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#26 2018-04-29 17:10:54

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,720

Re: Space X forging ahead with BFR

GW Johnson wrote:

Louis is putting words in my mouth that I didn't say.  I reverse-engineered the performance of the 2017 presentation's 9 m diameter BFS/BFR two-stage vehicle,  and posted those results over at my "exrocketman" site.  The numbers are there for all to see.

Apologies if that was what I was doing.  I appreciated your presentation on your website.   I can see how a theoretical analysis could end up with the v. high G entry figure...but I simply can't accept Space X are unaware of this issue...and that leads me to look at heat shielding, orbital capture and braking burns and ask "Is there really no way to slow down?"

GW Johnson wrote:

Those results for the return voyage at the max stated 50 ton return payload start from a fully-fueled BFS leaving Mars with all 1100 tons of propellant on board.  My best estimates say they need to reserve something like 60 tons of that propellant to cover boiloff losses,  a small midcouse manever,  and the final retropropulsive landing on Earth. 

Almost all of the rest is required to leave Mars on a min-energy Hohmann transfer.  I show a reserve delta-vee capability beyond that burn,  without touching the 60 ton reserve,  of only 1.6 km/s.  Compare that to around 7+ to leave Mars on a min-energy transfer trajectory.  You can come home faster than 8.5 months,  but not so very much faster.  Not so much at all.

There is no other propellant on board.  Period.  End of issue.

Well not just "end of issue". End of mission...

And that's what I can't accept.  I can't accept Musk is that dumb.

GW Johnson wrote:

Now,  if they save that 1.6 km/s capability and use it for a braking burn right before Earth entry,  then they fly the Hohmann min-energy trajectory home from Mars (the full 8.5 months!).  Under favorable orbital conditions,  entry speed would be 13 km/s or a little more.  If you brake right before entry,  that slows you to 11 or 12 km/s at entry,  roughly. 

Apollo came back from the moon at 11 km/s,  and experienced 11 gees doing so.  It was a capsule,  BFS is a lifting body craft,  not the same.  But it really is in the same class of gees.  Something like 11+ gees.  Higher,  if you choose a higher energy trajectory and hit Earth's air closer to 17 km/s. 

There IS NO WAY AROUND THAT!  If you shallow-out to lower peak gees,  you bounce off the atmosphere like a skipped stone,  at speeds above escape.  Dead crew lost in space!

You are looking at around (as a minimum) peak 11-12 gees imposed for a minute or so on a crew after suffering at the very least the medical damage of 8.5 months exposure to 0-gee.  That presumes Mars 0.38 gee is fully therapeutic,  and we don't know that,  yet.  Any way else you might slice it,  you are looking at high-gee stress on significantly-weakened hearts. 

Or,  I hope they think of sending BFS's home 2 at a time,  and providing spin gravity closer to 1 gee than 0.38 gee,  by docking tail-to-tail,  and spinning the pair up at 4 to 4.6 rpm.

If you cannot change the flight dynamics (and you cannot !!!),  then change the health (or lack thereof).

GW

I'll keep searching for more detail on the return journey. I haven't found much yet. But I have seen stray comments suggesting that not even a full tank is required for the return journey to Earth...


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#27 2018-04-29 18:46:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,522

Re: Space X forging ahead with BFR

That is because we did the moon 40 plus years ago and that was the only time we saw those velocities.

A bfr full tank is not the 150 tonnes of refueled earth orbit.

The full tank at mars is so that we can have the reserved fuel not used for mars escape velocity such that we can brake into earth orbit... Mass * acceleration equation...laws of momentum....

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#28 2018-04-30 04:00:28

elderflower
Member
Registered: 2016-06-19
Posts: 856

Re: Space X forging ahead with BFR

Would you say that 25 people  would be rotated out in the early days in one ship? That sounds more like emergency evacuation of the entire expedition in the early days. I don't expect normal returns to be direct entry to Earth atmosphere, so payload will have to be restricted to allow for a braking burn on arrival.
I would also expect that a bit later, when large return payloads are required, there would be a tanker in Mars orbit to top up the returning ship, as is to be done at Earth. Later still there will be new and upgraded vehicles.

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#29 2018-04-30 05:25:50

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,720

Re: Space X forging ahead with BFR

My guess would be 6 people for Mission One. The consensus here seems to be it will be well under 10.  For Mission Two you might go to 10. I doubt you'd be going over 20 before Mission Three.  Things might hot up after that, as more and more research teams come on board!

elderflower wrote:

Would you say that 25 people  would be rotated out in the early days in one ship? That sounds more like emergency evacuation of the entire expedition in the early days. I don't expect normal returns to be direct entry to Earth atmosphere, so payload will have to be restricted to allow for a braking burn on arrival.
I would also expect that a bit later, when large return payloads are required, there would be a tanker in Mars orbit to top up the returning ship, as is to be done at Earth. Later still there will be new and upgraded vehicles.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#30 2018-04-30 09:28:47

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,474

Re: Space X forging ahead with BFR

Regarding crew size and breakdown would be an excellent new topic which I may start. I was always very skeptical about the solo, 3 man, 4 man crews suggested for minimalist missions, vis a vis Mars Direct. An important underlying concept over and above "just getting there and back," is the overall workload on the selected individuals. It's one thing to sit here at home and plan the work sol for all these crew, and an entirely different thing to be called upon to perform everything the mission control geeks want done. NASA was probably correct with their desired 7 man crew being the smallest optimal number.

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#31 2018-04-30 10:25:24

GW Johnson
Member
From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,151
Website

Re: Space X forging ahead with BFR

My Mars Mission 2016 posted on "exrocketman" posits a 6 man crew organized into two complementary crews of 3.  The odd number aids decision-making and the use of a team leader,  as Oldfart1939 has pointed out.  I just envisioned two such 3 man crews,  one on the surface,  being watched-over by the other in low Mars orbit.  They alternate roles during the stay at Mars.

My mission plan could do this,  because it is very different from Zubrin's Mars Direct,  and from Musk's BFR/BFS plan.  I base from low Mars orbit,  using rendezvous to dock with previously sent supplies and equipment from Earth. The equipment includes reusable one-stage landers that use retropropulsion to touch down after the hypersonics,  much like Musk.  But the similarity ends there.

My mission plan uses an orbit-to-orbit transport with baton-style spin gravity,  and it spins while in Mars orbit,  too.  Excepting short durations during burns and docking activities,  the crew on board it always has access to up-to-1-gee spin gravity.  The crew on the surface is exposed to 0.38 gee,  but they alternate,  so it is not for the whole 13 months at Mars. This is very much like the Mars mission proposals of the 1950's,  except I updated the propulsion.  The men travel by impulsive rocket burns.  The pre-positioned supplies and equipment get sent there "slowboat" by ion thrusters.

My plan intends to recover the transport in Earth orbit for refit and reuse.  There is an emergency direct-entry bailout,  but the crew is fully fit to endure it.  Because of the spin gravity.

Uniquely,  my mission plan allows for the exploration and evaluation of multiple sites on Mars.  No other mission plan since the 1950's allows that option.  Not Mars Direct,  not Musk.  Not NASA.  Nobody.  And I rough-guessed the cost at ~ $50 billion,  not half a $trillion.

GW

Last edited by GW Johnson (2018-04-30 10:28:42)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#32 2018-06-08 16:49:11

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Have you queried for "Elon Musk, Running Ring lately?"

https://www.cnet.com/news/elon-musk-hin … -inspired/

http://fortune.com/2018/06/08/elon-musk … ing-track/

Quote:

Elon Musk Says SpaceX Spaceship Will Have Running Track Inspired by '2001: A Space Odyssey.

So, maybe that's how people stay a bit fitter on the trip to Mars and back.

......

And then for shortening the time, of travel, and adding safety there is this:
http://newmars.com/forums/viewtopic.php?id=8247&p=5
My post #106 which apparently gets invisible if I think it is something important to say.
Quote me:

Without ignoring you Louis or RobertDyke,
Kbd512,
The idea of using better propulsion is indeed sensible.  Perhaps electric propulsion to send a propulsive depot storage device to a location desired.
But for now I am going to work with the items that SpaceX apparently intends to produce, and also perhaps borrow from Vulcan.
1) BFR.  As far as I can tell this will be a relatively standardized device, but I would expect it to receive upgrades for some time.  It will likely become larger and more efficient.
2) BFS(s).  This will be a plurality of specialized versions, which you have listed in a prior post.
3) A device called a "Depot", which has not otherwise been technically specified.
I will make a suggestion.  While it could just be some tankage built in orbit, orbital construction is troublesome.  Better to stay simple.
Why not make it a daisy chain of BFS(s). 
This version would have removable engines which could be brought down to the Earths surface in the cargo bay of another BFS.  Or the engines could be stored in orbit.
The Depot BFS(s) could be daisy chained together.
And a Cargo or Passenger BFS could couple to such a daisy chained depot assembly of depot BFS(s) like a tug with barges on a river.
https://www.bing.com/images/search?q=ri … &FORM=IGRE
https://en.wikipedia.org/wiki/Barge
......
As for the Depot BFS(s) they might have a heat shield so that the engines could be reconnected at some point so it could land (It might only need one engine?).
Or it could be throw away without a heat shield.  Probably throw away if going to Mars, but then maybe not necessarily.  Perhaps some of them would return to Earth depending on how your mission propulsion was scripted.
Going to some other place where you are not going to do an aeroburn on arrival, then have the type you want.
......
Another possible option is to have the Depot BFS(s) have one landing engine, escort the Mars bound BFS to a high Earth orbit, and then they would disconnect, and return to Earth, or Earth orbit.
It is like Lego's very flexible.
And then indeed throw in other methods of propulsion, and you might really get things done.

But if history holds you guys will keep acting like it has not been mentioned.

Done.

Last edited by Void (2018-06-09 09:23:01)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#33 2018-06-08 21:15:12

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,522

Re: Space X forging ahead with BFR

I like the 2 groups of 3 as it makes each rocket and landers smaller but does rise the cost for the mission.
Gw could we use gyro's instead of fuels to make a rotating station for gravity as the ISS does use these for course changes saving on fuel...

Void the 2001 space running track will not produce enough gravity for man as he can not run fast enough to get the rotation speed.
4 rpm at a diameter of 56 m means = 176 meters x 4 revolutions in 60 seconds...or a running covered distance of 12 m per second or 26.8 Miles per Hour...

Fuel depot in open space are not catchable without expending fuel moving or not as you are trying to match conditions to be able to link up to the rocket. Having the depot try to catch via ion drive time might be a better chance to working. They work best in orbits only due to orbital timing as to match speed is a bit more easy with less fuel useage to catch or slow down.

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#34 2018-06-09 09:01:07

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Alright Spacenut.  I have respect for GW and O.F.  Within the constraints of a BFS passenger ship without additional resources, I have seen expressed concerns about crew health, and transit time, and lack of fuel for retro-propulsive entry to Mars.  I believe G.W. as long as the story stays inside of that "Box".  The box being that you have a singular BFS passenger ship put into transit to Mars without a running track and without additional assistance/resources.

I agree with O.F. that up to a point we have to go with the descriptions of BFR/BFS that have been supplied by SpaceX/Elon Musk/Gwynne Shotwell/ and others.  We can do a bit of speculation of Alternative BFR(s)/BFS(s).  But need to be careful to not presume too much beyond what is provided by the entities who are associated with BFR/BFS.

Spacenut, I feel that you replied to my material in a slanted way, in order to put them into the worst light possible.  In fact in you did a good/bad assessment on the running track.  Otherwise you ignored the true material I presented on additional assistive material goods, (Depots/External Tanks), and substituted the notion of in flight intercepts of Depots.

In fact in flight intercepts are possible and useful, at least in the case of LEO, and technically for a Martian Orbit Depot, which might be accessed for a return to Earth.  As I have stated previously, I don't currently expect BFS to utilize a Martian Orbit Depot.  It would however take some of the pressure off of the notion of sending a bunch of BFS(s) to the Martian surface and creating enough fuel/Oxygen for a return trip of 2 to 4 of them.  Instead you would only have to get enough fuel/Oxygen to get to the Martian Orbit Depot.

Spacenut said:

Void the 2001 space running track will not produce enough gravity for man as he can not run fast enough to get the rotation speed.
4 rpm at a diameter of 56 m means = 176 meters x 4 revolutions in 60 seconds...or a running covered distance of 12 m per second or 26.8 Miles per Hour...

I had said:

Quote:
Elon Musk Says SpaceX Spaceship Will Have Running Track Inspired by '2001: A Space Odyssey.
So, maybe that's how people stay a bit fitter on the trip to Mars and back.

Which still stands as absolutely correct.

I reported what supposedly Elon Musk tweeted.  Typically his tweets have some basis in truth, but are often mixed with humor.  For instance the Boring Company.

If they/he are contemplating a running track for BFS, then it can be stated that: So, maybe that's how people stay a bit fitter on the trip to Mars and back.

It is a matter of degrees.  Not a binary go/no go situation.  Some exercise is better than none, almost always.  I really hate the methods often used on this site against early presentations.  An early idea is often rough, and needs work.  Here ideas are given a go/no go test, and usually thrown out without a struggle.  It is very, very important to struggle to bring them to fullness.  Early dismissal is a moral crime.

I can think of at least 5 ways to enhance the running track, to make it more useful.  Some of them are more mass/cost expensive, some less.  I don't intend to speak for Elon Musk.  He can show us what he has in mind.

Spacenut said:

Fuel depot in open space are not catchable without expending fuel moving or not as you are trying to match conditions to be able to link up to the rocket. Having the depot try to catch via ion drive time might be a better chance to working. They work best in orbits only due to orbital timing as to match speed is a bit more easy with less fuel useage to catch or slow down.

Although perhaps you did not intend to, you have papered over my point #3, with something which comes from another discussion elsewhere and elsewhen.  It is one where you have claimed victory, but most likely you are not entirely correct.

Here is what I said in my point #3, most of which you did not reply to, and which has been obscured by you incorrect follow-up:
Quote:

3) A device called a "Depot", which has not otherwise been technically specified.
I will make a suggestion.  While it could just be some tankage built in orbit, orbital construction is troublesome.  Better to stay simple.
Why not make it a daisy chain of BFS(s). 
This version would have removable engines which could be brought down to the Earths surface in the cargo bay of another BFS.  Or the engines could be stored in orbit.
The Depot BFS(s) could be daisy chained together.
And a Cargo or Passenger BFS could couple to such a daisy chained depot assembly of depot BFS(s) like a tug with barges on a river.
https://en.wikipedia.org/wiki/Barge
As for the Depot BFS(s) they might have a heat shield so that the engines could be reconnected at some point so it could land (It might only need one engine?).
Or it could be throw away without a heat shield.  Probably throw away if going to Mars, but then maybe not necessarily.  Perhaps some of them would return to Earth depending on how your mission propulsion was scripted.
Going to some other place where you are not going to do an aeroburn on arrival, then have the type you want.
......
Another possible option is to have the Depot BFS(s) have one landing engine, escort the Mars bound BFS to a high Earth orbit, and then they would disconnect, and return to Earth, or Earth orbit.
It is like Lego's very flexible.
And then indeed throw in other methods of propulsion, and you might really get things done.

OK the above reference material provides both for using an assistive BFS, most likely a filled tanker to push a Passenger or Cargo BFS towards Mars.  The assistant serves as a orbital based booster.  It is either discarded into space or more likely recycled back to Earth after it has boosted the Passenger or Cargo BFS.

The other notion is using a Propellant/Materials Depot as an external tank for a Passenger or Cargo BFS.  That is it would come along all the way to near Mars or Mars itself.

And yes using ballistic capture, it might be possible to implant a Refueling BFS into Martian orbit prior to a landed mission.  That orbital tanker to help boost a Re-launched to orbit BFS.

In all of the above, I have relatively stuck to O.F.'s idea that we should not stray too far from technology which we have some assurance will be available within the next 5-15 years.

......

So, while I agree with GW that he knows what he is talking about in the case of an unassisted flight of a BFS to Mars from Earth, I assert that using components that are likely to exist within 5-15 years, it will be possible to offer assisted flights of BFS's to Mars from Earth.

That assistance availability takes us out of the box.  We are no longer constrained by the absolute limits of the contents of a single BFS on it's own.  And some physical therapy may occur using a running track (With 5 or more possible upgrades).

Unpaperedoverthen.


Done.

Last edited by Void (2018-06-09 09:33:39)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#35 2018-06-09 13:53:51

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,522

Re: Space X forging ahead with BFR

We already know that exercise in 0 g not rotating effects from the ISS but a BFR is not rotating so you are in free float no running is possible on a fixed internal track or treadmill. The track must move in a counter rotation as a treadmill does to create gravity based on movement on the person ruinning on a track with some means to stick the person to the track for it to work if the ship is not rotating. A track for the rotating ship would spin counter rotating to that of the ship for a person to stand on the track and then you would be able to walk or run without a means to pull you to the track as that force would be less.

Trying to combine Depots/External Tanks not going to work as its one or the other....in that a depot is a refuelable station keeping capable of having multiple tanks with a connecting port for a connection to couple the BFR for refueling transfer from those tanks. The unit would be refuelable for continued use.

External tank but smaller:
Space_Shuttle_fueltank_freefall.jpg

Bfr would require a means to bring up external tanks to the awaiting BFR which will require a new second stage that would be expendable. The second stage bfr with external tank would eject from the rest of the stage once the tank is attached to the bfr crewed as its dead weigh mass and the tank plus fuel connections to the connection points on the side of the crewed BFR would need to be added into a design that does not have them. External tanks are a use once and dispose as you would be carring dead weight mass once empty.

Final configuration with all the external tanks connected would look something like this:
Sprite_Microcosm.jpg

We are already at 5-6 bfr 150 t fuel launches just for a single bfr second stage to go to mars to be refueled. So are you thinking that we would add on that many more launches to provide that much more fuel to a single crewed bfr for what purpose?

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#36 2018-06-09 18:45:43

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Well thanks for the replies Spacenut. Really, you could have ignored me or just said I was stupid (Without so much verbage is you did in fact use) smile

I will very carefully return the favor: smile

Quote the Spacenut:

We already know that exercise in 0 g not rotating effects from the ISS but a BFR is not rotating so you are in free float no running is possible on a fixed internal track or treadmill. The track must move in a counter rotation as a treadmill does to create gravity based on movement on the person ruinning on a track with some means to stick the person to the track for it to work if the ship is not rotating. A track for the rotating ship would spin counter rotating to that of the ship for a person to stand on the track and then you would be able to walk or run without a means to pull you to the track as that force would be less.

Not strictly true as evidenced in Skylab:
https://www.bing.com/videos/search?q=ru … &FORM=VIRE

I am not going to imply that the benefits will be that much above "0", but it will be better than nothing.  For instance psychologically at least it may help a restless crew.  Further indeed if you exercise the muscles, you may shred some muscle, and that is an important process for maintaining muscle.  Similarly, if you do impact the bones, you may help them in not loosing as much mass.

Again, due to the above:
Quote:

Elon Musk Says SpaceX Spaceship Will Have Running Track Inspired by '2001: A Space Odyssey.
So, maybe that's how people stay a bit fitter on the trip to Mars and back.

Which still stands as absolutely correct. 

Note: "A bit" is not an actual unit of measure. However I interpret it to be >0 benefit.

I don't want to assume that I can see into Elon Musk's head.  However if it were me, I would spin the BFS to poopdeck speed.  (Sanitation Gravitation.  That is just me.  I want turds to drop into the bucket along with urine and tissues I have used to blow my nose.  I especially want other peoples items to go into such buckets as well.  Poopdeck synthetic gravitation would be that below nausea gravitation for the crew on the first flights, and a lesser value for the passengers on later flights.

So, now we have some small fraction of a 'g'.  We also can run in the track, even better.

For silliness we might ride bikes to get to a higher speed.  However if a crowd did that I would expect disaster sooner or later.  Also bikes may not stress the leg bones as well.

So, now I recommend that we ride our bikes on the ceiling smile  No actually modify them so that they do roll on the ceiling, but also include spring or pneumatic loaded downward compression on the body as the person runs.  This then pushing the person to the floor.  AI may be utilized with visual and other sensory capabilities to jack hammer the human body below appropriately to provide bone stresses.

Further, we might have bouncy magnetic shoes.  That is magnetic shoes, with bouncy pads under the magnets.  This may help.  Add in some elastic bands on legs, back, neck, and arms.

As for such things as blood pooling and eye damage, and immune system problems, I don't think this will help that much.  Maybe it would help a bit for the immune system, human spirits being uplifted.  Maybe it would help with the blood pooling.  It is possible that the body can regulate against the blood pooling for some value of synthetic gravity > 0 g.  Don't know yet.  Perhaps if the blood pooling is handled even with low g, then the eye damage will not be as bad.

Don't know yet.

A base on the Moon might help us find out.  So would spinning a BFS in LEO.

But I did not want to try to invent for Elon Musk.  He and SpaceX may invent/speak for themselves.  I just wanted to show that there may be possibilities worth exploring.

......
......
......

Now my Spacenut, the other thing:

Need to do some research, get an item that Kbd512 provide elsewhere.  I don't remember where so I have to find it. 

I found it!  See post #91 from this link:

http://newmars.com/forums/viewtopic.php?id=8247&p=4

FYI:  Kbd512 is in no way culpable for my crimes here.

Quote:

BFR-OT (Orbital Tanker) Concept: 1-1) specifically designed to deliver propellant to an orbital propellant depot
(First Group of Attributes/Methods):
1-2) * small habitable section, larger propellant tanks
1-3) * intended primarily for lunar exploration
1-4) * second variant to be flown and tested

Lets call the BFS-OT, (I corrected the name), an object as in a type of programming language.  Lets suppose that items listed for it after the word concept are "Attributes" or "Methods" as in a OOP programming language.

I will now take the license to add more "Attributes/Methods" for the BFS-OT.
(Second Group of Attributes/Methods):
2-1) *Part Time Orbital Booster for other BFS(s)
2-2) *Part time Depot.
2-3) *Part time External Tank.
2-4) *Self directed Depot/External Tank.  (Capable of migration to other space locations).

Then to explain further.....

Since SpaceX intends to use Hohmann transfers with intervals of 26 months???   And not yet or perhaps ever Ballistic Captures, then the BFS-OT(s) will be employed (while not assisting a mission to Mars each 26 months), in the first group of "Attributes/Methods".

So, there should be a number of them that could be conscripted to Martian launch service about every 26 months.

At that time they would likely cease Lunar activities, and prepare to be temporarily redirected to one of the Second Group Attributes/Methods.

Some would specialize to one of the secondary Attributes/Methods in a manner of a honeypot ant:
https://en.wikipedia.org/wiki/Honeypot_ant

Some of them would retain the task of workers to bring propellants from the Earth and or Moon, to fill these "Honeypots".

So, 2-1 could boost any daisy chained assembly of BFS(s), helping that assembly on it's way to Mars.  Ideally the 2-1 would not be sacrificed, but could be re-used, probably by return to Earth.  It would not escape Earth's gravity during it's 2-1 activities.

2-2 could fill a Mars bound BFS of the Passenger or Cargo type before launch from LEO, Or a higher Earth Orbit).

2-3 could be attached to a Mars bound BFS of the Passenger or Cargo type before launch from LEO, or a higher Earth orbit.  It could ride along all the way to Mars.  Approaching Mars the two would detach and each do their own aeroburn.  Perhaps 2-3 would aeroburn to orbit, and be waiting for the landing ship to come back up later, and would then supply propellants to it for return to Earth.

2-4 could be pushed to Mars, or to a NEO, and would not have to wait for the 26 month window necessarily.  In the case of Mars it could use a ballistic capture with possible aerocapture assist to achieve Martian orbit.  There it would wait to be of service.

A NEO of course would not have the 26 month window.

......

Per O.F. I have not included the further complications that using electric and other propulsive devices may add to the total system capabilities.

However I assert that the system capabilities are massive, with or without other propulsive capabilities.

......

Now you are likely to have a conniption fit about costs.

http://www.wisegeek.org/what-is-a-conni … youknowout

But if BFR/BFS occurs there are likely to be three major phases.

1) Establishment of a base with insitu capabilities.
2) Early rugged settlers.
3) Later common type settlers.

For #1, the options I have provided seem wise to me, as cost will be much less of a consideration.  Achievement within cost constraints will matter however.  Still you will not be trying to make a buck on transferring passengers.

This is much like digging a train tunnel through a mountain.  You are not going to make money on train tickets until you have the tunnel built.  Therefor you have to expect to expend capitol in order to dig the tunnel, and do that without procuring a profit.

For #2, then you would be getting special strong and adventurous types.  There will be some, but they will be a small percentage of Earths population.  During #2, you may get rid of the "HoneyPot" methods to save costs, as you will have established a refueling station on Mars.

For #3, you will have artificial gravity devices in orbit of both Earth and Mars.  I anticipate that the passenger ships will be enormous and will not land on either world as a rule.  They will likely have good radiation shielding, and synthetic gravity, and may then use Ballistic Capture instead of Hohmann Transfers.

......

That's quite a lot.  I look forward to a response.

Done.

Last edited by Void (2018-06-09 20:00:13)


I like people who criticize angels dancing on a pinhead.  I also like it when angels dance on my pinhead.

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#37 2018-06-09 20:21:23

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 12,522

Re: Space X forging ahead with BFR

I would not do that as that is not how we learn.

Thanks as I had not seen or remembered the skylab as having an area to do that in.

lossy-page1-556px-SkyLab_Isometric_2.tiff.jpg

or this black and white
sk003.gif

Nasa astronauts performing gymnastics on board the skylab

Still zero g for forces which makes it still the ISS level of exercise for health even running or exercise bikes or any other level of intense methods implemented to keep man in better condition.

I also agree that an acronym table for all the flavors of the BFR / BFS is something that we are going to need to help keep the features straight as it is quite confusing at times..

list of whats what as provided....

kbd512 wrote:

BFR-OC (Orbital Cargo) Concept: specifically designed to deliver cargo (spacecraft) to orbit
* small habitable section, unpressurized cargo bay
* intended primarily to deliver satellites or other spacecraft components
* first variant to be flown and tested

BFR-OT (Orbital Tanker) Concept: specifically designed to deliver propellant to an orbital propellant depot
* small habitable section, larger propellant tanks
* intended primarily for lunar exploration
* second variant to be flown and tested

BFR-MC (Mars Cargo) Concept: delivers heavy cargo (LOX/LH2 plants, PV arrays, robots, materials, etc) to Mars
* BFR-MC is just an internally reconfigured BFR-MP (has life support, but no seats or very few seats, just cargo space)
* Stays on Mars and continues to fetch heavy cargo from LMO
* third variant to be flown and tested

BFR-MP (Mars Passenger): delivers humans and light cargo (consumables) from the ITV to Mars
* Stays on Mars and continues to fetch people and consumables from LMO (has seats and personal living quarters)
* fourth variant to be flown and tested

ITV-P (Passenger): long duration deep space habitation
* beefed up for durability, redundancy, and protection
* first variant to be flown and tested

ITV-C (Cargo): long duration deep space cargo delivery
* ITV-C is just the engineering section of ITV-P and does not provide artificial gravity
* second variant to be flown and tested

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#38 2018-06-10 14:12:33

kbd512
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Registered: 2015-01-02
Posts: 1,911

Re: Space X forging ahead with BFR

Void,

I'll make an attempt at a feasible variation on your concept using BFS.

BFS-OPD = BFS Orbital Propellant Depot

Operational Considerations:
* composite construction to "spaghettify" tanks ruptured by overpressure
* delivered to an orbit below ISS to reduce the risk of an explosion damaging other spacecraft
* reentry heating intended to cause bursting from tank overpressure to assure tank disintegration
* limited use of metals to limit mass of debris fragments during reentry
Note:
1. OPD is designed to protect itself from approaching BFS, thereby protecting approaching BFS
2. approaching BFS fly under OPD, much like cargo carrying vehicles approaching ISS
3. OPD and BFS avionics use bi-directional communications and master/slave relationship to properly phase the orbits and precisely align both vehicles during approach and propellant transfer, with OPD acting as master
4. OPD automated approach system overrides BFS attitude control systems input to maintain minimum separation distance and manipulate closure rates as BFS overtakes the OPD, whereupon OPD's onboard gyro accomplishes precision alignment for the terminal phase of the approach and refueling probe mating in preparation for propellant transfer
5. an array of radar level gauges mounted to the tops of the tanks in the inter-tank area must create a surface image of the propellant levels to accurately determine fill volume, thus available propellant mass

Tankage:
* BFS upper stage diameter, but lengthened propellant tanks
* no common bulkhead between tanks to inhibit thermal energy transfer between oxidizer and fuel and provide a space for the refueling probes and radar level gauges
* built to same structural standard as BFR booster for improved durability
* no components or design features related to habitation, cargo, or header tanks for landings
* tanks lined inside and out with 100nm thick Reduced Graphene Oxide bi-layer to eliminate cryogen permeation through composite structure
* MLI insulation to minimize thermal radiation absorption induced boil-off
Notes:
1. thermal radiation absorption from conduction dominates in an atmosphere with significant pressure, but whereas vacuum jackets and aerogel bead insulation were determined to be most effective on Earth to inhibit conduction, they provide less heat rejection in the vacuum of space than MLI, where thermal radiation absorption from the Sun or reflection of the same from Earth dominates

Tanking Operations Mission Equipment:
* Multiple separate (3 oxidizer, 3 fuel) USAF style refueling probes for cryogen transfer to eliminate dead mass on other BFS variants and provide redundancy in the event that probes are damaged during operations
* refueling probes located between the two tanks to minimize piping and insulation
* Tank pressurization / depressurization for propellant dispensing provided by IVF, no goofball propellant settling maneuvers
* refueling probes protected from orbital debris by spring loaded hose doors
* pressure driven probe extension / retraction of flexible refueling probes using Thoraeus shape memory metal rubber to prevent damage to visiting BFS from probe collision
* keyed probe valve with PolyMagnets permanent magnet locking/unlocking cam surface ring to make dispensing of propellants without a solid seating impossible
Notes:
1. pushing on the probe once the nozzle is completely seated in the keyed receptacle to initial flow
2. pulling away closes the valve before the nozzle seal disengages
3. merely pushing on the tip of the probe does nothing because the magnetic cam surfaces can only engage when the nozzle is in the receiving BFS receptacle
4. go to the PolyMagnets website for more information about how this works

Depot Operations Support Equipment:
* IVF for vehicle electrical power, tank pressurization / depressurization, and gross attitude control
* gyro for fine attitude control

BFS Standard Design Equipment Alterations:
* ULA's IVF provides power, propellant pressurization / de-pressurization, and attitude control
* no heat shield for atmospheric reentry
* no delta wings for atmospheric reentry
* no header tanks for vertical landings
* no provisions for habitation or cargo storage
* ULA Vulcan first stage detachable engines with HIAD or PICA heat shield for returning the engines to Earth

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#39 2018-06-10 17:48:42

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 12,522

Re: Space X forging ahead with BFR

2006 article Orbiting gas stations key to interplanetary exploration

dn9259-2_600.jpg

safer refueling drop to target vehicle
dn9259-3_625.jpg


If we use hydrogen and oxygen they must be kept very cold, -253°C and -183°C respectively, to remain in their liquid state. While space is cold, the Sun is a powerful source of radiant heat, so any space-based gas station would have to be insulated and have solar-powered coolers to maintain the ultra-low temperatures.

NASA is trying to spur industry to develop such a fuel depot with the Fuel Depot Demonstration Challenge, one of NASA’s Centennial Challenges.
The $5 million will go to the first team to build, launch and test a model of a liquid hydrogen and liquid oxygen storage or production depot in Earth orbit. According to the draft rules, the tanks must be launched into low-Earth orbit and hold at least 20 kilograms of liquid hydrogen and 120 kilograms of liquid oxygen for 120 days. The deadline is 2012.

I guess this one was never completed....

THERMAL EXAMINATION OF AN ORBITING CRYOGENIC FUEL DEPOT

Technology Requirements for an Orbiting - Fuel Depot-A Necessary Element of a Space Infrastructure

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#40 2018-06-10 18:02:17

Void
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Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Yes I like both posts Kbd512 and Spacenut.

However they go quite further than I anticipated.  That is, as I see it if SpaceX makes all of the versions of BFS that Kbd512 mentioned, then the tanker:  (With some modifications of use I added), would be usable with little alteration for all the Attributes/Methods.

BFR-OT (Orbital Tanker) Concept: 1-1) specifically designed to deliver propellant to an orbital propellant depot
(First Group of Attributes/Methods):
1-2) * small habitable section, larger propellant tanks
1-3) * intended primarily for lunar exploration
1-4) * second variant to be flown and tested
Lets call the BFS-OT, (I corrected the name), an object as in a type of programming language.  Lets suppose that items listed for it after the word concept are "Attributes" or "Methods" as in a OOP programming language.
I will now take the license to add more "Attributes/Methods" for the BFS-OT.
(Second Group of Attributes/Methods):
2-1) *Part Time Orbital Booster for other BFS(s)
2-2) *Part time Depot.
2-3) *Part time External Tank.
2-4) *Self directed Depot/External Tank.  (Capable of migration to other space locations).

It would however make sense to be able to temporarily remove some of the engines in orbit if convenient for some of the "2" series, 2-3 and 2-4 in particular.

Of the "2" series Attributes/Methods, I see 2-1 as being by far the most important.

Where a tanker from Earth surface to LEO would be partially emptied, it could be topped off by another tanker, and then it could serve as a booster from LEO to High Earth Orbit, pushing a Crewed BFS to HEO for it's launch from HEO to Mars.  Therefore giving the Crewed BFS extra resources.

I have been concerned about GW's depiction of the BFS having too little resources for a rapid trip to Mars and also for a powered landing.
I want to quicken the trip if possible and allow for a powered landing with less aeroburn stress on the crew.

I also mentioned the running track because if it can keep the crew just a little more fit, then that of course is a good thing.

But indeed a Depot is also a desire.


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#41 2018-06-12 20:53:08

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Well, out of boredom, I have been doing queries for "BFS Tanker".  I have encountered some good stuff I feel.  Some of it about 9 months old or less +/-???.

I am euphoric about it!

Here is an example:
https://www.reddit.com/r/spacex/comment … e_onorbit/

In the various readings I have done, I have seen reference to the tanker being able to serve as a Depot.  So that is solid.

And if you have a Full Depot with rocket engines, you have a potential orbital booster to assist Cargo and Passenger BF Space Ships on their way to their destination, Mars or not.

And if you have a Full Depot with rocket engines, and it could be a orbital booster, one of them could be taken along with a passenger BFS, providing additional resources, and of course redundant propulsion options (Think Apollo 13).

And if you have a Full Depot with rocket engines, and full AI automation, you may send it to Mars alone, to await a launch from Mars of a BFS which could use propulsion assistance.  For BFS Cargo and also Tanker, there is no reason not to contemplate a Ballistic capture method.  In fact that may be the best if you intend to put a BFS tanker into Martian orbit.  Ballistic Capture allows much more flexibility on launch windows from Earth to Mars, as I understand.

And the articles I queried indicated that the BFS Cargo would look weird, whatever that means.  Some of the thinking indicates that SpaceX could go into the orbital refueling business for other entities.  And not just Methane.

......

Now to deviate a bit.....

I have wondered what engines you need on such a tanker, if it is not to very often land on Earth or Mars?  But maybe you would land it on Earth over long periods for servicing.  But what engines do you need to land?  To take off you need the full boat of engines.

So, looking at ULA's Vulcan:
http://www.businessinsider.com/how-vulc … reusable-9

I like it.  It has a refueling capability for it's orbital component.  So, great idea.  They also discard the tanks for the 1st stage booster, but save the engines and avionics I believe.

So, a different approach to the 1st stage.  Maybe parallel evolution in orbital processes such as refueling and depots, ect.

I really hope they can find a niche market for their process.

......

But now I am wondering about the BFS Tanker (Versions).  In some cases perhaps they will not need to land on Earth until after for several deployments of the device have been completed.  And I wonder if they do need to land, could they get by with just the one or two landing engines, or at least less of the big raptor engines?  This would reduce inertial mass of course if you could eliminate unneeded engines and other parts while the BFS Tanker Derivatives were in service in a vacuum environment.

This probably implies a space station with synthetic gravity, where such maintenance/modifications could be done.  Would the removed parts be stored there, or would a cargo BFS bring them down to Earth in their presumably mostly empty cargo bays?

Yes, I am jumping the gun a bit.  All this would take time.  But I think something like that might come.

......

And I am thinking about Elon Musk's hinted at "Running Track". 

I am thinking that with or without artificial gravity, it might be very good to look into some type of trolley system anchored into an electric track in the ceiling of the running track.

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

(Not a bus on a BFS!)

So a trolley robot anchored into a electric track above the human.  A frame/harness holding the human, the human running, the trolley machine keeping pace.  Of course it would involve a perceptive A.I., to do so.

So, in addition to the trolley machine pushing a human against the floor, it would not do so at a steady pace, but perhaps might do periodic (Mostly vertical) pushes, timed to simulate running in a gravitational field.  Simulated as best as is possible.

Alternately perhaps the runner will be able to operate controls somehow, regulating the pace, and the intensity of downward pushes.

Of course the intention being to stimulate the cardio-vascular system, stimulate bone growth, and perhaps tone the muscles.
For weight lifting (Resistance Training) some kind of robotic pushback system that simulates lifting weights?

*******************
Lets consider adding in electro-magnetic boots.  That to could be pulsed, while the push down from the trolley would simulate foot impacts, and perhaps spinal column stimulation, electromagnets could also make a contribution and could actually cause drag as the foot, leg was retracted upwards as in running.  This might simulate to a degree, moving your legs upward in a 1 g gravity field.  Necessary?  Well don't know.  Sounds good for the moment.
*******************

While there might be some spin generated synthetic gravity on the ship, I am thinking the device I describe above would be helpful with or without synthetic gravity.

So, I think that there may be some ways to overcome some of the problems of transit from Earth to "Elsewhere".
I hope so anyway.

Done.

Last edited by Void (2018-06-12 21:51:30)


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#42 2018-06-13 11:31:54

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

Continuing as a pestilence, and about the BFS tanker:
https://www.reddit.com/r/spacex/comment … post_from/

Quote: (This is a question I wanted answered)

Will the BFS landing propellants have to be actively cooled on the long trip to Mars?
The BFS has header tanks to store landing propellants.
When traveling to Mars they will have to be stored for months. Heat transfer slowly but surely rises the temperature of the tanks, eventually boiling off the propellants.
Will liquid methane and LOX have to be cooled - or is thermal insulation of the header tanks expected to be so good that no active cooling is required?
If cooling is required, what kind of system will the BFS use to manage the temperature of propellants in zero-gee?
The main tanks will be vented to vacuum, the outside of the ship is well insulated (primarily for reentry heating) and the nose of the ship will be pointed mostly towards the sun, so very little heat is expected to reach the header tanks. That said, the propellant can be cooled either with a small amount of evaporation. Down the road, we might add a cryocooler.
Isn't Methane capable of remaining as a liquid if it's pressurized?
Yes, but the pressure is extremely high. About 32 MPa/4600 psi, so the tank to hold that is way too heavy.
exactly

And there is a dark highlight on something I consider very important as well.  If the nose points to the sun most of the time, then can you spin the ship on it's long axis for some minimal synthetic gravity, and still have the solar panels deployed appropriately?  I think so.  The picture depictions of the solar panels had previously left me wondering, but the above verbal picture suggests that yes, solar power and spin, most of the time.

I really wonder about blood pooling in the body of a human in low g.  Is it proportional to the amount of g, or is there some minimum 'g' force that allows the body to cope with distributing body fluids per upper body <> lower body?

If it is proportional then that will be a persisting health problem even in the gravity field of Venus perhaps.  Putting people on the Moon, and/or spinning a BFR with a running track will tell much about the nature of that problem.

I certainly hope that the human body can balance fluids at low 'g'.

QUESTION 7
Will the BFS tanker's payload section be empty, or include extra propellant tanks?
You showed the BFS and the tanker in your slides at the 2017 AIC. In this CAD image the two ships have the exact same length and the exact same main tank layout.
It's not visible what's inside the tanker's payload section: will it be empty, or include extra propellant tanks?
At first, the tanker will just be a ship with no payload. Down the road, we will build a dedicated tanker that will have an extremely high full to empty mass ratio (warning: it will look kinda weird).

There is more to read about the tanker than this, but the above quote suggests that the tanker will start as a variant of a regular BFS, stripped down, and then will undergo evolutionary specialization.

I wonder if as part of the eventual specialization, it might make any sense for the BFS tanker to eject some of it's engines in it's assent flight, in a manner like that of Vulcan, to recover the engines expelled to the surface of Earth for eventual re-use.  Much more complex, but of course we are then talking about a very highly evolved BFS Tanker, eventually.

Certainly SpaceX is looking into recovering payload fairings from Falcon 9, so a similar technique perhaps.  Also there is the tweets about recovering the 2nd stage with a "Party Balloon and bouncy house", which suggests such methods to be learned by SpaceX, down the line.

This is an interesting question, but not well answered as far as I can see:
Quote:

QUESTION 12
Can the BFS delta wings and heat shield be removed for deep space missions?
In the BFS/2016 design the 'delta wings' were an integrated part of the main unibody BFS airframe.
The new BFS/2017 delta wings and heat shield appear to be additive components to the outer skin of the rocket.
Also, the BFS solar panels appear to be stored in the engine compartment close to the engines, not in the wings.
Was this (apparent) modularization done so that the delta wings and heat shield can be skipped during manufacturing, allowing lower dry mass expendable missions and deep space missions with no atmosphere at the destination - or are there other motivations as well?
Wouldn't call what BFS has a delta wing. It is quite small (and light) relative to the rest of the vehicle and is never actually used to generate lift in the way that an aircraft wing is used.
It's true purpose is to "balance out" the ship, ensuring that it doesn't enter engines first from orbit (that would be really bad), and provide pitch and yaw control during reentry.

......

About a BFS Tanker as a Depot:
https://www.reddit.com/r/SpaceXLounge/c … nevitable/
Quote:

Are BFR Fuel Depots Inevitable
Straight Orbital Refuelling
SpaceX have suggested orbital refuelling is an essential element of Mars colony flights using BFR. During his IAC Adelaide presentation Elon Musk suggested up to five BFS/tanker flights could be required to fully refuel Mars-bound spacecraft. This would seem a bottleneck for Mars flights because if you launch all the BFS/tankers on the same BFR booster it would need to be checked and prepped after each flight, which will inevitably take time. Additional BFR boosters/tankers could be launched from separate sites but that adds significant complexity and cost. In addition if any of the BFS/tanker flights fail to deliver on time it would significantly delay the Mars mission departure until a replacement tanker flight can be arranged. This would mean colonists sitting in orbit consuming food, water and life support, depleting resources which might otherwise prove vital for their long stay mission on Mars.
Orbital Propellant Depot
It has been suggested a dedicated BFR tanker will be produced later on, enabling more propellant to be shipped per flight, reducing the number of BFR refuelling flights required for each Mars mission. However, if a dedicated tanker could be placed in low Earth orbit, it could be used as an orbital propellant depot. Such a depot would enable outbound Mars flights to fully refuel with only one orbital rendezvous operation. This should minimise the time spent between launch and departure for Mars and minimise propellant boil off. In addition propellant stocks at the depot could be accumulated at a more leisurely and practical rate, in the many months prior to each Mars mission. It would seem wise to install a sunshield on any such fuel depot to minimise propellant boil off but this shouldn’t be a significant technical challenge compared to work already accomplished with BFR.

There is more to read such as a table.

......

Having all of that it would be insane to not consider the options of using Ballistic Capture, with or without aerocapture for missions to Mars and Venus, in the case of BFS ships that are not crewed.  In fact eventually if fitness can be maintained for the crew, and transit times can be favorable, perhaps even crewed missions may use Ballistic Capture and perhaps Aerocapture.
https://en.wikipedia.org/wiki/Ballistic_capture
Quote:

It is predicted to be
safer, as there is no time critical insertion burn,
can launch at almost any time, rather than having to wait for a narrow window of opportunity,
would be more fuel efficient for some missions.

I am not sure that the fuel savings apply only to Ion rockets.  Maybe
Ballistic capture probably does involve a flight time extension.  That would be a penalty of significance depending on the materials transferred, and if a crew can be physically protected for an extended period of time.
https://en.wikipedia.org/wiki/Aerocapture

For devices traveling from High Earth Orbit to LEO, would it be best to strip off the heat shield and other excess mass, or to do an Aerocapture? 

Done.

Last edited by Void (2018-06-13 12:15:47)


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#43 2018-06-13 19:24:48

Void
Member
Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

I guess I will finish my interest in this (I hope), by mentioning that if SpaceX can indeed bootstrap a startup of propellant production on Mars, and why not also the Moon, then there are still other items to think about.

Of course the Earths atmosphere might eventually be a source of propellants, but leaving that aside for now, there are:

Planetary Resources Company and Deep Space Industries.  Two asteroid mining companies.

https://www.planetaryresources.com/

https://deepspaceindustries.com/

Both for mining primarily NEA objects (Near Earth Asteroids).

The point being that they would fit very well with the BFR/BFS of SpaceX.

To begin with they could get rides and propulsive mass from SpaceX, and then if they do succeed in obtaining water, of course, then BFS tankers could move that to appropriate locations for use.

If you think I am over optimistic, I don't really think I am.  I estimate BFS of any kind in 10 years +/- 5 years.

Good chances I die before it gets into full swing.

Done.

Last edited by Void (2018-06-13 19:29:54)


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#44 2018-06-14 09:21:36

GW Johnson
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From: McGregor, Texas USA
Registered: 2011-12-04
Posts: 3,151
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Re: Space X forging ahead with BFR

Given the incompleteness of the information about BFR/BFS posted on Spacex's site,  I think pondering the details of variants of the design is really more debating angels on the head of a pin.  I did the best I could reverse engineering their design from their posted data,  and that scope included the crewed BFS,  with "best guesses" regarding the cargo and tanker versions.  That is posted over at my "exrocketman" site. 

This thing as a two-stage system makes a wonderful transport to low Earth orbit,  needing no refilling on orbit.  It can bring 150 tons per flight.  If the thing could be launched for an arbitrary guess of $250 M,  then that's $1.7M/metric ton delivered,  or $756/pound delivered.  That's even better than what is projected for Falcon-Heavy,  but not dramatically so. 

The beauty of the system is the reusable second stage.  It is inherently reusable because it was intended to be flown back and landed.  This is what the space shuttle was supposed to be,  but first attempts rarely ever pan out.  BFS has a better heat shield that is not so vulnerable to damage,  but does require replacement after "several" flights,  whatever that really means.  It cannot be dirt cheap,  as it is still among humankind's earlier attempts. 

With refilling,  that same second stage can go elsewhere in space:  the moon,  Mars,  etc.  It will get used for that until something better starts flying.  But the real point is,  it can do the missions.  The cost of refilling is inevitable for departure from LEO:  my best guess (based on the reverse engineering I did) was 6 tanker flights to put 1100 tons of propellant into one BFS to fly elsewhere. 

The thing seems capable of taking 150 tons to the moon,  and flying back to a free return landing at Earth without any refilling at the moon.  That would be with 50 tons or less payload on the return.  The delta-vee is just not there to stop in LEO instead of landing direct.  But refurbishment is easier on the surface instead of out in space.

The thing is capable of a one-way trip to Mars from LEO that terminates in a direct entry landing,  carrying up to 150 tons payload.  The delta-vee is just not there to capture into Mars orbit.  Like returning from the moon,  you must count on the aerobraking entry for much of your effective delta vee arriving at Mars.  It cannot return until you can refill it with 1100 tons of propellant made on Mars. 

There might be enough delta vee to support a 6 month trip outbound to Mars instead of the min-energy 8.5 months.  I think talking about 3-4 months is nonsense,  not at all possible carrying any significant payload,  much less 150 tons.  The mass ratio simply is not there.  I see little potential at all to shorten the homeward trip from the min-energy 8.5 months.  And that's with only 50 tons payload.

Don't forget,  any people on board,  plus all the supplies it takes to keep them alive,  are many tons of that payload!  You won't be flying one of these manned at zero payload. 

Decades later,  when better vehicles for deep space travel are flying,  the BFR/BFS will still be useful for launch to LEO. 

GW

Last edited by GW Johnson (2018-06-14 09:25:03)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#45 2018-06-14 18:02:18

Void
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Posts: 2,345

Re: Space X forging ahead with BFR

I am proud of what I have contributed here.  It is good.


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#46 2018-06-20 22:22:38

Void
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Registered: 2011-12-29
Posts: 2,345

Re: Space X forging ahead with BFR

I am afraid I am going to have to ask a brutal question.

What if the passenger BFS ships were approaching Mars now, with a global dust storm?

How do they survive?  Can they even land?  If they do land, can they work?

I have seen that SpaceX has revised it's plans before, I bet there may be another revision.

I won't speculate on what it could be.  I most likely would be off quite a bit anyway, and it would pay me no benefit.

I will say that I appreciate that SpaceX made the reach for Mars, but it appears to me that something more is required, unless the people in the BFS's want to roll dice on their success.



Done.

Last edited by Void (2018-06-20 22:26:45)


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#47 2018-06-21 02:45:46

louis
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Re: Space X forging ahead with BFR

As you all know, I am not an engineer (lol) but I would say, yes they can land. A rocket doesn't involve an intake system - it's all being blasted out, and any rocket landing on Mars is likely to kick up a lot of dust.

In fact that will be one of the landing site criteria - find somewhere that has a low level of surface dust. A dust storm does not equate to additional dust on the surface, Just more dust on the surface.

Space X know how to land in high winds:

https://twitter.com/SpaceX/status/718605741288894464

The max wind speed on Mars is 60 mph and the wind has much less force at the same speed, compared with Earth, owing to the near vacuum conditions.

They won't need a huge amount of energy to survive following landing. The crew won't attempt to disembark for several days. A combination of on-board batteries and, if necessary, methane-oxygen electricity generators will keep them powered up.  The BFS may also be able to deploy its PV to help recharge batteries. There may be a dust storm but insolation levels are unlikely to fall below 20%, so some power can be generated.  The six BFSs will have enough energy on board in the form of chemical batteries and methane/oxygen generators, plus air, water and food,  to ensure survival for hundreds of sols. This is an 800 tonne mission.

Most activity will be undertaken by robots and automated machinery. Best to avoid EVAs if at all possible, since dust is certainly a nuisance to deal with.

After a few days, the BFS can start unloading.







Void wrote:

I am afraid I am going to have to ask a brutal question.

What if the passenger BFS ships were approaching Mars now, with a global dust storm?

How do they survive?  Can they even land?  If they do land, can they work?

I have seen that SpaceX has revised it's plans before, I bet there may be another revision.

I won't speculate on what it could be.  I most likely would be off quite a bit anyway, and it would pay me no benefit.

I will say that I appreciate that SpaceX made the reach for Mars, but it appears to me that something more is required, unless the people in the BFS's want to roll dice on their success.



Done.


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#48 2018-06-21 07:48:09

GW Johnson
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From: McGregor, Texas USA
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Posts: 3,151
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Re: Space X forging ahead with BFR

To answer Void's question,  a BFS approaching Mars with a dust storm raging must land anyway.  There is no other choice with that system design.  It does not have the propellant to decelerate into orbit and wait out the storm.  This craft is moving slower than Mars itself about the sun,  when it reaches Mar's orbit about the sun.  Mars runs into it from behind. 

You control the collision geometry to be a grazing impact more-or-less tangent to the local surface in order to get the shallow angle required for an aerobraking direct entry.  Depending upon upon the details of your transfer orbit,  speed at entry relative to Mars will be 6-7 km/s. Aerobraking kills all but the last 0.7 km/s of this,  so you only need theoretically enough propellant for a 0.7 km/s retropropulsive landing.  I practical terms,  you really need about 1-1.4 km/s to land safely.   

In a dust storm,  you won't be able to see anything,  and radar may be degraded some.  Your landing accuracy will be poorer.  There is no help for that,  that I am aware of.  You're coming down through air with a significant rock dust particulate content.

What that means is extra heat shield erosion during the descent from the particulates suspended in the air.  I rather doubt there is any danger to the entering BFS at Mars,  but it raises the question of degraded heat shield integrity for a return at Earth,  where there is also no option to decelerate into orbit. 

As for degraded landing accuracy,  that means you will likely miss your intended landing zone,  by multiple km.  That not only causes post-touchdown logistical inconvenience,  it also means you may be making a blind rough-field landing.  The potential for toppling over and exploding is inherently higher.

GW

Last edited by GW Johnson (2018-06-21 07:52:04)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#49 2018-06-21 08:02:57

Oldfart1939
Member
Registered: 2016-11-26
Posts: 1,474

Re: Space X forging ahead with BFR

louis wrote:

As you all know, I am not an engineer (lol) but I would say, yes they can land. A rocket doesn't involve an intake system - it's all being blasted out, and any rocket landing on Mars is likely to kick up a lot of dust.

In fact that will be one of the landing site criteria - find somewhere that has a low level of surface dust. A dust storm does not equate to additional dust on the surface, Just more dust on the surface.

Space X know how to land in high wind.

Louis-I'll try to be polite here, but regarding landing a BFS on Mars, it reminds me of what my primary flight instructor told me: "A landing is done in a manner in which the aircraft is immediately reusable." Based on what we know about SpaceX's capabilities (near zero at this time) of landing on another planet, I seriously doubt that it would be successful under near zero visibility conditions. (An IFR approach and landing for small aircraft requires a minimum visibility of 1/2 mile). My instructor also told me that if I didn't accomplish a nice, smooth landing, he wanted the wreckage on the centerline of the runway. By the way, I have a LOT of experience in landing aircraft in windy conditions, but NOT under zero visibility conditions. On Mars, even a 60 mph wind acting on the huge surface area as a crosswind would blow the landing BFS off course by a substantial margin.

OK, then; what is the "bottom line" here?

Since the timeline for BFR/BFS has now shifted out to 10 years, it makes sense to me and others of my ilk, that a pioneer "Mars Direct" style mission should be flown first. Yeah, the hardware IS available in form of Falcon Heavy. Unlike some, I don't believe in "vaporware," and neither does Elon Musk. The only reason he shifted gears to BFR/BFS was due to the interference by NASA in his retropropulsion plans for Dragon 2, as well as difficulty in "man rating" the spaceship to nearly unachievable standards. I also think the BFR/BFS timeline is super-optimistic at 10 years; more likely will be 15 years. I will probably not live to see men on Mars.

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#50 2018-06-21 10:53:21

louis
Member
From: UK
Registered: 2008-03-24
Posts: 3,720

Re: Space X forging ahead with BFR

The BFR/BFS timeline has NOT shifted out to ten years. That was a misinterpretation of what Gwynne Shotwell said about an Earth-to-Earth system...that it would be in place within a decade. In fact for an Earth-to-Earth air service  to be in place implies the BFR/BFS will be available several years before that, in line with Musk's timeline (first hop test in 2019, first unmanned flight to Mars in 2022).

IIRC, Space X have landed a booster back on Earth at night. Is that not the case?

Oldfart1939 wrote:
louis wrote:

As you all know, I am not an engineer (lol) but I would say, yes they can land. A rocket doesn't involve an intake system - it's all being blasted out, and any rocket landing on Mars is likely to kick up a lot of dust.

In fact that will be one of the landing site criteria - find somewhere that has a low level of surface dust. A dust storm does not equate to additional dust on the surface, Just more dust on the surface.

Space X know how to land in high wind.

Louis-I'll try to be polite here, but regarding landing a BFS on Mars, it reminds me of what my primary flight instructor told me: "A landing is done in a manner in which the aircraft is immediately reusable." Based on what we know about SpaceX's capabilities (near zero at this time) of landing on another planet, I seriously doubt that it would be successful under near zero visibility conditions. (An IFR approach and landing for small aircraft requires a minimum visibility of 1/2 mile). My instructor also told me that if I didn't accomplish a nice, smooth landing, he wanted the wreckage on the centerline of the runway. By the way, I have a LOT of experience in landing aircraft in windy conditions, but NOT under zero visibility conditions. On Mars, even a 60 mph wind acting on the huge surface area as a crosswind would blow the landing BFS off course by a substantial margin.

OK, then; what is the "bottom line" here?

Since the timeline for BFR/BFS has now shifted out to 10 years, it makes sense to me and others of my ilk, that a pioneer "Mars Direct" style mission should be flown first. Yeah, the hardware IS available in form of Falcon Heavy. Unlike some, I don't believe in "vaporware," and neither does Elon Musk. The only reason he shifted gears to BFR/BFS was due to the interference by NASA in his retropropulsion plans for Dragon 2, as well as difficulty in "man rating" the spaceship to nearly unachievable standards. I also think the BFR/BFS timeline is super-optimistic at 10 years; more likely will be 15 years. I will probably not live to see men on Mars.


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