Author Topic: Mars Direct updated for the 21st Century  (Read 13444 times)

Offline Patchouli

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Re: Mars Direct updated for the 21st Century
« Reply #20 on: 10/19/2017 03:28 AM »

If you're leaving a return stage in LMO, why not leave the ERV hab there also?

I don't think there's any way to keep a ACES full of LH2 fueled long enough for a Mars return. Boiloff is going to catch up with it eventually.
Yah the hab could be left in LMO  if it's not being used on Mars such as a separate BFS being used for the surface hab I was mostly thinking about getting everything on one BFR.
I'm also not sure if ACES would have enough thrust to weight  it depends on the version and what engine is used but hydrogen boil off was one reason I figure the F9 US might be a better choice for an ascent stage.
The kerosene probably can sit inside it for the entire mission and lox can come from residual propellants in BFS or the Merlin can be switched to a derated Raptor or a cluster of Chase-10s and all the propellants can come for BFS.
If the BFS solar arrays could be removed and deployed on the ground they might be able to power enough ISRU for a small MAV just enough to lift a Dragon into LMO.

« Last Edit: 10/19/2017 03:39 AM by Patchouli »

Offline envy887

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Re: Mars Direct updated for the 21st Century
« Reply #21 on: 10/19/2017 07:32 PM »

If you're leaving a return stage in LMO, why not leave the ERV hab there also?

I don't think there's any way to keep a ACES full of LH2 fueled long enough for a Mars return. Boiloff is going to catch up with it eventually.
Yah the hab could be left in LMO  if it's not being used on Mars such as a separate BFS being used for the surface hab I was mostly thinking about getting everything on one BFR.
I'm also not sure if ACES would have enough thrust to weight  it depends on the version and what engine is used but hydrogen boil off was one reason I figure the F9 US might be a better choice for an ascent stage.
The kerosene probably can sit inside it for the entire mission and lox can come from residual propellants in BFS or the Merlin can be switched to a derated Raptor or a cluster of Chase-10s and all the propellants can come for BFS.
If the BFS solar arrays could be removed and deployed on the ground they might be able to power enough ISRU for a small MAV just enough to lift a Dragon into LMO.

It might be a lot easier to just to land a hypergolic ascent stage inside BFS and crane it to the surface with Dragon sitting on top. the total mass including Dragon would be about 35 tonnes.

Offline Patchouli

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Re: Mars Direct updated for the 21st Century
« Reply #22 on: 10/21/2017 02:22 AM »
The super Dracon could be used for ascent but it would need a vacuum nozzle for better ISP and possibly internal changes to handle firing for that long.
Could be a good excuse to keep the AJ-10 in production though the RD-861K or RD-0216 might be a better choice.
« Last Edit: 10/21/2017 02:33 AM by Patchouli »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #23 on: 11/07/2017 03:14 AM »
I was thinking. The only version of Mars Direct (genuinely direct - no Mars orbiting stuff) that has made sense to me is Elon's version.

I think Elon is more driven by reusability than by conceptual elegance.

I believe that the reailities of (very) large scale fuel manufacture on Mars means that any kind of direct return from Mars will come after earlier missions that don't depend on industrial scale mining. But its still worth contemplating.

So have you guys considered a scaled version of Elon's vehicles? Perhaps with the ability to land methane but with indigenous oxygen?

Offline Norm38

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Re: Mars Direct updated for the 21st Century
« Reply #24 on: 11/08/2017 04:16 AM »
Zubrin's original Mars Direct plan was presented as a response to NASA plans that were rapidly spiraling out of control, for little gain. Recall that the NASA plan had astronauts spending only 30 days on the surface but around 500 days in space. Mars Direct put astronausts on the surface for hundreds of days. Regardless of the transportation architecture, Zubrin won on that point.

Zubrin proposed something that could be built in with existing tech, rather than waiting decades. Of course now it's 20 years later anyway.  But the plan is still to use off the shelf tech or close to it. That means embracing rapid reuse. That extra mass in LEO gives us even more capable ships with achievable mass fractions. That means even less reason to brake into orbit, have separate landers, separate assent stages, orbital docking, etc.

Launch the ships, fuel them up and go.

Offline CuddlyRocket

Re: Mars Direct updated for the 21st Century
« Reply #25 on: 11/08/2017 11:37 PM »
I believe that the reailities of (very) large scale fuel manufacture on Mars means that any kind of direct return from Mars will come after earlier missions that don't depend on industrial scale mining. But its still worth contemplating.

So have you guys considered a scaled version of Elon's vehicles? Perhaps with the ability to land methane but with indigenous oxygen?

There won't be a scaled vehicle. That simply means additional development costs for a second vehicle for no apparent advantage. Scaling means you also scale propellant and cargo capacity and smaller rockets are less efficient.

As for taking methane to Mars; the BFS has a propellant mass of 1100t, 20% (220t) of which is methane. Its cargo capacity is 150t, so even if all the cargo is methane you can't take enough of it! You could take hydrogen - you only need 55t (plus tanks etc) - as long as you can accommodate everything else you need in the remaining cargo capacity.

You can get water and therefore hydrogen from the atmosphere. All you need is power and time (you could contemplate a mixture of such ISRU hydrogen and cargo hydrogen). Alternatively, you could mine it - 55t of hydrogen needs 495t of water; an 8-metre cube of ice will suffice!

I suspect that the first missions will have on-board ISRU propellant plants that will store propellant in their own tanks. Once there's enough, a manned mission will go. Eventually the plant will be removed from the initial spacecraft enabling them to return to Earth and be reused.

Offline guckyfan

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Re: Mars Direct updated for the 21st Century
« Reply #26 on: 11/09/2017 06:13 AM »
The payload capacity of a tanker is more than 150t. Also going back on an energy efficient trajectory won't need 100% propellant. In case of an emergency sending the methane for the return flight and sourcing the LOX locally would be entirely feasible.


Offline freddo411

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Re: Mars Direct updated for the 21st Century
« Reply #27 on: 11/09/2017 10:08 PM »
Initially I began a thread in the SpaceX department inquiring about applying the ITS booster toward the original Mars Direct effect vehicles.  MATTBLAK quoted:
Quote
The traditional Mars Direct by Robert Zubrin and David Baker had Direct vehicles of about 45 tons being sent on Trans-Mars Injection. This is about what the SLS Block II with 'Dark Knights' solid boosters could achieve with an Exploration Upper Stage. If the corestage was redesigned for 5x RS-25E and the EUS had slightly higher thrust engines, this could raise the Direct Vehicle's masses to about 50 tons.

We probably need to have a new thread about Mars Direct redesigned for alternate launch vehicles such as New Glenn, Vulcan/ACES and Falcon Heavy

When Baker and Zubrin conceived Mars Direct back in the 1990s there was only the space shuttle and, at best, the Titan rockets available with no signs of commercial rocketry beyond the ULA monopoly or perpetually-stalled-pie-in-the-sky plans within NASA.  20 years later now, we miraculously have a new world opening up despite the end of the space shuttle.  There may quickly be a huge range of options Mars Direct launchers to utilize for a plan created when there essentially were none.

The thread rules are the following:
1) Assume we wish to land 20+ metric ton vehicles onto the Martian surface with as minimal an architecture as possible - i.e. at least 2 but not more than 4 vehicles and launchers per expedition to Mars
2) Debate any launch vehicle from any company so long as it has the ability to throw over 20 metric tons to Mars
3) Focus discussion on launch vehicles that are active as of 2010 onward; we are trying to update Mars Direct's options
4) Discuss the ITS booster as a launcher but NOT the ITS spaceship as one; the spaceship isn't a launch vehicle by itself applicable to Mars


First off, let me state that Zubrin's Mars Direct architecture brought several new and important innovations into serious consideration.

* Utilizing several launches to accomplish the mission
* Surface rendezvous  (brings both benefits and risks)
* Prepositioning of supplies
* ISRU for a substantial portion of the mission's requirements
* Preference for long surface stay.
* Safety features in some redundancy of alternate vehicles.

These elements are widely considered to be reasonable, desirable and even most alternative architectures would include these or try to justify any lack of these with arguments about tradeoffs.

If we consider Musk's ITS architecture we notice some new and important innovations:

* more economical operational launch costs; reusablity;  -- cross subsidizes by commercial applications
* reasonable spacecraft / lander and booster development costs -- cross subsidized by commercial applications
* Serious effort to create a virtuous economic ecosystem to fund space travel.
* Serious work done on the EDL problem
* Embracing on orbit refueling  -- mass to Mars can scale upward
* Embracing ISRU on Mars -- Methalox rockets becoming a reality

Granted, Elon has not made the above list a complete, actual reality yet.   It is plausible to suppose that SpaceX will get there on its current trajectory.

To my eye, Elon's first couple of flights to Mars look very much like Mars Direct.   Zubrin's ideas did not have a hope to be funded.  It is not clear how Elon's Mars ambitions will be fully funded, but he does have both enormous financial and technical clout.   It is plausable to think that either private investors, philanthropists, and/or the government will step up and contribute the rest of money to make a Mars effort a reality.





Offline tdperk

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Re: Mars Direct updated for the 21st Century
« Reply #28 on: 11/12/2017 02:26 PM »
One of the things that grates on me about Musk's vision (apart from the absurdity of the whole idea of a colony) is the idea of sending civilians into space for several months of zero g and then subjecting them to 4 to 6 gs on Mars entry. I think we can and should do better than that.

A colony populated by those who can afford to go is only as absurd as launch prices / pound make it.  There is no reason why a mature MethaLOx launch system needs to be more than $500k to move 5 tons of settler and gear to Mars.

Why you think there is a issue sending people and cargo when there is no reason to doubt there will be many cargo only missions is a different question.

As for travel vs. EDL g's, there is nothing moving around can help them with in the way of surviving, so all they need to do for those few minutes is lay there.
« Last Edit: 11/14/2017 11:01 AM by tdperk »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #29 on: 11/30/2017 02:32 AM »
I can't comment on the absurdity of a colony because its off topic. But I can say that 5 tonnes per colonist is hopelessly unrealistic.

What I will say that is on topic is that 6gs is a lot of force on a civilian plucked at random. What makes it worse is months of bone loss in zero g.

Its not a case of grinning and bearing. Its a case of being stretchered out.

Offline MickQ

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Re: Mars Direct updated for the 21st Century
« Reply #30 on: 11/30/2017 11:40 PM »
I can't comment on the absurdity of a colony because its off topic. But I can say that 5 tonnes per colonist is hopelessly unrealistic.

What I will say that is on topic is that 6gs is a lot of force on a civilian plucked at random. What makes it worse is months of bone loss in zero g.

Its not a case of grinning and bearing. Its a case of being stretchered out.

Years ago when I was a lot younger and fitter I pulled 6.5 g in a jet fighter for about 20 seconds.  Not being a dedicated pilot, I was wrecked for a good 24 hours afterwards.  A barely trained person enduring those g's for 5+ minutes during EDL is going to suffer for days.

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #31 on: 12/01/2017 12:48 AM »
And we're not talking headaches either. We're talking a whole bunch of people with fractures and other medical issues strapped into chairs a long way up.

Online KelvinZero

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Re: Mars Direct updated for the 21st Century
« Reply #32 on: 12/01/2017 03:52 AM »
Years ago when I was a lot younger and fitter I pulled 6.5 g in a jet fighter for about 20 seconds.  Not being a dedicated pilot, I was wrecked for a good 24 hours afterwards.  A barely trained person enduring those g's for 5+ minutes during EDL is going to suffer for days.
What actually were the issues. Was it all the blood forced into your legs? Lack of blood to the brain?

If someone was flat in a properly supporting bed, wouldn't it be pretty similar to the pressure of being under 6 feet of water?

https://en.wikipedia.org/wiki/High-G_training

Vertical quote: This seems to be talking about vertical acceleration, as you would experience in a roller coaster or jet doing a turn:
The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An untrained individual not used to the g-straining maneuver can black out between 4 and 6 g, particularly if this is pulled suddenly. Roller coasters typically do not expose the occupants to much more than about 3 g

Horizontal quote: This seems to be talking about flat on your back.
The human body is considerably more able to survive g-forces that are perpendicular to the spine.
...
Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[3]

« Last Edit: 12/01/2017 05:10 AM by KelvinZero »

Offline guckyfan

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Re: Mars Direct updated for the 21st Century
« Reply #33 on: 12/01/2017 05:34 AM »
I am pretty sure the 6g mentioned in 2016 are a peak value, not sustained over the whole braking time. Also what about the new reentry method? More total braking over a longer period, but what about peak values? I suspect they will be lower, but don't know.

Earth reentry for point to point is different of course but there the max g will be in the range that commercial flight customers will be OK with it.

Offline tdperk

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Re: Mars Direct updated for the 21st Century
« Reply #34 on: 12/02/2017 06:39 PM »
What makes it worse is months of bone loss in zero g.

Its not a case of grinning and bearing. Its a case of being stretchered out.

Never yet been the case.

Offline Nathan2go

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Re: Mars Direct updated for the 21st Century
« Reply #35 on: 12/02/2017 10:09 PM »
To my eye, Elon's first couple of flights to Mars look very much like Mars Direct.   Zubrin's ideas did not have a hope to be funded.  It is not clear how Elon's Mars ambitions will be fully funded, but he does have both enormous financial and technical clout.   It is plausable to think that either private investors, philanthropists, and/or the government will step up and contribute the rest of money to make a Mars effort a reality.
Mars Direct was pitched as a government Mars program.  Government Mars missions have the handicap of requiring the Astronauts to come back within a short time frame, and this requirement drives a lot of cost&difficulty in the mission, perhaps to the point the mission is impossible.  Privately funded missions don't have this constraint.

I think a more likely outcome is that NASA finds a way to buy, say $2B worth of BRF launches every year, maybe for a lunar village, maybe for a Mars orbiting basecamp, whatever.  SpaceX uses the profits to fund their own Mars program.

In the SpaceX Mars program, the main reasons to send astronauts is so they can construct a space port (with a 150 ton cargo unloading crane) and propellant plant large enough to send back multiple BFS departures every 24 month window.  This could easily be a 3 year job for 10 people, and involve 4-10 single-use BFS payloads.  If something goes wrong, there is no emergency return option; the crew just waits until the next BFS arrives with spare parts and then continues their work.

Once the first re-usable BFS returns from Mars, likely empty (because why take the risk?), NASA would be shamed into funding a permanent government base and large exploration program.  The prudent NASA move would be to spend a few years building up cargo on the Mars surface, before ever sending the first NASA crew.  That way, SpaceX would have much experience getting the ships back to Earth before the first human return trip.

Zubrin convinced the space community that a 30 day surface mission was too short (i.e. "flags and footprints" is not a sufficient initial goal).  I think the first SpaceX crew will go for a 7+ year surface stay; it's the safest option, plus it creates a larger toe-hold for a future colony.  Eventually, crew rotations may shorten to 2 years, but initially, the rocket flights will be so dangerous that if you survive, you might as well stay a while.

I think that if SpaceX can self-fund an unmanned (expendable) BRS landing on Mars, then they will be able to find investors to back a larger program to build a base with propellant production.  At that point, NASA can't tell the public that Mars is to too hard, or it's 20 years in the future.  The big aerospace companies will be able to share a $100B NASA Mars program, so they'll push hard for it, including cutting deals with SpaceX and their investors.
« Last Edit: 12/02/2017 10:29 PM by Nathan2go »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #36 on: 12/04/2017 02:49 AM »
Its not comparable.

6 fert of water or roughly 2 metres exerts an isostatic pressure of roughly 20Kpa. That's a force of about 3.8 tonnes over the surface areacof an average male human. However we don't notice this because we are mostly bags of water and water and the internal pressure balances the external pressure.

An acceleration applied in one direction is an entirely different proposition. Everything gains "weight". Skin, muscle, in fact anything not rigid  applies oressure to wverything that is rigid. You wnd up with forces applied to joints and bones in directionsat odds with the direction of force they grew to support.

Now if you take a bunch of civilians and trained and screened them and subjected them to several minutes at 6 gs and they survived happily then I'd make the judgement call that they fit to land  in the immediate future.

However take the same people and give them months of weightlessness with resulting bone density loss - and all bets are off.

Large numbers of casualties stretched down from the top of a tall lander in space suits is a big exercise and it adds to other risks at a critical phase.

Online KelvinZero

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Re: Mars Direct updated for the 21st Century
« Reply #37 on: 12/04/2017 04:50 AM »
Russel, you skipped this bit.

https://en.wikipedia.org/wiki/High-G_training
The human body is considerably more able to survive g-forces that are perpendicular to the spine.
...
Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.


Offline MickQ

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Re: Mars Direct updated for the 21st Century
« Reply #38 on: 12/04/2017 10:52 AM »
Years ago when I was a lot younger and fitter I pulled 6.5 g in a jet fighter for about 20 seconds.  Not being a dedicated pilot, I was wrecked for a good 24 hours afterwards.  A barely trained person enduring those g's for 5+ minutes during EDL is going to suffer for days.
What actually were the issues. Was it all the blood forced into your legs? Lack of blood to the brain?

If someone was flat in a properly supporting bed, wouldn't it be pretty similar to the pressure of being under 6 feet of water?

https://en.wikipedia.org/wiki/High-G_training

Vertical quote: This seems to be talking about vertical acceleration, as you would experience in a roller coaster or jet doing a turn:
The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An untrained individual not used to the g-straining maneuver can black out between 4 and 6 g, particularly if this is pulled suddenly. Roller coasters typically do not expose the occupants to much more than about 3 g

Horizontal quote: This seems to be talking about flat on your back.
The human body is considerably more able to survive g-forces that are perpendicular to the spine.
...
Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[3]


I don't know the actual medical reason but I felt as if I had just done a full day's hard labour in about 5 minutes.  I was physically exhausted after the flight.

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #39 on: 12/04/2017 02:40 PM »
Kelvin that's still for healthy people who haven't lost bone density in zero g.