Asymmetrical LV

There are several limitations on the ability to expand a launch vehicle past certain sizes. One of them is tank diameter. On the smaller launchers, diameter limits might be dictated by available pipe sizes. A step up from there and tank diameter might be limited by available tooling. A couple of steps up from there and ground transport becomes an issue. Too large and it becomes somewhere between inconvenient and prohibitively expensive to transport from factory to launch site. Another limitation is height and fineness ratio. A launch vehicle gets into problems when the stack length is too large a multiple of tank diameter. 8″ irrigation tubing might be a good basis for a 10′ rocket, but gets into trouble before it reaches 20′. By the same token, the Atlases, Falcons, and similar vehicles are probably very close to the limits of length in relation to diameter. The standard build for a launch vehicle is, starting from the bottom, engines, fuel tank, inter tank structure or common bulkhead, LO2 tank, inter stage adapter, engine, fuel tank, inter tank structure or common bulkhead, LO2 tank, and payload. This is all in one long skinny cylinder except for a hammerhead shroud. To make the launch vehicle larger requires either more diameter, more length, or both, with the  manufacturing and transport problems from the diameter increase, or the structural problems from the length increase. There might be a way to double the size of a given vehicle class while holding the costs and other problems down. This idea is to build a vehicle that is asymmetrical around existing tooling. Also use a modular assembly technique to avoid both transport problems and the necessity of new tooling or construction techniques. Asymetrical LV   I still don’t have a computer that lets me draw cartoons all that well. The sketch is two possibilities for the vehicle concept. A stretched LOX tank built on existing tooling  that is as long as the original entire first stage. A stretched Kerosene tank proportionate to the LOX tank also built on existing tooling. These tanks are trucked separately to the launch site where they are clamped together along with the thrust structure. On the left the sketch has the helium tanks, avionics and such in the space above the shorter Kerosene tank with the second stage above the center line of the vehicle. The figure on the right has the second stage nested above the Kerosene tank with the helium tanks and such moved elsewhere. If this concept is feasible, a first stage could effectively double in size without causing problems in manufacturing and ground transport. Engines would double in number, but dome tank ends would not. The increased cost of the larger vehicle would be dominated by the engines. Eliminating the inter tank structures would eliminate a place for fumes to gather and possibly cause problems. The tank connectors could easily be lighter and cheaper than the normal inter tank structure. There would be no place at all for potentially explosive fumes to gather, which means that a leaking tank might be less of a problem. By going modular, any problem section could be swapped out with relatively little effort. The four modules being LOX tank, Fuel tank, thrust structure, and second stage. Two of these units could be flown together in a quad layout. Three of these units could act as boosters/first stage for a conventional  vehicle centered between them in the seven tank hexagon layout.

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SpaceX and Sea Launch

Another speculative thought. Suppose we have all been assuming that Falcons will try to land on a barge at sea or accept the payload penalty of RTLS, when all the tests have actually been in support of a launch at sea to a land recovery.

Sea Launch has the sea going craft to launch large rockets at sea. They are also, according to rumors, not making quite as much money as the investors would prefer. It seems possible that they might be at least semi-motivated to sell off the under performing launch assets.

What if the real intention of SpaceX is to acquire those assets at bargain prices for use in house. Launch a few hundred miles at sea from Vandenburg for a feet dry landing there, with the actual launch location dictated by the desired launch azimuth. The first stage would never have an IIP intersecting property on land, while the second stage would have an IIP that moved fast enough to minimize theoretical injury and property damage probabilities. A day out to launch and a day back. Twice a week seems possible.

From Brownsville the trip would be even shorter. A quick run to a point that gave the right launch  azimuth and distance from the cape for a Falcon recovery there. Possibly a day trip with the launch frequency that implies if the business develops.


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Falcon III H (R)

The vehicle SpaceX lost the other day has been described as a Falcon IX R with three engines. It is a bit intriguing to speculate on the purpose of three engines as opposed to the nine of the full up stage, or the one of the Grasshopper I.

The first and most likely thought is that more than one and less than nine are needed for the test flight profile. So three are required to do the job, but there is no financial sense in tying up, and possibly losing, six additional engines that are not required for this particular test program. The problem with that explanation for us in the peanut gallery is that it is boring and gives us nothing to speculate about.

An explanation that I find more fun and interesting is that there might be a financial and technical case for a three engine Falcon. A shortening of the stack for the lighter vehicle would produce a lower profile for a possible reusable version. Landing on a barge at sea would be with a vehicle with far less bending moments that a full Falcon IX stage. It seems possible that such a vehicle could land (barge) in a much heavier sea state than the larger vehicle. If that is a actual possibility, then Falcon III boosters could be attached to a Falcon IX stack with very low costs per mission if the mini boosters could be reused quickly and often.

Even a first take on such an arrangement yields some suggestive possibilities. A 66% increase in take off thrust would allow as much as 66% more take off mass and slightly more than that increase in payload with the additional staging event. With cross-feed, the Falcon III stages would drop off at under a minute and a half, barely supersonic, and fairly close to the launch site for a quick booster RTLS. The fully fueled Falcon IX would be in near vacuum conditions by that time with the considerable gain in Isp compared to a ground launch. A payload gain of over 2/3 for minimal cost could not be ignored if technically feasible.

For flights where the basic Falcon IX has enough performance to do the primary mission, but not enough for any recovery options, the Falcon III boosters could up the propellant reserve to allow core stage recovery. Small, quick turn around boosters enabling the recovery of a core for certain missions would be a nearly slam dunk decision if technically feasible.

For some Falcon IX missions, a Falcon III heavy could possibly deliver a bit more payload with the same number of engines. The engines being one of the major expense items could make not requiring more of them a sound business decision if the staging events become safe and routine enough. The extra payload would come from the same nine engines powering the stack for the first couple of minute as the normal Falcon IX, after which the two boosters drop off with the consequent dead mass reduction for the remaining stage. The remaining Falcon III would have the same velocity and remaining propellant as the base Falcon IX at this point, but would be boosting 1/3 of the engine and tank mass along with the upper stage and payload.

Last thought is on the difficulty of RTLS of stages entering from far down range. A barge landing is often mentioned, virtually always coupled with the words “good sea state” in some manner. This means that barge recovery is permanently dependent on  the sea not being too rough.  Some missions could be delayed by days or weeks to let the waves subside from a previous storm. Some whole seasons could be off limits if the recovery is sensitive enough.

The helicopter recovery I suggested a couple of years back might bear revisiting for lighter stages. The major objection to snagging a Falcon IX core in the air with a helicopter and flying it back to launch site was the excessive weight of the stage. A Falcon III stage might be air recoverable in a way the the Falcon IX stage could not be.


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Andrew Peregrin Goff

There are probably less than 5 people in the world who a) care about my family life, b) don’t follow me on twitter, c) don’t follow Tiffany on Facebook, d) didn’t get an email about this already, but e) do read this blog. So for those of you who fit in that category, I’d like to announce the birth of our son Andrew Peregrin Goff. Andrew is our fifth son after Jarom (deceased), Jonathan (9yrs old), James (7), and Peter (5).

Andrew was born this Wednesday evening at 5:20pm in Boulder. He was two weeks early (but still technically full-term), 6lb 11oz (3.03kg), and 19in (48cm) long. He’s doing great, and both he and his mother are home as of this afternoon.

If you’re wondering about the name, Andrew is my middle name. We also have several friends with Andrew as a first or middle name. It also fits with Peter, James, and Jonny (sort of) as a sort of semi-intentional Apostolic naming theme. We debated a lot of middle names–Andrew is somewhat tough to find good middle names to go with. Our two finalists were Sheridan after Tiff’s dad, and Peregrin (yes after Pippin from Lord of the Rings). We ended up going with Peregrin in the end. The good news is that with a middle name that can be shortened to Pippin, he’s set whether he’s a LOTR-fan nerd like his dad, or whether he gets into basketball…

After having picked the names, we found out that Andrew means “manly or brave”, and Peregrin (which amusingly enough was the word of the day on today) has connotations of wanderer, traveler, etc.

His current nicknames are spud, french fry, burrito, and self-eating-burrito.

Here are some pictures of baby Andrew:


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Dragon Tug

With the Dragon capsules fully capable of ISS interaction now, how hard would it be to use the dragons for ISS tugs as is?

One of the quite useful pieces of on orbit hardware is a space tug that off loads the critical maneuvering capabilities from the launch vehicles. A launch vehicle that does not need those capabilities will be simpler and cheaper, not to mention safer, than one that does require all the bells and whistles. I am wondering if the capability to accept cargoes from multiple  suppliers for the ISS has stealthed its’ way into operational use without any of us noticing.

It would be interesting to know if Atlas and Delta, or even Sea Launch and foreign suppliers, could deliver payloads to just outside the exclusion zone for a Dragon to tug to ISS. Financially it wouldn’t seem to make sense. Politically though it might get several more players pulling in a positive direction. If it suddenly became blindingly obvious that several suppliers could safely and reliably surge major tonnage to an orbital berth, the argument for the Big Rocket would take another hit.


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So I’m sitting in a friends yard watching the Blue Angels give it their best at the Sun-N-fun fly in thinking about how to modify their propulsion while all the people around me are oohing and aahing. Same with the F22 demonstration and various prop planes. I guess some of aren’t meant to watch these super skilled pilots do phenomenal things without focusing on the hardware.



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Certification and Rules-based Technology Regulations: Part of Why We Can’t Have Nice Things

Brian Wang over on Next Big Future brought up a point I’ve been thinking about for a while. In an article about why Canada is likely to beat the US to having molten salt nuclear reactors (in spite of the US pioneering the field back in the 60s), Brian hit on the key reason:

There is an important difference between the Canadian and the US regulatory authorities. The US is rule-based and Canada nuclear regulations are output-based. In the USA, anyone wanting to develop a new type of reactor will have to prove its safety before it exists. All of the US rules are based on light water reactors. In Canada, you will have to prove the safety of your concept while it is operating. Terrestrial IMSR seems to moving ahead very quickly. Canada’s nuclear regulators could allow a molten salt reactor to be built and operating in 6 years.

Simply put, US nuclear safety regulation is based on the idea that regulators from back in the 60s knew the best way to make a safe nuclear reactor, and that compliance to their rules was the best way to guarantee a new reactor was going to be safe. The problem is this kind of assumes that technology stands still and that new approaches with fundamental safety benefits aren’t likely. The sad reality is that this is why we have disasters like Fukishima–old reactors get grandfathered into the regulations, new reactors that could be dramatically safer or even passively safe get delayed so bad by regulations that they in many cases never get completed. So we’re stuck with older, less safe technology, all in the name of safety regulations.

You see similar dynamics in aircraft certification, and the current arguments about regulation of suborbital RLVs. George Nield, who I normally have a ton of respect for, recently argued against extending the “learning period” under the Commercial Space Launch Amendments Ac said that:

“The US has over 50 years of experience in human spaceflight,” he argued, providing a large set of lessons learned for commercial spaceflight providers. “For us to just put that aside and start over without taking advantage of what we’ve learned, I think is irresponsible.”

It’s true we have some experience, and that info should be provided to suborbital developers to build off of, but it makes the same fundamentally flawed assumption that’s stifling nuclear technology in the US–and which is making nuclear power less safe in the name of safety. We have a bit of experience now with manned capsules, and shuttle-type winged reentry vehicles. But assuming that we’ve now reached the pinnacle of reusable launch vehicle design is likely going to look laughably foolish in the future, possibly even the near future.

In some ways this line of argument might look like one a Department of Ground Transportation official could have made in 1907 about safety regulations for ground vehicles such as horse buggies and automobiles. After all, by that point, we had centuries of experience with design and operation of horse-driven ground transportation. We shouldn’t just throw that out and ignore it. We know enough to make reasonable safety regulations. I mean, how much are these automobiles going to change from horse buggies–heck the current ones even look really similar.

It would be sad if a few years from now safer launch vehicle and reentry vehicle technology had to go to places like Canada because the US was so sure it knew enough to make rules-based regulations to “certify” the safety of the industry.

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Introducing Taong Boondocks

FYI, I just created another blog, called Taong Boondocks, which will focus on all the non-space related topics I care about. Fair warning, I’ll be blogging about my family, hobbies, religious, political, and economic musings, etc. So if your only point of agreement with me is on space you might want to stick to Selenian Boondocks for now.

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Insert Lame Excuse Here

Hey guys, I apologize for not getting the follow-on posts for the “Slings and Arrows” and “Venus ISRU” series put up before I got overwhelmed with SBIR silly season (and several other work projects). I’m really going to try to get to them as soon as I come up for air, hopefully at the end of the month. I hope you’ve enjoyed my burst of blog productivity over the past two months. Hopefully once these proposals are knocked out, I can get back to things.

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The Slings and Arrows of Outrageous Lunar Transportation Schemes: Part 1–Gear Ratios

[Note: I haven't quite finished with my Venus ISRU series, but some of the articles I've read over the past few days drew me back to this series on propellantless lunar launch approaches that I started writing four years ago but never finished. While Venus ISRU is interesting, I still think it's pretty likely that the first operational ISRU (ie beyond demo or pilot-plant scale) will be on the Moon.]

One of many important issues that doesn’t get enough airtime when discussing lunar ISRU is how to efficiently get the propellants and other materials off the lunar surface. There seems to be a line of thinking that could be called “all we need is ISRU” that says that lunar ISRU is the most critical technology and everything else is just a distraction.

While it is possible to take propellant produced on the lunar surface up to LLO or to one of the Earth-Moon Lagrange points using similar rockets to what you landed with, and then deliver this to LEO using entirely propulsive tugs with no new technology, this isn’t very efficient. You end up spending a significant fraction of the lunar derived propellant lifting both the delivery propellant and the landing return propellant, as well as the propellant to ship the cis-lunar tanker back to LEO and bring it back for refueling near the Moon.

To give you an idea of how inefficient, I’m attaching a spreadsheet with some back-of-the-envelope level calculations to illustrate this point. In the spreadsheet I model a Lunar Surface to LLO or EML-2 and Back tanker, and then an LLO or EML-2 to LEO and Back tanker. In both cases, I assumed they were about Centaur size (~23tonnes), and used RL-10 based propulsion. For the reusable lunar surface tanker, I gave two propellant mass fractions–90% (aggressive once you factor in landing hardware) and 85% (more conservative). For the cislunar tanker, I assumed a 90% propellant mass fraction, and also analyzed cases where an aerobrake was provided that weighed 5% of the GTOW and 10% of the GTOW.

In the most extreme case of “all you need is ISRU” thinking, where you use entirely existing chemical propulsion systems for getting propellants from the lunar surface to LEO, only 9-11% of the propellant produced on the Moon actually makes it to LEO.  Alternately, this means you have a “gear ratio” (ratio of propellant extracted on the Moon to propellant delivered to LEO) of 9-11. Not only is this very wasteful, but it means that you would need to size your ISRU capacity significantly higher than if you had a more efficient system.

Of the approximately 12km/s of round-trip Delta-V from the lunar surface to LEO and back, there are several options you can use to improve your gearing ratio, each of which attack a different leg of the journey:

  1. Stage and refuel in LLO or EML-1/2 (which was already assumed for this analysis).
  2. Aerocapture/braking to go from your Trans-Earth Injection trajectory into LEO
  3. Propellantless methods for launching from the lunar surface to LLO, EML-1 or 2, or even directly to LEO.
  4. Propellantless methods for landing on the Moon from LLO or EML-1 or 2
  5. Propellantless or high-Isp methods for traveling from LEO to LLO or EML-1 or 2.

This series is focused on options #3 and #4, though #2 is also low-hanging fruit (and provides about a 2-3x gear ratio improvement over the baseline “all we nee is ISRU approach).

Next up: Five Propellantless Lunar Transportation Approaches

Posted in ISRU, Lunar Commerce, Lunar Exploration and Development, Space Settlement, Space Transportation | 66 Comments