Selenian Boondocks

There was an interesting piece about foreign policy linked to by one of the blogs I read on a regular basis (can’t remember who now). The piece was talking about the delay between when changes to the global order happen, and when elites finally start recognizing that something has changed:

Now… it seems to me that because of inertia or vested interests, members of the elites always fail to recognize the eroding influence of a declining great power. Economists refer to Recognition lag when they discuss the time lag between when an actual economic shock, such as sudden boom or bust occurs, and when it is recognized by economists, central bankers and the government. A similar time lag may explain why so many pundits are continuing to demand and/or expect the Obama Administration to reassert U.S. influence abroad and “do something” about this or that (depending on one’s favorite foreign policy agenda).

Interestingly enough, in a foreign policy seminar I led a while ago I asked my students to conduct a content analysis of how the leading powers were covered by the major international dailies in the aftermath of WWII. They were astonished to discover that until the mid 1950’s both Great Britain and France (by then bankrupted economic and military powers) were described as “great powers” more times than the U.S. and the Soviet Union. Only in the late 1950’s was “great” being dropped as an adjective when discussing the Brits and the French and “super” was applied to the Americans and the Soviets. A example of recognition lag in foreign policy.

I’ve been saying for some time now, that there may be a similar analogy in space policy discussions–the politics behind Shuttle Derived Launch Vehicles.

For many years, people have pointed out that the main reason why the Shuttle is still flying today is mostly due to inertia, and because it provides lots of jobs in important congressional districts.  The implied belief being that this will always continue to be such, so it doesn’t matter if a Shuttle Derived vehicle makes any technical or economic sense, becuase “political realities” will always guarantee that NASA employs tens of thousands of employees and contractors in much the same way as the are today.

This is historically naive in my opinion.

Much as the UK and France had their influence decrease after WWII, there have been many changes in our nation’s political structure recently.  The belief seems to go that somehow the loss of power by the party of which Utah, Texas, Alabama and Mississippi are all part will not effect in any way the political calculus on how NASA will proceed from here.  That retiring or outgoing people in key senate and congressional committees don’t matter.  That Senators and Presidents will stick out their necks to defend the jobs of people who didn’t vote for them.

While it is possible that inertia might prevail, I think the reality is that the winds have already changed in Washington, and that it’s just a matter of time before more space advocates start actually realizing this.

Here’s a quick thought on a way to use EELVs for launching Orion that I was thinking about tonight.   One of the reasons why the CEV is so big that it’s hard to launch on an existing EELV is because of the amount of service module propellant.  Basically, the CEV is sized to provide nearly 1800m/s of delta-V.  Now, you don’t actually need most of that for an ISS mission (except they use it as a contingency to provide enough delta-V during an abort over the North Atlantic in winter to make sure you can put the CEV down in a safer location), but you do for a lunar mission.

I don’t have the latest numbers, but some numbers I’ve seen for the CEV (from a presentation Pete Worden gave a few months back about using Orion for an NEO mission) put it at about 24.7klb dry and 20.5klb propellant.  In other words almost half of the CEV launch mass is NTO/MMH for the service module.  Once you factor in the much bigger tanks and engines for such a service module, the CEV isn’t really all that much heavier than a Dragon capsule for instance.  But once you include all that lunar return propellant, you now have a capsule that’s so big that it’s hard to loft on all but the biggest existing launchers.  In fact, due probably to the switch back to hypergols from the LOX/CH4 suggested in ESAS, right now in order to fit its mass targets, Orion is having to shed a lot of the redundancy and functionality it needs in order to perform its mission safely.

Right now, as I understand it, the current concept of operations is that the Ares-I puts the orion into a suborbital trajectory with most of the velocity needed for orbit.  The Orion then provides the circularization burn to put itself in orbit.

The question I had was, if you are already using the Orion somewhat like a third stage, what if you actually did use it as a third stage?  While you couldn’t launch a fully-fueled Orion into LEO on anything other than one of the EELV Heavies, transfer of hypergolic propellants is now a demonstrated capability, even in the US!  So, I was curious how small of an EELV you could use and still get Orion into orbit (with enough propellant left for rendezvous and docking maneuvers), if you assumed that for lunar missions you could tank-up the CEV on orbit.

I happened to have some mass numbers from previous conversations about the Atlas V Phase 1 and 2 concepts that ULA did, so I put together a spreadsheet. First, I took the payload numbers from ULA’s site, and the Centaur and CCB mass numbers I had sitting around and estimated the total delta-V to LEO for the stack. Then, I took the rough numbers for Orion I had above, and treated it like a third stage. The Orion payload adapter was added as a dry weight to the Centaur stage, and the LAS was added as a dry weight to the CCB stage (since it would likely be tossed immediately after stage separation). As you can see, a 1.5x Phase 1 Atlas V could do the job, leaving a bit of performance for margin and maneuvering delta-V. Of course, if someone were serious about doing this, you would likely oversize the Phase 1 upper stage a bit to provide extra margin, to relax the constraints on Orion. Call it a 1.6x or 1.65x (referring to 1.6 or 1.65 times the propellant load of an existing Centaur).

For ISS missions, you wouldn’t even need to top the propellant off, as you’d have enough leftover performance after arrival for rendezvous, docking, and deorbiting. For a lunar mission, you would need most of a second launch worth of propellant, but that propellant would be a very low cost cargo (and could also reasonably be launched by other lower-cost commercial suppliers). By using the service module as an upper stage, you would get to test out the engine thoroughly on the way to orbit, which might reduce your risks of unforeseen problems cropping up on your way home from the Moon. Also, if for some reason the upper stage fails (though it has engine-out capability now unlike the Ares-1 US), you still have the extra propellant for contingency maneuvers to avoid landing in the North Atlantic.

The single stick Atlas-Vs meet almost all of the old NASA human rating requirements (and NASA had to lower their standards enough for Ares-I to pass that most of the few human rating requirements that Atlas-V didn’t already meet are no longer there), and most of the remaining requirements are improvements that ULA wanted to do anyway for their Bigelow collaboration. The nice thing about a Phase-1 Atlas V is that the CCB is unchanged from the existing Atlas-V, and even the upper stage changes all have prior design heritage. The Titan Centaurs used the wider body diameter that the Phase 1 design would use, most earlier Centaurs were dual-engine, and between Lockheed and Boeing’s contributions to ULA, the friction stir welding techniques that would be needed are mostly developed and qualified already. And the engine that would be used, the RL-10 is an existing one with excellent heritage, and very benign operating characteristics.

Anyway, I just thought this analysis was kind of interesting. Such a system would still be able to loft a standard Orion, it wouldn’t require a ton of new development work (a little stage work, but a close derivative of an existing stage done by a team that has a proven track record from doing several such stages within the past decade or two), and since it would be a single-stick system, it would likely compare very favorably (LOM/LOC-wise) with the Ares-I.

Just a random thought.

guest blogger john hare

Work has picked up for us in the last several weeks, so I have been focusing on trying to make money instead of posting anything. Second reason for not posting is that several of the people that responded to my concept posts managed to effectively challenge the ideas in ways that I hadn’t expected. There was a far higher quality of critique than I usually see without writing a check. Continuing on with further possibilities on a concept in doubt is not very attractive, unlike throwing something controversial up once or twice. Over half the ideas on my short list of ideas to post now have known possible flaws that I have to rethink before moving on. Thank you to all the people that managed to get through to me exact problems in my conceptual visions, and to the ones that added to the ideas.

I had something of a grand scheme for a systems approach that seems to be better than most concepts I am aware of, to me at least. By breaking things down into the smallest subsystem I could describe, many answers to questions I hadn’t thought of came forth. I believe that if I had simply tried to throw the whole thing out there at once, it would simply have been dismissed (properly) as another  flawed champagne idea on a beer budget. The accurate information to divert me to other channels wouldn’t have happened.

The short version of the total idea was an HTHL flyback stage with a second stage that hits a tether. Both stages torus tank based with the upper nested in the donut hole of the first.  Two tipjet propellers on the first stage to provide cruise thrust and wingtip vortex control to get the induced drag down. Cagejet tuborockets in the vertical tails of the first stage for drag compensation and thrust to mach 1.6 (lightweight intake limit), with very high pressure, altitude compensating rockets kicking in at 20,000 or so feet and mach 0.6. Second stage uses whole bottom of vehicle as very high ratio aerospike from mach 6 to tether at mach 20. Tether reboost with 750 second tetherrocket. And so on  

In fighter aircraft there is a term called target fixation with a pilot so focused on his target that nothing else matters. Sometimes that focus results in getting kills, the scoreboard of fighter warfare. A high level of focus is required to hit a high speed twisting turning target. It has been noted many times that successful pilots are hunters, not hunted, and a very high level of self confidence is a job requirement. That only half the participants in a successful dogfight fly away is simply not useful information. 

Sometimes that focus results in getting shot down himself by the people on the other side that he excludes from his attention. Without a wing man or warning system that he will listen to, fighter pilots have an even lower life expectancy than normal with unfriendly people doing their best to do it to him first. When your buddy is yelling break break, it’s time to slam the stick over, stomp some rudder, and dump chaff and flares.

I am seeing a lot of this behavior in the rocket business, with many organizations so fixated on one target that they simply cannot see the guns on their six, and won’t listen to the people calling the break. Target fixation is a useful concept in the rocket business to distinguish between concentration on getting a job done, and setting yourself up for failure. The cannons of the fighter have a parallel in the march of technology, and the capabilities of the competition. Your business can be shot down by another company that is faster, smarter, or more agile in delivering what the customers want. The technology is simply one of the tools they use to get on your six.

The Griffenshaft is the most visible example at the moment, with billions poured down a rat hole of a flawed concept. The dozens of groups and members of his own calling the break seem to be unable to get his attention. The target fixation prevents the consideration of the quality of the target, whether there is a better target, and even if he is going to run out of fuel/funding pursuing this one. It is even worse if the wing men know they will be grounded and lose flight status if they call the break and interrupt his concentration.  You wouldn’t mind him getting shot down so much if he wasn’t taking so much useful hardware down with him. 

Commercial space has a few target fixations of its’ own that just might need to be addressed. I share in several of these so if I am pointing a finger, there are three others pointing back at me. The question in each case is whether we need to call a legitimate break, or if we are distracting people trying to make the shot.

Hydrogen is high on the list. I have joined many others in saying that hydrogen is more trouble than it is worth in almost all cases. Jon has pointed out that there are examples of existing hardware that are  mass competitive with  dense fuels for upper stages.

Clustering modules is very popular. Develop one stage properly and cluster as many as you need to get the job done. While attractive in some ways, getting 20 or more stages to play well together all the time seems like it might be tougher than building a bigger vehicle. Some very smart people are on both sides of this one. 

The single massive, do all rocket is one that comes up all the time. The Shuttle replacement or the Saturn replacement or the you name it is a dangerous fixation if a really good use for it is not justified. I think Kistler bit it on this one.

Pressure fed for simplicity is a standard for most newspace companies. You know where I stand on that one. With the rocket equation being what it is, a pump seems to be the inexpensive option compared to the sheer size penalty for low pressure orbital rockets. I have also seen plenty of complexity in the so called simple pressure fed systems. I never heard of a battery powered pump for a rocket until Paul started working on one.

High tech gets high performance. Sometimes high tech is just gingerbread. If it is not really needed, don’t waste your money trying to get wall to wall data on a pig that is designed wrong to begin with. 

ELVs being cheaper to develop is getting busted now, though some still believe it is cheaper to analyze problems than to test them. I don’t really care to depend on a vehicle with no flight history after a test flight program of perhaps two flights by similar vehicles. 

Vertical takeoff being lighter could possibly be flawed. A standard ELV on a runway trolley on a slight incline could possibly improve performance and reduce vehicle mass slightly. Side benefit is less ground infrastructure and therefore more potential launch sites.

Simpler is cheaper an more reliable. Not always.

There are many assumptions out there that really need to be examined. Focus on a single objective can result in making that objective, or in getting shot down by the competition that you ignore. Having been shot down in business a few times myself, I hope my friends out there have good wing men watching their six both technically and financially that they will listen to. I also hope the jamming from us wannabes doesn’t distract them from good targets.

With Christmas nearing, and lots of projects on my plate (one SBIR proposal, one abstract for an AIAA paper, and trying to put together some brief thoughts for the Obama NASA transition team), I doubt I’ll have much time to write very frequently any time soon.  Just wanted to give fair warning.

Now that silly season is over, and sanity is returning to most denizens of the blogosphere, Rand Simberg serves up some delicious satire about our intrepid Don Miguel De Grifo.  Of course, it would be funnier if it wasn’t as accurate.

A while ago, on aRocket, several people were discussing the concept of the launch loop.  Read the articles here and here to get caught up to speed on the details.  The idea is a non-rocket way of launching payloads to orbit.  The launch loop has a “stator” tube with an internal “rotor” comprised of ferromagnetic particles traveling at crazy speeds (faster than orbital velocity).  The momentum of the rotor is used to lift the main section of the loop to a sufficient altitude.  Payloads are accelerated using eddy currents to transfer some momentum from the rotor to the payload (and generating a lot of waste heat in the rotor which then gets dissipated).

Now, I wasn’t a huge fan of the launch loop for terrestrial applications, just due to the shear size of the system (we’re talking a cable 1000s of km long, 100s of MW of required power capacity, the cable has to hold a vacuum, and the failure modes if the vacuum system failed could be catastrophic).  I’m typically not a big fan of megaproject launch systems as a general rule.  But I realized a lunar launch loop might not be as crazy of an idea.

First off, the track length varies with the square of the velocity change.  At 3g’s of acceleration, getting up to earth orbital speeds (7400m/s after accounting for the equatorial rotational speed of the earth’s surface) requires an acceleration track of over 930km long.  However, lunar orbital velocity is much lower (something like 1850m/s), so at 3g’s you only need a track 58km long.

The actual equation is pretty simple: s = dV^2/2*a , where s is the track length in meters, dV equals the velocity change you’re trying to deliver, and a is the acceleration in m/s^2.

Now, I don’t understand all the math behind a launch loop, but it would appear that if you want to keep the same rotor density and stator density, that you’d only need a rotor speed of 4km/s.  Also, you probably don’t need as much stator weight, since you don’t need to get up to 80km to get over the atmosphere like you do with a terrestrial system, so your tethers can be much shorter/lighter.  Also you don’t need any vacuum containing systems.  So, you could probably make the rotor lower density, since it doesn’t have to support as much mass.  The original concept assumed about 10kg/m for both the rotor and stator and everything else, but it might be possible to halve that since you’re not trying to get as high of altitude.

Also, since your rotor would be a lot shorter and much slower, it would not require anywhere near as powerful of a power plant to keep it running or get it started up.  Also, the lower velocity of the rotor means that you dissipate less power providing the same accelerating force to the cargo, which means less heating, and less power has to be added back in to accelerate things.

You’re still talking a very massive system.  Even at 5kg/m, a 3g system would weigh around 580 tons, not counting the power plant.  But to put that in perspective that’s only about 30 lander loads of cargo.  Compared to a decent lunar base, it’s not entirely crazy.

And if I’m understanding things right, there are several significant benefits of such an approach over other non-rocket methods for launching lunar payloads (such as mass drivers).

1. The energy for a launch doesn’t have to be delivered rapidly.  This means no need for rapid discharge power systems such as you would need for a mass driver.
2. The majority of the system (and all of the moving parts) can be kept up far away from the lunar dust.
3. If the launch loop is located near one of the poles, you could hang solar panels off of the tethers, and could probably make an arrangement that guaranteed constant light, even if the underlying terrain turned out not to be in “eternal light”.
4. For loops away from the poles, the loop itself functions as a massive flywheel, storing lots of energy.  It might be possible to have such a loop to be “charged up” to a speed much faster than necessary to support the structure during the day, and then slowly tapping off some of that power during the night for the settlement near the loop.  So long as you did planning right, you could probably keep at least a lighter load of launches going even during the night.
5. There’s a tiny chance you might be able to use a lunar loop for “catching” payloads and soft-landing them.  This is a lot more dicey, since you need precision navigation, trying to hit a tiny target at high speeds, but it’s no crazier than other similar ideas I’ve heard over the years (for things like controlled lithobraking, eddy-current landers, rotating tethers, etc).  The good thing is that if you miss, you’re still a decent distance up off the ground, and depending on the design of the launch loop you may still have plenty of time to do an abort to orbit maneuver.

Anyhow, the idea is probably certifiable, and it’s going to be a long time before such a scheme would be even remotely possible.  But it’s an interesting approach for how to get lots of mass off the lunar surface in a hurry if we ever get to that point.  And if you can somehow make a launch loop in such a way that it can handle landings as well as takeoffs, it could really change the equation as far as lunar development is concerned.

I’ve written a lot about the technical and business implications of propellant depots, and I realized I ought to discuss some of my thoughts on the the public policy side of propellant depots.

On one hand, I think that propellant depots could probably be fielded eventually without any specific government assistance.  On many levels I dislike any form of government subsidy or industrial policy, and think that most central planning is doomed to failure (see: current financial situation).  While a purely market-driven approach would take a very long time to slowly bootstrap its way up to a full-service depot capability, I do think it is possible, and am currently trying to find ways to attack the problem from that direction.

On the other hand, I think it’s pretty clear that in many cases, there are existing public programs that are spending billions of dollars of taxpayer money that are being done in a less-efficient manner because propellant depots don’t yet exist.  Many NASA probes and its manned exploration programs could be done more cost effectively and accomplish more if depots existed.  I’ve also seen ways that the military could benefit from the existance of on-orbit refueling services and space tugs.

While I dislike government just giving away handouts, I think that in areas that our representatives have decided to spend our money, investing in ways to make those expenditures more efficient is prudent.

With that in mind, I have some thoughts on things that I think the government could do to help encourage propellant depots, as well as some ideas I’ve heard that I think the government should not do to encourage propellant depots.  I’ll start with the things I would not like to see:

1. I don’t think NASA should be allowed build or operate a propellant depot.  A NASA-run depot is going to be subject to the same political pressures that gave us the current ISS, and will probably end up being a multi-billion dollar megaproject that in the end delivers little of its original promise (but at least keeps lots of people employed at JSC, MSFC, GRC, etc, etc).  It’s not that there aren’t talented people at NASA working on technologies like this, it’s just that the institutional incentives NASA faces are probably incompatible with any sort of economically useful depot.  People use the ISS as “proof” that microgravity science isuseless, and that we shouldn’t do orbital assembly or build space stations.  We don’t need moer “existence proof” like that.  Another reason why NASA shouldn’t run a depot is that a NASA-run depot will be a lot more restricted on who it can buy and who it can sell propellant to.  While NASA could probably build a propellant depot, it’s just a bad approach all-around.
2. I don’t think NASA should have a contractor build and operate a depot either (think “United Space Alliance”).   While I believe Boeing when they say that they could respond to a NASA depot RFP with a $5B depot plan, I also don’t think this is the ideal way.  You end up picking winners, there will be a lot more political interference in business operations, and many of the same incentives issues that exist for NASA would exist for a “contractor run” NASA depot.
3. I don’t like the idea of Congress setting aside money to “just buy a bunch of propellant on orbit”.  Not only do I think it’s a political non-starter, but I hate handouts, and think it would probably end up causing more distortions and more harm than good.  NASA has existing and planned projects that can use propellant depots.   There’s no legitimate reason to set up programs to buy propellants not tied to actual needs.

So here’s my thoughts on things the government could/should do to promote propellant depots:

1. Continue to invest money into propellant depot research and technology development.  NASA is already doing this on a small level with its SBIR program, as well as other small research projects.  It would do well to reinstitute the approach O’Keefe took with the H&RT program of providing significant funding for important technology demonstration projects like this.  I think such programs should be focused on driving the technology to the level of flight demonstrations as quickly as possible. Proposed cryo fluid management test beds like LM/ULA’s Centaur Test Bed and possible suborbital analogs, should make it possible to actually start reducing more of these ideas to practice with actual flight demonstrations.
2. Fund the “Fuel Depot Demonstration” Centennial Challenges (early proposed rules can be found here), or something similar to it.  The Centennial Challenges program hasn’t been given a cent other than in its first year.  It’s used that money very carefully, and preserved most of the money for actual prizes.  But they had several other interesting prizes that they wanted to roll out that they haven’t been able to due to lack of funding.  This prize, for $5M nominally (though I think $10M might make it more interesting) was for a system that could store at least a certain amount of LOX and LH2 for at least 120 days.  While one can argue with the details of the rules, the idea of offering small prizes for technology demonstrations is important.
3. Fund the development of an Industry Standard for Passive Orbital Propellant Transfer Interfaces.  There’s been a lot of talk over the years of standardizing things like docking interfaces.  I think that most of those ideas are premature–docking interfaces are complex enough, and the tradespace has been sufficiently poorly explored that it’s too early to set things like that in stone.  Things like a passive propellant transfer interface are ironically probably closer to a point where they could be standardized.  By a passive interface, I just mean a set of quick disconnects, power/data transfer hookups, etc that could be added to the outside surface of a tanker or customer that could be connected-to manually, using robot arms, or tugs and hoses/cords.  Fund some well-accepted standards group (like ASME/AIAA or someone else) to do a study to see if things really are at a point where the interfaces can be standardized.  If they are, have them put together a draft standard, and get industry feedback on it.  Creating a simple, publicly available standard for propellant transfer will make it easier for tug developers, tanker developers, propellant depot operators, propellant transfer customers, etc. to develop their systems.
4. Once there is an accepted standard, mandate that all government flights beyond LEO be done with stages equipped with those standardized propellant transfer interfaces.  A simple passive interface might be able to be used for normal fueling purposes, and might be doable in a way that adds minimal extra weight to a rocket stage, and doesn’t cost a bunch.  By requiring all launch providers who want to sell to the government to incorporate that feature, that feature also becomes available to other non-government customers, allowing them to be able to take advantage of that capability without having to foot the bill for that development work by themselves.  A mandated standard interface like that also helps make it so prospective depot owners know that there will be stages that can accept transfered propellant for missions where they need the capability.
5. Some time after that mandated interface rule has kicked-in, require by law that NASA (and other government agencies if possible) procure propellant from a propellant-depot if available for all stages, satellites, probes, and landers outside of LEO that are too big to launch on a commercial, single-stick (ie no strapons) launch vehicle.  The “if available” clause means that if a depot operator doesn’t step-up, NASA isn’t under any obligation.  This might also be the case where they want to launch a mission into an inclination where they couldn’t use a depot.  But in cases where they could use a depot, it requires them to obey existing laws to procure services commercially when they are available.  So, in a way this is just a reaffirmation of existing statutes.  It has the benefit that it reduces the risk to a depot startup that NASA would just ignore them and build their own HLVs to launch their own propellant.  Lastly, by giving them the option to fly “single-stick” missions without depots, it at least allows the smaller, simpler missions that don’t actually need a depot to work to proceed unchanged.

Now, these are just some thoughts I’ve had over the past several weeks.  My goal here is to set up incentives that encourage the private development of depots, reduce the risk to depot operators of NASA ignoring the law and not buying from them if they take the risk to provide that capability, while still not forcing NASA to spend lots of money developing those capabilities and infrastructure itself.

But there may be flaws I’m not seeing.  What do you all think?  I’d particularly like feedback from people in the Space Policy community.

I just wanted to post a couple of short thoughts about the Falcon IX Upper Stage information that came out in the article I linked to in a blog post a few days ago. Specifically this picture from Figure 9 of the Asian Space Conference Paper (with my labels added) provides some interesting hints at how SpaceX is intending to recover the stage:

Just a few thoughts from seeing this drawing:

1. It looks like they’re planning on doing a nose-first reentry with a heatshield on the nose taking the brunt of the reentry heating.  A previous rumor (which I may deserve the ignominity of having first spread) was that they were going to try and reenter tail first using the big niobium extention of the engine nozzle as a sort of radiatively cooled TPS.  I asked Elon about this back in January (the only occasion I’ve had to meet him in person), and he just laughed, and then said something about using a normal heat shield and parachutes for landing.
2. With the main propellant tanks empty, the chunks of mass are the engines, the helium pressurant tanks inside the LOX tank, the heat shield, and those mysterious spheres in the front right behind the heat shield.  I’m not sure what those are, but my main guesses would be a) ballast, b) RCS propellants for deorbit and reentry.  There’s a long-shot third possibility as well–the heat shield might not actually be an ablative (or just an ablative) shield.  The tanks could be transpiration coolant.  But I think option “b” is the most likely.  Either way, by locating those tanks up front, it helps drag the CG forward during reentry, which makes the vehicle more aerodynamically stable.
3. Those big black panels at the back look like they could be aerodynamic control surfaces.   By moving them outward a bit, they can possibly drag the aerodynamic center of pressure back enough to make the stage aerodynamically stable.  Alternatively, they might allow a somewhat unstable design to fly by active controls.  There are plenty of examplse of aircraft that would rip themselves to shreds in seconds if it weren’t for their computer controls (due to being very aerodynamically unstable).

All in all, the more I look at it, the more I’ve come to the conclusion that SpaceX could actually pull off recovering this stage.  It may take them a few tries, and as their first stage recovery efforts have shown, there are lots of details that need to be just right for recovery to work.  Not to mention the fact that I still think that splashing turbopump-fed rocket stages in the ocean is a great way to make reusability a pain in the neck.  But I think the fundamental recovery concept is sound, and if they can be succesful enough with their launches, they’ll be able to stick around long enough to make reusability a reality.

I wonder if they can make this work if that will down the road lead others of their competitors to move in that direction for LEO launches.  Centaur is a fairly valuable stage, and I could see a similar configuration possibly making it be reusable as well (though the LM guys would probably use Mid Air Recovery instead of splashdown).  Wouldn’t make sense at current flight rates, but if things like Bigelow’s station come into reality, you might see enough demand to start justifying more creative incremental improvements like this.

I don’t think that these recoverability methods are the end-all, be-all of space launch.  And I don’t even think that many of them are even on the same evolutionary path as the ultimate direction things need to go.  But I do think they’re a useful improvement that could help lower the cost of heavier launches while small RLVs are getting their feet.

As I mentioned in the first post in this series, I wanted to paint the overall picture first, and then flesh out the details as time and interest permits. For this post, I want to discuss an interesting lander concept that could work well with the mission model I discussed in Part I. I may discuss some thoughts about how to do lunar lander reuse in a future post in this series.

By way of introducing the concept, I wanted to point out some material that LM/ULA came up with two years back that got me thinking in these directions. While many have read the AIAA paper ULA published in 2006 about various Centaur-derived manned lander schemes as alternatives to the ESAS LSAM, there was also some less-well-known material they had developed for Centaur-derived robotic landers that I found interesting. I just noticed today that a paper containing the information I had previously seen about this concept is up on the ULA site, here, so I figure it’s now ok to talk about this idea.

Basically, the second paper goes into some work LM/ULA had done for the Lunar Precursor Robotics Program back in the 2006 timeframe. They had looked into converting an existing Centaur into a lunar lander for robotics payloads, by adding a “Extended-Duration Mission Kit” and a “Lunar Lander Kit”. These kits, which the Centaur team has already detailed to some extent, would add things like better passive cryo insulation hardware, sunshields, solar panels, upgraded avionics and batteries, landing gear, landing propulsion systems, etc. The concept was based on launching the whole Centaur lander stack into LEO on an HLV.

Centaur-Derived LPRP Robotic Lander

The paper also went into a 4-person lander using the same Centaur-derived concept but extending it a bit further. A version of this concept was further discussed in the first paper. The manned lander would be two-stage with a hypergolic biprop system for ascent, and the lander would include hardware for supporting at least two-week lunar surface stays.

Centaur Derived Manned Lunar Lander

What I was interested in was what those concepts could do if they were used with in an architecture that included a LLO depot/waystation. In the case of the robotic lander, the lander itself also performs the TLI and LOI burns, which means that most of its propellant is used up before it gets to LLO. For the human lander, while they assumed the use of another stage to do the TLI/LOI burns, the system was constrained to be launchable with an Atlas V HLV, which meant that a full Centaur-load worth of propellant couldn’t be used for it either. Plus, with the use of a hypergolic ascent stage, the ascent fuel weighs a lot more than it would in a reusable scenario. Fortunately, this paper gives a mass budget, so we can do some number crunching.

For the robotic lander, it used a Centaur dry mass of 2500kg, a Extended Duration Mission Kit mass of 800kg, and a Lunar Lander Kit of about 1000kg, with 1500kg of LLK propellant, and 21000kg of Centaur propellant.  Now assume a mission concept where you tank the whole Centaur stage up in LLO, the Centaur propulsion provides most of the delta-V except for the final touchdown/hover, the hypergolic landing engines provide landing/hover thrust as well as enough ascent thrust to get the vehicle up a couple hundred meters before relighting the RL-10s for ascent.

Depot-Enabled Centaur-Derived Manned Landing Missions
Factoring in some extra hypergolic propellant for both a long-duration hover (>90s) during landing, and enough propellant to get the vehicle up to a decent altitude before lighting the RL-10s, I estimate a payload in the 7500-8850kg range (you can download a copy of the spreadsheet I used here).  The lower number was assuming a 2500m/s ascent delta-V (ie ascent DV plus some plane change propellants), while the higher payload was for a 2200m/s ascent delta-V, which is probably closer to what you would nominally need (when you have backup systems like tugs, depots, and a second lander in orbit, you don’t need as much in the way of contingency margins on any individual flight). 

By way of comparison, the mass of the Apollo LEM minus main propellants was 4200kg, and most of that was stuff that would already be provided by the lander.  So, it’s pretty safe to say you could haul at least four people up and down in such a system.  For another comparison, at the higher end of the hauling capacity, you could haul a full Bigelow Sundancer module to and from the surface. Lastly, comparing it to the two-stage lander that they analyzed, if you ditched the ascent propulsion system and propellants and used the Centaur stage, it looks likely that you could haul 6-8 people and several tons of cargo for a two week stay without much difficulty. I can check on that if I can get better numbers from somewhere of the mass breakdown for their concept–the numbers given in paper #2 aren’t very clear on which weight in the ascent stage is for stage and propulsion mass, and which is for crew accomodations, pressure shells, etc.

Note, that at that point, this is anything but a “light scout lander”.  Such a system would likely provide a substantial increase in capability compared to the ESAS LSAM, while only requiring a marginal 25-26 metric tonnes per mission worth of propellants/consumables.   I don’t have the latest ESAS numbers, but for a sortie mission from them, you’re talking at least 65 metric tonnes, for only 1/2 to 2/3 as many people.

Also note that all of this is based on the existing Centaur design, not the Wide Body Centaur/ACES stuff that ULA has been investigating over the past several years.

Depot-Enabled Centaur-Derived Cargo-Dropoff Lander Missions
Now, what if instead of hauling a crew module up and down from the lunar surface, you were just hauling one-way cargo down to the lunar surface? For that scenario, I’m getting about 23,900kg of landed mass. Which is probably enough to deliver a full Bigelow Nautilus module to the surface. Or just about any piece of equipment you could imagine. Once again, this is with a stage based on the existing Centaur stage, not anything fancy like the ACES stage.

Admittedly, getting a payload that big to lunar orbit is actually the bigger challenge. You would need to use something bigger than a single Centaur derived transfer stage like I had talked about in Part I. Solar electric tugs, multiple Centaur stages in series, or a WBC/ACES derived transfer stage would be required. Or just finding a way to offload a decent amount of weight from the module itself, and outfitting it in lunar orbit before landing it.

Anyhow, I think this concept shows that using propellant depots in lunar orbit can greatly enhance a lunar exploration/development program, while also making the transportation phase of the program much safer. This performance benefit is not just with tiny sortie missions, but also with missions much more capable than what could be done with the planned ESAS architecture. Depots just make too much sense.

I just saw two interesting SpaceX documents linked to on NASASpaceflight.com. The first is a paper that was presented at the Fourth Asian Space Conference back in October, and the second is a presentation from the von Braun Symposium, also back in October They’re both fairly interesting, and provide some extra insight into the direction SpaceX is looking at pursuing over the coming years. I wanted to post them here for you all to read and comment on.