Wednesday, April 15, 2015


A Chinook May Soon Capture a Rocket Engine from the Sky

 Because the capture barge thing is not working.

Al - Looks like Elon Musk and his guys at SpaceX Corporation need your help.

It is doable possibly.  Didn't the Air Force use CH-3 Sea King equipped with retrieval systems to snatch early spy drones out of the air after their flight over North Vietnam?  I am not sure what the weight of  the Falcon engine is though.


  1. mike

    Very interesting idea. Would like so see more details, as there are a variety of wrinkles that come to mind, not the least of which would be how they would keep the parachute from being inflated by forward flight and during descent.

  2. Back from life's business

    I have flown my fair share of sling loads that had aerodynamic lift potential. We recovered several Bird Dogs, but spoilers had to be put on the wings to keep them from developing lift. Our unit lost a crew of five when a poorly rigged Bird Dog lost the spoilers and immediately flw up into the rotor system of the Chinook slinging it. I was slinging a C-130 wing segment who's spoiler (mattresses) came lose. The only way to keep the load from flying up was to maintain a slow airspeed and a minimum 300 ft per minute rate of climb. Obviously, all I could do was jettison it into a jungle area.

    OH-23s were particularly unstable sling loads. Had to maintain very slow airspeeds to keep them from rotating and swinging. We tried a drogue chute to get one to "streamline", but that just caused the load to trail, with the chute rising. It was worse when descending.. Thus we had to use very long sling lengths, which just increased lateral instability.

    Whatever mechanism they develop, it will have to not only take normal parachute behavior into account and somehow restrain it, but what to do if the chute restraining system malfunctions.

  3. Musk isn't interested in the parachute snag idea, he wants the entire first stage back. The people who are interested in the parachute idea is the United Launch Alliance, the unholy union of the last two aerospace companies that provided monopoly-based pricing to the US government for the last 20 years.

    A rocket engine is NOT aerodynamic and I think the idea is that the helo would come down from above and capture something on the top of the parachute and the theory is that the weight of the engine would collapse the parachute. I'm also pretty confident that the ULA has NOT thought through the idea or tested it, Al's comments give us plenty of reasons to suspect that the idea would not work well.

    Previous mid-air captures have all been items that were small and light (which would not describe a rocket engine) and the exterior was designed to be captured (which I cannot imagine for a rocket engine).

    Summary of my thinking: Musk is going to land on the barge in the next two attempts and ULA engineers are going to wish the parachute idea had not been publicly mentioned when they go to conferences and other engineers giggle themselves silly asking about how the parachute is working out for them.

  4. Pluto

    I see it as wishful pipedreams as well.

    The longer the sling length, the less stable the load. I would be quite concerned with the total length of the snatch rig, the length of the collapsed chute and the risers. And yes, the chute may very well be collapsed by the weight of the load in level flight or whilst climbing, but the chute will tend to inflate during a descent, introducing additional destabilizing forces between the Helo and the weight of the rocket engine.

    Since the latest incarnation of the Chinook can carry a slingload of about the same weight as the Chinook, you are looking at the load being able to exert the same same force as the aircraft whilst it is swinging. I stopped flying the aircraft well before the 1:1 load to aircraft weight was reached, and I can assure you that an unstable load has a significant effect on aircraft control at even the lower force ratio.

    I guess the engineer types can design a snatch rig that allows enough leeway for eyeballing the snatch. Since the rig would be well behind the cockpit, and visual indicators for depth perception are virtually nil for such a snatch, some kind of instrumentation would be required so that rate of descent can be matched while also closing in on "contact". After all, it will have to be a diving snatch.

    The next issue is airspeed at time of snatch. Below about 20 kts, and the bird is hovering outside of ground effect, which requires more power. The bird is a bit less stable at such airspeeds. In short, a lot of stuff going on at once.

  5. Pluto: My bad on citing Musk. You are right about ULA. And I believe the Russian built RD-180 rocket engine is the one they want snatched during descent. Dimensions and weight below from wikipedia:

    Length 140 in (3.56 m)
    Diameter 124 in (3.15 m)
    Dry weight 12,081 lb (5,480 kg)

    Even with additional weight from tare I assume it should still come in as less weight than half of a Chinook.

    Rate of descent is ???. They would need a monstrous chute or chutes to get the rate down to 22 to 24 ft/sec.

    In any case I believe you are right that Musk and his crew will eventually land the Falcon on a barge. Hasn't he already done it (or a demo of it) on dry land?

  6. mike

    The Gemini capsules weighed in at about 8,300 lbs, and used a single chute. No idea of diameter. However, the greater the diameter, the longer the lines. (I said "risers" incorrectly above).

    23 ft/sec is 1380 ft/min, which is a healthy rate of descent. You would have to line up above the capsule, at a distance, and begin a slow approach, adjusting the Chinook's rate of descent to be within a couple of ft/sec of that of the descending capsule. And, of course, adjust for wind drift of the capsule.

    1. The video of the SpaceX attempts show the rocket comes down FAST, I cannot imagine a parachute being an effective tool in slowing down something that weighs 6 tons to the point where a Chinook could safely snag it without causing other problems.

  7. SpaceX has discovered that doing a successful demo on dry land under controlled circumstances is a LOT different than putting a 200+ foot unbalanced, nearly out of fuel, rocket stage on a barge at sea.

    The first time they ran out of hydraulic fluid at a bad moment (see right hand photo above) and crashed. The most recent landing attempt came close but the computer over-steered and the rocket crashed. Watching the video shows that they are very close to working out the problems.

    Nobody is sure about which rocket engine the ULA wants to eject and re-use. Russian-built rocket engines are not popular in Congress right now and 100% of the ULA business comes from Congress. Jeff Bezos (of fame) claims to have an economical liquid hydrogen rocket engine that will replace the Russian engine in a few years (2019?). But Bezos is well-known in the Aerospace groups as secretive, overly optimistic, and not exactly strong on delivering what he promises. If I were the ULA, I'd want a back-up plan.

  8. Pluto

    They had to slow the various manned capsules enough for the crew to survive splash down. However, the complexities and hazards in snagging a descending, parachute supported load with a helo are enormous, unless it is totally automated, which would be similar to target aquisition in nature. But that still doesn't address post snag difficulties, which, as far as I can see, would not lend themselves to management by automation.

  9. My personal opinion is the rocket body itself is allowed to "land" in the water, but like the Apollo capsules, inflatable balloons pop out the sides keeping the bloody thing afloat and available for retrieval. Thus avoiding the whole challenging the luck of a good Cuisinart pilot with a floppy, entangling length of "fuck-you and your luck!"

    just my opinion.