Author Topic: Taking the BFR Beyond Mars  (Read 17228 times)

Offline qraal

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Taking the BFR Beyond Mars
« on: 10/28/2017 07:17 AM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.

I've analysed using this technique to fly to Titan (all on a single tank!) with a reasonable aerobrake entry speed of ~7.7 km/s, to land on the surface. It's the easiest Outer System target to reach, but takes ~3 years, so it's an endurance mission. Launching there in a Parabolic solar orbit takes 2.5 years, but means a re-entry speed of ~10.5 km/s. That *might* be doable with a Magnetoshell braking system.

To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop. The BFS needs to aerocapture into Jupiter, then do a bi-elliptical transfer to Callisto. Shaving off ~1.5 km/s in the aerocapture from an entry speed of 60.7 km/s (it's a 500 day solar orbit, not a 1,000 day Hohmann) is the *hard* part. I feel it'll require some tricky tweaking of the TPS. Or a working Magnetoshell braking system. The BFS ends up in low Callisto orbit, so a pre-emplaced Tanker will be needed to land.

Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #1 on: 10/28/2017 07:25 AM »
Note: I am assuming a *small* crew of 10 for these missions. If 100 people are provisioned for 180 days on a standard Mars payload, then 10 can be provisioned for 1,800 days. ISRU will be needed for all the missions to get back to Earth or survival, if it's a one-way "settlement" mission.

Callisto has water ice, dry ice and some sort of organics available in its surface material.

Titan has methane, ethane, acetylene (!!) and water ice. Lots of organicky crud with the texture of instant coffee in those dunes (or something like that.) Plus nitrogen. It also has super-rotation in its upper atmosphere, which means we could use stratospheric tethered floating wind-turbines for power. Fill them with either methane or the 0.1% hydrogen in the atmosphere.

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #2 on: 10/28/2017 10:39 AM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)

Offline MATTBLAK

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Re: Taking the BFR Beyond Mars
« Reply #3 on: 10/28/2017 11:01 AM »
Apparently; Ceres requires a fair plane-change maneuver to reach it that is fuel-intensive, depending on the method of propulsion. Dawn had no worries because of it's high-Isp ion drive. I'm not sure what it's difference to the Earth's solar system ecliptic position is, but I think it's more than 7 degrees, but less than 10.
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Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #4 on: 10/28/2017 11:33 AM »
Apparently; Ceres requires a fair plane-change maneuver to reach it that is fuel-intensive, depending on the method of propulsion. Dawn had no worries because of it's high-Isp ion drive. I'm not sure what it's difference to the Earth's solar system ecliptic position is, but I think it's more than 7 degrees, but less than 10.
Yeah I have heard that Ceres is well off the plane of the ecliptic an this makes it very awkward.. just wondering why it was easier from Mars.

According to this there are about 200 asteroids greater than 100km in size.
https://en.wikipedia.org/wiki/Asteroid#Size_distribution

I think people assign far too much importance to Ceres. One of these 200 would surely be in a far more convenient orbit, depending what our goal is, and have a more convenient mix of ice and ore on the surface. >100km is plenty of material.

Offline Hauerg

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Re: Taking the BFR Beyond Mars
« Reply #5 on: 10/28/2017 11:41 AM »
I do not think that we assign too much importance to Ceres.
Looks like it had an OCEAN!

Offline MATTBLAK

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Re: Taking the BFR Beyond Mars
« Reply #6 on: 10/28/2017 12:17 PM »
Ceres is awesome - it should be the very next target for manned missions after Mars, no question - either by SpaceX or NASA. And more probes, too for that matter. At least one rover and another with a good drill - somewhat like the one on Mars Insight.
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Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #7 on: 10/28/2017 12:23 PM »
That's minor compared to the fact you need to propulsively brake into orbit around it. No aerobraking, no handy highly elliptical orbit momentum bank. From Mars, the delta-vee is lower overall. But the trip is a bit longer.

Apparently; Ceres requires a fair plane-change maneuver to reach it that is fuel-intensive, depending on the method of propulsion. Dawn had no worries because of it's high-Isp ion drive. I'm not sure what it's difference to the Earth's solar system ecliptic position is, but I think it's more than 7 degrees, but less than 10.

Offline Hauerg

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Re: Taking the BFR Beyond Mars
« Reply #8 on: 10/28/2017 12:30 PM »
10.6

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #9 on: 10/28/2017 12:42 PM »
Can you unpack that a bit for me?

10.6

Offline geza

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Re: Taking the BFR Beyond Mars
« Reply #10 on: 10/28/2017 01:00 PM »
I've analysed using this technique to fly to Titan (all on a single tank!) with a reasonable aerobrake entry speed of ~7.7 km/s, to land on the surface. It's the easiest Outer System target to reach, but takes ~3 years, so it's an endurance mission. Launching there in a Parabolic solar orbit takes 2.5 years, but means a re-entry speed of ~10.5 km/s. That *might* be doable with a Magnetoshell braking system.

If Titan is the easiest, let's talk about that! Certainly, it would worth to establish a research base there, if it possible. I guess, the return trip would be possible also on a single tank, after refueling on Titan surface. Could you calculate?

Online meekGee

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Re: Taking the BFR Beyond Mars
« Reply #11 on: 10/28/2017 02:20 PM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)
That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.

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Offline Kaputnik

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Re: Taking the BFR Beyond Mars
« Reply #12 on: 10/28/2017 10:12 PM »
What would a viable power source look like for a Titan mission- ASRG?
At least the methane ISRU would be easy- it's even subcooled for you already :D
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Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #13 on: 10/29/2017 12:12 AM »
RTGs would work better if optimised for convection cooling so a bit of redesign required.

What would a viable power source look like for a Titan mission- ASRG?
At least the methane ISRU would be easy- it's even subcooled for you already :D

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #14 on: 10/29/2017 12:28 AM »
I don't think you need to keep any landing fuel around for these tankers, right? They could aerobrake into earth orbit and be refueled before landing. It saves dragging that dead weight all around the solar system.

Offline Ludus

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Re: Taking the BFR Beyond Mars
« Reply #15 on: 10/29/2017 01:13 AM »
This also connects with BFR and science instruments thread. How much payload can a standard BFS cargo land on Titan?

How well does it work for Europa? No aerobraking so I suppose not well.

A cheap 50 ton robot Sub for the seas of Titan sounds pretty cool. Perhaps a variety of flying, swimming, crawling robots in the same payload.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #16 on: 10/29/2017 01:29 AM »
There's insufficient tank capacity for return in all the above cases. ISRU is needed.

In the case of Titan, the main need is oxidiser. Methane can be pumped straight out of the air, but there's nothing to burn it with. We're going to have to extract oxygen from either water or carbon dioxide. But how to minimise the needed oxygen?

Pondering the options led to a Google search and I found an old patent for a rocket engine using a mix of acetylene and ethane, with a smidge of oxygen, that might simplify things. That'd take development work on Titan, since acetylene isn't a forgiving compound to work with on Earth in pure form.

Acetylene + O2 gets an Isp of 415 seconds, so that's an encouraging start, but acetylene is touchy. Mixing it with N2 or CO would help stabilise it, but the N2 option would bring down the Isp quite a bit to a bit under 300 seconds. Acetylene + Carbon Monoxide as fuel gets an Isp of 350 seconds, which is quite exciting, so mining dry ice to crack into CO + O2 might mean local rocket propellant is straightforward to make, without the need for cracking water ice. The advantage over straight CH4+O2 is that the CO is used, rather than dumped, if CO2 cracking is how we're making O2.

Another option is acetylene/ammonia mix plus O2. Which the Russians have done some work on and got a decent discussion here back in 2013: Energomash Develops Revolutionary (?) Ammonia/Acetylene Rocket Engine ...but then the advantage against straight methalox isn't clear.

That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #17 on: 10/29/2017 01:36 AM »
I don't think robot subs mass 50 tons even on Earth. Remotely operated submersibles aren't over large and don't have to be as weighted down in 0.125 gee in a liquid half as dense as water. Going 200 metres down in methane/ethane probably means a pressure of less than 2 bar. To descend to 1,000 bar would need to penetrate the icy crust and go about ~80 km down. We're not likely to find access into the ice that deep, though we won't know until we go look ;-)

This also connects with BFR and science instruments thread. How much payload can a standard BFS cargo land on Titan?

How well does it work for Europa? No aerobraking so I suppose not well.

A cheap 50 ton robot Sub for the seas of Titan sounds pretty cool. Perhaps a variety of flying, swimming, crawling robots in the same payload.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #18 on: 10/29/2017 02:33 AM »
For the Trans Jupiter Insertion, quite right.

I don't think you need to keep any landing fuel around for these tankers, right? They could aerobrake into earth orbit and be refueled before landing. It saves dragging that dead weight all around the solar system.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #19 on: 10/29/2017 02:39 AM »
I assumed 150 tons, though most will be the life-support etc for the 10 crew. A cargo vehicle would need to be sent with it for setting up the base and ISRU. Personally I think the power should be sourced from in situ energy flows,
 rather than a reactor we've hauled across the solar system, though that will probably be needed initially. Wind power from high altitude seems more feasible on Titan than on Earth. Superconducting cables to floating wind-turbines seem perfectly suited to the job.

This also connects with BFR and science instruments thread. How much payload can a standard BFS cargo land on Titan?

Offline Norm38

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Re: Taking the BFR Beyond Mars
« Reply #20 on: 10/29/2017 03:46 AM »
Power for the ship is a real problem. Solar power is impossible for a crewed ship past Mars. RTG isn't going to cut it either. This isn't a probe that can run on 200W by trickle charging a battery for one daily pulse of activity.
Actual fission reactors are needed (discounting a fusion breakthrough). And those aren't coming anytime soon.

Offline Robotbeat

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Re: Taking the BFR Beyond Mars
« Reply #21 on: 10/29/2017 04:28 AM »
Power for the ship is a real problem. Solar power is impossible for a crewed ship past Mars. RTG isn't going to cut it either. This isn't a probe that can run on 200W by trickle charging a battery for one daily pulse of activity.
Actual fission reactors are needed (discounting a fusion breakthrough). And those aren't coming anytime soon.
Man, I disagree with almost EVERY sentence here.

Solar power isn't "impossible" beyond Mars. Even at Jupiter, you're only off the power produced at Mars by a factor of 11. And for Ceres, it's just a factor of 3 different from Mars. So a ship designed for, say, 200 people at Mars (in a pinch) could handle like 18 at Jupiter and still a healthy 65 or so people at Ceres. Those are huge crew sizes for typical NASA deep space plans, so power for crew is not going to be the ultimate limiting factor.

RTG would work, too. You'd need a lot of Pu238, but you can also use the cheaper Americium. A high performance 10 ton RTG/ASRG could produce like tens of kilowatts, plenty for a small crew. That much Americium would be hundreds of millions of dollars, but that's not too bad for a truly deep space mission.

Actual fission reactors are also not far away, either. NASA's Kilopower reactor tech is progressing fairly quickly. They did a small proof of concept test generating actual electricity using actual small-scale fission with Department of Energy help a couple years ago, and the prototype Kilopower reactor KRUSTY is pretty far along. Could easily be done within a decade if desired and fully funded.
« Last Edit: 10/29/2017 04:29 AM by Robotbeat »
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Offline Norm38

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Re: Taking the BFR Beyond Mars
« Reply #22 on: 10/29/2017 10:26 AM »
Has solar advanced that far?  Mars is about 1/2 Earth solar incidence. So it's factors of 6 and 22 for Ceres / Jupiter. Look at the ISS array size to keep 6 people alive.  A ship is not hauling 22 of those to Jupiter. What is it down to now? How is even a small integer practical?

1 ton RTG per 1-3kW sounds like a lot to me. Does that include the radiators? I'll go read up on Kilopower.

Offline tea monster

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Re: Taking the BFR Beyond Mars
« Reply #23 on: 10/29/2017 11:46 AM »
Once you add a decent sized reactor and cooling system, you pretty much have a deep-space tug. Chuck some 3X nested hall thrusters or a VASIMIR on that thing and you have a deep space vessel that can be used for all sorts of things like ferrying suites of probes to the outer planets - or pushing an ITS spacecraft out to the Jovian system. The ITS gets its power from the tug and the high-power ion engines can reduce trip time. The ITS can be used as a lander and a hab.

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #24 on: 10/29/2017 12:06 PM »
I've analysed using this technique to fly to Titan (all on a single tank!) with a reasonable aerobrake entry speed of ~7.7 km/s, to land on the surface. It's the easiest Outer System target to reach, but takes ~3 years, so it's an endurance mission. Launching there in a Parabolic solar orbit takes 2.5 years, but means a re-entry speed of ~10.5 km/s. That *might* be doable with a Magnetoshell braking system.

If Titan is the easiest, let's talk about that! Certainly, it would worth to establish a research base there, if it possible. I guess, the return trip would be possible also on a single tank, after refueling on Titan surface. Could you calculate?

Thanks to qraal for starting this thread! I played around a good bit with these numbers after the first ITS reveal last year. My take home: Titan is "easy" to get to and -for multiple reasons- a good place for a sustainable colony, but is is harder to get back from, so maybe overall a good target for one-way settlement voyages. Ceres is hard to get to but easy to get back from so -also for multiple reasons- an attractive target for building as much a possible on site with local materials and selling tankers full of volatiles back to Earth. Callisto is in principle reasonable for two-way traffic _if_ you can aerobrake at Jupiter, given scary-looking reentry speeds and radiation. And as been mentioned before, all of them are a lot easier from Mars orbit that from LEO, making Mars a promising gateway to parts further out.

Offline RonM

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Re: Taking the BFR Beyond Mars
« Reply #25 on: 10/29/2017 01:07 PM »
Has solar advanced that far?  Mars is about 1/2 Earth solar incidence. So it's factors of 6 and 22 for Ceres / Jupiter. Look at the ISS array size to keep 6 people alive.  A ship is not hauling 22 of those to Jupiter. What is it down to now? How is even a small integer practical?

1 ton RTG per 1-3kW sounds like a lot to me. Does that include the radiators? I'll go read up on Kilopower.

Solar panel tech has greatly improved since the ISS panels were made and research continues. Look at the Juno mission at Jupiter. It's solar powered and the panels were built about a decade ago.

By the time anyone is ready to fly BFR to Jupiter or Ceres, solar panels will not be a concern.

Offline guckyfan

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Re: Taking the BFR Beyond Mars
« Reply #26 on: 10/29/2017 01:13 PM »
By the time anyone is ready to fly BFR to Jupiter or Ceres, solar panels will not be a concern.

Maybe for the ECLSS for a crew of 10-20. But for the MW needed to produce propellant?

Offline RonM

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Re: Taking the BFR Beyond Mars
« Reply #27 on: 10/29/2017 01:32 PM »
By the time anyone is ready to fly BFR to Jupiter or Ceres, solar panels will not be a concern.

Maybe for the ECLSS for a crew of 10-20. But for the MW needed to produce propellant?

Just like Mars, it's going to take multiple ships to create an infrastructure before the first crewed mission. It will probably take a fission reactor for the propellent plant.

This isn't going to work with a single BFR flight.

Offline Ludus

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Re: Taking the BFR Beyond Mars
« Reply #28 on: 10/29/2017 01:42 PM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)
That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.

If you were using a filled Tanker as a departure stage, how would you do it? What would be the minimum mod to the standard BFS? Lock them heat shield to heat shield for the boost?

Offline philw1776

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Re: Taking the BFR Beyond Mars
« Reply #29 on: 10/29/2017 03:35 PM »
I believe that aerobraking a crewed ship at Jupiter leaves you with a soon to be dead crew after transiting Jupiter's intense radiation belts.  Some form of non-existant at this time magnetic field shield would be needed.
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Offline Robotbeat

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Re: Taking the BFR Beyond Mars
« Reply #30 on: 10/29/2017 03:42 PM »
I believe that aerobraking a crewed ship at Jupiter leaves you with a soon to be dead crew after transiting Jupiter's intense radiation belts.  Some form of non-existant at this time magnetic field shield would be needed.
Wrong.

You can use supplies, polyethylene, and water to block the radiation, which is lower energy than cosmic rays and closer to the easier-to-block solar particles.
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Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #31 on: 10/29/2017 03:46 PM »
By the time anyone is ready to fly BFR to Jupiter or Ceres, solar panels will not be a concern.

Maybe for the ECLSS for a crew of 10-20. But for the MW needed to produce propellant?

Just like Mars, it's going to take multiple ships to create an infrastructure before the first crewed mission. It will probably take a fission reactor for the propellent plant.

This isn't going to work with a single BFR flight.
It may well take a fission reactor to get propellant production started at a useful rate in a reasonable amount of time, but you'd also start by bringing solar panels from Earth, then bringing equipment to make solar panels locally, then equipment to make that equipment, etc., all with as much local material as feasible, so the rate of power (and propellant) production can ramp up (more than!) exponentially. For Ceres in particular, once you can fill up tankers there and send them out to refill spaceships "part way" to other destinations, a lot of beyond-Mars trips get a lot easier.

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #32 on: 10/29/2017 04:08 PM »
Not beyond Mars but another interesting non-Lunar destination might be Earth's quasi-satellite 2016 HO3 (https://www.jpl.nasa.gov/news/news.php?feature=6537), the closest deep space (i.e. beyond Earth's Hill Radius) object in a (quasi) stable orbit. At what looks like a bit under 100 meters across, it's too small for much propellant production for BFR-scale vehicles but if it's on the order of a million kilograms of mass, it could provide raw materials enough to make a small deep space hotel, just a few million kilometers from home. I can't think of any compelling orbital mechanics reason to use it, but it would be the easiest past-the-Moon tourist destination.

Online meekGee

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Re: Taking the BFR Beyond Mars
« Reply #33 on: 10/29/2017 04:23 PM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)
That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.

If you were using a filled Tanker as a departure stage, how would you do it? What would be the minimum mod to the standard BFS? Lock them heat shield to heat shield for the boost?
IMO I'd modify the tanker to be able to push.  Much lower acceleration than launch, everything still axial, and the BFS itself doesn't require any mods  so any mass penalty stays on Earth.
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Offline acsawdey

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Re: Taking the BFR Beyond Mars
« Reply #34 on: 10/29/2017 04:39 PM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)
That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.

If you were using a filled Tanker as a departure stage, how would you do it? What would be the minimum mod to the standard BFS? Lock them heat shield to heat shield for the boost?
IMO I'd modify the tanker to be able to push.  Much lower acceleration than launch, everything still axial, and the BFS itself doesn't require any mods  so any mass penalty stays on Earth.

One could imagine a structure that unfolds out of the cargo section of the tanker (assuming tanker is just BFS that doesn't carry cargo) and provides the same structural connections used to mate BFR to BFS, but in front of the ship. The structure has to carry the load down to the aft bulkhead of the cargo compartment which normally carries the cargo load. Might need to use only two Raptor vac engines at part throttle when boosting to keep the loads manageable. Normal load of 150 MT at 3g would mean you could push 1200 MT fuelled BFS at something like 0.4g. Or, maybe they build a tanker for boosting with heavier structure.

Online meekGee

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Re: Taking the BFR Beyond Mars
« Reply #35 on: 10/29/2017 04:44 PM »
To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop.
...
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.
A pet idea of mine is to use a full BFS Tanker as a departure stage to push the ship on it's way. The trick is that the trajectory could skim past earth, boosting just before closest approach for maximum Oberth effect, and also to allow the now empty tanker to be immediately recaptured at earth.

Why is Ceres a real pain from Earth but pretty simple from Mars? (honest layman's question)
That is one hell of an idea...

If BFS can hold propellant for long durations (Musk mentioned cryo coolers) then you can have all the inherent dV for braking and return.

That's very powerful.

If you were using a filled Tanker as a departure stage, how would you do it? What would be the minimum mod to the standard BFS? Lock them heat shield to heat shield for the boost?
IMO I'd modify the tanker to be able to push.  Much lower acceleration than launch, everything still axial, and the BFS itself doesn't require any mods  so any mass penalty stays on Earth.

One could imagine a structure that unfolds out of the cargo section of the tanker (assuming tanker is just BFS that doesn't carry cargo) and provides the same structural connections used to mate BFR to BFS, but in front of the ship. The structure has to carry the load down to the aft bulkhead of the cargo compartment which normally carries the cargo load. Might need to use only two Raptor vac engines at part throttle when boosting to keep the loads manageable. Normal load of 150 MT at 3g would mean you could push 1200 MT fuelled BFS at something like 0.4g. Or, maybe they build a tanker for boosting with heavier structure.
Might not need to unfold.

The tanker is a BFS without a cabin, and optimised structurally.

If there's a longitudinal member -basically an axial through tube - it'll transfer load straight through, and so the BFS can have a nose mounted pusher ring.

With that arrangement, you can pull off some insane dV flights.
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Offline Kaputnik

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Re: Taking the BFR Beyond Mars
« Reply #36 on: 10/29/2017 07:11 PM »
RTGs would work better if optimised for convection cooling so a bit of redesign required.

What would a viable power source look like for a Titan mission- ASRG?
At least the methane ISRU would be easy- it's even subcooled for you already :D

Do you mean 'better than ASRG'?
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Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #37 on: 10/31/2017 10:49 AM »
Ceres is awesome - it should be the very next target for manned missions after Mars, no question - either by SpaceX or NASA. And more probes, too for that matter. At least one rover and another with a good drill - somewhat like the one on Mars Insight.
A bit off topic, but I looked up some other possibles. Here are a few.

NameCeres24_Themis65_Cybele19_Fortuna
Size960km198km302×290×232225×205×195
Density2.16 g/cm³2.79 g/cm³0.99 g/cm³2.70 g/cm³
Orbit2.56-2.98AU2.7-3.5AU3-3.8AU2.0-2.8AU
Inclination10.6°0.76°3.6°1.573°
IceLotsCompletely covered
in surface ice
Ice on surface,
and density~1
Dunno, but similar
spectra to Ceres

Ceres is really really big, and has lots of ice. But these others are big enough.. so it is ok to look at other characteristics. 24_Themis has a much lower inclination for example. Im not sure, but the wording implied the ice might be more exposed on the surface also, perhaps.

(Im a bit puzzled why the density of 65_Cybele is so close to one.. possibly a misprint? I didn't google anyone talking about this odd coincidence)
« Last Edit: 10/31/2017 11:17 AM by KelvinZero »

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Re: Taking the BFR Beyond Mars
« Reply #38 on: 11/04/2017 11:23 AM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.
(Snip)
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #39 on: 11/04/2017 04:12 PM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.
(Snip)
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Maybe this goes without saying but I am assuming you mean easier from EML1 than Mars surface. I forget who did a nice post with delta-V calculations a ways back showing how Mars orbit is a very attractive staging point for destinations further out.

Also, just to re-iterate, the largest factor making Ceres a difficult target is not the orbital inclination but rather the absence of aerocapture, requiring a large delta-V at the destination. That changes once there is enough infrastructure on Ceres to fill tankers locally and send them out to meet incoming ships part way to supply propellant for the arrival delta-V.

Online rakaydos

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Re: Taking the BFR Beyond Mars
« Reply #40 on: 11/04/2017 09:21 PM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.
(Snip)
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Maybe this goes without saying but I am assuming you mean easier from EML1 than Mars surface. I forget who did a nice post with delta-V calculations a ways back showing how Mars orbit is a very attractive staging point for destinations further out.

Also, just to re-iterate, the largest factor making Ceres a difficult target is not the orbital inclination but rather the absence of aerocapture, requiring a large delta-V at the destination. That changes once there is enough infrastructure on Ceres to fill tankers locally and send them out to meet incoming ships part way to supply propellant for the arrival delta-V.
Sending out takers to rendevous with INBOUND ships? that's just...

Whatever the velocity the inbound rocket is at. The tanker needs to get BACK to the rocket, CANCEL it's backward velocity, MATCH velocity with the rocket, and still have enough fuel to slow the tanker AND rocket the required velocity. Basically 4 and a half times the DV requirement.

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #41 on: 11/04/2017 11:59 PM »
Sending out takers to rendevous with INBOUND ships? that's just...

Whatever the velocity the inbound rocket is at. The tanker needs to get BACK to the rocket, CANCEL it's backward velocity, MATCH velocity with the rocket, and still have enough fuel to slow the tanker AND rocket the required velocity. Basically 4 and a half times the DV requirement.
I think the trajectory to do this would be similar to designing a cycler trajectory, even if a cycler is not practical between earth and Ceres. You wouldn't send the tanker/depot towards the ship, but in the opposite direction. You are giving it the velocity a BFS would have as it shot on by. This trajectory has to encounter earth and return to Ceres.

Given the years this fuel would be travelling I suspect it would not end up looking like a BFS tanker.

The similarity of the problem to a cycler might make similar orbital inclination very appealing. There are an estimated 200 asteroids above 100km in size so there are probably very good candidates.

IDEA:
The cycler itself could become a more central destination than a specific world like Ceres. Maybe the next target after Mars could be a cycler well designed to revisit Mars regularly that dips deep into the asteroid belt.

Rather than being concerned with any specific target, which requires large varying delta-v, instead this cycler has a fleet of unmanned ARM-like asteroid grabbers that keep grabbing the low hanging fruit of low delta-v and high value asteroids, in "small" 1000 ton bites.. assuming we stuck with the tiny ARM sized variants.

You could end up with multiple of these cyclers visiting mars regularly, perhaps named after the constellation that is in conjunction when they return.

You would still have permanent colonies on places like Ceres, but they are not hubs. They have varying windows to reach mars, made possible by these cyclers. So the Cyclers become the hubs that connect Mars to the outer solar system.

In this analogy, specific asteroid colonies that produce materials but are not centers of trade are sort of like the "fly over states" :)

Im taking this too far off topic. Im really interested in this but it goes way beyond missions with a few BFR Tanker rendezvous.  I vaguely remember someone had a thread about the best targets within the asteroid belt.

Offline Spacer Dan

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Re: Taking the BFR Beyond Mars
« Reply #42 on: 11/05/2017 02:21 AM »
Station modules seem to by geared towards as large a volume as possible, constrained by the cargo capabilities of the BFF. I suggest, after the cargo, tanker, passenger stages are operational that a semi-expendable second stage would be built. Spacex has demonstrated a 12m fuel tank. A semi-expendible stage would be 12m in diameter with the propulsion engines in a 8m open truss at the bottom of the state. The 'power pack' would be detachable and 2-3 of then stored into a freighter to be brought back to earth. All you would leave in orbit would be the tanks. Payload could be 12m by 20 meter long station segments, massing up to 200+ tons.

Please don't take this sideways about expendable stages, I'm just saying that large station construction may require a more specialized vehicle if you want to put a 'Space Vegas' into low Earth orbit.  The tanks could be turned into large zero-G habitation at the station. The stages, refueled, would be massive tugs.

Offline Ludus

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Re: Taking the BFR Beyond Mars
« Reply #43 on: 11/07/2017 03:01 AM »
I assumed 150 tons, though most will be the life-support etc for the 10 crew. A cargo vehicle would need to be sent with it for setting up the base and ISRU. Personally I think the power should be sourced from in situ energy flows,
 rather than a reactor we've hauled across the solar system, though that will probably be needed initially. Wind power from high altitude seems more feasible on Titan than on Earth. Superconducting cables to floating wind-turbines seem perfectly suited to the job.

This also connects with BFR and science instruments thread. How much payload can a standard BFS cargo land on Titan?

This approach suggests that a BFS cargo could be sent on an expendable mission on land on an ice moon with over 100 tons of payload for less money than a conventional flyby probe massing a few tons. It could carry several 10 kW reactors. It would be interesting to see what different labs could come up with to include if the money was tight by typical standards but mass and energy requirements that liberal.

Offline DLR

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Re: Taking the BFR Beyond Mars
« Reply #44 on: 11/07/2017 07:40 AM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.

I've analysed using this technique to fly to Titan (all on a single tank!) with a reasonable aerobrake entry speed of ~7.7 km/s, to land on the surface. It's the easiest Outer System target to reach, but takes ~3 years, so it's an endurance mission. Launching there in a Parabolic solar orbit takes 2.5 years, but means a re-entry speed of ~10.5 km/s. That *might* be doable with a Magnetoshell braking system.

To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop. The BFS needs to aerocapture into Jupiter, then do a bi-elliptical transfer to Callisto. Shaving off ~1.5 km/s in the aerocapture from an entry speed of 60.7 km/s (it's a 500 day solar orbit, not a 1,000 day Hohmann) is the *hard* part. I feel it'll require some tricky tweaking of the TPS. Or a working Magnetoshell braking system. The BFS ends up in low Callisto orbit, so a pre-emplaced Tanker will be needed to land.

Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

What about skipping the aerobraking and capturing directly into Callisto orbit? If you time the encounter right, Callisto will be moving parallel to the spacecraft on its orbit around Jupiter, so you can deduct Callisto's orbital velocity when calculating orbital capture delta v.

This is from NASA'S HOPE study (2003):

L1 Departure: 0.58 km/s
TJI: 4.55 km/s
Callisto direct OI: 3.75 km/s

Time: 851 Days

Online tchernik

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Re: Taking the BFR Beyond Mars
« Reply #45 on: 11/07/2017 05:36 PM »
I assumed 150 tons, though most will be the life-support etc for the 10 crew. A cargo vehicle would need to be sent with it for setting up the base and ISRU. Personally I think the power should be sourced from in situ energy flows,
 rather than a reactor we've hauled across the solar system, though that will probably be needed initially. Wind power from high altitude seems more feasible on Titan than on Earth. Superconducting cables to floating wind-turbines seem perfectly suited to the job.

This also connects with BFR and science instruments thread. How much payload can a standard BFS cargo land on Titan?

This approach suggests that a BFS cargo could be sent on an expendable mission on land on an ice moon with over 100 tons of payload for less money than a conventional flyby probe massing a few tons. It could carry several 10 kW reactors. It would be interesting to see what different labs could come up with to include if the money was tight by typical standards but mass and energy requirements that liberal.

What I find exciting about these latest developments of rocketry, is precisely their power just by having a single one of them (for the mission, not for the preliminaries).

As qraal describes, they would enable truly incredible possibilities for exploration of the Solar System at large, just by having one or two from time to time.

But the real transformation comes from what they can achieve in groups, with several of them per year coming out of the rocket factories, with both reusable and expendable modes of operation available.

There is no reason why several pieces of that nice payload you say couldn't be taken to Ceres,  Titan or Callisto beforehand, enabling any manned  missions to have plenty of supplies and machinery in place when they arrive, including spare return ships.

And that's an actual human expansion and settlement of space scenario. Not just landing, but with permanent manned facilities with scheduled crew rotations on these amazing places.
« Last Edit: 11/07/2017 06:32 PM by tchernik »

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #46 on: 11/07/2017 06:36 PM »
The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.

[...]

To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop. The BFS needs to aerocapture into Jupiter, then do a bi-elliptical transfer to Callisto. Shaving off ~1.5 km/s in the aerocapture from an entry speed of 60.7 km/s (it's a 500 day solar orbit, not a 1,000 day Hohmann) is the *hard* part. I feel it'll require some tricky tweaking of the TPS. Or a working Magnetoshell braking system. The BFS ends up in low Callisto orbit, so a pre-emplaced Tanker will be needed to land.
[...]

What about skipping the aerobraking and capturing directly into Callisto orbit? If you time the encounter right, Callisto will be moving parallel to the spacecraft on its orbit around Jupiter, so you can deduct Callisto's orbital velocity when calculating orbital capture delta v.

This is from NASA'S HOPE study (2003):

L1 Departure: 0.58 km/s
TJI: 4.55 km/s
Callisto direct OI: 3.75 km/s

Time: 851 Days

I think it's a good idea, and I'll bet you can do even better with a multi-moon bank-shot to decrease the delta-V needed at the destination, a la the "Interplanetary Transport Netork" idea (https://en.wikipedia.org/wiki/Interplanetary_Transport_Network), but I don't think it totally obviates the need/benefit for aerobraking. The numbers you cite get you 8.83 km/sec to get to Callisto Orbit, but you'd still need another 1.7 km/sec or so to  land, and 10.5 km/sec total delta-V is more than the nominal BFS can do (though a tanker can).

Offline speedevil

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Re: Taking the BFR Beyond Mars
« Reply #47 on: 11/07/2017 11:39 PM »
The numbers you cite get you 8.83 km/sec to get to Callisto Orbit, but you'd still need another 1.7 km/sec or so to  land, and 10.5 km/sec total delta-V is more than the nominal BFS can do (though a tanker can).

On very beyond Mars (Saturn).

ISRU production is going to be annoying unless you get reactors, as solar is a percent or so of earth.
Getting reactors is going to be politically annoying.

Titan is unfortunately likely to not have well mapped available water ice even if you do get reactors.

Neglecting for the moment the difficulty of extracting this, and rendevous, and ...

How rich can you run a raptor before adding more methane is a bad thing for total impulse.
Would adding nitrogen ever be beneficial?
Wondering if this lets you stretch expensive imported oxygen.

Offline Ludus

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Re: Taking the BFR Beyond Mars
« Reply #48 on: 11/10/2017 02:05 AM »



Getting reactors is going to be politically annoying.

Titan is unfortunately likely to not have well mapped available water ice even if you do get reactors.


Reactors are going to be as necessary for humans being seriously spacefaring as reusable rockets so it’s gonna have to be addressed.

I had the impression that it was about half water in different mixes and pressures and the ground surface was often water ice rather than rock, though water ice is much like rock at those temperatures. I’d thought that insulating so waste heat doesn’t melt the ground under you was a bigger issue than finding ice.

Offline DigitalMan

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Re: Taking the BFR Beyond Mars
« Reply #49 on: 11/10/2017 02:17 AM »

Reactors are going to be as necessary for humans being seriously spacefaring as reusable rockets so it’s gonna have to be addressed.

I had the impression that it was about half water in different mixes and pressures and the ground surface was often water ice rather than rock, though water ice is much like rock at those temperatures. I’d thought that insulating so waste heat doesn’t melt the ground under you was a bigger issue than finding ice.

Perhaps in the future reactors can be fueled with off-world nuclear material
« Last Edit: 11/10/2017 02:18 AM by DigitalMan »

Offline Patchouli

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Re: Taking the BFR Beyond Mars
« Reply #50 on: 11/10/2017 02:23 AM »
The numbers you cite get you 8.83 km/sec to get to Callisto Orbit, but you'd still need another 1.7 km/sec or so to  land, and 10.5 km/sec total delta-V is more than the nominal BFS can do (though a tanker can).

On very beyond Mars (Saturn).

ISRU production is going to be annoying unless you get reactors, as solar is a percent or so of earth.
Getting reactors is going to be politically annoying.

Titan is unfortunately likely to not have well mapped available water ice even if you do get reactors.

Neglecting for the moment the difficulty of extracting this, and rendevous, and ...

How rich can you run a raptor before adding more methane is a bad thing for total impulse.
Would adding nitrogen ever be beneficial?
Wondering if this lets you stretch expensive imported oxygen.


BFS would need some kind of solar independent heat source such as RHUs to keep itself from freezing at distances beyond the asteroid belt.
It might even need them for Mars surface ops at higher latitudes so the nuclear politics thing is going have to tackled any way.
« Last Edit: 11/10/2017 02:30 AM by Patchouli »

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #51 on: 11/10/2017 03:25 AM »
They have found ice mountains on Titan.

BTW, rather than worrying about waste heat melting the ground out beneath you, engineer to exploit it. There is a whole list of arguments for melting down and creating a small ocean around you. Pretty much every icy body in the solar system could be terraformed this way, into an ocean world under an eggshell of ice.. and you can also start very small: Landers far far simpler than those speculated for Europa ocean missions could just melt down a few tens of meters and begin melting a body of water and provide an airlock into that cavity.

It is one of my hobby horses.

Offline Kaputnik

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Re: Taking the BFR Beyond Mars
« Reply #52 on: 11/10/2017 06:53 AM »
The numbers you cite get you 8.83 km/sec to get to Callisto Orbit, but you'd still need another 1.7 km/sec or so to  land, and 10.5 km/sec total delta-V is more than the nominal BFS can do (though a tanker can).

On very beyond Mars (Saturn).

ISRU production is going to be annoying unless you get reactors, as solar is a percent or so of earth.
Getting reactors is going to be politically annoying.

Titan is unfortunately likely to not have well mapped available water ice even if you do get reactors.

Neglecting for the moment the difficulty of extracting this, and rendevous, and ...

How rich can you run a raptor before adding more methane is a bad thing for total impulse.
Would adding nitrogen ever be beneficial?
Wondering if this lets you stretch expensive imported oxygen.


BFS would need some kind of solar independent heat source such as RHUs to keep itself from freezing at distances beyond the asteroid belt.
It might even need them for Mars surface ops at higher latitudes so the nuclear politics thing is going have to tackled any way.

I don't think RHUs are the answer for something the size of BFS. Perhaps useful for some small systems located away from the main cabin, but even then electrical heaters powered by the main power source might be easier.

On Mars, you can do everything with solar, unless you want to work at high latitudes in winter.
Waiting for joy and raptor

Offline jpo234

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Re: Taking the BFR Beyond Mars
« Reply #53 on: 11/10/2017 07:12 AM »
Titan is unfortunately likely to not have well mapped available water ice even if you do get reactors.

The solar system is soggy. Basically everywhere we have looked there is or was an abundance of water. The NASA article "The Solar System and Beyond is Awash in Water" says:

Quote
Perhaps the most surprising water worlds are the five icy moons of Jupiter and Saturn that show strong evidence of oceans beneath their surfaces: Ganymede, Europa and Callisto at Jupiter, and Enceladus and Titan at Saturn.

This puts Titan into the Ocean World category. More details found in "Titan's Underground Ocean":

Quote
The search for water is an important goal in solar system exploration, and now we've spotted another place where it is abundant.
« Last Edit: 11/10/2017 07:19 AM by jpo234 »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #54 on: 11/11/2017 03:19 AM »
Hi DLR

Oddly enough a Facebook friend suggested this very same thing to me...

As I envisaged it, the TJI would involve 3 vehicles, two of which are Tankers to top up the BFS. They'd have enough left to stage back to Earth for reuse.

Did the HOPE study quote the C3 value of that orbit?



What about skipping the aerobraking and capturing directly into Callisto orbit? If you time the encounter right, Callisto will be moving parallel to the spacecraft on its orbit around Jupiter, so you can deduct Callisto's orbital velocity when calculating orbital capture delta v.

This is from NASA'S HOPE study (2003):

L1 Departure: 0.58 km/s
TJI: 4.55 km/s
Callisto direct OI: 3.75 km/s

Time: 851 Days

The slide for using the BFS to land on the Moon and return has the BFS 'parked' in a HEEO while it tanks up. With a top delta-vee of ~6.4 km/s for the BFS, storing launch momentum in such an orbit allows a very effective Oberth Maneuver for Outer Planet missions.

I've analysed using this technique to fly to Titan (all on a single tank!) with a reasonable aerobrake entry speed of ~7.7 km/s, to land on the surface. It's the easiest Outer System target to reach, but takes ~3 years, so it's an endurance mission. Launching there in a Parabolic solar orbit takes 2.5 years, but means a re-entry speed of ~10.5 km/s. That *might* be doable with a Magnetoshell braking system.

To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop. The BFS needs to aerocapture into Jupiter, then do a bi-elliptical transfer to Callisto. Shaving off ~1.5 km/s in the aerocapture from an entry speed of 60.7 km/s (it's a 500 day solar orbit, not a 1,000 day Hohmann) is the *hard* part. I feel it'll require some tricky tweaking of the TPS. Or a working Magnetoshell braking system. The BFS ends up in low Callisto orbit, so a pre-emplaced Tanker will be needed to land.



Online mikelepage

Re: Taking the BFR Beyond Mars
« Reply #55 on: 11/11/2017 06:13 AM »
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Maybe this goes without saying but I am assuming you mean easier from EML1 than Mars surface. I forget who did a nice post with delta-V calculations a ways back showing how Mars orbit is a very attractive staging point for destinations further out.

Would be interested if you can find that.  I can imagine an argument that, from a dV perspective, Mars orbit is an attractive staging point... once Mars is already a thriving colony/hub and is generating whole tanker loads of propellent in excess to their needs, but logistically, I can't see how EML1 and the Deep Space Gateway are not going to be the most efficient staging points for decades to come.

(snip)
You would still have permanent colonies on places like Ceres, but they are not hubs. They have varying windows to reach mars, made possible by these cyclers. So the Cyclers become the hubs that connect Mars to the outer solar system.

In this analogy, specific asteroid colonies that produce materials but are not centers of trade are sort of like the "fly over states" :)

Im taking this too far off topic. Im really interested in this but it goes way beyond missions with a few BFR Tanker rendezvous.  I vaguely remember someone had a thread about the best targets within the asteroid belt.

That was me, and this thread here (although I was really focussing on NEOs):
https://forum.nasaspaceflight.com/index.php?topic=38820.msg1445943#msg1445943

What I think will happen now - and I'm writing a novel to depict this - is a "hub and spoke model" centred around cis-lunar space.  Of course the Mars colony will be the "fattest" spoke, but I think it will only be one of hundreds or more.  The rest will require the placement of "stepping-stone" colonies at Apollo asteroids which have the same/similar inclination & ascending node as desirable "anchor" locations, plus rendezvous opportunities with them.

I was originally using Ceres as my story's "anchor location" and the NEO Apollo asteroid 1999 JT6 as my "stepping stone colony".  Because of the inclination/distance factor, I've switched to 16 Psyche as the anchor location, and another Apollo as the stepping stone: 2008 EQ is a nothing rock, barely 50m across, but it's big enough to mine, and provide for a storm shelter/radiation protection, and most importantly flies by Earth every 7 years for the next century or more.

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #56 on: 11/15/2017 11:56 PM »
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Maybe this goes without saying but I am assuming you mean easier from EML1 than Mars surface. I forget who did a nice post with delta-V calculations a ways back showing how Mars orbit is a very attractive staging point for destinations further out.

Would be interested if you can find that.  I can imagine an argument that, from a dV perspective, Mars orbit is an attractive staging point... once Mars is already a thriving colony/hub and is generating whole tanker loads of propellent in excess to their needs, but logistically, I can't see how EML1 and the Deep Space Gateway are not going to be the most efficient staging points for decades to come.


Found it:
It was by metaphor
https://forum.nasaspaceflight.com/index.php?topic=41306.msg1597199#msg1597199
the file is its.ods

Offline DrRobin

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Re: Taking the BFR Beyond Mars
« Reply #57 on: 11/16/2017 12:37 AM »
Ceres, from Earth orbit, is a real pain. But it'd be pretty simple from Mars. Thus Mars will be the Gateway to Ceres and the Asteroids.

From LEO, perhaps. Way easier to go to Ceres/asteroids from EML1 than Mars though.

Maybe this goes without saying but I am assuming you mean easier from EML1 than Mars surface. I forget who did a nice post with delta-V calculations a ways back showing how Mars orbit is a very attractive staging point for destinations further out.

Would be interested if you can find that.  I can imagine an argument that, from a dV perspective, Mars orbit is an attractive staging point... once Mars is already a thriving colony/hub and is generating whole tanker loads of propellent in excess to their needs, but logistically, I can't see how EML1 and the Deep Space Gateway are not going to be the most efficient staging points for decades to come.


Found it:
It was by metaphor
https://forum.nasaspaceflight.com/index.php?topic=41306.msg1597199#msg1597199
the file is its.ods

In particular, for Ceres, metaphor's #'s are that from LEO it takes 5.5 km/sec dV to get to the right point in space but another 6 km/sec to match velocities and land -and 11.5 km/sec total is more than BFS can do. It's the same total dV from Mars surface but "only" 7.5 km/sec from Mars orbit, which would let BFS deliver a significant payload.

(I tried to re-do these calculations myself and I get somewhat different numbers: a bit lower for the transfer orbit but 1.2 km/sec higher for the dV at the destination, but then again, I am an orbital mechanics noob, so I'd be curious to know what more knowledgeable folks think.)

Offline tdperk

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Re: Taking the BFR Beyond Mars
« Reply #58 on: 11/16/2017 10:14 AM »
logistically, I can't see how EML1 and the Deep Space Gateway are not going to be the most efficient staging points for decades to come.

I believe there is no rational reason to believe the first SpaceX Mars landing will not have sufficient excess ISRU fuel capacity, for the sake of a safety margin in dispatching the next synods's vessels with the expectation of return, that it will not be generating available fuel from the get go.  Within one decade or less of that landing, agree with them on a price and you can fill your tanks there.

A staging orbit around the Moon looks good if the departure vessel is O2/H2 fueled, or when a CC asteroid is emplaced there as a feedstock for MethaLox.  It would be to SpaceX's long term advantage to do so if liquid fuels are not eclipsed by better tech by then.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #59 on: 11/17/2017 10:30 PM »
Hi

From my own calculations, the trip time quoted below is *nearly* Hohmann - a tiny bit of extra delta-vee is enough to shave off ~150-200 days. The delta-vee assumes a low orbit, rather than direct touch down.

A 1,000 day Hohmann would need ~5.4 km/s delta-vee for a direct touch down trajectory. A full tank delta-vee of 6.4 km/s would reduce the trip time to ~685 days. A bit quicker if the Isp gets as high as 385 seconds - I'm assuming a Block 1 Vacuum Raptor performance of 375 seconds.

Once on Callisto the first task would be ISRU acquisition. There's definitely H2O and CO2 ices, but I wonder if there's not trapped O2 from radiolysis of the ice? We know there's very likely such on Europa, probably Ganymede's poles, but confirmation on Callisto would ease the power requirements. Instead of electrolysis for making oxygen, it'd be just hydrogen feedstock for making CH4. Merely melting the ice would give us the O2 - though the energy cost-effectiveness would depend on its volumetric abundance.

Hi DLR

Oddly enough a Facebook friend suggested this very same thing to me...

As I envisaged it, the TJI would involve 3 vehicles, two of which are Tankers to top up the BFS. They'd have enough left to stage back to Earth for reuse.

Did the HOPE study quote the C3 value of that orbit?



What about skipping the aerobraking and capturing directly into Callisto orbit? If you time the encounter right, Callisto will be moving parallel to the spacecraft on its orbit around Jupiter, so you can deduct Callisto's orbital velocity when calculating orbital capture delta v.

This is from NASA'S HOPE study (2003):

L1 Departure: 0.58 km/s
TJI: 4.55 km/s
Callisto direct OI: 3.75 km/s

Time: 851 Days

[..]

To get to Callisto requires using two BFS Tankers which then transfer propellant to the BFS after all three boost into a Trans-Jupiter Insertion orbit. The Tankers can then return to Earth after a long loop. The BFS needs to aerocapture into Jupiter, then do a bi-elliptical transfer to Callisto. Shaving off ~1.5 km/s in the aerocapture from an entry speed of 60.7 km/s (it's a 500 day solar orbit, not a 1,000 day Hohmann) is the *hard* part. I feel it'll require some tricky tweaking of the TPS. Or a working Magnetoshell braking system. The BFS ends up in low Callisto orbit, so a pre-emplaced Tanker will be needed to land.



Offline oldAtlas_Eguy

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Re: Taking the BFR Beyond Mars
« Reply #60 on: 11/17/2017 11:15 PM »
Most miss the point that with an on orbit (in flight) refueling with a SC and tanker set architecture there is not actually a limit on the delta V possible with this system. It is only a matter of costs since for each 6.3km/s of delta V is an equation of 6.3*N where number of launches is = 5^N + 5^(N-1) +...+5(N-N)

N   DV (km/s)  Launches
1      6.3             6
2    12.6            31
3    18.9          156

The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.
« Last Edit: 11/17/2017 11:20 PM by oldAtlas_Eguy »

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #61 on: 11/17/2017 11:34 PM »
Nicely summarised. Thanks for the equation too! Quite right. I'm only looking at minimal architectures at this point, for initial feasibility. But faster flights will help!

Titan is very attractive as a target thanks to the aerocapture angle, but the long trip time is a problem. I don't think it's insuperable. Artificial gravity by spin should be perfectly feasible, if we're talking *Titan-gee* levels. It's a *pioneering* effort after all, not a programmatic mission, that I'm envisaging. A fast elliptical transfer or even a parabolic orbit can be done for less than a full-tank. Starting with a full tank and using the remaining fuel for initial power production will help expand the ultimate ISRU options, without presuming nuclear will be readily available. I'm hoping the Kilopower effort by NASA pays off and mini-reactors become commercially available for Outer Solar System ventures, but the more In Situ power supplies that can be tapped, the better. Thus the appeal of high altitude windpower that Titan seems to have plenty of.


Most miss the point that with an on orbit (in flight) refueling with a SC and tanker set architecture there is not actually a limit on the delta V possible with this system. It is only a matter of costs since for each 6.3km/s of delta V is an equation of 6.3*N where number of launches is = 5^N + 5^(N-1) +...+5(N-N)

N   DV (km/s)  Launches
1      6.3             6
2    12.6            31
3    18.9          156

The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.

Offline speedevil

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Re: Taking the BFR Beyond Mars
« Reply #62 on: 11/18/2017 02:42 PM »
The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.

If you're expending them, you can also in principle remove most engines, for some tons of weight saving.
Tankers that don't need to launch full, and never need to land can get by with many fewer.

At that point you might also consider how much an absolutely minimal tanker that had one raptor, and was carried to orbit mostly empty on cargo could cost.

Fuel is cheap, but at some point the exponentials of trying to recover tankers going quite fast away from you means that the logistics get expensive.

I do wonder on the cost of a simple aluminium one-raptor tanker, with very little else. (it would of course have a compatible base-frame for propellant transfer)
Expendable looks somewhat different if the margins required to launch to orbit don't need to be there, and you have a rapidly reusable (though expensive in terms of capital) propellant transfer for those expendables.

Online rakaydos

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Re: Taking the BFR Beyond Mars
« Reply #63 on: 11/18/2017 05:57 PM »
The problem comes in how to get the tankers back in some reasonable amount of time or if there is enough funds to expend them.

If you're expending them, you can also in principle remove most engines, for some tons of weight saving.
Tankers that don't need to launch full, and never need to land can get by with many fewer.

At that point you might also consider how much an absolutely minimal tanker that had one raptor, and was carried to orbit mostly empty on cargo could cost.

Fuel is cheap, but at some point the exponentials of trying to recover tankers going quite fast away from you means that the logistics get expensive.

I do wonder on the cost of a simple aluminium one-raptor tanker, with very little else. (it would of course have a compatible base-frame for propellant transfer)
Expendable looks somewhat different if the margins required to launch to orbit don't need to be there, and you have a rapidly reusable (though expensive in terms of capital) propellant transfer for those expendables.
At that point, it's no longer a tanker. "Flyback Drop Tank" is what you're looking for.

Probably has some use in the future, but I would expect a clean sheet design for a cheap external tank. Possibly an inflatable around the outer rim that also protects the main tanks from heating the same way the main tanks protect the header tanks, and plugs into the refueling pipes withoutblocking the engines.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #64 on: 11/26/2017 08:06 PM »
There's a Russian propellant combination which I think is really interesting in a Titan context - acetam / atsetam.

A 30/70 mix of acetylene/ammonia, with O2 oxidiser. Titan has acetylene deposits on the surface and very likely has ammonia. Of course, there's lots of methane and it's possibly the easiest for initial ISRU - but acetam seems to get an Isp in the low 400s.

If the ice on Titan is a eutectic of water/ammonia, then there'll be ammonia produced by water-mining for oxygen. Of course we might need to use dry ice for oxygen, so really ground-truthing local resources will decide.

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #65 on: 11/30/2017 03:02 PM »
This mentions doing a "solar fry by" that could also be useful for a fast HSF mission within the solar system.
https://www.centauri-dreams.org/?p=38728

Im thinking perhaps you could use this just to accelerate some fuel depots. The crew BFS could catch the depots as they fly past the earth, leapfrogging from the slowest up to the fastest.

Offline qraal

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Re: Taking the BFR Beyond Mars
« Reply #66 on: 12/01/2017 09:15 AM »
Coming from so close to the Sun means the orbits are nearly radially outwards, thus significantly different to an orbit that launches cotangentially to Earth's orbit, which is needed to minimise delta-vee.

Plus the "Solar Fryby" (a phrase I coined BTW) needs a Jupiter Gravity Assist to get so close to the Sun.

This mentions doing a "solar fry by" that could also be useful for a fast HSF mission within the solar system.
https://www.centauri-dreams.org/?p=38728

Im thinking perhaps you could use this just to accelerate some fuel depots. The crew BFS could catch the depots as they fly past the earth, leapfrogging from the slowest up to the fastest.

Offline KelvinZero

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Re: Taking the BFR Beyond Mars
« Reply #67 on: 12/01/2017 09:50 AM »
Coming from so close to the Sun means the orbits are nearly radially outwards, thus significantly different to an orbit that launches cotangentially to Earth's orbit, which is needed to minimise delta-vee.

Plus the "Solar Fryby" (a phrase I coined BTW) needs a Jupiter Gravity Assist to get so close to the Sun.

This mentions doing a "solar fry by" that could also be useful for a fast HSF mission within the solar system.
https://www.centauri-dreams.org/?p=38728

Im thinking perhaps you could use this just to accelerate some fuel depots. The crew BFS could catch the depots as they fly past the earth, leapfrogging from the slowest up to the fastest.

Yes, as I said you would use this just for depots. It could take a decade to set up but the goal is to minimise the transit time for the crew. Once there is constant traffic there would be no waiting for setup of course.

The goal can't be just to minimise delta-v. Im hazy here but I think if you do that you will always have very long flight times on the order of the year of your target.. im guessing roughly a 1/3? eg eight months to mars. Think how long it would be for Saturn with an orbital period of almost 30 years. Im guessing around 10 years.

Of course each depot can only vary from the previous by about 10km/s, or whatever a single BFS can do, and the first can only vary from earth's current velocity by the same amount.

Offline Patchouli

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Re: Taking the BFR Beyond Mars
« Reply #68 on: 12/31/2017 11:14 PM »
There's a Russian propellant combination which I think is really interesting in a Titan context - acetam / atsetam.

A 30/70 mix of acetylene/ammonia, with O2 oxidiser. Titan has acetylene deposits on the surface and very likely has ammonia. Of course, there's lots of methane and it's possibly the easiest for initial ISRU - but acetam seems to get an Isp in the low 400s.

If the ice on Titan is a eutectic of water/ammonia, then there'll be ammonia produced by water-mining for oxygen. Of course we might need to use dry ice for oxygen, so really ground-truthing local resources will decide.
Nuclear thermal engines can be designed to use strait ammonia as propellant which would get an ISP of 470 to 550 seconds?

Water also could be used as a propellant but the ISP is terrible but it's very dense and can be mined from Enceladus as well.
« Last Edit: 12/31/2017 11:54 PM by Patchouli »

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