Author Topic: Mars Direct updated for the 21st Century  (Read 2400 times)

Offline redliox

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Mars Direct updated for the 21st Century
« on: 05/01/2017 04:14 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
"Let the trails lead where they may, I will follow."
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Offline sevenperforce

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Re: Mars Direct updated for the 21st Century
« Reply #1 on: 05/01/2017 08:17 PM »
Build your 20-tonne vehicle with methalox engines, loft it as the upper stage on Falcon Heavy, refuel it in LEO, and send it on its way.

As long as you can aerobrake at Mars, you're golden.
« Last Edit: 05/01/2017 08:17 PM by sevenperforce »

Online KelvinZero

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Re: Mars Direct updated for the 21st Century
« Reply #2 on: 05/18/2017 10:32 AM »
This is something I sort of wanted to ask before but this makes it a bit more topical.

around the 3 minute mark, he says that if you can refuel a vehicle in orbit it's a very valuable thing to do.

Would it still count as Mars Direct (Updated for the 21st century) if it had many many refueling flights?

My loose understanding is that a large number of flights is against his philosophy.. but wouldn't that simply change if it became a standard proven practice?

The 21st century might be defined by F9R becoming mundane. The first stage to get that huge amount of fuel for an all chemical mission to mars into LEO is a huge part of the cost but IMO a small part of the architecture.

Online MATTBLAK

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Re: Mars Direct updated for the 21st Century
« Reply #3 on: 05/18/2017 11:52 AM »
Dual launches of 50+plus ton Commercial launchers could send 25-to-30 metric ton spacecraft on their way - be they Dragon-derived or the traditional 'Tuna Can' Mars Direct ships. Though, I've always had a bit of a soft spot for blunt-biconic spacecraft, which the Dragon 2.0 has more than a passing resemblance to. Using 2x Falcon Heavy in it's fully expendable mode allows for 120 tons into Low Earth Orbit. I once wrote a paper (too many details to reproduce here, and a bit obsolete in details) on how to do a basic 2 or 3 man Sortie/Flags/Footprints Martian mission to 'break the Dragon of impossibility's back and prototype a pioneering Manned Mars Mission. Larger, long stay missions could come later...

With the following, I'm drawing a broad sketch - some might go; "Yeah, but hang on - how does it..." Details might come later in a more detailed 'white paper' that I'll hammer out, if I get time. Then real engineers and scientists like Dr Pietrobon for instance could crunch the numbers, if they were so inclined...

A: A Dragon 2 based Earth Return Vehicle is pre-deployed to Martian orbit with a Transit Hab docked to it's nose - inflatable or stretched Cygnus-derived. The Dragon ERV has an extended Trunk that has a 'Propulsion Pallet' fueled by about 20 tons or more of hypergolics and powered by a cluster of Dracos. We broadly assume that this craft had been braked into Martian orbit previously by an expendable, storable propellant propulsion stage.

B: On the surface of Mars at a pre-chosen landing site are 2x upgraded Red Dragon Cargo landers. One contains a Solar/RTG/Stirling generator unit for ISRU and Expedition surface power. The other has food, water, tools and equipment - including a simple Apollo-style Martian Roving Vehicle - carried in a conformal, aerodynamic 'bulge' shell on the outside hull of the Dragon. A matching conformal shell on the other side carries other gear. Once emptied, this Cargo Lander can also act as a Surface Habitat.

C: As near as possible (200 meters or less) to the pre-landed Cargo/Hab Dragons is a third craft: A Dragon based Mars Ascent Vehicle. The only cargo this craft lands is a supply of Hydrazine fuel. A small robot rover unspools a power cable from the Power Cargo lander and plugs it into the Ascent Vehicle. The Ascent Vehicle sucks in and cracks Martian CO2, dumping Carbon Monoxide overboard and storing Liquid Oxygen in it's oxidizer tanks.

CREW LAUNCH: In fully expendable mode, a Falcon Heavy places into LEO a crewed Red Dragon spacecraft with a propulsion pallet-equipped Extended Trunk. It carries 2x Astronauts. A second Falcon Heavy launches with a small Transit Hab attached to the top of it's second stage. The Transit Hab will mass about 7 tons with it's supplies and equipment if it's based on an enhanced Cygnus, or lighter if an inflatable. The second Falcon Heavy's upper stage retains about 50 tons of propellant from it's ascent to orbit. The Crewed Dragon docks with the Transit Hab mounted atop the Falcon second stage and the combined crafts burn out of Earth orbit on Trans-Mars Injection; using all of the Falcon stage's propellant and most of the crewed Dragon's propulsion pallet. Enough fuel is retained in the propulsion pallet for 2 or 3 course correction burns or an abort burn past Mars if necessary later in the mission. The Transit Hab contains enough crew contingency supplies for a months-long cruise back to Earth if needed. But during a nominal mission; these supplies would be jettisoned, along with the Trans Hab.

The Crew Dragon cruises to Mars and when on final approach, the Transit Hab and Trunk are jettisoned and the crewed Red Dragon performs a direct entry descent to the Martian surface, right near the pre-deployed Dragon assets. Depending on when the precise years the Launch windows are set in, and on the trajectory used; the surface stay and exploration would be anywhere from two to four weeks. The crew would then have to board the now fully-fueled Mars Ascent Dragon and climb to rendezvous and dock with the Earth Return Dragon vehicle...

Now; this bare-bones basic mission concept could be augmented with extra equipment and modules launched every launch window - more Mars surface power units and supplies landed to increase the Martian stay to more than a year. An inflatable surface Habitat to allow the crew to increase to 3 or even 4 Astronauts... And a larger Transit Hab to allow room and supplies for a larger crew, outbound to Mars...

Yes; I know this isn't as grandiose or 'sexy' as either Elon's Interplanetary Colonial Transport system, or even NASA's slightly nebulous plans... But that's the point! Do it fast, do it minimalist and 'dirty', and break ground - 'guerilla' fashion. But it would still be asking a great deal of both the available technology and also the tech that is still to come.
« Last Edit: 10/06/2017 02:14 PM by MATTBLAK »
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Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #4 on: 10/06/2017 05:49 AM »
I haven't been here for a while, mostly because of other commitments.

However, going back over where I've been before and thinking about it freshly, there is still one thing that remains an absolute for me. That's a fully propulsive landing for the crew. 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.

What has changed however is Elon Musk has convinced me that its okay to burn a lot of fuel. This changes several things.

One is that you can afford to get people to Mars in more like 3-4 months than 6-8 months.

Another is I'm less worried about there being sufficient fuel for a propulsive Mars lander.

Another is that I don't have to worry about solar electric propulsion.

Can I do this with a minimal number of vehicle types. Pretty much.
Can I do this with a minimal number of launches. Perhaps.

No, I haven't thought through the detail but I still think its worth doing cargo and crew landings separately.
« Last Edit: 10/06/2017 05:52 AM by Russel »

Offline Archibald

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Re: Mars Direct updated for the 21st Century
« Reply #5 on: 10/06/2017 07:47 AM »
Musk wants BFR stage 2 to be able to land on Moon and Mars. The major differencies are delta-V and atmosphere.
 I feel that, in the days of BFR 2016 and Red Dragon, the plan was "screw Mars atmosphere, we will land fully propulsive on Mars just like on the Moon." Unfortunately, Mars atmosphere is a harsh mistress, and decided otherwise. Musk has to concede some kind of aerodynamic braking, see the small delta wing on 2017 BFR.

At the end of the day

a) Mars atmosphere is a giant PITA, no Earth, no Moon, but in the middle of the two. No heatshield and burns, but no full propulsive landing either, because stronger gravity and atmosphere.

b) using a similar vehicle to land on Moon and Mars is quite difficult. LEM and MEM were to be markedly differents.

c) Musk tactic to get around this is "think big". Big propellant mass provides large delta-V and with enough delta-V you can land anywhere on the solar system. This is really a brute force approach, but then again, Musk understand were are stuck with chemical propulsion for a very long time, and the only way to get around chemical propulsion is "think big" and "propellant depots".
« Last Edit: 10/06/2017 07:49 AM by Archibald »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #6 on: 10/06/2017 09:43 AM »
This is where I take exception with the commonly held concept that cargo and humans have to be landed together in one big ship and thus also where I take exception with Elon.

If you've got a very heavy vehicle then yes, Mars atmosphere is a pita and a fully propulsive landing is very expensive fuel wise. And that's precisely where you're at if you insist on landing people on the same vehicle as cargo.

However, if you separate cargo from people then the numbers work out a lot differently. You can land cargo exactly how Elon proposes. In fact without people on board there are optimisations you can perform because you have the freedom to pull even higher gs. Likewise, people don't weigh much and its not that costly to land them fully propulsively. Another point worth repeating is that you'd like a fast transit to Mars. That means more fuel. And if you're taking cargo on the same flight then that's even more fuel that you didn't need to use, which could be used to better advantage in other ways.

Again, where people go wrong is the almost universally held notion that it all has to come down to Mars surface in a single vehicle.
« Last Edit: 10/06/2017 09:44 AM by Russel »

Offline envy887

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Re: Mars Direct updated for the 21st Century
« Reply #7 on: 10/06/2017 02:02 PM »
This is where I take exception with the commonly held concept that cargo and humans have to be landed together in one big ship and thus also where I take exception with Elon.

If you've got a very heavy vehicle then yes, Mars atmosphere is a pita and a fully propulsive landing is very expensive fuel wise. And that's precisely where you're at if you insist on landing people on the same vehicle as cargo.

However, if you separate cargo from people then the numbers work out a lot differently. You can land cargo exactly how Elon proposes. In fact without people on board there are optimisations you can perform because you have the freedom to pull even higher gs. Likewise, people don't weigh much and its not that costly to land them fully propulsively. Another point worth repeating is that you'd like a fast transit to Mars. That means more fuel. And if you're taking cargo on the same flight then that's even more fuel that you didn't need to use, which could be used to better advantage in other ways.

Again, where people go wrong is the almost universally held notion that it all has to come down to Mars surface in a single vehicle.

There is no way to land on Mars (or the Moon) besides than propulsive landing. You can get rid of hypersonic retropropulsion, but you can't get rid of propulsive landing.

Offline the_other_Doug

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Re: Mars Direct updated for the 21st Century
« Reply #8 on: 10/06/2017 04:05 PM »
This is where I take exception with the commonly held concept that cargo and humans have to be landed together in one big ship and thus also where I take exception with Elon.

If you've got a very heavy vehicle then yes, Mars atmosphere is a pita and a fully propulsive landing is very expensive fuel wise. And that's precisely where you're at if you insist on landing people on the same vehicle as cargo.

However, if you separate cargo from people then the numbers work out a lot differently. You can land cargo exactly how Elon proposes. In fact without people on board there are optimisations you can perform because you have the freedom to pull even higher gs. Likewise, people don't weigh much and its not that costly to land them fully propulsively. Another point worth repeating is that you'd like a fast transit to Mars. That means more fuel. And if you're taking cargo on the same flight then that's even more fuel that you didn't need to use, which could be used to better advantage in other ways.

Again, where people go wrong is the almost universally held notion that it all has to come down to Mars surface in a single vehicle.

There is no way to land on Mars (or the Moon) besides than propulsive landing. You can get rid of hypersonic retropropulsion, but you can't get rid of propulsive landing.

And this is the crux of where people don't get how SpaceX is changing the paradigm.  If you think of each delivery vehicle as a truck, the old paradigm had you design and build a different type of single-use truck for each individual piece of cargo -- manned or unmanned.  SpaceX is building one multi-purpose truck that can carry all sorts of cargo to all sorts of places.  You don't spend a year optimizing a truck to carry cargo over the mountains -- you just add tire chains and head on up the hill.

The old paradigm would cost the better part of a trillion dollars to land four to six people on Mars.  The new one is planned to bring that down to a few billion.  You do the math... ;)
-Doug  (With my shield, not yet upon it)

Offline DreamyPickle

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Re: Mars Direct updated for the 21st Century
« Reply #9 on: 10/06/2017 04:13 PM »
The architecture proposed by SpaceX already has dedicated crew and cargo craft. The plan showed 4 cargo and 2 crew landings for the initial setup of the ISRU plant. Sending crew and cargo on different trajectories can already be done. Not much detail was shown for those cargo vessels but they might even be unpressurized and have large openings for unloading extremely voluminous cargo.

They chose to use a single outer-mold-line for all the S2 variants because reentry is difficult and it gets harder for bigger spacecraft. For Mars the current record is Curiosity at less than 1 ton. Developing *multiple* reentry systems would require a lot of extra effort for no gain.

Red Dragon (since cancelled) would have been nice to have for initial scouting. But it's not it would have been useful beyond the first couple of missions. It would be inefficient for cargo and using it for crew would imply a separate orbital-only transit habitat.

Having as few distinct components as possible is an excellent way to keep costs down.

Offline blasphemer

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Re: Mars Direct updated for the 21st Century
« Reply #10 on: 10/06/2017 04:20 PM »
This is where I take exception with the commonly held concept that cargo and humans have to be landed together in one big ship and thus also where I take exception with Elon.

Who says cargo will have to be landed together with people? I am sure there will be an unmanned, cargo only BFR spaceship variant as well as a manned one. But there is no point in designing entirely different vehicles for cargo and for crew, that would be a waste of resources, IMHO. In the end humans are just an especially fragile type of cargo anyway..

Online guckyfan

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Re: Mars Direct updated for the 21st Century
« Reply #11 on: 10/06/2017 04:32 PM »
This is where I take exception with the commonly held concept that cargo and humans have to be landed together in one big ship and thus also where I take exception with Elon.

Who says cargo will have to be landed together with people? I am sure there will be an unmanned, cargo only BFR spaceship variant as well as a manned one. But there is no point in designing entirely different vehicles for cargo and for crew, that would be a waste of resources, IMHO. In the end humans are just an especially fragile type of cargo anyway..

They could probably reduce g-forces for passengers when they don't have the max payload weight. Maybe that is what Russels post is pointing at. Otherwise I have no idea.

Edit: fixed quote
« Last Edit: 10/06/2017 04:33 PM by guckyfan »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #12 on: 10/06/2017 10:13 PM »
There is one thing you cannot escape with Elon's architecture

4 to 6 gs on Mars entry for passengers.

Offline Lars-J

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Re: Mars Direct updated for the 21st Century
« Reply #13 on: 10/06/2017 10:19 PM »
There is one thing you cannot escape with Elon's architecture

4 to 6 gs on Mars entry for passengers.

What way of landing do you propose that would have reduced G forces that differ significantly from that?

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #14 on: 10/07/2017 07:41 AM »
There is one thing you cannot escape with Elon's architecture

4 to 6 gs on Mars entry for passengers.

What way of landing do you propose that would have reduced G forces that differ significantly from that?

As stated - a fully propulsive landing.

As a rough guide. Velocity (relative to atmosphere) of Mach 5 at atmospheric interface (135Km altitude). Slowing to Mach 3 at roughly 50Km altitude. There is a velocity vs altitude envelope that results in acceptable heating for a vehicle with minimal thermal protection.

Such a landing does not require high g forces. Its a trade between efficiency (gravity loses) and fuel but its not that hard to constrain it to 2 gs and keep most of it under 1.5 gs.

Yes, it uses more fuel than an approach that relies on drag. But its a vehicle that doesn't require a massive heat shield and is exposed to lower aerodynamic stress. Hence the extra fuel is partly compensated for in a less massive vehicle.

Now the reason I bring this up in this thread is because Elon has basically said that we can get fuel into low Earth orbit cheaply. Therefore we don't need to be as obsessed with fuel mass as has been the case in previous architectures. He's saying that rocket fuel is cheap and big dumb rockets are cheap (especially when reusable), so why not have an architecture that does indeed burn a lot of fuel.

You still need to land cargo and there's no reason not to land it in the manner Elon proposes. However, humans are only a small proportion of the mass landed on Mars and we can afford to be generous with fuel for human landings. Especially if its less costly to get the fuel there in the first place.


Just for the sake of something concrete to talk about here.

Imagine we borrow the earth side of Elon's architecture. A big, reusable rocket. A big, reusable spacecraft with wings.

Let me add one more item. A lander with either drop tanks or an extra stage. How you package this is up to you, but its not large relative to the overall spacecraft.

On approach to Mars, the crew move to the lander, detach and at the correct time fire the engines or burn the extra stage and then fire the lander's engines.

The main part of the spacecraft lands ahead of the crewed lander.  The crew then land nearby.

The rest of the architecture is as Elon proposes. You have a reusable spacecraft sitting on Mars. You refuel that and travel directly back to Earth.

I can imagine all sorts of variations on this. I'm just putting it up as a starting point.


« Last Edit: 10/07/2017 07:56 AM by Russel »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #15 on: 10/12/2017 10:45 AM »
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


Having had more time to reflect on this I'll make some observations.

1. A lot of Mars architectures equate mass with cost which leads to a lot of time and energy being spent either on exotic propulsion (SEP), minimising the number of Earth launches, or on having impractically small interplanetary transport vehicles.

2. Elon makes the correct observation that rocket fuel is cheap and that with a big reusable booster, lofting hundreds or thousands of tonnes of fuel into LEO is not that expensive.

3. What really costs is development of complex, reliable systems. Another pointer towards reusability and adaptability of basic designs.

So, if you had an ITS scale reusable booster you have a lot of options in terms of throwing mass at Mars. That can allow us to do things that weren't previously considered - such as fuel depots in Mars orbit and fully propulsive crew landers.

I also admit to preferring Mars semi-direct over Mars direct. I didn't like sending people back from Mars on something that is unrealistically minimal and fragile. Likewise I don't like Elon's scheme because of the sheer scale of earthmoving and processing that would be involved.

I do like Elon's basic spaceship design. Yet another winged lander. I'm not suggesting copying the ITS spaceship or at least not something at the same scale. As stated before, I'm not fond of inflicting 4-6 gs on people but that doesn't stop us doing this to cargo.

So where does that leave me in a practical sense? As I understand it, the "winged" form lander (or indeed anything with some lift) could be used as an Earth return vehicle and lander and if so the g forces can be constrained. Correct me if I'm wrong. Certainly you could have a go at a double-dipped landing. So I'll work with that.

I do want people to land on Mars fully propulsively. It follows that they need the same or a similar vehicle to return to Mars orbit. Therefore the Earth return vehicle must be parked in Mars orbit and it must have sufficient fuel for the return to Earth. Again, if your starting point is an ITS scale booster then I think you've got a pretty good chance of throwing that quantity of fuel to Mars orbit.

So, now we have an architecture that looks something like this:

Start with something that looks like Elon's plan. A big reusable booster and a reusable spacecraft (only its not for 100 people. Its only for 6-8 people). A decently fast trajectory to Mars. Followed by a burn to reduce speed. Followed by an aerocapture pass. Now you're in Mars orbit.

Your crew now climb into a lander and descend. The lander features either an expendable first stage or drop tanks. At the end of the mission the crew use a similar or the same vehicle to ascend. They then use the same spacecraft left parked in Mars orbit to return to Earth and land.

What about cargo? Well why not use the same basic design. A "winged" spacecraft adapted for cargo (doesn't contain the life support) and sent on a direct entry to Mars. This can be done ahead of time and on a lower energy trajectory. Again, adapting a design saves development costs.

I'll leave the reader to fill in the blanks. All I'm saying is that if Elon can make the launch to Earth orbit costs low enough (and I believe he can) then things got a whole lot easier. We can afford to burn more fuel to get to Mars sooner and indeed we can do the same on the way back. That's one problem solved. We can be more generous with cargo (may take more than one cargo landing vehicle depending on scale). And we can afford to keep spare fuel in Mars orbit and given the scale of things we can afford to keep enough fuel in Mars orbit to supply multiple ascents/landings and have room left over for visiting Martian moons.

Offline Nathan2go

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Re: Mars Direct updated for the 21st Century
« Reply #16 on: 10/14/2017 09:38 PM »
I think the important change that NASA needs to make is to support the SpaceX Mars vision and plan, but to be politically viable, it can't entirely abandon its other "stuff".  For the moment, NASA has to keep SLS as part of the plan, but can say commercial companies will carry part of the mission payload. 

NASA has to get the first set of astronauts back, and can embrace ISRU, but I don't think they can go so far as to be dependent on water collection, and making enough propellant for a BFS on the first trip.  They have the MOXIE oxygen generator on the Mars 2020 rover, so I think they can plan to make oxygen (but not H2 or methane) for the return trip.

NASA should embrace the methalox BFR ship outer-mold-line, not as a reusable 2nd stage, but as an expendable lander/ascent vehicle for Mars and the Moon.  Shrink it sufficiently (e.g. 7m diameter, 120 ton landed mass) so that in addition to being compatible with the BFR booster, it could also be carried by SLS and New Glenn.

With the mission split between NASA/SLS and commercial companies, maybe some of the flights will load propellant in LEO, and maybe the SLS flights will load in a high orbit (like DSG) or avoid propellant transfer and dock with loaded departure stages.  But there's not much value in having a DSG or solar electric propulsion.

By the way, I still like the Mars Direct style direct return from the surface of Mars, to the surface of Earth.  Even if the crew space is very cramped, it's worth it because eliminating mission critical Mars orbit rendezvous operations makes it safer.  Doing it as a re-usable requires high performance engines and structures, but it should be manageable as an expendable, perhaps with 2 stages (booster plus capsule and service module).

The 9m dia. BFS has a gross landing mass of 150+85=235 tons on Mars.  A 7 m dia. scale-down should be able to land 117 tons.  Of that, say 40 tons is the Earth return vehicle with payload, and 53 tons is methane for the return trip.  It would make 190 tons of O2, for a Mars take-off mass of 283 tons (just 23% of BFS).  Unlike Mars Direct, the propellant is not made by a nuke before the crew arrives: the crew builds a solar PV array to power the system, which they can bring over by truck, since it may not fit in the same lander with the return vehicle.

As in Mars Direct, NASA would commission two kinds of landers: an Earth Return ship, and a single-use payload lander.  This modified mission also allows SpaceX to use their own lander to bring mission elements.  The crew can fly out on the SpaceX BFS, or the NASA payload lander (in a hab).

Once the base is built-up enough to have full methalox production, the BFSs can return home, and the NASA landers and return ships are no longer needed.  Of course SLS can be cancelled as soon as NASA is confident that private companies can launch the NASA landers.
« Last Edit: 10/14/2017 09:46 PM by Nathan2go »

Offline Russel

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Re: Mars Direct updated for the 21st Century
« Reply #17 on: 10/15/2017 03:06 AM »
Perhaps a topic for a separate thread but Mars Direct doesn't just result in cramped conditions. It compromises safety in numerous and often subtle ways. So whilst its fair to describe transfer in orbit as mission critical, the risks in Mars Direct are often unrecognised and understated.

Having wide margins and redundancy really does matter.  Anyhow I'll continue to advocate indirect until we have the kind of ISRU capability thst Elon advocates. And frankly I don't believe that can or will happen in early missions.