Temstar

It's conceivable but it doesn't seem likely to be the case given what we've seen of it. When they fired up the Ares 3 MAV's OMS engine it shot out two huge exhaust plumes (none of this 'puff of gas' type deal we see with regular monopropellant RCS blocks), was able to right the whole three stage vehicle against the storm and remained firing for quite some time. Given that Ares 4 MAV was dramatically lightened I get the feel that a working OMS would be able to impart significant amount of delta-V to it. It wouldn't really change the story either, they just have to have a second of two showing the Ares 4 MAV capsule firing the OMS after separation from the upper stage.

Why would you remove OMS to save weight (to get more delta-V) when you could just use the OMS to give you more delta-V?

Another thing that I thought was a bit goofy in The Martian was the MAV. MAV was a two stage vehicle which was fine. But on second stage burnout the spacecraft then separated from the rocket stage into an Apollo command module shaped capsule which was then drifting towards Hermes. This I thought was a pretty weird design, I don't get why there needs to be a stage separation there? Surely under its normal operating mode the "command module" part would still be attached to some kind of service module when it docks with the Hermes mothership. Then once the crew boards Hermes the whole MAV can then be deorbited to crash back on Mars. None of this require a staging event. The only thing I can think of that need staging is if the crew capsule part of the MAV has its own small built in motors and/or reaction control system, So that it can fly under its own power to complete the docking with Hermes. (Actually come to think of it we know this is true since they mentioned firing the Orbital Maneuvering System engine to counter the tilting, and the engine that was fired looked pretty beefy and was located in the nose where the crewed capsule was) In which case getting rid of the MAV upper stage will be a good idea. But if that was the case they surely would have used the same OMS to close the relative speed with the flyby Hermes?

Wait sorry it's 1000 bombs to orbit. Each bomb gave the craft a 10m/s delta-V. The other 1000 bomb was for going around to interesting places in the solar system. 10m/s was the limit that the ship could take, hence the much larger super Orion that weighed 8 million tons using 3 megaton bombs. The bombs increased in yield as you ascended in atmosphere and you needed to carry some half momentum charge to reset the pusher plate position in chase you get duds. The Orion bombs where nuclear shaped charges that produced a plasma fireball that was a cigar shape instead of a normal spherical fireball. They were definitely not neutron bomb or anything like that. The biggest fallout problem was I think strontium-90. I would trust the calculations done in Orion project - the guys involved where pretty good in maths in general and Dyson was particularly good, and they had no shortage of above ground nuclear bomb test data back in those days.

The point is 400m/s is not really a useful amount. You can't even reach KSO from LKO with that delta-V. Yeah you can land on Gilly a few times, but if you want to get back to Eve you still need a transfer stage, and if you need to use a transfer stage you need to be able to dock with it and your RCS system is already powerful enough for landing and reaching orbit: For orbital manoeuvring you need a bit of TWR, else burn time become unmanageable. So saying "well I can get heaps of delta-V with one ant engine and 100 tons of fuel" is a moot point - a spacecraft like that is unusable anyway. For practical application a deep space spacecraft need 1000+m/s of delta-V to go anywhere interesting and you need to be able to complete that burn in a burn time measured in minutes not hours. And pretty much in all such cases nuke is your best bit. Of course I can think of cases outside this: if you want to lower a probe to low, circular kerbol orbit for example then having burn time measured in hours is fine, and plentiful sunlight makes ion practial If you want to land on Tylo you need a lot of TWR, proper big chemical engines are needed here If you're making an small orbital runabout that only need to move between stations, then your delta-V requirement is so low that a small chemical engine will do If you want to land and take off from Gilly to meet up with a transfer stage, your RCS blocks will suffice For everything else, use nukes.

Nah nah they said and I quote directly "Instead of taking the Endurance into orbit around Miller's planet which will save fuel but we'll lose a lot of time, what if we take a wider orbit around Gargantua parallel with Miller's planet outside of this time shifter here" Didn't say L2 or anything. For all we know the plan was probably go into a Gargantuan orbit wider than Miller's planet's orbit. Then have the Ranger burn directly for Miller (not hohmann transfer orbit), land, then burn directly back towards the Endurance. After all Endurance will only be in this orbit for an hour and the Ranger is equipped with magical relativistic rocket engines.

It's both, time dilation on Miller's planet is caused by both the effects of special relativity (because it's orbiting at relativistic speeds) and general relativity (because it's in a region of highly curved spacetime). Miller's planet must be orbiting at relativistic speed because that's what "orbiting near the event horizon" means by definition. The Endurance is definitely not at L2 point of Miller's planet because Miller's planet has 130% earth's mass and it's orbiting a supermassive blackhole with millions of solar masses (hence the supermassive part). Because the ratio of mass is so extreme any Lagrange point would be so close to Miller's planet that there will be negligible difference in time dilation.

If cost of interplanetary transfer is an issue the answer is still nukes. Because yes the transfer stage will be bigger, however you simply reuse the transfer stage by refueling it LKO with SSTO tanker spaceplances and/or refuel at target planet from ISRU bases.Fuel is cheap, throwing engines away is not. Remember also launch from Kerbin itself can be done with a dry transfer stage which can then be fueled in LKO with SSTOs, thus cutting down cost of launch vehicles again. Yes nukes have bad TWR and long burns can be tricky, but it still doesn't mean you need to burn away from prograde - it's a simple matter of starting your ejection burn earlier so that by the time you reach your target velocity your ejection vector matches the phase angle for the interplanetary transfer. Your orbit will be "wider" from Kerbin than a short burn transfer with high TWR, but on an interplanetary scale that distance is negligible. It's not like nuke transfer stages need burns that last 30 minutes or something, it's only slightly longer.

The engines in Interstellar were so overpowered it's absurd. Given the time dilation difference between Endurance and Miller's planet it works out that Endurance's orbit has a velocity of about 33%c and Miller's planet orbit the blackhole at 55%c. So you are talking about a craft that can hold 3 guys and a robot (and pretty roomy interior), do a burn that charges the craft's velocity by 22% the speed of light, then land on a planet with 1.3G and atmosphere, then take off back into orbit, then change the craft's velocity by another 22% the speed of light to dock with Endurance again, all in a single stage. If you could build engines that good you wouldn't need to know how to manipulate gravity to lift space colonies into orbit, you will just build heaps of those engines and strap them to the space colony itself. With The Martian beside the storm the only thing that stood out to me was reducing hydrazine inside his hab to make hydrogen for burning. Hydrazine is pretty nasty stuff, about as awful as chemicals we've specifically invented to kill each other with (VX, sarin, all that good stuff). I'm pretty sure handling the stuff and bringing it indoor to react in a jury rigged reactor will kill you pretty quickly.

Suppose your rocket can boost a 10 ton spacecraft into orbit. The goal is to maximize the delta-V of this craft. Let's say out of this 10 ton payload, 2.5 ton is mission hardware, eg the reason why you're going into space in the first place, so you can't change this part. You start with a nuke engine, which is 3 tons, this leave you with 4.5 tons to play with. This happens to fit two Mk1 jet fuel tanks perfectly. These two tanks weights 4.5 ton, of which 4 ton is the fuel. So the dry weight of your craft is 2.5 + 3 + 0.5, or 6 tons. Plug 10 ton wet mass, 6 ton dry mass and 800s ISP into a delta-V calculator and you get 4007.59m/s of delta-V Now suppose instead of a nuke engine we use a LV-909 Terrier instead. It has same vac thrust as a nuke but only weights 0.5 ton, it has a lot lower ISP though at 345s. Because the engine is now 2.5 tons lighter, we free up 2.5 tons of payload capacity on our launch vehicle. Naturally since we want delta-V we devote all that 2.5 ton to more fuel. KSP fuel tanks have a 9:1 wet/dry mass ratio. So a hypothetical 2.5 ton fuel tank will have a dry mass of 0.278 tons. Good thing bipropellent has the same combined density as jet fuel as this makes calculation easy. So now, our chemical engined spacecraft has a dry mass of 2.5 + 0.5 + 0.5 + 0.278 tons, or 3.778 tons. We plug 10 tons wet mass, 3.778 tons dry mass and 345s ISP into delta-V calculator again and we get 3283.27m/s of delta-V. So as you can see, despite having much more of the craft being fuel, the chemical engined craft has much lower delta-V than the nuke powered version.

Yes definitely. Chemical engine only matter if TWR is an issue. Bop's gravity is so low that TWR is completely irrelevant. Even with the Mun the gravity is low enough that nuke powered craft's TWR is a non-issue. TWR is only an issue when you're dealing with world's like Tylo. Tylo's gravity is strong enough that you need a lot of thrust to safely land and take off, and here chemical engines start to look good again because of their much higher TWR.

The standard Apollo style layout is fine for the 3 men capsule, with two radial parachutes. During launch there would be a LES tower attached to the top. However this is my general purpose spacecraft that I use to go anywhere within Kerbin SOI, it has 1000+m/s of delta-V in its service module. If you want to make a craft that is only used to go between ground and LKO then this is overkill. If you look closely at the capsule you notice it has storage for both electricity and monoprop, turns out that's enough to deorbit the capsule without any service module at all! What you do in the VAB is to put the docking port on top, heat shield below and two radial parachutes around it. Then make sure the capsule has full electricity and monoprop and toggle usage for those two resources off for the capsule. Then attach two of those single direction RCS thrusts so they point forward. Then when you're in orbit (say, attached to a station with crew boarded waiting to come back) you just undock, switch on electricity and RCS in the capsule, tap the RCS thrust to back away, then point your capsule prograde and fire the RCS. The monoprop stored inside the capsule should be more than enough to deorbit it.

Basically any time you see the words "shuttle between" and "reusable" and "deep space only" the answer is NTR engine. For single use lightweight spacecraft then chemical engines become viable. There's a chart somewhere for this that shows what engine is best to use at a given TWR (ie the % of your craft that's engine determines which engine is best for most delta-V). But for crafts that always stay in vacuum and you will refuel and reuse over and over again the answer is always the nuke engine, because its ISP is THAT good.

Huh? It doesn't say that. Original plan called for launch directly from the ocean into orbit all with nukes (2000 bombs to get into orbit). And Dyson calculated that out to show that on average the fallout will kill somewhere between 0.1 to 1 person per launch globally. I consider that acceptable, consider the huge amount of payload each launch can loft up. Dyson said he would consider it acceptable if they could get it down to 0.01 person per launch.

Real rockets are actually tested in full test flight too. And just like in KSP the first test flights usually show some overlooked problems, eg Saturn V and pogo, N1 and its engine control, Falcon 9 and not enough struts etc etc. Only difference is real life space program usually don't do test launches with 80% of their budget that will sink or swim the whole program. That's an area of Career that could use some improvement. It would be nice to see some kind of government budget simulation where you get regular funding from the government to keep the program alive, so you are never in a situation where you can't afford to launch anymore just because of launch failures. That said if a singled failed launch has the potential to bankrupt your space program it probably mean you should attempt something less ambitions first to grow your budget.

Oh you Squad

It's a bit hard to scale things up since they don't scale up linearly. It's about 3500m/s to reach LKO and 10,000m/s to reach LEO, so LKO is much easier to reach. But on the other hand KSP rocket parts are rubbish compared to real life rocket parts so a Kerbal rocket with 10,000m/s of delta-v will have a tiny payload fraction (eg Eve ascent rocket). If you had Kerbal rocket parts on earth and you tried to make a rocket to launch a given payload you will need a much bigger rocket than the real life equivalent rocket for that payload. BTW, is it just me or does Kerbals enjoy huge amount of space per person in their capsules? Their one man and three man capsules are only a little bit smaller than Mercury and Apollo capsules, yet Kerbals are much much smaller than humans so per person space would be greater.

KVV is the best thing since sliced bread. And since the VAB/SPH now gives you dimensions of your craft I thought I'll spend some time creating a size comparison picture between real life manned spacecraft launch vehicles and a selection of my own launch vehicles in KSP to see the size difference: Interestingly while Nova II is close to the maximum height the VAB supports, the VAB still has plenty of room sideways. So in theory you should be able to fit the NASA space shuttle inside the KSC VAB. Although I doubt you can actually prep the Space Shuttle inside the KSC VAB for launch.

KVV is the best thing since sliced bread. And since the VAB/SPH now gives you dimensions of your craft I thought I'll spend some time creating a size comparison picture between real life manned spacecraft launch vehicles and a selection of my own launch vehicles in KSP to see the size difference:

That said, if you have an truly immense amount of delta-V then this type of transfer may be practical. This is called a brachistochrone trajectory where the ship more or less just accelerate directly at the target and fire its engine (and therefore accelerate) until the half way point, then flips around and fire it's engine retrograde so it can enter orbit upon arrival. Compared to low energy Hohmann transfer orbit a brachistochrone trajectory will get you to the target much much faster. Someone worked out that a ship capable of accelerate at 0.3G for hours will be able to reach Moon from LEO in about 6 hours, rather than 4 days that the Apollo spacecrafts took. Trip to Jupiter with this ship will take 2 weeks, and Saturn in 3 weeks. That is, assuming you have an engine that can fire continuously for hours and days and weeks, rather than minutes with chemical rockets. I recall someone actually did a brachistochrone to Mun in KSP. It should be doable with NTR engines given the much reduced distance compared to real life but it will still require a huge ship.

Yes for early career Mun flyby you need to enter Mun SOI in retrograde direction, which means you need to have Kerbin AP beyond the orbit of the Mun. All Apollo missions used this kind of trajectory for the same reason - flyby moon in retrograde orbit means you're doing a gravitational slingshot to reduce your velocity relative to Earth, so in the event that the service module engine fail to fire to insert you into Lunar orbit you'll just come back to Earth in 4 days without any burn required (more or less, it's more complicated than that). If you try to insert a spacecraft into prograde Moon orbit and your service module engine does not fire (or you're too low on fuel in KSP) then you'll do a slingshot and increase your velocity relative to Earth. Some of Apollo's S-IVB 3rd stage did exactly this and the moon slung them into solar orbits where they remain to this day. If this were to happen with a manned spacecraft that would be an automatic death sentence.

Back in the days AV-R8 was the go to part for landing legs as legs didn't exist. AFAIR struts always looked the same now and then.

0.17.1 - Apokee I, the first version of my general purpose manned spacecraft. Back then docking didn't exist, I had to hack together two different mods for this docking to work. [img]http://i64.tinypic.com/2yvs8rc.jpg[/img] 0.18 - Apokee II with Mun lander, stock docking now introduced, allowing me to now easily conduct Apollo style Mun landings [img]http://i63.tinypic.com/erh1jm.jpg[/img] 0.18.1 - Apokee III, first major redesign using the previous version's Mun lander service module, producing a smaller, cheaper yet almost as capable spacecraft. [img]http://i65.tinypic.com/24fgwwn.jpg[/img] 0.18.4 - Apokee IIIB, now includes a homemade LES tower for better crew safety. [img]http://i64.tinypic.com/2yzbw5c.jpg[/img] 0.19.1 - still using Apokee IIIB [img]http://i65.tinypic.com/28t9p36.jpg[/img] 0.23 - Apokee IIIC, now only uses 4 RCS block instead of eight, monoprop capacity reduced by 50% as I find I didn't need that much. Also solar panels are now four 1x6 with a gap in between ala Automated Transfer Vehicle, so that RCS block's gas can shoot through the gap [img]http://i64.tinypic.com/2niz05u.jpg[/img] And after a long break from KSP I came back recently just as 1.0.5 came around to start playing again: 1.0.5 - Apokee IV, now has heatshield that can survive steep reentry from anywhere within Kerbin SOI. Solar panels now retractable. LES tower change to use the stock one. [img]http://i67.tinypic.com/2111no0.jpg[/img]

Yeah but each lander has to leave LKO and get onto the interplanetary trajectory somehow, how do you propose to do that in a flotilla? If the answer is "integrated interplanetary transfer stage" for each lander then the mass of those stages have to be included. And if these are nuke stages which you then drop that's a lot of nuke engines that you are throwing away. Putting all those engines onto a mothership means they can be reused on later trips and there won't be any hot reactors flowing around Kerbol. When I did my Jool 4 mission the mission architecture was: 1. Launch mothership into LKO 2. Launch Bop lander to LKO, dock with mothership 3. Launch Tylo lander to LKO, dock with mothership 4. Launch Laythe/Vall double lander to LKO, dock with Mothership 5. Launch tanker rocket to refuel the entire stack 6. Mothership + 3 landers make a burn for Jool SOI using mothership's nuke engine cluster 7. Upon entering Jool SOI, Mothership makes trajectory adjustment for Jool aerocapture pass, after aerocapture AP is now at Tylo orbit 8. Tylo lander undock from mothership and adjust orbit for Tylo SOI encounter 9. Bop lander undock from mothership and adjust orbit to raise PE above Jool's atmosphere, then at PE it fires its engine again to raise AP to Bop orbit 9. Mothership adjust orbit to raise PE, so that after another aerobraking pass it's AP will change to Laythe orbit 10. Tylo lander enter Tylo SOI at its Jool orbit AP, fire engine to enter Tylo orbit 11. Mothership + Laythe/Vall lander enter Laythe SOI, adjust PE for Laythe aerocapture 12. Bop lander enter Bop SOI, fire engine to enter Bop orbit 13. Mothership + Laythe/Vall lander now in Laythe orbit after aerocapture pass 14. Tylo lander lands on Tylo surface, jettisoning orbital maneuvering fuel tanks in the process (no engine, only fuel for orbit change and deorbit burn) 15. Bop lander lands on Bop surface (polar orbit landing to visit Kraken) 16. Laythe lander undock from mothership and land on Laythe surface 17. Laythe lander jettison descent stage shortly after lift off, the ascent stage returns to the orbiting Mothership with empty tanks. The ascent stage now becomes Vall SSTO lander 18. Vall lander refuel from Mothership fuel reserve 19. Vall lander make a moon-to-moon tranfer burn, leaving Laythe for Vall 20. Mothership makes an ejection burn to leave Laythe SOI, pass through upper Jool atmosphere for aerobraking pass and settles down in Low Jool Orbit 21. Vall lander enter orbit around Vall, then lands on Vall surface 22. Bop lander launch from Bop surface, makes an ejection burn for Jool aerobraking pass 23. Tylo lander launch from Tylo surface, jettison ascent stage and makes an ejection burn for Jool aerobraking pass 24. Vall lander launch from Vall surface, makes an ejection burn for Jool aerobraking pass 25. The remaining sections of all three landers make aerobraking pass through Jools atmosphere and settle into Low Jool Orbit and dock with the Mothership. 26. Service modules of all three landers and jettisoned, leaving only the capsules attached to the mothership. Service modules deorbited into Jool's atmosphere for science 27. Mothership + capsules fires nuke engine cluster for interplanetary trip back to Kerbin 28. Mothership + capsules make aerocapture pass through Kerbin atmosphere and settles into LKO. 29. Shuttles bring crew and data back down to Kerbin, fuel tankers refuel Mothership to prepare for next trip. You're not suppose to take the Mothership everywhere, the Mothership is only responsible for carrying the landers to the parent body SOI, the landers then all undock and go onto complete their individual missions before rejoining the Mothership for the trip back. In my case my Mothership also pulled double duty bringing fuel for the Laythe/Vall lander. I considered this extra leg acceptable since you can aerocapture both ways between Jool and Laythe.

[quote] 2. The Mothership Here you dock the lander to the crew transport in LKO and send them out as 1 unit. Lander only has to get down, back up, and rendezvou, so is pretty small and light. However, the crew transport is bigger and more expensive than necessary because it has to get both itself and the lander out there (although only itself home). [/quote] This concept is not necessarily bigger than the flotilla concept because of one very important reason - the Mothership can be optimized for deep space only operation and lander can be optimized for landing/takeoff only. For example an Eve lander by necessity needs high TWR and engines that can work under high atmospheric pressure. Sure you could use such engines to make an interplanetary trip but they are not optimized for it. If instead you send the Eve lander to Eve with a nuclear thermal rocket powered mothership then you no longer need to refuel the lander before landing on Eve or need to build an integrated interplanetary stage to the lander. Also another important factor: once you designate your interplanetary mothership as "deep space only" this opens up the option of reuseability. Just like how the mothership remains in orbit while the landers land in the outward part of the trip, upon returning to Kerbin you can elect to park the Mothership in low Kerbin orbit. The crew and the data can return to KSC via SSTO space shuttles and the Mothership refueled by your orbital infrastructure and be prepared for the next trip. Also, for target worlds were SSTO landers are possible (so basically all of them except Eve and Tylo), once the landing is complete you simply leave the lander back in orbit and have the crew move to the mothership on the return leg of the trip. This means on the next trip to that world you already have a lander waiting in orbit and all the mothership have to do is bring fuel to refuel the lander for another landing. Here are some images of my interplanetary trips using this mothership-lander architecture: Duna + Ike double landing [img]http://i50.tinypic.com/2hzh4oz.jpg[/img] Landing on all four moons of Jool (Pol didn't exist back when I did this mission) [img]http://i42.tinypic.com/m8zhn9.jpg[/img] Eve + Gilly double landing, including an Eve rover for driving to the ocean [img]http://108.imagebam.com/download/pDGNiG6An__Fltu2YmOYJw/25596/255950333/screenshot1124.jpg[/img]