sevenperforce

When it comes to yield-to-weight, bigger is better. Of course you get into absurdities fairly quickly. The flight crew that dropped Tsar Bomba was not entirely expected to survive. A 1000-megaton bomb would probably have a mass 5-7 times greater than the Tsar Bomba, around 160 tonnes. The explosion would be the equivalent of a direct impact from a rocky asteroid 260 meters in diameter at 17 km/s. The zone of total destruction would be 200 miles across. It's just not realistic. And I don't know of any good way to drop 160+ tonnes on someone.

Well several hours of play later, I have craft that is 99 tonnes in low Kerbin orbit, so...evidently I didn't go minimal after all.

I don't think I've ever done a complete crewed mission to and from Moho before, so this should be fun. Can we get some sort of point bonus based on minimizing the size of our craft?

Someone forgot to select the "rigid attachment" modifier.

Update: tested it at actual interplanetary entry speeds and it still works.

Here's what I threw together in KSP just as a proof of concept. The view inside the extended fairing (this is just to show the main component fit, before I added the internal skycrane and external parts): Fun with Dunian entry: The money shot: Skycrane in action: And the hab on the ground with the expandable modules deployed (sans one broken solar panel): Full "mission" in the spoiler.

Another option I think I like better: use one half of the fairing as the heat shield and the other half of the fairing as the backshell. Adding PICA-X to one of the fairing halves couldn’t be too difficult, and you keep the existing separation mechanism (although you would need to have a modified PAF that separates from the Falcon upper stage). The fairing halves already have cold gas thrusters for orientation after separation; they would just need to be mounted with nozzles pointing through the backshell half of the fairing for orientation control during re-entry. Weight distribution would easily make it passively stable with lift, and the yaw thrusters would merely control the lift vector. The backshell half would also need an external supersonic chute a la Perseverance, and it could include fixed solar panels as well for power during coast. No matter if they burn off during entry. The hab is oriented sideways in the fairing with the base oriented toward the heat shield side, so as it descends through re-entry it remains base-side-down. Once through the seven minutes of hell, the drogue on the backshell half pops. Once it fully inflates, the heatshield half is jettisoned, exposing the base of the hab. A skycrane is inside the backshell half, which separates from the hab before the skycrane lowers it to the surface. This allows a central hab core room that’s up to 4 meters high and 4 meters wide, connected to two modules that can each contain expandable modules, with room for a logistics module on one end and a rover on the other. Low to the ground, maximum footprint.

Ooh - I missed that. Somebody is being a special little snowflake - just in time for winter! That article is absurd. Sure, environmental racism is a real thing. The burden created by environmental and ecological waste/neglect often falls heaviest on low-income communities, particularly communities with many POC. But raising the spectre of environmental racism in an article about a white lady from Ohio who owns two vacation homes? Please.

Satellites are small and space is big. It’s not a significant issue. Most orbital skyhook designs utilize relatively low orbital paths with solar-electric propulsion modules at each end and at the center of mass.

It can be adapted to either, but the phasing issues will probably be solved more readily with a conjunction class mission, if the surface hab can support that long of a stay. If you want a larger surface hab, you can do orbital assembly with an inflatable heat shield and use either an expendable, naked Falcon Heavy or an EUS for TMI.

Completely unnecessary. Skyhooks are very, very long; long enough that you don’t need high gees for a good launch.

I don’t imagine you’d need more than 400 m/s for landing. Perseverance popped its chute at 420 m/s airspeed, and so a couple of drogues should do plenty to get the descent speed down to something manageable. Of course, you need to reserve RCS props for the descent. Having a single descent/ascent element has an abort mode advantage, because if you have a landing problem you can simply fire your ascent stage and return to orbit. But if you’re willing to accept a separate ascent and descent element, there are definitely some advantages. You can use solar power to crack LOX out of the Martian atmosphere and eliminate more than half of your landed mass. And perhaps even more interesting: you can make your descent element do double duty. Most Martian landing architectures call for a pressurized rover that can dock to your hab. If you’re going to have a pressurized rover, then why not land your crew IN the rover? The lander module docks with your orbiter and the crew crawls through to the rover. The landing progresses much like Curiosity or Perseverance, albeit with a much bigger rover. Then the crew simply drives the rover over to a docking with the hab.

Oh, interesting. That is a cool concept. What's the limit of a skycrane landing? If it landed vertically, then presumably you'd have some sort of doors so you could drive a pressurized rover right out and onto the regolith. If horizontal, then you would drive the rover out the back end. For my more conventional approach, I was thinking of a two-stage skycrane. Put the hab and inflatable side modules behind an inflatable heat shield, and put a pressurized rover on top. The skycrane lowers the whole affair down to the ground, then severs the connection between the rover and the hab and lowers THAT to the ground next to it, then flies away.

Yes, if you were launching a Harmony sized module and a Tranquility sized module at the same time, you could weld them together and put them on Falcon Heavy. The important question, though, is how we would go about stuffing a Martian surface hab into a 5-meter diameter.

With the fairing stretch that Falcon Heavy is getting, it could loft both Harmony and Tranquility stacked end to end at the same time. I'm more curious about how deployment would work.

Falcon Heavy is fairly limited by its 5-meter fairing. What kind of a Martian surface hab can you realistically fit in that kind of cross-section?

I suggest you spend some time reading about skyhooks.

Yeah, the Dragon would really only be doing a handful of actual things: Fly independently from the Falcon 9 launch vehicle to rendezvous with the transfer hab; dock (exactly what it does with the ISS right now) Assist the transfer hab in holding position while the EUS mates to it Stay attached to the transfer hab during coast After Martian orbital insertion, assist the transfer hab in holding position while the return propulsion unit mates to it Assist the transfer hab in holding position while the descent/ascent element docks to it Stay attached to the transfer hab during the Martian surface mission After the Martian surface mission, assist the transfer hab in holding position while the descent/ascent element docks to it Stay attached to the transfer hab during coast Undock shortly before Earth entry interface, adjust course, and re-enter. Only a single docking-undocking sequence. No free flight. Of course, that's for an eyeballs-out burn. For a more pleasant eyeballs-in burn, the Dragon would need to carry the EUS mating adapter in its trunk. But I don't know whether the docking port on the nose of the Dragon is up for pushing an 18-tonne payload through TMI. The Red Dragon proposal would have landed on Mars using SuperDracos and I don't think there was any particular concern about how long the hypergolics would last. I suppose they call them storables for a reason.

It can take 210 days docked to the ISS before the radiation environment starts to degrade the electronics, particularly the solar arrays. A beefed-up Crew Dragon for the Martian return would presumably also have beefed-up radiation protection and rad-hardened electronics. Costly but not a lot of mass growth.

Fortunately this question has already been answered: Full explanation here.

If the question is "how do we send stuff to Mars without Starship?" then that might actually be a viable use case for SLS...not as a launcher, but as a way of throwing heavy stuff to Mars. It doesn't have the cadence to support orbital assembly but it might be able to finish everything out at the end. The new RL-10C-3s for the EUS are supposed to get 460.1 seconds of specific impulse. This familiar image outlines some of the capabilities that the EUS is supposed to have in comparison to Block 1: And here is this (which seems like a good an estimate as any for EUS): Trans-lunar injection is 3.2 kilometers per second. If EUS on SLS Block 1B Cargo can push 42 tonnes (plus its own 13.13-tonne dry weight) to TLI, then it would need to leave LEO with an m0 of 112.1 tonnes. Given that it would mass 155.4 tonnes at staging, this means it stages just 1,474 m/s shy of LEO. Now, the SLS core would stage at a higher velocity if it wasn't pushing a 42-tonne payload on top of the EUS. The SLS has a dry mass of 85.3 tonnes and a prop mass of 987.5 tonnes, for a total wet mass of 1,072.8 tonnes. Add the EUS and a 42-tonne payload, and that's a launch mass of 1,228.2 tonnes and a burnout mass of 240.7 tonnes. With the 452 second vacuum specific impulse of the RS-25s, that's a total of 7,224 m/s. We can use this since gravity drag, aerodynamic drag, and pressure drag will be roughly the same. Yes, I'm ignoring the boosters; they don't make much of a difference in this scenario. If you take off the 42 tonnes, then your launch mass becomes 1,186.2 tonnes and your burnout mass becomes 198.7 tonnes, for a total of 7,920 m/s. So a naked EUS would stage around 696 m/s faster than an EUS carrying a 42-tonne TLI payload, meaning it would only need to burn 778 m/s to reach LEO. It would have some sort of docking/berthing adapter, of course, but let's not worry about that just yet. It would only need to burn 18 tonnes of propellant to reach LEO, leaving it with 82.3 tonnes of residuals. Now we turn to our Mars payload, assembled in LEO using some combination of commercial launch vehicles. How big could it be? Well, at 460.1 seconds of specific impulse, a stack needs to burn 65% of its total weight to get the 3.6 km/s of dV required for a Hohmann transfer to Mars. 82.3 tonnes divided by 65% gives you a total stack weight of 126.6 tonnes and a burnout mass of 44.3 tonnes. Once we subtract the dry mass of the EUS, that's about 31 tonnes injected to Mars. Assuming you have to brake in with storables, that should give you about 23 tonnes to a high, eccentric Martian orbit (a la the "podsadka" approach referenced upthread) or 15 tonnes to low Martian orbit, before subtracting the dry mass of the propulsion unit. What does that give us? Well, not much. For a best-case scenario with the eccentric Martian orbit, that's probably around 21 tonnes of useful payload. Architecture would need to look something like this: Pre-positioned hab, 16.8 tonnes launch mass. Launched direct to TMI by FHe, performs direct EDL at Mars. Descent/ascent vehicle, 31 tonnes launch mass. Launched to LEO by FH(ce), then sent to TMI by EUS, then burns its own engines to enter eccentric Martian orbit. Return propulsion module, 16 tonnes launch mass. Launched direct to TMI by FHe, uses about 5 tonnes of its propellant to enter eccentric Martian orbit. Transfer hab and Martian orbital propulsion module, 18 tonnes launch mass. Launched to LEO by FH. Beefed-up Crew Dragon, 13 tonnes launch mass. Launched to LEO by Falcon 9, docks with the transfer hab, and then the whole stack is sent to TMI by EUS. The transfer hab would be spartan -- only about 8 tonnes. The orbital propulsion module attached to the transfer hab would brake it and Crew Dragon into eccentric Martian orbit, where the vehicle would rendezvous with the waiting descent/ascent vehicle and the return propulsion module. Checkouts would ensure that both were fully operational; if the return propulsion module showed issues necessitating an abort, the descent/ascent vehicle would have ample dV to perform the TEI burn. Crew would enter the descent/ascent element, reach the surface and the hab, have their Martian stay, and then return to the waiting transfer hab, Crew Dragon, and return propulsion module. Then the return propulsion module would burn for TEI with Crew Dragon and the transfer hab. Required launches: 2X Falcon Heavy Expendable 1X Falcon Heavy (core expended) 1X Falcon Heavy 1X Falcon 9 2X SLS Block 1B The two SLS launches would be two years apart, which solves the cadence problem. I believe all these mass budgets are roughly in line with what @RCgothic proposed upthread. The difference is that I'm using Falcon Heavy's expendable configuration where necessary and I'm using an eccentric Martian orbit rather than a low Martian orbit. I can use eccentric Martian orbit because using EUS for TMI allows for a very large monolithic descent/ascent element with the necessary dV to make up for needing to go past LMO. I'm also splitting the propellant budget up so that the crew vehicle doesn't have to brake all its return propellant into Martian orbit when it arrives.

Block 1B is supposed to be able to throw 42 tonnes to TLI. What can it throw to Mars? And what is our best estimate of what kind of propellant residuals EUS would have if launched empty to LEO?

"Approximately" because it could be varied realtime by the ballast sled. I don't know what L/D ratio TKS had, but Apollo's was around 0.35, not 0.4, and the 7K-L1 Zond only need an L/D of 0.2 for skip entry reducing the gees from 10-15 down to 4-7 (although this was increased to 0.3 to give better landing accuracy). In any case, an L/D of 0.24 is enough for a skip entry, so it's fine.

Approximately 0.24. It has a 120-kg ballast sled that can be moved back and forth behind the heatshield to adjust the L/D ratio in realtime.

But this is NASA we're talking about, so they would want to use their precious Orion. Probably with the tanks largely drained. I will point out that SpaceX offers both a 1,575-mm PAF and a 2,624-mm PAF, and for the latter, the Falcon User's Guide explicitly provides for payloads up to 19 tonnes. The User's Guide also says that Falcon can accommodate heavier payloads on request. Plus, if I recall correctly, Bridenstine talked about Falcon Heavy being able to launch both ICPS and Orion in a single stack, which would come to about 52 tonnes to LEO. Of course that would be flying expendable. But I don't think there is any reason to think Falcon Heavy couldn't do a 21-tonne monolithic payload to LEO (which is about what we would expect it to be capable of given its 8 metric tonne payload to GTO). Or Falcon Heavy can send a 16.8-tonne hab module to Mars in a single launch, flying expendable. Now, a 16.8-tonne hab might not be enough. They might want to do orbital construction of something a little bigger. But even so, a naked Falcon Heavy (either expendable or partially expendable) would be able to dock with it and push it to TLI. You can do a lot with 68 tonnes of residuals. What physical characteristics of Crew Dragon are you are unfamiliar with?