Rotor Kites as Alternatives to Parachutes

[fatalitymayoccur]

The rotor would be to heavey and complicated to operate, and require a lot of expensive training to operate.That auto rotation trick is not for the first day of piloting. what possible material could do this? You need to deal with a lot of physical stresses to spin something faster enough to auto rotate and you need something heat resistant, those two traits are pretty much opposite. Temperatures would be all over the place, things would be binding or breakling. Those parachutes are very fail safe and redundant. Pop a couple lines tear a hole they still work. One single chip on something spinning this fast and it shatters. The para chute system could be much more effective, if it was used in two stages, the first is like the current system to slow the capsule down, then a much bigger chute lands you softly.

[sgt_flyer]

autorotation is a mandatory skill for any helicopter pilots that want to aquire it's pilot license (planes have gliding, helicopters have autorotation - hence why pilots don't like the things like the V-22 osprey, which are bad in either gliding or autorotation :p).

for autorotation, you basically directly use the rotor as a giant flywheel to store energy (0 torque from the helicopter's engines are applied to it - so you don't even need a working tailrotor)

you can 'store' energy within the rotor by adjusting the blade's pitch, so the airspeed accelerate the blade's rotation, until it's enough to sustain a 'glide' (it's a mix between forward gliding and losing altitude, to maintain the rotor's speed). when nearing the ground, an helicopter will flare, while adjusting it's blade's pitch to 'discharge' all the stored energy to stop forward and vertical motion (only a few meters above ground) - then land on the remaining energy stored in the rotor.

 

advantages for autorotating capsules : you can control where you'll land compared to parachutes (much less drag than giant parachute canopies for the wind to act upon), softer landing

inconvenients : more mechanical parts, (so additionnal potential parts breaking down), if you miss your final flare, things are bad (and as you're only a few meters above ground, there's no time for a backup solution) - and in case of mechanical failure, you still need backup parachutes (hence why dragon V2 will still carry emergency parachutes - in case it's superdracos fail).

 

as for parachutes, those can weight quite a lot. Orion's parachutes weight 300lb each... - not sure an helicopter blade weight this much. (afterwards, you still have the rotor shaft weight to take into account though - and you still need a backup system :p)

 

http://www.space.com/21155-orion-parachute-test.html

[shynung]

There are other things to worry about. Rotor stowage and deployment, for instance.

Also, when the flare fails, solid rockets can be used to lessen the landing stresses, a la Soyuz.

Edited December 9, 2015 by shynung

[AngelLestat]

If spacex (with extra development) would remplace the grid fins by small-medium size autogyro blades, then the guiding would be a lot easier, and you can reduce a lot the braking speed and (corrections) made by the propulsion system.

Then I will like also to see an autogyro system for a dragonv3 capsule in remplacement of the parachutes, then the autogyro would be main option, and if that present fails, then the propulsion method as alternative landing method.

But this tech will take some years of development, because the deployment at big speeds is a challenge.

[shynung]

Why would they do that? A Falcon 9 stage have high thrust engines right underneath. Much simpler to pack more fuel for powered landing. the grid fins are there as control surfaces, not lifting surfaces, which is what autorotating rotors are meant to do.

Also, rotors for Dragon v3 seems unlikely. They already have a SuperDraco engine on the v2 version, no reason to weigh it further.

[sgt_flyer]

well, i guess he would put the rotors as a backup to the superdracos, like how dragonv2 uses parachutes a a backup / landing system in case of abort. 

;

though, for sure, parachutes seems to be a simpler, more reliable backup / abort landing system than the rotor. (the parachutes are still mechanically simpler than a rotor assembly - limiting possible points of failure.

if you're at the point you need a backup emegency landing system, you don't care where you'll land, so long as it can save your life).

besides, one of the possible failure modes of superdracos is the explosion of the engines, even if they installed within a casing capable to deflect  the  blast outwards, you'll still damage the outer hull, which will at least modify the capsule's drag (if not damaging something else also present on the sides of the capsule, like the folded rotors blades)

 

now, one possible usefulness for autorotation as a backup system, is if it can deploy and begin the autorotation descent from a much lower altitude than what the parachutes are capable of (given they need a bit of time to first eject the pilot pararachute, then the main chute, then fully deploy). - though, with the time it the rotor would need to accelerate to store enough energy, i don't think it would be faster  (as rotors on inflight helicopters are already turning at flightspeeds when the problem forcing them to go to autorotation happens after all)

[AngelLestat]

Ok, A lot of misunderstandings..

I meant for a future dragon version (I am not saying they would do that, I said that is the thing I would like to see).
Is not as backup for the draco thrusters.. Is the other way around, the draco thrusters would be the backup for the autogyro.
Because there is no other way of execute a soft and guided landing more reliable and dependable than autogyro.
The weight will be the same than parachutes.. so you remplace the actual parachutes with an autogyro.

About the stage1 booster, if you have short blades, enough to decrease the speed at 10m/s close to the surface "changing the pitch", then it will weight a bit more than normal grid fins, but you also save a lot of fuel that you need to use for guiding and the fuel needed to reduce the 100m/s.
And guiding and landing using rockets is a lot hard than using autogyro. The stage is too long which it makes too hard for a "force" to balance the stage from below than above. 

 

Edited December 10, 2015 by AngelLestat

[shynung]

Parachutes are much simpler than rotor blades. They don't need to be rotating at deployment to function properly, in addition to their deployment being pretty much a set-and-forget affairs. Sure, precision landing is rather difficult, but for a backup system, you'd want it to be extremely reliable, something tricky to do with stuff like deployable rotor blades or rocket engines.

What I'd propose would be this: the capsules have rotor blades as the primary descent control system, with parachutes as backup. The rotor blades contain a fuel line, connected to a monopropellant or hypergolic propellant tank at the capsule, and a small thruster at the tip. This constitutes a tip jet, a type of rotor propulsion system that doesn't need a tail rotor. The tip jets can be used to spin the propeller just after deployment, let it autorotate until final approach, then do a powered landing on tip jet thrust.

Also, F9's self-landing booster has a set of RCS thrusters near the top of the stage, just under the 2nd stage attachment point. At lower speeds, where grid fins have lower effectiveness, these thrusters, along with the stage engine gimbals, does most of the work.

[AngelLestat]

Autogyros are more reliable than parachutes and can face strong winds or turbulence with the mentioned bonus of guiding and soft landing.

You are replacing dracos by rotor blades, so you are losing the great benefic of the escape system which is a 40% or 60%  more light than the tower design, and you dont need to eject that (which contributes in the cost), you can also use that extra deltav in any emergency during orbit.

About rotor blade propulsion, you can have that even with compressed helium, this was being mentioned in the nasa study on this tech. It was not necesary, but increase the safety.
But well, I can not said that rotor blades will be more reliable than parachutes in the capsule or booster escenario, because the tech would be more complicated because it needs a good deployment system, only a good design and time testing will tell, personally is something that for me it will be a pleasure to see, I am tired to see how the world stay in the past just by fear or lack of inventiveness. Of course we can not ask more of Elon musk, he already did a lot, is the time for somebody else to try something new.

The RCS thrusters in the top booster stage just points the inconvenience of landing with a propulsion force from below. Surely you've tried this in KSP, not matter how strong are your tops RCS, once the angle is more than 2 or 4 degress, there is not going back.
Their software can be very good (in time) to ensure  +95% of recoveries, But with the other way would be ensure 100.  

PD: grid fins does not work at low speed, so the final touches are all rockets.

Edited December 10, 2015 by AngelLestat

[SomeGuy123]

Think like an engineer.

Alternative 1 :

  A complex subsystem.  At a minimum, you need folding rotors.  A deployment system (aka a cover to protect the rotors during reentry).  A bearing and hub where the rotors connect.  A system to pop out the rotors and get em spinning.  

All this adds mass.  Lots of mass, lots of big gears and rotor pieces and covers and pyro charges to pop the covers off at the right moment.  

All of this adds engineering complexity.  A small army of engineers will have to design this system.  Then test it.  Then redesign it because the first iteration was bad.  

And finally, in real life, human engineering, there are failure modes that complex systems have that basically no amount of engineering can remove.  No matter how much money you spend, a more complex machine tends to fail more often than a simpler machine.  And this is a very complex machine.

Alternative 2 : 

You make the propellant tanks for your hypergolic propellant thrusters larger.  These tanks are pressurized by helium and to fire the rocket engine, a servo motor opens 2 valves and the propellant flows into the engine chamber.  To turn the engine off you close the valve.  You fire the engines right before touchdown for a soft landing.

Not only is this technology 50 years old, while deployable rotors are not, but it's fundamentally simpler.  I think if you spent the same amount of money working on deployable rotors you could spend making the thrusters better, the thrusters will always be more reliable because there are less pieces and less stuff that has to happen.  

Even if the extra mass of the larger propellant tanks is more than the extra mass of the rotor assembly (seems unlikely but maybe), it's just a little more money to make the rocket bigger.  It's a lot more money to design and manufacture the rotors.

Edited December 10, 2015 by SomeGuy123

[shynung]

Autogyros need at least 2 blades to work, and those blades need to be symmetrical. If any one blade falls off, the vibrations its absence induces would shake the craft apart. A multi-canopy parachute system typical of space reentry capsules still work acceptably even when one or more canopies collapse and cease functioning.

Also, parachutes, by design, are more reliable than rotor blades. All it needs to function are airspeed, and nothing else. Rotor blades need to be rotated in the first place, something tricky to do in the tight confines of a space capsule, and need to be carefully controlled while in operation, lest the blades stall. Parachutes can be left alone after deployment, and it will work perfectly fine.

Edited December 11, 2015 by shynung