Deep Space Questions – Episode 10 – Relativistic Aerodynamics, Thermonuclear Warheads & Red Dragon

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Another batch of questions from supporters over at Patreon

This month I do some mental artithmetic about the density of the interstellar medium, ponder what it means for humanity to live in space, how to communicate to non scientists and other things.

  1. Todd RF

    I just finished reading the book you have on your desk. It’s well worth it.

  2. Chr Stian

    An onther problem with near lightspeed travel is the background-radiation
    As you speed up this will get more and more hard radiation due to the doppler effect.
    And at a certan point this will be gamma radiation.
    So you need to shield from this as well

  3. Sanket Savani

    From a DJ to one of the most NEEDY guy in Aerospace community 🔥

  4. James Tuck

    “Mongolian metal bands” must have been a reference to “The Hu”? A great band btw if you’ve not heard 😁

  5. Leo zanyk

    This format of videos is awesome, keep up the good work!

  6. James Millar

    Second stage implosion isn’t driven by radiation pressure, it’s an ablative process. The photon gas has the sole job of heating the exterior of the secondary.

  7. Arational

    First reference to Avogadro’s Number that I’ve seen on Youtube.
    Well done.

  8. Adam B

    “If humans were meant to live in Minnesota they would have fur.”
    As a fellow Californian I agree with this sentiment haha

  9. Ray Bell

    I greatly appreciate your insights, I am concerned about preventing fuel boiloff during the Starship journey to Mars. Could the Raptor engines run on Butane as it will stay liquid for longer than Methane.

  10. Destructor1701

    Watching Scott math scientific notation in his head at the beginning was terrifying to me for some reason. I guess it’s a “holy shit my brain sucks” moment.

  11. M G

    “If humanity were meant to live in Minnesota they would have fur” love that line Scott Manley… My response usually to those kind of people are if God did not intend us to do something God would not give us such big brains to do it and trying to figure it out for ourselves… And also to add on to your Minnesota reference I would also reply with if humanity was meant to live in Africa we would be born with elephant like ears like nearly all desert animals have

  12. tevvya

    Hey Scott, one small point in the phrase “flora and fauna” the “fauna” refers to animals and the “flora” is plants. While there are animals which are “grown” (e.g. silk worms) but overwhelmingly we talk about “raising” animals and “growing” plants. I love your channel–been a long time fan!

  13. ke6gwf - Ben Blackburn

    When you mentioned Mongolian Metal my throat starts hurting and my head starts banging thinking of The Hu – Wolf Totem.
    Now I have to watch it again! Lol

  14. steve polychronopolis

    I feel like we should expand on collisions with hydrogen in space at any speed.

  15. Jonathan Bush

    Great video as usual! I have a small quibble. 1:58 “Even if you’re traveling at 99% the speed of light, the drag is a million times less” This ignores the effect of time dilation. Once you reach about 71% of c, you will be traveling through one light year’s worth of interstellar material within one perceived year. Beyond that, the amount increases to multiple light-time units per perceived time units. So the ratio could decrease significantly below 10^6 once you reach 0.99c BUT this was what the original question was specifically NOT asking about.

  16. jazz itsw

    Hey Scott, I’m also into Hawaiian 🍕 toppings 😉, no doubt the best to have.
    Do you still know where you got that Shirt from? Greetings and fly safe!

  17. CrackerJakkTV

    When you referenced Mongolian heavy metal, were you talking about The Hu? If so, I agree. They make some good music.

  18. Yora

    “Jemenai” or “Jemenee”? Doesn’t matter, both are wrong. It’s Latin, so it’s a hard G.

  19. keco185

    While there are fewer particles hitting the spacecraft per unit time when traveling close to the speed of light in space, those particles are accelerated to a much higher speed when they do hit the spacecraft so the drag could probably still be higher in space

  20. Bob Blum

    Scott, I always enjoy trying to read the titles on the books you have in the background during your videos. Many I recognize. In this one on your left (our right) I see the title “Test God”; I can’t tell if it’s a book about someone well known as being the greatest when it comes to testing things, or a book about (dis)proving religious concepts! 😉

    Thanks as always for an enjoyable video!

  21. Fred Bloggs


    Last time I checked, the density of interstellar space is also too low.

    Which is annoying, the idea was great.

  22. RaDeus

    12:27 HERETIC, BUUURN HIM! /s

    I like kebab pizza myself, with the rare calzone/kebab variant being my favorite 😄

  23. Gewel ✔

    16:22 I absolutely love that voice!

  24. Robert Orton

    On the speed units question, I can recommend always using ℓP / tP to avoid arbitrary confusion. although the numbers do get very big/small in every day use and there is the inherent problems with floating point representations but conveniently the speed of light is 00111111100000000000000000000000, so there is that at least to help reduce the confusion over units.

  25. Scott Dorfler

    That’s the coolest nurd shirt I’ve ever seen!!!

  26. Jeff Evarts

    Newtons as the “correct unit”… ask the people at Wikipedia about this. Someone once wrote a clever robot that visited each page and changed all the “miles per hour” to “kph” and “pounds” to “kilograms”, etc… Good idea, except… I once found an agricultural page that listed the yield of grain in a locale… *in kilopascals* … the unit converter had seen “tons per acre” as the grain yield, and said “hrm, that’s force per area… which is newtons per square meter… which should be listed in Pascals…” not the right unit.

  27. Bob-a-FET

    Love The Hu they’re great – the Tuvan throat singing is such a different sound I often think of it as being like Pink Floyd’s experiment with singing as an instrument; The Great Gig In The Sky is what I’m thinking of from Dark Side Of The Moon. I often visualise this as what aurora borealis might sound like; which comes back to the album cover.

  28. jjbloon

    Do the Gemini rescue for stranded Apollo mission in KSP! that would be an awesome visual

  29. Elliot Robinson

    I think I’d thank the Alien overloads the day Scott gives us a DJ set

  30. Paul A

    The only newtons I understand are fig newtons. Thankyou for using pounds for me, and kg’s for those that understand them. I can at least ask Google to translate metric to Imperial so I can relate. Mind, I like metric better, but it was never taught in school so my mind is crippled with Imperial measurements.

  31. Kuba Ober

    I’d imagine that at a good fraction of c, the “airflow” tends to fuse with the “wings”. As in nuclear fusion. Not the best outcome for longevity of the thing.

  32. realulli

    10:30 Doing bespoke chips – I remember talking to some guys at the University of Freiburg, about 30 years ago. They were showing off their raster tunnel microscope, especially that they discovered they could pick up single atoms if they modulated the current going through the needle in just the right way.

    Now add the fact that carbon is a semiconductor when it is in a diamond grid. These guys were fantasizing about using their method to build computer chip diamonds (including doping the carbon) from scratch.

    What makes these chips very interesting for flying to Venus is that they could theoretically comfortably operate at temperatures of up to 800C, so the computers using those could be air-cooled even on the surface of Venus…

  33. Zach Billings

    I was listening to this in the background at work and I involuntarily winced when you said you like pineapple on pizza. Love the rest though!

  34. smockydevil

    Regarding the 1st question, and doing a similitude with standard aerodynamics, I think you forgot to notice that the drag includes the velocity squared. So even though density is extremely low, with the speed of light squared you get quite a lot of drag.
    Of course, if you consider relativistic behaviour things are probably not that simple though..

  35. Joel Tashinian

    Totally SOMA! “goes well woth most meds” put in 1000s of hours of mission control. Always relaxing when precussion is just too much. I could pass time to this stuff. Also Goa Psy and many more

  36. Marshall Garey

    Yes, another Hawaiian pizza fan! I especially loved that kind of pizza in Taiwan (I got it at Costco) since the pineapples are fresh and soooo much better than the pineapples we have in the US.

  37. Lucifer Satoshi

    The MASS of the rocket is expressed in kilograms, so it makes sense to talk about the thrust in kilograms or metric tons.

    If we are going to talk about trust in Newtons, then we should talk about the WEIGHT of the rocket in Newtons.

    This way we can quickly and intuitively derive the Thrust to Weight Ratio without a lot of conversions.

  38. Bookjunkie

    I really need to remember “My favourite pice of music is always the piece of music I’ve never listened to”, I’m totally with you on that one.

  39. Em Wintle

    So happy you’re still using the Pride rocket 🌈 🚀

  40. Steven Castellanos

    Newton😆 I love how Elon basically gave the same answer. He likes to use cost/ton for the raptor engines. I think it was Tim Dodd’s 1st video where he gave his opinion on silly units of measurement. Silly as why use it in that instance if you’ll have to convert it anyway.

  41. Hex System

    @17:25 Wasn’t there a tether experiment done about a decade ago where the tether broke? It was determined that we couldn’t produce a long enough tether with the appropriate tensile strength to make it a practical application at this time, or something like that. I may just be completely misremembering it. It has been a while.

  42. FalconWing 1813

    Yes ! please do the Gemini moon / rescue mission on Kerbal . Would like to see that!

  43. KantanLabs

    For the first part; relativistic aerodynamic, you forget to take into account that in aerodynamics the drag increases as the square of the velocity and even like the cube of the speed for very high mach numbers (the present case), so your order of magnitude computation does not hold and indeed crossing high-density nebula at light speed is going to be a problem. On the other side at low density and low temperature, the medium doesn”t behave as a fluid as the mean free path is very large (probably much larger than the starship), so that the physics behind is only a matter of high-energy impacts on the fuselage and on the total amount of momentum transferred to the medium particles through the inelastic collisions. Again the energy removed by collisions are proportionnal to the densiy (increased by the relativistic factor gamma), and the square of the speed. Pretty sure it is not negligible in high-density regions.

  44. docpaul

    Love SomaFM!! Not even thought about this station for over 10 years – thanks for reminding me!!

  45. Michael Pagan

    Re: magnetic cores for Venus “logic gates” – 1) magnetic cores were memory, not logic gates (the logic was done with discrete transistors). 2) magnets demagnetize at elevated temperature, not sure exactly what temp but they would likely be useless at Venusian temps

  46. Daniel Pierce

    Spooky action at a distance still blows my mind, I think about it a lot…

  47. Bill Donnelly

    Thnx for the sonafm yip – perfect background music for when I’m working on my projects!

  48. Joy L

    Very enjoyable episode again!
    Thank you so much Scott.
    You are a endless well of knowledge.

  49. Wesley Bantugan

    Best birthday upload! Thank you so much for all of your work!

  50. Oscar Sommerbo

    Damn, that booming outro music really cleared out my ear canal.

  51. kingawsume

    Thanks for pointing out SomaFM, this stuff is exactly what I didn’t know I wanted.

  52. Matthew Tarbet

    Pineapple and Ham on pizza- Thank you Scott, been my favorite since day 1!!!

  53. Invisifly2

    13:10 – If somebody knows that trying to pull petty bull over something minor will wind up causing them a major headache due to spiteful retaliation then they are less inclined to do so. Malicious compliance is the embodiment of this. Inotherwords spite helps make sure you have a good reason to bother people before doing so because they’re going to bother you right back. Self destructive spite is just the unhealthy extreme of perfectly functional social behavioral regulation.

  54. Dean Su

    1:50 I’d like to point out that drag scales as the velocity SQUARED, so if the density is 10^-14 times that in the atmosphere a flat plate would “only” really need 10^7 m/s to get the same drag as it would travelling at 1 m/s on Earth. Arguably it would be worse if we considered relativity because momentum scales nonlinearly near the speed of light.

    That being said, the drag you’d get at 3% the speed of light amounts to a stiff breeze on Earth, which would be the least of your problems considering the energies of said particles are literally cosmic-ray-level, so in the words of Winchell Chung it’s like “flying down the barrel of a particle accelerator”

  55. Todd Zircher

    Thank you for the maths on near-light speed aerodynamics.

  56. CuriousMarc

    Unfortunately the Achille’s heel of a magnetic core bi-stability has always been its sensitivity to temperature. The first core memories could only work in an oil bath with precisely controlled temperature. Later on, thermistors were used to sense ambient temperature and make the required fine current adjustments in the drivers. And then of course, above the Curie temperature, there are no good magnetic properties left. So not a viable candidate for Venus electronics unfortunately. They are very insensitive to radiation though, very good for that.

  57. S. Montgomery

    SomaFM’s still around and it is the greatest! I’m a GrooveSalad fan myself.

  58. Friday Californiaa

    Scott went totally nuts on this one 😂😂 I love it 😂

  59. Brandon Link

    As a Minnesotan I can confirm that fur would be a nice addition when it’s -40 in January, not so much when it’s 105/40 in August.

  60. J T

    Shuttle on the top of the stack as opposed to the side, seems like a very plausible solution. at the very least the crew compartment should have been designed as a completely “ejectable” module. Like a capsule. To be used in the case of Columbia. And possibly would have allowed Challenger crew to survive. Provided the parachutes survived the initial breakup.

  61. Skorj Olafsen

    “kilo-Newtons are a stupid unit, all we ever care about is tons of thrust” Elon Musk

  62. Jim Marburger

    Hey Scott, thanks for being one of my favorite space content creators. Before I get to my point, I like your selection of reading you have behind you, lol. I have a comment on the thermonuclear bomb you chose as the counter intuitive physics. It is outrageous to think of a device that is destroying itself as it works but in this case as in all of these weapons the time for the actual reaction as the core goes critical is very short. The US designers of the bomb (Fat Man in this example) calculated that it would take .8 microseconds to complete the 80 generations of neutrons hitting atoms, splitting and those going on to hit more. At that point, the core would be so distorted that it would drop subcritcal. I don’t know at what speed the explosive forces propagate but I have a feeling that it isn’t even beyond the case. With newer weapons I believe with reflectors, neutron sources and boosters it wouldn’t even take that long. My speculation though. Thanks Scott!
    BTW, the time for a neutron to travel the entire diameter of the core was dubbed a “Shake” as in the shake of a lambs tail…

  63. Moto Rick

    Scott says, “fly safe” like my mother says “clean your room”.

  64. John Vincent Pedregoza

    Now I don’t feel so alone with my choice of music as well! This was actually a blast! Looking forward to the next month’s DSQ.

  65. Ethan Pricco

    4:42 as someone living in Minnesota, having fur would really help in the winter.

  66. Blibby Blobby

    somaFM is my main choice on Tunein radio.
    The mission channel is still there …
    Just relax, stair at the stars and listen to the lucky ones do the thing that people thought couldn’t be done.

  67. bbertsch23

    Scott, listen to king Gizzard and the Lizard wizard, they span many genres, should keep you busy for a while

  68. RealPunkie

    Scott: “I like hawaiian, that’s my thing”
    me: Nooooooooooooooooooo!

  69. C Fudge

    One of my favorite songs for any Space Game Play is Clutch “Space Grass”. Definitely a play list add. Also fun driving song. Rock on Scott

  70. lance moore

    In “The Songs of Distant Earth” (1986) Arthur C. Clarke wrote about huge ice shields attached to the leading surfaces to act as an ablative shield from high speed particles.

  71. Tommy Huang

    I see the “What if?” book in the background Scott :) absolutely fantastic read

  72. Pedro Cardoso

    In the first question, dont you have to consider length contraction too? what if the lorentz factor is also 1000000?

  73. Zachary Hill

    I love these episodes! Please keep these up, I hope you can do them every month as well

  74. Brym Stone

    I’m surprised nobody’s asked you recently… granted, your audience has considerably widened over the years, but do you still play Eve from time to time?

  75. Itz_ Ultima

    “Mongolian Metal”

    The HU is 🔥

  76. Wiregold

    Pear, Gorgonzola, caramelized onion is the oddest-sounding but great tasting pizza.

  77. baze.djunkiii

    john peel…. he even played one or two records released on my labels back in the day. unfortunately i never heard the actual shows but i saw playlist arounds and i am forever grateful for that.

  78. Craig Jackson

    I enjoyed ya b4 but knowing you also like Hawaiian pizza..! You’re now definitely my favourite Scottish space nerd.

  79. TonyP

    Still amuses me that theres a game in the book case called “f*ck yeah games” :)

  80. bami2

    14:53, the way I understand it, the primary is boosted by injecting some fusible fuel (like tritium) into the core as it is collapsing. For variable yield, this boosting is adjusted (simply less tritium is injected into the core or injected at a different rate or something), so the primary delivers less radiation (pressure) into the secondary, which causes less of the fusion fuel to fuse, hence less total yield.

    So all of the dial-a-yield is done in the primary, not some constrictor device between the primary and the secondary. It’s not like any device could ever hold that back.

  81. The Legacy

    Pizza… and Nuclear Warheads?

    Now THAT’S a sentence I never thought I’d read. 😂

  82. Antonio Maglione

    Hello Mr. Manley,
    The “guy at NASA” about project Gemini – was Dr. Gilruth, I believe.
    He was there pushing for Mercury, Gemini and Apollo, as Chief of the Johnson Space Centre…
    Thanks for the video! I appreciated every single bit except the ananas on the pizza.

  83. RuKiddin06

    The idea of a nebula fusion ramjet is insane. I love it

  84. Mark Werley

    Spite has been shown to have a societal benefit. In games where all participants benefit from cooperation, but freeloaders can bring everyone down, adding a spiteful element can bring all players back into cooperation. There’s a cost to the spiteful player, and no obvious benefit except the satisfaction of teaching the freeloader a lesson, but everyone’s scores eventually go up. Personally, I don’t want to be the spiteful player, but I guess I’m glad they’re there.

  85. Logic?

    You forget that drag raises from velocity squared or cubed depending on case, in this case cubed more likely. Vacuum of space is around 10^-9 to 10^-20, and speed of light around 6*10^8 mph which squared is 3.6*10^16, making much vacuum in space equal to about drag from moving 1 mph in atmosphere on earth which can be big for large structures over time

  86. Astronist

    3:25 – reversing direction using the galactic magnetic field. The reference is: Mallove and Matloff, “The Starflight Handbook”, p.73-77. I once checked their figures and found a confusion between gauss and tesla, as the result of which (according to my calculation) the galactic magnetic field would be 10,000 times too weak to generate enough Lorentz force to move the ship as described.

  87. armr6

    recovering a S-V booster in the 70s-80s would give the whole “suicide burn” thing a new meaning.

  88. B D

    That was cool watching him do the maths in his head on the spot

  89. Lone Wolf

    oh thank you for the soma fm recommendation… its so hard to find good chillout on youtube its all full of bass and mixed up genres

  90. Leah C

    Love the T-shirt 😍

    Do you think maybe Accelerando may be the way we go ?

  91. Java Man

    One issue with high-speed relativistic travel (0.999999999…c) is that the cosmic microwave background (CMB) becomes blue-shifted into the gamma ray range and focused into a narrow cone directly ahead of the ship, so you need to shield against that radiation in addition to any particles in the interstellar medium impacting the spacecraft with extremely high energies.

  92. CHET M

    “If humanity were meant to live in Minnesota they would have fur” Scott Manley 2021

  93. Waffledraggin

    As a Minnesotan, I can confirm that Fargo is not a bad representation. Considering that it and it’s sister city split the ND MN border, it’s basically half Minnesotan anyway.

  94. Mark van wijk

    Keep up the good work, the content keeps getting better!

  95. Thomas Rogers

    Words cannot describe how motivational spite is for certain people.

  96. Valentine

    Nebula ram-jet is the single most awesome phrase I have ever heard

  97. Hicham Mohsen

    Can you please talk about the physics and math of deorbiting and reentering the atmosphere, precisely on how they predict landing sites when you have such a dynamic atmosphere!?

  98. Seán O'Nilbud

    Travelling at high speed the interstellar particles would be like nuclear bombs.

  99. Rita Loy

    I hope you can do this every month.

Comments are closed.