sevenperforce

There's absolutely an upside. Gravity is an incredibly harsh mistress. Gravity drag is the only thing that directly, linearly robs you of endpoint dV; if you have 100 m/s more gravity drag, then you stage at 100 m/s slower, and you reach final stage burnout (regardless of how many stages you have) at 100 m/s slower. Cutting gravity drag on the first stage provides a 1-to-1 boost to your final stage burnout velocity. Gravity drag comes in units of m/s just like any other source of dV and is the product of gravitational acceleration (g) and time. Every second the rocket spends in its boost phase is 9.81 m/s of dV lost. If a higher TWR means you can shave 1 second off your ascent, you stage at 9.81 m/s faster. If you can shave 5 seconds off your ascent, you stage at 49.05 seconds faster. During the first test flight, Falcon Heavy staged at T+373 seconds. If they can uprate the engines and increase TWR by just 2.5%, then they can stage at T+364 seconds instead, meaning they've shaved nine seconds off their ascent, which means around 92 m/s of dV gravity can't steal from them. The relationship between dV and mass fraction (all other things being equal) is logarithmic, so if the upper stage is trying to push a payload into GTO, starting with an extra 92 m/s is a significant advantage. They hope to recover this center core, but since they haven't recovered a center core to date, they are building a new one for the next flight out of an abundance of caution. If they recover this core they will probably break it down and inspect it heavily before flying again. It is essentially a brand new rocket.

The standard, baseline payload adapter tops out at around 10-11 tonnes but a custom payload adapter can be ordered that will allow much heavier payloads. We don't know the structural limits of the upper stage but the TEL can erect something that's 25-30 tonnes easily. I don't assume Bridenstine has perfect working knowledge of FH's capabilities but he said that putting Orion, the ESM, and the ICPS on top of the upper stage would actually work but that replumbing the pad for hydrogen and reengineering wind tunnel tests would pose the biggest challenges. I don't think the NASA engineers who studied the possibility would have considered it if they had concerns about the upper stage's structural limitations. If SpaceX had a reason to put a 60-tonne block of lead into LEO on FH, they would do it. At least one of the nose cones is reused.

Hey all -- the distributed launch article was moved behind Medium's paywall so I copied down the free link for sharing and for you guys... https://medium.com/@davidstarlingm/back-to-the-moon-61a47c60f78d?source=friends_link&sk=74918bf1b29cbd8606507be115f9d2ec I don't have Twitter...if anyone does, can you @ Elon the next time he is on a tweetstorm? Something like, "Hey, is it true that Dragon 2 and Falcon Heavy could push Orion to the moon? [link]" Not that Elon would do anything directly, but if he replies or discusses then there's a better likelihood of it getting up to NASA and Bridenstine.

That's Block 5 for you.

Thanks for the tip; I like that edit better. The docking port can take the load, for sure; we just aren't sure whether the Dragon V2 pressure vessel can take that much axial, compressive structural loading. I am more worried about whether D2 can effectively rendezvous and dock while still connected to FH's upper stage. Developing a brand new docking port with its own rendezvous capability (effectively making Falcon 9's upper stage an expendable space tug) would be tremendous but it would actually be a LOT of development work. Practically starting D2 dev over from scratch.

I wonder if the "mass sim" on EFT-1 was just structural and not actually the right weight. 28.8 tonnes to LEO means MECO-2 at 2.77 km/s short of LEO based on RL-10 isp and propellant load. With a 25.85-tonne payload, the DCSS can push 2.97 km/s, meaning only 200 m/s past LEO instead of ~1100 as I had anticipated. Let's run with those numbers. The FHUS will need to burn about 3 tonnes of props past LEO to get itself and D2 up to a matching orbit with Orion. Let's imagine, to add some margin, that D2 burns off half its props in the rendezvous and docking, saving us about 0.7 tonnes. This means the mated stack can get about 2.14 km/s more out of the FHUS, pushing a total of 2.341 km/s past LEO...safely above GTO and around 390 m/s short of TLI. Definitely within Orion's capabilities. DRO might be a stretch but NRHO would be easy enough. It was ridiculously muffled on the livestream.

"From the surface up to and including 1000 feet AGL"

Another thought... The whole concept was predicated on the fact that DIVH already put Orion into an elliptical orbit in EFT-1. I'm merely assuming it can repeat the same feat a second time. Orion's service module in EFT-1 was stated by NASA to be a dummy mass simulator, although I don't have confirmation that it was the same mass as the operational service module. It wouldn't make sense to call it a mass simulator if it didn't actually do the job of simulating the mass of the SM. That being said, if EFT-1's dummy SM was not actually on the order of 15 tonnes, then my math is screwed. However, the mission itself is not necessarily screwed. There are a lot of areas with margin. If D2 is lightened by the removal of internal systems (ECLSS etc) and burns off more of its props, and Orion can perform the final leg of the TLI, then it will still work. I also suspect that Falcon Heavy will have even more residuals after taking Dragon 2 to LEO. I used the stated expendable payload to GTO in estimating residuals in LEO, which introduces a fair bit of conservatism. If I am more aggressive, then we recognize that taking a 26.7-tonne payload to GTO (2.27 km/s past LEO) requires 29 tonnes of residuals on LEO. This means it burned 78.5 tonnes of prop to get that 26.7-tonne payload into LEO, which means it needed 2.86 km/s from MECO-2 to MVac startup. But if it was carrying only 10.9 tonnes of Dragon 2 from MECO-2 to LEO instead of 26.7 tonnes, then that 2.86 km/s would only cost 69.5 tonnes of props, leaving the Falcon upper stage plus Dragon 2 in LEO with 38 tonnes of residuals. Even if DIVH could not push Orion+SM past LEO at all (we know it can at least get it to LEO because Bridenstine said that math would work), those 38 tonnes of residuals would still be enough to push Dragon 2+Orion+SM 2.25 km/s past LEO, leaving about 480 m/s to Orion for completion of the TLI. Should leave Orion with enough dV to get in and out of DRO or at least NRHO.

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.

Does anyone know Scott's handle here on the forums?

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. 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. 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.

It never hurts! I think someone already tweeted it out once. Thank you! Exactly what I needed. Bridenstine got SO close but he didn't hit it.

On the topic of Orion in general: if anyone wants to forward this on to Bridenstine, send it to someone you know in the industry, or simply post on social media, I'd greatly appreciate it: https://medium.com/@davidstarlingm/back-to-the-moon-61a47c60f78d

Many of the newer ones should be back-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.

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

Final version: https://medium.com/@davidstarlingm/back-to-the-moon-61a47c60f78d Please share!

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

Just did a little mathing and the maximum gee-loading in the Constellation architecture would have been 1.08 gees at J-2X Earth Departure Stage burnout.

Never mind...

Are you sure? I thought Bridenstine said Pad 39A wasn't set up for hypergol loading. Can anyone with RO+RSS do a mockup and a couple of screenshots of Dragon 2, still attached to a Falcon 9 upper stage, mating with Orion and its service module in elliptic orbit?

Can anyone with RO+RSS do a mockup and a couple of screenshots of Dragon 2, still attached to a Falcon 9 upper stage, mating with Orion and its service module in elliptic orbit?

Finishing up this whitepaper...does anyone recall whether Dragon's prop load (D1 or D2) takes place before or after integration?

Correction: all Falcon 9 stages have black interstages; this is the natural color of the carbon composite they are made from. Before Block 5, the interstage was painted white, but this was found to be unnecessary and thus Block 5 flies without paint on the interstage. This is a brand new FH center core...either it began construction before the switch to unpainted interstages, or its higher entry interface meant that it was painted with ablative white paint.

The crew vehicle still needs to be accelerated to match the electric vehicle on its way to Mars, and that needs to happen with chemical propellants, but at least you only need to accelerate Orion rather than the entire stack. Remind me where I said the cancellation of ARM was an absolute disgrace.

I, for one, welcome our new golden-showering robot-spaceship-building overlords.......