The Myth of 25X

One item of contention that I've seen in the emerging space industry is about the relevance that suborbital spaceflight has for future orbital applications. With the exception of RpK, all of the current effort going into building reusable, safe, and operable launch vehicles has been focusing on suborbital vehicles first. However, while most of those companies are focusing on suborbital vehicles at first, and while most of us think we can close our business cases on suborbital, most of us fully intend to proceed on to orbital spaceflight if we can make a successful enough go at our first markets. That is one thing that MSS, XCOR, Armadillo, Blue Origin, TGV, SpaceDev, Canadian Arrow all have in common.

However the conventional wisdom in the industry is that orbital launch requires X times more energy (where X is a number that varies from 25-81 depending on who is throwing out the number) than suborbital launch, so suborbital launch really is an entirely different problem. While I will admit that suborbital spaceflight is a more benign flight regime in many ways, this particular piece of common knowledge is misleading at best, completely bogus at worst.

The origin of these numbers is the simple kinetic energy equation KE=1/2*m*v^2. Since kinetic energy is equal to the square of velocity, if you need 5 times more delta-V to get into orbit than to reach 100km, you end up needing 25 times as much energy.

The problem is that this is wrong. You don't need 5 times as much delta-V to get into orbit as you do for a suborbital vehicle. Or to put it more correctly, people making this argument don't seem to have a good handle on how much delta-V it really takes to make it even to 100km.

I can see where such people are probably making their mistake. If you take an extraordinarily naive first brush attempt at estimating the delta-V requirements for a 100km suborbital hop, you might just determine what cutoff velocity you would need to coast up to a 100km apogee. If you run the numbers it comes out very close to 1400m/s, which is about 1/5th of the theoretical minimum orbital velocity.

What both of those numbers (that for the suborbital delta-V requirement and for the orbital delta-V requirement) both ignore is air drag losses and "gravity losses". If we lived on a planet without an atmosphere, and if we had engines with infinite thrust-to-weight ratios, they might have a point.

Real world orbital launch vehicles typically need to deliver 8500-10000 m/s of delta-V (compared to the orbital velocity of ~7200m/s) to reach a low earth orbit. Somewhere between 1300 and 2800 m/s of delta-V ends up getting eaten up by drag and gravity losses.

To illustrate gravity losses, imagine a vehicle just after takeoff. It has a thrust to weight ratio of say 1.2 (about what Saturn V was IIRC). That means that at that point, 1/1.2=~83% of the rocket's thrust is just going into counteracting gravity. As an orbital vehicle gets out of the thickest part of the atmosphere, it quickly starts turning so it can start accelerating horizontally (most of reaching orbit is going fast enough sideways that you can fall without ever hitting the ground). If your engine is firing parallel to the ground, you aren't suffering any gravity losses because your engine isn't fighting against gravity. You are falling however, so you either need to get up to a sufficient height before you make that turn (called "lofting"), or you need to fly with your engine not quite parallel to the ground (so a tiny bit is providing some lift). But basically for orbital vehicles almost all of their drag losses occur very early on since they spend most of their flight flying horizontally. For a straight up and down suborbital flight, you might not have much higher gravity losses in nominal terms than an orbital launch vehicle, but as a percentage of the overall delta-V suborbital vehicles take a much bigger hit.

Drag also tends to impact suborbital vehicles (and reusable ones in particular) more than an orbital launch vehicle. Drag tends to scale with the frontal area of the vehicle. However, the mass tends to scale with the volume of the vehicle. If your vehicle was spherical with a radius of r, the force due to drag would scale with r^2, while the mass would scale with r^3, thus the acceleration due to drag would scale with 1/r. Basically smaller vehicles suffer much worse drag penalties than bigger vehicles. Another issue with suborbital vehicles (especially VTVL ones) is that they tend to have much squatter aspect ratios compared to orbital vehicles. Take a look at your average orbital launch vehicle, like Atlas or Delta. They are typically about 12-15x as long as they are wide (Ares I is a whopping 25:1!). Due to landing stability issues for VTVL vehicles, you're more likely to see aspect ratios of around 3 or 4 to 1 for single stage vehicles and 6 or 8 to 1 for orbital vehicles. Squatter vehicles tend to have much higher drag losses than longer skinnier vehicles, since they have more frontal area per unit mass. Between those two issues, and the fact that suborbital vehicles spend a lot larger percentage of their flight duration inside the sensible atmosphere, and you once again end up with drag losses accounting for a much higher percentage of the delta-V required for a suborbital vehicle.

The real eye-opener for me came when I tried to toss together a quick "1DOF" trajectory model a couple of days ago. The model included drag and gravity losses, with an exponential curve fit model for the atmospheric density at various altitudes. I ignored the performance increase you get at higher altitude (due to less backpressure losses), and just picked a "mission average Isp). I assumed an average drag coefficient (for the shapes we're interested in, the drag coefficient doesn't change too drastically over the various Mach numbers in question). To try out the model, I put in some numbers for a vehicle that was roughly equivalent to what you would need to compete in Level 2 of the lunar lander challenge (with a huge amount of reserve propellant). I was expecting to see us get close to 100km with it, since the design had a delta-V of over 2km/s. Instead of 100km, my model showed the vehicle peaking out at only ~25km. Even doubling the propellant mass while keeping the dry mass constant wasn't quite enough to make 100km.

The basic takeaway was that a ground launched VTVL RLV is going to take a pretty sizeable delta-V in order to actually make it even to 100km. While I didn't keep going on trying to see what it would take (since I had to get back to work), it looks like you might need 3-3.5km/s of delta-V just to reach 100km in real life. If you're trying to go to higher altitudes (as most of us are), you need even more delta-V.

Now, some may say that this still is only 30-40% of the delta-V needed to reach orbit, and that therefore you still need 6-9x as much energy to reach orbit, but even this is missing something important. Most orbital launch vehicles are "two-stage to orbit" vehicles, and most orbital RLVs will also be TSTO. If your first stage has 3.5km/s of delta-V with a payload equal to the fueled mass of your upper stage, and it also has 3.5km/s of delta-V, you've got 7km/s of delta-V overall. Which is between ~75-80% of the velocity you need to reach orbit. Which means a big VTVL "barely suborbital" vehicle with a much smaller "barely suborbital" VTVL vehicle stacked on top is going to have over 66% of the energy needed to reach orbit.

But 1.5X just doesn't sound as impressive as 25X does it?

Now, before I wrap this up (which I need to do soon since this post has spilled over into Sunday morning), I want to add a few caveats. First off, I don't know how the numbers pan out for ground launched HTHL vehicles. I know XCOR does, but doing a real analysis of an HTHL suborbital vehicle requires more than a simple 1DOF. My guess is that the basic conclusion, that the amount of delta-V you need to reach 100km ends up being a large fraction of the delta-V you would want out of a first stage of a TSTO orbital RLV, still holds.

Second, air launched suborbital vehicles take much smaller hits from drag losses, and can get away with much bigger expansion ratios. Which means they can get away with propulsion systems that tend to be lower performance (both from an Isp standpoint and a mass ratio standpoint) than ground launched RLVs. It also means that the delta-V required for being "barely suborbital" is lower, and hence you can build a suborbital RLV that actually is much, much lower performance than a comparable TSTO first stage. So, maybe some of the original criticism is fair--if you're talking about air launched suborbital RLVs.

Third, there are lots of issues other than raw delta-V performance that are more challenging for orbital vehicles. TPS is one of them. Figuring out the logistics of how to recover 1st stages that land down range (or how to make them high enough performance to be able to do a Return to Launch Site landing). How to handle vehicles that are physically bigger. Etc.

But in spite of all those caveats, the conclusion you should walk away with is that suborbital vehicles really aren't "dead ends" that have no relation to the challenges of orbital vehicles. They may deliver slightly less performance than an orbital launch vehicle stage, but the real energy difference may only be a factor of 1.5-4x, not 25x.

Benefits of Orbital Propellant Transfer: Adaptability, Capability, Etc.

[Editor's note: A good friend of mine from Santa Clara, Henry Cate, is starting up a Carnival of Space. I'm usually not a huge fan of blog carnivals, but I think this is a creative idea, and wanted to support him on this, so this is my first "Carnival" post.]

Of the top ten technologies that I discussed previously as being critical for a spacefaring society, one of the technologies that I've repeatedly stressed has been orbital propellant transfer and storage. And for good reason. Other than lower cost launch (which I think has been discussed to death already), these two technologies are probably the ones that can have the largest impact on space exploration and development. I'd just like to summarize some of the key benefits I see of using orbital propellant transfer and storage in a space transportation architecture.

Adaptability: Propellant transfer and storage technologies (especially in the form of propellant depots) allow a space transportation system to take advantage of improvements in launch vehicles over time. By separating the launcher from the interorbital transfer stages, landers, and other in-space hardware, it makes it a lot easier to take advantage of upgrades over time.

In a way it's kind of like the computer I'm writing this post on. This computer started out as a machine I bought on eBay back before my mission (in '99 I think). Over time as new chips and better hard-drives came out, I was able to incrementally upgrade things without having to fork out all the money for a brand-new machine. By now, the only hardware I have on this computer that was on the original machine is the smaller of the two hard disks. The modularity of a PC architecture has allowed me to inexpensively upgrade things as I had the time and money available, instead of forcing me to buy a whole new system. Now, not everyone does it that way, but the option is there if you want to.

Reusability:Propellant transfer and storage makes it much easier to move towards a more reusable transportation infrastructure. In fact, without the ability to transfer propellants on orbit, there are some segments of a lunar or Martian transportation infrastructure that really can't be reused. With propellant transfer capabilities (eventually augmented by ISRU capabilities), there really aren't any parts of the transportation architecture that need to be expendable.

The economics of reusing in-space hardware may actually be even more compelling than reusing orbital launch vehicles (and the case for reusing orbital launch vehicles is pretty darned compelling). Unlike orbital launch vehicles, reuse of on-orbit vehicles doesn't involve adding much if any hardware that wouldn't be needed already for just performing the basic mission. Design for reusability does tend to drive you in different directions from design for expendable vehicles (such as pushing you to multi-engine landers with engine-out capability instead of rolling the dice every time you land with a single-engine lander), but in many cases those changes can actually make things less expensive in the end.

But all of that is moot if you can't refuel the vehicles except on planetary surfaces.

Capability: Orbital propellant transfer and storage can allow for much more capable missions than you could perform without them. Dallas Bienhoff (of Boeing) recently presented a paper at the recent STAIF 2007 conference discussing how much you could increase the lunar surface mass of the planned ESAS architecture if you used orbital propellant transfer and "dry-launch" techniques for the EDS and LSAM (Dry Launch is where you launch the transfer stage and lander empty, and top them up on orbit from a depot or from fuelers). I don't have the exact numbers handy, but the increase was substantial. It may have been over double the cargo to the lunar surface.

More interestingly to me, these technologies can allow you to get much more capability even if you don't develop new launch vehicles. Every component of the planner lunar stack is light enough to be launched dry on existing EELV equivalent vehicles. And if you then top them off in orbit, you can send a lot more in a given mission than could be done with a non-dry-launch architecture. You could probably send 6-8 person missions, or land entire Sundancer modules along with the 4-6 person crew. All without needing heavy lift launch vehicles.

Dependability: In a world of expendable launchers, where launcher reliability is still depressingly low, a propellant depot serves as a buffer or capacitor between a lunar or martian mission, and the launch vehicles that put the components up. A commercial propellant depot can buy from whoever can launch to it, and with the likely propellant demands for even modest lunar transportation architectures, it will be buying from lots of suppliers. If one launcher starts having problems, the show still goes on. Much like how many companies will put UPS systems between their computers and the main power grid, especially in areas where the power can be flakey or unreliable.

Incremental Developability: [Yes, I think I may have just created that word on the spot.] One of the main issues raised with propellant depots, is that they sound like big, very complex projects. When people hear propellant depot they often think of some ISS sized monstrosity and then extrapolate that only NASA could run something like that, and therefore it would cost as much, take as much time, and be as poorly run as ISS. The reality is that the first "propellant depot" probably isn't going to be some sprawling 100% custom designed facility that has all of the features, bells and whistles. More likely you'll see a gradual buildup of capability.

At first, you might see missions that don't even use a depot--but transfer propellants directly from tanker to tankee without any special infrastructure. Some of that may be in the form of hitchiker satellites that tap the surplus propellants from their launcher so they don't have to store propellants onboard during the flight (thus reducing the risk to the main, paying customer). Then, you might see someone moving into a first generation propellant depot. This will probably be nothing more than an upper stage possibly docked to a Sundancer module. It won't have zero-boiloff capabilities, probably won't have fancy sunshields or meteorite protection, it probably will only handle two propellants, and much of the propellant handling may involve manual connections and valves. Only once there starts to be serious money being made by depots will you start seeing them branching out, growing in size, adding bells and whistles, etc.

You'll also likely see a lot of the technologies needed for these depots being developed not by big expensive NASA or DoD demonstration satellites like DART or Orbital Express, but by companies like Lockheed piggybacking experiments on the postflight portion of Atlas V launches, and other such, low-budget partially IR&D funded experiments.

Feasibility: One of the best things about propellant depots is that there really is a lot of prior art and experience that demonstrates that we should be able to make this a reality. Every time a Centaur upper stage performs an in-flight relight, it is settling propellants, transferring them through a series of valves and pumps, and then sending them into another system (in this case an engine). Starting with Gemini and Russian programs at the same time, we've demonstrated the ability to do orbital rendezvous and docking. The Russians have been doing autonomous rendezvous and docking for decades, and now that we finally got around to it with Orbital Express, we're doing it too. The Russians for decades, the Shuttle, many other programs, and now Orbital Express have demonstrated the ability to make fluid couplings between spacecraft, both with and without manned intervention.

There are subtleties and tricky parts to tying everything together in the case of cryogenic propellants, but almost all of the toughest techniques and technologies needed for transferring propellants on orbit have been demonstrated already. Based on the plethora of past experience, one can have high confidence that this orbital capability can be refined and brought into practice in the near term. There is a lot of detail work to be done, and it'll probably take a lot of hands-on experience and several iterations before we start converging on the best ways of doing things, but the initial capability is relatively low-risk, and near-term.


Anyhow, that's a basic introduction to some of the benefits I see from orbital propellant transfer and storage. I've got lots of other articles on this blog detailing some of the technical challenges and some ideas for how to handle them. I'd strongly suggest doing some searches if you have the time and are interested.

2007 ISDC (and Lunar Library) update

By guest blogger Ken

We're rapidly closing in on one month out from the ISDC and things continue to gel well. First and foremost, because I'll finally get to meet Jon face-to-face. The prep work certainly has not been an easy process, and if I had to grade myself on program management I'd have to give myself no better than a B-/C+. I recognized this would likely be the case early on, and so I made sure to have a co-chair (perhaps the chapter insisted a little [lot]). Carol Johnson has been active since before the NSS, and has been to most of the conferences to date, so I know she knows what needs to get done, and she's doing a phenomenal job compared to me (though I was strong in the earlier part). She also has hardware on orbit, so there.

There is still a lot of work because we've got a full plate lined up. We've arranged a lot of conference space at the hotel and will have a number of tracks each day.In a broad context it will look something like this:

Thursday -
ATWG wrap-up
Space Venture Finance Forum

Friday is Transport Day
The mornings are given over to plenaries and we're still finalizing schedules, but we're pretty confident on Congressman Nick Lampson, Shannon Lucid and Don Pettit for Friday morning. Friday lunch is given over to Robert Bigelow [Just found out today that Mr. Bigelow will not be able to be there Friday. We'll have to see how the overall weekend works out for him], and after 2pm the tracks kick in. Attendees will have their choice amongst the three main tracks - Frontier Transport/Moon & Cislunar Space Development/The Martian Frontier, as well as Space Settlement, ISS Science, Space Business, Education sessions, Space Law, as well as a number of NewSpace speakers in the big room used for plenaries.

Saturday is Moon Day
Ames Director Pete Worden will open the plenary for us and we'll have a number of speakers, including space hottie Laurie Leshin [um, I'm pretty sure she's married - is hottie appropriate?] as well as Paul Spudis and Jeff Volosin. Eric Anderson should be telling us about Space Adventures' $100Mn trip around the Moon (there are complications, understandably). John Carmack is going to talk in the Big Room about his Lunar Lander, and later on will be the Space Blogger Summit. I heard that about 35 folks were invited to that and about a dozen have responded with more expected. I've been given a sort of backdoor invite because of my work here and at the Lunar Library, so I may yet make a public appearance in something other than a Moon context. As before, the tracks open up at 2pm, and we've got again got Space Settlement, ISS Science, Education and Space Business, as well as Astrosociology, Space Solar Power, Space Outreach and the three main tracks.

Sunday is Mars Day
Bob is going to open the plenary, and Rusty Schweickart is going to be the lunch speaker. There's an international session that we're way behind on (I bear part, but not all, of the blame) being put together by the former president of CNES. We'll also have tracks on Space Medicine, FTc, Settlement, Business, Education, and Transport/Moon/Mars, with everything wrapping up in an Awards Dinner Sunday night.

Monday is just some miscellaneous bits and pieces, like one of the Moon Rock Cert. classes, so that everyone can travel home Monday afternoon and evening. D/FW benefits from being within ~4 hr flying distance of most major North American cities. If we had point-to-point suborbital travel that would be a global capability, but we're not quite there yet.

There's also all kinds of other stuff that will be going on as well. We're still trying to scare up displays for the front area. All of our Affiliates get a display table, and we're trying (without only a few successes) to get some vendors of space stuff in there. We'll have an Author's Area for presenters and others to sign books they've authored. Dallas Personal Robotics Group wants to put on an outdoor robot challenge with some groups in Austin and Houston, and perhaps others, back behind the hotel. We'll have a large Space Arts Track and Space Art area. We've got a small Kids Program. There's a Jim Baen's Universe writing competition tie-in, which stories are being processed as we speak. We've got a bunch of neat tours lined up. I'm already signed up for one of the Moon Rock classes we've arranged. There's also the 50th anniversary of space flight, the 20th anniversary of ISU, and others as well I'm sure.

Apogee Books, one of the few exhibitors, is apparently partnering up somehow with Launch Magazine, who I know will be there on a Media Pass, and because they're going to be doing some stuff with the Dallas Area Rocket Society. We've got a number of movies lined up, and the director of "Postcards from the Future" is working to get a special camera to the conference so that we can see it in all its 4K glory. We've also got "Microgravity", Chip Proser will be there to talk about his documentary "GaiaSelene", and the Mars guys have a cool flick as well.

So it's going to be a great conference. We do of course have various concerns that give each of us ulcers. My co-chair is disappointed that we don't have more deep space presentations for things like Hubble and Webb. I tried to drum up some support with the local JPL Solar System Ambassadors but had no luck. A few speakers have pulled out to date (typically after they are in some printed ad), and there seems to be an overall squirelliness about speakers and the Memorial Day weekend. I'm disappointed that we don't have more people showing off hardware or just corporate displays, but folks have been most parsimonious in that regard. My disappointment is that if we do get a fair amount of local turnout they will not have a whole lot of stuff to see, and so by extension it's still not a serious industry. Space companies need to spend less time showing off for each other and more time showing off for the public.

Because is there any doubt that this is a general space interest conference? NSS's goal is to get people living and working in space, and it turns out we do have a lot of friends in that regard.



Lessons learned:
-Have a high-speed internet connection and a solid e-mail host. Dial-up doesn't cut it anymore when you've got 17Mb files that need sending around. Hotmail, which I've been using since 1999 and have been able to access from places as diverse as a bar in Christianashavn to a bar in Cabo San Lucas (okay, maybe not so diverse), has been so-so. It's great in the global access regard, but it's a Microsoft site and so seems to have periodic fits, and is also slow at their end. It may be time to start migrating more stuff to the Lunadyne GMail account.
-When people give you a really good deal and you take it, they'll probably come back later to revisit the deal.
-Choose any weekend other than Memorial Day. It's too close to too many other traditional community/family activities. People in the space field don't want to spend their weekend doing space stuff. 2007 is an important year, so we have got a pretty impressive line-up of speakers, but it's not worth the heartache.
-When you live in the heart of the Bible Belt, the major local newspaper is likely to have other priorities than space and technology (our GuideLive.com submission isn't up yet, for example). The small niche papers seem to be the way to go.
-Try to make sure your leaders are people with initiative. If you can just give them general guidelines to work with and then they take the ball and run with it, you get great results. It doesn't always work that way, though.
-Take periodic vacations. Go far away and do not do any space stuff. I am sooo looking forward to one of those. I'm guessing it's about time for another trip to Eden. I'm just worried that I'll get a ticket from the State Trooper in Brady for still not having the front license plate (it was stolen, probably to get a vehicle to Mexico as they've gone after my inspection tag as well, and my topless beetle has a much prettier smile without it. DPS in Dallas has much more whacked out stuff to deal with than missing license plates).

So what happens afterwards? That's a good question. I've got close to a score of vacation days saved up. Ten of those are for prep and aftermath of the conference. In early June I'm going to use some vacation time to go to the Rutgers Symposium on Lunar Settlements. Then I'm going to start working on my next project - some kind of Lunar Academy program. The guys over at the Moon Society have a really good super-secret idea that ties in with that that I may be able to help out on.

I've got some work to do on the Lunar Library like getting more of the old papers up and compiling the first CentiLune. I've got over 100 Moon story reviews (and counting) linked into the Lunar Library. Amazingly, they average about 100 views per day and have since the beginning of the year. Much higher traffic than Google is showing for the site proper. It is kind of cool to see the search terms and realize that people are looking for titles they remember seeing on the site. Popular search or e-mail items have been the "Final Frontier" mini board game, the Spanish language version of the Braille Moon phase book, the "Moon in my Room" nightlight (which has apparently been selling like gangbusters [though not through my site :-(]), the "Earthrise" 8'x13' wall mural which is OOP, and "Kids to Space".

I'm also excited to hear that the guys at Orbis got an order for a large (probably 20') Moon globe. If they sell a few more large ones they'll be able to afford the processing time to render it down to the sizes I can afford, like the 1 meter. (These are high-definition renderings, unlike the inflatable Moon globe I have now) I'll definitely be picking up a few of the smallest (16") ones when they come out.

I'm also going to be buying a house by the end of the year (I'm anticipating some serious seller pain in the third quarter, but the first quarter of 2008 might be more opportune), so I will actually be able to put the LL in a real home. Ultimately it's bound for an institution (like the ISU Lunar campus), but it's still not quite there yet. So much work left to do...

Continued Light Blogging

Sorry guys, but the light blogging is going to continue for a while. I've got some ideas I'd like to write a bit about, but getting my thoughts together to a point where they'd be worth posting is going to take longer than I have at the moment. Here's a random sampling of the craziness that is my life:

Things are going fairly well at work, and I should be to the point where I can write up an official MSS Update either sometime later this week or early next week.

Last year I was asked to serve as a Webelos (Cub Scout) Den Leader for the three Wards here in Tehachapi. I finally got formal training for the position last month, and then was promptly released last week, and given a new (and probably more challenging) calling. I'm now the "2nd counselor" in the Elders Quorum for our Ward (Wikipedia has a semi-decent explanation for those not familiar with LDS jargon). It'll be a challenge, but an enjoyable one.

My thesis is actually moving forward a bit. I was able to get access to Maple (the computer program I'm using for doing my math models) again, so I've been making some progress getting my models put together. I was able to tie in the complex loss constants into my piezoelectric vibration model. It turns out that Maple eats Bessel functions with complex arguments for breakfast. I was also able to figure out a model for the pressure distribution in the nozzle (as a function of position, time, and the amplitude of the wall vibration). Interestingly enough, it turns out that you can actually have a negative pressure value in some cases. At first I thought that this meant that the fluid would cavitate at that point, but it turns out you can have negative pressure without cavitation in some instances. Weird, huh? Where I'm having trouble is coupling those two models together (the one that describes the piezoelectric crystal and nozzle with the second model that involves the nozzle wall and the actual fluid). Maple doesn't like that. Or more correctly, I keep crashing the program as it sits and crunches on the numbers. I'm making some progress, but the math is just really, really, really ugly. I'll go into the math a bit in a future post if anyone is masochistic enough to want to see it, but suffice it to say, my computer doesn't like me a the moment.

And on the homefront, I have a wonderful wife, and two cute little boys doing cute little boy things. I'll have to post some pictures with the incriminating evidence from Jonny's latest adventure sometime soon too.

Anyhow, but other than some thesis related stuff, and maybe some Jonny bloggin, I'm not going to be able to blog too much anytime soon.

Sorry.

Random Thought: ISS Module Delivery Without Shuttle

One of the reasons why I've started doing these "Random Thoughts" blog posts was in order to toss out some ideas that I just don't have the time to research completely, yet still sound interesting. On some of my more detailed posts, I can often spend 4-6 hours writing, doing math, looking figures up, etc. Because of that hurdle I post less frequently, and unfortunately I was noticing that some interesting ideas were falling completely by the wayside. It's generally considered bad to sacrifice quality for the sake of quantity, but I look at it more as it being better to let out an idea that is half-baked and get early feedback than to sit on it until I've forgotten about it.

So without further ado, my latest musing.

In case you haven't noticed, I don't like the Shuttle. I don't like Shuttle Derived Boosters. I spent half my life in Northern Utah, but I really don't like SRBs, and have never been that impressed with them. I'd really like to have a reason to retire the Shuttle sooner rather than later. I know it isn't going to happen, but a guy can wish can't he?

One of the key problems with retiring the Shuttle sooner (or even in 2010) is that there are many ISS modules and payloads that were designed specifically to be launched on the Shuttle, and can't just be launched on a standard EELV. The argument has gone that if we don't keep Shuttle flying, we can't complete ISS, and without ISS there won't be a market for COTS. Never mind the fact that NASA just undercut COTS by signing a contract with Russia for crew and cargo services out through, was it 2011?

So, for a long time I've been noodling alternatives to the Shuttle for launching such payloads.

So here's the idea. Well, here's some background first. CSI recently unveiled their LEOExpress idea for cargo delivery to space stations (ISS as well as Bigelow). The basic idea is you make a cargo canister that has a "Progress Nose" on both ends, and a cargo section in the middle. You launch this canister on any existing LV (Atlas, Delta, eventually Falcon or K-1 as well). The upper stage of the LV holds the canister in place until a Progress can undock from the space station, and rendezvous and dock with the canister. The LV upper stage then separates and deorbits, and the Progress hauls the cargo up to the station where the free-end of the cargo canister then docks into the Progress's original docking port. After use the progress then disposes of the canister and itself. It's a kind of cool idea that really doesn't feature a lot of new technologies, while still opening up a bunch of new capabilities.

Currently the canisters envisioned all have the same OD as the existing progress module. But what if you expanded those canisters? Say to the same internal volume and shape as the Shuttle payload bay? Use composite structures to transmit the loads from the ISS modules into the canister in the exact same manner as on Shuttle. Provide all the services packaged in so none of the modules have to be redesigned. Sure it's wasteful to toss away such a payload canister after each mission, but these are just stripped down payload bays with the minimum number of services for the job.

What most people don't realize is that while the Shuttle can put almost 30 tons into a due-east, minimal Low Earth Orbit, it can only put about half of that (~32,600lb IIRC) all the way to the station. This is because Shuttle has a very low MR "upper stage" and is operating at the bad end of the Rocket Equation. Vehicles like Atlas V 552 and Delta IVH could likely launch more to ISS, even once you take the hit for the "shuttle bay canister".

Anyhow, that's the idea. I've run the numbers, and the payload is heavy enough compared to the Progress tank capacity that you would need to deliver the cargo to just outside of the ISS operating area, and just have the Progress supply the "last-mile" so to speak. And I don't have specific numbers on how much Delta-IVH or Atlas V 551 or 552 can deliver to an ISS altitude and inclination, but at least from preliminary investigations such an idea could be doable. Since we're going to retire the Shuttle soon anyway, reverse engineering one of their cargo bays to make such an expendable cargo-bay-canister might actually be a good idea. There are some modules that are never planning on flying as is, and this might provide them a second chance. Plus if it were done quick enough, you might be able to retire the orbiters a year sooner, and funnel some of that money into more productive purposes.

Just a thought.

Space Venture Finance Symposium

I just wanted to put a quick word for a symposium that's going to be held in conjunction with ISDC this year that I thought some of you might be interested in. It's called the Space Venture Finance Symposium, and it will be held on May 24th (the day before ISDC begins). Details and registration information can be found here on the ISDC 2007 webpage.

While I did take as many business classes as they'd let me as part of my Mechanical Engineering Masters degree studies, I don't get to spend as much time these days doing things on the business side (other than my dabblings on this blog) as I would like. While a key part of symposiums like this is trying to help people who are interested in possibly investing in commercial space ventures meet some of the firms and get some introduction to the industry, I like going just to learn, to meet new people, and bounce ideas around.

I don't know all the major speakers there, but I can vouch for Stephen Fleming, Lee Valentine, and Esther Dyson. I always learn something new from them, and the coolest thing I've found is that they're perfectly willing (as time permits) to talk with and answer questions, even from younger folk like me. Oh, and I particularly need to make penance for missing half of Stephen and Esther's panel at Space Access...

So, if you're an investor looking for more info on this interesting new industry, or if you're a startup looking for ways to better raise money, or if you're just fascinated by this whole space entrepreneurism thing... I'll hopefully see you there.

Random Thoughts: Rocket Nozzles

Last night I ended up staying up a lot later than intended. It's a long story, so I'll spare you the details (other than that it involved a cold, a cat, an upcoming open-house, a gassy baby, a LLC competitor, and the RS-68--don't ask). While I was up, I got reading some of Ross Tierney's latests posts on Nasaspaceflight.com about his DIRECT concept (he's only recently reappeared on the scene after a couple month's absence). One of Ross's comments got me thinking again.

One of the biggest pieces of evidence used by Dr Stanley in his Q&A thread to call into question the merit of DIRECT was the large discrepancy between the RS-68 Regen numbers Ross had used, and some official numbers given by P&W. Ross had been claiming a vaccum Isp of ~435s or so, and the P&W guys released a formal performance summary stating that they only felt ~418s was reasonably attainable (compared to the existing 409s vacuum Isp). Ross mentioned that while the engineers working with him on the original study had investigated almost 100 different configurations, many of which used bog-standard existing RS-68s, they had taken the gamble of selecting the RS-68R version because they had it from a pretty good source that the higher performance numbers were doable.

One thing Ross mentioned suddenly gelled several different things I had been reading and thinking about over the past several months. Back when I did my quick "Random Thought" post about inflatable nozzles, I had noticed that the original J-2 engine had a vacuum Isp only a little bit above the RS-68, but the new J-2X NASA is working on has almost the same Isp as the SSME (~420s for J-2 and ~448s for J-2X), in spite of it being, I think, a gas-generator driven cycle. The big difference? A much larger expansion ratio. On the simplest level, as you increase the expansion ratio of a nozzle, more of the jet thermal energy is converted into kinetic energy.

The RS-68 and the RS-68R shown in the link above both use very small expansion ratios, while some other ground-lit LOX/LH2 engines use much, much higher expansion ratios. The reason? The RS-68 was designed initially for the Delta-IV. The simplest version of the Delta-IV relies 100% on the thrust of the RS-68 for liftoff. The SSME and Vulcain 2 on the other hand are used on vehicles where large solid rocket boosters provide the majority of the liftoff thrust. The main reason they're even lit on the ground is to avoid needing to air-start the engine, so all they have to do on the ground is light reliably, and not rip themselves apart due to flow separation. What this all means is that the RS-68 had to be optimized for a much lower altitude than the Vulcain 2 or SSME. This means a lower expansion ratio, and hence a much lower vacuum Isp.

The Ariane-5's Vulcain engine is a particularly enlightening example. The Vulcain engine is much lower thrust than an RS-68 (~240klbf for Vulcain vs ~700klbf for RS-68), but runs on the same propellants, has a chamber pressure that is very similar (102bar for Vulcain vs ~95 bar for RS-68), runs on a similar mixture ratio (6.2 for Vulcain, 6.0 for RS-68), the Vulcain has a regen cooled chamber with a dump-cooled nozzle, and both are gas generator cycles. However the Vulcain has an area ratio over twice the RS-68's, so it's vacuum Isp is 431s vs 409s for the RS-68.

Now, with a concept like DIRECT, most of the liftoff thrust would likely be provided by the SRBs anyway, unlike on the Delta-IV. So it would seem to make a lot of sense to pursue such a nozzle extension. You really don't need that much extra thrust on liftoff, and the Isp later on would be a lot more useful. Now, I'm not sure if you could package a longer-nozzle version of an RS-68 into the volume required for use with DIRECT, but the numbers look pretty convincing that you could get most of Ross's "magic Isp numbers" with a completely realistic redesign of the nozzle. You don't even need to go regen cooled to get most of the benefit. You just need to redesign the nozzle section for a slightly higher expansion ratio. Unless the throat somehow unchokes, downstream changes to a nozzle do not have any real effect on the upstream combustion processes. No new pump work or injectors, or combustion chamber changes would need to be made, just the nozzle skirt. As it is, the RS-68 is already throttleable down to 60%, so they know that they can operate the thing at much reduced exit pressures without flow separation. Doing a nozzle redesign like that for an ablative engine is a much easier task than resurrecting a 40 year-old design like the J-2X. Heck, such a change might even be useful for the core stage on a Delta-IVH.


Now, with all that said, Ross and his group are now focusing on a v2.0 of their DIRECT concept that uses existing RS-68s, SRBs, unstretched shuttle external tanks, etc. So, none of this musing really effects what they're doing. But I thought it was worth mentioning.

Oh, and I also ended up learning a lot more about nozzle design cleverness. While it's cool knowing that I've been part of a 4-person team that has designed, built, tested, and is about to start flying a fairly darned high-performance throttleable biprop engine, it's also fun learning more about ways to make those systems even better. Looks like I've got a new area to study out once I get this pesky thesis done...

speaking of which...

Lunar Tourism

For a long time, I've felt that translunar tourism was an interesting potential market, especially for guys like me who have the solution of propellant depots that is definitely searching for a problem. I was quite interested a few years back when David Anderman of CSI announced their whole "Lunar Express" idea of using a Soyuz to send space tourists around the moon. I thought the idea was pretty darned clever (the CSI guys are pretty good at being clever), and apparently so did Space Adventures, because they also started trying to drum up interest for a similar flight. The only problem I had with the whole concept was the price tag.

At $100M per person, I figured that the price was so high that nobody would bite. There just really aren't that many people in the world who even have $100M, let alone enough more than $100M that they could actually afford a $100M vacation. So, my focus has always been on trying to find ways to lower the price point at least to the commonly accepted (though probably quite inaccurate) $20M price for a ticket on a Soyuz. But if what Clark reports about what Eric Anderson was saying on NPR today is accurate, I may need to find some recipes for crow.

Now, I'm not exactly firing up the grill yet--it's pretty clear from Eric's comment that while they have people who've expressed interest, they most definitely do not have the full $100M in hand at the moment. But if his statement isn't total marketing hype (and you have to remember--these are the guys who've arranged for several ISS trips so far, so there's a real chance it isn't just hype), and he's actually able to get even one paying customer at that price point, that will be truly impressive. And it will likely provide a fairly nice prod to people with business plans for orbital propellant depots to start moving faster.

Random Thought: Dragon + Sundancer = CEV?

In a lot of conversations I've heard over the past year or so regarding COTS and its implications, many people trying to downplay the role of COTS (and explain why Orion has to be so heavy that only the Stick can launch it safely) have tried to play up the long duration features of the CEV. Basically they say "oh that Dragon capsule sure sounds nifty (if it ever flies), but it's only capable of barely getting people to LEO, it doesn't have all the features for exploration that the CEV does". After all, it's an exploration vehicle--it says so in the name!

Which is all well and good until you hear about what Orion doesn't have. It doesn't have a toilet (because nothing says exploration quite like Depends!) though it does have a "WCS", it doesn't have an airlock (so you have to depressurize the whole module if you need to do an EVA), and while much bigger than the Apollo CM, it only has about 19m^3 of volume inside (equivalent to a cube about 8.75ft on each edge, or smaller than the bathroom in my apartment complex). To be fair, it's a lot more capable than the Apollo CM, or Dragon all by itself.

But all of that got me thinking about an idea I had a while back--combining Dragon and a Sundancer module for use as a long-duration space transport. So, I ran the numbers. Interestingly enough, once you factor in the fact that the Orion SM has to provide about 100-300m/s of delta-V just to make it to orbit (even with the CLV delivering them to -11x100km now instead of -30x100km), the CEV only delivers about ~1380m/s of delta-V once on orbit. Now, once you factor in extra propellants and tankage on the Dragon/Sundancer stack to bring its total delta-V up to that level (ignoring how much propellant Sundancer itself has because I have no numbers for it), the total "Initial Mass in LEO" for both designs are almost identical: ~51.7klb. The difference is that the Dragon/Sundancer stack could be launched on Falcon IX's or Atlas V 401s.

Well, there's that difference as well as the fact that the Dragon/Sundancer combo also get you nearly 10 times the interior volume (about the size of my 2-bedroom apartment), a toilet, and (I think) an airlock. Oh, and the possibility of taking 7 people instead of just 4. If I were going on a multi-week or multi-month trip to an NEO, you can be sure what I'd want to ride in.

Now, to be fair, there would need to be some changes to the stock Dragon/Sundancer combo for this mission. Dragon would need a beefed up heat shield (which is already in their plans), Sundancer might need a slightly beefed up life support system (since it's only designed for three people for six months, it may not have enough "throughput" capacity to handle more than three or four people, and it is unclear how long Dragon could provide enough throughput for extra people), and there would probably be some communications and navigation upgrades you'd want for using those vehicles outside of LEO.

But it is interesting that they come out to such similar masses.

Now, one last thing. While a Dragon + Sundancer could probably be used as a CEV replacement, and could probably be used for a lower price than an Orion + Ares I, that's not the optimal way to use it. You'd preferably not want to toss away the Sundancer module after every mission if you could avoid it, which leads you to entirely different mission modes, and technologies like aerobraking. But I'll go into that more, some other day.

Jonny, Jimmy, and Us Bloggin

Just wanted to put some pictures up since it's been a while:








This last one is an oldie, but one of my favorites. It was a picture from when Tiff and I had just gotten engaged (which was four years ago Friday). It was sitting in my scriptures for most of the past four years, and I realized that I probably ought to scan it in, as I don't think I have any other copies of the picture.


And yes, before I got married, I was actually skinny. Thanks for asking.

Capacity and Priorities

Back when I was taking one of my Manufacturing Operations classes as an undergrad (which was long enough ago that even I am starting to feel downright old), we discussed an interesting concept. We were doing simulations of a factory, incorporating some complexities like maintenance downtime, variability, setup/changeover times, etc. The interesting thing that the closer you try to run a manufacturing facility to "100%" of its capacity, the more rapidly things get completely bogged down. There's some tipping point where actual throughput drops off rapidly, and the interesting thing is that it is often quite a bit below the supposed full capacity of the shop.

I was reminded of this phenomenon on our way home from Space Access. We were driving into San Bernardino, when all the sudden traffic slowed down to a near crawl for several miles. I figured that maybe there was an accident or some construction or something going on causing the delay. But all of the sudden traffic just started moving again. Dave pointed out that such behavior is predicted by chaos theory. At some point you just get enough cars on a given stretch of road, that with people needing to change lanes, merge in and out, etc that all of the sudden everything starts slowing down--even without an accident or some other choke-point.

I kind of feel that way right now, and for the last several weeks. Which is why I haven't been blogging so much. I got so many things going simultaneously on my plate that almost nothing was getting done. I'd want to blog, but I'd be so fried that I'd just sit there an play dippy Windows games like solitaire for an hour or so. Which gets depressing really fast.

Space Access helped a bunch. My spirits were up after getting to spend some time with the rest of my friends in the community. Space Access really is like a "Zone Conference" for rocket nerds. For those 99.9% of the people who read my blog who aren't LDS, a zone is a division of a church mission that typically contains 2-3 districts, for a total of 16-30 missionaries. Once every month and a half we'd have a big conference with 2-3 zones put together, or about 1/4 of the mission. There would be talks and training, but mostly it was a chance to catch up with old friends, check in on how people you cared about in previous areas were doing, swap stories, and generally recharge. I think that without Zone Conferences, most missionaries would go stark raving mad relatively quickly. I know I would've.

But even with Space Access, I was still feeling stretched way too thin.

This weekend, our church held its semi-annual General Conference. One of the concepts that really struck home to me was the importance of unencumbering our lives. Basically, the speaker was telling me something that had already been weighing on my mind for a while--that I've got too many commitments going on, and I need to prioritize, and pare back on some things.

As I was looking at priorities, I can think of four key priorities right now that are very important: my family, my job, my church calling (as a Cub Scout Den Leader), and my thesis. After that, I've got blogging, reading other peoples' blogs, and trying to change the alt.space world. But unfortunately it's pretty obvious that those have to be secondary priorities, not primary ones. Once I get my thesis done, I'll probably be able to move a new priority into its place, but for now, those four are what I have the most time for.

Now, this doesn't mean I'm going to quit blogging entirely. Quite frankly I spend a lot more time reading other peoples' blogs, forums, and newsgroups than I do actually blogging here. I'm going to try cutting back first on that and on trying to take too active of a non-blogging role in the alt.space world. Which might even mean that I get to blog more often, but we'll see.

What that does mean, is that you'll probably see less posts commenting on other people's blogposts, or ripping on ESAS, or talking about current space events, and more of a focus on original ideas, musings, etc...

So what I think I might be saying is: "The blog is dead...long live the blog!"