Space X and early colonisation of Mars

louis · 2020-05-23 19:28:01

Their presentation is a bit whacky but they deal with the issues quite methodically:

https://www.youtube.com/watch?v=-xGWSgxq-0k

louis · 2020-05-24 04:02:14

The video notes that the Erebus Montes potential landing sites (on the boundary between Amazonis and Arcadia) which we are fairly confident are the ones favoured by NASA and Space X are not only good for water resource but are also very low radiation risk (you would only reach your lifetime max after 7 years' outdoor exposure , and obviously most of the time you will be indoors, well protected from radiation).

The video suggests that 2029 is a realistic landing date for first humans on Mars, as opposed to the official 2024/25. Personally, I feel that is too pessimistic and the one after 2026/27 is definitely doable, given we could well see an orbital Starship by early 2021. That would give several years (5-6 years) for Earth landing trials, for lunar trials, for perfecting orbital refuelling and for test robot cargo flights to the landing areas. Also enough time to perfect the surface infrastructure for the Mars mission and work out how it will all be deployed, plus training time for the pioneers.

The video makers argue for a 300 person first Mission. That seems way over the top to me. Imagine the training requirement that would involve - getting 300 people Mars-ready, fully acquainted with all inflight and surface procedures! I think that's way over the top and would carry with it unnecessary risks. The more people, the more chance that one might have been harbouring some undetected infectious disease for instance and the more chance of factions and negative interaction. No - I would keep it to a small team, perhaps 10 max for the first mission, split between two Starships. A team of ten could do a huge amount of infrastructure work on Mission One, get the energy and propellant production facility operating smoothly and set up habs for follow up missions while doing lots of experimental work e.g. horticulture, 3D printing and making Mars bricks.

Last edited by louis (2020-06-13 04:57:47)

tahanson43206 · 2020-05-24 05:13:21

For Louis re new video and discussion ...

Your fantasy of factions is interesting .... Considering the funding levels that would be needed, the selection of a management team that would allow factions seems (to me at least) highly unlikely.

Did you pick up from the video any hint about funding?

I did not, but I might have missed it.

(th)

louis · 2020-05-24 07:34:33

There are always tensions between human beings, unspoken or overt. There was tension between Armstrong and Buzz Aldrin (Aldrin lobbied to be appointed Commander or at least first to step foot on the Moon). But these were people used to working in a very disciplined fashioned, often from a military background.

We are talking here about the critical Mission One. Maintaining unity of purpose and harmonious working among 300 people would be nigh on impossible in my view in the context of Mission One where you are actually having to construct a base. You wouldn't even be able to house them all in one hab, I suspect.

There are all sorts of negative aspects in my view. The chances of someone dying on the mission increase the more people there are. Supervision of safety procedure adherence becomes inherently more difficult with that number of people. What if there was a calamitous event and all 300 people died? That could set back Mars colonisation for decades.

It seems to me that piling 300 people into 10 Starships is complete overkill and raises risk in all areas. I would run with a mission of between 6 minimum and 10 maximum for Mission One, spread between two Starships. They would be able to put in place propellant production, the energy facility, a starter farm hab and accommodation for those who are to follow. Maybe for Mission 2 you could up the numbers to between 20 and 50.

I did skip some of the video but don't think they were focussed on funding in this, but I think in other videos they've mentioned the importance of Starlink in generating funds, and Space X themselves make clear that is at the heart of their business model.

tahanson43206 wrote:

For Louis re new video and discussion ...
Your fantasy of factions is interesting .... Considering the funding levels that would be needed, the selection of a management team that would allow factions seems (to me at least) highly unlikely.
Did you pick up from the video any hint about funding?
I did not, but I might have missed it.
(th)

Terraformer · 2020-05-24 07:45:53

Re. crew size, the military have plenty of experience managing groups of people in hostile environments. It's probably worth seeing what advice they have on the matter.

Wiki tells me the USS Ohio has a total crew of 155, around a single Monkeysphere in size. On the other hand, other research suggests the optimal size for groups is 60-80 people. I think that's a good size for a crew, if we go big.

GW Johnson · 2020-05-24 10:31:31

While I am rooting for Spacex's success, I believe NOTHING until I see it. Words are cheap. Accomplishments are not. Arguing about Mars colonization crew size is tantamount to arguing angels on the head of a pin, until there is a version of Starship ready to fly to Mars. If that actually happens, because a whole lot can go wrong, when your attempted accomplishments are so ambitious, difficult, and interlinked.

Starship has yet to fly even suborbitally here on Earth. The first few of those are likely to crash or blow up. After all, the first few Falcon-1's failed when Spacex first flew them. That's when they learned there is a vast gulf of a difference between knowing how to build and operate a rocket engine, and knowing how to fly a staged supersonic flight vehicle.

There is a vast gulf between being able to land a booster stage from around 70 km and 3 km/s speeds, and being able to land a second stage from a couple of hundred km altitude and 7-12 km/s speeds.

There is a vast gulf between landing that lifting-body second stage in Earth's atmosphere where you come out of the hypersonics over 40 km up, and in Mars's atmosphere where you come out of hypersonics under 5 km up and less than a dozen seconds from impact.

There is a vast gulf between reentry heat protection and construction materials approaches and choices for 3 km/s at 50 km, versus 7-12 km/s at 50 km. Just the effective temperatures are widely disparate: 3000 K class versus 7000-12,000 K class.

See what I mean?

Let's wait and see Starship fly successfully suborbitally here at home before we wrap ourselves around the axle worrying much about Mars crew sizes. I want to see them succeed, but the inevitable failures are cheaper and easier to overcome if they happen earlier. And such failures are inevitable.

They need to overcome the shortfalls in their design, not the least of which are (1) excessive bearing stress upon soft soil, and (2) excessively high (and therefore unstable) center-of-gravity relative to footprint. Unaddressed, those are FATAL SHORTFALLS on both the moon and Mars, and for any off-site abort out of low Earth orbit or even a suborbital flight abort.

It'll apparently take the flight test failure of an off-site abort to force them to address those shortfalls.

GW

Last edited by GW Johnson (2020-05-24 10:37:11)

louis · 2020-05-24 15:44:36

GW Johnson wrote:

While I am rooting for Spacex's success, I believe NOTHING until I see it. Words are cheap. Accomplishments are not. Arguing about Mars colonization crew size is tantamount to arguing angels on the head of a pin, until there is a version of Starship ready to fly to Mars. If that actually happens, because a whole lot can go wrong, when your attempted accomplishments are so ambitious, difficult, and interlinked.

Hardly angels on the head of a pin when they are about to take humans to ISS.

Starship has yet to fly even suborbitally here on Earth. The first few of those are likely to crash or blow up. After all, the first few Falcon-1's failed when Spacex first flew them. That's when they learned there is a vast gulf of a difference between knowing how to build and operate a rocket engine, and knowing how to fly a staged supersonic flight vehicle.
There is a vast gulf between being able to land a booster stage from around 70 km and 3 km/s speeds, and being able to land a second stage from a couple of hundred km altitude and 7-12 km/s speeds.

But we have seen pretty spectacular success with the FH9.

There is a vast gulf between landing that lifting-body second stage in Earth's atmosphere where you come out of the hypersonics over 40 km up, and in Mars's atmosphere where you come out of hypersonics under 5 km up and less than a dozen seconds from impact.

I've read or heard somewhere, that Space X intend to use deceleration orbits around Mars.

There is a vast gulf between reentry heat protection and construction materials approaches and choices for 3 km/s at 50 km, versus 7-12 km/s at 50 km. Just the effective temperatures are widely disparate: 3000 K class versus 7000-12,000 K class.

We do know how to deal with the temperatures don't we? Yes, they are on a learning curve but they are already attaching tiles to SN4 so one hopes they will learn quickly.

See what I mean?

I think we all appreciate they are climbing mountain but they are now experienced mountaineers, so I have a lot of confidence in them.

Let's wait and see Starship fly successfully suborbitally here at home before we wrap ourselves around the axle worrying much about Mars crew sizes. I want to see them succeed, but the inevitable failures are cheaper and easier to overcome if they happen earlier. And such failures are inevitable.

I think the point here is that if their target of humans landed on Mars by 2024/25 or even 2026/27 they would really need to have an idea now of crew size, because that will determine everything else (number of Starships required, minimum amount of cargo). I just thought it was worth pointing out the suggested Mission One size of 300 is not credible in my view. It just raises the risk profile all round. I think Space X are far more likely to focus on 6-12 people with them maybe being spread between two Starships.

They need to overcome the shortfalls in their design, not the least of which are (1) excessive bearing stress upon soft soil, and (2) excessively high (and therefore unstable) center-of-gravity relative to footprint. Unaddressed, those are FATAL SHORTFALLS on both the moon and Mars, and for any off-site abort out of low Earth orbit or even a suborbital flight abort.
It'll apparently take the flight test failure of an off-site abort to force them to address those shortfalls.
GW

It's one of life's ironies that there is no abort system for the billions of us everyday folk when we fly (remember that?) - not even a slim-chance parachute - but space pioneers are supposed to be able to abort and land in comfort.

louis · 2020-05-24 15:46:16

It doesn't seem likely that the Space X Mars Mission will be organised on military discipline. I think they are more likely to run with a kind of research team model, of the type you would find in a university science department.

Terraformer wrote:

Re. crew size, the military have plenty of experience managing groups of people in hostile environments. It's probably worth seeing what advice they have on the matter.
Wiki tells me the USS Ohio has a total crew of 155, around a single Monkeysphere in size. On the other hand, other research suggests the optimal size for groups is 60-80 people. I think that's a good size for a crew, if we go big.

SpaceNut · 2020-05-24 16:26:13

Jun 08, 2016 · Current agreements are valid to support ISS till 2024.
May 19, 2016 · NASA Chief Announces a 2028 Expiration Date for the ISS:
Jan 24, 2018 · The Trump administration is preparing to end support for the International Space Station program by 2025, according to a draft budget proposal reviewed by The Verge.

May 27, 2020 Demo-2 is designed to fully validate the Crew Dragon-Falcon 9 system, paving the way for operational crewed flights to and from the ISS. SpaceX holds a $2.6 billion contract to fly six such missions. Boeing, with a contract worth $4.2 billion.

Crew Dragon is capable of carrying up to seven passengers to and from Earth orbit, and beyond. The capsule is about 13 feet in diameter and 26.7 feet high, and can carry 13,228 pounds at launch.

Launched on the falcon 9 but not the heavy...

https://en.wikipedia.org/wiki/List_of_F … y_launches

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

FH9 has less than a dozen missions planned....

Terraformer · 2020-05-25 03:54:31

louis,

A university science department isn't a good model. An over-wintering Antarctic research base is the closest comparable situation, but we also have lots of experience (thousands of years of it) onboard ships that will be helpful.

louis · 2020-05-25 08:31:58

The references to the Antarctic bases and ships are both relevant but when referencing a research team in a university science department I was thinking specifically of people bound up together in one specific research project with a well defined goal. An Antarctic base would be more like a 300 person mission. We can learn from how ships and submarines on long voyagers are run and organised but I think their approach is probably too hierarchical.

Terraformer wrote:

louis,
A university science department isn't a good model. An over-wintering Antarctic research base is the closest comparable situation, but we also have lots of experience (thousands of years of it) onboard ships that will be helpful.

tahanson43206 · 2020-05-25 09:28:04

For Louis re #11

Thanks to Terraformer #10 for making a good point, which Louis was willing to acknowledge.

The funding authority for an expedition to Mars will determine the kind of organization and the kinds of people who will be invited to participate.

There exists ** no ** organization on the face of the Earth, able to fund a Mars expedition, that is going to tolerate an undisciplined, non-hierarchical organization, and they will sacrifice creativity for reliability ** every ** time. The creative people are welcome to remain safely on Earth, where they can ask questions of the highly disciplined onsite personnel, who will have the option of running the questions up to the CEO (whatever the title may be) and if the CEO says NO, then that will be the end of it.

(th)

SpaceNut · 2020-05-25 10:34:23

Which gives the corporate plan versus government for RobertsDyck topic as the funding level an worldly controls a must, which makes all providers of capability just a block to which makes the journey possible.

louis · 2020-05-25 11:39:49

It's a bit difficult to "not tolerate" something at a distance of 160 million kilometres. "OK Hanson, that's it. You're relieved of command." Reply comes back half an hour later. "Message recieved. Invalid request. Remain in Command." What do you do about it? Especially if the commander is in charge of the communications channel.

While I wouldn't expect a serious breakdown in discipline even on a 300 person mission, I think there are increased risks of negative interactions, the more people you have operational on Mission One.

Space X will be meticulous in their choice of crew but as already explained NASA still had issues with tensions and people lying to them about health status and so on.

tahanson43206 wrote:

For Louis re #11
Thanks to Terraformer #10 for making a good point, which Louis was willing to acknowledge.
The funding authority for an expedition to Mars will determine the kind of organization and the kinds of people who will be invited to participate.
There exists ** no ** organization on the face of the Earth, able to fund a Mars expedition, that is going to tolerate an undisciplined, non-hierarchical organization, and they will sacrifice creativity for reliability ** every ** time. The creative people are welcome to remain safely on Earth, where they can ask questions of the highly disciplined onsite personnel, who will have the option of running the questions up to the CEO (whatever the title may be) and if the CEO says NO, then that will be the end of it.
(th)

Last edited by louis (2020-05-25 11:41:39)

elderflower · 2020-06-13 03:43:20

Navies have protocols for dealing with unfit commanders in circumstances where communication with higher authorities is not possible.

louis · 2020-06-13 05:05:26

Maybe, but why create huge organisational difficulties for yourself on Mission One. There's simply no need for 300 people. The more people, the more the risk of an accident. With our hysterical media,one death would be enough to signal "failure". These are not robust times!

Personally I'd say go with a reasonably low number - perhaps a team of between 6 and 10 which gives you some redundancy should person A have an accident or fall ill...so you can have maybe 2 or 3 of everything: electrical engineers, gas production specialist, metal engineers, medics, comms, geologists, biologists and so on. Some people will have double or triple roles. That would suggest 6 is a minimum and 10 would be comfortable.

elderflower wrote:

Navies have protocols for dealing with unfit commanders in circumstances where communication with higher authorities is not possible.

elderflower · 2020-06-13 07:29:22

I would agree with your minimum for an effective mission, but it does depend on what you wish to do when you get there and how long you are going to stay.
A group of seven is the optimum team size for many tasks but we might need 9 or 11. Odd numbers so that group meetings don't end in deadlock.

GW Johnson · 2020-06-14 11:35:39

Arguing crew size for the first missions is tantamount to arguing angels on the head of a pin. You have a limited tonnage of payload you can send in a fully-refilled Starship, even with 8.5-month Hohmann min-energy transfer, and less if you try to fly faster. Spacex "promises" 100+ metric tons. My 2020 reverse-engineering estimate posted on "exrocketman" suggests 149 tons max, with 8 to 9 tanker flights required for the on-orbit refill.

Now each ton of that payload can be cargo or it can be a person plus all his life support supplies. As a rule of thumb for 9 month-class voyages, you can trade one ton of cargo for one person. Musk has NEVER talked about sending more than 100 people to Mars in a single Starship. Plus, much of that cargo has to be the life support supplies for the crew while they are there, and for the return voyage. Call it 3-4 tons per person if they all return ~2 years later. I'm probably not accurate, but it's in that class or ballpark.

If you send 100 tons of cargo (unspecified as to what) there is room for somewhere between 0 and (by my estimate) 49/3-to-4 =~12-to-16 people max. That's all still a wild guess, but the sense is clear: many tons of cargo and a small crew. Half a dozen, two dozen, what's the real difference? None at all.

But Elderflower is right, an odd number is better so that decision-making is not paralyzed by hopeless ties.

GW

Last edited by GW Johnson (2020-06-14 11:38:28)

louis · 2020-06-14 16:43:55

Sounds like you know better than the chief engineer for the Mars Mission GW! - pretty sure he said 5 or 6 refuel launches in a video, not your 8 to 9.

Crew size is clearly an important determinant in energy and cargo requirement (though propellant production will be by far the biggest call on energy usage on the Mars surface). I wouldn't disagree with your crew max for Mission One - 16 sounds like an absolute upper limit to me. There will be serious trade-offs the higher you go. All the Mission One crew really have to do is (a) mine water ice (b) produce propellant and (c) ensure the Starship is readied for take off and safe return to Earth.

GW Johnson wrote:

Arguing crew size for the first missions is tantamount to arguing angels on the head of a pin. You have a limited tonnage of payload you can send in a fully-refilled Starship, even with 8.5-month Hohmann min-energy transfer, and less if you try to fly faster. Spacex "promises" 100+ metric tons. My 2020 reverse-engineering estimate posted on "exrocketman" suggests 149 tons max, with 8 to 9 tanker flights required for the on-orbit refill.
Now each ton of that payload can be cargo or it can be a person plus all his life support supplies. As a rule of thumb for 9 month-class voyages, you can trade one ton of cargo for one person. Musk has NEVER talked about sending more than 100 people to Mars in a single Starship. Plus, much of that cargo has to be the life support supplies for the crew while they are there, and for the return voyage. Call it 3-4 tons per person if they all return ~2 years later. I'm probably not accurate, but it's in that class or ballpark.
If you send 100 tons of cargo (unspecified as to what) there is room for somewhere between 0 and (by my estimate) 49/3-to-4 =~12-to-16 people max. That's all still a wild guess, but the sense is clear: many tons of cargo and a small crew. Half a dozen, two dozen, what's the real difference? None at all.
But Elderflower is right, an odd number is better so that decision-making is not paralyzed by hopeless ties.
GW

SpaceNut · 2020-06-14 17:29:37

That was due to the higher efficiency engines for mass ratio for less needed engines for the task of getting the ship to orbit and changes to the tank design for landing fuel separate from the used to get to orbit or to mars once filled. That equates to more payload under the current plan level of 150mt not the original 100mt. This again is the creep factor of design when things are not fully tested and no longer in a state of value changing.

GW Johnson · 2020-06-14 18:28:03

Louis:

Doesn't matter what they tell the public. What matters is the numbers you can ferret-out that are verifiable. The rocket equation doesn't lie.

Spacex's website gives the propellant load as 1200 tons, and says "100+ tons" of payload. It also gives sea level and vacuum performance levels to expect, something I was able to verify for myself with real rocket ballistics analysis.

Musk's Boca Chica presentation admits the inert mass of Starship is currently 120 tons. He'd be happy to see that get down to 100 tons, but he admits the 85 tons they showed in the 2017 and 2018 presentations is nonsense. Although, he called out the 85 tons his slide still showed to be an error.

I used 120 tons, not his desired 100 tons, because in every vehicle development I ever heard of, inert weights grow. They never reduce. Remember, I used to do this shit for a living, and I was very, very good at it. If by chance the inert weight does reduce, then my performance estimates still hold. You just trade each ton of inert weight saved for another ton of payload.

Similarly, they publish a propellant loadout for Superheavy to be 3400 tons, but they give no inert. Their Falcon cores are running about 5% inert, where the booster "payload" is the whole second stage-and-payload stack. Since the Superheavy is so similar to the Falcon first stage core, I used the same 5% inert, where the "payload" is a fully-loaded Starship. It is really hard to argue with those numbers. They have to be rather close. Which means my estimate is quite realistic.

It is also very, very hard to argue with the rocket equation, given realistic jigger factors for drag and gravity losses, and the number for LEO velocity. I did the trades, including Superheavy flyback, staging velocity, and varying the onboard payload in Starship. I am showing about 1.8 km/s at staging, and a max 149 tons payload carried to LEO. I'm also showing about 10-20 tons propellant held in reserve to land a Starship. That assumes the low-altitude "belly-flop" velocity of 68 m/s published by Spacex is accurate. We'll see in flight tests for sure. I used a jigger factor of 1.5 on that as the mass ratio-effective landing delta-vee, and I also included the deorbit burn, which is of comparable size.

What that means is you need to refill a Starship on-orbit with around 1180-1190 tons of propellant to get a complete refill to the max 1200 tons, which is prerequisite for lunar or Mars missions. So how much can be delivered by a tanker? That deliverable number divided into the refill requirement IS the number of tanker flights, when you round-up to the nearest flight. Doesn't matter what the claims are, NO ONE can argue with the that kind of math!

Now, there are two concepts for the tanker per what Musk has claimed in public: (1) just fly a Starship with zero payload, which reduces its fuel burn to orbit, which also affects the stagepoint velocity and booster flyback, and then deliver what you didn't use getting up there. My numbers, done the same way as I did the loaded Starship, show 133 tons left to deliver, while still preserving 10-20 tons for landing the tanker. That option requires 9 tanker flights.

(2) Is a dedicated redesign to be a tanker. For that I simply assumed that the cargo deck and passenger accommodations get replaced by additional tanks, plumbed into the existing system. That way, the normal payload of 149 tons can be the delivered propellant. That requires 8 flights.

Now, who ya gonna believe? The math? Or a publicity claim with no supporting data? If you want the details, I published this analysis over at "exrocketman" a few weeks ago. Read it at your leisure.

GW

Last edited by GW Johnson (2020-06-14 18:36:05)

louis · 2020-06-14 19:46:41

I'm not going to choose between the two of ya! lol You do the math and they make the statements without showing the math...who to believe.

One thing I would say though is that I think I've heard their chief engineer say they will use orbital entry (I might have got the technical term wrong here) so that they are not trying to "brake" at full speed when they enter Mars orbit...they will have a few orbits...or maybe a month of orbit to reduce speed.

I have a feeling you have previously been a bit dismissive of orbital insertions (if that's the right phrase)....

Surely this is quite an important variable...if you are prepared to spend a month in orbit around Mars presumably the retro rocket firing is much reduced.

GW Johnson wrote:

Louis:
Doesn't matter what they tell the public. What matters is the numbers you can ferret-out that are verifiable. The rocket equation doesn't lie.
Spacex's website gives the propellant load as 1200 tons, and says "100+ tons" of payload. It also gives sea level and vacuum performance levels to expect, something I was able to verify for myself with real rocket ballistics analysis.
Musk's Boca Chica presentation admits the inert mass of Starship is currently 120 tons. He'd be happy to see that get down to 100 tons, but he admits the 85 tons they showed in the 2017 and 2018 presentations is nonsense. Although, he called out the 85 tons his slide still showed to be an error.
I used 120 tons, not his desired 100 tons, because in every vehicle development I ever heard of, inert weights grow. They never reduce. Remember, I used to do this shit for a living, and I was very, very good at it. If by chance the inert weight does reduce, then my performance estimates still hold. You just trade each ton of inert weight saved for another ton of payload.
Similarly, they publish a propellant loadout for Superheavy to be 3400 tons, but they give no inert. Their Falcon cores are running about 5% inert, where the booster "payload" is the whole second stage-and-payload stack. Since the Superheavy is so similar to the Falcon first stage core, I used the same 5% inert, where the "payload" is a fully-loaded Starship. It is really hard to argue with those numbers. They have to be rather close. Which means my estimate is quite realistic.
It is also very, very hard to argue with the rocket equation, given realistic jigger factors for drag and gravity losses, and the number for LEO velocity. I did the trades, including Superheavy flyback, staging velocity, and varying the onboard payload in Starship. I am showing about 1.8 km/s at staging, and a max 149 tons payload carried to LEO. I'm also showing about 10-20 tons propellant held in reserve to land a Starship. That assumes the low-altitude "belly-flop" velocity of 68 m/s published by Spacex is accurate. We'll see in flight tests for sure. I used a jigger factor of 1.5 on that as the mass ratio-effective landing delta-vee, and I also included the deorbit burn, which is of comparable size.
What that means is you need to refill a Starship on-orbit with around 1180-1190 tons of propellant to get a complete refill to the max 1200 tons, which is prerequisite for lunar or Mars missions. So how much can be delivered by a tanker? That deliverable number divided into the refill requirement IS the number of tanker flights, when you round-up to the nearest flight. Doesn't matter what the claims are, NO ONE can argue with the that kind of math!
Now, there are two concepts for the tanker per what Musk has claimed in public: (1) just fly a Starship with zero payload, which reduces its fuel burn to orbit, which also affects the stagepoint velocity and booster flyback, and then deliver what you didn't use getting up there. My numbers, done the same way as I did the loaded Starship, show 133 tons left to deliver, while still preserving 10-20 tons for landing the tanker. That option requires 9 tanker flights.
(2) Is a dedicated redesign to be a tanker. For that I simply assumed that the cargo deck and passenger accommodations get replaced by additional tanks, plumbed into the existing system. That way, the normal payload of 149 tons can be the delivered propellant. That requires 8 flights.
Now, who ya gonna believe? The math? Or a publicity claim with no supporting data? If you want the details, I published this analysis over at "exrocketman" a few weeks ago. Read it at your leisure.
GW

elderflower · 2020-06-15 03:56:47

Dont underestimate the power of publicity statements with no support from the numbers. People seem to love to believe that stuff.

louis · 2020-06-15 07:03:03

Good overview from Martian Colonist:

https://www.youtube.com/watch?v=bmcr2FaoWoU

GW Johnson · 2020-06-15 08:51:30

Louis:

You find all sorts of stuff said on the internet by all sorts of people, pushing all sorts of agendas. You find very few on the internet who actually understand how to run the numbers. The numbers don't lie, as long as you use the right ones in your equations. There is a garbage-in/garbage-out problem that many run afoul of. I usually don't, because I am one of those rare ones who actually did this stuff for a living. I have been long-retired from that, but the physics has not changed, and the technology has not changed very much.

If you look at the evaluations I did (posted on "exrocketman" for all to read) for the 2020 and 2019 versions of the Starship/Superheavy design concept, you will see that the 2020 version is less capable than what they thought in 2019. That is precisely because the inert mass is nearer 120 tons than 85 tons, despite the growth in propellant loadout from 1100 tons to 1200 tons. With a similar 100 ton increase in Superheavy propellant, I might add.

Now, what I showed for the 2019 version was no capability to enter Mars orbit. There was simply not the mass ratio in the design to support an orbit entry burn in addition to a Hohmann transfer and the powered landing. It had to reduce payload to reduce transit time with a faster trajectory.

There are those who point at entering an elongated capture orbit with repeated perigee aerobraking to capture at Mars, but that notion has two very critical downsides: (1) it has never been successfully done at Mars before, and (2) the results are erratically-factor-of-2 variable because the upper atmosphere density is factor-of-2 erratically variable at Mars.

This is aggravated by faster trajectories, because the bigger your initial approach velocity, the more likely you are to bounce off into deep space instead of capturing at all. There is no backup propulsion capability available, the mass ratio does not support that.

Now as I already said, the 2020 version is less capable. It carries less payload than the 2019 version. 2019 could not execute an orbit entry burn and carry any payload. 2020 most certainly cannot. The numbers say that without a doubt. And the enormous risks of attempting repeated-aerobraking capture into a variable atmosphere at extremely-marginal half-again-to-twice-escape-speed conditions make that notion wishful thinking at best, and most likely arrant nonsense.

I'm sorry, but the numbers do not lie. Not as long as you put the good stuff through the equations.

And, I would point out that the Mars entry simulation Spacex has had on its website shows a trajectory and an entry velocity incompatible with repeat-pass aerobraking. It is compatible with direct entry from the interplanetary trajectory, one just a tad faster than Hohmann min-energy transfer. The entry speed they show is 7.5 km/s max. Mars escape is 5.03 km/s. Entry from low Mars orbit would be 3.6-3.7 km/s.

GW

Last edited by GW Johnson (2020-06-15 08:58:17)

New Mars Forums

Announcement

#1 2020-05-23 19:28:01

Space X and early colonisation of Mars

#2 2020-05-24 04:02:14

Re: Space X and early colonisation of Mars

#3 2020-05-24 05:13:21

Re: Space X and early colonisation of Mars

#4 2020-05-24 07:34:33

Re: Space X and early colonisation of Mars

#5 2020-05-24 07:45:53

Re: Space X and early colonisation of Mars

#6 2020-05-24 10:31:31

Re: Space X and early colonisation of Mars

#7 2020-05-24 15:44:36

Re: Space X and early colonisation of Mars

#8 2020-05-24 15:46:16

Re: Space X and early colonisation of Mars

#9 2020-05-24 16:26:13

Re: Space X and early colonisation of Mars

#10 2020-05-25 03:54:31

Re: Space X and early colonisation of Mars

#11 2020-05-25 08:31:58

Re: Space X and early colonisation of Mars

#12 2020-05-25 09:28:04

Re: Space X and early colonisation of Mars

#13 2020-05-25 10:34:23

Re: Space X and early colonisation of Mars

#14 2020-05-25 11:39:49

Re: Space X and early colonisation of Mars

#15 2020-06-13 03:43:20

Re: Space X and early colonisation of Mars

#16 2020-06-13 05:05:26

Re: Space X and early colonisation of Mars

#17 2020-06-13 07:29:22

Re: Space X and early colonisation of Mars

#18 2020-06-14 11:35:39

Re: Space X and early colonisation of Mars

#19 2020-06-14 16:43:55

Re: Space X and early colonisation of Mars

#20 2020-06-14 17:29:37

Re: Space X and early colonisation of Mars

#21 2020-06-14 18:28:03

Re: Space X and early colonisation of Mars

#22 2020-06-14 19:46:41

Re: Space X and early colonisation of Mars

#23 2020-06-15 03:56:47

Re: Space X and early colonisation of Mars

#24 2020-06-15 07:03:03

Re: Space X and early colonisation of Mars

#25 2020-06-15 08:51:30

Re: Space X and early colonisation of Mars

Board footer