sevenperforce

Another issue is the propellant density. If you take an engine capable of running on multiple propellants (like an NTR or some variable-mixture tripropellant engines), increasing the density of the propellants while maintaining the same fuel flow increases thrust and decreases specific impulse. Hypergolic fuels are much higher-density than hydrocarbon fuels, and nitrogen tetraoxide is slightly higher-density than LOX, IIRC.

Okay, so....I do believe this qualifies. Flew for a total of about 15 minutes, but 13:05 is the highest value on the screenshot.

Yeah, upgrading the pad is definitely an improvement!

Yeah, I did a challenge almost identical to this a while back, but I believe I specified an 18-tonne pad limit. I'll see what I can do.

A dual-thrust-axis, atmospheric VTOL upper stage. It's a rather complicated problem, because you need to be balanced for ascent, but you also have to be aerodynamically balanced for entry, descent, and landing along an alternate axis. Getting center of mass and center of pressure correct is a big challenge.

A recent trade dispute (arising from an unfortunate misunderstanding wherein pinecones were mislabeled as pineapples and shipped to the Kerbalhouse Correspondents Dinner) has led to a ban on importing numerous products, including critical aerospace hardware. Among those items no longer available are parachutes, circular heat shields, and wheels. But the Kerbonauts still need to service the Space Station. To do so, they'll need to build an upper stage capable of re-entering and landing on its own. Jeb has decided he is tired of suicide burns, so he insists on a dual-thrust-axis lander. Your mission is to build a manned reusable integrated upper stage vehicle that can re-enter and land on auxiliary thrusters in a horizontal attitude (example here) at the KSC. The vehicle must reach orbit (presumably being launched by an initial stage of your own design), performing its own final circularization, then re-enter and land (on land) without losing any parts. All entries must be stock. Scoring is based on part count; the fewer parts you have in your vehicle, the better. EDIT: After a dizzyingly successful entry by @qzgy, it was pointed out by @MaxL_1023 that reaction wheels make this challenge all too easy. So, reworking the scoring table to make this more interesting. Scoring is based on payload into orbit and back down (pretend you're taking crew and/or cargo up to a space station and then returning). A kerbal counts as 0.1 tonnes; cargo mass counts as, well, cargo mass. You cannot count unburned fuel as cargo. Multipliers: No reaction wheels: x2 No reaction wheels or RCS (use only control surfaces and gimbaling): x3 Good luck!

Okay, that is what I assumed. So...whoever plays this mission for the longest wins? There needs to be a limit, like "you can only go to Minmus once" or "all the ore needs to come back in a single ship".

Dark, man. Very dark.

I did it Apollo Style...on my VERY FIRST FLIGHT! A little explanation: I've been playing the Demo for about a year, and I've flown some pretty cool missions, but I've never been able to do an Apollo-style LOR because the demo doesn't have docking ports. Anyway, I finally got the full game. So, I decided: why not replicate Apollo 11 on my very first flight in the full game? Ambitious, true, but I think I'm up to the challenge. Not too shabby for the very first flight in-game.

I did it Apollo Style...on my VERY FIRST FLIGHT! A little explanation: I've been playing the Demo for about a year, and I've flown some pretty cool missions, but I've never been able to do an Apollo-style LOR because the demo doesn't have docking ports. Anyway, I finally got the full game. So, I decided: why not replicate Apollo 11 on my very first flight in the full game? Ambitious, true, but I think I'm up to the challenge. With no further ado: Scoring: Single-stack ascent, LOR, manual piloting, BYOR: +30 3-man Mission +10 2-man Lander +10 2-stage Lander (leave the decent-engine on the Mun) +20 Launch escape system in place? +10 Lander stored behind the CM during ascent +20 Lander tucked away behind some kind of fairing? +5 Free return trajectory to the Mun +10 Flawless landing (no parts broke off, Neil Armstrong is watching you!) +10 After succesfull Mun landing dock CM and MM in munar orbit (no swapping ships without docking them first) +10 MM disposed by crashing it into the Mun (remove Kerbal first!) +5 Plant flag on the Mun (no cumulative, i.e. two flags don't get you 6 points) +3 TOTAL: Now, I really think I deserve a 100-point bonus for this literally being my very first flight in KSP, but that's not up to me!

I'm wondering -- do you have to bring the ore back to Kerbin for it to count? Your post never actually says that the ore needs to be recovered, only collected. Also, what limitations are there to prevent someone from just running the same mission over and over again to grind for ore, if multiple launches are possible?

The boosters have to essentially be SSTOs, though, which is problematic. With a smaller payload bay, an internal tank, and crossfeed, you could really get some good performance. Even better if you use methalox and make the wings wet.

I'm not sure if I am understanding you correctly or not, but one thing to note is that the dry mass must be excess; you can't say that a manned crew cabin or an occupied storage container is "dry mass". Now, if you are bringing an empty cabin or an empty storage container to represent your dry mass, that works just fine. A very good approach for getting your consumables there would be to add parts with liquid fuel storage. Liquid fuel can't be used by rocket engines, so it is a nice compact way to get that dry mass. If I was being a little more realistic I'd specify the need for some large-volume module to act as a transfer hab for astronaut space, but that would get messy. Once you've demonstrated reuse, you can carry the fuel you would need with crossfeed disabled.

Get the Kerbals there any way you want, but remember that you need to pack enough dry mass (in whatever form you'd like) for each leg of the trip, as I outlined above. Spaceplanes and inflatable heat shields are perfectly fine! But you can't land horizontally on Duna; that's a bit too unrealistic. So even if you use a spaceplane, it would need to land vertically, somehow. And you can't reuse inflatable heat shields, so that cuts into your score a bit. On reuse -- you don't have to actually reuse everything; you just need to demonstrate reuse. For example, if someone went the ITS route with a RTLS booster launching a persistent second stage, you'd only need to perform the RTLS once, though you'd need to reserve the same amount of propellant on all subsequent launches. That should save you some time.

If desired, we can do two leaderboards: one with RSS and one without. But this is more about mission configuration than getting everything perfect.

You're absolutely right, on all of your points. I'm not actually trying to solve for the minimum cost of getting to Mars; obviously it is easier to get to Duna in KSP than it is to get to Mars IRL. Of course, the engine TWRs and fuel tank fractions in KSP are a lot more punishing, but not enough to make up for it. But this challenge is more about finding a mission configuration and architecture that will permit the lowest overall cost, once things like consumables are factored in. Hope that makes sense.

When you mix physics and philosophy, both end up muddy. Causality in philosophy is a little different from causality in physics. Causality in physics is a physical constant, known more generally as the speed of light. Causality propagates at roughly 3e8 m/s. If space and time are inverted, as in a black hole or at the start of the universe, causality becomes undefined. Not absent, but actually undefined.

This is still kind of possible. Barely, but can be a viable choice if payload mass must be conserved at all costs. Barely, yes. There's not much mass saved, though, really. A lifting body only needs ~600 m/s of dV to land on Mars, whereas a ballistic capsule needs 1000 m/s or more. You can add chutes to drive this down a little, but that increases your dry mass. 600 m/s of dV is nothing compared to the 4.1 km/s your MAV will need to get back to Martian orbit, so there's no sense doing an Apollo-style EDL stage separate from the ascent stage. Plus, your ballistic heat shield needs to be much beefier than the TPS on a lifting body, so that's extra mass to deal with. The problem is something like Columbia; even if they had identified the foam strike while the orbiter was still on the mission, staging a rescue would have been almost impossible. The inclination couldn't be reached by the Soyuz, and even if they could have pushed Atlantis ahead to do a rescue, it would have required a dizzying set of EVAs. They didn't have nearly enough dV to abort to the ISS, either. The rescue mission approach is only possible if you had a large enough fleet of RLVs and androgynous docking ports, so a rescue mission could launch almost immediately, rendezvous, and dock for the crew transfer. Of course, that assumes the rescue vehicle has enough seats for all the crew onboard the crippled vehicle. I agree that in an abort before reaching orbit, the crew cabin is the only thing you need to save. The only reason I was thinking of having the stage be able to independently re-enter is so that you could swap out the same upper stage for payload launches and crewed launches, since the upper stage will be re-entering by itself after payload launches. Of course, if you want downmass capability, then you don't build a swappable upper stage at all; you build two different vehicles with the same-size tanks: a crew version and a cargo bay version. You'd want to use something like methalox and intertanks, like the ITS has.

One of the things Elon Musk said in his September 2016 speech about the ITS was that the cost of getting to Mars is essentially infinite right now. In his powerpoint, he put it at $10 billion per person. Now, the logistics of the ITS aside, I wonder how accurate this is. How much WOULD it cost to get humans on Mars? What are the different cost breakdowns of different approaches, and which mission configuration would be best? And, most importantly, what happens if we Kerbal it? The challenge is to send a few Kerbals to Duna, using only currently-available propulsion methods, with enough supplies to live on for the trip, as cheaply as possible. Rules: Propulsion. No nukes and no airbreathers. SABRE isn't up and running, and NTR isn't likely any time soon, so your propulsion needs to be chemical only. No ion engines; we need to assume you're running against some kind of a deadline. ISRU. Nope, sorry. We can't wait around on Duna forever. Payload. Send up to 12 Kerbals to the surface of Duna and bring them back to Kerbin. But they need consumables, right? Let's be very Spartan and say that they each need a total of 0.2 tonnes of food and other consumables for each leg of the trip. You can pack that extra payload any way you want; that's approximately two Science Jrs per Kerbal, and you can ditch up to half of them (they're empty, after all) before you enter Duna's SOI. Prop transfer. This is not only permitted, but encouraged. I highly recommend it. Reuse. Recovery of components is encouraged by a cost reduction as outlined below. Scoring. Your total score is the total mission cost divided by the number of Kerbals you actually land on Duna and return safely. Kerbals which stay in Duna orbit do not count, and dead Kerbals do not count. Any recovered components (reusable launch vehicles, etc.) are counted at 30% of their full cost. You do not have to include the cost of whatever you use for dry mass payload for consumables. The winner is whoever has the lowest score. Mods. No part mods and nothing that would affect scoring, but anything else is fine. I only have the Demo, or I'd make my attempt, but obviously this can be done. I'm mostly interested in seeing HOW it is done, what mission architectures are used, and so forth. Good luck!

For LEO, the main advantage is that a big fluffy re-entry vehicle is much safer and endures lower peak heating and lower gees than a smaller vehicle. That's true whether the crew vehicle is a capsule or a lifting body; the version which retains the stage will have an easier entry than the version which doesn't. For BLEO, you pretty much have to have your capsule and your stage connected for EDL, since you can't re-integrate for relaunch. So that's an absolute requirement. You can get around it for the moon, since there is no atmosphere to make entry sticky, but it's automatically necessary for Mars. I mean, you can do a capsule on top of an MAV on top of a heat shield, but...egads. If you're going to go the route of having the crew cabin detach from the upper stage, then you have to ask yourself whether the cabin is going to detach with or without ECLSS, the aeroshell, and so forth. If it detaches with ECLSS and aeroshell, then it is essentially a separate capsule that can serve as a lifeboat, and so you have to ask whether it makes sense to give it an independent emergency re-entry heat shield. And so forth.

Isn't that essentially the Apollo missions' configuration when going from Earth orbit to Lunar orbit? Rocket stage, lander, crew capsule? Not to say this isn't complicated. but it's not that complicated. Though, I tend to agree with the idea that combining the upper stage and the payload/crew module, a la ITS, is a better configuration. Not at all; they can dock together just fine, but they obviously can't re-enter together. That's the part I was highlighting. The only issue with combining the upper stage and the crew cabin a la ITS is that launch abort is really unpleasant.

For LEO operations, using an integrated second stage crew vehicle is a bit of a tossup. Flexibility is actually a little more limited, because you cannot use (or reuse) the same stage or stage configuration for crewed launches and payload launches. This isn't necessarily a dealbreaker, though; as long as the tanks and engines have the same dimensions for manufacturing purposes, the supply-chain production side of things can benefit from economies of scale. The immediate advantage of an integrated reusable second stage vehicle is that you have only one orbital EDL to worry about. Of course, the final advantage is disputable. Having a single vehicle to refurbish doesn't necessarily make everything easier, a point often missed by SSTO advocates. It may be cheaper to refurbish a capsule and an upper stage separately, as both are highly specialized. But it is definitely attractive to be able to use the large volume of the upper stage to help gently decelerate the crew capsule. For BLEO operations, on the other hand, having refuelable, reusable upper stage integrated with the crew vehicle seems like a no-brainer. You've got to take tanks and engines with you for the transfer burn anyway, and high-velocity re-entries really benefit from the extra volume of an upper stage. The ideal configuration, I suppose, would be an independently-recoverable upper stage and crew vehicle which can dock together and enter together. But that seems ridiculously complicated.

I'd wager that a majority of post-v.10 R&D was recovery-oriented, but not all of it. Even the fully-expendable Falcon 9 FT is a far, far more capable launch vehicle than v1.0 was. Remember that v1.0 couldn't even launch satellites; it had no clamshell fairing, no octaweb, nothing. Falcon 9 FT can send more to GTO than Falcon 9 v1.0 ever sent to LEO.

As an example: I get 23.2 tonnes to a 185x185, 28.5 degree LEO orbit, flying F9 expendable in its current incarnation. With eight engines (core engine removed), I get 22.7 tonnes. With seven engines (one pair of engines removed), I get 21.2 tonnes. With six engines (core and one pair removed), I get 20.5 tonnes. With five engines (two pairs removed), TWR has dropped low enough that propellant loading needs to be reduced. Reducing to 330 tonnes of fuel on the first stage so it can get off the pad, I get 18.0 tonnes. If an expendable Falcon 5 could still get more payload to orbit than Falcon 9 flying reusable, it doesn't make sense to build a second smaller "mini-Falcon-9" for expendable payloads. Just reserve the landing propellant and be done with it.

Remembering Falcon 5... If SpaceX wanted to do a cheaper expendable Falcon 9, the fastest way for them to do so would be to mount fewer engines on the octaweb. They can drop the center engine or any pair of outer engines without affecting balance. Then, simply fill the tanks a little less full than normal, and launch. Does this make sense? Absolutely not. But it would cost them less than building an entirely new shorter stage and still throwing away all nine Merlins.