Orbital Access Methodologies Part II: The Key Challenge of TSTO RLVs

Before I go into detail on any of the two stage to orbit (TSTO for the uninitiated) approaches that I mentioned in my post last week, I’d like to briefly discuss what I think is the key issue that drives the design and development tradeoffs for reusable TSTO launch vehicles. That issue is: how do you get the first stage back after a mission, and ready to fly again?

This article will focus on the key tradeoff that stems from this question: whether to try and recover the first stage downrange, or whether to try and perform some sort of return to launch site maneuver. The answer to this question is probably the number one driver of what approach one takes for developing a TSTO vehicle.

RTLS vs. Downrange Recovery
As I pointed out in my brief discussion about SSTO vs. TSTO approaches in Part I of this series, attaining orbit is mostly about building up a lot of horizontal velocity, and only a little bit about gaining vertical altitude. For performance optimized TSTO ELVs, the first stage often imparts a significant portion of the overall delta-V (especially for ELVs delivering satellites to GTO or GSO). This means that it ends up coming in hot, fast, and a long way downrange from the original launch site. Now, there are several different approaches to deal with this problem (or avoid it altogether).

One option is to just let the stage come down where it wants to, and recover it downrange. Downrange recovery can take several forms including recovering a stage out of the ocean after a splashdown, landing the stage at a downrange site and ferrying it back (either by rocket flight, a carrier plane, or by truck, train, or barge), or it could involve mid-air recovery of part or all of the first stage. While downrange recovery may is the general approach that probably imposes the smallest performance penalty, each of the actual approaches to down-range recovery have some pluses and minuses.

Splashdown Recovery
Let’s take splashdown recovery first. Falcon-1 is an example of the splashdown recovery. The stage separates where a typical ELV would want to have a staging event, and then (hopefully) it’s fished out of the ocean and refurbished for reuse. Some of the benefits of splashdown recovery:

  1. Splashdown recovery is probably one of the easiest and best understood methods for recovering a traditional ELV-like first stage.
  2. There’s a large experience base to use as a foundation for carrying out such a design.
  3. Even if your flight rate is low enough that it isn’t saving you much money, you’re still able to learn a lot from being able to perform post-flight inspection on the propulsion hardware. Thus, even if you aren’t flying enough to save a lot of money via recovery, it will help your reliability.
  4. Ocean splashdowns don’t require anywhere near as heavy of recovery equipment as land parachute landings.

But they also have several drawbacks:

  1. Trying to make a complicated rocket engine sea-water compatible, especially a turbopump-fed rocket engine, is not a trivial task. Material selection, and getting the stage out of the salt water (and cleaned out) as quick as possible are all required.
  2. There’s a lot of time and labor involved in hauling the stage back, cleaning it out, making sure nothing got damaged on reentry or splashdown, testing everything to make sure it’s still in working order, etc. This fundamentally limits how frequently you can refly a given stage. It also translates into a lot of extra personnel and labor-hours required above and beyond what you would normally need to just build, test, and fly an expendable vehicle.
  3. The wear and tear from ocean recovery, splash down, etc. are likely going to limit the number of reflights you can get on a stage or engine before major overhaul or outright replacement.
  4. Your potential launch sites are limited, since you need a large body of water on which you can drop big heavy hardware. Most likely (for US entities) that means flying out of one of the existing ranges like Wallops, Vandenberg, or Canaveral. These locations, while excellent for flying missiles, and while also improving their commercial friendliness over time, are still a long way from the environment you want to be operating a reusable launch vehicle out of.
  5. While it’s possible to design a launch vehicle splashdown recovery first stage in such a way that a first stage failure doesn’t necessarily imply the loss of your cargo, it is much harder to design such systems for graceful abort modes. Unless the upper stage is also designed for splashdown recovery (with the payload designed for it as well), a stage failure probably will result in loss of payload. This loses you one of the big potential advantages of reusability–graceful and intact aborts.

Mid-Air Recovery
The idea behind mid-air recovery is that instead of allowing the stage to crash down into the water, you instead snatch it (or a high-value part of it) out of the air using a helicopter or other sort of aircraft aircraft. This is similar to how Genesis was supposed to be recovered, and was the method used for recovering a lot of the film capsules from early spysats. There are actual serious players looking at this idea, but I don’t know if it’s supposed to be public knowledge yet, so that will have to be a post for another day. There was also a paper floating around by a company that does mid-air recovery work, including work for the SpaceHab ARCTUS project. If I can dig it up again, I’ll probably post about that as well.

Anyhow, here are some of the benefits of mid-air recovery:

  1. No salt water contamination in the rocket hardware! This greatly cuts down on the amount of work that needs to be done to turn a stage around. No need for decontamination. No need for stripping down hardware. Probably eliminates the need to “requalify” the propulsion system before reflight.
  2. Gentle, low-shock recovery is much less likely to damage stage or propulsion hardware, also making it more likely that the hardware can just be reused after some inspection.
  3. There are companies that specialize in this sort of thing, and you can just rent their services instead of trying to do this in-house. They aren’t cheap, but they’re a lot cheaper than building a new stage every time.
  4. Your propulsion system is going to be in about as close to the same condition as it was when the engine shut down as you’ll get for any recovery technique–this makes it a lot easier to get good reliable data on wear-and-tear on the engine, so you can improve the quality over time.

But here are some of the challenges:

  1. Complex recovery technique. Sure, you can practice it a whole lot for not too much money, but there is some increased risk of failing with the rendezvous or recovery operations, which could occasionally cost you a stage.
  2. Weight limits. Even with the latest techniques, which can recover payloads up to 80% of the maximum cargo capacity of the helicopters, you’re still limited to around 22klb or less. Depending on the size of your stage, this may mean that you can only recover part of the stage (like say the engines). That’ll still likely save at least some money, but it’s not as big of a win as getting the whole stage back intact.
  3. There may also be issues with trying to recover a big, but fluffy stage. Depending on the weight distribution, there could be some real oscillation issues (like what happened when they tried to move the Roton ATV under helicopter).
  4. Range issues. Depending on how far downrange your stage comes back, you might need to also rent not just a helicopter, but some sort of barge to operate the helicopter off of. This will increase the amount of time it takes to turn a stage compared to if you could just fly it back.
  5. Like with splashdown recovery, this method of recovery still doesn’t give you graceful and intact recovery methods in the case of a first-stage failure. With dump valves and two helicopters, and a mid-air recoverable upper stage, you might be able to recover the payload over part of the trajectory, but you’ll still have zones where a failure means sure loss of the payload (or a launch escape abort if you’re flying people). It isn’t a showstopper, but it does reduce the upside somewhat.
  6. Due to challenges #1 and #5, you probably still need to launch out over the ocean, which means that once again you’re still going to face the issue of launching out of an existing missile range. Basically, since there’s a chance you could biff the in-air recovery, you have to do this over an unpopulated area. And since your vehicle doesn’t likely have graceful failure modes, it’s more like an existing ELV than a more traditional RLV, and will probably be treated as such by the FAA and the ranges. Not a showstopper either, and it might just be possible to pull this off with an over-land launch if you can find a sufficiently deserted area, but definitely a challenge.

Mid-air recovery is probably too weight constrained for something like a complete (but dry) Falcon IX first stage, but might be an interesting option for recovering the Falcon IX upper stage or the Falcon I first stage. It’d also probably be just the right size for recovering the first stage if they hadn’t canceled the Falcon V. Other than the weight limit, there’s some real benefits of this approach over the traditional splashdown technique.

Downrange On-Land Recovery
This type of recovery can take several forms. It could be a powered VTVL landing at a downrange pad. It could be a powered or glide landing for a HTHL. It could be a parachute and airbags landing (like Kistler, just downrange). But basically you have the thing land, on the land, downrange, and then fly the thing back, or ship it back.

Here are some of the benefits:

  1. Much more efficient, performance-wise, than any of the RTLS approaches. You can still stage at the most optimal staging velocity, therefore making your upper stage design a lot easier. You also get a lot more payload per given takeoff (and dry) mass.
  2. At least some of the RTLS approaches can also sometimes use this as a performance enhancing option–in case you need to launch a bigger payload than you can handle with a normal RTLS trajectory.
  3. Unlike mid-air recovery, this recovery approach can scale up to fairly large sizes.
  4. In emergency cases for RTLS approaches, you may want to be able to land your vehicle at alternative downrange sites anyway.
  5. Unlike the other two downrange recovery options, this option is a lot more compatible with intact and graceful aborts.

And here are some of the challenges:

  1. A given launch site will typically have its launch azimuths (directions in which you can launch) restricted a lot more for downrange land recovery than it will for an RTLS vehicle. This is because you need to have a suitable place downrange where you can actually land. This makes downrange recovery vehicles less flexible than RTLS capable vehicles.
  2. You need facilities at both ends, especially if you intend to fly the stage back after landing.
    This may entail having almost as many launch support people at the downrange site as at the initial site, which greatly increases the fixed costs of such a system. Probably not quite double (since you don’t have payload processing facilities there), but it’s a non-trivial expense.
  3. If you do a rocket powered return, you’ve now effectively halved both your flight rate (as you have to do two launches, two landings, two ground preps, etc. per a single paying flight), and halved the number of revenue generating flights you can get out of a given airframe. Both of these directly affect the bottom line.
  4. If the return flight is a rocket-powered suborbital flight (as per AST’s definitions), I think that each of your downrange sites will need to be an FAA licensed launch site, and you will need launch licenses for all of the return flights. Now, once you have one launch license to base things off of, getting additional ones should be easier, but its still extra paperwork. Also, your Ec and MPL calculations are going to be different for the return flight, because your IIP will move at different rates over different areas under your groundtrack for the two trajectories (not to mention mission-critical operations will occur with your IIP over a different location). All of this stuff has to be taken into account.
  5. If you have a jet powered return (either using a carrier aircraft, or if the stage has built-in jet engines), you now need to deal with the aircraft side of FAA, which may entail getting the vehicle type-certified. I’m not certain, but having a vehicle that operates under both regimes is likely going to make things a lot harder, not easier. Being unusual is not a virtue when dealing with regulators. If you’re using an existing carrier craft, that’ll make things easier however, as it is purely a subsonic aircraft, and thus a lot closer to what FAA is used to dealing with.
  6. If you try to return the stage via trucking or train, now the stage has to be “roadable”. Which means making it skinny enough to fit on existing transports. While this may be feasible for some smaller, dense-propellant RLV stages (after all I think that Falcon IX is roadable), it is a constraint on the size of stage. And the aspect ratio roadability forces you into is not as ideal for VTVL stages. VTVL stages want to be shorter and squater than typical rocket stages.
  7. If you return the stage via trucking or train, you now need heavy moving equipment at any downrange sites, experienced heavy equipment personnel there, and it’s going to cost you a lot of extra time. All of these things add cost, and slow down your turn time.

Conclusions: The Case for RTLS
Now, I probably ought to clarify something. I don’t think any of these downrange recovery ideas are stupid. If done right, they can save a lot of money compared to a purely expendable system, while also increasing reliability by allowing for post-flight inspections and the like. Especially with the downrange land-landing techniques, you can get all of the benefits of traditional RLVs.

In other words, while there are some challenges with downrange recovery, there are often some real benefits. There are some cases where using these downrange recovery approaches really is the best choice. SpaceX and the others looking at these approaches aren’t being foolish by pursuing them. I just think that the inherent limitations of this sort of reuse (especially the first two options–splashdown and mid-air recovery) will probably prevent it from being a revolutionary as opposed to a modest, evolutionary improvement over a purely ELV approach. Now, in the near to medium term, even when RLVs first start flying, they’ll likely be relatively quite small compared to the EELVs (for reasons I’ll go into in a later post). Which means that approaches that allow existing ELVs to become somewhat more reusable, and improve their economics somewhat are actually useful. I think that while small RLVs will bump ELVs out of the people, light cargo, and propellant markets very quickly after they enter the field, there’ll still be payloads that are too big for RLVs that are small enough to be economically viable in the near-to-medium term. The ULA’s, SpaceX’s, and Sea Launch’s of the world will still have a useful role to play for some time yet. Particularly for launching bigger payloads like Bigelow stations, transfer stages, etc. So, having ways to improve them is good, even if they aren’t necessarily going to change the world all by themselves.

As for the last options–land recovery downrange, it actually does have the potential to be revolutionary. But the approach still has some serious economic and regulatory drawbacks that are sufficient to make one start looking at RTLS approaches, even though they may be less optimal from a purely performance-based standpoint. There are four primary (and one somewhat oddball) RTLS techniques/trajectories: pop-up, glideback, boostback, flyback, and once around return. Of these five approaches, the most well known (until recently) and thus most thoroughly studied is the flyback approach. However, the first three are the ones (pop-up, glideback, and boostback) that I think are the most promising and relevant to near-term orbital RLV endeavors, and thus will get the bulk of my focus for the remainder of this series (Parts III-V). But I’ll probably spill a few electrons discussing the last two as well. They are interesting after all.

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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22 Responses to Orbital Access Methodologies Part II: The Key Challenge of TSTO RLVs

  1. redneck says:

    One thing that sort of works with two of your posts is air launching with down range recovery at your main base. Not new of course. Fly some distance uprange to launch downrange toward your base with TSTO first stage recovery at home. Even a modest boost from a few hundred miles has major payload benifits compared to even air launched SSTO.

    Sea Launch could use this also. I think this is the same two base thing you said in the post except the launch position would be the minor base instead of the major one.

    If you investigate integrating the FLOC concept as well, air launch of really massive payloads might be feasible, on paper.

    As a really crazy scheme then, two aircraft fly several hundred miles uprange. They launch two TSTO vehicles, which impart a few thousand m/s to the uppers before doing a first stage recovery at base. During first stage boost, they keep close and the uppers dock after staging for FLOC fuel sharing. The drained upper becomes the only long downrange recoverable asset. It will be much smaller than a first stage and easier to transport home.

    I’m glad I don’t have a paycheck riding on my hobby class ramblings.

  2. Mike Puckett says:

    I wonder if there are any potential sites where a recovery from a fresh water lake would be possible?

  3. redneck says:

    If the recovery downrange is an air catch, then glider tow back might mitigate the mass limits. I would assume that a reasonable amount of lifting surface on the recovered stage would allow tow back by an aircraft not much larger than the stage.

    How much experience is there on mid air towline catching by gliders?

  4. Anonymous says:

    RTLS with ram-air canopy ala X-38 ? Being a sports skydiver, i trust my life to these parachutes quite often. With trash pack jobs like we often do, we still achieve about one in 1000 reserve rides. Packed properly, like reserves, they basically always operate.

    Nevertheless, the numbers wont probably add up at all for glide back landing. How about … adding a bit of propulsion ? A huge motored paraglider, bringing back your stage ..
    probably in the crazy land, but hey …

  5. Anonymous says:

    I, like many of you, have watched the stage separation of Saturn Vs. There seems to be a lot of damage to the lower stage when the next stage engine ignites. Not an issue on ELVs.
    To make the RLV stage work, it seems to need to be a) strong enough to withstand these forces/heat imposed – more mass/thermal shielding? or b) wait until a sufficient gap has occurred between stages to not get hit by the 2nd stage engine – how much velocity will be lost while this happens/how long do you wait?
    Would the additional mass/features/launch profile effect the RLV to an extent to offset any benefit of returned stage. At best you get a returned stage ready for launch after inspection but with reduced launch capability due to the additional strengthening/shielding, at worst you only get the bottom part (engines etc.) to reuse.

    I suppose one you has the landing legs/air bags/airbreathing engines/additional fuel for vertical landing/parachutes or whatever for you preferred approach – the additional mass etc to survive separation is not considerable.

    Thoughts?

    Andy

  6. gravity loss says:

    Nice stuff!

    Air catch could be an aircraft towing a ram air parawing, it doesn’t have to be a capture and carry. đŸ™‚
    The aircraft has to be very slow though.
    Parachutes have advanced massively in the last 30 years thanks to some crazy American and French adventure guys I guess.

    The Arctus team already did a subscale parawing helicopter capture test.
    Check the bottom here for video:
    http://www.arctus-spacecraft.com/media.htm

    Parawing is nice since you can chase it, it doesn’t fly straight down like a parachute. Hence the catch velocity difference and shock should be much less. Also low sink rate because it flies forward and has lift and not just drag. You can even flare.

    Incidentally I just read about Energia’s booster recovery.
    http://www.buran-energia.com/energia/energia-consti-1eretage.php
    nose forward re-entry with drag chute, then a normal parachute and landing skids for horizontal attitude touchdown! A retro motor in the chute line.

  7. Jon Goff says:

    John,
    One thing that sort of works with two of your posts is air launching with down range recovery at your main base. Not new of course. Fly some distance uprange to launch downrange toward your base with TSTO first stage recovery at home. Even a modest boost from a few hundred miles has major payload benefits compared to even air launched SSTO.

    D’oh! I can’t believe I missed that one. Yeah, that makes a lot of sense. You get all of the performance benefits of air launch, all the performance benefits of TSTO, and all of the operational benefits of RTLS…Not to mention, if the upper stage has a failure early in its burn (or right at separation), it will also be coming back right near your launch site.

    Methinks I need to add *another* part to my series.

    ~Jon

  8. Jon Goff says:

    Mike,
    Possibly, but then you’re really limiting your vehicle’s flexibility. I’ll go into this later, but basically I’m shooting for a booster that you could sell a couple dozen of, and have operated all over the world–not just in one or two corner case locations.

    ~Jon

  9. Jon Goff says:

    Gravity Loss,
    I’m not sure if the trick used for ARCTUS could easily be adaptable for a fixed-wing aircraft. As you point out, the stall speed would have to be really low, and you still have to find a way to get the stage to the ground at the end of the flight (unless your slow-flying aircraft can also reel the stage into its cargo bay…).

    There are probably ways around the 22klb limit, but I’m not really the guy to ask about it.

    ~Jon

  10. gravity loss says:

    True, if the stage is of decent size, the towing only helps with the down range part, not the landing…
    At which point it starts to resemble flyback.

  11. RĂ¼diger Klaehn says:

    I think that launch from a coast and powered vertical landing on a barge in the ocean would be a good idea.

    Of course you can not reach the barge if there is a total propulsion failure in the middle of the flight, but that is what redundant engines are for.

    Even when 1000km out, a barge could be towed back to the launch site in a day or so, assuming a tow speed of 25knots. You could check out and refuel the craft while it is being towed back.

    You would be limited to one launch per day. But for the time being that is quite a good flight rate.

    For smaller, high frequency payloads you could always fly a RTLS maneuver with your first stage. In fact, it might be best to start with a VTVL TSTO that does a RTLS maneuver, and use the barge when you need to double the payload for a space station once the system is reliable.

    regards,

    RĂ¼diger

  12. Iain McClatchie says:

    Jon,

    A CH-53E can lift 32,000 pounds: http://en.wikipedia.org/wiki/CH-53E_Super_Stallion

    Presumably it can generate a fair fraction of that lift as forward force.

    A paraglider has an L/D ratio of 8:1 or more: http://en.wikipedia.org/wiki/Paragliding

    If the CH-53E pulls with 20,000 pounds of force, and the wing is good for 8:1, that’s 160,000 pounds lifted. Incredibly, that’s only half of an empty Saturn 1C! It is, however, sufficient to move an empty Falcon 9 first stage, or one or even three empty Atlas V first stages.

    It seems like a big problem with mid-air recovery is that you must get the stage into a fairly small area to rendezvous with the helicopter/plane. If you have an engine-out abort, it might be hard to arrive in the same area as you would with a normal flight. Perhaps if the normal flight glides back towards base some amount.

    But this is getting into the RTLS flyback approach, which you will cover in your next post. I’m looking forward to it.

  13. Anonymous says:

    Parawing has still the advantage of being remotely steerable, so if you fail to catch, you can choose over which barn to land, to reduce liability issues.
    Parawing does not have the center of gravity shift issues that are the achilles heel of VTHL booster ideas, like shuttle flyback liquids.
    Iain, the parawing of this size will have its own significant mass to lift as well, so you gotta add some there.
    And flying with two ( some redundancy ) at both ends of the booster is also doable.

    Of course, packing one would be a b*tch, i hate packing even tandem canopies đŸ™‚

  14. gravity loss says:

    And we’re getting close to my favored approach: a subsonic flyback with a parawing.
    The rocket body can be suspended vertically or any way.

    It needs a small turboprop or jet engine to haul it back (can use rocket fuel). Speed is not essential. If it flies high enough, it is not weather sensitive except at landing.

    There are huge problems of course: the authorities don’t want a big unmanned (although it could be manned as well) parawing dangling a rocket stage flying in their airspace. And how is the final landing done? Some gears and feet are needed, which have mass and even if the stage is vertical in flight, it’s probable that it must be landed horizontally if it’s a thin cylinder by any measure. The interaction of the canopy, the lines, the rocket and the ground is not entirely simple.
    And what happens in gusty or crosswind landing? If the thrust is small and the parawing big, there can be real problems…

  15. Karl Hallowell says:

    I think the distinction between “revolution” and “evolution” is unhealthy here. IMHO, there’s a lot of room for the latter. For example, one can gradually reuse more and more of a launch vehicle as its launch rate increases and the economics start to favor reusability. A revolution on the other hand may fail simply because the business isn’t there to support the revolution.

    For example, someone pointed me to an extremely ambitious launch vehicle design called the Rombus. Basically, it was a huge reusable SSTO with 450 ton payload using 1960’s technology. Would have been revolutionary, if someone had built it. But no market exists for 450 tons to orbit at a frequency and price that would justify such a monster.

  16. Anonymous says:

    ::Some gears and feet are needed, which have mass and even if the stage is vertical in flight

    The simplest solution would be to hang it upside down, so that the expensive parts are up, and have a replaceable crush structure at the other end. Not really reuseable but probably good enough for any near term flight rate.

    But note that parawings flare, and can flare very well. With well tuned automatic landing system you can probably land without any significant vertical or horizontal velocity. Deployed skids could be enough.

  17. Randy Campbell says:

    Jon;

    Great series I’m looking forward to the next article!
    (Are we ‘done’ yet? :O)

    Seriously, I wanted to mention an air-launch idea I hadn’t seen yet, (still making my way through the comments…half the time I can’t check out your blog from work… other times I can… damn government filters) Chair-Force mentioned on his blog the Air-Launch methods study done a number of years ago, which I recall having its own method called “SwiftLaunch” which is carried by a large cargo aircraft such as a C5 or AN-225 which I was hopeing to get your comments on?

    Secondly, I noted that Mike Puckett asked:
    >I wonder if there are any
    >potential sites where a recovery
    >from a fresh water lake would be
    >possible?

    I’d think the ram-air/parawing chute would allow that given the right launch azmiths?
    While it might be more resrictive in landing sites, it would certianly give Minnisota a “leg-up” for an actual spaceport :o)

    I know that ROTON turned a lot of folks off to the idea of rotor recovery, but having read a study on a concept for rotor-recovery for the CEV capsule (using sub-sonic deployed extending blades) I’m wondering what the pros/cons of the idea really are?

    I’m personally anticipating the discussion on the idea of “once-around” RTLS booster return. I found an ESA paper on the concept of a first stage rocket plane that used skip-glide with external burning of fuel during the deeper parts of the skip to extend what is basiclly a Mach-12 to 18 speed of seperation (for the second stage) into a once-around-the-Earth RTLS 90 minute flight.
    (Mentioned is the fact that such a flight carrying passengers would be a HUGE hit for space tourism folks which is true :o)

    I’m also curious on your take on the concept of “Stage-and-a-half” to orbit such as the “Neptune” concept? Something along the lines of a “plug-nozzle” main engine section that is ‘staged’ and lands down range, especially combined with any of the above ideas seems to be feasible but I’m not a rocket engineer :o)

    Keep up the good work!

    Randy

  18. Anonymous says:

    my prediction: Jon is going to take a break from the orbital access methodologies discussion and sit speechless for a few weeks, because Mike Griffin just gave a speech about how ESAS was conceived.
    PDF link here.

    And oh my, its a riot. The common sense and logical conclusions thrown around in there ..

  19. redneck says:

    >>>>>Anonymous said…
    my prediction: Jon is going to take a break from the orbital access methodologies discussion and sit speechless for a few weeks, because Mike Griffin just gave a speech about how ESAS was conceived.
    PDF link here.

    And oh my, its a riot. The common sense and logical conclusions thrown around in there < <<<< He took a left turn about page 7, but I didn’t start screaming at the moniter until page 17. In my experience, people that constantly invoke common sense have the least of it.

  20. Anonymous says:

    On the subject of parachutes, have you checked into using a hemisflow hypersonic parachute to reduce reentry loads?

    For some reason Google isn’t recognizing my password, so I’m posting anonymously.

    stickmaker@usa.net

  21. Pingback: Selenian Boondocks » Blog Archive » Partial Rocket Reuse Using Mid-Air Recovery: A Review

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