Skylon

SpaceX Discussion Thread

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13 minutes ago, sevenperforce said:

Hey all...

Just finished my draft whitepaper/open letter to NASA Administrator Bridenstine. I think it's decent. Sharing a draft link here before I publish.

https://medium.com/@davidstarlingm/back-to-the-moon-61a47c60f78d

I don’t think KSP is the best choice for a visualization...

Sounds interesting. I don’t think he’ll read it, but it’s an interesting idea.

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I think before you submit it, you should use more accurate representations of Dragon V2 and Orion @sevenperforce :) 

You can get high quality, higher accuracy Dragon V2 and Orion parts with the Tundra Exploration mod by @damonvv and ReDirect by @benjee10!

https://forum.kerbalspaceprogram.com/index.php?/topic/166915-16x-tundra-exploration-v1305-march-6th-spacex-falcon-9-dragon-v2-and-starship/ and https://forum.kerbalspaceprogram.com/index.php?/topic/172187-16-redirect-stockalike-orion-sls-shuttle-derived-launchers-craft-files-v096/

I look forward to the final version :)! 

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20 minutes ago, Bill Phil said:

I don’t think KSP is the best choice for a visualization...

I've seen actual NASA coverage and meeting slides that have used KSP images (not sourced as such).

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Posted (edited)

and there was the ARM Collab between Squad and NASA a few years back.

 

Edited by Barzon Kerman

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35 minutes ago, Bill Phil said:

I don’t think KSP is the best choice for a visualization...

Sounds interesting. I don’t think he’ll read it, but it’s an interesting idea.

ESA did something with modded ksp mun missions a while back, you could easily tell it was in the kerbin system

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I don't mean to make this into a chore, but using RSS and visual enhancements might also be better. I did this for a class project a few weeks ago. I couldn't get Tundra working in 1.2, though, and I don't know if RSSVE is working for the most recent version.

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43 minutes ago, Bill Phil said:

I don’t think KSP is the best choice for a visualization...

 

Use Orbiter 2010?

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6 minutes ago, sevenperforce said:

If anyone is able to make more impressive screenshots then I will replace and credit them.

Do you know any 1.2 compatible Orion and Dragon 2 mods? If so, I can make them.

6 minutes ago, sevenperforce said:

If anyone is able to make more impressive screenshots then I will replace and credit them.

Also, are Orion and Dragon 2's docking ports compatible?

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4 minutes ago, Ultimate Steve said:

Do you know any 1.2 compatible Orion and Dragon 2 mods? If so, I can make them.

Many of the newer ones should be back-compatible.

4 minutes ago, Ultimate Steve said:

Also, are Orion and Dragon 2's docking ports compatible?

Yes, they are.

I'd love it if people could share the open letter on social media and send it to NASA with commentary. Can't guarantee it will get traction but you never know.

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20 minutes ago, sevenperforce said:
33 minutes ago, Ultimate Steve said:

 

Many of the newer ones should be back-compatible.

I tried Tundra, and at least the BFR portion didn't work. I'll see if I can get Dragon working. Any idea which Orion or Dragon mod would be best? Orion in particular, I've never looked at Orion mods before.

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SSTU has a great Orion, but it's 3.75m. You can always rescale it to more accurately match the Dragon mods.

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37 minutes ago, sevenperforce said:

I'd love it if people could share the open letter on social media and send it to NASA with commentary. Can't guarantee it will get traction but you never know.

I could throw it up on Twitter, but I’m a nobody,  can’t even guess if the right people would see it. 

Couple of suggestions: 

At the beginning, replace “temporarily replace SLS” with augment, supplement, complement, something along those lines. Sounds less, I dunno, confrontational, and we all know certain Congresscritters will be automatically hostile to anything that implies replacing SLS at all. 

Also, you said:  “...and no new mold miles.” Is miles the correct word there or did it autocorrect from lines?

Very impressive proposal you’ve got there. Part of me says, “it’s NASA! They’ve probably thought of that already. They’ve got a room of guys somewhere just thinking crap up and another room of guys backing them up...”  but another part reminds that part that when the semi got stuck under the bridge and the professionals couldn’t figure out how to remove it, it was a passerby who suggested just letting the air out of the tires... :D

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Just now, CatastrophicFailure said:

I could throw it up on Twitter, but I’m a nobody,  can’t even guess if the right people would see it. 

It never hurts! I think someone already tweeted it out once. 

Just now, CatastrophicFailure said:

Couple of suggestions: 

At the beginning, replace “temporarily replace SLS” with augment, supplement, complement, something along those lines. Sounds less, I dunno, confrontational, and we all know certain Congresscritters will be automatically hostile to anything that implies replacing SLS at all. 

Also, you said:  “...and no new mold miles.” Is miles the correct word there or did it autocorrect from lines?

Thank you! Exactly what I needed.

Just now, CatastrophicFailure said:

Very impressive proposal you’ve got there. Part of me says, “it’s NASA! They’ve probably thought of that already. They’ve got a room of guys somewhere just thinking crap up and another room of guys backing them up...”  but another part reminds that part that when the semi got stuck under the bridge and the professionals couldn’t figure out how to remove it, it was a passerby who suggested just letting the air out of the tires... :D

Bridenstine got SO close but he didn't hit it.

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Yeah, distributes launch discussed, but only one LV was odd.

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@sevenperforce I think I may have found a hole in your plan. We know (barring a redesign of Orion which may very well have happened) that Orion can withstand the g forces of acceleration. However, we don't know if Dragon 2 can. At 0.9g acceleration, docking to Orion and pushing it around would be akin to putting a 25 ton weight on top of Dragon in Earth gravity, more than twice Dragon's mass. I don't think it's designed to handle those forces.

Also, I don't know how deep the SuperDracos can throttle, but IIRC you said Orion needed another push even after the stage two burn. Maybe the Abort system on Dragon 2 has enough fuel for that, if operated at a very low throttle, perhaps with only 2 SuperDraco engines. Actually, at that point you may be better off just using the Dracos, they are more efficient but I'm not sure if they are pointing the right direction, so accounting for cosine losses the SuperDracos may be better...

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1 hour ago, sevenperforce said:

Bridenstine got SO close but he didn't hit it.

Which makes the cynic in me wonder if maybe someone did think of it, and it promptly got buried cuz it just might work.... <_<

@Ultimate Steve brings up a good point too. :P

HowEVer, just pulling this out of my, er, thin air, IIRC somewhere it was considered using Dragon 2 to reboost the Space Station. Dunno how the load compares, or if I’m just imagining it altogether...

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Max g on Crew Dragon ascent is above 3g, right? Admittedly, not on the docking port.

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9 hours ago, tater said:

Yeah, distributes launch discussed, but only one LV was odd.

It may be inertia. Delta IV Heavy is the vehicle with the high-energy hydrolox upper stage; if you're trying to send payload BLEO, you want hydrolox at the very end. It would be much better, from a pure rocket science perspective, to send Orion up to LEO on Falcon Heavy (recovering the side boosters and expending the core) and then have Orion mate to a naked DCSS from DIVH for the TLI burn. But of course this is problematic because you have to mate Orion to FH (which is not easy, as he pointed out) and you have to teach Orion to perform autonomous docking (again, a big undertaking). But swapping the vehicles, as wasteful as it may be from the rocket science angle, is what would allow this to work.

9 hours ago, Ultimate Steve said:

@sevenperforce I think I may have found a hole in your plan. We know (barring a redesign of Orion which may very well have happened) that Orion can withstand the g forces of acceleration. However, we don't know if Dragon 2 can. At 0.9g acceleration, docking to Orion and pushing it around would be akin to putting a 25 ton weight on top of Dragon in Earth gravity, more than twice Dragon's mass. I don't think it's designed to handle those forces.

Very good point! I admit that I hadn't considered this specific issue, so I appreciate you seeing it. That's the main reason why I wanted to discuss it on this forum -- everyone here is pretty savvy and you guys pick up on stuff like this.

It's not a straightforward question, since SpaceX has not (to my knowledge) published any structural load limit results on the Cargo Dragon or Dragon 2 pressure vessel. My baseline, heuristic assumption is that it won't be a problem. In the Constellation architecture, Orion would have mated to the top of the Ares V Earth Departure Stage using a docking port on the Altair lander, and the lander body would have transferred all acceleration loading through its structure into Orion during the TLI burn (which, as I point out in the letter, reached 1.08 gees at burnout). On a purely heuristic basis, I would be very surprised if the Altair ascent stage had greater structural integrity than Dragon 2, given that the latter has to handle the stresses of Max-Q, re-entry, chuted deceleration, and splashdown. 

Of course, I want to limit my references to an architecture that was ultimately canceled. There are, however, a few other points where we can try to assess how Dragon 2 copes with structural loading.

  • In an abort, Dragon 2 ends up with six gees of sustained acceleration at the SuperDraco mounting points. This doesn't represent loading on the entire vehicle but the load is still axial; the internal structure loading is therefore on the order of at least 65 tonnes (more at burnout, as props have been expended).
  • In a nominal re-entry, Dragon 2 has a pretty gentle time of things...but in a contingency situation where it undergoes a ballistic entry instead of a lifting entry, forces can shoot up to seven gees. This is without the trunk, of course, but that's still 60-70 tonnes of compressive, axial force. It's distributed through the heat shield rather than through the upper portion of the pressure vessel but it still gives us a ballpark of the kind of forces it can handle.
  • Dragon 1 could carry up to 6 tonnes of externally-manifested cargo. This cargo is "hung" inside the top of the trunk, but the loading on the trunk is still compressive. At MVac burnout, even with minimum throttle, gee-loading for a Dragon 1 (4.2 tonnes dry, 1.3 tonnes props) reaches 2.4 gees, which comes to 27 tonnes of compressive force on the trunk. The D1 trunk is not the D2 trunk but I imagine they are comparable.
  • Loading can be estimated to some degree based on staged chute deceleration. SpaceX stated that with three chutes, astronauts would experience up to 3 gees on main chute opening. Dragon 2 with half its props masses around ten tonnes, which means the load on the chutes (transferred off-axially to the pressure vessel) is 30 tonnes. This is tensile, not compressive, but still germaine.

So, all in all, I'm not terribly worried.

9 hours ago, Ultimate Steve said:

Also, I don't know how deep the SuperDracos can throttle, but IIRC you said Orion needed another push even after the stage two burn. Maybe the Abort system on Dragon 2 has enough fuel for that, if operated at a very low throttle, perhaps with only 2 SuperDraco engines. Actually, at that point you may be better off just using the Dracos, they are more efficient but I'm not sure if they are pointing the right direction, so accounting for cosine losses the SuperDracos may be better...

The FHUS can push Dragon 2 and Orion onto TLI with an 80 m/s margin, so there's no need for a further burn after S2 jettison. You'd merely need course correction burns, because realistically you'd put S2 onto a disposal orbit (either lunar impact or heliocentric ejection). Orion and Dragon 2 can perform their own course correction burns independently, since we're talking about a dozen m/s at most. Orion would want to orient for a capture burn into DRO; Dragon for a free-return. 

You would never want to use the SuperDracos for anything outside of the atmosphere.

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6 minutes ago, sevenperforce said:

The FHUS can push Dragon 2 and Orion onto TLI with an 80 m/s margin, so there's no need for a further burn after S2 jettison. You'd merely need course correction burns, because realistically you'd put S2 onto a disposal orbit (either lunar impact or heliocentric ejection). Orion and Dragon 2 can perform their own course correction burns independently, since we're talking about a dozen m/s at most. Orion would want to orient for a capture burn into DRO; Dragon for a free-return. 

You would never want to use the SuperDracos for anything outside of the atmosphere.

Oh, I read that wrong the first time and thought you came up 80m/s short and not 80m/s extra.

However, given boiloff, S2 will lose Delta-V over time, so unless the rendezvous is lightning fast, the 80m/s margin will evaporate quickly. In that case, would some sort of Dragon based burn be beneficial? Also, what would be bad about using SuperDracos for this? Acceleration would be manageable. 2 of them, even assuming they are mounted on axis, produce 142kN of thrust, and they can be throttled to 20%, so 28.4kN, giving a minimum acceleration of <0.1g, if I did my math right.

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Just now, Ultimate Steve said:

However, given boiloff, S2 will lose Delta-V over time, so unless the rendezvous is lightning fast, the 80m/s margin will evaporate quickly. In that case, would some sort of Dragon based burn be beneficial? Also, what would be bad about using SuperDracos for this? Acceleration would be manageable. 2 of them, even assuming they are mounted on axis, produce 142kN of thrust, and they can be throttled to 20%, so 28.4kN, giving a minimum acceleration of <0.1g, if I did my math right.

Yes, there will be some boiloff, though not a lot. D2 is intended to perform 6-hour rendezvous and docking with the ISS, and Orion would be responsible for performing adjustments to reach rendezvous.

Three reasons to eschew SuperDracos: first, cosine losses; second, underexpanded and low isp; third, Dragon 2 is not programmed to push external payloads like Falcon's upper stage is. If there is a remaining dV deficit, Orion can handle it on its own.

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