sevenperforce

It rolled out yesterday in the US but nothing like volume yet. Unrelated, Boris Johnson now in ICU.

Depends on the application. The Sprint Missile had virtually no time between second-stage burnout and warhead trigger. Other interceptors did have coast periods. Residual-thrust coast is not a likely scenario, however. The second stage of Sprint was a full stage. I would look at modern interceptors and investigate which ones tend to have coast periods in the atmosphere.

Magnetic fields ARE the thrust of a light craft. Motion of a charged particle produces magnetic fields, period. We call it "electromagnetic" because they are a single phenomenon.

It's going to depend weakly on overall size and much more directly on fineness ratio. What you're looking for is the L/D, or Lift-to-Drag ratio. L/D is usually measured in a wind tunnel and should be known for most shapes, including cones, cylinders, half-spheres, and so forth. L/D will be a function of airspeed and angle of attack (AoA). At an AoA of 0 degrees, the L/D of a cylindrical symmetric body will be zero. As it tilts relative to the airstream, its L/D will change. If you know the relationship between L/D and AoA, you can rearrange the equation to determine how much deflection you need to produce a desired amount of lifting force and from there determine how much thrust you need to use to deflect. These values depend on too many variables to be calculated de novo and so you need analytic solutions based on real-world data. A starting hypothesis for your purposes might be "aerodynamic control surfaces do not work well at hypersonic speeds during coast, but cold-gas-thruster-induced flow separation can be used to produce more lift-based diversion than divert thrusters of commensurate mass during the following flight regimes."

Well fudge. https://www.cnn.com/2020/04/02/health/aerosol-coronavirus-spread-white-house-letter/index.html

Yes, you have to go into suborbital spaceflight. So, a boost stage (or stages) that burn out under 35 km to put you onto a suborbital trajectory above 70 km. Realistically you will need to have an apoapsis at burnout well over 70 km in order to actually make it into space when coasting from 35 km. I expect people will use RCS to adjust trajectory, then a ballistic re-entry. You cannot use your main engine, though. Correction burns after crossing 35 km are fine as long as they do not use the main engine or add appreciably to the missile's kinetic energy. The point of the 35 km burn ceiling for a suborbital missile is to push people toward high-acceleration ICBMs that produce as much thrust early on as possible and involve a significant ballistic element. I also expect that most people will merely launch straight up from the pad at the KSC, pitch just slightly downrange, then fall back straight down. That's easiest, and it lets people focus on their rocket design rather than spending endless hours figuring out how to target KSC from the desert airfield or elsewhere. Nope -- it needs to go into space and then fall back down without thrust until impact.

Figured it out. They were too far inside the fairing, even though they were visible outside of it. If I blew the fairing they started working.

I've always loved the Nike Sprint ABM, with its ridiculous 100G acceleration and boost-phase skin temperatures rivaling re-entry energies. It was a marvel of rocket science and advanced engineering. Unfortunately, there isn't much of a way to introduce a high-acceleration ballistic interceptor into KSP challenges. You can replicate it, of course, but it's not really good for anything. There have been challenges where you try to get a rocket as close as possible to an orbiting target, but that takes a lot of effort and doesn't really play into design as much as dumb luck. But I thought of a challenge that might push people to design an ICBM-style vehicle, so here you go. Long-awaited funding for the Kartemis Missions has finally come through, and the VAB is due for a much-needed upgrade. An upgrade, of course, first requires a demolition, so the KSP agrees to build one final VAB rocket to get the job done. Ordinarily, a ballistic missile would carry a warhead, but to avoid damage to the surrounding buildings the impactor will be purely kinetic. The launch will also have a liftoff limit of 120 tonnes. Because the KSP complex will be evacuated for safety during the mission, the Deep Space Kerbnet will be shut down. Accordingly, all engine burns must take place before entering the upper atmosphere. The impactor must stay below 150 km altitude for its targeting systems to remain functional. Your mission is to destroy the VAB with a suborbital ballistic impactor. The impactor with the greatest kinetic energy (if you don't know how to calculate kinetic energy, Google it) wins, provided that your launch vehicle was less than 120 tonnes at liftoff, launch clamps and other ground assets excluded. No engine burn may be conducted after crossing 35 km altitude; your impactor cannot exceed 150 km altitude at any time. Because the KSP physics engine handles high-velocity impacts poorly, it is not necessary that the VAB actually be leveled; it is enough that your impactor strike the ground reasonably close to the VAB. Your score is your calculated kinetic energy at impact, modified by the following bonuses: Pinpoint Precision: Actually level the VAB. +3%. Sprint Style: Two-stage solid-fueled vehicle with liquid verniers on the first stage and no RCS. +5%. Super Sprint: Engine burnout below 15 km. +10%. GNOM Style: Ramjet boost stage launched from a mobile, wheeled platform. +5%. Accidental Elon: Single-stage liquid rocket which impacts engine-first and steers descent using fold-out fins, like a returning Falcon Heavy booster. +8%. Poseidon Style: Two-stage solid-fueled missile with vernier guidance on both stages, launched from underwater. Upper stage uses RCS once exoatmospheric for guidance, then releases a purely ballistic, unguided impactor. +12%. Pootin' Style: Final stage may fire engines within atmosphere up until impact, subject to the following limitations (+30%): Final/cruise stage may only carry Whiplash engines with infinite fuel enabled and can only ignite after re-entry Must launch vertically from either the Desert Airfield or Woomerang Max altitude limited to 100 km Kinetic energy calculation may only use mass of onboard RTGs at impact Kamikaze: Your launch vehicle will be crewed and otherwise unguided; the Kerbal must bail out (and survive) no more than 5 km in altitude, just before impact. (+20%). Kim Jung Boom Style: Single-stage liquid-fueled launch vehicle with a fixed main engine and four verniers; upper stage uses RCS once exoatmospheric for guidance, then releases a purely ballistic, unguided impactor. +10%. Von Braun Style: Single-stage liquid-fueled ogive missile with fixed external fins, like a V-2. Entire rocket must remain in one piece until impact. +6%. Good luck!

One thing to look into would be whether you could use cold-gas thrusters to produce flow separation around the base of the projectile during terminal flight, altering drag effects and thus producing differential torque. Might be possible with far less thrust than traditional RCS.

I should have specified. "The Oberth effect says that for any given orbital trajectory, the deeper you are in a gravity well..."

There have been several good explanations, plus some helpful math, but maybe this will give a way of thinking about the Oberth effect that will help conceptually. In 1920, the New York Times published an editorial which mocked rocketeer Robert Goddard and said it was preposterous to imagine a rocket working in space, where there is no air to push against. The Times posted a retraction of that on July 17, 1969, the day after Apollo 11 lifted off from Cape Canaveral: "Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere." As humorous as this was, it underscores a critical element in understanding the Oberth effect, along with all other types of rocketry. Rockets are not magical force engines which produce thrust by simply flipping a switch; they are reaction issues which gain thrust by pushing against exhaust gases. The harder and faster the exhaust comes out, the farther and faster the rocket will fly. The farther you throw the exhaust, the farther it will throw you. The Oberth effect says that the deeper you are in a gravity well, the more energy you will ultimately gain from a burn of specified length. But instead of thinking of it in terms of an engine's thrust, think of it in terms of the exhaust you are leaving behind. If you burn your engine while high in a gravity well, you're leaving your exhaust behind in its own orbit, one which has a high amount of potential energy relative to the bottom of the gravity well. The particles of exhaust will fall toward the bottom of the gravity well, their potential energy forever lost. By diving deeper into a gravity well, on the other hand, you convert the propellant's potential energy into kinetic energy first. A burn at periapsis leaves the exhaust behind close to the planet, rather than wasting momentum carrying it up into a high-potential-energy space to be lost.

Not trying to be a dick, but -- how were you going to 'save on fuel' by launching an entire new first stage to rendezvous with a re-entering orbiter, rather than just letting that orbiter descend all the way to the runway without using any fuel at all? MHD only works in the ionosphere where the atmosphere is already ionized. It will not work in the mesosphere or below. You should read about The Air-Breather's Burden. Also this old thread.

This is true. Anything that would make a great SSTO either has high thrust (making it a great first stage) or high efficiency (making it a great upper stage). Any SSTO concept you can imagine will have better performance if you use it as a first stage booster instead. The only drawback is that an SSTO gets a "free" RTLS by re-entering after one trip around. With staging you need either reserve propellants for a RTLS boostback or you need downrange recovery assets. The reason to use a sled is to reduce the mass of the landing gear and the size of the wings, since you no longer need to lift off horizontally at full load and the gear is only used on landing. The problem with this approach is that you lose non-catastrophic abort capability. Conventional rockets are single-use so if you encounter a problem on launch you either limp along to a lower orbit or you simply lose the vehicle, but with a reusable launch vehicle you really need the ability to turn around and fly back if something goes wrong. Can't do that if your gear is too small to land under full load. This is essentially the "starter kit" Skylon, using a suborbital version to deliver payloads that then boost into LEO under their own power. Keep in mind that the fueled Falcon 9 upper stage is 115 tonnes without payload. Frankly this part is a terrible idea, no offense. If the orbiter is capable of re-entry and atmospheric flight it should just glide back on its own. This would become super profitable if there was an independent market for suborbital hypersonic passenger and cargo delivery. Unfortunatelt this does not appear to be a thing. Nukes make a poor first stage, period.

And LES is more likely to injure you than a zipline. One would hope.

It may just be fire codes: any structure intended to hold people needs to have multiple avenues of escape in case of fire. I think there are stairs, and the elevator, but I also don't think Elevators count as an avenue of escape in the case of a fire, so they have zip-lines. I've wondered about this as well. Most rocket-related failures do not give advance warning. That being said, what if a fuel line springs a leak? It's not so severe that you want to trigger the LES but you definitely don't want to waste any time in an elevator.

Someone on Twitter asked how quickly you would die if you drank that amount of plutonium dissolved in the tea. The answer is somewhere between two hours and two seconds.

Fun fact: I did the math for this comic.

Why would you clip? Oscars are denser than any other case but their mass ratio is the same as every other tank. Clip them if you need to avoid drag, but this is a hover test where drag is nonexistent. Take a spaceplane into a suborbital flight until intake air is exhausted. Close the intakes. Re-enter and glide to a landing; stop. Open the intakes and restart. You'll note that there is intake air at zero forward airspeed.

Oh, I use it to complete circularization. Which means you don't need as much mass below.

I was building a model of the Sprint ABM being discussed by @p1t1o and I over in Science and Spaceflight, but when I tried to put the vanes (standard canards) on they didn't work, at all. I can't get them to actuate. They won't control the vehicle in flight; they won't even actuate on the pad. Other control surfaces (engine gimbal, etc.) on the vehicle works fine. Spent half an hour troubleshooting to no avail. Any ideas?

Tempted to try and hit every point item with a rocket that looks as little like the Saturn V as possible....

I missed the Worm.

Hmmmm, good point. Let's see here. The ion setup is 424 kg. The Ant+OKTO2+Oscar setup has a dry mass of 90 kg and a wet mass of 290 kg for 3612 m/s. Add another Oscar and you're up to a dry mass of 120 kg with a wet mass of 520 kg, for 4527 m/s. So more mass, less dV. You could try to add the Oscar (or a pair of Dumplings) as a drop tank but that adds complexity and dry mass. And you'd need guidance on the drop tank stage which hurts more. Plus, the Dawn can do useful things like firing at full thrust while occluded, which allows you to use it as a parallel stage while stacked serially. The disadvantage of the ion setup is that you either need to do a retrograde orbit or you need to do a zillion periapsis kicks.

Here's a (sadly low-quality) schematic showing the guide vanes. If @sahil saxena's application intercepts at higher velocities or under lower air pressure, or if it has a long coast phase, rcs might be better than vanes.

Doing the math...that's 3612 m/s. Dawn + OKTO2 + single 1x6 solar panel + small radial xenon tank = 5164 m/s. No contest.