If I lose comms after closing the vents but before launch, the LOX tank will
self vent at abt 750 psi through a burst disc. That should bleed down most of
the helium through the LOX regulator and the now open burst disc outlet. The
pressurized fuel tank is a little more difficult as it will require a manual
drain. If it's still intact on the pad, no big deal. The tank I'm using has
about 2.5x factor of safety. If it's crashed somewhere or blown up on the pad,
I'm not so interested in walking up to it and the rifle may be a better
solution. However once the engine starts, I plan to never close the main valve
so everything should eventually bleed down.
If I lose comms after a valve command, I see where you're going, hmmm, for a
skinned vehicle where everything is internal, it would be hard to tell the
position of a ball valve externally. The valve outlets are flush with the skin
so you can always look at the ball to see if it's open our closed but that
would require putting your eyeball up to the vehicle. Maybe some sort of flag
attached to the valve shaft but you'd have to have a window or viewing port to
see it.
- Bob
On Nov 10, 2015, at 18:37, Paul Breed <paul@xxxxxxxxxx> wrote:
The real issue is what do you do when you've lost communication with the
vehicle and its in unknown state.
Some external visual clues as to its current state would be very useful.
With blue and silver the main vent valve would visually pop open....
A good scoped rifle is a remote depress of last resort...
From 50 yards you should be able to reliably depress in a 2" circle.
For a liquid rocket I would retain such capability and ensure that I'm clear
down range...
Nothing worse than sitting in the bunker waiting for the lox tank to go boom
with no way to change the outcome....
I watched one group go out to a crashed burned pressurized lox rocket and
manually open a vent valve.... this was a vehicle that used cheap fire
extinguisher tanks... so the cost to ventilate the tank was low. I offered
them other tools... alas hoplophobia wins out over common sense.
Paul
On Tue, Nov 10, 2015 at 3:23 PM, Robert Watzlavick <rocket@xxxxxxxxxxxxxx>
wrote:
The opto controlled relays provide that capability. To enable power, the
switch providing power to the opto LED high side has to be on (either a
switch or shorting plug) and then a bit from the onboard computer has to be
set appropriately for the LED low side. For the smart servos, you also have
to send a command to get them to move (they power up in standby). The only
potential issue is that you're assuming the MOSFET on the output side of the
relay won't get turned on by itself. Seems really unlikely to me but still a
potential failure mode.
I was considering the Molex Mini-Fit Jr series of connectors (same series as
ATX power supplies) for power. They have a latch for internal onboard use
(vibration resistant)?and I can break off the latch for the ground supply
connector so it pulls away on liftoff.
-Bob
On Nov 10, 2015, at 16:35, Pierce Nichols <piercenichols@xxxxxxxxx> wrote:
I agree that any rocket should be able to sit on the pad under ground power
all day long. If its power draw is low, you could use a 1/4" phono plug --
they're cheap, low profile, have some spring retention for wind etc while
still being easy to pull straight out, and they can handle a few amps.
It seems like we need parallel safing systems -- a 'soft' system that can
be engaged and disengaged remotely and a 'hard' system that requires some
sort of physical intervention (pins, plugs, etc). So, in the re-safing
scenario, the operator engages the soft system and then someone runs up to
the rocket quickly and engages the hard system.
-p
On Tue, Nov 10, 2015 at 1:46 PM, Paul Mueller <paul.mueller.iii@xxxxxxxxx>
wrote:
Seems that a safe/arm system may have to be at least partially dependent
on onboard power, and then the question becomes how do you make onboard
power as reliable as possible for various failure scenarios? One way would
be a ground-based charging connection much like a laptop (runs on ground
power and keeps onboard batteries charged until you disconnect it). That
way you could sit on the pad, powered up, all day long if you need to, as
long as you have gas for your ground generator! You could have a magnetic
connection like an Apple laptop, which could be fairly easily reconnected
if needed with a rotating arm. Then do your arming/safing remotely via
something like a TV remote control or even a laser pointer aimed at a
photoreceptor on the side of the rocket. It would also be smart to have
LEDs indicating the arm status of your various systems (visible through
binoculars).
On Tue, Nov 10, 2015 at 2:33 PM, Paul Mueller
<paul.mueller.iii@xxxxxxxxx> wrote:
The re-safing problem seems to be the most difficult, as the concepts so
far seem to involve pulling a pin or a rare earth magnet with a long
string. It's hard to "push on a rope" to reinstall a pin, etc. from a
distance if necessary. I'm at a loss to figure out a contraption that
would allow you to remotely arm and safe the rocket mechanically. Maybe a
rail-mounted rotating arm that would return to the same spot (assuming
the rocket didn't move during a launch attempt, misfire, etc.)...?
On Tue, Nov 10, 2015 at 10:59 AM, Pierce Nichols
<piercenichols@xxxxxxxxx> wrote:
Here's a (half-baked) thought:
Make the shorting switches mosfets instead of physical switches and
drive the mosfet gates either with a single shorting plug or with a hall
effect switch. The cool thing about the hall effect switch is that you
can place it in the skin of the rocket with a small piece of steel. Then
your shorting plug become a rare earth magnet stuck to the outside of
the rocket... which can be easily pulled off with a long cord when it
comes time to arm the rocket. On the flip side, as long as there's
nothing else ferromagnetic near it, you can re-safe the rocket by
tossing a small magnet at it.
-p
On Tue, Nov 10, 2015 at 9:24 AM, Robert Watzlavick
<rocket@xxxxxxxxxxxxxx> wrote:
I have 5 opto relays I need to disable so I would need multiple
contacts - GOX igniter solenoid, fuel igniter solenoid, CDI module,
servo power, and recovery motor power. I could do a multi-pin connector
and shorting plug or go with a switch that grounds the + lead for all
the optos.
-Bob
On Nov 10, 2015, at 10:11, Paul Breed <paul@xxxxxxxxxx> wrote:
The Short across the opto with an external plug does not have to be to
ground, just short across the opto input pins. The 820 ohm resistor
will be more than enough to isolate the cpu from damage....
On Tue, Nov 10, 2015 at 7:04 AM, John Dom <johndom@xxxxxxxxx> wrote:
Actually, “Failure is not an option” is a Gene Kranz book. Not C.
Kraft.
jd
From: arocket-bounce@xxxxxxxxxxxxx
[mailto:arocket-bounce@xxxxxxxxxxxxx] On Behalf Of Nels Anderson
Sent: dinsdag 10 november 2015 13:48
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: Safing of liquid vehicle
Something similar was considered, though not actually done, when
NASA's first attempt launch a Mercury capsule resulted in a four-inch
flight in November 1961. From Wikipedia
(en.wikipedia.org/wiki/Mercury-Redstone_1):
"[T]he fully fueled and powered-up Redstone was now sitting on LC-5
with nothing securing it to the pad. Various other dangers existed as
well such as the capsule's retrorocket package and the range safety
destruct charges. Furthermore, the capsule's main and reserve
parachutes were hanging down the side of the rocket, threatening to
tip it over if they caught enough wind. Fortunately, the weather
conditions were favorable. Amid the panicked atmosphere in the
control room, the launch team was unable to come up with quick and
viable options to rectify the situation. Chris Kraft, the
now-frustrated flight director, rejected several unsafe
interventions, including getting a rifle and shooting holes in the
booster's propellant tanks to depressurize them. He eventually took
the advice of one of the test engineers to simply wait out the
battery discharge and let the oxidizer boil off."
Wikipedia cite's Kraft's biography, _Failure is not an Option_, as
its source.
On 11/09/2015 02:58 PM, Ben Brockert wrote:
Only an 'unreasonable' person would carefully shoot off a vent cap
with a .30-06 when the servo-actuated normally closed vent on their
spherical peroxide rocket doesn't actuate.
On Monday, November 9, 2015, Robert Watzlavick
<rocket@xxxxxxxxxxxxxx> wrote:
I've heard similar anecdotes - has this technique ever actually been
used?
-Bob
On 11/09/2015 01:40 AM, Michael Clive wrote:
.3006 will safe it pretty good and solid.
--
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