Blue Origin Thread (merged)

[Technical Ben]

Finally got my nose landing second stage in KSP working. I realized I'd beefed up the second stage too much (KSP is a bit over powered). I had to put more weight on the top, by adding a second fuel tank for the landing. If I had more mods installed (tweak scale, and some extra engines), I'd go for some alternative fuel possibly... but I guess a small liquid fuel system would work. I used air breaks near the rear engine for stability.

For Real Life, I've no idea if the super dracos or similar would work for the landing, as it's not human rated, it would only need the number it needs with no redundancy, so that would save on weight. Say, 2 to 4 of them could be used. Some retractable fins/etc near the main engine for help orienting too?

[Nightside]

Does anyone know why Falcon uses cold gas thrusters on the Falcon instead of SuperDracos?

[CatastrophicFailure]

6 minutes ago, Nightside said:

Does anyone know why Falcon uses cold gas thrusters on the Falcon instead of SuperDracos?

Quicker/easier turnaround. SuperDracos use hypergolic fuel, nasty nasty stuff to work with. Falcon's thrusters are just nitrogen gas. Lower power/ efficiency but much easier to "refuel and go."

Compare to the Space Shuttle, which also used hypergolic thrusters. After landing, they had to wait minutes/hours to even go near it due to the toxic fumes. 

[Technical Ben]

That, and they don't use the cold gas thrustsers FOR landing, just for orientation/adjustment, right? They would not be powerful enough. But for a manned landing, it's worth the expense.

[Wjolcz]

What about a SuperDraco redesigned to work with the fuel second stage uses? That would be the simplest solution, wouldn't it? All you have to do is slap two or three of these and run some additional plumbing from the tanks to the modified SuperDracos. Not sure what kind of performance would they have though.

Edited April 20, 2017 by Veeltch

[StrandedonEarth]

Just now, Veeltch said:

What about a SuperDraco redesigned to work with the fuel second stage uses?

It would need some sort of ignition system, and the mixture ratio would probably be different. So yeah, a total redesign. May as well be a blank sheet, aside from the chamber, and even that might need tweaking for the ignition system.

[Wjolcz]

3 minutes ago, StrandedonEarth said:

It would need some sort of ignition system, and the mixture ratio would probably be different. So yeah, a total redesign. May as well be a blank sheet, aside from the chamber, and even that might need tweaking for the ignition system.

Oh, yeah. Forgot the hypergolic ones don't need ignition. Anyhow, even if they developed a completely new engine that would be a pretty elegant solution IMO.

BTW, I'm not sure if it's been mentioned but the first flight of FH is scheduled for late summer.

[StrandedonEarth]

It seems to me the best way to make it recoverable would also be the simplest. Build a module that attaches to the payload adapter of a standard second stage, with the engines, fuel, legs and heatshield needed for reentry and landing, along with another payload adapeter. This package would probably be heavier than the Merlin, which is designed to be light. With that at the nose and the big, lightweight vacuum bell at the back to act as a shuttlecock, it might actually be aerodynamically stable. The stage itself would probably only need a thermal blanket, if that, since it can be shielded by the landing module.

 I just wonder how that thin bell would hold up to the buffeting when it's not under power, and without the stabilizer ring mentioned earlier (a page or three ago?) in the thread

[kerbiloid]

+1 t of the 2nd stage dry mass = -1 t of payload = -1/10 launch mass = +1/10 launch count = -1/10 of the 1st stage flight count.

 

[Skylon]

Is the G-force on splashdown just too much to keep the integrity of the engine/fuel tank? If it is just salt water getting to the engine, maybe just have airbags/other buoyancy devices at the sides for stability? Engine is more valuable

[Elthy]

I think the reasons for not landing the first stage in the ocean also apply to the second stage. If you can slow down enough to survive a splashdown its not hard to slow a bit more to land next to the launchsite, with the added benefit of not having to deal with saltwater. Im not sure how they will do this, but splashdown seems like the worst method to recover hardware.

[sevenperforce]

17 hours ago, _Augustus_ said:

Elon mentioned a "bouncy castle" for the fairings. What if they used the same thing for the second stage?

It's possible, but the second-stage engine is a LOT more fragile than the fairings are, so I'm unsure about that.

14 hours ago, Nightside said:

Does anyone know why Falcon uses cold gas thrusters on the Falcon instead of SuperDracos?

As everyone else said, the SuperDracos are heavier and require toxic fuel. They also aren't really needed. The Falcon 9 first stage uses its engine gimbals for pitch, yaw, and roll control on ascent; the cold gas thrusters are only used to adjust attitude/roll when the engines are turned off, and this requires only a very minimal amount of thrust since they are operating in a vacuum.

6 hours ago, Skylon said:

Is the G-force on splashdown just too much to keep the integrity of the engine/fuel tank? If it is just salt water getting to the engine, maybe just have airbags/other buoyancy devices at the sides for stability? Engine is more valuable

Splashdown wouldn't destroy the stage, but the saltwater getting to the engine would ruin it. Even if there were airbags or flotation bags, waves and spray could still saturate the engine before it could be recovered.

13 hours ago, StrandedonEarth said:

It seems to me the best way to make it recoverable would also be the simplest. Build a module that attaches to the payload adapter of a standard second stage, with the engines, fuel, legs and heatshield needed for reentry and landing, along with another payload adapeter. This package would probably be heavier than the Merlin, which is designed to be light. With that at the nose and the big, lightweight vacuum bell at the back to act as a shuttlecock, it might actually be aerodynamically stable. The stage itself would probably only need a thermal blanket, if that, since it can be shielded by the landing module.

 I just wonder how that thin bell would hold up to the buffeting when it's not under power, and without the stabilizer ring mentioned earlier (a page or three ago?) in the thread

The engine bell would not be able to act as a shuttlecock; aerodynamic loads would rip it apart. There's a reason it launches inside the interstage. However, there's a SpaceX rendering that shows panels around the engine which could conceivably pop out and act as a shuttlecock:

Spoiler

A "recovery module" would be straightforward enough, but fitting all the required parts into the form factor seems like it would be a pretty big challenge.

[sevenperforce]

1 hour ago, sevenperforce said:

A "recovery module" would be straightforward enough, but fitting all the required parts into the form factor seems like it would be a pretty big challenge.

Following up on this, consider what has to go into a "full" recovery module adapter:

• Heat shield
• Payload attachment points on/around/under heat shield
• Thrusters
• Propellant tanks
• Pressurant tank(s)
• Landing legs

There's a chance you could pressurize the legs and the thruster prop tanks from the main-stage pressurant COPVs, but that would require re-plumbing of the main tank, and I'm not sure the Falcon COPVs have enough helium pressure to successfully run pressure-fed thrusters. The SuperDracos have a chamber pressure of 6.9 MPa.

Consider also that the thrusters and the landing legs both need to be outside of the re-entry plasma impingement region. For the thrusters, this probably means being set significantly back inside the module with associated cosine losses. The landing legs are also problematic, since space is really limited. Using the Dragon 2's pop-out landing struts is not ideal due to the much greater height of the second stage; even a slight puff of wind would tip it over. The recovery module is also going to increase the effective height of the stage, significantly.

Geometry is a limiting factor, here.

EDIT: For example, here's what the difference might look like...

First from left is the current Stage 2. Second from left would be the second stage with recovery adapter and flaps added. Third shows recovery adapter and feathered flaps on re-entry; fourth shows landing burn (high cosine losses) with legs extended. Obviously it would be balanced; this only shows one thruster and one landing leg for the sake of simplicity. The tanks shown are helium pressurant and hypergolic bipropellant.

Edited April 20, 2017 by sevenperforce

[StrandedonEarth]

Perhaps an inflatable heat shield? Which would make the nose more draggy, not so good. Pros and cons

[Technical Ben]

The above design is probably what they will go for IMO if flipping the stage is really not an option. Payload size is not a worry at this point. If costs are reduced, you can just launch multiple times for multiple buses (instead of doubling up as they do often now). Or scale up later when the tech/industry and demand is proven.

 

The above design would fit either the top or bottom of the stage. So as this is not KSP, they could theoretically just run the numbers in a computer, program a landing system (we are limited by Mechjeb, or sitting there bug testing self made KOS scirpts ) that can orientate nose first. Even against a stupid COG that is rear ended, with cold gas thrusters/fins/fuel pumps/etc they could just hold it in place. Then flip back over last second to land. It's not unheard of, and of cause a lot of fighter jets actually fly this way nowadays.

[sojourner]

2 hours ago, sevenperforce said:

Following up on this, consider what has to go into a "full" recovery module adapter:

• Heat shield
• Payload attachment points on/around/under heat shield
• Thrusters
• Propellant tanks
• Pressurant tank(s)
• Landing legs

There's a chance you could pressurize the legs and the thruster prop tanks from the main-stage pressurant COPVs, but that would require re-plumbing of the main tank, and I'm not sure the Falcon COPVs have enough helium pressure to successfully run pressure-fed thrusters. The SuperDracos have a chamber pressure of 6.9 MPa.

Consider also that the thrusters and the landing legs both need to be outside of the re-entry plasma impingement region. For the thrusters, this probably means being set significantly back inside the module with associated cosine losses. The landing legs are also problematic, since space is really limited. Using the Dragon 2's pop-out landing struts is not ideal due to the much greater height of the second stage; even a slight puff of wind would tip it over. The recovery module is also going to increase the effective height of the stage, significantly.

Geometry is a limiting factor, here.

EDIT: For example, here's what the difference might look like...

First from left is the current Stage 2. Second from left would be the second stage with recovery adapter and flaps added. Third shows recovery adapter and feathered flaps on re-entry; fourth shows landing burn (high cosine losses) with legs extended. Obviously it would be balanced; this only shows one thruster and one landing leg for the sake of simplicity. The tanks shown are helium pressurant and hypergolic bipropellant.

I think your depiction of the recovery adapter is WAY too large.

[sevenperforce]

6 minutes ago, sojourner said:

I think your depiction of the recovery adapter is WAY too large.

The consumables tanks could probably be much smaller, but getting fold-out landing legs requires a lot of space.

[sevenperforce]

Another idea that is particularly promising...

Autorotation.

Terminal velocity on the first stage is (at present) slightly subsonic. I'm guessing it's somewhere around 300 m/s. The first stage masses four times the second stage, but since grid fin drag and pressure drag are the majority, this suggests terminal velocity that's roughly a quarter of that, or 75 m/s. It would actually be slightly higher because of the square term in the drag equation, but the new grid fins are larger so that's probably not much of a difference.

The new grid fins are supposed to be able to provide a 1:1 lift-to-drag ratio on the first stage. And that's where things get interesting. L/D on the second stage with the same size grid fins would be on the order of 4:1 or maybe even 5:1. So if the second stage was allowed to autorotate, it could conceivably get enough lift to reduce impact speed to something on the order of 15 m/s, which might be bouncy-castle-survivable.

[cubinator]

What about, in place of landing legs, some sort of "catcher" platform that would attach to the second stage and stabilize it as it finishes it's landing? They're already working on something similar for the first stage. That way you don't have the added mass of landing legs during flight, but you still don't tip over when you land.

[sevenperforce]

9 minutes ago, cubinator said:

What about, in place of landing legs, some sort of "catcher" platform that would attach to the second stage and stabilize it as it finishes it's landing? They're already working on something similar for the first stage. That way you don't have the added mass of landing legs during flight, but you still don't tip over when you land.

The RoombaX is intended to secure the first stage on the droneship, not catch it. It wouldn't survive the engine wash.

Might be different for a second stage, particularly if it had hover capability with a set of SuperDracos, but it would be tricky. Would potentially work for a RTLS but not for a droneship. A cradle with fixed vertical arms over a blast trench, maybe.

[Technical Ben]

It is smaller... the legs could be put in other ways. In KSP my build currently looks like the picture above, as it is stock, so I am limited on sizes/styles.

Why could the legs not flip out like scissors, then extend. That way they could be very compact, and not very tall when stowed. Not actual scissor reaching link:

 just scissor extension as in:

PS, sorry, seems KSP forums autoposts links to pictures now.

 

I'm having trouble finding a video/picture, but some JCB/cranes have the stability assisting legs fold out, then deploy. A horizontally stowed, instead of vehicle stowed, set of legs would take up less space in front of the fuel tanks.

Edited April 20, 2017 by Technical Ben

[cubinator]

48 minutes ago, sevenperforce said:

The RoombaX is intended to secure the first stage on the droneship, not catch it. It wouldn't survive the engine wash.

It could be a decent place to start nonetheless.

48 minutes ago, sevenperforce said:

A cradle with fixed vertical arms over a blast trench, maybe.

The second stage was portrayed doing a RTLS in the old video, so this could be plausible. You'd only need to integrate small attachment points in the stage itself instead of whole legs.

[sevenperforce]

1 hour ago, cubinator said:

The second stage was portrayed doing a RTLS in the old video, so this could be plausible. You'd only need to integrate small attachment points in the stage itself instead of whole legs.

Honestly, you wouldn't even need attachment points. The second stage is short enough that as long as it slides in, it's okay if it lists a little bit.

[Technical Ben]

So would it just be a giant net? I know they can do clever landings, but an actual catch in a crane? I think that is asking too much.

[sevenperforce]

35 minutes ago, Technical Ben said:

So would it just be a giant net? I know they can do clever landings, but an actual catch in a crane? I think that is asking too much.

It can land upright in a static cradle with vertical arms. Pinpoint landing isn't a problem, never has been.

Spoiler

The cradle would have wide open spaces for the exhaust plumes to exit through.

EDIT: Wait a minute. If it can RTLS and control its descent with grid fins enough to pinpoint a landing, it can literally just land in a net, suspended above the ground. No SuperDracos required. Terminal velocity would not be very high. Case in point: https://www.youtube.com/watch?v=6qF_fzEI4wU

 

Edited April 20, 2017 by sevenperforce