Deep Space Questions – Episode 8 – Heavy Payloads, Cool Rockets & The Most Difficult Question Yet

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Continuing to answer questions from supporters over at my Patreon

NASA’s open Source Software

Weakless Universe

Fundamental Physical and Resource Requirements for a Martian Magnetic Shield

American Rocketman – by Robert C Truax

Most of the questions are still taken from the first post:

  1. Brian Jaber

    Thank you for that Scott I completely enjoyed it although I completely enjoy everything you do, so I guess it’s just thank you so much and keep up the great job.

  2. Bob Burrough

    Scott, regarding a magnetic shield to protect Mars atmosphere, please see phys dot org “NASA proposes a magnetic shield to protect Mars’ atmosphere.” NASA suggested that you only have to protect two relatively small areas where atmosphere is escaping.

  3. Bryan Hensley

    The trip back from the moon probably took less time because they didn’t use free return trajectory and used power burns coming back. I’m just guessing though..

  4. wil6817

    Surely answer to the first question is earth has a greater magnetic field so it starts feeling the effects of earth’s gravity sooner over going to the moon which is where it would be fighting against the earth’s magnetic field before the moons takes over?

  5. Roger Stone

    Scott, PLEASE do a video explaining the graph of abundance of elements in the universe as at 9:40! Why does it have that double-line zigzag? Are elements alternately right- and left-handed? And why isn’t there a much bigger drop-off after you reach Iron, the heaviest element which can be directly made in a star?

  6. Remtech Shelby

    Hi Scoot, has the FAA ever done an environmental study of rocket maker?

  7. RickTheClipper

    Hi Scott, assumed Starship flies to Mars, what will happen to the LOX and Methan, will they boil off or freeze? In Zero G the liquids will form bubbles floating around in the tank. How to ignite the engine again in Zero G

  8. josh cheatham

    the first thought I had on that question was. Earths gravity. To the moon the were escaping it. On the way back they are pulled in. Also the time spent in parking orbit, dockings, much less weight.

  9. Michael Kilbourn

    The reason it took longer to get to the moon than coming home is because after TLI the spacecraft were decelerating because of the Earth’s gravity. When they enter the Moon’s gravity sphere they speed up again. But on the way home they are accelerating from the time they leave the Moon’s gravitational influence, which is only about 1/4 of the way home.

  10. 786otto

    Mars could use a teaspoon of a neutron star to get its magnetic field going.

  11. Hellboy Stein

    1-2Tesla would be made with superconductors in such a case.

  12. Martin Smyrk

    Absolutely loved watching you work through the first (Apollo return) question. Would definitely like to see a video once you’ve done your research.

  13. Nicholas Maude

    Talking about open-source software in aerospace, Scott, the Falcon 9’s first stage uses a guidance algorithm developed by NASA for its boost-back and landing perhaps you could do a video about that?

  14. John Kepa

    Hay Scott i have a question. After a long manned mission to mars. How fast would astronauts body’s adapt to gravity once on mars. As we all know body muscles, bones deteriorate. Could SpaceX integrate artificial gravity on starship?. After long missions on board the iss astronauts can’t move. Just a question

  15. danny234786

    Hey Scott, regarding the first question: At approach you have two fully fueled spacecraft. So to make it faster you have a very expensive burn – and that even twice (once when leaving the earth and once when decelerating at the moon). When going back you have only one spacecraft with less fuel so it’s much cheaper to speed up the mission time.

  16. TheeGrumpy

    Delta-v between ISS and Tiangong is within the capability of Soyuz landing thrusters (and a fire extinguisher), if Sandra Bullock taught me anything.

  17. T.

    Damn, I miss the Space Shuttle. ☹

  18. Starpartyguy

    On the way out, the earth being larger would be slowing the trip, while on the return it would be accelerating travel. The Earth’s gravity well extends farther than the moon and starts to influence velocity sooner on the way back than on the trip out.

  19. David Archbold

    Scott – regarding lunar and earth transit: did they use the same thrust when launching from earth and moon orbit?

  20. Mike DeMarco

    The heaviest landing WOULD HAVE BEEN Columbia, STS-107, with a fully loaded SpaceHab double module.
    It flew, unfortunately, without its robot arm to due to weight constraints, even to a more equatorial orbit.

  21. Mike DeMarco

    So, Salyut 7 and MIR were in the exact same orbital plane.

  22. Lew Sheen

    Scott: Outbound spaceflight has to overcome EARTH’S gravity – 6X the moons’, inbound spaceflight is falling into a 6X stronger gravity field than the origin on the moon. Not sure why this is hard to understand…

  23. RWBHere

    At 5:05 to 6:25 – What an interesting statement that is about the precision behind the structure of the universe! Thanks Scott.

  24. ElectricUrinal

    Regarding the first question: maybe the question was asking about the idea that command module reached something like 24,000 mph during the final stages of the return trip, and on the way out the spacecraft never moved that fast. Which of course the answer is because of the Earth’s much more powerful gravity pulling objects toward it.

  25. Daniel Son

    I would of thought that coming back from the moon would be quicker because of the mass and gravity of the earth compared to the moon there for tugging greater because of gravity.

  26. DJ Wooten

    I’m pretty sure going to the moon had to be slower because entering orbit required fuel and they had the mass of the lander. On the return there was no need for orbit and atmosphere could do the majority of bleeding the speed rather than burning.

  27. Jim Patrick

    My guess with the flight times to the moon is; the apogee for the free return trajectory is on the dark side, so it has further to travel whereas coming home the apogee is on the earth side.

  28. D.Eldon

    Regarding the shorter travel time to return from the Moon to the Earth, isn’t the Earth’s much larger mass the primary factor? Since the Moon has so much less mass, it takes less energy to escape and, since the Earth has so much more mass, its gravity exerts a much stronger pull on the returning spacecraft. Another way to look at it: Traveling from the Earth to the Moon requires the spacecraft to fight against gravity. On the other hand, traveling from the Moon to the Earth enables the spacecraft to cooperate with gravity.

  29. loonatic90

    0:50 Isn’t it related to going up Earth’s gravity well (constantly slowing down) the way to the Moon and down the well on the way back to Earth (constantly speeding up)? Maybe also position vs. Sun makes the difference?

  30. Frank Gulla

    Thank you, Scott, for another great Q&A.

  31. Em Wintle

    Wow, those were amazing questions. Thanks, everyone!

  32. Loren Maendel

    I think the answer to question one is simply earths gravity. On the way there they are fighting earths gravity where as on the way back its helping them and they are constantly accelerating and there acceleration is increasing too as they are basically falling back to earth.

  33. Colin Paddock

    Winchell Chung is the GOAT. Disclosure: I owe my avatar to him.

  34. Tetsujin

    5:07 – Sounds kind of like a creationist “fine tuning” argument…

  35. Manu blabla

    Slight addition to the isolation question:
    Minotaur IV also has one; BANANAPEEL

  36. Richard Loewen

    Scott, could you investigate the following?: Does Musk need to make one or more lightning towers TALLER than the launch / landing tower at Boca Chica? Is that not a necessary component of the not yet supplied FCC permission? (I love Musk and his endeavour, but I’m getting nervous.)

  37. Marco Francioni

    On the moon faster returns:
    The Moon transfer burn was performed after some orbit around the earth therefore the perigee was at least above 100km (probably 200km) while for the return the perigee was inside the atmosphere to exploit aerobraking therefore the orbital period is shorter

  38. Tim Ypp

    Imagine the amount of sea life it will kill, if the sea dragon ever gets off …

  39. Thomas Jager

    For the magnets, what about superconducting magnets? In my lab we’ve got a cryostat with a superconducting magnet that can put our samples under test (a bunch of IC dies) up to 2.5 T.

  40. Christian A

    The problem with a trebuchet on the moon is that they used to try and find the biggest tree around to build the trebuchet’s main arm. There are no trees on the moon.

  41. Manu le maboul

    You can’t aerobrake on the moon, and the moon’s orbital velocity is much lower than earth, so they had to arrive there with either a lower velocity or with enough fuel to brake; so slower for obvious reasons, hence the travel being longer I guess.

  42. Jeriku

    When you love rocket science and you are in the matrix

  43. BOB A

    transit time – its the gravitational delta between the earth and moon. 60hrs / 73hrs ~ = 5/6ths

  44. QwazyWabbit

    Re: Apollo trip times. It’s all about conservation of energy and initial mass at TLI. The kinetic energy (KE) at TLI was dependent on the mass of the vehicle which included a fully fueled and assembled LM and the mass of the S1B at the TLI burn. The velocity of the coupled CM/LM had to be calculated to give a specific velocity at the moon and a specific ΔV at LOI. The velocity was constantly decreasing on the way up, out of the gravity well of earth and slightly increasing once the force of lunar gravity matched the force of earth. KE=1/2mV^2. Separation from S1B reduced the mass arriving at the moon. We have now converted the KE of the vehicle at TLI to gravitational potential energy at the moon with a lower mass vehicle. Coming back, we are reduced to CM/SM mass plus a couple kg of rocks. The total KE at reentry must equal the KE at TLI and we have much lower mass so it results in a higher velocity on the way back and shorter return time. All this and the fuel budget was calculated on earth long before launch. The trajectory and course corrections had to be recalculated for Apollo 13 safe return because they were bringing the full LM back with them. Evaluate all the Apollo logs and compare them with Apollo 13’s to see the difference a change in vehicle mass makes. All the KE has to be dissipated in the atmosphere on reentry.

  45. TheKrimzonGuard

    Q1: Maybe the moon flyby alters the Earth-centric orbital parameters? In particular, is the apoapsis lowered? (Lowering the periapsis into Earth’s atmosphere is a very marginal shortening of the orbit, too.)
    Q4: The moon’s escape velocity is 2.38 km/s. It doesn’t seem possible to get the tip of a whip to go that fast, let alone a trebuchet…

  46. Julian Danzer

    should probably be 2*sin(a/2) but it’s all in a range where we can roughly approximate sin(a)=a so it doesn’t make a huge difference

  47. Julian Danzer

    in a 2 dimensional universe you’d expect literally everything to be a black hole

  48. MasterShishas

    I think it takes more time in the travel earth-moon that moon-earth cause when you go to the moon youre trading gravitatory potential for speed as you leave earth gravitatory well, and that takes a lot of energy, but from the moon to the earth you trade your gravitatory potential for speed cause youre aproaching the main body in cuestion. Its just a thought if anyone have a better explanation im happy to hear it.

  49. Taylor Lucy

    unresearched guess about the inbound vs outbound times for apollo:
    The perigee of the outbound flight was at orbital altitude
    The perigee of the inbound flight was in the atmosphere
    Therefore the inbound flight had a higher speed

  50. Dogmatic Pyrrhonist

    The shuttle would have needed the capability to land with it’s cargo for abort requirements.

  51. chrisw443

    It’s time to build the sea dragon.

  52. Phil

    On the first question my first thought was leaving a less massive object and falling to a more massive object on the way back, vs the opposite on the way there. Would that have anything to do with it?

  53. Leon Knauf

    Hey Scott. Any chance you could start uploading in 1440 or 2160p?

  54. michael shortland

    It is faster coming back because of the Earths gravity.

  55. Venusian Creative

    Listening to your answer to changing universal constants makes me think about creating super villains with these powers. That would make the Thanos snap look like a blown out birthday candle lol!

  56. John Kechagais

    Q1 perhaps they are coming back quicker and relying on the atmosphere of the earth to use that energy up.

  57. Chris Musix

    “I AM careful.” ~Jesus

  58. Axonteer

    wub dub dubudubu di dub dub – ah that intro never gets old

  59. Jim's videos

    Single crossbow to orbit on the Moon, why not? It’d be the Wile E. Coyote space program.

  60. Kirk Goins

    On Apollo return speed… What affect would the Earth’s mass and Gravity have vs the Moon on the outbound trip?

  61. William Gallop

    Apollo 10 made human speedrecord on way home 11.08 km/s, no human had ever travel that fast – and live.

  62. Ziginox

    Not only does not work poorly, as you discovered, but it’s also pretty insecure.

  63. hotdrippyglass

    First question thoughts; Leaving the larger gravity well of Earth required more effort and hence more time to reach the relatively smaller gravity well of the moon, which was moving and therefore absent from the target path, and therefore little to no gravity assist, for capture. The return trip leaving the smaller gravity well toward the larger gravity well of the Earth, which was not moving and therefore centered on the target path, would have had a much much larger gravity assist.
    Classic beer can math with no astronomical background at all, worth what you paid for it.

  64. Barack Obama

    Today I learned: Ingenuity runs on Linux.

  65. Samurai Nuts

    Im an 18 year old listening to the same man who got me into Kerbal (and by proxy: space and air flight, general physics, general chemistry, and general engineering) dang near 4 years ago. I think with a more critical mind now and like to think i know quit a bit about the world around me now just because the love of SCIENCE was put in me by a videogame and a very knowledgeable man. Its some crazy shiz to think about, i would have never gotten into space like i did if it wasnt for KSP and scott, and i think my life is forever changed because of it.

  66. Digital Dan

    My version of ImageMagick is more like IIIIIIImmmmmmmaaaaaaaggggggeeeeeeeMMMMMMaaaaa….
    If they’re actually using it onboard, I hope somebody has done some optimization.

  67. Ryan Katic

    Ok now i can’t wait for the Apollo video

  68. SocialDownclimber

    Lots of people commenting about why the return trip would be faster. Most of them need to spend some more time in KSP to get the concepts down.

  69. Rob Wilson

    Thanks again for your great content.

  70. Jerome Thiel

    Hot damn, those were some good questions!

    One thing i find that always separates people who actually know things from people who pretend to know things is how often they say “hmmm… I hadn’t thought of that, let me go and find out.”

    So i would class you, Scott, as someone who knows things. Because the more you know, the more how little you know. And that inspires you to go and learn more.

    People who are absolutely sue about things are liars, prophets, or politicians. Because in the real world, there is no certainty. There is only questions that need to be answered. And the answers change as we learn more.

  71. Shaylen Naidoo

    Isn’t the fact that the earth has stronger gravity that it would make the return trip a bit faster?

  72. MrMegaPussyPlayer

    6:21 Then someone has changed the constant of Gravity in my apartment more than once. Not only stuff seem to disappear into black holes, to never to be seen again, also there’s dust everywhere.

  73. marvin martin

    On the way to the moon, earths gravity holds craft back a bit like drag. On the way back the moons gravity doesn’t have as much drag as earths gravity. ? Also might depend on location. ? Where are you when reach the moon in relation to the distance to moon. Is it mirrored when leaving? . Do they leave from the same location.? Is the moon between earth and sun? When arrived other side. The more I think the more reason there are.

  74. John DoDo Doe

    There was a famous book decades ago that explained advanced physics concepts with short stories in scenarios with each fundamental constant changed to become easily perceptible. So there was a set of billard balls that had wave/particle duality. A Safari with similar elephants, a world with a lower speed of light so basic business travel induced age difference etc.

  75. Jeff Mason

    20 minutes well spent. Thanks Scott for all you do.

  76. redwalsh87

    My thought is on the way to the moon the moon’s orbit was catching up to where the LEM was positioned. On the way back the ship not only had to have the speed to escape the moon’s gravity but also had the moons orbital speed as it had been orbiting it.

  77. Launch Pad Astronomy

    I asked John Grunsfeld about returning Hubble many years ago. If I remember everything he said correctly, NASA looked into this, but by the end of SM4, HST had more than doubled its original mass. So a return mission would have necessitated four EVAs to remove instruments, the solar arrays, and batteries in order to fit within the shuttle’s landing weight, leaving behind a lot of space junk. Considering this would have mandated an end to HST within 2 years of SM4, I’m glad they didn’t do this mission 😀

  78. Joe Bloggs

    I would think you would want the Earth return to be slower, so as to reduce the amount of heating.

  79. Lovenought

    But wouldn’t the lower gravity on the moon make the counterweight have less power?

  80. Bobby L

    Regarding the Apollo timing: It’s easier to slow down in Earth’s atmosphere with a heat shield than it is with a rocket in space around the Moon.

  81. Jon Bradley

    Less mass on the return trip from the moon should cause more efficiency for the engines and thus, faster return time.

  82. Lost Pony

    They did do gravity assist so the trip home is powered by Earth instead of Luna.

  83. Matthias B.

    i bet the different travel time is caused by the gravity of earth. earth slows down while escaping and pulls on approach

  84. Jack-Ash sailing

    Maybe the outbound voyage has to be slower due to there not being an atmosphere to slow down but you can come back faster and dump excess energy in earths atmosphere?

  85. Greg Steehler

    So if we(the average person) is going to space, it will have to be cheep?! I wanna know more about the “big dumb booster” in the ocean please.

  86. Alasdair Munro

    Isn’t it just a matter of mass? On the way back they were moving just the command & service module. Quite happy to find I’m wrong, though.

  87. TacticalFluke09

    return time shorter because escaping the moon’s gravity (and atmosphere/lack thereof) is easier, so acceleration can be faster?

  88. Chris Edwards


  89. kjevers1

    Question 1. Lift off, pulling out out Earth’s gravity well 2. parking orbits 3.acceleration and deceleration. / Coming back/ Acceleration and splash down. No deceleration for 1/2 time. simple.

  90. Rad Donkey

    Could the mass of the earth contribute enough gravitational acceleration to cause a meaningfully shorter lunar return trip?

  91. David Woods

    Top video, as ever. On the Saturn V hydrogen tanks, the vehicle had two hydrogen tanks. The one in the third stage had insulation on the inside, as you said. The second stage’s hydrogen tank had insulation on the outside. Initially, the insulation was in the form of panels glued to the tank. This was problematic due to air pockets liquidising with the cold. From Apollo 13 onward, spray-on foam was used, a technology that was carried on to the Shuttle External Tank.

  92. Kiithnaras Ashaa

    Intuitively, a Moon trebuchet would have similar ballistic properties to a similarly-built earth trebuchet. Gravity would produce a lower release velocity proportional to the reduced gravitational effect on the arc of the projectile.

  93. Jeff Pudlo

    The Hubble was actually originally planned to be returned to earth via the shuttle for museum use or refurbishment, it was absolutely within limits. But that plan obviously got cancelled when the Hubble wound up outlasting the shuttle.

  94. Hadinos Sanosam

    8:04 A 1T magnet is really not that special nowadays: high-quality Neodymium magnets can be magnetized to around 1.4T according to Wikipedia, and I’ve personally estimated the surface field strength of some neodymium magnets I had lying around to be about 0.99T (hmm…)

  95. Raphaël Casimir

    Hi Scott, the Shuttle II concept from 1986 is quite interesting with a launch escape system which was effectively a small shuttle that could also re-enter the atmosphere. A KSP recreation would be glorious.

  96. Robin S

    The speed of approach to the Moon had to be low enough to minimize fuel consumption for a capture. On TEI, they could build all sorts of delta V to get home quicker.

  97. Jayson Pida

    As others posted -Earth’s much larger/stronger ‘gravity-well’ slowing them outbound & speeding them up inbound.

  98. V A

    What mission patch shirt is Scott wearing?

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