Armchair Rocket Scientist

EDIT: The TWR is off by .2 at launch. The value should be approximately 1.5, but is 1.7 at launch. I am not sure what the rate of change is on this as the shuttle climbs, but the launch values are definitely off. I will just have to wait until CSS is fully compatible. Thanks for trying to help, regex.

So, something I've been wondering about for a while: is it possible for the greenhouse effect in the atmosphere of a venus-like planet to raise its surface temperature so high that the entire surface becomes molten? First, according to this link, nearly all igneous rocks that would be found on a planetary surface should be molten at a temperature of 1200 *C, or 1500 K. I am assuming that this is still approximately accurate under a pressure of several hundred atmospheres. We can assume that a planet with a Venus-like atmosphere will have a nearly constant surface temperature across its entire surface, even if it is tidally locked to its star, because we know Venus's surface temperature varies by only a few degrees, and its rotation is so slow that it's solar day is over a hundred days long. We will also assume a near-circular orbit, giving a constant planetary temperature, and assume that the internal heat generated by the planet is negligible. Therefore, the planet should radiate the same amount of energy as it receives from its star, and we may use the equations here. Pin = Insolation * (1 - albedo) * pi * planet radius2, and Pout = emissivity * the Stefan-Boltzmann constant * 4 * pi * planet radius2 * T4. Setting these equal to one another: Insolation * (1 - albedo) = 4* emissivity * the Stefan-Boltzmann constant * T4 The original page sets emissivity equal to 1 for the black-body temperature, but we won't do that, so: T = ((1-albedo)*insolation/(4*Stefan-Boltzmann constant * emissivity))1/4 Note that the temperature is measured at the altitude where the atmosphere becomes effectively transparent to thermal radiation. This should be a bit lower than the actual surface temperature, but we will set them equal for convenience. We will set T = 1500 K, albedo = 0.90 (the same as Venus), and put the other constants together: (1500 K)4 = insolation * 0.1 / (4 * 5.67*10-8 W/m2*K4 * D2 * emissivity) insolation / emissivity = 1.48*107 W/m2 To make life easier, we will change insolation to units of Earths (1366 W/m2) This gives us emissivity = insolation / 10,800 earths. For a planet receiving the insolation of Venus, the required emissivity is therefore 1.77*10-4, which is about 16x lower than it would be for Venus (half the surface temperature, everything else is the same, and this is proportion to T4). With Mercury's insolation, this rises to 6.18*10-4. If the planet has equal emissivity to Venus, it must be roughly 4 times closer to the sun. Now, I still have some questions: 1. How do I determine at what temperatures and pressures CO2 will be stable? Note that unless photodissociation and ionization occurs, a rocky planet of Earth's mass or larger should have no problem retaining CO2, even at high temperatures. 2. How can I approximate a planet's emissivity from the amount of CO2 (mass per unit of surface area) in its atmosphere. 3. At higher insolations, will the sulfur clouds seen on Venus disappear, raising the planet's albedo?

1. Ganymede's atmosphere has a surface pressure of around a micropascal. Mars's atmosphere is 600 Pa and 0.145% oxygen according to Wikipedia. This means that the partial pressure of oxygen is close to a MILLION times higher on Mars than on Ganymede. Trying to compress Ganymede's atmosphere would be absurd. It would probably take many orders of magnitude less energy to electrolyze the water ice of Ganymede's regolith to produce oxygen, or to synthesize oxygen from Martian CO2. 2. Ganymede's ice is FAR more water than a colony would have any use for. Mars should have enough buried ice to support a colony. Also, for the record, Ganymede's ocean is below 150 km of ice/URL]. We can't drill through that with anything remotely resembling current technology. If you want to explore an ocean, going to Europa is a better bet. 3. As everyone else has pointed out, Ganymede's magnetic field isn't enough to protect it from Jupiter's much stronger one. Sure, you could shield a colony by placing it under a couple tens of meters of ice, but why bother? Aside from that, there are a couple of other important points to consider: First, travel to/from Ganymede will take much longer than travel to/from Mars. With a hohmann transfer, I believe it's 3-5 years vs. a few months. This means that a ship would need extremely thick radiation shielding, and use an very high dV transfer. Second, Ganymede takes a LOT of delta-V to reach compared to Mars. Assuming this delta-V map of our solar system is anywhere near accurate, it takes about 4500 m/s to reach the Martian surface from LEO, but 9500 m/s to reach Ganymede's surface. This is assuming you Aerocapture for both Mars and Jupiter. The actual dV needs will be even higher, because again you won't be using a Hohmann transfer. Ganymede has no atmosphere for aerobraking, and is about as hard to land on as the moon. Returning will be even harder; that dV map says that you'd need 6700 m/s to escape Jupiter's immense gravity well from a Ganymede transfer orbit. This is a huge requirement even for nuclear-powered spacecraft.

I think if jet engines were rebalanced to semi-realistic levels with no other changes the game would be made almost useless. However, with fixes to Kerbin's soupy air, planes should be able to fly with lower TWRs. It would also be extremely helpful to have 0.625m and 2.5m jet engines, probably with up to 250 kN of thrust or so. At the very least, we should have "basic jet engines" at each scale with good low-speed thrust, and "turbojets" up to mach 3 or so. Perhaps a pre-cooler part could be added to extend the thrust curve of jet engines to higher speeds. Anyway, however it's done, the jet engine rebalance should allow a well-built SSTO to have a larger payload fraction than a well-built multi-stage rocket (asparagus staging presumably won't be as powerful with aerodynamics fixes). Unless rockets and fuel tanks are dramatically rebalanced as well, this probably means allowing jets to keep producing usable thrust up to at least 1500-1800 m/s in some vehicle configurations.

That's how MESSENGER did it. One flyby of Earth, two of Venus, and three of Mercury before the final orbital insertion.

Honestly, with Procedural Parts the part counts aren't that bad. Anyway, to the main question, I found orbital launches to be too easy in stock KSP, even with FAR + DRE. However, rendering the larger planets is hard on my laptop's integrated graphics chip. Once I get a new computer, I plan on making a custom 10x scale config including the Outer Planets Mod.

Actually, Dragon's trunk is probably a lot lighter than most service modules: in most manned spacecraft, most of the propellant, thrusters, and some life support equipment is in the service module, while in Dragon these components are all in the back of the capsule, and the trunk only contains solar panels, radiators, and some space for unpressurized payloads.

I dislike when the "take visual / temperature / pressure readings on Kerbin" contracts generate surface sites on a cliff face. Also, the game needs an option for Wernher Von Kerman to pop up and say: "It looks like after staging is complete some parts of this vessel have a command pod, but no batteries or power-generating parts" or "There are no valid tanks supplying fuel to this engine." Kinda like Microsoft Sam.

What's the giant motor case on the right? It's hard to tell with perspective and all, but it looks like an "O" or bigger.

Goodspeed Aerospace also has hexagonal trusses, although I don't know whether it still works in 0.90. http://forum.kerbalspaceprogram.com/threads/72567-0-23-5-Goodspeed-Aerospace-Parts-v2014-4-1B

+1 on larger jet engines. In particular a giant 2.5m turbofan would be approximately to scale with the GE90, which is used on real aircraft. In addition, hopefully the less soupy aerodynamics in 1.0 will allow planes to get off the ground with lower TWRs: modern jetliners typically only have a TWR of 0.3.

I noticed the new version of mechjeb has an "Svel+" (pointing prograde relative to surface motion) option. Has anyone tried that for RSS launches?

You're calculating required vehicle masses linearly, when due to the nature of the rocket equation it's actually exponential: dV = g * isp * ln(wet mass / dry mass) wet mass / dry mass = e^(dv/g/isp) mass ratio = e^(dv/g/isp) So: mass ratio = (payload mass + fueled mass of rocket) / (payload mass + dry mass of rocket) = e^(dv/g/isp) Now, for a dV of 9000 m/s (by the way, this only BARELY gets you into orbit with nothing left for deorbit or orbital adjustment) and an isp of 450 (chemical fuel with hydrogen), the required mass ratio is about 7.68. For a more reasonable dV of 9.5 km/s, it's 8.60. Now, to get our payload fraction, we need to subtract the structural mass of the vehicle from the dry mass. Let's assume the structural mass is 5% of the fueled mass - this is comparable to a F9R first stage, and it uses kerosene fuel (high density + non-cryogenic = good tank mass fractions) and the highest TWR liquid-fueled engines ever flown, so this is VERY optimistic. So: (payload mass + fueled mass) / (payload mass + 0.05 * fueled mass) = 8.60. payload mass + fueled mass = 8.60 * payload mass + 0.430 * fueled mass 7.60 * payload mass = 0.570 * fueled mass fueled mass = 13.33 * payload mass. launch mass = 14.33 * payload mass, or 1433 tons for a 100 ton payload. This is much lighter than a Saturn V, but we used an unrealistic mass fraction for our rocket: it's more realistic to assume dry mass is around 10% of fueled mass for a cryogenic stage. This gives us a launch mass of about 5400 tons, which is close to double a fully fueled Saturn V (and the Saturn's payload is a bit more than 100 tons actually). Anyway, now let's switch out our hydrolox engines for a solid-core NTR with an isp of 900 s, and keep the mass fraction the same. With our higher isp, we get: (payload mass + fueled mass) / (payload mass + 0.10 * fueled mass) = 2.93. Our launch mass ends up being 373 tons for a 100 ton payload. Holy mackerel! Doubling our specific impulse didn't half our launch mass, it cut it by more than ten times! Unfortunately, our actual mass ratio won't be that high, since (a) nuclear engines and their associated shielding are heavy ( the vehicle needs to survive reentry for safety reasons, and © again for safety reasons we'll want fairly high structural safety margins. Now, let's look at a rocket with a dV of 19,000 m/s (enough to make a propulsive landing on an Earthlike planet with no atmosphere and launch back into orbit). With hydrolox engines, our launch mass must be e^(19000 / 9.81 / 450) = 74 * (dry mass of rocket + payload mass). Oops. Even the lightest rocket stage we've ever built, launched with no payload at all, is still three times too heavy. Let's try again with NTRs. (payload mass + fueled mass) / (payload mass + dry mass) = e^(19000/9.81/900) = 8.6 (hey, this number looks familiar). Turns out our nuclear rocket with a dV of 19 km/s DOES end up being about twice the size of a Saturn V, but a chemical-fueled one turns out to be utterly impossible. Fortunately for OP, if we can build a warp drive we can probably build a closed-cycle gas-core NTR (aka a "nuclear lightbulb"), which would have an ISP of at least 1500. Or, better yet, we could use some type of fusion reactor. For that matter, less than a gram of the antimatter used for the mothership will provide plenty of energy to reach orbit provided we can find some way of using it to make a jet or rocket engine usable in atmo. Also, if we're exploring the stars with a ship like this, it's reasonable to assume we're looking for potential colonization sites. If a planet has so little atmosphere that we can't aerobrake or run a nuclear-thermal jet engine (Mar's atmosphere makes both difficult but possible), then just leave and find another target, and send a small robotic lander to do some basic measurements on the feasibility of terraforming the place.

Skylon could be interesting, since its engines are pretty far from the center of mass. At low speeds it ought to be fine doing what you said, but at mach 3+ it's possible that an engine failure would push the vehicle into a flat spin before the other engine could be shut down (as has been experienced by pretty much anyone who's flown a multi-engine SSTO in KSP before the update with the RAPIER), which in real life would result in the vehicle breaking up. Here's an example of this happening with an SR-71: http://www.916-starfighter.de/SR-71_Waever.htm Once Skylon has performed its pitch-up maneuver following the transition to rocket mode, it will have almost no aerodynamic control. If an engine fails, it would have to immediately shut down the other engine completely (RCS would be much too weak to compensate for imbalanced thrust). It would still likely go into a spin, with associated problems from high centripetal accelerations, but wouldn't immediately break up and could slowly stop its rotation using RCS (heck, maybe use the LOX as a cold gas thruster, since it won't be needing it). However, it's possible that for a large part of the burn to orbit, an engine failure would result in a reentry too steep for the vehicle to survive. However, according to this: http://forum.nasaspaceflight.com/index.php?topic=33648.450;wap2 Skylon has the equivalent of four engines in rocket mode (I guess each SABRE has two turbopumps), so it's possible it could handle a failure in that regime with just a reduction of thrust.

Basically, a jet airliner moving at mach 0.8 and 30,000 feet, with wings optimized for flight in that regime and a TWR of 0.3, is VERY different from the space shuttle, which has a TWR over 1, is designed for hypersonic reentry, and may be flying at, say, mach 2 and 60,000 feet, or mach 10 and 200,000 feet, when an engine failure occurs. An airplane can pretty much always rely on being able to generate a pretty large yaw force with its tail to compensate for an engine failure, as well as throttling down. The Shuttle can't do that without going to a high angle of attack and risking breaking up, and in some cases throttling down would make the problem WORSE because the remaining engines would be unable to overcome the upward pitching moment produced by the SRBs. Its ability to make drastic trajectory changes is extremely limited with the external tank attached. Plus, in the event of an engine failure close to takeoff, the shuttle would have to either separate from the still-burning SRBs (very dangerous) or ride them all the way to burnout (in which case the vehicle must remain controllable). Longer after takeoff, it would be on a suborbital trajectory over the ocean, with no air to help with control. At best, if a failure resulted in inability to keep the thrust balanced with gimballing, it could ditch the ET and get out of the spin with RCS, but if it can't keep burning the main engines the OMS would probably be too weak to allow a Transatlantic abort. The shuttle's high stall speed means ditching in the ocean would almost certainly be unsurvivable, so crew would have to bail out. Again, this is very dangerous. http://en.wikipedia.org/wiki/Space_Shuttle_abort_modes Here's a chart of the shuttle's abort modes: http://en.wikipedia.org/wiki/File:ShuttleAbortPost51L.png Basically, anything after SRB sep is a flight regime where there isn't enough air for a vehicle to maintain control via aerodynamics alone, so without gimballing you have to shut the engines off entirely and immediately (equivalent to a 3-SSME failure) and use RCS to stop any rotation that was imparted. For the space shuttle, unless this happened very near the end of the burn you've got a vehicle loss and frequently a crew loss. This would be true for most spaceplanes of a "shuttle-like" design. AFAIK the only serious spaceplane design that doesn't have the ability to point its thrust vectors at the COM is Skylon. However, Skylon is again different from the space shuttle: an engine failure low in the atmosphere would be similar to one on a normal airplane, while at higher speed and altitude it could potentially shut its engines off, reenter, and wait until it reached a low enough speed and altitude for safe powered flight before returning to the runway on its single engine (most likely dumping all oxidizer and some of the fuel to reduce mass enough that reentry is safe).

Question regarding GTO launches: would it be viable to build a cheap, pressure-fed upper stage to perform the burn to GTO, and have the second stage stay in LEO?

Here's a formula that approximates it for bodies of constant density. http://en.wikipedia.org/wiki/Equatorial_bulge#Mathematical_expression. Note, however, that only a very small, non-differentiated body will be anywhere near constant density; real-world planet-sized objects are much denser at the center due to a combination gravitational compression and denser compounds sinking to the core.

Another approach is to put a set of rails on the inward-facing surface of the ring. A docking ship approaches at very low velocity, lines itself up, and grabs the rails with some sort of clamp. A linear motor (aka magnetic catapult) in the rack then accelerates the ship up to the station's tangential speed - or, from the station's perspective, brakes the ship until it's stopped relative to the station. The ship can then be transferred to a series of docking ports off to the side, allowing another ship to use the same "runway." For departures, the process is reversed, with the same catapult accelerating the ship backwards until its velocity is zero, at which point the ship disengages its clamps and manuevers away in microgravity. Note that for a station with spokes, the docking ports themselves can be between the spokes, while the runways themselves can be off to the side, preventing a collision between a ship and a spoke. For a "small" station of this type with a 1 km radius, the required tangential velocity is about 100 m/s, which is slow enough that the ships' clamping apparatus could be plain old wheels. For larger stations these could be replaced with a maglev system, but even with an immense 100 km radius ring, the tangential velocity is only 1 km/s. This is comparable to the speeds proposed for mass drivers used for launch into lunar orbit. Note that this is primarily useful with very large space-based colonies where the mass of an incoming ship is negligible. Such a station could also use more conventional docking ports at its hub for very large spacecraft, but it could only have two of these - one on each side.

That could work really well: instead of having to deal with TweakScale, OP can just directly edit the config to upscale that part 2x. It will obviously make the hatches larger than necessary, but so will any attempt to rescale a crewed part.

Off the top of my head, there's a 3.75m science lab in the parts pack with the Taurus HCV. It requires 3 kerbals, but a simple config edit could probably fix that. It also has small cargo bays. http://forum.kerbalspaceprogram.com/threads/75074-90-Taurus-HCV-3-75-m-Crew-Pod-and-other-parts-v1-4-Dec-15-2014 However, the Honey Badger appears to have an octagonal section, so normal 3.75m parts won't actually fit it. TweakScale won't help either. If you want to use the Honey Badger, your best option is probably to attach FTT's cargo bay and put the regular science lab inside. It's what players have been doing with awkward-shaped parts like B9 for quite a while. Finally, if the FTT pack has an octagonal crew module, you could config edit it to serve as a science lab, but it might not look that good.

70,000 years ago? So, most likely any Oort Cloud objects that were perturbed back then haven't had time to reach the inner solar system. Could this mean that in a few million years there will be a swarm of comets buzzing the inner solar system, possibly leading to a mass extinction on Earth?

IIRC, Skylon is supposed to be able to do this for larger payloads, approximately doubling its capacity from 15 tons to LEO to 33 tons. However, since the upper stage is expended, the cost per ton would likely be higher than flying as an SSTO.

Yeah, it's a very young system. And apparently there are gaps in the rings which may indicate moons forming. While this planet is apparently very large, and may even be a brown dwarf, this suggests that Jupiter and Saturn began life with accretion disks of a similar size.

There are plenty of gas giants in their stars' habitable zones. http://en.wikipedia.org/wiki/Category:Giant_planets_in_the_habitable_zone