Clark Lindsey has a lot of links.
[Update a few minutes later]
I said yesterday that they had a chute failure. But what I’m hearing now is that the stage broke up on entry, rather than when it hit the ocean, so the failure to open chutes was an effect of the vehicle breakup, and not the cause. That’s too bad, because a failure of chutes to deploy would be a lot easier thing to fix. I wonder how much of a setback this is to the goal of first-stage reusability?
This article was doing so well until…
…Sen. Bill Nelson’s plan to continue Ares 1 test flights from Kennedy Space Center is a smart approach that should be approved.
What could have caused it to break-up? Loss of pressure in the tanks?
Not an engineer, so if this is a stupid question I apologize. Why couldn’t they have launched the first stage with no second stage? That would allow them to test the chutes and everything else.
That would allow them to test the chutes and everything else.
They did test the chutes Chris and in the environment in which they will be used. Think.
It’s a good question, but only SpaceX knows the answer for sure.
My guess would be that reusability is not a requirement, just a nice-to-have-if-it-works-out-that-way. If it were a requirement, they went down a design path that gives very low odds of success. NASA did extensive studies on recovery of the Saturn V first stage, and concluded that the performance hit combined with the cost of refurbishment made it less economical than throwing the stage away. The same type of study was done for the Atlas booster engine package.
The shuttle SRBs are made of D6AC steel, and are practically indestructible. Still, the cost of recovery and refurbishment is equal to the cost of a new case, so the net saving is zero. I don’t think SpaceX will be recovering first stages any time soon, if ever. Their cost still appears to be way less than the competition’s, so they should do well.
If it turns out the first stage is not recoverable (and that would be a large shame) they will at least be able to lower the cost and increase the performance by removing recovery items from that stage.
This might also revive the F5 or perhaps an F5 heavy with 15 engines?
> Not an engineer, so if this is a stupid question I apologize. Why couldn’t they have launched the first stage with no second stage? That would allow them to test the chutes and everything else.
Because that would be almost as expensive as a launch with the second stage, and then they’d still need to launch again to test the second stage afterwards.
Because that would be almost as expensive as a launch with the second stage, and then they’d still need to launch again to test the second stage afterwards.
In other words, they went for an “all-up” test to verify both stages at once (obviously counting on 1st stage working to verify 2nd – high risk/ high payoff).
There was no point in flying a dummy 2nd stage because they’d need all the avionics from it anyway.
Yes, this was the cheapest way to test the recovery capability of the first stage, and it’s not a mission-critical capability. They’ll get to test it again with every flight, and eventually get it recoverable, or give up on it and make the stage lighter and cheaper by removing those items, as was suggested. Of course, they never expected, at least initially, to be able to reuse the stage. Part of the point of recovery was for forensics, and to at least reuse those bits (e.g., avionics) that could be.
It was observed by a few people that the second stage likely blasted the first after separation, so this could be a contributing factor.
Maybe the fix will be as simple as delaying the ignition, or deploying a streamer on the first stage to keep it upright.
What I read was that SpaceX wanted to first recover some of the more expensive components of the first stage, like the titanium thrust structure of the Falcon 1 (I don’t know if Falcon 9 has one of those also.)
“It was observed by a few people that the second stage likely blasted the first after separation, so this could be a contributing factor.”
That wouldn’t make the stage break up during reentry, though. I suspect the backblast wasn’t really that severe as it appears and was expected. Falcon 1 always had it (and they still received telemetry from the stage afterward), Delta II two.
In other words, they went for an “all-up” test to verify both stages at once (obviously counting on 1st stage working to verify 2nd – high risk/ high payoff).
If the first stage was ready for testing earlier than the second stage they might have done the first stage test earlier. I’m not saying that would have been worth it, but it could have been a consideration.
There was no point in flying a dummy 2nd stage because they’d need all the avionics from it anyway.
Doesn’t the first stage have its own avionics? Unusual, but I think I’ve read something to that effect.
“Doesn’t the first stage have its own avionics? Unusual, but I think I’ve read something to that effect.”
It’s got some avionics and a separate telemetry system, but the brain of the vehicle is in the 2nd stage, as in other vehicles.
There must be some drag-inducing mechanism that ensure the stage reenters heat shield first, otherwise it would naturally reenter engine first. It seems possible that mechanism, whatever it is, may have failed. If so, it could still be a reasonably fixable problem.
Bill: the base of the vehicle had better be heat resistant anyway, due to gas recirculation and radiant heating while the engines are operating.
Then why would they have fitted the top of the stage with a heat shield? The stage would naturally want to align itself heavy end down.
Bill: the entire stage is going to be exposed to some hot gas regardless of the orientation of entry. Is the heat shielding material just on the top, or does it cover the sides also? Aluminum weakens at moderately elevated temperature, so I think they’d have to cover everything.
(Not sure how much cooling the tankage would experience from residual propellant. If it enters base-first the top of the stage will be farthest away from the settled propellant.)
Clark Lindsey has a lot of links.
The Economist article is surprisingly good.
The sides are covered in cork to protect them during reentry. I believe I was mistaken about the heat shield on the top of the stage. That’s their plan for second stage recovery. There was a recent update that showed several canisters in the interstage for the first stage recovery parachutes, which implies the interstage stays attached to the first stage all the way down – so no heat shield there. I suppose they reenter engines first all the way down – just like you were saying.
The engine end is heavier but also has a larger cross-section than the upper end. Everything else being equal, the larger cross section end should trail, like a badminton birdie. The engine mass complicates things because it might exceed the differential drag force between the top and bottom cross-sectional areas, but maybe not by enough to insure a stable engines-first descent attitude. If the empty first stage lacks weight distribution and aerodynamics sufficient to make it assume a stable vertical orientation once effective atmosphere is re-encountered, it might just tumble. Rocket stages are designed to withstand forces mainly along their longitudinal axes. Violently variable bending moments over the stage’s length of ca. 100 ft. seem like they would be quite sufficient to break the thing up.
I assume the preferred orientation for recovery is engines down because the parachutes are packed in a space at the top of the first stage. The fix might have to be some additional item near the top end of the first stage sufficient to force and maintain the desired vertical orientation as early as possible after MECO. The two classes of mechanism that seem reasonable are active thrusters and deployable aerodynamic elements. Maintaining active control of a 100-foot mass that is not inherently stable would seem to require a lot of thruster activity and concomitant reaction mass. From a mass budget standpoint, redesigning the interstage structure to have its outer skin hinge outward and lock in flower petal/speed brake fashion shortly after MECO would turn the falling stage into a for-real giant badminton birdie. With sufficiently clever engineering, there might wind up being little or no mass penalty over the current interstage design.
I’ve never understood the economics of recovering the Falcon first stage, recovering relatively simple spent SRB casings is one thing (and still not profitable) but it seems to me that a liquid fueled rocket has too many intricate devices, machinery etc. to do well after a dip in salt water. Maybe if it were possible to allow the upper fuel/Lox tank to flood with sea water thereby raising the engine end of the vehicle out of the water… otherwise I don’t see it being worthwhile. That is assuming the vehicle actually survives reentry and water entry in the first place
Dick: I think you’re going to find the center of gravity of the first stage is well below the center of pressure. I think it should orient itself engines first, if it achieves a stable orientation.
The problem was not the salt water since the thing broke up during reentry.
I remember all the issues they had with cork peeling out of the vehicle some time ago. Plus I heard comments during this launch, by several people, that there were more ejecta than they expected. It could also turn out the vehicle tumbled down as some people here say, or that the reentry environment conditions are harsher than simulated. I doubt SpaceX has much experience on reentry. Few people have. That should change soon after they start launching actual capsules and retrieving them.
Frankly I am more concerned about that second stage rotation. Reusability would be nice to have but is a bit of an afterthought in this vehicle. Still it did reach the proper orbit, and many consumables wouldn’t mind some spinning around during launch.
They should just check and re-check everything in case there is something that could mess up with future flights. This one was seemingly fine.
I don’t think the main problem with seawater immersion is the salt but all the other gleep in ocean water, living and otherwise, that would get into places it would not be easy to clean it out of without expensive disassembly and purge processes.
The Merlin engine uses a pintle injector design and is throttleable. As a pintle injector is, to my understanding, anyway, an overgrown needle flow metering valve, it seems that simply commanding a throttle-down to zero at MECO and closing the tank vents would render the first stage innards effectively watertight. After recovery, a pressure wash with distilled or equivalently filtered water should serve to clean things up adequately for another go-round.
The parachutes are presumably spec’d to keep entry velocity below what would cause mechanical damage. The hot parts would still be warm, no doubt, but the hottest parts – the engine nozzles – also have a huge amount of surface area relative to their solid volume. They would rapidly dump their own residual heat, then act as radiator fins to suck heat out of the parts of the engine complex with less favorable intrinsic surface/volume ratios. I think the cool-down gradient for the engine complex is probably pretty steep as the stage descends under canopy (assuming SpaceX gets the bugs worked out sufficiently to allow parachute deployment to actually occur, of course).
The Shuttle SRB’s were, basically, open pipes that filled with seawater; a very different refurbishment situation.
Dick: I think you’re going to find the center of gravity of the first stage is well below the center of pressure. I think it should orient itself engines first, if it achieves a stable orientation.
It seems like this ought to be so, but the ratio of the linear distance between these points to the total length of the vehicle matters crucially for stability. Ideally, you’d want center of gravity and center of pressure at opposite extremes of the vehicle’s long axis. Too close and the thing will tumble anyway. I think the greater cross sectional area of the engine end, relative to the upper end, probably affects this relationship quite a bit. This would have the effect of moving the center of pressure from the top of the stage toward the bottom; i.e., toward the center of gravity.
I’m guessing SpaceX will have a definitive answer to the stability question in fairly short order from all the instrumentation telemetry. Whether we eager little creatures on the outside looking in will be told all the details is another matter, of course.
It seems like this ought to be so, but the ratio of the linear distance between these points to the total length of the vehicle matters crucially for stability.
The stage is very nearly a cylinder, so the CoP should be near the geometric center.
The engines + thrust structure constitute over half the dry mass of the first stage. The CoG will be displaced significantly from the center, less than 25% of the length of the stage from its base.
How plausible would stubby maple seed/helicopter winglets be?
Drag + gyro stabilization. Several different methods of retracting or swinging into position all allow adjustment of the drag.
One wonders how hard it would be to evolve the Falcon vehicles into VL stages like we have seen from Armadillo and Masten. Sure there would be a significant mass penalty mostly in propellant, but it might be worth it on the first stage at least. They already have most of the systems required and landing gear could be sized for landing only.
Alternatively, dispense with the parachutes and do a controlled vertical rocket landing into water.
“How plausible would stubby maple seed/helicopter winglets be?
Drag + gyro stabilization. Several different methods of retracting or swinging into position all allow adjustment of the drag.”
Gary Hudson, call your office!
Armadillo just re-lit their rocket engine mid-air 🙂
Did the first stage tumbling motors fire?
Let me back up… SpaceX knows you need to tumble the first stage if you plan to recover it, right? The Falcon 9 first stage does have tumbling motors, right? I didn’t get any useful google hits off “Falcon 9 tumbling motors”….
BBB
Um, the SRBs provide much less delta-V than the common first stage of a two-stage rocket.
In a “traditional” two-stage rocket, each stage is “sized” for roughly the same mass fraction. Say, the first stage is 400,000 lbs and has a 100,000 lb “payload” in the form of the second stage stack. The second stage is 80,000 lbs and has a 20,000 lb payload. The payload is thus about 1 out of 50 or about 2 percent of the launch weight — maybe this is optimistic and YMMV, but the numbers are somewhere in that ballpark.
What this means is that the spacecraft is going some large X-15-ish Mach number at burnout. When “they” were looking at Shuttle designs with a massive liquid-fueled and piloted “flyback” booster, they were talking 5:1 mass ratios, and the thermal protection requirements for the Booster, reentry from a high-Mach suborbit were almost as severe as for the Orbiter.
When they came out with the Shuttle they have now, they put all of the liquid fuel in that giant External Tank, equiped it with those record specific-impulse high-pressure SSME’s, and the solid are almost there just to overcome the “gravity loss” — the Shuttle is almost a SSTO as the SRBs are not a true “first stage” — I don’t think they stage all of that high, although they do a kind of “lofted” launch profile that the SRBs take them more “high” than “fast.”
Long story short: I don’t think the staging conditions on the SRB’s are as severe as the first stage on the Falcon 9.
Alternatively, dispense with the parachutes and do a controlled vertical rocket landing into water.
Why not controled onto barge?
Why not save some residual propellant on the first stage and then relight the center engine 10-15 secs or so after staging to provide slower and more controllable reentry–at least until you can deploy parachutes safely? I mean, if the F9 is already overpowered as they say it is, this should be doable even on a baseline F9.
The stage is very nearly a cylinder, so the CoP should be near the geometric center.
If it was an actual cylinder, yes. But it’s not. The engine cluster is square with faired, rounded corners that stick out beyond the tankage diameter. This means the heavy end has a cross sectional area at least 10 – 15% larger than the rest of the first stage. This differential is what will induce a tendency for the thing to want to swap ends in a free fall through atmosphere and that tendency will increase with atmospheric density. This will cause the CoP to be displaced downward from the longitudinal midpoint – quite a bit downward, I suspect.
Even a perfect cylinder with a significant weight bias toward one end is not especially stable in free fall, by the way. It would fall heavy end first, but would “tail wag” quite a bit too. That’s one of the reasons airplanes mostly have tails and why the ones that don’t tend to require active stability control systems in order to fly. Get the CoP as far back toward the trailing end as you can and things steady down just fine. That’s why I suggested the flower petal speed brake interstage. It adds fletching to the arrow at little or no mass cost and with no parasitic drag penalty on the way up.
Cecil,
The cost of liquid fuelled rocket engines is pretty high, depending on the model. Being able to recover them and reuse them would dramatically reduce the cost of getting to orbit. They easily account for more than half of the cost of an expendable launch vehicle. Being able to reuse them just once means reducing your cost to orbit by 25% or more.
“Alternatively, dispense with the parachutes and do a controlled vertical rocket landing into water.”
Why not controled onto barge?
A vertical landing in water is very forgiving and requires little new hardware (restartable engines, no parachutes, etc.). Landing on a barge would be much preferred but requires a barge, landing gear and a difficult landing on a small moving platform.
Without telemetry any speculation is likely to be far wide of the mark. One thing SpaceX has shown is the ability to understand and correct. I wonder how much telemetry they get from the first stage after separation?
Interesting. The Australian media have reports of people in Sydney seeing a UFO in the pre dawn sky about 45 minutes after the F9 launch.
Local astronomers have decided it was actually the second stage/dragon.
Must have been some excess fuel venting as they saw a spiral pattern around it which also means the stage was rolling at the time I guess.
Cecil,
The cost of liquid fuelled rocket engines is pretty high, depending on the model. Being able to recover them and reuse them would dramatically reduce the cost of getting to orbit.
Exactly, hence my wondering if flooding the forward portion of the stage causing it to sink would lift the engines out of the salt water.
Or, what about a detachable engine “pod” that separates from the rest of the stage, parachutes to the sea and then is floated clear of the sea water by inflatable bladders? Perhaps the pod could even be designed so as to enclose the engines entirely during the parachute recovery phase so that they never come into contact with the sea water at all.
I totally agree with Dick E. Once I heard it broke up it just seemed that if it was not feathered, shuttlecocked, or drogued in some way that it would just tumble end over end. Dick you said everything I want to say and certainly did so a lot better than I could have.
(Blush)
Thanks for the kind words Josh.
I eagerly await definitive word on the first stage loss – if any is forthcoming – from SpaceX. I have sort of a neighborly interest as I live less than three miles from their Hawthorne plant; the interior of which, by the way, does a cameo appearance as the home base of the bad guy billionaire defense industrialist nemesis of the hero in Iron Man 2 (shameless, but uncompensated – alas – plug). Elon has a couple of lines in a cameo appearance in a party scene too. Tony Stark tells him, “Those Merlin engines are great.” Keen judge of hardware, that Stark.
Mike,
[[[The cost of liquid fuelled rocket engines is pretty high, depending on the model. Being able to recover them and reuse them would dramatically reduce the cost of getting to orbit. They easily account for more than half of the cost of an expendable launch vehicle. Being able to reuse them just once means reducing your cost to orbit by 25% or more.]]]
Yes, which was the basis for Starbooster proposing a flyback system. Yes, there is a performance penalty, but more then made up for in reduced turnaround costs of having the entire booster land intact on land. That is why the USAF is pushing the mode with Lockheed for its flyback system. And of course you don’t need to worry about chutes failing.
Indeed, Thomas, and in technological stepping stones to space I included just such a side-mount strap-on liquid-fueled glide-back auxiliary booster as a “stepping stone” enabling technology, with Starbooster in mind. Such a device doesn’t even need to be manned, as UAV technology is a natural fit. John Hare has a similar idea for a VTVL RTLS sidemount.
It’s just one example of the sort of enabling technologies that NASA could be doing under the Flexible Path, which such notables as Neil Armstrong and Paul Spudis and some other credible voices view as a “directionless goal” for NASA and thus doomed to failure, a “path to nowhere”.
I disagree with that position. I think it could be the path to everywhere.