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Let's say I'm returning home in my near-future space capsule, but instead of the leisurely Mach 32 the Apollo astronauts experienced striking the atmosphere, through major [plot-device hand-wavium] interference, I re-enter at Mach 172.

What would happen?

I'm guessing I'm instantly vaporized. But what else? Is earth doomed as well?

Edit: Capsule specifics
Let's say my re-entry craft is about 6 meters in diameter and 4 meters tall in the classic gumdrop shape of Apollo era space capsules, with a weight of 10,000 kilograms.

My ablative shielding was designed to withstand up to 20km/s reentry speeds, but is recommended to only re-enter up to 16km/s.

Kallmanation
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    I do not see how this is world building. Even if it ssomehow is, it is too broad, as we do not know tech level, mass of the capsule, ablation shielding, shape, reentry angle, nothing... – Mołot May 22 '18 at 15:32
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    @Molot, I've added details about my vehicle. Tech level is near-future, so you can bend material science a little bit, but no unobtanium or adamatium constructions. If you think there's more details that would make this question better, I can try to expound. – Kallmanation May 22 '18 at 15:48
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    are you aware that giving a Mach number in the vacuum of space makes no sense? – L.Dutch May 22 '18 at 17:44
  • @L.Dutch: Indeed, Mach number is a variable, a function of atmospheric temperature, pressure, and composition: https://en.wikipedia.org/wiki/Mach_number#Calculation – jamesqf May 22 '18 at 17:52
  • @L.Dutch, Yes I know it depends upon atmospheric conditions and has no meaning in a vacuum. But it does have meaning once I re-enter, which is what my question is on, and I'll be traversing the whole of earth's atmosphere so quickly, I didn't think the difference in mach number between upper and lower atmosphere made much of a difference for me. So I felt reporting in Mach number was a good headline version of what's happening. – Kallmanation May 22 '18 at 18:01
  • Since your velocity is almost three times the maximum recommended in the manual, consider a few aerobraking passes through the atmosphere before your final approach. – user535733 May 22 '18 at 18:46
  • If you look at this image from Wikipedia, the sped of sound varies by something like 30% from 90km altitude down to 50km altitude. – Cort Ammon May 22 '18 at 19:09
  • I'm seeing a lot of VTC. If I may hazard a guess, it may help to amend the "What would happen" to be more focused on what happens to the earth. What would happen to the lander is very story specific, but what would happen to the earth is, as Wilik's answer shows, based more on the materials and sizes. Putting that in the bold part may help styme the VTC votes. – Cort Ammon May 22 '18 at 19:45
  • It would seem that all the VsTC are some kind of reaction to the discussion ongoing at Meta regarding what questions are on & off topic. This question, according to the present agreement, is perfectly on topic and should be reopened as far as I'm concerned. – elemtilas May 23 '18 at 19:01

5 Answers5

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You break up in the atmosphere. You make a sound as loud as heavy traffic.

Mach 172 is 57 km / second; a reasonable speed for a meteor. I used this site: https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/ and gave you 10 m diameter and the same density as ice.

Earth Impact Effects Program

Robert Marcus, H. Jay Melosh, and Gareth Collins

Your Inputs: Distance from Impact: 1000.00 meters ( = 3280.00 feet ) Projectile diameter: 10.00 meters ( = 32.80 feet ) Projectile Density: 1000 kg/m3 Impact Velocity: 53.00 km per second ( = 32.90 miles per second ) Impact Angle: 90 degrees Target Density: 2500 kg/m3 Target Type: Sedimentary Rock Energy: Energy before atmospheric entry: 7.35 x 1014 Joules = 175.68 KiloTons TNTThe average interval between impacts of this size somewhere on Earth is 28.8 years Major Global Changes: The Earth is not strongly disturbed by the impact and loses negligible mass.The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).The impact does not shift the Earth's orbit noticeably. Atmospheric Entry: The projectile begins to breakup at an altitude of 98800 meters = 324000 ftThe projectile bursts into a cloud of fragments at an altitude of 37000 meters = 121000 ftThe residual velocity of the projectile fragments after the burst is 39.7 km/s = 24.6 miles/sThe energy of the airburst is 3.23 x 1014 Joules = 0.77 x 10-1 MegaTons.No crater is formed, although large fragments may strike the surface.

The air blast will arrive approximately 1.87 minutes after impact.Peak Overpressure: 654 - 1310 Pa = 0.00654 - 0.0131 bars = 0.0929 - 0.186 psiMax wind velocity: 1.54 m/s = 3.44 mphSound Intensity: 56 dB (Loud as heavy traffic)

I was interested to see that something this size and speed hits earth's atmosphere every 28 years. Ho hum.

Mołot
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Willk
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  • Good info, but I think the capsule is probably much better equipped to survive the trip than a meteor – Josh May 22 '18 at 15:33
  • Chelyabinsk meteor was slower, but considerably bigger. It had an estimated energy of 400–500 kilotons of TNT (3x of the example here), and still it did not cause much trouble. – Alexander May 22 '18 at 16:31
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    You don't necessarily break up in the atmosphere. Assuming you have a strong capsule, a good heat shield, and the proper re-entry trajectory, atmospheric braking slows you to a speed where you can use parachutes &c. The Galileo probe entered Jupiter's atmosphere successfully at a speed not far from that: https://en.wikipedia.org/wiki/Galileo_(spacecraft)#Galileo_Probe – jamesqf May 22 '18 at 18:00
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    @jamesqf However, the OP's specs state "My ablative shielding was designed to withstand up to 20km/s reentry speeds, but is recommended to only re-enter up to 16km/s." When you're re-entering at over twice that, something's gotta give... and that something is you! – Cort Ammon May 22 '18 at 19:11
  • Adding a symbol for powers of ten would improve the answer. It took me a while to figure out why someone would write 7 \times 1014 joules, and why the number is so small. – Tommi May 22 '18 at 19:24
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    Rolled back last edit. Code syntax should never ba used for non-code content. Among other bad effects it makes content hardly accessible for visually impaired people using screen readers, as some (many?) of these tends to read code letter-by-letter if they do not recognize particular code syntax. – Mołot May 24 '18 at 18:26
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Mach 172 is about 57km/s. If your re-entry vehicle has the same mass as the Apollo Command/Service module of 11,900kg, then it will have a kinetic energy of about 7.7 terajoules. That's about 1.8 kilotons of TNT equivalent, so the size of a tiny tactical nuke. So the Earth is certainly safe, but if it was only intended to handle Apollo-level re-entry speeds, your craft certainly isn't, as it has about 29 times as much kinetic energy which needs to be dissipated.

Stephen
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The details depend on how much of your capsule survives the fall. I'm not sure if you'd be vaporized, but you'd definitely die of something. As for what happens to earth, are you familiar with project thor and the concept of kinetic bombardment?

The basic idea behind that weapon system is dropping a large mass from orbit to cause a kinetic explosion. (an explosion generated simply by kinetic energy, not by an explosive payload) According to the info in the link, 8 kilometers per second is a fast enough re-entry speed for a tungsten rod of approximately 20 square feet to cause a great deal of damage with an impact speed of mach 10. (comparable to a small nuke, according to some estimates) Your capsule is entering not at 8 kilometers per second, but at almost 60. It will have a great deal more drag than the tungsten pole, but also more mass, and I imagine after some atmospheric burning/vaporization, it will lose a lot of that drag.

So I think if your capsule is durable enough to make it to Earth in some form, everything nearby is in trouble, but the earth as a whole is safe. I'm going to keep researching to see if I can find an approximation of how much of a capsule could make it, and how much it would be slowed down. I'll update the answer with anything useful I find.

EDIT It was surprisingly hard to find information on temperatures during reentry at such high speed. I found a record of a supersonic jet reaching mach 20 and heating to around 2000C. Spacecraft seemed to hit around 1300C at a bit less than half that speed. NASA's heat shielding looks like it can take close to 4000C, but I could not find details on what happens above that temperature. (I'm sure it's not good) I'm not sure how the temperature grows as heat increases, so I'm not sure what the odds are that your capsule survives. My gut says that the temperature increase probably slows as the speed gets higher and higher, and your capsule will decelerate REALLY quickly, so I still think there's a good chance some of it will survive, but unfortunately I'm not going to be able to find a definite answer.

Josh
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You shatter and burn up in the upper atmosphere, assuming you're angle of approach approximates 90° to the ground, if you're off that by much you're still going to shatter but also bounce off the atmosphere at an acute angle and fall away into the universe. Bits of the capsule will probably make it surprisingly close to the ground due to being composed of heat resistant alloys.

Ash
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Even if your heat shield stands, the at this speeds high atmosphere is like concrete. Your spaceship, which is not designed to support that much external pressure, is crashed like an egg at 100 km of height.

Rekesoft
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