sevenperforce

Here's the final render for what should be the ultimate (achievable) Space Shuttle concept. I've pictured it with both the crew-carrying module and the payload module installed. At a little over 90 meters in length, it's a whopper, nearly three times the length of the Space Shuttle orbiter: It carries 42 linear aerospike engines. The two in the nose, pictured below, are only used at full throttle during takeoff and landing: With an internal tank volume exceeding that of the Space Shuttle's external tank, it can carry a huge amount of fuel. The rounded-body form factor allows the tanks to form structural elements, reducing total weight. The 30 forward main engines, eight on each centerbody sidewall and seven on each inner wing section, cause a vortex to form which travels down the length of the shuttle on each side: The vortex on this side is counterclockwise; the vortex on the other side is opposite. In atmospheric flight, the pressure differential of the vortex causes air to be sucked in from below and above and added to the total flow. The aft section contains two large aerospike engines angled directly back as well as eight additional wing-mounted engines which push against the vortex rotation to produce an evenly-directed propellant flow: During takeoff, all downward-pointed engines (the rear wing-mounted engines and the centerbody engines) fire simultaneously with sufficient force to lift the shuttle straight up off the ground, air being pulled down between the wings and the centerbody to augment thrust. Then, the rear engines fire to propel the shuttle forward, while the vortex is initiated by throttling up the upward-pointed wing-mounted engines. This mode, while requiring additional thrust and a very specific design, allows for the safest possible takeoff and landing operation with maximal reusability. The crew module contains its own fuel tank and six of the engines used for vertical takeoff, as well as four of the engines used for forward thrust. In any abort scenario, it can automatically detach from the rest of the craft and land propulsively. It is capable of independent re-entry. This design uses the majority of its main propulsive engines for VTOL and only has two engines not used for forward propulsion. This, in combination with maximal thrust augmentation, enables a high T/W ratio as well as a low thrust specific fuel consumption. So there you have it.

Horizontal attitude, not horizontal direction.

On the subject of liquid methane, would any of you rocketheads like to weigh in here?

You won't notice the dip, and if you time yourself your stopwatch will read just the same as his does, but you'll realize when you get to the end that he beat you.

It's complicated and simple at the same time -- once you get it, it makes a fair bit of sense, but until you do, it's really unpleasant. Let's say that you and your evil clone twin from an alternate universe are hanging out together in the park one day, and you decide to have a foot race. Because the two of you are identical in every respect (except, you know, him being evil), you both have identical reaction times and both start parallel to each other at exactly the same time. Your strides, breathing, speed, and everything are all exactly the same. An observer watching the pair of you from the sidelines would see that your feet kept hitting the ground at the exact same time, the exact same distance with each stride. Suddenly, suppose that you encounter a small dip in your side of the track. Traveling down into the dip and back up makes your side of the track just a couple of centimeters longer than his. You cross the dip and you're still traveling at the same speed, but the observer can now see that you're slightly out of step with your evil twin and just slightly behind him. That's what has happened here. The two laser beams have identical wavelengths (comparable to your stride length) and speed. However, the gravitational ripple extends the path length of one laser beam slightly. This causes the peak of that laser beam's wavelength to reach the interferometer a split second later than the peak of the identical laser beam coming from the perpendicular direction, instead of in perfect alignment.

Well, the interferometer does function based on the interference between the wavelengths of the two beams, IIRC, but it's the phase shift (due to the change in the total length of the beam) that is being measured; the wavelength change is not really detectable. Here, I'll try to do a visual depiction. Suppose you have two lasers that cross perpendicularly. Where they meet, they form an interference pattern: Now, suppose that a gravitational wave comes along from the left of your screen and changes the length of the horizontal laser: The interference pattern is now "bent" and points in a slightly different direction because the horizontal laser's phase meets the vertical laser's phase at a different point than it did before. Make sense?

Well, 1 mm is being stretched to 1.000001 mm for a split second, then it rebounds back. You'd never have any way of measuring that. But 1 mm on the perpendicular axis is being stretched to something like 1.000005 mm. So for that split second, the two rulers are 0.000004 mm out of alignment.

Not so much, no. But a laser beam running parallel to the motion of the gravitational ripple will be squeezed/stretched more than a laser beam running perpendicular to the motion of the gravitational ripple. The ripple squeezed the entire Earth, but it squeezed it along only one axis.

Indeed. With a single laser, you'd never be able to tell; you have no way of measuring the distortion. However, you can measure the difference between the two lasers. And since one laser is aligned with the direction of the ripple while the other is not, one laser will be distorted and the other will not be. And so they will register a misalignment even though you can't directly measure the distortion.

Oh, it does. But since the wave's direction of propagation is going to be better aligned with one cable than with the other cable (since the cables are perpendicular), the two cables won't have exactly the same change in length, and that's how you'll know. It's not a perfect analogy, because with the cable example you could simply feel the tug, and that's not quite right. It's more like the two cables don't quite touch, but cross at the pier, and you've balanced a pencil very carefully between the two of them. Now, if one of them becomes slightly longer than the other, it will change the alignment of the two cables and the pencil will fall off.

Each of the LIGO detectors use a pair of laser beams that extend several miles and meet at the center. An interferometer is installed to measure the precise alignment of these two beams; any change in beam shape will produce very noticeable misalignment. Because the two beams are perpendicular to each other, a gravitational ripple will always alter one of them more than it will alter the other. This is what produces the misalignment which trips the interferometer. Imagine that you're standing on a pier, holding cables that run to a pair of buoys each several hundred yards away. If a wave causes the buoys to shift their location, then one of the cables will pull more taut than the other based on where the wave came from, and you'll be able to feel this change. It's just that instead of cables, we have laser beams and a very precise interference measurement device. 60 solar masses is a pretty big black hole; it's hard to imagine there wouldn't be something swirling around or being lensed or something.

What the flying fudge.

It's a measurement of the change in the distortion of spacetime. Does anyone know if they immediately pointed Hubble toward the signal to see what they could see?

The Titius-Bode "law" is a discredited hypothesis from the era of alchemy. Sure, there will be a roughly logarithmic distribution of bodies in any system which forms by accretion from a circumstellar protoplanetary disc, but that's a consequence of a chaotic system, not an exception to it. Now, if the main bodies of our solar system were spaced linearly, or if they all had satellites exactly 1/100th their mass at exactly 1/10th of their Hill Radius, that would be more significant. But even then, we'd immediately start looking for what sort of drivers could produce such a system. As to Earth-Luna-Ceres: do you have any particular reason to suppose that a collision event would result in the ejecta coalescing into a series of bodies with uniformly descending radii ratios? Uniformly descending mass ratios, maybe, but radii is an implausible stretch.

You can really only do one nuke at a time this way, and only at the cost of a non-negligible amount of OMS fuel, and you're a sitting duck when your target realizes what hit them.

Too bad. Are there any metastable figure-eight orbits between Earth and Luna where we could build a semipermanent Earth-Moon transfer space station? So because one of the planets in one solar system has a density that makes the ratio of its diameter and the diameter of its primary satellite equal to the ratio of that satellite's diameter to another random object's diameter...suddenly the solar system must be designed by a math enthusiast? Gotta give me a bit more than that. Now, if all the planets and moons in our solar system had exactly matching ratios of diameter, mass, and orbital periods, then we might have something to investigate.

I thought the destabilization problem was only for low lunar orbit.

This is an Earth SSTO, not a Kerbal SSTO. I know it's not easy.

If you're building an SSTO spacecraft intended to make maximum use of air augmentation, using a single engine cluster from liftoff to orbit, what are some of the pros and cons of the best fuel combinations? The way I see it, fuel density is going to be fairly important because you want your SSTO to be fairly compact, and deep cryogens probably should be avoided to save tank weight because you can't drop the tanks. You'll also want something that can react at least a little with atmospheric air so that you can run fuel-rich from Mach 0.7 up to Mach 4 or so and get a little airbreathing assist. And you can't sacrifice too much ISP because air-augmentation is going to run out when your velocity equals your actual exhaust velocity, and at that point you're still depending on the same engine for orbital insertion. But if your primary working maas from launch to Mach 10+ is going to be diatomic nitrogen and diatomic oxygen, should you use a low-molecular weight fuel or something with really high heat capacity? Air augmentation is about delivering as much thermal energy to an airstream as possible, which is different from the usual vacuum rocket optimization parameters. What fuel will have optimal mixing in a duct? Would it be feasible/advantageous to use a triprop design, with a denser oxidizer for takeoff and max air augmentation and cryolox for the upper portion of the flight? Any thoughts/analysis would be appreciated.

If I recall correctly, earth is just on the edge of being able to sustain a stable orbit in Jupiter's Trojan points. It would not be stable in Saturn's.

In theory, a shield could be placed at the front of your projectile which ablated readily and shed gas in a sheath around your projectile to cancel compressive and form drag. If you don't want to bother with an engine to circularize, simply place a 10-mile-long space station in orbit with a large maglev track on it, then build an alectromagnetic launcher on the surface to fire your payload up and outside of the atmosphere such that it intersects the front of the space station as it passes overhead. Then the orbiting space station can maglev the projectile/payload up to orbital velocity.

How large of a body could stably orbit the moon? The Russians had showy stuff like the first satellite and first manned mission, but the US was first to get some of the really technically important stuff like first EVA, first orbital rendezvous, and other stuff that set them up for the moon shot.

Ah, yes, I forgot there were 12. Those robots weren't very anthropomorphic, but they were quite capable...I find it hard to believe they would not have been able to at least assess basic habitability.

I only watched it once, but IIRC the explanation had something to do with how only very simple signals could be sent back through the wormhole. A probe wouldn't be able to send back a large data stream, and presumably they couldn't trust a probe to make a full evaluation of all the criteria for habitability and send back a yes/no signal. So they sacrificed three astronauts instead. Of course, the fact that they have artificially intelligent talking walking robots that could almost certainly make as good or better an assessment as a human kinda clashes with this explanation. Plus, they landed on all three worlds anyway, so what was the point?

Exactly -- fewer failure modes, shorter turnaround time. I think this form factor can manage SSTO...it's got maximum internal volume, minimal ascent cross-section, and maximum re-entry cross-section. I don't like the idea of landing a crew module tail-first, which is why I had the notion for a tail-first suicide burn followed by a controlled nose-down to horizontal attitude on the forward SuperDraco-style thrusters. Extensible landing legs are all that would be required; once down, the ground crew can easily put wheels under the legs. A primary advantage of the forward removable crew module with really powerful thrusters is that it offers unparalleled abort capabilities. Catastrophic launch abort? No problem; the thrusters blast you away from the exploding orbiter and then land propulsively well clear of the fireball. Meteor or debris strike in orbit that renders the orbiter unsuitable for re-entry (e.g, Columbia scenario)? Again, no problem; the crew module can detach and re-enter alone, using its underbelly shielding to aerobrake (ablatively, but at this point reuse is no longer the main concern) and touch down again on its thrusters. And autonomous-return FH-style liquid-fueled boosters would be preferred to SRBs, but that's beside the point.