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Old 12-21-2015, 06:37 PM
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Continuing discussion of SpaceX launches [edited title]


We've had a few lively and informative threads around here about SpaceX, reusable rockets, and other developments in spaceflight, so I'd thought I'd let y'all know that a significant SpaceX launch is coming up.

Today, Dec. 21 at 8:29 PM Eastern Time (UTC 1:29 AM Dec. 22), SpaceX will attempt their first launch after the June 28 failure. Notably, the first stage will fly back and attempt to land at the launch site, rather than on a barge a couple hundred miles away from the coast. This is also the first launch of an upgraded Falcon 9 rocket that has up-rated engine thrust, and a slight tank stretch and oxidizer supercooling to carry more propellant. These upgrades give enough margins so that the first stage will be able to land after nearly any launch (previously it had to be expendable to launch heavier or higher orbit payloads).

SpaceX will stream the launch and landing live (official page, youtube mirror). The stream will begin about 20 minutes before the launch. There's also a live reddit thread that is frequently updated with every scrap of relevant information, if those streams aren't enough.

There's no guarantee of a launch today, however, and certainly no guarantee of a successful landing. The current forecast has about a 20% chance of cancelling the launch due to weather (don't want to launch through a cloud that has the slightest chance of producing lightning!) SpaceX has also had some technical issues dealing with the superchilled oxygen that's new on this rocket.

In any case, I'm going to be glued to my computer for the next hour or two...

Last edited by Idle Thoughts; 12-22-2015 at 01:05 PM.
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Old 12-21-2015, 07:38 PM
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First stage has landed!

Second stage has completed its burn and is in the correct orbit!

ETA: aww, no all caps?

Last edited by lazybratsche; 12-21-2015 at 07:38 PM.
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Old 12-21-2015, 07:40 PM
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Wow. Simply awesome!
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Old 12-21-2015, 07:43 PM
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I watched Star Wars yesterday and loved hit, but holy crap it doesn't begin to compare to the excitement and exhilaration when the Falcon first stage actually touched down. God damn! I can only imagine what it was like to actually be there.

Glad to see the Orbcomm satellites are beginning to deploy as planned as well.

SpaceX still has a long road to go before actual first stage reuse, but this was a hell of a first step.
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Old 12-21-2015, 07:46 PM
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And all 11 satellites have deployed successfully!
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Old 12-21-2015, 08:05 PM
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Entirely aside from the primary mission and first stage landing, this was also the first flight test of their up-rated "full thrust" engines, stretched second stage, and densified propellant. Not to mention that it's their return to flight after the previous launch failure. A huge success on all fronts.

For those wondering what densified propellant is: like most liquids, liquid oxygen (LOX) and kerosene (RP-1) get more dense as they get colder. You can thus pack it more densely in the tanks the more you chill them. Traditionally, the kerosene is kept at room temperature and the LOX at its boiling point. This is relatively easy to maintain, but with extra work you can chill the liquids in advance to increase their density.

Aside from tankage efficiency, this has another benefit: it increases the mass flow rate of the engine pumps. Denser propellant means more mass per second, which means more thrust. More thrust means you can take even more propellant along and still lift the rocket.

Densified propellants have been used before, but I believe SpaceX set another world first in that they've chilled the LOX to lower temperatures than anyone before them.
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Old 12-21-2015, 08:12 PM
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The landing site is a few miles south of it's launch site at SLC40. It's at the old SLC13 launch site so good viewing from the restaurants at Port Canaveral and the beach at Jetty Park.

I remember the old science fiction movies from the 50's and 60's of people going to Mars. The rockets always landed backwards on their tails. And so 60+ years later..... rockets can now land on their tails.

Heard from folks down there in CB, (Cocoa Beach) sonic boom of the landing rocket knocked some windows out.
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Old 12-21-2015, 08:20 PM
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Nearby residents were apparently warned about the sonic boom--first one since the Shuttle landings (at least from a returning spacecraft). A historic moment in and of itself.

Quick video with the booms here. The people seem concerned . Three quick pops, with the last two very close together. Maybe a shockwave from each of the engine side (the "front"), the top (the "rear"), and from the grid fins?
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Old 12-21-2015, 08:23 PM
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That was a lot of fun watching the world change.
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Old 12-21-2015, 08:27 PM
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There's also supposed to be some additional tests on the 2nd stage, to make sure that multiple engine restarts were working properly before upcoming missions that needed them to achieve geosynchronous transfer orbit. Has SpaceX done 2nd stage restarts before? Or was this just precautionary testing for the upgraded Falcon 9?

Meanwhile, Elon Musk has been teasing us about the next rocket SpaceX is working on, the Big Fucking Rocket and the Mars Colonial Transporter. "It's really big. There's not been any architecture like this described that I'm aware of." Various rumors have suggested that it'll be somewhere between substantially larger than the Saturn V to HOLY SHIT I CAN'T EVEN COMPREHEND. In the wilder speculations, the second stage will fly direct to Mars and land propulsively. For the return trip, it would generate fuel on Mars, and could even fly direct from the Martian surface all the way to landing on Earth.

I don't even know what to say without gibbering now.
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Old 12-21-2015, 08:44 PM
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The SpaceX Song
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Old 12-21-2015, 09:08 PM
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Wow! I think this is remarkable and astounding. What a great accomplishment.
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Old 12-21-2015, 09:12 PM
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Found some video of a crowd at mission control totally losing their shit.

https://youtu.be/1B6oiLNyKKI
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Old 12-21-2015, 09:17 PM
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I remember the old science fiction movies from the 50's and 60's of people going to Mars. The rockets always landed backwards on their tails. And so 60+ years later..... rockets can now land on their tails.
Did it? From the animation (the pencil being shot over the Empire State Building), it looked to me like it landed on its "nose" - in effect, it has engines at both ends; one for liftoff, and the other for landing.

Still, YAY SCIENCE!
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Old 12-21-2015, 09:25 PM
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Did it? From the animation (the pencil being shot over the Empire State Building), it looked to me like it landed on its "nose" - in effect, it has engines at both ends; one for liftoff, and the other for landing.
Nope; just one set of engines (per stage).

The first stage has nine individual engines. At takeoff, those nine provide only about 1.2 gees of acceleration. Only one of them is used for the final landing, however, and at close to its minimum throttle levels (rocket engines tend not to like being throttled to a small fraction of their full thrust levels).

Even at that, the stage has to perform a "hoverslam", which is to say that the minimum deceleration is more than one gee. So it can't just hover in place a bit to get its bearings; it has exactly one shot at the landing. It wouldn't have enough propellant to hover anyway.
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Old 12-21-2015, 10:02 PM
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Wake up, sheeple! They obviously just ran the film backwards!








Seriously, though, that was way cool.
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Old 12-21-2015, 10:35 PM
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A handful of particularly stunning photos:

Long exposure of launch and landing

Just before touchdown

First stage on the landing pad

There's probably going to be a hell of a lot more. I understand that the first stage is packed with GoPros, but up til now they've never been recovered.

Last edited by lazybratsche; 12-21-2015 at 10:37 PM.
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Old 12-21-2015, 11:04 PM
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High-res video of touchdown from an observation helicopter. Just like God and Heinlein intended.
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Old 12-22-2015, 01:57 AM
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Old 12-22-2015, 02:01 AM
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I want to see how they transport that thing (it's about 1.5x the size I was expecting) back to the factory for re-furb.

But: Christ. I was in Middle School when the first moonwalk was done.

Actually kinda glad I won't live long enough for Mars colonization. I don't think my mind could stretch that far.

(if there are martians, will they develop Cargo Cults and build model rockets to entreat the Gods to return with more goodies?)
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Old 12-22-2015, 04:42 AM
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I want to see how they transport that thing (it's about 1.5x the size I was expecting) back to the factory for re-furb.
I'm sure it'll be the same way they got it there: on a big truck. Part of the reason the Falcon 9 is so tall and skinny is so that it can be transported by road. They made sure that the diameter is low enough that it will pass under the bridges it needs to. The payload fairing is wider, but it splits in two and they can put it on a diagonal so that it still meets the height/width requirements.

I was surprised to see people walking around the vehicle so quickly after landing. I would have guessed that they'd wait a while before declaring it safed. Maybe there was so little LOX left that it boiled away almost immediately. The remaining propellant--kerosene and pressurized nitrogen--are fairly minimal hazards. There are no nasties like hypergolics, fortunately.

At any rate, they must need a hell of a crane to get it tipped over. At the pad, they have their custom-build strongback to lift it up; I'm really not sure what they'll use here.
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Old 12-22-2015, 09:22 AM
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At any rate, they must need a hell of a crane to get it tipped over. At the pad, they have their custom-build strongback to lift it up; I'm really not sure what they'll use here.
Yes, but at launch, the whole stack weighed about 540 tons. The returned 1st stage, with the fuel tanks empty, weighs only 19 tons or so. I think a conventional mobile crane can handle this.

Last edited by scr4; 12-22-2015 at 09:23 AM.
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Old 12-22-2015, 09:28 AM
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OK, it's cool that the landing was technically possible and that it was successful. But how much does it save? I recall NASA overselling the hell out of the savings of the reusable shuttle and its reusable boosters, so let's say you use the first stage 100 times. Between the extra cost to build in the capability to land and the cost of refurbishing after every use, what percent of the launch cost can be saved by using this?
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Old 12-22-2015, 09:56 AM
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OK, it's cool that the landing was technically possible and that it was successful. But how much does it save? I recall NASA overselling the hell out of the savings of the reusable shuttle and its reusable boosters, so let's say you use the first stage 100 times. Between the extra cost to build in the capability to land and the cost of refurbishing after every use, what percent of the launch cost can be saved by using this?
Excellent question. I'd be interested in learning those things, too.

However, I doubt that Musk has gotten this far in the process without crunching the numbers on how much it will cost to refurbish the reusable components. Yeah, they said the same thing about the shuttle, and each turn around wound up taking a lot more work than they planned. But, we've learned an awful lot since then. For one thing, their first stage uses 9 motors (didn't know that until last night) to the shuttle's 3. I imagine it's easier to tear down the smaller motors, and components like the pumps and seals probably aren't stressed nearly as much as they were on the shuttle.

So, yeah, the business case still has to prove itself, but the tech is fucking awesome!
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Old 12-22-2015, 09:57 AM
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OK, it's cool that the landing was technically possible and that it was successful. But how much does it save? I recall NASA overselling the hell out of the savings of the reusable shuttle and its reusable boosters, so let's say you use the first stage 100 times. Between the extra cost to build in the capability to land and the cost of refurbishing after every use, what percent of the launch cost can be saved by using this?
I've been wondering about this as well. It turned out the extensive effort required to refurbish the shuttles' rocket boosters made the savings pretty negligible.
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Old 12-22-2015, 10:04 AM
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However, I doubt that Musk has gotten this far in the process without crunching the numbers on how much it will cost to refurbish the reusable components. Yeah, they said the same thing about the shuttle, and each turn around wound up taking a lot more work than they planned. But, we've learned an awful lot since then. For one thing, their first stage uses 9 motors (didn't know that until last night) to the shuttle's 3. I imagine it's easier to tear down the smaller motors, and components like the pumps and seals probably aren't stressed nearly as much as they were on the shuttle.
I'm not so sure about that. Musk himself has a tendency to make overly optimistic promises. Every model of Tesla produced so far has missed its promised launch date at least once, and that affordable Tesla that was supposed to be out by now still hasn't left the drawing board as far as anybody knows.
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Old 12-22-2015, 10:17 AM
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I'm not so sure about that. Musk himself has a tendency to make overly optimistic promises. Every model of Tesla produced so far has missed its promised launch date at least once, and that affordable Tesla that was supposed to be out by now still hasn't left the drawing board as far as anybody knows.
Good points; maybe their projections will turn out to have been too optimistic. But they've come closer to making this work than anyone else has, and the tech is still fucking awesome.
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Old 12-22-2015, 10:17 AM
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For one thing, their first stage uses 9 motors (didn't know that until last night) to the shuttle's 3. I imagine it's easier to tear down the smaller motors, and components like the pumps and seals probably aren't stressed nearly as much as they were on the shuttle.
To be a devil's advocate, isn't this like saying it's easier to rebuild three 3-liter car engines than one 10-liter truck engine?
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Old 12-22-2015, 11:10 AM
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Has anyone seen anything like a map of the trajectory? I can't visualize where exactly it went.
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Old 12-22-2015, 11:14 AM
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But they've come closer to making this work than anyone else has, and the tech is still fucking awesome.
True. It is a very cool accomplishment, but it remains to be seen if reusing rockets is cost-effective, or even practical.
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Old 12-22-2015, 11:43 AM
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True. It is a very cool accomplishment, but it remains to be seen if reusing rockets is cost-effective, or even practical.
I would think SpaceX would have run the numbers on that before committing tens of millions of dollars to the technology.
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Old 12-22-2015, 01:05 PM
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Changed the title as you asked.
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Old 12-22-2015, 02:37 PM
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To be a devil's advocate, isn't this like saying it's easier to rebuild three 3-liter car engines than one 10-liter truck engine?
Maybe it is; you can do it assembly-line style, lift more of the pieces by hand instead of needing a crane...
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Old 12-22-2015, 02:41 PM
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So, just to make sure I've got this right. At separation the first stage is about 11 km downrange and moving at 7-8 kilometers per second is what I think I heard on the video. Then, after separation, it orients itself using cold gas thrusters and initiates a burn to start heading back to the launch site. How much extra fuel does it need to reverse it's downrange velocity and come back to the launch pad? If they are going to have to transport it over the road back to the factory anyhow, why not launch it from 22 miles further inland and have it land downrange?
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Old 12-22-2015, 03:18 PM
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Yes, but at launch, the whole stack weighed about 540 tons. The returned 1st stage, with the fuel tanks empty, weighs only 19 tons or so. I think a conventional mobile crane can handle this.
You're correct that it's quite light, but it is around 220 feet tall (bit more with the legs, I guess). At any rate, their fairly large crane is now at the pad.
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Old 12-22-2015, 03:28 PM
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Has anyone seen anything like a map of the trajectory? I can't visualize where exactly it went.
Here you go.

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So, just to make sure I've got this right. At separation the first stage is about 11 km downrange and moving at 7-8 kilometers per second is what I think I heard on the video. Then, after separation, it orients itself using cold gas thrusters and initiates a burn to start heading back to the launch site. How much extra fuel does it need to reverse it's downrange velocity and come back to the launch pad? If they are going to have to transport it over the road back to the factory anyhow, why not launch it from 22 miles further inland and have it land downrange?
From the image, you can see that its more like 70 km downrange at MECO (Main Engine Cut-Off), and gets up to 130 km before the burn is complete. Also, it's going more like 6000 km/h, or 1.7 km/s at that time (8 km/s is for orbit).

SpaceX's previous efforts have been to land on an ocean barge. They've failed but for reasons unrelated to it being over water. They'll probably try barge landings again at some point, and will virtually have to if they want to land the center core of the Falcon Heavy. I'll be going way faster than this one and they won't be able to afford a full burnback.

Unfortunately, I don't have figures on the propellant fraction they have to reserve for this maneuver. It's surprisingly little, however--at that stage in flight, almost all the mass is in the upper stage. Once the upper stage is gone, it's just a soda can with a few drops of fuel left in it. It doesn't take a huge amount to slow down and land. It's in the ballpark of a 30% hit on total rocket performance.
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Old 12-22-2015, 03:57 PM
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Pictures remind me of the model rockets I used to fly.
I wonder how long it will be until Estes brings out a flying model of this rocket.
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Old 12-22-2015, 04:07 PM
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Unfortunately, I don't have figures on the propellant fraction they have to reserve for this maneuver. It's surprisingly little, however--at that stage in flight, almost all the mass is in the upper stage. Once the upper stage is gone, it's just a soda can with a few drops of fuel left in it. It doesn't take a huge amount to slow down and land. It's in the ballpark of a 30% hit on total rocket performance.
I saw a graph once of performance figures for the Saturn V; lines for altitude, speed, mass, etc. as a function of time. I wish I could find it again, the numbers were jaw-dropping. The one I remember the most is mass. The rocket is about 3,000,000 kg at launch, and I think it was below 1,000,000 when it separates the first stage, in less than 3 minutes. If you don't throttle the engines down, you'll have 3x the acceleration (and 3x the Gs) as you did at liftoff.

I saw something similar on the webcast last night. There were numbers in the upper right showing speed and altitude. When the second stage fired the speed number was increasing pretty slowly. And then it started speeding up as the fuel was burned and the mass decreased.
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Old 12-22-2015, 04:22 PM
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I saw something similar on the webcast last night. There were numbers in the upper right showing speed and altitude. When the second stage fired the speed number was increasing pretty slowly. And then it started speeding up as the fuel was burned and the mass decreased.
Yep. The Falcon 9 second stage has about 180,000 pounds of thrust. With full tanks, the stage weighs around 220,000 lbs, so it starts off at somewhat under 1 gee. Empty, though, it's more like 15,000 pounds--that would be 12 gees without throttling down! They'll never let it get that high, of course, but it's a pretty crazy difference from start to finish.

Kerbal Space Program teaches this principle very effectively.
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Old 12-22-2015, 05:11 PM
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I don't know about cost effectiveness and yada yada blah blah, but that was incredibly cool! Is it overstating this to compare it with first stepping on the moon?
(edit: I feel like I just watched something really, really noteworthy- is why I ask.)

Last edited by bobot; 12-22-2015 at 05:12 PM.
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Old 12-22-2015, 05:38 PM
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We had the pleasure of watching the event from Titusville, right across the Indian River, where there is always a crowd gathered for launches. Yes, incredibly cool - the booster really did create that stream of orange light, and those with sharp enough eyes could see the first stage separation. The chest-shaking noise (quieter than an Atlas V but hey), the thunder to the lightning, arrived on schedule, surprisingly much later. Suddenly another stream of light closer to the ground, then it shut off while we all wondered if that had gone wrong. But it came on again, slower and even closer to the ground, while it visibly decelerated and shut off - success! Applause! Then the sonic boom that we all thought at first was a heartbreaking explosion until we remembered it was supposed to happen. A fun time was had by all.

Just one of the side benefits of living in Orlando.
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Old 12-22-2015, 05:59 PM
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Is it overstating this to compare it with first stepping on the moon?
It's overstating it. The Apollo program was a few orders of magnitude more difficult than what SpaceX did.

...however...

Apollo was an evolutionary dead end. Although it continues to be an unmatched standalone achievement, when the program stopped, that was it. We learned a lot from it, of course, but not much that wouldn't have been learned anyway. If and when we go back to the moon, it won't look like the Apollo program.

On the other hand, it may well be that in a couple of decades, all rockets are reusable. And if so, today's achievement will be seen as huge jump in the evolutionary heritage of those rockets, just as Robert Goddard's tests of liquid fueled rockets are in the history of every rocket today. In that sense, it may be just as important or even more so.

This isn't a guaranteed future--there's still a long ways to go. There was a lot of optimism at the start of the Shuttle program, and that was another dead end. The promise is there, though. If SpaceX succeeds, they will reduce the costs to space by a large factor, possibly an order of magnitude, and this will enable all kinds of new applications for space.
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Old 12-22-2015, 06:14 PM
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Pictures remind me of the model rockets I used to fly.
I wonder how long it will be until Estes brings out a flying model of this rocket.
SpaceX beat them to it.
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Old 12-22-2015, 06:17 PM
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Is it overstating this to compare it with first stepping on the moon?
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It's overstating it. The Apollo program was a few orders of magnitude more difficult than what SpaceX did.

...however...

Apollo was an evolutionary dead end. Although it continues to be an unmatched standalone achievement, when the program stopped, that was it. We learned a lot from it, of course, but not much that wouldn't have been learned anyway. If and when we go back to the moon, it won't look like the Apollo program.

On the other hand, it may well be that in a couple of decades, all rockets are reusable. And if so, today's achievement will be seen as huge jump in the evolutionary heritage of those rockets, just as Robert Goddard's tests of liquid fueled rockets are in the history of every rocket today. In that sense, it may be just as important or even more so.

This isn't a guaranteed future--there's still a long ways to go. There was a lot of optimism at the start of the Shuttle program, and that was another dead end. The promise is there, though. If SpaceX succeeds, they will reduce the costs to space by a large factor, possibly an order of magnitude, and this will enable all kinds of new applications for space.
In terms of pure technical achievement, Doc is quite right. But I was struck by the similarity, and differences, with the old footage from NASA's Mission Control in the '60s. There are still rows of consoles, and people monitoring them, but they're computers and flatscreens now. The controllers don't have crew cuts, white shirts, and skinny ties anymore. They hug each other when things go right. The room has glass walls so everyone can watch.

The glee that they showed last night is what I hope their counterparts felt 50 years ago, but expressed in a different way for a different time.
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Old 12-22-2015, 06:47 PM
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Apollo was an evolutionary dead end. Although it continues to be an unmatched standalone achievement, when the program stopped, that was it. We learned a lot from it, of course, but not much that wouldn't have been learned anyway. If and when we go back to the moon, it won't look like the Apollo program.
Apollo led to Skylab. And it only dead-ended there because NASA stopped developing the capability further to focus on the Shuttle. If NASA continued to build and update the Saturn-V, they may not be trying to reinvent it now.

Last edited by scr4; 12-22-2015 at 06:47 PM.
  #46  
Old 12-22-2015, 07:41 PM
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Originally Posted by scr4 View Post
Apollo led to Skylab. And it only dead-ended there because NASA stopped developing the capability further to focus on the Shuttle. If NASA continued to build and update the Saturn-V, they may not be trying to reinvent it now.
To be fair, the decision to end the Apollo program was taken out of the hands of the then-current NASA administration. Funding for Apollo 18 through 20 was deallocated (despite the fact that most of the hardware fabrication and subsystem testing costs had already been sunk), and NASA was put to the course of developing a spaceplane-like shuttle which could also perform various military and defense functions that the Air Force in no way asked for or wanted and which caused the already questionable decision toward a quasi-reuseable spaceplane concept to be burdened with ridiculously conflicting requirements that hobbled its basic functionality and reliability. The development of the Space Transportation System ("Shuttle") was supposed to presage a permanent orbiting platform but Skylab decayed before the first flight of Columbia to boost it into higher orbit, and it wasn't until the late 'Nineties that the ISS even began to be assembled. (By the way, there was not "a lot of optimism" about the Shuttle from the technical people working on it, who saw time and again technical compromises being made for political expediency and promises that it would never be able to deliver upon. One former Rocketdyne engineer who headed one of the development of one of the SSME critical subsystems told me that the engine was known to be "a self-cannibalizing piece of shit" from the start due to the machinations which forced Rocketdyne to partner with opponent Pratt & Whitney on the high pressure staged turbopump design rather than the lower pressure aerospike engine that Rocketdyne had designed, built, and qualified in-house using IR&D funding.)

If there is a failure that can be attributed to NASA, it was the failure to plan for and demonstrate a viable and necessary path for a continued crewed space program following the Apollo landings. And to be fair, it isn't clear that we need or can support a sustained crewed space program at the current state of the art either then or now; an ultimate sustained human presence demands either an absurdly cheap bulk material launch capability or in situ utilization of space resources; shipping consumables and critical hardware into space at even hundreds of dollars a kilogram (never mind the many thousands it costs now at the cheapest) is just not a sustainable model beyond transitory exploration for its own sake. (The SLS certainly isn't going to provide that capability; it is an absolute pig of a vehicle that shouldn't cost a tenth of the estimated per-flight cost.)

The failure of the destination-oriented model of the Apollo program should be a cautionary tale for advocates of a crewed Mars mission in the "soonest" timeframe; even if we could achieve such a goal with conventional propulsion and habitat technology (doubtful based on the studies I've worked on), even the cheapest budgets for a single mission (at a cost that would exceed the entire Apollo program) are vastly too expensive to support repeated missions. We need the technology and infrastructure development to perform a practical, useful interplanetary mission. Fortunately, this technology would come with its own benefits, including detection and mitigation of space hazards such as solar weather and potentially hazardous asteroids, fabrication of structures and complex processing of materials in space, enhanced communication and Earth surveillance, et cetera, all of which could provide a benefit to the world at large.

Back to the topic of the SpaceX landing, it is certainly an outstanding technical achievement, but I remain dubious that this alone will result in substantial reduction in flight costs. It may seem that being able to 'reuse' a stage would be a big savings, but the analogy to "throwing away an airliner after one flight" misses the point that launch vehicles are not airliners; rockets experience extremes of vibration, shock, thermal stress, and operating pressures that are beyond any other conventional engineered system. The useful lifetimes of many components in rocket engines such as valves, manifolds, seals, et cetera are measured in minutes rather than hundreds or thousands of hours. The operating and structural margins are necessarily slim in order to avoid excess mass. The use of supercooled (densified) propellants--done solely to allow enough remaining propellant for the flyback operation--presents additional processing challenges and risks which add to the expense and effort of processing the vehicle for flight, and it is this cost which is most significant in launch costs, and are potentially most amenable to reduction through simplification and automation.

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  #47  
Old 12-22-2015, 07:46 PM
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Originally Posted by lazybratsche View Post
A handful of particularly stunning photos:

Just before touchdown
It's not often you know the import of what you're seeing.

That's Kitty Hawk. That's one giant leap. That's a damned 21st-century Wonder of the World.
  #48  
Old 12-22-2015, 08:22 PM
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Originally Posted by UncleRojelio View Post
It has "recovery wadding". It doesn't land like the real thing, dammit!


Jesus Christ, it is 32" tall!

Last edited by carnivorousplant; 12-22-2015 at 08:24 PM.
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Old 12-22-2015, 10:30 PM
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To be clear, in no way have I intended to denigrate NASA for their achievements--Apollo, Shuttle, and otherwise. They behave according to the political environment they exist in, which does enable them to achieve great things, but low costs are not one of those things. I think the current approach of commercial partnerships is a good one and SpaceX would likely not exist without it.

There aren't enough public details to say how much SpaceX has been able to simplify their ground operations. The few public bits are promising, however. For instance, SpaceX avoids the use of pyrotechnic fasteners. Although straightforward to use, they are one shot deals and can't be reused. They're also unsuitable for non-destructive ground testing. Similarly, SpaceX uses pneumatic actuators for the stage separators and nitrogen cold gas thrusters for the ullage motors, as compared to the more usual solid motors.

From what I've seen, when given a choice, they've always taken the approach of spending extra mass to have a system which is resettable and which is more easily tested on the ground. A nitrogen thruster can be cycled and the tank refilled; the tank has sensors to verify that it is pressurized and there are no leaks. For a solid motor, you have to hope that your quality control several months ago was good enough and that nothing happened in the meantime.

The ideal is a rocket where you can press a button, it does a bunch of self-tests, and when it says OK you have high confidence that it will succeed. I'm sure SpaceX is still a ways off from this, but it's been a goal of theirs from the very beginning.
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Old 12-23-2015, 03:09 AM
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Originally Posted by Stranger On A Train View Post
Back to the topic of the SpaceX landing, it is certainly an outstanding technical achievement, but I remain dubious that this alone will result in substantial reduction in flight costs. It may seem that being able to 'reuse' a stage would be a big savings, but the analogy to "throwing away an airliner after one flight" misses the point that launch vehicles are not airliners; rockets experience extremes of vibration, shock, thermal stress, and operating pressures that are beyond any other conventional engineered system. The useful lifetimes of many components in rocket engines such as valves, manifolds, seals, et cetera are measured in minutes rather than hundreds or thousands of hours. The operating and structural margins are necessarily slim in order to avoid excess mass. The use of supercooled (densified) propellants--done solely to allow enough remaining propellant for the flyback operation--presents additional processing challenges and risks which add to the expense and effort of processing the vehicle for flight, and it is this cost which is most significant in launch costs, and are potentially most amenable to reduction through simplification and automation.
I posit that one reason rocket parts have historically been so fragile is that up until now, no-one has ever had any reason to design them otherwise. Now they do.
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