[X] My Assistant

[Paolo]

well this is sad but not unexpected
https://twitter.com/NASAInSight/status/1349760462854909957

One phase ends, and another begins…

Last weekend, the mole made a final attempt to dig farther underground on Mars. Even with all the steps we’ve taken to #SaveTheMole, it seems there’s just not enough friction in this soil to keep it moving downward.

[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

[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.