Armchair Rocket Scientist

I rather doubt it: "end-burning" solid rocket motors have two major drawbacks. 1. They burn a lot slower than other profiles. Even in smaller amateur rockets you can end up not having enough thrust for a safe flight. Even a sepatron-sized motor might burn for 30 seconds depending on the fuel composition. 2. In an end-burning motor the lower portion of the casing is exposed to exhaust gases, while in a core-burning motor it's insulated by the unburned fuel. Basically this means that larger endburning motors would need a very bulky and heavy ablative lining to avoid overheating and exploding.

Smallsat? The Ares I and Liberty concepts were supposed to be capable of putting 20 tons in LEO with cryogenic upper stages. A solid upper stage or two could probably still give it 5-10 tons. Also, such a large ICBM would be pretty much useless. With that much payload, you'd either be dropping something like a hundred MIRV warheads or an enormous bomb with a yield in the tens of megatons. I can't think of a viable strategic use for either of those, given that it would be much easier and cheaper to just send a bunch of smaller ICBMs.

2 miles? Wow! What HPR Cert level is he?

Could be interesting, although the only application I can see is if you're docking a rover to a lander, base, or another rover. One thing to consider is that both omni and mecanum wheels can just roll sideways without any traction. Good luck trying to drive a vehicle sideways up a slope. I'm not sure the hemispherical gimballed wheels work offroad at all. A better idea might be wheels that can swivel 360 degrees, as seen here:

There are a few things to consider there: 1. How long does it take your vehicle to ascend and descend from an altitude where it can cool down? You might have to go 30 km up to reach an air temperature of 200 *C. On Earth, a weather balloon can cover this in about an hour. However, on Venus the denser air means drag will be much higher (with no lift or updrafts, the equilibrium speed of an ascending or descending balloon has drag equal to the net buoyancy). It could take days for the probe to change altitude, meaning the time spent at unsafe altitudes is so long that you'd need a cooling system anyway, which makes the blimp concept kind of pointless. 2. What material are you planning to use for your envelope? It needs to be flexible enough to be inflated, strong enough to store your lifting gas (probably something like nitrogen) at a fairly large pressure difference (zero-pressure envelopes run out of gas after a few cycles), and finally it must be able to withstand Venusian surface temperatures without melting. You might be able to cool your electronics, but your envelope will quickly reach ambient temperature. 400+ degrees celsius is pushing the limits of even high-temperature polymers like kevlar. 3. The repeated changes in temperature and pressure could give your materials some fatigue problems they wouldn't experience if they just stayed on the surface.

This design uses a Stirling RTG, which replaces the thermocouple with a heat engine. This is several times more efficient than a conventional RTG, but they aren't normally used because they're more complex than a conventional RTG, and normally spacecraft don't need high power densities anyway. Oil vaporizing wouldn't be a concern either: the vehicle could use a dry lubricant. These are already used on spacecraft because in a vacuum oils vaporize even at temperatures encountered in LEO, and can also freeze. Dry lubricants can also operate at Venus's surface temperature without problems. The main concern I see is getting rid of the heat from the RTGs during interplanetary cruise; unlike a nuclear reactor an RTG can't be throttled or shut off. A fairly complex cooling system might be required. Also, 50 gallons of water would weigh as much as one of the Mars Exploration rovers, and would probably only last a few days at best. By comparison, this design has the potential to function for months, or even years.

For cheap, light stuff it's generally easier to just use a bunch of non-gimballing thrusters. The hardware to make an engine gimbal 180 degrees or even hemispherically is going to add a lot of weight and cost.

Seriously? You think people planning an interplanetary mission want to pack hundreds or thousands of pairs of shoes, potentially weighing over a ton?

In theory, it will slide and look like the orbit on the left. However, in real life a satellite's longitude of ascending node slowly precesses. At least for Earth, there is a set of orbits where the precession rate is exactly 360 degrees per year, meaning the orbital plane stays in the same alignment to the star. These are called Sun-synchronous orbits. These are commonly used by mapping satellites because they can always photograph the target area at the same time of day. Cubesats also love SSOs because they can be placed in a dawn/dusk orbit where the satellite is almost always in sunlight.

To play Devil's Advocate, that doesn't mean that it didn't lose cabin pressure due to having a hole poked in it, or was damaged in such away that parachute deployment was impossible or the capsule couldn't float if it made it to the water at a safe speed.

Honestly, no. Pressurized tanks aren't actually that heavy compared to the alternative, which is a solid-fuel motor casing designed to withstand chamber pressures of 100 bars or higher with a very high safety margin. Plus, the vehicle will undergo very high accelerations compared to a launch vehicle, and experience very high aerodynamic loading, which means that the structure is heavy anyway. For an amateur-sized vehicle capable of supersonic flight, you'd be very lucky to get 50% of your launch mass as fuel. I don't think the isp is that bad, although gasoline contains some compounds that would eventually mess up an engine. The main issue is that tankage for gaseous fuels is very heavy and takes up a lot of space. I doubt a GOX design would ever be used for a flyable vehicle. More likely oxidizers are nitrous oxide, which is relatively easy to work with and is used for most amateur hybrid rockets, or LOX if someone really needs the extra isp. Another potential oxidizer is hydrogen peroxide. For fuels, I know ethanol and methanol are common. Propane should also be a good fuel; it's commercially available and very easily liquefied at room temperature. However, commercial propane contains additives to give it detectable smell for safety reasons; these could mess up an engine.

Okay, first of all look up the laws on doing this in your country, any subnational jurisdictions, and municipality; the US is pretty permissive with sugar rockets but you have a bunch of different regulations to think about, including explosives regulations, aviation regulations, and fire codes. Doing amateur rocketry "safely" includes not being thrown in prison. Also, I don't have the book: what is your "ingenious apogee detector" and how does it work? It's possible that there are some better ideas. Now, provided all this is legal in your jurisdiction: If you are in the US, I would STRONGLY recommend buying some model rocket motors from Estes BEFORE you test-fly experimental motors. This will let you determine that you can successfully fly a rocket safely without the extra failure modes of your experimental motors. Second, do NOT try to fly a multi-stage rocket until you have succesfully flown a single-stage one, AND ground-tested your motors in the staged configuration to make sure your booster can actually ignite the sustainer. A few other points: There are two problems here. First, your black powder ejection charge on the booster stage will just blow your upper stage off without igniting it. Build your booster like the Estes booster engines: an endburning propellant grain without any end cap; at the end of the burn the remaining disc of propellant gets so thin it breaks, sending exhaust gases forward and up the nozzle of your second-stage engine. This will light it much more effectively than the brief explosion of a black powder charge. Also, for a rocket this small, a delay isn't very useful. Second, the "delay grain" method is reliable enough that on rockets of the size you will be building nearly everyone uses it, and it works quite well. Now, I'm assuming your airframes will be cardboard tubes; if they aren't, seriously rethink your materials selection. If your rocket is not minimum diameter, i.e. there is an outer airframe tube, and an inner tube that holds the motor casing, separated by rings, then you will make a coupler by taking a short length of tube, cutting a small amount off lengthwise, putting it back together and gluing it into the top of your first stage. It should stick up into the back of the upper stage at least 1/2 the airframe diameter, and extend as far into the lower stage. Make sure the rear centering ring on the upper stage is far enough into the airframe that the coupler will fit. Alternately, if you're using standard commercial tube sizes, just buy a coupler from the manufacturer. If your rocket is minimum diameter, i.e. the motor case fits right into the airframe, then have your second stage motor stick out the back of the airframe at least 1/2 a diameter, preferable 1 diameter. Make sure you leave room on the booster to insert it all the way. In either case, the joint between stages will stand up to the first-stage motor's thrust, but because it's only held together by friction they can easily slide apart when the first stage motor burns out and the hot gases push the first stage backwards and the second stage forwards. A couple other tips: for your first attempts, do not use more than 20 grams of sugar propellant per motor. And do NOT, even if it's legal in your jurisdiction, use more than 125 grams of propellant in a flying vehicle unless you really know what you're doing. For lower stage recovery, the lower stage will be unstable without a sustainer on top, and will be fairly light. It will simply tumble back to the ground from a low altitude. The only likely source of damage is thermal damage from the upper stage igniting. EDIT: I don't know if your book mentions this, but always test motors from behind a blast shield. If your propellant grain has large voids or cracks, it may burn much faster than you expected, overpressurizing the case and turning it into a pipe bomb. Assuming you're using a cardboard or plastic casing and under 20 g of propellant, most of your shield can be plywood. For parts you want to see through, use polycarbonate plastic, NOT glass or acrylic. Oh, and don't use a metal case; aluminum cases are for people who really know what they're doing, and steel cases are for people who REALLY know what they're doing, aka professionals. (here in the US, even the launches that let you fly 300 lb rockets 20 miles up in the air don't allow steel cases).

No you couldn't. What you're proposing is basically a mechanical version of the electronic timers which have previously been used on multi-stage rockets. The timer (which is pretty cheap and compact) uses an accelerometer to detect launch, then waits a pre-programmed amount of time before firing an electronic igniter on the second stage motor. If anything, this system gets the timing more accurate than a fuse would. As the first two videos demonstrate, a first-stage failure can easily result in the timer firing when the rocket is in an unsafe attitude. How is this device triggered? Manually via a radio signal? Now you're reliant on the operator's reaction time and ability to see the rocket A break wire? You'd be out of luck in the first video where the vehicle stays together. On the other hand, a flight computer using either an accelerometer-barometer combination (measuring altitude and velocity at a given time: if they're too low something's wrong) or a combination of accelerometers and gyroscopes that directly measures how far from vertical the rocket is can simply not fire the igniter. Furthermore, it will not fire if something happens like a spike of acceleration during a CATO or shred ripping the battery wires loose; the same cannot be said for any device which cuts a fuse.

There are several significant challenges for multi-stage amateur rockets. First, they are just flat-out more complex. There's two (or more) motors, two (or more) sets of electronics, etc. that can fail. Second, the connection between stages is placed under very high loads during supersonic flight, and is difficult to build robustly. Third, any motor that is "airstarted" needs a more advanced flight computer that can check that the rocket is flying close to vertical before igniting the motors. Why? If something goes wrong during the first stage burn, the second stage could ignite with the rocket pointing horizontally or even downward, which is extremely dangerous. and show what can happen if a simple timer is used to ignite upper stages. Either of those rockets could easily have killed someone.However, there are some good examples of successful multi-stage flights. is someone's 3 stager, and is a 2-stage flight to over 100,000 feet. For reference, it would take 2-4 times as much total impulse to reach that altitude on a single-stage rocket.

What you're proposing is basically a combined-cycle nuclear-thermal engine that can use either internal propellant (which should be stored as a liquid because high-pressure gas tanks have abysmal mass ratios and density) or external air. I'm not sure how feasible it would be to make one that worked well because your cooling channels need to be either compatible with both liquid and gas or you need multiple sets of cooling channels.

More likely there's no real reason to have a fast approach on an unmanned ship. Progress is solar-powered and I'm assuming has multi-week endurance on its own, so it doesn't really matter if it takes two days to reach the station. On the other hand, astronauts don't want to be cooped up in a Soyuz for two days.

For pump-fed engines, hydraulics driven by the engine's turbopump. It's just that nobody bothered to code having the gimbal stop working when the engine is turned off. The pressure-fed engines, like the LV-1R, the 24-77, and maybe the MK-55, probably have an electrical gimbal (or electrically-powered hydraulics for the MK-55 assuming it isn't pump-fed.

I have to say, I would IMMENSELY approve of this for reserving just the right amount of dV for landing on a recoverable first stage.

Allow me to translate: "Instead of adding cosmetic features that, while nice to look at, don't do much to improve gameplay, Squad overhauled a core gameplay feature that has been broken since the game was released, and which most of the community has been clamoring to have fixed since the game was released. I'm upset and hate Squad forever because my ridiculous aircraft don't work anymore." Seriously, come on. Complain all you want about Squad not fixing the aerodynamics BEFORE releasing 1.0, resulting in the fix being poorly balanced and subsequent post-release hotfixing breaking craft. But claiming Squad "ignored community suggestions for unneeded stuff" is utterly absurd since a large portion of the community has been asking for better aero for literally years. In fact, a lot of players have been angry at Squad for adding new features like asteroids and contracts when a core part of the physics engine was a placeholder.

They'd probably be screwed (IIRC it was deemed that trying to fire the SPS on Apollo 13 was too risky since the engine might have been damaged). But the astronauts would also be screwed if an Apollo 13 type accident happened while the LM was on the moon, or if a severe failure happened to the LM while it was on the moon, or if an Apollo 13 type accident happened while in lunar orbit and disabled the SPS (LM on its own couldn't put the whole stack on a return trajectory AFAIK. Ultimately, having redundant systems on the same spacecraft is safer than having multiple spacecraft where some systems are redundant but there are also plenty where a failure on EITHER spacecraft will kill the crew.

The superdracos are deeply throttleable IIRC, but even firing only two engines at 10% throttle would give you a TWR of almost 0.2, which is more than you actually need for operations in LEO (the Shuttle's OMS only had a TWR of about 0.05). Having such a high minimum thrust isn't that good for precision maneuvering (such as lining up an orbital rendezvous), and is only really useful for large burns like a TLI (which the Dragon doesn't have enough dV for anyway). Also, the SuperDraco has a relatively small nozzle, and is most likely optimized for atmospheric operation (an abort could be required anywhere from on the pad to first-stage burnout), so it should have worse vacuum ISP than the Dracos. Using them in orbit would just waste fuel.

Not necessarily. The Voyager probes are currently leaving the sun's Heliosphere, and are able to take various magnetic and chemical measurements of how the solar wind interacts with the interstellar medium. If their RTGs last long enough, they may be able to sample the interstellar wind directly. Kerbal spacecraft could take similar measurements of Kerbol's astrosphere. To decrease mission time, such a probe could use a jettisonable ion engine and solar panel stage that lasted until Jool's orbit, or use an NTR to make a high-dV burn as it flew past Jool.

Technically, IIRC ablative cooling only involves the vaporization or melting of a solid. What you're describing is evaporative cooling, which involves the use of a liquid. Incidentally, the human body automatically "sprays" water on its skin to cool down. That's what sweating is. A better water-based analogy for an ablative heat shield would be if you wet your finger before touching it to a dangerously hot surface (such as a red hot metal bar). The film of water, evaporates, absorbing almost all of the heat transferred from the metal. This buys you a little time before your skin gets hot enough to cause injury. This is pretty much exactly how ablative heat shields work: for a brief exposure to high heat fluxes, the vast majority of the heat will be sunk into vaporizing the ablative material. On the other hand, an evaporative cooling system like sweat can actually reduce an object's temperature by absorbing heat from that object and evaporating. If you tried using an ablator to deal with internal waste heat, you'd end up cooking yourself since most ablative materials are also excellent thermal insulators, and would heat up from the inside out. On the other hand, ablative cooling is used to deal with waste heat in some rocket engines, like the RS-68. However, ablative cooling is only useful for rocket engines because the nature of the design means the combustion chamber and nozzle are exposed to a fast-moving stream of very hot gas.

Only the fastest into Earth's atmosphere: the Galileo Atmospheric Probe entered Jupiter's atmosphere nearly four times faster.