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#101 2020-07-09 17:25:16

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 16,749

Re: Solving Mars mission docking with Phobos

For GW Johnson re #99, and SpaceNut re #100

Thank you both for your thoughtful analysis of the situation which will be faced by a ship's navigator approaching Mars on a Hohmann transfer trajectory.

This post is reserved for notes after (what I hope will be) careful study.

***
In another topic, RobertDyck has undertaken analysis of and creative thinking about a large scale passenger ship for Earth/Mars travel.

It is too early to know if that initiative will go further or if it has reached its natural conclusion, but it it does continue, the navigation of a large vessel in the vicinity of Mars will be of concern to the crew, and to the mission planners who will be providing the equipment and supplies needed to insure a safe journey for up to 1000 people.

I will endeavor to show that Phobos is capable of imparting (on the order of) 2 km/s of velocity change (acceleration) to a vehicle that engages with the mass of the moon on the backswing, and then rides along as Phobos travels around Mars.

That 2 km/s of velocity change will (and does) represent a savings of fuel and oxidizer which would otherwise be needed to enter orbit around Mars.

(th)

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#102 2020-07-11 16:22:18

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
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Re: Solving Mars mission docking with Phobos

Sending 1000+ people to Mars is way to hell and gone beyond anything currently contemplated,  even at Spacex.  That is most definitely a very large-scale colonization ship effort. 

My advice for that is to use nuclear pulse propulsion in a ship exceeding 10,000 tons,  starting from the backside of the moon,  to shield the Earth from the EMP of its departure "burn".  It will need to use an arrival at Phobos,  in order to shield those on the surface of Mars from the EMP of its arrival "burn".  Such "burns" would likely be thousands of thermonuclear devices,  not 1955-vintage fission devices.

Aerobraking for a ship of that capability will be entirely irrelevant.  You are looking at something about like a WW2 pocket battleship,  around 10,000 to 20,000 tons initial mass,  and over half the ignition mass is dead-head payload.  Because you are looking at 10,000 sec+ Isp at a vehicle acceleration in the 2-4 gee range.  Made from 2-inch thick steel armor plate.  Such a thing can reach Mars in 2-5 months single-stage,  two-ways,   and is big enough to easily spin for artificial gravity between "burns". 

There are a number of missing support technologies necessary to make such a thing possible.  Not the least of which is a nuclear propulsion development-and-test station on the moon,  where there is no air or water to pollute,  or neighbors to annoy,  if you have a problem.  You will need a way to transport that thousand people and all those thousands of tons of supplies to a location beyond the moon,  in order to board a vessel like that.  Plus a way to transport same from beyond Phobos to the surface of Mars.

You WON'T be launching things that large from Earth,  or landing them upon Mars,  because of the collateral-damage the EMP does.  Compared to that,  the radioactive fallout risk is trivial.

GW

Last edited by GW Johnson (2020-07-11 16:24:57)


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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#103 2020-07-11 17:24:33

tahanson43206
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Re: Solving Mars mission docking with Phobos

For GW Johnson re #102

SearchTerm:1000PassengerNuclear
SearchTerm:NuclearFissionPassenger

(th)

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#104 2020-07-11 19:16:14

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,352

Re: Solving Mars mission docking with Phobos

EMP is caused by gamma rays stripping electrons from air molecules in the upper atmosphere.  These are subsequently deflected by the Earth's magnetic field, resulting in a huge induced current lasting for nanoseconds - the so called E1 pulse.

The effects scale with the square root of yield and are more severe in single phase fission devices, because there is no surrounding compressive charge to absorb gamma rays.  Some mitigation options:

1. Smaller devices generate smaller pulse, all else being equal;
2. Gamma rays decline in intensity according to the inverse square law.  A burst at 40,000km will have only 1% of the intensity at ground zero of a burst at 400km, but will effect the entire hemisphere.  Unfortunately, launching at that height would pump the Van Allen belts with charged particles, which may damage satellites.
3. One could shield devices by encasing them in hydrogen rich materials to absorb gamma pulse.  This will increase weight and reduce effective energy density of the pulse units.
4. Fire small devices within some kind of enclosing engine bell, and use the radiated energy to heat hydrogen propellant.  That would do bad things to power to weight ratio and I expect the engine would need to be huge.
5. Launching from the poles would be advantageous, as there is no tangential magnetic field.

I doubt that the pulse rocket would need to launch from behind the moon.  But it may be advisable to launch from above the inner Van Allen belt to avoid damage to geo stationary satellites.

Mars has a thin atmosphere and no magnetic field.  I do not know how a EMP inducing event would play out under those conditions.  It has never been tested.

Any decent performance space drive is a weapon of mass destruction.  There is no way of releasing such huge amounts of energy without collateral damage.  Interestingly, I am not sure that a pure fusion inertial confinement drive would solve these problems.  The explosions are usually envisaged as being smaller, but there is no surrounding charge to absorb gamma rays.  Not an easy problem to solve.  Though there are solutions that would reduce the problem, maybe even making it tolerable.

If chemical propulsion can be used to ship people, propellant and freight to low earth orbit, then a large interplanetary transport ship using gas core nuclear thermal propulsion would be one way of avoiding EMP problems.

Last edited by Calliban (2020-07-11 19:31:31)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#105 2020-07-12 12:32:34

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,423
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Re: Solving Mars mission docking with Phobos

Sending 1000 people to Mars at time has nothing to do with exploration,  and everything to do with colonization or large base-building.  I personally consider that day a very long ways off,  especially for any government-led efforts. 

But if it is a long ways off,  then there is time to develop both gas core nuclear thermal and nuclear pulse propulsion,  and there is time to build a safe place to do that development work,  which in turn is a safe place from which to launch them. That safe place is the moon.  Which should be obvious to the casual observer. 

What you are looking at with gas core is either "nuclear light bulb" concepts (where the uranium is kept separated from the hydrogen) or open-cycle gas core,  where an intimate contact flow scheme must be devised that effectively sets the uranium throughflow at 1/1000 of the hydrogen throughflow. 

None of this has undergone any development at all,  but the early exploratory design work says the light bulb concepts might have Isp ~ 1300 sec max,  at engine thrust/weight greater than 1,  maybe a lot greater than 1. They were looking at double-walled quartz window separation,  cooled in between,  so that thermal radiation transmitted through from the core fireball to the hydrogen propellant.

The open cycle gas core operates at much higher gas core temperatures and power levels,  limited primarily by hydrogen transparency to thermal radiation when it gets hot enough.  There was also a limit where regenerative cooling of the chamber and nozzle bell was no longer feasible,  because the demand for coolant exceeded the supply (the engine throughflow of hydrogen). 

Open cycle gas core was thought possible with regenerative cooling up to ~ 2000 maybe 2500 sec Isp,  with engine thrust/weight exceeding 10,  maybe far above 10. That could actually be used to launch from the surface of the Earth,  if you can accept the radiation in the exhaust stream.

Such exhaust stream radiation is minimized but not eliminated,  if you get to the target 1000:1 flow ratio.  The fission products are there in the exhaust,  at best.  At worst,  there are products plus unused uranium,  all in very hot gas form,  and moving really,  really fast.

Operated at higher core power,  with powered active cooling and a gigantic 3500 F waste heat radiator,  open-cycle gas core could operate up to the transparency limit,  thought to be no more than about 10,000 sec Isp.  But nobody knew "for sure". Or how to actually build that radiator.  Or what from.

The first design target for development set this at 6000 sec Isp, in order to stay well away from the transparency limit.  This design necessarily includes the radiator and powered cooling circuit as part of the engine equipment,  with an effective engine thrust/weight well under 0.1.  Only suitable for in-space propulsion.

The other main attraction of open-cycle gas core over nuclear light bulb,  or any of the solid core concepts,  was safety after shutdown,  which is abortability.  Stop the flows,  and you have an empty steel can,  no reactor core at all.  It "cools" quickly in a radiation sense to levels that can be dealt with,  fairly easily. Nothing that retains a core,  solid or gaseous,  can do that.

Now as I said,  this was all early design speculation,  no real development testing was ever done with any of this.  But the potential really is there.

As for pulse propulsion,  it has not received any development at all,  since it was shut down in 1965.  The design was an armored hull with shock absorbers and a massive steel blast plate,  using small kiloton-range shaped-charge fission devices based on our 1955 technology.  It appeared mostly feasible at the time,  excepting the lack of feasible fractional-kiloton device technology in 1955,  needed to launch from the surface in the atmosphere. We have that now.

Many folks erroneously question the blast plate,  but it was essentially a massive heat sink with radiational cooling,  and pretty much survived in the same way as other massive steel items survived pretty much intact at Hiroshima,  Nagasaki,  and in the surface tests in Nevada.

This stuff actually works more efficiently in larger sizes.  It was barely attractive at a ship initial mass of 5000 tons.  But for ships in the 10,000 to 20,000 ton range,  you are looking at effective Isp in the 10,000 to 20,000 sec range,  and it is hard to hold the ship acceleration levels to the 2 to 4 gee range. In other words you are building vessels of steel armor plate that are the size of WW2 battleships.  And totally unlike electric propulsion,  the thrust levels are very high indeed. Even the Isp is higher than electric.

For really,  really large vessels transporting 1000-to-10,000 people at a time,  there is no other known choice but pulse propulsion.  Nothing else we know scales up that big.  It will scale up even larger.  Pulse propulsion just won't scale down effectively,  so it needs to be used only in such large applications,  not the smaller ones. It just needs an update to 2010/2020 nuclear technology.

For transporting 100-1000 people (or 100-1000 tons) at a time,  open-cycle gas core nuclear orbit-to-orbit ship designs might do well,  with far fewer side effects.  That's still early colonization or large base-building. Nothing to do with exploration.  These would have to be combined with chemically-powered transports of one kind or another,  at each end of the trip,  to get people and cargo between the ship and the surfaces.

On a smaller-still scale (10-100 people or tons),  the chemical and solid-core nuclear thermal schemes look practical.  That addresses both explorations and early small base-building.  These need not be orbit-to-orbit transports,  if one can accept the conflicting design requirements of orbit transports versus landers.  So,  guess why the Spacex Starship/Superheavy design is what it is,  and gets touted for this application. 

Just putting some perspective to this.

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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#106 2020-07-12 14:51:25

Calliban
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From: Northern England, UK
Registered: 2019-08-18
Posts: 3,352

Re: Solving Mars mission docking with Phobos

Thank you very much for an interesting post GW.

I get the feeling that we won't be colonizing Mars until the world stops being scared of radiation.  Both nuclear pulse and gas core nuclear rockets would bleed fission products into the atmosphere.  If the world stopped caring about that, we could launch colonization ships like the one you described from Antarctica, where magnetic field lines are close to vertical and avoid most of the problems from EM pulse.  We could have regular interplanetary transport.  But the price would be higher background radiation levels for anyone living back on Earth.

What kind of a nation would do that?  What kind of government?  Certainly none that I know today.  Maybe the Chinese are ruthless enough.  But the US and Europeans would need governments that are nothing like the ones they have today.  I just cannot imagine it.

Last edited by Calliban (2020-07-12 14:53:56)


"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."

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#107 2020-07-12 15:25:45

SpaceNut
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Posts: 28,747

Re: Solving Mars mission docking with Phobos

Radiation is solved on earth so why can we not do so for trips beyond LEO has to do with cost to lift the materials or sufficient mass which work. That is why we design with the water we must take, the food that is frozen, and with a variety of materials to make it so that less of that fear gets through.

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#108 2020-07-13 08:12:25

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 5,423
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Re: Solving Mars mission docking with Phobos

For exploration missions,  which might or might not establish a small outpost,  all you need is stuff like we already almost have,  launched from the surface of the Earth or from low Earth orbit.  That is exactly what the refilled/outside-LEO mission proposals for Starship / Superheavy are all about,  and it is exactly what NASA claims SLS / Orion is for,  even though it still cannot do such missions. 

Spacex has serious issues to resolve with docking tail-to-tail,  with transferring cryogenic propellants,  with inert mass fractions in their vehicle designs,  with landing pad bearing pressure on soft surfaces,  and with landing leg pattern lateral dimension vs cg height static stability issues on rough ground.  Resolving those is what the prototypes and testing is all about.  That takes time,  and failures are inherent in that.

NASA has serious issues to resolve,  too.  They have as yet no lander design for the moon,  and nothing at all for Mars.  They have no deep space habitat design ready to go,  and what they have does not address microgravity disease or solar flare radiation protection.  They do not have the throw weight capability in Block 1 SLS to do any of this,  and it is doubtful we will ever see Block 1B or block 2B,  because of the cost issue.  The cost issue is that,  pound for pound,  flying on SLS is at least 10 times as expensive as anything else. Maybe 100 times as expensive,  if one is honest with the book-keeping.  They literally cannot afford to use their own rocket.  And the flight rate is too low to do anything significant with it.

NASA's biggest problem is that it long ago devolved into a corporate welfare scheme for the big old-space contractors,  micromanaged in terms of funded projects by congress.  And that is exactly what congress wants from NASA,  to serve its own porkbarrel politics interests.

So,  you are looking at doing early exploratory-level stuff to the moon and Mars in the next several years.  The transportation that does it will most likely be things like Starship / Superheavy,  Falcon-9 / Falcon-Heavy,  Atlas-5,  Vulcan,  and maybe New Glenn.  I doubt that SLS will ever play much of a real role,  but I do think there will be a few stunt flights.  To this mix you need to add habitats resembling Skylab,  equipped with radiation shelters,  some scheme for at least partial spin gravity,  and,  phasing-in later,  some updated nuclear thermal propulsion,  most likely solid core,  if you want to seriously send any "bigger things" to Mars.

Its going to take many,  many years to build a mature transportation system between Earth and the moon,  routinely shipping mass tonnages and big passenger loads back and forth.  At that time is when we will need the advanced nuclear development station(s) on the moon,  and it is from there that the really big colonization-class vehicles will depart,  using that advanced nuclear propulsion.  None of us will live to see that.  All we can do is point the way for our descendants.

GW

Last edited by GW Johnson (2020-07-13 08:17:29)


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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#109 2020-07-13 08:58:09

tahanson43206
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Re: Solving Mars mission docking with Phobos

For GW Johnson re #108

SearchTerm:ForecastSpaceDevelopment
SearchTerm:OutlookSpaceDevelopment
SearchTerm:PredictionSpaceDevelopment

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#110 2020-11-22 18:05:01

SpaceNut
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From: New Hampshire
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Re: Solving Mars mission docking with Phobos

PHOBOS ON THE CHEAP proposes instead that we take a slow approach, incrementally building up towards an eventual manned landing.

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#111 2021-01-25 09:04:18

tahanson43206
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Re: Solving Mars mission docking with Phobos

This is for GW Johnson (hoping you're still keeping an eye on the forum) ....

Some time ago, you very kindly provided advice (and plenty of facts) to this topic.

I accepted the tyranny of the Hohmann Transfer orbit without question at the time.

However, recent discussion of an idea of Void led Calliban to make an observation about the velocity with which a delivery package would encounter Phobos.

I'm going to offer a question; Why are we obligated to only consider the Hohmann transfer orbit?

The Hohmann orbit has a lot going for it.  It puts a payload/vehicle ahead of Mars at the peak of its elliptical trajectory.

Mars catches up with the vehicle and pulls on it.  SpaceNut recently quoted SpaceX as expecting 7.5 kms for a Starship upon entry to the atmosphere of Mars.

Earlier in this topic, it was shown that the velocity of a vehicle approaching Phobos from a Hohmann orbit on the backside of Mars (ie, while Phobos is receding with respect to the arriving vessel) would be reduced by (about) 2 kms, as compared to the velocity relative to Mars.

I am now back asking the question: Why are we obligated to use the Hohmann orbit for package delivery?

A package delivery service is going to want to push the package off from Earth with a velocity calculated to exactly match the velocity of Phobos.

As I am imagining the trajectory right now (with the limited capability available to me) it would arrive at Phobos with exactly (or close to exactly) the velocity needed to dock gently with Phobos.

Is there such a trajectory?

This is a bulk material delivery vehicle, and time is not critical.

Energy invested in shipping the package is important, but it's safe arrival is even more important.

Thanks in advance for any assistance you may have time to provide.

Edit#1: The web page at the link below provides a discussion of the Hohmann transfer orbit at a high school level.

It makes the point that the Hohmann orbit is most efficient.

https://www.jpl.nasa.gov/edu/teach/acti … h-windows/

After thinking about the assertions made in the web site, I've come to wonder if the efficiency claimed includes actions needed at the destination to accelerate to match the velocity of Mars. 

Phobos provides a variable velocity of (about) +/- 2 kms to work with, for a total buffer zone of 4 kms.

Edit#2: The web page at the link below appears to offer an open source program developed by NASA ? that can be used to compute spacecraft trajectories.

https://www.nasa.gov/feature/goddard/20 … aft-design

Apparently the software can be downloaded, but I did not see how to do that in the article.

(th)

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#112 2021-01-25 15:06:51

GW Johnson
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From: McGregor, Texas USA
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Posts: 5,423
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Re: Solving Mars mission docking with Phobos

Tahanson43206:

Perhaps the best way to get you to the information you want is to refer you to my "exrocketman" article "Interplanetary Trajectories and Requirements",  dated 11-24-19.  The fast navigation tool is on the left of the page.  Click on the year (2019),  then the month (November).  You won't need to click on the title,  that article is the only one I posted that month.  Click on a figure to see any of them enlarged. 

The Hohmann transfer ellipse is the minimum-energy trajectory that can take you to Mars at all.  What recommends it,  is its lowest "cost" as measured by required mass ratio and propellant quantity.  You will always arrive with that energy relative to Mars,  at least.  Higher energy trajectories merely have you arriving at higher velocities with respect to Mars.  But you can NEVER get there slower than Hohmann!

The detailed numbers vary a little with exactly where Earth and Mars are in their elliptical orbits about the sun.  What's in the article is for average distances and average orbital velocities.  The effect is larger for Mars than Earth,  because Mars's orbit is a bit more eccentric than that of the Earth.  It's not a large effect,  but it is significant when you are actually designing systems. 

The difference between Mars's orbital velocity VECTOR about the sun,  and your velocity VECTOR on your transfer orbit about the sun at Mars's distance from the sun,  is the relative velocity VECTOR you have with respect to Mars,  "far" from Mars.  Only with Hohmann transfer are these vectors collinear,  so that you can do an arithmetic difference of the velocity magnitudes.  Higher energy trajectories require vector substraction,  and things do NOT happen at aphelion.  The article covers all that. 

Your velocity magnitude "far" from Mars gets increased as you get "close" to Mars by the effect of Mars's gravity drawing you closer.  There is a very simple kinetic energy equation by which you can convert speed far from Mars to speed close to Mars.  The article covers that,  too.  It depends upon local Mars escape velocity at the "near" distance of interest to you.

It's a bigger increase in relative speed going into low Mars orbit,  than it is going into an orbit at the distance of Phobos (which is what the corrections shown on the article are all about:  I failed to do that correctly the first time). 

At average planetary orbital conditions,  your far-from-Mars speed off of Hohmann transfer is about 2.6 km/s relative to Mars.  By the time you reach the distance of low Mars orbit,  it has increased to about 5.7 km/s,  give or take about 0.1 km/s for variation of planetary orbital positions.

If you use the higher-energy trajectory of a 2 year transfer orbital period (this is the free-return-abort orbit Zubrin favors),  you get off the trajectory at Mars at a higher speed "far" from Mars.  That is about 5.4 km/s.  At low Mars orbit distance,  the increase takes you to 7.4 km/s relative to Mars.  Add about 0.1 km/s for worst-case orbital position effects,  and you have the Spacex "worst case" free-entry figure of 7.5 km/s for its Starship to land directly on Mars!

Nice to know that orbital mechanics gives them the same answers as it gives me,  right?  These data are among the 4 cases shown in Figure 8,  out of 16 figures in the article.

For Phobos,  you arrive at the distance of Phobos,  where the escape velocity from Mars is lower at 3 km/s instead of 5 km/s.  That makes the kinetic energy increase "far" to "near" less.  Fig 16 in the article has those data (as I corrected them) for the various transfer cases.  From Hohmann,  your 2.6 km/s becomes 4.0 km/s instead of 5.4 km/s,  relative to Mars.  From the faster 2-year-abort trajectory,  your "far" 5.4 km/s becomes "near" 6.2 km/s,  instead of 7.4 km/s,  relative to Mars.

Now,  if you have timed everything correctly,  you arrive at Phobos's orbit about Mars,  with Phobos right there when you arrive.  You do this on the sunward side of Mars,  so that Phobos is "running at you" slower than Mars is,  so that you can subtract Phobos's orbit speed about Mars from your "near" velocity with respect to Mars. 

That difference is your "near" velocity with respect to Phobos,  essentially almost your delta-vee to land,  uncorrected for any gravity or drag losses,  and uncorrected for the escape velocity from Phobos (about 28 m/s).  Airless and almost gravitationless,  there are no effective corrections to make to the "near" velocity at Phobos,  so you are needing only to add the Phobos escape velocity,  for the actual delta-vee to land. 

The numbers are 1.9 km/s to land on Phobos from Hohmann,  and 4.1 km/s to land on Phobos from the faster 2-year-abort trajectory. That's what Figure 16 shows,  in the top right block of data. 

Now,  add in the departure delta-vee from low Earth orbit,  and a kitty for mid course and near-arrival corrections,  and you have the total one-way trip delta-vee requirements shown in Fig 16,  bottom block of data. The faster 2-year-abort trajectory puts you at 9.0 km/s delta-vee for the one-way trip,  versus 6.1 km/s for the min-energy Hohmann trajectory.  Give or take 0.1 to 0.2 km/s for non-average conditions.
 
Besides the mass ratio cost,  there is the time spent traveling,  which adds a lot of life support mass and energy if manned.  At average planetary orbital conditions,  this is 8.6 months one-way on min-energy Hohmann,  and only about 4.3 months one-way on the faster 2-year abort trajectory.

These numbers are pretty real,  and cannot be sidestepped with some "fancy trick" of orbital mechanics.  These trajectories have been known for many decades,  and in none of those decades has anything any better been found.

I'm no specialist in orbital mechanics,  but I did have to learn the basic subject to get my first engineering degree.  And I used it doing trajectory work on the "Scout" launcher as a graduate student,  about half a century ago.  Nothing has changed since. 

Which is why I can still do this stuff using the basic equations and a spreadsheet,  the way that I do in the article.  It's even slower with a slide rule as I first did upon entering the workforce,  but it is still the same pencil-and-paper-based process,  the same one I used to set up the confirming mainframe trajectory computer runs for "Scout".  Myself,  I have no computer codes for this.

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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#113 2021-01-25 18:31:30

tahanson43206
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Registered: 2018-04-27
Posts: 16,749

Re: Solving Mars mission docking with Phobos

For GW Johnson re #112

Thank you very much for your detailed reply, including the references to all the work you have done in your ExRocketman Blog!

The key information I am selecting is for support of the idea of Void, to deliver bulk materials to Mars using a ballistic system.

The numbers are 1.9 km/s to land on Phobos from Hohmann,  and 4.1 km/s to land on Phobos from the faster 2-year-abort trajectory. That's what Figure 16 shows,  in the top right block of data.

However, before I return to the Ballistic Delivery topic with the quote above, I'm going to set in place a few tags to try to help to find your post again when memory fades which is likely to happen (in my case, at any rate).

SearchTerm:Phobos docking from Hohmann transfer orbit by GW Johnson
SearchTerm:Hohmann Transfer orbit optimum performance arrival at Phobos

(th)

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#114 2021-05-30 17:52:15

Mars_B4_Moon
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Registered: 2006-03-23
Posts: 8,892

Re: Solving Mars mission docking with Phobos

Phobos and Deimos are Fragments of Larger Martian Moon, Study Suggests
http://www.sci-news.com/space/phobos-de … 09672.html

Another attempt at a PhobosGrunt mission?

https://en.wikipedia.org/wiki/Mars-Grunt

PADME was a NASA concept but it lost out to  Psyche and Lucy missions.
https://www.nasa.gov/press-release/nasa … ar-system/

DePhine from Europe but this mission was rejected
https://www.esa.int/Our_Activities/Spac … _for_study

Last edited by Mars_B4_Moon (2021-05-30 17:53:54)

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