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. 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, 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. 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
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