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#26 2019-11-20 20:19:30

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,631

Re: Solving Mars mission docking with Phobos

For SpaceNut … thanks for your follow up …

I apologize for beating a dead horse, but some earlier results using the online calculators were confusing (to me at least).

Here is a set of three calculations, using the figures you showed.

What is changing with the increase of mass of the object in the track is the total force on the track.

For mass of 1 kg

Radius 11.2654 km
Tangential velocity 332.27 m/s
Angular velocity 0.28165 rpm
Force 9.8 N
Effective mass 1.9993 kg
Centrifugal acceleration 9.8 m/s²



For mass of 10 kg

Radius 11.2654 km
Tangential velocity 332.27 m/s
Angular velocity 0.28165 rpm
Force 98 N
Effective mass 19.993 kg
Centrifugal acceleration 9.8 m/s²


For mass of 100 kg

Radius 11.2654 km
Tangential velocity 332.27 m/s
Angular velocity 0.28165 rpm
Force 980 N
Effective mass 199.93 kg
Centrifugal acceleration 9.8 m/s²

I am now persuaded that the leisurely rotation rate of 0.28 rpm will be very comfortable for passengers, since 1 rpm was the Gold Standard set for the Stanford Torus study.

Passengers will experience Earth Normal gravity while spending time in the rotating train.

Your observation about where passengers will be experiencing the floor and ceiling has been addressed previously, in studies for Dr. O'Neill's habitats, as well as the Stanford Torus and other similar systems.

The interiors of the compartments will be designed to provide a floor where "gravity" is pulling, and the ceiling will be on the opposite wall.  There will be NO acceleration toward the ends of the cars.

What passengers would experience would be lateral acceleration as they are brought up to speed to enter one of the compartments, but that acceleration would be of short duration.

Likewise, when passengers disembark, they will enter a deceleration pod via airlock from a rotating compartment, and then experience lateral force as the deceleration pod brakes to match velocity with an airlock to the interior of the Phobos station.

SearchTerm:PhobosTorus
SearchTerm:StanfordTorus

For those who may be curious, a Google search for Phobos and Torus yields a large result set which includes a number of citations about a torus of dust particles around Phobos. 

https://www.sciencedirect.com/science/a … 3583711322

https://agupubs.onlinelibrary.wiley.com … i006p00861

https://ui.adsabs.harvard.edu/abs/2016J … P/abstract

Above are the top 3 citations

Edit 2019/11/23: Design of a centripetal habitat strong enough to sustain 1 Earth gravity for passengers will be challenging.

It is possible to envision habitat compartments assembled from rocket bodies.  However, these need to be mounted on and secured to a strong backbone.

At present I am thinking the back bone would be metal, but the strength of Carbon fibers may argue in favor of using Carbon as the main component of the outer rim of the structure.

The rotating habitat needs to be protected by a thick layer of regolith, and that would be supported by hoops (or perhaps full rings) of material.

The system needs to be designed to facilitate convenient entry to and departure from habitat modules, so I would envision a second track running along side the primary one. 

Each module needs to be self-sufficient in the same way that a space transport would be.  However, power can come into the modules from an outside source, such as solar arrays mounted on the exterior of Phobos.

(th)

Last edited by tahanson43206 (2019-11-23 08:11:45)

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#27 2019-11-21 16:10:27

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Solving Mars mission docking with Phobos

Per my promise in post 16 above,  I have completed my article on orbit analysis and velocity requirements for Hohmann min-energy and faster-transit ellipses to Mars. 

These transfer analyses and the terminal area requirements feeds into 3 missions:  (1) depart LEO,  direct entry and propulsive landing on Mars,  direct departure from Mars,  with direct entry and landing on Earth.  (2) LEO-LMO orbit-to-orbit missions,  with 2-way lander from LMO to surface (return is to LEO,  Earth landing not included).  (3) LEO-Phobos-orbit orbit-to-orbit missions,  landing the transit vehicle upon Phobos,  and taking off to depart (return is to LEO,  Earth landing not included). 

The article is posted at my "exrocketman" site,  which is http://exrocketman.blogspot.com,  titled "Interplanetary Trajectories and Requirements",  and dated today (21 November 2019). 

I saw Earth departure delta-vees steadily increase with faster transfer ellipses,  as I expected.  But not the same for the free-entry velocities,  those at Mars peaked around 7.4 km/s,  while those at Earth steadily increased.   Faster transit appears to cost a lot of delta-vee,  meaning it cannot be had simultaneously with max payload.  But I have not re-run any "Starship" analyses to see how much less payload.

Meanwhile,  the explosion of a Mk1 prototype in Boca Chica is not the disaster it appears.  The time to find problems is during early testing.  Later on,  any problems uncovered are going to be really expensive to fix,  and far more likely to kill someone.  Take it from me,  you really do want all the explosions very early on.  The earlier in the development cycle,  the better.  Been there and done that. 

GW

Last edited by GW Johnson (2019-11-21 16:12:54)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#28 2019-11-21 18:00:44

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,364

Re: Solving Mars mission docking with Phobos

Its going to take a while to go through all of the content. One thing that is part of the answer for mars return is we do not need a full load of fuel to leave mars but what is the landing requirement for earth.

GW website Post commentor

Rob Davidoff wrote:

"lunar semi-Direct". It's sort of a lunar orbit rendezvous by way of depots, with a Starship twist. Basically, a Starship arriving at the moon spends a lot of prop braking the prop it needs for LLO-to-TEI to the surface, then lifting it again. With ISp 381, this takes about a mass ratio of 2.77. A Starship passing through LLO-to-TEI needs about 40 metric tons of prop by my calculations, and thus uses about another 70 metric tons just getting that 40 tons to the surface, then back into LLO to be burnt on the way home.

If a Starship approaching the moon kicks loose a one-time "minidepot" with the LLO-to-TEI prop, then does rendezvous and docking with it after ascent to retrieve it, it allows that 70 metric tons (minus the perhaps 4-6 metric tons of tankage to hold the 40 metric tons of propellant) to be spent instead on landing further payload, which seems like it might increase that 52 metric ton value to 70 or more.

we know the gravity of the moon and mars so we can use these numbers to show how full a mars refueled starship needs to be.

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#29 2019-11-22 06:16:29

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,631

Re: Solving Mars mission docking with Phobos

For GW Johnson re #27

Thank you for doing this work, and for including the Phobos docking.  I'm looking forward to studying it later today or certainly this weekend.

(th)

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#30 2019-11-24 11:29:37

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Solving Mars mission docking with Phobos

Tahanson43206:

I need to take a second look at the delta-vee requirements for the Phobos thing.  I'm not sure,  but I think I used a low-altitude escape velocity for the mechanical energy conservation thing,  when I should have used a high-altitude value.  If I did,  I'll post an update.  The rest is correct. 

GW

update 11-25-19:  I looked,  I had made that mistake,  and I have already corrected it.  See the update at the end of the posting on "exrocketman".

Last edited by GW Johnson (2019-11-25 09:26:20)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#31 2019-12-02 07:28:48

tahanson43206
Member
Registered: 2018-04-27
Posts: 1,631

Re: Solving Mars mission docking with Phobos

SearchTerm:StudyGWXRMPhobos

2019/12/01 First Review of Article in ExRocketMan blog.

(th)

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#32 2019-12-02 17:13:17

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Solving Mars mission docking with Phobos

I have run good numbers for Hohmann and faster orbits to Mars,  with both Earth and Mars at ther average distances from the sun.  Arrivals at Mars are for direct entry,  low Mars orbit,  and the orbit of Phobos with landing upon that moon.  Return would be the reverse,  except for the direct launch from Mars,  for which I also have numbers. 

I have included recommendations for a mass ratio-effective factoring process to increase the "theoretical" delta vees to the values one should really use to determine mass ratios (i.e., allowing for gravity and drag losses),  where appropriate.  Bear in mind that none of this applies to low-thrust micro-acceleration electric propulsion investigations. 

I have NOT (yet,  anyway) applied any of this to performance estimates for the Spacex Starship or any other vehicle.  Anyone is free to do that for themselves. 

But be careful:  what you assume about the delta vee requirements (especially those for landing,  for midcourse correction,  or for non-average planetary orbital positions) affects exponentially the mass ratios required of the mission. I will probably run a sensitivity study next on that issue.

Results so far are at http://exrocketman.blogspot.com,  dated November 2019,  and titled "Interplanetary Trajectories and Requirements".  That includes an update for corrected velocity requirements to Phobos. 

GW

Last edited by GW Johnson (2019-12-02 17:14:34)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#33 2019-12-07 14:40:24

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,756
Website

Re: Solving Mars mission docking with Phobos

OK,  I have run some sensitivity numbers for the 2019 version of "Starship" using the faster transfer orbits to and from Mars.  This is only for LEO departure - direct Mars entry,  and direct Mars launch - direct Earth entry.  I have NOT looked at entering Mars orbit or going instead to Phobos. 

The analysis looks at performance vs transfer orbit trip time,  based on average orbital distances.  It looks at the effects of worst case orbital distances,  vehicle inert mass growth,  and the need for a thrusted pull-up at Mars. 

I posted this stuff today (Sat 12-7-19) at "exrocketman".  That site is http://exrocketman.blogspot.com.  Look for "Analysis of Space Mission Sensitivity to Assumptions".

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#34 2020-01-12 20:35:41

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,364

Re: Solving Mars mission docking with Phobos

https://www.nasa.gov/sites/default/file … 6-ADD2.pdf
Mars Design Reference Architecture 5.0 – Addendum #2

pg 506 starts the planned mission to orbit and check out the moons before going to the surface of mars

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