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3 hours ago, Scotius said:

Holy hydrazine!!! Dragon with an airlock... If it works... Can Dragon be used to service Hubble, Kepler and other high-orbit space observatories? :confused:

Kepler is heliocentric and deactivated, so that probably won't happen, and Hubble needs the robotic arm to keep the vehicles together

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On 2/13/2022 at 12:26 AM, kerbiloid said:
On 2/13/2022 at 12:26 AM, kerbiloid said:

To the contrary, Raptor 2 has thrust levels significantly higher than what was estimated when the booster diameter was set.

And they still need a skirt. So, even Raptors 2 don't fit its diameter.

Thus, Raptor 1 looks unable even to lift it, and the diameter looks overoptimistically.

Don't they teach math in Russia?

All of this stuff is simple public knowledge that anyone can look up. It's not that complicated.

When the diameter was set at 9 meters at the 2017 IAC, they proposed 31 engines, each around 175 tonnes force, lifting a vehicle with a total mass of 4400 tonnes. At that time, the vehicle was expected to be 109 meters high, slightly less than the Saturn V. 

Here's what 31 engines looks like, optimally packed:

circle-packing.png

You will note that the diametric ratio is 6.292; for a 9 meter vehicle, this means each 1.3-meter engine has a 10 cm gap between it and each nearest adjacent engine...more, if you cluster the outside engines closely to allow more room for the inner engines to gimbal.

At this time, they were still planning on carbon fiber bodies, which would have used a thrust puck distribution on the booster. However, as @Rakaydos and others have pointed out to you, once they switched to stainless steel, the plan was to have the load path go straight up through the skin. This was also the design of the Saturn V first stage:

load-path.png

And as you can see, even in the 33-engine configuration, there is still plenty of space. They're intentionally positioning the outer ring of engines around the skin:

circle-packing.png

Lots of daylight between those central engines. They are obviously not area-limited.

Now, with more powerful engines, the whole vehicle has gotten a tank stretch so it now is taller than the Saturn V and has a higher liftoff mass than the original configuration.

On 2/13/2022 at 12:26 AM, kerbiloid said:

The cutouts have a visible gap to prevent the contact of the nozzle and the ring.
The nozzles are attached to the combustion chamber, not to the ring.

The nozzles are braced to the secondary stiffener ring, which is bolted to the cutouts.

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5 hours ago, Beccab said:

I see three options for the extra-vehicular activity:

1) Depressurizing the whole capsule during the EVA, like e.g. Gemini

2) if there is enough space, putting an airlock in the nosecone like e.g. the Inspiration 4 cupola

3) carrying an airlock in the trunk but attached to the second stage, so that the Dragon can rotate of 180 degrees once in orbit and dock, like e.g. the Apollo-Soyuz adapter; this way it doesn't impact the abort capabilities which are notoriously the reason the trunk on crewed flights is empty

I don't think there is enough space for an airlock in the nosecone, although I suppose they could try for an expandable one like Voskhod. That seems like a lot, though.

The flip-and-dock maneuver would be problematic because the only thrusters on Dragon 2 that don't have cosine losses are the ones in the nose, which would be blocked by a docked airlock.

My guess is that they go with a full de-press a la Gemini. Everything inside Dragon 2 is vacuum-hardened already. 

I'm particularly interested to see their EVA suit. I want them to solve the EVA issues in a cool and inventive way. Maybe an open hard shell that straps on over the existing IVA suits and prevents them from ballooning?

3 minutes ago, kerbiloid said:

They teach to look at photo and see what's actually assembled, instead of inventing how to pack circles.

Well then it is fortunate that I provided you the photo so  you can look and see how it is actually assembled.

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24 minutes ago, sevenperforce said:

Well then it is fortunate that I provided you the photo so  you can look and see how it is actually assembled.

Also they teach to look at the object from side, not in "exploded" by the photocamera focus view.

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37 minutes ago, sevenperforce said:

I don't think there is enough space for an airlock in the nosecone, although I suppose they could try for an expandable one like Voskhod. That seems like a lot, though.

The flip-and-dock maneuver would be problematic because the only thrusters on Dragon 2 that don't have cosine losses are the ones in the nose, which would be blocked by a docked airlock.

My guess is that they go with a full de-press a la Gemini. Everything inside Dragon 2 is vacuum-hardened already. 

 

 

 

 

 

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Will they be using the neutral buoyancy center for this? I wonder when they'll set up their own astronaut corps and training center. All these missions seem like a precursor to doing that, but they'll eventually need their own place to train their own astronauts.

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Busy news day. :confused:

Has anyone run the numbers to see how much extra delta-V might be left in the Falcon upper stage after typical orbit insertion? Getting up there is probably a simple case of relighting the S2 or just burning longer during launch to boost apogee to that higher point while keeping a low, possibly very low, perigee. Wouldn't be that long of a mission, after all. 

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15 minutes ago, CatastrophicFailure said:

Busy news day. :confused:

Has anyone run the numbers to see how much extra delta-V might be left in the Falcon upper stage after typical orbit insertion? Getting up there is probably a simple case of relighting the S2 or just burning longer during launch to boost apogee to that higher point while keeping a low, possibly very low, perigee. Wouldn't be that long of a mission, after all. 

It is different with every mission, but typically they burn the upper stage (nearly) to depletion in order to hand off any margin to the booster. For less massive payloads or lower-energy orbits, the vehicle will simply stage earlier in the ascent in order to give the booster more margin for recovery.

There are a number of things that the booster can do, depending on how much margin it has, to reduce overall stresses on the vehicle and make recovery easier. It can do a 1-3-1 landing burn or even a single-engine-only landing burn. It can do a longer entry burn that starts higher and continues for longer. It can do a partial boostback that lowers the distance that the droneship has to travel, or it can even do a full boostback and land on the pad where recovery is easiest.

Keeping this margin with the booster (rather than leaving extra dV in the upper stage) makes the most sense for two reasons. First, the upper stage is not recoverable. With the exception of stages that leave Earth's SOI (which are definitely not recoverable), the upper stage is going to be ditched into the ocean regardless, either by relight or a propulsive vent. The upper stage only has the single engine, so if something goes wrong with it, having extra margin on that stage isn't going to help. On the other hand, the first stage has nine engines; if there is a thrust shortfall or engine-out, the first stage can tap into that margin and burn longer to save the mission. Booster recovery is always the secondary mission; SpaceX would rather sacrifice a booster than not have a payload reach the intended orbit.

So the question we really want to ask is what Falcon 9's maximum performance is, with recovery, when it is carrying Dragon 2. 

 

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30 minutes ago, CatastrophicFailure said:

Right. Or perhaps, even... how much juice could be left in S2/Dragon stack if the did the nasty and expended the booster?

That would be sinful and wrong :( /j

That would give them more Delta-V for sure.

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Crew Dragon launches have had specified launch masses of 12.1-13 tonnes when launching to the ISS and a launch mass of 12.5 tonnes on the Inspiration4 launch to a 585 km circular orbit. In each of those cases, booster recovery was downrange on a droneship. We know that the largest payload SpaceX has launched to date was in each of the launches in the 550 km shell of Starlink satellites, with a 15.6-tonne payload mass, but we don't know exactly what orbit those are being released into (release altitude was 230 km in the one I saw but I don't know the apogee and perigee). More usefully, however, we know that Falcon 9 lifted a 14.5 tonne payload to a 435x425 km orbit at 53.2° inclination in the BlackSky rideshare Starlink mission on December 2, 2021.

In that particular mission, SECO-1 took place at 167 km and the stage coasted up to an apogee of 447 km. A few minutes later, it executed a small 71 m/s burn, probably with a slight radial component. Unfortunately, we can't simply take the altitude numbers at face value, because they are reporting altitude ASL and Earth is an oblate spheroid, not a sphere. The animation shows SECO-1 taking place at around 42 degrees north,  where the distance to the center of the Earth is approximately 6,368 km, for an estimated perigee of 6,535 km. The animation also shows apogee at approximately 51 degrees south, where the distance to the center of the Earth is approximately 6,366 km, for an estimated apogee of 6,813 km. Plugging all this into the vis-a-vis equation gives a perigee velocity of 7.89 km/s, 80 m/s greater than a circular orbit at 167 km altitude. MECO for the December 2 mission took place at a telemetry speed of 7,962 km/hr and altitude of 64.7 km. This is probably close to the peak of what the Falcon 9 first stage can do and still be recovered; the 15.6-tonne Starlink launch from November 13 had MECO at 7,864 km/hr and 66.6 km so that's about what you'd expect if they were both going all-out.

Applying simple arithmetic tells us that the Falcon 9 upper stage, then, has at least 80 + 71 = 151 m/s of dV margin when lofting a 14.5-tonne payload to a 167x167 km orbit. Estimating the Falcon 9 upper stage mass at 4.5 tonnes and the total usable propellant at 111.5 tonnes, the total dV in the upper stage with the 14.5 tonne mission is 6,576 m/s. A little more math tells us that if we replace the 14.5 tonne payload from the BlackSky mission with a 12.5-tonne Crew Dragon payload and assuming no appreciable difference at MECO, the total dV in the stage would be 6,903 m/s, giving it 327 m/s more. Accounting for the Hohmann transfer the BlackStar mission did from an effectively 167x167 km orbit, that means the Falcon 9 has 478 m/s of dV margin with Crew Dragon at a 167 km parking orbit.

This is when we pull the vis-a-vis equation out again, which tells us helpfully that adding 478 m/s to a 167 km parking orbit will raise your apogee distance to 8,423 km, or an altitude (taking the average Earth radius of 6,368 km) of 2,055 km, approximately 50% higher than the apogee of Gemini 11.

So Falcon 9 Block 5, with recovery, can easily take Crew Dragon much higher than Gemini 11. And that's not even accounting for all the dV onboard Crew Dragon. It could do a series of burns to raise its perigee, then raise its apogee even higher, then deorbit.

2 hours ago, CatastrophicFailure said:

Right. Or perhaps, even... how much juice could be left in S2/Dragon stack if the did the nasty and expended the booster?

With the booster expended, Falcon 9 can put 22.8 tonnes into LEO. With that large of a payload, the upper stage only develops 5,550 dV, meaning that expending the first stage provides roughly 1,353 m/s more than in a downrange recovery situation. If you add an extra 1,353 m/s to that same parking orbit as before, on top of the 478 m/s we were already accounting for, the apogee is 20,919 km, more than halfway to geostationary orbit and well past the Van Allen belts.

1 hour ago, StrandedonEarth said:

Too bad Falcon Heavy isn’t crew-rated… yet. 

Falcon Heavy could send a Crew Dragon nearly to GTO with three-core recovery and it could send Crew Dragon around the moon if the core was expended and the boosters were recovered downrange. 

Edited by sevenperforce
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3 hours ago, sevenperforce said:

So the question we really want to ask is what Falcon 9's maximum performance is, with recovery, when it is carrying Dragon 2. 

The initial mission is to ISS inclination (57°) for commonality with abort/recover operations—as Inspiration 4 was. So any work on what is possible needs to assume that inclination. Mission 2 I have to assume is polar. Isaacson expressed interest in that before Inspiration 4, and "polaris" has got to be a nod to that—and it would be another "first."

What would it take to crew rate FH?

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I want to revisit this whole,

15 hours ago, Beccab said:

with spacewalks (!) with a SpaceX-designed EVA suit

Do we think that Isaacman is basically fronting a bunch of money in a joint-venture with SX to design/build/sell these things?

Because, frankly, if they do put forth a working (and better) EVA suit than others have to date... they'll have a whole new market.  Except for the whole 'bespoke' part.  While SX's current suits are ridiculously bespoke, atm, it goes against the general design philosophy at SX (produce at scale to drive down costs).

Any further info on this?

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From the NASA spaceflight interview

  • entire crew will be exposed to vaccum for EVA
  • may use neutral bouancy facility, still in early stages of training
  • science payloads still being decided
  • one includes an implant into scott to measure cranial pressure before during and after flight
  • not doing an expendable launch 
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1 hour ago, JoeSchmuckatelli said:

Do we think that Isaacman is basically fronting a bunch of money in a joint-venture with SX to design/build/sell these things?

Because, frankly, if they do put forth a working (and better) EVA suit than others have to date... they'll have a whole new market.  Except for the whole 'bespoke' part.  While SX's current suits are ridiculously bespoke, atm, it goes against the general design philosophy at SX (produce at scale to drive down costs).

Any further info on this?

My suspicion is that while the current suits are bespoke, they’re not THAT bespoke. Like, you get someone’s measurements and then the computer tells you the sizes of the pieces to cut out and then it’s all standard from there.

I want to see them solve the ballooning problem in an inventive way. 

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