that. Even at $100Mn per Falcon 9 that's still less than $6.0Bn.

And the thing is, once you ramp up to that level of production, per-unit costs start coming down, which means that after a couple of years the D4s are down to $150Mn, A5s are $75-100Mn, and F9s are the Bic lighters of space. Okay, maybe a bit optimistic, but don't be bamboozled by the NASA finesse. They could be applying their skills towards 20mt Moon machines, or international interface standards (now that's useful!) for space vehicles instead of fussing over launch systems. NASA asked itself the question of whether it should be in the business of flying airplanes around. In most cases the answer was no. Should NASA be in the launch vehicle business? (Or provide engineering insight like they do with aircraft...)

Follow-up:

There has been a bit of discussion about the article on the internet (Space Politics, Transterrestrial Musings and the Space.com Uplink)

Some folks seem to be fixating on the 'Proximity Ops' issue as a killer for the deal, as if each and every thing that has to meet up with something else in space has to have a complete set of maneuvering devices and complicated and heavy equipment and you're sacrificing payload on an already tight 20mt limit and...

They seem to forget that this issue has already been looked at and the answer is tugboats and robot arms. You launch something near the ISS. A tugboat runs out and fetches it. The arm attaches it to the station or something else. The tugboat can also be used for releasing/retrieving free-flyers, ferrying s/c over to the fuel depot, and so forth.

This doesn't need to be a complicated machine. It doesn't even need to be pretty or aerodynamic. Just capable of moving stuff around in orbit. It's been variously called an OTV or OMV over the years. It's also a craft that would be functional at an L-1 station as well, so it's not just a mono-purpose or mono-location vehicle.

It's also the kind of design challenge that would likely excite more kids than updating their grand-dad's Apollo.

It's been said that NASA needs a serious infusion of young talent and fresh ideas. Perhaps this project is the catharsis that will have this infusion inflicted upon them...