sevenperforce

Took me a while to figure it out. Comma rolls left; period rolls right. Let's see here. Dragon 2 has four forward Dracos with a total thrust of 1.6 kN. You cannot fire a single SuperDraco but you can fire two pairwise, downthrottled to 20%. There are some cosine losses but there is also increased thrust because they are underexpanded in vacuum, so we'll pretend they cancel. Minimum SuperDraco thrust is therefore 28.4 kN. So you need to fire your forward Dracos for 17.8 seconds for every one second you fired your SuperDracos. Actually not as bad as I thought. I got it down to 3:26 with keyboard controls. Still in awe of you magnificent SOBs who can pull off anything under two minutes.

This was proposed very seriously as a subset of the Black Horse orbital concept. Black Horse was a horizontal takeoff/landing rocketspaceplane that would have loaded up with oxidizer from a tanker before continuing to orbit. One of the alternate possibilities was that two Black Horse spaceplanes would launch onto a suborbital trajectory and mate, then transfer props from one to the other, and then the second would continue to orbit while the first would go back. There's just not a lot of time for suborbital rendezvous.

sure

**slow clap** I see my first problem...you are using the keyboard; I was using my mouse.

Hot damn. I just got down to 3:58 and thought I was doing good. What is your failure rate tho?

I did it in 6:22 but I am still puzzled by @Ultimate Steve's time.

what the actual how on earth Are those minutes or seconds

I was going to say challenges but...

Yep, I was expecting to get a message that says "Congratulations! You've successfully docked. You used 44 lbs of maneuvering propellant. Automated docking takes between 11 and 18 lbs." In a proper fly-around you adjust pointing to a consistent view of the ISS. So my suggestion is that a fly-around takes either pitch or yaw through 360 degrees without losing view of the Harmony module. I went about 2/3 of the way around before I got bored so I know it is possible.

We should do races to see who can make it around the station AND dock successfully as fast as possible.

That's terrific. Does switching off gravity do anything?

Yeah, I got a successful docking on the first go as well. If you've played KSP it is pretty straightforward. I feel like it might be more difficult for the actual astronauts since they are likely to get induced pitch/yaw drift from translation. When I did it, all I had to do was cancel pointing drift once and it all stayed at 0.0 the whole time. Likewise.

Hmmm. Based on the above render, I would guess at the diameter of the inboard tanks at around 3.1 meters. 2.7 cm per pixel. Estimated internal volume of 41 cubic meters per tank. With methalox that would be 68 tonnes which is clearly nonsense.

Looks promising! It's fine to drop straight from high orbit to the pole without LLO circ.

How do you propose to make a nuclear reactor spin anything, or produce motion of any kind? The local air is useful reaction mass but is not going to generate any energy.

The vacuum isp here is a huge determiner due to the fixed mass fraction.

My guess is that it's like a radial decoupler attached to a docking port. So you dock the tanks using a reusable docking mechanism capable of high-pressure prop transfer, but when it is time to drop them, they are dropped using a sacrificial element. Once safely at NRHO (or perhaps even on the surface) you can carefully drop the discarded portion of the docking mechanism. I broke down and did the pixel count. Looks like the volume of the drop tanks is 238% the volume of the inboard tanks. My estimate had 7,768 kg of props on the inboard tanks and 10,290 kg of props on the outboard tanks, which is closer to 132%. Maybe the render is not very good.

Yeah, I had suggested something along these lines a few months ago. NASA's initial studies had proposed a notional three-stage lander with an ascent module at 9-12 metric tonnes, taking crew from the lunar surface to NRHO (2.6 km/s). If we assume Dynetics represents a bare-bones, minimum-mass "space taxi" design, then let's baseline that at 9 tonnes. I think Dynetics will use cryos, but let's suppose they used pressure-fed hypergolics, because that's what NASA was originally planning. The Apollo descent stage had a dry-mass-to-props ratio (legs and tanks) of 5.3:1; the Delta-K upper stage has a dry-mass-to-props ratio of 7.0:1. If we suppose the Apollo ascent module had ratios similar to a Delta-K upper stage, then that suggests the tankage and thrust structure of the Apollo ascent module massed around 336 kg with the engine and capsule massing 2011 kg. At 312 s isp, a notional 9-tonne vehicle would burn 5.15 tonnes of props to get from the lunar surface to NRHO. Borrowing the ratios from the Delta-K puts tankage and thrust structure at 736 kg, leaving engines and capsule massing 3114 kg. The engine of the Apollo ascent module massed 1.7% of its GLOW; if we use the same value (assuming TWR will be similar), then that puts the notional 9-tonne lander's engine at 157 kg and the capsule and payload at just 2957 kg, a mass growth of just 53% for having doubled the crew. Skinny. So let's use this value and plug in the numbers for the Dynetics launcher. To get from the lunar surface to NRHO is still 2.6 km/s but now we need an extra 500 m/s or so for final descent, approach, hover, and landing. It's okay if that seems a little high; I'll deal with it in a second. We also need to borrow values from the Apollo descent module because we are dragging along landing legs. Total propellant fraction needs to be 63.72%; props come to 7768 kg, which means inboard tanks and thrust structure of 1466 kg and a staging mass of 12.19 tonnes. At liftoff it's going to be 10.35 tonnes, which means matching Apollo will call for around 176 kg of engines, give or take. This cuts our total dV at staging to 3.025 km/s, leaving 425 m/s for descent, approach, hover, and landing, which will still work well enough. Now how do we get there? Well, we need to go from TLI to NRHO to LLO and then all but 425 m/s of the 1.87-km/s descent dV. It's 430 m/s from TLI to NRHO, 730 m/s from NRHO to LLO, and 1445 m/s from LLO to drop tank staging, for a total of 2.61 km/s. Propellant fraction will need to be 42.66%, but here we can use the better mass ratio of the Delta-K upper stage. We need 10.29 tonnes of props, 1942 kg of tankage, and a total TLI mass of 24.6 tonnes. The drop tanks themselves mass 12.236 tonnes. Note that this conveniently splits the total vehicle mass up into two almost exactly equal blocs, which is useful if you do a very very distributed launch. Total TLI mass of 24.6 tonnes actually brings this very close to the direct performance capabilities of a single expendable Falcon Heavy. It's definitely within range if you use a longer, cheaper NRHO transit, or if you switch over to cryos. Alternately, you can launch the capsule and inboard tanks to LEO on a single-stick Falcon 9 with droneship recovery, then launch the drop tanks on a Falcon Heavy with the center core expended, leaving more than enough props to perform the TLI. What's interesting is the cargo capabilities of this system. If we strip away the capsule, we get a drop-and-go potentially-reusable lander with a dry mass of 1.64 tonnes which can make some pretty interesting deliveries. It only needs 2.2 tonnes of props to return itself to NRHO after dropping off cargo on the lunar surface, which means it can deliver 6.1 tonnes if launched from TLI. If fueled up at NRHO, it can deliver a whopping 7.2 tonnes to the lunar surface. And of course if it needs to fly expendable it can send much more: 10 tonnes if launched from TLI; 11.2 tonnes if launched from NRHO. Imagine what NASA could do with an 11.2-tonne surface asset. Of course this pales in comparison to Starship, but so does everything.

Well, yes, I agree that's easier. @Ultimate Steve's point was that SLS is the only way to get to cislunar space without Earth Orbit Rendezvous.

Problem is powering the thing. This don't need fuel but it need power to run. The real challenge to this is the losses in ionizing the air in the first place. It's called a "low temperature plasma" because the electrons in the flow stream are at a different temperature than the rest of the fluid, but they still have a tremendous amount of energy. Air is not particularly happy about being ionized so it takes huge amounts of voltage to do it, and all the energy is wasted when the ions are fired out the back end. However, if there was a way to grab the ionized particles, they could be routed back around to the front end to offset the required voltage potential. That idea has...potential. You'd need a compressor fan at the front terminating in a high voltage drop to ionize the compressed air. You'd then use microwaves to heat it in a "combustion chamber" a la a conventional turbojet engine, and it would be expelled out the back end. You'd need to mix with compressor bypass to augment the thrust, then collect the ions in the rear of the thrust chamber while the accelerated un-ionized air roared out. An ionocraft works in a similar way: the ions themselves are not producing thrust, but rather they are bumping into ambient air to create ion wind and are then collected. But the force imparted to the ambient air is a function of the voltage drop, and it requires ridiculous amounts of voltage to ionize in the first place. This concept, on the other hand, would use microwaves to beef up the force imparted to the ambient air, so the voltage drop remains low (and can even be recycled). Nukes are not known for being helpful at creating low-temperature plasma. Or at creating electricity, unless you have a ton of coolant.

I do generally agree with you here, but I would note that if the cost of a single SLS launch was put into rapidly man-rating FH and testing D2's heat shield (perhaps with an aux propulsion unit in the trunk for LOI and return), you'd have Dragon 2 equipped to send people to NRHO in under a year. It's not as roomy as Orion but it's better than Apollo.

Ditto. One of the best.

I am one of the biggest opponents of SLS and one of the biggest reuse/newspace proponents out there, and I agree it will be awesome to see SLS fly.

I'm sure they would, but I think this is one of the things about the Dynetics lander that they said is a challenge. I am anticipating sacrificial elements if they do docked assembly. Basically, imagine mounting the docking port on top of a radial decoupler in the VAB, so the LOCV-critical bit is not the bit that is actually assembled on orbit. Doesn't matter if the docking connection is janky or gets stuck, because it is a one-way mate. I haven't re-run all the maths but I am pretty sure you can do this with full reuse on the first mission and an expended core on the second. So only one expended core and no elliptical staging orbit. Possible as long as the lander has storables. Definitely insufficient. Fully-expendable, Falcon Heavy can throw 26.7 tonnes to GTO (2.27 km/s past LEO). TLI is 3.2 km/s and NRHO is another 430 m/s. You can do some very low-dV three-body trajectories with multiple swingbys for 100 m/s but only if you use storables. It's just not possible. Wait, I misread what you said. Yes, yes, 100% yes. A naked FHUS can do this without sneezing. You only need 61 tonnes of props to get from LEO to NRHO with a 27-tonne payload, and FHe can deliver a nearly 65-tonne monolith to LEO, so it can definitely reach LEO with more than 65 tonnes of residuals. @tater will snap at me for saying it can deliver a monolith but he hasn't shown maths and I have. It probably could pull it off with side-core recovery. 311s is the isp of the underexpanded SL Merlin 1D burning in vac. The vac-optimized Merlin 1D pushes 348 seconds. If the lander has storables it is easier to give it extra dV and let it do a long transit. But yes, unless SLS is used, it will take SOME kind of orbital assembly. USSF-44 late this year will provide direct GEO insertion for a 4-tonne classified USAF payload, demonstrating operational endurance (they already did a delayed restart on the very first test flight). If they can do half a day they can do three days. Agreed. I think that we will not see elliptical staging orbits until Starship.