sevenperforce

Less SLS, more general NASA, but... All of the Mars surface missions we've launched used direct entry from a hyperbolic trajectory. However, a sample mission would need to carry a heat shield for Earth return. How punishing is re-entry from low Martian orbit alone, rather than hyperbolic entry? Using the Earth-return heat shield to aerobrake the entire stack into LMO before separating the lander (leaving the Earth return props and heat shield in orbit for a Martian orbit rendezvous) could allow for a much smaller EDL heat shield and a very small (perhaps solid-fueled) MAV. Feasible?

I love this thread! To answer this (very excellent) question, we need to look at two factors: energy and practicality. I'll start with the latter. Except for a very small class of frozen orbits, most low lunar orbits pass over mass concentrations (leftover from the Late Heavy Bombardment) buried just below the regolith; these mascons will aggressively perturb any low orbits and eventually cause surface impact. For this reason, microsatellite orbits originating from the surface are impractical. It's also impractical because you have to take extra mass down to the lunar surface; if you are already going to be in orbit at some point, and so you're much better off pulling an Apollo and just dropping the satellites while still in orbit. Granted, such maneuvers are limited to the plane of your manned vehicle's orbit, but if you have an active enough manned lunar landing program that you can afford the mass budget for a shoulder-fired orbital launcher, you can probably afford to come in for a landing (from LOP-G or whatever) in the desired plane. Even setting aside those considerations, it is hard to imagine a situation in which the risks of firing a rocket in close proximity to an astronaut on EVA would be outweighed by benefits. Would be much better to go tripod. Now, to the question of energy. As @magnemoe pointed out, the Stinger pushes 750 m/s; it deploys a 3-kg warhead. The very different (but also man-portable and nearly shoulder-fireable) Javelin launches an 8.4-kg warhead at up to 600 m/s. The shoulder-fired PZR Grom, from Poland, has a 1.3-kg warhead that reaches 650 m/s and has a ridiculous range of 5.5 kilometers. It is similar to the Russian 9K333 Verba, which launches a 1.5-kg warhead at similar speeds. The fastest shoulder-launched short-range SAM in the world is the two-stage British Starstreak, which launches a 2.7-kg cluster warhead to around 1400 m/s. Firing on the moon would obviously improve performance. Gravity drag would not be any different due to the high TWR of all these missiles, but aerodynamic control surfaces could be discarded and there is no drag. It would not be implausible to imagine a man-portable, shoulder-fired two-stage missile launcher that would get a 1-2 kg payload into a nearly orbital trajectory which could then self-circularize with ease. You only need about 1.7 km/s to get into low lunar orbit.

Perhaps; perhaps not. One thing that SpaceX has proven, Elon Time be damned, is that they test as they fly. Once they have an architecture capable of performing the bare minimum they need, they fly it, and then they iterate. Once they have a heat shield that will do the job, they will fly with it, and they will make whatever modifications they need thereafter.

They crop up periodically. Usually they need to have some kind of restrictions or they quickly become nonsensical. There is no limit if you are allowed to reach maximum speed outside of Kerbin's atmosphere. If it has to be done inside Kerbin's atmosphere then it gets interesting. If you restrict to airbreathing engines then you top out at 2100 m/s.

Then I'm sure you'll be at the top of the leaderboard As long as there is an actual leaderboard (based on weight or cost or part count or SOMETHING) then I will compete with @Ultimate Steve for that coveted spot.

You will find no bigger fan of manned missions than me, but sample return from Mars is absolutely science-worthy.

Well, the Romans obviously named Jupiter Jupiter and the name was traded through the Middle Ages. But it has different Names in different cultures. In modern times it was chosen to name planets after Roman deities, so Jupiter just kept its designation. One could as well have chosen Arabic names, as in high Middle Ages their astronomy was more advanced. But now it is as it is, and i too think that by coincidence the boss of the Roman pantheon became the boss of planets :-) Originally, Venus was not regarded as a planet, but as a star. This is because it orbits nearer the sun than we do. Mars, Jupiter, and Saturn all orbit farther from Earth, meaning that their positions across the sky are readily predictable using reasonably predictable epicycles, deferents, and so forth. We can observe Jupiter at many times of the year. In contrast, planets nearer the sun like Mercury and Venus are only visible close to sunset or sunrise, so it is more challenging to track their movements and recognize that they are, indeed, planets. In fact, Venus was originally imagined to be two different stars (the morning star and evening star) which appeared near to the sun. Jupiter was the brightest of the three distant planets known to the ancients and so it was regarded as the greatest of all.

Great question! Zeppelins were gigantic warships of the air, with lifting gas being stored in numerous separated cells. Even if you puncture one cell, the others remain full, and with a fabric exterior a bullet only leaves a tiny hole. The hydrogen inside was not under pressure, so there was nothing to make it "vent" or otherwise leak out...it could take days before a bullet puncture hole would leak out enough hydrogen to cause significant lifting problems. They were also effective because they could fly much higher than the planes of their time, meaning that fighter pilots were extremely exposed to the zeppelin's massive firepower. Incendiary rounds, which we know as the tracers that show up during machine gun fire in wars, were first invented as a way of igniting the hydrogen gas in zeppelins and thus taking them down with fewer bullets.

Cruel, but I like it! Put a scoring element in (lowest part count, lowest Eve liftoff mass, etc) and I'll do it.

Would be better to edit the rule to say "enough fuel for 120 seconds of additional flight time".

Right. It just becomes a question of making bigger and bigger LVs.

My concern is that this will end up being a competition over who has the biggest computer. Adding classes would not constrain imagination (you can have a "no limits" class) but it would give a new chance to compete.

@M_Rat13 A proposal..... In order to encourage low-part-count and low-mass solutions, why not have multiple classes? So it's still a race, but you have a "10 tonne or lower" class, a "50 tonne or lower" class, etc.

A promising architecture for a fully-reusable SL Eve TSTO would be to do parallel staging, like Energia+Polyus but with a Shuttle-C engine arrangement on the side-slung stage. That also fixes the difficulty with vertical integration, because the vehicles can be mated while erect, then fueled. The mated stack would launch from SL into a suborbital trajectory with crossfeed all the way up, then the upper stage would circularize before the lower stage performed the flyback and landing. You'd want support vehicles on the surface, but the whole thing would be fully reusable.

I worked on this for a good while. It's doable.

The complexity and challenges of large-scale orbital propellant transfer dictate a future mission architecture. We KSP players think nothing of refueling, but reality is not so easy. If ACES proves to be successful and we can readily toss props around on orbit, then we could see it form an integral part of the reusable lunar architecture, with a dedicated man-rated lander operating from something like the Gateway (or at least a DRO or frozen LLO), refueled at each mission by a reusable command module sent onto TLI by Starship. If orbital refueling proves to be more of a challenge, then we are more likely to see a single vehicle making the entire round-trip with direct ascent from the lunar surface and back to Earth. Paradoxically, the very thing which enables Starship's BLEO aspirations--orbital refueling--is the thing that would make it not nearly as useful BLEO.

With 150 tonnes to LEO, there are any number of fully-reusable lunar landers that could be proposed. Starship could also send a smaller lander direct to TLI in a single launch and then aerobrake itself back. Not sure which would be more efficient. Then with the Chomper you could bring the lander back and enter together, if desired.

Elon's transpiration cooling approach had me a little worried about margins for success, but with a metallic TPS as sacrificial fallback then it's much more viable. Even without actually landing Starship on the Moon, the ability to send 150 tonnes to LEO for unbelievably cheap enables virtually any lunar landing architecture anyone would want.

SSTO from Eve sea level is the next big stunt, I suppose. I have some ideas. A resorbable stock prop could do it, potentially. @Kergarin, have you ever had any success with a stock prop that can be detached and reattached indefinitely? Doing it with a Klaw is such a Kludge.... If you can land on Eve and refuel with ISRU, then you can land at SL, refuel, and fly to a higher takeoff point before repeating the process. That's straightforward enough. But actually doing it from SL without any further refueling is the real challenge.

Done, for the very first time, here: Whistance is a beast.

SpaceX beats BO by a year or two. I fanboy a bit over SpaceX sometimes, but on this point it is clear. Mars is aspirational; Luna is firmly within reach.

@Kergarin has pulled this off a couple of times. It's the holy grail of KSP. It can be done but not easily.

What if I go to Minmus with SRBs under 5 tonnes and under 10 parts? Kidding, kidding...THAT would be impossible. But going with SRBs only is easy.

Lander can sucks on Kerbin but it is perfect for Duna provided you launch at high altitude.

The chute's impact resistance is 12 m/s and a chute slows a 1.5-tonne stack to around 16 m/s at 3000-4000 m. My plan is to cut the chute just before impact and use the reaction wheels to flip chute-down and lithobrake it. My lander engines are arranged radially so they can burn around the rest of the stack. The Dawn can fire through the drop tank. Yeah, that would make no sense.