I don't know... I've always considered Battletech to be Hard SF, and it has ships which accelerate at 1G. 9.807 m/s^2 doesn't seem that impractical in the future.

IIRC, egocasting is primarily done with a neutrino transmitter. Neutrinos go through matter like it doesn't even exist, so I don't think there'd be any LOS issues. [On the other hand, how do you receive a signal that so easily passes through all matter! Chalk that one up to magic, I guess.]

Here is a bunch of approximations, which is how I think I will handle it: Distance If planet A and B orbit at radius r1 and r2 from the sun (ignoring elliptic orbits and inclinations) the average distance is approximately r1*sqrt(1+(r2/r1)^2) (the real expression is an ugly elliptic integral nobody in their right mind wants), and for even rougher rpg purposes one can say that if B orbits inside A's orbit the average distance is slightly more than r2, if both are in the same orbit the distance is 1.25*r2 and if B is much further out the distance is r2. Example: the average distance between Venus and Earth (r1=0.723 and r2=1 AU) is around 1.135 AU. The above formula gives 1.234 instead. Racer burns The fastest way of going a straight distance R is with a rocket that constantly accelerates at an acceleration A (see the table on page 347). This would take K sqrt(R/A) days, where K is 1.4285433 if we measure R in AU and A in G-s. A metallic hydrogen rocket can go 1 AU in just one and a half days! Unfortunately this is *extremely* fuel inefficient. The rocket equation, my least favourite law of nature, shows that the amount of reaction mass needed grows exponentially with the velocity (since you need to accelerate the mass too). Even with cheap energy and reaction mass this makes fast spaceflight hard since the sheer size of the ship will balloon. Slow trips The most fuel efficient way of going from point A to B in the solar system involves using the "interplanetary transport network", sending the vehicle orbiting in such a way that different gravitational effects nudge it from orbit to orbit. This is very slow; typically it takes many revolutions of the involved planets to get anywhere - going from Earth to Jupiter would take several years. If you are willing to use a bit of fuel to do two burns, then a Hohman transfer orbit is optimally cheap. The time taken is about half a period of the destination planet (e.g. going from Earth to Mars takes about half a Mars year, about 1.05 years). Unfortunately this only works at certain times when the start and destination are at the right points in their orbits. However, with a bit of extra fuel one can make another orbit that solves the Kepler problem and brings one from A to B. As a rough rule of thumb, this will also take about half an orbit for the outer planet. Middle-of-the road burns Spacecraft will normally travel somewhere between the absurdly fast constant acceleration trajectories and the efficient Kepler orbits. If you burn for time T at start and finish, you will get velocity AT for the coasting period (and assuming it is most of the journey) will arrive after time R/AT. If we measure R in AU, A in G-s and T in hours we get the travel time of around 49*R/AT days. Example: A fusion rocket burning for 4 hours at the start and destination, going from Mars to Jupiter (R is around 5.2 AU) will arrive after 26 days. Had it been a antimatter rocket it would have arrived after 6.5 days. Both burns have to long enough to bring the ship up to speeds comparable to the planets, typically some tens of km/s (Mercury 47.9 km/s, Earth at 29.8 km/s, Jupiter at 13.1 km/s to Pluto at 4.7 km/s). In reality these delta-v changing burns will depend quite a lot on where you want to go (and relative position: much of the burn is about changing the direction rather than size of your velocity). The time it takes to get to V km/s if one can thrust at A G-s is around 102*V/A seconds. Example: Getting to Jupiter from Mars may involve two burns at around 30 km/s, taking 1020 seconds if done with a metallic hydrogen rocket, 4.25 hours with an antimatter rocket and 17 hours with a fusion rocket. Comparing with the previous example, the fusion rocket needs a longer burn than four hours to match the orbital velocities, while the antimatter rocket is probably about OK with a 4 hour burn. All in all, celestial mechanics is fun, but one shouldn't overcomplicate things.

I built a very simple calculator back when this came up on RPG.net (which JSnead might remember): http://alfedenzia.com/misc/burn.php No accounting for interplanetary transport networks, Hohman transfer orbits, or even how much reaction mass the ship has to carry. The 'burn ratio' parameter in the third case is the percentage of time that the rockets are firing. While it defaults to 100%, for realistic results, it should be set lower. Much lower. (See Arenamontanus's comments on racer burns.) If you don't care too much about precision, it might be enough to get an order of magnitude for how long it takes to get from A to B.

For travel time, you're interested in the right-hand column. The checkbox at the top determines whether you want to stop at the end of your trip, or if you're trying to ram the target at full speed. Naturally, it defaults to the unsafe option. The text box labeled Burn ratio is what percentage of the trip you want to spend accelerating or decelerating. By default, it's assuming that you're firing the rocket the whole way. The checkboxes are for the different propulsion methods, based off of the acceleration figures provided in the rulebook. Later in the RPG.net thread, JSnead provided better figures, but this doesn't use them. You now have two options, indicated by the radio buttons. The first choice will calculate travel time for five configurable distances, measured in AU. There's no significance behind the default numbers there, beyond roughly exponential. One AU is, of course, the distance from the Earth to the sun. The second choice, labeled 'A to B' lets you chose one or more sources, and one or more destinations. Clicking the 'Compute' button will take every pairing of source and destination, and calculate the travel time when the source and destination are closest and furthest apart. Now that I have Arenamontanus's equation for calculating average distance, I might add that as well. Be careful choosing lots of sources and destinations, since you'll end up with 2 * s * d columns in the resulting table, which can grow very quickly. Note that once you click the button, the page will very gleefully forget all of the values that you just entered, so if you want to make minor changes, you'll have to hit back, or enter everything in again.

The left-most tells you, if you're accelerating at maximum speed with a given engine/propellant, how fast will you be after a given amount of time. The middle column will tell you how far you've gone in that time.

While HO and MH rockets are very likely incapable of racer burns, I'd imagine that the other types of propulsions systems are likely designed for that specific use... especially since they are supposedly designed for long-distance travel. Also, since they have 15 to 400+ times less acceleration than either of the former two systems, racer burns are likely necessary to actually get to your destination with any decent amount of time.