Aethon

Blue Origin Thread (merged)

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14 minutes ago, Camacha said:

Ehm. No? Landing in such a fashion is no different from a take-off, except, again, the direction of travel is in your favour. Slowing down to get out of the way is much easier than speeding up to outrun your rocket.

I think it's generally agreed that suicide burns/hoverslams are more precise and exacting than aborts, even if the g-forces of the latter are more severe. In an abort, you don't really care how much thrust you have, as long as it is enough to get you out of harm's way. In a hoverslam, you've got to have precisely the right amount of thrust at precisely the right amount of time so that your legs touch down exactly when your engines shut down. Any residual lateral velocity and you break a leg or tip over entirely.

Tipping over in a capsule isn't a big problem, because even if you did happen to lose a leg partially (Thiacom-8) or completely (Jason-3), you'll still be mostly upright. In the unlikely event that you come in at an angle like CRS-5 or tip over completely like CRS-6 (which almost certainly won't happen since the height-to-width ratio is so low), you end up rolling, which won't be much fun for the occupants but at least the capsule itself will probably remain intact.

But when you're thinking about landing a mini-ITS on its tail, with the crew perched on top, it's a lot more risky. A Thiacom-8 problem, and you're teetering on the top of a tower that's rocking back and forth while you hang on for dear life. Jason-3? You're dead. CRS-6? You're dead. CRS-5? You're so very very dead. 

And even in an ideal case, you're still perched on top of a tower with no way to get out on your own.

29 minutes ago, Rakaydos said:
32 minutes ago, sevenperforce said:

The methalox thrusters for the ITS will be hot-gas pressure-fed from the autogenous pressurization tanks configured with the Raptors.

Without the Raptor and its heat exchanger, then, there's no way to pressurize the tanks for the methalox thrusters.

I wouldnt say there's no way to solve that problem, but you are right in that an alternate heat source is something that needs to be engineered around.

Raptor and Merlin both have high specific impulse for their propellant type and high TWR because their chamber pressures are very high.

The ITS methalox thrusters are technically an autogenous pressure-fed cycle, which works fine in the ITS because it is using the Raptor as its heat exchanger, but wouldn't work otherwise. You could go to helium pressure-fed cycle, like the Kestrel, but that really hurts engine efficiency and TWR while driving up the dry mass of the stage. A hot-gas expander cycle could be used, but that's also inefficient and doesn't scale up very well.

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Posted (edited)
25 minutes ago, sevenperforce said:

I think it's generally agreed that suicide burns/hoverslams are more precise and exacting than aborts, even if the g-forces of the latter are more severe. In an abort, you don't really care how much thrust you have, as long as it is enough to get you out of harm's way. In a hoverslam, you've got to have precisely the right amount of thrust at precisely the right amount of time so that your legs touch down exactly when your engines shut down. Any residual lateral velocity and you break a leg or tip over entirely.

Tipping over in a capsule isn't a big problem, because even if you did happen to lose a leg partially (Thiacom-8) or completely (Jason-3), you'll still be mostly upright. In the unlikely event that you come in at an angle like CRS-5 or tip over completely like CRS-6 (which almost certainly won't happen since the height-to-width ratio is so low), you end up rolling, which won't be much fun for the occupants but at least the capsule itself will probably remain intact.

But when you're thinking about landing a mini-ITS on its tail, with the crew perched on top, it's a lot more risky. A Thiacom-8 problem, and you're teetering on the top of a tower that's rocking back and forth while you hang on for dear life. Jason-3? You're dead. CRS-6? You're dead. CRS-5? You're so very very dead.

And even in an ideal case, you're still perched on top of a tower with no way to get out on your own.

It seems you are creating problems where there are none, or where well tested solutions exist. Egress systems exist, have existed for quite a while and have been built and tested.

Jason-3? Very slow topple and therefore an easy escape. Fire your escape system and you are well clear of any explosion. CRS-6? Same story. CRS-5 is probably the most dramatic failure and even that provided ample time to egress. As long as the craft is not inverted or anywhere near that, you have the option of using the escape tower like system. That is exactly what they are designed for. Ejection seats save pilots from aircraft that were heading towards the ground uncontrollably, ejecting at about a 90 angle and close to the ground. Being on top of a rocket at near standstill is, by comparison, a much better starting position.

Being on top of a tower has been solved by humanity a while back and was successfully used in space and other bodies. All Apollo craft that reached the moon employed a ladder system to allow the crew to exit their craft.

 

 

 

Edited by Camacha

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10 minutes ago, Camacha said:

It seems you are creating problems where there are none, or where well tested solutions exist. Egress systems exist, have existed for quite a while and have been built and tested.

Jason-3? Very slow topple and therefore an easy escape. Fire your escape system and you are well clear of any explosion. CRS-6? Same story. CRS-5 is probably the most dramatic failure and even that provided ample time to egress. As long as the craft is not inverted or anywhere near that, you have the option of using the escape tower like system. That is exactly what they are designed for. Ejection seats save pilots from aircraft that were heading towards the ground uncontrollably, ejecting at about a 90 angle and close to the ground. Being on top of a rocket at near standstill is, by comparison, a much better starting position.

Ooooh, I see. We were comparing apples and oranges. I was talking about a tailsitter landing being bad for crew with something like the ITS, where you don't have any separate escape system at all. If a mini-ITS pulled a CRS-5, CRS-6, or Jason-3, everyone dies. Even a Thiacom-8 is a very, very bad day.

It's safe enough to use LAS engines as landing engines for a capsule like the Dragon 2, because the capsule will not RUD even if a leg breaks or it tips over. A mini-ITS would not have any escape system, which is why I said I didn't like the idea of landing it on its tail.

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4 minutes ago, sevenperforce said:

Ooooh, I see. We were comparing apples and oranges. I was talking about a tailsitter landing being bad for crew with something like the ITS, where you don't have any separate escape system at all. If a mini-ITS pulled a CRS-5, CRS-6, or Jason-3, everyone dies. Even a Thiacom-8 is a very, very bad day.

It's safe enough to use LAS engines as landing engines for a capsule like the Dragon 2, because the capsule will not RUD even if a leg breaks or it tips over. A mini-ITS would not have any escape system, which is why I said I didn't like the idea of landing it on its tail.

What do you do if the LAS engines blow up?'

I seem to recall some famus person reportedly saying "you can put all your eggs in one basket, as long as you make DAMN sure you protect that basket." That is the ITS's escape strat- a reliable second stage that doesnt blow up.

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27 minutes ago, Camacha said:

Being on top of a tower has been solved by humanity a while back and was successfully used in space and other bodies. All Apollo craft that reached the moon employed a ladder system to allow the crew to exit their craft.

Hah! Yes, this is true. But things were a bit different for the LM. For one thing, the height-to-width of the LM was less than 1, so tip-over during egress was never a possibility. Plus, it wasn't the terminal stage; during landing, the ascent stage could have aborted to the command module at any time. When you're landing on Earth, you kind of want to be able to reliably get out of your vehicle if there was an emergency. Being at the top of a tower is one thing; being at the top of an unstable tower still partly filled with a bucket o' dV is another thing entirely.

12 minutes ago, Rakaydos said:

What do you do if the LAS engines blow up?'

I seem to recall some famus person reportedly saying "you can put all your eggs in one basket, as long as you make DAMN sure you protect that basket." That is the ITS's escape strat- a reliable second stage that doesnt blow up.

In the Dragon 2, if the LAS engines fail you can pop the chutes and let the legs crush...it'll be a bumpy landing but you'll be okay.

Anyway I'm not concerned so much about the engine integrity. Using one set of engines for launch, launch abort, and propulsive landing (e.g. ITS) is fine and dandy, but even 100% reliable engines can't save you from an RUD if you're landing on your tail and you start to tilt.

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2 minutes ago, sevenperforce said:

Ooooh, I see. We were comparing apples and oranges. I was talking about a tailsitter landing being bad for crew with something like the ITS, where you don't have any separate escape system at all. If a mini-ITS pulled a CRS-5, CRS-6, or Jason-3, everyone dies. Even a Thiacom-8 is a very, very bad day.

In space flight, humans have always been a little bit better protected than unmanned spacecraft. It seems obvious to me that some sort of backup would be present, especially considering they generally always have and that SpaceX has already tested an egress system. Of course, even a singular landing system could be designed in such a way that failure does not have to be the end. Using multiple engines, controlled by separate systems means you have a built in backup system. That is one of the reasons the Falcon 9 has so many engines.

2 minutes ago, sevenperforce said:

Hah! Yes, this is true. But things were a bit different for the LM. For one thing, the height-to-width of the LM was less than 1, so tip-over during egress was never a possibility. Plus, it wasn't the terminal stage; during landing, the ascent stage could have aborted to the command module at any time. When you're landing on Earth, you kind of want to be able to reliably get out of your vehicle if there was an emergency. Being at the top of a tower is one thing; being at the top of an unstable tower still partly filled with a bucket o' dV is another thing entirely.

Yes. For this reason, your exit strategy is important. I will point again to jet fighters, which are essentially slow rockets with wings. Very light, very powerful and, more often than not, very filled with combustible go juice. If you want to land on a tiny huge metal sliver in an even huger ocean, you make sure you have a plan B if the cable essential to plan A does not cooperate.

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11 minutes ago, Camacha said:

In space flight, humans have always been a little bit better protected than unmanned spacecraft. It seems obvious to me that some sort of backup would be present, especially considering they generally always have and that SpaceX has already tested an egress system. Of course, even a singular landing system could be designed in such a way that failure does not have to be the end. Using multiple engines, controlled by separate systems means you have a built in backup system. That is one of the reasons the Falcon 9 has so many engines.

Yes. For this reason, your exit strategy is important. I will point again to jet fighters, which are essentially slow rockets with wings. Very light, very powerful and, more often than not, very filled with combustible go juice. If you want to land on a tiny huge metal sliver in an even huger ocean, you make sure you have a plan B if the cable essential to plan A does not cooperate.

Spacex has already tested an egress system? By egress, I mean physically entering and exiting the vehicle.

Ejection seats work very well for aircraft. They would work well enough for landing a spacecraft on Earth, but less so during launch, and not at all on orbit.

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Just now, sevenperforce said:

Spacex has already tested an egress system? By egress, I mean physically entering and exiting the vehicle.

They have tested the egress system I posted earlier. I have no knowledge of EVA tests.

Just now, sevenperforce said:

Ejection seats work very well for aircraft. They would work well enough for landing a spacecraft on Earth, but less so during launch, and not at all on orbit.

Are you talking about just a literal  seat? It seems obvious you need to adjust your solution to the application. The comparable solution for space flight is an escape tower or pod.

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6 minutes ago, Camacha said:

Are you talking about just a literal  seat? It seems obvious you need to adjust your solution to the application. The comparable solution for space flight is an escape tower or pod.

There are numerous instances in which you may need an escape system, each with their own complications.

  • 0/0 pad abort. You've got to go up very fast and get enough horizontal velocity that you come down, you don't land in fireball. You also need a way to come down without going splat.
  • MaxQ abort. You've got to get clear of a fireball in air too thin to breathe, while you're already going supersonic, avoid tumbling uncontrollably beyond the aerodynamic limits of your vehicle, and then come down without going splat.
  • On-orbit Lifeboat. For instances where your crew cabin is incorporated into your launch vehicle, you need a way to leave your launch vehicle behind on-orbit if its primary TPS or its structure is damaged during launch or on orbit (e.g., Columbia). Then you need to re-enter without burning up, and come down without going splat.
  • Landing snafu. If your vehicle is coming down too hard/fast, then see 0/0 pad abort as above.

Ejection seats work for the 0/0 pad abort and the landing snafu, but not for the MaxQ abort or the On-orbit Lifeboat. An ejectable capsule/cabin with its own pusher engines will work for a MaxQ abort, but it needs to be chuted down, and it will only work as an on-orbit lifeboat if it has its own TPS. And it may not work for a 0/0 pad abort or a landing snafu, depending on its orientation to the rest of the vehicle.

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2 minutes ago, DarthVader said:

Absurd, coming from a man who has consistently overhyped and under produced

Heh, everyone said that about reuse. But I hope it works out as well :) 

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59 minutes ago, DarthVader said:

Absurd, coming from a man who has consistently overhyped and under produced, but it might work: https://mobile.twitter.com/elonmusk/status/847882289581359104

@sevenperforce Welp, whatever the (nonexistent) details, it would appear they're a lot closer to second stage recovery than anyone thought. :/

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He mentioned that the fairing costs 6 M$. A new F9 launch sells for 62 M$.

Merlins are substantially cheaper than a fairing, apparently.

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Well, unless whatever test payload they put on the FH demo is very heavy or sent beyond LEO, the second stage on that flight is going to have a healthy margin of fuel left to play around with for a retro burn.  More so than on most operational flights.

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3 hours ago, DarthVader said:

Absurd, coming from a man who has consistently overhyped and under produced

Using the term under produced is rather brave, considering the achievements of SpaceX so far. We are not even mentioning the other companies.

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1 hour ago, Camacha said:

Using the term under produced is rather brave, considering the achievements of SpaceX so far. We are not even mentioning the other companies.

Maybe he meant to refer to Richard Branson?

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29 minutes ago, sojourner said:

Maybe he meant to refer to Richard Branson?

Well, the link obviously refers to a message from Musk. Whatever the case, few of us could ever dream to achieve what either Branson or Musk have. Both men have achieved remarkable things in their lives, far beyond any reasonable expectation.

I never quite understand the need some keyboard warriors have to put highly achieving people down. Besides, if you do not shoot for the stars, you will never end up there.

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I suppose that if Dragon flights land at sea instead of boosting back to land, that may leave enough margin to recover the second stage. Similarly, if F9 payloads that allow the booster to be recovered are moved to F9H, that should certainly leave enough margin to recover the second stage, likely with all boosters returning to dry land.

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Next launch seems to be NROL-76, NET April 16th. I asked around on Reddit, and interestingly enough, this will be horizontally integrated (despite the air force's requirement of vertical integration capability for certification). It will also be a return to land flight. So people are thinking that this is a small test payload, rather than a fully fledged mission. But as with all NRO launches, no information is provided, so it could be anything.

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12 hours ago, StrandedonEarth said:

I suppose that if Dragon flights land at sea instead of boosting back to land, that may leave enough margin to recover the second stage. Similarly, if F9 payloads that allow the booster to be recovered are moved to F9H, that should certainly leave enough margin to recover the second stage, likely with all boosters returning to dry land.

Second stage recovery will hit payload capacity a lot. With falcon heavy should will work however. 
And it will require an new upper stage, lots of changes is needed to be able to deorbit and land upper stage. 
 

 

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Posted (edited)

It is probably some military cheese... :sticktongue:

SpaceX has done a lot, and recovering a first stage is incredibly difficult. I don't know about the cost savings, but if they are enough that it is cheaper to refurbish than to build a new one, I think they've found a pretty good gold mine to do that with every launch.

The second stage would need a lot more fuel, and there would have to be something like the grid fins added for steering. It would have to survive the blistering reentry for longer because it is technically in orbit, just not a stable one. 

Thought: have a heat shield on the front of the stage where the payload sits, so it reenters forward...

Edited by Benjamin Kerman
More ideas

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11 minutes ago, Benjamin Kerman said:

Thought: have a heat shield on the front of the stage where the payload sits, so it reenters forward...


You still need thermal protection on the rest of the stage to protect from radiant heat.

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Mm.... Yeah, that would be a problem. But then again, the first stage has survived, but it's reentry was not as long. 

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30 minutes ago, Benjamin Kerman said:

-snip-

Thought: have a heat shield on the front of the stage where the payload sits, so it reenters forward...

Hmm... where have I seen this before?

Second stage recovery was part of the original plan afaik.

Musk on the upper stage: https://youtu.be/PULkWGHeIQQ?t=6m59s

 

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