Whilst testing our new interstellar system over the past week a number of changes have been made and this post summarises those changes.
A trip to another star is now two ordinary burns. A speed up burn on the way out and a slow down burn on the way in. The Transfer Planner plans both and the flight computer flies them just like any other auto burn. Time warp now goes up to 100 years per second so the years in between pass in minutes.
Here is what changed today and what we learned flying it.
MRS-1 Magnetic Scoop :- Collects interstellar hydrogen into the vessel's hydrogen tanks, between the planets or the stars. Switch it off with its Scoop Field toggle. Has a 1,000 km capture radius.
MTT-1 Magnetic Trap Tank :- Holds antihydrogen, the drive's antimatter. It is the only tank that can and it holds nothing else.
All of these parts are placeholder parts - and may not end up in the final game. They are all currently using placeholder models. None of them currently use or require Electricity to operate. - Yet.
The space between stars now contains 0.1 hydrogen atoms per cubic centimetre that the scoop can collect.
Both the speed up and slow down burns will run at full throttle.
The speed up burn stops at whichever comes first. Either we reach max speed, the antimatter is used up, hydrogen is used up, or we get halfway to the star.
The slow down burn is timed backwards from your arrival so that it ends at the destination at your selected final speed. The planner shows the circular orbit speed at arrival so you can pick a final speed that leaves you in orbit.
For each burn you see its length, what will cause it to end, the final speed and the antimatter and hydrogen it uses, followed by the coast in between and the total trip time.
Press Preview to see both flight plans drawn: the path out and the path after slowing down.
Once you hit calculate the planner re-times both burns against the real delta-v they need, which on the way out includes climbing out of the Sun's gravity and cancelling your orbital speed.
At full throttle the antimatter drive burns roughly 6.5 kg of hydrogen for every kg of antimatter.
The magnetic scoop matters on the coast and the slow down, not the speed up:
Each burn is limited by what is actually in the tanks when it starts, the coast refill is limited by tank space, and the slow down burn starts as heavy as a ship with full tanks minus the antimatter already burned.
A burn 4,700 years away now arrives in under a minute instead of over five hours.
Burning at high warp was slow for two reasons, and both are better now:
The flight computer debug window has a Long Burn Pointing section showing the pointing errors and what each part of the flight computer asked to be woken for.
Inside Alpha Centauri, a vessel moves between A, B and Proxima by their spheres of influence instead of jumping to whichever star is nearest.
Here is what changed today and what we learned flying it.
New parts
RAIR-1 Antimatter Ramjet :- Annihilates antimatter to push out hydrogen. It takes gas from a magnetic scoop before its own hydrogen. Produces: 500 kN thrust, 30 TW jet power, exhaust at 0.4c, 20 t, throttles down to 1%MRS-1 Magnetic Scoop :- Collects interstellar hydrogen into the vessel's hydrogen tanks, between the planets or the stars. Switch it off with its Scoop Field toggle. Has a 1,000 km capture radius.
MTT-1 Magnetic Trap Tank :- Holds antihydrogen, the drive's antimatter. It is the only tank that can and it holds nothing else.
All of these parts are placeholder parts - and may not end up in the final game. They are all currently using placeholder models. None of them currently use or require Electricity to operate. - Yet.
The space between stars now contains 0.1 hydrogen atoms per cubic centimetre that the scoop can collect.
Planning a Trip
Select Interstellar in the Transfer Planner. You will then need an antimatter engine currently active in the currently selected vehicle to then choose a destination star and a set of four sliders. The planner works out the rest.Both the speed up and slow down burns will run at full throttle.
The speed up burn stops at whichever comes first. Either we reach max speed, the antimatter is used up, hydrogen is used up, or we get halfway to the star.
The slow down burn is timed backwards from your arrival so that it ends at the destination at your selected final speed. The planner shows the circular orbit speed at arrival so you can pick a final speed that leaves you in orbit.
For each burn you see its length, what will cause it to end, the final speed and the antimatter and hydrogen it uses, followed by the coast in between and the total trip time.
Press Preview to see both flight plans drawn: the path out and the path after slowing down.
Once you hit calculate the planner re-times both burns against the real delta-v they need, which on the way out includes climbing out of the Sun's gravity and cancelling your orbital speed.
Fuel, hydrogen and the scoop
On the way out from a star the hydrogen will likely run out long before your antimatter.At full throttle the antimatter drive burns roughly 6.5 kg of hydrogen for every kg of antimatter.
The magnetic scoop matters on the coast and the slow down, not the speed up:
- Speeding up, it collects little. Collection grows with speed, so it is tiny early on. Above 0.2c at full throttle carried hydrogen is the better reaction mass.
- Coasting, it refills the hydrogen tanks.
- Slowing down, it does most of the braking. Gas hitting the scoop at 0.37c pushes back with about 6.5 MN, over ten times the drive's 500 kN.
Each burn is limited by what is actually in the tanks when it starts, the coast refill is limited by tank space, and the slow down burn starts as heavy as a ship with full tanks minus the antimatter already burned.
Flying it
Interstellar burns behave differently from normal burns in a few ways:- They light at the burn marker. A normal burn starts half its length before its node. An interstellar burn can run for months, so it starts exactly where its marker sits on the map, and the stretch flown during the first half is drawn in the burn's colour.
- They run for a planned time. The flight computer burns at full throttle for the time the planner worked out rather than until a delta-v target is met.
- Warp stops between burns. When an auto burn finishes or runs out of propellant, time warp drops to real time and the next burn loads, ready for you to hit Auto.
- The slow down burn adapts. If the speed up burn runs out of propellant early, you arrive slower and later than planned. The flight computer re-plans the slow down burn from the path you are actually on, keeping your final speed and antimatter allowance.
Getting there faster
Time warp now goes past 90 days per second, with new steps at 1, 5, 10, 50 and 100 years per second. They work everywhere, including auto warp to a burn.A burn 4,700 years away now arrives in under a minute instead of over five hours.
Burning at high warp was slow for two reasons, and both are better now:
- Physics steps. Velocity Verlet, our integrator for vessels under power is only accurate up to 2 second steps. Out in free flight, away from atmospheres and planets, steps longer than that now use an eighth-order Runge-Kutta method (Dormand-Prince). Coasting off rails for 15 days at 100,000x, it stayed within half a millimetre of the exact orbit where Velocity Verlet drifted 2.4 m in testing. It is worth noting that due to our architecture and decisions to do our own physics integration this kind of thing was achievable within one day. Something we simply could not have done using a game engine. Allowing us to do the most apropriate physics required for our use cases in the game allows us to deliver much more than we could have achieved with any game engine.
- Flight computer wake-ups. An auto burn used to wake the flight computer every 0.1 s to steer the vehicle, which capped every physics step at 0.1 s. A long burn that is on target now sleeps until its pointing drifts past a set error angle or rate, then corrects and sleeps again.
The flight computer debug window has a Long Burn Pointing section showing the pointing errors and what each part of the flight computer asked to be woken for.
Space is split between star systems
In the first post each star owned the space nearer to it than to any other star. Now that space belongs to whole star systems.Inside Alpha Centauri, a vessel moves between A, B and Proxima by their spheres of influence instead of jumping to whichever star is nearest.
Alpha Centauri
Alpha Centauri now moves like the real system:- A and B orbit their shared centre of mass with the pair's measured 80 year period. Before, B orbited A and took 110 years. This is achieved using an invisible Barycenter object.
- B and Proxima are real stars. They draw as stars rather than planets, and whichever one you are near lights the scene.
- B has a 3 AU sphere of influence. A vessel orbiting A is no longer captured by B the moment it burns.
- Proxima orbits 8,600 AU out and goes round in about 550,000 years instead of 1.4 million.
- The masses set the orbits. Changing a star's mass keeps the whole system consistent.
Known limitations
- Interstellar Burns are finite and immediate and not accurate as our current patched conics system uses immediate burns.
- Arrival accuracy. A flown speed up burn is not yet accurate enough to any kind of closest approach. Test flights predicted arrivals 156 AU to 1,700 AU out (as per the error angle and rate mentioned above).
- I have removed the target periapsis slider from planning until a flown burn can meet it.
- Burns at very high warp. A long burn still cannot reach the top warp steps without slowing the game down but coasting runs at full speed.
What's Next
- Steering the burns themselves onto the target periapsis.
- Improve the vehicle steering integration errors so we can improve the arrival accurancy and sim speed slow down issues at extreme timewarp speeds.
- Change Burns and Patched Conics / Flight plans to use impulsive burns for all flight plans.
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