The large Pioneer Multiprob deployed parachute so it could descend to surface of venus.

I am trying to understand the whole mortor and parachute system.
For those of you parachute experts.

When a mortor fires to pull out a pilot chute. What happens to the mortor after its fired?
I am guessing the mortor has a rope tail that it pulls out of the chute. Then the rope has a pilot parachute attached to it.
And then what..the mortor just files off leaving rope still attached to the pilot prachut or it takes the rope tail with it?
I have tough time finding info about the details of a mortor pilot chute relationship.
I am not even sure if the mortor really does have a rope tail connecting to pilot chute.
Also what does the mortar look like.

Is this same method used for the Hyguns and Galileo probes?
Thanks for any help.

A mortar isn't an object in itself that would get ejected - it's a technique. As I understand it (and I probably don't) Imagine a cylinder and a piston. The parachute is packed above the piston - with a retaining cover, and a charge packed below the piston. The charge is ignited and the piston is pushed upwards ejecting the chute at high speed out through the cover and into the airflow. It's similar to the way the nose-cone and chute get deployed on model rockets. I think.

Some use a spring instead of an explosive charge - but with spaceflight you really REALLY want the chute to deploy, quickly, so a small charge gets used.

Doug

(restrains impulse to comment on spelling)

The Huygens PDD (Parachute Deployment Device) was a mortar on the top
platform of the probe. A propellant cartridge is ignited by 2 NSI pyros and builds up
gas pressure behind an aluminium sabot held inside the PDD with 2 O-rings. The
pilot chute itself is packed above the sabot with a closure cap.

The pressure accelerates the sabot, chute (in a bag, with the riser and bridle) and
cap. When they have moved 42mm or so, they push out the breakout patch in
the aft cover (remember all this stuff has to be protected from the heating of entry)
which is held in place by shear pins.

So, sabot, chute and cover fly out. The sabot is unrestrained. The cover is attached to the
parachute bag. As the chute bag flies off, the bridle, then riser and lines come out, then the
canopy itself which begins to inflate as the bag comes off.

The bag, cover and patch are all connected together and fly off. Pilot chute inflation is
complete 1.4 seconds after PDD initiation.

Insofar as the thing is a tube with stuff hurled out by a charge, it's a mortar, but really it is a
more sophisticated system with lots of bits all of which get designed with care and whose
trajectories have to be modeled etc.

System was designed by Martin-Baker (UK) who make ejection seats etc (though the people
involved with Huygens split off to form their own company - Vorticity)

Hope this helps. Couldnt tell you anything about Galileo - this level of detail is rarely
found in public documentation for US systems, unlike ESA/Huygens. You can find some more
general background in 'Planetary Landers and Entry Probes'. Knacke's
Parachute Recovery Systems Design Manual is excellent, if dated and expensive.

Ralph

Doug has it pretty much right.

But the issue is less deploying the chute quickly as it is getting the canopy clear of the recirculating wake
of the probe. So you need enough momentum to get the chute into the clear air (rule of thumb -
though there are now sweet fluid-structure interaction models that can explore it explicitly - is you
need to be 9 probe diameters or so behind) to inflate reliably.

Huh. So you're saying that 9 vehicle diameters is a more-or-less constant for avoiding wake turbulence, at least to the degree needed for successful deployment? That seems almost too small, esp. at supersonic speeds as during Mars EDL. It also seems peculiar that such a relationship would exist between vehicle diameter & deployment distance (I would have expected that velocity & atmospheric density would be more significant influences). Is this 'constant' basically something derived from experience, or via laminar-flow modeling?

Not clear of any turbulence, just the bit of it that's recirculating and might trap the chute ( I think )

Doug

'seems almost too small' - based on what, may I ask ?

I believe this is an essentially empirical relationship - as are most parachute things
originally (hence I said 'rule of thumb') - only now is the field moving into a substantially
model-based approach.

I may be also conflating different requirements - the pilot and main (deployed supersonically)
were supposed to be 10 calibers behind, whereas the later stabilizer chute only needed to be 7
calibers (the issue there being not so much inflation as degradation of the steady-state drag
performance by being in the wake).

I believe in the Galileo program originally the trailing separation was not as large and they
discovered problems during testing which pushed them into the 9-10 calibers line/riser length

You're right in that in an ideal world you analyze everything with CFD (no reason to force it to
be laminar), then build it, test in a wind tunnel, then test in flight. But before/instead of going to
that, you use the rules of thumb that prior missions give you.

Prior experience may be deceptive of course (e.g. the effective porosity of a canopy will depend
strongly on Reynolds number, so that a porous fabric that works fine on Earth with nice
stable characteristics acts essentially impermeably in the low density Mars environment..)

Actually, based on aircraft departure procedures; the spacing between launches is hundreds of times the cross-sectional area of the aircraft themselves, but of course the primary sources of turbulence are the engines, so the airflow is considerably more chaotic.

However, I'm more inclined to accept your premise based on fighter aircraft landing behavior. F-4s deployed a drogue chute upon landing that was extended behind the aircraft far shorter than the horizontal dimension of the vehicle; the Shuttle does the same. So, again I ask, how did the 9X diameter touchstone arise? It does not seem to be intuitive.

Primary source of *noise* is the engines, but as far as I understand it, aircraft takeoff or landing spacing is
driven by the wingtip vortices (I've even hear the term vortex spacing) which can remain coherent
for quite some time (after all the weight of the aircraft is being deposited into downward momentum in the
air every second and since the tip vortices are separated by the aircraft span, the dissipative shear in the
vortex system is comparatively low)



You can ask again, but the answer is still the same - it is empirical. That doesnt mean it has a robust
theoretical background, nor even that it is right. But a pilot chute absolutely has to work, or else mission loss.
Drogue chutes for braking are helpful (after all, shuttle coped for years without one until they decided to
copy Buran) but perhaps less mission-critical.

Note also the wake behind the tail of a jet or even the shuttle is less likely to have a nasty street of vortices
or large recirculating region than is the very bluff shape of an entry probe (which is blunt for aerothermodynamic,
rather than aerodynamic reasons)

So, the justifiably conservative practitioners of the black art of parachute system design adopt that rule of thumb.
Question it at your peril.