Temstar

It is a good reason, unfortunately science has never been conducted that way. When HMS Beagle took off it was to do a hydrographic survey for the navy and Darwin basically hitched a ride. Similarly we went to the moon mainly to score political points and the science was an after thought. It's a bit unfortunate if you're the type that feel we should do science for its own sake. But I like to see it as an opportunity to continue to look for economic or political reason to go to Mars. If you can find such a reason then science will naturally follow in its wake.

No, fuel tanks are kept at constant pressure by pumping in inert glasses like helium as the tanks are emptied. The CoM change is only because liquid (which is heavy) are being removed from the bottom of the tank and replaced by gas which is much less dense.

The contract does actually tell you the object's length, width, height and mass.

It's this bit that doesn't sit well with me. Usually my criteria for design rocket is that I have to assume payload is a dumb lump of lead without any capability at all, which means I build the guidance package on the upper stage. It's probably overly restrictively as in practice I've never launched completely dead weight payload into orbit. The closest is propellant depots which don't have engine but have plenty of reaction wheel which then helps the rocket steer. Putting guidance into the payload, particularly reaction wheel and engines that complete the final orbit insertion starts to get into the grey area of "what's an upper stage and what's a payload" like Saturn V's upper stage. It also strongly couples payload to rockets in the manner of "this rocket can put your payload into orbit, assuming your payload can supply 500m/s of delta-V and 30 unit of torque in all three axis". But if you insist it's certainly doable as a challenge. In fact I have a rocket in mind already, I'll just get rid of the decoupler to merge the upper stage with the usual payload:

In real life fuel drains from the top down as well, assuming we're talking multi-stage rocket. This change would mess with asparagus staging and other such designs that rely on fuel flow logic.

New aero does mess with things a bit. Recently I had to put a manned rover with science lab on the Mun for a contract, not as big as MOLAB but still big enough that you couldn't really put it in a fairing. So if you look at the way the stages are arranged, the first two stages put the rover into orbit. I then hang onto the 2nd stage and dock the rover to my propellent depot to refuel that upper stage, putting 1381 m/s back in its tank. I then fired up the 2nd stage again to get the rover to Mun orbit, do the deorbit burn and get it close to the surface. Then the 2nd stage runs out of fuel and it gets cut loose to crash onto the mun while I switch the rover to belly landing mode (there's a probe core under the rover's belly), do a 90 degree flip in the air and fire up the integrated landing engines to soft land on the Mun.

Yeah it's a giant rover from KSP 0.19 days by yours truly: http://forum.kerbalspaceprogram.com/index.php?/topic/22798-0191-molab-heavy-manned-munar-rover/ That's around the time when rover wheels were first added so we were all experimenting with it. I recall someone wrote an excellent guide back then on the different landing methods available to put a rover down, let me try to find it. Edit: found it: http://forum.kerbalspaceprogram.com/index.php?/topic/26721-landing-rovers/&do=findComment&comment=351980

We can probably do better than that since marine reactors are designed to be compact with not much emphasis on weight. Space reactor need to be lightweight first and foremost. One easy way to get this is to use a shadow shield instead of shielding all the way around as with a marine reactor.

Craft file link now updated to KerbalX, the version in KerbalX has been slightly refined compared to the original version in the OP. It's slightly cheaper, and uses about 10% less part count.

For rovers on that kind of scale it's best if it lands using an integrated landing stage, that is the landing equipment is built into the rover. It only needs enough delta-V to land, it doesn't have to do the deorbit burn or anything, that can be handled by a rocket stage: Notice the wreckages of the orbital stage, jettisoned not long before switching to integrated landing engines shortly before touch down.

I think so. You can always angle the sail by angling the whole ship so that the laser bounces off with some angle and you can get thrust in any direction up to 180 degree off axis from the laser source. Basically much like the sail on a tall ship. I'm not 100% certain but I think there are ways to actually sail light sail against the motion of the incoming photon, but I think that requires several mirrors and a few bounces.

Are you two aware that you're replying to a thread from 2 years ago? Anyway you might have noticed that people's response from back in those early days are clustered around 1.7g to 2.0g for lift off. One of the big reason for this is cost was not a factor. Back then there was no career mode and all parts prices were only place holder and for academic interest only, Reliant (or rather LV-T30, as it didn't have its nickname then) and Mainsail had the same cost. So the only thing that mattered and people could use to compare rocket performance was payload fraction. If you ask about TWR at lift off nowadays you'll probably find people suggest somewhere between 1.3g-1.5g. The lower acceleration reduces aerodynamic forces so is easier on rockets with dodgy centre of pressure. But more importantly career mode is now a thing and parts prices actually matter. As with real rockets engines are expensive while fuel and fuel tanks are relatively cheap. So nowadays for career mode rockets cost per ton to orbit is much more important than payload fraction. And since engines are expensive you want to hang onto them for longer and get more bang out of the bucks you paid for them. Increase the fuel load for the first stage is a simple way to achieve this. By adding fuel to the first stage you decrease cost per ton to orbit (because your first stage is now doing more work for the same amount of engine) as well as payload fraction (because your rocket now suffers more gravity loss from low TWR first stage). For transfer stages I like to keep the TWR above 0.3g, for landing I prefer 1.5g-2.0g of local gravity.

I wish youtube would implement this functionality:

Dual-mode nuclear engine is a good idea, problem is it makes certain really challenging aspect of KSP (eg: Eve ascent) really easy. It needs some kind of drawback.

Patched Conics. Yes laugh all you want at the lack of Lagrange points and fuzzy orbits but patched conics vastly changed the game when it was introduced. Before that you played the whole game with basically Tier 1 tracking station. Every trip to the Mun or Minmus was a shot in the dark and every orbital rendezvous involved looking up tables, eyeballing AN/DN and using circular orbit.

You get the flyby if you have focus of the ship at the moment it enters or leaves the SOI of the thing it's meant to flyby. Yes logically entering into orbit means you must have been on a flyby trajectory at some stage, sadly the game doesn't care, it only accepts the above two very specific moments as having satisfied flyby.

There might be ways around this. The ISV Venture Star from Avatar for example only carries anti-matter for two burns and hydrogen for one burn for a round trip. On the outward burn from earth it acts as a light ship with its photon sail extended and vast lasers from Earth propel the ship. Since there are no laser stations on Pandora it has to fire its anti-matter catalysed fusion engine to enter orbit, using up half of its anti-matter and all of its hydrogen propellant. It releases two SSTO Valkyries to the surface. The two Valkyries from previous ISV is then dispatched from the surface to the parent gas giant Polyphemus to scoop up hydrogen from the upper atmosphere to refuel Venture Star. When its time to leave the ISV Venture Star then fire its fusion engines again for Earth, using up all of its anti-matter and hydrogen. When it arrive back in the solar system it extends its photon sail again and Earth's laser station slows the ship into orbit. It's quite a scary thought when you think about it, having a ship flying in Earth's general direction at 0.7c and relying on laser propulsion to stop. I suppose if something goes wrong with the photon sail and the ship looks like it will be unable to enter orbit the laser stations on Earth will then proceed to fry the ship for safety. You wouldn't want a mile long spacecraft travelling at some fraction of c slamming into your homeworld.

If you send a probe that will take 100 million years to get to Alpha Centauri, by the time it gets there it will probably find worlds teeming with humans.

Woo thanks for the feature. There are in fact now fully reusable versions of Hurricane Duo and Hurricane Trio now: KerbalX download numbers suggest people are divided between the convenience of 1.5 stage and slightly lower cost of fully reusable. Basically most of the saving is from recovering the rocket engines, recovering the engine-less external tank reduce the cost per ton only mildly, from $571 per ton to $411 per ton.

It has to be longer than that, 42.14km is only the half way station, you need more elevator above this point so that the whole elevator will be taut and in tension. It doesn't necessarily have to be much longer though, if you tether something heavy like say an E class asteroid on the far end then the upper section of the elevator can probably be pretty short.

It seems a bit premature to me to design a ship when it's core technology is still pretty much completely unknown. Isn't that a bit like Henry Ford trying to design a Lamborghini Aventador right after coming up with Model T?

No it's legit. Do you see us humans send rovers out with every day rubber tires? The wheels on the Apollo Lunar Roving Vehicle took many many years to develop because they had to work in a very unusual and hostile environment. There were all sorts of designs like the metal conical wheels and even archimedean screws that were designed and tested before it settled on a wheel made out of woven piano wire. Similarly with ladders, for the longest time no one thought to put hand holds on the outside of the spacecraft, not even after Ed White's space walk. Everyone thought White's little pressure gas gun or the later more advanced Astronaut Propulsion Unit was perfectly adequate for moving around on the outside of the spacecraft. We didn't know until Gemini 9A how hard EVA actually was if you needed to do work in space instead of just floating around and it wasn't until Gemini 12 (after neutral buoyancy tank was introduced so EVA procedure and equipment could be tested on Earth) that proper hand holds were added to the outside of spacecrafts. To me, rover wheels and space grade ladders and hand holds not being available at the start makes perfect sense. Here's a video where the GM people talk about the difficulties of designing the rover wheels: https://youtu.be/5aDSYTMqyQw?t=2m33s Here's detail on the specific wheel design that was chosen: https://youtu.be/5aDSYTMqyQw?t=20m26s Here's a video on the difficulties with EVA encountered during Gemini and how it was overcome: https://youtu.be/ytxcYLCf0nA?t=41m46s Here is Curiosity's wheel after 3 years on mars, just to show that even today rover wheel design is still not a solved problem.

Say if you're the president and Elon Musk finishes his BFR or MCT or whatever the big rocket is going to be called. Then he comes to you and say "before we send the colonist can I have some hydrogen bombs to drop on the Martian poles to thicken and warm up the atmosphere". What would you say?

Robert Zubrin is not exactly the most level headed person around. He's like an Elon Musk minus the money. And I still suspect Elon Musk could be a supervillain in disguise.

One other trick: remember if you really want to shave down the mass to orbit you can use the kerbalnaut him/herself as the final stage. The EVA suit's MMU has something like 600m/s of delta-v. So it's quite acceptable to design a lander that gets the kerbalnaut to suborbital velocity 400m/s short of LEO, then bail out of the lander, taking all the science with you and use the MMU to complete climbing to orbit with 200m/s as both reserve and fuel to get into the return craft.