Author Topic: BFS for point to point on Mars  (Read 5464 times)

Offline Steve D

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BFS for point to point on Mars
« on: 12/08/2017 06:45 PM »
Was wondering if BFS could be used for sub-orbital hops around Mars delivering people and cargo to different sites on Mars. With just the header tanks full and a mostly full cargo hold (say 100 tons) how many hops could it make on Mars?

Offline spacenut

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Re: BFS for point to point on Mars
« Reply #1 on: 12/08/2017 06:59 PM »
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. 

Offline Steve D

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Re: BFS for point to point on Mars
« Reply #2 on: 12/08/2017 07:07 PM »
Say the initial base is set up with a fuel production facility up and operating. 5000 km away a large ice deposit that is easily accessible is located.  Would it make sense to start another fuel facility at the new site also or to bring the water to the established facility? How much water could a BFS carry?

Offline ncb1397

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Re: BFS for point to point on Mars
« Reply #3 on: 12/08/2017 07:16 PM »
The record for electrically driven aircraft is ~30 km in NASA Helios. Air pressure is about 1000 pascals at that altitude. Pretty close to Mars average surface level pressure of 600 pascals. Factoring in that particles of Martian air are more massive and the 38% gravity(need less lift to counter-act gravity, airplane can be lighter structurally, wings can be longer), general aviation using propeller driven aircraft should be doable. It doesn't waste precious water like a rocket would.

Offline freda

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Re: BFS for point to point on Mars
« Reply #4 on: 12/08/2017 07:17 PM »
I wonder if the accurate Earth point-to-point relies on GPS? If so, accurate Mars p2p might be difficult?

Offline John Alan

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Re: BFS for point to point on Mars
« Reply #5 on: 12/08/2017 07:26 PM »
Point to point is best served with ground based transport... IMHO...

Look at the Crawlers pulling sleds overland near the south pole, for an earth bound example...
Or the Alaska Highway circa 1950's using trucks and crawlers... as another...

Electric Drive machines to build and maintain unpaved roads between bases and mines...
Electric Drive transports to travel the roads with people and materials...
From a least cost and least trouble to get going standpoint...
This is the best early way to move TONS around Mars...

My opinion...  ;)


Offline Steve D

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Re: BFS for point to point on Mars
« Reply #6 on: 12/08/2017 07:48 PM »
Point to point is best served with ground based transport... IMHO...

Look at the Crawlers pulling sleds overland near the south pole, for an earth bound example...
Or the Alaska Highway circa 1950's using trucks and crawlers... as another...

Electric Drive machines to build and maintain unpaved roads between bases and mines...
Electric Drive transports to travel the roads with people and materials...
From a least cost and least trouble to get going standpoint...
This is the best early way to move TONS around Mars...

My opinion...  ;)


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.
« Last Edit: 12/08/2017 07:59 PM by Steve D »

Offline Zed_Noir

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Re: BFS for point to point on Mars
« Reply #7 on: 12/08/2017 07:52 PM »
I wonder if the accurate Earth point-to-point relies on GPS? If so, accurate Mars p2p might be difficult?

No. If a Martian GPS system is not ready in time for Mars P2P. Then terrain contour-matching navigation with radar should suffice. The technology is quite mature. The USAF use it with their cruise missiles since the early 80's.

Offline ncb1397

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Re: BFS for point to point on Mars
« Reply #8 on: 12/08/2017 08:32 PM »
I wonder if the accurate Earth point-to-point relies on GPS? If so, accurate Mars p2p might be difficult?

No. If a Martian GPS system is not ready in time for Mars P2P. Then terrain contour-matching navigation with radar should suffice. The technology is quite mature. The USAF use it with their cruise missiles since the early 80's.

Cruise missiles have a success rate of about 85%. Probably not the best example to use. They get easily confused on flat terrain for instance. When GPS guided, they do much better.
« Last Edit: 12/08/2017 08:32 PM by ncb1397 »

Offline MickQ

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Re: BFS for point to point on Mars
« Reply #9 on: 12/08/2017 10:03 PM »
Just putting out a ground beacon or two should be enough for an accurate fix on any regularly used landing site.

Online Coastal Ron

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Re: BFS for point to point on Mars
« Reply #10 on: 12/08/2017 10:10 PM »
I wonder if the accurate Earth point-to-point relies on GPS? If so, accurate Mars p2p might be difficult?

Pilots on Earth started out using dead reckoning, and I'm sure it will be good enough for Mars too if needed. Especially since you will be able to be VFR all the time on Mars due to a lack of clouds...  :)
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline laszlo

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Re: BFS for point to point on Mars
« Reply #11 on: 12/08/2017 10:33 PM »
Point to point in a BFS would be a ballistic hop. That would only require a simple (especially by today's standards) inertial navigation system to get within a mile of the target zone. Some star sights during flight to update and correct the trajectory would get it close enough without the need for GPS. GPS is a convenience, not a necessity in this case. When you factor in the cost of the constellation, but even more, the ground operations center and staff to keep GPS running accurately, it's an extravagance in the early days.

Offline Steve D

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Re: BFS for point to point on Mars
« Reply #12 on: 12/08/2017 11:08 PM »
I guess my main question is this. Can a BFS carry enough water as cargo on a sub-orbital Mars hop to be worth it? Or would it use more fuel in the hop then it could make from the water? What would be the maximum amount of mass that it could carry on a Mars hop?

Offline AncientU

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Re: BFS for point to point on Mars
« Reply #13 on: 12/08/2017 11:13 PM »
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.
"If we shared everything [we are working on] people would think we are insane!"
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Offline Steve D

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Re: BFS for point to point on Mars
« Reply #14 on: 12/08/2017 11:33 PM »
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?

Offline Patchouli

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Re: BFS for point to point on Mars
« Reply #15 on: 12/08/2017 11:39 PM »
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. 

One possible solution replace the vacuum Raptors with BNTR engines and use liquefied CO2 as the primary propellant.

When it lands the engines operate in power reactor mode and recharge the tanks with Martian CO2.
The ISP would not be great but it would be good enough for sub orbital hops on Mars and probably could even achieve orbit.
« Last Edit: 12/08/2017 11:45 PM by Patchouli »

Offline tchernik

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Re: BFS for point to point on Mars
« Reply #16 on: 12/09/2017 02:56 AM »
If BFS has such reusabilty, why not? but it neds to be thoroughly validated first, given the harsh conditions such ships would be placed into (lots of dust and rough landings on unprepared terrain).

Most likely it would be used for long travels only (like going to the other side of the planet).

Nevertheless, I think it may not happen on the first visits, given the need of some redundant logistics and return ships at hand, and the abundance of places to visit nearby (a few tens of miles from the base camp) with ground vehicles.

But if there are several camps, placed thousands of miles away, that may give an incentive for a few long suborbital hops.

Offline DavidCar

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Re: BFS for point to point on Mars
« Reply #17 on: 12/09/2017 05:00 AM »
Was wondering if BFS could be used for sub-orbital hops around Mars delivering people and cargo to different sites on Mars. With just the header tanks full and a mostly full cargo hold (say 100 tons) how many hops could it make on Mars?

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.

Beyond just traveling point to point, a good program may require that a BFS be able to launch into Mars orbit, refuel in orbit, then land at some other point on Mars with enough fuel to launch into Mars orbit again.  That way if there was some point on Mars that was best for making propellant, then propellant could be made at that location then transferred to a different BFS while in orbit, after which the first BFS would return to the propellant plant.

It's not clear to me if that approach would be more economical than transferring liquid water for propellant production from point to point.  Both approaches sound expensive.

Online docmordrid

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Re: BFS for point to point on Mars
« Reply #18 on: 12/09/2017 10:48 AM »
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. 

One possible solution replace the vacuum Raptors with BNTR engines and use liquefied CO2 as the primary propellant.

When it lands the engines operate in power reactor mode and recharge the tanks with Martian CO2.

The ISP would not be great but it would be good enough for sub orbital hops on Mars and probably could even achieve orbit.

Or, a LOX/CO or LOX/CH4 vehicle designed for the purpose is taken to Mars in pieces and assembled there. Something along the lines of the container carrying Space 1999 Eagle, or the ACES/XEUS.
« Last Edit: 12/09/2017 10:53 AM by docmordrid »
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Offline KelvinZero

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Re: BFS for point to point on Mars
« Reply #19 on: 12/09/2017 12:08 PM »
This seems a nice topic. single stage p2p on Mars seems a no brainer if 2 stage p2p on earth is actually on the table.
(whether it is outcompeted by hyperloop is a much wider topic. I say just do some numbers first)

Questions I would have are:

(a) What cargo can a BFS deliver p2p on mars, assuming refueling exists at both ends, ie analogous to p2p on earth.

(b) What radius can a BFS explore, assuming it needs enough fuel to bring itself home (no cargo except perhaps crew)

(c) what radius can a BFS explore assuming some useful amount of cargo, and fuel to bring itself home empty.
(or instead of defining a useful cargo, we could define a useful radius and work back to max cargo)

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