Mars Penetrator Probes, Brilliant Balance Masses & Other Ideas Options

[JRehling]

Ah, mole, we never had a chance to see the data you would have collected.

I hope we see a re-fly of a heat flow measurement experiment soon. I like the idea of multiple penetrators dropping from one entry vehicle, using momentum to enter the soil, and enough safety in numbers that one or more failures still lets us get one success.

This seems like something that could ride along with some future stationary lander, regardless of the lander's other functions.

https://www.lpi.usra.edu/meetings/lpsc1996/pdf/1452.pdf

[HSchirmer]

...I like the idea of multiple penetrators dropping from one entry vehicle, using momentum to enter the soil, and enough safety in numbers that one or more failures still lets us get one success.
This seems like something that could ride along with some future stationary lander, regardless of the lander's other functions.
https://www.lpi.usra.edu/meetings/lpsc1996/pdf/1452.pdf

The brains of existing Textron BLU-108 cluster bomb "skeet" submunitions detect 2 color infra-red signatures , scan with lidar then steer themselves to likely targets. Reprogram them to aim for the wavelengths of hydrated minerals, do their lidar scan and upload a high resolution DEM model to the rover.
One "skeet" weights 7.5 pounds and samples about 16 acres. The 4 pack dispenser weights 64 pounds and covers around 64 acres.
Another recent advance are electronics that survive being fired out of 155mm howitzer and allow computer controlled artillery shells so a "lawn dart" penetrator could be an option.
http://midkiff.cz/obj/firma_produkt_priloha_120_soubor.pdf

[Steve G]

Can someone explain to me how these balance masses work? Just before entry, they eject two of the cruise balance masses as 70 kgs each. That's a 140 kgs (308 lbs) of weight. To put that in perspective, Mariner 4 was 260 kgs. During EDL, they drop more of these. Curiosity did the same thing, but it just seems like a heck of a lot of weight to be tossing away that could be added to the landed weight. Is there no way around using these?

[vjkane]

Can someone explain to me how these balance masses work? Just before entry, they eject two of the cruise balance masses as 70 kgs each. That's a 140 kgs (308 lbs) of weight. To put that in perspective, Mariner 4 was 260 kgs. During EDL, they drop more of these. Curiosity did the same thing, but it just seems like a heck of a lot of weight to be tossing away that could be added to the landed weight. Is there no way around using these?

During cruise, the capsule needs to be balanced so that it can spin for stability. During entry, the capsule needs to be unbalanced so that the capsule can use the unbalance to steer itself during entry. I'm sure that others here can give more detailed explanations.

There was a program to examine if there could be small science payloads that could be substituted for the dead weights that were used for Curiosity. Idea apparently didn't go anywhere. Not sure if it was for technical/risk reasons or lack of inspiring ideas for science payloads.

[mcaplinger]

There was a program to examine if there could be small science payloads that could be substituted for the dead weights that were used for Curiosity.

There are the cruise ballast masses (2*75 kg) dropped before entry and then 6*25 kg of ejectable mass that goes before chute deploy. It was the latter that were the subject of the contest: https://www.nasa.gov/content/nasa-announces...mass-challenge/

There was a proposal for a system that would pump ballast mass around but that ended up being heavier and more complicated than just dumping the mass. You need the mass offset during entry to fly the descent.

[JRehling]

It is tantalizing to realize that we're sending dead ballast almost all the way to Mars, but I'm sure that part of the challenge of making those into something actively useful is that they get ejected at a pretty unfortunate time in the sequence. If someone could figure out a way to turn one into a penetrator with heat probe, their next dinner is on me.

[mcaplinger]

I'm sure that part of the challenge of making those into something actively useful is that they get ejected at a pretty unfortunate time in the sequence.

The cruise balance masses would have to go through entry, but the smaller ones get ejected at more reasonable speeds and altitudes.

Having said that, one would have to make something that has the same mass and form factor as the balance mass, requires no power or data interfaces of any kind during cruise, survives the landing, communicates on its own, and does something useful. Perhaps doable, but certainly very challenging.

The winning challenge entry looks like it was completely passive, but I don't know the details.

Paradoxically, one of the biggest problems is probably making them heavy enough.

[Art Martin]

It is tantalizing to realize that we're sending dead ballast almost all the way to Mars, but I'm sure that part of the challenge of making those into something actively useful is that they get ejected at a pretty unfortunate time in the sequence. If someone could figure out a way to turn one into a penetrator with heat probe, their next dinner is on me.

My guess is creating the penetrator with a heat probe inside it is not as much the issue as ensuring that there's a way to transmit whatever data it found though electronics and power circuits capable of surviving the trauma of the penetration. The thing would basically look like an arrow where the pointed head would naturally seek down (essentially a lawn dart). Have we done such a task on Earth before? I suppose if we could pinpoint the spot it hit, the rover could find it and get signals from it at close range so the power levels could be substantially reduced.

[mcaplinger]

Mods: penetrator discussions have taken over several threads recently (off-topic; I'm as guilty as anyone) so perhaps a dedicated Mars penetrator thread could be created and this traffic moved.

[Phil Stooke]

The impact sites of the various MSL balance masses were imaged by HiRISE after the landing. Big dark splats. Presumably the new ones will be as well. There might be a bit of science from that, extending the range of impact effects of objects of known mass and velocity.

Phil

[JRehling]

Suddenly synergistic with the ballast thread, it's too bad that Insight wasn't located somewhere close to a subsequent landing site. Being heavy and thumping the ground is definitely a challenge that inert ballast can accomplish.

[Steve G]

Did Viking or MERs use mass balancing?

[djellison]

Neither used guided entry and thus didn’t need the offset CoG. Ditto MPF, MPL, PHX and InSight.

[mcaplinger]

Neither used guided entry and thus didn’t need the offset CoG. Ditto MPF, MPL, PHX and InSight.

Actually, while Viking was unguided, it was lifting (constant lift up), not ballistic. I'm not sure how/if they managed balance for parachute deploy. Viking entered from orbit, not directly, and in the cruise phase was 3-axis stabilized, not spin-stabilized, so the less-critical cruise balance could have been managed with fixed offsets on the orbiter.

It's worth noting that avoiding the use of balance masses doesn't directly translate to more landed mass. The more landed mass, the more fuel, heavier structure, etc -- there are many ripple effects.

Similarly, penetrators IMHO are one of those things that sounds easy enough to do but turns out being harder than expected.

[hendric]

MPL had the two failed DS-2 probes, but to be fair they were pretty small, only 2.4 kg apiece, and lacked the budget to do extensive validation before launch.

It does seem like a great missed chance for NASA to setup some contests by setting form-factor, interface, and mass/density constraints (one in which you must 'use up' all your mass would be very weird!) and letting university or private teams compete. The final winning designs would have to be reimplemented by NASA in order to meet planetary protection requirements, etc but would benefit from the innovation such a contest could provide.

Obviously there would need to be minimum density requirements, but giving teams a goal of 50 - 75% of the density of tungsten would still leave quite a bit of room for electronics.

I don't think the impact per se would be difficult to survive, the military has bunker-busting and runway-destroying munitions designed to penetrate feet of concrete.

But having to do so with a reliable battery that can also survive 18 months (since it would need integration well before launch) and a trip in deep space in a presumably non-heated portion of the craft, that will be tough. Haha, what about a clockwork spring that powers up the system as it is ejected from the cruise stage, or requires the impact to break the holding pin? That would be amazing! No need to worry about electrolytes freezing or plates cracking from G-forces. The void space could be filled with dense oil to keep the density high. Other teams could explore things like fuel cells or liquid electrolyte based systems.

If I had infinite time, monkeys, and access to a large tower, I would try some testing with a RaspPi and see how much it could survive with various configurations, such as being held in air, surrounded by mineral oil, expanding foam, epoxy, etc. That alone would be a fun project!