h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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Certain flying vehicles use rocket assisted braking. It
works. Other vehicles should benefit the same way.
- Jet assisted emergency braking for trains
- Jet assisted emergency braking for cars
- Jet assisted emergency braking for ships
- Jet assisted emergency braking for gliders
-
Jet assisted emergency braking for commercial
airliners.
- Jet assisted emergency braking for helicopters
- Anything that moves and carries passengers could
potentially benefit
The simplest example is a train. When the conductor
presses a big red "emergency stop button" a massive
rocket mounted to the roof of the train fires in the
opposite direction of the train's motion. It will safely
stop
the train before slamming into a line of gravel filled
wagons that accidentally detached from a previous
freight
train.
The toughest example (but most impressive) will be
something like a helicopter. Imagine that the
helicopter's
blade breaks off as a result of manufacturing defect.
The
helicopter loses all control and comes tumbling down as
hard as a sack of bricks. The helicopter is equipped with
6
rockets (up,down,left,right,forward,back). The onboard
computer looks at velocity, distance to ground, and
orientation to determine which combination of these
rockets should be fired seconds before impact. Instead
of
impacting the ground at 300 KM/h it will impact at a
more
reasonable 30 KM/h. With more than 6 rockets (or
steerable rocket), there is a potential for gentle 1 KM/h
landing. (Think moon landing)
How to stop a train by firing AK-47 rounds at it.
http://what-if.xkcd.com/18/
Not quite the same as the problem expressed in this idea, but similar. [hippo, Apr 16 2014]
C130 JATO braking
http://youtu.be/fSFjhWw4DNo?t=1m25s
[DIYMatt, Apr 16 2014]
similar version....except where it is different.
Vertical_20thrust_20braking
[Ling, Apr 17 2014]
Here's what happens when you try this...
http://www.military...sters/912500478001/
The fun begins at 2:00 and gets really good at 2:20 [normzone, Apr 17 2014]
[link]
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How big would that train rocket have to be? |
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Passenger train with 10 cars will weight roughtly
800,000 kg. Let's say it's only got 50 km/h
momentum left before coming to a stop. That's 12
m/s. 800,000 kg * 12 m/s = 9,600,000 Ns. That is a
class X motor. Same as they use on the space
shuttle. Ok so that won't be very practical, but it
would sure be cool to see in action. |
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Car might work bit better. Mass is 2000 kg. Let's
say it's speed is 70 km/h. That is roughly 38,000
Ns. Which is a Class O rocket motor. These
weight only ~150 kg and can be had by amateurs
without FAA license. |
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There's also the problem that in order to not make
the stop worse than the crash, the rocket has to be
mounted onto the last car in the train, which will
result in the rocket wash hitting the entire train. |
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I seem to remember covering it here, but you're
actually better off mounting the rockets vertically
(driving down), increasing the normal force on the
wheels and thus the stopping power of the existing
brakes. |
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Yes, a space shuttle sized rocket slamming into
another object would make a pretty big boom. Why
not mount more emergency rockets on it and eject it
into a nearby field if it doesn't do it's job in time?
Sure, it's a Rube Goldberg approach but with enough
engineering we'll get the kinks out (eventually) |
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//rockets should be fired seconds before impact//
No no no. You want the rockets to be firing as soon as an imminent impact is detected - longer deceleration means smaller forces. If you use a short, powerful, "last second" rocket blast, it's just the same as the impact, only earlier, and it roasts the "target" too. |
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Ah, the theory of unintended consequences. I personally think it would be pretty funny to obliterate the object you were about to crash into with your superheated plume of retro-rocket exhaust gasses. You would likely ablate away most of the offending object during the firing of your retro-rocket. |
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A couple hundred tonnes of APCP exhaust at 5000 or so metres a second is about as close to a death ray as I could imagine. |
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Next up - advanced ceramic armour and carbon-carbon composites for cars and trucks to protect against "safety" devices. I wonder what's worse? Dying from being run into by a train, or dying a fiery death as you and your car are picked up and hurled maybe a mile or so into the distance in a spectacular fiery plume? |
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I read this as rocket assisted bra, which has yet to be done on halfbakery...probably |
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I'm thinking along the lines of custardguts above, wouldn't it be easier to use the rocket to destroy whatever it is you're about to crash into? |
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It would be fun too. I'm sure [8th] will be along in a minute to bun this for irresponsible and gatuitous use of dangerous explosives. |
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Imagine being the driver of a large truck, fitted with the latest whizz bang retrocket kit, in heavy traffic. Some toolbag in a new bright green VW beetle pulls out in front of you, waving their middle finger and laughing, causing you to have to jump on the brakes. Do you a) apply appropriate pressure with your right foot to the brake pedal to prevent tragedy, or b) press the big red button and wipe them off the face of the earth? |
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Sooner or later, people would start choosing option b. Maybe, (or maybe not,) I want to live in that world. |
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This kind of reminds me of the launch escape
systems used on some spacecraft, except that those
worked and this wouldn't. |
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I think there should be a pedestrian version as well. You know when you are hurrying through a crowded city street and sometimes someone steps in front of you and you dont have time to stop or dodge aside. |
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Well carrying around a double barrel 4-bore rifle would have a similar
effect, both halting your forward movement, and similar downrange
effects too I imagine. |
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A couple of jatos aiming forward would have the
added bonus of blowing away whatever it was that
caused you to slam on the breaks if it was light
enough. |
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Anyone mad enough to climb into one of
those Heath-Robinson deathtraps deserves
everything they get. |
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The idea of using a mass of rockets to brake a
falling object was pioneered in the 1940's by
D.M.W.D.'s "Hajile" device, which was only
partly successful and was never deployed
operationally. |
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//The idea of using a mass of rockets to brake a
falling object was pioneered in the 1940's by
D.M.W.D.'s "Hajile" device, which was only partly
successful and was never deployed operationally.// |
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Also by the lunar lander and Soyuz reentry module. |
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Braking and landing aren't quite the same thing. |
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Breaking and landing sometimes are. |
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I seem to recall a recent successful Mars NASA event
in which braking rockets were used to slow down
entry. |
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What [Ling] said, only again... |
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Just to extend the idea, put a pair of small rockets on every
engine and every car. The rocket would be sized based on
the fully loaded mass of the car. An emergency signal would
ignite all rockets by RF signal. Bring the train to a 1G slow
and stop in about 1/10 the current stopping distance. Since
trains usually have lots of time to see an object in their way
before needing to stop. 1/10 of the stopping distance would
save a lot of lives. |
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If you aimed the train's rockets down where the wheels meet the
rails, you could melt away the low-friction shiny bits and really get
some braking traction. |
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For automobiles, I would build a retractable arm that extended out
behind the car, with the rocket pointed up and forward. When it fired,
the flame would go up over the car, roasting fewer pedestrians and
melting enough of the roof to discourage gratuitous use. Under the
end of the arm would be a friction pad that the rocket would force
onto the road surface (or, in the deluxe model, a plow blade). |
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(Or you could just be boring and mount the rocket in the car's trunk,
pointing up and forward, so the blast would both slow the car and
increase the downforce for better braking. (Or, in the deluxe model,
smash the back end of the car into the pavement so hard that it digs
a hole.)) |
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(By the way, a free-flight rocket cannot be stabilized by locating the
motor to pull, instead of push, so my idea is not going to help
steering.) |
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Weld the wheels to the rails with high current... |
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If a train engine weighs 100 tons and is going 56 mph, a
rocket with the thrust of a Titan I (40 tons) would slow it
to a stop in 6.4 seconds. In the recent train wreck in
Oxnard California the engineer applied the brakes 8
seconds before impact. The Titan weighs 50 tons, but
most of that weight is to produce a 140 second burn. This
would only need a 6 second burn, so it might only weigh
around 4 tons. Each burn of a Titan costs 1.3 million. So
each burn of this rocket would cost about 55 thousand
dollars. Every train car would need an appropriate sized
pair of rockets of its own. |
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Every car needs one, and a train might be a hundred cars in
length. That's $ 5,500,000 per stop. Spendy. Consider also
that you are lighting a mile long oxyacetylene jet around
often flammable cargo that might well be passing through a
highly populated area. Also, to equip the entire fleet,
including the cars that are shuttling back and forth lightly
loaded or empty will require an initial investment of
trillions of dollars, framed against the current situation of a
rail fleet that includes thousands of cars grandfathered into
use that cannot be brought to safety code but will not be
retired until they wear out due to toothless legislation. |
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