ApolloHoax.net
Off Topic => General Discussion => Topic started by: bobdude11 on August 20, 2017, 01:58:46 AM
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I have been watching the Falcon 9 videos and marveling at the progress made since Apollo; then a question came to mind:
Is the entry burn used as a form of heat shield for the 1st stage reentry or does it not get high enough to have to worry about the ionization heating during its return to terra firma?
Thanks in advance!
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I have been watching the Falcon 9 videos and marveling at the progress made since Apollo; then a question came to mind:
Is the entry burn used as a form of heat shield for the 1st stage reentry or does it not get high enough to have to worry about the ionization heating during its return to terra firma?
Thanks in advance!
Its the former. Since Stage 1 is not equipped with a heat shield, it would burn up if it wasn't slowed down
If you listen to the commentator on this youtube video of the latest flight (Auguit 14), you will hear him explain. I have cued to the correct time, but if cuing doesn't work, drag slider to 19m into video.
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I would just like to add that if you watch the video from the point of 1st stage separation, the two telemetry boxes in the top right of the screen are the Stage 1 altitude and speed.
Note that at MECO/staging, the vehicle reaches 6,000Km at about 60km altitude. The speed then immediately starts to drop as Stage 1 continues to climb due to its momentum. It continues to climb another 60 km to about 120km at a speed of just over 1600 km/h, then the speed it starts to increase again as Stage 1 begins falling back to earth. By the time it reaches the point of the re-entry burn its 52km up falling at over 4300 km/hr... it will either burn up or become severely damaged if its allowed to continue to accelerate. The re-entry burn sheds 1000 km/h off its rate of descent, bringing it down to about 3200 km/h, but as soon as the burn is done it starts accelerating again, but not as quickly because air-resistance starts to come into play, and ultimately, that air-resistance (assisted by the grid fins) begins to slow the descent down because its falling faster than its terminal velocity. At 4km about the ground its still plummeting earthwards at over 1100 km/h, when the landing burn kicks in, and slow it from 1100 km/h to zero in 30 seconds and a perfect, pinpoint landing.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
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I have been watching the Falcon 9 videos and marveling at the progress made since Apollo; then a question came to mind:
Is the entry burn used as a form of heat shield for the 1st stage reentry or does it not get high enough to have to worry about the ionization heating during its return to terra firma?
Thanks in advance!
Its the former. Since Stage 1 is not equipped with a heat shield, it would burn up if it wasn't slowed down
If you listen to the commentator on this youtube video of the latest flight (Auguit 14), you will hear him explain. I have cued to the correct time, but if cuing doesn't work, drag slider to 19m into video.
Thanks Smartcooky. I missed that initially. I think I was still under the impression that it was moving too fast to prevent burn up, but your explanations (this and the follow up) have cleared that up for me! Thanks!
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
I can believe that very little fuel is on board, but I find it difficult to believe zero and that is why I asked the question. Remember back to the videos of the unsuccessful attempts and the large fireball as the first stage toppled over and impacted on the deck of the recovery barge.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
A mostly-empty F9 booster can't hover - the T/W of the Merlin engine is too high. The stage would start climbing again if they didn't touch down at the right instant (the Grasshopper test article was ballasted to allow hovering).
They can't let the stage run completely dry at landing because the engine would not shut down cleanly, but they get close.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
A mostly-empty F9 booster can't hover - the T/W of the Merlin engine is too high. The stage would start climbing again if they didn't touch down at the right instant (the Grasshopper test article was ballasted to allow hovering).
They can't let the stage run completely dry at landing because the engine would not shut down cleanly, but they get close.
Right, so part of the calculation to get a perfect hoverslam (achieving 0 VS at 0 ALT) must take into account the ever diminishing fuel weight?
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
A mostly-empty F9 booster can't hover - the T/W of the Merlin engine is too high. The stage would start climbing again if they didn't touch down at the right instant (the Grasshopper test article was ballasted to allow hovering).
They can't let the stage run completely dry at landing because the engine would not shut down cleanly, but they get close.
Right, so part of the calculation to get a perfect hoverslam (achieving 0 VS at 0 ALT) must take into account the ever diminishing fuel weight?
That's pretty fundamental to any rocketry calculations.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
A mostly-empty F9 booster can't hover - the T/W of the Merlin engine is too high. The stage would start climbing again if they didn't touch down at the right instant (the Grasshopper test article was ballasted to allow hovering).
They can't let the stage run completely dry at landing because the engine would not shut down cleanly, but they get close.
Right, so part of the calculation to get a perfect hoverslam (achieving 0 VS at 0 ALT) must take into account the ever diminishing fuel weight?
Yup.
The fact that they're already making it look routine and easy is freaking insane. This thing is as tall as an 11-story building, it falls roughly 100 km through the atmosphere (after having pushed the payload uphill), and lands on a postage stamp (sometimes on the water) with no hover time. It's no wonder some people dismiss the landings as fake; between the size of the booster and the complexity of the operation, it's just brain-breaking to think about.
Like I said, they have to leave some reserve to guarantee the engine shuts down cleanly (running out of LOX before RP-1 or vice versa would have bad effects, and may result in the engine shredding itself). I don't have a reliable source, but my understanding is that it's on the order of a couple of hundred kg or so.
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A slight sidetrack, I have asked others in CQ approximately how much fuel remains at touch down. Does anyone know?
AIUI, there is supposed to be no fuel left, or at least very little. Stage 1 performs a "hoverslam", its designed to have the landing burn terminate at 0 altitude 0 rate of descent as the fuel runs out. There is certainly not enough fuel left to hover if the timing is off.
A mostly-empty F9 booster can't hover - the T/W of the Merlin engine is too high. The stage would start climbing again if they didn't touch down at the right instant (the Grasshopper test article was ballasted to allow hovering).
They can't let the stage run completely dry at landing because the engine would not shut down cleanly, but they get close.
Right, so part of the calculation to get a perfect hoverslam (achieving 0 VS at 0 ALT) must take into account the ever diminishing fuel weight?
Yup.
The fact that they're already making it look routine and easy is freaking insane. This thing is as tall as an 11-story building, it falls roughly 100 km through the atmosphere (after having pushed the payload uphill), and lands on a postage stamp (sometimes on the water) with no hover time. It's no wonder some people dismiss the landings as fake; between the size of the booster and the complexity of the operation, it's just brain-breaking to think about.
Like I said, they have to leave some reserve to guarantee the engine shuts down cleanly (running out of LOX before RP-1 or vice versa would have bad effects, and may result in the engine shredding itself). I don't have a reliable source, but my understanding is that it's on the order of a couple of hundred kg or so.
OK, lets put some numbers on this. According to Wiki, Falcon 9 lifts of with 146,000 litres of LOX and 94,000 litres of RP-1 in Stage 1
Lox is 1.41 kg/l, and RP-1 is 800g/l
- NOTE: I used https://www.aqua-calc.com/calculate/volume-to-weight for the conversions
Lox weight is 166,000 kg
RP-1 weight is 75,000 kg
Total is about 241,700 kg of fuel
If we take your figure of "on the order of a couple of hundred kg or so" as correct, then 200/242,700 = less than 0.1% of the starting fuel load left.
I also read somewhere that Stage 1 burns fuel at a rate of about 250kg/s, so if there really is only 200kg left on board, that is less than 1 second of fuel left on landing.
Holy Cow! Those are some razor thin margins for error!
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And they make it look so damn easy. Is there any idea when the next flight of a refurbished 1st stage will be?
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And they make it look so damn easy. Is there any idea when the next flight of a refurbished 1st stage will be?
"a reused Falcon 9 will launch the SES-11 communication satellite on early October."
http://www.launchphotography.com/Delta_4_Atlas_5_Falcon_9_Launch_Viewing.html
"The SES 11/EchoStar 105 satellite will likely ride a Falcon 9 first stage that first flew Feb. 19 with a Dragon supply ship heading for the International Space Station, one source said, but a firm assignment has not been confirmed. That vehicle returned to a vertical touchdown at Landing Zone 1 at Cape Canaveral Air Force Station."
"Liftoff from a Florida launch pad is scheduled no sooner than around Sept. 27, a couple of days after a United Launch Alliance Atlas 5 rocket is set to haul a classified payload into orbit for the National Reconnaissance Office, the U.S. government’s spy satellite agency. The Atlas 5 flight with a U.S. national security mission is already booked on the Air Force’s Eastern Range for Sept. 25, and will receive priority to launch first if it remains on schedule."
https://spaceflightnow.com/2017/08/04/ses-agrees-to-launch-another-satellite-on-a-previously-flown-falcon-9-booster/
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And they make it look so damn easy. Is there any idea when the next flight of a refurbished 1st stage will be?
As near as I can figure out...
► Aug. 24 (today) Falcon 9 • Formosat 5 - Vandenburg SLC-4E - First stage will return to landing on a platform downrange in the Pacific Ocean. (about 9 hours ago - 100% successful)
► Sept. 7 Falcon 9 • OTV-5 - Pad 39A - First stage will return to landing at Cape Canaveral
► Sept. 27 Falcon 9 • SES 11/EchoStar 105 - Pad 39A - The Falcon 9 rocket will launch with a previously-flown first stage (no mention of recovery type but IMO it looks like a heavy payload so perhaps it will return to land on a platform downrange in the Atlantic Ocean..
NOTE: With today's launch from Vandenburg, that is 12 successful missions this year so far, with nine Stage 1 landings attempted, all of them also successful. Two of the launches have used refurbished 1st stages.
So far, they really are making this look routine.
I read an interesting article a few days ago about Elon Musk wanting to work on a system to recover the 2nd Stage as well. IMO that is going to be a whole lot more difficult (by orders of magnitude) because we are talking much higher speeds.
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We'd probably be talking once around with the second stage rather than boost back.
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Higher speeds and digging into the payload more, since you'd need a lot more fuel and/or shielding to slow down from orbital speeds. Still, if they can make it work, not just as a concept but also commercially, props to them of the highest order.
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Here is a nice little youtube video by Everyday Astronaut that uses a few Kerbal Space Program simulations to explain how much harder it is to recover a second stage. It graphically demonstrates raven's comment about speed and payload.
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I also read somewhere that Stage 1 burns fuel at a rate of about 250kg/s,
The whole stage or just the single Merlin that is used for booster landings?
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Once again, I am glad I joined this community. You not only answered my question, but also the other one I was going to ask!
I always learn something new and in detail.
I want to thank you all for allowing a space fan (since I was little and watched Neil Armstrong walk on the moon) to ask questions and not feel stupid doing so.
I know computers and InfoSec fairly well (been in that industry for over 30 years doing InfoSec for 20), but aviation and space exploration are my passions. I was not smart enough to be part of the groups helping to do those things, but I sure do enjoy watching the progress.
Thank you all who are part of that for all you do and allowing the little boy that watched Apollo to live again each and every day! The astronauts are typically the face of space, but all of you engineers and other support teams are the real heroes.
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I also read somewhere that Stage 1 burns fuel at a rate of about 250kg/s,
The whole stage or just the single Merlin that is used for booster landings?
AIUI, that is the fuel consumption rate for all 9 engines
Falcon 9 v 1.1 = 235 kg/s
Falcon 9 FT (Full Thrust) = 270 kg/s
The Stage actually uses different numbers of the 9 engines for different things
9 for lift off
3 for the boostback burn (if required)
3 for the re-entry burn
1 for the landing
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Cool, thanks for the clarification.
Even with one engine burning there doesn't seem to be a massive margin for error!
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Welp, I've tried running actual numbers based on what info I can find on the F9 FT 1st stage. Grabbed most of my specs from the F9 Full Thrust (https://en.wikipedia.org/wiki/Falcon_9_Full_Thrust) and Merlin 1D (https://en.wikipedia.org/wiki/Merlin_1D) Wikipedia pages.
- Dry mass - 22200 kg
- Liftoff mass - 433100 kg
- Prop mass - 410900 kg
- M1D chamber pressure - 97 bar
- M1D Isp - 282 s
- M1D thrust - 845 kN (sl)
Given those M1D numbers, the mass flow rate is roughly 305 kg/s per engine at full throttle.
I got some loose timings from the CRS-12 launch, which can be divided into several phases:
- Liftoff to Max Q (roughly 78 seconds), 9 engines at full throttle
- Max Q to MECO (roughly 67 seconds), 9 engines throttled down to 80%(?)
- Boostback burn (roughly 10 seconds), 1 engine full throttle
- Re-entry burn (roughly 12 seconds), 3 engines full throttle?
- Landing burn(roughly 30 seconds), 1 engine 70% throttle
I'm pulling the throttle amount for Max Q out of thin air. I know they throttle down, but not sure by how much. 80% seems reasonable, but again, that's just pulled out of thin air.
Based on those numbers, I come up with remaning propellant at the end of each phase:
- ~196317 kg
- ~48860 kg
- ~45803 kg
- ~38100 kg
- ~31681 kg
So, definitely more than a couple of hundred kg left in the tanks at the end of the landing burn, so my assumption was pretty wrong. Then again, that assumes the above calculations have any basis in reality.
But it makes sense - given the T/W on the M1D, they need all the ballast they can get, even at 70% throttle.
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- Dry mass - 22200 kg
- Prop mass - 410900 kg
So each kilogram of spacecraft holds 18,5 kg of propellant. That really drives home how difficult and technologically demading reaching orbit with reasonable payload actually is.
Lurky
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They may throttle down for max q, but wouldn't they throttle up afterwards?
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They may throttle down for max q, but wouldn't they throttle up afterwards?
I doubt it - as the stage gets lighter, the G load gets higher for the same amount of thrust. ISTR them shutting down two engines on the V1.0 F9 at some point after Max Q to manage the G load.
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- Dry mass - 22200 kg
- Prop mass - 410900 kg
So each kilogram of spacecraft holds 18,5 kg of propellant. That really drives home how difficult and technologically demading reaching orbit with reasonable payload actually is.
Lurky
It ain't called "the tyranny of the Rocket Equation" for nothing. A linear increase in delta-V requires an exponential increase in propellant mass. And for a kerolox gas generator with a sea level Isp of 280-ish seconds, that's a lot of propellant mass to begin with.
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Frankly, it's amazing humans have gotten into space at all. For big rockets like the Saturn V, we're talking a small nuke's worth of energy.
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Imagine if we had a thicker atmosphere and more gravity.
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Imagine if we had a thicker atmosphere and more gravity.
If one reads a few flat earth beliefs, rockets don't actually go into orbit, just over the horizon(into the ocean?) never attaining orbit. ::)
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Imagine if we had a thicker atmosphere and more gravity.
Maybe we would launch our rockets from giant airships.
Lurky
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(https://assets.cdn.spaceflightnow.com/wp-content/uploads/2017/07/26015852/falconheavy_sep.png)
Apparently, when SpaceX launch their first Falcon 9 Heavy later this year (at this stage its down for November, but that could change) their intention is to use two previously flown Stage 1 cores as the boosters. Furthermore, they intend to recover all three parts of Stage 1, the two booster cores back to the Cape, and the centre Stage 1 core back to the downrange Atlantic platform.
https://spaceflightnow.com/2017/07/25/musk-sets-expectations-low-for-maiden-falcon-heavy-launch/
That is something I am looking forward to watching.
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(https://assets.cdn.spaceflightnow.com/wp-content/uploads/2017/07/26015852/falconheavy_sep.png)
Apparently, when SpaceX launch their first Falcon 9 Heavy later this year (at this stage its down for November, but that could change) their intention is to use two previously flown Stage 1 cores as the boosters. Furthermore, they intend to recover all three parts of Stage 1, the two booster cores back to the Cape, and the centre Stage 1 core back to the downrange Atlantic platform.
https://spaceflightnow.com/2017/07/25/musk-sets-expectations-low-for-maiden-falcon-heavy-launch/
That is something I am looking forward to watching.
Indeed that will be a special launch to watch.
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That is something I am looking forward to watching.
Indeed that will be a special launch to watch.
I've booked a week in Florida in the hopes I get lucky and see it! Fingers crossed
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That is something I am looking forward to watching.
Indeed that will be a special launch to watch.
I've booked a week in Florida in the hopes I get lucky and see it! Fingers crossed
Best of luck, then.
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I've booked a week in Florida in the hopes I get lucky and see it! Fingers crossed
Hopefully not this week.
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I bet it will take a couple launches to get the bugs ironed out, but I also bet they'll get it in time.
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Places where things will be "interesting" -
- Ignition - lighting up 27 engines at once will be fun (and probably very loud)
- MaxQ - that's where the fittings holding the boosters to the center core will be under the most stress
- Booster separation - that's where their aero modeling will be put to the test, making sure that the boosters fly away from the core instead of into it
I'm not worried about landing, although watching two boosters land at the same time will be quite a show.
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I bet it will take a couple launches to get the bugs ironed out, but I also bet they'll get it in time.
Musk has said that the chances of the first being successful are pretty low. I really hope that he's lowballing us!
I'm not worried about landing, although watching two boosters land at the same time will be quite a show.
If it all goes to plan there'll be three boosters landing. :)
<edit> not all at the same time though!
https://www.instagram.com/p/BXXiVWFgphb/
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I heard an interesting piece of information while watching the latest YT video from "Everyday Astronaut". Apparently, early in 2018, SpaceX intents to test the capsule abort and recovery system during a Falcon 9 launch. That should be an interesting watch.
On a side note, I really enjoy Tim Dodd's "Everyday Astronaut" and Amy Shira Teitel's "Vintage Space" (I'm a subscriber to both channels). Lately, Tim in particular has been covering off a lot of SpaceX stuff. Well worth the time to watch.
Everyday Astronaut
https://www.youtube.com/channel/UC6uKrU_WqJ1R2HMTY3LIx5Q
Vintage Space
https://www.youtube.com/channel/UCw95T_TgbGHhTml4xZ9yIqg
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Oh, and I should add, they are going to do this test at Max-Q!
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Oh, and I should add, they are going to do this test at Max-Q!
Which is where you find out just how good those SuperDracos are.
Don't know which is going to be more exciting in terms of mayhem potential - this, or the maiden FH launch.
Everyday Astronaut recently put up a good video on the challenges of bringing a used upper stage back to Earth using KSP. He came up with a system that worked, barely, but severely cut into the payload budget.
I think any reuse of the US will be on orbit, not on return to Earth.
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I've just watched Elon Musk's closing address Live from the IAC in Adelaide. Its about 50 minutes long, and well worth the watching the whole thing right through
http://www.spacex.com/mars
SpaceX are planning to start construction on BFR (Big Falcon Rocket) next year. It is to be fully reusable and will be able to be refuelled in orbit. Musk's intention is to have it make its first test and cargo flight to Mars in 2022.
Ambitious indeed, but he thinks its doable, and so far, you can't argue that he hasn't delivered on what he has outlined, even if not always on schedule.
Here are a couple of interesting slide from the address. First, a graphic showing a number of rockets arranged by payload capability, lowest on the left, highest on the right...
(https://www.dropbox.com/s/fbg8damv0orn78d/Launch%20Capability.png?dl=1)
But here is what happens when you sort them in order of launch cost per kg of payload, lowest on the left, highest on the right...
(https://www.dropbox.com/s/hcc7fjm8b6kuh4q/Launch%20Cost.png?dl=1)
Staggering if correct.
What do the rocket scientists here think?
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Assuming 100%, true "gas-n-go" reusability on the order of a modern airliner, then yeah, I can see it becoming one of the cheapest launch options over time (if not the cheapest), at least on a per-Kg basis. You have to amortize the cost of building the thing over multiple launches, but eventually all you're paying for is propellant, staff, and pad expenses, which are not that much relative to the vehicle itself. That becomes especially true if they can co-manifest multiple payloads like Ariane typically does (which they should be able to do given the (frankly insane) volume and lift capability).
It just has to, you know, work as advertised.
Last night I realized that this hits close to the original vision of the Space Shuttle, which was originally supposed to have a flyback booster and offer true "gas-n-go" reusability, but not on this scale. And of course, the STS orbiter was never meant to leave LEO - Elon claims the BFS can go anywhere from LEO to the outer solar system and back. What had me :o-ing was the idea that it has enough Delta-V to get to the Moon, land, and come back without refueling. That's kinda staggering. This thing is going to be effing huge.
Honestly, what gives me the cold pricklies is the idea of transitioning their entire business onto this new architecture. It's a hell of a risk. But of course, the only way they can pay for it is to make it the system.
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IMO, one of the key reasons the Space Shuttle couldn't reach its full potential was because it was weighed down with pork. Everything had to be compromised because of pork.
The porcine hindrances aren't a problem with private aerospace
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IMO, one of the key reasons the Space Shuttle couldn't reach its full potential was because it was weighed down with pork. Everything had to be compromised because of pork.
I wouldn't call the Shuttle "pork" the way I call SLS "pork". STS wasn't merely a jobs program designed to keep the legacy space manufacturing sector employed; it was actively used for real exploration. It would have been better to start with a proof-of-concept vehicle that could have been iterated as needs evolved, but the .gov doesn't work that way. Unfortunately, NASA had to get buy-in from many different stakeholders to build STS, and as a result the system was way over-scoped IMO. But, you know, you have to start somewhere.
SpaceX has the advantage in that they can see what NASA did right as well as wrong and improve on the vision. They also have the advantage of 40 years' worth of advances in materials and manufacturing technology. Looking back on it now, STS was damned ambitious for the mid-1970s.
It is true that SpaceX are not currently burdened with having to satisfy a bunch of different stakeholders with their own agendas, but don't believe for a minute that private aerospace is free of political wtf-ery.
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IMO, one of the key reasons the Space Shuttle couldn't reach its full potential was because it was weighed down with pork. Everything had to be compromised because of pork.
I wouldn't call the Shuttle "pork" the way I call SLS "pork".
I watched a documentary on the Challenger disaster last night. Now even thougn I am very familar with the details surrounding this, I tried to put that aside and go in as if I had fresh eyes as someone finding out this stuff for the first time.
What I saw was infuriating. The five engineers at Morton-Thiokol, including Roger Boisjoly, Robert Ebling and Arnie Thomson knew that Challenger was in grave danger of blowing up, and tried to stop the launch. They failed because they were overruled by bean counters who wilted under pressure from NASA executives who used thinly veiled threats about upcoming contract negotiations.
Of course its history that the actual cause of the explosion was the failure of the field joint, in particular, in the cold temperatures on launch morning compromised the rubber O-Ring's ability to expand into the joint to seal it off. The joint was a flawed design, but the more important issue is that there was no need for field joints in the first place, and there would not have been any had it not been for pork. There was a company (Aerojet) who could have built the SRBs in a single piece, and delivered them by barge to The Cape. They initially won the recommendation but thanks to some lobbying by some Utah politicians, NASA administrator Dr. James Fletcher overruled this and awarded the contract to Morton Thiokol in Utah. The SRB's could not be transported over land in one piece, so they had to be made in sections. From there, its simple logic. Sectioned SRBs require field joints, one piece SRBs do not.
One piece SRBs = no field joints = no Challenger disaster.
This article is about the SRBs and the political machinations behind the STS. It is well worth the read even 30 years after the disaster.
http://www.tsgc.utexas.edu/archive/general/ethics/boosters.html
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IMO, one of the key reasons the Space Shuttle couldn't reach its full potential was because it was weighed down with pork. Everything had to be compromised because of pork.
Not just pork, it had to comply with DoD requirements too.
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IMO, one of the key reasons the Space Shuttle couldn't reach its full potential was because it was weighed down with pork. Everything had to be compromised because of pork.
Not just pork, it had to comply with DoD requirements too.
Some, like the immense crossrange capability of those delta wings was never used. How sad is that? Almost as sad as the Soviet equivalent languishing, nay, rotting in a hanger until said hanger collapsed and destroyed it. Alas, poor Buran, we hardly knew ye.
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The most fuel-efficient hoverslam F9 landing would have no entry burn, and it would light all nine engines for the landing burn. The latter part is not practical because it would make the guidance and timing even more spectacularly critical than it already is, and the stage would break up on entry without an entry burn to slow it down.
Remember the "Oberth effect": the efficiency of a rocket is directly proportional to its speed, if we define "efficiency" as the amount of payload kinetic energy added (or removed, for a landing burn) per unit of propellant burned. That's where the hoverslam comes from in the first place; you wait as long as you can to build up as much velocity as possible, then remove it at the last possible moment as quickly as you can. You also want aerodynamic drag to do as much of the work for you as possible.
But that drag would be so great at re-entry that the stage would break (or burn) up, so you have to make it survivable by spending a little fuel before entry. Again, you want to wait until the last possible moment to do the entry burn, to build up velocity to maximize the efficiency of the entry burn.
In effect you are making two hoverslam landings, first "on" the atmosphere and then on the actual ground. It's just that only the second hoverslam (the real one on actual land) has to be done at zero velocity to be survivable; the first "landing" only has to be slow enough to survive the collision with the atmosphere.