I got into a discussion the other day about the Blue Origin/SpaceX barge landing issue. I suggested that it was very difficult to write such a comprehensive patent that there was no way to design around the restrictions. As an offhand illustration, I suggested that landing on a hovercraft was unlikely to be covered by a barge landing patent. Being called on it as an idea instead of mere talking point, I did a quick search to refute the point of hovercraft not having the capacity to handle the weight.
The two craft that remembered from TV documentaries I found in minutes. The Marine Corp LCAC is the Landing Craft Air Cushion and is rated for 60-75 tons and 40 knots speed. The operational radius apparently 200 miles. The English channel ferries that were retired after the Chunnel opened for business were rated for 52 cars and 60 mph. It is likely that there are hovercraft in these performance ranges available for sale in the world without having to build your own.
The point I couldn’t address was whether hovercraft of any size would be stable enough for a landing at sea. I didn’t find any definitive source on the relative stability of these vessels compared to anything else. Â In order to raise this thought to at least idea level I decided to assume that they could not be stable enough for the conventional landing we tend to think of.
The idea of any landing is to get the vehicle down without any damage whatsoever. This covers everything from model airplanes and rockets, to airliners, VTVLs, Â and Space Shuttles. Even a hovercraft like the LCAC capable of carrying an Abrahms tank wouldn’t seem to have the excess capacity for a full landing platform capable of landing a rocket stage and securing it against the rolling and pitching from even a fairly mild sea state. Horizontal landings of a serious rocket stage a la aircraft carriers is so absurd as to defy serious thought. Â I came up with the slant landing technique, as demonstrated by Masten Space Systems during the Lunar Lander Challenge.
So Vertical Take off and Slant Landing is VTSL. When Masten was testing vehicles in the Mojave wind, sometimes the vertical landing vehicles would be, I’ve read, leaning 20-40 degrees from the vertical to compensate for the extremely high winds for precision landings. An LCAC at high speed will produce relative winds of as much as 40 knots  (46mph,I think) plus the natural wind component for a total wind across  the deck of 50-70 mph. A stage landing on the fast moving vehicle will be leaning into the wind just as the Masten vehicles did. A net on a pair of pivoting booms could match the angle of the incoming stage to catch it at near zero relative velocity in a three axis capture.
The whole length of the vehicle could be soft netted simultaneously to avoid any ten story structures falling to the deck. As soon as netting secured is confirmed the hydraulics retract to the horizontal for the trip home. Being a hovercraft, the destination is inside the stage integration building instead of the barge dock. It seems likely that the listed 200 mile range of the LCAC is fully loaded with dangerous people and their tools. The hovercraft going for a stage capture could make the trip out with bladder tanks in the cargo area for a massive range extension
johnhare
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Suppose you didn’t elevate the net and left it horizontal, letting the rocket come in vertically, touch on a pair of legs, and then tip over? If need be, you could add a dedicated side-ways facing solid near the top of the stage to help brake the pitch-over prior to hitting the net, or given that you’re catching a cylinder, simply the net into rows of webbing going over pulleys, allowing you to control the force curve on each strap. Either way, you could still be leaning when you touched down, and could probably set it up so that it captures even better if you have a significant horizontal touch-down speed, snagging the landing legs, to aid the tip-over.
Considering the F9 has already had a zero velocity splash down it really should not be that hard to position a vehicle under it. If it could hold the weight of vehicle and a gantry net some tilt would only be needed in the last moments.
The whole thing sounds pretty straight forward and after the first couple of times would probably become quite routine. The velocities after all would be quite low, not like trying to snag it out of the air.
Thinking more about it… the only real problem I see is side to side movement. You would want to get the gantry to horizontal quickly or wind could be a problem.
A moving vehicle after capture would mitigate the wind problem.
Why not have the gantry with 2 clamps such that you motor up to the suspended rocket, the clamps close, there would be a ring on the rocket that would settle on the clamps, light off some airbags to cushion and hold it tight (similar to expanded foam packaging when shipping sensitive hardware), then lay down sally.
We aren’t talking too much weight…1st stage empty is what, 17-20 tons?
How about this totally whacked out idea…have a device similar to a trebuchet that could hook an eye on the top of the stage then hauls the stage in, the pick up would travel much like the dipping stick on an old steam shovel. Far too many moving parts and places to fail….but even though it’s way outside the box it’s food for thought (or a good laugh)
George,
While my concept may not work, yours has added four failure modes that I can see offhand. Long fall, uncontrolled tip over may not hit the net, various pulley issues that must be just right, and adding a sideways solid to the stage.
Ken,
Agree with your points.
Born1930,
It is fun to consider. I prefer simple systems with as few failure modes as possible. The slanted flight into the wind was well demonstrated five years ago by Masten Space Systems. The pivot boom is a variation on the roll off dumpster systems that are used thousands of times a day. Two understood systems on a new platform.
Funny you should mention the LCAC, as there is something similar used as a hover barge of sorts for arctic oil drilling resupply (towed by a CH-47 helicopter at a crazy angle to boot).
If size and performance are issues, perhaps a surface effect ship (SES), a hybrid between a catamaran and a hovercraft? There’s a japanese ship called the TSL Ogasawara that might be going to the ship breakers sometime in the future due to the scrap value of the aluminum. It’s a SES with waterjet propulsion, originally intended as a high speed long distance ferry, powered by somewhat fuel hungry gas turbines.
I doubt it is all that fuel hungry compared to the Falcon 9. 🙂 If the SES could enable the intact return of a stage that would otherwise be lost, I think the scrap value of aluminum would be less significant.
I can see slant landing into a net working, with a few minor catches.
– A larger net provides more available landing area.
– Some give on the net could allow for the net’s/rocket’s motion. Something with near constant static tension + motion damper seems ideal.
– The stage can be expected to roll and slide around some in the net.
– The landing legs as used by the Falcon9r would at best get in the way. Some kind of hook that grabbed the net once the stage was down would be useful, at both ends.
– The net needs to be a material that can handle at least a few seconds of engine exhaust.
– Winglets may be useful.
Winglets would be useful in three phases of the flight if they could be figured out. During ascent the winglets could provide a bit of lift to augment the rocket thrust for the first minute or so. During reentry the winglets could control the whole rocket to an alpha 90 entry (a la Scaled Composites) for maximum drag and minimum heating. At netting the winglets could provide that extra measure of control and fuel economy. It also seems possible that some fairly small winglets could provide a measure of redundancy during the landing/netting phase in case the vehicle ran a bit short of propellant.
This is if it could all be figured out of course.
One word. Velcro.
Last year I wrote quite a bit about the benefits of launching and landing stages when they were oriented horizontally. When a vehicle is well over a hundred feet long, standing it upright is time-consuming, expensive, and makes everything about accessing it difficult. If airliners sat on their tails then every airport would need dozens of VAB’s and crawlers.
For example, if you had an Army requirement for a solid-fueled short or medium range mobile ballistic missile, you could build a trailer that erects the missile vertically prior to launch, or you could just attach a JATO unit slightly forward of the missile’s center of mass and blast the missile 50 or so feet in the air while rotating it within 20 or so degrees of vertical, and then light the main engine, much like a submarine launched ballistic missile wobbling up out of the ocean.
But ignoring the launch (because that infrastructure is already built), you could still land the rocket stage horizontally with little performance penalty other than the dead weight of a few small engines. Three side-facing super Dracos should be sufficient to land a Falcon 9 first stage, and a horizontal orientation would simplify the stability and control problems, allow for short, light weight landing gear, allow for recovery on almost any flat surface in high-wind conditions, and eliminate the need to lower the stage from vertical to horizontal for subsequent transport. You could also more naturally utilize wings and wheels, bringing the design concept full circle to a glide landing on a conventional runway.
John, I think I’ve got it now (closed the business case) and could really use your critique. Click my name, thanks.
Ken,
I still can’t understand the reasoning behind your Mars business case. It still feels like you are picking up a piece of paper, writing “ONE MILLION DOLLARS”, putting it in your pocket, and claiming that you are a millionaire. (Or the legendary three guys on a deserted island who got rich selling each other sea shells.) There’s no business case there.