There are many hypothetical systems for bringing spacecraft of the near-future up to speed, some of which may attain some relativity-bending velocities. However, these systems, to achieve such high speeds, often waive extremely high mass ratios given to fuels and engines. Take laser propelled spacecraft, for instance. An inert mass hitchhiking a giant kite.

The problem with these systems is that they'd have trouble at the other end if it was outside their designers' intentions to perhaps slow down to non-relativistic speeds--and that, with a spacecraft left to show for. For the case of laser propulsion, the spacecraft would require a beam at its destination to decelerate.

But, what if we didn't have a beam? Better yet, what if our technology allowed us not to care? Could we be brute about this?

Consider some spacecraft whose exact dimensions, material make-up, and function is yet unspecified, traveling at ten percent light-speed toward a star system. Without any constituent unobtainium (with known materials), can some arbitrarily purposeful piece of the spacecraft (assume a microorganism-sized component) be made to withstand and survive a direct impact with an airless body of arbitrary mass at ten percent light-speed?

Constraints of creativity:

A direct impact with an airless body, say, the moon, at ten percent lightspeed would pull millions to billions of gees, not to mention the kinetic energy released. Microorganisms can be durable things and the closest I've come to researching their resistance to high rates of acceleration was through lithopanspermia. One may assume the smallest microorganisms, perhaps to the scales of viruses.

I would guess that this is predominantly an issue of finding some material that may withstand the involved energies and then scaling that up to protect some microorganism-sized component--the ultimate egg drop challenge. If you can do better than a measly cell-sized thing, larger is better.

The spacecraft can be made of anything, can have any (reasonable) dimensions (just keep it smaller than a thousand kilometers to a side, okay?), and can do anything it needs to do, whatever that may entail. It may also be assumed a light sail spacecraft if nothing else, though, it does not need to be.

I suppose this question is double-edged. The answer may either be No, for these reasons, or Yes, by this method. If you have suggestions for how some parameters may be adjusted--should the answer really, plainly be no--I'm all for it!

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    $\begingroup$ Do you want your destination to survive? $\endgroup$
    – Joe Bloggs
    Commented Dec 27, 2018 at 17:42
  • $\begingroup$ @JoeBloggs Its fate is trivial. $\endgroup$
    – user44399
    Commented Dec 27, 2018 at 17:52
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    $\begingroup$ There have been methods planned to use lasers from earth to both accelerate and decelerate. Take a look at The Flight of the Dragonfly/Rocheworld for a hard science example of how it could be done. $\endgroup$
    – Tim B
    Commented Dec 27, 2018 at 19:27
  • $\begingroup$ @Tim B: my first thought was launching retroreflectors ahead of the main ship, but then I decided a self assembling kilometre long crumple zone was cooler. $\endgroup$
    – Joe Bloggs
    Commented Dec 27, 2018 at 20:42
  • $\begingroup$ @JoeBloggs It's certainly a spectacular way to get things done. Just hope no-one is living near the impact zone or they may take it personally! In FotD they use the primary lightsail for acceleration then detach it at "turnaround" time and then use it as a focusing reflector back to a smaller lightsail still on the ship. $\endgroup$
    – Tim B
    Commented Dec 27, 2018 at 23:03

4 Answers 4


Yes, but as with many things size matters.

Imagine a shock absorber. It’s purpose is to absorb a sudden deceleration and provide a ‘buffer’ to turn it into a slower, more acceptable deceleration. The same principle goes for crumple zones. If a crumple zone can be stacked on another crumple zone then you have more ‘buffer’. Stack n crumple zones and the eventual size of the deceleration can be made almost arbitrarily small, especially with clever use of geometry etc.

Upon impact your initial crumple zones will pretty much vaporise, creating a gas/liquid substrate into which your secondary crumple zones can mash themselves and so on and so on, each layer of crumple robbing the total structure of energy until eventually your final payload can be ‘flicked’ off the top of the stack and land (hopefully) far enough from the now-hellish impact point that it will survive.

Now, the above paragraphs assume a couple of things: The most important is the absence of gravity. The reason for this is that your ‘buffers’ can be built en-route in space, letting you create kilometre long shock absorption zones to sink the energy of collision into. But if gravity accelerates the stack down at a greater rate than your crumple zones are decelerating the stack then you gain nothing at all but a lot of heat. This is a matter of materials engineering, and it’s why you should aim for a relatively small body rather than one like Earth, aiming to transfer (via a stupidly large array of shock absorbers, crumple zones and packing peanuts) as much momentum to the target as possible.

Wherever you hit you should expect widespread devastation.

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    $\begingroup$ The spacecraft assembling itself into a shock-absorber looks like a great idea! I'm no engineer, but I think shock-absorption, especially at high velocities, has everything to do with the speed of sound in the material doing the absorption. You want the material at the bottom to propagate its rebounding momentum to the material at the top, decelerating it. Except, the material at the top is pushing toward the material at the bottom at ten percent light-speed, likely faster than the speed of sound in that material. $\endgroup$
    – user44399
    Commented Dec 27, 2018 at 18:27
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    $\begingroup$ You could build a thousand-kilometer-long shock absorber, but for every inch the bottom particles attempt to propagate the rebounding wave upward, the top particles lunge downward another mile. Like a fish swimming upriver, except the river is flowing at terminal velocity. Am I missing something? $\endgroup$
    – user44399
    Commented Dec 27, 2018 at 18:32
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    $\begingroup$ @B.fox : think of it less as a shock absorber and more as a self assembling atmosphere of vaporised metal if you like. Or include some active absorption to transfer momentum from the rear of the vehicle to the front over the impact event. Or use magnetic shocks that transfer over non-material timescales. The end result is still a lot of fire! :-) $\endgroup$
    – Joe Bloggs
    Commented Dec 27, 2018 at 18:56
  • $\begingroup$ @Joe Bloggs "active absorption to transfer momentum" would be the key engineering challenge here. We need to have it transferred at 0.1c $\endgroup$
    – Alexander
    Commented Dec 27, 2018 at 19:10
  • $\begingroup$ @Alexander: nah, you just need to transfer it at 0.0001c per meter of buffer. $\endgroup$
    – Joe Bloggs
    Commented Dec 27, 2018 at 20:05

If I understand your question correctly...

  • Your ship with (I declare) cargo and crew are bookin' along at 0.1c.
  • It's covered with Cool Goo #18Ω, used to decelerate the ship upon impact with a relatively immovable object.
  • The final speed needs to be manageable, but let's call it zero (because I don't think it'll matter what other number it is).

We have some problems.

  1. Everyone inside is dead. There is no way to physically connect their bodies to the ship in such a way that every bone, every muscle, every organ, won't succeed in bursting through the skin and sticking to the windscreen upon deceleration. This is why shows like Star Trek use "inertial dampening" handwavium. Your eyeballs would come out of their sockets and burst into flame before they hit the inside of your spacesuit helmet. (It'd make a good horror movie, though.) Remember, your crew is moving at 0.1c and don't have the privilege of having Cool Goo #18Ω saturated throughout their cells (which also wouldn't matter. See below.)

  2. Your cargo is plasma for the same reason. You might succeed in holding down the creates such that their kinetic energy could transfer through the ship to the hull and connect with Cool Goo #18Ω, but the contents won't and can't without handwavium (let's call it "Clarkean Magic." I'm sure someone will invent a solution someday... but if it could be invented here, today, the inventor should be running to the patent office rather than posting an answer.) So, your cargo is destroyed.

  3. We'll ignore the fact that between your crew and your cargo the interior of the ship is destroyed.

  4. On the outside, your ship collides with, say, a rock in the rings of Saturn. One big enough to meet the demands of Newton's 3rd law. I'm going to suggest that Cool Goo #18Ω upon impact can absorb or convert a remarkably efficient 100% of energy experienced by the collision. What's left over is a rock tumbling along just as it was before and your ship calmly resting on its surface.

Well... Kinda...

You see, the energy must go somewhere. What is Cool Goo #18Ω going to do with it? Is it acting like a big battery? Is it converting it into an explosion (like ablative armor against the incoming projectile)? If it has the ability to retain the energy, dump what it can back into the ship's engines and slowly evaporate the rest as heat into space (that's serious handwaving, BTW), then the ship uses thrusters to move free of the rock and continues on its way.

If it explodes (actual ablative armor), then force is delivered against the ship that's equal and opposite to the motion of the ship (we'll ignore that some of it is actually against the rock...). That would reduce your ship to the proverbial crushed beer can. What if it just converts it to heat? Your ship (and the rock) would melt (or vaporize). What if it converts it to cold? That violates the laws of thermodynamics, but the ship and rock shatter from becoming infinitely brittle. What if it converts it to light? That would be one wailing cool light show, but photons have energy, and the number created would burn you and the rock to a crisp (think sunburn).

In the end, your real problem is what to believably do with the energy. I'm OK with using Cool Goo #18Ω to protect the ship while it collides with a honking big dirt clod, but the energy must go somewhere. It can't simply vanish (well... there's always subspace...). Note that this is why saturating your crew's cells with Cool Goo #18Ω won't help. The energy must go someplace.

You need to come up with a believable way to channel an inconceivably enormous amount of energy in a mind bogglingly short period of time somewhere. Off hand, I don't know where you can put it that isn't intrinsically destructive unless you use handwaving.

  • $\begingroup$ Dump it into the planet! If you’re aiming for Moon A then braking using Moon B isn’t a bad plan, since you can blow it up completely without any major worries! $\endgroup$
    – Joe Bloggs
    Commented Dec 27, 2018 at 20:40
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    $\begingroup$ On your last note, I was thinking I'd put all that energy somewhere in the ship (and, of course, the body of impact)! I'm okay with the ship transitioning into a brilliant cloud of expanding, super-heated gas, so long as its small payload turns up soundly. $\endgroup$
    – user44399
    Commented Dec 27, 2018 at 21:06
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    $\begingroup$ @B.fox, so the ship itself is expendable? Cool. Sounds expensive (suggests transit time is much more critical than transport cost), but cool. $\endgroup$
    – JBH
    Commented Dec 27, 2018 at 22:16
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    $\begingroup$ @B.fox, don't forget that every particle of mass is involved, and all those particles are not elastically connected to one another. It doesn't matter what's between the cargo/passengers and the immovable-object or how much energy it absorbs, it won't realistically absorbe the kinetic energy of the cargo/crew, which is are all destroyed. $\endgroup$
    – JBH
    Commented Dec 28, 2018 at 20:55
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    $\begingroup$ @JBH Yes, reflecting on *Loren's answer, I suspected molecular bonds would not be able to survive the resultant compression forces. You'd instead probably get an interesting soup of ions and fundamental particles $\endgroup$
    – user44399
    Commented Dec 28, 2018 at 21:40

There is a name for that, it's called lithobraking. If you are going to send live material in a lithobraking ship, you may as well replace the usual control center countdown with a presentation of those responsible, suffixed with "and this is Jackass".

Lithopanspermia relies on another form of deceleration, aerobraking, to bring a comet or whatever from a handful clicks per second to a few hundred meters per second in upper atmospheres, and possibly slower even. That is a few orders of magnitude less extreme than what you propose.

Especially, going relativistic against an obstacle will cause nuclear fission. The scenario you propose is similar to that of the following question:

What effects would propellant that expands at near light speed have on firearm technology?

And the result is very similar, so I'll quote my own answer from there:

The very first XKCD - what if article deals exactly with that. The scenario is a baseball being thrown at 90% of the speed of light. It is a very fun read, and, like many other XKCD what if's and questions that have the tag, anyone around the phenomenon proposed in the question gets disassembled into particles in a very spectacular way.

TL;DR: at near light speeds, particles with mass have enough energy to cause nuclear reactions. Here is Randall Munroe's artistic conception of what happens when the mass in case is that of a baseball:

My eyes! It burns!

You have a projectile that is one order of magnitude slower, but since you are sending a rocket, I imagine it is a few orders of magnitude more massive, so you get an even less favourable scenario. The lack of atmosphere doesn't help - there is no air to form a growing ball of plasma, but the ground and the ship are going to be turned into a mix of plasma and molten metal and rock - and even if they didn't, how would the microbes in the rocket survive the hard vacuum of space anyway?

  • $\begingroup$ Fusion, not fission. $\endgroup$
    – adrian
    Commented Dec 28, 2018 at 4:40
  • $\begingroup$ Bacteria can survive years in the vacuum of space $\endgroup$ Commented Dec 28, 2018 at 5:10
  • $\begingroup$ @AdrianZhang fusion requires more energy than fission. Fission is more likely in this scenario. $\endgroup$ Commented Dec 28, 2018 at 11:06
  • $\begingroup$ So, you suggest that, due to the amount of energy unleashed in such an interaction, that it is impossible? I wouldn't think the presence of an atmosphere would be advantageous given that our "spacecraft" is traversing it at 30,000 kilometers a second. For 100 km of atmosphere, that's about 3 milliseconds of potential drag-time. Also, "microorganisms" was just a placeholder for something fictionally synonymous that has no trouble in hard vacuum, perhaps nanomachines. $\endgroup$
    – user44399
    Commented Dec 28, 2018 at 17:16
  • $\begingroup$ @B.fox 3 ms would present no noticeable difference ; also, the atmosphere around the ship would suffer nuclear reactions and become a plasma hotter than the surfave of the sun. As for "Also, "microorganisms" was just a placeholder for something fictionally synonymous that has no trouble in hard vacuum, perhaps nanomachines", it's not what was asked, but the nanomachined would be vaporized as well. $\endgroup$ Commented Dec 28, 2018 at 17:42

Realistically, no.

Lets consider something weighing 1kg, impacting at 10% of lightspeed. That's 453,408,126,873,804 Joules of energy. 4.5E+14 J to keep it more manageable.

I'm not sure what is the hardest thing to vaporize but amongst the elements it's clearly Boron. (Perhaps there's a compound that will be harder, if so my google-fu isn't up to finding it.)

To raise 1kg from room temperature to it's vaporization point needs roughly 2.3MJ, plus 4.7Mj to melt it and another 45.3MJ to vaporize it. Thus 52.3MJ = 5.23E+7 J is absorbed into converting it into a gas that obviously isn't going to be in a position to do much more. Note that this is about 1 millionth of the energy that must be dissipated. I can't imagine a system that will be so efficient as to overcome this.

There's also the problem of being squashed flat. I'm breaking every calculator I find trying to input a large enough acceleration to stop it in 1km.

  • $\begingroup$ Yes, I imagine for a blunt mass this is the likely case, although, I don't think all of the energy would be redirected back into the colliding object. Some would be dissipated into the body it collided with and some into space as light. The compressive forces alone would probably be enough to destroy most molecular bonds. The result would likely be a lot of super-heated gas as you suggest. $\endgroup$
    – user44399
    Commented Dec 28, 2018 at 17:06

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