The SLS: too expensive for exploration?

Tom Kalbfus · 2016-06-01 10:08:15

How much is the SLS worth? What if SpaceX were to buy it, and the factories designed to build it? You think they could get it going? The could probably hire the folks they need to get it build and layoff all the rest. Maybe they could even modify the lower stage of the SLS so it can land, it is made with reusable shuttle engines after all.

GW Johnson · 2016-06-01 10:15:36

I don't see Spacex wanting to take over SLS at all. Why would they want to?

It was designed to be thrown away, not reused, which makes it extremely expensive inherently. You cannot change fundamental design flaws with tack-on band-aids. Flying back SLS first stages is not a realistic goal.

Plus, they got their hands full just keeping up with Falcon-9, Falcon-Heavy, and two (or maybe three) versions of Dragon. Look at their launch manifest: it is backlogged. That is driven by the production bottleneck, which is taking all their efforts to deal with. Simplifying the Falcon stage versions to a common core and side boosters was a big part of dealing with that.

Their Raptor methane-oxygen large engine , and the huge "Mars Colonial Transporter" rocket that Raptor is for, are years away. Those are just paper design notions right now.

GW

Last edited by GW Johnson (2016-06-01 10:20:14)

SpaceNut · 2016-06-03 06:03:58

Space x would need to create its own version of all the pieces that make of the SLS for them to be able to lower the costs that is the results of its current contractors.... So while they could make many parts without any thought there are a few that would need huge developement money by them in order to duplicate the performance of those parts.
First up would be the SRB or any powerful liquid type booster, Second would be the Lox/LH2 engines in the first stage of comparible size to the RS25.....next would be the upper stage engine and then a service module for support of the Dragon capsule.....

RobertDyck · 2016-06-03 09:44:04

If SpaceX were to develop a heavy lift launch vehicle, why make the same mistakes? Don't use LH2 for the first stage, and don't use solids. Saturn V used RP1/LOX for the first stage, because that makes the most sense and most cost effective. SpaceX already uses RP1/LOX for their Falcon 9 and Falcon Heavy, so just use that. If you want a liquid booster, Falcon Heavy already has them: a pair Falcon 9 core stages. The current fad is to use a sustainer stage and boosters instead of first and second stage, because you can use engines of the sustainer stage for initial launch and cross-feed propellant. So when boosters separate, the sustainer stage has full tanks. That makes sense, SpaceX would want to continue that. Only upper stage(s) would use LH2/LOX.

GW Johnson · 2016-06-03 11:28:31

Well, if your design has a lift-off thrust problem, but otherwise looks good, IMHO there is nothing wrong with adding solids to it. I think our shuttle experiences verify that we really don't want to reuse them, though.

Nor do we need them all the way to the typical first stage burnout (around 10,000 ft/sec = 3 km/s, essentially exoatmospheric). They are for thrust low down and slow, where thrust is far more important than Isp because weight is still so high. They are essentially just big JATO bottles to help get overweight stuff off the ground quicker.

And if you design them correctly, they will be safe for use on manned flights, too.

NASA still to this day does not know a proper, safe design from a tragedy-in-the-making. They still think the final SRB design was good. Stupid is as stupid does, clearly.

GW

RobertDyck · 2016-06-03 11:36:05

I would argue the solids on Delta IV and Atlas V make sense. The big solids on Shuttle did not. For exactly the reasons you stated. But SpaceX is using RP1/LOX, so continue that.

SpaceNut · 2016-06-04 19:02:11

So in order to get to that next level for Space x they will need to develope a stronger engine one more capable than where they are now as it takes to many engine to get the thrust level that is needed for that next step in tonnage.....

Tom Kalbfus · 2016-06-04 20:51:10

GW Johnson wrote:

I don't see Spacex wanting to take over SLS at all. Why would they want to?
It was designed to be thrown away, not reused, which makes it extremely expensive inherently. You cannot change fundamental design flaws with tack-on band-aids. Flying back SLS first stages is not a realistic goal.
Plus, they got their hands full just keeping up with Falcon-9, Falcon-Heavy, and two (or maybe three) versions of Dragon. Look at their launch manifest: it is backlogged. That is driven by the production bottleneck, which is taking all their efforts to deal with. Simplifying the Falcon stage versions to a common core and side boosters was a big part of dealing with that.
Their Raptor methane-oxygen large engine , and the huge "Mars Colonial Transporter" rocket that Raptor is for, are years away. Those are just paper design notions right now.
GW

A Mars Colonial Transporter would be in the scale of a Nova Rocket, having the SLS would be a step on the path towards building that! Why should SpaceX repeat the work of developing the SLS when they can just buy it from the government, the government can then be rid of it, and SpaceX will get a big head start towards building their Martian Colonial Transporter. What if they clustered SLS rockets together in the same fashion they clustered Falcon 9 rockets to make a Falcon Heavy, say an SLS Heavy for instance. Imagine 3 SLS bottom stages.
screen%20shot%202014-03-12%20at%204.36.44%20pm.png

The one on the right What if they did an "Heavy" version of that? That would come close to what a Martian Colonial Transporter would be, don't you think?

What if they built something like the rocket on the right?

Last edited by Tom Kalbfus (2016-06-04 21:09:29)

GW Johnson · 2016-06-05 12:28:39

Tom:

I don't have the patience or the time to explain to you why one organizations product designs are not usually properly replicated by another organization's employees, much less improved. Suffice it to say the background experience bases and the entire management cultures are alien to each other.

Not to mention that almost no organization I ever heard of (except a labor union) acts to preserve the art (the 50% of the how-to that was not written down). Those are the facts of engineering life, and if you choose to disbelieve, or to inject politics into it, well then, stupid is as stupid does.

An example happened when Boeing took over McDonnell-Douglas and inherited the popular DC-9/MD-80 family of aircraft. Boeing's production lines could not build those airplanes properly. As soon as they shut down the ex-McDonnell-Douglas production lines, production of those aircraft ended. Not because they were bad (they were actually quite good airplanes), but simply because one company cannot effectively build another company's products without making extraordinary efforts that are usually horribly expensive.

Ford building Consolidated Vultee B-24's during WW2 is NOT the counterexample you might want to think it is. Ford had very serious (to the point of fatal) delivered quality problems the first year that production line was open, precisely because the cultures and backgrounds were so different between the two companies. They literally had to make a crash effort to acquire the experience and background of Consolidated, and to recreate for themselves the unwritten art. I'm surprised it only took a year, but the WW2 effort was well-motivated.

THAT is why Spacex would never would never want to build SLS or "take over" its production in some way. THAT is why Spacex building an SLS is NOT a step along the way toward the Mars Colonial Transporter.

I'm very surprised you do not already know that.

GW

Last edited by GW Johnson (2016-06-05 12:31:59)

SpaceNut · 2016-06-05 19:21:10

The only thing Space x could do is provide off the shelf commodities or parts that could be substitued for what Lockheed and Boeing are making to be used in the SLS. Which still makes a profit for space x and possibility a lowing of costs to Nasa for builds of the SLS....

Tom Kalbfus · 2016-06-06 08:06:09

GW Johnson wrote:

Tom:
I don't have the patience or the time to explain to you why one organizations product designs are not usually properly replicated by another organization's employees, much less improved. Suffice it to say the background experience bases and the entire management cultures are alien to each other.
Not to mention that almost no organization I ever heard of (except a labor union) acts to preserve the art (the 50% of the how-to that was not written down). Those are the facts of engineering life, and if you choose to disbelieve, or to inject politics into it, well then, stupid is as stupid does.
An example happened when Boeing took over McDonnell-Douglas and inherited the popular DC-9/MD-80 family of aircraft. Boeing's production lines could not build those airplanes properly. As soon as they shut down the ex-McDonnell-Douglas production lines, production of those aircraft ended. Not because they were bad (they were actually quite good airplanes), but simply because one company cannot effectively build another company's products without making extraordinary efforts that are usually horribly expensive.
Ford building Consolidated Vultee B-24's during WW2 is NOT the counterexample you might want to think it is. Ford had very serious (to the point of fatal) delivered quality problems the first year that production line was open, precisely because the cultures and backgrounds were so different between the two companies. They literally had to make a crash effort to acquire the experience and background of Consolidated, and to recreate for themselves the unwritten art. I'm surprised it only took a year, but the WW2 effort was well-motivated.
THAT is why Spacex would never would never want to build SLS or "take over" its production in some way. THAT is why Spacex building an SLS is NOT a step along the way toward the Mars Colonial Transporter.
I'm very surprised you do not already know that.
GW

Just seems like a waste of taxpayer's money to spend billions of dollars on a project and then abandon it and start anew. If the problem is government mismanaging the project, then the solution would be to get new management, but that new management should start where the previous management left off, not throw out all the work previously done up to that point and starting anew. So how many billions were spent on the SLS? Do you just want to throw those billions already spend like it was garbage in a landfill? Of are you saying that all the employees that worked on the project simply took their paychecks and contributed nothing of value? Is all their previous work valueless, are they worthless employees that no one should hire in future projects?

GW Johnson · 2016-06-06 08:37:59

To the best of my knowledge, SLS/Orion is not being abandoned, though some say it should be. It is a congressionally-mandated porkbarrel project, primarily. It will be built. It may not get used very much.

As a moon rocket it lacks a sufficient service module, and lacks a lander entirely, so it cannot quite reprise the Apollo-8 round-the-moon mission, all it could do is loop around without attaining lunar orbit. It could perhaps reach something somewhere in cislunar space, if negligible delta-vee was required to rendezvous.

As an interplanetary vehicle, Orion is too heavy to serve properly as an Earth return capsule, and would require a much better heat shield for free return from Mars or Venus or the asteroids. It is entirely inadequate as an interplanetary crew transport vehicle. Only 3 weeks life support, and the crew would go insane not long afterward from the cramped conditions, even if they had the life support.

SLS could serve to fling big heavy things into space of course, but could never be made reusable in the sense that Spacex is attempting. It is a reprise of the Saturn-5 one-shot throwaway design using shuttle technology. And that's my point: it was designed from the outset to be one-shot/throwaway, with the same gigantic supporting logistical tail, just like Saturn.

Because of that gigantic logistical tail, it cannot ever be cheap to use, cannot even come close. That's why the argument is over the launch price: is it $0.5B or will it be closer to $1-2B? Atlas-5 and Falcon-9 are already cheaper to use, even if SLS launches for $0.5B. And Falcon-Heavy will launch things nearly as big and heavy, for way less than half the price of SLS.

GW

RobertDyck · 2016-06-06 09:13:30

Falcon Heavy: 54.4 metric tonnes to LEO, $90 million. According to the SpaceX website.
SLS block 1: 70 metric tonnes to LEO. You estimate at least $500 million?

However, small print says the $90M price is for "Up to 8.0 mT to GTO". Other small print says LEO = 28.5° inclination, GTO = 27° inclination. Performance data states 22,200kg (22.2 metric tonnes) to GTO. Further small print says "Performance represents max capacity on fully expendable vehicle". Ok, so that means lift to LEO (meaning 185km altitude @ 28.5° inclination) is 54.4 metric tonnes, but only on fully expendable vehicle. What is the lift to ISS (400km ±10km altitude @ 51.6° inclination) with reusable core stages?

Last edited by RobertDyck (2016-06-09 13:33:48)

GW Johnson · 2016-06-06 13:28:21

I noticed the same fine print. Before they started providing prices again, I had been using $80-90M for Falcon-9 to send 13 tons to LEO as an expendable, and $100-120M per Falcon-Heavy to send 53 tons to LEO as an expendable.

The reported prices today are lower and the payloads (especially -9) are higher. But I noticed the fine print qualifiers too. I think it means the price is higher if you fly full to lower orbit. But it's hard to tell. Not even any weasel words to parse out, really.

GW

RobertDyck · 2016-06-06 13:50:14

Your comment got me to look more closely, that's when I noticed it. I think it's pretty clear. The price is for 8 metric tonnes to GTO only. Your previous comment implied it may be for a share of a launch, but since the other small print says "Performance represents max capacity on fully expendable vehicle", I believe that means 8 metric tonnes only to GTO with a reusable vehicle. An expendable vehicle would cost more. Or does that mean 16 metric tonnes to GTO, with two payloads each charged $90 million? Eh, whatever. Cost per unit mass is still dramatically less than SLS.

SpaceNut · 2016-06-06 19:31:24

The biggest problem for SLS is not the number of launches per year but rather the dead weight army doing nothing for there pay.....and at a yearly budget of 3.5 billion now thats real pork......all the reductions possible for manufacturing the SLS does not equate to the bloated cost of the army doing nothing....that causes the cost to elevate and not come down.....

Tom Kalbfus · 2016-06-07 08:47:56

GW Johnson wrote:

To the best of my knowledge, SLS/Orion is not being abandoned, though some say it should be. It is a congressionally-mandated porkbarrel project, primarily. It will be built. It may not get used very much.

I agree the SLS itself is a secondary effect of the primary purpose of the project which is to create jobs in some politician's district and possible an exchange between the corporations involved and the politicians, the corporations donate to the politicians and the politicians in exchange provide the public money for the corporation's bottom line, in order to capture the public's imagination, something gets built, in this case that something is a giant rocket, intended to go somewhere, probably back to the Moon. That something, the SLS, is not without value in itself. I think if properly managed, and not used as a pork barrel project to create jobs and reelect the politicians, then that SLS vehicle can do something useful. I hate to throw the whole thing out just because its genesis is in question. I think someone like Musk can manage that program much more efficiently, the skills that went into its creation are valuable, at least some of those skills, and they shouldn't all be thrown out. Probably the SLS could have been built with less money, but what has been spent cannot be unspent, the only way we can get some of that value back is by using the SLS for something, if we just cancel it, we are throwing out all that value that has thus far been created. The same with Orion, I think it is close enough to completion that we should make a useful vehicle out of it, it should probably be sold to a private corporation that intends to use it profitably, to get the most value out of it.

GW Johnson wrote:

As a moon rocket it lacks a sufficient service module, and lacks a lander entirely, so it cannot quite reprise the Apollo-8 round-the-moon mission, all it could do is loop around without attaining lunar orbit. It could perhaps reach something somewhere in cislunar space, if negligible delta-vee was required to rendezvous.

Stand an Apollo era Lunar Module next to an SLS sitting on the launch pad, how much do you think that would cost next to the SLS? Do you really think it would take a large amount of money to develop and build a lunar lander next to the construction of the SLS? I think there is one Lunar Lander from the Apollo era that is in serviceable condition, we might be able to run an Apollo 19 mission with the SLS. (Apollo 18 was the link up with the Russian Soyuz in orbit in 1975 I believe) The LEM is old hardware however, better to build a new Lunar lander than to use a Museum artifact.

GW Johnson wrote:

As an interplanetary vehicle, Orion is too heavy to serve properly as an Earth return capsule, and would require a much better heat shield for free return from Mars or Venus or the asteroids. It is entirely inadequate as an interplanetary crew transport vehicle. Only 3 weeks life support, and the crew would go insane not long afterward from the cramped conditions, even if they had the life support.

3 weeks life support for a crew of 4 I believe, or is it 6? If one person was sitting in that capsule, he's have life support for 12 weeks!, or if the larger crew was assumed it would be 18 weeks! Lets work with this, What if we launched multiple Orions towards Mars, but they weren't all crewed. Each Orion has 3 weeks of life support for 4 people. 180 days of transit time to Mars would require 9 Orion Spaceships to get to Mars, and you would need 9 more Orion Capsules to get you back from Mars, the crew just transfers from one to another when the life support runs out in each one. All the Orions can travel in parallel courses to one another, you don't need a single spaceship. I think each Orion duplicates a lot of things that you don't need for the trip. I don't think you need 18 sets of acceleration couches, but technically the Orion alone can get you to Mars is you use enough of them and only 4 astronauts. With a cable, you can also pair up Orions and get them to spin for gravity, using one Orion as the counter weight for the other. One can make an interplanetary vehicle out of Orions, maybe not the most optimal use of such equipment, but it can be done.

GW Johnson wrote:

SLS could serve to fling big heavy things into space of course, but could never be made reusable in the sense that Spacex is attempting. It is a reprise of the Saturn-5 one-shot throwaway design using shuttle technology. And that's my point: it was designed from the outset to be one-shot/throwaway, with the same gigantic supporting logistical tail, just like Saturn.

If you throw something away, you get to build a new one each time, the only thing that gets reused is the design for it, and the thing is, each time you build a new one, you can build it a little different from the one before. One such reuse could be a landable bottom stage. One of the flaws of the Shuttle is you are stuck with the same vehicle that costs money to maintain, so you are stuck with the Shuttle's limited capabilities to low Earth Orbit. As mentioned before the Bottom Stage doesn't need the heat shields the Shuttle does in order to be reused, the only thing the bottom stage needs is the ability to land itself, and rocket engines that can be reused over and over again.

GW Johnson wrote:

Because of that gigantic logistical tail, it cannot ever be cheap to use, cannot even come close. That's why the argument is over the launch price: is it $0.5B or will it be closer to $1-2B? Atlas-5 and Falcon-9 are already cheaper to use, even if SLS launches for $0.5B. And Falcon-Heavy will launch things nearly as big and heavy, for way less than half the price of SLS.
GW

The SLS unlike the Shuttle is not a particular vehicle, but a design, the design can be altered for each mission and improvements can be made with each launch, same as was done with the Falcon 9. You really think its impossible to put landing legs on the bottom stage of the SLS, or save some fuel in its tanks or add controls that allow its engines to be re-used for landings?

I think this vehicle I proposed, by the way would require 6 solid rockets mounted on the 3 lower stages, I forgot to add that to the illustration, this would be the Extra-Super-Heavy version of the SLS. We probably should stretch the payload faring to make it bigger. Maybe the Colonial Transporter would look something like this, but with more falcon stages instead.

Last edited by Tom Kalbfus (2016-06-07 08:56:48)

RobertDyck · 2016-06-07 09:35:04

After Shuttle was cancelled, if Orion and SLS were not created, NASA could no longer justify Marshall, Michoud, Johnson would have some work due to ISS but would have to be dramatically shrunk, Kennedy would become a museum. Stennis would still exist but have little work. Remember the Johnson Space Center was created as a university campus so that it could become a campus of Rice university once Apollo was cancelled. That was how it was created in the first place. Today SpaceX launches from Cape Canaveral Air Force Station, in the same area as KSC but not part of KSC. SpaceX has leased complex 39 pad A, where Apollo 11 launched. That has been converted to Falcon Heavy. SpaceX works with KSC for its resupply missions. Orbital Sciences also works with them, although their launch pad is on Wallops Island. And work on CST-100 Starliner is actually done at KSC. So KSC now has a reason for being other than Orion & SLS, but I suspect that at the time that SLS and Orion were announced its existence was in question.

RobertDyck · 2016-06-07 10:11:51

My suggested Moon architecture started as a modification of Robert Zubrin's. Launch the Mars surface habitat to the Moon on SLS block 2 or 2B, but replace the ERV with an Apollo-style architecture. Looks like block 2 won't be built, so that would be 2B. I tried to minimize launch mass to fit on a single Falcon Heavy, but it wouldn't work. However, using Dragon and a new lunar module it would fit on SLS block 1. Constellation required 1 Ares V and 1 Ares I, SLS block 2 was intended to replace Ares V and block 1 replace Ares I. My suggestion is based on Robert Zubrin's, so Mars Society members should like it. Constellation hardware cannot be used in any way for Mars, but my architecture would land a Mars surface hab on the Moon (again Zubrin's idea) so prepare us for Mars. And the surface hab is much much MUCH bigger than the inside of an Altair lunar module. I've argued that Orion is too small to go to Mars without a Deep Space Habitat, and too large to go with one. Dragon is the largest capsule you could justify to accompany a DSH to Mars. So a deep space variant of Dragon also prepares us for Mars.

But look at this from perspective of a Congressman (or woman). My suggestion for the Moon would require all the NASA centers, so no one would lose their job. Congress would still retain all the jobs in their districts.

GW Johnson · 2016-06-07 14:02:07

"You really think its impossible to put landing legs on the bottom stage of the SLS, or save some fuel in its tanks or add controls that allow its engines to be re-used for landings?"

Quite unlike what does done at Spacex, all of the SLS hardware was never designed to hold landing loads at all. You would have to change literally everything to make such "additions". The extra "meat" to hold the landing loads simply isn't there, was never there, and is extremely unlikely to ever be there.

"The SLS unlike the Shuttle is not a particular vehicle, but a design, the design can be altered for each mission and improvements can be made with each launch, same as was done with the Falcon 9."

The Falcon was intended from the beginning to have landing legs. The only true upgrades it has received are (1) the uprated Merlin 1-D engine that fits in the same octaweb that the Merlin 1-C's fit, (2) that octaweb layout to support retropropulsion better (*). and (3) reducing the number of Falcon-9 1st stage configurations back to 2 from 3 to support better, faster production. Those 2 designs are the core and the boosters for -Heavy. And they are largely common to each other.

SLS is the same stages 1 and 2, in all configurations. Only the 3rd stage and the strap-on boosters differ. Having already spent untold billions on those stage 1 and 2 designs, no one in their right mind would ever propose changes to them, other than a thrust uprate of the engines, just as they did on the Saturns.

(*) I suspect without proof of any kind that the octaweb (versus the old rectangular 3x3 layout) gets some free expansion effects of the 8 against the center plume for a little better thrust as the vehicle climbs. I also suspect without proof that the more radially symmetric design has better retro-plume stability against the oncoming airstream, no matter how many or few engines are burning, for lower aerodynamic upsetting forces during stage reentry. And, finally, I suspect that the reto-plume spreading and reversing IS the "heat shield" for 10,000 ft/sec entry.

"As mentioned before the Bottom Stage doesn't need the heat shields the Shuttle does in order to be reused, the only thing the bottom stage needs is the ability to land itself, and rocket engines that can be reused over and over again."

Bullshit. Do not kid yourself about slower first stage entry speeds. At 10,000 fps (roughly Mach 10), stagnation zone temperatures and side-located recovery temperatures are in the 3000+ K range, limited to only that by ionization into plasma. No materials exist to withstand that without aid of some kind. Entry from orbital speeds is worse at ~8000 K, but once you're past the softening point of steel or titanium at ~800-900 K, it's all over. Aluminum is worse still, and aluminum lithium alloy is no better than plain old duralumin.

Something protects Falcon-9 aluminum-lithium tanks from Mach 10 entry heating. I suspect without proof the oncoming stream is diverted and kept away by the reversing engine plume or plumes. Even those engine plumes are very hot (~2800 K chamber ~ stagnation and recovery), so this is also a heat-sinking transient sort of operation, and residual propellant vaporization also probably plays some role. Somehow there is an adequately-cooled gas layer holding the plasma slipstream off the lithium-aluminum surfaces.

GW

Last edited by GW Johnson (2016-06-07 14:10:35)

RobertDyck · 2016-06-07 15:54:29

Here are a couple images. The first is from SpaceX themselves. Click the image for a larger view, with readable text.

The next is from Redit, the last a news service.

All show 3 engines burning during atmospheric entry. They say it slows entry, but notice the graphic from SpaceX shows a bow shock. I believe that is the effect GW Johnson talked about. Interesting, I read NASA tried that in early days, before Mercury. They found the vehicle actually entered the atmosphere faster, less deceleration. The rocket exhaust actually pushed air out of the way to reduce friction, so using a small rocket for deceleration actually reduced deceleration. I can only assume SpaceX is doing this to reduce heating of the stage during entry.

For completeness, only one engine is used for landing burn and soft touchdown.

This is a landed stage. Notice the black marks...
13164181_10157406441965131_7949724814525687889_n.png?oh=cee1579355adf10937e52d8a6fdb8cfc&oe=57D9F5CA
The bottom is covered in what looks like soot, with bright white paint where it was covered by closed legs. But the lower black stuff ends in a neat line, with bright white paint above. That makes me suspect the blackened stuff is ablative paint. Only painted so high? More blackened stuff above, but that has the random you would expect from turbulent hot air.

GW Johnson · 2016-06-07 17:24:33

Notice the grid fin deploy speed of Mach 3. That's close to 600 K total/recovery temperature in the air stream. Survivable with steels, but not aluminums. Heat sink transients plus propellant residuals vaporization might be enough to make up the difference for exposed aluminums. Just a guess on my part.

GW

Tom Kalbfus · 2016-06-07 18:12:13

The diagram doesn't mention this, and a bow shock would have appeared whether the engine was firing or not, it appears around any object that is entering the atmosphere. Perhaps you are right about the rocket exhaust though, its just that its not mentioned as what the rocket is doing. Though why else would you have a reentry burn? The Apollo capsule did not, it just hit the atmosphere with its ablative shields faced forward. Perhaps the rocket exhaust acts as an ablative shield, but this time ablating gas. The engine nozzle is designed to deal with high temperatures.

Last edited by Tom Kalbfus (2016-06-07 18:15:37)

SpaceNut · 2016-06-07 20:24:44

I think that I found the answer to the burn question and heatshielding for the Falcon at this link

http://space.stackexchange.com/question … n-re-entry

before image:

after

GW Johnson · 2016-06-08 09:27:22

Told ya it gets hot, even at only 10,000 ft/sec (3 km/s), now didn't I?

Based on their successes, it looks like retro-plume aerodynamic stability is less of a bugaboo than feared. I don't see any significant cant to the outer ring of 8 engines.

I have to wonder about the exposures of the inactive engine bells. Those only cool while fuel is flowing through the regenerative passages. Otherwise they are fragile structures that would overheat quickly.

Like I said, the shocked-down air mixing with the active engine plume(s) is very hot, as is the shocked-down active engine(s) plume that must reverse. Those gases are far too hot for the aft and lateral structures to tolerate. I wonder if they're running kerosene at low flow rate through the inactive engines? Its evaporation would cool the other gases, and leave soot all over everything, just like we see.

GW

Last edited by GW Johnson (2016-06-08 09:34:30)

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