Author Topic: Space Elevator for Mars  (Read 87673 times)

Offline Paul451

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Re: Space Elevator for Mars
« Reply #80 on: 11/25/2017 05:18 am »
Dr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?

Hard to say. The only Martin Lades I've seen involved in Space activities is an AI researcher in pattern recognition and neural networks; which doesn't seem related to to any special expertise in orbital mechanics.

And the page on ISEC about their "Martin Lades" reads, in full:

"Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit."

...making it a little difficult to profile the guy.

Your appeal-to-authority seems a little weak. If you've done the analysis, why not answer Meberbs questions instead hiding behind someone else?

Offline stefan r

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Re: Space Elevator for Mars
« Reply #81 on: 11/28/2017 10:41 am »
...What are some other plausible methods for ice removal?

Tether climbers use some sort of motor.  The motor needs a heat sink. 

A descending vehicle could simply slide.  Similar to snow removal from roads. Without sliding, compression could still liquefy water ice.  The grip pressure will be high.

Fullerenes are hydrophobic.  Is there reason to believe ice would collect?

Offline Paul451

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Re: Space Elevator for Mars
« Reply #82 on: 11/28/2017 11:57 am »
Fullerenes are hydrophobic.  Is there reason to believe ice would collect?

Hydrophobic surfaces don't prevent frost build up. There are surfaces that can, but they are all structural, harder to produce and wouldn't stand up to wear from the climber.

Offline stefan r

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Re: Space Elevator for Mars
« Reply #83 on: 12/03/2017 02:17 am »
...What are some other plausible methods for ice removal?

You could pluck it like a guitar string.  That would increase tension but when the climber is off the tether an increase should be manageable.   Could pull the tether below the pad where the tether is attached and then snap release back to normal.  That would keep all tension in one dimension. 

Some descending "climbers" could release and use parachutes/wings.  Time on the tether is tedious and prevents climbers from going up.  Releasing early on a descent allows direct delivery to locations far away from the tether pad(s).  A sudden release should send a wave down the tether.  Ice would detach due to inertia. A descending vehicle should be bending the tether with Coriolis forces.  The letting go wave would have both a vertical stretch component and a horizontal component.

I have not tested the efficiency of ice removal from guitar strings.  I believe all of the musicians I know would be offended if I asked for permission to test. 

Offline LMT

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Re: Space Elevator for Mars
« Reply #84 on: 12/05/2017 05:55 am »
Dr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?

Hard to say. The only Martin Lades I've seen involved in Space activities is an AI researcher in pattern recognition and neural networks; which doesn't seem related to to any special expertise in orbital mechanics.

And the page on ISEC about their "Martin Lades" reads, in full:

"Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit."

...making it a little difficult to profile the guy.

Your appeal-to-authority seems a little weak. If you've done the analysis, why not answer Meberbs questions instead hiding behind someone else?

Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask. 

And of course ISEC Director and research physicist Dr. Lades knows orbital mechanics well enough to mark our rocket equations -- is the difficulty of the Phobos/tether collision problem underappreciated?  Anyway, some c.v info.   

His current research on CNTs gives him insight into the achievement of space elevator tethers.   Notably, his Mars Lift tether is more easily achieved than an Earth tether or lunar tether.  Comparatively very short and light, and unpowered, the Mars Lift presents a first opportunity.  Implementation sets a technical basis for greater space elevators, at Mars and elsewhere. 

Maybe some thread participants would want to explore the possibilities.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #85 on: 12/05/2017 02:27 pm »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.

So why not answer Meberbs question instead of vague appeals to authority?

And of course ISEC Director and research physicist Dr. Lades knows orbital mechanics well enough to mark our rocket equations

So show your/his work. Why is that so difficult? Why should it take two pages of comments to get you to just show your work?

is the difficulty of the Phobos/tether collision problem underappreciated?

Off-equator tethers is an old concept, Lades didn't come up with that. (And I'm not accusing him of taking credit for that.) His own calculations of the minimum off-equator angle necessary to avoid Phobos are just geometry, not orbital mechanics.

Offline meberbs

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Re: Space Elevator for Mars
« Reply #86 on: 12/05/2017 04:37 pm »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.

You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V the implicit question for you to answer was for you to either accept that your statement was wrong, or to do math to justify your statement.

Discussing who did your proposal is irrelevant, because your statement was still wrong even if you had von Braun himself working for you.

Either way, you need to show your work for your architecture including what assumptions you made. Currently you have a spacecraft spending fuel for an Earth transfer, losing propellant during the transfer, spending fuel to arrive at Earth and rendezvous with another identical ship, and somehow fully fuel that other ship while reserving enough propellant to land on Earth. This self evidently leads to the ship needing to carry more fuel than fits in its tanks.

Since you don't seem to acknowledge the existence of questions if there is no question mark let me rephrase:

Do you acknowledge that your statement that adding 130 tons of dead weight/cargo to a spacecraft on orbit has no effect on performance is wrong? If not why?

Can you provide an explanation of your architecture using numbers to justify your claimed performance?

Offline LMT

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Re: Space Elevator for Mars
« Reply #87 on: 12/19/2017 08:33 pm »
is the difficulty of the Phobos/tether collision problem underappreciated?

Off-equator tethers is an old concept, Lades didn't come up with that. (And I'm not accusing him of taking credit for that.) His own calculations of the minimum off-equator angle necessary to avoid Phobos are just geometry, not orbital mechanics.

You're "not accusing" Dr. Lades of anything.  OK.  Nb:  no reason to accuse us of anything, either; you should clean that text.  ::) 

--

But really, imagining Dr. Lades' tether solution as "just geometry" is a severe underappreciation of the difficulty.  To find a solution, the space elevator feasibility condition must be satisfied and the off-equator tether shape equation must be solved, altogether within parameters set by Mars and Phobos, including osculation.   

Not "just geometry". 

Dr. Lades' BIS deck on the feasibility condition and our joint BIS deck on the Omaha Trail give some Mars Lift physics. 

--

Connection

CNT fiber is a plausible material for a Mars Lift tether.  ITS can deliver tether from Earth in 150-ton segments. 

These segments would be connected at the Arestation.  Ideal connections would be low-mass and fully automated.  The Tethers Unlimited SpiderFab spinneret might be modified for such purpose, but there are other possibilities to consider.  Has anyone at NSF explored the challenge of tether segment connection?

Offline LMT

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Re: Space Elevator for Mars
« Reply #88 on: 12/19/2017 08:40 pm »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.
You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V

Never said any such thing, obviously.  You should quote people fairly, and you really should apologize for the misunderstanding that fed your accusations here.

Would you like to see estimates of the transit delta-v and mass possible for an ITS craft on the Omaha Trail? 
« Last Edit: 12/19/2017 08:58 pm by LMT »

Offline Lar

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Re: Space Elevator for Mars
« Reply #89 on: 12/20/2017 01:25 am »
sterile. Stop it. Don't bring this bickering here.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline Paul451

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Re: Space Elevator for Mars
« Reply #90 on: 12/20/2017 01:36 am »
.

I've PM'd you previously with a suggestion about how you might change the way you are approaching this site and potentially get your Lake Matthew thread unlocked. You ignored the PM and seem to be doubling down on this.

It's your concept, so show your work instead of demanding that others do work for you. I don't think the mods would have a problem with that.
« Last Edit: 12/20/2017 10:13 am by Paul451 »

Offline meberbs

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Re: Space Elevator for Mars
« Reply #91 on: 12/20/2017 06:47 am »
Another strange post.  Naturally we calculated the Omaha Trail, as I said.  Rocket equation etc.  That answered the question Meberbs didn't ask.
You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V

Never said any such thing, obviously.  You should quote people fairly, and you really should apologize for the misunderstanding that fed your accusations here.
This is an exact quote below, you said that this adding 130 tons would have "no bearing" on available payload in transit. (Note that I said carrying capacity, not ascent cargo limit. Not really much difference either way, because this system will be designed by SpaceX such that one load of fuel = sending one full ascent load from LEO to Mars.)
You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.

It's a 130-ton water shield from Deimos.  What's unclear? 

As for "carrying capacity", ascent cargo payload limit applies during ascent.  It has no bearing in transit.

Would you like to see estimates of the transit delta-v and mass possible for an ITS craft on the Omaha Trail?
Paul451 and I have repeatedly asked you to provide numbers. If you actually answered questions and provided numbers, you wouldn't be upsetting the mods.

Offline LMT

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Re: Space Elevator for Mars
« Reply #92 on: 12/20/2017 05:50 pm »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

Delta-v Example:  DRL & Gravity Assist

If used efficiently, tethered systems at Mars, such as Deimos Dock, Deimos Rail Launcher (DRL) and Mars Lift could improve flight efficiency significantly. 

Example:  M/E transit with the Omaha Trail's proposed DRL.

Here 0.94 km/s DRL delta-v launches to Mars periapsis, and gravity assist.  At periapsis a small burn of 1.55 km/s gives approximate transfer to Earth.  This is a Mars perihelion transfer; near aphelion, the burn delta-v is less, ~0.8 km/s.

Options:  The Deimos Dock propellant load could be minimized for minimum periapsis delta-v, or else maximized for greater delta-v or greater payload.








The example GMAT script:

--

%  Contact:  [email protected]
%
%  Example Script:  Deimos Rail Launcher (DRL) on Omaha Trail
%
%  Sequence:  DRL EM launch, propagate to Mars periapsis, periapsis burn, propagate approximately to Earth intercept.
%
%  Links:
%  Sept 18 2017:  http://www.lakematthew.com/press/press-release-september-18-2017/
%  Nov 7 2017:  http://www.lakematthew.com/press/press-release-november-7-2017/
%
%----------------------------------------
%---------- User-Defined Celestial Bodies
%----------------------------------------

Create Moon Deimos;
GMAT Deimos.NAIFId = 402;
GMAT Deimos.SpiceFrameId = 'IAU_DEIMOS';
GMAT Deimos.OrbitSpiceKernelName = {'C:\Program Files (x86)\GMAT\R2016a\data\planetary_ephem\spk\mar097.bsp'};
GMAT Deimos.OrbitColor = Tan;
GMAT Deimos.TargetColor = DarkGray;
GMAT Deimos.EquatorialRadius = 7.5;
GMAT Deimos.Flattening = 0.3066666666666666;
GMAT Deimos.Mu = 0.0001588174;
GMAT Deimos.PosVelSource = 'SPICE';
GMAT Deimos.CentralBody = 'Mars';
GMAT Deimos.RotationDataSource = 'IAUSimplified';
GMAT Deimos.OrientationEpoch = 28990;
GMAT Deimos.SpinAxisRAConstant = 0;
GMAT Deimos.SpinAxisRARate = -0.641;
GMAT Deimos.SpinAxisDECConstant = 90;
GMAT Deimos.SpinAxisDECRate = -0.5570000000000001;
GMAT Deimos.RotationConstant = 190.147;
GMAT Deimos.RotationRate = 360.9856235;
GMAT Deimos.TextureMapFileName = 'GenericCelestialBody.jpg';
GMAT Deimos.3DModelFile = '';
GMAT Deimos.3DModelOffsetX = 0;
GMAT Deimos.3DModelOffsetY = 0;
GMAT Deimos.3DModelOffsetZ = 0;
GMAT Deimos.3DModelRotationX = 0;
GMAT Deimos.3DModelRotationY = 0;
GMAT Deimos.3DModelRotationZ = 0;
GMAT Deimos.3DModelScale = 10;

%----------------------------------------
%---------- Spacecraft
%----------------------------------------

Create Spacecraft OmahaTrailSpacecraft;
GMAT OmahaTrailSpacecraft.DateFormat = TAIModJulian;
GMAT OmahaTrailSpacecraft.Epoch = '28990';
GMAT OmahaTrailSpacecraft.CoordinateSystem = MarsMJ2000Eq;
GMAT OmahaTrailSpacecraft.DisplayStateType = Keplerian;

% Approximately Match Deimos
GMAT OmahaTrailSpacecraft.SMA = 23458.17634980082;
GMAT OmahaTrailSpacecraft.ECC = 0.0003144182911521799;
GMAT OmahaTrailSpacecraft.INC = 37.0000000000051;
GMAT OmahaTrailSpacecraft.RAAN = 43.99999999998535;
GMAT OmahaTrailSpacecraft.AOP = 193.1409087306092;
GMAT OmahaTrailSpacecraft.TA = 64.99999997766069;
GMAT OmahaTrailSpacecraft.DryMass = 850;
GMAT OmahaTrailSpacecraft.Cd = 2.2;
GMAT OmahaTrailSpacecraft.Cr = 1.8;
GMAT OmahaTrailSpacecraft.DragArea = 15;
GMAT OmahaTrailSpacecraft.SRPArea = 1;
GMAT OmahaTrailSpacecraft.NAIFId = -10032001;
GMAT OmahaTrailSpacecraft.NAIFIdReferenceFrame = -9032001;
GMAT OmahaTrailSpacecraft.OrbitColor = Red;
GMAT OmahaTrailSpacecraft.TargetColor = Teal;
GMAT OmahaTrailSpacecraft.EstimationStateType = 'Cartesian';
GMAT OmahaTrailSpacecraft.OrbitErrorCovariance = [ 1e+070 0 0 0 0 0 ; 0 1e+070 0 0 0 0 ; 0 0 1e+070 0 0 0 ; 0 0 0 1e+070 0 0 ; 0 0 0 0 1e+070 0 ; 0 0 0 0 0 1e+070 ];
GMAT OmahaTrailSpacecraft.CdSigma = 1e+070;
GMAT OmahaTrailSpacecraft.CrSigma = 1e+070;
GMAT OmahaTrailSpacecraft.Id = 'SatId';
GMAT OmahaTrailSpacecraft.Attitude = CoordinateSystemFixed;
GMAT OmahaTrailSpacecraft.SPADSRPScaleFactor = 1;
GMAT OmahaTrailSpacecraft.ModelFile = 'aura.3ds';
GMAT OmahaTrailSpacecraft.ModelOffsetX = 0;
GMAT OmahaTrailSpacecraft.ModelOffsetY = 0;
GMAT OmahaTrailSpacecraft.ModelOffsetZ = 0;
GMAT OmahaTrailSpacecraft.ModelRotationX = 0;
GMAT OmahaTrailSpacecraft.ModelRotationY = 0;
GMAT OmahaTrailSpacecraft.ModelRotationZ = 0;
GMAT OmahaTrailSpacecraft.ModelScale = 1;
GMAT OmahaTrailSpacecraft.AttitudeDisplayStateType = 'Quaternion';
GMAT OmahaTrailSpacecraft.AttitudeRateDisplayStateType = 'AngularVelocity';
GMAT OmahaTrailSpacecraft.AttitudeCoordinateSystem = EarthMJ2000Eq;
GMAT OmahaTrailSpacecraft.EulerAngleSequence = '321';

%----------------------------------------
%---------- Formation
%----------------------------------------

Create Formation OTS;
GMAT OTS.Add = {OmahaTrailSpacecraft};

%----------------------------------------
%---------- ForceModels
%----------------------------------------

Create ForceModel MarsProp_ForceModel;
GMAT MarsProp_ForceModel.CentralBody = Mars;
GMAT MarsProp_ForceModel.PointMasses = {Mars, Sun};
GMAT MarsProp_ForceModel.Drag = None;
GMAT MarsProp_ForceModel.SRP = Off;
GMAT MarsProp_ForceModel.RelativisticCorrection = Off;
GMAT MarsProp_ForceModel.ErrorControl = RSSStep;

Create ForceModel EarthProp_ForceModel;
GMAT EarthProp_ForceModel.CentralBody = Earth;
GMAT EarthProp_ForceModel.PointMasses = {Earth};
GMAT EarthProp_ForceModel.Drag = None;
GMAT EarthProp_ForceModel.SRP = Off;
GMAT EarthProp_ForceModel.RelativisticCorrection = Off;
GMAT EarthProp_ForceModel.ErrorControl = RSSStep;

Create ForceModel SunProp_ForceModel;
GMAT SunProp_ForceModel.CentralBody = Sun;
GMAT SunProp_ForceModel.PointMasses = {Sun, Earth, Luna};
GMAT SunProp_ForceModel.Drag = None;
GMAT SunProp_ForceModel.SRP = Off;
GMAT SunProp_ForceModel.RelativisticCorrection = Off;
GMAT SunProp_ForceModel.ErrorControl = RSSStep;

%----------------------------------------
%---------- Propagators
%----------------------------------------

Create Propagator MarsProp;
GMAT MarsProp.FM = MarsProp_ForceModel;
GMAT MarsProp.Type = RungeKutta89;
GMAT MarsProp.InitialStepSize = 60;
GMAT MarsProp.Accuracy = 1e-012;
GMAT MarsProp.MinStep = 0.001;
GMAT MarsProp.MaxStep = 2700;
GMAT MarsProp.MaxStepAttempts = 50;
GMAT MarsProp.StopIfAccuracyIsViolated = true;

Create Propagator EarthProp;
GMAT EarthProp.FM = EarthProp_ForceModel;
GMAT EarthProp.Type = RungeKutta89;
GMAT EarthProp.InitialStepSize = 60;
GMAT EarthProp.Accuracy = 1e-012;
GMAT EarthProp.MinStep = 0.001;
GMAT EarthProp.MaxStep = 86400;
GMAT EarthProp.MaxStepAttempts = 50;
GMAT EarthProp.StopIfAccuracyIsViolated = true;

Create Propagator SunProp;
GMAT SunProp.FM = SunProp_ForceModel;
GMAT SunProp.Type = RungeKutta89;
GMAT SunProp.InitialStepSize = 60;
GMAT SunProp.Accuracy = 9.999999999999999e-012;
GMAT SunProp.MinStep = 0.001;
GMAT SunProp.MaxStep = 160000;
GMAT SunProp.MaxStepAttempts = 50;
GMAT SunProp.StopIfAccuracyIsViolated = true;

%----------------------------------------
%---------- Burns
%----------------------------------------

% DRL EM Launch to Mars Periapsis
Create ImpulsiveBurn TOI;
GMAT TOI.CoordinateSystem = Local;
GMAT TOI.Origin = Mars;
GMAT TOI.Axes = VNB;
GMAT TOI.Element1 = 0;
GMAT TOI.Element2 = 0;
GMAT TOI.Element3 = 0.94;
GMAT TOI.DecrementMass = false;
GMAT TOI.Isp = 382;
GMAT TOI.GravitationalAccel = 9.810000000000001;

% Mars Periapsis Burn to Approximate Earth Intercept
Create ImpulsiveBurn EarthTxfr;
GMAT EarthTxfr.CoordinateSystem = Local;
GMAT EarthTxfr.Origin = Mars;
GMAT EarthTxfr.Axes = VNB;
GMAT EarthTxfr.Element1 = -1.55;
GMAT EarthTxfr.Element2 = 0;
GMAT EarthTxfr.Element3 = 0;
GMAT EarthTxfr.DecrementMass = false;
GMAT EarthTxfr.Isp = 382;
GMAT EarthTxfr.GravitationalAccel = 9.810000000000001;

%----------------------------------------
%---------- Coordinate Systems
%----------------------------------------

Create CoordinateSystem MarsMJ2000Eq;
GMAT MarsMJ2000Eq.Origin = Mars;
GMAT MarsMJ2000Eq.Axes = MJ2000Eq;

Create CoordinateSystem SunMJ2kEc;
GMAT SunMJ2kEc.Origin = Sun;
GMAT SunMJ2kEc.Axes = MJ2000Ec;

Create CoordinateSystem SunMJ2kEq;
GMAT SunMJ2kEq.Origin = Sun;
GMAT SunMJ2kEq.Axes = MJ2000Eq;

Create CoordinateSystem EarthSunRot;
GMAT EarthSunRot.Origin = Earth;
GMAT EarthSunRot.Axes = ObjectReferenced;
GMAT EarthSunRot.XAxis = R;
GMAT EarthSunRot.ZAxis = N;
GMAT EarthSunRot.Primary = Sun;
GMAT EarthSunRot.Secondary = Earth;

%----------------------------------------
%---------- Solvers
%----------------------------------------

Create DifferentialCorrector TOIDC;
GMAT TOIDC.ShowProgress = true;
GMAT TOIDC.ReportStyle = Normal;
GMAT TOIDC.ReportFile = 'DifferentialCorrectorTOIDC.data';
GMAT TOIDC.MaximumIterations = 25;
GMAT TOIDC.DerivativeMethod = ForwardDifference;
GMAT TOIDC.Algorithm = NewtonRaphson;

%----------------------------------------
%---------- Subscribers
%----------------------------------------

Create OrbitView MarsMJ2KView;
GMAT MarsMJ2KView.SolverIterations = None;
GMAT MarsMJ2KView.UpperLeft = [ 0 0.3382899628252788 ];
GMAT MarsMJ2KView.Size = [ 0.7997630331753555 0.8463444857496902 ];
GMAT MarsMJ2KView.RelativeZOrder = 15;
GMAT MarsMJ2KView.Maximized = true;
GMAT MarsMJ2KView.Add = {OmahaTrailSpacecraft, Sun, Earth, Mars, Deimos};
GMAT MarsMJ2KView.CoordinateSystem = MarsMJ2000Eq;
GMAT MarsMJ2KView.DrawObject = [ true true true true ];
GMAT MarsMJ2KView.DataCollectFrequency = 1;
GMAT MarsMJ2KView.UpdatePlotFrequency = 50;
GMAT MarsMJ2KView.NumPointsToRedraw = 0;
GMAT MarsMJ2KView.ShowPlot = true;
GMAT MarsMJ2KView.ShowLabels = true;
GMAT MarsMJ2KView.ViewPointReference = Mars;
GMAT MarsMJ2KView.ViewPointVector = [ 20000 -5000 20000 ];
GMAT MarsMJ2KView.ViewDirection = Mars;
GMAT MarsMJ2KView.ViewScaleFactor = 2;
GMAT MarsMJ2KView.ViewUpCoordinateSystem = MarsMJ2000Eq;
GMAT MarsMJ2KView.ViewUpAxis = Z;
GMAT MarsMJ2KView.EclipticPlane = Off;
GMAT MarsMJ2KView.XYPlane = On;
GMAT MarsMJ2KView.WireFrame = Off;
GMAT MarsMJ2KView.Axes = On;
GMAT MarsMJ2KView.Grid = Off;
GMAT MarsMJ2KView.SunLine = Off;
GMAT MarsMJ2KView.UseInitialView = On;
GMAT MarsMJ2KView.StarCount = 7000;
GMAT MarsMJ2KView.EnableStars = On;
GMAT MarsMJ2KView.EnableConstellations = Off;

Create OrbitView EclipticView;
GMAT EclipticView.SolverIterations = Current;
GMAT EclipticView.UpperLeft = [ 0 0 ];
GMAT EclipticView.Size = [ 0.7997630331753555 0.8463444857496902  ];
GMAT EclipticView.RelativeZOrder = 17;
GMAT EclipticView.Maximized = true;
GMAT EclipticView.Add = {OmahaTrailSpacecraft, Sun, Earth, Mars};
GMAT EclipticView.CoordinateSystem = SunMJ2kEq;
GMAT EclipticView.DrawObject = [ true true true true ];
GMAT EclipticView.DataCollectFrequency = 10;
GMAT EclipticView.UpdatePlotFrequency = 200;
GMAT EclipticView.NumPointsToRedraw = 0;
GMAT EclipticView.ShowPlot = true;
GMAT EclipticView.ShowLabels = true;
GMAT EclipticView.ViewPointReference = Sun;
GMAT EclipticView.ViewPointVector = [ 0 0 600000000 ];
GMAT EclipticView.ViewDirection = Sun;
GMAT EclipticView.ViewScaleFactor = 1;
GMAT EclipticView.ViewUpCoordinateSystem = SunMJ2kEq;
GMAT EclipticView.ViewUpAxis = Z;
GMAT EclipticView.EclipticPlane = Off;
GMAT EclipticView.XYPlane = On;
GMAT EclipticView.WireFrame = Off;
GMAT EclipticView.Axes = On;
GMAT EclipticView.Grid = Off;
GMAT EclipticView.SunLine = Off;
GMAT EclipticView.UseInitialView = On;
GMAT EclipticView.StarCount = 7000;
GMAT EclipticView.EnableStars = On;
GMAT EclipticView.EnableConstellations = Off;

%----------------------------------------
%---------- Mission Sequence
%----------------------------------------

BeginMissionSequence;
Maneuver BackProp TOI(OmahaTrailSpacecraft);
Propagate 'Propagate to Mars Periapsis' MarsProp(OTS) {OmahaTrailSpacecraft.Mars.Periapsis};
Maneuver BackProp EarthTxfr(OmahaTrailSpacecraft);
Propagate 'Propagate to Approximate Earth Intercept' MarsProp(OTS) {OmahaTrailSpacecraft.ElapsedDays = 195};





« Last Edit: 12/20/2017 06:47 pm by LMT »

Offline Lar

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Re: Space Elevator for Mars
« Reply #93 on: 12/20/2017 08:02 pm »
Code like that usually is just given as a text file attachment rather than pasted in en masse, but that's a nit.

I applaud showing your work this way. Keep it up. There is a reason that everyone is urging you to show your numbers, show your calculations, show your work in general... you're the one making claims, you get to back them up. You do NOT get to push any work onto those challenging your calculations.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline meberbs

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Re: Space Elevator for Mars
« Reply #94 on: 12/21/2017 12:26 am »
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.

Delta-v Example:  DRL & Gravity Assist

If used efficiently, tethered systems at Mars, such as Deimos Dock, Deimos Rail Launcher (DRL) and Mars Lift could improve flight efficiency significantly. 

Example:  M/E transit with the Omaha Trail's proposed DRL.

Here 0.94 km/s DRL delta-v launches to Mars periapsis, and gravity assist.  At periapsis a small burn of 1.55 km/s gives approximate transfer to Earth.  This is a Mars perihelion transfer; near aphelion, the burn delta-v is less, ~0.8 km/s.

Options:  The Deimos Dock propellant load could be minimized for minimum periapsis delta-v, or else maximized for greater delta-v or greater payload.
Thank you, that gives some numbers to work with.

First a couple notes about your numbers:
Quote
GMAT OmahaTrailSpacecraft.DryMass = 850;
...
GMAT EarthTxfr.DecrementMass = false;
GMAT EarthTxfr.Isp = 382;
Spacecraft mass is 85 tons dry (85000 kg), plus cargo (to compare with SpaceX's architecture  apples to apples, 50 tons return to Earth)
Isp of raptor vacuum is 375.
Neither of these matter, because you are telling the sim to ignore fuel consumption.

This is fine, but now you need to apply the rocket equation to determine fuel consumption. I'll do it for you this time to demonstrate the magnitude of the fuel consumed.

You would use 26.7% of your fuel for a 1 km/s delta v (towards the low end of the range you listed.) For the 1.55 km/s delta V, you would use 38.6% of your fuel, calling this a "small" delta-V does not seem accurate.

You would then lose fuel in transit to Earth (boil off), spend fuel during earth capture and rendezvous with another ship. Your architecture expects you to then fully fuel that other ship for it to transfer to Mars while still reserving propellant to land on Earth. This is clearly impossible because of how much fuel is spent just leaving Mars.

You also appear to be using a roughly Hohmann transfer, compared to the fast transfers that SpaceX plans on.

Offline Hop_David

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Re: Space Elevator for Mars
« Reply #95 on: 01/01/2018 09:49 pm »
Pedantry, because it's one of those things that always bugs me:


For a tether, the part in circular orbit is not at the centre-of-mass. Because centripetal acceleration is linear to distance, but gravitational acceleration is to the square, the balance point of the forces on a tether (and hence its orbit) is below the centre-of-mass.

Happy to see you point this out. Acceleration gradient isn't symmetrical about the balance point's circular orbit. It always makes me gnash my teeth when I hear people say it'd take a 36,000 km length above geosynchronous orbit to balance the 36,000 km length below. (Actually it'd take about a 100,000 km length).

But acceleration gradient gets more symmetrical as you get closer to the balance point's circular orbit. I attached a pic of acceleration gradient. You can see the top of the "hill" is less lopsided.

In the case of the two lunar cube sats, the upper and lower points are only separated by 180 kilometers.

Let's say the ends of this tether each mass a tonne. If the balance point's circular orbit is at 100 kilometers altitude the cube sat 90 kilometers below this orbit would exert a downward force of 2.25 newtons and the upper end 90 kilometers above the circular orbit would exert an upward force of 2.04 newtons.

In the case of that proposed lunar mission, the balance point is very close to the COM. It is a forgivable approximation. Still, I wish they hadn't given it that label, it helps to perpetuate a popular misconception.
« Last Edit: 01/01/2018 09:52 pm by Hop_David »

Offline Nilof

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Re: Space Elevator for Mars
« Reply #96 on: 01/02/2018 02:46 pm »
Solid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.

As noted in Isaac Arthur's video, the advantage of orbital rings is that the ring's shell is stationary WRT to the surface, but vastly lower than geostationary (or areostationary) orbit (in theory even inside the atmosphere). That drastically lowers the strength requirements of the ground cables. And since you can use the ring for fast point-to-point ground transport, you end up with a lot of ground cables, stabilising the ring.

I admire Isaac Arthur. But I am skeptical that the rings he describes would be stable. Even with an interior counter rotating ring, both parts feel the same GM/r^2. If Mars center coincides with rings' center of rotation, a decrease in r also means a decrease in ω^2 r, regardless if the inner ring is retrograde. So dipping closer to Mars means stronger gravity and weaker centrifugal force. The instability remains.

The inner and outer component of a low Mars elevator would be moving at greater than orbital speed with regard to one another. That would be more than 3.4 km/s. How far apart are the inner and outer rings? Should they come in contact with one another, the failure mode would be spectacular.

And we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference. What is the mass of this ring? Isaac Arthur has been talking about megastructures that might come to pass in the distant future.

My focus has been elevator to payload mass ratios. The less ambitious Deimos  and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.

You can tether an orbital ring to the surface to make it stable, since it can be built just above the atmosphere. The point where the tethers to the ground attach can be used to exchange momentum with the body it orbits. That's something that Niven's ringworld couldn't do.

With that said, Mars is so much smaller than Earth that the advantages of an orbital ring don't make a lot of sense. You can use aerobraking to land, and for going up, building a mass driver on one of Mars's giant volcanoes makes more sense. The top of Olympus Mons is close enough to a vacuum, with a pressure more than two orders of magnitude lower than the pressure at the exit of the proposed Startram.

With that said, a good Mars SSTO should have a payload fraction on the order of 50% so *shrugs*. There's not that much point in using launch assists. Mars orbit delta-v is in the range where chemical propulsion comes reasonably close to the optimal energy efficiency for delivering things to orbit, and Mars SSTO's can be built with way more margin than Earth-based launchers.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Paul451

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Re: Space Elevator for Mars
« Reply #97 on: 01/02/2018 06:13 pm »
You can tether an orbital ring to the surface to make it stable, since it can be built just above the atmosphere.

If the rotor (the super-orbiting ring) is fully enclosed and evacuated, you could actually build it inside the atmosphere.

With that said, Mars is so much smaller than Earth that the advantages of an orbital ring don't make a lot of sense.

Not for Mars. Certainly not with a large anchor mass so conveniently close to the planet. The tether length/mass from Phobos leaves any orbital ring, or mass accelerator, or other launch/entry assist system for dead. And can drop the delta-v for launch down to below 1km/s.

OTOH, once orbital rings were a standard technology, proven around the Earth and the moon, it's likely that a Mars colony would say "Me too". They make everything so much easier. I don't need to drive my car to work, but it's much more convenient.

Offline Nilof

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Re: Space Elevator for Mars
« Reply #98 on: 01/02/2018 09:05 pm »
Orbital rings are not a form of space launch by themselves. They are just a convenient platform to build a mass driver above the atmosphere. You still need to build some kind of accelerator on your orbital ring. The top of Olympus Mons happens to give you a nice platform with an atmospheric pressure comparable to Earths atmosphere at 60 km altitude, without having to build your own.


As for space tethers, several of the posts here seem to overstate the utility of a tidally locked tether. In an earlier space elevator thread, I made some computations for a climber and came to the conclusion that trying to climb a space elevator with chemical energy is strictly less efficient than getting to orbit with a chemical rocket. So space elevators and tidally locked tethers in general require a dedicated remotely-powered climber vehicle with good performance to outperform chemical.

It would be more efficient to use a rotating tether in order to do the tethered equivalent of a gravity assist to steal orbital energy from Phobos.
« Last Edit: 01/03/2018 01:32 am by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline LMT

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Re: Space Elevator for Mars
« Reply #99 on: 01/03/2018 01:42 am »
As for space tethers, several of the posts here seem to overstate the utility of a tidally locked tether. In an earlier space elevator thread, I made some computations for a climber and came to the conclusion that a space elevator with chemical energy is strictly less efficient than getting to orbit with a chemical rocket. So space elevators and tidally locked tethers in general require a dedicated remotely-powered climber vehicle with good performance to outperform chemical.

Climber & Rappeller Utility

Yes, a climber would need something other than chemical energy.  Even HVDC power lines are inefficient and unsuitable over MSE distances.  It may be that areosync PV + a superconducting tether power line will be needed, to power an MSE climber system with performance superior to Mars launch.

A cargo descent rappeller is more efficient than a climber:  it uses 0 kW.  :)  And it does so while saving the tremendous energy that would otherwise be devoted to propellant manufacture on Mars, for the cargo ship's surface launch. 

There's utility in that, yes?

It would be more efficient to use a rotating tether in order to do the tethered equivalent of a gravity assist to steal orbital energy from Phobos.

Centripetal Tethers & Rail Launchers

Dr. Lades looked at a locked Phobos L1 (lower) tether for cargo delivery, as in slides 46-47, but couldn't find an economic case.  As for an upper tether, of course David did his own analysis; e.g., a 6155 km tether for Earth return of small masses. 

If David's centripetal launch tether were feasible on Phobos, it would also be feasible on Deimos, and at least as useful.  And as David noted, "...parking at Deimos would save a lot of time and delta V." 

One would deploy this tether from a Deimos base station much as the DRL was itself deployed.  (tether added at lower right)



The 1 AU centripetal tether would give delta-v to Earth only slightly greater than that of the DRL, and it would launch a smaller mass.  Would this be enough to justify construction?  Maybe not.  But Deimos is envisioned as a proving ground, so perhaps this first centripetal tether could serve as proof-of-concept: a precursor to even stronger and longer tethers for greater launches, to the asteroid belt and beyond. 

Conceivably a greater Deimos centripetal tether could be scaled to accommodate ITS mass, for extension of the Omaha Trail.  To that end we can note also that helical coil launchers are bidirectional, accelerating in either direction by design.  So one might reduce the centripetal tether's very great tension by incorporating this tether within a new DRL; one having shorter length than a stand-alone tether.  This DRL would launch not inward toward Mars, but outward.  Here the DRL acceleration and centripetal acceleration would be additive, and cumulatively very great, if all forces can be managed.

Q:  Might the synergy between DRL acceleration and centripetal acceleration be a key to efficient and rapid transit from Mars to, say, Callisto?

Q:  How might a rotator be usefully incorporated, if at all?

« Last Edit: 01/03/2018 02:17 am by LMT »

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