How many Gs would a hard-landing Europa Lander face upon Impact/landing?

[fredinno]

So, apparently, according to SciShow Space, the Europa Clipper Mission's lander would need 8000 kg of fuel to soft-land on Europa. That's really unacceptably high, and is a sure-fire way of putting Europa Clipper in development hell (not to mention the fact not even SLS Block IB would be able to send Europa Clipper there without gravity assists.)

HOWEVER, what if a probe did not need to soft-land? The Galileo Reentry probe had to face up to https://en.m.wikipedia.org/wiki/Galileo_Probe 230Gs of impact force. However, this was in the 80's. Today, using airbags, better shock absorbers, and equipment, a hard impact-lander might survive over 260Gs of force. 

How much impact force would a Europa lander face upon hard impact, assuming no propulsive slow down? I'm pretty sure the ice meting from the impact might cushion the probe slightly.

Edited February 17, 2016 by fredinno

[Hannu2]

I do not know exact number but you can assume it to be infinite for every practical purposes. Anything which hit to ice at several km/s will be destroyed in millisecond. Galileo Probe entered to Jupiter's atmosphere. It may be thick and nasty atmosphere, but it is surely softer than ice at -150 C. G value of icebraking would be several orders of magnitude higher in spite of any imaginable air bag contraption.

8000 kg of fuel sounds great. What the heck they are going to land on Europa? Have they hired Whackjob to plan real probes?

[GDJ]

8,000 kg's of fuel isn't unreasonable, especially when a probe is slowing down from between 15 and 18 kilometres per second to zero in a short time.

Actually I expected the number to be more than that actually. Chemical rockets are punchy, but rather inefficient.

Edited February 17, 2016 by GDJ

[cantab]

It will hit at at least Europa's escape velocity, so about 2 km/s. That is twice the speed of a rifle round. I question how useful any "probe" that could survive that would be.

[Interplanetary Engineer]

While a clever row of gravity assits around Jupiter's (almost wrote "Jools") moons should slow you down very much from interplanetary speeds, but you would most probably need at least some manner of breaking by rocket propulsion. No need for a soft landing though when you have a sturdy enough probe, and a bullet-shaped one could also reduce the G's faced greatly.

Edited February 17, 2016 by Interplanetary Engineer

[magnemoe]

2 minutes ago, cantab said:

It will hit at at least Europa's escape velocity, so about 2 km/s. That is twice the speed of a rifle round. I question how useful any "probe" that could survive that would be.

Yes, expect 10-30.000g think artillery shell. Downside is the heavy casing and payload restrictions. Theoretical you could use an long spear to brake on or use as crumble zone but you will not get under 1000g.
nerva or an reactor powered vasmir sounds like more realistic option here. 

[fredinno]

42 minutes ago, cantab said:

It will hit at at least Europa's escape velocity, so about 2 km/s. That is twice the speed of a rifle round. I question how useful any "probe" that could survive that would be.

I assumed the impact takes 3 seconds, and the impact G would be 68 G. 2 seconds, and 102 G. 1 second, and 204 Gs. That seems like a reasonable G load, and might be achievable with the use of airbags.

45 minutes ago, GDJ said:

8,000 kg's of fuel isn't unreasonable, especially when a probe is slowing down from between 15 and 18 kilometres per second to zero in a short time.

Actually I expected the number to be more than that actually. Chemical rockets are punchy, but rather inefficient.

It's not going to go from Jupiter Transfer to Europa impact- just Jupiter Orbit to Europa Imapct.

[Ravenchant]

1 hour ago, fredinno said:

I assumed the impact takes 3 seconds, and the impact G would be 68 G. 2 seconds, and 102 G. 1 second, and 204 Gs. That seems like a reasonable G load, and might be achievable with the use of airbags.

But the impact is not going to last nearly that long- the probe is colliding with a solid surface. For a basic order-of-magnitude calculation, let's assume constant deceleration during impact. From a velocity of 2 km/s and a one-second impact duration, this gives us a deceleration distance of approximately 1 km. Of course the ice would vaporize during the impact, possibly softening the blow, but we're still talking hundreds of meters. Can we send airbags which would measure hundreds of meters across to jupiter? Even a gas-filled sphere a mere 100 m across filled with hydrogen at 1 bar and room temperature would have a mass of, like, 50 tons. Yeah...

 

Edit: airbags might be useful in a scenario where the lander's only braking propulsion is, say, a solid motor. Fire at the right time, decouple, inflate and let the final couple dozen m/s be cushioned. But this kind of landing profile seems an unlikely choice today.

Edited February 17, 2016 by Ravenchant

[magnemoe]

Don't make Danny2462 design the impactor, he is likely to destroy Europa, perhaps Jupiter too. www.youtube.com/watch?v=ds2iSXvngRo

Had it not been for all the poor moons who would get hurt this would be an nice KSP challenge

 

[fredinno]

28 minutes ago, Ravenchant said:

But the impact is not going to last nearly that long- the probe is colliding with a solid surface. For a basic order-of-magnitude calculation, let's assume constant deceleration during impact. From a velocity of 2 km/s and a one-second impact duration, this gives us a deceleration distance of approximately 1 km. Of course the ice would vaporize during the impact, possibly softening the blow, but we're still talking hundreds of meters. Can we send airbags which would measure hundreds of meters across to jupiter? Even a gas-filled sphere a mere 100 m across filled with hydrogen at 1 bar and room temperature would have a mass of, like, 50 tons. Yeah...that's not going to happen.

Ok, so maybe we should do a little propulsive deceleration- getting the speed down to 1000m/s before the 0.5s impact, results in 204 Gs. On the other hand, 1000m/s speed and a 0.35s impact results in a 292 G impact, and a deceleration distance of 0.35km, or 350 m. Is that more reasonable? I mean, only 300kg or so is allocated for a Europa Lander, so...

[Ravenchant]

22 minutes ago, fredinno said:

Ok, so maybe we should do a little propulsive deceleration- getting the speed down to 1000m/s before the 0.5s impact, results in 204 Gs. On the other hand, 1000m/s speed and a 0.35s impact results in a 292 G impact, and a deceleration distance of 0.35km, or 350 m. Is that more reasonable? I mean, only 300kg or so is allocated for a Europa Lander, so...

Probably more trouble than it's worth. Obviously no descent is going to be without gravity losses, but if we include a 500 m/s margin (for a total delta-v of 2500 m/s) and an engine with a specific impulse of 306 s (certainly not outlandish for storable propellant), a 300-kg probe could afford around 130 kg dry mass. I'm no expert, but that seems doable.

[fredinno]

10 minutes ago, Ravenchant said:

Probably more trouble than it's worth. Obviously no descent is going to be without gravity losses, but if we include a 500 m/s margin (for a total delta-v of 2500 m/s) and an engine with a specific impulse of 306 s (certainly not outlandish for storable propellant), a 300-kg probe could afford around 130 kg dry mass. I'm no expert, but that seems doable.

Still, even a small impact of 50-100m/s could allow for easy sampling of the interior from the impact crater, sciecne on how impact craters form on icy bodies, and radiation shielding from the surrounding ice. Not to mention shave off a few kg of fuel mass.

[cantab]

This is what happens when a complex and relatively fragile mechanical object (a car, or a space probe) collides with a much more solid object (a solid steel plate, or the super-cold ice surface of Europa) at a mere 300 m/s.

https://youtu.be/Nl8xTqTUGCY?t=1m30s

Nothing but the most hardened solid objects, with limited electronics, is going to survive an impact like that. And such a hardened probe would itself have a huge mass of metal compared to its useful payload.

[PB666]

6 hours ago, fredinno said:

Still, even a small impact of 50-100m/s could allow for easy sampling of the interior from the impact crater, sciecne on how impact craters form on icy bodies, and radiation shielding from the surrounding ice. Not to mention shave off a few kg of fuel mass.

Why are we having this discussion. Suppose the satellite is a meter cube, now suppose the instrument is on the non-impact side, suppose lets be liberal it digs a hole 10M into the ground.

Speed is 2 km/sec. Do the math dv = A*t  11 = 1/2at2 22 = at2  t = 22/2000 = 0.011 sec A = 2000/t = 181888 a, of course it does not survive. The energy of the collision itself, assuming the satellite weighs 100kg is 0.5  100 2000 2000 =   200,000,000 joules which means you also have a pretty nice fireball of molten and vaporized materials, not just the impact forces but also the heat.

[fredinno]

3 hours ago, PB666 said:

Why are we having this discussion. Suppose the satellite is a meter cube, now suppose the instrument is on the non-impact side, suppose lets be liberal it digs a hole 10M into the ground.

Speed is 2 km/sec. Do the math dv = A*t  11 = 1/2at2 22 = at2  t = 22/2000 = 0.011 sec A = 2000/t = 181888 a, of course it does not survive. The energy of the collision itself, assuming the satellite weighs 100kg is 0.5  100 2000 2000 =   200,000,000 joules which means you also have a pretty nice fireball of molten and vaporized materials, not just the impact forces but also the heat.

We kind of already realised this was a bad idea.

[Spaceception]

It makes sense on why it has so much fuel; We've never been there long enough to know what surface conditions are like.