Realistic Science Fiction: What did Interstellar/the Martian get wrong?

[KAL 9000]

Well, in Interstellar, they did use a lot of real science. I really liked the story in Interstellar, it was a great movie!

[billbobjebkirk]

I just want to back up the idea that people should read The Science of Interstellar before trying to criticize... the science of Interstellar. There are some legitamate oversights, including the ridiculously overpowerd small spacecraft, but with regards to physics, the movie gets almost everything right.

[AngelLestat]

15 hours ago, ChrisSpace said:

Both Interstellar and the Martian kind of completely ignore radiation

I forget about this one, not sure in the Martian, but interstellar does not ignore the radiation factor, the black hole accretion disk as you can ""see"" in the movie bright on the visible spectrum..  That is because is a old residuary accretion disk in cooling process. 

What I ignore is the radiation blue-shift when you get close to the black hole from the accretion disk.

[KerikBalm]

1 hour ago, AngelLestat said:

I prove it :P, and the friction coefficient that I took was correct,

Proof by unsupported assertion?

Not logically valid.

You came up with some numbers for a coefficient of friction, and assert that they are true.

The air density, the drag coefficient, the coefficient of friction, etc, all have large error bounds. You can get any result you want by asserting certain values. You have nothing to prove your friction coefficient was correct... I suspect it was off by at least a factor of 2.

[RainDreamer]

I always wonder how in Interstellar, the planets manage to hold themselves together when they are close enough to the black hole to experience such serious time dilation. And heck, the kind of time dilation between the water planet orbit and its surface is so crazy insane for such an astronomically short distance.

[Hcube]

@SomeGuy123 saying 2K Sv is a 10% fatal cancer chance is totally wrong. 1)for any given dose it's impossible to predict "there's a xx % chance you'll get cancer. You can just say that under 100mSv is veeery unlikely to get you cancer, and that over 3Gy you'll probably be dead before you get any cancerous cells !   2) : 2k sieverts, even if given slowly during, like, a year,  will boil you down before anything happens ! You're basically dead at 5Sv... (On a more pedantic note the dose is usually measured in Gy when it's higher than 1Sv, it's kinda funny isn't it ?)

 

Did you mean 2Sv instead ? Because That's way more probable and also will likely give you cancer, being a medium dose.

 

Let's just suppose they have very good radioprotection in their spaceships ?

[KAL 9000]

1 hour ago, KerikBalm said:

Proof by unsupported assertion?

Not logically valid.

You came up with some numbers for a coefficient of friction, and assert that they are true.

The air density, the drag coefficient, the coefficient of friction, etc, all have large error bounds. You can get any result you want by asserting certain values. You have nothing to prove your friction coefficient was correct... I suspect it was off by at least a factor of 2.

Let's stop fighting like babies.

[Neil1993]

I saw an interesting lecture by Kip Thorne. He actually went over a few of the things that were wrong in Interstellar and were changed for theatrical effect. This includes:

1. Passing through the wormhole. It was all dramatic when, in reality, it would have been unnoticeable if you weren't looking out a window
2. The Accretion disc on the wormhole, which should have been red-shifted on one side and blue-shifted on the other. Nolan didn't think it looked good

There were more things but I can't name them off the top of my head.

Edited December 2, 2015 by Neil1993
wrong word used

[Robotengineer]

30 minutes ago, Neil1993 said:

I saw an interesting lecture by Kip Thorne. He actually went over a few of the things that were wrong in Interstellar and were changed for theatrical effect. This includes:

1. Passing through the wormhole. It was all dramatic when, in reality, it would have been unnoticeable if you weren't looking out a window
2. The excretion disc on the wormhole, which should have been red-shifted on one side and blue-shifted on the other. Nolan didn't think it looked good

-snip-

There were more things but I can't name them off the top of my head.

*Accretion disk. Last time I checked black holes didn't excrete.

[Neil1993]

1 minute ago, Robotengineer said:

*Accretion disk. Last time I checked black holes didn't excrete.

Whoops! good catch!

[AngelLestat]

6 hours ago, KerikBalm said:

Proof by unsupported assertion?

Not logically valid.

You came up with some numbers for a coefficient of friction, and assert that they are true.

The air density, the drag coefficient, the coefficient of friction, etc, all have large error bounds. You can get any result you want by asserting certain values. You have nothing to prove your friction coefficient was correct... I suspect it was off by at least a factor of 2.

I took that friction value from a table of different type of surfaces, and I choose gravel and dust, but one thing that I dint notice then is the value is measure at 40% of humidity that we have on earth, if we dry that dust and gravel to mars levels, the friction coefficient will reduce by 40%, then we need to add the temperature which any trace of water it becomes in ice dust. This is also why NASA said is too easy to drill on mars, because the friction coefficient is very low.

Also if you look the friction angle on mars for all different rovers and surfaces measure it, you find values between 14 degress to 40 degress!

http://onlinelibrary.wiley.com/doi/10.1029/2010JE003625/pdf   Page 36 of 38

In addiction, the fact that we never measure 400kmh in mars means nothing, I never saw winds higher than 130kmh in my decades of living, but I know that are circustances and places where you can have 500kmh, besides you dont need a storm with constant winds of 400kmh, there is something called gusts or twisters generated when 2 front of winds collide that can produce 400kmh winds over a short time scale.

For finish, if you walk under a storm with almost not visibility, you will not have a constant friction force in your boots because the terrain is not regular.

But well, maybe your purpose is just negate anything that I said because is easier than admit that can happen :S

Yes, looks like a childish behavior.

 

6 hours ago, RainDreamer said:

I always wonder how in Interstellar, the planets manage to hold themselves together when they are close enough to the black hole to experience such serious time dilation. And heck, the kind of time dilation between the water planet orbit and its surface is so crazy insane for such an astronomically short distance.

Is explained above.

Edited December 2, 2015 by AngelLestat

[lukethecoder64]

The only two things about the martian movie that I think were unfeasible and that bothered me were only two things:

• The landscapes are horribly incorrect - everywhere Watney goes it is just dunes and these weird hill-like formations (pic) whereas we know that some places that he went (like the pathfinder landing site) are very different.
• He fixes the airlock hole with cellophane and duct tape. Duct tape is OK, but CELLOPHANE!? Correct me with math if I am wrong, but I'm pretty sure cellophane can't hold 1ATM. (In the book he uses hab canvas + resin)

There are other inaccuracies, but those are the only things that bothered me.

Luke

[cubinator]

In Interstellar, one thing I noticed after watching it for like the third time was that when they were leaving Earth for Duna Mars they could see a full Earth out the window. From the transfer time (8 months) it seems like a Hohmann transfer, but that was definitely not a hohmann transfer for them to be seeing a full Earth at that distance. There must have been some secret Venus transfer they never told us about for that to work.

In The Martian, one thing that really bothered me (besides the storm of course) was that after he fixed the hole from the airlock incident, the canvas was flapping all over the place during a storm. This shouldn't be possible without gas-giant scale winds with the puny Martian atmosphere. Since the Hab is far more pressurized that the outside, the canvas should have just blown up like a balloon and stayed that way. It was good plot-wise as it emphasized the danger of depressurization, but IRL it wouldn't actually flap that much if it wasn't already depressurized.

Yes, I actually mixed up Mars and Duna. Really! I do it all the time. Mun/Moon, Mars/Duna, Jupiter/Jool, it's all the same.

[Temstar]

Another thing that I thought was a bit goofy in The Martian was the MAV. MAV was a two stage vehicle which was fine. But on second stage burnout the spacecraft then separated from the rocket stage into an Apollo command module shaped capsule which was then drifting towards Hermes.

This I thought was a pretty weird design, I don't get why there needs to be a stage separation there? Surely under its normal operating mode the "command module" part would still be attached to some kind of service module when it docks with the Hermes mothership. Then once the crew boards Hermes the whole MAV can then be deorbited to crash back on Mars. None of this require a staging event.

The only thing I can think of that need staging is if the crew capsule part of the MAV has its own small built in motors and/or reaction control system, So that it can fly under its own power to complete the docking with Hermes. (Actually come to think of it we know this is true since they mentioned firing the Orbital Maneuvering System engine to counter the tilting, and the engine that was fired looked pretty beefy and was located in the nose where the crewed capsule was) In which case getting rid of the MAV upper stage will be a good idea. But if that was the case they surely would have used the same OMS to close the relative speed with the flyby Hermes?

Edited December 3, 2015 by Temstar

[lukethecoder64]

5 minutes ago, Temstar said:

(Actually come to think of it we know this is true since they mentioned firing the Orbital Maneuvering System engine to counter the tilting, and the engine that was fired looked pretty beefy and was located in the nose where the crewed capsule was) In which case getting rid up the MAV upper stage might be a good idea. But if that was the case they surely would have used the same OMS to close the relative speed with the flyby Hermes?

IIRC The OMS on the ares 4 MAV was removed to save weight.

[Temstar]

2 minutes ago, lukethecoder64 said:

IIRC The OMS on the ares 4 MAV was removed to save weight.

Why would you remove OMS to save weight (to get more delta-V) when you could just use the OMS to give you more delta-V?

[SomeGuy123]

8 hours ago, Hcube said:

@SomeGuy123 saying 2K Sv is a 10% fatal cancer chance is totally wrong. 1)for any given dose it's impossible to predict "there's a xx % chance you'll get cancer. You can just say that under 100mSv is veeery unlikely to get you cancer, and that over 3Gy you'll probably be dead before you get any cancerous cells !   2) : 2k sieverts, even if given slowly during, like, a year,  will boil you down before anything happens ! You're basically dead at 5Sv... (On a more pedantic note the dose is usually measured in Gy when it's higher than 1Sv, it's kinda funny isn't it ?)

 

Did you mean 2Sv instead ? Because That's way more probable and also will likely give you cancer, being a medium dose.

 

Let's just suppose they have very good radioprotection in their spaceships ?

Dude, don't nitpick.  You know I meant 2k mSv, you could have figured it out from the other context in the calculation and everything else I said.  And yes, 1 Sv is supposed to be a 5% extra chance of fatal cancer.  Linear is a reasonable assumption at medium radiation doses, it is probably not linear at very low doses but no one has direct evidence either way.

For that matter, when you say "impossible to predict", no, they have data on this...Over a population, these numbers are correct.  Like rolling dice, every crewmember might get fatal cancer with a 1 Sv dose or none, but if you exposed enough people this is what the numbers say will happen.

There's no such thing as "very good radioprotection" for a spacecraft.  Check out the wiki article on it.  You trade off more and more kilograms of lead for marginally better results.  By the time you have the kind of shielding they put on nuclear reactors, the spacecraft is too heavy to be practical.

Edited December 3, 2015 by SomeGuy123

[Neil1993]

 

4 minutes ago, Temstar said:

Why would you remove OMS to save weight (to get more delta-V) when you could just use the OMS to give you more delta-V?

OMS systems aren't designed to put out huge amounts of Delta-v. Rather, they are for fine attitude and translation adjustment and quick response. It is conceivable that eliminating this system rather than using it in flight would result in a net gain in Delta-v.

[lukethecoder64]

9 minutes ago, Temstar said:

Why would you remove OMS to save weight (to get more delta-V) when you could just use the OMS to give you more delta-V?

I dunno why (my guess would be b/c mono has horrible isp and hence more regular fuel would be better) but they did. Page 328 of the hardcover:

Quote

"The orbital maneuvering system had three redundant thursters. We'll get rid of those."

 

Edited December 3, 2015 by lukethecoder64

[Temstar]

1 minute ago, Neil1993 said:

 

OMS systems aren't designed to put out huge amounts of Delta-v. Rather, they are for fine attitude and translation adjustment and quick response. It is conceivable that eliminating this system rather than using it in flight would result in a net gain in Delta-v.

It's conceivable but it doesn't seem likely to be the case given what we've seen of it. When they fired up the Ares 3 MAV's OMS engine it shot out two huge exhaust plumes (none of this 'puff of gas' type deal we see with regular monopropellant RCS blocks), was able to right the whole three stage vehicle against the storm and remained firing for quite some time. Given that Ares 4 MAV was dramatically lightened I get the feel that a working OMS would be able to impart significant amount of delta-V to it.

It wouldn't really change the story either, they just have to have a second of two showing the Ares 4 MAV capsule firing the OMS after separation from the upper stage.

[Neil1993]

14 minutes ago, Temstar said:

It's conceivable but it doesn't seem likely to be the case given what we've seen of it. When they fired up the Ares 3 MAV's OMS engine it shot out two huge exhaust plumes (none of this 'puff of gas' type deal we see with regular monopropellant RCS blocks), was able to right the whole three stage vehicle against the storm and remained firing for quite some time. Given that Ares 4 MAV was dramatically lightened I get the feel that a working OMS would be able to impart significant amount of delta-V to it.

It wouldn't really change the story either, they just have to have a second of two showing the Ares 4 MAV capsule firing the OMS after separation from the upper stage.

It sounds like you may be using evidence from the movie. I'll have to take your word for it since I actually haven't seen the movie (this is an even more terrible sin when you consider the fact that I had received tickets to a pre-screening but have them to some friends because I had too much work that night).

It might be possible that the OMS system that was removed were just the sections used for attitude adjustment or it was like Luke suggested where they just removed redundant components.

 

Edited December 3, 2015 by Neil1993

[KerbMav]

Weir used handwavium for the hab canvas to make the hab safe from radiation. I guess if they have a material that shields against radiation and being only that thick, the ship would be equally safe.

[Hcube]

6 hours ago, SomeGuy123 said:

Dude, don't nitpick.  You know I meant 2k mSv, you could have figured it out from the other context in the calculation and everything else I said.  And yes, 1 Sv is supposed to be a 5% extra chance of fatal cancer.  Linear is a reasonable assumption at medium radiation doses, it is probably not linear at very low doses but no one has direct evidence either way.

For that matter, when you say "impossible to predict", no, they have data on this...Over a population, these numbers are correct.  Like rolling dice, every crewmember might get fatal cancer with a 1 Sv dose or none, but if you exposed enough people this is what the numbers say will happen.

There's no such thing as "very good radioprotection" for a spacecraft.  Check out the wiki article on it.  You trade off more and more kilograms of lead for marginally better results.  By the time you have the kind of shielding they put on nuclear reactors, the spacecraft is too heavy to be practical.

Yeah, but that's irrelevant : the 10% number is a statistic number calculated from data from thousands of people, but if a single person, or a crew of 6 receives this dose you can't predict that there's a 10% chance since the variability is very high !

The wiki contains a lot of errors : it for example gives some values for halving thicknesses without precising any energy, wich makes no sense at all.

And then it's just a sci fi movie, we can just figure out they have a new fictional material very good at stopping gamma...

 

[peadar1987]

@Hcube:

That is literally the definition of probability. There is a 10% chance. Doesn't matter if it's a small group or a huge group, there will be a 10% chance.

To be honest, I'd take the risk. A 1Sv dose over a period of years gives a smaller increase in cancer risk than smoking, and we never see people complaining that films "totally ignore the smoking aspect", because they don't tend to show a small proportion of the smokers they feature developing a cancer they otherwise would not have.

You shield the spacecraft as well as you can within your mass budget, and the crew members accept the risks.

[SomeGuy123]

A 10% or 15% extra fatal cancer risk over the astronaut's lifetime isn't as bad as it could be.  First of all, there are experimental drugs that may reduce the damage radiation has on the body if they are taken at the same time you are exposed to radiation.  You would expect the Hermes would have that onboard.  Second, when I said no practical radiation shielding, I misspoke.  You could nestle the crew quarters in among the propellant tanks, essentially using the cryogenic liquid propellant stored in the tanks as a radiation shield. (probably liquid hydrogen)

This only helps you when you have significant amounts of propellant remaining, and the books seem to say the Hermes basically returned to earth with just fumes left.  

The problem is in the movie, and in the book, it shows these cool centrifuge nodes where the crew spend most of their time, and they appear completely exposed, with massive windows exposed to space.  Radiation shielding them would also increase their mass and thus the stress put on the centrifuge assembly.  

Finally, they could have frozen the bone marrow of the Hermes crew before departure, then done a bone marrow transplant on the crew when they returned.  Maybe by the 2030s we'll have a practical method to expand the stem cell population in a bone marrow sample.  That would at least protect against leukemia, one of the more common forms of cancer that results from radiation exposure.

 

Edited December 3, 2015 by SomeGuy123