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.

Technology Lock-in
One of the most interesting points made in the paper was how often technology can get locked-in by early decisions in a field, often made in situations of very limited data.  As documented in the paper, the engineers developing the Apollo docking  system admitted that “The selection of a docking system for the Apollo Program was based on limited knowledge because experience with actual hardware in space or from ground-based docking simulations was almost nonexistent.”  These early conceptual downselects, in this case with only a few half-scale air-bearing experiments to provide any data at all, often are not revisited in future developments.  This puts us in a situation where hasty decisions made early-on, based more on “engineering judgment” end up getting stuck with for many decades after the fact.   While this paper was focused on rendezvous and docking techniques, there are plenty of other examples of similar technology lock-ins in aerospace and elsewhere in industry.

Illustration of Boom Rendezvous
I found the following illustration, pulled from a NASA presentation given by Kirk Sorensen of MSFC (one of Joseph’s coconspirators on many topics including air launch, MXER tethers, and Thorium Liquid Flouride Reactors), to be the best illustration of the concept:

Much like modern mid-air refueling of helicopters and jets, a low-inertia connection is made at the end of booms extended from both vehicles, instead of trying to actively fly the two vehicles into each other.   In this case, the boom is on the order of 10-100m long, giving plenty of space to avoid collisions while hooking up the booms.

Boom Design Concept

The preferred approach for the extendable boom was to use a system like the Bi-STEM, which has been manufactured by Northrop-Grumman for in-space applications for decades:

The Bi-STEM system is sort of like a pair of tape-measures.  The coils of spring-steel form into arcs as they are spooled out, and their ends are interlocked, creating a tube that can be actively lengthened and shortened using electric motors or the spools.  A polymer tether can be easily run down the center of the assembly, adding greatly to the system’s tensile strength:

The whole assembly can be mounted on a gimbal or a Camfield Joint allowing full 6DOF pointing, using electric actuators.

Advantages

The main advantages of Boom Rendezvous, as detailed in the paper linked to, include:

• Greatly decreased probability of collisions during rendezvous.  Of all the possible rendezvous failures, collisions are the most likely to badly damage one or both vehicles.  Being able to greatly reduce the probability of damage due to failed docking is critical for operations like propellant depots that may require hundreds or thousands of successful docking operations over their lifetime.  With Boom Rendezvous, a missed connection goes from being a serious hazard to being the kind of thing you can easily try again, with the only risk being the ego risk of getting razzed by your fellow astronauts after the fact.
• Greatly reduced propellant requirements for the docking maneuvers.  Instead of the hunting problem often faced in current real-world docking operations, the closing is performed almost entirely by electric motors.
• Elimination of plume impingement problems.  When maneuvering two rocket-powered vehicles close together, impingement of the jets from the maneuvering vehicle on the other vehicle structures can be a severe problem.   Impinging plumes can spall off structural material or contaminate surfaces and optics.  Since all the maneuvering close-in is done using the booms, this is eliminated.
• Much lighter and simpler connection interfaces, since the booms can eliminate any remaining rotational or angular misalignments, and since the booms up close have enough compressive strength that you can very precisely control the final connection loads.  Without those extra loads, you can eliminate the heavy backing plates, shock absorbers, and guide petals common in modern docking adapters.  And without having to have those in the middle, the latching mechanisms, seals, and fluid/electrical connections can be made a lot more straightforwardly.
• Reduced sensor requirements for the rendezvous/docking.  You no longer need to know anywhere near as much about the target vehicle’s velocity and orbit, which allows you to use less sensitive, more robust sensors to make the hookup.
• Less precision required in the initial rendezvous orbit.  This may allow for the upper stage of the launch vehicle to do the rendezvous burn, allowing the payload to be much simpler and “dumber” than your typical modern prox-ops stage (like Dragon or Cygnus).  This will be important for depot operations as well, because the less smarts the tanker has to have, the lower it’s cost can be, and the more space can be left for the actual useful cargo or propellant.

Applications of Boom Rendezvous
While Boom Rendezvous has many benefits compared to the existing probe-and-drogue based docking systems in-use today, it has a few areas where it really shines:

• Rapid Rendezvous situations.  These include MXER tethers, apogee tugs, exo-atmospheric suborbital refueling, and other situations where the vehicle needs to hook-up very quickly.  Trying to do that with the high-inertial close-in maneuvering typical of today’s rendezvous and docking systems is begging for a crash.
• Depots and other space facilities.  The ability to have the actual docking with a depot occur several meters away from sunshields, tanks, and other hardware increases the odds of the depot being able to last long enough to be economically useful.  In fact, it may be possible using Boom Rendezvous for the Tanker/Tankee to offload or onload propellants without ever actually touching the depot itself.
• RLVs.  Most early-generation RLVs are likely going to be rather weight constrained.  By providing a potentially lighter docking system that doesn’t require as many demanding subsystems, more weight can be reserved for payload and recovery systems.
• Space Tugs.  Boom Rendezvous makes it a lot easier to divide the docking up into as many tugs as are necessary for safe operations.  Much like how more than one tug boat can be used when bringing a large oceanliner in to dock.

Concluding Thoughts
Boom Rendezvous and Docking is a rather promising approach that I hope sees more investigation.  The cool thing is that with the advent of suborbital vehicles, this is the kind of system that could be rapidly matured and demonstrated “in-space” for a tiny fraction of what it would cost to do with purely orbital systems.  Hopefully, the changing technological maturation situation provided by reusable suborbital launch vehicles can allow us to finally revisit hasty decisions made during Apollo.

1. Parallel Ascent Air-Launch Glide-forward TSTO with Exo-Atmospheric Refueling.  A crazy idea I’ve been stewing on involving the intersection between air-launched TSTOs, propellant transfer, FLOC, and Boom Rendezvous, and my attempt at making it seem a little less crazy than it sounds.  If it can be made to work, it might allow for fully reusable manned orbital launch off of carrier planes as small as WK2.
2. Boom Rendezvous.  An introduction to a clever rendezvous and docking technique that I think deserves more investigation.
3. Dual Fluid Propellant Depots.  A little more in-depth discussion of my favorite depot concept from my prop depot paper.
4. Refuelable Un-Crasher Stages for Early Lunar Lander Reuse. A discussion of a lunar lander architecture I came up with that leverages propellant depots to enable early reuse of a significant part of the lunar lander system, while still allowing impressive (ie >>ESAS) landing capabilities.
5. The Slings and Arrows of Outrageous Lunar Transportation Schemes.  A discussion of several of the non-rocket methods for getting payloads off of (and in some cases back onto) the Moon.  Including pro’s, con’s, and technology hurdles.

Not too much yet on the why’s, but I’ve been keeping these how’s bottled up for too long.  Which of these sounds most interesting to you guys?  In the comments, pick your favorite one or two, and say why.

I’ve been so busy lately that I’m only now getting a few spare minutes to show off some rather cool pictures I was sent a week ago.  A week ago Monday, I got an email from Claire Flanagan of the Johannesburg Planetarium in South Africa, asking about some strange pictures, including the one taken above by Mitchell Krog of Livingcanvas.co.za (check out some of his nature photographs–they’re breathtaking!). She had reason to believe that these bubbles had something to do with last week’s Atlas-V DMSP launch.

This was the launch I mentioned in my propellant depot paper, where after delivering the spacecraft they did a series of cryo-fluid management tests, including several tests on centrifugal propellant settling. BTW, I hear they got some good data from the tests, but I’ll let the ULA guys speak for themselves once the data is fully analyzed.

Anyhow, after helping the Johannesburg Planetarium gals/guys get in contact with ULA, they were (with Case Rijsdijk’s help) able to resolve the mystery. But I’ll let you read what Case and the Planetarium had to say about it, instead of just repeating it.

Kudos to Mitchell and Claire for letting me post some of the pictures and links.

First, the propellant depot paper I keep talking about: AIAA 2009-6756 Near-Term Propellant Depots: Implementation of a Critical Spacefaring Technology (also available on the ULA publications page), and the presentation that went along with it: SPACE 2009 Prop Depot Paper Presentation.

For those who’ve read most of the rest of my posts on propellant depots, there’s only a few key new concepts:

• The Single-Launch Dual-Fluid Depot concept that Frank Zegler and myself both independently came up with this year (which I’ll go into more in a later blog post).  This idea holds a lot of promise because it shows how a single EELV launch with existing fairing sizes can put up a depot capable of storing 75-114mT of LOX/LH2.
• The realization that unless you have some sort of high-Isp or propellantless propulsion system (like an ED tether) for stationkeeping purposes, that Zero-Boiloff storage might not be very useful for an LEO depot.  The amount of propellant you lose to boiloff is less than the amount you would’ve spent for stationkeeping anyway, so it’s effectively free.
• The realization that LEO depots really ought to be treated as “use-it-or-lose-it”, high-throughput depots, and that its L1/L2 depots that should be used for longer-term storage.

I had been avoiding discussion of the dual-fluid depot concept for a while, mostly so I wouldn’t be stealing my own thunder.  Now that the paper is presented and out in the public, I hope to have the time soon to discuss the concept a bit.  I also have some space transportation architecture ideas using that depot concept that I may flesh out a bit either here on the blog or in some white papers (which I’ll post on the blog).

The second paper, which was mostly written by Robert Frampton of Boeing talks about a project to use our XA-0.2 vehicle as a testbed for demonstrating autonomous landing systems for planetary landers: AIAA-2009-6571 Planetary Lander Dynamic Model for GN&C

I’m not really sure what I’m allowed to say about the project that isn’t spelled-out in the paper, but I figured I’d bring it to people’s attention, and hopefully at some point in the future I can discuss things more on the MSS blog.

Depot-Centric Human Spaceflight: Strengthening American Industry, Creating a Robust Beyond-LEO Exploration Program, and Enabling the Commercial Development of Space

Anyhow, Jeff managed in 25 minutes to address human rating, depots, whether or not we need heavy lift, technology maturation and R&T investment, and the need for NASA to find new ways to interact with business. I don’t think he could have hit more of my hot-button issues in 25 minutes if he had tried.

Anyhow, I hear that the HSF committee will have video of today’s proceedings up online soon (possibly tonight) for those who didn’t get up at 5:30am PDT to watch. I’ll comment more later.

Whew! I haven’t had this much hope for this nation’s space program in years!

[Update:  Here's the link to the subgroup's presentation (warning, it's a 14MB powerpoint presentation).  All of it is interesting, but Jeff's part starts on page 76 and goes through page 89.  Chris Chyba's section was the last three pages.]