What would it take to do "Mars Direct," let alone MCT?

[guckyfan]

* There is the famous problem of HSF scale payloads having insufficient drag, but this can be somewhat offset by the low density of one of your most basic requirements: space.

Sounds like a good idea.

[Oli]

Well MCT is in other aspects more unrealistic (they way its usually described here at least).

But I didn't say landing a "huge rocket" is unrealistic. I think Mars Direct is unrealistic because it assumes it can get away with a tiny return hab/stage.

7100 kg crew cabin for four people (1775 kg per person). Compared to what MCT is expected to get away with:

Well the hab in MCT is only a payload and not its own reentry vehicle. I don't know whether 100t for 100 people one way is realistic. Not something you'd want to sell to NASA but it might be survivable.

[Impaler]

Follow up on ADEPT, a 200 mt entry mass using a 72 m diameter ADEPT type deploy-able decorator would have a very low terminal velocity at mars, just 190 m/s assuming a drag coefficient of 0.5 and atmospheric density of 0.02 kg/m^3.  Naturally a vehicle will take time to decelerate fully to terminal velocity and it will likely reach point when a landing burn must start before fully reaching that velocity, but it dose seem that the required terminal landing burn would be greatly reduced, perhaps to under 500 m/s.  This would translate directly into saved propellant at atmospheric entry.

[Oli]

I love HIAD, because shows promise as a large payload EDL technology when combined with SRP (especially when the landed payload fraction can be 40-50% of the total mass at entry). But a HIAD would be disposed after Mars entry, and people are expecting the feasibility of a reusable MCT while at the same time having the whole thing land on Mars. (I know, it's supposed to go back to Earth with only 1/4th its outbound payload capacity)

I think as long as you take the slow way back (~7.25km/s), MCT might be possible even without HIAD. But it will be absolutely huge. Several 1000s of tons fully fueled if you ask me. I just don't see such an approach being economical. But we'll see, I'm really curious to see what Musk will present us.

[FinalFrontier]

Going to post this here, discussion regarding possible Pre-MCT Mars Architecture using FH came up in another thread.

Premise is basically the fact that FH will be operating before MCT, and (IMO) not likely that at least a small scale crewed mission would not be attempted using FH.
Post string below:

The BFS not only serves as the upper stage, but as a tanker (probably in modified form), crew launch vehicle, transfer vehicle, lander, surface hab, and ascent vehicle.

I also think that the idea of an 'ERV' as envisaged by Zubrin is flawed. It's aksing way too much to support a crew of four for six months in a vehicle which can also land on and ascend from Mars.

And that is the Mars Direct/MCT double standard. We need to say that the Mars Direct Earth Return Vehicle is feasible before assuming a vehicle that is far more ambitious in scope.

You realize that I am not the same person as Kaputnik.

Also, realize that Kaputnik's quote was from 2008... That was before supersonic retropropulsion (a key enabler for landing heavy loads on Mars) was demonstrated (by SpaceX, I might add) and before we knew there was THIS much water available in so many places on Mars (making full propellant ISRU much easier).

Using quotes from different people and from like 8 years apart in time (during relatively rapid developments related to Mars ISRU and EDL tech) is not what I'd call a "double standard."

Indeed, but Mars Direct is still considered a "pipe dream" in recent times, because

Mars Direct assumes a crew cabin of 7.1t with 1.6t consumables for a crew of 4 for the trip home, at least according to the information that can be found on the internet.

while this is considered a reasonable goal for MCT (I know, it's from different people. But it seems to reflect the general attitudes and expectations towards MD and MCT):

Bring the dry mass per passenger of the vehicle very low, like down to less than 500kg per person.

But I can agree that the "two-launch architecture" of MD is a pipe dream.

There's also a difference: MCT is going to be way overbuilt (in size and mass) for initial crewed missions. Only later will it get similar mass and consumption requirements per crew member as Mars Direct, and you also would have decades of tech improvement between when Mars Direct was first proposed and by the time MCT is going for full 100 passengers per trip. Additionally, there's a very real economy of scale that you'd get: Making a life support system that can support 100 people is not going to be 25 times as massive as one that can support just 4 people.


...additionally, I think the Mars Direct craft is doable.

And this is the wrong thread!!! There's already a thread on this topic!

Not totally wrong thread its totally relevant.

I highly doubt MCT or an MCT architecture will be the first vehicle to go to Mars, even by SpaceX. Far more likely to be a Falcon Heavy driven vehicle+stack first for initial missions. Again, worth pointing out that there is still (serious) talk of a possible un-crewed Dragon V2 sample return mission to Mars using F9H being flown prior to or around 2020.  Should that happen, and should it work properly, there really would be no obstacles to replicating the mission profile with a larger stack (HAB ect) and a crew.

Yeah, the obstacle would be you need to spend billions developing a stack that will only fly like once because it'll be replaced by BFS.

Red Dragon and uncrewed missions that ensure ISRU and everything are running, sure. A whole pre-MCT SpaceX human Mars architecture? No. I don't see that happening.

The big advantage of MCT is that you're not really spending more than the architectures of old, you're just leveraging refueling and reuse and ISRU in a very powerful way so that you can quite feasibly use the same piece of hardware for half a dozen roles. SpaceX would be more than doubling their costs if they tried to ALSO recreate Mars Direct.

Mars Direct used a few different vehicles, but needed only 2 HLV launches. MCT would need perhaps more than 2 HLV launches (and the HLV would be larger), but it'd need fewer unique hardware elements and it can leverage reuse. So MCT trades greater IMLEO and greater ISRU requirements for a lot fewer unique hardware developments and more capability from the get-go.

I think that's realistic, and it may actually cost less than Mars Direct (as originally envisioned) would for the first mission.

I don't see it happening as a true architecture. I do see it as feasible for perhaps 1-3 missions, depending on exactly what the flight profile and propulsion would be, since these items drive how long you will be in transit and how much hardware would be needed for the stack. MCT would most likely utilize only one HLV launch as currently envisioned anyway, just going off what SpaceX has said its a single vehicle, but who knows what they actually end up producing. 

I do see the issues however. Really comes down to just one thing: how much stack hardware do you actually need for your planned flight profile? Also: can you buy off the shelf hardware somebody else is making or do you  have to entirely design and build it yourself? Which actually given how SpaceX goes about design this might be cheaper, since they could potentially just build their own HAB in the plant.  In fact that would be what I would expect, doubt they'd buy off the shelf they would probably just build their own components.

In that regard the question becomes how much would it cost SpaceX to build their own stack components and how many would they need

I really do see your point however, it doesn't make alot of sense to produce hardware for one flight profile, then ditch all of it for MCT, but there are time and design related factors involved as well. If they think they can do a crewed mission on FH on the cheap prior to MCT coming online they will probably try it. I just find it really hard to see something small not being attempted using FH considering how large MCT will be and how much will be involved in vetting it. 


In any case to top this off, so Mars Direct VS MCT, is there really anything lost in trying both ? (but picture Mars Direct for flags and footprints only pre-MCT).

[Robotbeat]

The big thing comes down to the ascent vehicle:

You could travel using some Bigelow or Cygnus-derived hab. You could land in a Red Dragon, in principle, and somehow stick them together ala Mars One. But you'd be stuck on the surface, just like Mars One.

You need an ascent vehicle. And building an ascent vehicle along with the ability to land it on the surface of Mars is no simple task! It could cost nearly as much as a BFS itself!

Mars Direct assumed a two-stage Earth Return Vehicle and a surface hab or two (which are landed separately and each need a landing system), along with a NTR in-space stage and an expendable HLV (several launches) and several heat shields that are expended along the way.

MCT assumes a fully reusable HLV that is refueled in orbit by another reusable HLV of the same type (though operating as a tanker). The upper stage of that RHLV carries the crew, and is big enough to operate as the hab throughout the whole trip. It also operates as the in-space stage (so no NTR stage needed), the EDL and lander vehicle (somewhat redundant, but this means you keep your heatshield and landing legs and can use them on the way back to Earth), plus the ascent/Earth return vehicle.

...that one rocket stage does the work of like 4-6 separate rocket stages in the Mars Direct architecture (depending on how you count), and the crew portion takes care of the rest. This is what reuse, extensive refueling, and ISRU buys you. A huge reduction in how many pieces of hardware need to be designed, qualified, built, and launched.


...what the two architectures have in common is the need for surface power (nuclear or solar), some ISRU equipment. For ISRU, the original Mars Direct assumed bringing hydrogen all the way from Earth, which is pretty tough engineering-wise due to boil-off and large volume, but MCT assumes you're mining/collecting it on the surface in the form of water. So MCT needs to land a significant robotic water-collection system, able to mine hundreds of tons of water per year at a minimum, to give a rough figure of merit. But that's actually not too bad: one or two tons per day. This would've been laughed off the stage in the early 1990s, but now even NASA's architecture planning conferences take this large amount of available water as a given and is used for site-selection.

So what MCT needs is HUNDREDS of kilowatts (at a minimum) and a robotic rover or two to process a bunch of regolith to extract the (apparently fairly abundant) water (though Mars Direct also assumed rovers, but for manned use... so this isn't a big difference either). That's like a few SP-100s (or perhaps an SP-100 at the top end of considered designs) instead of just one SP-100 (or equivalent in solar+batteries) in Mars Direct, but that's a pretty good trade, in my opinion, to greatly simplify the rest of the architecture and make it fully reusable (thus much cheaper to do each mission once you build it out) and much more capable.

So I actually think that Mars Direct might've actually cost more money than MCT will!

[Robotbeat]

It's a certainty that SpaceX will be sending robotic missions ahead of the crewed missions to prepare the ground and test ISRU technology. It's possible they could send a subscaled BFS in the form of their Falcon 9/Heavy Raptor-based (presumably reusable) upper stage as the lander for these robotic trips instead of a Red Dragon, but I'd be putting my money on a Red Dragon at this point, then they'd probably send an uncrewed BFS (and possibly return it).

[Pipcard]

The technological risks and challenges are higher with a "jack-of-all-trades" vehicle. It's like trying to integrate Dragon with the F9 second stage, and making that all reusable. Also, a lunar mission with a single integrated command+service+lander module (that doesn't even stage when taking off from the Moon); it would need staging after TLI, but the delta-v won't be SSTO level, like what you've said about MCT. Would that have a shorter development period and less development costs, or would that just be impractical to achieve? Even a reusable system would need staging at the L1 or L2 points.

The plan for Mars Direct/Semi-Direct was to land on a chosen location on Mars, have astronauts explore the surrounding area, and repeat that process, each time landing a few hundred kilometers away. Later on, a suitable location for a base would be found. It would make sure that the planet is scouted out first before anyone starts moving there.

I've seen MCT described as a "colonize first" architecture. It is dependent on whether thousands of people are actually willing to move to Mars. A "build it and they will come" strategy. As MCT is focused on one-way colonization, being that its return payload is less than the payload sent to Mars, how would the people who could afford the $500,000 ticket (which is also dependent on dozens of thousands of people going to Mars, so initial tickets would cost even more) have the incentive to permanently move from the comforts of Earth to a much more hostile environment?

A Japanese space tourism SSTO concept known as the Kankoh-maru was supposed to have the same "build it and they will come" strategy: aside from the technical issues that come up with SSTOs, it was expected that an entire fleet of Kankoh-marus would be built, that a million people would be using the system every year, and that the flight rate would bring down the cost per person to $20,000. This would only work if that many people were willing to go. Now, one might say that LEO isn't much of a destination, other than for sightseeing. But for that, infrastructure (such as space hotels) would have to be constructed. Same thing goes with Mars right now: there needs to be infrastructure. (and I know, tourism is not the same thing as colonization)

edit: In spite of the skepticism I am showing for MCT, I don't want to completely dismiss it. In fact, I am still very fascinated and excited for its belated reveal.

[Robotbeat]

The tech risk is a little higher, but not much so, if you retire the risk with early tests, as SpaceX does. The modular, many different stages approach is good for splitting up the work among multiple centers and contractors, but I doubt it's more cost-effective or reliable over the long-run.

And let's be clear, here: This isn't just a "jack of all trades" type capability like the Shuttle which relied on engineering prowess to enable a bunch of different capabilities, this is a case of hugely overlapping requirements. Refueling and ISRU are the things which make all this possible and to beat the iron triangle of trade-offs. This is a genuine improvement over previous concepts.

If you have refueling and plan on reuse anyway, then there's no reason to take the typical multiple stage approach that you're forced to do without refueling.

You're not going to save money by developing 5 different rocket stages and a couple different EDL schemes at large scale over one BFS which can refuel multiple times.

Things look very different when IMLEO is no longer the primary constraint!

[Pipcard]

Things look very different when IMLEO is no longer the primary constraint!

So that's it, the main things that justify what I have been calling a "double standard" are:
- a fully reusable TSTO HLV for cheap lift
- demonstrated supersonic retropropulsion for Mars EDL

(and allowance for orbital assembly/refueling, in comparison with the original Mars Direct/Semi-Direct)

[Impaler]

While a reusable HLV (really we should be calling it ULTRA heavy lift because were talking about payloads more then 3 times the actual 'Heavy' criteria), can be considered a game changer.  I would not consider SRP alone to be that impact-full, the payload mass fraction for a lander using SRP is simply not high enough to make MCT work, additional breakthroughs are necessary in the EDL department are needed.

[Pipcard]

But I'm still wondering, would the "reusable all-in-one" architecture still be good for only 1 Mars exploration mission every 2 years, to a different location on Mars each time? (basically, what if the whole idea of mass colonization doesn't pan out?)

[Impaler]

I think that hinges entirely on how many propellant production pre-deployment missions need to occur in a location before manned landings can be performed, and particularly how many if any of these pre-deployment vehicles can be recovered.

Best case would be 1 pre-deplyment lander on the synod before manned landing with the ability to recover the pre-deployed lander at some future date (perhaps the synod after the manned landing).  Under this scenario a campaign of multiple widely spaced landings is quite feasible.

On the opposite extreme your looking at several landers being needed and for non to be recoverable, this makes the campaign considerably more costly though it may still be within NASA's budget if the landing vehicle itself is not terribly expensive.  I expect this to be the initial pattern in any case as colonization simply cant happen until the pioneering work is done and only NASA can absorb that kind of risk.

Lastly I believe the fixed location 100 km radius exploration model NASA is currently exploring should be replaced with a 'Caravan' system in which all the surface exploration and habitat elements are mobile.  With each MCT unloading one large vehicle and a group of said vehicles forming a redundant long range convoy a huge area of the Martian surface could be explored in a single synod and the crew could rendezvous with multiple other landers for supplies or for Earth return as the situation dictates.

[Robotbeat]

While a reusable HLV (really we should be calling it ULTRA heavy lift because were talking about payloads more then 3 times the actual 'Heavy' criteria), can be considered a game changer.  I would not consider SRP alone to be that impact-full, the payload mass fraction for a lander using SRP is simply not high enough to make MCT work, additional breakthroughs are necessary in the EDL department are needed.

Youre wrong. ssr and a biconic or some similar shape with a high mass fraction but an okay lift, plus minor aerosurfaces like the legs or find on F9 first stage would be sufficient.

Direct entry is not required. Neither is landing at high altitudes.

[Burninate]

While a reusable HLV (really we should be calling it ULTRA heavy lift because were talking about payloads more then 3 times the actual 'Heavy' criteria), can be considered a game changer.  I would not consider SRP alone to be that impact-full, the payload mass fraction for a lander using SRP is simply not high enough to make MCT work, additional breakthroughs are necessary in the EDL department are needed.

Youre wrong. ssr and a biconic or some similar shape with a high mass fraction but an okay lift, plus minor aerosurfaces like the legs or find on F9 first stage would be sufficient.

Direct entry is not required. Neither is landing at high altitudes.

How do you use SSRP and a biconic at the same time though?  This gets back to the geometry thing I was asking about.

[Robotbeat]

While a reusable HLV (really we should be calling it ULTRA heavy lift because were talking about payloads more then 3 times the actual 'Heavy' criteria), can be considered a game changer.  I would not consider SRP alone to be that impact-full, the payload mass fraction for a lander using SRP is simply not high enough to make MCT work, additional breakthroughs are necessary in the EDL department are needed.

Youre wrong. ssr and a biconic or some similar shape with a high mass fraction but an okay lift, plus minor aerosurfaces like the legs or find on F9 first stage would be sufficient.

Direct entry is not required. Neither is landing at high altitudes.

How do you use SSRP and a biconic at the same time though?  This gets back to the geometry thing I was asking about.

Flip and do Ssrp right before landing. Like Delta Clipper. DC-X even demonstrated the swan dive you'd need.

[Impaler]

While a reusable HLV (really we should be calling it ULTRA heavy lift because were talking about payloads more then 3 times the actual 'Heavy' criteria), can be considered a game changer.  I would not consider SRP alone to be that impact-full, the payload mass fraction for a lander using SRP is simply not high enough to make MCT work, additional breakthroughs are necessary in the EDL department are needed.

Youre wrong. ssr and a biconic or some similar shape with a high mass fraction but an okay lift, plus minor aerosurfaces like the legs or find on F9 first stage would be sufficient.

Direct entry is not required. Neither is landing at high altitudes.

I was initially optimistic about a bi-conic and SRP configuration, but my research hasn't turned up anything better then around a 20% payload fraction with this configuration and our estimates are the MCT needs something near 50%.

Also I'm not even assuming direct entry OR high altitude landings.  Neither of which is even very relevant here because entry speed primarily determines the thermal and g-loads on the vehicle during peak deceleration which occurs well before SRP and all vehicles will be going the same speed at the point of SRP initiation regardless of entry speed.   

Landing altitude has little effect once you stop using parachutes for deceleration, current landing tech depends on chutes and is thus altitude sensitive.  But under SRP landing altitude just dictates the length and intensity of your terminal landing burn and it will have little effect on payload fraction as your still basically shedding the same velocity propulsive and that's the same propellant mass if you do it fast or slow.

[JulesVerneATV]

NASA-funded pulsed plasma rocket concept aims to send astronauts to Mars in 2 months

https://www.yahoo.com/tech/nasa-funded-pulsed-plasma-rocket-100000198.html