BFR and the space industry

[Lars-J]

The BFR is a fine idea, the BFS is daft, SpaceX will either go with a simple reusable second stage by themselves, or Blue Origin will show them how to do it.

Unnecessary problems with BFS:

Integrated Fairing  The payload is bigger in volume than the upper stage.  That fairing is huge and heavy (the F9 fairing is about the same mass as the second stage!) and as you say is expensive to take to orbital velocity and back.  I don't think it should come down on its own, because then you need ships out there to get it regardless of where the booster is landing.  It should be a part of the BFR and land with that.  This means it encapsulates the second stage as well as the payload, but that's got benefits as well as costs.

Heat Shield  PICA-X is great stuff, but like the Shuttle tiles it's porous.  The BFS design puts it on the outside of the spacecraft to get rained on while on the pad.  The absorbed water will freeze while in orbit and can break the tiles, and can also break tiles while vaporizing during reentry.  The Shuttle had lots of delays and work associated with its exposed heat shield.

The obvious place for the heat shield is inside the fairing.  It'll still need refurb because it gets exposed to moisture after landing, but for high-tempo operations they might conceivably get the PICA inside a controlled low-humidity atmosphere before it gets cold.

Legs  They will have the technology to land on a cradle.  I'm not as exercised about this as the fairing, as the legs are 1/6th as much mass.

People  Since the vast majority of upmass in ten years will be comsats, people and their related gear should go in something that doesn't affect the comsat launching missions.  If I was going to Mars, I'd want to see something that had an inflatable part that aerobrakes but doesn't reenter, and maybe large propellant tanks that get filled while in orbit around Mars.

I thought you were arguing for a *simpler* reusable upper stage.   

[su27k]

I think the idea of manufacturing in space is just bonkers.  The future seems pretty obvious to me.  It's going to be LEO comsat constellations. 

That's like saying the obvious application of better 3D graphics card is better 3D games, yes it's obvious but it is also missing the unknown unknowns. It turns out better 3D graphics card has a huge usage outside games and enables a whole new industry to emerge, this was not obvious at the time.

[envy887]

Well said.

I'm especially fine with the scale.  They are going to need gobs of lift for the comsat constellation.  Elon is right on point when he says that chartering a 747 from North America to Australia, and back, costs about what a new Cessna 206 goes for.  A 747 is 220 tonnes.  Last year's iteration of BFR was penciled at 275 tonnes, this year it's smaller.  It'll be an evolutionary step for building large composite airframes.

I'm a little less impressed with the switch from 12m to 9m.  Rockets don't scale well with height.  Essentially you are lifting a tank of LOX on a base of compressed gas.  If that column gets taller the average pressure at the base must get larger.  Booster engine exit pressure wants to be around 40-50 kPa, and average base pressure can increase with increasing chamber pressure... but it's not 1:1.  So once the rocket is as tall as the Saturn V, stop scaling height and scale diameter instead.  Also, SpaceX should budget for lower density payloads, which implies larger diameter fairings.  The 3.6m road transport standard was a smart move, but once they commit to barging it they should go big and squat.

Unnecessary problems with BFS:

Integrated Fairing  The payload is bigger in volume than the upper stage.  That fairing is huge and heavy (the F9 fairing is about the same mass as the second stage!) and as you say is expensive to take to orbital velocity and back.  I don't think it should come down on its own, because then you need ships out there to get it regardless of where the booster is landing.  It should be a part of the BFR and land with that.  This means it encapsulates the second stage as well as the payload, but that's got benefits as well as costs.

Heat Shield  PICA-X is great stuff, but like the Shuttle tiles it's porous.  The BFS design puts it on the outside of the spacecraft to get rained on while on the pad.  The absorbed water will freeze while in orbit and can break the tiles, and can also break tiles while vaporizing during reentry.  The Shuttle had lots of delays and work associated with its exposed heat shield.

The obvious place for the heat shield is inside the fairing.  It'll still need refurb because it gets exposed to moisture after landing, but for high-tempo operations they might conceivably get the PICA inside a controlled low-humidity atmosphere before it gets cold.

Legs  They will have the technology to land on a cradle.  I'm not as exercised about this as the fairing, as the legs are 1/6th as much mass.

People  Since the vast majority of upmass in ten years will be comsats, people and their related gear should go in something that doesn't affect the comsat launching missions.  If I was going to Mars, I'd want to see something that had an inflatable part that aerobrakes but doesn't reenter, and maybe large propellant tanks that get filled while in orbit around Mars.

The first problem with a fairing on the booster is that F9 stages before fairing sep, and BFR will stage even sooner. Atlas can get away with it because the booster is 10x as large as Centaur, but the BF booster is barely 2x the size of BFS and will stage low and slow enough that many payloads still need cover.

The other problem is you need an aerodynamic profile on the way up AND on the way down, so shedding your aero nose upon reaching space causes significant issues for the return. Now you can't get your large and expensive satellite dispenser system back, and you have to mount the payload dispenser through the heatshield.

Water ingress can be solved by covering or spraying the heatshield on the ground. IMO they will have to put a frame around the BFS for transport and lifting atop the BF booster anyway (see the frame around the F9 fairing), so a heatshield cover could be built right into that frame and only removed shortly before launch.

Edit: the F9 fairing is heavy mostly because it carries the full weight of the payload and PAF during integration. The BFS will probably not do vertical encapsulation like F9, so the "fairing" never has to carry payload mass, and is load-limited either by Max-Q (most likely) or reentry (probably not).

[oiorionsbelt]

IIRC the silver-ish coating on the Dragon PICA X heat shield is exactly that. A waterproof covering.

[IainMcClatchie]

The first problem with a fairing on the booster is that F9 stages before fairing sep, and BFR will stage even sooner. Atlas can get away with it because the booster is 10x as large as Centaur, but the BF booster is barely 2x the size of BFS and will stage low and slow enough that many payloads still need cover.

As you point out, it's possible to stage earlier or later.  The current F9 stages about 20 seconds before fairing separation.  It's possible to stage later.  Why would BFR stage sooner?

Also, Starlink satellites are going to 1000 km orbit.  That's a more lofted trajectory than the 400 km ISS or 650 km LEO sat orbits, so there is less performance loss associated with staging right around fairing sep.

Finally, if the later staging ended up being a performance issue, BFR could land on a barge, partially refuel, and then boost back to its launch site.  I expect this would only show up as a problem once orbital deliveries were in full swing.

The other problem is you need an aerodynamic profile on the way up AND on the way down, so shedding your aero nose upon reaching space causes significant issues for the return. Now you can't get your large and expensive satellite dispenser system back, and you have to mount the payload dispenser through the heatshield.

I agree that the dispenser is now no longer reusable.  That's a drawback.

Dragon mounts to its trunk around the heatshield, and the BF2 can mount to its payload in some similar way.

Water ingress can be solved by covering or spraying the heatshield on the ground.

IIRC the silver-ish coating on the Dragon PICA X heat shield is exactly that. A waterproof covering.

This is a good idea.

Edit: the F9 fairing is heavy mostly because it carries the full weight of the payload and PAF during integration. The BFS will probably not do vertical encapsulation like F9, so the "fairing" never has to carry payload mass, and is load-limited either by Max-Q (most likely) or reentry (probably not).

That's odd.  The weight of the payload and PAF are all borne through the base of the fairing, where it attaches to the second stage, right?  Isn't this where the external frame used during horizontal integration attaches as well?  So why would those loads go through any part of the fairing except the ring at the base?

[rakaydos]

That's odd.  The weight of the payload and PAF are all borne through the base of the fairing, where it attaches to the second stage, right?  Isn't this where the external frame used during horizontal integration attaches as well?  So why would those loads go through any part of the fairing except the ring at the base?

Leverage and torque. With several tons suspenced sideways from 1 side, the fairing would be reinforced to not let the payload droop, and as a rigid structure the weight of payload+fairing is distributed such that supporting the top of the fairing makes sencse.

[envy887]

The first problem with a fairing on the booster is that F9 stages before fairing sep, and BFR will stage even sooner. Atlas can get away with it because the booster is 10x as large as Centaur, but the BF booster is barely 2x the size of BFS and will stage low and slow enough that many payloads still need cover.

As you point out, it's possible to stage earlier or later.  The current F9 stages about 20 seconds before fairing separation.  It's possible to stage later.  Why would BFR stage sooner?

Ratio of delta-v available from each stage determines staging velocity, which with trajectory shaping (lofting) determines altitude. BFR will fly a lofted trajectory, but it will also stage early for RTLS. Remember that BFR only does RTLS as far as we know, not downrange landing. Higher staging velocity and distance makes RTLS exponentially more difficult.

[IainMcClatchie]

Remember that BFR only does RTLS as far as we know, not downrange landing.

Why would that be?  SpaceX is committed to making BFR able to refly reliably.  Why not just land on a barge, refuel, and fly home?

The infrastructure for sea launch seems daunting, but note that it's just the infrastructure for launch, and not the infrastructure for integrating the payload.  They are already talking about it with the P2P trips.

Moving the fairing from the second to the first stage cuts nearly in half the amount of mass that must be landed from orbit.  That is a very significant benefit.  The cost of staging 20 seconds later seems small in comparison.  However, I have not done the simulations yet to show this.  I do have a simulator, but it's 2D and not at all as good as the other simulators here.

[Robotbeat]

Whether down range landings are worth it or not depends on the ratio between first stage and upper stage refurbishment costs for the tanker.

[Lars-J]

Remember that BFR only does RTLS as far as we know, not downrange landing.

Why would that be?  SpaceX is committed to making BFR able to refly reliably.  Why not just land on a barge, refuel, and fly home?

Because it will only be economical if it flies a lot. And reduces time and expense of refurbishment. This is why the plan is to land back at the launch mount - They don't even want to spend time moving it between a landing area and its launch pad. So this is why it is RTLS only.

You can dream up other scenario for your "perfect launcher" all you want, but this is what SpaceX is doing.

[2552]

I wonder if a better way to go than downrange landing + refuel + relaunch is to add a pair of strakes like New Glenn has to the sides of the booster but still RTLS directly. The lifting reentry would eliminate the reentry burn and allow staging later for the same amount of boostback fuel, because the boostback burn wouldn't need to move the IIP all the way back to the launch site, since the lifting reentry would take care of the rest of the distance back.

This could possibly increase payload to 180 tons or a bit more. It would also avoid the need for a ship to land on, fuel tankers to ship relaunch fuel to it, nosecones that need to be robotically attached to the booster before launch, and a second launch and reentry. Also reduces engine starts for recovery to 2 vs the 3 of current SpaceX boostback, reentry and landing burns.

[livingjw]

The first problem with a fairing on the booster is that F9 stages before fairing sep, and BFR will stage even sooner. Atlas can get away with it because the booster is 10x as large as Centaur, but the BF booster is barely 2x the size of BFS and will stage low and slow enough that many payloads still need cover.

As you point out, it's possible to stage earlier or later.  The current F9 stages about 20 seconds before fairing separation.  It's possible to stage later.  Why would BFR stage sooner?

Ratio of delta-v available from each stage determines staging velocity, which with trajectory shaping (lofting) determines altitude. BFR will fly a lofted trajectory, but it will also stage early for RTLS. Remember that BFR only does RTLS as far as we know, not downrange landing. Higher staging velocity and distance makes RTLS exponentially more difficult.

We did a "RTLS" staging trade off years ago and found that for a high performance staged combustion HC rocket the optimum (minimum takeoff mass) staging velocity was around 6500 ft/s.

John

[IainMcClatchie]

I wonder if a better way to go than downrange landing + refuel + relaunch is to add a pair of strakes like New Glenn has to the sides of the booster but still RTLS directly. The lifting reentry would eliminate the reentry burn and allow staging later for the same amount of boostback fuel, because the boostback burn wouldn't need to move the IIP all the way back to the launch site, since the lifting reentry would take care of the rest of the distance back.

This could possibly increase payload to 180 tons or a bit more. It would also avoid the need for a ship to land on, fuel tankers to ship relaunch fuel to it, nosecones that need to be robotically attached to the booster before launch, and a second launch and reentry. Also reduces engine starts for recovery to 2 vs the 3 of current SpaceX boostback, reentry and landing burns.

Note that if the fairing is part of BFR, there is no need to mess with nosecones.

I think the reentry burn is to protect the bottom of the booster from the shockwave heat, and not so much to slow it down.  If you eliminate the retroburn you need to figure out how to survive the heat, and in particular how the engines are going to survive the heat.

[envy887]

I wonder if a better way to go than downrange landing + refuel + relaunch is to add a pair of strakes like New Glenn has to the sides of the booster but still RTLS directly. The lifting reentry would eliminate the reentry burn and allow staging later for the same amount of boostback fuel, because the boostback burn wouldn't need to move the IIP all the way back to the launch site, since the lifting reentry would take care of the rest of the distance back.

This could possibly increase payload to 180 tons or a bit more. It would also avoid the need for a ship to land on, fuel tankers to ship relaunch fuel to it, nosecones that need to be robotically attached to the booster before launch, and a second launch and reentry. Also reduces engine starts for recovery to 2 vs the 3 of current SpaceX boostback, reentry and landing burns.

Note that if the fairing is part of BFR, there is no need to mess with nosecones.

I think the reentry burn is to protect the bottom of the booster from the shockwave heat, and not so much to slow it down.  If you eliminate the retroburn you need to figure out how to survive the heat, and in particular how the engines are going to survive the heat.

The entry burn is both to slow the booster and push the shockwave away.

New Glenn is planned to forgo the entry burn and reduce heating by using lift to get more deceleration in the upper atmosphere. This is fine for downrange landings where the entry angle is low and the vehicle spends a lot of time in the upper atmosphere, but does not work for RTLS where the vehicle is plunging almost directly down, passing through the thin upper atmosphere very quickly.

[envy887]

Remember that BFR only does RTLS as far as we know, not downrange landing.

Why would that be?  SpaceX is committed to making BFR able to refly reliably.  Why not just land on a barge, refuel, and fly home?

The infrastructure for sea launch seems daunting, but note that it's just the infrastructure for launch, and not the infrastructure for integrating the payload.  They are already talking about it with the P2P trips.

Moving the fairing from the second to the first stage cuts nearly in half the amount of mass that must be landed from orbit.  That is a very significant benefit.  The cost of staging 20 seconds later seems small in comparison.  However, I have not done the simulations yet to show this.  I do have a simulator, but it's 2D and not at all as good as the other simulators here.

Landing from orbit allows 99% of the downrange energy to be dissipated by the heatshield, while for RTLS it has to be entirely propulsively dissipated, plus return energy added. At some point, it's more payload efficient to carry more mass to orbit than to carry your booster further downrange, and I'm sure SpaceX is evaluating this tradeoff.

One thing you're missing is that Elon wants a Mars lander, and he's going to make that Mars lander be a vehicle that can be used for everything else (sat launch, Moon support, Earth returns) because that's the only way to pay for it. A Mars lander means lots of downmass through atmospheric entry (and upmass atmospheric launch, because the same vehicle has to be used for Earth return because $$$). Any design that does not get significant downmass to Mars and Earth is right out for SpaceX.

SpaceX has little use for a vehicle that's mostly reusable (potentially fully) but doesn't get significant downmass. They have Falcon 9 already, and it does the same thing.

[oldAtlas_Eguy]

The first problem with a fairing on the booster is that F9 stages before fairing sep, and BFR will stage even sooner. Atlas can get away with it because the booster is 10x as large as Centaur, but the BF booster is barely 2x the size of BFS and will stage low and slow enough that many payloads still need cover.

As you point out, it's possible to stage earlier or later.  The current F9 stages about 20 seconds before fairing separation.  It's possible to stage later.  Why would BFR stage sooner?

Ratio of delta-v available from each stage determines staging velocity, which with trajectory shaping (lofting) determines altitude. BFR will fly a lofted trajectory, but it will also stage early for RTLS. Remember that BFR only does RTLS as far as we know, not downrange landing. Higher staging velocity and distance makes RTLS exponentially more difficult.

We did a "RTLS" staging trade off years ago and found that for a high performance staged combustion HC rocket the optimum (minimum takeoff mass) staging velocity was around 6500 ft/s.

John

1.981 km/s

[ZachF]

Remember that BFR only does RTLS as far as we know, not downrange landing.

Why would that be?  SpaceX is committed to making BFR able to refly reliably.  Why not just land on a barge, refuel, and fly home?

The infrastructure for sea launch seems daunting, but note that it's just the infrastructure for launch, and not the infrastructure for integrating the payload.  They are already talking about it with the P2P trips.

Moving the fairing from the second to the first stage cuts nearly in half the amount of mass that must be landed from orbit.  That is a very significant benefit.  The cost of staging 20 seconds later seems small in comparison.  However, I have not done the simulations yet to show this.  I do have a simulator, but it's 2D and not at all as good as the other simulators here.

Landing from orbit allows 99% of the downrange energy to be dissipated by the heatshield, while for RTLS it has to be entirely propulsively dissipated, plus return energy added. At some point, it's more payload efficient to carry more mass to orbit than to carry your booster further downrange, and I'm sure SpaceX is evaluating this tradeoff.

One thing you're missing is that Elon wants a Mars lander, and he's going to make that Mars lander be a vehicle that can be used for everything else (sat launch, Moon support, Earth returns) because that's the only way to pay for it. A Mars lander means lots of downmass through atmospheric entry (and upmass atmospheric launch, because the same vehicle has to be used for Earth return because $$$). Any design that does not get significant downmass to Mars and Earth is right out for SpaceX.

SpaceX has little use for a vehicle that's mostly reusable (potentially fully) but doesn't get significant downmass. They have Falcon 9 already, and it does the same thing.

They have transferred more impulse on to the second stage in the new iteration versus the old one.

ITS 2016 had a 6,975 tonne first stage and a 2,100 tonne second stage (sans payload); 3.32:1
BFR 2017 has a ~3,065 tonne first stage and a 1,185 tonnes second stage (again w/o payload); 2.59:1

[IainMcClatchie]

Landing from orbit allows 99% of the downrange energy to be dissipated by the heatshield, while for RTLS it has to be entirely propulsively dissipated, plus return energy added.

This statement is misleading.  In particular, landing from orbit must take at least as much fuel as landing downrange.  The heatshield (and mostly the atmosphere) can dissipate much of the excess energy.

If SpaceX is forgoing downrange landings for BFR (and I doubt they are certain of that yet), then they must think those downrange ops cost more than the lost payload of BFS vs something closer to a traditional second stage (I'm calling that BF2 here).  Maybe they are thinking that (a) satellite payloads won't scale up to what BF2 could deliver, and BFS is good enough, and (b) nobody else is going to compete with BFS, in particular, ULA and BO will both fail to field a big rocket, in an environment where the Air Force is willing to spend more than SpaceX has so far to ensure two competitors are flying their payloads.  That could happen, as Air Force payloads are small compared to BFS scale payloads.  I wouldn't bet on it.

One thing you're missing is that Elon wants a Mars lander, and he's going to make that Mars lander be a vehicle that can be used for everything else (sat launch, Moon support, Earth returns) because that's the only way to pay for it. A Mars lander means lots of downmass through atmospheric entry (and upmass atmospheric launch, because the same vehicle has to be used for Earth return because $$$). Any design that does not get significant downmass to Mars and Earth is right out for SpaceX.

Agreed.  If they stick to this idea they'll have a system which is inefficient for the majority of launches, and they'll get their asses handed to them by Blue Origin and fail to make enough profit to get to Mars.

[cppetrie]

Landing from orbit allows 99% of the downrange energy to be dissipated by the heatshield, while for RTLS it has to be entirely propulsively dissipated, plus return energy added.

This statement is misleading.  In particular, landing from orbit must take at least as much fuel as landing downrange.  The heatshield (and mostly the atmosphere) can dissipate much of the excess energy.

If SpaceX is forgoing downrange landings for BFR (and I doubt they are certain of that yet), then they must think those downrange ops cost more than the lost payload of BFS vs something closer to a traditional second stage (I'm calling that BF2 here).  Maybe they are thinking that (a) satellite payloads won't scale up to what BF2 could deliver, and BFS is good enough, and (b) nobody else is going to compete with BFS, in particular, ULA and BO will both fail to field a big rocket, in an environment where the Air Force is willing to spend more than SpaceX has so far to ensure two competitors are flying their payloads.  That could happen, as Air Force payloads are small compared to BFS scale payloads.  I wouldn't bet on it.

One thing you're missing is that Elon wants a Mars lander, and he's going to make that Mars lander be a vehicle that can be used for everything else (sat launch, Moon support, Earth returns) because that's the only way to pay for it. A Mars lander means lots of downmass through atmospheric entry (and upmass atmospheric launch, because the same vehicle has to be used for Earth return because $$$). Any design that does not get significant downmass to Mars and Earth is right out for SpaceX.

Agreed.  If they stick to this idea they'll have a system which is inefficient for the majority of launches, and they'll get their asses handed to them by Blue Origin and fail to make enough profit to get to Mars.

Inefficient how? In fuel? Who cares; fuel is cheap. Based on the architecture they’ve described, the capital cost of the machine is high but is fully reused 100s of times meaning the portion of machine cost per launch is small. The cost of launch is driven by fuel and ops, which are being designed to be cheap. Spend more on machine to reduce cost of operations. The economics of this model are well-proven in other industries such as air travel as is cited regularly. Now, whether this architecture is achievable is another question altogether, but I don’t think you can argue with the economics of what is described. The same basic plane designs are configured in numerous ways to accomplish many operational missions (passenger, cargo, etc.). The unique purpose-built plane that is designed for one specific use case (e.g. the guppy) is the rarity. If SpaceX is able to realize the architecture they have proposed, they will be just fine.

My 2 cents, anyway.

[envy887]

Landing from orbit allows 99% of the downrange energy to be dissipated by the heatshield, while for RTLS it has to be entirely propulsively dissipated, plus return energy added.

This statement is misleading.  In particular, landing from orbit must take at least as much fuel as landing downrange.  The heatshield (and mostly the atmosphere) can dissipate much of the excess energy.

If SpaceX is forgoing downrange landings for BFR (and I doubt they are certain of that yet), then they must think those downrange ops cost more than the lost payload of BFS vs something closer to a traditional second stage (I'm calling that BF2 here).  Maybe they are thinking that (a) satellite payloads won't scale up to what BF2 could deliver, and BFS is good enough, and (b) nobody else is going to compete with BFS, in particular, ULA and BO will both fail to field a big rocket, in an environment where the Air Force is willing to spend more than SpaceX has so far to ensure two competitors are flying their payloads.  That could happen, as Air Force payloads are small compared to BFS scale payloads.  I wouldn't bet on it.

One thing you're missing is that Elon wants a Mars lander, and he's going to make that Mars lander be a vehicle that can be used for everything else (sat launch, Moon support, Earth returns) because that's the only way to pay for it. A Mars lander means lots of downmass through atmospheric entry (and upmass atmospheric launch, because the same vehicle has to be used for Earth return because $$$). Any design that does not get significant downmass to Mars and Earth is right out for SpaceX.

Agreed.  If they stick to this idea they'll have a system which is inefficient for the majority of launches, and they'll get their asses handed to them by Blue Origin and fail to make enough profit to get to Mars.

Blue has to launch at all, and then launch cheaper. SpaceX does not optimize for per-launch efficiency, they optimize for cost. Sending a spaceship that is twice as big as it needs to be to LEO? No problem, as long as its the cheapest because it's the same ship they use for everything else.

And you are assuming that SpaceX cannot profit sufficiently from downmass. If someone finds something that's profitable to bring to space and back (like people) or manufacture in space and return to Earth (ZBLAN fiber, perhaps) than that downmass is worth a lot of money.