BFS for point to point on Mars

[docmordrid]

A) thorium or other raw materials which are regionally concentrated.

[philw1776]

Since BFS can deliver according to Musk about 1/4th it's to Mars payload upon return to Earth, looking at delta V, BFS could do Mars ptp and return with around that payload both ways.  In other words, the entire planet would be accessible.
Propellant will be at such an energy premium, especially is solar is the power source, it will be a while before ptp is done.  Maybe NASA/ESA/JAXA, etc. pays for exploratory hops.

[KelvinZero]

Since BFS can deliver according to Musk about 1/4th it's to Mars payload upon return to Earth, looking at delta V, BFS could do Mars ptp and return with around that payload both ways.  In other words, the entire planet would be accessible.

That is a pretty good start. That could be useful for substantial crewed missions to anywhere on the planet. No longer a "mission per synod" situation. You are getting vastly better use from your BFS then, same as around earth. It is the travel time that cuts into it's reuse.

Anyone prepared to estimate the one way p2p cargo tonnage, if you bring the empty BFS back without refuelling?

That could be very useful for setting up a new base, maybe not self sufficient but eg a thorium mine like mentioned above. Or maybe you are just transporting a whole bunch of startup prospecting equipment, from an existing base that no longer needs it, to investigate a new location.

[Ludus]

It might be a good idea initially, but eventually a good ground transportation system would be needed.  Hyperloop would probably be best as it would not be affected by Martian dust storms, hub to hub.  All terrain electric ground rovers and trains may come first. 

BFS would probably require too much fuel to process unless traveling half way around Mars.

Hyperloop on Mars wouldn't require tubes. 
That is why it is being developed and operated at a half percent of an atmosphere.

I am not talking 20 or 30 years after colonization begins. Before you build a hyperloop you need somewhere to go. I am thinking 1 settlement and maybe a scattering of outposts. Can a BFR carry enough water to make it worthwhile?

Mars has quite a lot of water ice, that’s a major reason settlement makes sense. Any settlement would be located by a major source. BFS doing hops on Mars may make sense but transporting water isn’t the killer app.

[alexterrell]

Yes but you have to get them to mars first... On the 1st expedition to Mars musk said it will consist of 4 cargo and 2 passenger BFS's. Once you unload the cargo ships they would be immediately available for use. Why not use them? And what about the drivers? Crossing thousands of miles of Martian desert in a crawler would be a very dangerous thing to do.

Drivers? There won't be drivers. There might just be a manual drive option, but any long distance driving will be done by the computer. It's already safer on Earth, and Mars will be a lot easier. A GPS would be useful for that, but terrain recognition could also work.

Speaking of which, GPS needs lots of satellites. Would it be possible to put one satellite in Mars Stationary Orbit, and it optically tracks each rover (maybe they have a laser), and reports its position to it. That could provide 10m accuracy.

[Ludus]

Yes but you have to get them to mars first... On the 1st expedition to Mars musk said it will consist of 4 cargo and 2 passenger BFS's. Once you unload the cargo ships they would be immediately available for use. Why not use them? And what about the drivers? Crossing thousands of miles of Martian desert in a crawler would be a very dangerous thing to do.

Drivers? There won't be drivers. There might just be a manual drive option, but any long distance driving will be done by the computer. It's already safer on Earth, and Mars will be a lot easier. A GPS would be useful for that, but terrain recognition could also work.

Speaking of which, GPS needs lots of satellites. Would it be possible to put one satellite in Mars Stationary Orbit, and it optically tracks each rover (maybe they have a laser), and reports its position to it. That could provide 10m accuracy.
[/quote]

Before the first unscrewed BFS to Mars, SpaceX will have experience with specialized BFS satellite dispenser ships that do nothing but launch Starlink Constellation satellites. The most profitable part of SpaceX business will be mass producing and operating satellites. The same Mars Constellation could provide high speed low latency internet everywhere on Mars, GPS, 24/7 observation of the entire surface for weather and exploration. It would be surprising if SpaceX didn’t launch a Constellation around Mars very early in the settlement project.

[philw1776]

Since BFS can deliver according to Musk about 1/4th it's to Mars payload upon return to Earth, looking at delta V, BFS could do Mars ptp and return with around that payload both ways.  In other words, the entire planet would be accessible.

That is a pretty good start. That could be useful for substantial crewed missions to anywhere on the planet. No longer a "mission per synod" situation. You are getting vastly better use from your BFS then, same as around earth. It is the travel time that cuts into it's reuse.

Anyone prepared to estimate the one way p2p cargo tonnage, if you bring the empty BFS back without refuelling?

That could be very useful for setting up a new base, maybe not self sufficient but eg a thorium mine like mentioned above. Or maybe you are just transporting a whole bunch of startup prospecting equipment, from an existing base that no longer needs it, to investigate a new location.

Off to a Christmas party soon so can't build a spreadsheet model but based on a quick look at existing spreadsheets I'd say a couple hundred tonnes to anywhere with tiny return payload.  Plenty.  Getting to Mars orbital velocity requires ~4Km/sec Delta V which lets you go pretty much anywhere.  Need another 4 Km/sec back but no couple hundred tonnes payload.  BFS can do roughly 7Km/sec with a 200 T payload.

Gonna be a long time before mines needed for thorium assuming you have the non-existant reactors; easier to hall the minimal thorium mass from Earth than to set up a remote mining base.

Again the gating factor is energy to produce the 1100+ tonnes of propellant per round trip flight.  For the first several synods it's all about producing enough to get the BFSs back to The Green Hills of Earth.  A BIG challenge.

[CuddlyRocket]

I assume a good early unmanned Mars exploration program would require that a BFS on Mars next to a propellant plant must be able to launch, land at some other point on Mars, then relaunch, land back near the propellant plant and automatically reattach itself.

I think concerns might be expressed at the idea of a flying blowtorch and potential bomb landing or taking off next to or even near your very valuable, difficult to replace and highly flammable propellant plant and storage facilities! Of course, 'near' is a relative term - though 'automatically reattach' implies fairly close - but I suspect significant safety margins will be thought advisable.

[philw1776]

Since BFS can deliver according to Musk about 1/4th it's to Mars payload upon return to Earth, looking at delta V, BFS could do Mars ptp and return with around that payload both ways.  In other words, the entire planet would be accessible.

That is a pretty good start. That could be useful for substantial crewed missions to anywhere on the planet. No longer a "mission per synod" situation. You are getting vastly better use from your BFS then, same as around earth. It is the travel time that cuts into it's reuse.

Anyone prepared to estimate the one way p2p cargo tonnage, if you bring the empty BFS back without refuelling?

That could be very useful for setting up a new base, maybe not self sufficient but eg a thorium mine like mentioned above. Or maybe you are just transporting a whole bunch of startup prospecting equipment, from an existing base that no longer needs it, to investigate a new location.

Off to a Christmas party soon so can't build a spreadsheet model but based on a quick look at existing spreadsheets I'd say a couple hundred tonnes to anywhere with tiny return payload.  Plenty.  Getting to Mars orbital velocity requires ~4Km/sec Delta V which lets you go pretty much anywhere.  Need another 4 Km/sec back but no couple hundred tonnes payload.  BFS can do roughly 7Km/sec with a 200 T payload.

Gonna be a long time before mines needed for thorium assuming you have the non-existant reactors; easier to hall the minimal thorium mass from Earth than to set up a remote mining base.

Again the gating factor is energy to produce the 1100+ tonnes of propellant per round trip flight.  For the first several synods it's all about producing enough to get the BFSs back to The Green Hills of Earth.  A BIG challenge.

I apologize and retract my statement about P2P and return capability. 
I realized last night that I did not account for the Km/sec needed for the landing burns each way.  Unlike Earth where the atmosphere slows the BFS down to under 0.2 Km/sec and minimal propellant is needed for landing, Mars' atmosphere provides some but far less reduction in velocity.  If I can get a good # for the terminal velocity of a craft re-entering from Mars orbit, I could be more specific about the BFS but I no longer believe it can do P2P and back to anywhere on Mars.  Sorry for posting mis-information.

[speedevil]

I apologize and retract my statement about P2P and return capability. 
I realized last night that I did not account for the Km/sec needed for the landing burns each way.  Unlike Earth where the atmosphere slows the BFS down to under 0.2 Km/sec and minimal propellant is needed for landing, Mars' atmosphere provides some but far less reduction in velocity.  If I can get a good # for the terminal velocity of a craft re-entering from Mars orbit, I could be more specific about the BFS but I no longer believe it can do P2P and back to anywhere on Mars.  Sorry for posting mis-information.

From the multiplanetary talk, and the transcript.

35:30 '[Slide: Mars Entry: Real Time: Over 99% of energy removed aerodynamically. Supersonic retropropulsion for landing burn. Graph of Altitude (km) plotted against Mach: 5 km @ Mach 2.5; 2.5 km @ Mach 2.4; 0.7 km @ Mach 0.5; 0 km @ Mach 0.]'

This is presumably 99% of 7.5km/s mentioned on the previous slide, so landing delta-v is under 750m/s.
The animation/graph at 35:44 and on is useful. This is presumably representative of an orbital entry (looking only at the sub 4.1km/s bit).
The pure aerodynamic bit ends with ignition at mach 2.4 or so, so ~570m/s and 2.2km altitude.
A rough eyeball says that at that point it's descending along its thrust vector some 30 degrees from the horizontal, down to 120m/s, at which point it pitches vertical.
An initial speed of 570m/s being 500m/s horizontally and 290m/s vertically.
It takes  15 seconds to get to 120m/s. (both in the video time, and in the clock on the video).
35m/s^2 as a first guess seems plausible for thrust, which matches reasonably with the angle estimate to kill most of the vertical velocity, and nearly all of the horizontal.
Then we're at ~120m/s and 700m altitude, and it throttles back moderately, goes vertical and lands in 23s or so.

This is an average vertical speed of 30m/s - which is extraordinarily cautious from 'hoverslam' perspectives.

So, a moderately close ballpark would seem to be 35m/s^2*15s + 100m/s to cancel remaining velocity, and 70m/s of gravity losses in the latter period when it's mostly vertical and decelerating at almost exactly 1g.

So, 700m/s in the landing phase, and a few tens of meters a second in the reentry burn phase.
This seems plausible, and is moderately better than 1km/s.

Perhaps down to 600m/s if the hoverslam gets rather more aggressive, with 35m/s down to the last five seconds.

[oldAtlas_Eguy]

A cargo BFS would deliver greater than 240mt of prop to Low Mars Orbit (LMO).

The problem of the no refueling on surface of second location is the landing and reentry mass.

In order to get back just to LMO completely empty and no payload it would need to land with 230mt of prop still on board + the payload weight. It might be capable of this but it would seriously challenge the reentry and landing. Note this scenario uses only a 15mt payload outbound with 0 return is feasible if you can reenter and land with that much on-board prop 245mt total extra mass 95mt above normal landing payload mass.

But for point to point a stop off in LMO would deliver up to 130mt of prop as well as carrying 150mt of payload. The extra 130mt of prop would have to be offloaded at LMO to some other BFS parked in LMO. 8 one way leggs (4 round trips) would fill a BFS left in LMO tank.

But these scenarios all assume prop manufacture is ongoing at significant rates at both ends of the P2P (with a stop-off in orbit to offload extra prop).

added:
Partial prop loads of 620mt would do a one way P2P with 150mt payload so it would take 1240mt of prop (620mt loaded at each end of the P2P) for a round trip with 150mt both ways.

P2P is possible but requires prop manufacture at both ends.

[Steve D]

I am thinking more of a takeoff from the main base empty of cargo. Land at an outpost and load up with water as a cargo and return with it to the main base without refueling. How many km/sec would be required for a suborbital hop of say, 2000 miles? How much cargo can it bring back to base without refueling?

[DavidCar]

Maybe the answer to my question is clear to someone who understands the math in the previous posts, but would a p2p roundtrip be possible with propellant manufacture on only the initial end if the BFS tanks were larger?  Or is the limitation more complicated than that?

It seems such p2p round trips from an initial base would be useful for a good Mars exploration program prior to determining the best location for a larger base.

[philw1776]

I am thinking more of a takeoff from the main base empty of cargo. Land at an outpost and load up with water as a cargo and return with it to the main base without refueling. How many km/sec would be required for a suborbital hop of say, 2000 miles? How much cargo can it bring back to base without refueling?

You'd spend more water making propellant for the flight than you could bring back.  Pointless.

[Steve D]

I am thinking more of a takeoff from the main base empty of cargo. Land at an outpost and load up with water as a cargo and return with it to the main base without refueling. How many km/sec would be required for a suborbital hop of say, 2000 miles? How much cargo can it bring back to base without refueling?

You'd spend more water making propellant for the flight than you could bring back.  Pointless.

Have you got the numbers to back that up? What would be max payload for mars point to point in the 2000 km distance range? Could it be done with just the fuel in the header tanks? With Mars gravity and air pressure being so much lower then earth the cargo mass should be much higher.

[KelvinZero]

Hi Steve, I can't do the numbers, but given the BFS tanks take something like a 1000 tons and the typical payload discussed is in the 50 to 200 ton range, Im not sure it could even carry enough in a one way trip. The cargo you could carry on the second leg of a two way trip without refueling just has to be far far worse even than that.

I don't think anyone has been debating the assumption that the absolute #1 requirement for the main base is an access to water, so that the BFS can return home. This was certainly very clear in Elon Musk's presentation.

You may be unaware of how much evidence there is for water on mars, even quite near the equator. As a last resort we might even be able to extract it from the atmosphere.

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

[Steve D]

Hi Steve, I can't do the numbers, but given the BFS tanks take something like a 1000 tons and the typical payload discussed is in the 50 to 200 ton range, Im not sure it could even carry enough in a one way trip. The cargo you could carry on the second leg of a two way trip without refueling just has to be far far worse even than that.

I don't think anyone has been debating the assumption that the absolute #1 requirement for the main base is an access to water, so that the BFS can return home. This was certainly very clear in Elon Musk's presentation.

You may be unaware of how much evidence there is for water on mars, even quite near the equator. As a last resort we might even be able to extract it from the atmosphere.

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

Lots of evidence yes, but until you get your hands on it...... Just trying to see what options the first crews will have if abundant water is not found where they land. I am assuming the first 6 BFSs will not be carrying autonomous electric powered water tanker trucks. What they will have are 4 cargo ships that when emptied could carry large amounts of cargo. If a good source of water is found at a distance that is too far for whatever rovers they have could handle, could a BFS be used for that?  I am assuming a suborbital hop would not need full fuel tanks on the BFS. After all it is capable of returning to earth without refueling.

[philw1776]

Chemistry makes flying a BFS elsewhere to haul back water is a losing proposition.  Takes roughly 9Kg water to yield 1Kg of hydrogen.  In other words haul back 90 tonnes of water and get 10 tonnes of hydrogen.  You spent a couple hundred tonnes of methane CH4 to do this.

[Steve D]

Chemistry makes flying a BFS elsewhere to haul back water is a losing proposition.  Takes roughly 9Kg water to yield 1Kg of hydrogen.  In other words haul back 90 tonnes of water and get 10 tonnes of hydrogen.  You spent a couple hundred tonnes of methane CH4 to do this.

You still need the 80 tons of o2 that you get from it.

[Dalhousie]

Hi Steve, I can't do the numbers, but given the BFS tanks take something like a 1000 tons and the typical payload discussed is in the 50 to 200 ton range, Im not sure it could even carry enough in a one way trip. The cargo you could carry on the second leg of a two way trip without refueling just has to be far far worse even than that.

I don't think anyone has been debating the assumption that the absolute #1 requirement for the main base is an access to water, so that the BFS can return home. This was certainly very clear in Elon Musk's presentation.

You may be unaware of how much evidence there is for water on mars, even quite near the equator. As a last resort we might even be able to extract it from the atmosphere.

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

Lots of evidence yes, but until you get your hands on it...... Just trying to see what options the first crews will have if abundant water is not found where they land. I am assuming the first 6 BFSs will not be carrying autonomous electric powered water tanker trucks. What they will have are 4 cargo ships that when emptied could carry large amounts of cargo. If a good source of water is found at a distance that is too far for whatever rovers they have could handle, could a BFS be used for that?  I am assuming a suborbital hop would not need full fuel tanks on the BFS. After all it is capable of returning to earth without refueling.

1) You don't go where there are no water resources.
2) you make sure that your initial mission has sufficient reserve in case your site selection got it badly wrong.
3) Spend future missions to a different site.

There are many sites on mars where potential water resources extend for 100s if not thousands of km to depths of many metres .  You build your station on top of these.