Space X News - lunar tourism and delayed BFR hop

GW Johnson · 2018-09-17 16:01:03

Hi Void:

I'm no expert on conjunction vs opposition class missions, or gravity assist flybys. I don't know anything about skyhooks or space elevators.

I'm just an old engineer who started in the slide rule days doing rocket and ramjet missile propulsion. I did some space launch work on the old LTV Scout launcher. Did hypersonic wind tunnel testing on the Space Shuttle as a grad student. Got laid off after 20 years along with over 1.5 million others, and had to switch careers.

Did a little civil/mechanical stuff, some aviation alt fuels research, and mostly teaching. Anywhere from 7th grade math to grad school level engineering. Did some automotive alt fuels on my own time.

Now retired, building custom farm implements for sale, and advising a few launch startup teams. And still driving E-35 blends in all my 4-stroke equipment as a drop-in fuel, plus running my ancient farm tractor on straight E-85.

GW

Last edited by GW Johnson (2018-09-17 16:01:54)

kbd512 · 2018-09-17 18:32:39

Void,

The amount of drag depends on how you construct the Skyhook. If you just put a giant counterweight on a really long and strong string, then you're gonna need quite a bit of propulsion to get it back to an acceptable altitude. Thankfully, there are other ways of getting the job done.

kbd512 · 2018-09-17 19:13:42

GW,

Instead of simply killing all those cactus, can they be harvested and turned into ethyl alcohol fuel?

SpaceNut · 2018-09-17 19:41:53

Void we can use just about anything that is out there for insitu resource to make oxygen, fuel and water with so long as it does not come at the expendature of fuel to do so.
As for the different transits to mars from earth we need to be able to launch more often and the same for returning from Mars. This may mean a mix of ion even for crews if it means we get there in a period shorter than waiting for the next cycle....

SpaceNut · 2018-09-17 19:43:12

kbd512 wrote:

GW,
Instead of simply killing all those cactus, can they be harvested and turned into ethyl alcohol fuel?

I was thinking of send Bourtiques of them to washington....

Void · 2018-09-17 21:01:37

Hmm... Got a lot of respect for you GW but let you get away from my nonsense.

kbd512:
The skyhook I am thinking of would most likely be rotating. While it would dip into the Venus atmosphere, the relative speed would be kept a low as possible between the hanging element, and the high level atmosphere. I would not intend to snag solid objects, but molecules.

Just lifting molecules would require make-up inertia to be added to the machine. Also any clumsy drag where the hanging element would stir the air would end in a pointless loss of energy. Some of that has to happen. Machines are only so efficient at their best.

How to make up for the loss of inertia and prevent the machine from entering the Venus atmosphere? Well I plan solar sailing of the solar wind type. A magnetic field at some portion of the machine above the atmosphere and where the solar wind gushes by. It could be throttled as the device orbited Venus, to receive more or less of a push from the solar wind as is appropriate to keep a reasonably desirable orbit, and to yet pull materials up to orbit from the upper Venus atmosphere.

I was excited because I hoped that BFS might not only be suitable for Earth/Luna and Mars, but also Venus. I am not yet disappointed by that potential revelation. Perhaps I will later be.

In this case however I do not intend that BFS will ever intentionally enter the Venus atmosphere to land, rather to change it's inertia by aeroburn method, and to exploit the gravity well of Venus above it's atmosphere.

So with that we then might have the potential to arrive at a Venus vacuum orbit with BFS and it's potential contents, and to also mine the upper atmosphere of Venus for it's materials.

Then if devices like BFS would open access to Earth, Luna, Mars, and Venus, we may hope to have commerce in materials between them.

If the skyhook would work, then Carbon, Oxygen, Nitrogen, and Argon may be pulled up to Low Venus Orbit by a rotating skyhook. Then these things may be provided to the Moon, and/or various customers. The Moon could very likely be a place where large habitats could be manufactured from solid substances. Those enclosures could be launched by the rocket propellant of your choice. I am thinking solid rocket methods from Lunar materials. Those enclosures sent to Venus, and to aerobrake to the orbit of Venus. Those enclosures then assembled into orbital habitats to be filled with Oxygen and Nitrogen. Carbon materials to be used to add strength to these Venus orbiting habitats.

Now then happy habitats for people migrating from Earth. Lots of solar energy, no dust storms, but Mars also.

Spacenut. Of course you are not wrong, but you are too Mars centric in my opinion. Four worlds soon. Earth, Luna, Mars, and Venus.

Isn't that better if you can pull it off? I am trying to find a method to pull it off.

Its late.

I'm Done for now.

Last edited by Void (2018-09-17 21:18:51)

GW Johnson · 2018-09-17 23:54:23

Cactus to ethanol? Yes, but the yield is very low. The fruit makes really tasty jam, if you know how to peel it without getting covered by the tiny thorns.

The crunching sound of cactus being smashed under my implement provides great emotional satisfaction. Especially after 15 years of fighting it and failing, before I figured out how to do it right.

I've got this down to nothing but "driving around drinking beer on a tractor" work. Never picked up or disposed of anything. Composted right in place.

It does knock the long thorns off the pads. So the cattle can eat them safely. Sometimes they follow me around the same way birds follow someone plowing.

I just cannot plow here: 4 inches of dirt, then rocks, then monolithic stone. Anything planted has to be no-till. Grazing is most practical.

GW

Last edited by GW Johnson (2018-09-17 23:55:35)

SpaceNut · 2018-09-18 16:52:22

I think you may have missed my posts in those topics of syphoning gasses and venus cloud city use in those other topics to which this particular topic is neither of them.

elderflower · 2018-09-19 06:13:34

GW Have you tried making jelly rather than jam with your prickly pear fruit. You wouldn't have to peel them to get rid of the thorns, just stick them in a jelly bag and pressure cook them.
Another thought: How about cider?
And another: What would a goat do with prickly pear? They seem adept at eating every thing else. Not so easy to milk though.

louis · 2018-09-19 07:31:54

A good video from Martian Wolf updating on the BFR project.

https://www.youtube.com/watch?v=h1tLEv9j3OE

GW Johnson · 2018-09-19 10:24:03

I finally saw the footage of the moon passenger announcement. It is posted on the Spacex website. About an hour and 44 minutes long, but there is about half an hour of title and nobody on stage yet up front. Unedited footage, obviously.

My evaluation of the revised design is given in posts 13 and 21 above, with some rocket nozzle evaluation in post 22 above. To that, I would add only that the "fin articulation" I suspected goes even further than I thought. They don't just fold dead broadside during entry, they actually fold about 45 degrees from the fixed vertical fin. They stay like that until almost touchdown during an Earth entry, which animation Musk showed (twice) during the presentation.

During an Earth entry, there is no pitch-up into a tail slide maneuver. I do not know what they now plan for Mars, since the previous 2017 design iteration did pitch up into a tail-slide at Mars. On Earth, they go dead broadside to the slipstream descending dead vertical once subsonic, falling at under half a Mach number. Close to the surface, they pitch up tail first and fire an engine or two, and fold the two actuating fins around 120 degrees apart for landing.

The odd looking flat surfaces in the stage base around the engines is aft cargo volume, supposedly 88 cu.m worth. The forward section has 1000-1100 cu.m payload volume, which sounds like that is not yet finalized.They have built a cylinder section 9 m in diameter, presumably part of the tankage section, but they have no domes yet. Musk talked about building domes and the engine section next, so the inboard profiles from 2017 seem still notionally accurate.

I looked very closely at the Raptor engine test footage, and saw no bleed dump from any turbopumps. So the engine cycle has to be different from the Merlins, which do have turbopump bleed dumps. With no dumped massflow and a 300 bar operating pressure, that may explain the Musk statement of 380 s specific impulse. Thrust is "200 tons" per Musk.

GW

Last edited by GW Johnson (2018-09-19 11:13:02)

Void · 2018-09-19 13:38:39

Yes, I do care what you have to say. It is very valuable.

It appears they can swap out engines? That is types or number of??? This would be per mission requirements???

I am thinking space stations in Earth orbit where you can deposit and withdraw engines, after your acquire orbit? Down the road a bit.

Done.

Last edited by Void (2018-09-19 13:39:20)

louis · 2018-09-19 15:24:45

Not sure if anyone's linked to Musk's recent presentation but anyway here it is:

https://www.youtube.com/watch?v=DV2TLnMfoYo

16:24 view of the first cylinder section - it's really happening folks!!!

Last edited by louis (2018-09-19 15:52:18)

louis · 2018-09-20 07:52:19

https://www.youtube.com/watch?v=8mbMAvDu-3g

I think it's great that Space X are bringing art and space together in the lunar orbital project.

We know that space can have huge cultural impact on Earth (probably the Earthrise photo is the greatest example of that).

I have long maintained that art could be an important element in Mars colonisation. For one thing adventurous artists will want to experience Mars and be the first to put their stamp on it so to speak. Many of the world's greatest artists are fabulously wealthy and so could afford to pay their way, thus filling up Space X's coffers.

Artists could also remotely create sculptures, paintings and other art work on Mars. This would create a Mars based art market. The art objects could be sold back on Earth and Space X could take a proportion of the revenue - say a 30% commission. Also, some artists would pay for Space X to take their art works to Mars.

louis · 2018-09-20 10:52:11

Interesting presentation by the Everyday Astronaut on the latest BFR design:

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

Void · 2018-09-20 18:27:54

It's quiet.... To quiet.... and I think Louis is lurking just outside the campfire.

As a person who was in maintenance, I think that way.

I read an article about carbon aircraft and the methods that are used to repair them. I am wondering about certain possibilities where a BFS might be injured by a hit from space junk or a small outer space object. Or maybe some other partially crippling event.

I guess you might use your best orbital patch method, and presume that perhaps your ability to do the full aeroburn belly flop down to Earths surface should be modified (Maybe it could be).
1) Get the non-essential people off the ship.
2) Remove dead weight store in orbit.
3) Use BFR fueling ships to fully fill the injured BFR.
4) Use more retro propulsion than is ordinarily used to cut the burn in hazard.
5) Probably a robotic landing.
6) Avoid the belly flop burn in as much as possible, but likely you can belly flop once you are past the worst heat danger.

Maybe salvage the ship with no human life loss. Repairs on the surface of Earth then I suppose.

Done.

Last edited by Void (2018-09-20 18:34:20)

GW Johnson · 2018-09-21 11:09:18

I've been thinking some, about how this BFS lands.

Based on what they showed for a Mars landing simulation with the 2017 design, versus what was an Earth landing with this 2018 design, I'm guessing the Mars landing is still a low-altitude pull-up into a tail-slide, with immediate retro-propulsive touchdown.

The Earth landing is different, since end of hypersonics is 35-40 km altitude, not ~5 km as on Mars. The vehicle pitch attitude goes to 90 degree angle of attack as the trajectory steepens into a vertical descent at very subsonic speed. Pitch goes to 180 angle of attack (tail first) just before retro-propulsive touchdown.

I don't yet understand how they expect to seal inherently-porous carbon-composite tank structure against leakage of their cryogenic contents. Nor do I understand yet how they expect the airframe to survive dead-broadside air loads during descent, unless they gas-pressurize these tanks to levels approaching the wind pressure acting externally. Either way, these structures are going to be thicker and heavier than first projected with the inert weights posted for the 2017 design.

This basic space transportation design has some marvelous advantages, but it also has some very serious vulnerabilities. The basic approach is the same as for commercial airliner design: if you lose the airplane, you lose everybody aboard. Spacex hasn't flown crews yet, so the have not yet had to face the reality of my infamous quote: "there is nothing so expensive as a dead crew".

As for space junk or meteors punching holes, Spacex had better be prepared to patch them. If my suspicion is correct, entry survival will depend upon the ability to pressurize the empty tanks. On an interplanetary trajectory headed for entry, there is no diversion and there is no rescue. Period.

GW

Void · 2018-09-21 11:50:20

I support what you say, although honestly I will not pretend to be up on the details of all of your concerns.

Last video from Dr. Zubrin, indicated that he thinks that BFS is best as a Earth/Luna craft, getting mass to the edge of the Earth's orbitsphere. Then some method to complete the passage to Mars.

I applaud the ability to get to Mars, get a bit concerned about the plans to then at that place at the start be able to insitu get the resources you need to return the BFS. Really I have been thinking about it a lot.

I think Dr. Zubrin indicated that he thinks that the idling of a BFS during a mission to Mars, would waste vast amounts of it's abilities.

So, I really think the device may not leave the Earth/Moon system, or not the type designed to work in the Earth/Moon system. It's fuzzy, and I did note your concerns about even getting the BFS to work with reasonable safety in the surface to LEO and back to surface mode.

It's going to be interesting. Thankfully they apparently can fully test the device without humans on board.

I have had an interesting morning, I think I am going to mess around in the "Alternate BFR" section.

Thanks for your good information. I do like to learn.

louis · 2018-09-21 15:59:42

Couple of points:

1. Apollo was a "one craft" mission. As we saw with Apollo 13 if the craft failed then ultimately the crew's lives were at risk. I think when you are pioneering you have to accept a degree of risk ie death.

2. Do you think they are really planning to land on Mars on fin points? Seems counter-intuitive to me. But Space X always surprise...so maybe they have worked out plan to create a landing pad on Mars?

GW Johnson wrote:

I've been thinking some, about how this BFS lands.
Based on what they showed for a Mars landing simulation with the 2017 design, versus what was an Earth landing with this 2018 design, I'm guessing the Mars landing is still a low-altitude pull-up into a tail-slide, with immediate retro-propulsive touchdown.
The Earth landing is different, since end of hypersonics is 35-40 km altitude, not ~5 km as on Mars. The vehicle pitch attitude goes to 90 degree angle of attack as the trajectory steepens into a vertical descent at very subsonic speed. Pitch goes to 180 angle of attack (tail first) just before retro-propulsive touchdown.
I don't yet understand how they expect to seal inherently-porous carbon-composite tank structure against leakage of their cryogenic contents. Nor do I understand yet how they expect the airframe to survive dead-broadside air loads during descent, unless they gas-pressurize these tanks to levels approaching the wind pressure acting externally. Either way, these structures are going to be thicker and heavier than first projected with the inert weights posted for the 2017 design.
This basic space transportation design has some marvelous advantages, but it also has some very serious vulnerabilities. The basic approach is the same as for commercial airliner design: if you lose the airplane, you lose everybody aboard. Spacex hasn't flown crews yet, so the have not yet had to face the reality of my infamous quote: "there is nothing so expensive as a dead crew".
As for space junk or meteors punching holes, Spacex had better be prepared to patch them. If my suspicion is correct, entry survival will depend upon the ability to pressurize the empty tanks. On an interplanetary trajectory headed for entry, there is no diversion and there is no rescue. Period.
GW

GW Johnson · 2018-09-21 18:56:09

Louis, I'm surprised you have provided so many links to interpretations of Musk's presentation, but apparently you have not seen the presentation itself, posted on Spacex's website!

Musk himself says the vertical fin is less of an aerodynamic item and more of a landing leg. Between that comment and the illustrated tip pods on all 3 fins, how could these fins be anything but landing legs?

The video he shows (twice!!!) clearly shows a final retro-propulsive touchdown on the tips of 3 fins located about 120 degrees apart. For most of the entry trajectory, the two "bottom" fins are clocked only about 45 degrees away from the vertical fin. Musk says the hinge forces to move the fins like that are mega-newton class.

By the way, that simulation video is of an Earth landing, not a Mars landing. You can tell because of the long vertical fall dead broadside to the wind to the touchdown. That cannot happen that way in the thin air on Mars.

Those three fin tips provide a wider footprint relative to vehicle length than the previous four landing legs did in the 2017 presentation. Somebody at Spacex has understood something about the rough field instability problem. Not yet well enough, but better than it was.

As for unsurvivable risks, both the Mars entry and the Earth entry are single-point failure possibilities (with multiple ways to fail at each entry) with no way out. As is refilling propellants on Mars.

GW

Last edited by GW Johnson (2018-09-21 19:04:20)

SpaceNut · 2018-09-21 19:46:04

That single point of failure was a hard lesson to learn when a chunk of frozen foam hit the wing making a small hole on the leading edge. From that point on an inspection was performed to limit that risk factor of failure for a return home.

The refueling on mars is slightly different in risk reduction methods as we need to look at what risks are present with which fuels used under staged or unstaged condition of fuel and oxidizer for the return plus the type of fuels used as well for supplied or made insitu in whole or in part.

For insitu if all we can guarantee is oxygen then send, to stage the return fuel and if oxygen is out then send hydrogels instead or the materials to make it on mars.

louis · 2018-09-22 03:49:01

Yes I saw that part of the presentation. But this was in the context of a lunar tourism announcement and as you point out what was shown was an Earth landing...I did specify landing on Mars in my question. My thinking was that in the context of Mars, landing on unprepared ground with fin points is asking for trouble. With - what is it? - a few hundred tonnes of mass above in cargo, unused propellant, and structure, isn't there a risk anything with a point is going to dig in, or if you are landing on a flat rock bed, find some fracture in the rock and become unstable? That's what led me to wonder if Space X are thinking in terms of getting some landing pad laid out on Mars. How they would do that, I don't know as I imagine it would have to mass at least a tonne, so firing by mini rocket from the cargo BFR is unlikely to work...I guess you would have to have a dedicated robo-vehicle that is craned down automatically from the BFR (no mean feat I would suggest) and tows or carries a (folded) landing pad to the desired location. Alternatively I guess a landing pad could be ejected from the BFR as it comes down to land...

Re propellant production failure I think the crew could last a couple of years to the next mission potentially. So maybe a medium risk of death.

GW Johnson wrote:

Louis, I'm surprised you have provided so many links to interpretations of Musk's presentation, but apparently you have not seen the presentation itself, posted on Spacex's website!
Musk himself says the vertical fin is less of an aerodynamic item and more of a landing leg. Between that comment and the illustrated tip pods on all 3 fins, how could these fins be anything but landing legs?
The video he shows (twice!!!) clearly shows a final retro-propulsive touchdown on the tips of 3 fins located about 120 degrees apart. For most of the entry trajectory, the two "bottom" fins are clocked only about 45 degrees away from the vertical fin. Musk says the hinge forces to move the fins like that are mega-newton class.
By the way, that simulation video is of an Earth landing, not a Mars landing. You can tell because of the long vertical fall dead broadside to the wind to the touchdown. That cannot happen that way in the thin air on Mars.
Those three fin tips provide a wider footprint relative to vehicle length than the previous four landing legs did in the 2017 presentation. Somebody at Spacex has understood something about the rough field instability problem. Not yet well enough, but better than it was.
As for unsurvivable risks, both the Mars entry and the Earth entry are single-point failure possibilities (with multiple ways to fail at each entry) with no way out. As is refilling propellants on Mars.
GW

Void · 2018-09-22 07:16:39

Just a couple of minutes available: (Titanium alloy equipment for the Moon and Mars & Magnetic SharkFin Drive for interplanetary travel).

The BFS now has a cargo ring at it's base. This suggests the possibility of dropping small robots to the surface to do scouting and maybe even move rocks and perhaps even more. Of course to do this you first must land a robot BFS to the Moon or Mars.

SpaceX/Elon Musk has discussed building landing pads remotely, but did not have the assurance yet that they knew how.

The SharkFin drive is certainly interesting, but to me puzzling. Don't understand quite a lot of it.

Therefore I cannot vouch for either, but will be watching.

I think the idea in the SharkFin drive, is an Aerogel Ship Body, which holds and thermally insulates some very special self cooling super conducting coils.

So, a couple of things to watch.

I know that your are a very rigid thinker which can be good or bad, depending on the moment and situation.

Above I have presented materials, make whatever you want of it or not. Don't ask me to vouch for it. Please no reptilian brain responses.

SpaceNut · 2018-09-22 08:34:40

Only 3 points to land on with what seems a flexed degree of angle will make for a very unstable ship setting on the lunar survice. The distance between the landing contact is also not going to be very large as they are out in the open for the entire flight from launch with a large pad needed for the landing that is unable to move out of the way.

GW Johnson · 2018-09-22 09:26:56

Tripod stance is less stable than quadruped stance, because the distance from the middle to the nearest edge of the outline is shorter. These fin tips are much further away from the centerline than the 4 landing legs were in the 2017 design iteration. So, it looks marginally more stable against overturn instability. However, I have no numbers to analyze.

I have noticed there are no inert weights or even propellant weights associated with this 2018 design iteration. However, those should be at least roughly comparable to the previous iteration. I looked at soil bearing loads when I reverse-engineered the 2017 design. That stuff is in one of the updates to the later-dated article I posted at "exrocketman". With something near 10 sq/m of pad area, soil bearing loads looked OK for desert hardpan, but NOT sand. Obstacles 1 m in size under a pad were a real risk of overturn; that should still be true. Same is true for unevenness in the ground contours.

They added a lot of fin mass while deleting landing leg mass. Net inerts probably went up, which is why payload went down by 50 tons. By the time the air loads analyses are completed for the entry sequences, inerts will probably rise some more. You'll very likely see yet another design iteration on this, I predict.

And, no, I don't think a probe could be sent ahead from the new aft cargo spaces. This design does not have the delta-vee capability to stop in orbit, or otherwise delay its entry, direct from the interplanetary trajectory. Even if it did have the capability to stop in Mars orbit, it would be stranded there, totally out of propellant.

Delta-vee to land is utter-theory-min 0.7 km/s, practical ~1 km/s. Delta vee to stop in Mars orbit from a min energy Hohmann transfer is 1.8 km/s, higher still from a faster trajectory. You're short by 0.8+ km/s delta vee, and that's fatal to all aboard.

Earth orbit departure delta-vee is 3.85-3.90 km/s for a min energy Hohmann transfer. 3.9 to depart, 1.0 to land. That's a required min 4.9 km/s delta-vee required of the BFS. Go play with the rocket equation yourselves (I already did). The mass ratio is just barely there at all. Remember, your payload, inert, and propellant mass fractions MUST sum to unity !!!! Propellant mass fraction is 1 - 1/MR where MR is the mass ratio.

GW

Last edited by GW Johnson (2018-09-22 09:39:35)

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#26 2018-09-17 16:01:03

Re: Space X News - lunar tourism and delayed BFR hop

#27 2018-09-17 18:32:39

Re: Space X News - lunar tourism and delayed BFR hop

#28 2018-09-17 19:13:42

Re: Space X News - lunar tourism and delayed BFR hop

#29 2018-09-17 19:41:53

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#30 2018-09-17 19:43:12

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#31 2018-09-17 21:01:37

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#32 2018-09-17 23:54:23

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#33 2018-09-18 16:52:22

Re: Space X News - lunar tourism and delayed BFR hop

#34 2018-09-19 06:13:34

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#35 2018-09-19 07:31:54

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#36 2018-09-19 10:24:03

Re: Space X News - lunar tourism and delayed BFR hop

#37 2018-09-19 13:38:39

Re: Space X News - lunar tourism and delayed BFR hop

#38 2018-09-19 15:24:45

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#39 2018-09-20 07:52:19

Re: Space X News - lunar tourism and delayed BFR hop

#40 2018-09-20 10:52:11

Re: Space X News - lunar tourism and delayed BFR hop

#41 2018-09-20 18:27:54

Re: Space X News - lunar tourism and delayed BFR hop

#42 2018-09-21 11:09:18

Re: Space X News - lunar tourism and delayed BFR hop

#43 2018-09-21 11:50:20

Re: Space X News - lunar tourism and delayed BFR hop

#44 2018-09-21 15:59:42

Re: Space X News - lunar tourism and delayed BFR hop

#45 2018-09-21 18:56:09

Re: Space X News - lunar tourism and delayed BFR hop

#46 2018-09-21 19:46:04

Re: Space X News - lunar tourism and delayed BFR hop

#47 2018-09-22 03:49:01

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#48 2018-09-22 07:16:39

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#49 2018-09-22 08:34:40

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#50 2018-09-22 09:26:56

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