Blue Origin Thread (merged)

[Skylon]

Just now, Veeltch said:

It's the current plan, I believe.

2020 vision? No? Yes?

[Wjolcz]

Just now, Skylon said:

2020 vision? No? Yes?

YES.

[Rakaydos]

2 hours ago, Skylon said:

What is the reason for having more satellites? Is there no way you could increase the capacity of a satellite while increasing the mass? Does a bigger satellite equal less satellites? I imagine not

Does Elon Musk still want to have their first mars mission in 3 year's time? So the 2020 vision?

A single big satelite can only be in one place at a time. Lower altitudes have better latency, and more managable signal strengths, but limit individual satelite "uptime" where the ground can see the satelite. The answer is more satelites.

[mikegarrison]

2 hours ago, Rakaydos said:

It's more a problem at, ironically, the higher altitudes. At low altitudes the dangerous schrapnel that sustanes a kessler cascade has too much drag to stay in orbit, and falls back to earth.

And the satelites arnt actually that close together. Imagine if there were only 40,000 cars in the entire world, roughly equally far apart.

And yet ... https://en.wikipedia.org/wiki/2009_satellite_collision

[magnemoe]

3 hours ago, Rakaydos said:

A single big satelite can only be in one place at a time. Lower altitudes have better latency, and more managable signal strengths, but limit individual satelite "uptime" where the ground can see the satelite. The answer is more satelites.

Yes, satellites in low orbit give less latency, You will also get more capacity as each satellite only serves the area below it, and the frequency band can be reused for other satellites. 
An satellite in higher orbit could use multiple antennas to service multiple areas but this would not work for uplink and you get higher latency.
 

 

[tater]

Given the talk by Elon of attempting stage 2 recovery (even if to start it's a soft water landing, like early booster landing attempts), has anyone seen data on the sea level thrust of the vacuum optimized Merlin 1D? 

Or would serious recovery use parachutes, or sacrifice payload for the mass of superdraco engines and props?

Edited April 12, 2017 by tater

[tater]

So I re-watched the old SpaceX video of reuse of the entire Falcon vehicle and Dragon (with the song  "Uprising" as soundtrack). When S2 lands, the Merlin is not doing the work, there are 4 small engines it looks like, around the vac engine.

[Skylon]

32 minutes ago, tater said:

Given the talk by Elon of attempting stage 2 recovery (even if to start it's a soft water landing, like early booster landing attempts), has anyone seen data on the sea level thrust of the vacuum optimized Merlin 1D? 

Or would serious recovery use parachutes, or sacrifice payload for the mass of superdraco engines and props?

I remember in the original animations it used thrusters which looked like cold gas thrusters for landing. I think they may do parachute-assisted propulsive landing. Really it is just a test of reentry I think.

Ninja'd!

Edited April 12, 2017 by Skylon

[sevenperforce]

51 minutes ago, tater said:

Given the talk by Elon of attempting stage 2 recovery (even if to start it's a soft water landing, like early booster landing attempts), has anyone seen data on the sea level thrust of the vacuum optimized Merlin 1D? 

Or would serious recovery use parachutes, or sacrifice payload for the mass of superdraco engines and props?

The MVac would have catastrophic flow separation at sea level. Not to mention that a retrograde burn (even a subsonic one) would shred the thin, ultra-lightweight nozzle extension. It would need to land on auxiliary thrusters for sure.

If Elon is serious about landing the second stage, my best guess is that he'll have his people design a mini-Dragon-2 (heat shield, SuperDracos, tanks, and legs) that attaches to the standard S2 payload adapter. Then it would simply be a matter of adding grid fins and a bit of TPS to the second stage body.

Edited April 12, 2017 by sevenperforce

[Mad Rocket Scientist]

34 minutes ago, sevenperforce said:

The MVac would have catastrophic flow separation at sea level. Not to mention that a retrograde burn (even a subsonic one) would shred the thin, ultra-lightweight nozzle extension. It would need to land on auxiliary thrusters for sure.

[...]

They show an MVac with an extendable bell @1:24 in this video: 

But they also show other engines being used for landing.

I'm not sure if the second stage + MVac has enough TWR to land, but I suppose it'd be almost empty.

 

[RCgothic]

I notice that 'fully reuseable' craft doesn't reuse the trunk!

[sevenperforce]

1 hour ago, Mad Rocket Scientist said:

They show an MVac with an extendable bell @1:24 in this video: 

But they also show other engines being used for landing.

I'm not sure if the second stage + MVac has enough TWR to land, but I suppose it'd be almost empty.

That's not an extensible bell; that's apparently a nozzle that retracts in and extends out of the stage body...presumably to shorten the interstage and protect it during re-entry. That's not the direction SpaceX has gone with the MVac at all.

The MVac is useless at sea level. Fire it up, and it will be so underexpanded that flow separation inside the nozzle would tear it to pieces. Even if this didn't happen, the aerodynamic turbulence would shred it; that nozzle is ridiculously thin, to the point that it's practically pressure-stabilized in flight. Watch the S2 startup from one of the SpaceX live launch videos; the entire nozzle flexes during startup transients.

And, even if it could do controlled flow separation and could somehow avoid aerodynamic turbulence, the TWR at minimum would be around 12, waaaaay too thrusty for a hoverslam. 

23 minutes ago, RCgothic said:

I notice that 'fully reuseable' craft doesn't reuse the trunk!

That's why we need an integrated S2+Dragon!

[magnemoe]

5 hours ago, sevenperforce said:

That's not an extensible bell; that's apparently a nozzle that retracts in and extends out of the stage body...presumably to shorten the interstage and protect it during re-entry. That's not the direction SpaceX has gone with the MVac at all.

The MVac is useless at sea level. Fire it up, and it will be so underexpanded that flow separation inside the nozzle would tear it to pieces. Even if this didn't happen, the aerodynamic turbulence would shred it; that nozzle is ridiculously thin, to the point that it's practically pressure-stabilized in flight. Watch the S2 startup from one of the SpaceX live launch videos; the entire nozzle flexes during startup transients.

And, even if it could do controlled flow separation and could somehow avoid aerodynamic turbulence, the TWR at minimum would be around 12, waaaaay too thrusty for a hoverslam. 

That's why we need an integrated S2+Dragon!

Currently the bell is fixed and inside the interstage.
The reuseable version launch with the bell retracted to make room for the landing legs inside interstage, after seperation the legs go out and the bell expands.
After deobit burn the bell retract and the legs folds in to protect them. after reentry, the second stage flips and the legs expands for landing. 

I agree with you about the twr issues. 
 

[sojourner]

Why not put heat resistant grid fins at the base of the stage that would open up in a "shuttle cock" configuration? Could that achieve enough stability for re-entry? We already know that F9 Block 5 is getting titanium grid fins that are more heat tolerant. Maybe they are thinking of 2nd stage recovery as well with that change?  Heck, with some smart engineering they could even integrate the landing leg system into the gird fin/shuttlecock system.  If you're going to add weight make it work for you too..

[Lukaszenko]

I don't think it's that simple. Reentry vehicles are especially shaped to push the hot plasma away and create a cooler boundary layer between the vehicle and the hot gas. And even then, they use special materials and various tricks to withstand the extreme heat. A grid fin, at first glance, is a smack in the face to this design concept. You're basically asking it to go directly through the hot plasma, and even adding extra surface area for it to impinge upon. 

I'm confident that using everyday materials such as titanium as a heat shield would be catastrophic. I'm also confident that a grid-fin out of purpose-made reentry material (if even possible) would fail. 

A titanium grid fin though? There would be no chance. 

Edited April 13, 2017 by Lukaszenko

[TheEpicSquared]

Didn't China once experiment with using wood for heat shields? I haven't read up fully on that (and I have no idea if it would be successful) but that's an idea...

 

Edit: Oh, looks like this is my 1000th post!  

Edited April 13, 2017 by TheEpicSquared

[rkarmark]

13 minutes ago, TheEpicSquared said:

Didn't China once experiment with using wood for heat shields? I haven't read up fully on that (and I have no idea if it would be successful) but that's an idea...

Cork works really well as a heat sheld

[kerbinorbiter]

34 minutes ago, TheEpicSquared said:

Didn't China once experiment with using wood for heat shields? I haven't read up fully on that (and I have no idea if it would be successful) but that's an idea...

 

Edit: Oh, looks like this is my 1000th post!  

 Congratulations on the 1000th post 

21 minutes ago, rkarmark said:

Cork works really well as a heat sheld

Just think of it, cork is basically a wood can you imagine a slab of wood protecting you from the same temperature as the sun practically that would be scary 

[Kryten]

1 hour ago, TheEpicSquared said:

Didn't China once experiment with using wood for heat shields? I haven't read up fully on that (and I have no idea if it would be successful) but that's an idea...

Their early FSW sats used oak impregnated with an ablative treatment. Not very efficient in terms of mass, but it worked.

[KSK]

1 hour ago, kerbinorbiter said:

 Congratulations on the 1000th post 

Just think of it, cork is basically a wood can you imagine a slab of wood protecting you from the same temperature as the sun practically that would be scary 

No more scary than relying on carbon-carbon composites (hey carbon burns right?) as the Space Shuttle did on the most demanding parts (nose cone and wing leading edges) of its thermal protection system.

As @rkarmarksaid, cork works well as a heat shield, at least in principle. Phenolic impregnated cork has been studied by NASA as a possible thermal protection material for aerocapture at Mars and as an ablator for heat shields in general. A successful moulded cork heat shield was apparently produced and tested back in the 70s and established as a realistic product. From the paper linked to in that article:

" The properties which make cork a potential ablative insulating material are, of course, its low density, low thermal conductivity, inherent stability, and the way in which it burns... *snip* The burning characteristics of cork are naturally related to its low thermal conductivity Cork, as a  natural wood, burns on ignition, but with its foam-like structure the heat of combustion simply is not transferred very deeply into the material. Thus, the formation of successive layers of char is dependent upon a constant supply of heat. As soon as heat is removed, the cork will self-extinguish..."

So there you go.  

Edit. I'm unsure why cork wasn't adopted as a heatshield material despite the fact that it was found to be a realistic product. Possibly that  reliably obtaining large enough pieces of cork of the required quality (it is a natural product after all) may have been too hard.

Edited April 13, 2017 by KSK

[Brent Kerman]

Scott Manley did a very good video on wood heat shields and how they would work in real life, he said oak was the best because it was so dense.

[sevenperforce]

10 hours ago, sojourner said:

Why not put heat resistant grid fins at the base of the stage that would open up in a "shuttle cock" configuration? Could that achieve enough stability for re-entry? We already know that F9 Block 5 is getting titanium grid fins that are more heat tolerant. Maybe they are thinking of 2nd stage recovery as well with that change?  Heck, with some smart engineering they could even integrate the landing leg system into the gird fin/shuttlecock system.  If you're going to add weight make it work for you too..

Yeah, I've been curious as to whether the new titanium grid fins will be square, like the current ones, or switch to something like the diamond-shaped ones depicted for the ITS Booster.

Simply placing a cork lip around the base of the second stage should be enough to keep it on track.

3 hours ago, TheEpicSquared said:

Didn't China once experiment with using wood for heat shields? I haven't read up fully on that (and I have no idea if it would be successful) but that's an idea...

The TPS panels currently used for the Falcon 9 first stage are cork.

[sevenperforce]

1 hour ago, Brent Kerman said:

Scott Manley did a very good video on wood heat shields and how they would work in real life, he said oak was the best because it was so dense.

I'm not sure if density is the key factor. IIRC the efficacy of an ablative heat shield is a combination of its heat capacity, its heat conductivity, and its total mass. You want something with a high heat capacity so it takes a lot of heat to ablate a given mass away, and you want something with very low heat conductivity so that each microlayer must ablate away completely before the next layer feels any significant heating. 

[Frozen_Heart]

18 hours ago, RCgothic said:

I notice that 'fully reuseable' craft doesn't reuse the trunk!

Shush. You'll give elon ideas.

[softweir]

The problem with cork, wood and other natural materials is that they are prone to having internal flaws such as splits and inclusions of more volatile materials. Splits and similar flaws can potentially conduct heat deep into the material, seriously damaging its insulating capability, and inclusions of more volatile materials can potentially expand explosively, seriously compromising the integrity of the heat shield. At their worst, natural materials under such extremes of heat can fail catastrophically leaving the re-entry vehicle unprotected.

There are techniques for getting around this, such as using large numbers of very fine layers of material that have been carefully inspected and tested for flaws. However the cost of doing this starts to approach the cost of using completely artificial materials, so the motivation for using natural materials is reduced.