IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)

[KelvinZero]

If the engineers are in doubt, perhaps the mars version could have wider legs?

Hey, has there been speculation for positioning of reaction control thrusters? Perhaps same as Shuttle?

https://en.wikipedia.org/wiki/Reaction_control_system#Location_of_thrusters_on_spaceplanes

How much of the detail of the shuttle would be relevant to the surface of the BFR? That could make for a more fleshed out CGI model. It is almost a shame that physics and basic optimisation makes the 9m BFR look sort of plain. It is basically the profile of the shuttle main tank. The shuttle orbiter has way more fiddly hull shapes.

We have some good CG modellers here, but they are sort of hamstrung by the fact the BFR profile sort of looks like an amateur modeller's first experiment with the lathe tool

[Negan]

From SpaceX's Mars page quote below I also see the possibly that none of the first six ships will be coming back, and those first crews will the building launch/landing pads for the BFRs that will return.

"A second mission, with both cargo and crew, is targeted for 2024, with primary objectives of building a propellant depot and preparing for future crew flights. The ships from these initial missions will also serve as the beginnings of our first Mars base, from which we can build a thriving city and eventually a self-sustaining civilization on Mars."

Edit: Also makes sense because the initial crew will also setup the propellant depot (the presentation slide says "propellant production plant". No depot (or plant), no return.

[oldAtlas_Eguy]

What would it take to create an improved landing pad?

First two earth moving robots. A front loader and a scraper/leveler.

Once the area is smoothed out the area needs to be packed and then re-leveled. The packer could be a drum device or a pounding device that pounds a spot then moves to the next spot and pounds it. The pounding device/robot would do a better job of creating a packed surface.

Next is to re-level surface then pack again.

Next is to re-level for final time.

Now is the use of a microwave device that  fuses the packed and leveled regolith into a solid surface. It does this one small area at a time with an overlapping fusing pattern. This will create a single solid large hardened high load bearing surface.

The last step is to paint the outside circle and the SpaceX logo in the center.

Equipment needed:(only 1 of each is actually needed but second is spare for redundancy)
2 Front loader robots
2 Scraper/leveler robots
2 Pounder robots (It is possible that the pounder, fuser and painter are just different end effectors on the same robot)
2 Fuser robots (It is possible that the pounder, fuser and painter are just different end effectors on the same robot)
2 Painter robots (It is possible that the pounder, fuser and painter are just different end effectors on the same robot)

=10 robots each on a single palet of a size like 2mX2mX3m. If it was the density of water would be 12mt each pallet but more likely <4mt per pallet or total of <40mt.

With pounding and fusing being significantly time consuming having three end effectors on each of up to 6 robots could shorten the time to perform the tasks. since these are somewhat sequential in nature.

780 days is a long time for small pads of just 50m diameter.

These robots would have multiple uses latter in mining, roadway preparation, and habitat site preparation. NOTE the painter is used to mark the sites for alignments for later tasks and not just to paint logos. The painter has to have a very high quality IMU/surveyer to produce precise paint markings of just a few cm wide (like 2cm). On hardened surfaces a corner or X could be done at mm precision.

So for BFS it would not be difficult to create "improved" landing pads on Mars it would just take time.

[speedevil]

September 2022 is a while off yet.
Assuming for the moment that that milestone is hit,or looks plausible to hit, for launch and arrival at the tail end of 2022.

If 2018/19 goes as planned for F9/F9H, it seems likely that they will have burned through all of their non commx payloads, and be more or less queue free, perhaps with the beginnings of starlink revenue coming in.

In August 2020, there is a window to mars landing at the end of 2020.

If they are not confident about the capacity for BFR to land on an unprepared surface, a small rover, launched by F9H and drawing on the red dragon plans (what there was of them) might considerably reduce risk by scouting an area in very great depth.

This of course has risks of its own, but  some form of vehicle on the surface even if only to drag pipes and setup solar panels would be nice, and doing it early as a combined risk mitigation for landing which is not strictly required for mission success has some plusses.

Of course, this would be at the same time as the mars 2020 rover, which would be very odd.

More than just a levelled ~15m circle with the loose large rocks scraped off and surveyed for pockets of dust and terrain that might sink a foot would be hard to do with what you can fit in Red Dragon.

[Negan]

If they are not confident about the capacity for BFR to land on an unprepared surface, a small rover, launched by F9H and drawing on the red dragon plans (what there was of them) might considerably reduce risk by scouting an area in very great depth.

Seems like the biggest concern is the rocket plume when landing and its destabilizing affects on the soil, but considering they're sending two ships on the first go, they must have some kind solution in mind to avoid this.

Edit: As in the plume creates a hole under the ship which could collapse which could in turn tip the ship over.

[jg]

If they are not confident about the capacity for BFR to land on an unprepared surface, a small rover, launched by F9H and drawing on the red dragon plans (what there was of them) might considerably reduce risk by scouting an area in very great depth.

Seems like the biggest concern is the rocket plume when landing and its destabilizing affects on the soil, but considering they're sending two ships on the first go, they must have some kind solution in mind to avoid this.

The biggest issue I see is not the first landing; but subsequent landings, due to the rocket plume possibly creating projectiles that might damage other ships or other installations.

So maybe you punt to begin with by choosing topography that will shield one BFS from the other; they can't be all that close together, but you have to be able to move things around on the surface anyway.

Eventually, you want prepared pads...

Given the temperature on Mars, maybe you just saturate the ground with water and have a ice/regolith
pad..

[matthewkantar]

I know of a spot here on Earth that is nearly flat granite 150 feet wide. If a spot like that could be found on Mars convenient to other desired features, that would be ideal. Whatever dust and rocks remaining after the landing could be removed with a hand truck and a broom.

Matthew

[john smith 19]

If they are not confident about the capacity for BFR to land on an unprepared surface, a small rover, launched by F9H and drawing on the red dragon plans (what there was of them) might considerably reduce risk by scouting an area in very great depth.

Seems like the biggest concern is the rocket plume when landing and its destabilizing affects on the soil, but considering they're sending two ships on the first go, they must have some kind solution in mind to avoid this.

Edit: As in the plume creates a hole under the ship which could collapse which could in turn tip the ship over.

IIRC during the DC-X landing trials the RL-10 engines dug quite deep holes in the salt flats of White Sands. Keep in mind a)Total thrust of the DC-X was about 68 000 lb, The multiple Raptors will be much greater.
b) the 1/3g surface gravity will allow dust to say airborn much longer.

An FH delivered rover sounds like a useful risk reduction idea if SX can spare the staff to design and build it.

[docmordrid]

I would think the chassis and drive system could be farmed out to Tesla. There already seems to be a fair amount of synergy between the two companies.

[oldAtlas_Eguy]

I would think the chassis and drive system could be farmed out to Tesla. There already seems to be a fair amount of synergy between the two companies.

Not only that but the solar power systems as well that will become fixed features on the surface. Besides Tesla is already the experts in AI software for fully self driving in complex difficult environments. Tesla has the expertise they only need some experienced engineers with the environment that the systems will operate in to inject the right requirements and do the design verification against the environments the designs would operate.

That just leaves the comm systems and the end effectors/tools to be developed and integrated onto the chassis/rover robots to be done by SpaceX.

The item most miss in this arrangement is that SpaceX would eventually buy possibly such rover chassis in the thousands and the solar power systems in the many square kilometers. That's $Bs in purchases from Telsa. So Tesla would do most of the development work on Tesla's own dime. This stretches SpaceX's cash for BFR development by offloading the ancillary development work and costs to Tesla.

[Lar]

Thousands?

I would expect stuff like implements to be farmed out to CAT or another commercial vendor even if Tesla makes the chassis.

[oldAtlas_Eguy]

Thousands?

I would expect stuff like implements to be farmed out to CAT or another commercial vendor even if Tesla makes the chassis.

Initially maybe just a couple of dozen like 10-20 every 2 years for a few synods then an ever increasing number probably ~5 on each flight. With out year being as many as 20 flights per synod that's 100 chassis every 2 years at the 10 year point.

Having someone else do the stuff to add to the chassis is a good idea if SpaceX can achieve it.

[TomH]

Keep in mind...b) the 1/3g surface gravity will allow dust to say airborne much longer.

The 0.0059 density of Martian atmosphere (in relation to Earth's atmosphere) will not support particle suspension. The stuff will drop quickly back to the surface as there is almost no gas to support it, not quite, but almost as fast as on the lunar surface.

[TomH]

Thousands?

I would expect stuff like implements to be farmed out to CAT or another commercial vendor even if Tesla makes the chassis.

I can't see that at all. CAT makes stuff from heavy steel. They know nothing about designing lightweight gear more suitable to being flown a couple of hundred million miles through space.

And BTW, I used to own a tractor and about 20 implements/attachments. Most of these type items are not made by CAT. CAT makes the chassis and engines of immense machines. Most tractors use either towed implements, made by a dozen or so other companies, or attachments driven by the PTO (power take off). These things are made by people who are used to designing implements whose utility depends upon high mass and fabricated via simple means from basic steel. They have little experience in fabricating low mass/high strength tools that depend upon advanced geometrical structures and advanced materials to achieve a task. I guarantee you, things that have to be transported hundreds of millions of miles through space and landed on another planet will be designed and engineered by someone other than any of the companies who build traditional tractor and earthmoving gear.

[Lar]

Keep in mind...b) the 1/3g surface gravity will allow dust to say airborne much longer.

The 0.0059 density of Martian atmosphere (in relation to Earth's atmosphere) will not support particle suspension. The stuff will drop quickly back to the surface as there is almost no gas to support it, not quite, but almost as fast as on the lunar surface.

What are dust storms then? I thought they were (very fine) particles suspended in the atmosphere, perhaps with some component of wind to help keep them aloft? (if that's the case then calm air will not hold dust and windy are will carry it away from the landing area)

[Negan]

Would using a stripped down one-way BFS to Mars orbit up the possible rover payload to the surface?

[TomH]

Keep in mind...b) the 1/3g surface gravity will allow dust to say airborne much longer.

The 0.0059 density of Martian atmosphere (in relation to Earth's atmosphere) will not support particle suspension. The stuff will drop quickly back to the surface as there is almost no gas to support it, not quite, but almost as fast as on the lunar surface.

What are dust storms then? I thought they were (very fine) particles suspended in the atmosphere, perhaps with some component of wind to help keep them aloft? (if that's the case then calm air will not hold dust and windy are will carry it away from the landing area)

Have you ever studied fluid dynamics? There is a huge difference between the flow of a fluid and the ability of a resting fluid to hold particles in suspension. Regardless of density, if a fluid is moving fast enough, it can pick up and carry particles. A resting fluid must have a high enough density to support particles in suspension.

Think about a sandstorm on Earth. Imagine there are only particles of quartz in the 1-2 mm diameter range. A hundred mph wind comes along and easily drives the particles into the air. When the wind stops, those pieces of sand immediately fall back to the ground. They are far too large for our atmosphere to hold in suspension. In like manner, Mars' atmosphere is too low density to suspend most of the particles that can float in Earth's atmosphere.

[speedevil]

Would using a stripped down one-way BFS to Mars orbit up the possible rover payload to the surface?

You could in principle remove some of the engines, but this is likely to be a rather small number, and would change how the heatshield works.

The above hypothesis I raised was a Red Dragon, launching on a falcon heavy a couple of years before, so the rover would be in the ton range, at most, to prepare the site for BFR landing in 2022.

It would be able to move moderate sized rocks that a human could probably push with hand tools at most, and do detailed surveying of dust properties and thicknesses, as well as provide a location beacon and wind/... to aid some in improving landing accuracy, as well as perhaps a light 1kg helicopter or three as planned for the mars 2020 rover for in depth mapping of the surrounding area.

It would not have any way of preparing the surface other than shifting intermediate size rocks and removing loose dust perhaps at most.

With a 150 ton BFS payload, even without stripping, a really quite large fleet of construction equipment without much attention being paid to mass reduction, and a large solar/battery array and a garage could be made.


It seems unlikely they'd dedicate a BFS to this, and it seems dramatically more unlikely that it'd be ready to go in summer 2020.



Something a little larger than this, 'winterised', with a hutch and solar array.

[Lar]

Thousands?

I would expect stuff like implements to be farmed out to CAT or another commercial vendor even if Tesla makes the chassis.

I can't see that at all. CAT makes stuff from heavy steel. They know nothing about designing lightweight gear more suitable to being flown a couple of hundred million miles through space.

Try this Google search  https://www.google.com/search?q=caterpillar+lunar+mining&ie=utf-8&oe=utf-8

https://www.caterpillar.com/en/news/caterpillarNews/innovation/nasa-caterpillar-collaboration-for-technology-advancement.html
https://www.equipmentworld.com/caterpillar-to-develop-loaders-with-nasa-for-lunar-mining/

Both from 2013

https://nma.org/2017/08/30/caterpillar-bringing-mining-innovation-deep-space/

From 2017

Several good hits for stories about CAT and NASA collaborating on... mining equipment. You might think they will fail, and maybe they will, but they are a logical place to start seeking third party equipment.  You might do a bit of research before just dismissively pontificating that they can't do it. ("they know nothing")

Keep in mind...b) the 1/3g surface gravity will allow dust to say airborne much longer.

The 0.0059 density of Martian atmosphere (in relation to Earth's atmosphere) will not support particle suspension. The stuff will drop quickly back to the surface as there is almost no gas to support it, not quite, but almost as fast as on the lunar surface.

What are dust storms then? I thought they were (very fine) particles suspended in the atmosphere, perhaps with some component of wind to help keep them aloft? (if that's the case then calm air will not hold dust and windy are will carry it away from the landing area)

Have you ever studied fluid dynamics? There is a huge difference between the flow of a fluid and the ability of a resting fluid to hold particles in suspension. Regardless of density, if a fluid is moving fast enough, it can pick up and carry particles. A resting fluid must have a high enough density to support particles in suspension.

Think about a sandstorm on Earth. Imagine there are only particles of quartz in the 1-2 mm diameter range. A hundred mph wind comes along and easily drives the particles into the air. When the wind stops, those pieces of sand immediately fall back to the ground. They are far too large for our atmosphere to hold in suspension. In like manner, Mars' atmosphere is too low density to suspend most of the particles that can float in Earth's atmosphere.

Oddly enough I DID take fluid dynamics in college and if you read what I wrote, I hypothesized the very same conclusion you came to, but without the introductory snark.

You need to work on your tone. I've seen you be this way with others as well. Don't be that way. Be collegial. We are all here to learn together and figure things out.

[john smith 19]

Have you ever studied fluid dynamics? There is a huge difference between the flow of a fluid and the ability of a resting fluid to hold particles in suspension. Regardless of density, if a fluid is moving fast enough, it can pick up and carry particles. A resting fluid must have a high enough density to support particles in suspension.

Think about a sandstorm on Earth. Imagine there are only particles of quartz in the 1-2 mm diameter range. A hundred mph wind comes along and easily drives the particles into the air. When the wind stops, those pieces of sand immediately fall back to the ground. They are far too large for our atmosphere to hold in suspension. In like manner, Mars' atmosphere is too low density to suspend most of the particles that can float in Earth's atmosphere.

I mentioned the suspension of particles due to this presentation



You can skip the first 14 minutes with no real loss of data.  The key element regarding airbourne dust is at 28:15. 

A key question would be what is the dust particle size that all those weather cycles and radiation exposure reduced the surface to? What won't stay in the air for more than a few seconds at > 2mm in dia may be very different to what, and how much can stay airbourne at 100 micrometers or less.  We know that despite a static air pressure 1/160 that of Earth SL Mars dust storms can last for months, despite the sunshine level (which is a major driver of global weather systems) being 1/4 that of Earth IE neither the energy input nor the air that's being energized are as great as that on Earth, yet the effects are enormous. The missing factor is the "settling force" is 1/3 what it is on Earth.