Layer 1: RPi runs Linux. Good luck with the exe. Layer 2. RPi comes without any internal storage to install this on. They'd need to include it in SD images Layer 3. RPi is a tinkerer's machine, the malware wouldn't survive a day. Layer 4: "The exe creates a desktop shortcut to our website" - you need.exe for that? Layer 5: even if it does - most RPis are run headless. And many of these with screens run without network...there are more if you think about it.
The Boostback can be - and will be forfeited for heavier payloads. The rocket will travel in a ballistic trajectory instead of looping back to the launchpad.
The reentry burn - that highly depends on the rocket's speed. Not viable for orbital reentry but quite realistic for this - we're dealing with energy roughly 16 times lower. A drogue chute is often used in a later phase for these purposes - most Russian reentry vehicles used one. Another option is airbrakes - even disposable(ablative) ones.
Then the landing, upon which we mostly agree. Discarding the parachute some 50m above the landing would mitigate the headaches of it dragging the rocket upon landing.
Yes, it's not entirely simple, but it's neither as bad as you present it.
Maybe I saw it wrong. I'm on mobile net and Youtube just refuses to load the video, but I'd swear I saw it somewhere around 8-9th minute of https://www.youtube.com/watch?...
Q: "How does the mass of the necessary parachute compare to the mass of the fuel needed to do the same job?".
A: Quadratically, vs linearly.
In the range of speeds where the parachute works at all, its efficiency is proportional to square of airspeed. The engine provides deceleration directly proportional to the speed change needed.
That means that even a very modestly sized parachute could adequately replace the middle burn and a major part of the final burn. It can do wonders at high airspeeds, but it's lousy for the last several m/s that make the difference between a crash and a landing.
But it also really sucks for precision of the landing. If the landing pad was a dry salt lake, it would be a no-brainer solution. But for a barge landing it would be rather risky.
I seriously doubt it uses ONLY one engine as they form a ring without a central engine (they showed the bottom of F9 during the stream), so the thrust would be way off-center. (and since there are 9, it has a 3-way symmetry but no 2-way symmetry). But isn't it throttleable BY 70%, instead of TO 70%?
I saw different articles citing different numbers. I saw 16mln too.
I believe the sum of 80mln is including their commercial mark-up - the price for the customer. And while recovery will drop the cost by 16mln, the "price" will be halved, firstly because the expensive development can slow down, and besides because Musk wants space travel to become more accessible, more ubiquitous, and above all to force the competition to step up their efforts.
There were 9 total (fatal or nonfatal) dangerous accidents on Soyuz missions over its 940+ launches, so below 1%. There were 10 total dangerous accidents involving the Shuttles. So above 13%. (source: https://en.wikipedia.org/wiki/...)
Not really splitting hairs. Both the Shuttle and Falcon 9 discard and lose a good part of their spacecraft - the Shuttle loses the whole (huge) LF tank, F9 loses the whole (big and pretty complex) second stage. Apples to apples, Falcon 9 loses more, "percentage-wise".
The real difference though is in cost of refurbishing of what is recovered.
Refurbishing the shuttle and preparing it for a launch (800mln) costs about 10x more than building the Falcon 9, both stages, from scratch (80mln)!
And then recovery of Falcon 9 first stage about halves these costs.
So, the real difference isn't really in what, how much is recovered, how it flies and lands. The real difference is the absolutely vast reduction of costs. 80mln was already something very competetive. Halving it is a total game-changer!
First, it operates on three out of its nine engines, and then Merlins are exceptionally deeply throttleable, so I wouldn't be surprised if it could hover... OTOH without payload, almost without fuel, that thing must have insane peak TWR at that point and might not be throttlable enough...
Actually, the rocket could just as well burn H2, creating water vapor. Though Falcon 9 uses kerosene.
The problem with "a lot of available energy" is when "a lot" becomes "too much". Soyuz needs to dissipate around 0.2 gigawatt of energy during peak-Q of reentry.
Some big problems with parachutes: - they work only in certain velocity range: they will be ripped apart at very high speeds and they will never slow you down below a couple m/s. And they need fairly thick atmosphere. And they are unsteerable.
But a hybrid system could work (like in Soyuz which launches small SRBs last 3 meters above the ground). It could be that - in case of Earth surface landing - a modestly sized parachute could be deployed on some last kilometer or so, It's not viable for the barge landing though.
The principal concept was actually developed in [Germany](https://en.wikipedia.org/wiki/Wernher_von_Braun) but Russians perfected it enough to reach space, and later enter orbit.
Actually, the *concept* is quite simple. It's the mind-boggling numbers pushing the envelope on material science and engineering that make it so difficult. Eight kilometers per second. 32 megajoules of kinetic energy per every kilogram in orbit. Dissipating that energy on reentry and ascent. Tsiolkovski's rocket equation and its tyranny that boils down to taking many times the weight of the vehicle in fuel. Managing extreme energy density cryofuels - extremely corrosive liquid oxygen and explosive liquid hydrogen. Working with temperatures between 70 and 3500 Kelvin. Void, cosmic radiation, extreme temperature differences, lack of convective cooling. Attitude monitoring and control.
Each of these problems taken alone is a moderately difficult engineering challenge. But if you put them all together this becomes a byzantine puzzle.
There was this site with "lessons" in using some API or library. There were code examples. And if you tried to select and copy, to paste an example into a compiler, a dialog would pop up telling you that the content is copyrighted and you're not allowed to copy it.
And at the bottom of the page was a survey, "What can I do to improve these lessons?"
I filled it out, with my email and a sarcastic comment about the copy restriction - that maybe forcing people to retype the examples isn't the best way of teaching. The owner of the site wrote me with a solemn apology, informing me that she didn't even notice the (dis)functionality was in place, and that it just got installed with the CMS and she didn't disable it because she didn't know it was there...
> What precisely did the shuttle show is impractical? I think comparing this to the shuttle seems like an apples to oranges comparison.
Two factors.
1. Excessive cost of $/kg to orbit. 2. Design flaw making it inherently unsafe (the foam pieces falling during launch).
The situation with the SRBs wasn't that bad. They are very simple devices so no wonder after burn-off there was very little left to recover. The solid, hard shell was recovered and it was fully reusable. The rest had to be restored, because it was actually all "consumables". No big deal, they were the cheapest part anyway.
The huge LF tank was lost. It wasn't exactly cheap, but not terribly expensive.
The shuttle, though, had to be refurbished after each flight. And being an incredibly complex device, it took excessive time and cost to perform the inspection and repairs.
And then most of the fuel burned, most of the construction to carry that fuel, most of infrastructure to support that huge construction - was there to lift the cargo bay, the landing gear, the wings, the heat shields on all that, and there was relatively little left for the actual cargo.
For the Shuttle the reusability was a liability, not a boon.
SpaceX still loses the whole second stage. That's not a small loss. But it seems they actually save up a lot on the reuse of the first stage - the cost of preparing it for another launch is nowhere near to the cost of rebuilding it from scratch - and the cost of building it from scratch is nowhere near the cost of preparing the Shuttle for another launch.
Unless they get a private island, the barge is going to stay for heavier payloads. The burnback maneuver will cost far less if you don't need to fly back where you came from.
the kernel loads normally. It's the init system (which is already userspace) that gets hijacked. The whole authentication system runs on userspace side - and in this case isn't run, replaced by plain bash. You still need to issue 'mount -a' to mount all the filesystems but they work okay.
that's what init=/bin/bash is for. You boot directly to bash shell with root privileges bypassing all authentication. Then you can either create a passwordless alias for the root account, or install any rootkit you like.
They wouldn't find the generated 24-char ones. Either the passwords were stored in plaintext or easily crackable crypt (unlikely), or the hackers hijacked the login system and collected the passwords as they were used for login.
As for heating, they need only to heat a very tiny portion of it to ignite the fusion; it will sustain itself later on - so lasers or masers... The power losses come from the containment requirements - the reactor doesn't break even with that but the fusion does produce power to heat itself - just not enough surplus to power the magnets.
It really takes spending a little time with WolframAlpha to pull up some numbers to understand how much sci-fi underestimates the difficulty of space travel.
Take reentry. Some flames, some shaking, right? How much of a problem is it, and why do some parts burn in the atmosphere while others don't? The communicational blackout, some weird quirk... right?
Well, take your Soyuz capsule. Take the time of "communicational blackout", find speed before, speed after, and then calculate kinetic energy at the two moments. Then divide by time for average energy dissipation.
Well, the figure you obtain is about 0.2 gigawatt for some four minutes. This is the amount of energy produced and dissipated as heat, light, sound and about all of spectrum, from deep ultraviolet far past microwaves. No wonder no radio can push from a noise like that. No wonder superior heat shielding is needed with heating like that. And the capsule MUST descend rapidly into thicker atmosphere, because even if less heat was produced during more flat reentry, the thin atmosphere wouldn't be as good at removing it - superheated ablator is blown away before its heat can penetrate deeper into the ship; remove it slower and the inside will heat up!
Or take the LEO speed. About 9 km/s. That's a meaningless number to most, but maybe 26 mach is closer to your heart. Most ammo doesn't exceed 1.5km/s. So energy of impact is roughly 36x of equivalent bullet. Or an object 1/36 as big as a bullet can cause the same damage.
Then we can get started on how big space is, and how much effort matching orbits is... how the Gravity movie was such a bullshit.
Slashdot Mirror
Layer 1: RPi runs Linux. Good luck with the exe. .exe for that? ...there are more if you think about it.
Layer 2. RPi comes without any internal storage to install this on. They'd need to include it in SD images
Layer 3. RPi is a tinkerer's machine, the malware wouldn't survive a day.
Layer 4: "The exe creates a desktop shortcut to our website" - you need
Layer 5: even if it does - most RPis are run headless. And many of these with screens run without network
The Boostback can be - and will be forfeited for heavier payloads. The rocket will travel in a ballistic trajectory instead of looping back to the launchpad.
The reentry burn - that highly depends on the rocket's speed. Not viable for orbital reentry but quite realistic for this - we're dealing with energy roughly 16 times lower. A drogue chute is often used in a later phase for these purposes - most Russian reentry vehicles used one. Another option is airbrakes - even disposable(ablative) ones.
Then the landing, upon which we mostly agree. Discarding the parachute some 50m above the landing would mitigate the headaches of it dragging the rocket upon landing.
Yes, it's not entirely simple, but it's neither as bad as you present it.
Maybe I saw it wrong. I'm on mobile net and Youtube just refuses to load the video, but I'd swear I saw it somewhere around 8-9th minute of https://www.youtube.com/watch?...
Solaris didn't exist back then. It was still SunOS... what number? 2? 3? Or did even that exist?
I was a user of SunOS 4 and I can tell hands down any Linux distro today is far better than that.
Q: "How does the mass of the necessary parachute compare to the mass of the fuel needed to do the same job?".
A: Quadratically, vs linearly.
In the range of speeds where the parachute works at all, its efficiency is proportional to square of airspeed. The engine provides deceleration directly proportional to the speed change needed.
That means that even a very modestly sized parachute could adequately replace the middle burn and a major part of the final burn. It can do wonders at high airspeeds, but it's lousy for the last several m/s that make the difference between a crash and a landing.
But it also really sucks for precision of the landing. If the landing pad was a dry salt lake, it would be a no-brainer solution. But for a barge landing it would be rather risky.
Ok. Merlin 1D used in stage 1 is throttleable to 70%. Merlin 1D-Vac is throttlable to 39%.
I seriously doubt it uses ONLY one engine as they form a ring without a central engine (they showed the bottom of F9 during the stream), so the thrust would be way off-center. (and since there are 9, it has a 3-way symmetry but no 2-way symmetry).
But isn't it throttleable BY 70%, instead of TO 70%?
I saw different articles citing different numbers. I saw 16mln too.
I believe the sum of 80mln is including their commercial mark-up - the price for the customer. And while recovery will drop the cost by 16mln, the "price" will be halved, firstly because the expensive development can slow down, and besides because Musk wants space travel to become more accessible, more ubiquitous, and above all to force the competition to step up their efforts.
If you haven't noticed, Linux has quite progressed since the times when it was just a UNIX knock-off.
Comparing today's Linux to the UNIX of these times is... really, Golden Gate to Erector set.
Last Soyuz fatality was in 1971. The Shuttle program began in 1977. So, "at that time" there were no fatal Soyuz failures.
To date there's been over 940 successful launches of Soyuz with a total of 2 fatal accidents involving 4 astronauts. The Shuttles over their two accidents killed 14 astronauts.
There were 9 total (fatal or nonfatal) dangerous accidents on Soyuz missions over its 940+ launches, so below 1%.
There were 10 total dangerous accidents involving the Shuttles. So above 13%. (source: https://en.wikipedia.org/wiki/...)
Not really splitting hairs. Both the Shuttle and Falcon 9 discard and lose a good part of their spacecraft - the Shuttle loses the whole (huge) LF tank, F9 loses the whole (big and pretty complex) second stage. Apples to apples, Falcon 9 loses more, "percentage-wise".
The real difference though is in cost of refurbishing of what is recovered.
Refurbishing the shuttle and preparing it for a launch (800mln) costs about 10x more than building the Falcon 9, both stages, from scratch (80mln)!
And then recovery of Falcon 9 first stage about halves these costs.
So, the real difference isn't really in what, how much is recovered, how it flies and lands. The real difference is the absolutely vast reduction of costs. 80mln was already something very competetive. Halving it is a total game-changer!
First, it operates on three out of its nine engines, and then Merlins are exceptionally deeply throttleable, so I wouldn't be surprised if it could hover... OTOH without payload, almost without fuel, that thing must have insane peak TWR at that point and might not be throttlable enough...
Well then, in that sense, SpaceX's Falcon 9 is just a clone of a Nazi Germany's V-2 technology.
Just. The. Same.
Actually, the rocket could just as well burn H2, creating water vapor. Though Falcon 9 uses kerosene.
The problem with "a lot of available energy" is when "a lot" becomes "too much". Soyuz needs to dissipate around 0.2 gigawatt of energy during peak-Q of reentry.
Some big problems with parachutes: - they work only in certain velocity range: they will be ripped apart at very high speeds and they will never slow you down below a couple m/s. And they need fairly thick atmosphere. And they are unsteerable.
But a hybrid system could work (like in Soyuz which launches small SRBs last 3 meters above the ground). It could be that - in case of Earth surface landing - a modestly sized parachute could be deployed on some last kilometer or so, It's not viable for the barge landing though.
The principal concept was actually developed in [Germany](https://en.wikipedia.org/wiki/Wernher_von_Braun) but Russians perfected it enough to reach space, and later enter orbit.
Actually, the *concept* is quite simple. It's the mind-boggling numbers pushing the envelope on material science and engineering that make it so difficult. Eight kilometers per second. 32 megajoules of kinetic energy per every kilogram in orbit. Dissipating that energy on reentry and ascent. Tsiolkovski's rocket equation and its tyranny that boils down to taking many times the weight of the vehicle in fuel. Managing extreme energy density cryofuels - extremely corrosive liquid oxygen and explosive liquid hydrogen. Working with temperatures between 70 and 3500 Kelvin. Void, cosmic radiation, extreme temperature differences, lack of convective cooling. Attitude monitoring and control.
Each of these problems taken alone is a moderately difficult engineering challenge. But if you put them all together this becomes a byzantine puzzle.
Sometimes they don't even notice.
There was this site with "lessons" in using some API or library. There were code examples. And if you tried to select and copy, to paste an example into a compiler, a dialog would pop up telling you that the content is copyrighted and you're not allowed to copy it.
And at the bottom of the page was a survey, "What can I do to improve these lessons?"
I filled it out, with my email and a sarcastic comment about the copy restriction - that maybe forcing people to retype the examples isn't the best way of teaching. The owner of the site wrote me with a solemn apology, informing me that she didn't even notice the (dis)functionality was in place, and that it just got installed with the CMS and she didn't disable it because she didn't know it was there...
So... whoops?
> What precisely did the shuttle show is impractical? I think comparing this to the shuttle seems like an apples to oranges comparison.
Two factors.
1. Excessive cost of $/kg to orbit.
2. Design flaw making it inherently unsafe (the foam pieces falling during launch).
The situation with the SRBs wasn't that bad. They are very simple devices so no wonder after burn-off there was very little left to recover. The solid, hard shell was recovered and it was fully reusable. The rest had to be restored, because it was actually all "consumables". No big deal, they were the cheapest part anyway.
The huge LF tank was lost. It wasn't exactly cheap, but not terribly expensive.
The shuttle, though, had to be refurbished after each flight. And being an incredibly complex device, it took excessive time and cost to perform the inspection and repairs.
And then most of the fuel burned, most of the construction to carry that fuel, most of infrastructure to support that huge construction - was there to lift the cargo bay, the landing gear, the wings, the heat shields on all that, and there was relatively little left for the actual cargo.
For the Shuttle the reusability was a liability, not a boon.
SpaceX still loses the whole second stage. That's not a small loss. But it seems they actually save up a lot on the reuse of the first stage - the cost of preparing it for another launch is nowhere near to the cost of rebuilding it from scratch - and the cost of building it from scratch is nowhere near the cost of preparing the Shuttle for another launch.
Unless they get a private island, the barge is going to stay for heavier payloads. The burnback maneuver will cost far less if you don't need to fly back where you came from.
TBH this time the rocket landed a perfect bull's eye in the middle of the big X on the launchpad.
the kernel loads normally. It's the init system (which is already userspace) that gets hijacked. The whole authentication system runs on userspace side - and in this case isn't run, replaced by plain bash. You still need to issue 'mount -a' to mount all the filesystems but they work okay.
that's what init=/bin/bash is for. You boot directly to bash shell with root privileges bypassing all authentication. Then you can either create a passwordless alias for the root account, or install any rootkit you like.
press backspace 28 times [enter]
write_word 0x7eb514e 0x90909090[enter]
normal[enter]
Enter 'edit mode'
append init=/bin/bash to the linux entry
F10
They wouldn't find the generated 24-char ones.
Either the passwords were stored in plaintext or easily crackable crypt (unlikely), or the hackers hijacked the login system and collected the passwords as they were used for login.
As for heating, they need only to heat a very tiny portion of it to ignite the fusion; it will sustain itself later on - so lasers or masers...
The power losses come from the containment requirements - the reactor doesn't break even with that but the fusion does produce power to heat itself - just not enough surplus to power the magnets.
And with proper main thrusters and RCS. Not a backpack, a bunch of landing SRBs and a fire extinguisher.
It really takes spending a little time with WolframAlpha to pull up some numbers to understand how much sci-fi underestimates the difficulty of space travel.
Take reentry. Some flames, some shaking, right? How much of a problem is it, and why do some parts burn in the atmosphere while others don't? The communicational blackout, some weird quirk... right?
Well, take your Soyuz capsule. Take the time of "communicational blackout", find speed before, speed after, and then calculate kinetic energy at the two moments. Then divide by time for average energy dissipation.
Well, the figure you obtain is about 0.2 gigawatt for some four minutes. This is the amount of energy produced and dissipated as heat, light, sound and about all of spectrum, from deep ultraviolet far past microwaves. No wonder no radio can push from a noise like that. No wonder superior heat shielding is needed with heating like that. And the capsule MUST descend rapidly into thicker atmosphere, because even if less heat was produced during more flat reentry, the thin atmosphere wouldn't be as good at removing it - superheated ablator is blown away before its heat can penetrate deeper into the ship; remove it slower and the inside will heat up!
Or take the LEO speed. About 9 km/s. That's a meaningless number to most, but maybe 26 mach is closer to your heart. Most ammo doesn't exceed 1.5km/s. So energy of impact is roughly 36x of equivalent bullet. Or an object 1/36 as big as a bullet can cause the same damage.
Then we can get started on how big space is, and how much effort matching orbits is... how the Gravity movie was such a bullshit.