Pilot Chutes and Mortars Options

[ncc1701d]

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.

[nprev]

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?

[rlorenz]

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?

'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..)

[nprev]

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

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.

[rlorenz]

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.

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)

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.

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.