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#1 2019-12-03 07:18:41

tahanson43206
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Registered: 2018-04-27
Posts: 3,082

Phobos

For SpaceNut ....

This topic is created to allow for focus on Phobos.

Phobos has received attention in a large number of posts in the NewMars forum.

The posts are scattered over a great number of topics.

If anyone has the time and energy to collect links to discussions of Phobos, please add them to this topic.

The idea I have in mind is to assist future visitors to the forum to investigate conversations about Phobos more directly than is possible by entering a search for the word Phobos.

SearchTerm:IndexPhobos

(th)

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#2 2019-12-03 07:22:58

tahanson43206
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Registered: 2018-04-27
Posts: 3,082

Re: Phobos

Construction of Landing Platform for Phobos

On the assumption Phobos is destined to become a major Port of Entry to the Mars environment, this post is offered to begin discussion of how the infrastructure for landing vessels inbound from Earth (or elsewhere) can be constructed from local materials.

A concept that came to me recently is the jigsaw puzzle model.  Pieces of a platform can be molded of molten regolith, in shapes which interlock as the pieces of jigsaw puzzles do.   This would allow for small scale manufacture of pieces of a landing platform, while contributing to a large scale structure when the pieces are assembled.

(th)

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#4 2019-12-03 18:32:15

SpaceNut
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#5 2019-12-03 19:22:47

tahanson43206
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Registered: 2018-04-27
Posts: 3,082

Re: Phobos

For SpaceNut re #3 and #4

Thank you for finding all those topics!

It was interesting to see the robust discussions from 2003, as just a first impression.

FYI ... the images from the Soviet Phobos mission don't appear to still be available.  Perhaps the web site is long gone.

The Mars Express image is impressive.

(th)

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#6 2019-12-03 19:50:18

SpaceNut
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Posts: 19,222

Re: Phobos

The are hundreds more topics with the casual meantion or more with in then and would take to much time to dredge through each one to collectively add all of those post into this one topic.
So what do you want this topic to be is up to the questions posed and ideas on how to press forward to a mission to the little moons of mars.

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#7 2019-12-11 18:04:49

knightdepaix
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Re: Phobos

While mining would be going on on Phobos, does loss of mass slow down or stop its deceleration so the Phobos would not be broken apart?

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#8 2019-12-11 19:27:37

SpaceNut
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Re: Phobos

Relative to mars its orbit should speed up with mass lose, relative to phobos its gravity will drop but what happens to its rotation rate is a question?

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#9 2019-12-12 07:03:10

tahanson43206
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Registered: 2018-04-27
Posts: 3,082

Re: Phobos

For SpaceNut re #8

There should be no change to rotation rate.   Phobos is tidally locked.

There should be no change in orbit characteristics as mass is added or removed.  Any change would happen as a result of thrust that might be imparted as mass is added or subtracted.  Scooping up a rock from a body in motion, as is being done with probes visiting various objects today, will have no effect whatsoever on the motion of the primary object.

If you have a resource that would show otherwise, I would be interested to see it.

(th)

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#10 2019-12-12 17:59:08

SpaceNut
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Re: Phobos

The centriplical force of mars on to phobos is the tidal locking and its related to mass. F=M*A where F is Mars pull on Phobos.
Like you meantion its not until its light enough that the forces of rockets would start to alter how phobos would behave.

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#11 2019-12-13 08:55:15

Terraformer
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Re: Phobos

If we use tethers on Phobos, it will lose or gain momentum and energy as mass is transferred. Dropping mass down to Mars will raise its orbit, as will catching payloads at a higher orbit, and conversely we can use it as a momentum bank export mass from Mars.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#12 2019-12-13 13:22:33

GW Johnson
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Re: Phobos

When you consider that a direct entry is the way to do arrival delta-vee without rocket power,  I see little advantage to orbit about Mars,  or even going to Phobos.  Not unless other constraints drive you there.  And they might.

That being said,  I'm unsure of what advantage Phobos might have over low Mars orbit.  The delta-vee to and from low Mars orbit to the surface of Mars is lower than to and from Phobos.  Unless there is some sort of usable resource on Phobos,  then what is point?

Delta vee is rocket,  or it is aerobrake.  We do not have any tether or mass-driver technologies ready to apply.  We have rockets,  and we have heat shields.  Big difference between ready-to-apply,  and "here's an idea".

Now,  what makes anyone on these forums believe there will be usable volatiles on Phobos (or any small asteroid)?  And just what exactly can you really do with small stones,  sand,  and rock dust,  anyway?

The bodies like that which sometimes show comet-like tails are the ones with the volatiles,  and they are all very much larger:  hundreds,  not tens,  of km in size.  Smaller bodies seem to be dry rubble piles,  for the most part.  And with insufficient gravity to hang together to hold any significant internal pressure in a mined-out space. 

So I ask again,  what is the point of going to Phobos instead of straight to low Mars orbit or to a direct entry?  I'd really like to know.

GW

Last edited by GW Johnson (2019-12-13 13:29:25)


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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#13 2019-12-13 14:08:44

tahanson43206
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Re: Phobos

For GW Johnson re Why Phobos?

The answer is straight forward ... Human Nature.

Human beings cannot be trusted to land anywhere on Mars and do anything they want to do on Mars.

As a veteran of the Cold War, I suspect you are well aware of the realities of how human nature will impact the Mars project.

However, there is a period of time, before anyone is actually ** on ** Mars, when idyllic visions of peaceful interactions fill the heads of starry eyed visionaries.

We are (apparently) very much IN that period of time.

As soon as possible, people who set up shop on Mars are going to be concerning themselves with quarantine of arriving shipments from Earth, or from anywhere else, so that diseases can be blocked before they enter the fragile environment that will exist in Mars habitats for many years. And that is just ONE threat that will inevitably arrive from Earth or elsewhere.

Phobos is just about ideal for Customs Inspections, so I would expect it will receive a LOT of attention.

As this reply illustrates, there are even people alive on Earth today who are starting to think about management of borders around Mars.

(th)

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#14 2019-12-13 17:30:33

GW Johnson
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Re: Phobos

I think it premature to talk about colonies when we haven't even landed there briefly yet. 

The first visits to Mars will likely resemble the Apollo landings,  in that it's a whole lot more about just getting there and back again.  I would hope to run some real experiments aimed at processing local materials into life support supplies and propellant.  I would hope these would be left running when the explorers leave,  but those explorers will be using life support supplies,  and probably propellant,  brought from Earth. 

That last assertion is actually a backup plan to Spacex's plan:  send 6-8 "Starship" tankers to Mars before the first manned "Starship" goes there.  It seems unlikely to me that a propellant plant is really going to work adequately,  before those first folks are forced to return,  or else die there.  Propellant manufacturing plant hardware is simply not yet an existing item,  lab bench top experiments notwithstanding.  And nobody out there is working on this in any serious way,  to the best of my knowledge.

Without return propellant,  some 1200 tons of it per ship,  "Starship" is a one-way ticket to Mars.  And death,  in the cold,  and the dark,  without even air to breathe.

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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#15 2019-12-13 18:09:02

SpaceNut
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Re: Phobos

If there was a commercial off the shelf for home use we would be really ready for mars as safety would be built into what we would take to mars. The biological approach does work to make methane from anything that will decompose with the aid of bacteria but not likely to produce the amounts that man needs and even the seasonal release would not do if we can not get at its source.

Thats the 100 mT for each ship carefully planned manefest but keep in mind that we are send duplicates on the first few as we are still not sure of the landing. A test landing even out in the desert here on earth would bring up the confidence levels for doing so.

The next issue is how to link up the ones that do land close enough, get cargo out and setup for all aspects to get fuel and oxygen surplus for man's use.

The ability to save surplus water is another carefull action item that must work as well as the gathering of water to make the process work to begin with.

Another is the long term collection of a co2 atmospher without getting the filter plugged up or having compressors die..

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#16 2019-12-14 11:34:17

GW Johnson
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From: McGregor, Texas USA
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Re: Phobos

OK,  from "Interplanetary Trajectories and Requirements" posted 21 November 2019 on my "exrocketman" site,  here are the average (not worst-case,  but average) velocity requirements for going to Mars from LEO by Hohmann min-energy transfer.  These data are from Figure 10,  excepting Phobos,  which got corrected in Figure 16 in the update. Where it says "factored",  the kinematic velocity requirement has been factored for gravity and drag losses by about 2%,  or by 1.5 for landing hover and divert requirements.

First is for direct entry:

item         dV, km/s
departure    3.659
midcourse    0.5
landing      0.45
total        4.609
speed at entry interface 5.689 km/s

Second is for deceleration into low Mars orbit.  Note that I listed the surface excursion (split out 2-ways) as a separate item).

item         dV, km/s
departure    3.659
midcourse    0.5
arrival      2.129
total        6.288

deorbit      0.050
landing      0.45  (factored)
total        0.500
speed at entry interface ~3.6 km/s

ascent       3.629 (factored)
rendezvous   0.2
total        3.829

2-way total  4.329

Third is for deceleration into Phobos's orbit,  followed by rendezvous and landing upon that moon,  which transfer is only slightly different from low Mars orbit.  I did not compute requirements for an excursion to the surface of Mars from Phobos,  but bear in mind that they are significantly higher than from low Mars orbit,  because of the much greater semi-major axis size of the transfer ellipse. 

item         dV, km/s
departure    3.659
midcourse    0.5
arrival      1.882
landing      0.028
total        6.069
       
That same article has the return requirements,  and the effects of faster trajectories,  things NOT included here.  These data would apply to anybody's vehicle designs.  Faster trajectories increase the delta-vee requirement dramatically,  and not symmetrically for outbound vs return voyage. Direct entry interface velocities at Mars and Earth are also higher for faster trajectories.

So here's the bottom line:  if you choose direct entry,  the vehicle that takes you there must have a heat shield for aerobraking,  but need only supply about 4.609 km/s delta-vee.  This means you land regardless of conditions on Mars,  there is no aborting the landing.  It also means you are restricted to exploring the one landing site,  period.

If you choose low Mars orbit,  your transfer vehicle needs no heat shield,  but must supply about 6.288 km/s worth of delta-vee.  From orbit,  you may dispatch different lander vehicles to any sites you wish,  anytime you wish,  thus responding to local conditions on Mars. 

For a one-way cargo lander,  the delta vee is only about 0.5 km/s,  but you do need a bit of a heat shield.  For a two-way "landing boat" vehicle,  you need a heat shield for descent,  and an ascent delta-vee capability near 3.829 km/s,  which includes a kitty for rendezvous.  If you choose to do all of that in a single stage,  the total delta-vee is only 4.329 km/s. (That's actually doable with any of the hydrazines and nitrogen tetroxide.)

If you choose to go to Phobos and "base" there,  the transfer vehicle needs no heat shield,  and must be capable of about 6.069 km/s delta-vee,  which is only trivially different from low Mars orbit,  given the uncertainties in these calculations.  However,  the delta-vee requirements for surface excursions to Mars are quite a bit higher than from low Mars orbit.  I didn't figure them,  but the two-way trip might fall in the 5+ km/s class,  which is getting very demanding for a single stage vehicle with a heat shield to survive the entry.

Why make the lander problem harder,  when the transfer delta-vee is only trivially different?  Low Mars orbit looks a lot more attractive to me than basing on Phobos,  precisely because of the lander problem. 

The 6.1-6.3 km/s delta-vee required for the transfer vehicle is just the price you pay for being able to respond to local conditions upon arrival and/or to explore more than one site,  when you get there. Otherwise,  direct entry and landing cuts that well under 5 km/s,  at the potentially very high cost of not being able to abort the landing because of poor conditions. 

Only if we had real (!!!) reason to believe that there are usable resources on Phobos,  would basing there look attractive.  As I have said elsewhere,  the presence of volatiles is unlikely due to the small size,  based on our current estimates for stony asteroids.  It's probably just a dry,  unconsolidated rubble pile.

Phobos might make sense later,  when there is a colony on Mars,  as a sort of border-crossing gateway and entry point.  But that is NOT pertinent to the first several landings.

GW

PS:  the same trivial transfer delta-vee advantage vs strong surface excursion delta-vee DISadvantage is exactly why NASA's lunar Gateway station makes absolutely NO sense anywhere but in low lunar orbit.  NASA is driven to base it wrongly because Block 1 SLS is incapable of putting it in low lunar orbit.


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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#17 2019-12-21 21:24:47

SpaceNut
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Posts: 19,222

Re: Phobos

poke... marsexpress-schematic-phobos-phase-angles-image-capture-hg.jpg

Mars Express tracks the phases of Phobos

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#18 2020-06-08 21:27:08

SpaceNut
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Re: Phobos

Scientist captures new images of Martian moon Phobos to help determine its origins

Wide range of temperatures over the years of taking images as our probes pass by.

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#19 2020-06-09 06:31:34

tahanson43206
Member
Registered: 2018-04-27
Posts: 3,082

Re: Phobos

For SpaceNut re #18

Thank you for this report of the image processing by (Dr?) Edwards!

Of particular interest for ** this ** topic is the short paragraph at the bottom:

Edwards added, "JAXA, Japan's space agency, is sending a whole mission to investigate Phobos and Diemos (Mars' other moon) called the Martian Moons eXploration (MMX), so we're providing some good reconnaissance data for that upcoming mission!"


Related Links
Northern Arizona University
Mars News and Information at MarsDaily.com
Lunar Dreams and more

The Japanese expedition planning must be well along.  If anyone can find any documents or web sites that cover the planning, the reports would seem a good fit for this topic.

One other note from the article ... the material observed on Phobos is reported to be primarily basaltic.  This is worth noting, for those who are thinking of making basalt thread for various purposes, such as the wrapping concept explored in Calliban's asteroid topic.

(th)

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