Author Topic: Modelling Mars  (Read 122126 times)

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #540 on: 03/11/2017 01:46 AM »
I stand corrected, and granted it's been a year since I've read the story, and I don't have a copy.  LH2 shielding was my first thought on as to why the accident wasn't considered plausible.  Furthermore, I know the accident created a propellant leak that would have vented the protective LH2 as time went on.

Honestly, this whole tragedy could have been avoided if the test was unmanned, but RL NASA sent pilots on the first space shuttle flight, and they do sometimes toss safety aside (which played roles in both RL space shuttle disasters), so it's not implausible for this to happen in the story.  Honestly, I never saw it as implausible except that I think NASA might have had more failsafes built into a test NERVA and fly it unmanned.

It's just hard to say.

Also, I meant to say "containment failure."  I missed that error.  What I was thinking about was an electronic failsafe that would turn the graphite moderators to a full position to try to shut down the core if temps exceeded a certain threshold (and a temp increase did precede the explosion IIRC).  Containment failure would be the NERVA shielding blowing and spreading radiation out.

I have a limited knowledge of NERVA and nuclear reactors, so I'm prone to make mistakes.

It would be interesting to model the radiation field of an exposed NERVA core.  IIRC, only part of the shielding was busted, and it busted out the side, so I wonder how the radiation would spread out.

« Last Edit: 03/11/2017 01:55 AM by Nittany Tiger »

Offline Archibald

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Re: Modelling Mars
« Reply #541 on: 03/11/2017 02:14 PM »
There actually was an unmanned test that (of course) went perfectly. :(

The 1/72 scale Ranger is pretty cool, 1/72 was my favorite scale ten years ago (before I stopped modeling)

I wish there could be a Big Gemini add-on either in Kerbal or Orbiter. If anybody can help :p

ETS and my own TL Explorers started exactly the same  premise (entirely coincidentally) but they are entirely different. Ranulf, how is your TL going ?
« Last Edit: 03/12/2017 09:40 AM by Archibald »

Offline brickmack

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Re: Modelling Mars
« Reply #542 on: 03/12/2017 02:03 AM »
There actually was an unmanned test that (of course) went perfectly. :(

The 1/72 scale Ranger is pretty cool, 1/72 was my favorite scale ten years ago (before I stopped modeling)

I wish there could be a Big Gemini add-on either in Kerbal or Orbiter. If anybody can help :p

ETS and my own TL Explorers started exactly the same  premise (coincidentally) but they are entirely different. Ranulf, how is your TL going ?

Big Gemini is included in FASA for KSP (along with several other Gemini-derivatives) and is compatible with Realism Overhaul too

Offline Archibald

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Re: Modelling Mars
« Reply #543 on: 03/12/2017 09:39 AM »
very cool. What is FASA ?

Offline brickmack

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Offline Nittany Tiger

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Re: Modelling Mars
« Reply #545 on: 03/14/2017 05:31 PM »
Yeah, FASA has Big Gemini, MOL, the Saturn C-8, the M-1, and the 156" UA SRBs for any Saturn MLV you want to make.  It doesn't have stretched S-I, S-II, or S-IVB stages, but you can install procedural parts and add the stretching yourself.

Frizzank isn't working on FASA anymore, but I think someone else is updating it for people who want to use it in Real Solar System + Realism Overhaul installs.  You can get a stock version from them as well.

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #546 on: 06/27/2017 03:21 PM »
Hey.  Finally got a copy of Voyage a few weeks ago courtesy of a friend.  It's interesting how things differ between my interpretation on KSP and what happens in the book, especially during the launch sequence.  For instance, I started throttleback for Max Q sooner because I didn't think 40 kPa dynamic pressure was acceptable (I can use MechJeb to give me Q, and the mod Ferram Aerospace Research will give a high dynamic pressure warning if Q exceeds 40 kPa).  I also eject the launch escape tower sooner, and I chose my time based on studies.  I'm actually not sure when the "right" time is to jettison a LES and go to a Mode II+ abort mode.

Offline Ronpur50

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Re: Modelling Mars
« Reply #547 on: 06/29/2017 10:22 PM »
Definitely after SRB jettison!  I would assume shortly after S-II ignition, like was done on Apollo.

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #548 on: 06/30/2017 06:03 AM »
In the book, LES jettison is done shortly after S-II ignition like in a standard Saturn V launch.  I've seen videos of this mission having the LES jettison occur shortly after SRB sep though, while the MS-IC is still firing.  After reading this paper, I went with the latter.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19720017278.pdf

From what I gather, the LES was best used while the LV was still in the atmosphere and mostly vertical.  After SRB sep in my launches, the LV is 72 km high and at a pitch of around 35 degrees.  It also has a high vertical velocity, so it's going to be crossing the Karman line pretty quickly.  Therefore, I jettison the LES at 80 km, where the MS-IC is still firing.  I imagine in an abort, the engines would be commanded to shut down and the SPS would fire to push the CSM away from a potentially-catastrophic explosion.

I'm truly not sure of the logic behind when to transition from using an LES for aborts to using a different abort option.  I just went with what I felt was best based on that paper, and it just happens to differ from what's in the book just like how my F-1A throttling timing differs from the book.  I'm not a NASA rocket scientist, so I can't say my way is "correct," but it works well with respect to KSP RSS/RO, which is pretty close to reality.

Offline Ronpur50

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Re: Modelling Mars
« Reply #549 on: 07/02/2017 08:41 PM »
I have always read that the LES was best used in those times as well.  The other part of the LES is the Boost Protective Cover, and it really only had a use in the atmosphere.  So once that was behind, and the SPS could take over, there was no longer a need to carry the extra weight.  I can't wait to see what you are coming up with!!

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #550 on: 07/02/2017 08:56 PM »
Thanks.  I need to get back on the project since it's 90% complete.  I left off on testing the Venus probe, where I used the Huygens probe as a stand-in for the Venus probe.  I didn't know the book actually had a description of the probe, but that's OK for now.  I plan on doing a test run of the mission.

I wonder if they guided the probe for a direct hit with Venus, or just aimed it at the limb of the planet for aerocapture?  The latter seems more likely because of the fewer g-forces on the probe and longer time spent in the atmosphere.  A direct descent is insane, and I've had probes explode from g-overload and overheating trying to aim it straight on (and these probes are rated for 50 Gs in-game I believe, and I can edit the tolerances, but I don't want to create a magical device).

I think I did read about the LES being used as a forward heat shield for ascent, so like you said, it would be logical to just ditch it when the rocket is above the majority of the atmosphere where shock heating is negligible to non-existent because it's just dead weight. 

I know Baxter did his homework for the novel, but he might have taken some artistic liberties, and he might have let some things slide since it's science fiction, and the focus of the book is the story of Natalie and the challenges of a Mars mission in an alternate post-Apollo NASA, not the hardcore technical and scientific details of the mission itself.  I've had a lot of fun researching and simulating the rigorous details of the mission though.  It almost makes me feel like I work at NASA right now given how much I've accomplished for this one mission.  I just want to make something special for it like a video or series.

Was also thinking of pictures and descriptions like what you did with the models, except using KSP screenshots.
« Last Edit: 07/02/2017 10:38 PM by Nittany Tiger »

Offline Ronpur50

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Re: Modelling Mars
« Reply #551 on: 07/03/2017 09:59 PM »
I imagined the Venus Probe to be the same as Pioneer Venus.  Since that never existed in Voyage, it made sense to me that the first probe would be that.  But it is also described as a pie dish, which sounds more Huygens-like.

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #552 on: 07/28/2017 05:54 AM »
There is a description of the probe I think, and they mention it being a sphere with fins within a pie-shaped dish.

"The pressure vessel was a sphere of thick metal.  There were vanes on the sphere to make it spin, so that it was stabilized during its fall, and there were tough little windows cut into the surface so that the probe's instruments could see out."

It's page 470 in my copy.  The pressure vessel is the part of the probe in the pie-shaped heat shield that falls out after the probe gets so far down in Venus that the atmosphere is a superfluid.  In KSP RSS, you can float probes down this way since the terminal velocity is so low that it's lower than many part's crash tolerances.

I'm planning the flight in KSP RSS now.  Might have to move the planets around a bit since planetary motions aren't perfect in RSS.  I've advanced my game to March 17th, 1985, but finding a Earth -> Venus -> Mars trajectory is tricky even with tools for finding flybys.

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #553 on: 08/24/2017 03:49 PM »
If anyone is interested, I started my first full run of my Ares recreation in KSP RSS.  It's more of a practice run, but it goes from launch to landing.  Already learned some interesting things about the mission and what the real Ares might have done versus the mission in the book.

Already, one big discrepancy is the Venus flyby.  I can't get a darkside flyby that doesn't result in a lower heliocentric orbit versus a higher one.  However, KSP uses a simple two-body gravity model.  It can be enhanced with a mod called Principalia I think, which introduces n-body physics into KSP, and maybe a dark-side flyby could result in a higher orbit in KSP there.  Overall, I'm interested in working out the vector math and even calculus to see if a dark-side Venus flyby could get you to Mars and not Mercury.  I'm also not sure if, when I approach Venus, that my trajectory will actually be on the dark side.  KSP's trajectory planning tools show a light-side encounter even in local body frame of reference mode (shows trajectories with respect to the dominant body in each sphere of influence).

Another discrepancy that I figured out was the G-forces apparently experienced by the Ares breaking into Mars orbit.  Baxter describes the Ares experience 4.6 G's max as it breaks into Martian orbit.  This is with a MS-II powered by 4 J-2S engines pushing a fully-fueled MS-IVB (minus boil-off) and Ares Command Stack.  However, during the launch, at least in my simulation, the MS-II (I used an MS-II) of the Saturn VB with five J-2S engines reached only 2+ Gs pushing just the Ares Command Stack into orbit.  There's no way the Ares Propulsion Module could produce a 4.6 G acceleration with one less engine and more mass to push.  I think even if you consider mass loss due to waste disposal and cryogenic boil-off, you're not going to get 4.6 Gs of acceleration from the APM breaking into Mars orbit.  This might be "artistic licensing" in action though, and Baxter broke reality to add to the drama of the scene.  I can forgive that.

Offline Ronpur50

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Re: Modelling Mars
« Reply #554 on: 08/25/2017 01:26 AM »
I know Baxter had help from JSC on the mission profile, including the flyby.  I have only a very vague understanding of the math involved in orbits.  So I can't give you any help.  You may also want to look at the Mars One Crew Manual, it uses an almost identical Venus flyby. 

Have you messaged any of the others who have modeled the mission in KSP?

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #555 on: 08/25/2017 07:44 AM »
The only other person I know who's done the mission is Chris P. Bacon.  Some have replicated the Ares, but did conjunction-class missions instead of opposition-class as in Voyage.  Again, I haven't got to Venus yet in my attempt, nor do I know if KSP does model flybys perfectly with it's simplistic gravity model (patched conics model I think it's called), so it's possible that Baxter's version is doable.  To answer your question, though, I have not contacted anyone else who's done an opposition-class Mars mission about how their attempt went.

I'll snap a pic of what my orbit plan looks like tomorrow.  I had a bug with a mod, so I didn't get to Venus today because I need the mod to move crew around between parts of my ship.

Offline Nittany Tiger

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Re: Modelling Mars
« Reply #556 on: 08/27/2017 04:13 AM »
I thought about the problem and did conclude that KSP's patched conics gravity model doesn't take into account momentum transfer between a planet and another body flying by it.  You can also see it as the game not taking frame of reference velocity into account in gravitational interactions.  This means that only directional accelerations are possible with KSP's base gravity model, and this is why a flyby on Venus on the dark side lowers the orbit instead of raises it.

I came to this conclusion experimenting with the maneuver node system.  I found that a maneuver node right after leaving Venus' SOI having the velocity components shown gives the trajectory found in the novel.  The pericytherian at Venus is very close to what's in the book, and it's a dark-side flyby.



It gives an arrival date at Mars of March 23rd, 1986, which is two days from canon.

The delta v of that maneuver node is about 6,537 m/s.  Some rough calculations show that the velocity difference between the orbit before and after the encounter is about 9 km/s, which I would put a +/- 2 km/s difference on that since I couldn't get exact orbital specifics, did change that maneuver node a bit, and I'm doing a very rough calculation of orbital velocities.  Finally, the difference between Earth and Venus's velocity is 5,409.3 m/s give or take.

Point is, Venus does add its velocity to the craft during the flyby.  I can make a better mathematical proof of this later when it's not 12 AM, but I think the rough numbers show that the issue with my flyby is just KSP's fault and not Baxter's.

Online mike robel

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Re: Modelling Mars
« Reply #557 on: 08/27/2017 05:31 AM »
Cool Stuff.  I wish I had the patience to do such modeling, but alas, I don't.  Well, I do.  But it is directed toward military wargaming.

Offline Pipcard

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Re: Modelling Mars
« Reply #558 on: 09/14/2017 07:25 AM »
If Blue Origin existed in the universe of "Voyage," their fourth launch system would be called "New York."

Offline Ronpur50

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Re: Modelling Mars
« Reply #559 on: 09/14/2017 05:56 PM »
If Blue Origin existed in the universe of "Voyage," their fourth launch system would be called "New York."


Perfect!

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