Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)  (Read 204314 times)

Offline jpo234

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1280 on: 02/12/2018 07:11 PM »

According to THERMAL ENGINEER, REUSABLE THERMAL PROTECTION SYSTEMS their aim is:

Quote
Develop materials necessary to make thermal protection systems reusable for thousands of low earth orbit reentry flights on future SpaceX vehicles.

In other words, they want BFR to be used like an airliner.
No. They want BFS to behave like an airliner.

BFR will continue to act as a very large booster stage, like the F9 booster stage.

Interestingly they are especially interested in people with ceramic TPS experience, suggesting they don't think PICAX has enough stretch to deal with this task.

When talking about BFS, Elon keeps talking about how "some aspects of reentry heating scale to the 8th power" so for a potential fast intersteller transit, that's going to be a lot of scaling.

Shocked by SpaceX's sudden huge mission creep
Contingency planning in case Mars is a dud.
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Online wannamoonbase

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1281 on: 02/12/2018 08:15 PM »
I don't believe their prices for a second. Even with Falcon 9 the expended second stage doesn't make up even a majority of the launch costs. Chinese firms are also coming up with smallsat launchers that undercut electron by half already.

Ditto, the prices Elon stated are at best, the price if they hit every goal for development cost, reliability, turn around and reuseability.

But it's a good goal and if they are off by a large percentage, then it's still a huge improvement.

Like the Falcon series, BFR is going to take years and multiple iterations.  However, if in 10 years they are flying the 2nd or 3rd iteration out to the moon and back then perhaps it's worth it anyway.
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Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1282 on: 02/12/2018 10:45 PM »
But it's a good goal and if they are off by a large percentage, then it's still a huge improvement.

Like the Falcon series, BFR is going to take years and multiple iterations.  However, if in 10 years they are flying the 2nd or 3rd iteration out to the moon and back then perhaps it's worth it anyway.
It's true the Moon won't allow aerobraking or capture but the total delta V is substantially less to get there and back than from Mars. 150 tonnes to Mars gives plenty of room for a lighter loaded BFS to run a complete Lunar surface mission while still having a very substantial payload to (and from) the surface by Apollo standards.

Unfortunately NASA's fondness for "competition" is likely to make this quite a bizarre process. Does anyone recall that Shuttle didn't allow plug nozzle engines as only one company actually had experience of the technology, and therefore there would be no "competition"?
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Offline Negan

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1283 on: 02/12/2018 10:51 PM »
It's true the Moon won't allow aerobraking or capture but the total delta V is substantially less to get there and back than from Mars. 150 tonnes to Mars gives plenty of room for a lighter loaded BFS to run a complete Lunar surface mission while still having a very substantial payload to (and from) the surface by Apollo standards.

I think it would be very interesting to see how many tankers would be needed per how many tonnes of payload. Also the same for circumlunar and LLO missions.
« Last Edit: 02/12/2018 10:54 PM by Negan »

Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1284 on: 02/12/2018 11:40 PM »
1. You don't think there is a market for the BFR (even though its goal is to be the cheapest $/kg by far).

It's not just the relative price ($/kg) but also the absolute price ($/launch).
It's the $/launch price that is crucial. It means, that BFR can profitably launch with even comparatively tiny payloads.

Assuming for the moment that BFR/BFS cost $400M per pair, and reflights cost $500K in labour and fuel.

You need to hit around 8 reflights to get below the cost price to spacex (not price per kilo) of FH.
Perhaps 10 for Falcon 9, 12 for Pegasus, and over a hundred for Rocketlabs Electron.

Neglecting the cost of any groundside infrastructure.

More reuses - perhaps 1.5* these would be needed to get to the point you could sell these services to customers at a profit.


.
$400 million for a pair is equivalent to the 2016 ITS, which is twice the thrust: http://www.spacex.com/sites/spacex/files/making_life_multiplanetary_2016.pdf
The 2017 IAC BFR should be close to half that value, let’s say $200-250 million. Just 5 reuses, then, are necessary.


The interesting thing is: suppose they can make 25, $50m Falcon 9s per year. If they have a similar workforce manufacturing BFRs and at least as much revenue coming in to pay for them, that means they can add 5 BFRs to their fleet every year. If those are each capacle of launching hundreds or thousands of times each, that means that they’ll be able to launch thousands of times per year with no more manufacturing footprint than they have right now.

That’s millions of tons IMLEO over a decade. That’s enough for serious Mars settlement and space infrastructure.
« Last Edit: 02/12/2018 11:44 PM by Robotbeat »
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Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1285 on: 02/13/2018 12:02 AM »

According to THERMAL ENGINEER, REUSABLE THERMAL PROTECTION SYSTEMS their aim is:

Quote
Develop materials necessary to make thermal protection systems reusable for thousands of low earth orbit reentry flights on future SpaceX vehicles.

In other words, they want BFR to be used like an airliner.
No. They want BFS to behave like an airliner.

BFR will continue to act as a very large booster stage, like the F9 booster stage.

Interestingly they are especially interested in people with ceramic TPS experience, suggesting they don't think PICAX has enough stretch to deal with this task.
Not at all. The issue isnít with PICA-Xís performance. PICA-X and PICA can handle just about any entry scenario.

The issue is turnaround. An ablative heatshield, even if you can technically get away with using it several times, is non-ideal if you want to fly as often as a transpacific airliner.
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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1286 on: 02/13/2018 12:20 AM »
1. You don't think there is a market for the BFR (even though its goal is to be the cheapest $/kg by far).

It's not just the relative price ($/kg) but also the absolute price ($/launch).
It's the $/launch price that is crucial. It means, that BFR can profitably launch with even comparatively tiny payloads.
Absolutely.

I tried to make that point via the "fuel is cheaper than ..." point but I was pretty circuitous. It's a skill. :)
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Offline JamesH65

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1287 on: 02/13/2018 08:44 AM »
$400 million for a pair is equivalent to the 2016 ITS, which is twice the thrust: http://www.spacex.com/sites/spacex/files/making_life_multiplanetary_2016.pdf
The 2017 IAC BFR should be close to half that value, letís say $200-250 million. Just 5 reuses, then, are necessary.

I don't think the cost/size ratio is that linear. I'd expect 300-350M but that is a WAG.

Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1288 on: 02/13/2018 12:53 PM »
Sure, not totally linear. But Falcon 9 has about the same cost per dry mass as SpaceX's assumptions for ITS, so linear canít be TOO far off, particularly since a smaller BFR means theyíll need to make more of them.
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Offline M.E.T.

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1289 on: 02/13/2018 07:06 PM »
Veering off the cost discussion briefly. I was wondering if BFR is capable of delivering satellites into Martian orbit. If SpaceX wanted a Martian GPS network, or wanted communication and other satellites in place to support their Mars program, would BFR be the vehicle to deliver these satellites?

From a previous discussion my understanding is that BFS is not capable of decelerating into Martian obit, and instead needs the Martian atmosphere to bleed off 99% of its energy prior to landing. If so, does this mean that BFS is not able to slow down, open its cargo door and just  pop out a half dozen satellites around Mars?

And if not, would a Falcon Heavy be a better option to launch satellites to Mars?
« Last Edit: 02/13/2018 07:07 PM by M.E.T. »

Online envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1290 on: 02/13/2018 07:11 PM »
Veering off the cost discussion briefly. I was wondering if BFR is capable of delivering satellites into Martian orbit. If SpaceX wanted a Martian GPS network, or wanted communication and other satellites in place to support their Mars program, would BFR be the vehicle to deliver these satellites?

From a previous discussion my understanding is that BFS is not capable of decelerating into Martian obit, and instead needs the Martian atmosphere to bleed off 99% of its energy prior to landing. If so, does this mean that BFS is not able to slow down, open its cargo door and just  pop out a half dozen satellites around Mars?

And if not, would a Falcon Heavy be a better option to launch satellites to Mars?

BFS should be able to aerocapture and then aerobrake into a LMO. It's not substantially harder than direct entry to a pinpoint landing.

The hard part is having enough fuel to return home.

Online speedevil

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1291 on: 02/13/2018 09:05 PM »
From a previous discussion my understanding is that BFS is not capable of decelerating into Martian obit, and instead needs the Martian atmosphere to bleed off 99% of its energy prior to landing.
 If so, does this mean that BFS is not able to slow down, open its cargo door and just  pop out a half dozen satellites around Mars?

'No.'
BFS needs to aerobrake, in order to get from interplanetary to Mars orbit.
This however does not mean that it has to land.
In this thread, I was noting that in the nominal as presented at IAC landing, at 4.5km/s or so, after slowing from the 7km/s or so transit aerodynamically, BFS is aerodynamically diving down, in order to keep inside the atmosphere.
If, around this time you flip the vehicle 180 degrees or so, and begin to thrust up at the right point, you end up in a 40km periares orbit. (all aerodynamically, with no main engine thrust).

You then just need several tens of m/s to circularise, and can drop payload as you like at this point.

If you then drop more than a few tons of satellites, you may actually save on propellant, as you do not need to spend propellant landing these satetellites.

There are variants of this.
In this thread I was wondering about the smallest Martian lander - beagle 2 was 30kg or so, and there have been penetrators which have been 3 kg only.

You can, a week before entry of BFS, kick out at tens of meters a second atmospheric probes that will either directly enter and land on the surface on their own, or be floating through the atmosphere giving precise information on the composition in the minutes before entry.

Similarly, a _lot_ of tiny probes could be dropped that will all do lifting entries ala-BFR and go into their own orbits after circularisation at different inclinations.
This is obviously harder on the payloads design side.

Dropping off a hundred lightly modified Starlink sats, in LMO, with solar-electric propulsion, before reentry does not require any extra propellant, as you save on the landing propellant. (every four tons you drop off means you need one ton less of landing propellant, this rapidly exceeds the amount needed to circularise and do the entry burn).

Offline biosehnsucht

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1292 on: 02/14/2018 01:20 AM »
TL;DR : How much payload mass could a BFS get to TMI, then  brake back into Earth orbit after releasing the payload? Less than the advertised payload to LEO? More? Assume refueling on orbit is a thing and thus you can do this with maximum prop load. For bonus cool points, can it do a Martian fly-by without landing and come back to Earth?

Assuming a suitably small-yet-still-useful payload mass for satellite(s)/lander(s) to be deployed to Mars, could a BFS get close enough to Mars to deploy satellites and then return to Earth (neither landing nor staying in orbit at Mars)? Possibly just accelerating the payload to TMI, ejecting it, and then slowing down to return to Earth orbit?

This assumes the payload has the propellant and/or aerodynamic ability to capture at Mars, but seeing as how that's been done before (we've got Martian probes already orbiting Mars), that doesn't seem that hard to do one way or the other.

The more interesting method would be to have the BFS "free return around Mars", keeping the payload(s) protected until reaching Mars, but even just getting payloads to TMI would be something.

Googling a bit... the active orbiters masses including prop at launch (so everything they needed to brake into orbit)
MOM : 1,337.2 kg (2,948 lb)
MAVEN : 2,454 kg (5,410 lb)
ExoMars Trace Gas Orbiter : 3,755 kg (8,278 lb)
MRO : 2,180 kg (4,810 lb)
Mars Express : 1,120 kg (2,470 lb)
Mars Odyssey : 758 kg (1,671 lb)

So it seems the typical orbiter, including prop to enter orbit on it's own, is in the range of masses for typical geosynchronous satellites. With refueling in orbit (as would be done for actual journeys to Mars), at least the release payload from TMI and return to Earth option should be doable, right? You might even be able to get half a dozen or so payloads launched in one BFS launch, though you might need some fancy dispenser to do it with. It seems that it would take very few BFS launches to deploy a Martian Starlink, as long as the payloads can survive the interplanetary journey? Alternatively to dispensing many smaller payloads from a BFS just after TMI, deploy a large single payload that can brake into Martian orbit, and then dispenses the actual Starlinks.

I'd assume any such Martian Starlinks would have not just telecommunications packages but also some useful scientific instruments which don't need to be singularly amazing but combined could provide sufficiently detailed data on atmospheric conditions and such for any inbound BFS landing attempt.

I didn't look at all the Martian lander masses, but I assume you could similarly shotgun a bunch of landers using a BFS to get them to TMI, if you wanted to pepper a potential landing site with instrumentation that could both provide solid terminal navigation (either by itself like LORAN or combined with satellites like DGPS) and useful data on ground conditions, etc.

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1293 on: 02/14/2018 01:43 AM »
TL;DR : How much payload mass could a BFS get to TMI, then  brake back into Earth orbit after releasing the payload? Less than the advertised payload to LEO? More? Assume refueling on orbit is a thing and thus you can do this with maximum prop load.

Is a useful first step.
http://www.quantumg.net/rocketeq.html as a second one.
Assuming 380s ISP, 1185t wet, 85t dry, gives a delta-v of 9812m/s.
This is considerably more than twice the minimum energy transit to Mars from LEO.
So, we can throw stuff at Mars from LEO and come back.
Going from an orbit like GTO, will cut the delta-v from around 3800 to perhaps 3000.
So, 6000m/s delta-v required or so.

Going back to the rocket equation calculator tells us that we can do 6000m/s with a 150 ton payload, but this is misleading, as in fact we need to end up with 85 tons, in order to have it work out most payload.
So, 85 tons at the end of the mission, 3km/s gives 190 total tons before the burn back to same initial velocity.
.
Initial burn is at 1185t+payload,  3000m/s, and needs to end at 190 tons + payload mass.

Taking a guess at 300 tons, that is an initial mass of 1485, 3000m/s, leading to 663 tons, or 363 tons, or 160 tons of fuel extra.

600 tons gives 797 tons afterwards, which is 7 tons of fuel spare.

This is however, 600 tons of payload which will need its own mid-course correction, and landing gear, unless you want to smack it into Phobos at 5km/s.




Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1294 on: 02/14/2018 10:49 PM »
It's true the Moon won't allow aerobraking or capture but the total delta V is substantially less to get there and back than from Mars. 150 tonnes to Mars gives plenty of room for a lighter loaded BFS to run a complete Lunar surface mission while still having a very substantial payload to (and from) the surface by Apollo standards.

I think it would be very interesting to see how many tankers would be needed per how many tonnes of payload. Also the same for circumlunar and LLO missions.
Good question.  The joker is payload Vs needed delta V.

The Moon was not (AFAIK) a design driver destination for BFS design. Wings are completely redundant for it. I'm guessing SX would want to go with a minimal mission. The ideal basic mission is no refueling. Just the BFS flying to the Moon, (landing?) and returning.

I'm not sure that's possible so the minimal after that is 1 tanker launch.  AFAIK SX has no plans to build any kind of Lunar habitat so anything beyond landing, taking off and returning to Earth would (I presume) be expected to be handled by other people.

In principle BFS has the size, payload capacity and operating costs to undercut any potential launch services supplier for any plausible architecture.  A case of "If you have the habs and the rovers we can get you there."
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Offline Robotbeat

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1295 on: 02/14/2018 11:04 PM »
They need a bunch of tanker flights to send BFS to the Moon, landing, and returning. Actually, several more than it takes to just send BFS to Mars.
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Offline GORDAP

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1296 on: 02/14/2018 11:15 PM »
It's true the Moon won't allow aerobraking or capture but the total delta V is substantially less to get there and back than from Mars. 150 tonnes to Mars gives plenty of room for a lighter loaded BFS to run a complete Lunar surface mission while still having a very substantial payload to (and from) the surface by Apollo standards.

I think it would be very interesting to see how many tankers would be needed per how many tonnes of payload. Also the same for circumlunar and LLO missions.
Good question.  The joker is payload Vs needed delta V.

The Moon was not (AFAIK) a design driver destination for BFS design. Wings are completely redundant for it. I'm guessing SX would want to go with a minimal mission. The ideal basic mission is no refueling. Just the BFS flying to the Moon, (landing?) and returning.

I'm not sure that's possible so the minimal after that is 1 tanker launch.  AFAIK SX has no plans to build any kind of Lunar habitat so anything beyond landing, taking off and returning to Earth would (I presume) be expected to be handled by other people.

In principle BFS has the size, payload capacity and operating costs to undercut any potential launch services supplier for any plausible architecture.  A case of "If you have the habs and the rovers we can get you there."

I know that Methane is probably a non-starter for lunar ISRU, but what about the LOX?  I thought I'd read that it would be fairly simple to extract O2 from lunar rocks using a solar furnace.  If so, would it make sense to send a BFS to the Moon with the LOX expended during landing, but with enough Methane left over for the return flight?   Then just refuel the LOX tank for the trip home.  And if that works, would it significantly increase the possible payload(s)?

Offline biosehnsucht

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1297 on: 02/14/2018 11:30 PM »
This is however, 600 tons of payload which will need its own mid-course correction, and landing gear, unless you want to smack it into Phobos at 5km/s.

Well, that's quite a payload! To even put that much on a BFS you'd have to use multiple launches to LEO and then move it in space to a single BFS, right?

So generally, if you can fit your payload(s) into a Cargo BFS somehow, it can put it on a TMI trajectory. If we're being lazy and not doing on-orbit payload assembly to get to 600t, that is still up to 150t to TMI, right? That is pretty crazy. Even after factoring out whatever mass you spend on braking into TMI, you're going to have an insane amount of mass left for an orbiter or lander, etc.

So assuming that BFS/BFR launching goes as planned, and in-space refueling, they can start lobbing anything they want "on the cheap" at Mars.

With so much mass that can be thrown, should be able to take a lazy approach to engineering with overbuilt / redundant systems and excess maneuvering / orbit braking dV etc. Without a need to save every kg of mass, should be possible to do some interesting things.

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1298 on: 02/15/2018 01:34 AM »
This is however, 600 tons of payload which will need its own mid-course correction, and landing gear, unless you want to smack it into Phobos at 5km/s.

Well, that's quite a payload! To even put that much on a BFS you'd have to use multiple launches to LEO and then move it in space to a single BFS, right?<snip>

With so much mass that can be thrown, should be able to take a lazy approach to engineering with overbuilt / redundant systems and excess maneuvering / orbit braking dV etc. Without a need to save every kg of mass, should be possible to do some interesting things.

Pretty much.
BFS-chomper can have it loaded pretty easily in orbit, but it's even somewhat density constrained.
Much under the density of water, and you actually run out of volume.

Offline niwax

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #1299 on: 02/15/2018 01:52 AM »
One thing that has emerged from this thread is that with BFR, we truly are beyond anything seen before in spaceflight. Every way people try to approximate cost or come up with missions sound slightly to very off compared to any traditional vehicle.

If turnaround costs of $0.5m and times of a day or two hold and the vehicle does not show significant depreciation per launch, there is no question of replacing even tiny launch vehicles. They can simply have a small payload option that will throw you sat into orbit for $1-2m between big, properly profitable launches the same way software startups tend take on contracts to design websites and such between actual customers to get more optimal utilization. Another option that hasn't been discussed is more aggressive batching of small payloads. Who cares if they're headed for significantly different orbits when you're literally only using 2% of your capacity. They can run it like a bus service, offering a bunch of cheap slots on a regular basis, pretty much wiping out the custom small launcher market.

By the same numbers, a BFR that doesn't need to hit amortization targets when used by SpaceX internally would cost them on the order of $0.5m for the inital orbit and say $3.5m for subsequent refueling flights. If they can pull that off, they can really throw stuff at Mars as they wish. Even according for the price of the Mars vehicle that won't be available for commercial missions during that time they may be able to push a Mars launch into current F9 territory.

These number sound like, and probably are, completely wrong. But that's what makes me so excited. We're finally talking about a rocket that is so different we can't quite grasp it.

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