Where are we now?

spacetechsforum · 2018-08-18 06:35:05

Hello.
I am doing some research on mars missions and i found this great forum. There is a lot of valuable resources here but i would like to get some summary on the subject, and so.. If you were to decide today (using available technologies, not inventing new ones!) on the next step towards mars colony, what would it be?

The data i gathered until now suggest this:
Sending probe with mining and research equipment to Deimos to check for water.
Why? Most agree that without fuel supply near Mars there is no way to feasible conduct missions. The means of water extraction on Mars are being developed and that water can be processed into fuel but to lift it from Mars one would need to create a lot of it. Possible source on some smaller body that can resupply the spacecraft in orbit would be (in my present opinion) best option for moving object from Mars orbit to LEO.

What do you think?

Last edited by spacetechsforum (2018-08-18 06:36:14)

GW Johnson · 2018-08-18 09:44:05

We don't yet know enough about the characteristics of small bodies like asteroids, comets, and small moons like Deimos to reliably determine which might really have exploitable water or other volatiles.

That will take more unmanned and some manned missions to find out. Until we know, we are forced to do it the hard way.

But you are right: propellant production in places with small or nonexistent gravity wells makes much more long-term sense.

GW

louis · 2018-08-18 13:18:21

I don't see any fundamental problem with Space X's mission design, which involves propellant production on the surface of Mars. Certainly post Mission One it is non-problematic in my view. But for Mission One you have to be as certain as you can that you have a water source available, unless you land in summer and have large dehumifidiers working full time on extracting water from the atmosphere.

spacetechsforum wrote:

Hello.
I am doing some research on mars missions and i found this great forum. There is a lot of valuable resources here but i would like to get some summary on the subject, and so.. If you were to decide today (using available technologies, not inventing new ones!) on the next step towards mars colony, what would it be?
The data i gathered until now suggest this:
Sending probe with mining and research equipment to Deimos to check for water.
Why? Most agree that without fuel supply near Mars there is no way to feasible conduct missions. The means of water extraction on Mars are being developed and that water can be processed into fuel but to lift it from Mars one would need to create a lot of it. Possible source on some smaller body that can resupply the spacecraft in orbit would be (in my present opinion) best option for moving object from Mars orbit to LEO.
What do you think?

SpaceNut · 2018-08-18 17:54:17

As GW Johnson indicated unknowns when it comes to water quantity on the moons of mars and other locations with only somewhat a knowledge is available for the surface of mars at this time.
We have suggested a small mission that carries the means to return within its landed cargo support with the equipment required for mining and processing that water for a follow up mission to make use of. This first mission is a preperation style mission that makes the most of exploration, science and making ready for future missions.

spacetechsforum · 2018-08-18 19:53:17

Sorry. I did not state clearly that I am suggesting unmanned prepare mission, that should confirm the presence of the water and next expand into automatic production plant on Deimos.
The goal is self sustaining colony on mars surface, not just landing and returning like in the spacex mission. The question to be more precise is: what infrastructure should be placed before mars manned mission and in what order (actually the single next thing, not the all pices). Regarding my research I found some data and did some math, that needs to be checked (the option with "truck" spacecraft that would go back and forth between mars and earht orbits, variant without resupply on mars). Can I post it here to get verification?

LEO→LMO: 4.697 km/s
LMO→LEO: 2.75 km/s
Engine Isp: 4.53km/s

Trip to mars
Fuel 250.00t
Ship 12.39t
Cargo: 100.00t
Return needs: 23.39t

Total (no fuel): 135.77t
Total: 385.77t

ln(m1/m2) 1.04

dv needed 4.70km/s
dv provided 4.73k m/s

Retrun To Earth
Fuel 11.00t
Ship 12.39t
Cargo 0.00t

Total (no fuel)12.39t
Total 23.39t

ln(m1/m2) 0.64

dv needed 2.75km/s
dv provided 2.88km/s

Last edited by spacetechsforum (2018-08-18 20:00:23)

SpaceNut · 2018-08-18 20:59:32

GW Johnson is the expert on the rocket equations... but here are some references to the question of water....

https://en.wikipedia.org/wiki/Deimos_(moon)

Unmanned mission would be the way to find out but a manned use would suck...
https://en.wikipedia.org/wiki/Phobos_An … nvironment

Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. Deimos (the outer moon of Mars) should have water ice at depth. It is a guess based on what is a density question. So we really do not know for sure and the amount will not last for very long most likely. But this is the intent to mine it if its there.

the_deimos_water_company.2.gif

http://space.nss.org/media/Space-Manufa … ompany.pdf

https://blogs.agu.org/martianchronicles … nd-deimos/

http://www.planetary.org/blogs/jason-da … t-mmx.html

louis · 2018-08-19 16:05:24

I think you are misunderstanding Space X's plans. They plan to establish a permanent colony beginning in 2024. If the BFR rocket works there's nothing implausible about their plans, given they aim to land six rockets (cargo and human passenger) between 2022 and 2024
(meaning they can put at least 600 tonnes of cargo on the surface)...I guess there might possibly be a brief period of non-occupation of the colony in 2026. I don't personally see Mars Moon operations as having any great merit...seem more like a diversion now with the BFR on the horizon. We know there's plenty of water either in glaciers, the atmosphere or the permafrost on Mars. The key factor now is a propellant production process design that we can be assured will work.

spacetechsforum wrote:

Sorry. I did not state clearly that I am suggesting unmanned prepare mission, that should confirm the presence of the water and next expand into automatic production plant on Deimos.
The goal is self sustaining colony on mars surface, not just landing and returning like in the spacex mission. The question to be more precise is: what infrastructure should be placed before mars manned mission and in what order (actually the single next thing, not the all pices). Regarding my research I found some data and did some math, that needs to be checked (the option with "truck" spacecraft that would go back and forth between mars and earht orbits, variant without resupply on mars). Can I post it here to get verification?
LEO→LMO: 4.697 km/s
LMO→LEO: 2.75 km/s
Engine Isp: 4.53km/s
Trip to mars
Fuel 250.00t
Ship 12.39t
Cargo: 100.00t
Return needs: 23.39t

Total (no fuel): 135.77t
Total: 385.77t

ln(m1/m2) 1.04

dv needed 4.70km/s
dv provided 4.73k m/s

Retrun To Earth
Fuel 11.00t
Ship 12.39t
Cargo 0.00t

Total (no fuel)12.39t
Total 23.39t

ln(m1/m2) 0.64

dv needed 2.75km/s
dv provided 2.88km/s

SpaceNut · 2018-08-19 17:43:20

Louis the rocket that spacetechsforum has described is not BFR....
This is BFR where the passengers are kept, at a pressurized volume of 825 cubic meters or with a mass payload up to 150 tons.
It will have a dry mass of 85 tons, plus a propellant mass of 1,100 tons.
The fuel tanks hold 240 tons of methane, while the oxygen tank holds 860 tons of liquid oxygen.

Here is the reference that GW has on his website
http://exrocketman.blogspot.com/2017/10 … ge-of.html

louis · 2018-08-19 18:04:37

Spacetechsforum made this claim at the outset:

"Most agree that without fuel supply near Mars there is no way to feasible conduct missions."

I don't accept that and I don't think most people do. You could either have a Space X style mission where propellant production takes place on the surface or you could have an Apollo Mission where you drop a smallish craft to the surface.

SpaceNut wrote:

Louis the rocket that spacetechsforum has described is not BFR....
This is BFR where the passengers are kept, at a pressurized volume of 825 cubic meters or with a mass payload up to 150 tons.
It will have a dry mass of 85 tons, plus a propellant mass of 1,100 tons.
The fuel tanks hold 240 tons of methane, while the oxygen tank holds 860 tons of liquid oxygen.
Here is the reference that GW has on his website
http://exrocketman.blogspot.com/2017/10 … ge-of.html

kbd512 · 2018-08-19 18:33:12

Louis,

Someone needs to test the concept behind making CH4 on Mars with equipment that actually fits inside BFR. This is something that doesn't exist, at present. The only way to make it "leap into existence" is a government R&D program to produce the required hardware and test it on Mars at sub-scale to discover all the inevitable problems that will arise. From a functional standpoint, that means NASA or the US military and their contractors. That's how things like cell phones, the internet, GPS, lasers, interplanetary rockets, etc all "leaped into existence".

If the upper stage used LOX/LH2 instead of LOX/LCH4, then the technology required already exists, at a purchase price of about $26M, and all that's required is a lot of electrical power to split H2O into H2 and O2. I take no issue whatsoever with using LOX/LCH4 for boosters because Earth has plenty of CH4 reserves. There are no identified reserves of CH4 on Mars. It doesn't mean it's not there, but the multi-billion dollar question is "Where?".

RobertDyck · 2018-08-19 18:42:08

My mission plan is a modification of Mars Direct. It fits the proposal by spacetechsforum. The idea is reusable ITV with expended propulsion initially, but switch to reusable propulsion after infrastructure is established. To answer his question, next step is a self-contained robotic Mars sample return mission. To demonstrate ISPP and end-to-end systems for return. I suggested keeping it small to keep it affordable; perhaps a Scout class mission like Phoenix with a rover the size of Sojourner to collect samples. Dr Robert Zubein pointed out a mission the size of Curiosity could include a rover the size of Spirit or Opportunity.

If you want to use Mars ice on the first manned mission, instead of carrying LH2 from Earth, the you will need to prove there is ice at the landing site before astronauts arrive. In 2005 the Canadian Space Agency proposed a rover the size of Spirit or Opportunity but with a multi-segment drill: 10 segments each one metre long. But Canadian Parliament didn't approve funding.

Last edited by RobertDyck (2018-08-19 23:19:33)

kbd512 · 2018-08-19 18:59:17

Robert,

I'm all for sending another rover to confirm where the water is. Maybe you can convince Canadian Parliament of the importance of finding water on Mars. At present, ISPP is the only practical way to make a mission more than just flags and footprints.

SpaceNut · 2018-08-19 19:32:49

https://en.wikipedia.org/wiki/List_of_m … e_missions

https://en.wikipedia.org/wiki/Exploration_of_Mars

spacetechsforum · 2018-08-19 19:40:16

Louis,
It is just my bad english understanding. I assumed that Mars surface is "near" mars (like mars + moons) and i think that you too agree that at least one of those places needs fuel production site.

The Deimos production plant + mars fuel production (in next step) in my opinion is better since you do not need to lift fuel from Mars to go back to Earth (you can refuel again in orbit). I did not look at fuel production tech on mars yet so I am very worried about the mars refinery efficiency - can it product enough fuel in time?

Most of the crafts will carry one way cargo, not humans, so they actually do not need to land, rather just "drop" the cargo, refuel in orbit and go back. I am working on concept of such craft like that right now actually, as the figures are really promising.
The greatest improvement compared to BFR is the possibility to use better engines, since atmospheric starts are not required (Isp-v = 4.53 vs 3.75 in BFR). This difference can compensate for taking the fuel for empty ship return, but that is no the best thing i like in that design.
Spacecraft like that would work with, and not against the BFR. Great reduction in LEO costs would also reduce ITV refuel needs so this always will be the least expensive option for "bulk" cargo, but only BFR can land with humans.

May I ask for the contact to GW to double check my calculations?

Last edited by spacetechsforum (2018-08-19 19:44:09)

SpaceNut · 2018-08-19 20:59:37

https://www.relativitycalculator.com/ro … ions.shtml

https://www-istp.gsfc.nasa.gov/stargaze/Smars2.htm

https://engineering.purdue.edu/people/j … ndMars.pdf

Something else to consider for the mining robotic methods is ION drive since we do not care how long it taks to come and go to mars and this will also allow for even larger payloads of water and equipment to be moved....

RobertDyck · 2018-08-19 23:36:01

kbd512 wrote:

Maybe you can convince Canadian Parliament of the importance of finding water on Mars.

I have tried. Marc Garneau was CSA president when he proposed the rover. He was Canada's first astronaut. When he retired from that, he became CSA president. Now he's a federal MP, but not a cabinet minister. I talked to a few MPs about this, and candidates for leadership of the party in 2006 and 2009. They appear to have no problem finding money to spend on stupid stuff, but don't like the idea of spending money on Mars. In fact, the previous administration (the other party) increased funding to CSA, while the current government is trimming the budget. During the Paul Martin administration (2004-2006, Liberal), CSA received $300 million per year. Yes, I said million, not billion. Marc Garneau said to fund the Mars rover, CSA funding would have to be increased to $450 million; that's a 50% increase. During the Stephen Harper administration (2006-2015, Conservative), CSA budget was increased to $450 million, but they didn't spend it on Mars or any other planetary exploration. They did build a new RADARSAT Constellation Mission project, which is due to launch this fall. There is no major project approved after that. The current administration (Justin Trudeau, Liberal, 2015-) has trimmed CSA budget, they appear to have a goal of $300 million per year again. To be precise, CSA budget for 01-April-2015 through 31-March-2016 was set for $483 million, but after the election of October 2015 they only spent $388 million. Budget for 2018-2019 is $348.9 million.

Last edited by RobertDyck (2018-08-19 23:38:53)

louis · 2018-08-20 04:44:23

I accept all that. But 600 tonnes of cargo allows for potentially a huge amount of equipment and the Sabatier reaction process is well established. Also dehumidification is a well established process. IIRC NASA did a study which showed an 800 kg machine could produce 3 kgs of water per sol during the Mars summer. With economies of scale perhaps for 200 tonnes you could get to the sort of levels of water required. Or you might have some sort of balance between a hydrogen feedstock (say 100 tonnes) you take with you, a large water supply you have with you (maybe another 100 tonnes), some dehumidification machinery (50 tonnes) and some water mining equipment (50 tonnes). The propellant production machinery might come in at 50 tonnes...so 350 tonnes dedicated to the propellant production process on the first critical mission. That would explain why Space X are intending to land so much cargo. If it was simply a local water mining operation and propellant production facility you probably wouldn't need more than 100 tonnes.

My understanding from what I've read on the internet is that handling hydrogen creates all sorts of demands in terms of special materials and processes - methane handling is cheap and cheerful in comparison.

kbd512 wrote:

Louis,
Someone needs to test the concept behind making CH4 on Mars with equipment that actually fits inside BFR. This is something that doesn't exist, at present. The only way to make it "leap into existence" is a government R&D program to produce the required hardware and test it on Mars at sub-scale to discover all the inevitable problems that will arise. From a functional standpoint, that means NASA or the US military and their contractors. That's how things like cell phones, the internet, GPS, lasers, interplanetary rockets, etc all "leaped into existence".
If the upper stage used LOX/LH2 instead of LOX/LCH4, then the technology required already exists, at a purchase price of about $26M, and all that's required is a lot of electrical power to split H2O into H2 and O2. I take no issue whatsoever with using LOX/LCH4 for boosters because Earth has plenty of CH4 reserves. There are no identified reserves of CH4 on Mars. It doesn't mean it's not there, but the multi-billion dollar question is "Where?".

louis · 2018-08-20 04:59:36

I think it would be possible to design a mission where you sent say 3 BRFs into Mars orbit. One would contain the equivalent of an Apollo lander/ascender - so much bigger than Apollo, maybe around 80 tonnes. Another would contain a smaller return vehicle, which would be fuelled by the third BFR, which would be essentially a fuel tanker. The three BFRs would be abandoned in Mars orbit. You can of course make it 4 BFRs if you want, if you think there's not enough fuel. The Mars return vehicle might itself contain a tiny return capsule like the Apollo return vehicle, so they land by parachute.

I accept the Deimos proposal has theoretical advantages as out of the gravity well somewhat but I expect there are lots of issues to do with operation - it's not going to be an even surface for landing and operating water mining equipment for instance. "Dropping" delicate equipment is not that easy...yes there is Skycrane but so far that has landed equipement only up to about a tonne I think. I don't know how far you would scale up and the Skycrane is not reusable is it? So that's a huge financial loss each time you use one. Comparing delivery of 100 tonnes by a BFR to the surface to 100 individual drops by Skycrane illustrates one problem area, I think.

I do think longer term it would make sense for people transfer to involve a kind of ISS hotel where BFRs docked and then smaller reusable craft ferried people to the Mars surface. In that scenario, I don't know whether the BFRs would still need to refuel for the return journey but if they did then it would make sense to have fuel produced on Deimos if possible.

spacetechsforum wrote:

Louis,
It is just my bad english understanding. I assumed that Mars surface is "near" mars (like mars + moons) and i think that you too agree that at least one of those places needs fuel production site.
The Deimos production plant + mars fuel production (in next step) in my opinion is better since you do not need to lift fuel from Mars to go back to Earth (you can refuel again in orbit). I did not look at fuel production tech on mars yet so I am very worried about the mars refinery efficiency - can it product enough fuel in time?
Most of the crafts will carry one way cargo, not humans, so they actually do not need to land, rather just "drop" the cargo, refuel in orbit and go back. I am working on concept of such craft like that right now actually, as the figures are really promising.
The greatest improvement compared to BFR is the possibility to use better engines, since atmospheric starts are not required (Isp-v = 4.53 vs 3.75 in BFR). This difference can compensate for taking the fuel for empty ship return, but that is no the best thing i like in that design.
Spacecraft like that would work with, and not against the BFR. Great reduction in LEO costs would also reduce ITV refuel needs so this always will be the least expensive option for "bulk" cargo, but only BFR can land with humans.
May I ask for the contact to GW to double check my calculations?

spacetechsforum · 2018-08-20 06:20:14

Damn.. this is slowly evolving into theoretical discussion without the numbers and facts, the only thing that i would like to avoid.
The BFR will most likely be useless for any other mission than trip from Earth surface to Mars surface and back. The fuel used in design and versatile engines capable of lifting and space travel are not efficient for space mission.
The BFRs data: dry weight: 85t, payload: 150t, fuel: 1100t. This gives the delta-v equal to 6.51 km/s.
The simple spacecraft designed with 4xRL-10B-2 (1t) engines + SLWT tank (26.5t for 600t of fuel) + constr (added to compare) + payload 150t needs 755t of fuel to get the same delta-v. That is 345t less mass to LEO, assuming lifting with current best solution (Falcon Heavy $1411/kg) we have $486,795,000. Furthermore the construction weight added to compare the solutions will be much smaller, since no landing gear is required (or the landing gear may be attached to "droped cargo" so constructions becomes payload in "drop" mission). Again, this does not work for humans and delicate cargo needs proper landing gear, but everything else (food, construction materials, lander, space station)? yes, also may be used in missions to other objects, not only mars, plus gets more efficient with better lifting to LEO solutions (perfect fit for LEO reusable Spacex vessels).

louis · 2018-08-20 07:02:34

It all depends what your objective is - fuel efficiency or effective colonisation. The virtue of the BFR system is the amount of cargo that can be quickly delivered to the surface in a reusable craft. Once you have your water mining operation and propellant production facility in place, then I think it can operate with v. minimal supervision. There will be no taxes to pay, no licence fees to pay, no land rent to pay: effectively the marginal cost of propellant production will be much lower than the cost on Earth. So, I think one shouldn't get hung up on propellant cost/efficiency.

The cost of a BFR payload will I believe reduce drastically especially as the development costs are being amortised over a range of businesses: ISS supply, satellite launches, an orbital internet, orbital tourism, lunar tourism, E2E transport and Mars colonisation. That's seven separate revenue streams. Also, the BFR will be fully reusable, so effectively reducing the manufacture cost.

Add to that ,there will no shortage of sponsors, Universities and Space Agencies eager to "get on board", then I think costs are covered. The real restraint is not cost but probably launch infrastructure on Earth and shortage of skilled staff. If you wanted to say carry out 200 launches of BFRs in a short space of time, perhaps a couple of months launch window, from existing launch facilities that would likely be impossible owing to the lack of appropriate launch facilities and insufficient number of engineers, ground control staff, IT technicians and so on with the requisite skills and experience.

I really think the cost/efficiency of propellant usage is way down the list of what is potentially preventing a colonisation project.

spacetechsforum wrote:

Damn.. this is slowly evolving into theoretical discussion without the numbers and facts, the only thing that i would like to avoid.
The BFR will most likely be useless for any other mission than trip from Earth surface to Mars surface and back. The fuel used in design and versatile engines capable of lifting and space travel are not efficient for space mission.
The BFRs data: dry weight: 85t, payload: 150t, fuel: 1100t. This gives the delta-v equal to 6.51 km/s.
The simple spacecraft designed with 4xRL-10B-2 (1t) engines + SLWT tank (26.5t for 600t of fuel) + constr (added to compare) + payload 150t needs 755t of fuel to get the same delta-v. That is 345t less mass to LEO, assuming lifting with current best solution (Falcon Heavy $1411/kg) we have $486,795,000. Furthermore the construction weight added to compare the solutions will be much smaller, since no landing gear is required (or the landing gear may be attached to "droped cargo" so constructions becomes payload in "drop" mission). Again, this does not work for humans and delicate cargo needs proper landing gear, but everything else (food, construction materials, lander, space station)? yes, also may be used in missions to other objects, not only mars, plus gets more efficient with better lifting to LEO solutions (perfect fit for LEO reusable Spacex vessels).

SpaceNut · 2018-08-20 19:50:04

Since the goal is to mine water in a low gravity well location I am thinking that speed of transport of that water is not important and that rocket fuel saved to get it from place to place is of great importance.

This is where the ION thrust comes in for space tugs to move large masses with just a little fuel and an energy source to make it work.

https://en.wikipedia.org/wiki/Space_tug

Cislunar transportation: the space trucking system

http://www.astronautix.com/s/spacetug.html

https://en.wikipedia.org/wiki/Propellant_depot

GW Johnson · 2018-08-21 15:23:44

To answer Spacetechsforum's question in post 14 above, you can email me at gwj5886@gmail.com. I have a lot of stuff posted over at http://exrocketman.blogspot.com. There is a navigation tool on the left, which works by year, then month, then title.

The most updated and comprehensive reverse engineering I have done so far of Spacex's BFR/BFS system is actually a 2018 article posted at "exrocketman" in April on the 17th, and titled "Reverse-Engineering the 2017 Version of the Spacex BFR". It supersedes the 2017 posting in the link Spacenut posted.

The methods by which these back-of-the-envelope estimates were made are partly documented in that, and other similar articles, on that site. I have one in the works for a September posting, that pulls all those "rocket equation" techniques into one place. I have already posted how delta-vee requirements are determined for Hohmann transfer, and might update or replace that one.

You have to understand what the BFR/BFS really is. It s really a highly reusable giant transport to low Earth orbit, requiring no refilling at all for that job. It will haul as much or more to low Earth orbit as the SLS, and at a tiny fraction of the cost. By the time it flies, there may be some competitors from ULA and Blue Origin, and maybe France, that will be comparable in economy, but not as capable in payload size.

The way Spacex chose to make the second stage (BFS) reusable was to make it a lifting body entry vehicle, with the capability to do a pitch-up late in the trajectory to a tail-first attitude for a retro-propulsive landing. That is something not seen before, except in 1950's science fiction. This approach deletes payloads within payload shrouds entirely, as the BFS carries its payload internally, sort of like an airplane. It comes in 2, maybe 3 versions: the passenger/cargo version, an all-cargo version, and possibly a tanker version we have not seen depicted yet.

It is because this thing is so big, and so inherently reusable, that the BFS second stage can double as an interplanetary spacecraft for certain types of missions. It requires on-orbit refilling in low Earth orbit to fulfill this function. That requires a number of tankers for full refill that has yet to be published by Spacex, but I think it is 6.

So-refilled in low Earth orbit, it has the mass ratio to haul 100-ton-class payloads to direct-entry missions one-way to the surface of Mars, including the final touchdown retro-propulsion allowance. It does NOT have the mass ratio to stop in Mars orbit, that is a much larger delta-vee.

It must be refilled on Mars by local propellant production in order to return. If fully refilled on the surface of Mars, it has the mass ratio to escape directly onto the interplanetary trajectory with a 50-ton-class reduced payload, and then make a free-return direct entry trajectory, with the allowance for its final retro-propulsive landing. It does NOT have the mass ratio to capture into Earth orbit, that is a far, far larger delta-vee.

If you reduce the return payload significantly, it has the mass ratio to leave Earth orbit for the moon, and land directly on the surface with 100-ton-class payloads. It still has enough propellant to leave the moon at reduced payload, and make a direct entry to land on Earth, with the touchdown allowance, all without any refilling on the moon. It does NOT have the mass ratio to stop in Earth orbit, and by far, not even at zero return payload, unless refilled to one extent or another, on the moon.

GW

Last edited by GW Johnson (2018-08-21 15:48:00)

louis · 2018-08-21 16:56:20

Great summary of why the BFR is a game-changer, GW...while we are on the subject, do you have a rough estimate of how big an equivalent Apollo-style lander for Mars would have to be, to be able to land from LMO and then return (in a small ascent vehicle) to LMO? The Apollo lunar lander/ascender system had a mass of 15 tonnes (including fuel/cargo). I looked into it before and I think I came up with a multiple of x5, making it 75 tonnes...would that be about right?

GW Johnson · 2018-08-22 08:33:22

Louis:

I put an article up at "exrocketman" recently dealing with two types of Mars Landers. The one-stage two-way reusable machine has a higher inert fraction because of the reusable features and large volume, and is almost 300 tons for a 3 ton dead-head internal payload. The two-stage two-way non-reusable machine has lower inerts because it is not reusable, and not so large, and is around 15 tons for the same 3 ton dead-head internal payload. Right now it is the latest thing posted, dated 8-6-18, and titled "Exploring Mars Lander Configurations".

One thing I didn't point out above in post 22 is that BFR/BFS is its own interplanetary spacecraft and lander, given you accept the cost of refilling in Earth orbit. The 150 ton payload is delivered to the surface of the moon or Mars in total.

SLS cannot do that, and will never be able to do that. It can boost a 130 ton payload to LEO in its block 2 form, maybe 100 tons or less on a trajectory to Mars, but that payload must include the interplanetary spacecraft and lander, which subtracts from the net delivered payload to the surface of the moon or Mars. Payload plus carrier spacecraft/lander must equal SLS's payload capacity. Block 1 = 70 tons, block 1B = 100 tons.

If the spacecraft/lander resembles my two-stage nonreusable Mars lander concept, with the ascent stage replaced by payload in a container, then the lander payload fraction is about 50%. That presumes ONLY a direct-entry trajectory, NO propellant for stopping in low Mars orbit. Thus a $1B SLS block 2 launch can deliver no more than 50 tons of useful payload to the surface of Mars. That's roughly $20M/ton delivered, and if you believe that a Block 2 SLS launch will only cost $1B, then I have beachfront property in Atlantis to sell you. Beautiful ocean view, 1200 feet straight up.

Now, BFR/BFS can deliver the entire 150 tons of useful payload to the surface of Mars, but requires tanker refilling in Earth orbit to do it. No one yet knows the real launch price, or how many tankers. I think it takes 6, Spacenut has been saying 4. Taking a wild guess of $200M per launch (and it could work out to less than half of that), and 7 total launches, that's $1.4B to send that payload to Mars. That works out to $9M per delivered ton on Mars as a high figure, and around $4M/ton if the launch price is instead under $100M.

Lower price per delivered useful ton on Mars, and more delivered tons by well over a factor of 2 for each flight! The new Spacex approach definitely has the far superior potential, and I have verified the performance potentials really exist. Now the real questions are, will it actually fly successfully, and will it actually work out the way they predict? And can it make a rough-field landing reliably and safely? Or do we have to send a precursor to prepare a paved landing pad? From whom will they buy the propellant production equipment that has been field-tested and verified to work at full scale, in the harsh conditions on Mars? All very good questions.

GW

Last edited by GW Johnson (2018-08-22 08:56:28)

SpaceNut · 2018-08-22 16:41:50

Good point GW on the capacity of the tanks on the "BFR/BFS" but we do know that its got to be an increment of 150 x some unknown count with maybe a few 100 t loads to finish it off. The other thing to note is if we are using it to go to the moon the filling up will not need to be the same as if you were going to mars. So that might be where the 4 x tanker fill ups might be coming from.

If Nasa gets smart sooner rather than later they will alter what the SLS can do for its second stage to make it refuelable at the minimum... I do not think they will ever get a first stage to be reuseable but thats just me...

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