SpaceX recovery vessel Mr Steven officially departed Port of Los Angeles on the evening of July 23 and is speeding towards its first Falcon 9 fairing recovery attempt since a major series of refits and upgrades. With massive new arms and usable net area increased fourfold, chances are better than they’ve ever been for the iconic clawboat to at last snag its first true ‘catch’ of a parasailing payload fairing.
Set to be stationed roughly 900 km (600 mi) southwest of the California coast, Mr Steven’s vast new net should dramatically even the playing field, cutting the effective error margin for each fairing catch attempt by as much as 60% on its own. An extra ~30 meters of net both length and width-wise would functionally act as a cushion for the ~50-meter accuracy the fairings have demonstrated thus far (i.e. halves missed Mr Steven’s smaller, original net by 50 m).
Still, the question remains for many people: how exactly does Mr Steven ‘catch’ a clamshell fairing half, and how does that fairing half find its way to Mr Steven?
A parasail and a prayer
Each Falcon 9 fairing is a two-piece 1600 kg sandwich of carbon fiber composites and aluminum honeycomb, as well as internal dressings of soundproofing panels, cold nitrogen gas thrusters for attitude control in vacuum, and finally the parafoil and control hardware/avionics necessary to safely recover the fragile halves. Stretching 13m long and 5.2m wide (43ft x 17ft), SpaceX has partially worked with contractors already experts in the art of autonomously guiding parasails with payloads up to 10,000 kg (22,000 lb), and doing so with some level of accuracy.
Ultimately, GPS-guided parafoils have been done successfully many times over in the past two or so decades. For the most part, the problems preventing SpaceX from recovering fairings in Mr Steven’s net have been almost entirely solved: the fact that six or more halves have been recovered intact after their Falcon 9 launches confirm that much. SpaceX engineers have somehow found a way to allow a highly flexible, lightweight, and aerodynamically awkward lifting body to survive a journey from heights of 110+ km and speeds of several kilometers per second.
Per the extraordinarily minimalist appearance of each half’s parafoil recovery hardware and the lack of any clear control mechanism, it’s very likely that SpaceX has sided with an in-canopy (canopy=the parachute) system of actuators tasked with subtly warping the parafoil, comparable in functionality to a crude replica of a bird’s wing.
When in doubt, copy birds
Birds fly with such extraordinary precision thanks to granular control surfaces known by most as “feathers”, whereby slightly tweaking the location of feathers or changing the shape of the wing can result in a huge range of behaviors. In-wing actuation and control is an elegant – if complex – solution for the problems posed by parafoil guidance. In this case, SpaceX’s contractor (MMIST) likely deserves at least some of the credit for several nearly successful catch attempts thus far, delivering each unpowered fairing half from an altitude of 110+ kilometers, speeds of more than 2 kilometers per second, and parabolic trajectories stretching over 800 kilometers to a square roughly 100m by 100m.
If each halve’s accuracy can be cut by 75% of that to an area of 50m by 50m, SpaceX and Mr Steven should have no trouble in reliably and routinely catching Falcon 9 payload fairings for rapid reusability, perhaps one day translating into a similar approach for the recovery of Falcon 9’s orbital upper stages and SpaceX’s Crew and Cargo Dragon spacecraft. Mr Steven’s new net upgrade is meant to accomplish exactly that by offering a much larger surface area for Falcon fairings to ‘aim’ at.
By tweaking, pulling, and tensing or loosening any number of those lines with servo motors and actuators, one can very accurately control the flight characteristics of a parafoil. (NASA)
Once the massive 800-kilogram components can be captured in flight by Mr. Steven, it should be a fairly simple prospect for SpaceX to move from recovery to reuse, potentially saving as much as 10% ($6m) of the cost of each Falcon 9 and Falcon Heavy launch in one simple, fell swoop. Perhaps even more importantly, fairing reuse would remove some of the pressure placed on SpaceX’s composite production floor, which currently must support the fabrication of dozens of fairing halves, booster interstages, payload adapters, Falcon Heavy nose cones, and much more, including smaller subassemblies required for both Crew and Cargo Dragons.
BFR is gonna need all the composite design and manufacturing expertise it can get.
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