Crumple zone landings

[Nich]

For my senior design project I did a crumple zone lander for a mars rover and found that it is actually about 1/2 the weight of LFO for the corresponding dv.  Of course there are complications involved including g-forces, uneven ground, and final orientation.  I decided to do some testing.

I created a lander put some fuel on it and engines so I could hit the ground faster.

With no landing gear the craft had 846 dv

4 Micro landing gear the craft had 817 dv had a top speed of about 45 m/s.  This was a savings of 16dv.  11 dv if we put in a 5 m/s safety cushion.  If you account for the fuel not wasted burning against gravity during touchdown it will be significantly higher.

What was really surprising where the cubic octagonal struts.  4 sets of 4 only reduced the dv to 838 but also allowed the craft to hit up to 70 m/s.  This was a saving of 62 dv or 57 including a safety cushion.  Additional gains from not fighting gravity would be even larger. With a TWR of 2, 140 dv has to be expended to get 70 dv when going vertical and this assumes a perfect suicide burn.  As TWR goes up this becomes less and less important but with lower TWR lighter craft are possible for the same dv.

[Fearless Son]

In other words, you did deliberate, non-ironic lithobreaking.  A rare thing among KSP players (who tend to lithobreak accidentally.)

[Archgeek]

8 hours ago, Fearless Son said:

In other words, you did deliberate, non-ironic lithobreaking.  A rare thing among KSP players (who tend to lithobreak accidentally.)

Lithobraking. Lithobreaking is what you get when it's not actually successful.

[bewing]

I was doing somewhat similar testing recently -- to test out the real capabilities of the micro landing gear. I wanted to know what that "150 m/s impact tolerance" really meant. I stuck 3 of them on a 1.5 ton craft on the launchpad. Launched it up to 250m, 300m, 350m, etc. and let it fall back to the launchpad unpowered. I especially wanted to know what happened with "locked" vs. "unlocked" suspension.

With unlocked suspensions, I was surviving impacts of 100m/s undamaged. With a locked suspension, the legs started falling off and then exploding when it landed at a little over 30 m/s. But otherwise, the rest of the craft survived.

 

[Nich]

I did do some experiments with cubics and struts but I ran into the problem of not being able to brake all 4 struts at the same time without destroying the craft.  If you don't destroy all 4 struts it will force a tip over.

[cubinator]

Interesting. An actual, scientific study of intentional lithobraking techniques.

[Stewcumber]

That's very weird, was thinking about this today! How many empty fuel tanks do you need to stop /slow down to a survivable speed from 100m/s, 200m/s etc, and how angle will affect that. Does the craft disintegrate in one go if it hits a surface at say greater than 100m/s regardless of crumple zones?

[Nich]

75 was a hard limit for me more cubics would not help. Reducing mass would not help. Cubics and landing gear were getting up to 100 but the extra mass of landing gear barely make it worth the risk effort

[bewing]

5 hours ago, Stewcumber said:

That's very weird, was thinking about this today! How many empty fuel tanks do you need to stop /slow down to a survivable speed from 100m/s, 200m/s etc, and how angle will affect that. Does the craft disintegrate in one go if it hits a surface at say greater than 100m/s regardless of crumple zones?

No, the lower parts explode, which tends to shoot the upper parts back in to the sky -- where they proceed to fall and crash again. The second impact will usually destroy what you were trying to save.

 

[Aloriel]

I kind of did this unintentionally.

For a while, I was using a return module that included the capsule, a storage bay with science in it, a science senior, solar panels on the sides, parachutes on the top, and a MSI-LS supply container on the bottom (with heat shield, of course).

My parachutes were insufficient to slow the module enough, and most landings were around 20m/s. This crushed the supply container, but everything else survived intact.

As such, I considered the effort a success and continued to use that design. I mean, what do Kerbals need with supplies when they've returned to Kerbin anyway?

 

Anyway, I think it's great that you are designing this concept intentionally. That is some serious fuel savings!