How to deal with nose flip when parachutes deployed IRL

[Xavven]

Hi! In KSP career mode, your first craft probably consists of a Mk1 Command Pod, a parachute, and a flea booster, but no stack decoupler. If you notice, the center of mass is actually quite high when the fuel is expended, giving the rocket a tendency to dive nose-first on decent which the parachute in its semi-deployed state cannot counteract.

Thus, if you don't use the (extremely) overpowered reaction wheels on the capsule, you'll end up with this situation:

[img]http://i.imgur.com/8gXMIPO.png[/img]


Followed by this situation:


[img]http://i.imgur.com/PkAjtIB.png[/img]


I can only imagine this is extremely uncomfortable to the occupant. How did engineers deal with this problem in real life?

As an aside, it seems this happens to model rockets, too. I found some videos where the camera is mounted to the rocket, and there always seems to be a violent flip when the parachute opens.

[SargeRho]

Real capsules are built so that they automatically orient themselves with the flat side down.

[Xavven]

[quote name='SargeRho']Real capsules are built so that they automatically orient themselves with the flat side down.[/QUOTE]

Thanks! I get that. Were there no manned flights that lacked a stack decoupler?

[SargeRho]

None that were done with capsules. I believe one Mercury mission reentered with the deorbit motor still attached, because a sensor indicated that the heat shield was loose, but that doesn't really count.

[_Augustus_]

[quote name='SargeRho']None that were done with capsules. I believe one Mercury mission reentered with the deorbit motor still attached, because a sensor indicated that the heat shield was loose, but that doesn't really count.[/QUOTE] Yep. It was actually Friendship 7 xD

[Armchair Rocket Scientist]

The simplest answer: you can't simply "deal with" this problem because it's part of physics. If a vehicle is aerodynamically stable flying nose-first, then it will be travelling nose-first when the parachute deploys, and subsequently have to "flip" around. There are only two ways to "fix" this.

1. Deploy the parachute from somewhere other than the nose, resulting in an "on-its-side" descent attitude. This is similar to the "rogallo wing" concepts for Gemini, as well as ballistic chutes for airplanes. For a capsule, you're lying on your back in normal flight, so with the capsule on its side you're sitting upright. For an airplane, the vehicle is in close to its level flight attitude. You can also deploy the chute from the tail, but for a manned vehicle you'd be hanging upside down for the descent so this is usually avoided.

2. Make the vehicle aerodynamically stable flying tail-first. This is what all "capsule-style" manned spacecraft do: during a normal reentry and descent, when the parachute deploys the spacecraft has already jettisoned the launch vehicle, service module, etc. and is already falling with the heat shield pointing downward.

The only time something like this could come up in manned flight is during a launch abort scenario. In [URL="https://www.youtube.com/watch?v=AMdYAg5mrnU"]this video[/URL] of the DragonRider's pad abort test, when the trunk, which includes fins to keep the vehicle stable nose-first during the LES burn, is jettisoned, the capsule violently flips over, although this is due not to the parachutes but due to it now being stable in a heat-shield-first attitude. The parachute deployment causes additional rocking and swaying. However, while it might be uncomfortable, this is definitely survivable, and would only occur in a launch abort scenario where crew discomfort and minor injuries are acceptable.

[Xavven]

Great! This was just was I was looking for. Thanks for the answers. I did some reading on John Glenn's re-entry and watched that video.

In the end, it seems like a safer bet in KSP to do launchpad "science" first to unlock decouplers before doing a first launch. I know these little green guys can take a lot and don't seem to mind, but I enjoy the design challenge of building something that flies a little more gently.

[Shpaget]

Model rockets eject their parachutes from a mostly intact rocket (even if it's a multistage rocket, the final stage is still aerodynamically stable and wants to fly nose first). The timing for the parachute ejections is most commonly done by delayed fuse in the motor itself, and more sophisticated devices are employed only on larger rockets. This timing is not ideal, because engine manufacturers can't know how your rocket will perform, so they take a guess. Ideally the parachute would deploy at apoapsis, but this blind guess makes it unlikely to happen then.
More advanced hobby rockets use apoapsis detector mechanisms to deploy the chute more accurately, and the jerking is less pronounced.

For KSP, don't put the parachutes on the SRB, put them on the pod, as high as possible.

[Alshain]

[quote name='SargeRho']None that were done with capsules. I believe one Mercury mission reentered with the deorbit motor still attached, because a sensor indicated that the heat shield was loose, but that doesn't really count.[/QUOTE]

I just want to add.. it wasn't. The sensor malfunctioned.

[prophet_01]

If you have something that is not stable at all, like a tall top heavy lander, you could also deploy grid fins at the top of your craft (somewhat similar to air brakes on a plane). The additional drag will help to stabilize you.
Some reusable booster concepts use that kind of thing in combination with a gimbaling engine or a chute to keep a correct orientation during the landing. Edited November 23, 2015 by prophet_01

[magnemoe]

[quote name='Armchair Rocket Scientist']The simplest answer: you can't simply "deal with" this problem because it's part of physics. If a vehicle is aerodynamically stable flying nose-first, then it will be travelling nose-first when the parachute deploys, and subsequently have to "flip" around. There are only two ways to "fix" this.

1. Deploy the parachute from somewhere other than the nose, resulting in an "on-its-side" descent attitude. This is similar to the "rogallo wing" concepts for Gemini, as well as ballistic chutes for airplanes. For a capsule, you're lying on your back in normal flight, so with the capsule on its side you're sitting upright. For an airplane, the vehicle is in close to its level flight attitude. You can also deploy the chute from the tail, but for a manned vehicle you'd be hanging upside down for the descent so this is usually avoided.

2. Make the vehicle aerodynamically stable flying tail-first. This is what all "capsule-style" manned spacecraft do: during a normal reentry and descent, when the parachute deploys the spacecraft has already jettisoned the launch vehicle, service module, etc. and is already falling with the heat shield pointing downward.

The only time something like this could come up in manned flight is during a launch abort scenario. In [URL="https://www.youtube.com/watch?v=AMdYAg5mrnU"]this video[/URL] of the DragonRider's pad abort test, when the trunk, which includes fins to keep the vehicle stable nose-first during the LES burn, is jettisoned, the capsule violently flips over, although this is due not to the parachutes but due to it now being stable in a heat-shield-first attitude. The parachute deployment causes additional rocking and swaying. However, while it might be uncomfortable, this is definitely survivable, and would only occur in a launch abort scenario where crew discomfort and minor injuries are acceptable.[/QUOTE]
This going nose first is mostly an issue with parachute deployment as you risk running into you chute while its deploy.
Dragon uses its trunk to be stable nose first and drop it to rotate, this is also true for the cargo version who now get an software update to perform an abort.