While I was standing there looking at this pretty darned impressive hole in the ground, I started thinking about Larry Niven’s quip about how “Dinosaurs went extinct because they didn’t have a space program”. As I said on Twitter during the drive, I don’t think our space program would actually do us much good in stopping an extinction-level meteor strike, even if we had 5-10 years advanced notice (which we most likely wouldn’t have because we’re not doing the NEO search in the way that would actually give us much advanced warning).

I think a better way of thinking about this would be to say that “Dinosaurs went extinct because they weren’t spacefaring. Unfortunately, neither are we–yet.”

Speaking of spacefaring, I think that Paul Spudis’ article about the seafaring vs. aviation analogy for space was spot-on in illustrating this point. This is why I’m worried that the destination/mission focus of so much of the space debate is driving things in foolish directions. I actually side with Paul in thinking that cislunar space (including the surface of the Moon) is where it makes the most sense for us to develop ourselves into a spacefaring (and not just space-visiting) civilization. I just think a lot of the debate is on destinations versus whether we want to be forever stuck with one-off missions or whether we want to establish the kind of transportation infrastructure that enable something more like what Paul described (and ultimately what would be required if we want to be able to avoid repeating the fate of the Dinosaurs if it turns out some rock out there is addressed with our name on it).

Jeff made the point that you can look at space policy from a framework that has Goals at the top, with Strategies that help you achieve those Goals, Objectives that provide you measurable steps to gauge your progress at those Strategies, and then Tactics that determine what tools you use for meeting those Objectives. I really like this framework, and in fact it helped me clarify my thinking about Altius’ corporate goals and strategies (but that’s a blog post for another time, and probably over on the ASM blog).

After giving a few analogies (WWII military policy and the Space Race), Jeff then made the argument that “space settlement” was actually the policy of the United States. For me, my motivating goal for space development is a very closely related but slightly different focus–tapping the resources of space for the benefit of mankind here on earth. Now, there are challenges for both of these goals. As Jeff right pointed out, there are many who are afraid of openly proclaiming goals like these, because they are afraid that they might not actually be realistically achievable. In the case of settlement, there are questions of whether humans can actually reproduce outside of a 1g field, or if we can ever get to the point where we can economically support life indefinitely off planet. In the case of tapping space resources for humanity’s benefit, there’s the “minor technical detail” that most of these resources are extremely subeconomic right now.

I actually discussed the topic of subeconomic resources back in the early day of this blog, but I figure a revisiting of the topic is worthwhile. To recap, a subeconomic resource is one that you can’t profitably extract and sell under current conditions. Pretty much all space resources currently fall under this category. While you hear a lot of comments on space forums about the importance of better space property rights, the reality is that even if there was a clear way you could homestead a chunk of the Moon or a NEO or Mars, and sell anything you could harvest for it, I still don’t think you could actually close an honest business case around resource extraction today. With how much it would cost and how long it would take to go from where we are right now to the point where you could actually sell your first kg of lunar platinum or put the first drop of lunar derived LOX or LH2 into a customer’s tank in LEO, there’s no way you could actually make the ROI work for doing that privately, stand-alone. In fact, I’ve even got a certain coblogger who has made the argument that it’s impossible to ever mine a resource in space and send it back to earth for a net profit.

While I’m pessimistic on the current economics of space resource extraction, I think my friend is wrong. The point I made in my previous article on the topic and that I wanted to remake today is that resources that are currently subeconomic don’t have to stay that way. What got me thinking about this was actually reading a sign at the Hogle Zoo last week while on vacation. One of the donors for the zoo was the Kennecott Copper Mine, a major open-pit mine located in the mountains on the west side of the Salt Lake Valley. While this mine is one of the most productive mines in the world, there was still a time in the not-to-distant past, where even if you knew exactly how much gold, silver, copper, and molybdenum there was in there, that it wouldn’t have been possible to economically exploit that. But as transportation systems became more mature, affordable, and reliable, commerce spread, and eventually mines like it or deep-sea oil rig operations also became feasible and even profitable.

Now don’t get me wrong, just because it’s possible for some subeconomic resources to become economic over time, that doesn’t guarantee that a specific resource will do so. Personally, I’d be really surprised if anyone ever harvests Helium-3 from the moon for use in fusion reactors, for instance. But I think there’s a reasonable case that a space program run with the goals I mentioned earlier (settlement and resource utilization), and with a suitably well-thought-out and implemented strategy, can enable at least some extraterrestrial resources to become economically extractable for mankind’s benefit.

Imagine for a second that the White House actually proposed such a goal, and a strategy like Jeff’s “planet hopping” strategy, and found a way to get Congress on-board with such a strategy, and NASA to competently execute it’s part of that strategy long enough to get us past our first two major objectives (depots in LEO and L1 and a working lunar ISRU operation capable of delivering respectable amounts of LOX/LH2 to L1). Also imagine that the idea of prepping these new capabilities for a handoff to commercial operations was built-in from the get-go instead of being an afterthought like it usually is. By that point, we would have already started some virtuous cycles. By providing an anchor tenancy need for propellant in LEO, you’ve now provided a large enough stable market to close the business cases for several lower-cost launch providers. You’ve also helped establish infrastructure and systems to allow sending large amounts of crew, cargo, and other materials to the lunar surface. You’ve also established the first market for propellant in L1 (servicing missions both to the Moon and also to NASA’s next steps in the “planet hopping” strategy). If the price point of propellant in L1 from lunar sources really is cheaper than shipping it from home, you’re also getting the start of a transportation system that has a made a lot of progress towards being able to extract and ship home Lunar PGMs at an economically useful price point. While you might not yet be all the way there, you’ve now lowered the amount of additional work that has to be covered by a lunar PGM extraction business plan substantially, and also removed a lot of content and time between fundraising and when that first bar of platinum can be sold on earth. Also, by providing steady demand for propellant in L1, NASA has also provided an economic incentive for people to improve the cost of delivering stuff to L1 (say by improving the reusability of lunar landers, building a small lunar mass driver, rotovator, launch loop, sling, or a lunar beanstalk). By providing an anchor tenant for LEO and L1 propellant, NASA has also made it easier for other people with business ideas to factor those into their company’s plans, or their country’s space program.

To summarize what has now become a much longer blog post than I intended, I think a properly done settlement/resource extraction goal with a “planet hopping” strategy could actually start making lunar resources economically extractable even before we’ve managed to put a human foot on Mars, even if such resources are currently nowhere near economically feasible today.

May 25th, 2010, Mojave, CA, USA: XCOR Aerospace and Masten Space Systems, two of the leaders in the New Space sector, have announced a strategic business and technology relationship to pursue jointly the anticipated NASA sponsored unmanned lander projects. These automated lander programs are expected to serve as robotic test beds on Earth, on the lunar surface, Mars, near Earth objects and other interplanetary locales, helping NASA push the boundaries of technology and opening the solar system for future human exploration.

Masten’s award winning automated vertical take off, vertical landing (VTVL) flight vehicles combined with XCOR’s strong experience in liquid oxygen (LOX) / methane powered propulsion systems and nonflammable cryogenically compatible composite tanks, brings to NASA a powerful and competitive combination of innovative talent with a proven record of producing exceptional results quickly and affordably.

Last October, Masten won the $1 million first prize for Level II of NASA’s Lunar Lander Challenge, beating out a host of New Space rivals, and demonstrating they are the leading VTVL development group in the country. In 2007 XCOR Aerospace’s LOX/methane engine, developed for NASA, was named by Time Magazine as one of the “Inventions of the Year”, recognizing XCOR’s successive advancement in the state of the art of both pump and pressure fed reusable, throttle-able rocket propulsion systems. XCOR and Masten have also demonstrated the ability to rapidly take from concept to live fire, new propulsion and control system designs using innovative rapid prototyping techniques that surpass client requirements in much shorter periods of time than traditional aerospace methods.

Dave Masten, founder and President of Masten Space Systems commented “Masten Space and XCOR are next door neighbors here in Mojave. We’ve worked together on many tactical problems over the years and our corporate cultures mesh well. Working together on something like this simply made too much sense. We can’t wait to start working with Jeff, Dan, and the XCOR team to help NASA build affordable and responsive landing platforms.”

“Our company work ethic and styles are very compatible, and with XCOR propulsion and Masten VTVL technology, we can solve problems of national interest, and I am excited about the possibilities,” said Jeff Greason, CEO and Founder of XCOR.
Andrew Nelson, Chief Operating Officer of XCOR added, “It’s a no brainer, Dave’s team is the absolute best New Space company when it comes to VTVL and autopilot unmanned operations – they demonstrated that in October by winning NASA’s lander challenge. And we feel our LOX/methane engines are unsurpassed in the trade space today by anyone. We should bring this tandem set of best in class capabilities to NASA, it just makes sense for them and for us.”

XCOR and Masten will be jointly marketing their skill sets and services to the NASA community as prime contractors, and as joint teaming partners for larger systems integrators and prime contractors servicing the NASA community.

# # # # #

Masten Space Systems is a Mojave, CA based aerospace company developing fully reusable vertical takeoff, vertical landing (VTVL) launch vehicles, rocket-related products, and engineering services. The company’s 6000 square foot production facility and 200,000 square foot testing facility is located on the Mojave Air and Space Port. The company designs and builds aerospace solutions that focus on durability, long operational lifetimes, and minimal per-flight maintenance. For more information on the company see http://masten-space.com

XCOR Aerospace is a California corporation located in Mojave, California. The company is in the business of developing and producing safe, reliable and reusable rocket powered vehicles, propulsion systems, advanced non-flammable composites and other enabling technologies for responsive private space flight, scientific missions, upper atmospheric research, and small satellite launch to low earth orbit. The Lynx is a piloted, two seat, fully reusable, liquid rocket powered vehicle that takes off and lands horizontally. The Lynx production models (designated Lynx Mark II) are designed to be robust, multi-commercial mission vehicles capable of flying to 100+ km in altitude up to four times per day. XCOR’s web address is: www.xcor.com.

Contact:
Michael Mealling
Masten Space Systems
Phone: +1-888-488-8455 x102
Email: mmealling@masten-space.com

Mike Massee
XCOR Aerospace
Phone +1-661-824-4714 x127
Email: press@xcor.com

I can’t speak for the company, but personally I’m really glad we were able to find a way to make this partnership work. I’ve got nothing but respect for the XCOR team, and have been trying to find a way to work with them for years. As Jeff said at Space Access, it’s deals like this that show that the industry is starting to grow up.

• The land grant size proposed is too big–about 4x the surface area of California for a single base.  While this allows you to raise lots of money off of a pretty crappy land valuation ($40B raised at $100/acre), I still have to wonder if you’d really be able to sell this.  I mean, what’s the value other than speculation for any of the land parcels much more than say 10-20 miles beyond the base?  Here on earth, where you can breath the air, and where the dust isn’t viciously abrasive, it still takes a huge amount of effort to bring even a reasonable fraction of that land area into productive use.  I think a better strategy would be sticking with more reasonable land area grants (say tied to the distance you can travel on the ground in a day or two), with the goal being to charge a higher value per acre over a smaller number of acres.
• I just can’t help feeling this is super premature.  Part of why land prices on the Moon in this scheme are assumed to be low is that it isn’t clear how we’d make money on the Moon, and our methods of reaching the Moon are still utterly primitive and barbaric.  Once we have things like depots, and have had some robotic landers on the lunar surface, and maybe commercial crew in LEO and a few other things (ie sometime in the next 10 years), we might actually be close enough to a lunar venture that this might be more useful.
• That said, once we’re ready for it, having something like this in place might not be a bad way to help raise revenue for the initial venture.  I’m just worried that if we jump the gun too far, the more likely result is going to be people getting burned, and investors getting a bad taste in their mouth for lunar ventures.

Just some quick thoughts.

Here is the humor slide I started out with:

We Don’t Need No Steeking Propellant Depots!

My actual presentation:

RLV Friendly Depots

Bernard Kutter’s presentation for ULA:

Near Term Depots

and Dallas Bienhoff’s presentation for Boeing:

Space Transportation Impedance Matching

I haven’t been given a copy of Rand’s presentation yet.

[Edit, here it is, Rand says he'll probably get some annotations up later]

Anyhow, a few quick random thoughts that I don’t think anyone else has really hit upon on the intarwebs:

• One of the concepts out of Dallas’s presentation I liked was the idea of having a space transfer tug that takes landers from EML1 (L2 would also work) to some perilune trajectory, and then returns to EML1.  I’ve been toying with variants of this idea for some time.  With a Centaur-sized trasnsfer tug, fully-tanked-up in EML-1/2, you can actually bring pretty darned big landers most of the way to the lunar surface (ie leaving 1000m/s or less of delta-V for the descent), while still having enough propellant to return to lunar orbit and from there to the L-point station.  That segment is probably one of the easiest in-space segments to start doing reusable stages, since you don’t need an aerobrake, and don’t have to deal with lunar dust, just propellant transfer, and lots of engine relights.
• In a conversation with Jeff Greason late one night at the conference, we got off onto the topic of RLVs and propellant depots.  One of Jeff’s opinions is that in order to really have an industry for some service, you need enough demand to allow for 2-3 healthy competitors.  With only one provider, you get monopolies, three is ideal.  But for RLVs you probably want a small fleet (~3 vehicles) of RLVs so that you can provide dependable service even if you either have a mishap or have to pull one of the vehicles for maintenance or repair.  Having a single vehicle may work during the development phase where you’re transitioning into operations, but once you’re in full operations, you want enough demand for 2-3 companies with probably 2-3 vehicles per year.  And for each of those vehicles, in order to get the per flight price in a really good range, you need to fly often–Jeff says 100 times per year, but I’ve heard numbers as low as 30-50 (but any way you slice it, it’s a lot of flights).  That comes out to somewhere in the 120-900 flights per year range.  The interesting thing that Jeff mentioned was that if you postulated very small RLVs to start with (say 300-500lb to LEO net payload capacity), just one lunar mission per year would be enough to provide enough demand for an entire healthy industry by itself.  Towards the lower ends of that scale, you’d only need one “soyuz around the moon” flight, or 1-3 GEO flights that used a propellant tank-up in LEO (say using a Falcon 1 with a mini-Raptor type LOX/LH2 upper stage?) to provide enough demand for at least the starting of an industry.
  • While 300-500lb to orbit sounds tiny, that’s actually a pretty reasonable size for a first-generation RLV.  The first stage doesn’t end up being that much bigger than existing or planned suborbital vehicles, doesn’t have to have much more capability either.  The upper stage ends up down in the middle of the size range for proposed suborbital vehicles.  While it has a much higher performance requirement, and much nastier reentry environment, it’s on a size that you can realistically work with a lot easier.  Also, a lot of the TPS work can be refined by flying “expendable” upper stages on these first generation commercial suborbital launchers.
  • This would definitely require the sort of RLV-friendly depot setup I described in my presentations–you’d have to have tugs that carry all the rendezvous/docking smarts, and keep the RLV-side of the propellant system as dumb as possible
  • Propellants are a much less demanding payload than people.  Not only does this keep up-front development costs down, but it also reduces the business risk if you happen to lose a vehicle occasionally.  While high flight-rate RLVs should be capable of high reliability, we’re also talking about 1st or 2nd generation systems here, where we’re still learning a lot–and learning can be painful.
• I also liked Bernard Kutter’s graphic of the simple, single-launch, dual-fluid depot concept.  This is a simpler version of the ideas Frank Z and I came up with last year (it uses a stock Centaur-sized tank for the LH2 side of the depot), but is still quite capable–on the order of 30mT capacity is nothing to sneeze at.  With one of those in LEO and one in L2, that’s actually enough to do an ESAS-capacity lunar transportation system without Heavy Lift.
  • One of the really interesting possibilities is that if something like this demonstrator depot were chosen as a part of the money Obama has proposed for orbital refueling technology demonstration (it wouldn’t need anywhere near the full $400M-1B that Obama mentioned per technology area), if the demo system worked, it would actually be operationally useful.  Sure, you’d want to replace it and/or upgrade it down the road with lessons learned, but I’m a fan of pressing technology demos into operational service, as that’s a good way to get a lot more data out of the deal.
• I also liked how Bernard explained a lot of the cryo storage issues.  A lot of this stuff still needs to be proven in space, but they (ULA, LM, and Boeing) have a lot more experience doing related tasks than most people realize.

I probably have some more thoughts on the matter, but I’m home at sick with a cold today, so I’ll leave it at that.

Traditional Aerobraking and Aerocapture
One of the challenges of orbital mechanics is that it takes just as much energy to descend into a gravity well as it does to ascend out of it. One technique that has been used for lowering the propellant cost of descent into the gravity well of a planet with an atmosphere is aerobraking. Aerobraking is the process of taking a spacecraft in an ellpitical orbit around a planet with an atmosphere, and using atmospheric drag at the lowest altitude portion of its trajectory to slowly decrease the altitude of the high end of the elliptical orbit. This process has been used now on about a half-dozen planetary missions, in some cases reducing the propulsion requirements by 1km/s or more, over the course of a couple hundred passes. Aerobraking has been traditionally been done by satellites that aren’t explicitly shaped like a reentry vehicle–in fact most of the drag for typical aerobraking vehicles is produced by using the spacecraft’s solar panels as massive drag brakes!

Artist's Impression of MRO Aerobraking (credit JPL and Wikipedia)

A more aggressive maneuver called aerocapture takes a spacecraft in a hyperbolic (interplanetary) orbit and in a single pass decelerates that vehicle into an elliptical orbit around a planetary body.  Typically the term refers to maneuvers where the ending orbit has an apoasis near the altitude of a circular orbit, though it could also be used to describe a maneuver that uses a single pass through the atmosphere to replace the “capture braking burn” that would normally be used. Aerocapture is a lot more challenging, since the deceleration has to take place a lot lower in the atmosphere in order to provide the required deceleration in such a short distance. This implies much higher forces and heat-fluxes, which require some sort of aeroshield/TPS system.

Here are a few of the main challenges of aerobraking and aerocapture:

1. Dynamic Pressure Loads: Dynamic pressure is the pressure felt on the vehicle by the impingement of the atmospheric molecules.  The equation for dynamic pressure is q = 1/2 * rho * V^2, where lower case q is the dynamic pressure, rho is the instantaneous atmospheric density, and V is the instantaneous relative velocity.  For MRO, the dynamic pressure limits were set at 0.35 Pascals, which correlates to moving at about .76m/s at sea level (ie a slow walking pace).  To give you an idea of how this compares with orbital reentrythe peak dynamic pressure of say a Soyuz in its emergency ballistic reentry mode, is over 40,000 Pa of dynamic pressure, and even a low-G lifting reentry is still in the 10kPa+ range.  Direct entry into the Venusian atmosphere from a hyperbolic interplanetary orbit gets you into the 1MPa range!  Another fun comparison is that the max-Q Xombie or Xoie have seen in flight was around 250Pa.Most of the very low allowable dynamic pressure load for past aerobraking efforts has been driven by the fact that most aerobraking craft to-date have used large flimsy solar panels as their main drag structure.
2. Peak Heat Flux:  The shockwave caused by slamming into gas particles at hypersonic velocities compresses and heats the gas particles to substantial temperatures.    Heat from this shock wave is convected and radiated into the aerobraking spacecraft.  The equation for heat flux is Q = 1/2 * rho * Ch * V^3.  Capital Q is the heat flux (in W/m^2), rho and V are the same as before, and Ch is the heat transfer coefficient.  The heat transfer coefficient, I think, represents what portion of that heating goes into the vehicle itself instead of being carried off by the now quite ruffled atmospheric gas molecules who didn’t see you coming.  Yes it is confusing that dynamic pressure is lower-case q, and heat flux is capital Q.Once again, to give you some scale, the worst case pass for Odyssey had an estimated heat flux of about 500 W/m^2,  which is about 40% of the heat you get in LEO from the solar radiation. For that Soyuz reentry case mentioned earlier, the total heat generated at max-q is in the 240 MW/m^2 range–several times higher than the heat flux at the throat of the SSME or RD-180.  The Venusian direct entry example according to one source would actually be in the 4000MW/m^2 range! Fortunately, I think that for atmospheric reentry the Ch term is relatively low–most of that heat gets carried away by the atmosphere.As with dynamic pressure loads, the reason why peak heating rates are kept so low for most aerobraking missions is that you’re using the large solar panels as most of the drag surface, and they can only take so much heating before their temperatures rise to levels that could permanently degrade their performance.
3. Atmospheric Density Variations: If atmospheric density was nice, constant, and well-known, aerobraking could proceed a lot faster and in a lot fewer passes.  The problem is that at the altitudes where aerobraking takes place (100+km), the density can vary significantly over length scales as small as 20km.  This can be driven by many processes including variations in the solar wind and solar radiation due to sun cycles, weather effects like dust storms for Mars aerobraking, and other effects.  Going off of some data from the Odyssey mission, variations as big as 2-3x were seen in density from pass to pass.   A second-order effect of density variations is that both the drag coefficient and the heat transfer coefficient will vary with atmospheric conditions by noticeable amounts.  Unfortunately,  in many cases you don’t know the density along a given trajectory in advance, so you have to plan for not the average density, but the worst case pass density.   Which means that most of the time you’re getting less deceleration and heating than you could actually withstand, but some of the times you might actually find yourself pushing your limits more than you would like.   This drives you to taking more passes than you’d really like to take in an ideal situation.  These variations get more and more pronounced at higher aerobraking altitudes, where atmospheric density is measured in kilograms per cubic kilometer.Once again, this is an area where using large, sensitive solar panels as your drag devices really hurts. Because you can’t stand high dynamic pressures or heat fluxes, you have to do your passes higher up in the atmosphere. But due to variability in density at those higher altitudes, you end up getting driven even further up to deal with worst case variations. That said, even aerocapture trajectories are high enough altitude that atmospheric variations can be important challenges to deal with.
4. Aerobraking Duration: For most previous Mars and Venus aerobraking missions, velocity changes in the 1-1.2km/s range have taken between 70-150 days, over several hundred passes.  While this is fine for unmanned missions, it’s harder to do for manned missions, where radiation concerns make you want to minimize your time spent in-transit.  The large number of cycles is also a difficulty for missions aerobraking at earth, where each pass will take you through the Van Allen belts.  Lastly, for reusable in-space transports, the total turn-time is an important economic parameter–the more missions you can fly in the same period of time, the fewer vehicles you need to support a given mass throughput.

A couple more quick observations before we jump into using MHD forces to enhance aerobraking:

• For typical aerobraking, the parameter you can control easiest is the periapsis altitude, and thus indirectly the average density.  In other words, if you want to double the drag on a pass, you lower your periapsis to an altitude that has about double the average density.  This also means that to a first order approximation (ie ignoring the relation between density and the heat transfer coefficient) heat flux for traditional aerobraking is going to scale fairly linearly with drag.
• Ballistic coefficient ends up being really important for aerobraking as well–this is the whole reason why the solar panels are used unstowed for aerobraking.  Higher ballistic coefficients mean that you have to dip lower into the atmosphere (and thus get a higher heat flux) to get the same amount of deceleration per pass.
• In spite of the disadvantages of using solar panels as your drag brakes, there are some real advantages to being able to use a aerobraking scheme that doesn’t require your vehicle to be explicitly crammed into a typically reentry-vehicle shape behind a massive heat shield.  It would be nice for instance to be able to get tanker vehicles or orbital tugs back from lunar trajectories or martian trajectories without them having to carry a big aerobraking shield like you see in all the old literature.

Anyhow, that was a quick introduction to aerobraking by a complete non-expert.

Some Backstory on Why I’m Interested in Aerobraking
I started looking into this a few months ago as an alternative to propulsive retrobraking for Centaur-derived cislunar tanker vehicles.  While a Centaur stage actually can do a lunar round trip fully propulsively, with at least some payload delivered to the Moon, the “gearing ratio” (initial mass in LEO compared to payload delivered to LUNO or the Lunar Surface) was pretty pathetic.  Just to use some ballpark numbers, without digging up my more precise calculations, I’m getting around 8000lbs payload to LUNO if you drop it off in orbit and the Centaur only returns to earth, dropping to only 2500lb if the Centaur has to haul the payload all the way there and all the way back propulsively.  However, if you could do 3km/s worth of aerobraking (assuming about 1200m/s worth of burns between the Trans-Earth Injection burn and any periapsis raising maneuvers, including the final circularization), all of the sudden you’re talking about almost 20,000lb of payload on the dropoff mission, and about 13000lb on the round-trip maneuver.  Depending on how massive and expensive the aerobraking system weighs, it makes a massive difference in the performance of a reusable cis-lunar architecture.  For a long time though, I had sort of dismissed aerobraking, because any aeroshield big enough to allow single-pass aerobraking (or few enough passes to be interesting) also ended up looking like it would either be very heavy, or very bulky, or require lots of orbital assembly or some sort of new deployable technology.  Not that any of those other than being too heavy was a total show-stopper, but it definitely made it less attractive for a near-term commercial operation.

Another line of thought I had been wondering about recently was manned cislunar transportation, especially in light of the Augustine Committee report.  One of the big suggestions they made that rubbed a lot of HLV-advocates wrong was the idea of launching the crew on commercial LEO taxi vehicles, and flying Orion up to LEO unmanned.  A lot of people said this was just silly–if you’re launching Orion may as well launch it manned, even though this would require adding launch escape and emergency detection capabilities to the HLV.  I started thinking down the lines of what Orion could look like if it was designed from the start not to carry astronauts until they got to space.  The LAS would go away, as would all the structural requirements for taking those sorts of loads, being able to rapidly drop the service module, etc.  The whole thing could fit inside a fairing, thus simplifying aerodynamics and loads on the front end of Orion.  Heck, it could even be attached to the rest of the stack in whatever orientation made the most sense for mission ops–it wouldn’t be constrained by needing to be on the top in an orientation where the capsule could “get out of Dodge” in a hurry if something “went south” with the HLV.  The more I thought about it, the more I realized that Orion could end up looking like a drastically different vehicle if it was optimized for in-space use and reentry instead of needing to also handle manned ascent to orbit as well.  Then I made an interesting leap of logic.  What if Orion was only meant to be used in space?  I originally sort of dismissed this, since most single-pass aerobraking schemes I knew of would require the thing to be designed like a reentry capsule anyway.

Jumping back to the Centaur-based tug idea, I toyed around with the idea of doing a blog series, seeing if I could make an aerobraking simulator to figure out if a Centaur could without any sort of fancy aerobraking shield actually do a multi-pass aerobraking mission that would get it back to LEO within a reasonable amount of time (say three weeks or less).  However, I stumbled on the papers about magnetic aerobraking right about this point in my thought process, which may possibly provide a solution to both of these problems.

While I don’t have anywhere near the analytical chops to know for sure how far you can push this technology, if it could enable single-pass or at least small number of pass aerobraking without requiring a huge traditional aerobraking shield, interesting things might become possible. Magnetic aerobraking could potentially revolutionize cislunar transportation, enabling low-cost reusable manned and unmanned deliveries based on modified versions of existing LOX/LH2 upper stages, and could allow fully-reusable in-space only manned vehicles that weren’t just an overglorified 1960s-style reentry capsules.  But more on that later.

For now let’s get back to how we can use magneto-hydrodynamic interactions to enhance traditional aerobraking, and see if we can figure out if this idea has merit at all.

Magnetic Aerobraking
Going back to our previous two discussions, one of the key takeaways was that the enhanced braking and thermal protection provided by strong magnetic fields was strongest at high altitudes where atmospheric density was lowest. At high altitudes, the ambient atmospheric density is low, but Joule heating caused by the interactions between ions in the shock layer and the superconducting magnet keeps the electrical conductivity of the plasma in the shock layer high. Also, for aerobraking or aerocapture short of reentry, by definition you are both always at a speed and altitude high enough that you don’t have to worry about the shock layer losing sufficient conductivity for MHD effects to dominate aerodynamic drag effects. The magnetic interaction parameter (Qmhd) introduced in my first post in this series can easily be in the 250-1000+ range at high altitudes compared to down in the 5-50 range you might see during atmospheric reentry. For example, the paper I cited in my first article (Otsu et al) showed that for a vehicle coming back from a GTO-like orbit, you could cut the return time by 70% with a 0.1T magnet, which is about 5x weaker than the magnet assumed for most of the reentry magnetic TPS studies.   While magnetic effects may be helpful for reentry, they truly come into their own for aerobraking and aerocapture.

A few other thoughts:

• While the total drag for a magnetic aerobraking concept can actually be several times the drag of a similar non-magnetic vehicle, the gas-dynamic portion of the total drag actually decreases substantially in the case of magnetic aerobraking.  This is due to a much lower velocity behind the shock layer in the magnetic case.  Figure 9 from the Fujino et al paper I used in the last post (“Numerical Analysis of Reentry Trajectory Coupled with Magnetohydrodynamics Flow Control”, JS&R Vol 45 No 5, pg 911-920) illustrates this beautifully:
• For a vehicle using magnetic braking, most of the total drag force is actually reacted electromagnetically through the magnet itself, not through the surface of the vehicle.  The dynamic pressure that the vehicle surface itself sees is greatly reduced compared to what you would expect at that altitude and entry velocity.
• While in the above case, the dynamic pressure reduction was about 4x at ~75km, this effect is likely to be even more pronounced at the altitudes used for aerobraking (90-120km) where the electromagnetic interaction parameter is substantially higher (40-160x higher) than it is in the case shown above for atmospheric reentry.
• The heat flux seen by the aerobraking vehicle will also be greatly reduced compared to a non-magnetic aerobraking system at a similar altitude and velocity.  This is due to the much thicker shock layer standoff distance and the lower velocity of the particles behind the shock layer.  The Fujino et al paper estimated that the heat flux would roughly be cut in half at 75km with a 0.5T magnet (due to a boundary layer between the bow shock that is twice as thick at that magnetic interaction parameter).
• For higher parameters in the 100-1000 range that you would likely see for aerobraking, this effect should be even more pronounced.  The trend in shocklayer thickness vs. Qmhd shown in Fig 3 of Fujino et al  was linear over the Qmhd range of 0-6.  If it continued out linearly up into the Qmhd 100-1000 range, the shock layer standoff distance would be in the range of 100-125x thicker than without MHD effects, implying a drastically reduced heat flux at aerobraking altitudes.  Unfortunately without having them run the actual analysis, it would be hard to know precisely how well this would work.
• All these factors mean that the same vehicle could use a lower periapsis with a magnetic braking system than without.  The dynamic pressure and heat flux that the vehicle sees at a given periapsis altitude is going to be at least 2-4x and possibly more than an order of magnitude less than it would be without the magnetic field.  Even in the most conservative case (ie assuming that the effect at 100km and aerobraking speeds is no better than at 75km in spite of having a Q 40-160x higher) this would allow you to go to an altitude with at least double the density while keeping the heat flux and dynamic pressure loads within tolerances.  With an effective total drag 4x higher at a given altitude combined with being able to go to a lower periapsis, you get bare minimum a 8x reduction in total aerobraking time compared to the non-magnetic case.
• For the aggressive, “I don’t know if I’m extrapolating way too far” case, you could get even larger reductions in aerobraking time.  Going back to my linear extrapolation on shock layer standoff vs. Qmhd (and thus heat flux vs Qmhd), at Qmhd=250 this would put the shock layer standoff at about 25-30x thicker than the non-MHD case.  The example in Otsu et al gave a Qmhd of 250 using a 0.1T magnet and a 100km periapsis.  Since Qmhd is proportional to B^2 and inversely proportional to rho.  If you increased the magnetic field from 0.1 to 0.5T (similar to what was being suggested for the reentry studies done by Fujino et al and some of the others), you could maintain a Qmhd of 250 even if you increased the local density by a factor of 25.  At Qmhd of 250, the effective drag coefficient is about 3x higher than the non magnetic version.  That would give up to a 75x reduction in aerobraking time compared to the non-magnetic case.
• One other advantage of magnetic aerobraking is that you can drastically vary your effective drag coefficient electrically.  Also, the heating and dynamic pressure are far more driven by the magnetic field strength than by the atmospheric density for the MHD aerobraking case.  These mean that you can afford to take deeper passes without having to worry as much about variability.  If the density is higher than expected, and you have some head-room on your magnet, you can increase the MHD field strength a bit to keep the shock layer back and the dynamic pressure down.  This also could cut trip times in half just by allowing you to base your planning off of the average atmospheric density instead of having to take the mean + 3 standard deviations as your predicted atmospheric density.

I’m rapidly coming up to the point where I’m pretty sure I no longer know what I’m talking about.  At least from here, it looks like there’s a good chance that MHD aerobraking could allow for aerocapture (at least into a high eccentricity elliptical orbit), and very rapid aerobraking down to a circular orbit compared to the non-magnetic case. I think you can extrapolate the conclusions of these papers in these ways, but without having the people with the analysis tools actually verify these claims, I’d still take them with the appropriate sized grain of salt.   Also, my intuition on how a MHD aerobraking vehicle would compensate for density variations is not very good.  That alone could be a paper or a thesis.

So, whether this ends up being a mild curiosity that ends up only being useful in niche applications, or a game-change remains to be seen, but the potential for this being a game-change is real.

In my last post in this series, I’ll go more into some of the implications of what this could do if it works, and some thoughts on how to actually flight-demonstrate MHD aerobraking.

[Edit: It turns out I had misspelled Fujino's name in the original post. Fixed that and added the title of the paper in case people want to get a copy--it's free if you have a JS&R subscription, $15 if you're an AIAA member without a JS&R subscription, and something like $30 if you're not an AIAA member--highly recommended if you're interested in this topic]

Horse-Trading on Even Earlier Markets
A good point that was made on the same day by Wes Johnson in comments, and my boss Dave on the carpool down to Mojave, was that the “horse-trading” trick at the center of the business concept I gave could work even before manned landings. One of the big challenges with any lunar surface robotic exploration is the lack of a suitable lander. The big up-front development cost of a lander (especially one done the traditional way, without leveraging the capabilities of us VTVL developers) usually makes it harder to get these projects funded. If you could do a deal where the PI for a proposal only had to come up with the launch costs plus the marginal cost of the science payload such as rover(s), ISRU technique demonstrators etc., it might make it easier to close their proposal. More importantly, as Wes pointed out, PI’s on science missions have a lot more leeway on negotiating details of how to get the payload to the destination. You’d give them the same deal as the others–in exchange for covering the launch cost, you give them free delivery to the lunar surface, and get to sell the other half of the payload.

Robotic Precursor Missions
An interesting development in the NASA budget proposal that has gotten almost no real discussion in the blogosphere, was the funding for a series of robotic lander missions on the Moon and possibly other destinations. These could be a very interesting potential market for the initial lander work. I could imagine the private entity trying to build up to the manned one-way missions could set up a Space Act agreement with some of the groups at NASA to facilitate sharing of information on lander systems, then possibly using a combination of more traditional aerospace and newere entrepreneurial space entities (“OldSpace” entities since they tend to have a wider range of specialized knowledge, and “NewSpace” entities since they tend to have ways to flight test hardware cheaper, and to do cheaper rapid prototyping), could develop the lander in support of these missions. The money for the lander development could be mostly made back by selling the remaining hardware space to one or more up-and coming space countries that wants to get a leg-up on their competition (say either India, China, Japan, or South Korea). Groups that aren’t actively planning lunar landers in the near-term, or which might be a bit behind their competitor might be the most natural targets. Imagine South Korea being able to beat Japan to the lunar surface by partnering with a private space company? Or India beating China. South Korea has already demonstrated its interest and willingness to partner with commercial space companies to get a leg-up in regional technical rivalries. Just food for thought.

Also, this might tie into stuff like Project M, a youtube of which has been floating around the intertubes for a week or so. JSC has been working in the background on trying to put together a plan to do a quick robotic lunar lander, “within 1000 days of go-ahead”. If they don’t get the money to do such a project entirely themselves as-planned, teaming with a private entity might still allow them to pull such a feat off.

Lunar Surface Systems
After thinking this over and talking with some of the commenters, I think this is one area that I was being overly optimistic on. There is going to be a fair deal of expense for lunar rovers, life support systems, habitats, ISRU experiments (including stuff like systems to try out regolith fusing), power sources, etc. Some of these could be supplied as “demo units” by companies interested in selling future versions to other private or public expeditions, some could be supplied by governments wanting to pretest systems before sending their own people, but ultimately some of these systems would likely need to be developed by the private developer running the project. The good news is that if you can get initial revenue from selling some robotic flights on the lander, it might be possible to raise enough money to invest in the lunar surface systems.

Anyhow, just some thoughts. I just think it would be ironic if due to the lunar precursor lander funding, Obama’s “Evil Exploration Eradicating NASA Budget Proposal” somehow enabled the US to beat the rest of the world back to the Moon and ultimately cemented its lead in lunar exploration. All without having to blow tens of billions on new launchers.

As far as implementing this idea, the technology isn’t the hard part. Technologically, this is something that could’ve been done in the 70s. Modern technology and modern launch services make it a whole lot easier and more feasible, but the technology isn’t the key obstacle. Money is and always has been the biggest obstacle. But I think I have an idea, and it’s just crazy enough that I want to share it.

Any business plan whose first step is “first we convince a billionaire to give us lots of money” usually deserves to be laughed off the stage. But this isn’t a business plan competition entry, or some pitch before VCs that I’m demanding to be taken seriously, so I’m going to suggest just that. Even with a wealthy philantrocapitalist, I think you’d still want a concept that both gives you a reasonable chance of making the money back if things go well as well as minimizing your losses if it doesn’t work out.

Anyhow, this is a bit of a long-shot, and definitely not fully-baked, but here’s what I have so far. The business case revolves around a few core concepts:

• A privately developed simple lander and an ITAR approved method for launching it on both US and domestic launchers.
• Using barter with various space agencies with domestic medium-lift vehicles to provide both the startup launches and the sustaining launches
• Making revenue off of selling remaining space to corporations, research institutions, and smaller countries that are interested in lunar experiments, but lack indigenous launch capabilities
• Possibly offsetting initial lander development by selling rover delivery services to NASA or other large space agencies.

Some of these sound a bit crazy, so why don’t I explain them in turn.

Private Landers
The key technology piece in the project is obviously the lander. As discussed before, I’m thinking of something in the 10-20klb IMLEO range, with a payload in the 4-6klb range. The propellant combination for the lander doesn’t hugely matter. It could use storables like Martijn likes, it could use space storables like LOX/Methane or LOX/Propane. Heck, it could even use LOX/LH2. While the state of the VTVL industry isn’t quite mature enough where you could just order one of these custom and have it delivered to your launch pad 6 months ARO, a lander in these capability ranges isn’t a huge stretch for the commercial space industry, especially if they can partner wisely with some of the more traditional space companies or work with NASA via Space Acts. DC-X was actually a much bigger, probably more complicated system, and was done by a traditional aerospace company for around $100M in current dollars. A bare-bones lander, developed leveraging the emerging capabilities in the entrepreneurial community could probably be fielded for less than that. Possibly in the $50M range. You don’t need to push too hard on mass fractions or engine performance (you need to push a bit, but it isn’t as weight critical as some of the Apollo LM systems), and the technology is a lot more mature than it was in the 60s.

An important part of this process is not just developing the lander, but also working from the start with ITAR to make sure a process is in place that will allow you to launch on as many international launch vehicles as is feasible. This may not be fun, but is probably doable with appropriate precautions.

International Horse-Trading
Most space agencies prefer to spend money within their own borders, and interact with other agencies on a barter basis as much as possible. While this can sometimes lead to suboptimal solutions, it might just work in this situation. On the launch side, the barter would go something like this–the private entity would provide a lander, all lander ops, and physical launch integration work, and the space agency (NASA, ESA, RSA, JAXA, ISRO, or CNSA) would provide the lifter and upper stage for the mission. The launching country would get a certain share of the lander’s cargo space for their own experiments, a certain portion would be reserved for consumables and spare parts, and the remainder would be owned by the private entity to resell to other countries without launch capabilities (say a 40/40/20 split). In addition to transportation of the space hardware, the launching country would also get a share of the astronaut’s time on the surface. So basically you’re providing them with transportation and manned experimentation on the lunar surface in exchange for them providing a launch done by their own people. If one of the countries is willing to take some additional risks, they could even “buy” one of the two initial astronaut slots, in exchange say for a commitment to a certain higher share of the logistics launches per year. In exchange they’d get both the prestige of having one of the initial lunar crew, as well as a higher share in the available time. Over time, as the risk decreases, the initial crew could also be expanded (once again on barter terms that would have the agency in question shouldering a larger share of the required launches).

It should be mentioned how crazy of a bargain this really is for them in comparison to the typical lunar mission approach. Look at Constellation. It will be a lot more capable, but ultimately, somewhere around $10B/yr (and about $150B up-front), you get 4-person years/yr (2x 4-man crew rotations) and about 75klb of cargo (2x 17mT landings) on the moon once you have a base setup. Calling it a 60/40 split on costs (for manned vs cargo flights), that comes out to $1.5B per person-year, and about $53k/lb on the lunar surface–ignoring development costs. With a program like this, say you gave a country 1/4 of a man-year per launch, and about 1800lb, at a cost to them of call it a $200M launcher plus extra upper stage for the transfer. Splitting that $200M the same way (60/40), that gives you $480M per person year, and about $45k/lb on the surface. You don’t save a huge amount per pound of cargo on the surface, but your cost per person hour is about 1/4 as much (which is once again not too surprising–you’re not rotating crews, and not having to carry enough propellant to get them home–which takes about 4x as much mass per mission compared to a one-way manned landing). And you don’t have to spend tens of billions up-front, and you can buy your lunar program “by-the-slice”. Paying for an extra launch every year (and some lunar systems costs) is well within the budget capabilities of many of these agencies. While they might not be willing to take the risk of flying their own astronauts, or of “owning” the program, they are a lot more likely to be interested in a program like this, where someone else is shouldering the key risks, and they’re just getting a cheap deal. Even if they have their own lunar ambitions down the road, using a service like this would allow them to drastically reduce their technological risk moving forward, and might allow them to get a lot more benefit out of their investment when they eventually get that capability themselves.

“Sovereign Customers”
One of the key markets Bigelow is looking at for his inflatable space habitats is providing smaller countries with a way to participate in space for much cheaper than trying to do everything in-house themselves. By lowering the cost to participate, it makes it a lot more feasible for smaller countries, and even some corporations or research institutions to participate. This may be a country like South Korea wanting to send a rover that can get maintained by the astronauts over time. It may be a country wanting to do its own sample return mission–with the ability to have a human on the ground helping to presort/preprocess samples to maximize the bang for the buck. It could be a company like Catepillar that wants to get involved in lunar surface systems for future exploration programs sending a bunch of bearing concepts to test exposed to the lunar environment. It could be some small startup that has a crazy idea for lunar dust mitigation that it wants to try selling to future government programs, but needs testing and debugging first. There are many possibilities. The key here is that since the launch is already paid for, the private entity running all this can price the payloads however makes the most sense. You do need to cover lander costs, ground-ops costs, and the time of the scientists, but it might be possible to offer these slots at a price that is lower than they could buy commercially to try and stimulate demand, or if there is enough demand already you could price it high enough to make a decent profit. If there’s enough demand, you might even be able to justify paying for an additional “purely commercial” flight or two per year. You would want to save up some of the money to cover contingencies–like if something breaks down and you have to fly an emergency resupply flight on short notice, or if you decide for one reason or another to throw-in-the-towel after a few years, you can send enough propellant to get the settlers home. But depending on the interest level, this could easily be a business that has revenues in the low hundreds of millions per year.

Minimizing the Initial Risk
One additional market for the lander, and one that could allow the initial investment to be recovered a lot faster, would be to see if you could sell it to one of the space agencies for landing a rover or some other scientific package. The key here is that the lander is getting developed, on the philantrocapitalist’s own dime regardless of if he can presell any lander slots. This makes it easier to sell it as a commercially available service instead of a government funded development program. Using a light Atlas vehicle for instance (maybe with one or two strapons) you could probably short-load the vehicle enough to put a couple hundred pounds of useable payload onto the lunar surface. For a bundled price of say $200-250M for the launcher and lander, it would still be a steal transportation-wise for your customer, but could possibly pay off the initial costs of the project in one shot, even before the initial landings. The good news is that while its great if you can presell the landers for other applications, it isn’t the end of the world if you can’t.

One other way of minimizing the downside may be to see if you can prearrange the initial several launches. If you can line up enough international partners, it may be possible to get the initial setup done without having to actually buy any of the launches yourself. You’d still have to pay for the landers, but this way your total capital at risk for the startup is only the cost of 3-4 landers.

Anyhow, comments? thoughts? attempts to send nice young men in their clean white jackets to cart a certain space blogger away?

Let’s turn to the Augustine Report itself for some information. On pages 83 and 84 they discuss implementing the Program of Record on entirely unconstrained budgets–ie if we gave the program the full funding it needs to execute, and allot it to move at the full pace it can realistically move at, what do we get?

• A $145B pricetag over the 2010-2020 timeframe, which doesn’t even get us to the point of having Ares V and the LSAM ready for operations, much less a moonbase.  This would require almost $5B extra per year–ie a 25% increase in NASA’s topline budget.
• An international space station deorbited within 5 years of its completion, during which time the only method of access would be by paying the Russian government for flights.
• A crew launch vehicle that becomes available two years after its first destination is deorbited, and whose operational costs have to be carried for over half a decade until we have any of the tools that would be necessary to actually use it for anything.  But don’t worry, we can spend $2B+ per year to send even fewer astronauts flying in even more useless circles.
• A seven plus year manned orbital spaceflight gap in the US.
• Almost no investment in long-term technology development (not much more than the current SBIR budget, and entirely focused on short-term Constellation needs, not on making future missions safer, more affordable, and more valuable).
• No stimulation of commercial industry beyond the CRS contracts which wouldn’t be extended since the ISS would be gone by 2016.  No investment or early market for commercial crew delivery
• No money to actually develop hardware for actually doing anything on the Moon, since almost all of the money will go to figuring out how to go there while maximizing employment in Shelbyville.
• No more robotic orbiters or landers for years to follow-up on the work LCROSS did.

But hey, at least if we do it this way, sometime 15+ years from now, we’ll have the ability to send 8 people to the moon every year at the cost of an “exploration” program that costs almost as much per year as NASA’s entire current budget!

If you assume that there are parts of NASA outside of Huntsville that actually matter (ie that NASA != Northern Alabama Space Administration), the situation gets even worse.  In order to fund Constellation at full speed without splashing the space station almost as soon as it’s completed, you would need $159B over that timeframe, which constitutes a $7B per year increase for NASA.  That increase still:

• Gets you a space station you can’t access without the Russians for most of its operational lifetime (why does Congress trust Russian commercial space more than American commercial space, btw?).
• Gets you no real investment in long-term technologies, ensuring that the cost, safety, and efficiency of manned spaceflight will be stagnant for another couple decades.
• Gets you no real investment or encouragement of the commercial industry (in direct contravention of the laws of the land and NASA’s charter I might mention).
• Gets you no more robotic follow-ons for LRO and LCROSS for over 15 years.

Compare this with the Flexible Path option that Mark likes to mock so much.  For less than half as much of an increase per year, you get:

• Robust ISS utilization through 2020, with multiple methods of providing crew and cargo delivery that aren’t all dependent on Russia
• Investments in commercial space that can help keep the US in the forefront of space technology and utilization
• Robust investments in high-payoff medium-term technologies like propellant depots, space radiation, space nuclear power, aerocapture and other EDL techniques, ISRU, and other high-payoff technologies that can vastly lower the cost of future exploration missions, allowing us to accomplish more for less and at lower risk.
• A manned lunar landing program that at most is only 3-4 years behind the current PoR, but when it gets there, it provides a much more affordable, more commercially and internationally interesting program, and has much greater capabilities once you get there.
• A manned spaceflight program that is much more capable of exploring the whole inner solar system, and not just doing a few flags and footprints landing on the Moon.
• A manned spaceflight program that builds on and leverages our impressive achievements in robotic space exploration.
• A program that in spite of doing a lot more looking, also allows a lot more touching of new destinations like NEOs and Phobos/Deimos, all on about the same timeframe that the PoR would at best be going for its first lunar landings.

Where I come from, we tend to think that getting a heck of a lot less while paying a heck of a lot more is usually the sign of a sucker.  I just wish that a few space pundits and public figures didn’t keep enabling Senator Shelby and his ilk from hijacking NASA’s budget to enrich his campaign contributors at the rest of our expense.

[Note: As an aside, am I the only one who finds Shelby's latest childish tantrum accusing the Augustine Committee of being compromised by biased by evil commercial lobbyists to be richly and hilariously ironic?  When it comes to lecturing people about the evils of lobbyists corrupting the political process for their own personal gain, Senator Shelby has about as much moral standing as Tiger Woods does when it comes to lecturing people about marital fidelity.]

Anyhow, I probably would’ve figured it out a little quicker if I had been more interested in NEOs.  I’ve always been a planetary chauvanist, and a Moon Firster at that.  I always just waived away the much easier access to NEOs (which turns out not to have been as much easier as I thought) with the argument that while the transportation delta-V requirements were less, the trip times were a lot longer, and the difficulty of operating that far from home would likely drive the costs up a lot higher than just shear delta-V numbers alone would indicate.

So this misconception sat uninvestigated (and fortunately mostly harmless) for several years until earlier this week I was running some numbers regarding the so-called “Flexible Path” approach that was discussed by the Augustine Committee.  To my surprise when I actually looked up the numbers, the closest and easiest to reach NEOs all required delta-Vs from Low Earth Orbit of greater than 3.8km/s (which is approximately delta-V needed to reach Earth-Moon L-1 or one of the Earth-Sun L-points).  In fact some required over 10km/s of delta-V just for rendezvous!  After thinking it through, it actually made plenty of sense.  NEOs aren’t orbiting earth, they’re orbiting the Sun.  So it makes sense that you would need to do an earth escape maneuver first (3.2km/s right there) plus some more to change your orbit to intersect there, and a final burn to match their orbits and rendezvous.

So where the heck did the 60m/s number come from?  It turns out that the 60m/s number is the delta-V needed to depart the closest of earth-crossing NEOs in a trajectory that intersects with earth’s atmosphere.  If you actually wanted to bring the returning vessel into LEO, unless you have a really good aerobrake you’re talking about at least 3.2km/s just to decelerate from an escape trajectory, and honestly it’s probably the same amount of delta-V to return from an NEO into LEO as it is to depart LEO and rendezvous with the NEO–as it typically is in orbital mechanics.

What this means to me is that the round-trip delta-V’s needed for NEOs, especially for missions that don’t just go directly to reentry, are actually a lot more demanding than I had ever suspected.  Without extensive aerobraking, for a round-trip you’re looking at at least 7.6km/s of delta-V, ie nearly SSTO levels of delta-V.  Even with aerobraking and in-situ propellant production at the NEO, you’re still talking at ~4km/s of delta-V on the outbound leg–which means that with a LOX/LH2 system, only about 1/3 of your LEO mass will even reach the asteroid.  This also makes a propellant depot/transportation node at one of the Earth-Moon L-points look a lot more interesting for missions to NEOs.  The delta-V from L-2 to most of those locations is around 1-2km/s, which means that most of your mass that leaves L-2 will arrive at the destination (about 65-80% for a LOX/LH2 stage, depending on your target).

In summary, I still think that NEOs have their place, and I still think that they do have some transportation advantages compared to going down into the lunar gravity well.   But now that I’ve cleared up my misconception, it looks like actual near-term commercial exploitation of NEOs is not likely going to be any easier than commercial exploitation of the Moon.